Processes

The worldwide increase in energy consumption and the ambitions of efficient energy use are leading to a growing demand for high-quality materials for energy transmission and conversion. There is also a demand for technological and plant engineering solutions for improving properties that can be integrated into existing production processes and lines.

One area of application is the optimization of the magnetic properties of grain-oriented electrical sheet, which is preferably used for transformer cores. Targeted laser treatment can reduce the losses that occur during transformer core remagnetization and thus increase the efficiency of energy transmission.
 

Domain Refinement of Electrical Sheets 

The process engineering approach is based on the refinement of the magnetic domains. For this purpose, local stresses (thermal domain refinement) or structural defects in the form of trenches (heat-resistant domain refinement) are created in the material. The laser beam acts as a tool whose energy input can be influenced by the optimum choice of process parameters and optical configuration. The laser beam, which is moved perpendicular to the rolling direction, generates lines at an equidistant distance and thus influences the domain dimensions.

The system technology solution developed with partners allows integration into production lines and enables continuous treatment of the strip at speeds of up to 160 m/min.

System Technical Solution

The lasertronic®SAO x.x/12D laser beam deflection optics was developed for laser domain refinement of continuously moving grain-oriented silicon steel strip. The beams from up to four laser sources are focused on the material surface. The single laser spot is moved at speeds up to 300 m/s perpendicular to the direction of the moving strip. The light energy absorbed by the sheet generates thermal stresses in the structure of the material. As a result, the magnetic domains are refined. The lasertronic®SAO x.x/12D system uses 12 galvanometer scanners in a patented arrangement to generate 800 parallel lines on a 1 m wide strip with four independent laser beams per second.

The unique LMDR test system developed at Fraunhofer IWS is used for process and system development. The system has two independent laser beam paths and a setup corresponding to the production systems. The uniaxial material transport is performed via a sample table. The use of different laser sources allows, for example, the influence of the wavelength to be investigated. Adapted processing parameters can be worked out for customer materials, which can be implemented directly with production systems. The changes in magnetic properties determined for single strips or Epstein sets are an optimization criterion.

Technology and System Engineering Development for High-rate Laser Ablation on Copper Pins

Electric vehicle drive motors require maximum current levels, which have led to the development of pin or hairpin technology. New assembly and contacting processes have been developed in which the individual pins are electrically contacted by welding or soldering. The joints must be metallically bare, i.e. locally stripped and free of residues.

A technology and the associated system solution have been developed for the local stripping of continuously moving copper conductors. The use of a continuously emitting laser beam source in the kW range in conjunction with a highly dynamic beam deflection enables stripping rates greater than 1000 mm²/s. The division of the laser beam into two individual beams was used to realize all-round, parallel processing. The high reflectivity of the copper compared to the laser wavelength used presented a challenge with regard to the arrangement of the processing optics and the ablation sequence.

Technological investigations were carried out for the client to determine the processing wavelength, the required laser power and the achievable ablation rate. Based on these findings, an optical concept was developed and the system technology was selected and qualified. The developed adapted system solution made it possible for the customer to integrate continuous stripping into the production line. The system technology was transferred to the end user, the technology was put into operation and the necessary instruction and training were carried out. The laser processing system is designed in such a way that it can react flexibly to changing environmental conditions or production requirements.

Based on a profound understanding of the process, Fraunhofer IWS develops technologies for high power laser ablation that meet the requirements. From this, the boundary conditions for the design of the system technology are derived and production-relevant concepts are designed. A control hardware and software tailored to the individual benefit completes the solution.

High-rate Laser Ablation for Defined Surface Roughnesses

LIGHTblast is a consistent further development of laser microstructuring, with a continuously emitting beam source replacing the pulsed laser. The high precision of micro material processing gives way to a surface structure distributed over a wide area. The significantly higher average laser power and an alternative physical operating principle enable a surface rate 100 times higher than known from micromachining.

Using specially developed software, application-specific processes can be efficiently implemented for a wide variety of materials with any desired starting surfaces and different target roughnesses. The advantages of the process are obvious: the absence of a physical abrasive eliminates contamination, reduces operating costs and minimizes the amount of waste to the material actually removed. Any influence on quality due to abrasive wear can be ruled out. There is no need to change blasting media for different target roughnesses and this is controlled by the processing parameters of laser power and speed.

The working point of the laser has a diameter of less than 50 µm and can be guided on the surface with an accuracy of 10 µm. Masking of the surfaces to be processed is done intuitively in the programming software developed in-house with standard CAM functionalities. Compared to sandblasting, process automation is necessary, but pays off immediately through reduced part cycle times and exact process results without fluctuations.