Cost–Tolerance Function. A New Approach for Cost Optimum Machining Accuracy

Abstract

Tolerances contribute both to the accuracy and quality of a mechanical product and to the manufacturing cost of the product. Tolerance optimisation taking into account the relevant machining cost is effected by making use of various empirical and/or analytical and computer-aided techniques and methodologies, with varying degrees of success. Among them, cost-tolerance functions play a major role. On the basis of the available industrial knowledge and the published work, the paper presents the development of a new analytical costtolerance model. This model is more inclusive than the previous ones, has a wider field of applications and, as it is shown, produces results that lie closer to industrial practice. It takes into account the size of the toleranced dimension, the tolerance size, the size of the initial tolerance before machining starts, the size of the workpiece surface that has to be machined to the specified tolerance (-es). Its use is demonstrated and discussed in an application example.

Multi-objective optimization for optimum tolerance synthesis with process and machine selection using a genetic algorithm

“…A number of trials have been carried out for the two different cases outlined in Table 4 for different numbers, from 7 bits to 21 bits, for all the objective functions mentioned in Table 8. For demonstration purposes, Table 9 shows the outcome of the objective function of minimizing the manufacturing cost for different bit numbers (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). For case 1, the best results are obtained in the bit numbers between 11 and 14.…”

“…Kenneth [12] described several methods for performing tolerance allocation to reduce the overall cost of production while meeting target quality. Diplaris et al [13] formulated a new analytical cost tolerance model, which produces results closer to industrial practice based on the available industrial knowledge and earlier published data.…”

Activity-Based Tolerance Allocation (ABTA) – driving tolerance synthesis by evaluating its global cost

“…Since they highly depend on the context (material, machining operation and condition, tool and machine used, cost labour...) it is both difficult and expensive to evaluate them [11] (mainly with experimental designs). Moreover these parameters, when they are assessed, are considered as strategic data then companies do not publish any information about them……”

A geometric accuracy design method of multi-axis NC machine tool for improving machining accuracy reliability

“…It is influenced by machining errors belonging to several categories, e.g. geometric errors caused by mechanical-geometric imperfections, misalignments, wear of the linkages and elements of the machine tool structure, by the non-uniform thermal expansion of the machine structure, and static/dynamic load induced errors [8]. Geometric errors include pitch errors of the lead screws, straightness errors of the guide ways, angular errors of machine slides, and orthogonal error among machine axis [3].…”