The effect of the stop limiting the automatic feed of long bar workpieces on the accuracy of their axial positioning in a lathe
DOI:
https://doi.org/10.31649/2413-4503-2025-22-2-71-80Keywords:
machine tool, optimization of cutting, modeling of part dimensional errors, system regularities, feed reliability, precision machining of rotating bodies, automation of the control system, stability of the dynamic system, surface accuracy, vibration prediction, stability and failure analysis, cutting edge positionAbstract
The influence of a rigid restriction of the automatic feed of a long bar on the accuracy of its axial positioning in a lathe is presented. It is shown that a rigid stop forms a non-stationary mode where the impact changes the boundary condition at the free end of the bar, excites longitudinal stress waves, and causes phase-dependent compression, which is accidentally captured by the clamping chuck. A criterion for a non-rebound mode and an equivalent limit for the bar approach speed are derived, which serve as tools for selecting feed modes, taking into account its length, stiffness, and friction forces. An expression has been obtained for finding the residual dynamic error, which determines the minimum time required to reduce the amplitude of oscillations. A non-monotonic dependence of the parameters of the axial positioning process on the actual length of the fed rod has been analytically demonstrated. It is shown that it is fundamentally impossible to ensure a constant “zero” base with a passive stop throughout the rod consumption cycle due to changes in its mass and stiffness, changes in friction, and degradation of contact with the stop. The practical value of the results obtained also lies in the ability to: calculate the speed of the bar's approach to the stop, the required amount of force to push the bar for given values of its actual length; determine the time delay of vibration damping; evaluate the effect of the stop stiffness on the reduction of bar compression; justify the transition to an active axial positioning scheme.
The novelty of the results obtained lies in interpreting the interaction of the elements of the “pusher-rod-stop” system as a problem of matching wave impedances with an explicit non-rebound criterion and in introducing the envelope of the maximum rod displacements during rebounds as an engineering metric of the guaranteed error at the moment of clamping. The proposed approach forms the theoretical basis for the synthesis of feed modes and design parameters of the stop and opens up the possibility of constructing closed-loop control systems.
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