Abstract
Organic sheets made out of fiber-reinforced thermoplastics are able to make a crucial contribution to increase the lightweight potential of a design. They show high specific strength- and stiffness properties, good damping characteristics and recycling capabilities, while being able to show a higher energy absorption capacity than comparable metal constructions. Nowadays, multi-material designs are an established way in the automotive industry to combine the benefits of metal and fiber-reinforced plastics. Currently used technologies for the joining of organic sheets and metals in large-scale production are mechanical joining technologies and adhesive technologies. Both techniques require large overlapping areas that are not required in the design of the part. Additionally, mechanical joining is usually combined with “fiber-destroying” pre-drilling and punching processes. This will disturb the force flux at the joining location by causing unwanted fiber- and inter-fiber failure and inducing critical notch stresses. Therefore, the multi-material design with fiber-reinforced thermoplastics and metals needs optimized joining techniques that don’t interrupt the force flux, so that higher loads can be induced and the full benefit of the FRP material can be used. This article focuses on the characterization of a new joining technology, based on the Cold Metal Transfer (CMT) welding process that allows joining of organic sheets and metals in a load path optimized way, with short cycle times. This is achieved by redirecting the fibers around the joining area by the insertion of a thin metal pin. The path of the fibers will be similar to paths of fibers inside structures found in nature, e.g. a knothole inside of a tree. As a result of the bionic fiber design of the joint, high joining strengths can be achieved. The increase of the joint strength compared to blind riveting was performed and proven with stainless steel and orthotropic reinforced composites in shear-tests based on the DIN EN ISO 14273. Every specimen joined with the new CMT Pin joining technology showed a higher strength than specimens joined with one blind rivet. Specimens joined with two or three pin rows show a higher strength than specimens joined with two blind rivets.
Highlights
Weight reduction in the automotive sector is still achieved by using materials such as aluminum alloys and high strength steels
This article focuses on the characterization of a new joining technology, based on the Cold Metal Transfer (CMT) welding process that allows joining of organic sheets and metals in a load path optimized way, with short cycle times
Carbon-fiber-reinforced plastics (CFRP) with a thermosetting matrix are used in the automotive sector, which leads to a multi-material-mix in the final products
Summary
Weight reduction in the automotive sector is still achieved by using materials such as aluminum alloys and high strength steels. Carbon-fiber-reinforced plastics (CFRP) with a thermosetting matrix are used in the automotive sector, which leads to a multi-material-mix in the final products. This is a big challenge for the joining technology, since the different properties of the materials need to be respected to get the intended results [2]. Applied technologies for the joining of FRP-parts with metal structures are frictional and form-locking joints as well as adhesive bonds, whereby for these technologies the joining components need to be prepared in a complex way. The process allows the one-sided, fault-tolerant and fiber-fair joining of the different material groups in short cycle times With this new joining technology, overlapping areas can be reduced drastically, when compared to usual riveting techniques. Areas in which loads are introduced don’t have to be reinforced, so that weight advantages can be achieved
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