Optimal selection of machining datum and machining tolerance allocation through tolerance charting
09 Jul 2012-International Journal of Manufacturing Technology and Management (Inderscience Publishers)-Vol. 25, pp 135-160
TL;DR: An optimisation model is formulated for selecting machining datum and tolerances and implemented with an evolutionary algorithm namely differential evolution (DE) in process planning.
Abstract: The main purpose of tolerance charting is to determine the optimal allocation of working dimensions and working tolerances such that the blueprint dimensions and tolerances can be achieved to accomplish the cost objectives. The selection of machining datum and allocation of tolerances are critical in any machining process planning as they directly affect any setup methods/machine tools selection and machining time. In order to reduce the machining time and cost, an optimum process plan should be designed. Due to the existence of intermediate machining operation, a large number of intermediate part features may be used as the datum for the machining of others. This paper mainly focuses on the selection of optimum machining datums and machining tolerances simultaneously in process planning. In this work, an optimisation model is formulated for selecting machining datum and tolerances and implemented with an evolutionary algorithm namely differential evolution (DE).
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TL;DR: A review of existing tolerance charting methods, and of an algorithm developed in the course of simplification, can be found in this article, where the authors discuss the tolerance allocation problem and its application with reference to over 50 published works.
Abstract: The tolerance chart is a tolerance analysis tool used by process planners in the determination of the working dimensions and tolerances of components during their manufacture. The control of tolerances is important in determining production cost and functionality. However, its merits are not exploited by small and medium–size industries, as compared to the larger automobile and aircraft corporations. This paper is a review of existing tolerance charting methods, and of an algorithm developed in the course of simplification. The specification of blueprint dimensions can to be justified by process and machine capability and the considerations of economics of production. The tolerance allocation problem and its application are discussed with reference to over 50 published works. Is tolerance charting an ultimate answer to our search for automated manufacturing competitiveness?
1 citations
01 Jan 2021
TL;DR: It was concluded that the method of tolerance chart and respectively a method that takes into account a statistical processing of the results accumulated over time are methods likely to lead to an efficient solving of the problem of determining the intermediate dimensions.
Abstract: Among other problems to be solved, the design of a technological process of machining by cutting a part involves establishing the dimensions that can be achieved in the pre-final machining of the same surface of the part. There are distinct ways to calculate the so-called intermediate dimensions and, in particular, to define the dimensions for adjusting the position of the cutting tool tip before starting the actual machining process. The paper analyzes some such ways of establishing the intermediate dimensions, highlighting the conditions under which they can be applied, their advantages and limitations of use. Subsequently, the double-entry matrix method was applied to identify one or more methods with wider possibilities of use. It was concluded that the method of tolerance chart and respectively a method that takes into account a statistical processing of the results accumulated over time are methods likely to lead to an efficient solving the problem of determining the intermediate dimensions.
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TL;DR: In this article, the importance of setup planning to tolerance control in process planning is discussed and a graphical approach is proposed to generate optimal setup plans based on design tolerance specifications, where setup and setup datums should be identified.
Abstract: Operational dimensioning and tolerancing play an important role in process planning. It ensures that resultant part dimensions and tolerances do not exceed specified design values. Tolerance chart analysis is an effective technique for process planners to calculate mean values and tolerances of operational dimensions. However, a tolerance chart can be built only after all the intial engineering decisions have been made concerning the process plan. Specifically, setups and setup datums should be identified. While many researchers focused their attention on tolerance chart analysis, the selection of setups and setup datums (setup planning) was overlooked. No systematic approaches for setup planning can be found in the literature. This paper discusses the importance of setup planning to tolerance control in process planning. A graphical approach is then proposed to generate optimal setup plans based on design tolerance specifications.
55 citations
"Optimal selection of machining datu..." refers background in this paper
...Ji (1994), Ngoi and Kuan (1995) and Zhang et al. (1996) presented various optimisation techniques by considering different parameters and objectives to generate optimised allocation of dimensions and tolerances....
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TL;DR: In this article, a simplified approach of deriving the working dimensions between surfaces of a workpiece during tolerance charting is presented, which does not require any representation of the machining sequence.
Abstract: We present a simplified approach of deriving the working dimensions between surfaces of a workpiece during tolerance charting. Unlike other methods, it does not require any representation of the machining sequence. The dimensional chains are first formulated into a matrix and it is then solved by applying the Gauss elimination technique. We also describe an elegant method of deriving the balanced tolerances of a workpiece during tolerance charting. The process links between surfaces are derived by using a special tracing technique. With the process links obtained, the balanced tolerances are solved by using a separate mathematical model. An example is used to illustrate the method.
49 citations
"Optimal selection of machining datu..." refers background in this paper
...Ngoi and Fang (1994) presented the branch and link method....
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TL;DR: In this article, the feasibility to build a mathematical model for computer aided process planning (CAPP) to find the optimal machining datum set and machining tolerances simultaneously for rotational parts was explored.
Abstract: In machining process planning, selection of machining datum and allocation of machining tolerances are crucial as they directly affect the part quality and machining efficiency. This study explores the feasibility to build a mathematical model for computer aided process planning (CAPP) to find the optimal machining datum set and machining tolerances simultaneously for rotational parts. Tolerance chart and an efficient dimension chain tracing method are utilized to establish the relationship between machining datums and tolerances. A mixed-discrete nonlinear optimization model is formulated with the manufacturing cost as the objective function and blueprint tolerances and machine tool capabilities as constraints. A directed random search method, genetic algorithm (GA), is used to find optimum solutions. The computational results indicate that the proposed methodology is capable and robust in finding the optimal machining datum set and tolerances. The proposed model and solution procedure can be used as a b...
37 citations
"Optimal selection of machining datu..." refers background or methods in this paper
...A rotational multi-step sleeve part (Li et al., 2000) is used as an example to illustrate the proposed methodology....
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...Machining cost units obtained Datum selection Using GA (Li et al., 2000) Using DE Datum selection set 1 NA 88....
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...Since there are large numbers of constraints need to be checked in each optimisation iteration, Li et al. (2000) introduced a two-end-recorded tolerance chart tracing algorithm in the kernel....
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...Li et al. (2000) proposed a method for the generation of feasible machining datums are as follows: Step 1 Generate a feasible datum pool for the part feature by considering the machining processes and the part setup methods involved in the manufacturing of that part....
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...Li et al. (2000) addressed the simultaneous optimisation of datum selection and machining tolerance allocation using genetic algorithm (GA)....
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TL;DR: In this paper, the relationship between process and blue-print dimensions can be expressed as an array of linear equations and inequalities, and the desired working dimensions and tolerances can be solved using LINDO, a linear programming optimization software.
Abstract: This paper introduces a simple and direct method to derive process links between feature planes. Consequently, the relationship between process and blue-print dimensions can be expressed as an array of linear equations and inequalities. By applying appropriate constraints to these models, the desired working dimensions and tolerances can be solved using LINDO, a linear programming optimization software. An example is also included to illustrate the method.
29 citations
TL;DR: A proportional smoothing approach is described with a numerical example, which can assign appropriate tolerances automatically and systematically, based on the requirements of both blueprint dimensions and process capabilities, and is extended to a statistical tolerance model.
Abstract: There are two dimensional sets in a tolerance chart: the blueprint (B/P) dimensional and the working dimensional group. The interrelation between these dimensional groups makes it very difficult to assign appropriate tolerances to individual working dimensions. This paper deals with the automatic tolerance assignment problem in a tolerance chart, especially for computer-aided tolerance charting. After the manual methods of tolerance assignment are briefly discussed, a linear programming model is analysed. Owing to the impractical solution from the linear programming (LP) model, a proportional smoothing approach is described with a numerical example, which can assign appropriate tolerances automatically and systematically, based on the requirements of both blueprint dimensions and process capabilities. The result from this approach is compared with that of the LP model and the original manual procedure. Finally, the approach is extended to a statistical tolerance model.
23 citations
"Optimal selection of machining datu..." refers background in this paper
...Ji (1994), Ngoi and Kuan (1995) and Zhang et al. (1996) presented various optimisation techniques by considering different parameters and objectives to generate optimised allocation of dimensions and tolerances....
[...]