The overall objective was to advance the state of the art of emerging spot like joining techniques, enabling the adoption of Friction Stir Spot Welding (FSSW) in the manufacturing industry, particularly in automotive and aircraft manufacturing industries, where there is a strong interest in the use and joining of lightweight alloys, due to the increasing utilisation of lightweight designs. The advantages offered by FSSW include, among others: possibility of joining dissimilar multi-materials combinations; low heat input with relatively low maximum temperatures; no production of toxic fumes, gases or environmental contaminants; excellent bonding with fine microstructure; automatic and highly repeatable process. Hence, the potential for the use of FSSW in the manufacturing industry is extremely large and the benefits of replacing traditional joining techniques are significant.
The main objectives were i) to study the feasibility of using FSSW in replacement to conventional spot like technologies (mechanical fastening –clinching, riveting, self-piercing riveting– and fusion based techniques –resistance and laser spot welding–) and ii) industrially apply in automotive or other components production (i.e. mass production) as well as other manufacturing sectors.
The achieved results are the following:
a) Process Technology:
- established the range of parameters for production of high quality friction stir spot welds in different lightweight alloys (heat treatable aluminium alloys, in sheet and honeycombe geometry);
- demonstrated the combined use of spot like process and application of polymeric sealants or adhesives for corrosion protection, which is not possible with laser or resistance spot welding due to the high temperatures achieved during the process.
b) Application to relevant lightweight alloys and multi-material joints:
- demonstrated friction based spot welding applications on simple demonstrator components;
- established the economic case for using FSSW in components production or other manufacturing products in comparison with more established welding processes. Estimated energy consumption and equipment investment reduction up to 99% and 40%, respectively in comparison to resistance spot welding.
The SPOTLIGHT project has developed knowledge based FSSW process methodologies allowing joining of difficult to weld lightweight alloy grades, i.e. grades which might have not experience a wider application simply due to the lack of an appropriate technology to weld them.