Process planning for laser-assisted forming

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Abstract

Laser forming has emerged as a viable means of assisting conventional forming processes with geometrical accuracy-related problems. By combining the incremental nature of laser forming with conventional processes such as brakeforming which forms material by a single continuous movement of the tooling, the exact specified bend angle and radius of curvature of the bent component may be approached. This may be achieved by sequential or simultaneous application of the conventional tooling and the laser beam. The laser beam may be applied once to the forming zone or multiple laser beam scans may be used.

The combined process allows the forming of highly accurate sheet metal products in a cost effective way, through the possibility to make corrections to the bend angle in a controlled way. Furthermore, the combined process makes it possible to form intricate products that cannot be bent on a press brake due to collision problems or problems emanating from spring-back.

Consequently there are new implications for process planning in brakeforming when a laser beam is used in combination. These implications are discussed for some primitive applications.

Section snippets

Introduction—laser forming

Laser forming is a non-contact forming process realised by introducing thermal stresses into the surface of a workpiece with a laser beam to induce plastic strains that results in forming as shown in Fig. 1. It may proceed by two primary forming mechanisms which includes out-of-plane or in-plane strain. The mechanism activated is dependent on the laser processing parameters employed, the geometry of the workpiece and the material properties. Out-of-plane deformation is induced by the

Accuracy-related problems with conventional forming

A simple box is shown in Fig. 4. The overlap conditions between front, back and side sections give constraints for the bending sequence. This is a result from the necessity to overbend the bends under loading in order to compensate for spring-back. Normally, the overlap conditions will be such that the shorter bends are processed first as this allows processing of all the bends with one set of tools.

When bending sheet metal, variations in bend angle can occur, mainly due to the variations in

Hybrid processing

The advantages of combined conventional and laser processing have been described generally in [5]. Below, the specific advantages of possible hybrid processes are described on the basis of the example of the sheet metal box.

Process planning for hybrid processing

A process planning application for hybrid processing may be part of a larger design and process planning system. The functionality for the application itself may be fairly limited (Fig. 7). An ‘information aorta’ forms the connection between various design and process planning components and arranges access to and flow of information. The main process planning components required for the applications that have been described in this paper are:

  • 1.

    Manufacturing information identification. This

Experimental

Experiments were carried out on some mechanically folded parts to investigate the feasibility of laser adjustment for correcting spring-back. No attempt was made to develop a control loop for the adjustment process here. One common engineering material was examined as described in Table 1. The bends were made with an RS folding machine. The bends were produced by bending the workpiece in one movement of the tooling to a nominal angle of 90° as shown in Fig. 9.

The laser parameters were tuned

Potential for control

As described previously even in an open loop, the laser is able to perform small adjustments. The simplest form of control for the process is the ability to close the sides of the box until they physically meet, or exploit the possibility that the laser beam is masked from the correction zone once the bend has reached 90°. The latter, however, would require the box to have no lips on the vertical sides (to allow the laser beam through), or the axis of the laser beam would have to be offset by

Conclusions

This paper has shown the potential to combine the benefits of two radically different forming techniques to improve geometrical accuracy and flexibility in sheet metal part processing. The collision problems can be largely circumvented by underbending the component and then finishing the forming in the final stages by using a laser. It was discussed how the same laser beam could be used to weld the seams of the box closed, and to cut features from the box, which may have shifted out of

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