Quality measurement of production process plan using tolerance chart

Abstract

This paper presents a new method for assessing the quality of production process plans using tolerance chart to lower production cost. The tolerance chart is used to predict the accuracy of the part that is to be produced following the process plan, and to carry out the quantitative measurement on the quality of the process plan. By comparing the values of design tolerances and their corresponding resultant tolerances calculated using the tolerance chart, the process plan that is incapable of satisfying the design requirements and the faulty production operations can be identified. Similarly, the process plan that imposes unnecessarily high accuracy and wasteful production operations can also be identified. For the latter, a quantitative measure on the quality of the process plan is introduced. The higher the unnecessary cost of the production, the poor is the quality of the process plan. A process plan quality measurement coefficient is introduced. This coefficient also incorporates two weighting factors to reflect the difficulty of manufacturing operations and number of dimensional tolerances involved. To facilitate the identification of the machining operations and the machined surfaces, which are related to the unnecessarily tight resultant tolerances caused by the process plan, a rooted tree representation of the tolerance chart is introduced, and its use is demonstrated. Several examples are presented to illustrate the new methods. This research introduces a new quantitative process plan evaluation method that may lead to the optimization of process plans.