FRICTION STIRRING INTERLOCKING OF DISSIMILAR MATERIALS
A new solid-phase technique called Friction Stir Interlocking (FSI) will be developed for joining lightweight metals to composites, composites, thermoset plastics, or other non-metallic materials. FSI will enable joining of magnesium (Mg) and aluminum (Al) to non-metals and would fill a critical technology gap identified by VTO for multi-materials joining. In FSI, mechanical interlocks (i.e. fasteners) can be created with a variety of patterns and cross sections as illustrated in the adjacent figure. As a friction stir process, numerous interlocks can be created quickly and uniformly, in a single pass, offering reduced cost and improved process efficiency compared to conventional metal-to-non-metal fasteners. Technical Approach:Two approaches for joining Mg and Al to non-metals are described as follows. The first approach is illustrated in the adjacent schematic. Here, pins that match the material of the metal sheet are inserted up through holes cut in the metal and non-metal sheets ending flush with the top of the metal sheet. A specially designed FSW tool then traverses the joint and welds the pins to the metal sheet to complete the joint. The large hydrostatic pressure in the plasticizing metal during welding will fill any small tolerance gaps, between the pin OD and CF hole ID. A thermally activated adhesive film, such as 3MTM 583 for example, can be applied between the metal-non-metal interface prior to welding to improve joint strength. The film will also serve as a barrier to galvanic corrosion by sealing against electrolyte imbibition into the joint interfaces. The joint could certainly be made without the added step of an adhesive film if desired. The short process time (a few seconds) and low process temperature (as low as 250 degrees C for Mg) make the FSI approach attractive for joining Mg and Al to CF without substantially degrading the CF material properties. Key tasks to be completed on this project are 1) tooling design, 2) process development, 3) property characterization and 4) modeling and simulation. The second approach is illustrated in the schematics below and involves embedding metal inserts within the non-metal and subsequently friction stir welding Mg or Al sheet to the metal insert. In friction stir scribe welding of metals to composites, the stirring action and high input act to disrupt the fiber and weaken the matrix. Furthermore process speeds are extremely slow. If metal inserts can be inserted during the fabrication process of the composite, mechanical interlocks can be created without degrading material properties. Metal plates can then be welded to the embedded inserts. This offers improved joint strength and dramatically improved process speeds. A similar FSW welds to inserts may lead to a cost competitive, production viable solution for metal to carbon fiber joining Below are schematics of cross sections of various interlock configurations. For this concept it is appropriate for bar inserts that run the entire course of the weld. Alternatively inserts can be smaller inserts to accommodate spot or stitch welds. The primary invention in the second approach is to embed an insert in the composite during manufacture of the composite blank to create an interlocked metal surface on the composite such that an FSW metal to metal weld can be made joining a metal part to the embedded insert. The primary invention is the process of embedding an insert during fabrication of the composite blank (examples: injection molding, compression molding, winding, layups etc. for the purpose of effectuation a composite to metal joint by FSW (or FSW variant) of a metal part to a metal insert embedded in the composite.
John Shilling
Sandro W. Lubis, PhD
Laura Fierce
DREAM2
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