Comparison between ps- and µs-laser radiation for drilling holes for force transmission elements in CFRP-preforms

Abstract

Current lightweight strategies in automobile, aerospace and wind energy applications include composite structures consisting of metal and fiber reinforced plastics for minimum weight, maximum force transmission and high material efficiency. Therefore, economic and technological beneficial material processing for the integration of force transmission elements such as inserts are crucial for these high performance materials.Current state of the art of machining carbon fiber reinforced material is to drill or mill the work piece after the consolidation process. Conventional mechanical and water jet processes lead to high tool wear and often non-repairable defects in the work piece such as delamination, fiber pullout, cracks in matrix and fibers, and deformation. Laser processing of the consolidated material can prevent force induced defects but leads to degradation of the matrix and leaves freestanding fibers inside the drilling hole which can damage the protective surface of subsequently inserted force transmission elements. This is especially critical for the lifetime and performance during operation of the structural part. One solution is to drill the non-consolidated work piece, the so called preform, prior to the infusion process, insert force transmission elements and subsequently infuse the preform with resin. Ultra sonic excited cutting knifes are not applicable for cutting hole diameters of a few millimeters with high aspect ratios. Punching as well as water jet cutting drop out due to force induced interaction with the textile or necessity of a subsequent drying process. Laser material processing could be an adequate solution to circumvent the above mentioned issues.Within this work, non-crimp carbon fiber (NCF) preforms with different amount of layers are investigated regarding laser processing via ultra-short pulsed and microsecond (fiber laser) radiation. The influence of different process parameters such as scanning speed, repetition rate and laser power are being evaluated regarding geometrical and materialographical quality such as conicity, textile swelling and heat affected zone (HAZ). The temperature distribution during laser processing is important for the estimation of when and where the knitting yarn, which keeps the carbon fiber plies together, disintegrates. Without the knitting yarn swelling occurs which is not desired for subsequent process steps.An ultra-short pulsed laser beam source from AMPHOS with 7 ps pulse duration and an average power of up to 400 W will be compared regarding process time and hole quality to a 6 kW pulse peak power micro-to millisecond pulsed IPG 600/6000- QCW fiber laser source.Current lightweight strategies in automobile, aerospace and wind energy applications include composite structures consisting of metal and fiber reinforced plastics for minimum weight, maximum force transmission and high material efficiency. Therefore, economic and technological beneficial material processing for the integration of force transmission elements such as inserts are crucial for these high performance materials.Current state of the art of machining carbon fiber reinforced material is to drill or mill the work piece after the consolidation process. Conventional mechanical and water jet processes lead to high tool wear and often non-repairable defects in the work piece such as delamination, fiber pullout, cracks in matrix and fibers, and deformation. Laser processing of the consolidated material can prevent force induced defects but leads to degradation of the matrix and leaves freestanding fibers inside the drilling hole which can damage the protective surface of subsequently inserted force tran...