EFFECT OF TOOL WEAR ON CUTTING FORCES IN THE ORTHOGONAL CUTTING OF UNIDIRECTIONAL GLASS-FIBER-REINFORCED PLASTICS

Orthogonal cutting tests were carried out on unidirectional glass fibr e-reinforced plastic composites, holding the cutting direction paralle l to the fibre direction. The tools were made of high speed steel, wit h rake angle alpha = 0 degrees; two relief angles gamma, namely 7 degr ees and 15 degrees, were adopted. A very low cutting speed was utilize d, in order to avoid thermal effects on both the tool and the work mat erial. The experimental results show that, under the selected operatin g conditions, the tool wear essentially consists of a very rapid round ing of the tool nose (nose wear). The face wear evolution is practical ly independent of the relief angle, whereas the latter affects the fla nk wear rate, which is slightly lower for the higher gamma value. Both the horizontal and the vertical cutting forces exhibit notable increa ses with tool wear. The force data are interpreted in the light of a p reviously presented model, aiming to predict cutting forces as a funct ion of the cutting parameters. It is shown that the observed increase in the horizontal force can be simply attributed to the increase in th e vertical force at the tool flank, whereas the chip-tool interaction forces occurring at the tool face seem to be unaffected by wear phenom ena. Finally, a strict correlation is found between the flank wear and the recorded vertical force variations.