Driver Sheet Research Articles

Formability and mechanism of ultra-thin titanium foil under the elevated temperature and high strain rate in electromagnetic forming

Electromagnetic forming (EMF) is a high-speed forming process with significant potential for manufacturing bipolar plates. However, titanium's low conductivity requires the use of a driver sheet in traditional EMF, limiting its formability improvement. This study proposed a novel electromagnetic forming method with independent loading of the magnetic field and current (EMF-ILMFC), enabling separate application of electromagnetic force and Joule heating. The dynamic deformation behavior of ultra-thin titanium was investigated using three different loading methods: quasi-static (QS), electromagnetic bulging with driver sheets (EMB-DS), and electromagnetic bulging with the new method (EMB-ILMFC). The study revealed that the forming limit under EMB-ILMFC was significantly higher than under EMB-DS and QS, with a maximum improvement of 139.1%. Numerical simulations and experimental analyses were conducted to elucidate the thermal effects on formability during dynamic deformation. The results indicate that thermal effects reduce flow stress, extend the duration of inertia and high strain rates, and thereby improve the formability of titanium.

Investigation of sheet thickness in the electromagnetic welding of aluminum‐stainless steel

AbstractThe goal of present research is to investigate the effect of thickness of aluminum, stainless steel and driver sheets on the ultimate tensile strength, weld width and hardness of aluminum‐stainless steel joint in the electromagnetic welding. First, the finite element analysis was applied to predict the joint formation between aluminum and stainless steel sheets by using the weldability window. Then, the experiments were conducted using the response surface methodology and desirability function to attain the desirable values of sheet thickness. Eventually, the microstructure of weld interface was observed by optical and scanning electron microscopy to evaluate the quality of welds. It was observed that the values of ultimate tensile strength, weld width and hardness can be simultaneously improved by selecting the thickness of aluminum, stainless steel and driver at 0.78 mm, 0.37 mm and 0.96 mm respectively. The microstructure analysis exhibited that the detrimental effects of intermetallic layers on the weld strength can be limited by reducing the thickness of intermetallic to 4 μm.

Electromagnetic impacting medium forming (EIMF): a new method forming process for magnesium alloy sheet

A new forming process for magnesium alloy sheet, namely, electromagnetic impacting medium forming (EIMF), is proposed. Medium is compressed by strong magnetic force which is produced from varied magnetic field between coil and driver sheet. Magnesium alloy sheet can be deformed by a strong force from medium. In EIMF, once impacting or more times impacting is easily implemented, that is difficulty in conventional electromagnetic forming. Effects of different discharge energy and temperature were investigated. Peak forming heights increased linearly with increasing discharge energy and temperature. Distribution of contour and thickness had been revealed. Strains could be improved by increasing temperature and discharge energy. Twice impacting process was carried out. The forming height was enhanced obviously in contrast with results obtained at once impacting. Fracture morphology and optical microstructure were analyzed. It is found that brittle fracture at room temperature and ductile fracture at 200 °C appeared. Due to high strain rate forming process, deformation mechanism (non-basal slip systems) has limit effect. And at 200 °C, twinning is also a main mechanism for AZ31 sheet deformation in EIMF. In further work, EIMF for formability of AZ31 sheet will be improved by affected the deformation mechanism.

Effect of the Radial Dimension of the Driver Sheet on the Electromagnetic Driven Forming

Electromagnetic forming has attracted more and more attention in the advanced manufacturing field as a promising technology to improve the formability of lightweight alloys at room temperature. Electromagnetic forming employs the electromagnetic force between the drive coil and the workpiece to complete the forming. The low conductivity materials such as titanium alloy usually cannot gain enough electromagnetic force to deformation due to the low induced current on the workpiece. The forming performance of low conductivity material can be improved using high conductivity driver sheet which increases the eddy current and the forming force acted on the workpiece. Some efforts to improve and optimize the performance of the electromagnetic driven forming were made. In this study, a copper driver ring for the electromagnetic driven forming of titanium alloy is proposed based on the electromagnetic force distribution. The effect of the radial dimension of the driver ring on the forming result is studied with the numerical simulation model which is verified by the experiment. It is found that the outer radius of the driver ring mainly effects the maximum forming depth, and the inner radius of the driver ring influences the forming profile of the workpiece. The numerical results suggest that the forming depth can be improved and the forming contour can be adjusted while the proposed driver ring is applied in electromagnetic driven forming.

Deformation behaviour of AZ31 magnesium alloy sheet hybrid actuating with Al driver sheet and temperature in magnetic pulse forming

In this paper, formability of AZ31 sheet in magnetic pulse forming hybrid actuating with driver sheet and temperature were investigated. The effects of discharge parameters, driver sheet and temperature were investigated on bulging by the experimental analysis. Forming height, thickness of AA1060 driver sheet, forming limit curve (FLC), fracture morphology and microstructure were performed to analyze causes of deformation behaviour for driver sheet and temperature. Analysis of driver sheet and temperature effects reveals that the optimum thickness of the driver sheet and temperature are 1 mm and 200 ℃, respectively. The FLC results show increased by increasing temperature from 25 ℃ to 200 ℃, and then decreased by increasing the temperature such as 250 ℃. Compared with quasi-static forming, the temperature effect for formability is unremarkable in magnetic pulse forming with driver sheet. Demonstrating similar drawability and strechability of AZ31 sheet appeared. Microstructure reveals that high strain rate effect, yield strength decreasing (because of temperature effect) and grain refinement are main reasons to affect the formability of AZ31 sheet in magnetic pulse forming with driver sheet and temperature. However, dynamic recrystallization (DRX) is not observed which is usually accompanied at temperatures higher than 150 ℃ in quasi-static forming.

Experimental and numerical research on magnetic pulse forming of DP600 high-strength steel with driver sheet

Magnetic pulse forming is high velocity forming technology, which requires the workpiece with better conductivity. However, high-strength steel with lower conductivity is difficult to deform by magnetic pulse forming. In this paper, AA1060 sheet was employed to drive DP600 sheet which was used to solve the forming problem of high-strength steel in magnetic pulse forming. Experimental tests and numerical method were used to investigate the deformation characteristic of DP600 sheet. Effects of drive sheet and discharge voltage for DP600 sheet deformation were analyzed. Forming height increases with increasing discharge voltage and optimal thickness of driver sheet is 2 mm. Forming profile and thickness of deformed DP600 sheet were provided. Distribution of magnetic field line and magnetic force were presented by numerical simulation. Higher magnetic flux density and magnetic force can be produced by 2 mm Al driver sheet. Deformation process, velocity, strain rate, and principal strain were investigated. During the driving process, DP600 sheet was accelerated and got higher velocity about 252 m/s with 2 mm driver sheet and C = 615 μF/U = 3.38 kV. Principal strain increases with discharge voltage increasing. And the varied trend can be described by quadratic equation.

An integrated pseudo-spectral simulation of high-speed discharging at an electromagnetic forming conveying a conductive driver sheet

An integrated computational methodology is implemented based on a pseudo-spectral solution of governing differential equations in a high-speed discharging of the flat spiral coils, which is used in the electromagnetic-forming systems. Both conductive driver sheet and coil are divided into several peripheral segments. Also, eddy currents induced by each segment are computed as well as the fields generated by each wire of the coil corresponding to defined local source points. The model will be established based on the Chebyshev polynomials to calculate spatial and temporal distributions of the magnetic fields. The Houbolt marching method is applied for the time discretization of the Maxwell equations. By adopting a backward process for implicit boundary conditions and summing up overall components of the magnetic fields at the lower surface, it leads to obtaining an integrated response to the problem. A multiple regression analysis is implemented based on the least square error norm to remove additional equations generated in the spectral discretization. An exponential filtering is used to control aliasing phenomenon due to collocation treatment of the mathematical terms. Validation is carried out by comparisons of the results with other works related in the literature.

Effects of temperature and driver sheet for magnesium alloy sheet in magnetic pulse forming

Thermal effect from warm temperature is always used to improve the formability of AZ31 magnesium alloy sheet. However, it is seldom employed to deform AZ31 sheet in magnetic pulse forming process, due to increasing resistivity and decreasing effect of high strain rate. In this study, Al driver sheets without heating were used to strength effect of high strain rate and drive AZ31 sheet with warm temperature to deform. Method of numerical simulation was used to analyze magnetic pulse forming of AZ31 sheet with driver sheet and temperature. Magnetic flux density and magnetic force with and without Al driver sheet (thickness of 1, 1.5, and 2 mm) and different temperature (25, 100, 150, 200, and 250°C) were investigated. Deformation processes and velocity with Al driver sheet and different temperature were analyzed. The results indicate that it is better for formability of AZ31 sheet to adopt 1-mm Al driver sheet at higher discharge energy and warm temperature.

Laser Indirect Shock Welding of Fine Wire to Metal Sheet.

The purpose of this paper is to present an advanced method for welding fine wire to metal sheet, namely laser indirect shock welding (LISW). This process uses silica gel as driver sheet to accelerate the metal sheet toward the wire to obtain metallurgical bonding. A series of experiments were implemented to validate the welding ability of Al sheet/Cu wire and Al sheet/Ag wire. It was found that the use of a driver sheet can maintain high surface quality of the metal sheet. With the increase of laser pulse energy, the bonding area of the sheet/wire increased and the welding interfaces were nearly flat. Energy dispersive spectroscopy (EDS) results show that the intermetallic phases were absent and a short element diffusion layer which would limit the formation of the intermetallic phases emerging at the welding interface. A tensile shear test was used to measure the mechanical strength of the welding joints. The influence of laser pulse energy on the tensile failure modes was investigated, and two failure modes, including interfacial failure and failure through the wire, were observed. The nanoindentation test results indicate that as the distance to the welding interface decreased, the microhardness increased due to the plastic deformation becoming more violent.

Parametric study on numerical simulation of the electromagnetic forming of DP780 steel workpiece with aluminium driver sheet

The purpose of this study is to investigate the influences of numerical parameters on the electromagnetic forming (EMF) simulation. The 3-dimensional coupled electromagnetic- mechanical simulations were conducted to predict the deformation behavior of the advanced high strength steel (AHSS) sheet receiving support in EMF with aluminum driver sheet. Dual phase (DP) 780 steel workpiece was formed into a hemi elliptical protrusion shape with aluminum alloy AA1050 driver sheet using a flat spiral coil actuator and open cavity die. The deformed shape of the DP780 workpiece and the computation time with respect to element size, N cycle number and time step of electromagnetic (EM) solver were analysed.

Effect of an aluminum driver sheet on the electromagnetic forming of DP780 steel sheet

Some experimental studies have proved that materials with low electrical conductivity and even nonconductive materials can be formed using driver sheets with high electrical conductivity. This study investigated the effect of an aluminum driver sheet on the forming peak height of advanced high-strength steel sheet (AHSS) in the electromagnetic forming (EMF) process. DP780 workpieces were formed into a hemi-elliptical protrusion shape, analogous to a reinforcement rib, with various thicknesses, sizes, and material types of the aluminum driver sheets. These experiments were performed with a flat spiral coil actuator connected to the EMF system with a high energy capacity. In addition, three-dimensional coupled electromagnetic-mechanical finite element (FE) simulations were conducted to analyze the effect of the aluminum driver sheet on the forming peak height of the high-strength steel sheets and to predict the proper configuration of the aluminum driver sheet.

Abstract T P255: QCI-NASCAR - Quality Care Improvement with Nursing-driven Acute Stroke CARe

Objective: To observe the impact on stroke code time metrics after applying a “pit stop” model of bedside nursing for telestroke encounters. Background: Despite the recent push for target treatment times in acute stroke codes, no guidelines exist for optimizing practices specific to stroke care via telemedicine. Effective telestroke is dependent on efficient data gathering by remote staff, and lengthy metrics for real-world telestroke often preclude timely tPA treatment. By co-opting “pit stops” as inspiration, an optimized nursing workflow for telestroke can be created on the following principles: Identification of Shared Goals; Organized Urgency with the Removal of Gatekeepers; Multi-personnel, Non-Sequential Processes; Focus on Defined Staged Roles; and Empowered Engagement/Responsibility. Methods: The QCI-NASCAR protocol was implemented in Oct 2013, and data was collected prospectively on consecutive stroke code activations through Apr 2014 at St. Paul University Hospital (Dallas, TX), a telestroke spoke site. The nurse-driven protocol was reinforced by a paper checklist (i.e. “Driver Sheet”), which doubled as a data collection form. Timestamps were recorded in real time for: door time, MD at bedside, CT arrival, needle time, and/or code cancellation. The primary outcome was Door-to-CT (D2CT) times to reflect the portion of the stroke code most impacted by the nursing protocol. Results: Mean D2CT times were: all cases (n=152, 33.2 min), intervention-eligible cases (n=71, 27.0 min), and thrombolytic-eligible cases (n=57, 22.2 min). A trend for lower D2CT times and standard deviations was noted in comparing the first half of the data (n=76, 38.04 ± 58.1 min) to the second (n=77, 27.8 ± 19.1 min; p<0.05). A similar pattern was noted in the subset of intervention-eligible cases: first half (n=36, 29.4 ± 37.4 min) vs. second half (n=35, 24.3 ± 18.6 min; p<0.05). IV tPA was administered 3 times, including an institutional best door-to-needle time of 32.0 min. Conclusion: QCI-NASCAR demonstrates the feasibility of implementing a nursing-driven protocol for telestroke encounters. A larger, multi-institutional trial will demonstrate if such a protocol can significantly and reproducibly lower stroke code metrics to national guideline parameters.

Magnetic pulse forming of AZ31 magnesium alloy shell by uniform pressure coil at room temperature

The magnetic pulse forming process of AZ31 magnesium alloy shell using uniform pressure coil at room temperature was investigated. ANSYS FEA software was used to analyze the distribution of magnetic flux density of the uniform pressure coil and magnetic pressure for loading on the AZ31 sheet. The characteristic of forming process of AZ31 shell was revealed, and magnetic pulse forming process of AZ31 shell and effect of Al alloy sheet with different thickness were presented by experiments. Due to impact between sheet and die, the rebound profiles on the bottom of deformed sheets were observed. In order to remove the rebound profile, AA5052 sheets were employed to drive the deformed AZ31 sheets. The section contour of R = 30 mm (R means bottom radius of die) shell deformed by 0.5-mm thickness of driver sheet driving once and R = 15 mm shell deformed by 1-mm thickness of driver sheet driving twice are good agreement with die, not only width direction (AB direction) but also length direction (CD direction). However, there was a big obstacle to deform the AZ31 shell with R = 2 mm, because the die had small bottom radius and sidewall section. Variation of effective strain and velocity with width direction and length direction during magnetic pulse forming without driver sheet and with Al driver sheet were analyzed by simulation.

Effects of driver sheet on magnetic pulse forming of AZ31 magnesium alloy sheets

In this work, the formability of AZ31 magnesium alloy sheets was investigated by electromagnetic bulging experiments with driver sheet. Al (0.5 mm, 1 mm, and 2 mm thick) and Cu (1 mm thick) driver sheets were used to accelerate the AZ31 sheet in electromagnetic forming (viz magnetic pulse forming) process. In order to evaluate the effect of impact induced by driver sheet, the electromagnetic bulging experiments with gap between AZ31 sheet and driver sheet were investigated. Compared with quasi-static forming limit results, increases in the major and minor principal strains (with 0.5 mm, 1 mm driver sheet, and without driver sheet) of approximately 68 % and 72 % were achieved, respectively. However, the major and minor principal strains with 2 mm Al driver sheet increased about 148 % and 184 %. When the energy is up to 2.788 kJ after the first crack (with 1 mm Al driver sheet) producing, the major and minor strains increase about four times compared to the quasi-static condition.

Formability of Ti–6Al–4V titanium alloy sheet in magnetic pulse bulging

In order to investigate the formability of Ti–6Al–4V titanium alloy sheet in high speed forming process, electromagnetic forming (EMF) namely magnetic pulse forming with an Al driver sheet is performed experimentally. Formability under EMF is compared with that in quasi static condition. Fracture analysis for the titanium alloy Ti–6Al–4V is then carried out to study the fracture mechanism and material response. Results indicate that the formability undergoing EMF process with a driver sheet is increased beyond that exhibited in quasi-static tests. In electromagnetic free bulging, the forming limit of Ti–6Al–4V increases by 24.37%, which is more optimistic than AA5052-O. Fractography analysis using SEM determines that the Ti–6Al–4V titanium alloy sheet fails in a combination of ductile fracture and shear fracture when subjected to the electromagnetic bulging process while only ductile fracture develops in quasi-static condition.

Formability of AZ31 magnesium alloy sheets during magnetic pulse bulging

Electromagnetic forming (EMF), i.e., magnetic pulse forming, with and without an Al driver sheet is experimentally performed to investigate the formability of an AZ31 magnesium alloy sheet during high speed forming. The formability of the magnesium alloy AZ31 during EMF is compared with that during traditional quasi-static tests. The results show that the formability of the magnesium alloy sheet undergoing the EMF process without the driver sheet is increased compared with that during quasi-static tests. To improve the energy efficiency of and to accelerate the AZ31 sheet, an Al driver sheet was used. The energy efficiency increases from 0.2% (no driver) to 1.8% (with a 2mm driver sheet). The forming limits of the magnesium alloy samples with the 2mm driver sheet are dramatically higher than those during quasi-static tests. The major and minor principal strains with the 2mm Al driver sheet increase by approximately 148% and 184%. The forming limits with 0.5 and 1mm driver sheets are similar to those during the EMF process without the driver sheet, enabling the AZ31 sheet to be formed at a higher strain. Increases in the major and minor principal strains with the 0.5mm driver sheet of approximately 68% and 72%, respectively, are achieved. According to the analysis of the crack fracture observations of the samples with the driver sheets, the fracture surfaces have obvious plastic dimples, which exhibit typical ductile rupture. The test results indicate that the formability could be significantly improved. The EMF process could be used in the manufacturing of AZ31 magnesium alloy sheet parts at room temperature.

Application of magnetic pulse welding technique for flexible printed circuit boards (FPCB) lap joints

The magnetic pulse welding (MPW) is a high speed solid state welding process which has been used successfully to provide metallurgical and electrical bonds between flexible printed circuit board (FPCB) with using: (1) welding with aluminum driver sheet and (2) without driver sheet. The optimum bank energy for reliable bonding was about 1kJ with 160–180kA maximum current. The maximum tensile shearing for most welded samples was nearly same as tensile shearing strength of copper layer of FPCB sheet.

Effects of process parameters on electromagnetic forming of AZ31 magnesium alloy sheets at room temperature

In this work, the effects of process parameters on AZ31 magnesium alloy sheets were investigated by electromagnetic bulging experiments. The bulging height increases with increasing discharging energy, which is adjusted by tuning discharge voltage and capacitance. The limit dome height of electromagnetic forming is markedly improved as compared to quasi-static forming. In order to improve the efficiency of the energy, 0.5- and 1-mm thick Al driver sheet were used to accelerate the magnesium alloy sheets. For rupturing the AZ31 sheet, the discharging energy can be reduced from a maximum value of 4.356 kJ (no driver) to 2.304 kJ (with1-mm Al driver sheet). The numerical simulation for the electromagnetic forming of AZ31 sheet is performed by means of ANSYS FEA software. The change of velocity, strain rate, and plastic strain energy were analyzed by simulation. Compared with quasi-static forming limit results, increases in the major and minor principal strains of approximately 68 and 72 % were achieved, respectively.

Electromagnetic impact welding of copper-to-copper sheets

Copper (Cu) has some properties, similar to aluminium (Al), like high thermal conductivity, high thermal expansion coefficient, relatively low melting point, brittleness at elevated temperatures and less viscosity of molten metal. These properties make the welding of Cu and Cu alloys difficult as compared to welding of carbon steels. The present study investigates the feasibility of electromagnetic impact welding of Cu-to-Cu sheets by using Al as the driver sheet. A study has been carried out to characterize the electromagnetic impact welding of 0.5 mm thick Cu sheets. The results of the microstructure and tensile shear strength tests are reported.

Electromagnetic impact welding of aluminum to stainless steel sheets

Welding of aluminum (Al) to stainless steel (SS) is difficult due to the difference in their melting temperatures. The processes, which are available for welding of Al-to-SS, are friction welding, laser welding, electric discharge welding, etc. The present study investigates electromagnetic impact welding of Al-to-SS by using Al as the driver sheet. The effects of process parameters such as energy, standoff distance and coil geometry on the tensile shear strength of the welds are examined. A study has been carried out to characterize the effectiveness of the process of welding 1 mm thick Al sheet to 0.25 mm thick SS sheet. The results of the microstructure and tensile shear strength tests are also reported.