Tolerance Design of Mechanical Parts Considering Degradation and Quality Loss in Manufacturing Process and Operating Conditions

Dehghani Tafti, Mohammad Saleh | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52979 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Khodaygan, Saeed; Asempour, Ahmad
  7. Abstract:
  8. The tolerance stack-up in mechanical assemblies is closely related to the quality of finished products and to the costs of production. In practice, choosing a large tolerance range will result in performance reduction. On the other hand, with small tolerances considered, production costs will increase. Tolerance allocation is a useful tool to control the dimensional and geometric variables of the product, so design engineers can control the final product quality level, production cost, and other variables. The proposed method for tolerance design considers the effects of degradation and quality loss over time and allocates tolerances so that, the functional key characteristic satisfies, as well as it has the lowest cost of manufacturing and quality loss. Concerning this, at first, wear as one of the most important and comprehensive mechanisms of degradation has been scrutinized and the formulation for obtaining the amount of wear on the surface profiles of objects has been attained. Then a general method for tolerance analysis affected by degradation is presented. Then the tolerance allocation problem is described, and the method is determined by specifying the cost-tolerance function and the quality loss function over time. The constraints of the tolerance allocation problem including constraints of the manufacturing process and constraints of the assembly function are examined. The friction clutch case and cam and follower mechanism have been studied to implement the proposed method. Tolerance analysis and tolerance allocation for each case have been carried out considering the effects of degradation over time and finally the efficiency of the proposed method has been investigated using the obtained results. The results show that considering these effects can reduce the total costs during operation as well as to satisfy design constraints
  9. Keywords:
  10. Tolerance Allocation ; Quality Loss ; Tolerance Design ; Tolerancing ; Degradation Effects

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