Resistance spot welding for light weight design (Spot Light)

Purpose and goal

It is important to be in the knowledge front line regarding manufacturing processes and manufacturing technologies, in order to strengthen Swedish vehicle industries competitiveness and keep production in Sweden. The project supports long term strengthening of research environments within production technology in order to find solutions to problems arisen by increased environmental demands and demands for crash performance. Requirements for less fuel consumption are increasing. This is driven by both environmental concerns and fuel cost. The requirements leads to increased usage of materials that contributes to lighter bodies and cabs with kept or increased strength performance. Simultaneous requirements for increased crash performance tend to increase weight, and low weight materials have to be used to counteract. Resistance spot welding is today the dominating joining technology for car and cab bodies and will so remain in the foreseeable future. It has great advantages as for production cost and time. Spot welding must however be developed in order to handle the new materials and the new material combinations which will be used in future light weight bodies. The project will lead to reduced production preparation time by developing and verifying simulation techniques for spot welding. The project will develop spot welding so that steels can be spot welded in thicker stacks with increased number of sheets than today considered possible. Special interest will be devoted to joints with thin sheets for weight reduction. Special problems with cracking at spot welds in crash loading will be addressed. New innovative techniques for spot welding of aluminum will be developed. Innovative techniques for electrode dressing will also be evaluated. New techniques for robotized NDT of spot welds will be demonstrated and evaluated. Finally a new approach will be made to the optimization of number of spot welds in a component or body through a systematic robust procedure.

Results and expected effects

The project will develop techniques supporting optimized and efficient quality assured spot welding of metals which will reduce the weight of a vehicle, as high strength steel and aluminum, including new combinations. The project will also deliver a FEM-based simulation tool verified by experiments and ready for implementation. The results will be spread through research reports, guidelines, training documentation and a NDT demonstrator. The results will be valuable both for academy and industry, and a considerable increase of competence is foreseen. A PhD student is planned within the project. This PhD student will focus on simulation and determination of the spot welding process parameters by simulation. The results will all together contribute to strengthening of the Swedish vehicle industry competitiveness, and will support reduction of CO2 and other emissions, by reduced body and cab weight. Materials investigated in the project will also have a positive impact on crash performance. Reduced lead time for production preparation (manufacturing engineering) of new material combinations in spot welding with the help of simulation tools. A techn. lic. exam in production preparation of spot welding Spot welding guide lines for multi sheet stackups, also combined with thin sheets. Guide lines how to avoid certain cracking problems in crash loading of spot welds with Boron steels Weight reduction of components by using UHSS Guide lines for spot welding of aluminum and magnesium. Reduced cost compared to mechanical joining. Weight reduction of components by using aluminum or magnesium. Efficient tip dressing of spot welding electrodes. Cost reduction for NDT of spot. Demonstrated technologies for NDT of spot welds. Methodology for cost reduction by optimization/reduction of number spot welds in bodies. Handbook and guide lines for spot welding of sheet combinations which are not regarded as possible now.

Approach and implementation

The project is divided in work packages (WP), each with specific targets and milestones. The manning is not the same in all WP, but matched to fit need, knowledge and available resources. Some WP will have common meetings to improve communication and reduce administration and travelling. The project partners have positive experience from this way to organize a big project. All tasks/WP can be and are clearly specified, and the partners individual competence is utilized efficiently. In brief the project will: Develop cost efficient spot weld processes for new steels and for aluminum alloys. Develop methods for spot welding of thicker joints and a greater number of sheets than now allowed in the vehicle industry. Propose an innovative tip dressing technology for electrodes used for steel and aluminum respectively. Develop, build and evaluate a demonstrator for automated non destructive testing (NDT) of spot welds. The choice of technology will partly be based on experience from earlier projects. Develop techniques for virtual simulation of process parameters in order to shorten the lead time for manufacturing engineering. Develop techniques for quality assured optimization of spot weld number, in order not to weld more than justified by product strength requirements. Develop new directions and guide lines for spot welding based on the project achievements.