can be simple and affordable, but have less strength than RSW. And, in most cases, mechanical joining techniques are combined with adhesive bonding to increase the static and fatigue strength of joints and prevent corrosion of joints caused by the contact between the dissimilar metals. Although RSW is the typical strategy for joining steel stampings together into a completed body, it has been problematic when applied to aluminum. Additionally, when applying RSW to the joining, dissimilar materials present numerous challenges. Issues can appear due to different melting points, different chemical structures, the formation of intermetallics and corrosion problems.
Friction Welding Offers an Alternative Friction welding, a type of solid-state
joining, creates mechanical friction between workpieces in relative motion to one another, heating the materials until they reach a plas- tic state (nonmelting) at the joint interface. The materials are then forged together by force, creating a joint. It offers numerous benefi ts over other joining techniques including elimination of fi ller metal or fl ux, higher quality joints, a very small heat affected area, and no coarse grain formation. A proven joining methodology, friction welding can be applied as friction spin (or rotary) welding, linear friction stir welding (LFSW or FSW) or refi ll friction stir spot weld- ing (RFSSW), as well as multiple variants of each approach. While most rotary friction welding is used on round, sym- metrical parts, linear friction stir welding and RFSSW allow solid-state welds on a wider range of part geometries. A major advantage of friction welding is that it allows dis- similar materials to be joined. In fact, nearly half of the welds made through friction welding are for joining of dissimilar materials. Normally the wide difference in melting points of the two materials would make it impossible to weld using tra- ditional techniques, and would require some sort of mechani- cal connection. Friction welding provides a “full-strength” bond with no additional weight.
As a variant of friction stir welding, RFSSW has become a focus as a solution for spot welding aluminum and dissimilar materials. It shows great potential to be a replacement of single- point joining processes like resistance spot welding and riveting.
Refi ll friction stir spot joining is similar in principal to LFSW, although generally applied as a joining technology for overlap- ping or stacked sheet material. Both techniques use a rotating tool with a specially designed pin and shoulder. However, with LFSW the tool travels along a seam between two metal plates versus the tool staying in one spot in friction spot joining. Coldwater Machine fi rst began development of its friction welding solutions in 2003, originally developing and integrat- ing friction spin welding solutions. Since then, it has designed
A panel of SpotMeld sample welds.
dozens of its SpinMeld systems for installation at a variety of Tier suppliers and OEMs in both automotive and nonautomotive markets. Given the increasing use of lightweight materials, and especially aluminum in automotive body applications, Coldwater has applied this friction welding experience to the challenge of spot welding of aluminum and dissimilar materials.
Developments in Refi ll Friction Stir Spot Welding In 2014, the SpotMeld RFSSW solution, based upon technology developed and patented by Helmholtz-Zentrum (Geesthacht, Germany) was announced. For integration of the technology into high-production environments, Coldwater con- tinues to partner with the Helmholtz Institute and weld-head provider Harms & Wende. SpotMeld uses a three-piece tool to join two or more faying surfaces. Basically, heat is generated between the tool and materials being mated to create a soft, plastic-like region. Coldwater has had success in spot welding aluminum (1000–7000 series), magnesium, nonferrous and dissimilar sheet materials, making SpotMeld a viable alternative to single-point joining processes like resistance spot welding, laser welding and riveting.
65 — Motorized Vehicle Manufacturing 2016
Images courtesy of Coldwater Machine Co.
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