EP2888064B1 - Forming method - Google Patents

Description

The invention relates to a tumble forming or rotary forging process in which a workpiece is brought to a certain temperature range and formed by means of a forming tool, the forming force transmitted during the forming by an upper, first tool of the forming tool that is tilted and rotated relative to the workpiece a partial area of an essentially rotationally symmetrical first deformation surface of the workpiece to be deformed acts, and the partial area which does not exceed the size of a sector of the first deformation surface with a reduced area compared to the entire first deformation surface is continuously changed during the action of the essentially constant deformation force, so that at the end of a cycle the entire first forming surface was subjected to the forming force,
and wherein the forming tool acts with a lower, second tool that is also tilted in relation to the workpiece and is rotatingly moved on a partial surface, which is congruent to the partial surface of the first forming surface, of a second forming surface of the workpiece opposite the first forming surface,
wherein the two tools of the forming tool are moved synchronously with one another in uniform rotational movements.

Such a method is known from DE 195 25 868 A1 . A ring-like component is forged in that two punches, each at an angle from above and below, carry out a synchronously tumbling movement and pressing the workpiece between them. In addition, the workpiece is enclosed by a toothed die, in the gaps between the teeth of which material displaced outwards flows during the forming process.

Another double tumbling process is from the JP S62 77145 A known.

A double rotary forging process, which differs from the aforementioned double wobble forming process essentially in the choice of the axis of rotation of the punches, is from JP S62 21439 A known.

The FR 2 819 203 A1 . discloses the rapid manufacture of short stub shaft sections. A tubular shaft blank is advanced step by step by means of a feed tool, so that its end face by means of a tumbling Forming punch can be formed into a flange. The feed tool then moves back and leaves the machined part standing so that a finished stub shaft section can be sheared off. The feed tool then moves forward again in order to bring the new end face of the blank into the machining position.

The WO 93/01906 A1 relates to a wobble press with a wobbling first die half and an axially parallel moving second die half. The products of the mass and the distance from the center of gravity should cancel each other out by means of a counter mass, and continuous operation with increased wobble frequency and a reduction in the forming time of a workpiece, especially in the half and hot range, should be achieved. The second half of the die is not moved.

Also the SU 1430146 A discloses a tumbling process with a tumbling upper die half and a fixed lower die half.

The WO 2001/034323 A1 discloses a method for axial forming rolling or stamping of workpieces by means of two rotors with axes of rotation inclined to one another. For this purpose, several tools are arranged exactly opposite one another on the circumference and close to form a cavity when the rollers come into contact.

The DE 10 2005 027 259 A1 describes a forging process for the production of metallic components by warm forming of blanks made of alloys with a superplastic structure. As a result, the forming pressure in the forming tool is kept well below the forming pressure of the corresponding alloy required for forging.

The DE 10 2007 023 087 A1 relates to a method for producing cams from a hardenable steel material for a camshaft in an internal combustion engine of a motor vehicle. The manufacturing method comprises a reshaping of a semi-finished product to produce a cam blank and a subsequent heat treatment of the cam blank. In order to facilitate the forming, the bar material or the cam disk can, depending on the material, be heated to a temperature of up to 400 ° C - 500 ° C before the forming, so that the forming takes place as warm forming. Such a temperature increase naturally increases the deformability. The temperature is selected in such a way that the deformation takes place without impairing the structure and no scaling occurs.

Through the WO 2005/021177 A1 a method for forming sheet metal, in particular for warm or hot forming of blanks, in a forming tool is known. A high degree of deformation proves to be advantageous due to the use of warm or hot deformation in contrast to, for example, cold deformation such as deep drawing. In this way, the pressing tools used in particular can be spared.

The DE 10 2009 025 023 A1 relates to a method of manufacturing a camshaft using warm pressing.

Warm forging uses lower temperatures than hot forging, which means that there is generally no material hardening. For example, however, high-strength materials can be used which already have high-strength properties. In this case, the temperature only needs to be increased in areas that facilitate forming - in particular to temperatures below 850 ° C., preferably between 500 ° C. and 700 ° C.

The basic rule is that high degrees of deformation require a high deformation temperature. For example, hot forming in the temperature range between 1,000 ° C and 1,200 ° C achieves a high formability of ϕ> 4. However, this is associated with a high consumption of energy when heating the workpiece to the high temperature. Another major disadvantage associated with hot forming is the high cost of post-machining, in particular due to the need to remove the scale that arises at high temperatures, for example by means of blasting. Furthermore, the loss of material proves to be disadvantageous because considerable oversize must be provided to compensate for the deviations and inaccuracies that occur. Due to the layers of scale, it is also impossible in practice to integrate several process steps into one tool, since disruptive scale could impair the function.

In contrast, the advantage of forming at lower temperatures, for example in the area of lukewarm forming and cold forming, lies in the lower energy consumption for heating and the high level of accuracy that can be achieved in this way, with no scaling at the same time. Compared to deformation at high temperatures, however, there is a significantly lower deformability at high deformation forces.

From the DE 32 02 254 C2 a method for producing a rack by cold forming is known, in which a cylindrical blank is formed between an upper and lower tool. A die part performs a tumbling motion on the blank during the pressing process. Due to the partial deformation area compared to upsetting, a lower normal stress is achieved, which leads to an increase in the tool life.

In a method for producing a blank for a rack according to FIG DE 198 39 428 A1 a starting material with a substantially circular cross-section is inserted between the molding tools in a first step using an embossing device with at least three molding tools movable relative to one another. In a second step, a force is then exerted on at least one of the molding tools in a direction through which the molding tools move relative to one another. As a result, the starting material is formed into a blank for the rack, which in the axial area of the rack teeth is given a shape that deviates from a circular cylinder. By introducing a force into the three molds that are movable relative to one another, the starting material can be shaped without major strain hardening in those areas of the blank which experience major deformations in the further course of the production of the rack. An additional advantage of this method is that a blank shape can be achieved in a simple manner with which burr formation is avoided in a subsequent forming process, in particular in the case of a tumbling process.

Against this background, the invention is based on the object of making a method of the generic type more energy-efficient and precise.

This object is achieved in connection with the features of the preamble of claim 1 in that the forming process is carried out between 50 ° C and 450 ° in the temperature range of lukewarm forming of the workpiece and with a degree of deformation of ϕ> 4.

A forming process is therefore provided in which the forming force transmitted by the forming tool acts during the forming process only on a small sub-area as a partial area of the forming area of the workpiece to be reshaped, the sub-area being in particular continuously changed during the effect of an essentially constant reshaping force, so that after At the end of a cycle, a deformation force is applied to the entire surface. The invention is based on the knowledge that at a comparatively low temperature, in the area of cold forming or only slightly above and thus far below the temperature of warm forming, a significantly improved formability can be achieved if the forming force is not transmitted to the entire forming surface at the same time, but acts successively on a step-by-step or continuously changing partial surface until the entire forming surface is at least once with the Forming force is loaded. In particular, the deformation force is thus partially or incrementally transferred to the sub-area, the selected sub-area being changed, in particular continuously, in relation to the deformation area after a predetermined cycle.

In the temperature range of lukewarm forming, a surprisingly high formability of L> 4 can be achieved, which corresponds to the formability of hot forming and even clearly exceeds the formability of warm forming. Although the physical effect on which this excellent deformability is based has not yet been fully understood, it is currently assumed that due to the variable partial surfaces, a swelling force introduction occurs in connection with shear forces, which opposes the purely axial force introduction customary according to the prior art with a reduced deformation moment . As a result, the forming process according to the invention at lukewarm forming temperatures combines the advantages of hot and cold forming. Compared to hot forming, the amount of energy that is otherwise required to heat the workpiece is reduced. Furthermore, the time-consuming removal of scale is no longer necessary, with high accuracy being achieved at the same time. This means that small oversizes are required, which lead to significantly less reworking and at the same time to material savings. Compared to warm forming, the energy expenditure for heating is also significantly reduced, as well as the increased formability with lower forming forces. Furthermore, the cost of purchasing the devices used for forming can also be reduced. In addition, tool wear is also minimized. However, compared to cold forming, there are also significant advantages with regard to the high forming capacity described with reduced forming forces at the same time. Special tumble forming and rotary forging processes are provided for forming, which will be discussed in more detail below. The forming process can preferably be carried out without intermediate annealing. In addition, the effective direction of the deformation force can have both a horizontal and a vertical orientation.

According to the invention, the forming process is used in a temperature range between 50.degree. C. and 450.degree. A particularly advantageous embodiment of the method is also implemented in that the workpiece is heated to a temperature between 100 ° C. to 300 ° C., in particular is heated between 150 ° C and 250 ° C and that the temperature is kept essentially constant during the deformation. According to current knowledge, this temperature range constitutes an optimum in terms of formability and the required post-processing effort.

It has proven to be particularly practical if the forming force is kept essentially constant during a cycle. As a result, due to the friction caused by the forming tool, which is moved along the surface of the workpiece and thereby loads a constantly changing partial area, the desired sudden improvement in the forming capacity is achieved. At the same time, the control effort is reduced, which would otherwise require additional effort for the new relative positioning when the tool is separated from the respective partial surface of the workpiece.

As a result, the transformation from an initial state to a predetermined target geometry can be carried out during a single cycle or several complete cycles. The manufacturing effort is thus significantly reduced. At the same time, a matching deformation force is ensured in each partial area in a simple manner.

The forming tool can be designed in such a way that different positions can be set and thus partial areas of different sizes can be acted upon in order to increase the pressure locally. In contrast, it is particularly expedient if the partial areas acted upon by the deformation force are dimensioned to be essentially the same size during a cycle. This ensures constant introduction of force and thus homogeneous deformation. At the same time, the surface is smoothed and high dimensional accuracy is guaranteed.

Since the forming tool has an adjustable active surface or is arranged interchangeably on a tool holder, the size of the partial surfaces can easily be predetermined.

In the forming method according to the invention it is further provided that the change in the partial area takes place continuously, so that the relative movement between the forming tool and the surface of the workpiece is carried out continuously parallel to the surface. In this way, homogeneous deformation is achieved, which leads to a further improvement in the material quality.

The forming process according to the invention is limited to certain workpiece geometries, namely to shapes in which the surface to be formed is point-symmetrical or essentially rotationally symmetrical, the partial surface on which the forming tool acts during the transfer of the forming force, the size of a sector with a reduced area compared to the surface to be formed Area share does not exceed.

For example, workpieces are suitable in which an in particular at least partially cylindrical blank made of steel is used. The workpiece can be fixed in place during the forming process or it can be moved relative to the forming tool. The partial introduction of the forming force results essentially from an inclination of the forming tool in that the active surface of the forming tool is not aligned parallel to the partial surface of the workpiece.

According to the invention it is provided that the forming tool acts with a first tool on a partial surface of the first forming surface of the workpiece and with a second tool acts on a partial surface of a second forming surface of the workpiece that is in particular uniform to the partial surface of the first forming surface. This realizes a double partial reshaping in which both tools are tilted relative to the workpiece. This results in low friction both on the upper and on the lower tool. In addition, high degrees of deformation can be achieved on both outer surfaces of the workpiece, which means that, for example, spur gears can be optimally manufactured. As a result, the method is also suitable, for example, for spur gears with a small toothing module or for high toothing, which for the first time can be produced by forming at temperatures below the scaling limit.

The two tools are moved synchronously with one another, that is to say in particular carry out uniform rotational movements.

The two tools preferably each have a tool axis which, for example, also enclose an angle between 0 ° and 7 ° that also coincides with the central axis of the workpiece. Of course, the tools can also have different angles with respect to the workpiece. Furthermore, both tools or only one tool can perform a feed movement.

A substantial increase in the degree of deformation that can be achieved can be achieved by applying a liquid or solid lubricant to the workpiece or the forming tool prior to forming.

Fig. 1

eine Seitenansicht auf ein Umformwerkzeug und ein Werkstück während der Durchführung eines Umformverfahrens gemäß Stand der Technik;

Fig. 2

eine Draufsicht auf eine Umformfläche des Werkstücks;

Fig. 3

eine Seitenansicht auf ein weiteres Umformwerkzeug mit zwei Werkzeugen während der Durchführung des erfindungsgemäßen Umformverfahrens;

Fig. 4

eine perspektivische Darstellung eines mit dem erfindungsgemäßen Umformverfahren hergestellten Kegelrades;

Fig. 5

eine perspektivische Darstellung eines mit dem erfindungsgemäßen Umformverfahren hergestellten Stirnrades.

The invention allows numerous embodiments. To further clarify its basic principle, one of them is shown in the drawing and is described below. This is shown in a schematic diagram in

Fig. 1

a side view of a forming tool and a workpiece while performing a forming method according to the prior art;

Fig. 2

a plan view of a deformation surface of the workpiece;

Fig. 3

a side view of another forming tool with two tools while the forming method according to the invention is being carried out;

Fig. 4

a perspective view of a bevel gear produced by the forming process according to the invention;

Fig. 5

a perspective view of a spur gear produced by the forming process according to the invention.

The forming process according to the prior art is used below to clarify the basic principle with reference to FIG Figures 1 and 2 described in more detail. Figure 1 shows a side view of a forming tool 1 for producing a workpiece 2 designed as a toothed component in a wobble or rotary forging process known per se. For this purpose, the forming tool 1 has a rotationally symmetrical tool 3 which, in order to transmit a forming force to the workpiece 2 held in a die 4, is set in a tumbling movement relative to the central axis 5 or a rotary movement around the tilted tool axis 6. So there is no reversing, but a revolving, rotating movement. As a result, a deformation force F of the tool 3 acts on the workpiece 2 held in a die 4 in the area of a partial surface 7, corresponding to a momentary contact surface starting from the central axis 5 to the periphery of the workpiece 2, the deformation force F being between the central axis 5 and a periphery of the molded part has its maximum F _max and its minimum F _min in the edge area. In that the workpiece 2 is heated to a temperature of approx. 200 ° C and the forming force F is not applied to the entire, in Figure 2 recognizable deformation surface 8 is transferred, but acts successively on a gradually or continuously changing partial surface 7 until the entire deformation surface 8 is loaded at least once with the deformation force F, surprisingly high degrees of deformation can be achieved with comparatively little force.

As in particular in Figure 2 Recognizable in a plan view of the forming surface 8, the forming force F is partially transferred to the respective partial surface 7, the selected partial surface 7 changing continuously with respect to the forming surface 8 after a predetermined cycle. The different partial areas 7, 7 ', 7 ", 7"' determined in this way each have a corresponding size and are in FIG Figure 2 indicated. Due to the continuously progressing force F on different partial surfaces 7, 7 ', 7 ", 7'", a swelling force introduction is generated in connection with shear forces, which opposes the purely axial force introduction common according to the prior art with a reduced deformation moment. As a result, the forming process according to the invention at lukewarm forming temperatures combines the advantages of hot and cold forming.

In Figure 3 a representation of a forming tool 9 which can be used in the forming process according to the invention and which has two tools 3, 10 is shown while the forming process is being carried out. The forming tool 9 acts with a first tool 3 on an in Figure 2 Partial surface 7 of the first forming surface 8 of the workpiece shown in more detail and, with a second tool 10, on a partial surface of a second forming surface 11 of the workpiece 2 that is equal to the partial surface 7 of the first forming surface 8. Since the two tools 3, 10 are each not loaded over their entire surface, a low level of friction with simultaneously high degrees of deformation is achieved on both outer surfaces of the workpiece 2. The two tools 3, 10 each have a tool axis 6, 12 which enclose a matching angle with respect to the workpiece 2, so that the tool axes 6, 12 of the two tools 3, 10 are each arranged inclined with respect to a workpiece center axis.

Finally, in the Figures 4 and 5 a workpiece 2 produced by the forming process according to the invention is also shown as a toothed component, with FIG Figure 4 a bevel gear and in Figure 5 a spur gear is shown.

List of reference symbols

1

Forming tool

2

workpiece

3

Tool

4th

Die

5

Central axis

6th

Tool axis

7th

Partial area

8th

Forming surface

9

Forming tool

10

Tool

11

Forming surface

12

Tool axis

F.

Forming force

F _max

Max. Forming force

F _min

Min. Forming force

Claims (7)

1. Wobble-forming or rotary-forging method in which a workpiece (2) is brought to a specific temperature range and is formed by means of a forming tool (1, 9), wherein the forming force (F) transmitted during the forming by an upper, first tool (1) of the forming tool (1, 9) that is tilted with respect to the workpiece (2) and moved in a rotary manner acts on a partial surface (7) of a substantially rotationally symmetrical first forming surface (8) to be formed of the workpiece (2), and the partial surface (7), which does not exceed the size of a sector of the first forming surface (8) having a surface portion that is reduced compared to the entire first forming surface (8), said workpiece being continuously modified during the action of the substantially constant forming force (F) so that the entire first forming surface (8, 11) has been subjected to the forming force (F) after completion of one cycle,
   and wherein the forming tool (9), with a lower, second tool (10) which is likewise tilted with respect to the workpiece (2) and moved in a rotary manner, acts on a partial surface of a second forming surface (11) of the workpiece (2) opposite the first forming surface (8) that is congruent with the partial surface (7) of the first forming surface (8),
   wherein the two tools (1, 9) of the forming tool are moved synchronously with one another in uniform rotational movements,
   characterized in that
   the forming method is carried out between 50°C and 450°C in the temperature range of the lukewarm forming of the workpiece and with a degree of forming of in part ϕ > 4.
2. Wobble-forming or rotary-forging method according to Claim 1, characterized in that the workpiece (2) is heated to a temperature between 100°C and 300°C, in particular between 150°C and 250°C, and in that the temperature is kept substantially constant during the forming.
3. Wobble-forming or rotary-forging method according to at least one of the preceding claims, characterized in that the forming is carried out in a single stroke without intermediate annealing.
4. Wobble-forming or rotary-forging method according to at least one of the preceding claims, characterized in that the forming from an initial state to a predetermined desired geometry is carried out during a single cycle or a plurality of complete cycles.
5. Wobble-forming or rotary-forging method according to at least one of the preceding claims, characterized in that the partial surfaces (7) respectively acted upon by the forming force (F) during a cycle are dimensioned to be of substantially the same size.
6. Wobble-forming or rotary-forging method according to at least one of the preceding claims, characterized in that the forming surface (8, 11) is substantially circular, wherein the partial surface (7) does not exceed the size of a sector having a surface area that is 25% of the forming surface (8, 11).
7. Wobble-forming or rotary-forging method according to at least one of the preceding claims, characterized in that the two tools (3, 10) each have a tool axis (6, 12) forming an angle corresponding to the central axis of the workpiece (2).

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