Milling Mechanism of Sheet Fiberglass Plastic by a Tungsten Carbide Tool with Diamond and Diamond-like Wear-Resistant Coatings

ABSTRACT: The study focuses on identifying the specific mechanisms of the FR4 fiberglass composite milling process using tungsten carbide end mills with wear-resistant diamond-like and diamond coatings. The processing was carried out at cutting speeds from 115 to 300 m/min and feed of 0.075 and 0.15 mm/tooth. At the same time, the vibroacoustic signal was recorded in three formats: changes in the RMS value and the amplitude of the acoustic emission in the low-frequency and high-frequency ranges, as well as the parameter K_f, which is the ratio of the RMS amplitudes of the signals in the low-frequency and high-frequency ranges. It is shown that the coating material has a predominant effect on the surface roughness. The minimum roughness value was R_A = 0.2 µm for the case of a diamond-coated tool. In addition, the coating improves processing performance by increasing the cutting speed for tools with DLC by 1.3 times and for tools with diamond coating by 1.7 times, provided that the R_A increases slightly but does not exceed 0.36 µm. When processed with an uncoated instrument, the mill captures the fiber, bends it and breaks it into bundles, creating grooves. The mechanism of glass fiber destruction by a DLC mill is similar, with the difference that the length of the fragmented fiber sections is noticeably reduced due to reduced friction. The mechanism of cutting fiberglass with a diamond-coated milling cutter is significantly different. There are characteristic scratches on the worn sections of the fiber, and there are no signs of destruction of the composite between the matrix and the fiber. Studies of vibration signals have shown that frequency ranges up to 20 kHz and from 33 to 48 kHz are informative enough to diagnose the fiberglass milling process. The most significant values of the K_f parameter were observed at large amplitudes of low-frequency vibrations, typical for processing with uncoated and DLC milling cutters. The lowest K_f values were obtained using diamond-coated milling cutters. A correlation was found between the values of the K_f parameter and the roughness values of the treated end surface of the fiberglass plate.