DE102017130680A1 - Die for a press and method for producing at least one green compact with such a press - Google Patents

Abstract

The invention relates to a die (1) for arrangement in a press (2), wherein the die (1) extends along an axial direction (3) between a first end face (4) and a second end face (5) and between the end faces (4, 5) an inner circumferential surface (6) for receiving a, by at least one along the axial direction (3) movable punch (7) compressible material forms, wherein the die (1) starting from the inner peripheral surface (6) along a radial Direction (8) towards an outer peripheral surface (9) and towards at least one, in the radial direction (8) on an outer diameter (10) arranged centering surface (11) extends; wherein the die (1) spaced from the end faces (4, 5) comprises a pressing zone (12) and the inner peripheral surface (6) in the pressing zone (12) has at least one first diameter (13) extending along the radial direction (8) ; wherein the die (1) has a pretensioning device (14) with at least one pressure chamber (20) arranged at least partially at a height (22) with respect to the axial direction (3) with the pressing zone (12) and can be acted upon by a pressurized fluid (19) ), by which at least the first diameter (13) during a pressing operation, in which the inner peripheral surface (6) with a in a direction of a normal vector (15) acting on the inner peripheral surface (6) proportion of a maximum pressing force (16) is applied, is expandable to a first value (17) and during a demolding operation subsequent to the pressing process with at least reduced pressing force (16) to a second value (18) which is larger than the first value (17).

Description

The invention relates to a die for a press, in particular for a powder press for the production of green compacts. With the press in particular sinterable green compacts are produced, ie green compacts, which can be sintered after the pressing process. In particular, metallic and / or ceramic powders can be pressed into green bodies in the matrix.

Known matrices of this type include a so-called shrink ring, wherein within the shrink ring if necessary, a core (in particular made of hard metal) is arranged, which forms the inner peripheral surface of the die. The inner peripheral surface of the die forms on the one hand the receptacle for the powder or the green product to be produced. Via an upwardly open first end face of the die, at least one upper punch of the press can travel into the die along an axial direction. The at least one upper punch slides along the inner peripheral surface of the die and increasingly compresses the powder. In particular, at least one lower punch can additionally be provided, which moves into the die via a downwardly open second end face of the die along the axial direction, or moves in the die between an upper position and a lower position. Between the at least one upper punch and the at least one lower punch, the powder is pressed into a green compact, wherein the inner peripheral surface of the die defines a lateral contour of the green compact.

The die has a collar on an outer peripheral surface, via which the die can be received and clamped in the press. The collar extends in a radial direction over the outer peripheral surface, so that the die can be placed or supported on a support of the press. Incidentally, such matrices are designed substantially cylindrical, wherein the cylindrically shaped outer peripheral surface is usually received via a radial play in the press, so that a centering of punch (s) and die to each other, so a coaxial arrangement of punch (s) and die, can be enabled.

A die may each have stamp guide zones on the end faces, wherein a press zone is present at a distance from the end faces and adjacent to the die guide zones. The press zone is the zone in which the powder with the highest press force is compressed. The press zone in the die is clearly defined and limited along the axial direction. Furthermore, a demoulding zone can be provided at least on one end face, ie. H. a zone of the die, through which the green body from the die pushed out (demolded) and is provided for removal from the press. When pressing the powder is pressed by the high pressure, the inner peripheral surface of the die also heavily. At this time, the inner peripheral surface of the die in the radial direction (or in the direction of a normal vector present on the inner circumferential surface, which is perpendicular to the respective surface of the inner peripheral surface), is deformed by a pressure acting in the radial direction which is in a certain proportion to that in the axial direction acting pressing pressure, elastically expanded. This expansion in the press zone leads to strong frictional forces during demolding, which in turn can lead to an increase in the temperature in the die. These frictional forces can be present in the demolding zone, because the die is usually cylindrical and therefore has a substantially constant stiffness or a substantially constant resistance to an elastic expansion in the radial direction.

This expansion only in the press zone of the die also leads to the fact that the green compact can not be produced accurately. In particular, a conicity of the green body may occur during demoulding of the green compact. In this case, the die in the press zone and with progressive demolding also in the adjoining area back to the front side over which the demolding takes place, so that the green body at the lower end, which is finally demoulded from the die, more and more constricted and so that it becomes conical overall.

To reduce these frictional forces Entungsungsschrägen could be provided on the inner peripheral surface of the die, so that with the movement of the green body along the axial direction from the press zone and through the Entformungszone through to the front side, a relaxation of the green body occurs. However, there is a risk of cold welding due to the possible drawing in of powder between die and punch by the increasingly narrowing gap.

On this basis, it is an object of the present invention, at least partially solve the problems described with reference to the prior art. In particular, unwanted, but previously process-related conicities are to be avoided on the green. It should also be able to produce non-rotationally symmetric components with high accuracy. Furthermore, it should preferably be possible to reduce the frictional forces that occur during demoulding of the green compact, wherein demolding slopes may not be required. A reduction of the frictional forces can in particular significantly reduce otherwise occurring tool wear.

To solve this problem, a die according to the features of claim 1 is proposed. Advantageous developments are the subject of the dependent claims. The features listed individually in the claims can be combined in a technologically meaningful manner and can be supplemented by explanatory facts from the description and details of the figures, with further embodiments of the invention are shown.

For this purpose, a die contributes to the arrangement in a press, wherein the die extends along an axial direction between a first end face and a second end face and forms an inner circumferential face between the end faces. The inner peripheral surface is provided for receiving a, by at least one movable along the axial direction stampable material. The die extends from the inner peripheral surface along a radial direction toward an outer peripheral surface and toward at least one centering surface disposed in the radial direction at an outer diameter. The die has spaced apart from the end faces on a pressing zone. The inner circumferential surface has at least one first diameter extending in the radial direction in the pressing zone. The die comprises a pretensioning device having at least one wall which is arranged with respect to the axial direction at least at a height with the pressing zone and which can be acted upon (at least in the axial direction by a pressure) and deformable thereby (at least in the axial direction). At least the first diameter is adjustable to a first (predeterminable) value during a pressing operation in which the inner circumferential surface is acted on by a portion of the maximum pressing force acting in a direction of a normal vector on the inner peripheral surface and during one of the Pressing following Entformungsvorgangs at least reduced pressing force to a second value relative to the first value increased second adjustable.

The die is intended in particular for a powder press for the production of green compacts. With the press in particular sinterable green compacts are produced, ie green compacts, which can be sintered after the pressing process. In particular, metallic powders and / or ceramic powders can be pressed into green bodies in the matrix.

In particular, the die comprises a so-called shrink ring, wherein within the shrink ring, if necessary, a core (in particular made of hard metal) is arranged, which forms the inner peripheral surface of the die. The inner peripheral surface of the die forms on the one hand the receptacle for the powder or the green product to be produced. Via an upwardly open first end face of the die, at least one upper punch of the press can travel into the die along an axial direction. The at least one upper punch slides along the inner peripheral surface of the die and increasingly compresses the powder. In particular, at least one lower punch can additionally be provided, which moves into the die via a downwardly open second end face of the die along the axial direction. Between the at least one upper punch and the at least one lower punch so the powder is pressed into a green compact, wherein the inner peripheral surface of the die defines in particular a lateral contour of the green body. About the stamp, the pressing force is introduced into the powder. The pressing force is held or adjusted via the punches and the die. In this case, a proportion of the pressing force in the direction of the normal vector acts on the die.

The die has in particular (possibly immediately adjacent) at the end faces in each case a stamp guide zone as zones, wherein spaced from the end faces and (possibly immediately) adjacent to the stamp guide zones is a press zone. In the press zone, the powder with the highest pressing force is compressed. In particular, the pressing zone is defined by the region along the axial direction in which the powder is disposed during the application of the highest pressing force.

Furthermore, there is a demoulding zone, in particular at least on one of the end faces, ie. H. a zone of the die, through which the green body from the die pushed out (demolded) and is provided for removal from the press.

In particular, the die in the press is aligned with the punches (at least roughly) via the at least one (outer) centering surface. However, a centering of the die relative to the punches is in particular also over other surfaces, for. B. parts of the outer peripheral surface or the inner peripheral surface possible. Specifically, between the centering surface (or the respective surface used for centering) and the press, there is the smallest radial clearance between the die and the press in the radial direction (with connections for cooling pipes, etc. excluded). In particular, the at least one centering surface lies on the outer diameter of the die, i. H. the die extends only within the outer diameter.

In particular, the centering surfaces, or the top and bottom of the die are used in the immediate vicinity of the centering as a collar for clamping the die in an adapter of the press. It may alternatively or additionally other Surfaces of the die and be adapted to serve as a collar for clamping the die in an adapter of the presses.

The die may have integrated cooling lines and / or heating lines, which are required for a temperature of the die during the pressing operations.

The biasing means of the die is arranged so that during the pressing operation, at least the first diameter during a pressing operation is adjustable to a first value.

The first diameter of the inner circumferential surface may be measured on the die when the biasing means is activated and without a pressing force acting on the die. By means of the pretensioning device, the first diameter is reduced in relation to the stress-free initial dimension (eg to a first value). When applying the pressing force, a proportion of the pressing force acts outward in the direction of the normal vector on the inner peripheral surface. This is widened as a result of the pressing force (or the proportion of the pressing force). By the biasing device, this expansion is at least reduced or completely compensated. The first diameter is equal to or greater than the first value, but always less than the second value or equal to the second value is activated with biasing means and no pressing force.

The biasing means of the die is arranged so that the first diameter can be increased during the demoulding process. During the demolding process, a portion of a reduced pressing force acts in the direction of the normal vector on the inner circumferential surface in relation to the previously applied maximum pressing force. This proportion of the reduced pressing force in the direction of the normal vector during the demoulding process can be less than 50%, in particular less than 25%, preferably less than 10%, particularly preferably less than 5% of the proportion of the maximum pressing force, or even (almost) the value Reach zero.

With the biasing means of the die, tensile stresses acting on the core of the die, which is usually made of hard metal, can at least be reduced.

The widening of at least the first diameter of the inner peripheral surface at least in the pressing zone during the demoulding process in particular means that the frictional forces can be at least reduced during demolding of the green body from the die. In particular, draft angles on the green body or on the inner peripheral surface of the die are no longer required, so that very dimensionally stable and cylindrical outer circumferential surfaces of the green body can be produced. Furthermore, the stress of the die is reduced by the friction during demolding, so that the wear of the die can be reduced. With the biasing device, the restoring forces of the die are reduced or compensated for during the demoulding of the green body on the one (first) end face, so that the green compact is less constricted and therefore has a very little or even no (unwanted) conicity.

The die comprises pretensioning means by which at least the first diameter is set to a first value during a pressing operation in which the inner peripheral surface is acted upon by a portion of the maximum pressing force acting in a direction of a normal vector on the inner peripheral surface (with the pretensioner activated) a demolding process following the pressing process can be set to at least a second value which is greater than the first value, given at least a reduced pressing force (and when the pretensioning device is deactivated). For this purpose, a force can be introduced directly into the die via the biasing device, in particular during the application of the maximum pressing force (or even before), by the expansion of the first diameter due to the pressing force in particular at least reduced or fully compensated. In particular, the first diameter (without application of the maximum pressing force) can be reduced by the (activated) pretensioning device (to the first value or to a further value reduced in relation to the first value).

By the activated biasing device, in particular a desired contour of the green compact is defined, wherein the deactivated biasing means of the improved demolding of the green body is used.

In the demolding operation following the pressing process, the pressing force (applied in the axial direction) and thus also the portion of the pressing force acting in the direction of the normal vector on the inner peripheral surface are reduced and the pretensioner can be deactivated (partially or completely). The first diameter of the inner peripheral surface of the die can expand to the second value, wherein an elastic spring back of the die during demoulding and thus concomitant constriction of the green body no longer occurs or can be prevented.

The pretensioning device can be activated before the application of the maximum pressing force, in particular even before the filling of the receptacle with the powder or the material to be compacted, so that at least the first diameter is set to the first value or to another value that is smaller than the first value.

The die can be deformed (elastically) by the pretensioning device, wherein when the pretensioning device is deactivated, the first diameter widens (elastically), in particular to the second value (when the green compact is still arranged in the pressing zone).

In particular, the second value of the first diameter can exclusively by actuation of the biasing means (ie without the influence of pressing force, temperature or other parameters influencing the first diameter) to an amount of at least 0.005 millimeters, preferably at least 0.01 millimeters, more preferably at least 0.002 millimeters or even at least 0.05 millimeters larger than the first value to be set. It is appropriate that the second value is not more than 0.2 millimeters larger than the first value.

In particular, the die comprises an activatable pretensioning device, by means of which, when the pretensioning device is activated, at least the first diameter can be reduced to at least a first value and the second diameter can be widened by the first diameter when the pretensioning device is deactivated to a second value which is larger than the first value. For this purpose, a force is introduced directly into the matrix via the activated pretensioning device, by means of which the first diameter can be reduced from a second value to a first value (or to a further value smaller than the first value).

The biasing device is formed in particular by at least one (at least in the axial direction) deformable wall between the inner peripheral surface (or the core) and the outer peripheral surface. The wall can z. B. limit a pressure chamber and be deformed by acting on the pressure chamber with a pressurized fluid. This deformable wall extends at least partially at an angle to the radial direction (the angle extending from the radial direction to the axial direction), so that by applying a force (a pressure) to the wall (in the axial direction) , z. B. on the pressurized fluid, a deformation of the inner peripheral surface in the radial direction can be effected.

The wall acts in particular in the manner of a membrane, which can be converted by a force acting on the wall of a curved shape into an elongated shape, wherein the wall in the elongated shape causes a deformation of the inner peripheral surface.

In particular, the biasing device comprises in this embodiment, a force introduction device, for. B. a piston-cylinder unit through which the force can be applied to the wall. On the other hand, the wall may define a pressure chamber arranged in the die, which can be acted upon by a pressurized fluid. About the pressure fluid, the wall can be deformed.

It is preferred that the biasing means comprise at least one pressure chamber acted upon by a pressure fluid, which is arranged in the die. In particular, the biasing device is activated when the pressure chamber is acted upon by the pressure fluid. A pressurization occurs, for example, when the pressure chamber is acted upon by the pressure fluid at a pressure of at least 10 bar, in particular at least 50 bar, preferably at least 100 bar, more preferably at least 200 bar or even at least 300 bar. In particular, the pressure chamber is acted upon by the pressure fluid at a pressure of less than 1000 bar, in particular less than 500 bar, preferably less than 350 bar.

In particular, the biasing means is deactivated when the pressure chamber has no (atmospheric) overpressure or the pressurized fluid pressurizes the pressure chamber and in particular at a pressure which is at most 80% of the pressure, preferably at most 60% of the pressure with activated biasing means. In particular, the biasing device is deactivated when the pressure chamber is acted upon by the pressure fluid at a pressure of less than 10 bar.

In particular, the at least one pressure chamber completely surrounds the inner circumferential surface along a circumferential direction.

In particular, the at least one pressure chamber is arranged at least partially or even completely with respect to the axial direction in the press zone or at a (common) height with the press zone.

Specifically, the at least one pressure chamber is arranged along a circumferential direction in the die and configured to have a first diameter (starting from the second value) at a height at a first position along the circumferential direction by a first amount (to a first value) and a second diameter present at a second position along the circumferential direction is variable by a second amount deviating from the first amount (to another first value).

Preferably, the biasing means comprises a plurality of pressure chambers, which are arranged one above the other along the axial direction.

In particular, at least between two pressure chambers arranged adjacently in the axial direction there is a cavity with a volume in the die, wherein the volume can be reduced when a pressurized fluid is acted upon by the pressure chamber.

Preferably, the biasing means comprises a plurality of pressure chambers, which are arranged side by side along the circumferential direction.

In particular, the inner circumferential surface can be deformed at different positions in different ways by the at least one wall or by the at least one pressure chamber (with respect to a first value and a second value).

• a) Anordnen eines Pulvers in der Aufnahme;
• b) Verfahren des mindestens einen Stempels in die Matrize entlang der axialen Richtung und Verpressen des Pulvers zu einem Grünling in der Presszone durch Aufbringung einer maximalen Presskraft über den mindestens einen Stempel;
• c) Entformen des Grünlings aus der Matrize über eine Stirnseite der Matrize; wobei während Schritt b) zumindest ein erster Durchmesser durch die Vorspanneinrichtung auf einen ersten Wert eingestellt und nach Schritt b) und vor Schritt
• c) der erste Durchmesser bei zumindest verringerter Presskraft auf einen zweiten Wert vergrößert wird.

It is further proposed a method for producing at least one green compact with a press, wherein the press has at least one template proposed here and at least one punch which can be moved over an end face of the die in a formed by the inner peripheral surface receptacle for the green compact along the axial direction is. The method comprises at least the following steps:

• a) placing a powder in the receptacle;
• b) moving the at least one stamp into the die along the axial direction and pressing the powder into a green compact in the press zone by applying a maximum pressing force over the at least one punch;
• c) removing the green body from the die via a face of the die; wherein during step b) at least a first diameter set by the biasing means to a first value and after step b) and before step
• c) the first diameter is increased at least reduced pressing force to a second value.

In particular, the pretensioning device is activated before application of the maximum pressing force, in particular even before filling the receptacle with the powder or the material to be compacted in accordance with step a), so that at least the first diameter starting from the stress-free or pressure-free state on the first value or to another value which is smaller than the first value.

In particular, the die is deformed (elastically) by the pretensioning device, wherein when the pretensioning device is deactivated, the first diameter widens (elastically), in particular to the second value (when the green compact is still arranged in the pressing zone).

1. i. Aktivieren der Vorspanneinrichtung und dadurch Reduzieren zumindest des ersten Durchmessers auf zumindest einen ersten Wert; und
2. ii. Ausgehend von dem ersten Wert Deaktivieren der Vorspanneinrichtung und dadurch Aufweiten des ersten Durchmessers auf einen gegenüber dem ersten Wert vergrößerten zweiten Wert.

In particular, a method is proposed for deforming a matrix, in particular a matrix described above, wherein the matrix comprises an activatable biasing device. The method comprises, in particular starting from the stress-free or pressure-free state of the die, the following steps:

1. i. Activating the biasing means and thereby reducing at least the first diameter to at least a first value; and
2. ii. Starting from the first value, deactivating the pretensioning device and thereby widening the first diameter to a second value which is larger than the first value.

The steps i. and ii. can be repeated several times or many times, of course also in reverse order.

In particular, this variant describes the function of the die even without green, d. H. This method can be carried out and understood from the template even without filling a powder and without producing a green body.

In particular, when the pretensioning device is activated, a force is introduced directly into the matrix via the activated pretensioning device, by means of which the first diameter can be reduced from a second value to a first value (or to a further value smaller than the first value).

In particular, the pretensioning device comprises at least one pressurizing chamber which can be acted upon by a pressurized fluid and which is arranged (at least partially at a height with the pressing zone) in the matrix, wherein the pressurizing chamber is acted on at least temporarily during step b) by a pressurized fluid ( Activation of the pretensioner). A pressure in the at least one chamber is reduced before step c) (deactivation of the pretensioning device).

In particular, the biasing means is activated when the pressure chamber is pressurized with the pressure chamber. A pressurization is present, for example, if a pressure of at least 10 bar, in particular at least 50 bar, preferably at least 100 bar, particularly preferably at least 200 bar, is present in the pressure chamber via the pressure fluid.

In particular, the biasing means is deactivated when the pressure fluid pressurizes the pressure chamber with no or at least (at least 20%) lower pressure than when the biasing means is activated and in particular with a pressure of less than 10 bar.

The comments on the die are particularly applicable to the said methods and vice versa.

The particular shape of the matrices proposed here can of course be produced using the known production methods such as turning, milling, sawing, drilling and grinding, wire cutting, die sinking and hard milling, as well as welding and soldering. It is particularly advantageous, however, the die or at least the shrink ring by so-called additive method, eg. As laser sintering (3D printing process, for the production of spatial structures of powdery starting material by sintering, workpiece is produced in layers) to produce. As a result, a truly free design of the die is possible, wherein the weight of the die can be reduced as much as possible.

By way of precaution, it should be noted that the numerical terms used here ("first", "second",...) Primarily serve (only) to distinguish a plurality of similar objects or quantities, that is to say, in particular, do not require any dependence and / or order of these objects or variables on one another pretend. If a dependency and / or order are required, this is explicitly stated here or it obviously results for the person skilled in the art when studying the concretely described embodiment.

• 1: eine bekannte Matrize in einer Seitenansicht im Schnitt;
• 2: die Matrize nach 1 in einer Draufsicht;
• 3: eine weitere, der Matrize nach 1 und 2 zumindest ähnliche Matrize, in einer perspektivischen Ansicht im Schnitt;
• 4: eine Matrize gemäß einer ersten Ausführungsvariante in einer perspektivischen Ansicht im Schnitt;
• 5: die Matrize nach 4 in einer Seitenansicht im Schnitt;
• 6: eine Matrize gemäß einer zweiten Ausführungsvariante in einer Seitenansicht im Schnitt;
• 7: eine Matrize gemäß einer dritten Ausführungsvariante in einer Seitenansicht im Schnitt;
• 8: eine Matrize gemäß einer vierten Ausführungsvariante in einer Seitenansicht im Schnitt;
• 9: die Matrize nach 8 in einer perspektivischen Ansicht im Schnitt;
• 10: ein Detail der Matrize nach 8 und 9, wobei die Vorspanneinrichtung aktiviert ist; und
• 11: ein Detail der Matrize nach 8 und 9, wobei die Vorspanneinrichtung deaktiviert ist.

The invention and the technical environment will be explained in more detail with reference to FIGS. It should be noted that the invention should not be limited by the embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and findings from the present description and / or figures. In particular, it should be noted that the figures and in particular the illustrated proportions are only schematic. The same reference numerals designate the same objects, so that explanations of other figures can be used if necessary. Show it:

• 1 a known template in a side view in section;
• 2 : the matrix after 1 in a plan view;
• 3 : another, the female after 1 and 2 at least similar template, in a perspective view in section;
• 4 a template according to a first embodiment in a perspective view in section;
• 5 : the matrix after 4 in a side view in section;
• 6 a die according to a second embodiment in a side view in section;
• 7 a die according to a third embodiment in a side view in section;
• 8th a die according to a fourth embodiment in a side view in section;
• 9 : the matrix after 8th in a perspective view in section;
• 10 : a detail of the matrix after 8th and 9 wherein the biasing means is activated; and
• 11 : a detail of the matrix after 8th and 9 with the pretensioner deactivated.

1 shows a known template 1 in a side view in section, in a press 2 , 2 shows the matrix 1 in a top view. 3 shows another, the female 1 to 1 and 2 at least similar template 1 , in a perspective view in section III-III to 2 , The 1 to 3 will be described together below.

The matrix 1 includes a so-called shrink ring 31 , being inside the shrink ring 31 a core 32 is arranged, then the inner peripheral surface 6 the matrix 1 forms. The inner peripheral surface 6 the matrix 1 on the one hand forms the receptacle for the powder or the green product to be produced 28 , Over a first open top side 4 the matrix 1 can a (top) stamp 7 of the press 2 along an axial direction 3 into the matrix 1 drive into. The (upper) stamp 7 slides along the inner peripheral surface 6 the matrix 1 and increasingly squeezes the powder. Here is an additional (sub) stamp 7 provided, (during assembly of the die 1 ) via a downwardly open second end face 5 the matrix 1 along the axial direction 3 into the matrix 1 goes in and up to disassembly of the die 1 within the matrix 1 moved up and down. Between the (upper) stamp 7 and the (sub) stamp 7 so does the powder by a pressing force 16 to a green body 28 pressed, the inner peripheral surface 6 the matrix 1 in particular a lateral contour of the green body 28 Are defined.

The matrix 1 has an outer peripheral surface 9 a collar over which the die 1 in the press 2 can be absorbed and tightened. The collar extends in a radial direction 8th up to an outside diameter 10 and forms a centering surface there 11 , The matrix 1 is cylindrical, wherein the cylindrically shaped outer peripheral surface 9 about a radial play in the press 2 is added, so that a centering of stamps 7 and die 1 So, a coaxial arrangement of stamps 7 and die 1 , can be made possible.

The matrix 1 points to the first front page 4 a first stamp guide zone 29 and at the second end face 5 a second die guide zone 30 on. Distanced from the end faces 4 . 5 and adjacent to the die guide zones 29 . 30 lies a press zone 12 in front. The press zone 12 is the zone in which the powder with the highest pressing force 16 is compressed. Here is the press zone 12 in the mold 1 clearly defined and along the axial direction 3 limited. Next lies on the first front side 4 a demoulding zone (here the first die guide zone 29 ), ie a zone of the die 1 through which the finished pressed green body 28 from the matrix 1 pushed out (demoulded) and for removal from the press 2 provided.

When pressing the powder is due to the high pressure, the inner peripheral surface 6 the matrix 1 heavily used. In this case, the inner peripheral surface 6 the matrix 1 in the direction of the normal vector 15 elastically expanded. This expansion in the press zone 12 now leads to strong frictional forces during demoulding. These frictional forces are up to the Entformungszone inside, as the die 1 is usually cylindrical and therefore has a substantially constant stiffness (ie a substantially constant resistance to an elastic expansion in the direction of the normal vector 15 ) along the axial direction 3 having. This expansion only in the press zone 12 the matrix 1 causes the green body 28 can not be produced accurately. During demolding of the green body 28 may be a conicity of the green 28 to adjust. At the same time the die is springing 1 in the press zone 12 with progressive demolding back, leaving the green body 28 (here at the lower end) constricted more and more conical.

4 shows a die 1 according to a first embodiment in a perspective view in section. 5 shows the matrix 1 to 4 in a side view in section with a press 2 , The 4 and 5 will be described together below. On the description of 1 to 3 is referred to.

The matrix 1 includes a so-called shrink ring 31 , being inside the shrink ring 31 a core 32 is arranged, then the inner peripheral surface 6 the matrix 1 forms. The inner peripheral surface 6 the matrix 1 on the one hand forms the receptacle for the powder or the green product to be produced 28 , The interaction of the matrix 1 with the stamps 7 was referring to the 1 to 3 described.

The matrix 1 extends along an axial direction 3 between a first end face 4 and a second end face 5 and forms between the end faces 4 . 5 an inner peripheral surface 6 for receiving one, by at least one along the axial direction 3 movable stamp 7 made of compressible material. The matrix 1 extends from the inner peripheral surface 6 along a radial direction 8th towards an outer peripheral surface 9 and toward at least one, in the radial direction 8th on an outside diameter 10 arranged, centering 11 , The matrix 1 has spaced to the end faces 4 . 5 a press zone 12 and the inner peripheral surface 6 in the press zone 12 at least one, along the radial direction 8th extending first diameter 13 on. The matrix 1 includes a biasing device 14 through which at least the first diameter 13 during a pressing operation in which the inner peripheral surface 6 with one in a direction of a normal vector 15 on the inner peripheral surface 6 acting proportion of the maximum pressing force 16 is applied to a first value 17 adjustable and during a demolding process following the pressing process with at least reduced pressing force 16 to one over the first value 17 enlarged second value 18 is expandable.

The pretensioner 14 is here by a deformable wall 33 between the core 32 and the outer peripheral surface 9 educated. This deformable wall 33 extends at least partially at an angle 34 to the radial direction 8th , so by applying a force 35 on the wall 33 (in the axial direction 3 , see arrow) a deformation of the inner peripheral surface 6 in the radial direction 8th can be effected.

6 shows a die 1 according to a second embodiment in a side view in section with a green compact 28 , 7 shows a die 1 according to a third embodiment in a side view in section. 8th shows a die 1 according to a fourth embodiment in a side view in section. 9 shows the matrix after 8th in a perspective view in section. The 6 to 9 will be described together below. On the description of 1 to 3 and FIGS. 4 to 5 are referred to.

The matrix 1 includes a so-called shrink ring 31 , being inside the shrink ring 31 a core 32 is arranged, then the inner peripheral surface 6 the matrix 1 forms. The inner peripheral surface 6 the matrix 1 on the one hand forms the receptacle for the powder or the green product to be produced 28 , The interaction of the matrix 1 with the stamps 7 was referring to the 1 to 3 described.

The matrix 1 extends along an axial direction 3 between a first end face 4 and a second end face 5 extends and forms between the end faces 4 . 5 an inner peripheral surface 6 for receiving one, by at least one along the axial direction 3 movable stamp 7 made of compressible material. The matrix 1 extends from the inner peripheral surface 6 along a radial direction 8th towards an outer peripheral surface 9 and toward at least one, in the radial direction 8th on an outside diameter 10 arranged, centering 11 , The matrix 1 has spaced to the end faces 4 . 5 a press zone 12 and the inner peripheral surface 6 in the press zone 12 at least one, along the radial direction 8th extending first diameter 13 on. The matrix 1 includes a biasing device 14 through which at least the first diameter 13 during a pressing operation in which the inner peripheral surface 6 with one in a direction of a normal vector 15 on the inner peripheral surface 6 acting proportion of the maximum pressing force 16 is applied to a first value 17 adjustable and during a demolding process following the pressing process with at least reduced pressing force 16 to one over the first value 17 enlarged second value 18 is expandable.

In the second, third and fourth embodiment of the die 1 includes the pretensioner 14 at least one with a pressurized fluid 19 acted upon pressure chamber 20 in the matrix 1 is arranged. The pretensioner 14 is activated when the pressure chamber 20 with the pressurized fluid 19 and pressurized.

Here the pressure chambers surround 20 the inner peripheral surface 6 along a circumferential direction 21 full.

At least one of the pressure chambers 20 is at least partially or completely with respect to the axial direction 3 in the press zone 12 or at a height 22 with the press zone 12 arranged.

At least one pressure chamber 20 is along a circumferential direction 21 so in the matrix 1 arranged and configured that one at a first position 23 along the circumferential direction 21 present first diameter 13 (starting from the second value 18 ) by a first amount (to a first value 17 ) and one at a second position 24 along the circumferential direction 21 present second diameter 25 (which is different than the first diameter 13 ) (starting from another second value 18 ) by a second amount deviating from the first amount (to another first value 17 ) is changeable.

Visible, the embodiments of the biasing device 14 each a plurality of pressure chambers 20 on that along the axial direction 3 are arranged one above the other. At least between two in the axial direction 3 adjacent pressure chambers 20 a cavity 26 with a volume 27 in the mold 1 before, the volume 27 when pressurizing the pressure chamber 20 with a (pressurized) pressurized fluid 19 is reducible.

10 shows a detail of the matrix 1 to 8th and 9 wherein the biasing means 14 is activated. 11 shows a detail of the matrix 1 to 8th and 9 wherein the biasing means 14 is disabled. The 10 and 11 will be described together below. On the remarks to the 6 to 9 will be referred.

The pretensioner 14 here comprises two at least in the axial direction 3 elastically deformable walls 33 between the inner peripheral surface 6 (or the core 32 ) and the outer peripheral surface 9 , The walls 33 limit a pressure chamber 20 and are about an admission of the pressure chamber 20 with a pressurized fluid 19 deformed. These deformable walls 33 extend (at least with deactivated biasing device 14 ) at least partially at an angle 34 to the radial direction 8th (where the angle 34 starting from the radial direction 8th towards the axial direction 3 extends), so that by the application of a force 35 (a pressure) on the walls 33 (in the axial direction 33 ) over the pressurized fluid 19 a deformation of the inner peripheral surface 6 in the radial direction 8th can be effected.

The wall 33 acts like a membrane through a wall 33 Acting force 35 of a curved shape ( 11 ) in a stretched form ( 10 ) is convertible, the wall 33 in the stretched form, deformation of the inner peripheral surface 6 causes.

The process for producing at least one green compact 28 with a press 2 , the press 2 the matrix 1 and at least one stamp 7 which has an end face 4 . 5 the matrix 1 in through the inner peripheral surface 6 formed admission for the greenling 28 along the axial direction 3 is movable, comprises in step a) arranging a powder in the receptacle and in step b) the method of at least one stamp 7 into the matrix 1 along the axial direction 3 and pressing the powder to a green compact 28 in the press zone 12 by applying a maximum pressing force 16 about the at least one stamp 7 , In step c) becomes the green compact 28 from the matrix 1 over a front side 4 . 5 the matrix 1 removed from the mold. During step b) at least a first diameter 13 through the pretensioner 14 to a first value 17 set and after step b) and before step c) the first diameter 13 at least reduced pressing force 16 to a second value 18 increased.

Without greenling 28 The method can also be implemented by the steps i., namely the activation of the pretensioning device 14 and thereby reducing at least the first diameter 13 on at least a first value 17 and ii., namely deactivating the biasing means 14 and thereby widening the first diameter 13 to one over the first value 17 enlarged second value 18 to be discribed.

When the pretensioner is activated 14 is via the activated pretensioner 14 a force 35 or a pressure directly into the die 1 initiated by the first diameter 13 starting from a second value 18 to a first value 17 (or to one over the first value 17 reduced further value) can be reduced.

LIST OF REFERENCE NUMBERS

1

die

2

Press

3

axial direction

4

first end face

5

second end face

6

Inner circumferential surface

7

stamp

8th

radial direction

9

Outer circumferential surface

10

outer diameter

11

centering

12

press zone

13

first diameter

14

biasing means

15

Direction of the normal vector

16

pressing force

17

first value

18

second value

19

pressure fluid

20

pressure chamber

21

circumferentially

22

height

23

first position

24

second position

25

second diameter

26

cavity

27

volume

28

Greenfinch

29

first stamp guide zone

30

second stamp guide zone

31

shrink ring

32

core

33

wall

34

corner

35

force

Claims (11)

Die (1) for placement in a press (2), wherein the die (1) extends along an axial direction (3) between a first end face (4) and a second end face (5) and between the end faces (4, 5 ) an inner peripheral surface (6) for receiving a, by at least one along the axial direction (3) movable punch (7) compressible material forms, wherein the die (1) starting from the inner peripheral surface (6) along a radial direction (8) extending to an outer peripheral surface (9) and towards at least one, in the radial direction (8) on an outer diameter (10) arranged centering surface (11); wherein the die (1) spaced from the end faces (4, 5) comprises a pressing zone (12) and the inner peripheral surface (6) in the pressing zone (12) has at least one first diameter (13) extending along the radial direction (8) wherein the die (1) comprises a biasing means (14) having at least one, with respect to the axial direction (3) at least at a height (22) with the press zone (12) and at least in the axial direction (3) with a Force (35) acted upon and thereby deformable wall (33) through which at least the first diameter (13) during a pressing operation, wherein the inner peripheral surface (6) with a in a direction of a normal vector (15) on the inner peripheral surface (6). acting portion of a maximum pressing force (16) is applied, to a first value (17) and during a subsequent demolding on the pressing process in at least reduced pressing force (16) is adjustable to a relation to the first value (17) enlarged second value (18). Die (1) after Claim 1 , wherein only by operation of the biasing means (14) the second value (18) is greater than the first value (17) by an amount of at least 0.005 millimeters. A die (1) according to any one of the preceding claims, wherein the biasing means (14) comprises at least one pressure chamber (20) which can be acted upon by a pressurized fluid (19) and which is arranged in the die (1) and which passes through the at least one wall (33). is limited. Die (1) after Claim 3 wherein the at least one pressure chamber (20) surrounds the inner circumferential surface (6) completely along a circumferential direction (21). Die (1) according to one of the preceding Claims 3 and 4 wherein the at least one pressure chamber (20) is arranged at a height (22) with the pressing zone (12) with respect to the axial direction (3). Die (1) according to one of the preceding Claims 3 to 5 wherein the at least one pressure chamber (20) along a circumferential direction (21) in the die (1) is arranged and configured such that at a height (22) at a first position (23) along the circumferential direction (21) present first Diameter (13) by a first amount and at a second position (24) along the circumferential direction (21) present second diameter (25) is variable by a second amount different from the first amount. Die (1) according to one of the preceding Claims 3 to 6 wherein the biasing means (14) comprises a plurality of pressure chambers (20) arranged one above the other along the axial direction (3). Die (1) after Claim 7 in which at least between two pressure chambers (20) arranged adjacently in the axial direction (3) there is a cavity (26) with a volume (27) in the matrix (1), the volume (27) acting on the pressure chamber (20). with the pressure fluid (19) by a deformation of the at least one wall (33) is reduced in size. A die (1) according to any one of the preceding claims, wherein the biasing means (14) comprises a plurality of pressure chambers (20) arranged side by side along a circumferential direction (21). Method for producing at least one green compact (28) with a press (2), wherein the press (2) has at least one die (1) according to one of the preceding claims and at least one stamp (7) which is connected via an end face (4, 5 ) of the die (1) in a through the inner peripheral surface (6) formed receptacle for the green compact (28) along the axial direction (3) is movable; the method comprising at least the following steps: a) placing a powder in the receptacle; b) moving the at least one stamp (7) into the matrix (1) along the axial direction (3) and pressing the powder into a green compact (28) in the press zone (12) by applying a maximum pressing force (16) over the at least one a stamp (7); c) removing the green body (28) from the die (1) via an end face (4, 5) of the die (1); wherein during step b) at least a first diameter (13) by the biasing means (14) set to a first value (17) and after step b) and before step c) the first diameter (13) at least reduced pressing force (16) a second value (18) is increased. Method according to Claim 10 wherein the biasing means (14) comprises at least one pressure chamber (20) which is acted upon by a pressure fluid (19) and which is arranged in the matrix (1); wherein the pressure chamber (20) at least temporarily during step b) with a pressurized fluid (19) is acted upon; wherein a pressure in the at least one pressure chamber (20) before step c) is reduced.

Images