EP1602472B1 - Process and apparatus for preparing a powder compact - Google Patents

Description

The invention relates to a method for producing a molded part from powder, in particular metal powder, from a doughy material containing a powder, from a flowable material containing a powder or from pre-pressed material, wherein a device is used which comprises: a die which consists of a base body and a die sleeve inserted therein, wherein the die sleeve has a preferably at least partially cylindrical contour which forms a molding surface for the molding, and at least one press die, which enter into the defined by the preferably cylindrical contour of the die sleeve opening and in can compact through the preferably cylindrical contour defined space located powder or material. The invention further relates to an apparatus for producing a molded part from powder, from a doughy material containing a powder, from a flowable material containing a powder or from pre-pressed material.

Such a method or a corresponding device are the contribution of Holownia BP "Balanced The Method For Metal Powder Compaction" in Powder Metallurgy, Metal Society, London, GB, Vol. 39, No. 3, 1996, pages 207 to 209 , known. Similar solutions reveal the US Pat. No. 6,324,970 B1 and the DE 197 22 779 A1 ,

With methods and devices of the generic type, it is possible to produce molded parts from metal powder by pressing and subsequent sintering. It is known to use for the pressing of powdery material stamp-like tools that compress powder introduced into a die by an axial pressing movement. For this purpose, at least one ram is required, which penetrates into the die. In this case, the die has a cavity which is open to the punch side. The die opening is closed - except for a slight play - by the stamp. The stamp builds up by its penetration into the Matrizenhohlraum necessary for compression pressure.

It can also be provided that a plurality of punches are used, which can move in an axial direction. The punches can dive into an axially closed on one side mold or come in an axially open in both directions die from both axial directions. Occasionally, through mandrel rods are used, but primarily have no compression function, but a positive displacement function. The punches can also dip laterally into the die to create undercuts or other geometric shapes. To demould the molded part, these radially dipping punch are withdrawn so far that the demolding is not hindered.

The die usually consists of a die ring (matrix base body) and a die bushing or sleeve inserted therein with the workpiece contour. Since the stamping pressure is transferred from the powder to the die wall, the die expands during the pressing process. If, after completion of the pressing operation, the pressing dies are withdrawn again, the elastic, widened die presses the powder radially together. However, since the powder has already become a molded part (compact) whose properties are comparable to those of a solid, the shaped part of the spring back resists the matrix.

At first, the resulting molded part gives way plastically. If the radial pressure of the die has reached the yield point corresponding to the current stress state, the plastic deflection ends; it remains an elastic tension between the compact and die.

The elastic tension causes high friction forces during removal of the molding from the die. These frictional forces lead to wear of the die and damage to the molding.

The difference between the diameter of the demolded molding and the die is referred to as "radial springback".

The size of the Springback depends on the flow limit of the molded part. When using the same powder mixture, the yield point increases with the level of pressing force. This results in a dependence of the geometry of the formed molded part of the maximum applied punching force. The Springback is bigger, the more elastic the die is. Because tungsten carbide has a significantly higher modulus of elasticity than steel, die liners made of tungsten carbide are therefore used to reduce the springback.

Particularly problematic are elongated moldings. In connection with the mostly circular die bending forces act. As a result, the elastic springing in the middle of the molding is greater than at the two ends.

Due to the axial pressing, a multiaxial stress state is formed. There is a significant difference between the magnitude of the radial stresses and the magnitude of the axial stresses. The exact description of this state of stress requires inter alia the consideration of the internal friction of the powder and the friction on the die walls. Therefore, an exact statement about the actual conditions in the pressurized tool is very difficult. For a simplified assessment, however, empirically determined diagrams are available.

To facilitate demolding of the molding from the die, a lubricant is often added to the powder. Depending on the amount added, this lubricant influences the density of the molded part more or less adversely. As a result, in turn, the strength of the finished molded part is reduced. The more lubricant added, the lower the density and strength of the molding.

It is therefore fundamental to strive to keep the lubricant content as low as possible, but nevertheless to ensure a good demoulding.

From the WO 02/32655 A1 is a powder press tool is known, which is provided that it is formed in a Auspressabschnitt so that the Auspresskanal supporting die walls are becoming increasingly thin. By thinning walls in this area, a gradually increasing compliance of the tool is achieved, whereby the demolding is to be facilitated.

After DE 198 30 601 A1 a pressing device for powdery and granular material is provided, in which two matrices whose end faces include the contour of the molded part, by means of guides einschießen an angle, the surfaces of the end faces of the matrices when reaching the final contour of the molding directly close to each other. In such segment matrices, in which the contour of the molded part is formed by a number of pressing segments, there is the great disadvantage that powder can penetrate between the individual segments, which leads to a frequent disturbance of the production process.

For the production of moldings with an undercut - seen in Entformrichtung of the molding - is from the DE 195 08 952 C2 a press device with a die and a plurality of dies is known, wherein a segment slider is used, which can be moved by means of appropriate feed and retraction devices also during the pressing operation for the molding after closing the mold.

To generate the pressing pressure on the ram itself, it is from the EP 1 097 801 A1 It is known to provide a device in which, in order to achieve a compact design, a hydraulic element cooperates with a piezoactuator.

An alternative to the axial compaction of powdered materials as described above is hydrostatic compaction. In this process, the compact is exposed to stresses that are approximately the same size in all axes. As a result, the unfavorable shear stresses are largely avoided. Due to the hydrostatic compression method, compacts with higher density and better material properties can be produced. The process usually takes place in a high pressure liquid container. The powder is surrounded by a flexible shell, so that an approximately equal compression takes place in all axes.

However, since the hydrostatic compression method can not deliver accurately molded compacts on all sides, it can not be used for many applications.

The invention is therefore in the light of the problems described above during pressing and demoulding of the molded part from the die, a device of the type mentioned in such a way that it is possible to facilitate the pressing and demolding and thus a total of the powder molding process to improve. Furthermore, possibilities are to be created to make the method of powder pressing so that an improvement of the process and the product are possible.

This object is achieved by the invention according to the method in that during the production cycle of a molding at least once a preferably radial compression or expansion with subsequent decompression or relaxation of a located in a die, preferably at least partially cylindrical die sleeve is made, wherein prior to insertion or during the insertion of at least one press ram into the die sleeve of the die, the preferably radial compression or widening of the die sleeve takes place in such a manner that a forming surface of the die sleeve assumes a desired caliber dimension.

This approach allows a particularly advantageous way to compensate for wear.

Before the demolding of the molded part from the Matrizenhülse the decompression or relaxation can take place. Furthermore, during the production cycle of a molded part, a repeated, pulsating, preferably radial compression or expansion with subsequent decompression or expansion of the die sleeve can be carried out.

A variant of the method is based on the fact that several means arranged along the direction of movement of the press die or in more than one plane perpendicular to this direction for applying a force to at least a part of the outer or inner wall of the die sleeve are actuated or actuated, that along the direction of movement of the press die or a time-variant course of the compression or expansion of the Matrizenhülse with subsequent decompression or relaxation takes place. It can in particular be provided that the time-variant course of the compression or expansion of the die sleeve followed by decompression or relaxation along the direction of movement of the press die or waves.

The die sleeve can also be subjected to varying degrees of local force by actuators. By specifically acting differently on the die sleeve or socket punch forces of the actuators can be a bending deformation with a larger deformation path and rotating waves produce. For the compact results in a uniform deformation result.

The big advantage of this approach is that then the demolding of the molding is possible in a particularly simple manner.

The device for producing a molded part from powder, in particular metal powder, from a doughy material containing a powder, from a flowable material containing a powder or from pre-pressed material, comprises: a die consisting of a base body and a die sleeve inserted therein wherein the die sleeve has a preferably at least partially cylindrical contour, which forms a molding surface for the molding, and at least one ram, which enter the opening defined by the preferably cylindrical contour of the die sleeve and located in the defined by the preferably cylindrical contour space powder or compressing material, wherein in a preferably radially outwardly or inwardly extending to the outer or inner wall of the Matrizenhülse space are arranged means with which a preferably radially inwardly or outwardly directed force at least a part de r outer or inner wall of the die sleeve can be applied. According to the invention it is provided that the means of at least one actuating element which between a wall of the space in the base body of the die and the outer or inner wall of the die sleeve a preferably radially directed force, and preferably consist of at least one pressure transmitting member which transmits the force generated by the actuating element to the outer or inner wall of the Matrizenhülse, wherein a number of actuators and associated pressure transmitting members disposed over the circumference of the wall of the space in the main body of the die are and wherein the pressure transmitting members are formed as a plunger which taper or widen at its the outer or inner wall of the die sleeve facing the end.

The actuating element is preferably a hydraulic piston-cylinder system.

The pressure transmitting members may be tapered such that their ends facing the outer wall of the die sleeve substantially or completely surround the circumference of the outer wall of the die sleeve adjacent to one another. Alternatively, it may be provided that the pressure transmission members widen so that their inner wall of the Matrizenhülse facing ends adjacent to each other largely or completely surround the circumference of the inner wall of the Matrizenhülse. This is the preferred procedure in the production of a substantially annular shaped body.

It can also be provided a single actuator having a preferably concentric with the Matrizenhülse formed, sealed to the environment space, and an element with which a hydraulic fluid under a predetermined pressure and / or with a predetermined volume flow into the room can be entered, wherein the preferably radially inwardly or outwardly facing end surface of the space adjacent to a number of pressure transmitting members. In order to simplify the sealing of the hydraulic fluid applied space to the pressure transmitting members can be provided that between the radially inwardly or outwardly end face of the space and the pressure transmitting members an elastic band is arranged. The band is preferably formed as a steel sleeve with a small thickness.

The die sleeve can be made in several parts and consist of several composite segments. Another embodiment of the invention provides that along the direction of movement of the press die or in more than one plane perpendicular to this direction separately controllable or actuatable means are arranged, with which the force at least on a part of the outer or inner wall of the Matrizenhülse can be applied.

With these means, it becomes possible to influence the die sleeve in terms of their effective inner diameter in the preferably cylindrical part, which can be used very advantageously both for the manufacturing process and for demolding, as will be explained in detail later.

The process according to the invention can be further optimized by supporting the process by heat, by vacuum and by special lubricants, binders and pouring agents. The method can also be used especially for multilayer and multilayer molded parts.

The proposed device and the associated method provide various advantages:

With the radial pressing and relieving the die sleeve, which can be generated metered with the proposed device, it is advantageously possible to effect favorable effects during molding, ie during the pressing process, and during demoulding, so when exposing the shaped body.

Because of the achievable improved demolding conditions, ie by the possibility of demolding with reduced extrusion force of the molding from the die, It is now possible to make do with smaller amounts or even without any lubricant, which is optionally added to the powder for ease of removal from the die. This improves the material properties of the molded parts, in particular the density and the strength. Furthermore, this reduces the risk that free cracks occur on the molded part.

Due to the reduced ejection force during demoulding of the molded part from the die, the wear on the radial inner wall of the die sleeve can furthermore be considerably reduced.

Furthermore, more cost-effective material can be used for the die, since the frictional forces are lower during demolding.

Due to the compression of the powder material not only in the direction of the axial movement of the ram, but according to the invention in the radial direction, there is a molded part with improved material quality.

It also becomes possible to influence the caliber of the die sleeve, whereby wear can be compensated. Consequently, a matrix which has become too large due to wear or a cavity in the center of the die can be adjusted.

The caliber of the matrix is set with reference to the theoretical Sinterschwundes sintering based on the finished size. In the case of deviations from the desired final dimension, post-processing after sintering may be necessary. This can be compensated with the device according to the invention by appropriate application of a radial force.

So it is possible to improve the quality of the molding, while reducing the Matrizenverschleißes. New molding geometries are made possible, whereby higher pressing forces can be realized. This is especially true in elongated moldings where the known methods and devices reach their limits. In particular, a controlled influencing of the geometry and dimensional deviations can take place, in particular during wear. Also, the risk of internal cracks and peeling on the molding can be reduced.

It is also possible to make a flexible adjustment of the radial geometry of the molding to compensate for tool wear, to compensate for thermal expansion and to compensate for dimensional changes due to the change in the pressing pressure.

Fig. 1

eine Prinzipdarstellung des Pressens von Metallpulver;

Fig. 2

eine Seitenansicht einer schematisch dargestellten Vorrichtung zum Pulverpressen;

Fig. 3

die Draufsicht auf eine Matrize dieser Vorrichtung;

Fig. 4a

im Schnitt die Seitenansicht und

Fig. 4b

im Schnitt die Draufsicht auf eine erste Ausführungsform der Matrize;

Fig. 5a

im Schnitt die Seitenansicht und

Fig. 5b

im Schnitt die Draufsicht auf eine andere Ausführungsform der Matrize;

Fig. 6a

im Schnitt die Seitenansicht und

Fig. 6b

im Schnitt die Draufsicht auf eine weitere Ausführungsform der Matrize;

Fig. 7a

im Schnitt die Seitenansicht und

Fig. 7b

im Schnitt die Draufsicht auf eine vierte Ausführungsform der Matrize;

Fig. 8a

im Schnitt die Seitenansicht und

Fig. 8b

im Schnitt die Draufsicht auf eine fünfte Ausführungsform der Matrize;

Fig. 9a

im Schnitt die Seitenansicht und

Fig. 9b

im Schnitt die Draufsicht auf eine sechste Ausführungsform der Matrize;

Fig. 10a

im Schnitt die Seitenansicht und

Fig. 10b

im Schnitt die Draufsicht auf eine siebte Ausführungsform der Matrize;

Fig. 11a

im Schnitt die Seitenansicht und

Fig. 11b

im Schnitt die Draufsicht auf eine achte Ausführungsform der Matrize;

Fig. 12a

im Schnitt die Seitenansicht und

Fig. 12b

im Schnitt die Draufsicht auf eine neunte Ausführungsform der Matrize;

Fig. 13

eine Draufsicht auf eine Matrize mit lokal unterschiedlich starker Beaufschlagung der Matrizenhülse mit Stempelkräften; und

Fig. 14

einen sich mit der Beaufschlagung nach Fig. 13 ergebenden Durckverlauf.

Further features and details of the invention will become apparent from the claims and the description of illustrated in the drawings embodiments of the invention. Show it:

Fig. 1

a schematic representation of the pressing of metal powder;

Fig. 2

a side view of a schematically illustrated device for powder pressing;

Fig. 3

the top view of a die of this device;

Fig. 4a

in section the side view and

Fig. 4b

in section the plan view of a first embodiment of the die;

Fig. 5a

in section the side view and

Fig. 5b

in section the plan view of another embodiment of the die;

Fig. 6a

in section the side view and

Fig. 6b

in section, the top view of a further embodiment of the die;

Fig. 7a

in section the side view and

Fig. 7b

in section the plan view of a fourth embodiment of the die;

Fig. 8a

in section the side view and

Fig. 8b

in section the plan view of a fifth embodiment of the die;

Fig. 9a

in section the side view and

Fig. 9b

in section the plan view of a sixth embodiment of the die;

Fig. 10a

in section the side view and

Fig. 10b

in section the plan view of a seventh embodiment of the die;

Fig. 11a

in section the side view and

Fig. 11b

in section, the top view of an eighth embodiment of the die;

Fig. 12a

in section the side view and

Fig. 12b

in section the plan view of a ninth embodiment of the die;

Fig. 13

a plan view of a die with locally different strong loading of the die sleeve with punching forces; and

Fig. 14

one with the admission after Fig. 13 resulting Durckverlauf.

In Fig. 1 schematically a device is shown, with which a metal powder 15 can be pressed into a molded part. The device has a die 1, which consists of a hollow cylindrical base body 2, into which a die sleeve 3 is coaxially inserted. So that the die sleeve 3 is highly resistant to wear, it preferably consists of hard metal. The die sleeve defines a cylindrical molding surface 4. The metal powder 15 is introduced into the space formed by this molding surface. Both from above and from below then a respective ram 5 are inserted into the respective openings of the die sleeve 3 and axially moved towards each other. In this case, a pressing force F _{P is} exerted on the punches 5, so that the powder 15 is compressed.

It should be noted that the invention is not only suitable for the processing of powder. Often an already preformed compact is re-pressed in a further step, especially in the final pressing with higher Press, which is a particularly important application of the device according to the invention and the corresponding method.

The overall device for powder pressing is in Fig. 2 shown. In a base frame 16 stamping cylinders 17 are installed, which act on the press ram 5 with the pressing force F _P to press the shaped body 18.

To control and monitor the manufacturing process pressure sensors 19 and 20 and displacement sensors 21 and 22 are present. Further, a radial displacement sensor 23 is provided, with which the radial position of the wall of the die sleeve 3 can be determined. The controller 24 initiates the process of the manufacturing process.

Based on Fig. 3 , from which the plan view of the die 1 of the device can be seen, the principle of the pressing concept is clear: Between the radially outwardly directed outer wall 6 of the female die 3 and a radially inwardly directed wall 11 of a substantially cylindrical recess in the base body 2 of Die 1 (defined here by recesses for piston-cylinder units), a space 7 is formed in the means 8 are arranged, with which a radially directed force F _R can be generated. These means 8 press on the outer wall 6 of the die sleeve 3 and can thus radially compress them or - when the force F _R is removed again - expand radially. This is used to achieve the advantages outlined above.

A first embodiment of this concept is based on FIGS. 4a and 4b out. Here, the means 8 for generating the radially directed force F _{R of} the space 7 itself, which is designed as a sealed or sealed space for receiving hydraulic fluid. Via an element 9 for introducing hydraulic fluid (line with pump, not shown), the hydraulic fluid in the space 7 and 8 is passed (in the present case, there are two subspaces, in the axial direction of the die 1 are arranged offset), where it causes an expansion of the space and thus a radial compression of the die sleeve 3. In the present case, the reference numeral 9 also designates the hydraulic fluid or the line and the elements for influencing the hydraulic fluid with respect to pressure and / or volumetric flow.

About the height of the hydraulic pressure p, the radial compression of the die sleeve 3 can be adjusted in a targeted and metered.

This embodiment is very simple in construction but requires high pressures p to operate efficiently. The die sleeve 3 should be designed as thin as possible here. It is also important that the extent of the space 7 in the axial direction is sufficiently large.

Another type is in the FIGS. 5a and 5b to see. Here, an actuating element 10 in the form of a piston-cylinder system is provided for acting on the die sleeve 3 with the radial force F _R. The piston is acted upon by an element 9 for inputting hydraulic fluid (see above) with fluid predetermined pressure p, which urges him from the wall 11 radially inwardly. The force generated by the hydraulic fluid is transmitted to a pressure transmitting member 12 which transmits the force to the outer wall 6 of the die sleeve 3 and thus radially compresses them.

There are a number of actuators 10 each arranged with their pressure transmitting members 12 distributed over the circumference in the space 7. The pressure transmitting members 12 - formed as a pressure stamp - taper in this case in the direction of the die sleeve 3, that their ends together completely surround the circumference of the die sleeve 3. This is achieved in an advantageous manner that it comes to a uniform radial compression of the sleeve 3.

In the Figures 6a and 6b an embodiment is shown which is similar to that in the FIGS. 5a and 5b is. In contrast, it is merely provided that the actuating elements 10 - also formed here as piston-cylinder systems - are set back in the region of the base body 2 of the die 1 behind the space 7. This has the advantage that the cross-sectional area of the piston or cylinder are larger, which enables the generation of higher forces. So that the pressure transmission members are also suitable for the transmission of the highest forces, they can be made of hard metal.

A further increase in the pressure force by the actuators 10 is possible with a variant as in the FIGS. 7a and 7b is shown. Here are piston-cylinder systems are used, which work with two pressure chambers and thus can generate a significantly higher power. It is a solution in which a series of multiple piston surfaces is connected in order to increase the forces; the effective piston area is thus increased.

One of the filigree construction in the FIGS. 5 to 7 arrangements shown deviating execution is in the FIGS. 8a and 8b shown. It is only a single sealed annular space 13 is formed, which is supplied via an element 9 with hydraulic fluid. Adjacent to the end surface 14 of this space 13 are a number of pressure transmitting members 12, which are pressed radially inwardly upon application of hydraulic fluid to the space 13 and expansion of the space 13 thereafter to radially compress the die sleeve 3. Advantageously, the end surface 14 is quite large, so that it may be the adjacent surfaces of the pressure transmitting members 12. Thus, the radial force is large, which is passed from the pressure transmitting members 12.

The gaps in the circumferential direction between the individual pressure transmission members 12 in the region of the abutment against the end face 14 must be sealed. This can be avoided if the annular space 13 is closed inwardly by a band, at the radially inner surface then only the pressure transmission members 12 abut. The individual segments of the pressure transmitting members 12 are thus strapped over the elastic band.

By using several cylinders, it is possible to make the die 1 the same stiff at all points. As a result, unsymmetrical or elongate shaped parts can be manufactured with high quality, while in the conventional method locally different springback occurs with the influence on the dimensional accuracy and damage of the workpiece.

In the FIGS. 9a and 9b It is shown that by accepting bending and maintaining the peel-off surface at the top, by expanding the hydraulic space downward, a larger pressurizing area can be achieved.

The Figures 10a and 10b show an embodiment with various piston-cylinder elements in the application for the production of an elongated molding.

In the Figures 11a and 11b an alternative embodiment of the invention is to be seen in which not - as in the above solutions - a radially inwardly directed pressure is exerted on a cylindrical shaped body, but in which it is about the production of a ring-shaped compact. Shown is a die 1, which identifies an outer hollow-cylindrical basic body part 2 and an inner cylindrical basic body part 2, which adjoins the die sleeve 3 on the radially outer surface.

Inside the cylindrically shaped main body part 2, a sealed space 13 adjoining an inner wall 11 is formed which, in the manner already explained, can be acted upon by hydraulic fluid via elements 9 and expanded therewith. The expansion of the space 13 leads via a ring-shaped metal band to a radially outwardly directed movement of the pressure transmission members 12, which in turn press radially outwards onto the die sleeve 3. The powder or a precompressed body located in the space between the die sleeve 3 and the outer, hollow-cylindrical base body part 2 is thereby pressed into an annular component.

In the Figures 12a and 12b is a further embodiment of the invention can be seen. In contrast to the solutions described above, it is provided here that a number of pressure-transmitting members 12 with their respective actuating elements 10 are arranged one above the other in the direction of movement of the press die 5 (ie in the axial direction of the die 1). The individual actuating elements 10 can be actuated separately or in groups. This is in Fig. 12b to see that at various points hydraulic fluid can be entered, which is indicated by the reference numerals p1, p2 and p3. It can thus be achieved that the centrally arranged die sleeve 3 can be acted upon along its longitudinal axis with different compression forces.

In Fig. 12a is shown enlarged how - caused by appropriate control of the various actuators 10 - the die sleeve 3 is deformed and with it also the powder located in its interior.

The actuating elements 10 can in particular be controlled such that one or more compression waves along the circumference of the die bushing 3, along the die sleeve 3 in the direction of the axis of the ram 5 or be introduced in a superposition of both movements on the die sleeve 3 in the powder.

The proposed procedure is suitable for producing longer compacts in the axial direction of the die 1 than has hitherto been the case. The wall friction reduces the pressure on the powder with increasing length. Due to the possibility of drastically reducing the wall friction due to the radial movement of the die sleeve 3 in spite of a high axial pressure, it is now possible to drive the axial pressure much further into the compact.

To further increase this effect, the in Fig. 12a and 12b sketched arrangement of several axially staggered arranged and independently controllable systems for generating and transmitting the pressure exist.

A special mode of operation of this arrangement is in a hydraulic control, which is characterized by specific order of pressurization or pulsating pressurization with phase offset for the individual zones (analogous to the wiring of a three-phase motor or a three-phase linear motor).

As a result, a wave motion can be generated on the side of the die sleeve 3 facing the powder. The effect achievable thereby is even stronger when such waves run axially on both sides of the center of the compact.

Such regional circuits can also be applied radially or in other preferred directions. As a result, local filling and compression problems can be solved, especially in complicated shaped parts.

The Fig. 13 shows a variant in which the die sleeve 3 is applied locally differently with the punching forces P 1 to P 6, which can achieve a uniform deformation result for the compact, with a pressure curve, as in the diagram Fig. 14 outlined.

As already stated, the hydrostatic compaction is a particularly favorable type of compaction, since an all-round compression of the powder takes place. However, the required for such a compression radial movement of the die sleeve 3 using the means 8, as a rule, exceed the possibilities of the described elements. Therefore, the radial movement of the means 8 and the corresponding radial compression of the die sleeve 3 must be used so that the greatest possible benefit can be drawn.

A permanent active control allows the greatest possible influence on the process of manufacturing the molded part. But even waiving elaborate controls can be significant improvements of the process - compared with previously known methods - realize. The exact parameters of the process must be defined in the individual process. The freedom of choice of parameters is limited by the available radial forces as well as the amount of allowable elastic strain of the die sleeve. Furthermore, it must be noted that the ram should not be clamped during the movement. In the resting state, however, they may be pressed radially. They dodge elastically inwards. The tool gap must not be too large, because then powder can get between the ram.

If only a facilitated Ausformen be achieved, a template is used with a certain excess. Before pressing, the die is narrowed by the means 8 by application of the radial forces. In hydraulic systems, it is sufficient, depending on the embodiment already, to pressurize the actuators prior to pressing with pressure, to lock the oil supply and before the Remove after pressing then open the lock again to reduce the oil pressure and let the die sleeve expand again. As a result, the Ausformkräfte can be significantly reduced.

Optimal is the procedure when the oil pad is only as flat as the re-deformation of the molding requires it. During pressing, the oil can then escape from the pad into a reservoir and store the return spring force there. The wall of the Matrizenhülse can then abut firmly against a certain pressure on a much stiffer contour. Only at the re-deformation it comes again to a cross-compression of the molding. After actuation of the shut-off valve, the workpiece is then easy to demould.

It may be that the molded part is transversely deformed in a phase in which the axial force is low. This can lead to cracks and damage. This damage to the molded part due to the transverse deformation can be significantly reduced if the active transverse deformation takes place under high pressure. The "active die" now offers the possibility of carrying out the required radial movement in a controlled manner with a mainly rigid mold.

In the case of a standard die, when switching from presses to offloading, the lateral elastic springback of the die has a destructive effect on the molded part. An improvement can already be achieved by applying force to the die walls in such a way that the contact surface with the powder remains unchanged in its position unchanged.

An expedient for the molding expiration consists in an axial compression up to the maximum axial pressing force. Thereafter, the standard die leads due to their elasticity during load change of the ram from pressing to unloading springback from. In this case takes place at low axial stress radial deformation. There may be internal sliding in the molded part, which is the Can damage the molded part. In the controlled die, however, the control force can be applied so that the inner contour of the female sleeve is seemingly rigid. The risk of damage to the molding is thereby significantly reduced.

If the die was already narrowed in this process before the beginning of the pressing, it is possible to completely reduce the stresses still remaining in the molded part after the discharge and to remove the molded part almost without friction.

An alternative procedure is to start the pressing process in the untensioned state of the die sleeve and during the pressing process to apply only the at least necessary pressure to the die sleeve in order to narrow the die sleeve at maximum axial pressing pressure. During compaction, however, a radial pressure must also be applied in order to avoid that the relatively thin wall of the die sleeve is pushed through. At the highest pressure then takes place a radial compression. This compression should be calculated to achieve the hydrostatic state. Then, the axial and the radial pressing force is synchronized shut down until the lack of tension is brought about.

In an ideal process, there is only so much bias of the die sleeve that a secure detachment of the molding from the wall of the die sleeve is achieved.

Whether in this process the hydrostatic pressure can be achieved during the pressure reduction entirely or only in approximation, depends on the size of the radial deformability of the die. In any case, however, there is an improvement over the conventional manufacturing process.

Another possibility is to keep the tool gap constant during the pressure build-up. For this, the Matrizenhülse is narrowed before the pressure build-up. During compaction, the ram increases in size due to its transverse strain and due to heating. According to this magnification, the radial compression of the die sleeve can then be reduced. If tools are used both for normal pressing and for hot pressing, the otherwise occurring clamping is avoided.

Overall, therefore, a low-friction demolding is achieved as well as an improvement of the pressing process by controlling the multiaxial stress state. On the geometry of the molded part can be actively influenced, and also a correction of the tool wear is possible. Furthermore, it is possible to influence the instantaneous tool gap or the contact force between die sleeve and ram. By repeatedly reducing the radial pressure during the pressing and demolding process, a reduction in the effects of friction can occur. Finally, the molded part has a better homogeneity when multiple radial opening and closing takes place during the pressing of the molded part.

While the use of the device according to the invention and the associated method is frequently indicated in the case of shaped bodies which at least partially have a cylindrical part, the invention is equally applicable if this is not the case, ie if the shaped body is not cylindrical, either in sections, and the die sleeve consequently likewise does not have a cylindrically shaped section.

LIST OF REFERENCE NUMBERS

1

die

2

body

3

die sleeve

4

form surface

5

press die

6

outer wall

7

room

8th

Means for generating a radially directed force

9

Element for inputting hydraulic fluid

10

actuator

11

wall

12

Pressure transmitting member

13

sealed room

14

end face

15

powder

16

base frame

17

press cylinder

18

moldings

19

pressure sensor

20

pressure sensor

21

displacement sensor

22

displacement sensor

23

Radial displacement sensor

24

control

F _P

pressing force

F _R

radially directed force

p

hydraulic pressure

Claims (14)

1. A method for producing a moulded part from powder, particularly metal powder, from a pasty material containing a powder, a flowable material containing a powder, or a pre-compacted material, wherein a device is used that comprises:

   - a die (1) consisting of a base body (2) and a die bushing (3) inserted therein, wherein the die bushing (3) has a preferably at least partially cylindrical contour, which forms a mould surface (4) for the moulded part, and

   - at least one press punch (5) that is able to enter the opening defined by the preferably cylindrical contour of the die bushing (3) and compact the powder or material located in the space defined by the preferably cylindrical contour,

   characterised in that
   a preferably radial compression or expansion with subsequent decompression or relaxation of a preferably at least partially cylindrically shaped die bushing (3) located inside a die (1) is carried out at least once during the production cycle of a moulded part, wherein the radial compression or expansion of the die bushing (3) takes place before the insertion or during the insertion of at least one press punch (5) into the die bushing (3) of the die (1), in such manner that a mould surface (4) of the die bushing (3) takes on a desired bore dimension.
2. Method according to claim 1,
   characterised in that
   the decompression or relaxation takes place before the moulded part is demoulded from the die bushing (3.)
3. Method according to claim 1,
   characterised in that
   a pulsed, preferably radial compression or expansion is carried out, followed by a decompression or relaxation of the die bushing (3), multiple times during the production cycle of a moulded part.
4. Method according to claim 1,
   characterised in that
   a plurality of means (8) arranged along the direction of motion of the one or more press punch(es) (5) and perpendicular to said direction in more than one plane for applying a force (F_R) to at least a part of the outer or inner wall (6) of the die bushing (3), is actuated or operated in such manner that a time-variable progression of compression or expansion of the die bushing (3) followed by decompression or relaxation takes place along the direction of motion of the press punch (5).
5. Method according to claim 4,
   characterised in that
   the time-variable progression of compression or expansion of the die bushing (3) with subsequent decompression or relaxation takes place along the direction of motion of the press punch (5) in the manner of a wave.
6. Method according to claim 1,
   characterised in that
   the die bushing (3) is subjected to locally varying levels of load by actuating elements (8, 10).
7. Device for producing a moulded part from powder, particularly metal powder, from a pasty material containing a powder, a flowable material containing a powder, or a pre-compacted material, comprising:

   - a die (1) consisting of a base body (2) and a die bushing (3) inserted therein, wherein the die bushing (3) has a preferably at least partially cylindrical contour, which forms a mould surface (4) for the moulded part, and

   - at least one press punch (5) that is able to enter the opening defined by the preferably cylindrical contour of the die bushing (3) and compact the powder or material located in the space defined by the preferably cylindrical contour,

   wherein means (8) are arranged in a space (7) that extends preferably radially outwardly or inwardly to the outer or inner wall (6) of the die bushing (3), with which means a preferably radially inwardly or outwardly directed force (F_R) can be applied to at least a part of the outer or inner wall (6) of the die bushing (3),
   characterised in that
   the means (8) consist of at least one actuating element (10) that is able to generate a preferably radially directed force (F_R) between a wall (11) of the space (7) in the base body (2) of the die (1) and the outer or inner wall (6) of the die bushing (3), that the force (F_R), as well as preferably consisting of at least one transmission member (12), generated by the actuating element (10) is transmitted to the outer or inner wall (6) of the die bushing (3),
   wherein a plurality of actuating elements (10) and associated pressure transmission members (12) are arranged along the periphery of the wall (11) of the space (7) in the base body (2) of the die (1), and
   wherein the pressure transmission members (12) are in the form of compression dies, of which the ends closest to the outer or inner wall (6) of the die bushing (3) are tapered or flared.
8. Device according to claim 7,
   characterised in that
   the actuating element (10) is a hydraulic piston-cylinder system.
9. Device according to claim 7,
   characterised in that
   the pressure transmission members (12) are tapered in such manner that the ends thereof closest to the outer wall (6) of the die bushing (3) abut and largely or completely encompass the periphery of the outer wall (6) of the die bushing (3).
10. Device according to claim 7,
    characterised in that
    the pressure transmission members (12) are flared in such manner that the ends thereof closest to the inner wall (6) of the die bushing (3) abut and largely or completely encompass the periphery of the inner wall (6) of the die bushing (3).
11. Device according to any of claims 7 to 10,
    characterised in that
    a single actuating element (10) is provided, which comprises a space (13) that is formed preferably concentrically with the die bushing (3) and sealed off from the outside, and an element (9) with which a hydraulic fluid may be introduced into space (13) under a predefined pressure (p) and/or with a predefined volume flow, wherein a plurality of pressure transmission members (12) abut the preferably radially inwardly or outwardly directed end surface (14) of the space (13).
12. Device according to claim 11,
    characterised in that
    an elastic band is arranged between the preferably radially inwardly or outwardly directed end surface (14) of the space (13) and the pressure transmission members (12).
13. Device according to any of claims 7 to 12,
    characterised in that
    the die bushing (3) is constructed in multiple parts and consists of a plurality of assembled segments.
14. Device according to any of claims 7 to 13,
    characterised in that
    separately actuatable or operable means (8) are arranged along the direction of motion of the one or more press punch(es) (5) and perpendicular to said direction in more than one plane, with which means the force (F_R) can be applied to at least a part of the outer or inner wall (6) of the die bushing (3).

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