SI9300258A - Process for radial extrusion with tube wall reduction - Google Patents

Abstract

A subject of the invention is the radial extrusion process combined with inside tube ironing, which is an essence a cold extrusion process and can be reckoned among bulk metal forming processes. It enables tube shaped metal semiproducts to be formed into different final shaped parts or parts that are intended for additional working, for example by machining. The process is grounded on insertion of a tube (1), which may be on one end previously expanded, into a proper shaped die (3), where on one side there is a punch (4) which is retained with a determined force (F1) and inside which lies a free movable mandrel (5), while from the other side in working stroke the counter-punch (2) extrudes the difference of tube volume which results from ironing of the tube (1), in the direction of counter-punch (2) travel so, that the material fills up the starting clearance between the mandrel (5) and the tube (1), the space between the tube (1) and the punch (2) and arbitrary shaped space (B) in the punch (2) or in the die (3).

Description

RADIAL PRESSURE PROCEDURE

BY REDUCING THE PIPE WALL

The subject of the invention is a radial extrusion process with pipe wall reduction, which is essentially cold extrusion, which is referred to as a mass transformation process, which allows the transformation of metal semi-finished tube-shaped products into various shapes, which may be final or intended for further processing, e.g. with cutting procedures.

The invention belongs to Class B 21D 22/00 of the International Patent Classification.

- 2 A technical problem that is successfully solved by the present invention is the determination and implementation of such a process that will allow the transformation of simple workpieces cut from standard thin or medium-thick tubes, or at one end previously expanded into transformations of more complex axisymmetric shapes, characterized by a longer cylindrical stem that converts to a shape that can capture a sharp increase in diameter and sudden changes in the thickness of the wall and the shape of its cross-section.

The characteristic shapes of the parts that can be made by the process according to the invention are shown in Figure 2, in which the shapes on the left represent the initial symmetry and on the right the final states after transformation.

The production of elongated thin-walled rotationally symmetrical shapes by cold forming the tubular billets is desirable especially in the case of heavily loaded parts. In this way, on the one hand, better strength properties resulting from the plastic hardening of the material and the fibrous structure are achieved, and on the other hand, the plastic deformation is relatively small in order to produce such shapes from the pipes with respect to the geometric similarity of the initial and final shape, which eliminates the need for multi-stage transformation due to intermediate recrystallization annealing while maintaining sufficient material toughness.

In the case of bulky production, we transform tube-shaped semi-finished products mainly by processes where changes in wall thickness are not the goal but a consequence of changes in diameter and length. Such processes are bending, spreading, narrowing, hydrostatic expansion and thrust molding.

For example, a deliberate change in wall thickness occurs in processes such as reduction, direct extrusion, radial extrusion, thrusting, rotary forging, and rotary shrinkage of pipe ends. A particular problem is the transformation of the pipe, which requires a local rotational symmetric increase in the thickness of the pipe wall or a sudden change in the shape of the cross-section of the wall.

- 3 Rotationally symmetric increase of wall thickness can only be achieved by bending the pipe in the axial direction, which in the case of unsupported pipe causes rotation symmetrical folds, which is usually prevented by supporting the wall from the inside and the outside with a mandrel or. matrix. Due to the large friction surface, the influence of friction is greater in this case, the greater the friction, the smaller the wall thickness compared to the diameter and the greater the supported length of the pipe through which the active force of shrinkage is transmitted. The problem of friction is particularly large in the case of a radial extrusion of pipes, in which to achieve the desired plastic flow of material in the area of the transformation zone, compressive stresses may be required, which may also be several times greater than the flow stresses. The known radial extrusion process, in which the working stroke of the tool is transmitted through the ends of the pipes, is therefore only useful for the transformation of shorter pipes or. pipes with larger wall thicknesses.

The method of radial extrusion by reducing the wall of the tube according to the invention is based on the insertion of a tube which may be pre-extended into one appropriately shaped die at one end, with a force held on one side by a pin in which a freely moving mandrel lies while on the other In the working movement of the pipe, a counterbore whose diameter is larger than the inner diameter of the pipe, while reducing the pipe wall, squeezes the difference of the tube volume in the direction of the pistil by filling the initial gap between the mandrel and the tube, or the empty space in the die or tube. pesticu.

I will describe the invention in greater detail on the basis of an embodiment and illustrations, of which:

FIG. 1 shows, in a specific embodiment, a radial extrusion process with reduction of the pipe wall according to the invention in the initial and final stages. FIG.

- 4 In Fig. 1, a radial extrusion process with reduction of the pipe wall according to the invention in the initial and final stages is shown in a specific embodiment. Said method according to the invention can be performed on vertical or horizontal hydraulic or mechanical presses with at least two, preferably three independent actuators.

Pipe 1, the upper part of which can be previously expanded, is inserted into the die 3, which is attached to the machine table. Then we move the piston 4, which must be held at all times by a certain force Fp, which ensures that the required hydrostatic pressure is maintained in the deformation zone A, in which the process of radial extrusion takes place. In the piston 4 there is a freely movable mandrel 5 whose diameter is slightly smaller than the initial internal diameter of the tube 1 for ease of entry. Instead of a freely movable mandrel 5, it is also possible to use a counter-mandrel which has an extension at the top of which the diameter corresponds to the diameter of the mandrel 5 The working stroke is made with a counter-pin 2 whose extended part is thicker than the initial inner diameter of pipe 1. During the working stroke, therefore, the difference of the tube volume is extruded in the direction of the pin 4, first filling the initial gap between the pin 5 and tube 1, and then with a sudden increase in hydrostatic pressure to a value conditioned by the force Fp with which the piston 4 is held, a vacant space B is made in the piston 4, whose shape later determines the final shape of the attachment. Depending on the final shape we want to achieve, the empty space B can also be made in matrix 3. The exact final shape of the product, which is defined by the shape of the matrix 3, the pin 4, the counter 2, the mandrel 5 and the length of the working movement of the counter 2, is obtained at a sufficiently high hydrostatic pressure, which is otherwise limited by the force F _v. When forming a tooth in space B, as shown in Figure 1, the friction between the mold (tube 1) and the mandrel 5 is also significantly assisted. Due to the hydrostatic pressure in deformation zone A, there was also a flow of material in the opposite direction to the movement of the pistil (in Fig. 1 in the downward direction). This is prevented by the proper design of the thickened part of the counterpart

- 5 2, especially the length of the thickening Lp, on which the friction acting in the direction of the movement of the counterpart 2. Depends on the unwanted counter-flow of the material, partly prevented by the rigidly supported ejector sleeve 6, through which only enough force can be transmitted. causes axial contraction of the tube under the thickened part of the counterpane 2.

A particular advantage of the process according to the invention is that the influence of friction on the forming force F2 can be controlled even at larger lengths of cylindrical branches, by properly dimensioning the diameter of the mandrel 5 and the diameter of the thickened part of the counterpart 2. In this way, it can be achieved filling the gap between tube 1 and mandrel 5, followed by an increase in the hydrostatic pressure in zone A and thus the friction force acting on the counterpart only at the back of the counter movement.

Figure 2 shows three typical shapes of products that can be produced by radial extrusion by reducing the pipe wall according to the invention, with the cross sections on the left being the symmetrical shapes of the workpieces and on the right the final shapes of the longitudinal sections. In the case of the products of Figures 2a and 2b, which may form part of a high-pressure armature, a preliminary transformation of the straight tube by the expansion or expansion process is envisaged. narrowing from the initial pipe diameter to the diameter D ₄ oz. D ^. The shape of the product in Figure 2c, which may be part of the coupling, can be made from a straight tube of outer diameter Dt and inner diameter Dq. Typical of the radial extrusion process of the invention is that the length of the blade remains approximately the same, but the initial inner diameter of the tube D _o in the stem region increases to the diameter of the thickened portion of the counterpart Dj. however, in the transition to the radial extrusion zone, the inside diameter is reduced to the diameter of the mandrel D ₃ .

Claims (3)

PATENT APPLICATIONS A method of radially extruding by reducing the wall of a tube, characterized in that the tube (1) with the previously expanded upper portion is inserted into a suitably shaped die (2), with a pin (3) being held on one side by a certain force. a freely movable mandrel (4) lies, while on the other hand, in the working motion, the counter (5) extends the difference of the volume of the tube (1) resulting from the reduction of the tube wall in the direction of movement of the counter (2) so that the material fills the formed initial slot between the mandrel (5) and the hose (1), the line between the hose and the hub (4), and any free space (B) formed. 2. The radial extrusion method by reducing the wall of a pipe according to claim 1, characterized in that the diameter of the inserted tube (1) is the same lengthwise. 3. Radial extrusion method by reducing the wall of a tube according to claim 1, characterized in. that an extension whose diameter corresponds to the diameter of the mandrel (5) is made in place of the freely movable mandrel (5) on the upper part of the counter-tip (2). Mag. Janez Pipan, B.Sc. ing. Figure 1 Figure 2a Figure 2b Figure 2c Mag. Janez Pipan, B.Sc. ing.