The Fraunhofer Institute for Laser Technology ILT will be presenting the latest results of two collaborative projects at Euroblech from 25 to 29 October in Hanover, Germany. Both projects aim to improve the processing of lightweight, high-strength materials used in automotive production through improving the separation, joining and heat treatment processes involved.
High-strength steel sheets are commonly used in the production of passenger cars for their ability to absorb large amounts of kinetic energy in collision situations. The two Fraunhofer ILT projects – ‘Local Laser Heat Treatment of Cold Strengthened Steels for Improvement of Forming and Functional Characteristics’ and ‘Klasse’ – aim to improve the production processes of these sheets by both removing the metallurgical effects that often occur in production – which can adversely alter a material’s ability to absorb kinetic energy (in a collision for example) – and by increasing the efficiency and capabilities of the tools involved.
The cold-strengthened steels used in automotive manufacturing are generally subjected to overall recrystallisation annealing. In this cold-strengthened state, the thickness of the steel sheets can be reduced, but the material can only be deformed to a lesser degree, and its ability to absorb energy in the event of a crash is reduced significantly. By introducing a local heat treatment into the production of this steel with a laser, the crash properties of resulting automotive components can be improved through the introduction of soft zones. Combining this heat treatment with the initial cold rolling can prevent cracks from occurring in the subsequent forming process at particularly stressed areas, typically at the edges of shaped components.
The development of this process is the focus of the ‘Local Laser Heat Treatment of Cold Strengthened Steels for Improvement of Forming and Functional Characteristics’ project being carried out at Fraunhofer ILT and the Metal Forming Institute (IBF) at RWTH Aachen University. For the project, the institutes are first determining correlations between the temperature-time profiles and the resulting properties and mechanical properties of the steel. Deformation tests will then be carried out and simulated in production and operation. Future development steps in the project will see the heat treatment process integrated optimally into production.
Taking a separate approach to improving steel production processes, the ‘Klasse’ project – which is being carried out by Fraunhofer ILT along with partners from the automotive industry and laser plant construction – has led to the development of a combined processing head which can minimise production set-up times and improve process efficiency by offering increased flexibility. The combi-head contains a hybrid laser beam source consisting of a diode laser for heat treatment and a fibre laser for cutting, in addition to a recently integrated powder nozzle which enables the head to carry out additive manufacturing steps by means of laser metal deposition. The combi-head can also be used to cut composite materials, e.g. carbon-fibre reinforced components, which are becoming increasingly popular in car body manufacturing due to their low weight and excellent mechanical properties.