Experimental and Numerical Coupling Proof of Conical Frictional Joints

Conical rings are used to joint a shaft with other mechanical parts through frictional forces induced by clamping of the inner ring into the outer one. In design, their coupling strength and the allowable torque are determined with the well known analytical formulas. However, the assumption of rigid and smooth contacts considered in the analytical solution generates technical uncertainties for reliability of conical joints especially for their small dimensions. The coupling strength of the conical rings is investigated at a set-up and by using Finite Element (FE) Method. A FE model of the analytically analysed conical joint is created with friction contact conditions on all interfaces of the joint. For a very fine mesh with the smooth interfaces, the FE contact forces differ remarkably from the analytical solution. This confirms that the elasticity of parts has to be taken into account in the design process. To assess an influence of real contact profiles on the coupling performance, contours of contact surfaces are measured at a Mitutoyo coordinate measuring machine. Based on the measured height variation in the normal to the contact plane, the surface profiles are extrapolated by approximation functions. Then, the FE mesh is modified locally on the contact with respect to the extrapolated profile functions and coupling strength of the conical joint is computed with friction sliding. According to the obtained results, the implementation of the real profile of the contact is needed in the design process to avoid failures under real operation conditions of conical joints. According to the obtained FE static results, the contour irregularities induces local separations in the contact, which can be monitored by measuring electrical resistance between the outer and inner conical rings.