Sequential tolerance control in discrete parts manufacturing

Abstract

Abstract:The machining of complex parts typically involves a sequence of n operations on m machine tools. Conventional tolerance control specifies a fixed set point for each such operation and permissible variation about this set point to insure compliance with tolerance specifications. However, this approach may be inadequate for complex, low-volume, highvalue added parts. This paper introduces the concept of Sequential Tolerance Control (STC), an approach that uses real-time measurement information at the completion of a stage to exploit available space inside a dynamic feasible zone and reposition the set point for subsequent operations so as to optimize the production of an acceptable part. It is also demonstrated that the measurement information acquired during STC can be used to compensate for systematic variation such as tool wear. STC is then used in the context of an implicit enumeration approach to select an optimal subset of technological processes required to execute a process plan. Finally, a probabilistic approach to the problem of optimal selection of technological processes under conventional tolerance control is presented and the First Order Second Moment Method (FOSMM) is used to estimate yield.Introduction: Interchangeability in mechanical assemblies and satisfactory functional aptitude of parts and products are only possible when component dimensions and other geometric features are produced inside prescribed tolerance zones. The drawing or print of a part translates the above requirement into a sketch of exact part geometry augmented by dimensional and geometric tolerance information; tolerance information specifies permissible deviations from perfect geometry. In machining, final specifications of a mechanical part are arrived at via a logical, chronological sequence of material removal operations. This sequence may involve several machine tools with each machine tool performing one or more material removal operations, under one or more distinct set-ups. During the processing of a complex part, design specification datums and manufacturing operations datums do not always coincide. This leads to the commonly encountered situation where, even under the best of manufacturing plans, a large subset of part specifications are satisfied by the combination of two or more manufactured dimensions. Knowing that the output of each manufacturing operation (dimension produced) x j will fall within a certain tolerance range such that ] , [

A method for determining cost-efficient inspection strategies in multistage production systems

“…A more recent contribution is e.g. the work of Fraticelli et al (1997), in which sequential tolerance control is introduced, suitable for components moving through a sequence of n operations. The approach uses realtime measurement information at the completion of stage j to reposition the set point for operations j + 1 tot n.…”

Sequential Design of Optimum Sized and Geometric Tolerances

“…This method, however, is suitable for mass, batch, and automated production. A new method termed STC for production of complex, low-volume, and high-value-added parts was introduced (Fraticelli et al, 1997;Fraticelli et al, 1999;Wheeler et al, 1999;Cavalier & Lehtihet, 2000;Mcgarvey et al, 2001;Huang & Zhong, (in press)). The method essentially used real-time measurement information at any completion stage of operations to exploit available space inside the dynamic feasible zone and recalculate the working dimensions and tolerances for remaining operations.…”

“…Though STC strategy is able to enhance the working tolerances and acceptance rate of manufactured parts (Fraticelli et al, 1997;Cavalier & Lehtihet, 2000), how to extend this method to complex 3D manufacturing is still a new problem when sized, angular, and orientational tolerances are included simultaneously. Based on the basic principle of STC introduced by Fraticelli et al (Fraticelli et al, 1997), the purpose of this paper is to extend the new methodology to deal with 2D sized, angular, and orientational tolerances of 3D parts. The proposed approach essentially utilizes STC strategies to dynamically recalculate the working dimensions and tolerances for remaining operations.…”

“…Though this method was suitable for mass production in automatic lines, it had limitations to produce low-volume and high-value-added parts such as those found in aircraft, nuclear, or precision instrument manufacturing industry (Fraticelli et al, 1997). To increase the acceptable rate of a machined part, a method named sequential tolerance control (STC) for design and manufacturing has been presented (Fraticelli et al, 1997;Fraticelli et al, 1999;Wheeler et al, 1999;Cavalier & Lehtihet, 2000;Mcgarvey et al, 2001). This method essentially used real-time measurement information of the complete operations to dynamically recalculate the working dimensions and feasible tolerances for remaining operations.…”

An adaptive design method for understanding tolerance in the precision stamping process

“…A new functional tolerancing method was presented for a geometrical functional requirement to geometrical specification (Yang et al, 2010). Meanwhile, some other research related to computer-aided tolerance design were being proposed, such as sequential tolerance control (STC) (Fraticelli et al, 1997;, some extension applications of sequential tolerance control (Cavalier and Lehtihet, 2000), a low-cost fault tolerance approach (Vakili et al, 2009), material selection strategy for optimal structural design (Qiu et al, 2013), and a multi-physics coupling field finite element analysis (Zhao et al, 2009).…”