The FLEXFORM project has demonstrated the applicability of laser bending for industrial use. Design prototypes can be manufactured very fast and with good repeatability. By means of numerical control, design changes can be made very rapidly by software adaptation. These changes occur frequently for examined parts like motor brackets. However, there is a limitation in the achievable 3D complexity of the parts. Formation of deep cups or surface depressions must be supported by external pressing tools and clamping devices, thus reducing system flexibility. As a new potential application of laser forming the straightening of sink marks in sheet metal after stamping was identified during the project. The results in this technology were very promising, although a robust strategy for process control does not yet exist.
The material properties of laser formed parts are different from mechanically bent parts. In the heat affected zones, the laser power can cause various changes of hardness, grain size, surface finish, tensile and fatigue properties. While the surface finish is usually deteriorated, tensile and fatigue strength seem to profit from the laser treatment. For aluminium specimen the tensile strength can decrease. The percentage of change is moderate so that generally, laser bent prototypes should be suitable for the planned applications.
Several fully working prototype set-ups were used for flexible laser bending. The set-ups showed that laser power of <3 kW is sufficient for sheet metal thickness of up to 2 mm. Nd:YAG lasers are preferable over CO(2) lasers due to the higher absorptivity and easier beam guiding. For on-line process monitoring of bending angles a distance sensor is sufficient. In the case of thin materials with a risk of melting a temperature control is recommended to protect from overheating.
The objective of this project is to develop a new flexible laser forming process for the production of complex sheet metal parts for automotive prototyping..
At present, sheet metal prototyping by conventional techniques e.g. deep drawing today takes much time and causes high costs due to the fact that special forming tools are needed for the forming process. In the automotive industry, which is one of the major applicants for sheet metal prototyping, tool costs for example achieve 14 million ECU on average per year in only one company. Therefore the demand for new, more flexible prototyping processes which permit prototypes to be manufactured more economically and, above all more quickly, is correspondingly high.
The course of development for the process contains the following areas of work :
- Process development for basic form features (angle sections, cones, cylinders) of steel and aluminium steels and layout of process diagrams.
- Development of transferability criteria for different materials and sheet thicknesses
- Development and test of process strategies for production of complex shapes.
- Test of different measurement techniques (temperature, shape) for process control.
- Design of a prototype laser sheet metal forming machine tool.
The expected cost savings in sheet metal prototyping are in the range of 15-30 million ECU per year. Therefore the competitiveness of the European automotive industry will be improved. The developed new forming process will also be suitable for application in other branches of industry.
Funding SchemeCSC - Cost-sharing contracts
CV4 9DB Coventry