Quality of Drilled and Milled Rivet Holes in Carbon Fiber Reinforced Plastics

摘要

In this paper, a conventional drilling process and a circular milling process are compared with respect to delamination and fiber protrusion when machining carbon fiber reinforced plastics (CFRP). The tool design (tool orthogonal clearance, drill-point angle) and the parameters (feed rate, cutting speed) are varied when drilling. The axial feed force and the spiral angles of the cutting edges can cause damages to the CFRP when circular milling. In this study, the possibilities to reduce those errors by the application of end mills with no spiral angle at the circumference cutter and no feed in axial direction are investigated. This milling process requires pre-drilled holes, and the final rivet hole dimension is then machined by circled movements without any motion in axial direction. For this special circular milling process, the tool design (rake angle of the circumference cutters) as well as the setting parameters (depth of cut, feed rate, cutting speed, up and down milling) are varied. The machining quality of both processes is compared. This is done by measuring the delaminations using an optical microscope. The fiber protrusion are visually identified with the help of an adapted imageprocessing algorithm. The diameters of the rivet holes are measured on two planes of the hole by a coordinate measuring machine. The cylindricity of the holes is determined using an instrument for roundness measurement.