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Development of a new method to determine bending sequence in progressive dies
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In progressive dies, two or more stations are used to produce sheet metal components. In each station, one or more processes are applied. The progressive dies reduce thetime and cost of producing complex sheet metal components.However, the design and manufacture of these dies are difficult. CAD/CAM systems have been proved to be very useful tools for this task. The main problem of CAD/CAM systems used in progressive die design is determining the bending operations sequence. In this paper, a new method for determining the sequence of the bending operations is described. In this method, sequencing is done in two stages. First, the bending operations, which can be carried out simultaneously, are defined by a classification method. In this method, all the bends are initially pided according to their bending directions (feed direction or perpendicular to it). Then for each direction, the bends are pided into operation groups according to classification rules. Three rules are used to determine the bending operation groups in this paper. These rules are based on relations between the bends in the component. The sequence of the bending operation groups is then determined using fuzzy set theory. Four components taken from industry and previous papers are used to show the capabilities of the proposed method..7685
Keywords: Bending sequence . Progressive dies . Fuzzy set theory
1 Introduction
One of the most common processes used for sheet metal forming is bending. The bending process has many applications including electrical, automotive and in aircraft industries.
Bending dies are designed according to the sheet metal component shape, its dimensions, and tolerances [1]. Thus,several types of dies are used in sheet metal bending. When the number of parts is large and the shape is complex, the designers often use progressive dies to reduce lead time and production costs.
Inpidual operations in a progressive die are often relatively simple. But when the die contains several stations where in each station a few of these inpidual operations are to be combined, it is often difficult to plan the most practical and economical strip design for optimum operation of the die.
The sequence of operations is the most important problem in progressive die design. In other words, the sequencing is the key to progressive die design.
Most research in sheet metal working involves using analytical and experimental methods which address problems of sheet metal behavior in forming process. Although much work has been carried out on sheet metal behavior, little work has been done on the automation of die design and the sequence of operations in progressive dies.
In this paper, a new approach for sequencing bending operations in progressive dies is described. In this method, sequencing is done in two stages. First, the bending operations which can be carried out simultaneously are defined by a classification method. The sequence of the bending classes is then determined by using fuzzy set theory.
2 Related work
Shaffer, Fogg, and S. Nakahara [2, 3] were the first people to work on computer-aided progressive die design systems. The early systems attempted to use basic computer graphics facilities and programs written in FORTAN to improve the productivity of die design [2]. These systems were mostly used for piercing and blanking operations.
In recent years, some researchers have focused on the bending process in progressive dies. De Vin et al. [4] have described the use of a tolerance tree in sequencing procedures
for bending operations. This was used in an integrated computer-aided process planning (CAPP) system.Ong et al. [5] used a fuzzy set system to determine the sequence of bending operations in press brake machines. Gupta et al. [6] have developed a process planning system for sheet metal components. They applied a greedy algorithm to determine the bending sequence. Prof. Duflou et al. [7] suggested a penalty function method and the traveling salesman problem method to determine bending sequences in press brake machines. Most researchers have worked on the bending operations performed by press brake machines or robot-assisted bending [8–10].