Towards Geometry Assurance of Laser Processed Sheet Metal Components

Licentiate thesis, 2019

Stricter emission norms have propelled the automotive industry towards lightweight transportation solutions to reduce the environmental impact. The industry has adapted to cost effective lightweight sheet metal solutions to control the vehicle weight as well as maintain the safety standards of the vehicle. Also, the industry continues to explore for innovative manufacturing techniques to achieve further vehicle weight reduction. Novel laser processing techniques for sheet metals have slowly gained prominence in the automotive industry. Specifically, the selective laser heat treatment process has gained interest for its ability to locally modify material properties to enhance formability and strength. Consecutively, it widens the horizon for lightweight design. However, some challenges remain in order to utilize this process to its fullest. Geometrical variation related effects from local heating is an area of concern. Also, integrating them into the virtual product development setup is necessary to enable accurate decision making.

In every manufacturing process the component produced varies from the desired values. This is further affected by variation in fixtures and subsequent assembly processes. It affects aesthetical characteristics and functionality of the product in its operating environment. It is expensive to either make adjustments in the final stages of the production process or to totally eliminate the variation sources. This could be overcome by making the design insensitive to the effects of such variation through the concept of robust design. Implementing the robust design concept requires adequate understanding of geometrical variation related effects due to local heating, an area which remains scarce. As a result, this phenomena is unaccounted for in the methods and tools that are in practice today.

The goal of this research is to understand the phenomena and gain sufficient knowledge to develop methods and tools for geometrical variation simulation that considers selective laser heat treatment effects. In this thesis, boron steels are the material in focus. Through literature studies, the geometrical variation influencing factors are identified and further investigated through experimental studies for deeper understanding. Sufficient knowledge on the influencing factors are developed which forms the major outcome of this thesis. This lays the foundation for developing methods and tools to perform accurate robust design assessment for selective laser heat treated sheet metal components.