Software Development for Setup Planning of Rotational Part

An innovative approach was developed to solve the problem of setup planning, which is the most critical problem in process planning for discrete metal parts. Setup planning is the act of preparing detailed work instructions for setting up a part. The major objective of this research is to improve the performance of CAPP systems by developing a systematic approach to generate practical setup plans based on tolerance analysis. A comprehensive literature review on tolerance control in CAPP was conducted. It was found that tolerance chart analysis, a traditional tolerance control technique, is reactive in nature and can be greatly improved by solving the problem of setup planning. In order to develop a theoretically sound foundation for tolerance analysis-based setup planning, the problem of tolerance stack up in NC machining was analyzed in terms of manufacturing error analysis. Guidelines for setup planning were then developed based on the analysis. To systematically solve the setup planning problem, a graph theoretical setup planning algorithm for rotational parts was then developed for automated and integrated setup planning and fixture design. Its efficiency and effectiveness evaluated. The result is promising. The algorithms were then computerized. A setup planning program was developed under the Microsoft Windows environment using C.

Graph-Based Process Planning for Rotational Part Machined with Tolerancing

This paper investigates a methodology and corresponding graph modeling of process planning for cylindrical machined parts with tolerancing. Methods and techniques for representing possible process plans, reducing the complexity and eliminating over-toleranced plans are developed. The method first maps each feature of a part into feasible finishing processes that are capable to achieve the specified tolerances associated with the feature. All possible process plans are then developed by expanding preceding processes of each finishing process. The expanded processes form a graph, or a forest, with processes as nodes and process sequence as links. Processes with same specifications can be further merged and pruned to reduce the complexity of the graph. Tolerance stack-up of each possible plan for simplified results is also further computed by tolerance chart such that over-toleranced plans are eliminated. As there are often many feasible plans for machining a part, the qualified plan that satisfies design specifications is achieved by traversal through the graph imposing tolerance chart. An example is also demonstrated to illustrate the approach and the model. The merit of this method is to employ a unified graph model for representing and reasoning.

Virtual Part Arrangement in Assemblies for Automatic Tolerance Chart Based Stackup Analysis

Manual construction of design tolerance charts is a popular technique for analyzing tolerance accumulation in parts and assemblies, even though it is limited to one-dimensional worst-case analysis. Since charting rules are GD&T (geometric dimensioning & tolerancing) specification dependent, and the user has to remember all the different rules to construct a valid tolerance chart, manual charting technique is time-consuming and error-prone. The computer can be used for automated tolerance charting, which can relieve the user from the tedious and error-prone procedure while obtain the valid results faster. The automation of tolerance charting, based on the ASU GD&T mathematical model, involves (1) automation of stackup loop detection, (2) formulation of the charting rules for different geometric tolerances and determination of the closed form function for statistical analysis, (3) automatic part arrangement for an assembly level chart analysis, (4) development of the algorithms for chart analysis and automatic application of the charting rules. Since the authors’ previous DETC/CIE’03 paper already discussed tasks 1~2 and part of task 4, this paper will focus upon task 3, i.e. virtual part arrangement in assemblies for tolerance charts, and update the analysis algorithm (related to task 4). These two papers together will provide a complete coverage of automated tolerance charting technique popularly used in industry. The implementation will be briefly discussed as well, and case studies will be provided to demonstrate the approach to virtual part arrangement.

A Complete Variation Algorithm for Slot and Tab Features for 3D Simulation-Based Tolerance Analysis

Development of tolerance analysis methods that are consistent with the ASME and ISO GD&T (geometric dimensioning and tolerancing) standards is a challenging task. Such methods are the basis for creating computer-aided tools for 3D tolerance analysis and assemblability analysis. These tools, along with the others, make it possible to realize virtual manufacturing, in order to shorten lead-time and reduce cost in the product development process. Current simulation tools for 3D tolerance analysis and assemblability analysis are far from satisfactory because the underlying variation algorithms are not fully consistent with the GD&T standards. Better algorithms are still to be developed. Towards that goal, this paper proposes a complete algorithm for 3D slot features and tab features (frequently used in mechanical products) for 3D simulation-based tolerance analysis. The algorithms developed account for bonus/shift tolerances (i.e. effects from material condition specifications), and tolerance zone interaction when multiple tolerances are specified on the same feature. A case study is conducted to demonstrate the algorithm developed. The result from this work is compared with that from 1D tolerance chart method. The comparison study shows quantitatively why 1D tolerance chart method, which is popular in industry, is not sufficient for tolerance analysis, which is 3D in nature.

A CAD/CAM Representation Model Applied to Tolerance Transfer Methods

This paper presents the adaptation of tolerance transfer techniques to a model called TTRS for Technologically and Topologically Related Surfaces. According to this model, any three-dimensional part can be represented as a succession of surface associations forming a tree. Additional tolerancing information can be associated to each surface association represented as a node on the tree. This information includes dimensional tolerances as well as tolerance chart values. Rules are then established to infer tolerance chains or stack up along with tolerance charts directly from the graph. This way it becomes possible to combine traditional one dimensional tolerance transfer techniques with a powerful three-dimensional representation model providing high technological contents.