Wesley A. Salandro

Thermomechanical modeling sensitivity analysis of electrically assisted forming

Recent research by the authors has resulted in the conception of several methods of accounting for direct electrical effects during an electrically assisted manufacturing process, where electricity is applied to a conductive workpiece to enhance its formability characteristics. This modeling and analysis strategy accounts for both mechanical effects and heat transfer effects due to the applied electrical power. This study presents a sensitivity analysis and explanation of several key material and process inputs during an electrically assisted forming test on Stainless Steel 304 and Titanium Grades 2 and 5 specimens. First, the effect that the specific heat (Cp) value has on the model will be discussed and compared with another lightweight material. Second, the significance of all three heat transfer modes (conduction, convection, and radiation) will be noted, and any possible simplifications to the existing heat transfer model will be highlighted. Third, the general electroplastic effect coefficient profile shape for the Stainless Steel 304 material will be compared to that of titanium alloys. Fourth, a frequency analysis will be done on the data taken during the experiments, by way of a Fast Fourier Transform, and the variation of frequency response with the electric input is studied. Overall, this study provides insight into several factors affecting a material’s electroplastic effect coefficient profile and also compares resulting electroplastic effect coefficient profiles of various materials.

A thermal-based approach for determining electroplastic characteristics

Recent development of electrically assisted manufacturing processes proved the advantages of using the electric current, mainly related with the decrease in the mechanical forming load, and improvement in the formability when electrically assisted forming of metals. The reduction of forming load was formulated previously assuming that a part of the electrical energy input is dissipated into heat, thus producing thermal softening of the material, while the remaining component directly aids the plastic deformation. The fraction of electrical energy applied, which assists the deformation process compared to the total amount of electrical energy, is given by the electroplastic effect coefficient. The objective of the current research is to investigate the complex effect of the electricity applied during deformation, and to establish a methodology for quantifying the electroplastic effect coefficient. Temperature behavior is observed for varying levels of deformation and previous cold work. Results are used to refine the understanding of the electroplastic effect coefficient, and a new relationship, in the form of a power law, is derived. This model is validated under independent experiments in Grade 2 (commercially pure) and Grade 5 (Ti–6Al–4V) titanium.

Thermo-Mechanical Investigations of the Electroplastic Effect

Recent development of Electrically-Assisted Manufacturing processes proved the advantages of using the electric current, mainly related with the decrease in the mechanical forming load and improvement in the formability when electrically-assisted forming of metals. The reduction of forming load was formulated previously assuming that a part of the electrical energy input is dissipated into heat, thus producing thermal softening of the material, while the remaining component directly aids the plastic deformation. The fraction of electrical energy applied that assists the deformation process compared to the total amount of electrical energy is given by the electroplastic effect coefficient. The objective of the current research is to investigate the complex effect of the electricity applied during deformation, and to establish a methodology for quantifying the electroplastic effect coefficient. Temperature behavior is observed for varying levels of deformation and previous cold work. Results are used to refine the understanding of the electroplastic effect coefficient, and a new relationship, in the form of a power law, is derived. This model is validated under independent experiments in Grade 2 (commercially pure) and Grade 5 (Ti-6Al-4V) titanium.© 2011 ASME

Modeling and Quantification of the Electroplastic Effect When Bending Stainless Steel Sheet Metal

Automotive manufacturers are continuously striving to meet economic demands by designing and manufacturing more efficient and better performing vehicles. To aid this effort, many manufacturers are using different design strategies such to reduce the overall size/weight of certain automotive components without compromising strength or durability. Stainless steel is a popular material for such uses (i.e. bumpers and fuel tanks) since it possesses both high strength and ductility, and it is relatively light for its strength. However, with current forming processes (e.g., hot working, incremental forming, and superplastic forming), extremely complex components cannot always be easily produced, thus, limiting the potential weight-saving and performance benefits that could be achieved otherwise. Electrically-Assisted Manufacturing (EAM) is an emerging manufacturing technique that has been proven capable of significantly increasing the formability of many automotive alloys, hence the “electroplastic effect”. In this technique, electricity can be applied in many ways (e.g., pulsed, cycled, or continuous) to metals undergoing different types of deformation (e.g., compression, tension, bending). When applied, the electricity lowers the required deformation forces, increases part displacement or elongation, and can reduce or eliminate springback in formed parts. Within this study, the effects of EAM on the bending of 304 Stainless Steel sheet metal will be characterized and modeled for different die widths and electrical flux densities. In previous works, EAM has proven to be highly successful on this particular material. Comparison of 3-point bending force profiles for non-electrical baseline tests and various EAM tests will help to illustrate electricity’s effectiveness. An electroplastic bending coefficient will be introduced and used for modeling an electrically-assisted bending process. Additionally, the springback reductions attained from EAM will be quantified and compared. From this work, a better overall understanding of the effects and benefits of EAM on bending processes will be explained.Copyright

Introduction to Electrically Assisted Forming

Electrically assisted forming (EAF) is a recently introduced metal-forming technique capable of enhancing a metal’s formability during deformation and reducing springback after deformation.

Modeling the Electroplastic Effect During Electrically-Assisted Forming of 304 Stainless Steel

Over the last decade, the Electrically-Assisted Manufacturing (EAM) technique, where electricity is applied to a metal during deformation, has been experimentally proven to increase the workability of many lightweight alloys which are highly desirable to the automotive industry. Recent research by the authors has led to ways of accounting for the formability increases due to the applied electricity, by way of an Electroplastic Effect Coefficient (EEC), and by utilizing this coefficient, simple EAM forming tests can ultimately be modeled.This work provides insight into the authors’ EAM modeling methodology and how it differs from previous EAM modeling attempts. Additionally, from the Electrically-Assisted Forming (EAF) experiments, two methods of accounting for the electroplastic effect will be discussed and compared. Ultimately, these methods will be integrated into the thermo-mechanical model to predict compressive stress-strain profiles for electrically-assisted forming tests under various current densities and die speeds. Finally, the efficiency of applying electricity to the deformation process will be discussed.© 2012 ASME

Tribological Aspects in Electrically-Assisted Forming

This study investigates the influence of electricit y on the different lubrication mechanisms by evaluating lubr icant performance in an electrically-assisted forming (EA F) process and identifying potential lubricant candidates for EAF. The tribological conditions have a significant influence on the fric tional forces occurring at the die/workpiece interface, thus on t he forming load, part quality, and achievable form. When electricity is applied, the lubricant is exposed to high localized temperatures and current fields. Electrically-assisted ring compression test s are conducted and the performance characteristics of several lubr icants are studied. By combining the experiments and finite el ement simulation results, friction coefficients can be es timated, and the effect of electric current flow on friction charact eristics quantified.

Evaluation of lubricants for electrically-assisted forming

The automobile and aerospace sectors are increasingly turning their attention to the opportunities created by the use of lightweight alloys with large strength-to-weight ratios, such as aluminium, magnesium, stainless steel, and titanium alloys. However, when using conventional forming processes, these light materials create processing challenges: low formability and high yield strength. Electrically assisted forming (EAF) is a method that can overcome these limitations. Specifically, EAF is a novel forming process where electricity is applied to the metallic workpiece during deformation. Previous investigations have shown that EAF creates a reduction in flow stress, an increase in formability, an ability to reduce/eliminate springback, and an improved precision. This study investigates the influence of electricity on lubricant performance and identifies lubricant candidates for EAF. When electricity is applied, besides the changes due to surface expansion at the interface that occur in conventional processes, the lubricant is exposed to high localized temperatures and current fields. Electrically assisted ring compression tests are conducted and the performance characteristics of three lubricants are evaluated. By combining the experiments and finite element simulation results, friction coefficients can be estimated, and the effect of electric current flow on friction characteristics quantified.

Sensitivities When Modeling Electrically-Assisted Forming

Recent research by the authors has resulted in the conception of several methods of accounting for direct electrical effects during an Electrically-Assisted Manufacturing (EAM) process, where electricity is applied to a conductive workpiece to enhance its formability characteristics. The modeling and analysis strategy accounts for both mechanical effects and heat transfer effects due to the applied electrical power.This work presents a sensitivity analysis and explanation of several key material and process inputs during an Electrically-Assisted Forming (EAF) test on Stainless Steel 304 and Titanium Grades 2 and 5 specimens. First, the effect that the specific heat (Cp) value has on the model will be discussed and compared with another lightweight material. Second, the significance of all three heat transfer modes (conduction, convection, and radiation) will be noted, and any possible simplifications to the existing heat transfer model will be highlighted. Third, the general electroplastic effect coefficient (EEC) profile shape for the Stainless Steel 304 material will be compared to that of Titanium alloys. Fourth, a frequency analysis will be done on the data taken during the experiments, by way of a Fast Fourier Transform (FFT), and the variation of frequency response with the electric input is studied.Overall, this work provides insight into several factors affecting a material’s EEC profile, and also compares resulting EEC profiles of various materials.Copyright

Applications of Electrically Assisted Manufacturing

Within this book, a modeling strategy for the EAF technique is explained for both compression and tension. Both strategies separate the thermal softening effects from the direct electrical effects and thus produce temperature and force profiles for their respective processes. However, in the real world, manufacturing processes are rarely exclusively compression or tension. Therefore, within this chapter, manufacturing processes that can be applicable to EAF will be explained. These include bending, stretch forming, machining, friction stir welding, and miscellaneous other EAF-industrialization research by researchers other than the authors. In addition, this chapter will include experimental EAF findings for compression, tension, channel formation, springback, and various types of forming.