CUTTING FORCES IN ORTHOGONAL CUTTING OF UNIDIRECTIONAL GFRP COMPOSITES

The results of orthogonal cutting tests carried out on unidirectional glass fiber reinforced plastic composites, using HSS tools, are presen ted and discussed. During the tests, performed on a milling machine at very low cutting speed to avoid thermal effects, the cutting speed wa s held constant and parallel to the fibre direction. Three parameters, namely the tool rake angle alpha, the tool relief angle gamma, and th e depth of cut t, were varied. According to the experimental results, the horizontal force per unit width, F-hu, undergoes a dramatic decrea se, never verified for metals, with increasing alpha. Besides, F-hu is only negligibly affected by the relief angle, and linearly increases t. Similarly to metals, an effect of the depth of cut on the specific energy (size effect) is found also for composites. However, the presen ted results indicate that the size effect can be analytically modeled in a simple way in the case of composites. The vertical force per unit width, F-vu, exhibits a marked reduction when the relief angle is inc reased. F-vu is also very sensitive to the rake angle: the lower alpha , the higher is F-vu. It is shown that this behavior probably reflects a strong influence of the rake angle on the forces developing at the flank. A linear dependence of the vertical force on the depth of cut i s also demonstrated. Finally, the experimental data are utilized to ob tain empirical formulae, allowing an approximate evaluation of cutting forces.