The Influence of the Base Scheme in the First Operation on the Value of the Allowance for Boring Holes in the Blanks of Body Parts on Tuned Machines

Abstract

Three variants of the scheme of basing the body part billet on the first machining operation are considered. The first two options solve the problem of providing dimensional communication between treated and untreated surfaces; the third option is the task of removing the minimum uniform allowance from the surface of the main hole.

The aim of the work is to identify the influence of the base scheme in the first operation of the technological process of machining a batch of body parts on a tuned machine on the quantitative values of allowances for the main hole boring. The studies were carried out on the example of machining a workpiece of a part of the "Bearing housing" type under mass production conditions. To determine the allowances, the calculation and analytical method proposed by Professor V. M. Kovan was used. For the three variants of basing schemes, all elements of intermediate allowances, minimum, maximum and general allowances are calculated. It is established that the use of the first two variants of the base scheme causes the magnitude of the displacement of the hole axis in the initial billet relative to the technological bases for the operation of its boring approximately ten times greater than the use of the third variant of the base pattern. The magnitude of the offset of the axis of the hole in the original billet is determined by building the appropriate technological dimensional chains.

An assessment of the possibility of using standard values of allowances, determined without taking into account the base scheme at the first operation, showed that if the value of the minimum start-up is significantly influenced by the offset value of the bore axis in the original billet relative to the technological bases, then for its full account in specific technological conditions should use the analytical method.