TARGET SEQUENCE OF LOCAL ELECTROHYDRAULIC STAMPING OF LARGE SHEET METAL PARTS

Abstract

This article considers the sequence of local loading required for various technical requirements in electrohydraulic forming of large-sized sheet bottoms. Electrohydraulic forming technologies for relatively small sheet parts are widely known. In such technologies, the energy release technology is created on one electrode pair, which allows for the deformation of small parts. Original electrohydraulic presses with high stored energy (up to 500 kJ) have been developed, which allows for the release of energy simultaneously in many zones of the working space above the workpiece. And this, in turn, allows the workpiece to be loaded only in certain zones.

Various technical requirements may be imposed on large sheet bottoms, i.e. limiting the deformation of thinning in certain zones, minimal elastic grooving of the part or especially high accuracy of its surface.

A comparative analysis of the stress-strain state at the initial and subsequent stages of forming large-sized round bottoms under different variants of the sequence of pulse loading was carried out. With pulse loading, which is uniform over the entire surface of the workpiece, compression zones appear in the flange zones, which leads to the appearance of wrinkles. As well as to the accumulation of thinning deformations in the center of the part. These harmful features of the process limit the technological capabilities of electrohydraulic stamping. With pulsed local loading of the flange part of the workpiece at the first stages of forming, the workpiece bends itself in this part, which makes its shape more rigid and partially leads to strengthening of the material in this part. This reduces the likelihood of wrinkles. At the subsequent stages, the deformation of the load is carried out in the central zone, which ensures a decrease in thinning deformations in the dangerous zone. This technology for forming bottoms with a diameter of more than a meter was tested experimentally and the positive results of these experiments are given in the work.

The proposed technology allows for the manufacture of large sheet metal parts of not very high accuracy, but when using one forming element of the equipment at one workplace.

For the manufacture of especially precise bottoms, for example, mirrors of space communication antennas, a double-stage manufacturing technology is proposed. With this technology, the workpiece is pre-freely formed to a certain deflection in the center under the action of local electro-hydraulic load on simple technological equipment. At the second stage, the peripheral zones of the workpiece are formed on a partially convex tooling. The results of the stamping process of antenna mirrors with a diameter of 250 and 900 mm are shown. The deviation from the parabolic surface of the matrix was 0.03…0.05 mm. Other positive properties of such a technological process are given.

As a result of the research, a rational sequence of local loading was proposed for some variants of the requirements. Some variants of the development were confirmed experimentally. A direction of mathematical modeling of the process was proposed. The purpose of the work is to establish a rational sequence of local loading to fulfill the proposed technical requirements during one technological operation.