Force Relations and Dynamics of Cutting Knife in a Vertical Disc Mobile Wood Chipper

摘要

The force relations and dynamics of cutting knife in a vertical disc wood chipper were investigated. The tool geometry determined include: rake angle (20o); Shear angle, ( f = 52.15o); the mean frictional angle, ( t = 5.71o). The analysis and comparison of the cutting forces has shown that the chips separated from the wood are being formed by off cutting, since normal applied force N is compressive in nature, the magnitude of the forces used by the knife on the wood is expected to increase as the cutting edge of the knife goes deeper into the wood until the value of the resisting force acting against the cut wood F_f is reached and exceeded. The evaluated forces acting on the knife and the chip are: F = 3.63Nmm^-1; N = 34.7 Nmm^-1; F_s= 27.45Nmm^-1; F_n =31.92 Nmm^-1; F_t = -8.46Nmm^-1; F_c = 33.85Nmm^-1. The resultant force acting on the tool face, Pr = 34.89Nmm^-1. The specific cutting pressure, P_c and cutting force needed to cut the timber, F_c, are 1.79 × 10⁶ N/m² and 644.84N respectively. The energy consumed in removing a unit volume of material is 69.96kJ/mm^-3 and the maximum power developed in cutting the chip is 3591.77W (4.82hp). The chipper efficiency (86.6%) was evaluated by the highest percentage of accepted chip sizes.