Drilling is a key manufacturing process in the industrial machining of CFRP. According to its own figures, AIRBUS performs around 150 million drillings in CFRP each year as part of its aircraft production. The IPMT investigates drilling using methods commonly employed in the aviation industry, ranging from hand-held machines and semi-automatic drilling feed units to industial robots and machine tools. Our focus is on developing, optimising and investigating drill geometries, diamond coatings and cooling solutions for drilling CFRP and CFRP-metal stacks. A key objective is to ensure the required component quality and avoid rework. To this end, we analyse how drill geometry, diamond coating and tool wear influence quality characteristics such as peel-up and push-out delamination, as well as fibre protrusions.

Curved circular cutting (CCC)

IPMT has developed and patented a curved circular cutting process (WO002014131823A1). Conventional contouring processes, such as milling, circular cutting, sawing and laser cutting, have significant disadvantages that are specific to the process. For example, in milling, productivity is limited by low feed rates and delamination caused by wear. Cut-off grinding and sawing only allow straight cuts on flat components. Laser beam cutting is only suitable for thin-walled components and can cause significant thermal damage. The CCC process enables curved, 3D cuts to be made by continuously adjusting the tool axis during cut-off grinding or sawing. Using electroplated diamond grinding wheels reduces tool costs and minimises thermal damage. This allows higher feed rates and thus high productivity. To date, critical delamination has not occurred when machining with CCC.

Scratching of the top layer when milling CFRP

During peripheral milling of CFRP, the top layer delaminates as the tool wears. To prevent this, the IPMT has developed a solution: in a preliminary process, the top layer causing delamination is removed to a depth of a few micrometres. This process involves 'scratching' the top layer, which prevents delamination even with heavily worn end mills, as the lower layers continue to be supported by the upper layers. Several methods of scratching, such as laser cutting or grinding, have been implemented at the IPMT.