A special V-shaped tool for trimming composite materials

The results of trimming tests carried out on unidirectional carbon fibre reinforced plastics using a conventional tool and a purposely designed, V-shaped tool, are presented and discussed. The main objective was to verify the effect of the new geometry on the cut quality. From previous works, this seems to be a topical aspects in composite machining, due to the fact that multiple cracks deeply penetrating into the worpiece are often generated by the tool action, impairing the material integrity, especially when the fibre orientation θ with the respect to the cutting direction assumes particular values. During the experimental activity, the depth of cut and cutting speed were fixed, whereas θ was varied in the range 0° to 180°. From the examination of the damaged morphology after trimming, three parameters were assumed to quantitatively evaluate the cut quality: the deepness of the splitting failures emerging at the specimen sides, the deepness of the internal splits, and the roughness Ra of the cut surfaces. All the quality parameters revealed an improvement of the cut surface when the V-shaped tool was substituted to the conventional one. Apparently, the qualitative dependence of cutting forces on fibre orientation was not influenced by the tool geometry. Comparing the principal force for the conventional and the special tool, it was found that in general the latter requires a higher principal force for a given θ value. A limited number of cutting tests was also performed doubling the width of the samples in order to verify whether the cutting forces are linearly dependent on this parameter.