Techniques for Improving Weldability and Testing of Weld-bonded Joints

Abstract: Increased understanding of improving the weld-bonding process is essential in order for the automotive industry to constantly develop their designs and production processes for the energy-efficient vehicles of the future. The joining method of weld-bonding, a hybrid method of adhesive joining and resistance spot welding, has introduced new challenges in the manufacturing and design of auto bodies. At the same time as adhesives are more incorporated in the joint configurations’, continuous development and implementation of ultra-high-strength steels, the complexity of the weld-bonding process increases. This thesis presents new approaches of parameter set-up and testing methods for weld-bonded joints. Aiming to displace the adhesive from the welding zone new parameters are tested by producing 1-D weld lobes that are analyzed in a screening matrix to find the factor with greatest effect on the weldability. Laser displacement measurement is a new method used to measure the amount of adhesive present in the joint during the welding cycle. The amount of adhesive plays an important role in the process and the intention is to get an assessment of how different thicknesses affect the weldability. The results showed that the different parameters have different influential behavior depending on the sheet thickness of the welded material. From the main effect screening, cap type has the greatest influence on the weld current range followed by the addition of an extra pre-pulse. The measured amount of adhesive present immediately before the weld pulse is very small. An interesting observation is that samples showing the largest increase in weld current range, compared to the corresponding reference were the samples which had most adhesive present in the contact area. The study showed that there are new parameters that improve the weldability of a weld-bonded joint that can be utilized using existing welding equipment. Finally, the study has shown that many possibilities exists to continue exploit within the field of weld-bonding, to be able to further utilize the effectiveness of weld-bonded joints in future lightweight autobody design.