DE2425501A1 - METHOD AND DEVICE FOR FLOW EXTRUSION OF THICK-WALLED HOLLOW BODIES - Google Patents

Description

Cable and metal works Gutehoffnungshütte Aktiengesellschaft

3-265

May 21, 1974

Method and device for cup extrusion of thick-walled hollow bodies with a bottom

The invention relates to a method for cup extrusion of thick-walled hollow bodies with a bottom, made of massive Raw parts of plastically deformable materials, especially metals.

When producing thick-walled hollow bodies by cup extrusion Often particular difficulties arise due to the occurrence of cracks in the interior of the workpiece. In Figure 1 is the Location of such cracks shown. They run at the transition from the floor to the wall at a short distance from the inner surface of the Workpiece. .

The origin of the cracks is due to the material flow of the cup extrusion. Especially when making thick-walled bowls, i. H. In the case of small decreases in cross-section, a so-called "rigid zone" is created in front of the extrusion die. This "rigid zone" is a hemispherical material vium in front of the punch, which is subject to only very small changes in shape and can therefore be described as rigid to a good approximation. Especially clear could this effect by material flow studies at Backward cup extrusion by KAST (Dieter Käst, model laws during backward extrusion of geometrically similar cups, reports from the Institute for Metal Forming Technology, University Stuttgart, No. 13) and by SCHMITT (Gerhard Schmitt, investigations on reverse cup extrusion of steel at room temperature, reports from the Institute for Metal Forming Technology, University Stuttgart, No. 7).

509850/0042

_ ₂ _ 24255Q1

The hemispherical border of the "rigid zone" represents a
Area of intensive change in shape. The locally very high changes in shape along this boundary ultimately lead to the exhaustion of the deformation capacity and thus to the occurrence of the cracks described, which are also known as so-called "shear cracks". As KAST was able to show on the basis of his material flow studies, the peculiarity of the material flow described above in cup extrusion is all the more pronounced, the smaller the decrease in cross section. This is the reason why, in practice, when producing particularly thick-walled cups, the risk of shear cracks occurring is greatest.

Another very important influencing factor is the deformability of the material. While the occurrence of such cracks in the forming of pure aluminum was not yet known, it poses a considerable problem in the forming of steels «This is particularly true for the processing of heavier formable steels (for example Ck 45, St 52.3) and for raw part diameters over
60 mm. The larger raw part diameters present particular difficulties because the forging of the bars during the rolling process is insufficient and thus the deformability of the
Material in the core of the raw part is particularly low.

Such severe shear cracks often occur during cup extrusion of steels on that to avoid them, the forming process in two to divided into three sub-processes and to restore the deformation ability A recrystallization annealing must be switched on between each of the sub-processes. This approach is, compared to the usual cup extrusion, associated with a considerable additional effort. Further economic disadvantages arise from the fact that the faulty parts can be found is very difficult because the crack does not emerge on the surface and a simple visual inspection is therefore ruled out.

SG985G / Ö (H2

The invention is based on the object of preventing shear cracks to be avoided in the manufacture of thick-walled bowls.

This task is performed in a method of the type mentioned at the beginning solved in that, according to the invention, exiting from the annular nozzle formed by the cup press ram and extrusion bush Material a counterforce is exerted axially against the exit direction. This counterforce can both be applied thereby be that the free end of the cup rests against an annular counter-holder, which is of an adjustable counterforce is acted upon, as well as in that a pressure medium acts directly on the free end of the cup. As a cup molding process Both reverse cup extrusion (FIG. 2) and forward cup extrusion (FIG. 3) can be used.

In a particularly advantageous embodiment of the method it is achieved by suitable measures that the counterholder force over is not constant over the entire commute, but rather shows an upward trend.

In a further advantageous embodiment of the method, achieves that the counter-holder force does not work over the entire period sweg, but only acts in the section of the work path in which the shear cracking would occur without counterholder force.

The advantage of the process is that it is possible to produce thick-walled hollow bodies with a bottom in one operation instead of as otherwise required, to produce in several operations.

The invention is shown schematically in FIGS. 1-3 illustrated embodiments explained in more detail.

In Figure 1, a thick-walled hollow body is shown, which by cup extrusion according to the conventional method in one operation was produced.

5 0 9 8 5 0 / Q (H 2

The dashed lines show the fiber orientation. With this known method, shear cracks 1 occurred at the transition the floor to the wall at a small distance from the inner surface of the workpiece.

FIG. 2 shows the method according to the invention in reverse cup extrusion. A blank 3 is inserted into the cup extrusion sleeve 2. When the press ram moves downwards, the cup press die k moves with the counter holder 5 downwards until both hit the blank 3. When the Napfpreßstempeis k penetrates into the blank 3, material is displaced counter to the movement of the punch by the annular nozzle formed by the Cuppreßstempel k and the press sleeve 2. The displaced volume of material pushes the counter holder 5 against a counterforce in front of it. Since an increase in the counterholder force simultaneously increases the tool load, the counterforce should only be as great as is necessary to avoid shear cracks. So should not exceed approx. 20 % of the punch force.

But it is also possible to let the necessary counterforce act directly on the emerging material. In the annular space 6 located above the cup wall there is then a pressurized medium, which is fed through the opening 7 and kept under pressure (right half of FIG. 2)

In Figure 3, the application of the method according to the invention to cup forward extrusion is shown.

A blank 3 is inserted into the cup press sleeve 2. Counterholder and cup press die k are at the same height at the beginning of the process. With Vorcfrngen of the press ram 8 material is pressed out through the annular nozzle formed by the cup press ram k and the press sleeve 2, the emerging material pushing the counter holder 5 in front of it while overcoming the opposing force. In the right half of FIG. 3, the counterforce is applied in that a hydraulic medium acts under pressure on the emerging material.

509850 / ÖD42

Claims (6)

Cable and metal works Gutehoffnungshütte Aktiengesellschaft 3-265 May 21, 1974 Claims (1.! Method for extrusion of thick-walled hollow bodies with a bottom, made of solid raw parts plastically umfortnbaren substances, in particular metals, characterized in that a counterforce is exerted axially against the exit direction on the material emerging from the annular nozzle. 2. The method according to claim 1, characterized in that the counterforce is variable in size during the entire duration of action. 3. The method according to claim 2, characterized in that the counterforce increases steadily in the course of the forming process. 4. The method according to claim 1, characterized in that the counterforce acts on the workpiece only during a part of the duration of the forming process. 5. The method according to claim 1 or one of the following, characterized in that the counterforce is applied via a gaseous or liquid medium. 6. A device for carrying out the method according to one or more of claims 1 to 4, consisting of a Napfpreßbüchse features, a press ram and a counter-punch, characterized ge, that in the annular space Napfwandung forming a counter-holder is disposed. 503850/0042 Blank page