الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Dimensional and geometrical tolerances play a basic role in both the design and manufacturing processes. Allocating dimensional and geometrical tolerances to the components of any mechanical assembly significantly affects the resulting manufacturing costs and quality. The determination of an optimal tolerance whereby the designer, manufacturer and customer’s objectives are met is highly relevant to the tolerance allocation issue. The purpose of this study is to introduce a general platform for solving the dimensional and geometrical tolerance allocation problem in the design stage that satisfies both design and manufacturing requirements. A description and identification of the problem provide the basis for developing the proposed solution. Numerous studies have identified the tolerance allocation problem in order to minimize manufacturing cost and quality loss. The bulk of the previous models are concerned with allocating only dimensionaJ.• tolerances in order to simplify the allocation problem by reducing the number of unknowns. It is also essential to note that most researchers take only the machining costs as an objective of minimization under functional constraints. Moreover, a general procedure for simplifying the allocation problem was rarely considered.
This study is mainly concerned with developing a mathematical model for estimating the optimal values of dimensional and geometrical tolerances in mechanical assemblies. The estimated tolerances will not only minimize a stated objective function but also satisfy the required functional and design constraints. The suggested model formulates a relation between dimensional and geometrical tolerances, and machining costs. This model aIsoinvestigates both inspectional cost and quality loss in the objective function. This thesis will show how to formulate the constraints of the allocation problem including design function, process capability and measuring equipment suitability constraints.
The proposed model is a Mixed Integer Nonlinear Programming (MINLP) due~ to the continuous variables of tolerance values, and the binary variables for selecting the suitable machining processes and inspectional equipment for each assembly component. The proposed model can be used in linear or non-linear cost-tolerance functions with or without tolerance limits in a design function. Furthermore, it can be used for linear or non-linear constraints and is also generalized for complex assemblies with any number of entities.
In order to simplify the allocation problem, a generalized procedure for allocating dimensional and geometrical tolerances for any product assembly is provided. Some flow charts are proposed to help designers allocate the minimum sufficient number of geometrical tolerances based on the different geometrical features interrelations.
To examine the model. a one-way clutch assembly problem is solved by the proposed model and the resultant tolerances are compared to the tolerances resulting nom solving the same problem using two different models namely the Lagrange Multipliers method and nonlinear IP model.
The proposed model is also adopted to solve four assembly problems; journal bearing assembly, gearbox assembly, ratchet assembly and comparator stand assembly problems, as examples for two dimensional and three dimensional assembly products. Different accumulation models are used to construct the design function constraints for the four mentioned assembly problems. The solution for these numerical examples .proves the model capability to find the optimal value of dDnensional and geometrical tolerances, the machining process selection, and the inspectional equipment selection at the design stage. Furthermore, an effective procedure for solving redesign problem is proposed in order to simplify the process of tolerance reallocation when modifications are required to improve the product performance .