LeichtKupu

Lightweight construction - cutting of FVK with high-energy short pulsed CO₂ laser radiation

Aim of the development

Machining processes for fibre composites usually cause high wear of the tool. Laser beam cutting, on the other hand, works without contact and therefore wear-free. However, this process causes thermally induced damage to the cutting edges, which usually requires subsequent machining. For this reason, a solution was sought with which laser beam machining can be realized with the least possible cutting edge damage.

Advantages and solutions

Both the plastic matrix of the material and the fibers absorb laser radiation of the wavelength 10.6 µm very well. Short, high-energy pulses cause a temporary energy input. High cutting speeds further minimize the interaction time of the laser energy with the cutting edge. An additional cooling effect can be achieved by using cutting gas. Therefore, a novel short-pulse CO2 laser beam source together with a highly dynamic 6-axis motion system was used in the project for cutting fiber composites. The laser beam source was characterized by a pulse duration of 200 ns, a pulse peak power of 100 kW and a maximum average power of 1 kW. The motion system achieves processing speeds of up to 100 m/min at accelerations of up to 1.5 g. With this method the thermal damage in the area of the cutting edge should be greatly reduced, in the best case completely prevented. Spectral and high-speed temperature measurements were used to investigate the thermal interaction between laser radiation and material in a broad parameter field in order to counteract heat build-up at the cutting edge. During the investigations, the "Multiscan" machining strategy proved to be more suitable than the classical contour cut. Here, due to the high cutting speed, little thermal damage is caused, but the cut must be repeated several times. With the first results of the high-speed temperature measurements, it was then possible to optimize the pause time between the individual scan repetitions in order to avoid heat accumulation at the cut edge. Furthermore, the project succeeded in cutting 3 mm thick CFRP with a commercially available short pulse fiber laser (120 ns pulse duration and 1064 nm wavelength). The process could be optimized for 0.5 mm thick CFRP to such an extent that the area of thermal damage was reduced to 20 µm. This is an important result for the application of the developed processes, as the necessary laser sources are more easily available and more cost-effective.

Target market

The application of the developed process can be implemented for lightweight products with medium and small quantities, for which the production of tools would be uneconomical. The laser is a flexible and wear-free tool and can give each workpiece an individual contour. Great application potential lies in the automotive sector. The introduction and testing of new technologies can already be observed there in small series. For example, the L-PBF process is already being used here, in which parts are manufactured additively from metal powder using the laser beam - a process that is considered innovative and is also still being intensively researched and optimized at ifw Jena. Similar developments are also expected for the laser processing of CFRP. In addition, lightweight construction helps to reduce emissions, which is becoming increasingly important in the automotive sector. Fiber-reinforced plastics and their precise processing make a decisive contribution to this. Furthermore, lightweight construction plays a central role in the aerospace sector. Whether for drones, aircraft or satellites: weight reduction is a relevant factor in every case. Because any geometries can be realized with the laser without using special tools, the developed process is particularly advantageous for prototype construction, the production of individual pieces and small series. Last but not least, the results achieved are relevant for laser and machine manufacturers: They can target their portfolio specifically at customers who are involved in the assembly of lightweight materials. The users of the lightweight components themselves benefit from the following advantages resulting from the process development:

• Full geometric flexibility of the processing for each individual workpiece
• Reduced heat-affected zone at the cutting edges and thus increased mechanical skill of the workpiece
• Short process time without prior tool production

The transfer of the results is achieved both through publication at events and in journals and through direct contact with industrial partners. ifw Jena offers the following services around the process:

• Consulting
• Sample and small series production
• Further process development
• Support for process integration into the partner's equipment.