Design criteria for the pin-foot ratio for joining adhesion-incompatible polymers using pin-like structures in vibration welding process

Joining technologies have a crucial role in the product development process, e.g. to achieve local part properties or functional integrations. This often requires multi-material joints, which are challenging for conventional joining processes. Therefore, innovative processes are needed to generate bonds between adhesion-incompatible material combinations, such as joining using pin-like structures in the vibration welding process. Investigations into this novel process have provided initial findings; however, a specific pin design is not possible at this time. For this reason, the influence of the pin-foot width of the two joining partners was analyzed numerically by simulation. The results of the simulation were validated by experimental tests. The investigations show, that the simulation model is suitable for predicting the bond quality as well as the fracture behavior of the multi-material joint based on pin-like structures. The developed correlations between material, pin-like structure, and resulting bond quality allow design criteria for the pin-like structures to be derived. These allow a specific dimensioning of the pin-foot ratio depending on the used material combination. Thus, for example, the fracture behavior of the multi-material connection can be selectively adjusted, as well as the bond strength can be maximally utilized.

Study on the effect of the welding environment on the dynamic recrystallization phenomenon and residual stresses during the friction stir welding process of aluminum alloy

Various methods have been proposed to modify the friction stir welding. Friction stir vibration welding and underwater friction stir welding are two variants of this technique. In friction stir vibration welding, the adjoining workpieces are vibrated normal to the joint line while friction stir welding is carried out, while in underwater friction stir welding the friction stir welding process is performed underwater. The effects of these modified versions of friction stir welding on the microstructure and mechanical characteristics of AA6061-T6 aluminum alloy welded joints are analyzed and compared with the joints fabricated by conventional friction stir welding. The results indicate that grain size decreases from about 57 μm for friction stir welding to around 34 μm for friction stir vibration welding and about 23 μm for underwater friction stir welding. The results also confirm the evolution of Mg2Si precipitates during all processes. Friction stir vibration welding and underwater friction stir welding processes can effectively decrease the size and interparticle distance of precipitates. The strength and ductility of underwater friction stir welding and friction stir vibration welding processed samples are higher than those of the friction stir welding processed sample, and the highest strength and ductility are obtained for underwater friction stir welding processed samples. The underwater friction stir welding and friction stir vibration welding processed samples exhibit about 25% and 10% higher tensile strength compared to the friction stir welding processed sample, respectively. The results also indicate that higher compressive residual stresses are developed as underwater friction stir welding and friction stir vibration welding are applied.

Vibration welding of components with angled areas in the direction of vibration

Conventional manufacturing processes for plastic products, such as injection molding or extrusion, often limit the achievable component geometries. Therefore, it is necessary to join components in order to generate highly complex geometries. Vibration welding is one way of joining components. This process is frequently used and is characterized by short cycle times, high energy efficiency, and the possibility of joining large components. In vibration welding, plastic components are heated by an oscillating friction movement of the joining surfaces, then plasticized and subsequently welded together. The joining of three-dimensional seam geometries is therefore a challenge for vibration welding, as the components can be lifted off by the linear movement and the surfaces do not plasticize sufficiently. Previous investigations have shown that angles of up to 20° can be welded in the direction of vibration, but that the deviation from the plane considerably reduces the weld strength. In order to weld three-dimensional weld seam geometries with short cycle times and simultaneously achieve a high weld seam strength, a process is being developed which is intended to extend the design freedom in vibration welding.