EP4302897A1 - Method for producing a tubular component - Google Patents

Abstract

The invention relates to a method for producing a pipe component with the following steps:
a. Providing a pipe 1 made of steel with a first end 2 and with a second end 3;
b. Reducing the outer diameter of the first end 2 by means of a relative movement between the tube 1 and a die 4 internally receiving the tube 1, the die 4 having an inner diameter ID3 that is smaller than the outer diameter AD1 of the tube 1, and the relative movement for forming of the tube 1 in the axial direction of the tube 1;
c. The outer diameter AD1 is reduced by increasing the wall thickness WD1 of the first end 2 by the relative movement of the tube 1 against a counterforce element 6 in the die 4, which exerts a force F1 exclusively on an end face 7 of the first end 2.

Description

The invention relates to a method for producing a pipe component according to the features of patent claim 1.

As part of the further processing of steel pipes, the outer diameter of the pipe end is often reduced using axial forming. The procedure is also known as retraction. Here, an external tool with a smaller inner diameter is moved axially over the end of the pipe. This process automatically results in an increase in the pipe wall thickness when drawn in, i.e. H. in the area with reduced diameter.

There are applications, such as rotor shafts, where a significant increase in wall thickness in the area of the retracted ends is required. The required increase in wall thickness can be greater than the wall thickness resulting from the Pulling in results. This goal can be achieved using partial hot forming. Here, the area to be formed is heated locally, in particular to temperatures above 800°C, and then formed. In addition to the additional energy input, a hot forming process is usually significantly more complex and places higher demands on the production technology compared to cold forming.

Another possible solution is cold extrusion. What is characteristic here is that in the last of several forming stages, the tool forms the negative of the finished component. In this final stage, the required contour of the workpiece is created using high forming forces. Since the entire workpiece is plasticized, high degrees of deformation are possible. The necessary manufacturing technology is complex and cost-intensive due to the high forming forces required.

The invention is based on the object of demonstrating a cost-effective method that can be carried out with little manufacturing effort for producing a pipe component with an end region of reduced diameter, the increase in wall thickness in the end region being greater than that which results from the mere drawing in during axial cold forming .

This task is solved in a method with the features of patent claim 1.

The subclaims relate to advantageous developments of the invention.

The method according to the invention for producing a pipe component includes providing a pipe or a piece of pipe made of steel with a first end and a second end. The outside diameter of the first end should be reduced. This is done by means of a relative movement between the tube and a die that accommodates the inside of the tube. The die has an effective inside diameter that is smaller than the outside diameter of the pipe. The relative movement for forming the tube takes place in the axial direction of the tube. The relative movement can be achieved by moving the die relative to the stationary tube or by moving the tube relative to one fixed matrix. The term relative movement also covers the movement of both components.

The term effective inside diameter refers to the inside diameter that comes into effective engagement with the pipe. The effective inner diameter can decrease in the further course, particularly starting from an opening of the die. The shape of the inner diameter is particularly funnel-shaped on the mouth side of the die.

The forming takes place using a single forming stroke. The forming stroke corresponds to the relative movement of the second end of the tube with respect to the die. The first end of the tube to be formed carries out a relative movement with respect to the die that deviates from this relative movement. The second end of the pipe is guided. This second relative movement is a guided relative movement.

The relative movement of the first end is unguided in a first forming phase and is guided in a second forming phase that immediately follows.

In the first forming phase, the outside diameter of the first end is reduced to the smallest effective inside diameter in the die with free relative movement. This means that one face of the first end has passed through a funnel-shaped mouth and has reached the narrowest point of the die.

According to the invention, it is provided that the outer diameter is reduced while increasing the wall thickness of the first end by the relative movement of the tube in the second forming phase taking place against a counterforce element in the die. The counterforce element is preferably located at a short distance from the funnel-shaped mouth area of the die and is ready for contact with the approaching end face of the first end in order to exert said force upon contact and to influence the deformation of the first end through its braking effect. It is moved so that a certain axial relative movement of the first end is continued until the forming stroke is completed. The relative movement of the first end is guided in this forming phase.

The method according to the invention therefore provides for retraction in combination with a counterforce. When retracting without counterforce, the retracted end of the tube is typically elongated slightly and the wall thickness increases slightly. When pulled in with counterforce, the pipe hardly elongates, but the wall thickness is significantly increased.

The counterforce element presses on the face of the retracted end. The process can be carried out in one step and cold, i.e. the area to be formed is preferably not heated locally. Compared to hot forming processes, the entire forming process is significantly simpler and places fewer demands on production technology. In addition, due to the lack of heating, energy is saved and scaling of the surface and subsequent blasting are avoided.

The method according to the invention cannot be assigned to axial cold extrusion, since the resulting increase in wall thickness does not occur because a mandrel delimiting the inside diameter of the reduced end is inserted into the pipe, but because the inside diameter is formed exclusively by applying a force to the end face of the first end is exercised. The counterforce element does not intervene in the inside diameter of the tube in a shaping manner, i.e. either not at all or at least not with the aim of coming into contact with the inside of the first tube end in order to define or limit the inside diameter during shaping. As a result, the effort required to pull in the pipe end is significantly lower than if the pipe end is completely plasticized at comparatively high degrees of deformation. As a result, a manufacturing technology that is cheaper than cold extrusion and is also less complex can be used. In the method according to the invention, the increase in wall thickness occurs without shaping contact of the counterforce element with an inside of the first pipe end.

The invention does not rule out that the counterforce element has a radially central region that projects into the end to be formed, but not in order to limit a radially inner mold cavity or to influence the wall thickness. The wall thickness is formed without any internal contact. i.e. the material of the pipe is not moved from radially outside to radially inside against a shaping element Internal mandrel pressed, but only limited in its flow movement in the axial direction. This limitation in the axial direction causes compression.

The position of the counterforce element within the die is regulated or controlled during the relative movement of the tube, so that increasing the wall thickness and reducing the outside diameter can be carried out in a one-step process step. A counterforce according to the invention that is well coordinated with the pulling-in process results in the wall thickness of the pipe increasing significantly beyond the natural dimension during the pulling-in process. The additional increase in wall thickness can be controlled via the level of the counterforce. The movement of the counterforce element can be force-controlled, that is, depending on the force with which it presses on the end face.

It is possible to produce workpiece contours that would otherwise only be possible by using significantly more complex forming tools (hot forming, cold extrusion, etc.). The process and the necessary technology for pulling in a pipe end with counterforce are somewhat more complex than simply pulling in without a counterforce element, but are significantly less complex than the alternatively mentioned forming concepts.

Typically, when pulling in the pipe end, the die is moved axially over the first end of the pipe. Meanwhile, the movement of the counterforce element is decoupled from the movement of the die. Preferably, the movement of the counterforce element takes place in such a way that the counterforce element presses against the end face of the tube with a constant force. The force with which the counterforce element pushes is smaller than the driving force with which the tube is moved relative to the die. The driving force is always greater because this force simultaneously presses against a shoulder of the die to reduce the pipe diameter. In the context of the invention, constant force means a force that does not fluctuate more than +/-20% around a nominal force during reduction.

However, it is also conceivable that a force that is variable over the forming time or the forming path is specifically set in order to set defined wall thickness profiles or to even out the wall thickness profile.

The outside diameter at the first end is preferably reduced by at least 10%. The outside diameter is not reduced to such an extent that the end of the pipe is closed. It remains permeable in the axial direction, only the outer diameter in the retracted area of the first end should be reduced. However, according to the invention, it is not excluded that the tube is completely closed in further processing steps in other tools. When the pipe end is pulled in, a conical transition area is created between the first end, which has a reduced outside diameter, and the second end of the pipe. The tube is in particular circular cylindrical.

Preferably, the outside diameter is uniformly reduced at the first end. Uniform means that the outer diameter is reduced evenly over the entire outer circumference. In the case of pipes with a circular cross-section, the matrices are also circular. The counterforce element preferably has a contact surface that runs parallel to the end face of the pipe end. In this case, all areas of the end face are evenly subjected to the force of the counterforce element. The end face of the tube is also preferably arranged perpendicular to the axial direction, so that there is a uniform compression over the entire circumference of the tube.

The compression should increase the wall thickness in some areas by at least 10%. Increasing the wall thickness occurs without internal support. The wall thickness can vary in areas over the axial length of the first end. At least in one length range, the wall thickness should be increased by at least 5%, preferably at least 8%, in particular at least 10% compared to the initial thickness. This means that a smaller increase in wall thickness can occur in other areas of the first pipe end, particularly in the immediate vicinity of the counterforce element, ie in the area of the end face of the pipe. Tests have shown that a greater increase in wall thickness can occur at a distance from the counterforce element by pushing the pipe and the greater plasticization there than at the end face. The degrees of deformation in the first pipe end are therefore greater at a distance from the end face than at the end face itself. This results in a non-constant axial wall thickness progression in the area of the first pipe end, which has a reduced diameter.

The method according to the invention is carried out in particular with pipes made of tempered martensitic steel, or also with pipes made of hardenable steel alloys, which are hardened or tempered in particular after the forming described above.

Further process steps can include hardening or tempering before reducing, surface hardening or coating after reducing for the purpose of corrosion protection.

The process is particularly suitable for producing rotor shafts.

Figur 1

einen Längsschnitt durch eine Matrize mit einem umgeformten Endbereich eines Rohrs gemäß dem Stand der Technik;

Figur 2

einen Längsschnitt durch eine Matrize mit einem umgeformten Endbereich eines Rohrs gemäß der Erfindung und

Figuren 3 bis 6

Längsschnitte durch eine Matrize mit einem Endbereich eines Rohrs bei 0%, 30%, 50% und 100% Fortschritt der Umformung.

The invention is explained below using exemplary embodiments shown schematically in the drawings. Show it:

Figure 1

a longitudinal section through a die with a formed end region of a tube according to the prior art;

Figure 2

a longitudinal section through a die with a formed end region of a tube according to the invention and

Figures 3 to 6

Longitudinal sections through a die with an end region of a tube at 0%, 30%, 50% and 100% progress of the forming.

Figure 1 shows, according to the prior art, a pipe 1 with a first end 2 and a second end 3. The pipe 1 is made of steel. The tube 1 has an original outside diameter AD1 and, after pushing a die 4 onto the first tube end 2, a reduced outside diameter AD2. The first end is now retracted, i.e. reduced in outside diameter.

The original inside diameter ID1 was reduced to the reduced inside diameter ID2 at the first end 2. The original wall thickness WD1 increased to the wall thickness WD2 within the first end 2. The first end 2 was compressed. The compression was carried out without any counterforce from tools within the die but only by axially displacing the tube 1 against a funnel-shaped or conical insertion funnel 5 of the die 4.

The exemplary embodiment of the Figure 2 shows the method according to the invention. In the method according to the invention, the tube 1 is also inserted into the die 4, but there is a counterforce element 6 in the die 4, which in a second forming phase exerts a force F1 on an end face 7 of the first end 2 of the tube element 1. The second forming phase begins when the end face 7 touches the counterforce element 6. The previous first forming phase, which is characterized by the lack of contact with the counterforce element 6, ends at this point in time. The forming is not stopped between these two forming phases, but is continued continuously. The wall thickness WD2 in the area of the first end 2 increases more due to the compression by means of the force F1 than during free forming without a counterforce element 6, as shown in Figure 1 is shown. The increase in wall thickness occurs without shaping internal parts that protrude into the tube, ie the mold cavity is open radially inwards. An inside 8 of the first end 2 of the tube 1 is not contacted by the counterforce element 6 for shaping. The counterforce element 6 is displaceable within the die 4 in the axial direction of the tube 1. Its outer diameter is adapted to the inner diameter ID3 of the die 4.

The invention assumes that both the tube 1 and the die 4 are circular cylindrical. The invention further provides that the outer diameter AD1 of the pipe 1 is reduced by at least 10% and, in addition, the wall thickness WD2 in the circumferential area shown is increased by at least 10% compared to the initial wall thickness WD1.

In a manner not shown in detail, the position of the counterforce element 6 within the die 4 is controlled so that the counterforce element 6 presses against the end face 7 of the first end 2 of the tube 1 with a predetermined force F1. The force F1 is smaller than the driving force FA with which the tube 1 is pressed into the die 4 against the insertion funnel 5.

The Figures 3 - 6 show a possible production sequence. At the beginning of the manufacturing process, the cold tube 1 is inserted into the dies 4 ( Figure 3 ). The outside diameter is reduced ( Figure 4 ). The counterforce element 6 is located at a distance from the narrowest point of the insertion funnel 5 of the die 4. Therefore the counterforce element 6 is not initially touched by the partially retracted tube 1. As soon as the tube 1 touches the counterforce element 6, the counterforce element 6 is displaced in the same direction as the tube 1, ie to the left in the image plane into the die 4, ie in the forming direction. The displacement takes place in such a way that a sufficiently large counterforce is built up so that the retracted end 2 of the tube 1 is compressed and the wall thickness increases to the desired extent. The Figure 6 shows the final position of the counterforce element 6 after the forming has been completed.

For the next pipe 1, the counterforce element 6 is in the starting position according to Figures 3 and 4 relocated.

The Figures 3 to 6 show that the tube 1 is displaced relative to the die 4. The invention includes that the die 4 with the counterforce element is pushed over a stationary tube 1.

Reference symbol:

1 -

Pipe

2 -

first end of 1

3 -

second end of 1

4 -

die

5 -

Introductory funnel

6 -

Counter force element

7 -

front side

8th -

inside

AD1 -

outer diameter

AD2 -

outer diameter

F1 -

Power

FA -

Driving force

ID1 -

Inner diameter

ID2 -

Inner diameter

ID3 -

effective inner diameter of 4

WD1 -

Wall thickness

WD2 -

Wall thickness

Claims (12)

Method for producing a pipe component with the following steps: a. Providing a steel tube (1) having a first end (2) and a second end (3); b. Reducing the outside diameter (AD1) of the first end (2) by means of a relative movement between the tube (1) and a die (4) which accommodates the inside of the tube (1), the die (4) having an effective inside diameter (ID3). is smaller than the outer diameter (AD1) of the tube (1), and the relative movement takes place in the axial direction of the tube (1), so that the first end (2) has a free first relative movement within the die (4) resulting from the forming. relative to the die (4) and that the second end (3) has a guided second relative movement outside of and relative to the die (4); c. in a first forming phase of a forming stroke, the outside diameter (AD1) of the first end (2) is reduced to the smallest effective inside diameter (ID3) in the die (4) with free relative movement; d. In a second forming phase of the same forming stroke, which immediately follows the first forming phase, the further relative movement of the first end (2) is guided by a counterforce element (6) in the die (4), the counterforce element (6) applying a force (F1) to a End face (7) of the first end (2) exerts to increase the wall thickness (WD1) of the first end (2). Method according to claim 1, characterized in that the counterforce element (6) is moved in the same direction as the first end (2). Method according to claim 1 or 2, characterized in that the counterforce element (6) exerts a force (F1) exclusively on the end face (7). Method according to one of claims 1 to 3, characterized in that the increase in the wall thickness (WD2) of the first end occurs without contact of the counterforce element (6) with an inside (8) of the first end (2). Method according to one of claims 1 to 4, characterized in that the position of the counterforce element (6) within the die (4) is regulated or controlled during the relative movement of the tube (1), so that the increase in wall thickness (WD2) and that Reducing the outside diameter (AD1) takes place in a single forming stroke. Method according to one of claims 1 to 5, characterized in that the movement of the counterforce element (6) is decoupled from the movement of the die (4). Method according to one of claims 1 to 6, characterized in that the counterforce element (6) is displaced depending on the force (F1) with which it presses against the end face (7). Method according to one of claims 1 to 7, characterized in that the force (F1) with which the counterforce element (6) presses against the first end (2) is smaller than the driving force (FA) with which the pipe (1 ) is moved relative to the die (4). Method according to one of claims 1 to 8, characterized in that the outer diameter (AD1) at the first end (2) is reduced by at least 10%. Method according to one of claims 1 to 9, characterized in that the outer diameter (AD1) is uniformly reduced at the first end (2). Method according to one of claims 1 to 10, characterized in that the wall thickness (WD2) at the first end (2) is increased in some areas by at least 5%, preferably at least 8%. Method according to one of claims 1 to 11, characterized in that the tube (1) consists of a tempered martensitic steel, or of a hardenable steel alloy and is hardened and/or tempered after reducing the outer diameter (AD1).

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