H.J.J. Kals

FIXES, a system for automatic selection of set-ups and design of fixtures

This paper reports on the development of a computer aided planning system for the selection of set-ups and the design of fixtures in part manufacturing. First, the bottlenecks in the present planning methods are indicated. A brief description is given of the CAPP environment PART, in which FIXES is incorporated. The planning procedure of FIXES consists of two parts: the selection of set-ups and the design of a fixture for each set-up. The automatic selection of set-ups is based on the comparison of the tolerances of the relations between the different shape elements of the part. A tolerance factor has been developed to be able to compare the different tolerances. The system automatically selects the positioning faces and supports the selection of tools for positioning, clamping and supporting the part. A prototype implementation of FIXES is discussed.

XPLANE, a Generative Computer Aided Process Planning System for Part Manufacturing

This paper reports on the development of XPLANE, a generative computer aided process planning system for part manufacturing. Described is its position and functioning as a part of a more extended computer aided manufacturing system that includes a link to CAD systems, as well as systems for computer aided design and selection of jigs and fixtures, NC part-program generation, tool management and capacity planning. The XPLANE system automatically selects tools, machining operations and their sequence starting from a full part description created by a boundary-representation solid modeller. Apart from the description of the CAM environment the paper focuses on some of the most important specifications of XPLANE, the knowledge driven expert system, i.e. the knowledge representation, the inference engine, the explain facility and the knowledge-base editor.

Fixture Design with FIXES: the Automatic Selection of Positioning, Clamping and Support Features for Prismatic Parts

FIXES is a computer aided system for the automatic generation of set-ups and for fixture design for prismatic parts, to be used in an integrated process planning environment. The generation of set-ups having been described in a previous paper [9], this paper concentrates on fixture design, in particular the automatic selection of the faces for the positioning, clamping and support of workpieces. The selection procedures described are based on both the topology of the prismatic part and the geometric relations between the different part elements (features). The geometric relations are evaluated with the aid of a so-called Converted Tolerance Scheme.

The Integration of Process Planning and Shop Floor Scheduling in Small Batch Part Manufacturing

In this paper we explore possibilities to cut manufacturing leadtimes and to improve delivery performance in a small batch part manufacturing shop by integrating process planning and shop floor scheduling. Using a set of initial process plans (one for each order in the shop), we exploit a resource decomposition procedure to determine schedules to determine schedules which minimize the maximum lateness, given these process plans. If the resulting schedule is still unsatisfactory, a critical path analysis is performed to select jobs as candidates for alternative process plans. In this way, an excellent due date performance can be achieved, with a minimum of process planning and scheduling effort.

A computer aided tolerancing tool II: tolerance analysis

A computer aided tolerance analysis tool is presented that assists the designer in evaluating worst case quality of assembly after tolerances have been specified. In tolerance analysis calculations, sets of equations are generated. The number of equations can be restricted by using a minimum number of points in which quality of assembly is calculated. The number of points needed depends on the type of surface association. The number of parameters in the set of equations can be reduced by considering the most critical direction for the assembly condition. The latter direction, called virtual plan fragment direction, is determined using a virtual plan fragment table, based on an analogy to the plan fragment table used in degrees of freedom (DOF) analysis. This reduced set of equations is then solved and optimized in order to find the maximum/minimum values for the assembly condition using simulated annealing. This method for tolerance analysis has been implemented in a feature based (re-)design support system called FROOM, as part of the functional tolerancing module.

Cost Decision Support in Product Design

The constraints addressed in decision making during product design, process planning and production planning determine the admissible solution space for the manufacture of products. The solution space determines largely the costs that are incurred in the production process. In order to be able to make economically sound decisions, costing data support must be integrated into the decision making processes. Regarding product design, the designer must be supplied with transparent costing data, that is ready for direct application. In this paper a functional architecture for costing data support during product design, as well as a corresponding data structure are presented.

A Tolerancing Tool Based on Kinematic Analogies

A computer aided tolerancing tool is presented that assists the designer in functional tolerance specification. The theoretical concepts for subsequent tolerance analysis are also provided. The computer aided tolerancing tool is part of a feature based object oriented (re)-design support system, called FROOM. FROOMs assembly modelling capabilities provide basic information for functional tolerance specification. Assembly constraints are satisfied by means of degrees of freedom (DOF) analysis. This method is based on the use of kinematic analogies. The rotations and translations (macro--DOFs) that components are allowed to have, are inferred using this technique. The tolerance representation in FROOM is based on the TTRS method, by Clment et al., which is also based on kinematic analogies. In this method, the small displacements that are allowed in the tolerance zone can be described by a tolerance torsor or transformation matrix. Using the tolerance torsor or transformation matrix, tolerances are described as constraints. The small displacements that are still allowed by means of the torsor are referred to as micro-DOFs. For tolerance analysis, the torsor approach offers a mathematically correct description of tolerance zones, although a lot of equations are generated. These are reduced by applying a kind of degrees of freedom analysis considering both the macro-DOFs and the micro DOFs (tolerances).

Conceptual graphs in constraint based re-design

This paper elaborates on the use of conceptual graphs for the representation of different types of objects and constraints in a re– design support system. Conceptual graphs, or conceptual structures, have been proposed for use in natural language processing and for representing mental models. However, recently they have also been proposed for use in the field of CAD/CAM. Conceptual graphs are graphs with two different kinds of nodes: concepts and conceptual relations. ReAesign support involves the modelling of assemblies and components, which on their turn are composed of features and geometric elements. The assemblies, components, features and geometric elements are represented by the concepts in the conceptual graph. The constraints between these entities are represented as conceptual relations. Constraints, such as geometric, kinematic, and manufacturing constraints are represented using conceptual graphs. Thus, conceptual graphs provide for an elegant way of representing hods functioning and manufacturing constraints. Constraints are satisfied using a ‘mukibrid’ constraint satisfaction approach, employing geometxy related domain knowledge for the geometry related constraints and an algebraichmmeric approach for the remaining constraint equations. The combination of the constraint satisfaction mechanism and the conceptual graphs allows for a unified way of handling assembly, comprnent and feature related information, Conceptual graphs are not only used in representing assemblies, components, features, and constraints, but also in supporting a mixed topiown and bottom-up design style,

Tolerancing and sheet bending in small batch part manufacturing

Tolerances indicate geometrical limits between which a component is expected to perform its function adequately. They are used for instance for set-up selection in process planning and for inspection. Tolerances must be accounted for in sequencing and positioning procedures for bending of sheet metal parts. In bending, the shape of a part changes not only locally, but globally as well. Therefore, sheet metal part manufacturing presents some specific problems as regards reasoning about tolerances. The paper focuses on the interpretation and conversion of tolerances as part of a sequencing procedure for bending to be used in an integrated CAPP system.

Conceptual Graphs in CAD

This paper elaborates on the use of conceptual graphs in a prototype of a computer based support system for re-design. Re-design support involves the modelling of assemblies and components. The requirements of the components to be modelled are a compromise between the functioning of the assembly and the manufacturability of the individual components. Conceptual graphs provide for an elegant way of representing both functioning and manufacturing aspects. In the prototype system, conceptual graphs are used for representing and defining assemblies, components and features as well as the relations between these entities. Constraints, such as kinematic, tolerance and manufacturing constraints are also represented using conceptual graphs.