L.J. de Vin

The generation of bending sequences in a CAPP system for sheet-metal components

An important process-planning task in sheet-metal manufacturing is the determination of bending sequences for individual components. Computer-aided generation of these sequences, as part of a computer-aided process-planning (CAPP) system, can relieve the workload of process-planning departments, this being especially important in small batch manufacturing environments. This paper discusses the functions that have to be performed during the determination of bending sequences, focusing on accuracy aspects. The generation of bending sequences is also put into the broader perspective of an integrated CAPP system such as PART-S, which is under development presently in the authors laboratory.

Suitability of sheet bending modelling techniques in CAPP applications

The use of CNC machine tools, together with decreasing lot sizes and stricter tolerance prescriptions, has led to changes in sheet-metal part manufacturing. In this paper, problems introduced by the difference between the actual material behaviour and the results obtained from analytical models and FEM simulations are discussed against the background of the required predictable accuracy in small-batch part manufacturing and FMS environments. The topics are limited to those relevant to bending along straight lines. Applications of analytical and empirical models in the area of CAPP and adaptive control are discussed. Process planning for sheet bending, however, should not be treated as an individual task but must be related to other process-planning tasks. An integrated CAPP system for sheet metal, part-s, is introduced briefly.

The Accuracy Aspect in Set-up Determination for Sheet Bending

Tolerance prescriptions, defined on a component, must be taken into account in manufacturing and in process planning. For the bending of sheet metal parts, the accuracy aspects must be addressed in sequencing and positioning procedures. 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 describes the use of the so-called “tolerance tree” in sequencing procedures for bending to be used in an integrated CAPP system.

Process planning for small batch manufacturing of sheet metal parts

The paper describes process planning for order-based small batch sheet metal part manufacturing. In this domain, general purpose CNC machinery and standard tools are being used. An example of a process planning system is given and some areas of special interest are discussed in more detail. Process planning for sheet bending and tolerance reasoning are important and intricate tasks within process planning, whereas abstractions in design and nesting are important due to their relations with other manufacturing functions. In general, manufacturing functions tend to become increasingly intertwined and traditional boundaries become blurred. Sheet metal industries, customers and suppliers alike, can benefit from this.

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.

Tolerance reasoning and set-up planning for brakeforming

Brakeforming is widely applied in high-variety small-batch manufacturing of sheet metal components to form bends that have a straight axis and a constant radius. The process typically involves a relatively large number of set-ups. The paper describes the appropriate search technique to solve the set-up planning problem as well as some of the manufacturing rules that can be applied. Special attention is paid to the accuracy aspect in the selection of set-ups for non-90° bend angles. As an example, the set-up planning procedure is demonstrated for a sheet metal bracket.