Effect of tool wear on cutting forces in the orthogonal cutting of unidirectional glass fibre-reinforced plastics

Orthogonal cutting tests were carried out on unidirectional glass fibre-reinforced plastic composites, holding the cutting direction parallel to the fibre direction. The tools were made of high speed steel, with rake angle alpha = 0 degrees; two relief angles gamma, namely 7 degrees and 15 degrees, were adopted. A very low cutting speed was utilized, in order to avoid thermal effects on both the tool and the work material. The experimental results show that, under the selected operating conditions, the tool wear essentially consists of a very rapid rounding of the tool nose (nose wear). The face wear evolution is practically independent of the relief angle, whereas the latter affects the flank wear rate, which is slightly lower for the higher gamma value. Both the horizontal and the vertical cutting forces exhibit notable increases with tool wear. The force data are interpreted in the light of a previously presented model, aiming to predict cutting forces as a function of the cutting parameters. It is shown that the observed increase in the horizontal force can be simply attributed to the increase in the vertical force at the tool flank, whereas the chip-tool interaction forces occurring at the tool face seem to be unaffected by wear phenomena. Finally, a strict correlation is found between the flank wear and the recorded vertical force variations.