Tolerance Allocation with Minimun Machining Cost- A Case Study for the Spindle of A Machine tool

• Main Authors: Jeng-De Huang, 黃政德
• Other Authors: Jhy-Cherng Tsai
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/r54qe6

碩士 === 國立中興大學 === 機械工程學系所 === 97 === Machine tool can procedure each kind products of processing equipments, thus is called “mother of machinery”. Promotes unceasingly along with the machining performance, the machining accuracy request is also higher. Spindle is the critical component. The relate tolerance design technique of a spindle usually is a question. Designer often depended on many years’ experiences by oneself or referred to others’ design methods to make the improvement strategies. They did not have exactly methods to follow. The purpose of this study is according to specification of original tolerance to allocate it for reduces the product processing cost as the goal. The research method was aimed to engineering graphics of the spindle system applied the tolerance analysis. For example, searched two critical dominant path and calculated the tolerance stack-up in the assembly. These methods include the establishment of product hierarchy via product and feature decompositions, the establishment of tolerance network of the mandrel system, and variation analysis based on the path of the tolerance network. Tolerance allocation is according to the precision variation requirement and product processing cost. The method used for sequential quadratic programming (SQP) algorithm. In the optimum model, the objective is to minimize the summation of product processing cost and then to construct the tolerance stack-up constraint conditions and the self-tolerance boundary constraint conditions. The self-tolerance boundary constraint conditions by using standard operating procedure (SOP) method to set it as a reference of tolerance allocation. The tolerance allocation method is according to tolerance adjusting strategy. It includes the following 3 methods: (A) Keeping the same precision variation but reducing production cost. (B) Increasing the precision variation with maximum reduction of production. (C) Decreasing the precision variation while keeping low production cost. The result of tolerance allocation on the mandrel system shows that the cost of route 1 reduces 5.6% as the accuracy and variation of spindle are not changed. If increasing 20% and 30% of variations, the costs 4.7% and 6.4% increasing. If loosing 11% of accuracy, the cost 6.4% decreasing. For route 2, the accuracy of spindle maintains the same, the cost 5.1% decreasing. If increasing 26% and 42% of variations, the costs 16.6% and 32.5% increasing. If loosing 5.3% of accuracy, the cost 8% decreasing. We know that the original design through tolerance adjustment and allocation can be the basis for tolerance allocation of spindle assembly.