GB2092041A

GB2092041A - Upsetting and swaging hollow bodies

Info

Publication number: GB2092041A
Application number: GB8137276A
Authority: GB
Original assignee: GFM Gesellschaft fuer Fertigungstechnik und Maschinenbau AG
Current assignee: GFM Gesellschaft fuer Fertigungstechnik und Maschinenbau AG
Priority date: 1980-12-22
Filing date: 1981-12-10
Publication date: 1982-08-11
Also published as: AT366938B; FR2496511A1; DE3142480A1; ATA623780A; JPS57134228A; DD201393A5

Abstract

To locally increase the wall thickness of a shell of a hollow body, that portion of the hollow body in which the wall thickness is to be increased is heated and the hollow body is then subjected to an axial pressure sufficient to upset said heated portion. In order to permit a fast and economical formation of a portion of increased wall thickness of virtually any desired shape on the shell even of a thin-walled hollow body without any risk of a formation of folds or cracks, the heated shell portion is upset and is simultaneously subjected to a swaging operation by which the material which tends to bulge outwardly under the axial pressure is confined within the desired shape of the outside surface of the shell portion which has been increased in wall thickness. <IMAGE>

Description

SPECIFICATION Process of locally increasing the wall thickness of shells of hollow bodies This invention relates to a process of locally increasing the wall thickness of shells of hollow bodies, wherein that portion of the hollow body in which the wall thickness is to be increased is heated and in a heated state is upset by th application of axial pressure.

Shells of hollow bodies, particuiarly cylindrical tubes used as blanks in the manufacture of numerous structual elements for vehicles container and plant, must often be locally increased in wall thickness in order to stiffen the shell and to increase its strength or for a subsequent shaping of the hollow body by a forming or machining operation. For such a local increase in wall thickness, the shell of the hollow body is locally heated to a temperature at which it can be upset and the heated portion is then upset by the application of axial pressure. That portion cannot be freely upset in the longitudinal direction because even a small upsetting will cause material to flow to the outside and that flow of material will result in the formation of an annular internal fold and of cracks.In order to prevent a flow of material to the outside, upsetting has mainly been performed in a mold. Although an upsetting in a mold is restricted by the friction between the workpiece and the mold. When it is desired to effect a relatively large increase of the wall thickness of a shell, two or more upsetting steps carried out in respective upsetting molds may be required.

Besides, hollow bodies cannot be upset at all unless they have a suffieciently large wall thickness and it is not possible to upset, e.g., thin-walled tubes.

An entirely different upsetting process has been proposed, in which an axially proceeding portion of the hollow body is heated by an annular heating inductor, which surrounds the hollow body, and the hollow body is subjected at the same time to an axial pressure that is sufficient to upset the heated portion.

The annular heating inductor heats a narrow annular portion of the workpiece to temperature at which the workpiece can be upset and the annular heating inductor is moved along the workpiece so that said heated zone is also moved along the workpiece. The pressure which is applied at the same time then causes the workpiece to be upset as desired. In that process an outward flow of the material is prevented by pressure-applying rollers, which contact the outside surface of the workpiece and are moved along the workpiece together with the annular heating inductor. The workpiece is rotated so that the rollers roll on the outside surface of the workpiece and prevent an outward flow of material. That upsetting process involves a considerable expenditure and can be performed only at a very low speed so that it is not economical.

It is an object of the invention so to improve a process of the kind described first hereinbefore that shells of hollow bodies, even of thin-walled tubes, can be increased in wall thickness to virtually any desired shape in a fast, economical operation without danger of a formation of folds or cracks.

This object is accomplished in accordance with the invention in that the heated portion of the shell of the hollow body is upset and at the same time is subjected to a swaging operation by which the material which under the upsetting pressure tends to bulge outwardly is confined to the desired shape of the outside surface of the shell. By the swaging operation performed as the material is upset, any portion of the material which flows outwardly as it is upset is confined so that the upset material can flow only inwardly. As the outside dimension of the upset portion of the hollow body will be determined by the inner dead center position of the swaging dies, the wall thickness can be increased only inwardly or only outwardly or inwardly and outwardly by the upsetting operation. The swaging during the upsetting operation always prevents an undesired folding of the material.Owing to the oscillatory motion of the dies, the faces of the dies contact the workpiece only for short periods of time so that the swaging will not obstruct the flow of the material in the longitudinal direction during the upsetting operation. As a result, even thin-walled hollow bodies can be upset in a singie operation virtually as desired without a formation of folds and cracks. It is essential, however, that the swaging dies will swage the entire periphery of the workpiece portion which is being upset. This can be ensured without difficulty in known manner by the provision of swaging dies having properly shaped die faces and provided in a suitable number and by a suitable relative rotation between the workpiece and the dies.

According to a preferred further feature of the invention, the swaging operation is continued when the upsetting has been terminated and the continued swaging operation is used to shape the hollow body for instance in that portion of its shell which has been increased in wall thickness. This can be effected in that the application of the upsetting pressure is discontinued when the material has been sufficiently upset. The workpiece can then be swaged to the desired final shape on th same machine in a conventional swaging operation.

This sequence of operation can be automatically controlled, if desired.

If the swaging operation performed in accordance with the invention is effected by swaging on a mandrel, the workpiece can be swaged at the same time to the desired interior shape. In that case the workpiece may be upset as far as to the mandrel, during the upsetting operation or may be swaged inwardly only after the upsetting operation. It will be understood that the workpiece can be swaged to the desired inside and outside shapes by means of suitably designed dies.

In accordance with a preferred further feature of the invention, the application of the axial pressure and the swaging operation are continuerl until the hollow body has been shaped so as to close its interior cavity. As the simultaneous swaging and upsetting operations permit a substantial upsetting without a formation of folds of cracks, the inwardly directed upsetting and possibly a subsequent swaging may cause the material to flow to gsther so that the hollow body is closed.

The upsetting and swaging process according to the invention and the optional subsequent swaging of the workpiece may be carried out in a simple manner on conventional swaging machines, provided that they can apply required upsetting pressure by the exertion of a feeding force by means of a gripping head and a holder-up. The swaging machine can be freely selected in dependence on the nature of the swaging operation to be combined with the upsetting operation and may consist, for instance, of a swaging machine with or without a mandrel, a swaging machine comprising an annular traveler, a swaging machine comprising means for rotating the workpiece, or a machine comprising two or more dies.

The invention is illustrated in the accompanying drawing, which in Figures 1 to 3 shows diagrammatically two successive steps performed in the process accordance with the invention to make a hollow body which has an end portion that is smaller in diameter and a transitional portion which has a larger wall thickness.

The workpiece 1 consists initially of a tubular blank and in th end portion 2 which is to be upset is heated to a temperature at which the workpiece can be upset. The temperature profile is controlled to match the desired upset shape and that portion which is to be upset to the largest extent is heated to the highest temperature (Fig. 1).

The heated blank is delivered to a swaging machine, the gripping head 3 of which comprises a collet chuck 4, which grips the workpiece 1 at that end which has not been heated. By means of the gripping head 3, the workpiece 1 is then moved between the dies 5 to a stop 7, which is formed by a holder-up 6. The feeding force exerted by the gripping head 3 is then increased so that an axial pressure sufficient to upset the heated portion of the workpiece 1 is applied to the latter between the stop 7 and the collet chuck 4.

During the upsetting operation, the workpiece is rotated and its end portion is swaged by the oscillating dies 5, by which the material which tends to bulge outwardly as it is upset is confined within the original shape of the outside surface of the workpiece so that the material of the latter flows only inwardly at 8.

This inward flow of material is provisionally limited by a mandrel 9, which has been inserted into the workpiece 1 (Fig 2).

When the workpiece 1 has been shortened to a predetermined extent by the upsetting operation, the latter is terminated and the upset workpiece 1 is moved by the collet chuck 4 opposite to the feeding direction and away from the stop 7 out of the range of the smooth portions 5a of the die faces, which smooth portions 5a serve to swage the workpiece as it is upset, into the range of second portions 5b of the die face, which second portions 5b serve to shape the outside contour of the end portion that is smaller in diameter. The swaging operation is then continued. As the workpiece 1 is swaged on the mandrel 9 by means of the portions 5b of the die faces, the workpiece 1 is formed with the end portion 10 which is smaller in diameter and has the desired exterior and interior shapes (Fig. 3).

The combination of upsetting and swaging operations in the process according to the invention permits an upsetting of large quantities of material even in thin-walled tubes in one operation without a formation of folds and without need for upsetting dies and permits an upsetting of hollow bodies and a subsequent swaging thereof to certain shapes virtually in a single operation.

Claims

1. A process of locally increasing the wall thickness of shells of hollow bodies, wherein that portion of the hollow body in which the wall thickness is to be increased is heated and in a heated state is upset by the application of axial pressure, characterized in that the heated portion of the shell of the hollow body is upset and at the same time is subjected to a swaging operation by which the material which under the upsetting pressure tends to bulge outwardly is confined to the desired shape of the outside surface of the shell.

2. A process according to claim 1, characterized in that the swaging operation is continued when the upsetting has been terminated and the continued swaging operation is used to shape the hollow body, for instance, in that portion of its shell which has been increased in wall thickness.

3. A process according to claim 1 or 2, characterized in that the workpiece is swaged on a mandrel.

4. A process according to claim 1 or 2, characterized in that the application of the axial pressure and the swaging operation are continued until the hollow body has been shaped so as to close its interior cavity.