Calculation of operational dimensions using techcard software

Abstract

An important stage in the design of technological processes is the calculation of the operational dimensions. In most cases, several machining paths for the blank are possible, and the corresponding dimensional structure of the process will be different for each path. The technologist must select the best of the possible alternatives on the basis of some criterion—for example, machining at the lowest cost. In practice, this problem is complicated by the need to take account of the accuracy of dimensions obtained in previous operations on the accuracy of the dimensions obtained in subsequent operations. Often, in practice, the design dimensions specified in the drawings cannot be ensured, since they are obtained indirectly through interrelated technological dimensions based on different criteria. As a result, the actual precision of the design dimension depends on the precision of several technological dimensions at once. This situation arises unless uniform bases are adopted. In designing the technological process, the interrelationship of the dimensions, taking account of the influence of the accuracy of the technological dimensions on the accuracy of the design dimensions, may be simulated by comparing specific technological dimensional chains and solving the corresponding equations. Dimensional analysis is based on multiple refinement of the structure of the model graph and the identification of closed loops in the dimensional chains, with qualitative evaluation of these loops and quantitative calculation of the balance of the tolerances. However, in traditional (nonautomated) design of the technological process, it is very challenging to formulate the structural diagram of the changes in dimensions of the blank, to establish the corresponding loops of the dimensional changes, and to solve the relevant equations. Therefore, in practice, technologists generally do not attempt complete dimensional simulation of the technological process being designed but confine themselves to particular calculations for a few operations, drawing on their own experience and intuition. Ultimately, the technological process must be refined in the production shop. This is associated with loss of product quality and added production costs. Thus, automation of the calculation of operational dimensions is of great importance. The various systems currently used to automate design processes are not fully suited to the automatic calculation of the operational designs. We will consider the example of the Techcard program developed by Intermekh production facility (Minsk, Belarus) and used at OAO NPO Saturn (Rybinsk) to automate the preparations for production.