Heat effect on the material removal in the machining of fibre-reinforced polymer composites

This paper aims to investigate the heat effect on the material removal mechanisms in the machining of fibre-reinforced polymer (FRP) composites. A coupled thermal-mechanical microstructured-model was established to investigate the cutting processes both with and without ultrasonic tool vibration. A systematic cutting experiment was also conducted to assess the reliability of the theoretical predictions. It was found that the cutting temperature influences significantly the material removal process, but has a little effect on the cutting forces. The fibres and matrix deform and fracture in brittle modes when the temperature is below the glass transition point of the matrix material, Tg. The matrix material becomes softer and its deformation turns to be ductile when the temperature exceeds the glass transition point. This consequently brings about significant deformation and fracture of fibres in the subsurface. During cutting, with increasing the cutting time, the cutting-induced heating zone spreads quite ahead of the cutting edge. However, with the assist of ultrasonic vibration, the high-frequency motion of the cutting tip dramatically reduces the tool-work interaction time at each vibration cycle; thereby slows down the heat generation and temperature rise. The high-frequency motion also leads to rapid chip removal and reduces temperature rising rate and heat accumulation. As a result, both the tool and workpiece temperature can be maintained to be below the Tg of the matrix material. Nevertheless, the advantage of the vibration-assisted process becomes trivial once the feed rate is larger than its maximum vibration speed.