Electrically Assisted Wire Drawing Polarity Effects

Electrically assisted manufacturing is the direct application of an electric current or field to a workpiece during a manufacturing operation. In addition to resistive heating, various anomalous effects have been observed experimentally. Since its conception in the 1950s, scientists continue to debate the existence of these so called electroplastic effects (EPEs) due to conflicted results shown throughout literature. A popular theory of electroplasticity is the electron wind, which postulates that there is a transfer of momentum between electrons and dislocations, which assists their motion during deformation. Though refuted both mathematically and experimentally in other types of tests, the electron wind theory, and therefore the existence of electroplasticity, is interestingly supported by the existence of polarity effects in wire drawing. A detailed review of the literature that has shown polarity effects in wire drawing is conducted. While the authors of these publications failed to fully disclose all test parameters, requiring several assumptions to be made, it appears that no mathematical/logical trends could be established. It is hypothesized herein that the velocity of the wire in a wire drawing application can influence the drift velocity of electrons, thereby increasing or decreasing current flow explicitly through the moving section of the wire. In order to test this hypothesis, a fixture was constructed which is capable of passing a current through a moving wire at common wire drawing speeds. Modern sensing equipment was used to measure various electrical parameters during testing. The wire speed effect hypothesis was refuted by experimental testing. While the results of experimental testing thus far indicate the existence of electroplasticity, further testing that includes drawing and force measurements must be conducted in order to fully conclude its existence in the wire drawing application.

Force Controlled Electrical Pulse Assisted Forming

Electrically-assisted manufacturing refers to the direct application of electrical current to a workpiece during a manufacturing process. This assistance results in several benefits such as flow stress reduction, increased elongation, reduced springback, increased diffusion, and increased precipitation control. These effects are also associated with traditional thermal assistance. However, for over half a decade it has been argued whether or not these observed effects are due to electroplasticity, a term which describes effects that cannot be fully explained through resistive heating. Several theories have been proposed as to the mechanism responsible for these purported athermal effects. Conflicting results within literature have enabled this debate over electroplasticity since its discovery in the mid 20th century. While the effects of electrically-assisted manufacturing are clearly characterized throughout literature, there is a lack of research related to control systems which may be used to take advantage of its effects. Typically, control systems are developed using an empirical approach, requiring extensive testing in order to fully characterize the stress-strain behavior at all conditions. Additionally, current research has primarily focused on reducing flow stresses during electrically-assisted processes without regard for the strength of the material subsequent to forming. Therefore, there is a strong need for a control system which can quickly be deployed for new materials and does not significantly reduce the subsequent strength of the material. Herein, a novel control approach is developed in which electrical pulses are triggered by a predetermined stress level. This stress value would be set according to the manufacturer’s stamping die strength. Once the material reaches this stress value, current is deployed until a minimum stress level is reached. At that point, the electricity is turned off and the material allowed to cool; at that stage the stress begins to elevate and the cycle continues. This approach does not require extensive pre-testing and is robust to a range of strain rate. This type of implementation can also be adapted to different levels of capability. For example, since the current is controlled by force and not by time, a low-current power supply will stay on for each pulse longer than a power supply with higher capabilities; however, each will achieve a similar effect. This study investigates the effect of several different minimum stress levels and strain rates. The strain rates chosen are relatively similar to common stamping process. This system was experimentally tested using 1018 CR steel. This control approach was found to be a successful method of maintaining a desired stress level.

A Numerical Study on Rotational Tube Flaring Process

A substantial increase in demand on the sheet metal part usage in aerospace and automotive industries is due to the increase in the sale of these products to ease the transportation. However, due to increase in the fuel prices and further environmental regulation had left no choice but to manufacture more fuel efficient and inexpensive vehicles. These heavy demands force researchers to think outside the box. There are many advanced manufacturing processes to produce optimized part are single and double point incremental forming, Reuleaux forming, hydroforming, explosive forming, electrically assisted manufacturing. In this project, a numerical study on rotational tube flaring process will be studied. Tube flaring is one of the most commonly used processes under tube forming. In this process, a conical tool contacts and forces the end of the tube while another end of the tube is fixed. This is called conventional flaring process. In contrast to this process, a tool rotational technique was utilized for this work. The rotation and the feed of the tool will be analyzed to have the best formability of the tool. The strain path and failure will be analyzed. The strain and thinning pattern will be discussed.

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.

The Effect of Multi-Point Electrical Paths on Global Springback Elimination in Single Point Incremental Forming

Automotive and aerospace industries are interested in implementing die-less forming processes in order to reduce part costs and the required forming energy. One method of die-less forming is incremental forming, in which a sheet metal part is formed; typically with a hemispherical tool that deforms material as it pushes into the material and passes along the surface to create the desired part geometry. One problem with incremental forming is global springback, which occurs after the part has been formed and is released from the forming fixture. This effect is caused by residual stresses that are created during part deformation and result in geometric inaccuracies after the clamping force has been released. In this paper, the effect of post-deformation applied direct current on the springback of pre-formed sheet metal will be investigated. This is a process is a type of electrically assisted manufacturing (EAM). This paper is a continuation of previous works presented at MSEC 2015–2016. The initial feasibility study described herein already achieves a springback reduction of 26.3% and is dependent on the regions of high stress concentration as well as current density. Future work will extend this reduction through further testing of complex configurations.

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.

Effect of Applied Electricity on Springback During Bending and Flattening of 304/316 Stainless Steel, Titanium AMS-T-9046 and Magnesium AZ31B

One of the major issues with forming sheet metal is the tendency for parts to spring back towards their original shape when the applied loading is released. Springback is a form of geometric inaccuracy and is the result of residual stresses, which are created as the part deforms. As a result, forming intricate parts require specialized equipment and calculations to compensate for springback. Transportation industries that rely on forming high strength parts currently use complicated machinery that takes up time and energy to meet specifications. This research investigates the effects of electrically assisted manufacturing (EAM), a process in which electrical current is applied while a material is being manufactured, on springback. Bending and flattening testing will be performed on 4 metals: stainless steel 304 and 316, ASM-T-9046 titanium, and AZ31B magnesium. Additional testing will be performed on stainless steel, observing the effect of changing thicknesses, pulse durations, and current densities on springback. It was observed that an increase in pulse durations results in decreased springback for all the materials. Applying electricity to decrease springback was more effective for bending than flattening procedures in stainless steel and titanium, though it was equally effective for magnesium. For the additional testing on stainless steel, a change in thickness affected results when comparing it to current density, but not when observing similar applied current.