An experimental investigation on tool wear and surface damage in milling carbon fiber reinforced polymer composites [EMBARGOED]

Abstract

Involved in the aerospace and automotive industries over the years, carbon fiber-reinforced polymer (CFRP) composites are nowadays in demand because of their excellency in mechanical properties, which including high stiffness and high strength-to-weight ratio. Milling and drilling are commonly used in the finishing process to achieve dimensional tolerances and product quality in CFRP as it is a near-net-shape product. However, the abrasiveness of CFRP due to its structure and properties causes rapid tool wear when subjected to conventional machining, which could produce poor surface quality of CFRP with delamination, fiber pull-out, and matrix cracking eventually degrading the CFRP performance. Until recently, there has been little discussion on the relationship between tool wear of carbide tools induced, surface roughness, and damage mechanisms of the CFRP’s machined surface when milling CFRP. A proper selection on cutting parameters such as depth of cut, cutting speed, cutting conditions, feed rate and tool material selection, are critical to reduce time consumption and post-machining costs. Thus, this study was carried out to investigate the influence of different cutting speed and feed rate toward progression of cutting tool wear, the surface roughness of CFRP, and its damage mechanisms during the milling operation. This study focuses on milling of CFRP for a 20-meter machining distance using an 8-mm uncoated tungsten carbide end mill tool at 100, 150, and 200 m/min of different cutting speeds and 450, 600, and 850 mm/min of feed rates in dry cutting conditions. The cutting tool wear progression and mechanism, surface roughness and damage of CFRP were observed throughout the 20-meter machining distance. The wear mechanism of carbide tool and the damages induced on the CFRP’s milled surface were analyze using a scanning electron microscope (SEM). a Dinolite digital microscope was applied to measure cutting tool wear, while the roughness of the machined surface of CFRP was assessed using an Alicona SL 3D profiler. As a result, it was observed that an increase in cutting speed has a notable influence on tool wear with 62.1% compared to an increased feed rate with a 42.7 % of the percentage difference. The maximum tool wear, 0.107 mm, and surface roughness, 3.120 µm, were achieved when milling CFRP at the highest cutting speed and feed rate, 200 m/min and, 850 mm/min,respectively. It was analyzed that the CFRP’s surface condition was severely deteriorated with the occurrence of surface damage such as delamination, fiber fracture and pull-out, and matrix cracking. It also noticed that appearance of the matrix smearing on CFRP’s machined surface suggests that the matrix resin was thermally degraded as heat generated during machining increased. Overall, milling of CFRP with low feed rate and cutting speed could minimize wear development and damage occurrence on machined surface of CFRP, hence lowering the roughness value to fabricate a preferable surface quality of the CFRP finishing surface.