Dynamic Accuracy of Hybrid Profiling Mechanisms in Cam Manufacturing

Abstract

Dynamic accuracy in cam production using hybrid profiling mechanisms in turning with a single point cutting tool is investigated. A profiling mechanism consisting of a four-way, critical-centered spool valve and a symmetrical volume power cylinder with a fixed piston is mathematically modeled and simulated on a hybrid computer to study its dynamic behavior. The model includes the dynamic cutting forces and their interaction with the velocity response of the mechanism, the nonlinear dry friction in the copying slide, and the dynamic behavior of the copying slide, control valve, and the stylus. The kinematic displacement of the stylus in time domain is formulated from the cam profile characteristic and is used as the input function for the simulation. The response of the mechanism to this input describes the shape of the manufactured cam profile in time domain. Based on the results of this investigation, it can be concluded that for a minimum manufacturing error in cam profiling, hybrid profiling mechanisms should be designed with low stylus inertia and high stylus stiffness. Operating a profiling mechanism with high supply pressure, low exhaust pressure, smaller depth of cut, and low angular velcoity of master cam also give high dynamic accuracy. The influence of dry friction in the copying slide and the copy-slide angle γ on the manufacturing error is also presented. Plots are also developed to be used as a guide in the design and operation of these hybrid profiling mechanisms.