EP0726823B1 - Process for forming hollow stepped shafts of cold-formable metal by internal high pressure - Google Patents

Abstract

PCT No. PCT/DE94/01300 Sec. 371 Date Jul. 12, 1996 Sec. 102(e) Date Jul. 12, 1996 PCT Filed Nov. 3, 1994 PCT Pub. No. WO95/12466 PCT Pub. Date May 11, 1995The invention relates to a process for forming hollow stepped shafts of cold-formable metal by internal high pressure with the following steps: provision of a tube outlet section and filling it with fluid; sealing at least the tube section to be widened; application of a suitable high internal pressure for widening the tube section; calibration of the workpiece by applying a high calibration pressure; maintenance of the calibration pressure while heading the tube along the longitudinal axis. Internal tools, also spring-loaded tools, are provided as supports in the tool.

Description

The invention relates to a method for hydroforming of hollow stepped shafts made of cold formable Metal according to the preamble of claim 1, such as it is known for example from EP-A-0497 438.

In general, a tube section is used in hydroforming with straight or not straight longitudinal axis simultaneous effect of internal pressure Pi and axial force Pa reshaped. Some hydroforming processes are e.g. in the conference proceedings of the 14th Metalforming Colloquium in Hannover 1993 on p. 9 described in more detail.

The internal high-pressure forming of conventional hollow shaft Workpieces are usually made in accordance with FIGS. 1 and 2 in two forming phases. After filling the pipes, this is done first expanding. Here the laws of the free, i.e. Tool-free expansion. The pipe surface is arched at the end of this first forming phase resulting contact between workpiece and tool extends initially only over a partial area of the workpiece surface. In the further forming phase, the workpiece by calibrating to complete contact with the inner shape brought the mold. The wall thickness profile in longitudinal section of hollow shafts generated in this way is usually around 15% of the initial wall thickness So the pipe sections (Fig. 3). The wall thickness curve is in primarily depending on the stretchability of the pipe materials. The free expansion length or kink limit is in the previously known hydroforming processes Max. 2xdo, where do is the diameter of the exit pipe is.

Document US-A-4,730,474 discloses a method of Relieving residual stress in a metal pipe. To do this a pipe by applying an axial pressure load in Longitudinal axis direction deformed, one compared to the internal high pressure reduced pressure of a fluid during forming inside the metal pipe is applied to the friction between the forming tool and the outer surface of the tube to reduce.

European patent application EP-A 497 438 discloses furthermore a method and a device for hydraulic Expanding tubular, hollow profiles. Here a provided tube is filled with fluid and sealed. A suitable internal high pressure is created by this fluid applied to expand the pipe section, wherein controlled movable inner tools for applying a Support force is provided on the pipe section to be expanded are. According to the teaching of this document, the internal tools after the flow limit of the material has been exceeded moved outwards in a controlled manner.

The object of the present invention is a to create an improved hydroforming process, that makes it possible to produce sophisticated hollow shafts.

According to the invention, the object is achieved by the method according to Claim 1 solved.

The method according to the invention is particularly suitable for such hollow shafts as e.g. in application DE 40 07 284 A1 are described. Here it is e.g. around Drive shafts of a motor vehicle with a central tube area larger outside diameter with thin wall thickness and bilaterally formed end areas with thicker Wall thickness. The wall thickness differences on these waves and the free flare length exceeds that of Hydroforming known process limits by a Multiples.

1. Herstellung von Hohlwellen mit Wanddickenverlauf im Längsschnitt mit Wanddickenunterschieden von weit mehr als 15% bezogen auf S_o.

2. Herstellung von Hohlwellen mit einer Aufweitlänge von weit mehr als 2xdo.

The following advantages are achieved by the method according to the invention:

1. Production of hollow shafts with a wall thickness profile in longitudinal section with wall thickness differences of far more than 15% based on S _o .

2. Production of hollow shafts with an expansion length of far more than 2xdo.

Fig. 1

ein schematisches Innenhochdruckverfahren;

Fig. 2

eine Folge von Verfahrensschritten zur Herstellung eines teilweise aufgeweiteten Rohrs

Fig. 3

den Wanddickenverlauf eines aufgeweiteten Rohrs,

Fig. 4

ein Beispiel eines erfindungsgemäß hergestellten Gegenstandes und

Fig. 5

schematisch einen anschließenden Verfahrensschritt.

The method according to the invention is explained in more detail below with reference to the drawing. It shows:

Fig. 1

a schematic internal high pressure process;

Fig. 2

a sequence of process steps to produce a partially expanded tube

Fig. 3

the course of the wall thickness of an expanded pipe,

Fig. 4

an example of an object manufactured according to the invention and

Fig. 5

schematically a subsequent process step.

As can be seen in particular from FIG. 2, it becomes a process product 4 thereby produces that first Pipe with a fluid that is also a gas or a highly volatile Liquid can be filled. Then follows expanding by sealing the pipe ends in itself known manner and application of an internal high pressure. To expanding in phase 1 and calibrating the hollow body in In phase 2, the high calibration pressure is maintained in phase 3 or even increased.

According to the invention, as can be seen in particular from FIG. 5, upsetting the molded long tube is performed.

The first part of the task is solved in that the two Forming phases a third according to Fig. S added becomes. After expansion in phase 1 and calibration in phase 2, the high calibration pressure is maintained in phase 3 or even increased. This high internal pressure enables one Pushing the pipe ends together without wrinkling in the Pipe wall. There is an inevitable upsetting of the wall the workpieces in the pickup area by almost any Amounts. Such a process can be done by appropriate Implement control technology of the forming machine. A suitable one Pipe wall thickness So you have to choose the optimal one Wall thickness gradation of the thinner expansion area and the to achieve a thick end region.

The second part of the task is done by tooling Measures solved (Fig. 6). Support elements in the tool, the can also be sprung, prevent the buckling of the long tube shafts. Depending on the length of the pipe shafts, a or several elements arranged in the longitudinal direction of the tool become.

Claims (2)

1. Process for forming hollow stepped bodies of cold-formable metal by internal high pressure, having the following steps:

   a) inserting a tube blank of a predetermined wall thickness (So) into a tool which is provided with internal tools for supporting the tube blank to be formed;

   b) sealing off the tube portion to be expanded;

   c) filling the tube blank with fluid;

   d) applying an internal high pressure suitable for expanding the tube portion;

   e) calibrating the workpiece by applying a high calibrating pressure;
   characterized in that,
   for forming hollow shafts with an inner portion expanded to up to twice the diameter of the end portion,
   the following steps are provided:

   f) maintaining or increasing the calibrating pressure while upsetting the tube in the direction of the longitudinal axis, and thereby

   g) increasing the wall thickness of the tube, at least on opposite sides of the expanded tube portion, in such a way that it becomes greater than the wall thickness (So) of the tube blank.
2. Process according to Claim 1, characterized in that the internal tools are sprung tools.

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