Master's thesis at RISE: Mechanical joining of megacastings

Robust joining process with self-pierce riveting (SPR) for mega castings.

Background
Aluminium offers significant potential for circular manufacturing through material recycling. However, cast aluminium alloys, and recycled aluminium alloys, also lead to material properties which are challenging for joining with self-pierce riveting, a joining process used extensively in car body manufacturing. To achieve lower weight, fewer parts, and reduced manufacturing complexity compared to conventional steel sheet parts, the use of aluminium cast parts is increasing. For these reasons, Volvo Cars will soon produce their own cast parts and their future car bodies will consist of a few very large castings, also called mega castings. Mega castings were recently introduced in the automotive industry by Tesla and several other manufacturers are also known to investigate this concept.  RISE, Volvo Cars, Stanley Engineered Fastening, Atlas Copco and BTM Scandinavia are working together to create stable and reliable joints in mega castings and enable the introduction of recycled aluminium into structural parts within the FFI project RobuCAP (Robust mechanical joining of cast aluminium components (RobuCap) | Vinnova (https://www.vinnova.se/en/p/robust-mechanical-joining-of-cast-aluminium-components-robucap/))

Problem description
Without heat treatment the as-cast properties of aluminium are strongly dependent on the microstructure achieved after casting and most often have low ductility, which is challenging for mechanical joining processes. For mega castings heat treatment should be avoided due to costs and energy consumption. This means the cast part will have local variations in its properties resulting from the casting process.

This creates a challenge in determination of the joinability of cast parts with mechanical joining processes like SPR, that are highly depending on good ductility in the material. Is the ductility low (e.g. in recycled aluminium), cracks in the casting can occur which can be a problem for the joint strength and corrosion protection.The possible variations between parts, casting batches, and locally in the part makes the evaluation of joinability quite complex and new qualification methods need to be found. Cracking of the castings need to be avoided and optimal process parameters or process modifications need to be developed.

Objective
Possible scopes include:

• Microstructural and mechanical analysis of properties and variations in mega casting parts
• Correlation of component properties with cast test specimens
• Image analysis for crack quantification and distribution
• Joining tests for process optimisation and/or investigation of local heat treatment for improved joining results
• Strategies for crack identification,crack avoidance and repair
• Process and material simulation

Location Gothenburg, Mölndal.

Number of students: 1-2.

Project work period: Start during autumn 2023 or spring 2024.

Target group: Manufacturing engineering, material science and engineering, joining technology.

The application deadline is November 10, 2023.

Contact

Andreas Reeb

andreas.reeb@ri.se

+46 10 228 47 27