EP2123377A1 - Method for manufacturing a workpiece, in particular a forming tool or a forming tool component - Google Patents

Abstract

The method comprises providing a heat resistance form (2) with a first form part (2a) and a second form part (2b) in a evacuable chamber (1), filling a metal containing material in the heat resistance form, generating a vacuum in the evacuable chamber and holding the vacuum over a period, generating a inert- or reduction gas atmosphere in the evacuable chamber after expiration of the period, heating the metal containing material, and condensing the heated metal containing material in the heat resistance form through hot pressing under vacuum conditions. The method comprises providing a heat resistance form (2) with a first form part (2a) and a second form part (2b) in a evacuable chamber (1), filling a metal containing material in the heat resistance form, generating a vacuum in the evacuable chamber and holding the vacuum over a period, generating a inert- or reduction gas atmosphere in the evacuable chamber after expiration of the period, heating the metal containing material, and condensing the heated metal containing material in the heat resistance form through hot pressing under vacuum conditions in the inert- or reduction gas atmosphere. A number of rinsing of the evacuable chamber is performed with a reduction gas and/or an inert gas, before the vacuum in the evacuable chamber is generated. A high vacuum is generated in the evacuable chamber. The hot press of the heated metal containing material is performed under high vacuum conditions. The metal containing material in the form of a layer of a metal containing powder or a metal containing powder mixture is filled into the heat resistance form. Two layers or area are produced with different chemical composition while filling the metal containing powder or a metal containing powder mixture. The metal containing material is melted partially and condensed partially in a fluid condition. A cold pressure welding is carried out before heating-up the metal containing material. The process heat is selectively discharged after condensing the metal containing material. An independent claim is included for a device for manufacturing a shaping tool or a shaping tool part.

Description

The present invention relates to a method of manufacturing a workpiece, in particular a forming tool or a forming tool part. Moreover, the present invention relates to an apparatus for producing a workpiece, in particular a forming tool or a shaping tool part.

Methods and devices of the type mentioned for producing a workpiece, in particular a forming tool or a forming tool part, are known from the prior art in different embodiments. Two of the most common methods of producing, for example, forming tools or forming tool parts, are the casting and (mechanical) machining of forged blocks.

When casting a forming tool or molding tool part, an alloy having the desired composition is first melted. The melt is then poured into a mold whose shape is already close to the desired final shape of the forming tool or forming tool part. When the molten alloy is solidified in the mold, it is first coarsely worked, then heat treated and then finely finished.

When forging forged blocks, the liquid melt is first poured into a billet. When the billet is solidified, it is extracted, then reheated and then forged - usually in several steps - to bars or blocks. The rods or blocks obtained in this way are then reheated to initiate an annealing process, which the subsequent post-processing simplified. When the rods have healed, they are usually cut into blocks of the desired dimensions. These blocks are then formed in a roughing step into a shape that is already close to the final shape of the forming tool or forming tool part. This is followed by a heat treatment and a finishing as in the casting method described above to complete the production of the forming tool or molding tool part. The processing of the bars or blocks is relatively complex, so that the processing costs in this process are many times higher than the cost of materials.

Looking more closely at the two manufacturing methods described above, the question arises as to why molding tools or forming tool parts are even made from forged blocks. In fact, casting processes for the production of forming tools or forming tool parts seem to make more sense at first glance, since they are considerably less expensive than the machining of forged blocks. On the other hand, the mechanical properties of the forming tools or forming tool parts obtained by the two methods described above are very different. It is the resulting toughness / ductility of the forming tools or forming tool parts, which makes the process technically much more complex and therefore much more expensive processing forged blocks advantageous. Namely, during the forging process, the relatively brittle carbide networks of the casting are destroyed and the toughness / ductility can thereby be even doubled. If the parts are relatively large (greater than 600 mm for most cold work tool steels and 200 mm for most high speed steels) this effect is not achieved in the core area of the billet or bar, where the relatively brittle casting structure is maintained.

If even higher toughness / ductility of the forming tool or forming tool part is desired, an even more complex process is often used. This is what is known as powder metallurgy (PM for short). The melt is not filled in a cast block, but in a nebulizer, which usually has at least one nozzle, in which a gas is burned against the liquid metal stream, which causes the metal to small, substantially spherical particles (powder) is evaporated. The metal powder thus obtained is then poured into steel containers which are substantially cylindrically shaped. The steel containers are then evacuated to maintain a degree of vacuum and introduced into a hot isostatic press apparatus in which high temperatures and pressures are generated to deform the steel containers and cause the metal powder to densify to form a billet is obtained. When the container material has been removed, there remains a billet which can be forged and subjected to all of the processing steps detailed above in the description of the "Forged Block Machining" method. This manufacturing process increases the cost of production while still. On the other hand, the achievable toughness / ductility can be many times higher than in the conventionally melted and forged blocks. This can be achieved in particular if the alloy has a relatively high content of a brittle ceramic phase.

On the one hand, forging increases the toughness / ductility of the forming tool or forming tool part, but on the other hand induces some undesirable properties, the most important of which is anisotropy. Namely, the forging creates a material structure which leads to different properties in the forging direction compared to the directions running transversely to the forging direction. This anisotropy may be particularly detrimental during the heat treatment of the forming tool part as it results in workpiece distortion, leaving more material to be left over for finishing.

Another method for producing a forming tool or a forming tool part is the sintering of a metal powder. In this case, a metal powder or alternatively a mixture of several metal powders is pressed in order to obtain a body with the desired geometric shape and with a suitable nature, so that it can subsequently be further processed. Such a body is often referred to as a "green body". The green body is then sintered at high temperature for a sufficient period of time to promote diffusion bonding. If a high density is desired, a final hot isostatic pressing step is performed. Different variants of such a method are for example in DE 198 252 23 C2 , of the WO 02/20863 A1 , of the DE 195 08 959 C2 , of the DE 197 52 505 C1 , of the DE 698 148 96 T2 , of the EP 1 281 461 A1 and the EP 0 919 635 A2 disclosed.

The industrial demand for workpieces and components with tailor-made properties has recently risen sharply. Therefore, new concepts, such as the intelligent tooling has been developed. For many purposes, the simplest way to obtain a component with tailored properties is to use a forming tool or part with appropriately graded properties.

From the DE 195 089 59 C2 For example, a molded article of a ceramic, powder metallurgy or composite material is known. Further, a method for producing such a molded article is disclosed in the aforementioned document. Within the shaped body, the material composition and / or the structure changes in one, two or all three spatial directions. The changes can be continuous or discontinuous. To produce the shaped body, one or more starting powders are processed into one or more moldable masses. This moldable mass / masses is / are processed in one, two or all three spatial directions continuously or discontinuously to give a shaped body and then cured, the application of the moldable mass or masses being effected as a function of the degree of property to be finally achieved.

It is also known from the prior art to use concrete (despite its very low strength and toughness in comparison to other materials) for the production of shaping tools. In the DE 699 08 273 T2 For example, a press tool is described which mainly consists of concrete.

In the international patent application WO 2006/056621 A2 For example, a method of making a forming tool by superplastic deformation or by hot compacting a metallic powder in a cement mold is described. The Characteristics of the forming die obtained by hot compacting the powder are not particularly good in consideration of strength and toughness / ductility. The cause lies in particular in the surface oxidation of the metallic powder, which prevents its optimal compression. It is an object of the present invention to provide a method for producing a workpiece, in particular a forming tool or a forming tool part, which enables near-net-shape production of a workpiece having an advantageous combination of high strength and at the same time favorable toughness and ductility properties , In addition, the present invention has the object to provide a device for producing a corresponding workpiece, in particular a forming tool or forming tool part available.

This object is achieved with regard to the method by a method having the features of claim 1. A further inventive solution provides a method having the features of claim 4. With regard to the device, the object underlying the present invention by a device having the features of claim 10 is achieved. The subclaims relate to advantageous developments of the invention.

• Bereitstellen einer hitzebeständigen Form mit einem ersten Formteil und mindestens einem zweiten Formteil in einer evakuierbaren Kammer,
• Einfüllen eines metallhaltigen Werkstoffs in die hitzebeständige Form,
• Erzeugen eines Vakuums in der evakuierbaren Kammer,
• Erwärmen des metallhaltigen Werkstoffs,
• Verdichten des erwärmten metallhaltigen Werkstoffs in der hitzebeständigen Form durch Heißpressen unter Vakuumbedingungen.

According to claim 1, a method according to the invention for producing a workpiece, in particular a shaping tool or a shaping tool part, comprises the following steps:

• Providing a heat-resistant mold with a first molded part and at least one second molded part in one evacuable chamber,
• Filling a metal-containing material in the heat-resistant form,
• Creating a vacuum in the evacuable chamber,
• Heating the metal-containing material,
• Compacting the heated metal-containing material in the heat-resistant form by hot pressing under vacuum conditions.

According to claim 1, the workpieces, such as forming tools or forming tool parts, under vacuum conditions by compacting the heated metal-containing material, which may be present for example as a solid metal-containing body, produced in a heat-resistant form. The production of the workpiece takes place in an evacuable chamber in which the vacuum can be generated and in which optionally also an inert gas atmosphere and / or a reducing gas atmosphere can / can be generated. The method according to the invention makes it possible in a particularly advantageous manner to produce near-net shape, locally isotropic workpieces (for example shaping tools or forming tool parts), which can be obtained by the casting methods known from the prior art, with mechanical properties such as those known from the powder metallurgy methods can be obtained. By generating a vacuum, in particular the oxygen content in the residual gas can be reduced within the evacuable chamber, so that an oxygen contamination of the Surface of the metal-containing material largely prevented, but at least can be significantly reduced and thus workpieces, such as forming tools or forming tool parts, can be produced of particularly high quality.

In order to further reduce the oxygen content within the evacuatable chamber after the metal-containing material has been introduced into the heat-resistant mold, it is proposed in a particularly advantageous embodiment that a number of flushings of the evacuatable chamber be carried out with a reducing gas and / or an inert gas, before the vacuum is generated in the evacuable chamber. Advantageously, a vacuum can be generated in the evacuable chamber between two flushings with the inert gas or reducing gas (at least for a short time). The vacuum does not need to be a high vacuum. Due to the generation of the vacuum following the flushes, the residual gas level within the evacuatable chamber is relatively low.

In a particularly preferred embodiment, it is proposed that in the evacuatable chamber a high vacuum is generated and the hot pressing of the heated metal-containing material is carried out under high vacuum conditions. The pressure range of the high vacuum generated within the evacuatable chamber is advantageously on the order of between about 10 ^-3 and about 10 ^-7 mbar. By generating a high vacuum, in particular the oxygen content in the residual gas within the vacuum chamber can be further reduced, so that an oxygen contamination of the surface of the metal-containing material can be further reduced.

• Bereitstellen einer hitzebeständigen Form mit einem ersten Formteil und mindestens einem zweiten Formteil in einer evakuierbaren Kammer,
• Einfüllen eines metallhaltigen Werkstoffs in die hitzebeständige Form,
• Erzeugen eines Vakuums in der evakuierbaren Kammer und Halten des Vakuums über einen Zeitraum t_Vakuum,
• Erzeugen einer Inertgasatmosphäre oder Reduktionsgasatmosphäre in der evakuierbaren Kammer nach Ablauf des Zeitraums t_Vakuum,
• Erwärmen des metallhaltigen Werkstoffs,
• Verdichten des erwärmten metallhaltigen Werkstoffs in der hitzebeständigen Form durch Heißpressen in der Inertgasatmosphäre oder Reduktionsgasatmosphäre.

According to claim 4, an alternative method according to the invention for the production of a workpiece, forming tool or forming tool part comprises the following steps:

• Providing a heat-resistant mold having a first molded part and at least one second molded part in an evacuable chamber,
• Filling a metal-containing material in the heat-resistant form,
• Generating a vacuum in the evacuable chamber and maintaining the vacuum for a period of time t _vacuum ,
• Generating an inert gas atmosphere or reducing gas atmosphere in the evacuatable chamber after expiration of the period t _vacuum ,
• Heating the metal-containing material,
• Compacting the heated metal-containing material in the heat-resistant form by hot pressing in the inert gas atmosphere or reducing gas atmosphere.

In this alternative solution according to the invention, the densification of the heated metal-containing material in the heat-resistant form by hot pressing thus takes place not under vacuum conditions, but in an inert gas atmosphere or reducing gas atmosphere. As a result, an oxygen contamination of the metal-containing material can also be effectively prevented. This process according to the invention likewise makes it possible to produce in a particularly advantageous manner near net shape, locally isotropic forming tools or forming tool parts, as can be obtained by the casting process, with strength properties, such as can be obtained by a powder metallurgy process.

An advantage of the method according to the invention presented here is that the achievable workpiece tolerances are so small that a usually subsequent rough machining step (for example by means of machining processes) of the workpiece can likewise be eliminated. Preferably, a workpiece (forming tool or forming tool part) produced by the method presented here has a notched impact strength of more than 50 J / cm ² , while the degree of hardness is preferably greater than 58 HRC.

In a particularly preferred embodiment, it is proposed that the hot pressing be carried out with a constant expansion rate. The expansion rate can be kept constant, for example, by changing the feed rate of a metal cylinder, by means of which a pressure is exerted on the mold and thus on the metal-containing material.

It can be provided in an advantageous embodiment that the metal-containing material is filled in the form of at least one layer of a metal-containing powder or a metal-containing powder mixture in the heat-resistant mold. The method then comprises in particular the step of hot-pressing the metal-containing powder or the metal-containing powder mixture in the heat-resistant form, which preferably has only a small amount of water added. That for the production of the workpiece metal-containing powders used can be made entirely of one material. The metal-containing powder may, for example, also be a mixture of a metal powder with ceramic particles, wherein the ceramic particles in turn may have a coating.

For many applications, the ability to use mixtures of different metal-containing powders or multiple layers of different metal-containing powders and to introduce them into the refractory form may be particularly advantageous. In a particularly advantageous embodiment, it is therefore proposed that at least two layers or regions of different chemical composition are produced during the filling of the metal-containing powder or the metal-containing powder mixture. This makes it possible in a particularly advantageous manner to produce workpieces (in particular shaping tools or shaping tool parts) with tailor-made mechanical and / or physical properties, which can also be graded within their volume. In this way, in other words, workpieces can be produced which have different mechanical and / or physical properties within their volume in one, two or all three spatial directions. The property gradients may be continuous or discontinuous.

Of particular interest in this context is the possibility of mixing a metal powder with comparatively hard coated or uncoated particles. Thereby, a better balance between toughness / ductility and wear resistance can be obtained. The coated particles that can be mixed with the metal-containing powder, however, are usually relatively expensive. The ones described here Methods allow the use of such particles without degrading their intrinsic properties, and further allow only the minimum required amount of these particles to be used. Namely, the particles can be placed only in those areas of the forming tool part where they are actually required, so that the manufacturing cost of the workpiece can be kept as low as possible. Some coated particles require controlling certain diffusion parameters (especially temperature and time) during the process to avoid deterioration of the intrinsic properties or to obtain optimal properties, the methods presented here being particularly well suited for this. In particular, it is possible to introduce different types of metal-containing powders or metal-containing powder mixtures into different working and carrier zones of a forming tool or forming tool part in order to obtain tailor-made tool properties in this way.

In a particularly preferred embodiment, it is proposed that the densification of the heated metal-containing material takes place in a superplastic state of the material. The heating of the metal-containing material in the heat-resistant form to achieve the superplastic state is preferably carried out comparatively slowly. The superplastic state of a metal-containing material is (depending on the material and depending on the strain rate) usually achieved at a temperature of about 800 ° C to about 1050 ° C. The densification of the heated metal-containing material in the superplastic state is particularly advantageous if the material is in the form of a preformed body in its geometry. This is the case, for example, for a pre-compacted, dimensionally stable green body. If the metal-containing material is present in powder form, the hot pressing can also take place in a non-superplastic state, although here too compacting in the superplastic state is particularly advantageous.

In order to be able to produce the greatest possible density within the workpiece, in particular in the case of a metal-containing material in powder form, a particularly preferred method variant provides for the metal-containing material to be heated further to its diffusion acceleration temperature after the superplastic state has been reached. This diffusion acceleration temperature is alloy-dependent and is, for example, about 1150 ° C for a tool steel. On the other hand, alloys of molybdenum have a higher diffusion acceleration temperature over 1800 ° C, and alloys of copper have a diffusion acceleration temperature lower than 900 ° C. Preferably, the diffusion acceleration temperature is maintained for an extended period of time, usually over a period of more than 30 minutes. The holding time depends in particular on the diffusion acceleration temperature and the pressure exerted. It can possibly be several hours or even several days.

In a further advantageous embodiment, it is proposed that the metal-containing material is at least partially melted and compacted in an at least partially liquid state. The metal-containing material need not be completely melted. For example, there is the possibility that only one phase of the metal-containing material is melted before compacting. This embodiment of the method may be advantageous for some applications.

1. a) ausreichend Zeit und eine ausreichend hohe Temperatur, damit der Diffusionsprozess stattfinden kann;
2. b) ein ausreichend hoher Druck, damit das metallhaltige Pulver fließen und die Leerstellen auffüllen kann (ein Bereich der superplastischen Deformation des metallhaltigen Pulvers ist dabei, wie oben bereits erwähnt, besonders vorteilhaft);
3. c) das Fehlen von Sauerstoff, um eine Oberflächenoxidation des metallhaltigen Pulvers zu vermeiden.

In order for a metal-containing powder or a metal-containing powder mixture to reach its maximum density during hot pressing, the following process conditions in particular must be observed

1. a) sufficient time and a sufficiently high temperature for the diffusion process to take place;
2. b) sufficiently high pressure to allow the metal-containing powder to flow and fill in the voids (a region of superplastic deformation of the metal-containing powder is particularly advantageous, as mentioned above);
3. c) the absence of oxygen to avoid surface oxidation of the metal-containing powder.

The pressure exerted on the heated metal-containing material during hot pressing (for example by means of a metal cylinder) is preferably greater than 20 MPa. The pressure during compaction of the metal-containing material may, depending on the load capacity of the molding material, be in particular between about 20 MPa and about 250 MPa.

In a further advantageous development of the method, a cold pressing step can be carried out before the heating of the metal-containing material. This is particularly advantageous when using a metal-containing powder or a metal-containing powder mixture. By the cold pressing step, the porosity of the metal-containing powder or the metal-containing powder mixture can be closed to leave as little coherent porosity as possible in the material.

After the cold pressing step, the evacuatable chamber can optionally be rinsed with a reducing atmosphere before proceeding with the remaining process steps. In an alternative variant, the metal-containing powder or the metal-containing powder mixture can also be entered in a controlled atmosphere environment. Regardless of which process is pursued, it is important to avoid the presence of oxygen between powder grains as much as possible.

In a particularly preferred embodiment, it is provided that the process heat after the compression of the metal-containing material, preferably by means of a cooling device, is deliberately dissipated. One purpose of such targeted heat removal may be to speed up the overall manufacturing process. In addition, the microstructural properties of the workpiece can be adjusted by the targeted heat dissipation. It is particularly advantageous if the pressure exerted on the metal-containing material pressure during the targeted removal of the process heat (cooling phase) is maintained. By this measure, geometry deviations, in particular shrinkage of the workpiece, can be largely prevented.

In a further advantageous embodiment, it is proposed that the step of compacting the metal-containing material or the removal of the process heat is followed by at least one post-processing step. This at least one post-processing step may in particular comprise the implementation of a finishing and / or hard-machining method. For example, grinding, high-speed milling or thermally-assisted laser machining can be used. The at least a post-processing step is not carried out under vacuum conditions or under a gas atmosphere.

In summary, the methods presented here for producing a workpiece, in particular a forming tool or a shaping tool part, allow tailoring of functionalities which can be derived directly from the metallurgical and microstructural composition of the metal-containing material used (in particular a tool steel).

• Verschleißbeständigkeit,
• Wärmeleitfähigkeit,
• elektrische Leitfähigkeit,
• Beständigkeit unter thermischer und/oder mechanischer Beanspruchung,
• sensorische und aktuatorische Funktionalitäten auf der Grundlage piezoelektrischer Effekte, eines Formgedächtniseffektes oder der Absorption elektromagnetischer Wellen.

Such functionalities are for example

• Wear resistance,
• thermal conductivity,
• electric conductivity,
• Resistance under thermal and / or mechanical stress,
• sensory and actuatory functionalities based on piezoelectric effects, a shape memory effect or the absorption of electromagnetic waves.

In this case, such a location-variable distribution of functionality can follow different motivations.

1. Integral temperature management

In the area of sheet metal forming, the technology of press, mold or profile hardening is of increasing interest in the production of such components which meet the highest safety and energy efficiency requirements in your application have to. On the one hand, such processes are characterized by the utilization of a significantly increased shape-changing capability at high process temperatures, and on the other hand by the thermal treatment taking place immediately after or already taking place with the shaping. If such a thermal treatment is a hardening, it is desirable for technological reasons, but also for reasons of process productivity on the one hand to achieve a rapid removal of heat stored in the workpiece, on the other hand, however, a premature curing further formation by a Permanently impair the reduction in the ability to transform. The consequences are increased shaping forces up to component failure due to cracking. The risk of premature heat dissipation occurs in the area of the sheet metal holder during press hardening, since the first contact of the tool workpiece still occurs before the beginning of the actual forming process and thus well before reaching the final contour of the workpiece. The associated premature cooling can be avoided or reduced in their effect that local low thermal conductivity for the tool material are provided in this area. Due to the time-delayed contact between the tool and the workpiece in the other areas, however, a correspondingly higher thermal conductivity is quite desirable.

2. Time and place variable temperature management

If the goal is to produce components that have complex microstructural property profiles by variabilizing the thermal process conditions in the sense of spatially and time-variable thermomechanical process conditions, then such complex process strategies are quite complex Requirement profiles for the tool. Locally variable Wärmeleitfähigkeiten are only one embodiment feature, other features may consist of the use of local variable electrical, piezoelectric effects, even shape memory effects even up to the absorption of electromagnetic waves, this flexibility in terms of sensory and aktuatorische tasks in terms of a targeted adjustment of local thermal and / or mechanical process conditions.

• eine evakuierbare Kammer,
• eine hitzebeständige Form, die in der evakuierbaren Kammer untergebracht ist und ein erstes Formteil und mindestens ein zweites Formteil aufweist, die einen Formhohlraum bilden, wobei ein metallhaltiger Werkstoff, insbesondere ein metallhaltiges Pulver oder eine metallhaltige Pulvermischung, in den Formhohlraum einfüllbar ist,
• Mittel zum Erzeugen eines Vakuums in der evakuierbaren Kammer,
• Mittel zum Erwärmen des metallhaltigen Werkstoffs in der hitzebeständigen Form,
• Mittel zum Verdichten des erwärmten metallhaltigen Werkstoffs in der hitzebeständigen Form durch Heißpressen.

According to claim 10, a device according to the invention for producing a workpiece, in particular a forming tool or a forming tool part comprises:

• an evacuable chamber,
• a heat-resistant mold accommodated in the evacuable chamber and having a first mold part and at least one second mold part forming a mold cavity, wherein a metal-containing material, in particular a metal-containing powder or a metal-containing powder mixture, can be filled into the mold cavity,
• Means for creating a vacuum in the evacuable chamber,
• Means for heating the metal-containing material in the heat-resistant form,
• Means for compacting the heated metal-containing material in the heat-resistant form by hot pressing.

The device according to the invention is particularly suitable for carrying out a method according to one of claims 1 to 9, so that workpieces, such as, for example, shaping tools or shaping tool parts, can be manufactured with the advantageous properties described above. The heat-resistant mold used to make the workpiece should, in terms of its mechanical design, be capable of withstanding the pressure required to flow a metal-containing powder or metal-containing powder mixture. The pressure acting on the metal-containing material during compaction may be between about 20 MPa and about 250 MPa, depending on the load capacity of the molding material.

In a particularly advantageous embodiment it is provided that the device moreover comprises means for generating an inert gas atmosphere and / or a reducing gas atmosphere. The densification of the metal-containing material can be carried out in such an embodiment of the device in an inert gas atmosphere or a reducing gas atmosphere. As a result, an oxygen contamination of the surface of the metal-containing material can be prevented.

In a particularly preferred embodiment, the heat-resistant form may be a ceramic-containing and / or graphite-containing form. The pressures acting on the molding material from which the heat-resistant mold is made are generally greater than 20 MPa, often greater than 30 MPa to 40 MPa, so that concrete, mortar or cement with a low water content and containing at least one Ceramic material as materials for producing the heat-resistant form are particularly advantageous. In this case, Al ₂ O ₃ , zirconium oxide, silicon carbide or SiO _{2 is} the preferred filler material for the production of the heat-resistant mold. Preferably, the concrete, cement or mortar may have a content of at least 40%, preferably of at least 60%, in particular of at least 80% Al ₂ O ₃ . It may, for example, also be provided that the concrete, cement or mortar has a strength which is higher than 150 MPa (preferably higher than 200 MPa).

The means for heating the metal-containing material may in a particularly advantageous embodiment comprise at least one heating element, which may for example be embedded in the heat-resistant mold. Preferably, the at least one heating element extends in the circumferential direction of at least one of the mold parts (preferably at a distance of about 10 to 20 mm from the mold cavity), so that a uniform heating of the metal-containing material can be achieved. The at least one heating element may for example consist of a Ni-Cr resistance wire or an Fe-Cr-Al resistance wire. Other resistance heating wires, which may be made of molybdenum or tungsten, for example, may also be used. An inductively operating heating element can also be used.

Furthermore, in a preferred embodiment, at least one cooling device may be provided, which may also be embedded in the heat-resistant mold, suitable for selectively cooling the metal-containing material within the heat-resistant mold. As a result, a cooling possibility for the metal-containing material filled into the heat-resistant mold can additionally be made available. The cooling device may, for example, comprise a number of cavities which are introduced into the heat-resistant mold when defined. Through these cavities, a liquid or gaseous cooling fluid can flow, which by means of a supply device or the like can be promoted in order to be able to cool the metal-containing material in the heat-resistant form after compacting targeted.

For example, the cooling device may comprise at least one tube embedded in the refractory mold and through which a liquid or gaseous cooling fluid may circulate. The evacuable chamber may also be flooded with a gaseous cooling fluid (for example with nitrogen or argon). Preferably, the gaseous cooling fluid from a pressure tank or a compressed gas cylinder can flow into the cavities, the tube or the evacuable chamber, since the gas continues to cool as it expands. There is in particular the possibility that the cooling device forms a cooling circuit, within which the cooling fluid can circulate and within which, for example, a heat exchanger or a compression stage can be provided.

In addition, at least one temperature detection means and control means may be provided to control the temperature of the metal-containing material in the mold.

To create the heat resistant mold, a model is first made having the desired geometry of the workpiece (eg, a forming tool or forming tool part). This mold model can be made of different materials (for example polystyrene, polypropylene, wood or aluminum). Many other thermoplastics, metals or even ceramics may be used to make the mold model. To obtain the mold model, conventional process techniques or so-called rapid prototyping techniques (for example mechanical editing, stereo lithography, three-dimensional wax printing, casting and so on).

With the mold model thus obtained, the mold can be produced by, for example, casting the heat-resistant molding material, especially when the molding material contains a powder or powder mixture, concrete, mortar or the like. When the mold is manufactured in this way, it is very easy to embed at least one heating element (in particular a resistance heating element or an induction heating element), a cooling element and possibly also temperature detection means in the mold. If the mold is produced by a three-dimensional ceramic printing technique or by a comparable technique which allows to obtain the heat-resistant mold directly, ie without further intermediate steps, no corresponding mold model has to be produced. The same is true when the heat-resistant mold is obtained by directly machining a solid block of a heat-resistant molding material.

For example, when making the heat-resistant mold from concrete, the concrete is poured into the mold model along with a small amount of water and preferably an admixture of a ceramic material. In order to avoid pore formation and also to fill in more complicated geometries with the molding material, the filling of the mold model should take place as quickly as possible. Subsequently, the mold is cured at a high temperature (for example, about 1200 ° C), so that the residual moisture can escape from the concrete. It is also possible to vibrate the mold model during filling of the molding material, for example, on a vibrating table or the like. It has been found that this can significantly reduce the porosity of the mold.

After the mold has been produced in the manner described above and provided in the evacuable chamber, the mold cavity can be at least partially filled with the metallic material, in particular with a metal-containing powder or with a metal-containing powder mixture. This is followed by the remaining process steps for the production of the workpiece.

In a particularly preferred embodiment, it is proposed that the surface of the mold cavity of the heat-resistant mold has, at least in sections, a ceramic layer and / or a release and lubricant layer. The ceramic layer may be, for example, an oxide layer (for example, zirconia) or a carbide layer (for example, silicon carbide). Any other ceramic that does not react with hot metal can also be used. The release and lubricant layer may be, for example, graphite, molybdenum disulfide, sulfur, phosphorus, boron nitride, mica, or other material that can withstand the relatively high process temperatures. It is also highly desirable that the molding material used has a relatively low thermal conductivity so that it can serve as an insulator between the heating zone in which the metal-containing powder and the metal-containing powder mixture is heated, and the outside of the mold, in particular, when the heat-resistant mold in an advantageous embodiment has a prestressed reinforcing ring made of metal. Such a prestressed reinforcing ring can create compressive stresses in the mold to compensate for the tensile stresses created when compacting the heated metal-containing material.

In order to avoid a reaction of the metal-containing material with the mold material of the heat-resistant mold, the surface of the mold cavity may, in a particularly advantageous embodiment, at least in sections have a color layer or dispersion layer. By applying a color or dispersion, the surface of the mold cavity can be made chemically inert. Also lubricants can be used for this purpose. It may also be advantageous to increase the emissivity of the surface of the ceramic mold in order to make the process more energetically efficient and to keep the heat where it is needed. The active material of the paint or dispersion may be, for example, zirconia, boron nitride, molybdenum disulfide or other graphite, phosphorus or sulfide based components (to name a few).

In particular, in order to increase the shear strength of the heat-resistant mold, it may be provided in a preferred embodiment that the heat-resistant mold is reinforced with metal particles and / or metal rods and / or metal wires and / or metal wire fabrics. The material can be iron or steel. For high temperature applications, however, particularly refractory metals, such as tungsten or molybdenum and their alloys, as well as nickel or cobalt based alloys may be more advantageous. In addition, textile fibers and / or polymer fibers and / or ceramic fibers and / or glass fibers and / or long-fiber fabric of these materials can be used to reinforce the heat-resistant form.

The means for compacting the metal-containing material may in particular comprise a metal cylinder, which is in operative connection with the second molded part of the heat-resistant mold. During operation of the device, the metal cylinder can exert sufficiently high pressure on the heat-resistant mold or a part of the heat-resistant mold, thereby to densify the metal-containing material in the mold.

Fig. 1

eine schematisch stark vereinfachte Darstellung einer Vorrichtung gemäß einem bevorzugten Ausführungsbeispiel der vorliegenden Erfindung, die zur Durchführung eines Verfahrens zur Herstellung eines Werkstücks, insbesondere eines Formgebungswerkzeugs oder eines Formgebungswerkzeugteils, geeignet ist.

Other features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings. It shows

Fig. 1

a schematically simplified view of a device according to a preferred embodiment of the present invention, which is suitable for carrying out a method for producing a workpiece, in particular a forming tool or a forming tool part.

An apparatus which is suitable for carrying out a method for producing a workpiece, in particular a forming tool or a forming tool part, comprises an evacuable chamber 1 with a vacuum system, by means of which a vacuum, preferably a high vacuum in the order of magnitude between 10., Is provided in the interior of the evacuatable chamber 1 ^-3 and 10 ^-7 mbar can be generated. The vacuum system may include, for example, a rotary vane pump and a turbomolecular pump connected thereto. The rotary vane pump generates a pre-vacuum for the turbomolecular pump. Furthermore, pressure sensor means are provided so that the pressure within the evacuatable chamber 1 can be measured and continuously monitored.

The device further comprises a heat-resistant mold 2, which may be, for example, ceramic-containing and / or graphitic, and a first (lower) mold part 2a with a mold cavity and a second (upper), relative to the first mold part 2a movably guided molding 2b includes. It can be seen that the inner diameter of the first mold part 2a is larger than the outer diameter of the second mold part 2b, so that the second mold part 2b can be inserted into the mold cavity of the first mold part 2a. The two heat-resistant molded parts 2a, 2b are preferably made of concrete and a ceramic material (for example, Al ₂ O ₃ ) and have only a small amount of water.

In the first mold part 2a, a heating element 3 is embedded, so that the first mold part 2a can be heated in the implementation of the method. Preferably, the distance of the heating element 3 from the inner surface of the mold cavity of the first mold part 2a is about 10 to 20 mm. The heating element 3 is required to reach the temperature required for the production of the workpiece. It is advantageous if the heating element 3 is embedded directly in the heat-resistant mold 2 as in the embodiment shown here. The heating element 3 may for example be a resistance heating element or an induction heating element, the latter variant being more advantageous because of shorter heating times and better insulation, although it is somewhat more difficult to calibrate. Furthermore, a (in Fig. 1 not explicitly shown), by means of which a cooling of the metal-containing workpiece in the mold 2 is possible.

In Fig. 1 For example, a possible position of the heating element 3 within the first mold part 2a of the heat-resistant mold 2 is shown. Alternatively, the first molded part 2a may also be of modular construction and may have, for example, an inner contact layer adjacent thereto, the heating element 3 and finally an insulation shield. In addition, in the here shown Embodiment embedded in the first mold part 2a, a temperature detecting means 4, which may in particular comprise a conventional thermocouple. This allows the process temperature to be continuously monitored during the performance of the process. By providing the at least one heating element 3, (optionally a cooling device), the temperature detection means 4 and a control device, the process temperature during the implementation of the method can be controlled very precisely.

Furthermore, the device has a metal cylinder 5, by means of which a pressure in the direction of arrow can be exerted on the second (upper) mold part 2b. The surface of the mold cavity of the heat-resistant mold 2 can advantageously be coated with a ceramic layer and / or with a release and lubricant layer. The ceramic layer may be, for example, an oxide layer (for example, zirconia) or a carbide layer (for example, silicon carbide). Any other ceramic material that does not react with the hot metal within the mold cavity may also be used. The release and lubricant layer may be, for example, graphite, molybdenum disulfide, sulfur, phosphorus, boron nitride, mica or other material that can withstand the high process temperatures. In addition, it is possible to use a glass powder as a release agent. Glass has the advantage that forms a glass separating layer at high temperatures, which can effectively prevent adverse surface reactions with the ambient atmosphere.

A metal-containing material in the form of a metal-containing solid body or at least one layer or a portion of a metal-containing powder or a metal-containing powder mixture from which the workpiece is to be produced is in the Form cavity of the first mold part 2a is introduced and heated therein according to a first embodiment under high vacuum conditions using the at least one heating element 3. In order for the compaction of the metal-containing powder or of the metal-containing powder mixture to take place as quickly as possible, the generation of a high vacuum in the interior of the evacuatable chamber 1 during compaction is particularly advantageous. Characterized in that the heating is carried out under high vacuum conditions in the evacuatable chamber 1, an oxygen contamination of the metal-containing material can be effectively prevented, but at least significantly reduced. This is of particular importance when using a metal-containing powder or a metal-containing powder mixture in order to obtain optimum tool properties.

The generation of a high vacuum is quite difficult with most mold materials from which the mold can be made, since they tend to outgas especially at higher temperatures. It is extremely important to have no oxygen as possible, which deteriorates the quality of the powder surface and prevents the complete compaction and diffusion bonding of the metal-containing powder or powder mixture. One way to obtain better process conditions is to cure the refractory mold 2 in a reducing gas atmosphere so as to ensure that voids within the molding material are filled with the reducing gas atmosphere. Alternatively, the heat-resistant mold 2 may be heated in the evacuable chamber 1 prior to filling the metal-containing material, then a vacuum is generated, and then the chamber 1 is filled with a reducing atmosphere to fill the voids within the mold material.

In order to further reduce the oxygen content in the evacuatable chamber 1 and thus further improve the process conditions, there is moreover the possibility that several flushes of the evacuatable chamber 1 are carried out with a reducing gas atmosphere and / or an inert gas atmosphere, before finally the high vacuum in the evacuatable Chamber 1 is generated. Advantageously, a vacuum in the evacuatable chamber 1 can be generated at least for a short time between two flushes.

According to a second embodiment, after the metal-containing material has been introduced into the heat-resistant mold, a vacuum is initially generated in the evacuatable chamber 1 and held for a certain period of time t _vacuum . After expiration of the period t _vacuum , an inert gas atmosphere or reducing gas atmosphere is generated in the evacuatable chamber 1 and the metal-containing material is heated. The densification of the heated metal-containing material in the heat-resistant mold 2 is then carried out by hot pressing in the inert gas atmosphere or reducing gas atmosphere.

The metal-containing material is heated in both embodiments after filling in the mold cavity of the first mold part 2a of the heat-resistant mold 2 and optionally placed in a superplastic state, which (depending on the material) is achieved at temperatures between about 800 ° C and about 1050 ° C. If the metal-containing material is in the form of a metal-containing body, the hot pressing is preferably carried out in this superplastic state. The hot pressing is advantageously carried out with a constant rate of expansion and a constant feed rate of the metal cylinder 5. The pressure which is generated during the hot pressing of the metal cylinder 5 and on the second mold part 2b on the metal-containing material within the first molding 2a may be between about 20 MPa and about 250 MPa. The pressure can act continuously or only in phases on the metal-containing material within the heat-resistant mold 2.

If the metal-containing material is in the form of a metal-containing powder or a metal-containing powder mixture, the hot pressing can also take place under non-superplastic conditions. However, it is particularly advantageous to densify the metal-containing powder or the metal-containing powder mixture by hot pressing in the superplastic state. Subsequently, the metal-containing powder or the metal-containing powder mixture can be heated to its diffusion acceleration temperature over a certain period of time (for example about two hours). By this measure, the largest possible material density can be generated in the workpiece. The diffusion acceleration temperature is alloy-dependent and is, for example, about 1150 ° C for a tool steel. In comparison, alloys of molybdenum have a higher diffusion acceleration temperature over 1800 ° C, and alloys of copper have a diffusion acceleration temperature lower than 900 ° C. Preferably, the diffusion acceleration temperature is maintained for an extended period of time, usually over a period of more than 30 minutes. The holding time, which may possibly be several days, depends in particular on the diffusion acceleration temperature and the pressure exerted. It can also be provided that the metal-containing material is at least partially melted and compacted in an at least partially liquid state. The metal-containing material need not be completely melted.

For example, there is the possibility that only one phase of the metal-containing material is melted before compacting. This embodiment of the method may be advantageous for some applications.
For example, there is also the possibility that in the heat-resistant mold 2 at least two layers or areas are filled with different metal-containing powders or metal-containing powder mixtures. A layer structure with at least two layers allows the production of a workpiece (for example a forming tool or forming tool part) with graded tool properties with the aid of the method presented here in a particularly advantageous manner. For example, it is possible to produce shaping tools or forming tool parts with different mechanical and / or physical properties within their volume. A property grading in volume can be generated in one, two or all three spatial directions (continuous or discontinuous). Often, a comparatively hard and wear-resistant tool surface is desired, whereas a softer tool base body, on the other hand, is sufficient or even particularly advantageous.

In order to reduce the costs for the forming tool or the forming tool part, a layer-related or partially different material composition is also advantageous. Thus, the optimum tooling properties, which are usually associated with high costs, can be provided only where they are actually needed. The remaining part of the forming tool or forming tool part can be built from a material with sufficient properties and significantly lower material costs.
It can also be provided that the process heat is removed selectively after the densification of the metal-containing material by means of the optionally provided cooling device. One purpose of such targeted heat removal may be to speed up the overall manufacturing process. In addition, the microstructural properties of the workpiece can be adjusted by the targeted heat dissipation. It is particularly advantageous if the pressure during the targeted removal of the process heat (cooling phase) is maintained. As a result, geometry deviations, in particular shrinkages of the workpiece, can be largely prevented in an advantageous manner. The cooling device may, for example, comprise a number of cavities which are introduced into the heat-resistant mold 2 in a defined manner. Through the cavities, a liquid or gaseous cooling fluid can flow, which can be conveyed by means of a supply device in order to be able to specifically cool the metal-containing material in the heat-resistant mold 2.

The cooling device may, for example, also comprise at least one tube embedded in the heat-resistant mold 2 and through which a liquid or gaseous cooling fluid may circulate. The evacuatable chamber 1 can also be flooded with the cooling fluid (for example with nitrogen or argon). Preferably, the gaseous cooling fluid from a pressure tank or a compressed gas cylinder can flow into the cavities, the tube or the evacuatable chamber 1, since the gas additionally cools down during the expansion. In particular, there is the possibility that the cooling device forms a cooling circuit within which the cooling fluid can circulate and within which For example, a heat exchanger or a compression stage can be provided.

Claims (19)

Method for producing a workpiece, in particular a shaping tool or a shaping tool part, comprising the steps: Providing a heat-resistant mold (2) with a first molded part (2a) and at least one second molded part (2b) in an evacuable chamber (1), - filling a metal-containing material in the heat-resistant mold (2), Generating a vacuum in the evacuable chamber (1), Heating the metal-containing material, - Compressing the heated metal-containing material in the heat-resistant mold (2) by hot pressing under vacuum conditions. A method according to claim 1, characterized in that a number of flushes of the evacuable chamber (1) with a reducing gas and / or an inert gas is carried out before the vacuum in the evacuable chamber (1) is generated. Method according to one of claims 1 or 2, characterized in that in the evacuable chamber (1), a high vacuum is generated and the hot pressing of the heated metal-containing material is carried out under high vacuum conditions. Method for producing a workpiece, in particular a shaping tool or a shaping tool part, comprising the steps: Providing a heat-resistant mold (2) with a first molded part (2a) and at least one second molded part (2b) in an evacuable chamber (1), - filling a metal-containing material in the heat-resistant mold (2), Generating a vacuum in the evacuable chamber (1) and maintaining the vacuum for a period of time t _vacuum , Generating an inert gas atmosphere or reducing gas atmosphere in the evacuable chamber (1) after the expiration of the period t _vacuum , Heating the metal-containing material, - Compressing the heated metal-containing material in the heat-resistant mold (2) by hot pressing in the inert gas atmosphere or reducing gas atmosphere. Method according to one of claims 1 to 4, characterized in that the metal-containing material in the form of at least one layer of a metal-containing powder or a metal-containing powder mixture in the heat-resistant mold (2) is filled. A method according to claim 5, characterized in that when filling the metal-containing powder or the metal-containing Powder mixture at least two layers or areas of different chemical composition are generated. Method according to one of claims 1 to 6, characterized in that the metal-containing material is at least partially melted and is compressed in an at least partially liquid state. Method according to one of claims 1 to 7, characterized in that before the heating of the metal-containing material, a cold pressing step is performed. Method according to one of claims 1 to 8, characterized in that the process heat is dissipated specifically after compacting the metal-containing material. Device for producing a workpiece, in particular a forming tool or a forming tool part, comprising an evacuable chamber (1), a heat-resistant mold (2) accommodated in the evacuable chamber (1) and having a first mold part (2a) and at least one second mold part (2b) forming a mold cavity, a metal-containing material, in particular a metal-containing powder or a metal-containing powder mixture can be introduced into the mold cavity, Means for generating a vacuum in the evacuable chamber (2), Means for heating the metalliferous material in the heat-resistant form (2), - Means for compacting the heated metal-containing material in the heat-resistant mold (2) by hot pressing. Apparatus according to claim 10, characterized in that the device further comprises means for generating an inert gas atmosphere and / or a reducing gas atmosphere. Device according to one of claims 10 or 11, characterized in that the means for heating the metal-containing material comprise at least one heating element (3) embedded in the heat-resistant mold (2) and in that the device comprises at least one cooling device suitable for selectively cool the metal-containing material within the heat-resistant mold (2), wherein the cooling device is preferably embedded in the heat-resistant mold (2). Device according to one of claims 10 to 12, characterized in that the heat-resistant mold (2) consists of concrete, cement or mortar with an admixture of at least one ceramic material. Apparatus according to claim 13, characterized in that the concrete, cement or mortar has a content of at least 40%, preferably of at least 60%, in particular of at least 80% Al ₂ O ₃ . Apparatus according to claim 13 or 14, characterized in that the concrete, cement or mortar has a strength which is higher than 150 MPa, preferably higher than 200 MPa. Device according to one of claims 10 to 15, characterized in that the device comprises a mechanically prestressed reinforcing ring, suitable to generate compressive stresses in the heat-resistant mold (2). Device according to one of claims 10 to 16, characterized in that the surface of the mold cavity of the heat-resistant mold (2) at least partially has a ceramic layer and / or a release and lubricant layer. Device according to one of claims 10 to 17, characterized in that the heat-resistant mold (2) is reinforced with metal particles and / or metal rods and / or metal wires and / or metal wire fabrics. Device according to one of claims 10 to 18, characterized in that the means for compressing the metal-containing material comprise a metal cylinder (5) which is in operative connection with the second mold part (2b) of the heat-resistant mold (2).

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