Effect of feedrate, depth of cut, tool material, and toolpath on dimensional accuracy and surface roughness of milled CFRP

Abstract

This thesis investigates the effect of different factors on Carbon Fiber Reinforced Polymers (CFRP) milling, like feedrate, tool material, and cutting speed. CFRP offers excellent material properties, which led to the increase of the material in today's manufacturing industry. CFRP offers up to 2.25 times steel's modulus of elasticity at about a fifth of the weight and excellent thermal properties, which allow the use of this material in applications with high heat like automobiles. Many industries have implemented the use of CFRP in their applications, like airplanes and automobiles, which lead to a decrease in weight and increase in strength. A literature review was conducted to determine the research gap, which resulted in 132 articles, of which 72 were relevant. The literature review results showed no specific machine settings were recommended, and neither was the type of material to use. Almost all reviewed articles used different tool materials and machine settings, with little work done in comparing various tools and settings regarding surface roughness and dimensional accuracy. A CNC mill was used to make slots in a CFRP workpiece using different combinations of the factors listed above. An initial experiment was conducted to determine the optimal toolpath, using Autodesk Fusion 360, that achieves the highest accuracy and lowest surface roughness. The slots were then analyzed using a profiler and a digital caliper to determine which toolpath to use for the experiment. After determining the toolpath, the factor level determination was conducted. Four different tool coatings were tested at three different levels of feedrate and depths of cut on a Tormach PCNC 1100. Multiple bits were used to reduce the effect of tool wear. Data was then collected on the slots' accuracy and surface roughness using a digital caliper and the Dektak XT Stylus profilometer, respectively. The data obtained were then analyzed in JMP to determine the optimal settings to mill CFRP. The analysis showed feedrate, tool coating, depth of cut, and their interaction effects have a significant effect on dimensional accuracy and surface roughness.