@article{pang_ngaile_2023, title={A Robust Bubble Growth Solution Scheme for Implementation in CFD Analysis of Multiphase Flows}, volume={11}, ISSN={["2079-3197"]}, DOI={10.3390/computation11040072}, abstractNote={Although the full form of the Rayleigh–Plesset (RP) equation more accurately depicts the bubble behavior in a cavitating flow than its reduced form, it finds much less application than the latter in the computational fluid dynamic (CFD) simulation due to its high stiffness. The traditional variable time-step scheme for the full form RP equation is difficult to be integrated with the CFD program since it requires a tiny time step at the singularity point for convergence and this step size may be incompatible with time marching of conservation equations. This paper presents two stable and efficient numerical solution schemes based on the finite difference method and Euler method so that the full-form RP equation can be better accepted by the CFD program. By employing a truncation bubble radius to approximate the minimum bubble size in the collapse stage, the proposed schemes solve for the bubble radius and wall velocity in an explicit way. The proposed solution schemes are more robust for a wide range of ambient pressure profiles than the traditional schemes and avoid excessive refinement on the time step at the singularity point. Since the proposed solution scheme can calculate the effects of the second-order term, liquid viscosity, and surface tension on the bubble evolution, it provides a more accurate estimation of the wall velocity for the vaporization or condensation rate, which is widely used in the cavitation model in the CFD simulation. The legitimacy of the solution schemes is manifested by the agreement between the results from these schemes and established ones from the literature. The proposed solution schemes are more robust in face of a wide range of ambient pressure profiles.}, number={4}, journal={COMPUTATION}, author={Pang, Hao and Ngaile, Gracious}, year={2023}, month={Apr} }
 @misc{li_peng_meng_xu_wang_ngaile_fu_2023, title={Energy field assisted metal forming: Current status, challenges and prospects}, volume={192}, ISSN={["1879-2170"]}, DOI={10.1016/j.ijmachtools.2023.104075}, abstractNote={To meet the various and critical manufacturing requirements including high precision, low cost, good manufacturability, and more demanding from product service and performance aspects such as high performance, light-weight, less energy consumption and low carbon emissions in today's era of rapid product development with short product life circle, it is crucial to re-innovate and re-invigorate metal forming technologies and enable it to play an even more important role in manufacturing arena. Historically, introducing new kinds of energy fields into the forming process drives the innovative advance and rejuvenating of forming technologies due to the physically interactive mechanisms of energy field and certain material deformation behaviors such as thermal-mechanical coupling effects. In this paper, a classification of energy-aided metal forming processes is orchestrated and presented, and three kinds of energy-assisted metal forming technologies, viz., electrically-assisted forming, ultrasonic vibration assisted forming, and electromagnetic field supported forming, are reviewed and delineated as they are currently receiving a widespread attention with promising application potentials. In this paper, the physical essence and the effects of these introduced energy fields on deformation behavior, process performance, microstructure evolution are elucidated and analyzed. The constitutive modeling of these forming processes is recapitulated, and the newly established energy field assisted metal forming technologies are exemplified and discussed. Based on the advantages and limitations of these unique metal forming processes assisted by additional energy fields, the process capacity and application potentials are unraveled and examined. Finally, from the aspects of exploring physical mechanisms, establishing high-fidelity models, coupling the multiple energy fields, and developing intelligent equipment and realizing these forming processes, the current challenges and future prospects were discussed, summarized and articulated in such a way to present a panorama of the research, development and application of the energy-assisted forming technologies.}, journal={INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE}, author={Li, H. and Peng, L. F. and Meng, B. and Xu, Z. T. and Wang, L. L. and Ngaile, G. and Fu, M. W.}, year={2023}, month={Nov} }
 @article{ngaile_avila_2023, title={Improving Material Formability and Tribological Conditions through Dual-Pressure Tube Hydroforming}, volume={7}, ISSN={["2504-4494"]}, DOI={10.3390/jmmp7040126}, abstractNote={Dual-pressure tube hydroforming (THF) is a tube-forming process that involves applying fluid pressure to a tube’s inner and outer surfaces to achieve deformation. This study investigates the effect of dual-pressure loading paths on material formability and tribological conditions. Specifically, pear-shaped and triangular cross-sectional parts were formed using dual-pressure modes where fluid pressure on the inside of the tubular blank was alternated with pressure on the outside surface of the tubular blank, causing the tube to expand/stretch and contract. During expansion, the tube conformed to the die’s cavity, while during contraction, the contact area between the die and the workpiece reduced, leading to decreased friction stress at the tube–die interface. Additionally, the reversal of pressure loadings caused the tubular blank to buckle, altering the stress state and potentially increasing local shear stress, improving material formability. Dual-pressure THF has demonstrated that the pressure loading paths chosen can substantially influence material formability. Comparing the geometries of parts formed by dual-pressure THF and conventional THF shows a significant increase in the protrusion height of both the pear-shaped and triangular specimens using dual-pressure THF.}, number={4}, journal={JOURNAL OF MANUFACTURING AND MATERIALS PROCESSING}, author={Ngaile, Gracious and Avila, Mauricio}, year={2023}, month={Aug} }
 @book{ngaile_montmitonnet_dohda_2022, place={Baech, Switzerland}, title={Tribology in manufacturing processes : selected peer-reviewed full text papers from the 9th International Conference on Tribology in Manufacturing Processes and Joining by Plastic Deformation (ICTMP2021 : November 24-26, 2021, Chennai, India}, ISBN={9783035717242}, publisher={Scientific.Net, Trans Tech Publications Ltd}, year={2022} }
 @article{pang_ngaile_2022, title={Utilization of Secondary Jet in Cavitation Peening and Cavitation Abrasive Jet Polishing}, volume={13}, ISSN={["2072-666X"]}, DOI={10.3390/mi13010086}, abstractNote={The cavitation peening (CP) and cavitation abrasive jet polishing (CAJP) processes employ a cavitating jet to harden the surface or remove surface irregularities. However, a zero incidence angle between the jet and the surface limits the efficiency of these two processes. This limitation can be improved by introducing a secondary jet. The secondary jet interacts with the main jet, carrying bubbles to the proximity of the workpiece surface and aligning the disordered bubble collapse events. Through characterizing the treated surface of AL6061 in terms of the hardness distribution and surface roughness, it was found out that the secondary jet can increase the hardening intensity by 10%, whereas the material removal rate within a localized region increased by 66%. In addition, employing multiple secondary jets can create a patched pattern of hardness distribution. Another finding is that the hardening effect of the cavitation increases with the processing time at first and is then saturated.}, number={1}, journal={MICROMACHINES}, author={Pang, Hao and Ngaile, Gracious}, year={2022}, month={Jan} }
 @article{ngaile_rodrigues_2021, title={Die Design Architecture for Enhancing Tool Life Via Manipulation of the Elastic Strain Field of the Dies During Extrusion Processes}, volume={143}, ISSN={["1528-8935"]}, DOI={10.1115/1.4048265}, abstractNote={Abstract}, number={3}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Ngaile, Gracious and Rodrigues, Daniel Santiago}, year={2021}, month={Mar} }
 @article{pang_ngaile_2021, title={Modeling of a valve-type low-pressure homogenizer for oil-in-water emulsions}, volume={160}, ISSN={["1873-3204"]}, DOI={10.1016/j.cep.2020.108249}, abstractNote={The geometric configuration of a valve-type homogenizer can have a significant influence on the performance of the emulsification process. Three new variants of low-pressure valve-type homogenizers which differ from one another by how the valve nose profiles and the upstream fluid chamber geometries are constructed were used to study fluid flow characteristics. All the three variants were conceived such that hydrodynamic cavitation can be induced as the oil-in-water emulsion passes through the valve. The computational fluid dynamic (CFD) simulations showed that by changing the valve nose shape from smooth profile to serrated nose profile, a substantially higher strain rate in the gap can be achieved, leading to higher stress on the droplet thus increasing the emulsification efficiency. The CFD simulations have also demonstrated that, incorporating a stagnation bluff in the upstream chamber results in a violence collapse of cavitating bubbles. This in turn promotes turbulence inertial and viscous effects which are essential parameters for enhancing emulsification efficiency. Droplet size analysis of oil-in-water emulsions from the physical experiments found that the serrated nose valve profile and the bluff in the chamber resulted in a mean droplet size of about 95 nm.}, journal={CHEMICAL ENGINEERING AND PROCESSING-PROCESS INTENSIFICATION}, author={Pang, Hao and Ngaile, Gracious}, year={2021}, month={Mar} }
 @article{rahman_ngaile_hassan_2021, title={Non-contact temperature control and stereo digital image correlation for high-temperature testing of miniature tubular specimens}, volume={92}, ISSN={["1089-7623"]}, url={https://doi.org/10.1063/5.0055718}, DOI={10.1063/5.0055718}, abstractNote={Component failures very often occur due to high temperature and multiaxial stress states arising at critical component locations. To imitate such loading conditions, a multiaxial miniature testing system (MMTS) with axial, torsional, and internal pressurization capabilities for high-temperature testing of miniature tubular specimens has been developed. Among many challenges of developing the MMTS, uniform heating, temperature measurement and control, and surface strain measurement on a miniature tubular specimen at high temperatures have significant difficulties. This paper addresses two significant challenges: first, the development of a non-contact temperature control system using infrared thermography to uniformly heat a miniature specimen of 1 mm outer diameter (OD), and second, the development of a stereo digital image correlation (stereo-DIC) setup for strain measurement on the miniature specimen subjected to high temperature. The developed control system maintains the test temperature through a closed feedback loop and employs a fail-safe mechanism to protect the MMTS load frame components against unanticipated temperature rises. The thermocouple wire-size effect on the measured temperature was examined for three different wire sizes: 0.05, 0.25, and 0.5 mm for accurate emissivity determination required for infrared thermography. Emissivities of the specimen surface at different high temperatures were experimentally determined. Inherent error analysis of the developed high-temperature stereo-DIC setup showed acceptable strain measurement uncertainty. The effectiveness of the developed non-contact temperature control system and high-temperature stereo-DIC setup has been verified by performing tensile testing of a 1 mm OD specimen at 500 °C.}, number={11}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Rahman, Farhan and Ngaile, Gracious and Hassan, Tasnim}, year={2021}, month={Nov} }
 @article{rahman_ngaile_hassan_2021, title={Optimized stereo digital image correlation setup for miniature round specimen: framework development and implementation}, volume={144}, ISSN={["1873-0302"]}, DOI={10.1016/j.optlaseng.2021.106555}, abstractNote={For the advancement of micro- and nano-technologies, multiaxial material testing at a small length scale is imperative. A novel multiaxial miniature testing system (MMTS) is under development for testing a tubular specimen of outer diameter (OD) as small as 1 mm. Because of the small specimen size of MMTS, stereo-Digital Image Correlation (DIC) is the preferred strain measurement technique. Although theoretically, stereo-DIC is length-scale independent, the implementation of stereo-DIC, particularly for miniature testing, faces experimental setup related challenges. For this reason, although stereo-DIC is strongly recommended over 2D DIC, researchers are sometimes compelled to use the latter. It is shown in the present study that the experimental setup related difficulties, particularly for miniature round specimen testing, can be overcome by a systematic development of a mathematical framework for stereo-DIC implementation. This framework addresses all setup decisions concerning stereo-DIC implementation, such as selections of stereo angle, speckle size, camera position, camera sensor size, lens focal length, dimensions of camera and lens bodies, calibration grid size, etc., as well as stereo-DIC analysis parameters, such as subset and step size. Besides serving the need of building a stereo-DIC setup for MMTS, since the developed mathematical framework treats all stereo-DIC setup decisions as variables, it can be used to develop an optimized stereo-DIC setup for any application. Examples of two general cases are reported. Since this general framework serves as a tool to solve the stereo-DIC experimental setup related challenges, the developed framework will contribute to the wider adoption of stereo-DIC over 2D DIC.}, journal={OPTICS AND LASERS IN ENGINEERING}, author={Rahman, Farhan and Ngaile, Gracious and Hassan, Tasnim}, year={2021}, month={Sep} }
 @article{li_chan_ngaile_hassan_2020, title={A novel gripper for multiaxial mechanical testing of microtubes at elevated temperatures}, volume={91}, ISSN={["1089-7623"]}, DOI={10.1063/5.0007150}, abstractNote={The success of a microtube hydroforming (μTHF) process heavily depends on the material properties of microtubes, which can reveal the material response under multiaxial stress and influence the formability of hydroformed products. However, these material properties are not well understood because of the limited availability of material testing apparatus that would permit control of axial force and internal pressure simultaneously to mimic realistic μTHF loading. The main purpose of this study is to develop a set of grippers that can transfer required testing loads under fully coupled combinations of axial force and internal pressure. The grippers are designed so that they may be kept at the safe working temperature even when tests are carried out at higher temperatures. The grippers are also designed to fit in a load frame that is integrated in a scanning electron microscope for in situ material testing. The capabilities of the grippers are demonstrated by performing uniaxial and multiaxial material tests on SS304 microtubes with 1 mm outside diameter and 0.15 mm nominal tube wall thickness. The finite element simulations and experimental results show that the designed grippers can firmly hold the specimen and thus enable tensile, compression, torsion, and microtube bulge material tests to be accurately performed.}, number={5}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Li, Lin and Chan, Yu-Chin and Ngaile, Gracious and Hassan, Tasnim}, year={2020}, month={May} }
 @article{pang_ngaile_2020, title={Formulation of SiO2/oil nanolubricant for metal forming using hydrodynamic cavitation}, volume={234}, ISSN={["2041-1975"]}, DOI={10.1177/0954405420933120}, abstractNote={ A novel hydrodynamic cavitation–based dispensing process was developed to disperse SiO2 nanoparticles into the base oil, and the effects of process parameters on dispersity and tribological properties of SiO2/oil nanolubricants were studied using the dynamic laser scattering and ring compression tests. With this process, nanolubricants with fine nanoparticles (139–1240 nm) were formulated. A mean particle size reduction of 78% was achieved in 60 min. This process can be scaled up for mass production with relative ease. The formulated SiO2/oil nanolubricants exhibited better tribological performance over that of base oil. Lubrication mechanisms of the SiO2/oil nanolubricant in metal forming were ascertained through analysis of the dispersity of nanolubricants and characterization of dents appearing on the surface of the deforming material. The study revealed the importance of formulating nanolubricants with specific particle size distribution that relate to the surface morphology of the deforming material. In this study, a nanolubricant with particle size of 3.6 μm exhibited better lubrication on ring samples with dent depth of 4.7 μm, implying that most nanoparticles were encapsulated in the dents facilitating hydrostatic lubrication. }, number={12}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Pang, Hao and Ngaile, Gracious}, year={2020}, month={Oct}, pages={1549–1558} }
 @inbook{kinsey_mori_ngaile_2019, title={Deformation Processes}, ISBN={9789813271012 9789813271036}, DOI={10.1142/9789813271029_0005}, booktitle={Handbook on Manufacturing}, publisher={World Scientific Publishing}, author={Kinsey, Brad L. and Mori, Ken-ichiro and Ngaile, Gracious}, editor={Huang, Y. and Wang, L. and Liang, S.Y.Editors}, year={2019}, pages={277–382} }
 @article{pang_ngaile_2019, title={Development of a non-isothermal forging process for hollow power transmission shafts}, volume={47}, ISSN={["2212-4616"]}, DOI={10.1016/j.jmapro.2019.08.034}, abstractNote={This paper presents a new forging process for hollow power transmission shafts. The key aspect of the process is altering the flow characteristics of the material via differential heating of the tubular stock. The process is conceived in three main stages namely, partially heat the tubular stock with induction heating; upset the heated section of the tube to form a solid section; and finally shape the solid section into a flange or a conical head by further upsetting the workpiece. Parametric study was also carried out for various internal diameter to external diameter (ID/ OD) tube ratios. With the aid of finite element analysis (FEA), the feasibility of the process was evaluated based on formability, forming loads and dimensional accuracy. FEA results showed that it is feasible to produce hollow axle shafts, stepped gear shafts, and pinion gear shafts. Scaled down models of hollow axle shaft and hollow pinion gear shaft were successfully fabricated using the proposed methodology.}, journal={JOURNAL OF MANUFACTURING PROCESSES}, author={Pang, Hao and Ngaile, Gracious}, year={2019}, month={Nov}, pages={22–31} }
 @article{rahman_ngaile_hassan_2019, title={Development of scanning electron microscope-compatible multiaxial miniature testing system}, volume={30}, ISSN={["1361-6501"]}, url={https://doi.org/10.1088/1361-6501/ab1ca6}, DOI={10.1088/1361-6501/ab1ca6}, abstractNote={Knowledge of deformation and failure mechanisms at micro- to nano-length scales is important for the prediction of material behavior as well as the development of new materials with desired properties. In situ multiaxial testing with scanning electron microscopes (SEM) can reveal physical deformation mechanisms under realistic multiaxial loading conditions. Although in situ SEM testing has gained traction in recent years, there is currently no multiaxial in situ SEM testing stage available with axial-torsional loading capabilities which can generally be used in any SEM. In this study, we report the development of a multiaxial miniature testing system (MMTS) with a unique capability for performing axial-torsional testing of a tubular specimen with a 1–2 mm outer diameter, inside most SEMs. The different challenges of developing a multiaxial in situ SEM testing stage, such as small load frame size, appropriate specimen position, high vacuum compatibility of MMTS load frame components, as well as the development of installation accessories, were addressed. A custom SEM stage door was developed for the MMTS load frame. Verification tests have confirmed the successful development of the MMTS for in situ SEM testing. In addition, digital image correlation was used with recorded SEM images during the test to determine the surface strain.}, number={10}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, publisher={IOP Publishing}, author={Rahman, Farhan and Ngaile, Gracious and Hassan, Tasnim}, year={2019}, month={Oct} }
 @article{wang_lowrie_ngaile_fang_2019, title={High injection pressure diesel sprays from a piezoelectric fuel injector}, volume={152}, ISSN={["1359-4311"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85062213294&partnerID=MN8TOARS}, DOI={10.1016/j.applthermaleng.2019.02.095}, abstractNote={Increasing injection pressure can increase combustion efficiency in direct injection (DI) diesel engines attributing to enhanced atomization. In this paper, a high pressure experimental setup was built to generate ultra-high fuel pressure. An intensification unit was used to magnify the pressure by about 10 times. Preliminary testing of the high pressure system produced a peak pressure of about 8700 bar. Due to the pressure limitation of the commercially available diesel fuel system, the maximum pressure tested in a practical piezoelectric fuel injector was 2500 bar. A high-speed imaging technique was used to visualize the fuel injection events and spray images were taken by a high speed camera for quantitative analysis. A Schlieren technique was used to visualize the shock waves generated during spray penetration. The near nozzle early stage spray development was also studied using a long distance microscope and an intensified charge coupled device (ICCD) camera. Results show that the spray penetration velocity increases with the increase of the injection pressure, while a higher injection pressure leads to a later opening of the piezoelectric injector. The spray angle first has a large value, then remains relatively steady throughout the injection process. Schlieren results clearly demonstrate detached shock waves during the spray penetration. The near nozzle results show that during the very early stage the spray penetration is quite linear for different injection pressures and the spray angle also appears to be very large at the beginning, which is consistent with the high-speed imaging results. Both high-speed imaging and near nozzle results were compared with published empirical equations. The high-speed imaging result shows a good match with the linear stage of empirical equation, while near nozzle result shows lower penetration velocity, indicating that there exists a very short “acceleration stage” for spray development at the starting moment of fuel injection.}, journal={APPLIED THERMAL ENGINEERING}, author={Wang, Libing and Lowrie, James and Ngaile, Gracious and Fang, Tiegang}, year={2019}, month={Apr}, pages={807–824} }
 @article{carcaterra_ngaile_2019, title={Investigation of energy storage in bolted joint components and the development of a geometry selection design tool for Belleville washers}, volume={178}, ISSN={["1873-7323"]}, DOI={10.1016/j.engstruct.2018.10.049}, abstractNote={Despite the advantages and widespread use of bolted joints in manufacturing, one major problem is their tendency to loosen, which can ultimately cause the joint to fail. This research evaluates strain energy storage in the Belleville washer, to determine how the washer's design could be modified to counteract relaxation in the bolt, which causes loosening. Finite Element Analysis (FEA) is used to study the strain energy, bolt preload, deflections, and other parameters of various geometric configurations of Belleville washers and shows that the strain energy is not optimally utilized with conventional Belleville washers, which have constant wall thickness. Tapering the Belleville washer reduces its weight significantly, thereby increasing the washer's energy storage capacity. The FEA data are used to develop a tool for helping to design Belleville washer geometry that can prevent bolt loosening. One of the tool's inputs is the bolt deflection relaxation within the acceptable bolt preload window. This work opens further research avenues for analyzing anti-loosening joints from the perspective of the elastic energy stored in the joint and thereby predicting when the joint might fail.}, journal={ENGINEERING STRUCTURES}, author={Carcaterra, Brian and Ngaile, Gracious}, year={2019}, month={Jan}, pages={436–443} }
 @article{pang_ngaile_2018, title={Development of a Non-isothermal Forging Process for Hollow Power Transmission Shafts}, volume={26}, ISSN={2351-9789}, url={http://dx.doi.org/10.1016/J.PROMFG.2018.07.087}, DOI={10.1016/J.PROMFG.2018.07.087}, abstractNote={This paper presents a new forging process for hollow power transmission shafts. The key aspect of the process is altering the flow characteristics of the material via differential heating of the tubular stock. The process is conceived in three main stages namely, partially heat the initial tubular stock with induction heating; upset the heated section of the tube to form a solid section; and finally shape the solid section into a flange or a conical head by further upsetting the workpiece. Parametric study was also carried out for various ID/ OD tube ratios. With the aid of finite element analysis (FEA), the feasibility of the process was evaluated based on formability, forming loads and dimensional accuracy. The FEA results showed that it is feasible to produce hollow axle shafts, stepped gear shafts, and pinion gear shafts.}, journal={Procedia Manufacturing}, publisher={Elsevier BV}, author={Pang, Hao and Ngaile, Gracious}, year={2018}, pages={1509–1516} }
 @article{ngaile_lowrie_2018, title={Punch design for floating based micro-tube hydroforming die assembly}, volume={253}, ISSN={0924-0136}, url={http://dx.doi.org/10.1016/J.JMATPROTEC.2017.10.049}, DOI={10.1016/J.JMATPROTEC.2017.10.049}, abstractNote={Conventional punches used in tube hydroforming (THF) are hollow to facilitate supply of pressurized fluid to the die cavity. The fabrication of hollow micro-punches for micro-THF which can sustain punch loads presents a challenge. This study proposes different types of micro punch designs that can be used in conjunction with floating based micro-tube hydroforming (THF) die set-up. Finite element analysis was carried out to determine the feasibility of the proposed punch design variants followed by Micro-THF experiments. The experiments were carried out to hydroform Y, T, and bulge shaped parts from SS 304 1 mm and 2 mm tubular blanks. The study has demonstrated that notched punches can effectively be used in micro-THF. The major benefit of using notched punches is that, longer micro-punches with the desired strength can be fabricated with ease using electrical discharge machining (EDM).}, journal={Journal of Materials Processing Technology}, publisher={Elsevier BV}, author={Ngaile, Gracious and Lowrie, James}, year={2018}, month={Mar}, pages={168–177} }
 @article{lowrie_ngaile_2018, title={Scalability of conventional tube hydroforming processes from macro to micro/meso}, volume={232}, ISSN={["2041-2975"]}, DOI={10.1177/0954405416683736}, abstractNote={ Due to the increasing demand for small, complex parts, researchers are putting a great deal of effort into applying the metal forming process to the micro and meso world. However, the tube hydroforming process is yet to be fully realized on this small scale because of the difficulties which arise in scaling the conventional tooling to the microscale. This article discusses the difficulties that arise as a result of simply shrinking the traditional hydroforming tools to the microscale. A simple mathematical model is then proposed as a way to help designers determine the limits of the conventional punch with a tapered nose commonly used in tube hydroforming. The model is then validated by performing a finite element analysis of the punch, and the results of the model are discussed in relation to the scaling concepts posed at the beginning of this article. It is determined that as the punch shrinks down, the stresses on the punch rise significantly as a result of changing aspect ratios of the workpiece and the inability to accurately machine very small holes through the punch body. A nonconventional tube hydroforming method may therefore be required to perform micro-tube hydroforming operations, especially on harder materials. }, number={12}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Lowrie, James and Ngaile, Gracious}, year={2018}, month={Oct}, pages={2164–2177} }
 @article{li_ngaile_hassan_2017, title={A Novel Hybrid Heating Method for Mechanical Testing of Miniature Specimens at Elevated Temperature}, volume={5}, ISSN={["2166-0476"]}, DOI={10.1115/1.4035954}, abstractNote={A novel hybrid heating method which combines the conventional electric-resistance specimen heating with microcoil heating of specimen ends to achieve uniform heating over the gauge length is presented. Resistive heating of a miniature specimen develops a parabolic temperature profile with lowest temperature at the grip ends because of the heat loss to the gripper. Coil heating at the specimen ends compensates for this heat loss resulting in uniform temperature distribution over the central segment of the specimen. Thermo-electric finite element simulations were carried out to analyze the transient and steady temperature distribution in miniature specimens followed by experimental validation.}, number={2}, journal={JOURNAL OF MICRO AND NANO-MANUFACTURING}, author={Li, Lin and Ngaile, Gracious and Hassan, Tasnim}, year={2017}, month={Jun} }
 @article{lowrie_ngaile_2017, title={Analytical modeling of hydrodynamic lubrication in a multiple-reduction drawing die}, volume={27}, ISSN={1526-6125}, url={http://dx.doi.org/10.1016/J.JMAPRO.2017.05.003}, DOI={10.1016/J.JMAPRO.2017.05.003}, abstractNote={The hydrodynamic lubrication regime is reported to exist in numerous metal forming applications, such as wire drawing and hydrostatic extrusion, but it is difficult to achieve in the drawing of large diameter rods due to the relatively low drawing speeds common for larger parts. By creating a stable fluid film between the workpiece and the die during the drawing process friction and die wear could be significantly reduced, leading to energy savings, increased achievable reductions, and increased die life. An analytical model of the hydrodynamic drawing process is proposed which considers the geometry of the workpiece and die, as well as, the material properties (including work hardening effects), and (temperature dependent) fluid properties to determine the fluid film thickness over the reduction die. This model is then used to analyze several case studies, including a multiple reduction die with high pressure lubricant supplied to the space between the dies. It is shown that a stable fluid film can be established for low drawing speeds through the combination of a multiple reduction die and a supply of lubricant at high pressures to the inlet of the dies.}, journal={Journal of Manufacturing Processes}, publisher={Elsevier BV}, author={Lowrie, James and Ngaile, Gracious}, year={2017}, month={Jun}, pages={291–303} }
 @article{pang_lowrie_ngaile_2017, title={Development of a Non-isothermal Forging Process for Hollow Axle Shafts}, volume={207}, ISSN={1877-7058}, url={http://dx.doi.org/10.1016/J.PROENG.2017.10.804}, DOI={10.1016/J.PROENG.2017.10.804}, abstractNote={This paper presents a novel non-isothermal forging process for a hollow axle shaft. The process consists of three operations: i) partially heat the initial tubular stock via induction heating, ii) deform the heated section into a solid, rod-like structure by upsetting the workpiece, and iii) shape the new ‘solid’ section into a flange by further upsetting the workpiece. The commercial finite element software Deform 2D is used to simulate the process and evaluate its feasibility. It is determined that the non-isothermal forming process does not require excessive forming loads and can be completed using the presses that are currently employed for axle shaft forging. Furthermore, the strains encountered in the process are reasonable for a hot forming process and the dimensional accuracy of the final product is acceptable. Future optimization of this process may lead to improved strain distributions and forming loads.}, journal={Procedia Engineering}, publisher={Elsevier BV}, author={Pang, Hao and Lowrie, James and Ngaile, Gracious}, year={2017}, pages={454–459} }
 @article{lowrie_pang_ngaile_2017, title={Weight reduction of heavy-duty truck components through hollow geometry and intensive quenching}, volume={28}, ISSN={["1526-6125"]}, DOI={10.1016/j.jmapro.2017.04.021}, abstractNote={Increasing environmental awareness has put pressure on heavy duty truck manufacturers to improve the fuel economy and reduce the emissions of their vehicles. Light weighting efforts are a useful tool in meeting these goals. As a demonstration of how light weighting practices can be applied to the power trains of heavy duty vehicles, this paper focuses on reducing the weight of the rear axle shaft. Two methods are focused on, i) hollow shaft geometry and ii) intensive quenching, as possible avenues to shed mass from the shaft. Load mapping is used to establish a finite element model which can be used to evaluate the light weight designs and techniques proposed in the paper. It is discovered that weight savings of around 26% can be achieved by changing the traditionally solid axle shaft into a hollow shaft. The intensive quenching process is shown to be superior to the oil quenching process in regards to both residual stresses and strength, allowing for material removal accounting for 3% of the shaft weight. Additionally, the compressive residual stresses created on the surface of the part during the intensive quenching process may also serve to slow crack initiation and increase fatigue life. Further optimization of the intensive quenching process may provide additional weight reduction opportunities.}, journal={JOURNAL OF MANUFACTURING PROCESSES}, author={Lowrie, James and Pang, Hao and Ngaile, Gracious}, year={2017}, month={Aug}, pages={523–530} }
 @inproceedings{li_ngaile_hassan_2016, title={A novel hybrid heating method for elevated temperature mechanical testing of miniature specimens}, DOI={10.1115/msec2016-8852}, abstractNote={The lack of robust testing systems to generate uniform elevated temperatures on specimens in material tests is hindering the advancement of small specimen testing technology (SSTT). The purpose of this study is to develop a novel hybrid heating method combining coil heating and electric-resistance specimen heating to uniformly heat micro specimens in material tests. In a hybrid heating process, two heating coils are used to heat the local temperatures on the specimen ends, and electric current is conducted through the specimen to generate Joule heat and compensate the heat transfer effects of natural convection and radiation around the specimen center area. In this way, a highly uniform temperature distribution can be generated on the specimen between the heating coils. In this study, Thermal-Electrical and Transient Thermal FEA simulations are applied to analyze the temperature distributions and preheating times on the micro specimens under coil heating, electric-resistance specimen heating, and hybrid heating respectively. According to the simulation results, it can be concluded that hybrid heating method can provide the ability to generate highly uniform elevated temperature conditions on different micro tubular specimens with short preheating times.}, booktitle={Proceedings of the ASME 11th International Manufacturing Science and Engineering Conference, 2016, vol 1}, author={Li, L. and Ngaile, G. and Hassan, T.}, year={2016} }
 @article{lowrie_ngaile_2016, title={Analytical Modeling of Hydrodynamic Lubrication in a Multiple-Reduction Drawing Die}, volume={5}, ISSN={["2351-9789"]}, DOI={10.1016/j.promfg.2016.08.058}, abstractNote={The hydrodynamic lubrication regime is reported to exist in numerous metal forming applications, such as wire drawing and hydrostatic extrusion, but it has not been achievable in the drawing of large diameter rods due to the relatively low drawing speeds common for larger parts. By creating a stable fluid film between the workpiece and the die during the drawing process friction and die wear could be significantly reduced, leading to energy savings, increased achievable reductions, and increased die life. An analytical model of the hydrodynamic drawing process is proposed which considers the geometry of the workpiece and die, as well as, the material properties (including work hardening effects), and (temperature dependent) fluid properties to determine the fluid film thickness over the reduction die. This model is then used to analyze several case studies, including a proposed multiple reduction die with high pressure lubricant supplied to the space between the dies. It is shown that a stable fluid film can be established for low drawing speeds through the combination of a multiple reduction die and elevated lubricant pressure in the inlet of the dies.}, journal={44TH NORTH AMERICAN MANUFACTURING RESEARCH CONFERENCE, NAMRC 44}, author={Lowrie, James and Ngaile, Gracious}, year={2016}, pages={707–723} }
 @article{lowrie_ngaile_2016, title={New punch design for the elimination of punch ejection load through manipulation of the elastic strain field in the punch nose}, volume={22}, ISSN={["1526-6125"]}, DOI={10.1016/j.jmapro.2016.01.008}, abstractNote={The extreme tribological conditions present during both the forward stroke and the punch ejection stroke of a backward cup extrusion process can adversely affect the quality of the extruded part and diminish the life of the punches. A novel punch design based on the segmentation of the extrusion punch into a main body and a nose cone insert is proposed to reduce or eliminate the pressure between the punch and work piece during the punch removal stroke. This is facilitated by manipulating the elastic strain field at the punch nose. With the aid of the finite element analysis, a parametric study on the segmented elastic punch assembly was carried out to establish optimal conditions and punch design guidelines. Experiments were carried out to determine the effectiveness of the segmented elastic punch. A significant reduction in the punch ejection load was observed along with a reduction in material pickup on the punch and galling on the surface of the part. The elastic deflection of the punch also allowed the researchers to discover that a significant amount of damage could occur during the punch ejection stroke.}, journal={JOURNAL OF MANUFACTURING PROCESSES}, author={Lowrie, James and Ngaile, Gracious}, year={2016}, month={Apr}, pages={49–59} }
 @article{alzahrani_ngaile_2016, title={Preliminary Investigation of the Process Capabilities of Hydroforging}, volume={9}, ISSN={["1996-1944"]}, DOI={10.3390/ma9010040}, abstractNote={Hydroforging is a hybrid forming operation whereby a thick tube is formed to a desired geometry by combining forging and hydroforming principles. Through this process hollow structures with high strength-to-weight ratio can be produced for applications in power transmission systems and other structural components that demands high strength-to-weight ratio. In this process, a thick tube is deformed by pressurized fluid contained within the tube using a multi-purpose punch assembly, which is also used to feed tube material into the die cavity. Fluid pressure inside the thick tube is developed by volume change governed by the movement of the punch assembly. In contrast to the conventional tube hydroforming (THF), the hydroforging process presented in this study does not require external supply of pressurized fluid to the deforming tube. To investigate the capability of hydroforging process, an experimental setup was developed and used to hydroforge various geometries. These geometries included hollow flanged vessels, hexagonal flanged parts, and hollow bevel and spur gears.}, number={1}, journal={MATERIALS}, author={Alzahrani, Bandar and Ngaile, Gracious}, year={2016}, month={Jan} }
 @article{ngaile_wang_gau_2015, title={Challenges in teaching modern manufacturing technologies}, volume={40}, ISSN={0304-3797 1469-5898}, url={http://dx.doi.org/10.1080/03043797.2014.1001814}, DOI={10.1080/03043797.2014.1001814}, abstractNote={Teaching of manufacturing courses for undergraduate engineering students has become a challenge due to industrial globalisation coupled with influx of new innovations, technologies, customer-driven products. This paper discusses development of a modern manufacturing course taught concurrently in three institutions where students collaborate in executing various projects. Lectures are developed to contain materials featuring advanced manufacturing technologies, R&D trends in manufacturing. Pre- and post-surveys were conducted by an external evaluator to assess the impact of the course on increase in student's knowledge of manufacturing; increase students’ preparedness and confidence in effective communication and; increase students’ interest in pursuing additional academic studies and/or a career path in manufacturing and high technology. The surveyed data indicate that the students perceived significant gains in manufacturing knowledge and preparedness in effective communication. The study also shows that implementation of a collaborative course within multiple institutions requires a robust and collective communication platform.}, number={4}, journal={European Journal of Engineering Education}, publisher={Informa UK Limited}, author={Ngaile, Gracious and Wang, Jyhwen and Gau, Jenn-Terng}, year={2015}, month={Jan}, pages={432–449} }
 @article{hummel_ngaile_2015, title={Die-less hydroforming of multi-lobe tubular structures}, volume={229}, ISSN={["2041-1975"]}, DOI={10.1177/0954405414528166}, abstractNote={ The process capability of die-less hydroforming for producing tubular structures of complex geometries was investigated. Multi-lobe tubular structures were chosen for this study as they are capable of carrying higher loads than normal tubes of the same weight. The forming characteristics of three variants of tubular geometry with longitudinal lobes, circumferential lobes, and helical lobes were studied through numerical analysis. The parameters that were investigated were tube wall thickness, tube diameter, tube length-to-diameter ratio, pressure loading paths, and lobe-forming patterns. The finite element analysis showed that the length of the tube does not influence the lobe formation for all three tube variants. The finite element analysis results also demonstrated that lobe wall thinning varies linearly with hydroforming pressure for all multi-lobe tube patterns studied. The strength-to-weight benefit of the tubular structures was also verified through finite element analysis for annealed stainless steel tube sample of 200 mm length, 40 mm diameter, and 2 mm wall thickness. The longitudinal lobed geometry, circumferential lobed geometry, and the helical lobed geometry all were able to carry significantly larger loads as compared to a blank tube of the same mass under compressive, flexural, and torsional loading conditions. To test the viability of the die-less hydroforming process, a longitudinal lobed tubular structure was fabricated and formed. The results from this study indicate that a die-less hydroforming manufacturing process is viable and capable of producing strong, lightweight parts of complex geometries. Besides being capable of producing complex tubular structures, the costs associated with die-less hydroforming are significantly lower due to the absence of a press and dies. However, preparation of tubular blanks requires reliable weld seams and rolling operations. }, number={3}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Hummel, Steve and Ngaile, Gracious}, year={2015}, month={Mar}, pages={435–452} }
 @article{lowrie_ngaile_2015, title={Novel extrusion punch design for elimination of punch ejection load and enhanced lubrication}, volume={5}, ISSN={2213-8463}, url={http://dx.doi.org/10.1016/J.MFGLET.2015.04.003}, DOI={10.1016/J.MFGLET.2015.04.003}, abstractNote={The extreme surface expansion and pressures observed during the backward cup extrusion process can adversely affect the surface of the work-piece and diminish the life of the punches. To reduce or eliminate punch ejection load and galling commonly encountered in the backward extrusion process, a punch system composed of a main body punch and a punch nose insert is proposed. The nose insert is both an elastic strain field generator to facilitate punch removal and a gateway for lubricant transport. The preliminary test results have shown a marked reduction in both galling and the load required to eject the punch.}, journal={Manufacturing Letters}, publisher={Elsevier BV}, author={Lowrie, James and Ngaile, Gracious}, year={2015}, month={Aug}, pages={12–16} }
 @inproceedings{lowrie_ngaile_2015, title={Novel extrusion punch design for improved lubrication and punch ejection}, DOI={10.1115/msec2015-9496}, abstractNote={The extreme surface expansion and pressures observed during the backward extrusion process can have adverse effects on the surface of the workpiece and the life of the punches used in the process. After the forming process is complete, the ejection of the punch can further damage the part surface and reduce tool life because the pressures on the land of the punch remain quite high. The research presented in this investigation aims to reduce or eliminate the galling and surface damage for the backward extrusion process by creating a new class of punch which can create the opportunity for lubrication transport to the area underneath the punch and lessen the damaging conditions during punch ejection. The proposed tooling divides the traditional punch into two pieces, a hollow punch body and an insert with micro channels for lubrication transport. The tooling was developed and used in a series of tests to determine the benefits of the new punch. Preliminary data shows that the extrusion loads for proposed punch are similar to the conventional punch, but the surface finish is significantly enhanced using the modified punch design and the galling is minimized. Furthermore, there is a marked reduction in the ejection load required to remove the punch from the part after forming.}, booktitle={Proceedings of the ASME 10th International Manufacturing Science and Engineering Conference, 2015, vol 1}, author={Lowrie, J. and Ngaile, G.}, year={2015} }
 @article{alzahrani_ngaile_2014, title={Analytical and Numerical Modeling of Thick Tube Hydroforging}, volume={81}, ISSN={1877-7058}, url={http://dx.doi.org/10.1016/J.PROENG.2014.10.312}, DOI={10.1016/J.PROENG.2014.10.312}, abstractNote={Hydroforging is a hybrid forming operation whereby a thick tube is formed to a desired geometry by combining forging and hydroforming processes. Through this process hollow structures with high strength-to-weight ratio can be produced for applications in power transmission systems, etc. In this process, a thick tube is deformed by pressurized fluid contained within the tube using a multi-purpose punch assembly, which is also used to feed tube material into the die cavity. An analytical model for determining pressure-feed loading paths is formulated for the hydroforging process. The model is derived based of plasticity theory and deformed shape evolution. Stepwise solution schemes are used to calculate instantaneous pressure, material feed, stresses, strains, and other geometrical parameters. The derived analytical model can be used for preliminary process design before embarking in extensive FE simulations. The model is also ideal for rapid establishment of loading paths for different geometrical configurations. Thus, time spent in trial-and-error finite element simulations carried out to determine optimal loading path for a specific part can be reduced significantly.}, journal={Procedia Engineering}, publisher={Elsevier BV}, author={Alzahrani, Bandar and Ngaile, Gracious}, year={2014}, pages={2223–2229} }
 @article{ngaile_lohr_lowrie_modlin_2014, title={Development of chemically produced hydrogen energy-based impact bonding process for dissimilar metals}, volume={16}, ISSN={["2212-4616"]}, DOI={10.1016/j.jmapro.2014.07.005}, abstractNote={There has been a growing demand in the fabrication of dissimilar metal parts for application in the automotive, aerospace, defense, chemical and nuclear industries. Welding of dissimilar materials can be accomplished via impact welding, which can minimize the formation of a continuous inter-metallic phase, while chemically bonding dissimilar metals. This paper discusses an innovative technique for bonding dissimilar metals by chemically produced hydrogen energy by reacting aluminum powder and water. Experiments were carried out to study impact bond characteristics using copper and stainless steel cylindrical billets. The influence of nosed flyer billet angle and billet mass on bonding characteristics were studied. The test results have demonstrated that the nosed flyer billet angle has significant influence on wavy bond patterns at the interface. Among the three flyer billet nose angles of 9°, 12° and 15°, the billets with a flyer angle of 15° resulted in a complete wave morphological pattern along the whole sample cross-section. This study shows the potential of developing a cost effective system/machinery where discrete metal parts can be bonded at near net shape.}, number={4}, journal={JOURNAL OF MANUFACTURING PROCESSES}, author={Ngaile, Gracious and Lohr, Peter and Lowrie, James and Modlin, Rhyne}, year={2014}, month={Oct}, pages={518–526} }
 @inproceedings{lowrie_ngaile_2014, title={Enhancement of tribological performance via innovative tooling design for extrusion processes}, DOI={10.1115/msec2014-4170}, abstractNote={Due to the expense and negative environmental impact of commonly used conversion coating type lubricants a new method for reducing the friction in the extrusion process is desired. This paper investigates the possibility of modifying the die set to better the tribological conditions and reduce friction in the extrusion process. A novel design of extrusion tooling is proposed, in which the die set is segmented into three separate pieces, a punch, a wall die, and a bottom die. Additionally, the wall die is given the freedom to move along the axis of the punch and a high pressure lubricant is supplied to the interface between the wall and bottom dies. Preliminary tests of the segmented tooling show that, if the tribological conditions are severe enough, the forming load will decrease in comparison to a conventional extrusion system.}, booktitle={Proceedings of the ASME 9th International Manufacturing Science and Engineering Conference, 2014, vol 2}, author={Lowrie, J. B. and Ngaile, G.}, year={2014} }
 @article{ngaile_lohr_modlin_lowrie_2014, title={High-velocity impact bonding of dissimilar metals by chemically produced hydrogen energy}, volume={2}, ISSN={2213-8463}, url={http://dx.doi.org/10.1016/J.MFGLET.2014.01.003}, DOI={10.1016/J.MFGLET.2014.01.003}, abstractNote={There has been a growing demand in the fabrication of dissimilar metal parts for application in the automotive, aerospace, defense, chemical and nuclear industries. Welding of dissimilar materials can be accomplished via impact welding, which can minimize the formation of a continuous inter-metallic phase, while chemically bonding dissimilar metals. This paper discusses an innovative technique for bonding dissimilar metals by chemically produced hydrogen energy by reacting aluminum powder and water. Experiments were carried out to bond copper and stainless steel billets. Preliminary test results show the potential of this technique for near-net-shape impact bonding of discrete parts.}, number={2}, journal={Manufacturing Letters}, publisher={Elsevier BV}, author={Ngaile, Gracious and Lohr, Peter and Modlin, Rhyne and Lowrie, James}, year={2014}, month={Apr}, pages={40–43} }
 @article{ngaile_kinsey_kapoor_2013, title={Editorial}, volume={15}, ISSN={1526-6125}, url={http://dx.doi.org/10.1016/J.JMAPRO.2013.02.005}, DOI={10.1016/J.JMAPRO.2013.02.005}, number={2}, journal={Journal of Manufacturing Processes}, publisher={Elsevier BV}, author={Ngaile, Gracious and Kinsey, Brad L. and Kapoor, Shiv G.}, year={2013}, month={Apr}, pages={181–182} }
 @inbook{ngaile_2013, place={Boston, MA}, title={Hydroforming Tribology}, ISBN={9780387928968 9780387928975}, url={http://dx.doi.org/10.1007/978-0-387-92897-5_1067}, DOI={10.1007/978-0-387-92897-5_1067}, booktitle={Encyclopedia of Tribology}, publisher={Springer US}, author={Ngaile, Gracious}, year={2013}, pages={1765–1774} }
 @article{alzahrani_ngaile_yang_2013, title={Part 1: Analytical modeling of symmetric multi-nose tube hydroforming}, volume={15}, ISSN={1526-6125}, url={http://dx.doi.org/10.1016/J.JMAPRO.2013.01.004}, DOI={10.1016/J.JMAPRO.2013.01.004}, abstractNote={Part 1 of this series of papers presents an analytical model for a multi-nose tube hydroforming process based on a mechanistic approach. In this process, the tube is surrounded by a number of evenly distributed circular dies. The model was established based on equilibrium conditions, yielding criteria, geometrical relationships, and a volume constancy condition. The system of equations was derived and solved for various process parameters. The model validation was performed using finite element analysis and experiments. The model has the ability to predict process parameters such as stresses, strains, internal pressure, geometry variables, and thinning rate distribution. The model could be applied to regular planar tube hydroforming of polygonal shapes such as square, pentagon, or octagon. Details for establishing governing relationships for polygonal shape hydroforming from the multi-nose analytical model are given in Part 2 of this series of papers.}, number={2}, journal={Journal of Manufacturing Processes}, publisher={Elsevier BV}, author={Alzahrani, Bandar and Ngaile, Gracious and Yang, Chen}, year={2013}, month={Apr}, pages={273–286} }
 @article{alzahrani_ngaile_2013, title={Part 2: Analytical modeling of regular planar polygon tube hydroforming as a special case of symmetric multi-nose tube hydroforming}, volume={15}, ISSN={1526-6125}, url={http://dx.doi.org/10.1016/J.JMAPRO.2013.01.002}, DOI={10.1016/J.JMAPRO.2013.01.002}, abstractNote={Part 2 of this series of papers presents an analytical model for regular planar polygon tube hydroforming (THF) as a special case of the analytical model for symmetric multi-nose tube hydroforming. The governing equations derived for multi-nose THF in Part 1 were evaluated by taking the limit of die geometric variables, resulting in a new set of governing equations for regular polygon THF. The model was validated using finite element analysis and a THF experiment, where good agreement was obtained. The model is able to predict field variables such as stresses and strain distribution, thinning rate distribution, and deformed shape at a particular pressure.}, number={2}, journal={Journal of Manufacturing Processes}, publisher={Elsevier BV}, author={Alzahrani, Bandar and Ngaile, Gracious}, year={2013}, month={Apr}, pages={287–297} }
 @article{ngaile_welch_2012, title={Optimal load path input in tube hydroforming machines}, volume={226}, ISSN={["0954-4054"]}, DOI={10.1177/0954405411428421}, abstractNote={ Tube hydroforming (THF) is a metal-forming process in which a tube is plastically deformed to conform to the die cavity by injecting a pressurized fluid inside the tube. To ensure that enough material is supplied to the die cavity, the tube ends are usually pushed towards the die cavity to feed the material. To successfully hydroform a part, good coordination between fluid pressure and material feed is necessary. This pressure–material displacement relationship is known as a load path. The load path is specific to a part, and it is entered in a THF machine as pressure versus time and displacement versus time input variables. A methodology of decomposing the pressure–displacement loading path as a time variable to obtain pressure–time and displacement–time variants that are optimal for the THF machine system is presented. The THF experiments for double T-shaped parts are carried out to demonstrate that using different pressure–time and displacement–time variants can result in a significant increase in the maximum power required by the THF machine actuators. }, number={B4}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Ngaile, G. and Welch, G.}, year={2012}, month={Apr}, pages={694–707} }
 @article{ngaile_kinsey_2011, title={Advances in Plastic Forming of Metals}, volume={133}, ISSN={["1087-1357"]}, DOI={10.1115/1.4005461}, abstractNote={Metal forming through plastic deformation is one of the most efficient, robust, and economical manufacturing processes available to produce products for unique applications at various length scales. To assist manufacturers address ever increasing and often seemingly conflicting demands (e.g., lightweight products with increased structural rigidity), researchers from around the world are actively engaged in efforts to continuously improve the processes. In this special issue, 28 research papers and four technical briefs are presented to highlight such efforts. These submissions are from researchers in academia, industry, and national laboratories from 12 countries and include experimental, numerical, and analytical efforts. The goal of this special issue is to present the latest developments, trends, and research solutions pertaining to plastic forming of metals to aid both industry and researchers alike. Highlights of the papers categorized by topic areas are given below.}, number={6}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Ngaile, Gracious and Kinsey, Brad}, year={2011}, month={Dec} }
 @article{ghosh_deshmukh_ngaile_2011, title={Database for real-time loading path prediction for tube hydroforming using multidimensional cubic spline interpolation}, volume={211}, ISSN={["0924-0136"]}, DOI={10.1016/j.jmatprotec.2010.09.012}, abstractNote={Tube hydroforming (THF) is a metal-forming process that uses a pressurized fluid in place of a hard tool to plastically deform a given tube into a desired shape. In addition to the internal pressure, the tube material is fed axially toward the die cavity. This process has various applications in the automotive, aerospace, and bicycle industries. Accurate coordination of the fluid pressure and axial feed, collectively referred to as a loading path, is critical to THF. Workable loading paths are currently determined by trial and error, which can be time consuming. This study discusses an innovative technique for developing an interactive, real-time database that would be able to predict loading paths for many THF components and hence reduce the computational time required. By classifying most of the commercial THF parts into families, parameters such as material properties, part geometry, and tribological factors were simulated by category and stored in the database. Multidimensional cubic spline interpolation was implemented to enable an end user to request from the database a loading path for a wide range of conditions. Test results from the database for different THF families were shown to approximate the simulated results. In addition to reducing the computation time, the use of interpolation techniques eliminates the need for carrying out multiple simulations for similar THF parts.}, number={1}, journal={JOURNAL OF MATERIALS PROCESSING TECHNOLOGY}, author={Ghosh, Angshuman and Deshmukh, Karan and Ngaile, Gracious}, year={2011}, month={Jan}, pages={150–166} }
 @inproceedings{ghosh_deshmukh_ngaile_2011, title={Database for real-time loading path prediction for tube hydroforming using multidimensional cubic spline interpolation}, DOI={10.1115/msec2010-34099}, abstractNote={Tube Hydroforming (THF) is a metal-forming process that uses a pressurized fluid in place of a hard tool to plastically deform a given tube into a desired shape. In addition to the internal pressure, the tube material is fed axially toward the die cavity. This process has various applications in the automotive, aerospace, and bicycle industries. Accurate coordination of the fluid pressure and axial feed, collectively referred to as a loading path, is critical to THF. Workable loading paths are currently determined by trial and error, which can be time consuming. This paper discusses an innovative technique for developing an interactive, real-time database that would be able to predict loading paths for typical classes of THF products and hence, reduce the computational time required. By classifying most of the commercial THF parts into families, parameters such as material properties, part geometry, and tribological factors were simulated by category and stored in the database. Multidimensional cubic spline interpolation was implemented to enable an end user to request from the database a loading path for a wide range of conditions. Test results from the database for different THF families were shown to approximate the simulated results. In addition, by reducing the computation time, the use of interpolation techniques eliminates the need for carrying out multiple simulations for similar THF parts.}, booktitle={Proceedings of the ASME International Manufacturing Science and Engineering Conference 2010, vol 1}, author={Ghosh, A. and Deshmukh, K. and Ngaile, G.}, year={2011}, pages={609–618} }
 @article{bunget_ngaile_2011, title={Influence of ultrasonic vibration on micro-extrusion}, volume={51}, ISSN={["1874-9968"]}, DOI={10.1016/j.ultras.2011.01.001}, abstractNote={Micro-forming is a miniaturization technology with great potential for high productivity. Some technical challenges, however, need to be addressed before micro-forming becomes a commercially viable manufacturing process. These challenges include severe tribological conditions, difficulty in achieving desired tolerances, and short tool-life due to inability of available die materials to withstand the forces exerted on miniature dies and punches. Some of these problems can be mitigated using ultrasonic technology. The principal objectives of this work were to investigate the possibility of applying ultrasonic vibrations in the micro-forming process, to design a set of tooling for ultrasonic micro-extrusion and to observe experimentally how ultrasonic oscillations influences the forming load and the surface finish. The test results showed a significant drop on the forming load when ultrasonic vibrations were imposed, and also a significant improvement in the surface of the micro-formed parts. Based on the preliminary test results, the study demonstrated high potential for using ultrasonic oscillations as a way to overcome the difficulties brought by the miniaturization.}, number={5}, journal={ULTRASONICS}, author={Bunget, Cristina and Ngaile, Gracious}, year={2011}, month={Jul}, pages={606–616} }
 @article{yang_ngaile_2011, title={Preform Design for Tube Hydroforming Based on Wrinkle Formation}, volume={133}, ISSN={["1528-8935"]}, DOI={10.1115/1.4005118}, abstractNote={A two-stage preforming process based on wrinkle formation is developed for the tube hydroforming process to accumulate material in the forming zone, thus reducing the thinning rate and improving the formability. In preforming stage one, the wrinkle onset is triggered with limited axial compression. In preforming stage two, the wrinkle grows stably and uniformly to a certain height. Then, the preformed wrinkles are flattened to conform to the die shape in the final tube hydroforming process. An analytical model based on bifurcation analysis and postbuckling analysis of the elastic-plastic circular cylinder under axial compression and internal pressure is used to study the wrinkle evolution characteristics in tube hydroforming. The analytical results offer valuable guidance to the process design of the two-stage preforming process. To validate this methodology, preform die sets for two axisymmetric parts were designed and tube hydroforming experiments were carried out on SS 304 tubing. Through this methodology, an expansion rate of 71% was achieved.}, number={6}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Yang, Chen and Ngaile, Gracious}, year={2011}, month={Dec} }
 @article{ngaile_yang_kilonzo_2011, title={Real-Time Friction Error Compensation in Tube Hydroforming Process Control}, volume={133}, ISSN={["1087-1357"]}, DOI={10.1115/1.4005430}, abstractNote={Tube hydroforming (THF) is a metal-forming process that uses a pressurized fluid in place of a hard tool to plastically deform a given tube into a desired shape. In addition to the internal pressure, the tube material is fed axially toward the die cavity. One of the challenges in THF is the nonlinear and varying friction conditions at the tube-tool interface, which make it difficult to establish accurate loading paths (pressure versus feed) for THF. A THF process control model that can compensate for the loading path deviation due to frictional errors in tube hydroforming is proposed. In the proposed model, an algorithm and a software platform have been developed such that the sensed forming load from a THF machine is mapped to a database containing a set of loading paths that correspond to different friction conditions for a specific part. A real-time friction error compensation is then carried out by readjusting the loading path as the THF process progresses. This scheme reduces part failures that would normally occur due to variability in friction conditions. The implementation and experimental verification of the proposed model is discussed.}, number={6}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Ngaile, Gracious and Yang, Chen and Kilonzo, Obadiah}, year={2011}, month={Dec} }
 @article{yang_ngaile_2010, title={Preform design for forging and extrusion processes based on geometrical resemblance}, volume={224}, ISSN={["2041-2975"]}, DOI={10.1243/09544054jem1799}, abstractNote={ Preform design in multi-stage forging processes is critical to ensure the production of defect-free parts. Moreover, owing to the geometry and material-flow complexities in forging processes, finding the optimal preform shapes could be difficult and time consuming. This paper proposes an efficient preform design methodology based on geometrical resemblance, which requires several finite element analysis simulation iterations to obtain a good preform shape. The initial and subsequent simulations are carried out by constructing a slightly larger part that geometrically resembles the desired part. Initial finite element analysis simulation of the larger part is performed with a reasonably guessed preform shape, whose forming defects or flash formation would be corrected in subsequent steps. Then a series of intermediate parts of similar shape and between the largest part and the desired part in size are constructed. The undeformed shape corresponding to an intermediate part can be obtained by backwards tracing of material flow from the simulation results of the larger part. This undeformed shape is then taken as the preform shape of the intermediate part. The procedure is repeated until the intermediate part is geometrically close to the desired part, which leads to the preform shape. In order to verify this preform-design methodology, several case studies on forging and extrusion processes have been carried out. The methodology has been shown to be computationally efficient, requiring as few as three finite element iterations to obtain a good preform shape. }, number={B9}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Yang, C. and Ngaile, G.}, year={2010}, pages={1409–1423} }
 @article{ngaile_yang_2009, title={Analytical Model for the Characterization of the Guiding Zone Tribotest for Tube Hydroforming}, volume={131}, ISSN={["1528-8935"]}, DOI={10.1115/1.3090888}, abstractNote={Common part failures in tube hydroforming include wrinkling, premature fracture, and unacceptable part surface quality. Some of these failures are attributed to the inability to optimize tribological conditions. There has been an increasing demand for the development of effective lubricants for tube hydroforming due to widespread application of this process. This paper presents an analytical model of the guiding zone tribotest commonly used to evaluate lubricant performance for tube hydroforming. Through a mechanistic approach, a closed-form solution for the field variables contact pressure, effective stress/strain, longitudinal stress/strain, and hoop stress can be computed. The analytical model was validated by the finite element method. In addition to determining friction coefficient, the expression for local state of stress and strain on the tube provides an opportunity for in-depth study of the behavior of lubricant and associated lubrication mechanisms. The model can aid as a quick tool for iterating geometric variables in the design of a guiding zone, which is an integral part of tube hydroforming tooling.}, number={2}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Ngaile, Gracious and Yang, Chen}, year={2009}, month={Apr} }
 @article{ngaile_yang_2009, title={Application of Finite Element Method in Metal forming Tribology}, volume={37}, journal={Transaction of the North American Manufacturing Research Institution of SME}, author={Ngaile, Gracious and Yang, Chen}, year={2009}, pages={379–386} }
 @article{ngaile_yang_2008, title={Analytical model for characterizing the pear-shaped tribotest for tube hydroforming. Part 1}, volume={222}, ISSN={["0954-4054"]}, DOI={10.1243/09544054JEM1057}, abstractNote={ An analytical model to characterize the pear-shaped tribotest is presented. In this test, a tubular specimen is pressurized, forcing the material to flow towards the apex of a pear-shaped die. The height of the pear-shaped tube is a function of the magnitude of friction stress at the tube—die interface. Through a mechanistic approach, a closed-form solution for field variables die—tube contact pressure, effective stress/strain, longitudinal stress/strain, and hoop stress/strain can be computed as a function of input pressure loading. The model has been validated by finite element analysis. The closed-form solution can be used rapidly to establish the calibration curves for determination of friction coefficient in the pear-shaped tribotest. Of equal importance, the analytical model can be used to optimize both process and die geometric variables to suit specific needs such as die wear studies through monitoring local interface pressure loading, types of material to be tested, tube sizes, and so on. Details on the applications of the developed analytical model can be found in Part 2 of this paper. }, number={7}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Ngaile, G. and Yang, C.}, year={2008}, month={Jul}, pages={849–863} }
 @article{yang_ngaile_2008, title={Analytical model for planar tube hydroforming: Prediction of formed shape, corner fill, wall thinning, and forming pressure}, volume={50}, ISSN={["0020-7403"]}, DOI={10.1016/j.ijmecsci.2008.05.006}, abstractNote={An analytical model for planar tube hydroforming based on deformation theory has been developed. This analytical model can be used to predict hydroformed shape, corner fill, wall thinning, and forming pressure. As the model is based on a mechanistic approach with bending effects included, local strain and stress distribution across the wall thickness can be determined. This includes strain and stress distributions for the outer layer, inside layer, and middle layer. The model is validated using finite element analysis and tube hydroforming experiments on irregular triangular, irregular quadrilateral, and pentagonal hydroformed shapes.}, number={8}, journal={INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES}, author={Yang, Chen and Ngaile, Gracious}, year={2008}, month={Aug}, pages={1263–1279} }
 @article{ngaille_yang_2008, title={Applications of analytical model for characterizing the pear-shaped tribotest for tube hydroforming. Part 2}, volume={222}, ISSN={["2041-2975"]}, DOI={10.1243/09544054JEM1058}, abstractNote={ Applications of the analytical model for characterizing the pear-shaped tribotest are presented. Details on the derivations of the analytical model can be found in Part 1 of this paper (published in Proceedings of the Institution of Mechanical Engineers, Journal of Engineering Manufacture, 2008, Vol. 222). In this test, a tubular specimen is pressurized, forcing the material to flow towards the apex of a pear-shaped die. The height of the pear-shaped tube is a function of the magnitude of friction stress at the tube—die interface. The analytical model is used rapidly to establish the calibration curves for determination of friction coefficient in the pear-shaped tribotest. The model is also used to optimize both process and die geometric variables to suit specific tribological needs. The paper presents examples of how optimal pear-shape tribotest conditions pertaining to die geometry, tubular material properties, tube sizes, and pressure loading can be achieved via this model. }, number={7}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Ngaille, G. and Yang, C.}, year={2008}, month={Jul}, pages={865–873} }
 @article{ngaile_bunget_2008, title={Influence of Ultrasonic Vibration on Microforming}, volume={36}, journal={Transaction of the North American Manufacturing Research Institution of SME}, author={Ngaile, Gracious and Bunget, Cristina}, year={2008}, pages={137–144} }
 @article{ngaile_botz_2008, title={Performance of graphite and boron-nitride-silicone based lubricants and associated lubrication mechanisms in warm forging of aluminum}, volume={130}, ISSN={["0742-4787"]}, DOI={10.1115/1.2805432}, abstractNote={Although water/oil-graphite emulsions are widely used in warm forging processes, they carry environmental concerns. In an attempt to replace graphite-based lubricants in warm forging of aluminum alloys, two variants of boron-nitride-silicone lubricants were formulated. The two variants were made by dispersing boron nitride powder in polydimethyl siloxane oil at concentrations of 1% and 8%. The formulated lubricants were initially tested for their thermal degradation characteristics using a thermogravimetric analyzer and compared to the thermal degradation behavior of graphite and silicone oil lubricants. Ring compression tests were then carried out at 260°C and 370°C. Boron-nitride-silicone lubricant variants did not show significant difference in performance as die temperature was increased from 260°Cto370°C. This is in contrast to graphite, which performed much better at 260°C than at 370°C, due to thermal oxidation. On the other hand, silicone oil exhibited the worst performance at 260°C and the best performance at 370°C. In both boron nitride lubricant variants, the polydimethyl siloxane facilitated hydrostatic/hydrodynamic lubrication at 260°C, with boron nitride acting as a barrier film that reduced friction. However, the lubrication mechanisms changed at 370°C, where the depolymerization of polydimethyl siloxane led to formation of silica due to thermal oxidation. Silica, together with boron nitride, acted as a film barrier with low shear strength. The dual lubrication mechanisms make boron-nitride-silicone lubricants suitable for a wide range of aluminum forging temperatures.}, number={2}, journal={JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME}, author={Ngaile, Gracious and Botz, Frank}, year={2008}, month={Apr} }
 @inbook{ngaile_2008, place={Cambridge, England}, title={Tribological aspects in hydroforming}, ISBN={9781845693282}, url={http://dx.doi.org/10.1533/9781845694418.1.144}, DOI={10.1533/9781845694418.1.144}, booktitle={Hydroforming for Advanced Manufacturing}, publisher={Woodhead Publishing/Elsevier}, author={Ngaile, Gracious}, editor={Koç, M.Editor}, year={2008}, pages={144–178} }
 @book{bunget_ngaile_2008, title={Ultrasonic microforming}, ISBN={9783639000559}, publisher={Saarbrucken: VDM Verlag Dr. Muller}, author={Bunget, C. J. and Ngaile, G.}, year={2008} }
 @article{ngaile_saiki_ruan_marumo_2007, title={A tribo-testing method for high performance cold forging lubricants}, volume={262}, DOI={10.1016/j.wear.2006.08.009}, abstractNote={A tribo-testing method based on inducing different deformation patterns at the tool–workpiece interface developed by the authors was used in rating the performance of high quality lubricants. Dies which can induce different levels of maximum surface expansion under localized rod drawing set up were used. The maximum local surface expansion induced ranged from 20 to 500%. The basic feature for this test lies under the assumption that the surface expansion is proportional to the lubricant thinning and breakdown at the tool–workpiece interface. The experimental set up is coupled with die heating facilities used to raise the temperature at the interface so that the influence of temperature on the performance of the lubricant is studied. The performance of several coating-based lubricants was studies under this method. One of the goals of screening the lubricant was to identify possible lubricant candidates for replacing zinc phosphate coating based lubricant for medium forging processes. The results have demonstrated that, the effectiveness of the lubricants varies considerably with changes in the maximum local surface expansion induced at the interface and the change in the interface temperature. Of the six lubricants studied, two lubricants based on calcium and sodium soap were found to be at the same performance level as the conventional zinc phosphate coating + metal soap.}, number={5-6}, journal={Wear}, author={Ngaile, G. and Saiki, H. and Ruan, L. Q. and Marumo, Y.}, year={2007}, pages={684–692} }
 @article{gariety_ngaile_altan_2007, title={Evaluation of new cold forging lubricants without zinc phosphate precoat}, volume={47}, ISSN={["0890-6955"]}, DOI={10.1016/j.ijmachtools.2006.04.016}, abstractNote={Zinc phosphate coatings plus metal soap lubrication system is required in nearly all steel cold forging operations. However, the chemical byproducts of this lubricant system are difficult to dispose of and have a negative environmental impact. In order to replace zinc phosphate based lubricants partially or completely, candidate lubricants were sought from lubricant manufacturers worldwide. The performance evaluation of these lubricants was conducted using the double cup backward extrusion test developed at the Engineering Research Center for Net Shape Manufacturing (ERC/NSM). With the use of the commercial FEM code DEFORM, friction factor calibration curves, i.e. cup height ratio vs. punch stroke, were established for different friction factor values. By matching the cup height ratio and the punch stroke from experiment to that obtained from FE simulations, the friction factor of the lubricants was determined. Three lubricants; namely, MEC Homat, Daido AquaLub, and MCI Z-Coat, were found to perform comparable to or better than zinc phosphate.}, number={3-4}, journal={INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE}, author={Gariety, Mark and Ngaile, Gracious and Altan, Taylan}, year={2007}, month={Mar}, pages={673–681} }
 @article{ngaile_cochran_stark_2007, title={Formulation of polymer-based lubricant for metal forming}, volume={221}, ISSN={0954-4054 2041-2975}, url={http://dx.doi.org/10.1243/09544054jem659}, DOI={10.1243/09544054JEM659}, abstractNote={ A new metal forming lubricant based on polymeric materials has been developed. The lubricant has been developed through emulsion copolymerization. Copolymers with the common composition of stearyl methacrylate and 2-hydroxyethyl methacrylate acid phosphate were made with three secondary polymers: methyl methacrylate, butyl acrylate, and 2-hydroxyethyl methacrylate. The performance of the developed lubricant was evaluated using the ring compression and twist compression tests. The performance of the polymeric lubricant was compared against a zinc-phosphate-coating-based lubricant, commonly used in forging, and three other commercial lubricants. The polymeric lubricant exhibited at least equal performance in all tests conducted at room temperature. Preliminary test results show that the developed lubricant can be used effectively for non-severe deformation processes such as cold heading and extrusion processes with low surface expansions. }, number={4}, journal={Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture}, publisher={SAGE Publications}, author={Ngaile, G and Cochran, J and Stark, D}, year={2007}, month={Apr}, pages={559–568} }
 @article{ngaile_stark_cochran_2006, title={Development of Polymeric Based Lubricant for Cold Forging Processes}, volume={34}, journal={Transaction of the North American Manufacturing Research Institution of SME}, author={Ngaile, Gracious and Stark, David and Cochran, Joseph}, year={2006}, pages={563–570} }
 @article{ngaile_gariety_altan_2006, title={Enhancing tribological conditions in tube hydroforming by using textured tubes}, volume={128}, ISSN={["0742-4787"]}, DOI={10.1115/1.2197849}, abstractNote={The effects of textured tubes on the tribological performance in tube hydroforming (THF) are discussed. Textured surfaces, namely sand blasted, knurled, electrical discharge machined (EDM), and as rolled surfaces, were tested under various interface pressure conditions. Sand blasted textured tubes were found to have the best tribological performance. The study has demonstrated that the increase in the interface pressure between the tube and the die can result in either lower or higher interface friction depending on the surface texture conditions. The study has also shown that different surface texture treatment methods can alter the hardness of the tube surface with significant influence on the tribological performance.}, number={3}, journal={JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME}, author={Ngaile, Gracious and Gariety, Mark and Altan, Taylan}, year={2006}, month={Jul}, pages={674–676} }
 @article{altan_jain_shi_ngaile_pax_harman_homan_2006, title={Progressive die sequence design for deep drawing round cups using finite element analysis}, volume={128}, ISSN={["1528-8935"]}, DOI={10.1115/1.2039942}, abstractNote={A methodology for progressive die sequence design for forming round cups using finite element method (FEM) based simulations is discussed. The process sequence design developed was applied to forming of an automotive part and was compared with the design obtained from past experience. The methodology proposed in this paper has shown that the integration of design experience and FEM simulations can enhance the robustness of the procedure for die design sequence and reduces the die development cost considerably.}, number={1}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Altan, T and Jain, NT and Shi, XX and Ngaile, G and Pax, B and Harman, B and Homan, G}, year={2006}, month={Feb}, pages={366–369} }
 @book{altan_ngaile_shen_2005, place={Materials Park, OH}, title={Cold and Hot Metal Forging: Fundamentals and Applications}, ISBN={978-0-87170-805}, publisher={ASM International}, author={Altan, Taylan and Ngaile, Gracious and Shen, Ganshu}, year={2005} }
 @article{chandrasekharan_palaniswamy_jain_ngaile_altan_2005, title={Evaluation of stamping lubricants at various temperature levels using the ironing test}, volume={45}, ISSN={["1879-2170"]}, DOI={10.1016/j.ijmachtools.2004.09.014}, abstractNote={Lubricants are employed in stamping operations in order to (a) improve the material flow into the die cavity, (b) reduce wear and galling in the die and (c) obtain good surface finish of the part. Process conditions such as high temperatures and pressures could cause the lubricant to fail, thus resulting in galling or tearing of the part, damage to the tooling, and lost production. Therefore, selection of an appropriate lubricant based on the process conditions is important in the stamping industry. Several benchmark tests emulating stamping operations have been developed and are used to evaluate the performance of candidate lubricants. The major drawback of most of these tests is their inability to emulate high contact pressures and sliding velocities, which are crucial parameters for lubricity, especially in the case of high-speed progressive or transfer die operations involving ironing. Moreover, most of these tests are conducted at room temperature, while in reality; the process temperature can reach as high as 200 °C. The ironing tribotest developed at the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) induces high contact pressures and temperatures, thus emulating the conditions in a production environment. Application of the test to screen candidate lubricants for stamping operations involving the ironing process is discussed in this paper.}, number={4-5}, journal={INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE}, author={Chandrasekharan, S and Palaniswamy, H and Jain, N and Ngaile, G and Altan, T}, year={2005}, month={Apr}, pages={379–388} }
 @inbook{ngaile_gariety_2005, place={Materials Park, Ohio}, title={Friction and Lubrication}, ISBN={9781627083003}, DOI={10.31399/asm.tb.chffa.t51040067}, booktitle={Cold and Hot Forging: Fundamentals and Applications}, publisher={ASM International}, author={Ngaile, Gracious and Gariety, Mark}, editor={Altan, Taylan and Ngaile, Gracious and Shen, GangshuEditors}, year={2005} }
 @inbook{ngaile_shirgaokar_2005, place={Materials Park, Ohio}, title={Near-Net shape forging and new development}, ISBN={9781627083003}, DOI={10.31399/asm.tb.chffa.t51040319}, booktitle={Cold and Hot Forging: Fundamentals and Applications}, publisher={ASM International}, author={Ngaile, Gracious and Shirgaokar, Manas}, editor={Altan, Taylan and Ngaile, Gracious and Shen, GangshuEditors}, year={2005} }
 @inbook{ngaile_2005, place={Materials Park, Ohio}, title={Plastic Deformation: Complex state of stress and flow rules}, ISBN={9781627083003}, DOI={10.31399/asm.tb.chffa.t51040051}, booktitle={Cold and Hot Forging: Fundamentals and Applications}, publisher={ASM International}, author={Ngaile, Gracious}, editor={Altan, Taylan and Ngaile, Gracious and Shen, GangshuEditors}, year={2005} }
 @inbook{ngaile_shirgaokar_2005, place={Materials Park, Ohio}, title={Plastic Deformation: Strain and Strain Rate}, ISBN={9781627083003}, DOI={10.31399/asm.tb.chffa.t51040017}, booktitle={Cold and Hot Forging: Fundamentals and Applications}, publisher={ASM International}, author={Ngaile, Gracious and Shirgaokar, Manas}, editor={Altan, Taylan and Ngaile, Gracious and Shen, GangshuEditors}, year={2005} }
 @inbook{ngaile_shirgaokar_shen_2005, place={Materials Park, Ohio}, title={Process Modeling in Impression-Die Forging Using Finite-Element Analysis}, ISBN={9781627083003}, DOI={10.31399/asm.tb.chffa.t51040193}, booktitle={Cold and Hot Forging: Fundamentals and Applications}, publisher={ASM International}, author={Ngaile, Gracious and Shirgaokar, Manas and Shen, Gangshu}, editor={Altan, Taylan and Ngaile, Gracious and Shen, GangshuEditors}, year={2005} }
 @book{cold and hot forging: fundamentals and applications_2004, ISBN={0871708051}, publisher={Materials Park, Ohio: ASM International}, year={2004} }
 @article{gutscher_wu_ngaile_altan_2004, title={Determination of flow stress for sheet metal forming using the viscous pressure bulge (VPB) test}, volume={146}, DOI={10.1016/S0924-0136(03)00838-0}, abstractNote={In sheet metal forming operations the mechanical properties of the sheet material (i.e. flow stress or stress–strain curve) greatly influence metal flow and product quality. Therefore, accurate determination of the flow stress is of paramount importance in process simulation via finite element method (FEM). In this paper the use of the viscous pressure bulge (VPB) test for determination of flow stress under biaxial state of stress is discussed. With the VPB test, larger strains, which are relevant for stamping operations, can be achieved compared to the standard tensile test used to-date. In this study, FEM simulations and experiments have been performed in order to study the interrelationship of the geometric and material variables such as dome wall thinning, dome radius, dome height, strain hardening index, material strength coefficient, and anisotropy. From the study a robust method to determine the flow stress under biaxial deformation conditions using a viscous material as pressure medium has been developed.}, journal={Journal of Materials Processing Technology}, author={Gutscher, G. and Wu, H.-C. and Ngaile, G. and Altan, T.}, year={2004}, pages={1–7} }
 @article{palaniswamy_ngaile_altan_2004, title={Finite element simulation of magnesium alloy sheet forming at elevated temperatures}, volume={146}, DOI={10.1016/S0924-0136(03)00844-6}, abstractNote={The use of lightweight magnesium (Mg) alloy offers significant potential to improve automotive fuel efficiency. However, the application of formed magnesium alloy components in auto-body structures is restricted due to this material’s low formability at room temperature and lack of knowledge for processing magnesium alloys at elevated temperature. In this study, non-isothermal finite element (FE) simulation has been conducted for forming round cups and rectangular pans from Mg alloy AZ31B sheet at elevated temperatures. The results were compared with experiments, conducted at the Technical University, Hanover. Simulation and experiments predicted increase in limiting draw ratio (LDR) with increase in temperature. Maximum LDR was obtained at the forming temperature of 200 °C. FE simulation results agreed well with experimental observations.}, journal={Journal of Materials Processing Technology}, author={Palaniswamy, H. and Ngaile, G. and Altan, T.}, year={2004}, pages={52–60} }
 @article{shirgaokar_ngaile_altan_yu_balconi_rentfrow_worrell_2004, title={Hydraulic crimping: Application to the assembly of tubular components}, volume={146}, DOI={10.1016/S0924-0136(03)00843-4}, abstractNote={The crimping process using a polyurethane tool and hydraulic pressure can be used in the assembly of tubular components. This crimping operation was evaluated with the aid of the finite element method (FEM) and its application to the assembly of tubular components was investigated. The goal was to enhance the performance of the assembly by determining the optimum process and geometrical parameters, such as the material properties of the tube, the interference between the inserted rod and the tube and the rod–tube interface friction. FE simulations were used to evaluate the crimping operation under various process conditions. The crimping process of a double grooved rod/bullet with a tubular casing was evaluated as a case study. It was possible to determine the effect of manufacturing tolerances and misalignment between the rod and the casing on the quality of the final assembly in terms of the pullout force.}, journal={Journal of Materials Processing Technology}, author={Shirgaokar, M. and Ngaile, G. and Altan, T. and Yu, J.-H. and Balconi, J. and Rentfrow, R. and Worrell, W. J.}, year={2004}, pages={44–51} }
 @article{ngaile_jaeger_altan_2004, title={Lubrication in tube hydroforming (THF). Part I: Lubrication mechanisms and development of model tests to evaluate lubricants and die coatings in the transition and expansion zones}, volume={146}, DOI={10.1016/S0924-0136(03)00850-1}, abstractNote={The lubrication mechanisms that occur at the tool–workpiece interface for the transition and expansion zones are discussed. Suitable lubrication systems for the transition and expansion zones are reviewed based on the mechanics of deformation and material flow at the interface. Details of two model tests for evaluating the performance of tube hydroforming (THF) lubricants and die coatings are given. The optimization of die geometries for the model tests is based on sensitivity analysis through the finite element method together with experimental verification. The details of these tests are given and their development is discussed.}, journal={Journal of Materials Processing Technology}, author={Ngaile, G. and Jaeger, S. and Altan, T.}, year={2004}, pages={108–115} }
 @article{ngaile_jaeger_altan_2004, title={Lubrication in tube hydroforming (THF). Part II: Performance evaluation of lubricants using LDH test and pear-shaped tube expansion test}, volume={146}, DOI={10.1016/S0924-0136(03)00851-3}, abstractNote={Two model tests to evaluate lubricant performance under realistic tribological conditions occurring in the transition and expansion zones of a tube hydroforming (THF) process are presented. The model test for the transition zone is based on the limiting dome height (LDH) test principle. For the expansion zone, a pear-shaped tube expansion test (PET) developed by the authors is employed. Four lubricants were tested and ranked based on (a) dome wall thinning behavior (for LDH), (b) tube wall thinning, tube protrusion height (PH), tube bursting pressure (for PET), and (c) surface topography. Friction coefficients for the lubricants were estimated by matching the experimental and FE results.}, journal={Journal of Materials Processing Technology}, author={Ngaile, G. and Jaeger, S. and Altan, T.}, year={2004}, pages={116–123} }
 @article{palaniswamy_ngaile_altan_2004, title={Optimization of blank dimensions to reduce springback in the flexforming process}, volume={146}, DOI={10.1016/S0924-0136(03)00841-0}, abstractNote={In sheet metal forming operations, springback of the part during unloading largely determines whether the part conforms to the design dimensions and tolerances. Finite element simulations were performed in order to study the interrelationship of the blank dimensions and interface conditions on the springback for an axisymmetric conical part manufactured by flexforming. Sensitivity analysis done using the finite element method (FEM) demonstrated that the magnitude of springback and the overall dimensional quality are highly influenced by the initial dimensions of the blank. A conventional optimization method combined with FEM was used to obtain optimum blank dimensions that can reduce springback.}, journal={Journal of Materials Processing Technology}, author={Palaniswamy, H. and Ngaile, G. and Altan, T.}, year={2004}, pages={28–34} }
 @article{shirgaokar_cho_ngaile_altan_yu_balconi_rentfrow_worrell_2004, title={Optimization of mechanical crimping to assemble tubular components}, volume={146}, DOI={10.1016/S0924-0136(03)00842-2}, abstractNote={The crimping process is used often in the assembly of tubular components. In this study, with the aid of the finite-element method (FEM), the mechanical crimping operation was evaluated and optimized for a specific application. The effect of various process variables, such as the geometry, alignment and stroke of the crimper and the friction at the crimper–tube interface were investigated. Thus, it was possible to optimize the process so that the effect of springback could be reduced and the assembly quality, as indicated by the pullout force, could be improved. The crimping process of a single-grooved rod with a tube was evaluated as a case study. Based on the FE simulations, it was possible to determine the optimum alignment and the optimum design for two types of crimper geometries.}, journal={Journal of Materials Processing Technology}, author={Shirgaokar, M. and Cho, H. and Ngaile, G. and Altan, T. and Yu, J.-H. and Balconi, J. and Rentfrow, R. and Worrell, W. J.}, year={2004}, pages={35–43} }
 @article{aue-u-lan_ngaile_altan_2004, title={Optimizing tube hydroforming using process simulation and experimental verification}, volume={146}, DOI={10.1016/S0924-0136(03)00854-9}, abstractNote={The success of a tube hydroforming (THF) process is highly dependent on the loading paths (axial feed versus pressure) used. Finite element (FE)-based simulation was used to determine optimum loading paths for hydroforming of structural parts with different tubular materials. Experimental and simulation results have demonstrated that FE-based loading paths can significantly reduce trial and error, enhance productivity and expand the THF capability in forming complex parts. The test results also demonstrated that the reliability of the FE-based loading paths is highly dependent on the accuracy of the material properties of the blank, interface friction, and how close the properties of the welding zone are to the base material of the tubular blank.}, journal={Journal of Materials Processing Technology}, author={Aue-u-lan, Y. and Ngaile, G. and Altan, T.}, year={2004}, pages={137–143} }
 @article{wenning_ngaile_altan_2003, title={Design of a fastener clinching process using FEM}, volume={31}, journal={Transaction of the North American Manufacturing Research Institution of SME}, author={Wenning, Patrick H. and Ngaile, Gracious and Altan, Taylan}, year={2003}, pages={17–24} }
 @article{cho_ngaile_2003, title={Simultaneous determination of flow stress and interface friction by finite element based inverse analysis technique}, volume={52}, DOI={10.1016/s0007-8506(07)60570-8}, abstractNote={A finite element based Inverse analysis technique has been developed to determine the flow stress and friction at the tool/workplace interface simultaneously from one set of material tests. The Inverse problem is aimed at minimizing the error between experimental data and predictions made by rigid-plastic finite element simulations. The ring compression test and the modified limiting dome height test (sheet blank with a hole at center stretched with a hemispherical punch) were selected for evaluating the method for bulk forming and for sheet forming, respectively. The determined flow stress data were compared with corresponding data obtained Independently using the well-lubricated cylinder compression test and hydraulic bulge test. Results show that the method discussed In the study is efficient and accurate.}, number={1}, journal={CIRP ANNALS-MANUFACTURING TECHNOLOGY}, author={Cho, H and Ngaile, G}, year={2003}, pages={221–224} }
 @article{ngaile_federico_tibari_altan_2001, title={Lubrication in Tube Hydroforming (THF)}, volume={29}, journal={Transaction of the North American Manufacturing Research Institution of SME}, author={Ngaile, Gracious and Federico, Vicenzo and Tibari, Khaled and Altan, Taylan}, year={2001}, pages={51–57} }
 @article{saiki_marumo_ruan_ngaile_2000, title={Evaluation Method of Tribological Conditions in Net Shape Cold Forging of Products with Concave-Convex Profiles}, volume={41}, number={477}, journal={Japanese Technology of plasticity}, author={Saiki, Hiroyuki and Marumo, Yasuo and Ruan, Liqun and Ngaile, Gracious}, year={2000}, month={Oct}, pages={1036–1040} }
 @article{ngaile_saiki_1999, title={Cold forging tribo-test based on variation of deformation patterns at the tool-work piece interface}, journal={Journal of tribologist and lubrication engineers (STLE)}, author={Ngaile, Gracious and Saiki, Hiroyuki}, year={1999}, month={Feb}, pages={23–31} }
 @article{saiki_ngaile_ruan_1997, title={Characterization of adhesive strength of phosphate coatings in cold metal forming}, volume={119}, ISSN={["0742-4787"]}, DOI={10.1115/1.2833867}, abstractNote={A test method is proposed to characterize adhesive strength of phosphate coatings based on the various deformation patterns at the tool-workpiece interface. The deformation patterns were induced by tools of different surface geometrical profiles, i.e., flat surface, sinusoidal surface, saw-tooth surface and multi-surface profiles, in a localized rod drawing technique. With change in the tool geometry, three deformation regimes were observed, i.e., full film lubrication regime, mixed regime, and seizure regimes, which were categorized by the level of friction coefficient attained, and the degree of galling observed on the surface of the drawn specimens. The full film lubrication regimes were noticed when flat dies were used. In this case, the friction coefficient was maintained at nearly μ = 0.065, irrespective of the change in the surface roughness of the tools and reduction. With sinusoidal surface and other non-flat dies, mixed regime and seizure regimes were observed, and the friction coefficient varied from μ = 0.1 to 0.3. To complement the friction data, surface analysis of the tool-workpiece interface was also conducted. The frictional range of μ = 0.065 to 0.3 obtained in this study, therefore, provides for a manageable characterization of phosphate coatings for cold metal forming of objects with intricate shapes.}, number={4}, journal={JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME}, author={Saiki, H and Ngaile, G and Ruan, L}, year={1997}, month={Oct}, pages={667–671} }
 @article{saiki_ngaile_ruan_1997, title={Influence of die geometry on the workability of conversion coatings combined with soap lubricant in cold forming of steels}, volume={63}, ISSN={0924-0136}, url={http://dx.doi.org/10.1016/s0924-0136(96)02629-5}, DOI={10.1016/s0924-0136(96)02629-5}, abstractNote={Abstract Tribological conditions pertaining to the plastic deformation of zinc-phosphate coated specimens under localized bar drawing experiments were investigated. Dies of different surface profiles namely; sinusoidal, saw-tooth, flat and multi-surface profiles were used to induce various deformation patterns at the tool workpiece interface. Significant changes in the interface friction with change in both the die geometry and the mean interface temperature were observed. In order to correlate the surface expansion behavior defined by the tool geometries with the distribution of lubricant film at the tool-workpiece interface, tool indentation simulations using Two Dimensional Rigid Viscoplastic Finite Element Method (2D-FEM) were also conducted.}, number={1-3}, journal={Journal of Materials Processing Technology}, publisher={Elsevier BV}, author={Saiki, Hiroyuki and Ngaile, Gracious and Ruan, Liqun}, year={1997}, month={Jan}, pages={238–243} }
 @article{ngaile_mshana_sigh_1995, title={A New Prototype of a pineapple peeling machine}, volume={19}, number={2}, journal={Uhandisi Journal}, publisher={University of Dar Es Salaam}, author={Ngaile, Gracious and Mshana, J. and Sigh, A.}, year={1995}, month={Dec}, pages={117–132} }