WO2004037469A1

WO2004037469A1 - Method and apparatus for rapid manufacturing of metal, ceramic and metal-ceramic products

Info

Publication number: WO2004037469A1
Application number: PCT/NO2003/000351
Authority: WO
Inventors: Roald Karlsen; Jim Bakkelund
Original assignee: Sintef
Priority date: 2002-10-23
Filing date: 2003-10-23
Publication date: 2004-05-06
Also published as: NO20025082D0; NO317085B1; AU2003274844A1

Abstract

Method and apparatus for rapid manufacturing of metal, ceramic and metal-ceramic products from building powder(s) of the relevant materials, comprising: I) at least one powder receptor (1), ii) at least one charging element (2) arranged to charge powder receptor (1), iii) at least one light source (3) arranged to illuminate powder receptor (1) with a product-adapted pattern, iv) at least one powder magazine (4) arranged to supply powder to powder receptor (1), v) at least one charging element (6) arranged to facilitate transferral of powder from powder receptor (1) to a transporting device (13), vi) a transportation device (13) arranged to receive powder (10) in a predetermined pattern from powder receptor (1) and to transport said powder to a sintering die, vii) a sintering die (18-21) arranged to receive powder layer from transporting device (13), envelope the powder layer in contact with the product being built and raise pressure and temperature in layer (17) so that the powder sinters and becomes part of the product being built.

Description

Method and apparatus for rapid manufacturing of metal, ceramic and metal-ceramic products

The present invention relates to a method and an apparatus for rapid, manufacturing of metallic, ceramic and metal-ceramic products in layers, by way of a layer by layer deposition and sintering of powder. Such rapid manufacturing is priory known only in connection with synthetic products or the like or for models of products that do not require the quality of functional products.

Background

Layer Manufacturing Technology (LMT) or Rapid Prototyping (RP) is a common term for several processes by which physical objects are built directly from a 3D CAD drawing. Any physical object may be divided into thin slices. And oppositely thin slices may be put together to obtain any geometry. This is the basic foundation for rapid prototyping. By assembling thin slices a 3 dimensional task is reduces to a 2 dimensional task. It is only required to manufacture the plane elements (slices) in stead of a full volume specification of the object.

Rapid Prototyping already functions well for numerous different synthetic materials. From the first LMT machine was built in 1987 the development has focused on reducing the layer thickness (the thickness of each slice). The most recent systems offer a layer thickness of 0.025 mm. Further development (3 to 5 years on) is expected to concentrate around building materials. Today there is no industrial solution for the manufacture of functional products of metal and ceramic materials, i.e. products with a strength and durability rendering the products suited for use industrially, not only as prototypes.

US patent 4.453.820, 5.153.618 and 6.212.352 Bl all describe various designs of the xerography process, by which a toner is deposited in a thin layer on a substrate. These patents concentrate on printing in two dimensions, not constructing objects in three dimensions. US patent No. 6.251.330 Bl teaches a method for the manufacture of thin plastic plates based on xerography. The US patent Nos. 5.088.047, 6.066.285 and 6.206.672 Bl concern rapid manufacture of objects from powders with a basis in the Xerox principle. None of these inventions, however, provide an apparatus for the manufacture of "real" materials. It is particularly the consolidation process of the manufacturing that has been left out, or does not have the required condition for being employed with metallic and ceramic materials. One of the major challenges in building products in 3 dimensions is to deposit the powder particles on the successively growing object. The particles have to be transported from a photoreceptor to the exact position on the object before the sintering can commence. This transportation may be performed as a one-step process or with the aid of an intermediate transportation medium.

A method for the deposition is presented by US patent 6.066.285. According to this method the deposition is supposedly facilitated by charging previously deposited layers with opposite charge to attract the powder on the photoreceptor. A charge element (corona wire) is moved beyond the previously deposited powder layer to thereby charge it. This will, however, not work well in practice. The induced charge will be spread around the entire object and not be limited to the top surface of the object, which is a condition for this principle to work. Various geometries, materials and structures will influence on the electrical field and cause an uncontrolled transferal of the powder particles. The technology employed in laser writers and copiers for depositing a toner on a sheet of paper is not directly transferable to the task of deposition on 3-dimensional objects. In US patent No. 5.088.047 an intermediate conveyor belt is used for transporting the powder from the photoreceptor to the object. Two depositions, one from the photoreceptor to the conveyor belt and one from the conveyor belt to the object, increase the risk of inaccurate deposition of the powder particles. Immediately prior to its deposition on the object, the powder is made sticky by applying liquid or heat. According to the inventor of said patent this will cause the powder to remain on the object when the conveyor belt is forced against the priory deposited layer. Investigations by the present inventors have revealed that this does not work well in practice. Some of the particles remain on the conveyor belt, resulting in an uneven deposition. A flexible pressure and heat resistant conveyor belt with desired electrostatic properties may be difficult or impossible to find.

None of the inventions described y the US patents No. 5.088.047, 6.006.285 and 6.206.672 Bl are able to provide complete products in metal or ceramic materials. Iron and steel require a temperature of about 1000 °C to sinter. The machines described in these patents are neither able to generate or work at such high temperatures. US patent No. 5.088.047 admits that the powder needs to be a special mixture containing also low melting particles. The three mentioned patents all describe machines that at best produce "green" objects, i.e. objects that stick together so that it is possible to move them to another apparatus for consolidating them. They are thus not machines for direct, rapid manufacturing of functional products. Consolidation of metals and ceramic materials require high pressures and temperatures. The part of the pressure element that takes care of the packing will in most cases be in direct contact with the powder layer. Thus, a heating of the powder layer will imply a temperature increase in the pressure element and in worst case particles will stick to the piston with a resulting flaw in the product. This is a major challenge for the manufacture of materials with high melting points.

In US patent No. 6.066.285 is suggested to consolidate the powder layer with a hot roll that rolls over the powder layer. To sinter materials like iron and steel an enormous amount of heat has to be developed in the contact zone between the roll and the powder. The risk of powder getting stuck to the roll is high. This will eventually lead to flaws that are transmitted throughout the powder layer as the roll rolls on. Investigations performed by the current invention have revealed that pack elements of metal often lead to flaws even with good water cooling.

An alternative sintering method implies use of microwaves to raise the temperature. US patent No. 6.183.689 Bl concerns sintering of "green" powder objects and is not related to rapid manufacturing. US patent No. 6.243.616 Bl suggests to use a concentrated microwave beam to draw a relevant plane geometry on a deposited powder layer in connection with a layer by layer build-up of an object. This is the same technique as the one used in the laser sintering machines described below. There is not provided any suggestions on packing prior to or during the laser treatment to obtain a functional end product with high density. To focus energy to perform a spot-sintering is a time consuming process that is suited only for small products.

Accordingly there is no good prior art solution for rapid manufacturing of real functional products in metal and ceramic materials. In addition to the required speed and accuracy of the manufacturing process, the apparatus therefore must be able to operate at high pressures and temperatures.

Objectives It is an object of the present invention to provide a method for rapid, layer by layer, manufacturing of functional products. Functional products means products made of metal and/ or ceramic materials that through consolidation obtain such strength and integrity that they may be used industrial machines and processes in the same way as products of these materials are commonly used, be that as tools, spare parts for machinery or for other purposes.

The invention

The invention comprises according to a first aspect a method for rapid manufacturing of metal, ceramic and metal-ceramic products from powders of the relevant materials, said method being characterized by the features disclosed by claim 1.

Preferred embodiments of this aspect of the invention are disclosed by the dependent claims 2-20.

According to a second aspect the invention furthermore comprises an apparatus for rapid manufacturing of metal, ceramic and metal-ceramic products from powders of the relevant materials, said apparatus being characterized by the features disclosed by claim 21. Preferred embodiments of this aspect of the invention are disclosed by the dependent claims 22-35.

The present invention has solved the challenge of transferring the metal and/ or ceramic powder from containers therefore via powder receptors to a manufacturing tool where the powder is deposited layer by layer in an accurate position along with a support powder that temporarily fills the voids in the manufacturing tool that shall not constitute part of the finished product. The method according to the invention also provides a solution to how the consolidation of each new layer is to be performed with a rate suited for industrial manufacturing. Furthermore a consolidation process comprising a complete sintering of the powder to solid metallic or ceramic material is described, i.e. materials suited for common use of such materials. None of the known methods are close to providing such a solution.

The area of application of the present invention may be anything from large objects with internal geometries to mass production of small complex details. The production of so-called FGMs is a particularly interesting area. An FGM is an object in which the microstructure changes gradually from one material to another, like from a metallic material to a ceramic material. This is achieved by a layer by layer increase of the relative amount of ceramic material at the sacrifice of metallic material or vice versa. In this manner may be avoided disadvantages related to different properties of the two materials, for example thermal expansion. The method according to the invention may render spare parts rooms superfluous in many different connections, e.g. at car repair shops, on aircraft carriers, on space stations etc. With basis in a computer drawing and required data hardware and manufacturing apparatus, as well as the required powder(s), the method according to the invention renders it possible to build a physical clone of the computer drawing in a matter of hours.

Computer based multi production systems have no readjustment delay and are not affected by the degree of geometric complexity. They use only the required amount of raw material (nothing has to be cut away) and they are equally well suited for 0-series production as for mass production. Contradictory to traditional manufacturing processes where excess material is removed from a blank stock, these new systems build products by a punctilious assembly of extremely small building blocks (powder particles). This opens for completely new combinations of materials and allows manufacturing of "intelligent" multifunctional products. Metals, and even more so ceramic materials, require a high temperature to sinter. To ensure a sufficiently high density in the end product, packing of the powder is important. "Packing" means that the powder is subjected to a direct pressure before and during sintering.

The method according to the invention includes a combination of several steps that may be seen as independent of each other and that in combination is truly unique.

A first step consists in fetching building powder from one or more powder receptors and positioning it on a powder receptor in a highly accurate pattern calculated separately for each layer of the product. This first step of the invention generally corresponds to the photoreceptor of an ordinary copying machine. The photoreceptor is designed of several thin layers with different electrical properties. A photoreceptor may be charges and will thereafter keep its charge until it becomes illuminated.

In parallel with the positioning of the building powder in the said pattern, a support powder is positioned on a separate photoreceptor so that the pattern of the support powder is complementary to the pattern of the building powder, i.e. the support powder is positioned to fill all areas of each layer that is not occupied by building powder. In order for the support powder to work as intended, it may not melt or sinter during the process; instead it will remain as a powder even after the building powder has been consolidated. Subsequently the support powder may easily be removed and reused. The support powder not only makes it possible, it also makes it simple, to manufacture products with advanced shapes, protrusions, overhangs and recesses.

A second step consists in depositing the building powder on the powder receptor on a transporting device, or more precisely to a part of a transporting device having an area and a shape that generally corresponds to the cross-section of the sintering die that the product is sintered in. The mentioned support powder is deposited on complementary parts of the same general area of the transporting device. The said area(s) of said part of the transporting device being covered by either building powder or support powder corresponds to the internal shape of the sintering die.

In a third step the transporting device brings the deposited powders to an exact position over the sintering die that with exception of the deposition of the very first layer, already contains one or more layers of powder that has already been sintered, so that they constitute a uniform, incomplete part of the end product. The positioning of the transporting device may be performed in several ways and is explained in more detail with reference to the drawings.

In a fourth step the sintering die closes and the pressure therein is increased to obtain the required packing of the powders. This is most conveniently made by means of an upper and a lower piston that are arranged to move against each other. The temperature in the sintering die is increased to rapidly and uniformly sinter the deposited building powder(s) to a true metal/ ceramic product layer.

During sintering the powder particles are grown together by atomic diffusion thereby building a uniform material where the traces of the individual particles and layers vanish. In order that the sintering shall result in compact materials, it is required not only to increase the temperature but also the pressure. For the method according to the invention it has been shown that the manufactured products obtain a density that is as dense as casted products, for instance with a density of more than 90% and e.g. up to 98%. By laser sintering such a true sintering based on atomic diffusion as obtained with the present invention, is not obtainable. Instead a local melting of the particles takes place. When materials like steel and titanium is to be included with laser sintering, additional binding substances that makes the end product more porous and weaker, has to be added. Furthermore, such coated powders are very expensive. To increase the density (reduce the porosity) some amounts of copper particles or the like, with properties inferior to steel and titanium, are commonly included. Products manufactured with laser sintering are therefore not functional products. Another disadvantage of laser sintering is that an entire layer cannot be sintered at once, only small areas at the time. Laser sintering is therefore very slow and also for this reason not suited for most industrial applications.

While both building powder and support powder are generally deposited in each layer, it is naturally possible that the building powder occupies the entire area of the sintering die, so that the relative amount of support powder for a certain layer is zero. On the other hand the amount of the building powder may not be zero in any layer unless the product is to be a discontinuous one, leaving the sintering die as two or more separate parts. For some products that do not exhibit any variation in a certain dimension, the support powder can be omitted completely. Step iii) of the method then becomes an "empty" step, as in this case there is no area of the transporting device corresponding to the internal shape of the sintering die that lacks building powder.

The sintering die may comprise more than one chamber and such more than one chamber may be identical or different from each other, so that two or more products may be built in parallel. For example the sintering die may comprise a matrix of 2 x 1 or 2 x 2 or m x n identical products. This may be convenient when each product has small dimensions, as the maximum dimension of the sintering die is limited. Details of the invention with reference to the drawings

Figure 1 is a schematic view of a preferred embodiment of the entire method (system) according to the invention.

Figure 2 is a schematic view of a section of the system of Fig. 1, showing the principles of supplying and returning powder particles from and to a magazine therefore.

Figure 3 shows a different section from that of Fig. 2, illustrating how the consolidation of a layer of powder is conducted. Figure 4 shows an alternative method for consolidation of a powder layer.

Figure5 shows a layer comprising several materials and microstructures, the layer being one of many that together constitute an artificial hip bone.

Figure 6 shows how several powder materials may be sequentially deposited so that they together constitute an entire powder layer. Figure 7 is an illustration of an embodiment of the entire method that is different from the embodiment of Figure 1.

Figure 1 is an illustration of the entire system or method according to the invention. Some details are, however, left out for the sake if simplicity. The following Figures show partial processes of the invention. In the following an explanation of how one layer of powder is fabricated and consolidated according to the invention is given. Cylindrical powder receptor 1 rotates clockwise with even rotational speed. Primary corona wire 2 charges powder receptor 1. This is indicated by the shown ionized gas molecules 8 attached to the surface of the powder receptor. A light emitting rod 3 illuminates the powder receptor very accurate in accordance with the geometry of the layer next to be fabricated. Light emitting rod 3 is typically a "LED printer head" type comprising many very small light emitting diodes that are arranged to illuminate the receptor with the relevant pattern from a very short distance. Thereby a difference in surface potential between illuminated and non-illuminated areas of the powder receptor is obtained. In Fig. 1 this is indicated by showing that certain gas molecules 9 that is detached from the powder receptor. When the illuminated powder receptor passes feed entry from a powder magazine 4, powder 10 will be drawn to receptor 1 in accordance with its illumination pattern. Powder that does not attach to receptor 1, falls into a tray 5 and is returned to powder magazine 4. The transporting device comprises a conveyor belt 13 arranged to gradually or stepwise to be rolled off a supply reel 14 and onto a collector reel 22. Conveyor belt 13 has a movement that is synchronized with the rotation of powder receptor 1 so that the mutual relation between the individual powder particles is maintained during deposition from powder receptor 1 to conveyor belt 13, ensuring that the pattern drawn by the particles on the cylindrical powder receptor, is drawn correspondingly on the conveyor belt's plane surface. Conveyor belt 13 is rolled off a supply reel 14. Immediately upstream of the powder receptor a preheating element 15 may be arranged in close proximity to the conveyor belt for, when activated, making the conveyor belt somewhat sticky. Under conveyor belt 13, straight under powder receptor 1, a secondary corona wire 6 is localized. This secondary corona wire 6 generates ionized gas molecules 11 at the lower surface of conveyor belt 13. The adhesion forces between gas molecules 11 and powder particles 10 are larger than the forces holding the powder particles to powder receptor 1. This way the powder pattern of powder receptor 1 is transferred to conveyor belt 13. Powder particles 12 that might remain on the receptor after having passed over conveyor belt 13 are removed with a scraper device 7 or the like. When the powder constituting a complete layer has been deposited as described above, it is transported to the sintering die for deposition and consolidation, i.e. sintering.

The conveyor belt must be appropriately rigid sp that the powder deposited thereon will not become displaced during transportation. Like a roll of film it may exhibit perforations along the sides to ensure even movement thereof. It must have such a composition that at the relevant sintering temperature or at a lower temperature, it decomposes without leaving behind harmful remains in the product. Suited materials for the conveyor belt are polyethylene and polypropylene and particularly high density variants of such materials.

To the left in Figure 1 is shown a sintering die 18-21 that is described in further detail below. Figure 1 also shows a closed metal housing 21 that envelopes the sintering die and a collector reel 22 for conveyor belt 15. Finally Figure 1 shows supporting rolls 16 that contributes to an even and accurate movement of conveyor belt 13.

Figure 2 is a schematic view illustrating the combined function of the powder magazine and a powder receptor 1. The technique is not entirely different from the one used in copiers but differences with respect to the properties of metallic particles like iron (which is magnetic) compared to toners used in copiers, obstruct a direct transfer of the technology.

The simplest form of a powder magazine to be used according to the invention has a shape like that of an hourglass, where a narrow, preferably adjustable passage leads towards the powder receptor in a way such that gravity may facilitate the transferral of the particles from the powder magazine to the powder receptor. Excess powder is collected in a tray 5 and lead back to powder magazine 4 by means of a conveyor screw 23. The distance between the feeding entry from the powder magazine and the powder receptor may have to be adjusted in accordance with the kind of particles used in each case.

Figure 3 shows how a new layer of powder comprising support particles 27 and building particles 28 is positioned accurately over an unfinished product 29. The temperature increase required for the sintering is, according to Figure 3, provided by allowing an electrical current to pass through the powder layers that is sequentially deposited on top of one another.

Pistons 18, 19 are connected to a source 32 of electrical power. Both upper 18 and lower 19 piston (also denoted "building table") have end elements 24 and 25 respectively in e.g. graphite, to avoid a direct contact between the metallic part of the pistons and the object/ the powder layers. The end elements have two functions during sintering. It has a high heat tolerance and ensures that the object does not get stuck to the pistons. In addition the end element becomes hot when the current passes through it, so that the entire powder layer is heated uniformly. When the current form power source 32 passes through the layer and sintering occurs, at least one of the pistons are allowed to move in sufficiently to maintain the pressure. Pistons in the context as used herein means primary an ordinary piston moving in a cylinder, but may also be any piston-like movable element able to set a product under manufacture in the sintering die under pressure.

The current will always take the route of least resistance. A local breakthrough of current before the layer has reached required sintering temperature will cause incomplete sintering and flaws in the object. Graphite element 24 ensures that this does not happen. The powder layer is also subjected to hot pressing from the graphite element; while at the same time heat is developed within the powder layer itself as electrons forces their way therethrough.

Support powder 27 is of a material that does not lead electrical current and/ or has a melting temperature that is substantially higher than that of the building powder. The part of product 29 that has been consolidated has a good electrical conductivity and is therefore only moderately heated. The heat development is thus concentrated to the powder layer. For electrically conductive materials sintering with current has proved to be very effective.

As also shown by Figure 3, the sintering die has inner walls 26 that define the outermost boundary of any layer. The inner walls will cause the support powder that remains a powder during the entire process, to lay steady until the product is finished, and ensure that building powder that is deposited in layers subsequently placed on top of the object is not allowed to be displaced. Lower piston 19 will gradually/ stepwise be lowered as new layers are deposited and the height of the object under manufacture correspondingly increased, so that the conveyor belt's path may remain unchanged independent of the height of the gradually growing product.

The area of the conveyor belt supporting building powder and support powder of each successive layer is enveloped in the die together with the powder. Conveyor belt 13 will normally consist of a synthetic material which, when heated, decomposes and is converted to carbon dioxide and evaporated water. The area of the conveyor belt that is enveloped in the die will thus decompose. To maintain a continuous conveyor belt, the belt must be wider than the die. Thereby the edges of the conveyor belt is unaffected of the heated/ sintering and is useful for the successive movement of the conveyor belt and the continuity of the supply of successive layers of powder. "Used" conveyor belt 13 with even holes from each sintering is rolled onto collector reel 22 and may be returned for recycling. Figure 4 shows an alternative way of performing the sintering compared to the method described with reference to Figure 3 and which is particularly relevant when building with a powder that is not electrically conductive. Microwaves have properties making them useful for sintering. Materials having low dielectric loss properties will not be heated significantly by microwaves. It is thus possible to control the heat development to the building powder in each powder layer. At their ends, pistons 18, 19 have protective coating 30 and 31 respectively which are not affected by microwaves. Die wall 26, that supports the powder sideways, is made in a corresponding material. Support powder 27 is chosen so that it is not affected by the microwaves and/ or has a significantly higher melting point than building powder 28. Microwaves have a quite limited penetration depth in solid metal. That means that the part of product 29 that is consolidated/ sintered, is not heated significantly but reflects the microwaves back to the powder layer. This effect is smaller when using ceramic materials, but the microwaves are still directed to the powder layer for a best possible heating. Several sources 20 of microwaves may be arranged around the product in order to obtain a rapid and even heating. AN example of a material suited for use in pistons and die walls for microwave sintering is aluminium oxide (A1₂0₃). Typical values for compressive strength and dielectric loss coefficient are 1720 MPa and 0.0005. Such a low loss coefficient means that the material does not become significantly heated when exposed to microwaves.

Independent of heating method and in spite of the heating principally being directed towards the last deposited powder layer, the "completed" parts f the product close to the most recently deposited powder layers are subjected to repeated cycles of heating. Investigations show that such repeated heating does not negatively affect the microstructure of the product.

The metallic part of the pistons in Figures 3 and 4 will typically be water cooled to avoid excessive heating. A metal housing 21 enveloping the die has several functions. It provides safety against squeeze hazard and high temperatures. It stops microwaves if microwaves are used for sintering. Furthermore it renders it possible to control the atmosphere (use of certain gases) in the die in order to affect the sintering process, thereby ensuring optimal properties of the finished product.

A complete layer of powder will always comprise at least one building powder and almost always a support powder. The method according the invention allows deposition of several building powders within the same layer. This in turn allows manufacture of optimal, complex products comprising various materials and structures. One example is layer (A) comprising different materials and structures of an artificial hip bone (B), as shown in Fig. 5. Base material (C) is protected by a wear resistant coating (D). Inside the hip bone there are cores (or elements) of a ductile material (E) to avoid that the bone breaks when exposed to heavy tensions. In attachment zone (F) is deposited a powder material where all particles have the same size, which ensures a porous material subsequent to consolidation and allows body tissue to grow into the artificial hip bone. This in turn ensures that the new body part remains in position and does not come lose after a while, which is a common problem with prior art hip bones. Building materials (C, D, E, F) that together constitute a layer of the hip bone, are surrounded by a support powder (G). The distribution of the various powders is made on the basis of the object geometry, function and a calculation of the strength requirements. Figure 6 shows how two powders may be deposited (sequentially) in the same layer, which is a requirement for products like the one shown in Fig. 5. By the present invention it is thus possible to build advanced objects by increasing the number of "stations" 33, 34 etc. One powder 35 (e.g. a metallic one) is deposited from a first powder receptor in a first station 33 and the layer is supplemented with a second layer 36 (e.g. a ceramic one) from a different powder receptor in a second station 34. This way different parts of any layer may be supplied with different types of building powders, where the properties of the end product as mentioned above may be thoroughly controlled.

Figure 7 shows in the same manner as Figure 1 the entire method and the entire system according the present invention. The difference between the two embodiments consists in that Fig. 7 shows a transporting device 112- 116 that is not based on a continuous conveyor belt, but rather on discrete absorption elements 112 that sequentially receive powder from powder receptor 101. Furthermore powder receptor 101 is of an alternative embodiment, having the shape of an endless belt running over two rolls or wheels, instead of (like in Fig. 1) having the shape of a cylindrical drum. When referring to powder receptor 101 below, we generally think of the belt of the powder receptor. The operation of this embodiment of the invention is explained below. Powder receptor 101 rotates counter clockwise with an even speed. Primary corona wire 2 charges powder receptor 101. Light rod 3 illuminates the powder receptor in accordance with the geometry of the powder layer to be manufactured.

When the illuminated powder receptor passes a powder magazine 4 powder particles 10 are attracted in accordance to the illumination pattern as a result of electrostatic forces. The powder receptor movement is synchronized with a transportation device comprising several absorption elements 112. Each powder layer 39 being positioned in a limited area (corresponding the die cavity) of powder receptor 101 , is accompanied by such an absorption element 112. A stationary charging element 116 is connected to an electric power source and localized in a way so that it comes into contact with each absorption element 112 when the latter passes by. An electric field is thus created between powder receptor 101 and absorption element 112, which causes the powder layer to be drawn up and temporarily attached to the lower side of absorption element 112 that priory has been provided with a wax coating 115 in a waxing station 114. Absorption element 112 with the powder layer on its lower side is transported to the die 18-21 where it is mechanically attached to the lower end of piston 18. Piston 18 is lowered until the powder layer contacts the product 129 being built (layers already sintered) and desired pressure has been obtained. The absorption element 112 is typically made of a material with high thermal conductivity and comparatively high dielectric loss coefficient (rapidly heated when microwave sources 20 are activated). An example of such a material is silicon carbide (SiC). The heat that develops in absorption element 112 is transferred to the powder so that the powder layer sinters. Any support powder present will have a significantly higher sintering temperature than the building powder, and will remain a powder. A preheating of the absorption element may be performed by activating the microwave sources as soon as the lower part of piston 18 is within metal housing 21. The preheating must not be excessive in order not to affect wax layer 115 negatively. During sintering the pressure is held constant by a required movement of at least one piston as described with reference to Fig. 3 above.

When the powder has sintered and become part of the object, piston 18 is raised. Absorption element 112 is released from the piston and lead to a cleaning and cooling station 113. Any remains of powder are removed and then absorption element 112 is allowed to slide along a cooling element of station 113. Absoφtion element 112 moves on to a waxing station 114 where it receives a new layer of sintering friendly wax 115. The wax ensures that powder particles cannot recombine electrically subsequent to being drawn to absoφtion element 112, which would cause them to fall off. The mechanism for movement of absoφtion element 112 in the closed loop preferably includes a magazine, so that a new layer of powder is drawn from the powder receptor belt simultaneously with the sintering of the previous layer. The mechanism for moving absoφtion element 112 in the closed loop is not crucial, as long as it does not negatively affect the properties mentioned or described above. It is preferred that the system is largely automated or allows being automated and that is versatile so that each of the absoφtion elements 112 may be moved independently of each other. Areas of powder receptor 101 (the belt) that have been coated with powder particles must be discharged and cleaned before new layers of powder may be drawn up from powder magazine 4. The discharging is conducted with a secondary corona wire 106 being connected to a source of alternating current. This is a technique also used in copiers. Powder receptor 101 is then cleaned with a scraper device 107.

To drawn different powder materials to the same layer, a plurality of powder receptors are arranged side by side. Each powder receptor has its own powder magazine. Absoφtion element 112 is moved over more than one powder receptor and picks up the different powder particles sequentially. Powder particles from different powder magazines may be combined prior to being drawn to a powder receptor in order to make a particular alloy or microstructure in the product being built, as explained with reference to Figures 5 and 6.

Sintering initiated by electricity requires absoφtion elements 112 and an end piece of lower piston 19 being made in a material with a certain electrical conductivity (for e.g. graphite), cf. discussion with reference to Fig. 3 above.

A further possible variant (not shown) which is independent of the transportation device is to combine different powders in one and the same powder receptor. In such a case powder magazines (two or more) containing separate powders and having separate feeding funnels with a control mechanism that allows a continuous control of the amount of powder supplied to the electrically charged and illuminated powder receptor. This way the mixture ratio between the different building po ders may be gradually changed and/ or changed individually for each separate layer of the product. Within each layer the powder combination will be uniform unless the latter technique is used in combination with the technique discussed with reference to Fig. 6 above. In practice the manufacturing process based on the present invention will be controlled by a computer processor principally the same way as any other CAD/ CAM production. That means that a processor with relevant connections to a powder magazine, powder receptor, light rod, transportation device and die etc., controls all these units step by step, layer by layer in accordance with a 3-D model of the product. The processor also needs information about production parameters like building materials, sintering temperatures, power requirements, distances, speeds etc. The adaptation of the relevant information (software) to the application in question is one which may be performed by the skilled artisan and dies not constitute part of the present invention.

Claims

1. Method fro rapid manufacturing of metal, ceramic or metal-ceramic products from powder of relevant material(s), hereinafter called building powder, characterized by a layer by layer deposition and sintering of the building powder in a sintering die, comprising the following steps: i) for each layer building powder is supplied from a powder magazine to at least one powder receptor that is electrically charged by a charge element illuminated with a light source in a pattern describing the shape of the layer in question, ii) each layer of the building powders is deposited from the powder receptor(s) onto a part of a transporting device which has a dimension adapted to the cavity of the sintering die, iii) to any area of the said transporting device, corresponding to the internal area of the sintering die, that is not covered by building powder for the layer in question, a support powder in a material that does not sinter or melt at the relevant temperature is deposited from a separate powder receptor that is electrically charged and illuminated as described in step i), iv) the transportation device transports each complete layer of building powder and support powder to an exact position on top of any previously deposited and sintered layers in the sintering die, v) the sintering die is closed and the powder set under pressure by means of at least one moveable piston, while the temperature at least in and near the most recent deposited layer is raised so that the building powder is sintered, and vi) subsequent to the depositing and sintering of the last layer, the product is removed from the sintering die and the support powder is removed.

2. Method as claimed in claim 1, characterized in that as charge element of step i) is used a corona wire.

3. Method as claimed in claim 1, characterized in that combinations of different types of building powder are supplied from two or more powder magazines to one and the same powder receptor.

4. Method as claimed in claim 3, characterized in that the mixture ratio of the different types of building powder is adjusted individually for each layer, preferably by means of a computer.

5. Method as claimed in claim 1, characterized in that any excess of building powder supplied from the powder receptor in step i) is returned to the powder magazine from which it was supplied.

6. Method as claimed in claim 1, characterized in that any excess support powder supplied to the powder receptor in step iii) is returned to the powder magazine from which it was supplied.

7. Method as claimed in claim 1, characterized in that the light source illuminating the powder receptor in step i) is a LED type light source.

8. Method as claimed in claim 1, characterized in that the temperature of the most recently deposited layer in the sintering die is raised by means of microwaves.

9. Method as claimed in claim 1, characterized in that the temperature of the most recently deposited layer in the sintering die is raised by directing an electric current through the layer, preferably by establishing an electrical voltage between a movable piston and another electrically conductive element in the die, like another movable piston.

10. Method as claimed in claim 1, characterized in using a sintering die that substantially comprises a lower part that rests on a vertically movable piston and an upper part that is movable by means of a vertically moveable piston and that the pressure in the sintering die is controlled by the force supplied to said pistons.

11. Method as claimed in claim 10, characterized in that the lower movable piston is positioned with a step motor that for each deposited and sintered layer is lowered in correspondence with the layer thickness.

12. Method as claimed in claim 1, characterized in that the parts of the sintering die which is contacted by the building powder are made in a material that does not stick to the building powder.

13. Method as claimed in claim 1, characterized in that the support powder that is removed from the finished product according to step vi) is returned to the powder magazine from which it was supplied.

14. Method as claimed in claim 1, characterized in that the part of the transportation device mentioned in step ii) and iii) on which the support powder is deposited, is one of a plurality of absoφtion elements that run in a closed loop from the powder receptor to the sintering die and during sintering according to step v) is enveloped in the die and after sintering is moved on to a cleaning and cooling station and from there to a waxing station, before returning to the powder receptor.

15. Method as claimed in claim 14, characterized in that each of the absoφtion elements during sintering is attached to the end of a movable piston within the die.

16. Method as claimed in claim 14, characterized in that the lower side of each absoφtion element is coated with a sintering friendly wax before being returned to the powder receptor.

17. Method as claimed in claim 1, characterized in that the part of the transportation on which the building powder and the support powder are deposited according to step ii) and iii), is constituted of an area of a conveyor belt with a width larger than the width of the die cavity, and that the same area of the conveyor belt in step v) is enveloped by the die and decomposed when the building powder is sintered.

18. Method as claimed in claim 17, characterized in that the conveyor belt is made of a synthetic material with low elasticity, preferably based on polyethylene or polypropylene.

19. Method as claimed in claim 17, characterized in that the conveyor belt is preheated prior to the deposition of powder thereon.

20. Method as claimed in claim 17, characterized in that the conveyor belt is advanced by means of at least one step motor controlled by a computer.

21. Apparatus for rapid manufacturing of metal, ceramic and metal-ceramic products from a powder of the relevant material(s), hereinafter called building powder, characterized in that it comprises at least the following elements: i) at least one powder receptor (1, 101) for a building powder, said powder receptor being based on the same operational principle as a photoreceptor of a copier, ii) at least one charging element (2) arranged to charge powder receptor (1, 101), iii) at least one light source (3) arranged to illuminate powder receptor (1, 101) with a pattern corresponding to the shape of the product layer in question, iv) at least one powder magazine (4) arranged to supply powder to powder receptor (1 , 101) subsequent to the powder receptor has been charged by charging element (2) and illuminated by light source (3), v) at least one charging element (6, 106) arranged to facilitate the transfeπ-al of powder from powder receptor

(1, 101) to a transportation device (13, 112-116), vi) a transportation device (13, 112-116) arranged to receive powder (10) in a predetermined pattern from powder receptor (1, 101) and to transport such powder with a high degree of accuracy to a sintering die, vii) a sintering die (18-21) arranged to receive powder layer (17) from the transportation device (13), envelope said powder layer in contact with the product being built and raise pressure and temperature in said layer so that sinterable parts of the powder sinters to and becomes an integral part of the product being built, and viii) computer hardware and software for by means of per se known principles, controlling the individual elements i) - vii) of the device in accordance with a 3-D product drawing.

22. Apparatus as claimed in claim 21, characterized in that each of the charging elements (2, 6, 106) is a corona wire.

23. Apparatus as claimed in claim 21, characterized in that it comprises two or more powder magazines (4) for the supply of different types of building powder to one and the same powder receptor (1, 101).

24. Apparatus as claimed in claim 21, characterized in that the apparatus is provided with means to recycle excess building powder and support powder to the magazines from which they are supplied.

25. Apparatus as claimed in claim 21, characterized in that light source (3) illuminating the powder receptor according to step iii) is a LED type light source.

26. Apparatus as claimed in claim 21, characterized in that said sintering die (18-21) comprises a microwave generator to raise the temperature of the powder supplied to the die.

27. Apparatus as claimed in claim 21, characterized in that sintering die (18-21) comprises means to establish an electric voltage over the powder supplied to the die for thereby raising its temperature.

28. Apparatus as claimed in claim 21, characterized in that sintering die comprises a lower part supported by a vertically movable lower piston φ) and an upper part which is movable by means of a vertically movable upper piston (18) and that the pressure in the sintering die is controlled by the force being supplied to the pistons.

29. Apparatus as claimed in claim 28, characterized in that lower piston (19) is arranged to be gradually lowered by a step motor (no"t t shown) in steps corresponding to the thickness of each powder layer, as the product is successively growing.

30. Apparatus as claimed in claim 21, characterized in that the parts of sintering die (18-21) that are contacted by the building powder are made in a material that does not stick to the building powder or provided with a coating of such material.

31. Apparatus as claimed in claim 21, characterized in that transportation device mentioned in steps v) and vi) comprises a plurality of absoφtion elements (112) that are arranged to move in a separate loop from powder receptor (101) to sintering die (18-21), from sintering die (18-21) to a cleaning and cooling station (113), from cleaning and cooling station (113) to a waxing station (114) and from waxing station (114) back to powder receptor (101) where it passes a charging element (116).

32. Apparatus as claimed in claim 21, characterized in that transportation device mentioned in steps v) and vi) comprises a conveyor belt (13) arranged to in an area at powder receptor (1) to be charged by secondary charging element (6) thereby receiving from powder receptor (1) a layer of powder, while conveyor belt (13) subsequent to having received a layer of powder is arranged to be advanced to a position wherein the layer may be enveloped in sintering die (18-21).

33. Apparatus as claimed in claim 32, characterized in that conveyor belt (13) is made in a synthetic material with low elasticity, preferably based on polyethylene or polypropylene.

34. Apparatus as claimed in claim 32, characterized in that it comprises a step motor (not shown) for accurate advancement of conveyor belt (13).

35. Apparatus as claimed in claim 32, characterized in that the step motor is arranged to be controlled by a computer.