No abstract

Industrial SummaryThe cost of tooling in sheet metal industries contributes a considerable part to the overall cost of manufacturing a component. It is therefore imperative to keep down this cost by ensuring that the tool works for a long period in production without interruption. One way of achieving this objective is to reduce the stress on the tool during punching/blanking. This paper deals with the study of this problem by using the finite-element technique. 3-D finite-element models of various type of punching/blanking tools have been developed, these models enabling the analysis of the effects of variations in tool geometry on the punching/blanking force and on the deformation of the punch, a parameter highly relevant to the assessment of tool performance in terms of the accuracy of the manufactured components. The model caters also for variation in the characteristics of the tool material, in the sense that a highly wear-resistant tool is normally composed of carbide tips around its cutting profile. Computed results by FE models are checked against design standards by American Society of Manufacturing Engineers (SME). Some suggestions are offered as to how the efficiency of a punching/blanking tool can be improved.

A so called 'three-section' model for air bending is presented. It is assumed that a state of plane strain exists and that Bernoulli's law is valid. The material behaviour is described with Swift's equation, and the change of Young's modulus under deformation is addressed. As compared with other models, the model described in the paper is capable of generating information such as required punch displacement and the unfolded blank size, very accurately. With in-process measurement of the spring-back angle, the punch displacement can be calculated even more accurately.

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 PARTS , which is under development presently in the authors' laboratory.

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