The lightweighting of vehicle structures has become imperative in order to further improve efficiency within the transportation industry. One method of lightweighting is through the extensive use of multiple materials, offering the ability to selectively add strength where needed while eliminating the addition of extraneous mass. Though effective in design, multi-material automotive structures are difficult to manufacture. One challenge which arises is the joining of these structures, which often cannot be achieved through traditional joining methods.Friction element welding (FEW) is a process capable of joining aluminum sheets to a steel substrate. An advantage of this process is that it does not require any pre-hole drilling. Instead, the aluminum material is softened through frictional heat caused by the rotation of the fastener and forced to flow around the fastener shaft by applying an axial load. When joining high-strength aluminum alloys, this flow becomes diminished due to these materials’ relatively low ductility, resulting in the formation of sharp edges which protrude from the head of the fastener in an irregular manner. These protrusions, termed chips, accelerate corrosion and are a significant defect.In a previous study, thermal assistance has been confirmed as a viable method of reducing chipping by improving the flow of aluminum. Thermal assistance requires that an additional process is added to the FEW process. Therefore, a rapid and efficient method for heating the workpiece must be pursued. An application method of such a process is developed and tested herein, which utilizes a direct electrical current applied locally to the joint region. The electrical flow in this configuration was limited to the workpiece only and was turned off prior to contacting the element. Therefore, electroplasticity was largely insignificant in these tests and only thermal effects can be assumed. The temperature rise was simulated and determined experimentally using a prototype modified downholder. This downholder design locally applied the electrical current near the joint area in order to maximize efficiency by reducing the redundant heating of surrounding materials. Electrical heating was found to be a viable method to efficiently and rapidly heat a workpiece in an FEW process. Furthermore, the overall energy consumption of the electrically assisted FEW process can be reduced relative to traditional FEW. A modified downholder design is proposed which will not add any additional process time. Another configuration is also explored which passes the electrical current through the element to the workpiece, resulting in significantly faster and more localized heating. However, this was only performed in simulations since electrical isolation of the spindle requires complex modifications to the FEW machine, which is outside the scope of this work.

Resistance Heat Assisted Friction Element Welding

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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