Method of producing a multilayer body by coalescence and the multi-layer body produced

Abstract

A method of producing a multilayer body by coalescence, characterised in that the method comprises the steps of a) filling, a pre-compacting mould with a start material in the form of powder, pellets, grains and the like, b) pre-compacting the start material at least once and c) compressing the material in a compression mould by at least one stroke, where a striking unit emits enough kinetic energy to form the body when striking the material inserted in the compression mould, causing coalescence of the material, d) at least one further material being inserted into the mould in the form of powder, pellets, grains and the like, either in step a), after compacting in step b) or after compressing the first material in step c), e) if necessary, further pre-compacting and/or compressing being performed after the insertion of the at least one further material.

Description

[0001] The invention concerns a method of producing a multilayer body by coalescence as well as the multilayer body produced by this method.

STATE OF THE ART

[0002] In WO-A1-9700751, an impact machine and a method of cutting rods with the machine is described. The document also describes a method of deforming a metal body. The method utilises the machine described in the document and is characterised in that a metallic material either in solid form or in the form of powder such as grains, pellets and the like, is fixed preferably at the end of a mould, holder or the like and that the material is subjected to adiabatic coalescence by a striking unit such as an impact ram, the motion of the ram being effected by a liquid. The machine is thoroughly described in the WO document.

[0003] In WO-A1-9700751, shaping of components, such as spheres, is described. A metal powder is supplied to a tool divided in two parts, and the powder is supplied through a connecting tube. The metal powder has preferably been gas-atomized. A rod passing through the connecting tube is subjected to impact from the percussion machine in order to influence the material enclosed in the spherical mould. However, it is not shown in any embodiment specifing parameters for how a body is produced according to this method.

[0004] The compacting according to this document is performed in several steps, e.g. three. These steps are performed very quickly and the three strokes are performed as described below.

[0005] Stroke 1: an extremely light stroke, which forces out most of the air from the powder and orients the powder particles to ensure that there are no great irregularities.

[0006] Stroke 2: a stroke with very high energy density and high impact velocity, for local adiabatic coalescence of the powder particles so that they are compressed against each other to extremely high density. The local temperature increase of each particle is dependent on the degree of deformation during the stroke.

[0007] Stroke 3: a stroke with medium-high energy and with high contact energy for final shaping of the substantially compact material body. The compacted body can thereafter be sintered.

[0008] In SE 9803956-3 a method and a device for deformation of a material body are described. This is substantially a development of the invention described in WO-A1-9700751. In the method according to the Swedish application, the striking unit is brought to the material by such a velocity that at least one rebounding blow of the striking unit is generated, wherein the rebounding blow is counteracted whereby at least one further stroke of the striking unit is generated.

[0009] The strokes according to the method in the WO document, give a locally very high temperature increase in the material, which can lead to phase changes in the material during the heating or cooling. When using the counteracting of the rebounding blows and when at least one further stroke is generated, this stroke contributes to the wave going back and forth and being generated by the kinetic energy of the first stroke, proceeding during a longer period. This leads to further deformation of the material and with a lower impulse than would have been necessary without the counteracting. It has now shown that the machine according to these mentioned documents does not work so well. For example are the time intervals between the strokes, which they mention, not possible to obtain. Further, the document does not comprise any embodiments showing that a body can be formed.

OBJECT OF THE INVENTION

[0010] The object of the present invention is to achieve a process for efficient production of multilayer products at a low cost. These products may be both medical devices such as medical implants or bone cement in orthopaedic surgery, instruments or diagnostic equipment, or non medical devices such as tools, insulator applications, crucibles, spray nozzles, tubes, cutting edges, jointing rings, ball bearings and engine parts. Another object is to achieve a multilayer product of the described type.

[0011] The term multilayer is used here to define a product composed of different parts integrally joined to each other. These parts may be in the form of flat layers or have any other suitable form provided that the form of the different parts fit closely together. One part may have a convex surface fitting around a concave surface on another part. Examples of different multilayer products are shown in FIGS. 2a-2f. The different parts may be made of the same type of material or of different types of material. It is possible to combine a ceramic material with a layer of a polymeric material. It is also possible to have a multilayer product with layers or parts of different polymers.

[0012] It should also be possible to perform the new process at a much lower velocity than the processes described in the above documents. Further, the process should not be limited to using the above described machine.

SHORT DESCRIPTION OF THE INVENTION

[0013] It has surprisingly been found that it is possible to compress different multilayer products according to the new method defined in claim 1. The material to be compressed is for example in the form of powder, pellets, grains and the like and is filled in a mould, pre-compacted and compressed by at least one stroke. The machine to use in the method may be the one described in WO-A1-9700751 and SE 9803956-3.

[0014] The method according to the invention utilises hydraulics in the percussion machine, which may be the machine utilised in WO-A1-9700751 and SE 9803956-3. When using pure hydraulic means in the machine, the striking unit can be given such movement that, upon impact with the material to be compressed, it emits sufficient energy at sufficient speed for coalescence to be achieved. This coalescence may be adiabatic. A stroke is carried out quickly and for some materials the wave in the material decay in between 5 and 15 milliseconds. The hydraulic use also gives a better sequence control and lower running costs compared to the use of compressed air. A spring-actuated percussion machine will be more complicated to use and will give rise to long setting times and poor flexibility when integrating it with other machines. The method according to the invention will thus be less expensive and easier to carry out. The optimal machine has a large press for pre-compacting and post-compacting and a small striking unit with high speed. Machines according to such a construction are therefore probably more interesting to use. Different machines could also be used, one for the pre-compacting and post-compacting and one for the compression.

SHORT DESCRIPTION OF THE DRAWINGS

[0015] On the enclosed drawings

[0016] FIG. 1 shows a cross sectional view of a device for deformation of a material in the form of a powder, pellets, grains and the like,

[0017] FIGS. 2a-2f shows the forming of different types of multilayer products and

[0018] FIGS. 3-4 are diagrams showing results obtained in the embodiments described in the examples.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The invention concerns a method of producing a multilayer body by coalescence, wherein the method comprises the steps of

[0020] a) filling a pre-compacting mould with a start material in the form of powder, pellets, grains and the like,

[0021] b) pre-compacting the material at least once and

[0022] c) compressing the material in a compression mould by at least one stroke, where a striking unit emits enough kinetic energy to form the body when striking the material inserted in the compression mould, causing coalescence of the material,

[0023] d) at least one further material being inserted into the mould in the form of powder, pellets, grains and the like, either in step a), after compacting in step b) or after compressing the start material in step c),

[0024] e) if necessary, further pre-compacting and/or compressing being performed after the insertion of the at least one further material.

[0025] The pre-compacting mould may be the same as the compression mould, which means that the material does not have to be moved between the step b) and c). It is also possible to use different moulds and move the material between the steps b) and c) from the pre-compacting mould to the compression mould. This could only be done if a body is formed of the material in the pre-compacting step.

[0026] According to one embodiment the first material is only pre-compacted before the insertion of the second material. Thereafter, a second pre-compaction is performed and the multilayer material is struck with at least one stroke to achieve coalescence and form an integral product. It is also possible to insert the further material or materials in powder form before the pre-compaction or the first or start material. All materials will be compacted and struck together in this case.

[0027] According to another embodiment the first and second materials are inserted in powder form beside each other or as layers above each other, whereafter pre-compaction and striking are performed.

[0028] According to a third embodiment the first material is pre-compacted and struck to make a coalescent element, whereafter this element is placed in a second mould on top of a powder of the second material or surrounded by the second material. The first element together with the second material are pre-compacted and struck with a coalescing stroke.

[0029] In the description below any step described may refer to a process performed on one layer or element of the multilayer product or on several layers or elements together.

[0030] The device in FIG. 1 comprises a striking unit 2. The material in FIG. 1 is in the form of powder, pellets, grains or the like. The device is arranged with a striking unit 3, which with a powerful impact may achieve an immediate and relatively large deformation of the material body 1. The invention also refers to compression of a body, which will be described below. In such a case, a solid body 1, such as a solid homogeneous multilayer body, would be placed in a mould.

[0031] The striking unit 2 is so arranged, that, under influence of the gravitation force, which acts thereon, it accelerates against the material 1. The mass m of the striking unit 2 is preferably essentially larger than the mass of the material 1. By that, the need of a high impact velocity of the striking unit 2 can be reduced somewhat. The striking unit 2 is allowed to hit the material 1, and the striking unit 2 emits enough kinetic energy to compress and form the body when striking the material in the compression mould. This causes a local coalescence and thereby a consequent deformation of the material 1 is achieved. The deformation of the material 1 is plastic and consequently permanent. Waves or vibrations are generated in the material 1 in the direction of the impact direction of the striking unit 2. These waves or vibrations have high kinetic energy and will activate slip planes in the material and also cause relative displacement of the grains of the powder. It is possible that the coalescence may be an adiabatic coalescence. The local increase in temperature develops spot welding (inter-particular melting) in the material which increases the density.

[0032] The pre-compaction is a very important step. This is done in order to drive out air and orient the particles in the material. The pre-compaction step is much slower than the compression step, and therefore it is easier to drive out the air. The compression step, which is done very quickly, may not have the same possibility to drive out air. In such case, the air may be enclosed in the produced body, which is a disadvantage. The pre-compaction is performed at a minimum pressure enough to obtain a maximum degree of packing of the particles which results in a maximum contact surface between the particles. This is material dependent and depends on the softness and melting point of the material.

[0033] The pre-compacting step in the Examples has been performed by compacting with an axial load of about 117680 N. This is done in the pre-compacting mould or the final mould. According to the examples in this description, this has been done in a cylindrical mould, which is a part of the tool, and has a circular cross section with a diameter of 30 mm, and the area of this cross section is about 7 cm2. This means that a pressure of about 1.7×108 N/m2 has been used. For hydroxyapatite the material may be pre-compacted with a pressure of at least about 0.25×108 N/m2, and preferably with a pressure of at least about 0.6×108 N/m2. The necessary or preferred pre-compaction pressure to be used is material dependent and for a softer multilayer it could be enough to compact at a pressure of about 0.2×108 N/m2. Other possible values are 1.0×108 N/m2, 1.5×108 N/m2. The studies made in this application are made in air and at room temperature. All values obtained in the studies are thus achieved in air and room temperature. It may be possible to use lower pressures if vacuum or heated material is used. The height of the cylinder is 60 mm. In the claims is referred to a striking area and this area is the area of the circular cross section of the striking unit which acts on the material in the mould. The striking area in this case is the cross section area.

[0034] In the claims it is also referred to the cylindrical mould used in the Examples. In this mould the area of the striking area and the area of the cross section of the cylindrical mould are the same. However, other constructions of the moulds could be used, such as a spherical mould. In such a mould, the striking area would be less than the cross section of the spherical mould.

[0035] The invention further comprises a method of producing a multilayer body by coalescence, wherein the method comprises compressing a solid body of a first or start material (i.e. a body where the target density for specific applications has been achieved) together with at least one further material in the form of powder or in the form of a solid body in a compression mould by at least one stroke, where a striking unit emits enough energy to cause coalescence of the material in the body. Slip planes are activated during a large local temperature increase in the material, whereby the deformation is achieved. The method also comprises deforming the body.

[0036] The method according to the invention could be described in the following way. 1) Powder is pressed to a green body, the body is compressed by impact to a (semi)solid body and thereafter an energy retention may be achieved in the body by a post-compacting. The process, which could be described as Dynamic Forging Impact Energy Retention (DFIER) involves three mains steps.

[0037] a)Pressuring

[0038] The pressing step is very much like cold and hot pressing. The intention is to get a green body from powder. It has turned out to be most beneficial to perform two compactions of the powder. One compaction alone gives about 2-3% lower density than two consecutive compactions of the powder. This step is the preparation of the powder by evacuation of the air and orientation of the powder particles in a beneficial way. The density values of the green body is more or less the same as for normal cold and hot pressuring.

[0039] b)Impact

[0040] The impact step is the actual high-speed step, where a striking unit strikes the powder with a defined area. A material wave starts off in the powder and interparticular melting takes place between the powder particles. Velocity of the striking unit seems to have an important role only during a very short time initially. The mass of the powder and the properties of the material decides the extent of the interparticular melting taking place.

[0041] c)Energy Retention

[0042] d)

[0043] The energy retention step aims at keeping the delivered energy inside the solid body produced. It is physically a compaction with at least the same pressure as the pre-compaction of the powder. The result is an increase of the density of the produced body by about 1-2%. It is performed by letting the striking unit stay in place on the solid body after the impact and press with at least the same pressure as at pre-compaction, or release after the impact step. The idea is that more transformations of the powder will take place in the produced body.

[0044] According to the method, the compression strokes emit a total energy corresponding to at least 100 Nm in a cylindrical tool having a striking area of 7 cm2 in air and at room temperature. Other total energy levels may be at least 300, 600, 1000, 1500, 2000, 2500, 3000 and 3500 Nm. Energy levels of at least 10 000, 20 000 Nm may also be used. There is a new machine, which has the capacity to strike with 60 000 Nm in one stroke. Of course such high values may also be used. And if several such strikes are used, the total amount of energy may reach several 100 000 Nm. The energy levels depend on the material used, and in which application the body produced will be used. Different energy levels for one material will give different relative densities of the material body. The higher energy level, the more dense material will be obtained. Different materials will need different energy levels to get the same density. This depends on for example the hardness of the material and the melting point of the material.

[0045] According to the method, the compression strokes emit an energy per mass corresponding to at least 5 Nm/g in a cylindrical tool having a striking area of 7 cm2 in air and at room temperature. Other energies per mass may be at least 20 Nm/g, 50 Nm/g, 100 Nm/g, 150 Nm/g, 200 Nm/g, 250 Nm/g, 350 Nm/g and 450 Nm/g.

[0046] There may be a linear relationship between the mass of the sample and the energy needed to achieve a certain relative density. However, for some materials the relative density may be a function of the total impact energy.

[0047] These values will vary dependent on what material is used. A person skilled in the art will be able to test at what values the mass dependency will be valid and when there may be a mass independence.

[0048] The energy level needs to be amended and adapted to the form and construction of the mould. If for example, the mould is spherical, another energy level will be needed. A person skilled in the art will be able to test what energy level is needed with a special form, with the help and direction of the values given above. The energy level depends on what the body will be used for, i.e. which relative density is desired, the geometry of the mould and the properties of the material. The striking unit must emit enough kinetic energy to form a body when striking the material inserted in the compression mould. With a higher velocity of the stroke, more vibrations, increased friction between particles,. increased local heat, and increased interparticular melting of the material will be achieved. The bigger the stroke area is, the more vibrations are achieved. There is a limit where more energy will be delivered to the tool than to the material. Therefore, there is also an optimum for the height of the material.

[0049] When powders for a multilayer product are inserted in a mould and the materials are struck by a striking unit, a coalescence is achieved in the powder material and the material will float. A probable explanation is that the coalescence in the material arises from waves being generated back and forth at the moment when the striking unit rebounds from the material body or the material in the mould. These waves give rise to a kinetic energy in the material body. Due to the transmitted energy a local increase in temperature occurs, and enables the particles to soften, deform and the surface of the particles will melt. The inter-particular melting enables the particles to re-solidify together and dense material can be obtained. This also affects the smoothness of the body surface. The more a material is compressed by the coalescence technique, the smoother surface is obtained. The porosity of the material and the surface is also affected by the method. If a porous surface or body is desired, the material should not be compressed as much as if a less porous surface or body is desired.

[0050] The individual strokes affect material orientation, driving out air, pre-moulding, coalescence, tool filling and final calibration. It has been noted that the back and forth going waves travels essentially in the stroke direction of the striking unit, i. e. from the surface of the material body which is hit by the striking unit to the surface which is placed against the bottom of the mould and then back.

[0051] What has been described above about the energy transformation and wave generation also refer to a solid body. In the present invention a solid body is a body where the target density for specific applications has been achieved.

[0052] The striking unit preferably has a velocity of at least 0.1 m/s or at least 1.5 m/s during the stroke in order to give the impact the required energy level. Much lower velocities may be used than according to the technique in the prior art. The velocity depends on the weight of the striking unit and what energy is desired. The total energy level in the compression step is at least about 100 to 4000 Nm. But much higher energy levels may be used. By total energy is meant the energy level for all strokes added together. The striking unit makes at least one stroke or a number of consecutive strokes. The interval between the strokes according to the Examples was 0.4 and 0.8 seconds. For example at least two strikes may be used. According to the Examples one stroke has shown promising results. These Examples were performed in air and at room temperature. If for example vacuum and heat or some other improving treating is used, perhaps even lower energies may be used to obtain good relative densities.

[0053] The multilayer product may be compressed to a relative density of 60%, preferably 65%. More preferred relative densities are also 70% and 75%. Other preferred densities are 80 and 85%. Densities of at least 90 and up to 100% are especially preferred. However, other relative densities are also possible. If a green body is to be produced, it may be enough with a relative density of about 40-60%. Load bearing implants need a relative density of 90 to 100% and in some biomaterials it is good with some porosity. If a porosity of at most 5% is obtained and this is sufficient for the use, no further post-processing is necessary. This may be the choice for certain applications. If a relative density of less than 95% is obtained, and this is not enough, the process need to continue with further processing such as sintering. Several manufacturing steps have even in this case been cut compared to conventional manufacturing methods.

[0054] The method also comprises pre-compacting the material at least twice. It has been shown that this could be advantageous in order to get a high relative density compared to strokes used with the same total energy and only one pre-compacting. Two compactions may give about 1-5% higher density than one compacting depending on the material used. The increase may be even higher for some materials. When pre-compacting twice, the compacting steps are performed with a small interval between, such as about 5 seconds. About the same pressure may be used in the second pre-compacting.

[0055] Further, the method may also comprise a step of compacting the material at least once after the compression step. This has also been shown to give very good results. The post-compacting should be carried out at at least the same pressure as the pre-compacting pressure, i.e. 0,25×108 N/m2. Other possible values are 1.0×108 N/m2. Higher post-compacting pressures may also be desired, such as a pressure which is twice the pressure of the pre-compacting pressure. For hydroxyapatite the pre-compacting pressure should be at least about 0.25×108 N/m2 and this would be the lowest possible post-compacting pressure for hydroxyapatite. The pre-compacting value has to be tested out for every material. A post-compacting effects the sample differently than a pre-compacting. The transmitted energy, which increases the local temperature between the powder particles from the stroke, is conserved for a longer time and can effect the sample to consolidate for a longer period after the stroke. The energy is kept inside the solid body produced. Probably the “lifetime” for the material wave in the sample increases and it can affect the sample for a longer period and more particles can melt together. The after compaction or post-compaction is performed by letting the striking unit stay in place on the solid body after the impact and press with at least the same pressure as at pre-compacting, i.e. at least about 0.25×108 N/m2 hydroxyapatite. More transformations of the powder will take place in the produced body. The result is an increase of the density of the produced body by about 1-4%. Also this possible increase is material dependent. When using pre-compacting and/or after compacting, it could be possible to use lighter strokes and higher pre- and/or after compacting, which would lead to saving of the tools, since lower energy levels could be used. This depends on the intended use and what material is used. It could also be a way to get a higher relative density.

[0056] To get improved relative density it is also possible to pre-process the material before the process. The powder could be pre-heated to e.g. ˜200-300° C. or higher depending on what material type to pre-heat. The powder could be pre-heated to a temperature which is close to the melting temperature of the material. Suitable ways of pre-heating may be used, such as normal heating of the powder in an oven. In order to get a more dense material during the pre-compacting step vacuum or inert gas could be used. This would have the effect that air is not enclosed in the material to the same extent during the process.

[0057] The body may according to another embodiment of the invention be heated and/or sintered any time after compression or post-compacting. A post-heating is used to relax the bindings in the material (obtained by increased binding strain). A lower sintering temperature may be used owing to the fact that the compacted body has a higher density than compacts obtained by other types of powder compression. This is an advantage as a higher temperature may cause decomposition or transformation of the constituting material. The produced body may also be post-processed in some other way, such as by HIP (Hot Isostatic Pressing).

[0058] Further, the body produced may be a green body and the method may also comprise a further step of sintering the green body. The green body of the invention gives a coherent integral body even without use of any additives. Thus, the green body may be stored and handled and also worked, for instance polished or cut. It may also be possible to use the green body as a finished product, without any intervening sintering. This is the case when the body is a bone implant or replacement where the implant is to be resorbed in the bone.

[0059] Before processing the materials for the multilayer product could be homogenously mixed with additives. Predrying of the granulate could also be used to decrease the water content of the raw material. Some multilayers do not absorb humidity, while other multilayers easily absorb humidity which can disturb the processing of the material, and decrease the homogeneity of the worked material because a high humidity rate can raise steam bubbles in the material.

[0060] The multilayer materials may be chosen from the group comprising a metallic, polymeric or ceramic materials such as stainless steel, aluminium alloy, titanium, UHMWPE, PMMA, PEEK, rubber, alumina, zirconia, silicon carbide, hydroxyapatite or silicon nitride. The multilayer may comprise a composite material containing reinforcements fibres or powders from the group comprising carbon, metals, glass or ceramics such as alumina, silica, silicon nitride, zirconia, silicon carbide.

[0061] The compression strokes need to emit a total energy corresponding to at least 100 Nm in a cylindrical tool having a striking area of 7 cm2 for multilayer products or layers. The compression strokes need to emit an energy per mass corresponding to at least 5 Nm/g in a cylindrical tool having a striking area of 7 cm2 for multilayer products.

[0062] It has been shown earlier that better results have been obtained with particles having irregular particle morphology. The particle size distribution should probably be wide. Small particles could fill up the empty space between big particles.

[0063] The first or second material may comprise a lubricant and/or a sintering aid. A lubricant may be useful to mix with the material. Sometimes the material needs a lubricant in the mould, in order to easily remove the body. In certain cases this could be a choice if a lubricant is used in the material, since this also makes it easier to remove the body from the mould.

[0064] A lubricant cools, takes up space and lubricates the material particles. This is both negative and positive.

[0065] Interior lubrication is good, because the particles will then slip in place more easily and thereby compact the body to a higher degree. It is good for pure compaction. Interior lubrication decreases the friction between the particles, thereby emitting less energy, and the result is less inter-particular melting. It is not good for compression to achieve a high density, and the lubricant must be removed for example with sintering.

[0066] Exterior lubrication increases the amount of energy delivered to the material and thereby indirectly diminishes the load on the tool. The result is more vibrations in the material, increased energy and a greater degree of inter-particular melting. Less material sticks to the mould and the body is easier to extrude. It is good for both compaction and compression.

[0067] An example of a lubricant is Acrawax C, but other conventional lubricants may be used. If the material will be used in a medical body, the lubricant need to be medically acceptable, or it should be removed in some way during the process.

[0068] Polishing and cleaning of the tool may be avoided if the tool is lubricated and if the powder is preheated.

[0069] A sintering aid may also be included in the material. The sintering aid may be useful in a later processing step, such as a sintering step. However, the sintering aid is in some cases not so useful during the method embodiment, which does not include a sintering step. The sintering aid may be yttrium oxide, alumina or magnesia or some other conventional sintering aid. It should, as the lubricant, also be medically acceptable or removed, if used in a medical body.

[0070] In some cases, it may be useful to use both a lubricant and a sintering aid. This depends on the process used, the material used and the intended use of the body which is produced.

[0071] In some cases it may be necessary to use a lubricant in the mould in order to remove the body easily. It is also possible to use a coating in the mould. The coating may be made of for example TiNAl or Balinit Hardlube. If the tool has an optimal coating no material will stick to the tool parts and consume part of the delivered energy, which increase the energy delivered to the powder. No time-consuming lubricating would be necessary in cases where it is difficult to remove the formed body.

[0072] A very dense material, and depending on the material, a hard material will be achieved, when the multilayer material is produced by coalescence. The surface of the material will be very smooth, which is important in several applications.

[0073] If several strokes are used, they may be executed continually or various intervals may be inserted between the strokes, thereby offering wide variation with regard to the strokes.

[0074] For example, one to about six strokes may be used. The energy level could be the same for all strokes, the energy could be increasing or decreasing. Stroke series may start with at least two strokes with the same level and the last stroke has the double energy. The opposite could also be used.

[0075] The highest density is often obtained by delivering a total energy with one stroke. If the total energy instead is delivered by several strokes a lower relative density may be obtained, but the tool is saved. A multi-stroke can therefore be used for applications where a maximum relative density is not necessary.

[0076] Through a series of quick impacts a material body is supplied continually with kinetic energy which contributes to keep the back and forth going wave alive. This supports generation of further deformation of the material at the same time as a new impact generates a further plastic, permanent deformation of the material.

[0077] According to another embodiment of the invention, the impulse, with which the striking unit hits the material body, decreases for each stroke in a series of strokes. Preferably the difference is large between the first and second stroke. It will also be easier to achieve a second stroke with smaller impulse than the first impulse during such a short period (preferably approximately 1 ms), for example by an effective reduction of the rebounding blow. It is however possible to apply a larger impulse than the first or preceding stroke, if required.

[0078] According to the invention, many variants of impacting are possible to use. It is not necessary to use the counteracting of the striking unit in order to use a smaller impulse in the following strokes. Other variations may be used, for example where the impulse is increasing in following strokes, or only one stroke with a high or low impact. Several different series of impacts may be used, with different time intervals between the impacts.

[0079] A multilayer body produced by the method of the invention, may be used in medical devices such as medical implants or bone cement in orthopaedic surgery, instruments or diagnostic equipment. Such implants may be for examples skeletal or tooth prostheses.

[0080] According to an embodiment of the invention, the material is medically acceptable. Such materials are for example suitable multilayer products containing an element or layer of hydroxyapatite or zirconia.

[0081] A material to be used in implants needs to be biocompatible and haemocoinpatible as well as mechanically durable, such as hydroxyapatite and zirconia or other suitable multilayer materials.

[0082] The body produced by the process of the present invention may also be a non medical product such as cutting tools, insulator applications, crucibles, spray nozzles, tubes, cutting edges, jointing rings, ball bearings and engine parts.

[0083] Here follows several applications for some of the materials which may be used in the present multilayer products. Applications for silicon nitride are crucibles, spray nozzles, tubes, cutting edges, jointing rings, ball bearings and engine parts. Alumina is a good electrical insulator and has at the same time an acceptable thermal conductivity and is therefore used for producing substrates where electrical components are mounted, insulation for ignition plugs and insulation in the high-tension areas. Alumina is also a common material type in orthopaedic implants, e.g. femoral-head in hip prostheses. Hydroxyapatite is one of the most important biomaterials extensively used in orthopaedic surgery. Common applications for zirconia are cutting tools, components for adiabatic engines and it is also a common material type in orthopaedic implants, e.g. femoral-head in hip prostheses. The invention thus has a big application area for producing products according to the invention.

[0084] When the material inserted in the mould is exposed to the coalescence, a hard, smooth and dense surface is achieved on the body formed. This is an important feature of the body. A hard surface gives the body excellent mechanical properties such as high abrasion resistance and scratch resistance. The smooth and dense surface makes the material resistant to for example corrosion. The less pores, the larger strength is obtained in the product; This refers to both open pores and the total amount of pores. In conventional methods, a goal is to reduce the amount of open pores, since open pores are not possible to get reduced by sintering.

[0085] It is important to admix powder mixtures until they are as homogeneous as possible in order to obtain a body having optimum properties.

[0086] A coating may also be manufactured according to the method of the invention. A coating may for example be formed on a surface of an element or of a multilayer product. When manufacturing a coated element, the element is placed in the mould and may be fixed therein in a conventional way. The coating material is inserted in the mould around the element to be coated, by for example gas-atomizing, and thereafter the coating is formed by coalescence. The element to be coated may be any material formed according to this application, or it may be any conventionally formed element. Such a coating may be very advantageous, since the coating can give the element specific properties.

[0087] A coating may also be applied on a body produced in accordance with the invention in a conventional way, such as by dip coating and spray coating.

[0088] It is also possible to first compress a material in a first mould by at least one stroke. Thereafter the material may be moved to another, larger mould and a further material be inserted in the mould, which material is thereafter compressed on top of or on the sides of the first compressed material, by at least one stroke. Many different combinations are possible, in the choice of the energy of the strokes and in the choice of materials.

[0089] The invention also concerns the product obtained by the methods described above.

[0090] The method according to the invention has several advantages compared to pressing. Pressing methods comprise a first step of forming a green body from a powder containing sinterinc, aids. This green body will be sintered in a second step, wherein the sintering aids are burned out or may be burned out in a further step. The pressing methods also require a final working of the body produced, since the surface need to be mechanically worked. According to the method of the invention, it is possible to produce the body in one step or two steps and no mechanical working of the surface of the body is needed.

[0091] By the use of the present process it is possible to produce large bodies in one piece. In presently used processes it is often necessary to produce the intended body in several pieces to be joined together before use. The pieces may for example be joined using screws or adhesives or a combination thereof.

[0092] A further advantage is that the method of the invention may be used on powder carrying a charge repelling the particles without treating the powder to neutralize the charge. The process may be performed independent of the electrical charges or surface tensions of the powder particles. However, this does not exclude a possible use of a further powder or additive carrying an opposite charge. By the use of the present method it is possible to control the surface tension of the body produced. In some instances a low surface tension may be desired, such as for a wearing surface requiring a liquid film, in other instances a high surface tension is desired.

[0093] Here follow some Examples to illustrate the invention.

EXAMPLES

[0094] The following material were tested: Silicone nitride, hydroxyapatite, Alumina, titanium, Co-28Cr-6Mo, PMMA and UHMWPE.

[0095] Silicone nitride was a pure freeze granulated powder. Hydroxyapatite and alumina was not pre-processed at all. The metal and polymer powder was initially dry-mixed for 10 minutes to obtain a homogeneous particle size distribution in the powder.

[0096] A multilayer has many applications areas e.g. implants.

[0097] Six different multi layers was tested with different material combination.

[0098] 2Two horizontal layers

[0099] 3Three horizontal layers

[0100] 1.One horizontal and two vertical layers

[0101] 2.Two vertical layers

[0102] 3.Two horizontal layers and two vertical layers

[0103] 4.Four vertical layers.

[0104] The main goal was to evaluate the possibility to obtain solid layers bonded to each other with chemical bonding.

[0105] The weight specified in the test specification of each constituent of the multilayer was divided by the number of layers in the multilayer. This means that the impact energy to obtain a visibility index for the weight specified in the test specification also has to be divided by the number of layers. If a horizontal layer consisted of two vertical layers then the material with the lowest hardness has to be consider when choosing impact energies. A polymer was never processed like material 1 as a single horizontal layer.

[0106] Following test scheme was general for all different layers:

[0107] 1Pre-compacting procedure for layer 1

[0108] 1.1Pre-compacting by hand

[0109] 1.2Pre-compacting with the striking unit, 12000 kp axial load.

[0110] 2Impact energy levels for layer 1 before adding material 2

[0111] 2.1Strike with an energy corresponding to visibility index 1

[0112] 2.2Strike with an energy corresponding to visibility index 2

[0113] 2.3Strike with an energy corresponding to visibility index 3

[0114] 3The multilayer impact stroke will be performed with machine pre-compacting and the maximum allowable impact energy for material 2 and 3 respectively. Depending if the multilayer has two or three horizontal layers.

[0115] A approximately theoretical density was calculated for the different multilayer by dividing the total mass of the three layers with the sum of each material mass divided by the materials specific theoretical density, &rgr;multilayer=mtotal/(ma/&rgr;a+mb/&rgr;b+mc/rd+mc/&rgr;d+.mc/&rgr;d)

[0116] After each layer the over die was removed and next powder was poured and processed. When the multilayer was complete then the tool parts were dismounted and the sample was released. The diameter and thickness were measured with electronic micrometers which rendered the volume of the body. Thereafter the weight was electronically established. Out of these results the density 1 was obtained by taking the weight divided by the volume.

[0117] To be able to continue with the next sample, the tool needed to be cleaned, either or only with acetone or polishing the tool surfaces with an emery cloth to get rid of the material rests on the tool.

[0118] Table 1 shows the different powders used in this study. 1 TABLE 1 Silicone Properties nitride Hydroxyapatite Alumina Co-28Cr-6Mo Titanium PMMA UHMWPE Particle size <0.5 <1 <0.5 <150 <150 <600 (micron) Particle — <1 0.3-0.5 2% > 150 −5% <250 distribution balance < 150   5%  25-355 (micron)   10% 355-500   45% 500-710   35% <710 Particle Cubic Irregular irregular Irregular Irregular Irregular morphology Powder Granulated Wet chemistry Grinding Water atomised Hydrided ex-reacted production precipitation Crystal structure 98% alfa Apatite alfa 85% alpha phase, HCP amorphous 2% beta 15% carbides (hexagonal) Theoretical 3.18 3.15 3.98 8.5 4.5 1.19 density (g/cm3) Apparent density 0.38 0.6 0.5-0.8 3.4 1.8 — (g/cm3) Melting 1800 1600 2050 1350-1450 1660 125° C. temperature (° C.) Sintering 1820 900 1600-1650 1200 1000 — temperature (° C.) Particle hardnes 1570 450 1770 460-830 60 M92-100 (HB)

[0119] Two Horizontal Layers

[0120] FIG. 2a shows the look of a two horizontal layer. The different material combinations used are specified in table 2.

[0121] There were no solid samples obtained after compressing hydroxyapatite and UHMWPE together. The hydroxyapatite could be solid before adding the polymer but then it cracked when the polymer was added and struck. Compressing hydroxyapatite and titanium gave a similar result for the hydroxyapatite. The titanium became a solid body after pre-compacting with the machine but when the titanium as material 2 was struck it cracked the hydroxyapatite. The best result was obtained by handcompacting the hydroxyapatite and then add the titanium powder.

[0122] Alumina and silicone nitride has not been successfully compressed as a single material and the same result was obtained in the multilayer compressing series. The ceramic material felled apart and could not bind to the added material 2.

[0123] Compressing titanium together with UHMWPE or PMMA gave solid samples when the titanium first was struck to a solid body and then the polymer was struck. The polymer had to melt and get plastic to bond to the titanium. If the titanium only were hand compacted the polymer seemed still to be powder.

[0124] Co-28Cr-6Mo has also been complicated to solidified as a single material. It was compressed together with PMMA and UHMWPE. Some solid samples were obtained with UHMWPE when Co-28Cr-6Mo was struck to a solid material body first. No fine samples for the Co-28Cr-6Mo/PMMA two-layer were obtained. 2 TABLE 2 Number of Material 1 Material 2 samples Hydroxyapatite UHMWPE 2 Hydroxyapatite Titanium 6 Alumina UHMWPE 8 Titanium PMMA 7 Titanium UHMWPE 5 Co-28Cr-6Mo PMMA 8 Co-28Cr-6Mo UHMWPE 9 Silicone nitride Titanium 5 Silicone nitride UHMWPE 5

[0125] Three Horizontal Layers

[0126] FIG. 2b shows the look of a three horizontal layer. The different material combinations used are specified in table 3.

[0127] It was difficult to obtain solid sample when three layers were compressed together. Often was the single layer solid but there was no obtained mechanical or chemical bonding between the layers. The best results were obtained when both the first and second material where only hand compacted or pre-compacted with the machine and then struck with a high impact energy. It seemed to be a mechanical bonding between the layers and the material body was solid.

[0128] Table 3 shows the different material combinations tested in three horizontal layers. 3 TABLE 3 Number of Material 1 Material 2 Material 3 samples Hydroxyapatite Titanium UHMWPE 28 Silicone nitride Titanium UHMWPE 28

[0129] One Horizontal and Two Vertical Layers

[0130] FIG. 2c shows the look of a multilayer with one horizontal layer and two vertical layers.. The different material combinations used are specified in table 4.

[0131] The best results were obtained for a pre-compacting and then striking the two materials. It was difficult to obtain a plastic polymer that could bond to metal or hydroxyaptite. The samples were often brittle and easily broken be hand. 4 TABLE 4 Number of Material 1 Material 2 Material 3 samples Hydroxyapatite Titanium UHMWPE 5 Titanium Hydroxyapatite UHMWPE 5 Hydroxyapatite Co-28Cr-6Mo UHMWPE 1

[0132] Two Vertical Layers

[0133] FIG. 4 shows the look of a two horizontal layer. The different material combinations used are specified in table 5.

[0134] Pre-compacting the two materials together with the machine and then strike with the highest allowable impact energy gave the best result. The samples obtained were solid and did not fall apart 5 TABLE 5 Number of Material 1 Material 2 samples Co-28Cr-6Mo UHMWPE 3

[0135] Two Horizontal Layers and Two Vertical Layers

[0136] FIG. 2e shows the look of a two horizontal layer. The different material combinations used are specified in table 6.

[0137] The samples fell apart. It was difficult to melt the PMMA and UHMWPE together using these impact energy levels. The titanium layer was solid but did not bond to the other materials. 6 TABLE 6 Number of Material 1 Material 2 Material 3 Material 4 samples Hydroxyapatite PMMA UHMWPE Titanium 8

[0138] Four Vertical Layers

[0139] FIG. 2f shows the look of a two horizontal layer. The different material combinations used are specified in table 7.

[0140] The second layer containing two vertical layers was twisted 180 degrees to obtain a cross in the centre of the multilayer.

[0141] The titanium get solidified but the polymer did not phase changes completely and the different materials could not be successfully bonded to each other.

[0142] Hydroxyapatite obtained finest samples when it was compacted together with titanium by first only hand compact or pre-compact with the machine the first two vertical layers and then strike the two other vertical layers. No solid samples were obtained compressing hydroxyapatite compressed together with UHMWPE. The hydroxyapatite felled apart and the polymer did not phase change. 7 TABLE 8 Number of Material 1 Material 2 samples Titanium UHMWPE 3 Titanium Hydroxyapatite 5 Hydroxyapatite UHMWPE 5

[0143] This was a screening test for compressing multi layers. The densities that could be measured with scale and micrometers were considered very approximately, therefore has no diagrams over densities been presented.

[0144] Due to machine and tool limitations could not all planned tests be performed. When the material was struck before adding the second or third material the tool parts got swollen and were sometimes impossible to remove from the tool, which meant that the tests could not be finished.

[0145] To obtain a bonding between solid layers it was concluded that the first layer has only to be pre-compacted by hand or by the machine. The reason is probably that pre-compacted the material still has a high porosity where the powder particles from the two or three layers can bind to each other.

[0146] If the material is nearly completely solid with a relative density around 90 -95% is it difficult to bind the material together. The solidified material has taken up possible energy and is not able to bind to another material.

[0147] The ideal could be to strike one material and then add a thin layer of powder which only is pre-compacted and the add the third layer which is completely solidified. The material in the centre can then bind the two solid layers together.

[0148] All multilayer containing a polymer material, UHMWPE or PMMA, was difficult to obtain a bonding at low energy levels. The polymer had melt and get plastic before it can adhere to another material.

[0149] Post-processing for a multilayer is complicated, because of the different material properties between the components. A polymer can for example not be sintered and the sintering parameters between different metals or between a metal and a ceramic material are very different. One solution could be to compress one layer and then remove the material and sinter the sample. After the sintering is the material placed in the tool and next sample or powder is added and compressed. This compressing process can also compress or deform solid samples which means that all layers in a multilayer could be compressed and sintered and then compressed to one solid material body.

[0150] The samples has only been visually studied and it is therefore difficult to conclude if there is a mechanical or chemical bonding between the layers in the solid samples.

[0151] To obtain a real chemical bonding between the layers and a relative density near 100% for the complete multilayer the process should probably be performed in vacuum. If a included component is a ceramic materials the powder should be pre-heated before the compressing.

Example 2

Di-Layer of Stainless Steel and 316L-Rubber

[0152] These di-layer samples consist of one layer of ss 316L and another layer of rubber above the ss 316L. Earlier tests with each of the material types separated have shown that solid samples have been obtained with a high relative density. In this study the main object to is to investigate if a chemical bonding occurs between the two layers and how the stroke sequence should be performed to obtain the best bonding between the material types. Applications are not well developed today, but with this new manufacturing process applications within the e.g. car industry, where both metal and rubber are present, could be one possible application area.

[0153] If desired material properties would be obtained directly after this manufacturing process a following post-processing could be avoided. That would partly cut down the total process cost and partly avoid no environmental additives to the rubber. If a further post-processing is needed manufacturing steps could be cut comparing with conventional manufacturing methods.

[0154] The ss 316L powder was prepared by dry mixing for 10 minutes to obtain a homogeneous particle size distribution. The rubber powder was not prepared partly due to that the particles would glue together and partly that the particle size was homogeneous.

[0155] Five samples were totally produced. For all samples, ss 316L was first poured into the moulding die. Different types of compacting followed before the rubber powder was poured into the moulding die above the ss 316L. An impact stroke followed, always with a certain impact energy. This impact energy was determined by earlier tests. The stroke was stricken with an impact energy corresponding to maximum impact energy in tests with pure rubber. Because of that two material types were present the weight of each material was half the normal weight, which means that this stroke was stricken with half the maximum impact energy of rubber. Depending on what sample that was to be produced compacting was different between the two layers. With the first sample the ss 316L was compacted by hand with a rod before the rubber was poured into the moulding die. Second sample a pre-compacting was performed and third sample a stroke at the lowest impact energy possible (150 Nm). The last (fifth) sample was stricken by half the maximum impact energy of the earlier test with pure ss 316L. The forth sample was stricken by an impact energy in between the impact energy of the third and the fifth sample.

[0156] After each sample had been manufactured all tool parts were dismounted and the sample was released. The diameter and thickness were measured with electronic micrometers which rendered the volume of the body. Thereafter, the weight was established with a digital scale. All input values from micrometers and scale were recorded automatically and stored in separate documents. Out of these results the density 1 was obtained by taking the weight divided by the volume.

[0157] To be able to continue with the next sample, the tool needed to be cleaned with acetone to get rid of the material rests on the tool.

[0158] To easier establish the state of a manufactured sample three visibility index were used. Visibility index 1 corresponds to a powder sample, visibility index 2 corresponds to a brittle sample and visibility index 3 corresponds to a solid sample.

[0159] The theoretical density was taken from the manufacturers. Out of that a theoretical density has been calculated that corresponds to this certain mix between 50% rubber and 50% ss 316L. The relative density is obtained by taking the obtained density for each sample divided by the theoretical density.

[0160] No density 2 was measured on multilayer samples due to that in some cases (not this material combination) there were samples where pieces were lost. In those cases the theoretical density is hard to determine.

[0161] The dimensions of the manufactured sample in these tests is a disc with a diameter of ˜30.0 mm and a height between 5-10 mm. The height depends on the obtained relative density. If a relative density of 100% should be obtained the thickness is 5.00 mm for ss 316L rubber. That is the reason to the half weight of each material type.

[0162] Powder properties are given in Table 9 and test results in Table 10. 8 TABLE 9 Properties Rubber ss316L  1. Particle size (micron) ˜496 <  2. Particle distribution 99.8 wt % < 1.0 mm 0.0% > 150 mic 42.7% < 115 mic  3. Particle morphology Irregular Irregular  4. Powder production Polymerised thereafter Water atom grinding to powder  5. Type of material Elastomer I  6. Theoretical density 0.99 7.90 gc  7. Apparent density — 2.64 gc  8. Melt temperature (° C.) Not applicable I  9. Sintering — 1315   temperature (° C.) 10. Hardness 40 shore A 160-190 HV

[0163] 9 TABLE 10 Sample weight (g) 15.8 Number of samples made 5 Number of stroke sequences per sample 2 Minimum impact energy of the first stroke (Nm) 150 Maximum impact energy of the first stroke (Nm) 2000 Impact energy of the second stroke (Nm) 1050 Relative density 2 of first obtained body (%) 96.0 Maximum relative density 2 (%) 98.4 Impact energy of the first stroke at maximum 2000 relative density 2 (Nm)

[0164] FIGS. 3 and 4 show relative density as a function of impact energy per mass and of total impact energy.. The following described phenomena could be seen for all curves.

[0165] All samples had visibility index 3.

[0166] What can be seen is that the two first samples, where the first material type is either hand compacted or pre-compacted by the machine, render a higher relative density than the third sample, where the first material type is stricken with the lowest impact energy. When the impact energy of the first stroke increases the relative density increases and ends up at a higher relative density than the two first samples. The maximum relative density, 98.4%, is obtained when the first stroke is struck with the highest impact energy.

[0167] The samples were all intact, but the volume was difficult to establish because the rubber part of the samples were elastic. But the ss 316L part stabilised it compared to pure rubber and density 1 shows well an indication of the obtained relative density.

[0168] Discussion:

[0169] 1.ss 316L

[0170] ss 316L has a melting temperature of 1427° C. Even though it is quite high the ss 316L part of the samples got dense. The local increase of temperature among the particles, due to transmitted energy, makes the particles to soften, deform and the surface of the particles to melt. This inter-particular melting enables the particles to re-solidify together and dense material can be obtained.

[0171] Furthermore, the ss 316L powder is softer than e.g. CoCrMo. The hardness of ss 316L is ˜160-190 HV and CoCrMo ˜460-830 HV. The softer a material is the more soften and deformed the particles get. That enables the particles to get well soften, deformed and compressed before the inter particular melting occurs.

[0172] A pre-treating process to increase the relative density of the ss 316L could be to pre-heat either only the powder or both powder and the tool. The material could possibly be heated to ˜250° C. in in air without any reactions of the powder occur.

[0173] Other critical parameters, that could effect the compressing result, besides the already mentioned, melting temperature and hardness, could be the particle size, particle size distribution and particle morphology. According to earlier tests' that were performed in Phase 1, better results were obtained with an irregular particle morphology, than spherical morphology. Inter-particular melting occurred when irregular particles were tested, but less when spherical particles were tested. When irregular particles get in contact with each other, due to that they are pressed together, the contact surface is much larger comparing with spherical particles. The big contact area could possibly enable the particles to easier fuse during the process and, with this theory, less impact energy is needed to be transmitted to the powder.

[0174] With big particles more space is present between the particles than with small particles. That makes it harder to obtain a dense and well compressed sample. The advantage with big particles, compared with small particles, is that the total surface of bigger particles is less than with small particles. A large total surface makes the surface energy high, and correspondingly higher impact energy could be required to reach desired results. On the other hand, small particles could possibly reach a higher compressed rate because the space between the particles is smaller than between large particles. The optimal particle size is still a question that needs to be answered.

[0175] The particle size distribution should probably be wide. Small particles could fill up the empty space between big particles.

[0176] It is important to obtain samples with less than 5% pores because the pores ate with that closed in the material. If there are more than 5% pores canals in the material, humidity can get into the canals of the material. That results in corrosion of the material, and the properties of the manufactured sample are low. If there are more than 5% pores the samples must be sintered to eliminate the canals and pores of the material.

[0177] To obtain a total dense sample, i.e. 99-100%, the atmosphere might need to be different from the present used in this test. If air is included in the material, the density decreases. To obtain a dense material, vacuum could be an alternative.

[0178] One alternative could be to sinter the ss 316L part first. Thereafter could the ss 316L part be put in the moulding die again and the rubber could be added above the ss 316L. It seems to that rubber bonded to ss 316L in this test and therefore it could be possible that rubber would bond to the sintered ss 316L as well. In that case the sample, at least the metal part, has probably reached the desired properties though the metal part has been sintered.

[0179] Rubber

[0180] The hardness of materials affect the results. The hardness of rubber is lower comparing with e.g. PMMA. PMMA required a higher amount of transformed impact energy compared with rubber to obtain a sample with visibility index 2. The softer a material is the more soften and deformed the particles get, which easily has occurred with the rubber particles. That enables the particles to get softened, deformed and compressed before the inter-particular melting occurs.

[0181] The particles could still be determined in the sample. Therefore should probably a post-processing follows. The rubber normally processes as a thermoplastic polymer where vulcanising follows. The vulcanising renders a high elastic material, elastomer, due to that the material gets cross-linked.

[0182] There exists hitherto no corresponding powder metallurgy for polymers and therefore it could be difficult to find what and how the parameters should be changed. But probably could some of the discussion be valid to polymers as well. Other critical parameters, that could effect the compressing result, besides the already mentioned, melting temperature, could be the particle size, particle size distribution and particle morphology. When irregular particles get in contact with each other, due to that they are pressed together, the contact surface is much larger comparing with spherical particles. The big contact area could possibly enable the particles to easier fuse during the process and, with this theory, less impact energy is needed to be transmitted to the powder.

[0183] If big particles are used more space is present between the particles than with small particles. That makes it harder to obtain a dense and well compressed sample. The advantage with big particles, compared with small particles, is that the total surface of bigger particles is less than with small particles. A large total surface makes the surface energy high and correspondingly higher impact energy could be required to reach desired results. On the other hand, small particles could possibly reach a higher compressed rate because the space between the particles is smaller than between large particles. The optimal particle size is still a question that needs to be answered.

[0184] The particle size distribution should probably be wide. When different particle sizes are used small particles could fill up the empty space between big particles. Thus there are particle surfaces that are in contact with other particles everywhere in the sample. That increases the possibility to succeed in inter-particular melting (e.g. small particles' surfaces against big particles' surfaces).

[0185] Rubber is an amorphous polymer. In this fast manufacturing process the sample is already room tempered when it is released from the mould. That means that the cooling process is much faster than other manufacturing processes. Due to this fast cooling process this manufacturing process could perhaps suit amorphous polymer production better than crystalline polymer production. The structure of crystalline polymers is in the form of lamellas and amorphous polymers' structure is not a well organised structure. To obtain this organised structure of crystalline polymers the cooling time could probably need more time than for amorphous polymers. This cooling process could possibly effect the structure and material properties of the rubber. Therefore is there an importance of investigating the microstructure and the material properties.

[0186] Layer

[0187] Between these two material types there is some kind of bonding. Exactly how these material types are bound together will be shown in the microstructure test. How will the highest relative density be obtained of both material, and in the mean time obtain a chemical bonding between the material types? As can be seen in the figures the relative density is higher when the first material type is compacted, not stricken with low impact energy. ss 316L and rubber particles can possibly get in contact with each other if the surface is somewhat rough compared with the samples where the a low impact energy is transformed to the powder. When particles can be in contact before the stroke process they can be more packed, and more integrated.

[0188] But if the impact energy of the first stroke increases the relative density increases as well. That could be that rubber could bind to a “polished” surface where a stroke has been performed due to the softness of rubber. Rubber could possibly act as glue on the ss 316L surface.

[0189] The invention concerns a new method which comprises both pre-compacting and in some cases post-compacting and there between at least one stroke on the material. The new method has proved to give very good results and is an improved process over the prior art.

[0190] The invention is not limited to the above described embodiments and examples. It is an advantage that-the present process does not require the use of additives.

[0191] However, it is possible that the use of additives could prove advantageous in some embodiments. Likewise, it is usually not necessary to use vacuum or an inert gas to prevent oxidation of the material body being compressed. However, some materials may require vacuum or an inert gas to produce a body of extreme purity or high density. Thus, although the use of additives, vacuum and inert gas are not required according to the invention the use thereof is not excluded. Other modifications of the method and product of the invention may also be possible within the scope of the following claims.

Claims

1. A method of producing a multilayer body by coalescence, characterised in that the method comprises the steps of

a) filling a pre-compacting mould with a start material in the form of powder, pellets, grains and the like,

b) pre-compacting the material at least once and

c) compressing the material in a compression mould by at least one stroke, where a striking unit emits enough kinetic energy to form the body when striking the material inserted in the compression mould, causing coalescence of the material,

d) at least one further material being inserted into the mould in the form of powder, pellets, grains and the like, either in step a), after compacting in step b) or after compressing the start material in step c),

e) if necessary, further pre-compacting and/or compressing being performed after the insertion of the at least one further material.

2. A method according to claim 1, characterised in that the pre-compacting mould and the compressing mould are the same mould.

3. A method according to any of the preceding claims, characterised in that the material is pre-compacted with a pressure of at least about 0.25×108 N/m2, in air and at room temperature.

4. A method according to claim 3, characterised in that the material is pre-compacted with a pressure of at least about 0.6×108 N/m2.

5. A method according to any of the preceding claims, characterised in that the method comprises pre-compacting the material at least twice.

6. A method of producing a multilayer body by coalescence, characterised in that the method comprises compressing a solid body of a start material in a compression mould by at least one stroke, where a striking unit emits enough energy to cause coalescence of the material in the body, at least one further material being inserted in the mould, either in the form of powder, pellets, grains and the like or in the form of a solid body, the at least one further material also being struck by the striking unit, either in the first stroke or in a later stroke so that the at least two materials form an integral body.

7. A method according to any of claims 1-5 or claim 6, characterised in that the compression strokes emit a total energy corresponding to at least 100 Nm in a cylindrical tool having a striking area of 7 cm2in air and at room temperature.

8. A method according to claim 7, characterised in that the compression strokes emit a total energy corresponding to at least 300 Nm in a cylindrical tool having a striking area of 7 cm2.

9. A method according to claim 8, characterised in that the compression strokes emit a total energy corresponding to at least 600 Nm in a cylindrical tool having a striking area of 7 cm2.

10. A method according to claim 9, characterised in that the compression strokes emit a total energy corresponding to at least 1000 Nm in a cylindrical tool having a striking area of 7 cm2.

11. A method according to claim 10, characterised in that the compression strokes emit a total energy corresponding to at least 2000 Nm in a cylindrical tool having a striking area of 7 cm2.

12. A method according to any of claim 1-5 or claim 6, characterised in that the compression strokes emit an energy per mass corresponding to at least 5 Nm/g in a cylindrical tool having a striking area of 7 cm2 in air and at room temperature.

13. A method according to claim 12, characterised in that the compression strokes emit an energy per mass corresponding to at least 20 Nm/g in a cylindrical tool having a striking area of 7 cm2.

14. A method according to claim 13, characterised in that the compression strokes emit an energy per mass corresponding to at least 100 Nm/g in a cylindrical tool having a striking area of 7 cm2.

15. A method according to claim 14, characterised in that the compression strokes emit an energy per mass corresponding to at least 250 Nm/g in a cylindrical tool having a striking area of 7 cm2.

16. A method according to claim 15, characterised in that the compression strokes emit an energy per mass corresponding to at least 350 Nm/g in a cylindrical tool having a striking area of 7 cm2.

17. A method according to any of the preceding claims, characterised in that the multilayer body is compressed to a relative density of at least 60%, preferably 65%.

18. A method according to claim 17, characterised in that the multilayer body is compressed to a relative density of at least 70%, preferably 75%.

19. A method according to claim 18, characterised in that the multilayer body is compressed to a relative-density of at least 80%, preferably at least 85% and especially at least 90% up to 100%.

20. A method according to any of the preceding claims, characterised in that the method comprises a step of post-compacting the body at least once after the compression step.

21. A method according to any of the preceding claims, characterised in that the materials in the multilayer body are chosen from the group comprising metallic, ceramic and polymeric materials..

22. A method according to claim 21, characterised in that one of the materials in the multilayer body contains a reinforcing phase which is chosen from the group comprising carbon, glass, metal, polymeric and ceramic material.

23. A method according to claim 21, characterised in that the multilayer materials are chosen from the group comprising UHMWPE, PMMA, nitrile rubber, aluminium alloys and titanium.

24. A method according to any of the preceding claims, characterised in that the body produced is a medical implant, such as a skeletal or tooth prosthesis.

25. A method according to any of the preceding claims, characterised in that the method comprises a step of post-heating and/or sintering the body any time after the compression or the post-compacting.

26. A method according to any of the preceding claims, characterised in that the body produced is a green body.

27. A method of producing a body according to claim 27, characterised in that the method also comprises a further step of sintering the green body.

28. A method according to any of the preceding claims, characterised in that the materials are a medically acceptable materials.

29. A method according to any of the preceding claims, characterised in that the at least one of the materials comprises a lubricant and/or a sintering aid.

30. A method according to claim 6, characterised in that the method also comprises deforming the body.

31. A product obtained by the method according to any of claims 1-30.

32. A product according to claim 31, characterised in being a medical device or instrument.

33. A product according to claim 31, characterised in being a non medical device.