Electrically-Assisted Manufacturing Research Articles

Investigation of thermal and mechanical effects during electrically-assisted compression of CoCrFeNiW0.5 high entropy alloy

Electrically-assisted manufacturing (EAM) has many advantages than ambient temperature manufacturing and thermoforming for the building of hard-to-deform alloys. The EAM technique of High entropy alloys (HEAs), a newer alloy category, is an issue worth of research, especially the deformation mechanism in the process of EAM. In the paper, the electrically-assisted compressive mechanical behavior of CoCrFeNiW0.5 HEA composed of face centered cubic phase and μ phase precipitate was studied under current density and strain rate region of 0–40 A/mm2 and 0.0005 s−1-0.1 s−1, respectively. At high current density and strain rate, the reduction of yield stress is remarkable. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques were utilized to analyze the effect of current density on the flow stress behaviors and microstructure evolution under plastic deformation. The results show that the introduced electric current enhances the movement and annihilation of dislocations as well as dynamic recovery, resulting in the continuous decrease of flow stress. Additionally, we can clearly observed that the dislocation-free ring or some very low dislocation density regions around the μ phase precipitates, that's because μ phase precipitate can lead to severe lattice distortion and thus increase the electron scattering, and then the local high temperature appeared around the defect regions due to local Joule heating effect, which is recognized as the principal reason leading to the significant decrease of mechanical properties during electrically-assisted compression.

Electrically assisted manufacturing of microchannels with enhanced filling quality and microstructural performance for thermal management

The printed circuit heat exchanger (PCHE) with arrayed microchannel structures is ideal for the extreme thermal management of hypersonic flight vehicles. Electrically assisted manufacturing (EAM) has a remarkable predominance in fabricating microchannels on sheet metals. By conducting EA micro-embossing experiments at current densities of 20, 25, and 40 A/mm2, respectively, the filling behavior and microstructural evolution of SUS304 sheets under the influence of current were elucidated in this study. The results indicated that a higher current density shortens the initial extrusion stage's duration and facilitates the material flow transition to the filling stage. Moreover, the current can simultaneously enhance the filling height and profile quality by minimizing the stress and stress differential in the deformation region of the filling section. The results of electron backscatter diffraction (EBSD) demonstrated that recrystallization occurs due to the synergistic effect of deformation and current. The degree of recrystallization in different regions of the filling section has a huge discrepancy. The region beneath the tooth exhibits considerable recrystallization and contains abundant refined grains. At the current density of 20 A/mm2, a number of dislocations accumulated in the deformed grains, and the filling section mainly consisted of 〈1 1 1〉 fiber texture and 〈1 0 1〉 deformation texture. In the process of continual dynamic recovery and recrystallization, dislocation packing relives at the current density of 40 A/mm2, which is one reason for the increase in filling quality. The 〈1 1 1〉 texture and 〈1 0 1〉 deformation texture are weakened and rotate as the forming temperature rises. Additionally, the 〈1 0 1〉 texture transforms into a 〈0 0 1〉 recrystallized texture. The diminished 〈1 0 1〉 deformation texture, the rotated 〈1 1 1〉 texture, and the appearance of 〈0 0 1〉 recrystallized texture enhance the homogenous strain distribution of the filling section, which is an additional explanation for the improvement of filling quality at high-density current. Based on the above results, a high-performance PCHE prototype with a pressure bearing capacity of 23 MPa and a heat transfer coefficient of 22 kW/(m2·K) was manufactured by EAM, confirming that the EAM technique is capable of achieving high-quality and eco-friendly fabrication of the enhanced microchannels.

“Target effect” of pulsed current on the texture evolution behaviour of Ni-based superalloy during electrically-assisted tension

Electrically-assisted manufacturing (EAM) has been proved to be very efficient in homogenizing the alloy with heterogeneous grain distribution due to the local Joule heating effect, which completely differs from the common heat treatment. However, the interaction between pulsed current and texture evolution during deformation have been rarely investigated even though texture is critical for the plastic behaviour of anisotropic material. Here, the effect of pulsed current on texture evolution behaviour has been studied by comparing the evolution behaviours of a Ni-based superalloy under electrically-assisted and quasi-static tension. The result showed that the evolution of easy-to-deform texture into hard one was promoted by the pulsed current, but the further enhancement of the hard-to-deform texture’s intensity was inhibited. This difference could be attributed to the more pronounced local Joule heating effect in the hard-to-deform grain due to larger lattice distance here, and then the softened hard-to-deform grain could rotate itself towards other orientations more easily. This is called “target effect” of pulsed current on the hard-to-deform texture in present work, which further indicates that EAM is effective in the control of homogeneous behaviour of anisotropic materials not only from the microstructure distribution but also from the mechanical property.

Electrically assisted pulse forming using closed-loop force control

The direct application of an electric current to a metallic workpiece during a manufacturing process, more commonly known as electrically-assisted manufacturing (EAM), produces many beneficial effects. During forming, significant flow stress reductions can be achieved. While there is much literature characterizing the effects of an electric current on the mechanical properties of materials during deformation, few feasible control systems for use in industrial processing have been developed. One such method is developed and tested herein using tensile testing in which electric current is triggered once a user-defined stress level is reached. The current then remains on until the stress reaches a desired minimum level. This cycle repeats until fracture occurs. The influence of several process parameters is discussed and an empirical formulation for determining the pulse frequency and the required energy per pulse is developed. This control method was found to be successful for forming metals while not exceeding a desired stress level. Furthermore, its application towards industrial use is also discussed.

Electrically-Assisted Manufacturing for Reduction in Forging Forces of Bearing Steels

The aerospace industry regularly uses three high-strength steel alloys in the manufacture of their bearings: M50, M50 NiL, and Pyrowear P675. The high strength of these alloys causes increased force, friction, and temperature rise during forging operations, resulting in residual stresses and creating issues with distortion and springback in subsequent machining operations. Electrically-assisted manufacturing (EAM) has been studied for reduction or elimination of these issues in magnesium, aluminum, and titanium alloys as well as A2 tool steel and 304 stainless steel. This research determined the threshold current densities for EAM of Pyrowear P675, M50, and M50 NiL steels. Threshold current densities were determined for each material at 33, 48, and 37 A/mm2 respectively. Once the test reached this threshold a significant reduction in yield stress occurred and the samples had an increase in hardness near the exterior, the authors assess the probability of a phase change due to resistive heating during this forming operation.

Electron force-induced dislocations annihilation and regeneration of a superalloy through electrical in-situ transmission electron microscopy observations

What effect does electric current do on dislocation evolution of metals keeps being a confusing question to be answered and proved. To this end, the dislocation evolution of a superalloy with electric current was directly observed by electrical in-situ transmission electron microscopy in this work. Dislocations annihilation at first and then regeneration was found for the first time, which directly proves the existence of electron force during the electrically-assisted manufacturing. Dislocations regeneration would be driven by the electron force and the resistance softening by the local Joule heating effect. Resultantly, a base could be provided for future electrically-assisted research.

Electro-Thermal Modeling and Design of High-Current Pulse Power Supply for Electrically Assisted Manufacturing

Electrically assisted manufacturing (EAM) is a promising and rapidly developing metal processing method. The power supply is a key sub-system for EAM, which needs to be designed properly. This paper proposes the model-based design of a low-voltage high-current pulse power supply used for EAM based on converter-level electro-thermal modeling. The thermal stress of key components is obtained by converter-level finite element simulations. A simplified thermal modeling method is proposed to reduce the computation burden of the FEM simulation to obtain the dynamic thermal profile under pulse current operation. The impact of the duration of the current pulse on the maximum temperature and temperature variations of MOSFETs is investigated based on the thermal model. A case study of a 10V/500A pulse power supply is presented to demonstrate the theoretical analyses and verification. The outcomes contribute to the design optimization and virtual prototyping of pulse power supplies for EAM applications.

Electroplastic Drilling of Low- and High-Strength Steels

When postforming machining operations are required on high-strength structural components, tool life becomes a costly issue, often requiring external softening via techniques such as laser assistance for press-hardened steel components. Electrically assisted manufacturing (EAM) uses electricity during material removal processes to reduce cutting loads through thermal softening. This paper evaluates the effect of electric current on a drilling process, termed electroplastic drilling, through the metrics of axial force, and workpiece temperature when machining mild low carbon steel (1008CR steel) and an advanced high strength press hardened steel. A design of experiment (DoE) is conducted on 1008CR steel to determine primary process parameter effects; it is found that electricity can reduce cutting loads at the cost of an increased workpiece temperature. The knowledge generated from the DoE is applied to the advanced high strength steel to evaluate cutting force reduction, process time savings, and tool life improvement at elevated feedrates. It is found that force can be reduced by 50% in high feedrates without observing catastrophic tool failure for up to ten cuts, while tool failure occurs in only a single cut for the no-current condition. Finally, the limitations of the developed model in electroplastic drilling are discussed along with future suggestions for industrialization of the method.

Mechanism for the macro and micro behaviors of the Ni-based superalloy during electrically-assisted tension: Local Joule heating effect

Electrically-assisted manufacturing (EAM) is used for forming difficult-to-form materials such as the Ni-based superalloy in recent years. Compared to the hot deformation, EAM is a more convenient and effective method. However, the mechanism for the macro and micro behaviors of the materials with EAM is still a controversial issue. Thus, in this work, the electrically-assisted (EA) tension tests of the Ni-based superalloy were carried out with different parameters, and the macro and micro behaviors of the material were studied and discussed. Besides the reduction of yield strength (YS) and flow stress, the Portevin-Le Chatelier (PLC) effect appears during the EA tension and is more significant than that during the hot tension at the same temperature. The critical temperature for the PLC effect is the same with different strain rates under a fixed peak current density. Essentially, the directional distribution of dislocations and the earlier precipitation of the second phase can also be the main causes for the PLC effect. According to the existing theories and the electric treatment experiments that the higher percentage of defects or the second phase in metal result in more significant temperature rise, the local high temperature which induced by local Joule heating effect exists in the critical areas. It may be the main mechanism resulting in the macro and micro behaviors of alloy during the EA tension. Furthermore, recrystallization is experimentally observed when the measured temperature is much lower than the critical temperature for recrystallization due to the local Joule heating effect.

A Review of Electrically-Assisted Manufacturing With Emphasis on Modeling and Understanding of the Electroplastic Effect

Increasingly strict fuel efficiency standards have driven the aerospace and automotive industries to improve the fuel economy of their fleets. A key method for feasibly improving the fuel economy is by decreasing the weight, which requires the introduction of materials with high strength to weight ratios into airplane and vehicle designs. Many of these materials are not as formable or machinable as conventional low carbon steels, making production difficult when using traditional forming and machining strategies and capital. Electrical augmentation offers a potential solution to this dilemma through enhancing process capabilities and allowing for continued use of existing equipment. The use of electricity to aid in deformation of metallic materials is termed as electrically assisted manufacturing (EAM). The direct effect of electricity on the deformation of metallic materials is termed as electroplastic effect. This paper presents a summary of the current state-of-the-art in using electric current to augment existing manufacturing processes for processing of higher-strength materials. Advantages of this process include flow stress and forming force reduction, increased formability, decreased elastic recovery, fracture mode transformation from brittle to ductile, decreased overall process energy, and decreased cutting forces in machining. There is currently a lack of agreement as to the underlying mechanisms of the electroplastic effect. Therefore, this paper presents the four main existing theories and the experimental understanding of these theories, along with modeling approaches for understanding and predicting the electroplastic effect.

Experimental study and analysis on the electrically-assisted tensile behaviors of Inconel 718 alloy

Abstract The effect of pulsed current on tensile deformation of Inconel 718 superalloy with different initial microstructures was studied by experiment, which is of great importance for the subsequent application of electrically-assisted manufacturing (EAM) technology. The results show that the pulsed peak current with a density of 10 A/mm2 has no effect on stress responses, while the yield strength (YS) and ultimate tensile strength (UTS) are reduced when the peak current density is above 25 A/mm2. The higher peak current density and frequency lead to more obvious thermal effect and thus result in the decrease of YS, UTS and elongation. For samples cutting from different directions, i.e. transverse direction (TD) and rolling direction (RD), no difference in YS can be observed with EAM. For samples with different initial microstructures, e.g., the as-received and the heat-treated samples, more significant decrease in flow stress and higher elongation can be observed for the former than for the latter. Notably decreasing YS was achieved without deteriorating the ductility at a peak current density of 25A/mm2 and a frequency of 400Hz. The physical mechanism for the obtained rules was revealed.

Effect of pulsed electric current on dissolution of Mg17Al12 phases in as-extruded AZ91 magnesium alloy

In this study, the tensile deformation behavior of as-extruded AZ91 magnesium alloy under pulsed electric current has been investigated based on microstructural observations. The flow stress decreased and the elongation increased remarkably on applying electric current in comparison with non-pulsed tensile test at both room temperature and at 70°C. The results of EBSD and EDS analysis showed that dissolution of the Mg17Al12 phase obviously occurs during pulsed tensile test due to thermal effect caused by Joule heating and athermal effect of electric current. To distinguish the athermal and thermal effects of electric current, the induction heat treatment (IHT) that follows the temperature cycle measured during pulsed tensile test was carried out using a dilatometer, which could control the temperature of specimen by an induction heater in a vacuum. Additionally, electropulsing treatment (EPT) was conducted and compared with the conventional heat treatment (CHT) under the same condition. The fraction of Mg17Al12 phase after pulsed tensile test and EPT was obviously lower in comparison with IHT and CHT, respectively. The results prove that applying electric current accelerates dissolution of Mg17Al12 phase in as-extruded AZ91 alloy with a distinct effect from Joule heating during deformation. It is proposed that electrically-assisted manufacturing (EAM) technique can improve the efficiency of forming process for as-extruded AZ91 alloy.

Influence of Continuous Direct Current on the Microtube Hydroforming Process

Research of the microtube hydroforming (MTHF) process is being investigated for potential medical and fuel cell applications. This is largely due to the fact that at the macroscale the tube hydroforming (THF) process, like most metal forming processes, has realized many advantages, especially when comparing products made using traditional machining processes. Unfortunately, relatively large forces compared to part size and high pressures are required to form the parts so the potential exists to create failed or defective parts. One method to reduce the forces and pressures during MTHF is to incorporate electrically assisted manufacturing (EAM) and electrically assisted forming (EAF) into the MTHF. The intent of both EAM and EAF is to use electrical current to lower the required deformation energy and increase the metal's formability. To reduce the required deformation energy, the applied electricity produces localized heating in the material in order to lower the material's yield stress. In many cases, the previous work has shown that EAF and EAM have resulted in metals being formed further than conventional forming methods alone without sacrificing the strength or ductility. Tests were performed using “as received” and annealed stainless steel 304 tubing. Results shown in this paper indicate that the ultimate tensile strength and bust pressures decrease with increased current while using EAM during MTHF. It was also shown that at high currents the microtubes experienced higher temperatures but were still well below the recrystallization temperature.

Study of electrically-assisted indentation for surface texturing

Electrically-Assisted manufacturing is a promising hybrid manufacturing process for improved ductility and elongation during plastic deformation of metals and decreased spring-back. Most studies have focused on the deformation of a whole material by applying electric current through the whole material, and many electrically-assisted manufacturing processes including forging, rolling, and sheet metal forming have been introduced. However, plastic deformation processes on a surface, such as indentation, embossing, and scribing, are also important for functional surface texturing and marking, among other uses. In this study, the effect of a continuous electric current on indentation in stainless steel and titanium was investigated using Vickers hardness test. The hardness was decreased by the electric current during indentation with a diamond tip. The amount of decreased hardness depended on the amplitude of the electric current and the positions of two electrodes. The electric current density passing through the surface was calculated by finite element analysis, and the hardness decrease was proportional to the electric current density.

A review of electrically-assisted manufacturing

The mechanical properties of metals change temporarily or permanently under application of electric currents under deformation. This phenomenon is often referred to as electroplasticity. The electroplasticity of metals and their alloys has been investigated under various loading conditions including tensile, compressive, bending, and hardness tests. Electrically-assisted manufacturing (EAM) utilizes this electroplasticity in manufacturing processes. Due to its technical advantages such as enhanced formability and reduced springback, EAM is energy efficient with reduced process time. Recent developments in EAM include various bulk deformation and sheet metal forming processes. This paper summarizes previously reported electroplastic behaviors of various metals or metal alloys and recent EAM processes. In addition, contemporary EAM patents are briefly reviewed.

Experimental Study on Electroplastic Effect in AISI 316L Austenitic Stainless Steel

Electrically Assisted Manufacturing (EAM) is a recently developed method for materials forming based on the Electro-Plastic Effect (EPE) induced by electric current on the flow properties of the material and enhancing their workability. In this technique, the concept of dislocations/electrons interaction and the localized resistive heating provided by electric current were found to be the main responsible for the observed increase in materials formability. However, the joule heating may hinder the induced EPE, since heat and electricity are contemporarily both present, and separation between these two contributions is mandatory to better understand the solely effect of electricity on plastic flow. The present experimental work on an AISI 316L austenitic stainless steel is aimed to study EPE by separating the effects of current from those of heating during EAM uniaxial tensile test, in order to ascribe the relative contributions.

Several Factors Affecting the Electroplastic Effect During an Electrically-Assisted Forming Process

Recent development of electrically-assisted manufacturing (EAM) processes proved the advantages of using the electric current, mainly related with the decrease in the mechanical forming load and improvement in the formability. From EAM experiments, it has been determined that a portion of the applied electrical power contributes toward these forming benefits and the rest is dissipated into heat, defined as the electroplastic effect. The objective of this work is to experimentally investigate several factors that affect the electroplastic effect and the efficiency of the applied electricity. Specifically, the effects of various levels of cold work and contact force are explored on both Grade 2 and Grade 5 Titanium alloys. Thermal and mechanical data prove that these factors notably affect the efficiency of the applied electricity during an electrically-assisted forming (EAF) process.

Electroplastic Modeling of Bending Stainless Steel Sheet Metal Using Energy Methods

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, and 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 three-point bending force profiles for nonelectrical 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 (EA) 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.