Search Results

Aluminum alloys are increasingly utilized in automotive body panels and crash components to reduce weight. Accurately assessing formability of the sheet metal can reduce design iteration and tooling tryouts to obtain the desired geometry in aluminum stampings. The current ISO forming limit curve (FLC) procedure is a position dependent technique which produces the FLC based on extrapolation at the crack location. As aluminum sheet metal use increases in manufacturing, accurate determination of the forming limits of this material will be necessary prior to production. New time dependent methods using digital imaging correlation (DIC) account for variations in material behavior by continuously collecting strain data through the material necking point. This allows more accurate FLC determination that is necessary for efficient design in the automotive stamping industry.

Deformation Resistance Welding (DRW) is a process that employs resistance heating to raise the temperature of the materials being welded to the appropriate forging range, followed by shear deformation which increases the contacting surface area of the materials being welded. Because DRW is a new process, it became desirable to establish variable selection strategies which can be integrated into a production procedure. A factorial design of experiment was used to examine the influence of force, number of pulses, and weld cycles (heating/cooling time ratio) on the DRW process. Welded samples were tensile tested to determine their strength. Once tensile testing was complete, the resulting strengths were observed and compared to corresponding percent heat and percent reduction in thickness. Tensile strengths ranged from 107 kN to 22.2 kN. A relationship between the maximum current and the weld variables was established.

Conductive heat resistance seam welding (CHRSEW) is a new process developed at Edison Welding Institute for creating butt joints on aluminum sheet. The process uses conventional resistance seam welding equipment, and takes advantage of steel cover sheets on either side of the intended joint. Resulting joints are fusion in character, and can be manufactured at very high welding speeds (∼ 3 to 4 m/min). In this study, the conductive heat resistance seam welding process was extended to some new applications. These included joining a 7075-T6 alloy, and a dissimilar thickness 1- to 2-mm 5754 configuration. The former is generally considered unweldable by fusion methods, and is of considerable interest for aerospace applications. The latter is representative of a tailor welded blank for automotive applications. Resulting welds were evaluated using metallurgical examinations and mechanical testing.

Laser welding has long been evaluated as a joining technique for galvanized steels in a lap-joint configuration in the automotive industry. However, a problem associated with the low boiling point of zinc limits the application of the laser process in a lap-joint configuration. Zinc-coatings at the interface of the two coated sheets vaporize during welding and the volume of the zinc vapor expands rapidly. The venting of the zinc vapor from the weld pool causes expulsion of the molten metal during welding and a portion of zinc vapor remains in the weld as porosity after welding. To improve the weld quality of galvanized steel, many efforts have been attempted worldwide, but limited success has been reported. Edison Welding Institute (EWI) investigated the laser weldability of galvanized steel in a lap-joint configuration with no gap using a dual beam laser welding technique.

Weldability study has been performed on Polypropylene (PP) and PC/ABS samples to investigate how the paint layer along the weld joint affects the vibration weldability. The plastic used for this study were PP representing semicrystalline thermoplastics and PC/ABS representing amorphous thermoplastics. Both resins were molded to generate sample plaques for the study. Design of Experiment (DOE) studies were initially conducted with unpainted plaques and then repeated with the painted plaques for comparison. Optimal welding parameters were determined through DOE and the maximum weld strength under optimized welding conditions were determined and compared. Following each DOE, a regression analysis, using the weld strength as a response, was performed.

An experimental evaluation to systematically study a hot air cold stake joining process was conducted with injection molded samples. Twelve material combinations consisting of six stud plate materials were matched with two hole plate materials (GDT 6400 and 18% talc filled PP). Seven stud designs with variations in size and geometry were used for each material combination. A proper heating temperature was first determined by heat characterization trials. Different heating times and stake heights were studied in the staking experiments. Pull tests were conducted to determine the strength of the joints and their failure mode. Results showed that material characteristics, material combinations, and process parameters all could contribute to variations in pull strength and different failure modes.

Resistance welding control systems utilizing secondary current feedback receive widespread utilization both in Europe and Japan. However, these types of control systems are only beginning to be used in any extended basis in this country. Currently, two variants of these systems are available; so called “self-teaching” systems, and “learning curve” systems. Either system has been shown to be capable of providing a stable secondary resistance welding current within two cycles. Recent work has indicated, however, that the self-teaching type control systems may be adversely affected by non-optimum set-up conditions, particularly poor fit-up and the introduction of organics (sealers or adhesives) at the faying surface. This work examines the performance of learning curve type constant current control systems under these adverse set-up conditions. Six conditions were selected for study; three degrees of progressively poorer fit-up, with and without an organic sealer.

Many automotive production plants are using various prepulse schedules for resistance spot welding thin gauge galvanized steel. The claimed reasons are that wider current range and longer electrode life are obtainable in comparison to the conventional schedule. However, data to support this are not available. The objective of this program was to determine the effect of prepulsation on spot weldability of galvanized steel. In this work, several prepulse resistance spot welding schedules were evaluated in two full factorial experiments. The effect of the number of prepulse cycles, the prepulse heat level and the effect of cool time were studied in detail. Weldability was evaluated using an electrode life test procedure in which the current range was periodically examined over the life of the electrodes. Generally, the results indicate that prepulsation has a negative effect on the resistance spot weldability of thin gauge galvanized steel.

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. It was found that the addition of the Ferrophos bearing paints had pronounced effects on weldability. Typically, required current levels were reduced by several thousand amps, and effective current ranges were increased by 50 to 100 percent. During electrode life testing significant reductions were also noted both in the rates of electrode face diameter increase, and the degree of electrode pitting.