A New Drilling Tool for Machining of CFRP-Metal-Hybrid Components

Abstract

In many industrial sectors, lightweight construction with fiber-reinforced plastics have been in use for many years. In aviation, for example, about half of the aircraft weight of current airliners consists of carbon fiber reinforced plastics (CFRP). These materials are combined with metals to obtain hybrid materials in order to improve their mechanical properties. For a secure and accurate fitting connection of the resulting components, both materials must be drilled simultaneously in one machining operation. This represents a significant technological challenge due to the contrasting requirements of both material groups on the machining process and the tools used. Standard tools are only adapted to one material at a time and the machining parameters can only be adjusted to a limited extent during the drilling process. As a result, one component of the hybrid material is damaged during the drilling process. This damage must be removed in an additional machining step in order to meet the high quality requirements.

In this paper, a new tool concept is presented, which allows high-quality drilling of hybrid materials made of CFRP and metal in a single manufacturing operation without subsequent rework. For high quality machining, the drilling process is carried out in three steps. At first, the hybrid material is pre-drilled with a universal cutting edge. The resulting material damage occurs in a small area around the bore edge, depending on the selected cutting parameters. Then, two independent sets of cutting edges, which are adapted to the respective material components, are used in a finishing process to remove the damage caused during the pre-drilling. By using a movable cutting edge, the tool works in two directions during the drilling process. Machining tests proved that the tool concept is able to achieve reproducible high-quality bores in hybrid materials made of CFRP in combination with high-strength aluminum, steel and titanium alloys.

Keywords: Drilling in two operating directions; multi-material-machining; mechanical manufacturing processes