Modelling the unidirectional fibre composite milling force oscillations through capturing the influence of the stochastic fibre distributions

Although high frequency variation of cutting forces is an inherent characteristic when milling composites, studies and models on the explanation and time-domain simulation of such processing forces seem to be missing in the literature. This paper first claims that the variation of the composite milling forces comes from three aspects: i) the variation of chip thickness caused by the cycloid trajectories of the cutting edge; ii) the random fibre placements within the composite and iii) the continuous variation of the cutting direction relative to the fibre orientation due to the rotational motion of the milling cutter. Moreover, the cutter's helix angle leads to each section of the cutting edge engaging different fibre orientations simultaneously, adding additional challenges in understanding and predicting the resultant forces. Thus, this paper develops an analytical approach which can be utilised to accurately simulate the milling forces in time domain for unidirectional fibre composites. The approach calculates the chip thickness, estimates the stochastic fibre placements and defines variable cutting coefficients for different fibre orientations to integrate their effects on the force variability. Besides, the helical cutter is discretized into several slices to simulate the force acting on each engaged part at its relevant fibre cutting angle, resulting in a procedure of simulating the composite cutting force with helical milling cutter. Both straight and helical milling cutters are taken into account to validate the model, the effects from the concluded three aspects are separately investigated to provide an in-depth understanding of the force variation and support the developed model. It is observed that the variation of milling forces follows a Gaussian distribution when the cutting direction of the fibre is fixed. Furthermore, the simulated milling forces show a satisfactory agreement with the experimental results, especially their oscillations illustrate a high degree of consistency.