Jerry E. Gould

Analysis of the Electromagnetic Impulse Joining Process with a Field Concentrator

Estimation of the electromagnetic pressure is a key step in the analysis of the electromagnetic impulse joining process. This information is essential to understanding process physics, judging coil reliability, and predicting mechanical behavior of the workpiece. In the present work, a comprehensive analysis of the compressive joining processes with a magnetic field concentrator was developed using an equivalent inductance and circuit approach. The analysis is able to incorporate the complex coupling of the system components to a single input‐output unit. With the input capacitor bank parameters or current in the coil, the induced current in the workpiece, and magnetic pressure acting on the workpiece can be calculated in one step. The analytical approach is verified by comparing numerical solutions with experimental results.

Development of spot weld failure parameters for full vehicle crash modelling

Abstract A cost and time effective process was developed to create spot weld failure parameters for crash models implemented in LS-DYNA. The process includes a design of experiment (DOE) approach for coordinating data collection, welding and testing, finite element modelling, statistical analysis, validation, and implementation. The DOE approach was used to coordinate testing of a reduced set of samples over a large range of material strengths and gauges. This testing included cross-tension, lap shea, and coach peel type evaluations. Computer models for each metal combination and sample geometry were developed to obtain normalised tensile, shear and bending stress at the incidence of weld failure. These normalised loads were then regressed to extend these results to all possible material combinations within the DOE space. These results were then used to estimate the spot weld failure parameters for all the stack-ups of interest. A set of multiweld T-section samples were then welded, physically tested and computer modelled to validate the failure parameters developed from the small single weld tests.

Weldability and electrode wear characteristics of hot-dip galvanized steel with and without a ferrophos containing primer

This study examined the effect of primers containing a conductive pigment on the resistance spot weldability of hot-dip galvanized steel. The pigment used was ferrophos, essentially Di-iron phosphide. Basically, two types of tests were used in this work. Current range tests were used to establish the effect these primers have on the effective ranges of weldability. Limited electrode life tests were used to infer the long term performance of the hot-dip galvanized steels with and without this paint

A detailed examination of weldability lobes for a range of zinc-coated steels

The objective of this study was to investigate the weldability of four tyes of coated steels. These materials include: uncoated, hot-dipped galvanized, electro-galvanized and galvannealed steels. «Statistically significant» weldability lobes were evaluated for each material. Dynamic resistant traces were also evaluated

Estimations of compatibility of supercapacitors for use as power sources for resistance welding guns

Supercapacitors offer potential for several kilojoules of energy to be proved in a small package with limited charge voltage (few volts). A preliminary examination of supercapacitors suggests that both the voltages used and retainable energies are well matched for resistance spot welding applications. Utilization of supercapacitors as resistance welding power supplies offers significant weight reduction over conventional (transformer and power supply) approaches, with subsequent economic advantages. In this work, some preliminary analyses have been done to assess the potential for using supercapacitors as resistance welding power supplies. This was done by integrating two separate analyses: one to assess the inductive response of specific weld gun designs and the second to define the current response of supercapacitors matched with that inductance. Results demonstrated potential for achieving desired currents and pulse widths with the proper selection of supercapacitor type and arrangement as well as secondary gun configuration. These analyses were further used to understand implications of system design on overall deliverable current capability. While the results described here only describe potential, some recommendations are made for next steps advancing supercapacitor-based resistance spot weld gun technology.

Development of Appropriate Spot Welding Practice for Advanced High Strength Steels (TRP 0114)

This program evaluated the effects of common manufacturing variables on spike-tempering effectiveness. The investigation used design-of-experiment (DOE) techniques, and examined both dual-phase and martensitic grades of high-strength steels (HSS). The specific grades chosen for this project were: Dual-phase (DP) 600, galvannealed (GA), 1.55 mm (DP) 600; Dual-phase (DP) 980 (uncoated), 1.55 mm (DP) 980; and Martensitic (M) 1300, 1.55 mm (M) 1300. Common manufacturing conditions of interest included tempering practice (quench and temper time), button size, simulated part fitup (sheet angular misalignment and fitup), and electrode wear (increased electrode face diameter). All of these conditions were evaluated against mechanical performance (static and dynamic tensile shear). Weld hardness data was also used to examine correlations between mechanical performance and the degree of tempering. Mechanical performance data was used to develop empirical models. The models were used to examine the robustness of weld strength and toughness to the selected processing conditions. This was done using standard EWI techniques. Graphical representations of robustness were then coupled with metallographic data to relate mechanical properties to the effectiveness of spike tempering. Mechanical properties for all three materials were relatively robust to variation in tempering. Major deviations in mechanical properties were caused by degradation of the weld itself. This was supported by a lack of correlation between hardness data and mechanical results. Small button sizes and large electrode face diameters (worn electrodes) produced large reductions in both static and dynamic strength levels when compared to standard production setups. Dynamic strength was further degraded by edge-located welds.

An examination of electric servo-guns for the resistance spot welding of complex stack-ups

In this program, the capabilities of medium-frequency direct current (MFDC) electric servo resistance welding guns for the welding of complex stack-ups were investigated. Capabilities of interest from these guns include the ability to apply forge forces and currents, as well as the ability to sequence the current and forging profiles. The complex stack-up under study included a 1-mm outside sheet attached to two 2-mm sheets. Work was done using design of experiment (DOE) techniques. The experiment included a range of processing variations deliverable from the MFDC servo-gun, as well as two electrode variations (materials and sizes). Heat balance during resistance welding of this stack-up was found to be dominated by the electrode variations. As electrode variations are not considered a solution for automotive complex stack-up applications, a best practice was defined from the DOE that included similar-sized class 2 electrodes. This best practice included short overall weld times, a moderate forge force, a significant (40 %) increase in current during forging, and a weld time relative to the forging portion of the weld schedule. This yielded nugget penetrations of roughly 50 % into the thin attached sheet. It was noted that, at these penetrations, indentations on both sides of the joint reached 0.45 mm and that process variations could be used to trade off penetrations with overall indentations.

Preliminary Investigations of Joining Technologies for Attaching Refractory Metals to Ni-Based Superalloys

In this study, a range of joining technologies has been investigated for creating attachments between refractory metal and Ni‐based superalloys. Refractory materials of interest include Mo‐47%Re, T‐111, and Ta‐10%W. The Ni‐based superalloys include Hastelloy X and MarM 247. During joining with conventional processes, these materials have potential for a range of solidification and intermetallic formation‐related defects. For this study, three non‐conventional joining technologies were evaluated. These included inertia welding, electro‐spark deposition (ESD) welding, and magnetic pulse welding (MPW). The developed inertia welding practice closely paralleled that typically used for the refractory metals alloys. Metallographic investigations showed that forging during inertia welding occurred predominantly on the refractory metal side. It was also noted that at least some degree of forging on the Ni‐based superalloy side of the joint was necessary to achieve consistent bonding. Both refractory metals were readily weldable to the Hastelloy X material. When bonding to the MarM 247, results were inconsistent. This was related to the higher forging temperatures of the MarM 247, and subsequent reduced deformation on that material during welding. ESD trials using a Hastelloy X filler were successful for all material combinations. ESD places down very thin (5‐ to 10‐μm) layers per pass, and interactions between the substrates and the fill were limited (at most) to that layer. For the refractory metals, the fill only appeared to wet the surface, with minimal dilution effects. Microstructures of the deposits showed high weld metal integrity with maximum porosity on the order of a few percent. Some limited success was also obtained with MPW. In these trials, only the T‐111 tubes were used. Joints were possible for the T‐111 tube to the Hastelloy X bar stock, but the stiffness of the tube (resisting collapse) necessitated the use of very high power levels. These power levels resulted in damage to the equipment (concentrator) during welding. It is of note that the joint made showed the typical wavy bond microstructure associated with magnetic pulse/explosion bond joints. Joints were not possible between the T‐111 tube and the MarM 247 bar stock. In this case, the MarM 247 shattered before sufficient impact forces could be developed for bonding.In this study, a range of joining technologies has been investigated for creating attachments between refractory metal and Ni‐based superalloys. Refractory materials of interest include Mo‐47%Re, T‐111, and Ta‐10%W. The Ni‐based superalloys include Hastelloy X and MarM 247. During joining with conventional processes, these materials have potential for a range of solidification and intermetallic formation‐related defects. For this study, three non‐conventional joining technologies were evaluated. These included inertia welding, electro‐spark deposition (ESD) welding, and magnetic pulse welding (MPW). The developed inertia welding practice closely paralleled that typically used for the refractory metals alloys. Metallographic investigations showed that forging during inertia welding occurred predominantly on the refractory metal side. It was also noted that at least some degree of forging on the Ni‐based superalloy side of the joint was necessary to achieve consistent bonding. Both refractory metals were re...

Evaluation of GRCop-84 for use as a resistance spot welding electrode material through experimental and analytical techniques

In this program, a NASA-developed Cu alloy, GRCop-84. was examined for application in resistance welding electrodes. The GRCop-84 alloy was developed for a combination of high thermal and electrical conductivity as well as elevated temperature strength. Electrode life testing for resistance spot welding (RSW) galvanized steel was conducted with both this material and a C15000 Cu alloy (Cr-0.1 % Zr) for comparison. To assist in this comparison both materials were evaluated with an EWI-developed model for electrode life. This model allowed the performance of the electrode materials to be more directly compared to the underlying material properties of the respective alloys. Results suggested that for the as formulated GRCop-84 alloy, there was no advantage compared to the C15000 material. In fact, the electrode life results were substantially poorer for the GRCop-84 material. The modelling results suggested that this was largely related to the lower yield strengths of the GRCop-84 compared to the C15000 (about 60 %) throughout the temperature range of interest (room temperature to 1000 °C). This reduced strength resulted in deeper forge depths at the electrade face, causing excessive mushrooming and premature electrode life failure of the GRCop-84.