Computer aided tolerance analysis and process selection for AutoCAD Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s1784n875

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  • The fundamental objective of a design engineer in performing tolerance technology is to transform functional requirements into tolerances on individual parts based on existing data and algorithms for design tolerance analysis and synthesis. The transformation of functional requirements into tolerances must also consider the existing process capabilities and manufacturing costs to determine the optimal tolerances and processes. The main objective of this research is to present an integrated but modular system for Computer Aided Tolerance Allocation, Tolerance Synthesis and Process Selection. The module is implemented in AutoCAD using the ARX 1.1 (AutoCAD Runtime Extension Libraries), MFC 4.2, Visual C++ 4.2, Access 7.0, AutoCAD Development System, AutoLISP, and Other AutoCAD Customization tools. The integrated module has two functions: a. Tolerance analysis and allocation: This module uses several statistical and optimization techniques to aggregate component tolerances. Random number generators are used to simulate historical data used by most of the optimization techniques to perform tolerance analysis. Various component tolerance distributions are considered (Beta, Normal, and Uniform). The proposed analysis technique takes into consideration the distribution of each fabrication of the component, this provides designers . The proposed tolerance analysis method takes into consideration the distribution of each fabrication process of the assembly. For assemblies with non-normal natural process tolerance distributions, this method allows designers to assign assembly tolerances that are closer to actual assembly tolerances when compared to other statistical methods. This is verified by comparing the proposed tolerance analysis method to the results of Monte Carlo simulations. The method results in assembly tolerances similar to those provided by Monte Carlo simulation yet is significantly less computationally-intensive. b. Process Selection: This thesis introduces a methodology for concurrent design that considers the allocation of tolerances and manufacturing processes for minimum cost. This methodology brings manufacturing concerns into the design process. A simulated annealing technique is used to solve the optimization problem. Independent, unordered, manufacturing processes are assumed for each assembly. The optimization technique uses Monte Carlo simulation. A simulated annealing technique is used to control the Monte Carlo analysis. In this optimization technique, tolerances are allocated using the cost-tolerance curves for each of the individual components. A cost-tolerance curve is defined for each component part in the assembly. The optimization algorithm varies the tolerance for each component and searches systematically for the combination of tolerances that minimizes the cost. The proposed tolerance allocation/process selection method was found to be superior to other tolerance allocation methods based on manufacturing costs.
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