DE19745283C2 - Process for manufacturing components from powder - Google Patents

Description

The invention relates to a method for manufacturing of components made of powdered starting materials, aptly as hot flow compaction can be designated. They are different most powder in a tool and pressed, so that the shape of the component by the pressure trains. As a rule, a green is produced in this way body subsequently decreased, so that the bond between the powder enlarged and accordingly the Density and strength is increased.

With known methods, components can easily are produced in which components with rear cuts to be made or construction partial form follows the pressing direction and in the cases where cores for training, for example Holes are drilled in the tool, it is in In these cases, a flow of the material is required fes to reach transverse to the pressing direction. Become such Shapes usually appear, cracks occur, which the strength and stability of the manufactured Limit component so far that their use is eliminated.

With the known methods, it is only in a few special cases possible in this way  Undercuts with powdered starting materials to manufacture. There are therefore rigid straight-walled ma triciform tools used that are just simple Have shapes and therefore simply out can be shaped to destroy when molding to avoid.

For the production of components with powders as Starting materials with complicated designs Undercuts or cross holes are known various possibilities, but the gene rell require increased manufacturing costs.

For example, it is known that component by Pressing the powder used, as already mentioned, to produce in a simple form and in Follow-up to this by machining desired contour or drill the hole. A another way is to do that accordingly simply trained components after the press by joining several such components (soldering, Welding, gluing) into the desired complex shape bring.

Furthermore, it is known if the respective Hin cuts only due to a slight offset during construction are marked by horizontal use separate dies, the components can be demolded to ma chen. Has the respective undercut to be made just a small groove in the component or a nose on the building part, it can be demolded using an auxiliary stamp become. The undercuts must be in proportion to the component, since the powder movement during Always press crosswise to the direction of the cracks on the Edges of the undercuts  Term "cross flow cracks" or appearance image of the cracks in English accordingly "dead water crack" naturalized.

In a third way of making Hin cuts and cross holes in such components is that known metal powder injection molding to use. The starting powder is wax and Polymer added in an amount so that it matches the processes known from plastic molding can be processed. The metal powder injection molding procedure (MIM process), however, requires additional Process steps such. B. the required off drive the high binder content, otherwise that Component when heating to sintering temperature again would melt or the high shrinkage of the building component les occur during sintering (risk of warping), so that only relatively large tolerances in those to be manufactured Dimensions of the components can be observed.

Such manufacturing processes are in Werner Schatt, Klaus-Peter Wieters: "Powder Metallur gy-processing and materials "; European Powder Metal lurgy Association (EPMA) Shrewsbury; UK, 1997, R. M. German: "Powder Metallurgy Science", Metal Powder Industries Federation; Princeton; New Jersey; 1984 and Randall M. German, Animesh Bose: "Injec tion molding of metals and ceramics "; metal powder Industries Federation; Princeton; New Jersey; 1997 have been described.

Based on this, it is an object of the invention to provide a Possibility to create with the complex trained Components made from powdered raw materials with little effort and avoidance  of cross flow cracks can be produced.

According to the invention, this object is achieved with the features of claim 1 solved. Advantageous design tion forms and developments of the invention when using the subordinate An characteristics included.

With the invention it is now possible to use verrin process costs a much higher form complexity of the components to be manufactured  chen than this so far with the conventional axial Pressing process is possible. Another advantage be is that the building made by pressing partly disappears less than with the known one Powder injection molding was the case.

In the method according to the invention, the ther moplastic properties of a temporary binder, which is added to the starting powder. Here, heating and softening or Liquefaction of the binder also the fluidity of the Powder starting material are improved so far that also avoiding cross flow cracks altransport in one tool Shape for the components made transversely to the pressing direction can.

The powdery starting material already a relatively dense component by pressing get and there can be a density of the component that is almost 100% of the theoretical density Powder and binder sourced and at least above 70% of the theoretical density (based on the powder gen) can be achieved. However, it rises during the entire shaping process.

According to the invention, the procedure is such that such a high density in a powder pack is that by adding a small amount the properties of a pressing aid (binder) th of the starting powder are influenced so that it exhibits viscous behavior. It is invented According to the proportion of binder chosen so that the applied pressure when heated and at least Softening the binder the mixture of starting powder  and can cause binder to flow, but avoided is that due to the proportion of binder, the dead weight of parts of the green compact, the yield point of which at Heating to sintering temperature exceeds.

Commercially available powder can conveniently be used as Starting material used, which is a certain Proportion of fine powder can be added. Here the fine portion of the powder can have the same consi stenz like the normal powder. It can but also certain alloy fractions in the fine fraction be included, which the achievable components can influence specific sciences.

The powder can then be mixed with the binder used to be mixed. The binder can be used as a mixture from a polymer and wax with the powder at one Temperature are mixed at which the polymer be already softened and the wax has flowed. Thereby can the fine powder particles through the binder the coarser powder particles bound and the coarser ones Particles of powder from a binder layer with fine NEN powder particles are surrounded. That said Delte powder is still easy to handle and trickle capable and is available as a composite powder.

This composite powder can pre-temperature be warmed, where the binder softens again and then into a heatable split tool in which the shape of the component to be manufactured is included, be introduced. The preheating of the Compound powder externally or in a heated tool respectively.

When a correspondingly high temperature is reached,  where the binder is at least softened, it will Powder with at least one press ram in the tool compacted and exerted pressure on the powder. This will compact the powder, as it already does from the state of the art in powder metallurgical Method is known and if the powder through the Stamp printing is so compacted that the binder forms a continuous phase, sets a viscous Flow in. This viscous flow then ensures white ter that also cavities in the tool that cross to Press direction of the stamp (s) are formed with the powder binder mixture. So can also areas that are in the slipstream of in the tool picked up cores lie with sufficient density be filled.

The green body prepared in this way can then be opened of a split tool demolded and in a known Be sintered in a way that the binder content is small is, the flowability of the starting powder improved, but prevents that during sintering The weight of the parts is sufficient to prefabricate it let the component melt and the components regardless of the binder relatively quickly can be heated to the sintering temperature.

Through the added fine fraction of the starting powder the sintering activity increases and consequently also the final density of the sintered finished components.

In contrast to the known methods, the Density increase on the shape during compression by pressing and by shrinkage when sintering distributed. In contrast, conventional Pressing the starting powder only loosely packed  and the compression takes place mainly in the mold exercise step in pressing. With metal powder spray the increase in density is only moved during sintering carried out and the shaping runs almost without Compression.

With the method according to the invention, the ver various components by pressing in the complex most forms, especially with undercuts, Boh stanchions transverse to the pressing direction, as a through hole or blind holes. The Bores or blind holes without additional moving Stamps are created in the component and it can be used for this simple cores are used. Moreover can also cores with threads applied be put out of the green part, compact can be screwed. Such verses with threads Henen bores can in the pressing direction and also across be aligned to the pressing direction and by the The threads with the Starting material filled. Net-SHAPE- Threads are made, however, in each Fall through the corresponding shrinkage during sintering appropriate design of the respective cores must be viewed.

The various relatively complex buildings parts can usually already be matched chend trained form are made without additional movable or auxiliary stamps required are and they are sufficient only for pressing required stamp. You can use the stamps acting in the same direction or counter to each other be pressed.  

Due to the higher fluidity and better movement Powder particles (since they are in a viscous Phase can be moved) better homogeneity the density in the finished component can be achieved as this with the conventional method (e.g. matrices press) is the case.

As already mentioned, a proportion of fine powder can be added to the starting powder to increase the packing density and a proportion of fine powder between 5 and 40% by volume can be maintained. At least all powders that are smaller than the d ₅₀ value of the starting powder fall under fine fraction.

A starting powder also has a similar effect which the particle size over a relatively large size Outside area is distributed, so that in addition to small very fine particles, medium particles also large par items are included.

A wide variety of mate can be used as the starting powder rialien be processed according to the invention. Leave it components from a wide variety of ceramics, Manufacture plastic materials and glass.

The process for processing is particularly suitable processing of metal powder.

It can be used for such metal powder, for. B. Iron Ba sis alloys with a grain size below 150 µm, which is advantageously a fine powder with a Grain size below 25 µm, particularly advantageous below half 10 microns can be added. The fine fraction should preferably be between 5 and 20% by volume, the rest being 100% coarse powder  complements.

Possible grain sizes for ceramic powder as a starting point material are of the same order of magnitude, whereby for ceramics, the coarse grain fraction may also be somewhat larger can.

Starting with the starting powder or with a fine fraction The starting powder can then be mixed with a binder Proportion of 0.5 to 4 mass% are added, wherein these proportions are preferred for metallic powders should be set. For powder with less output The binder percentage can be more dense than this Range must be increased accordingly.

The thermoplastic binder softens when reached a specific temperature for the binder and takes off when it heats up due to the Thermal expansion a larger volume fraction than this is the case at room temperature, this being the Start shaping at a higher processing temperature increases. Only as much binder should be used that the applied pressure of the powder binder Ge mix can flow, thereby the bin the upper limit is limited by the fact that the stretch limit of the green body when heating up during the sin terns is not exceeded and the green compact through the dead weight of parts not during sin terns is destroyed.

Examples of binder compositions are:

• a) polyoxymethylene (POM) with approx. 4 mass% Paraffin,
• b) polymethyl methacrylate (PMMA) with approx. 4% by mass Paraffin,
• c) Polypropylene (PP) with 2% paraffin and 2% Stearic acid.

These specifications ensure that the binder proportion remains so small that there are no additional ones Expulsion processes, like this with metal powder spraying pour the case is necessary.

The actual shaping in the tool takes place at a temperature above room temperature at which the Binder is soft or even liquid. There is one Warming only required to the extent that the binder the corresponding temperatures are reached and the starting powder has no property in this regard changes. It is obvious, that the temperature range required for this, esp especially for starting powders made of metal, ceramic or Glass is much lower because the softening or Melting temperature of the binder is much lower.

With the method according to the invention, in the green body a larger after pressing and before sintering Density can be achieved with certainty above that can be achieved with metal powder injection molding lies.

The method according to the invention can be used for the manufacturer development of components in various complexes trained forms are used. Examples for this, components with flanges or collars are on the middle, multi-speed sprockets, parts with cross bores, parts with offset bores, threads bores and. a .. Thereby contours and in particular Right undercuts made of powdery starting material materials are manufactured by pressing, such as this was impossible before the invention. Also first Sometimes components could be powder metallurgically won which are produced in such a process.  

In addition to the already mentioned Aus materials also used with other powders become. Powders with a wide range Grain size distribution and in several particle sizes are available.

The invention is based on exemplary embodiments len are explained in more detail.

Show:

Figure 1 shows an example of a tool that can be used in the inventive method who can.

Figure 2 is a schematic representation of an accordingly manufactured component.

Fig. 3 is a micrograph of the middle portion of the component shown in Fig. 2;

Fig. 4 is a photomicrograph of an edge region of the component shown in Fig. 2;

Fig. 5 shows a further example of a component produced according to Inventive;

Fig. 6 is a micrograph of the component from a central area of the component;

FIG. 7 shows a micrograph with a relief crack on the component shown in FIG. 5;

Fig. 8 is a micrograph of the component of Figure 5 in an edge region.

Fig. 9 shows the density distribution of the flowable compacted material in a component determined;

Fig. 10 is a photographic representation of such a component;

Fig. 11 shows a component with undercuts ver different width;

FIG. 12 shows a micrograph from a central region of the component shown in FIG. 11;

FIG. 13 is a micrograph of an edge region of the component shown in Fig. 11;

Fig. 14 is a photographic representation of a component according to the invention with transverse bore and

Fig. 15 several micrographs of a ausgebil Deten in a dung OF INVENTION prepared according component thread.

With the example shown in FIG. 1, tool 1, which is divided in the drawing or in plane A, can build parts of a powdered starting material according to the method according to the invention are prepared. It is already, as mentioned in the general part of the description, the prepared powder-binder mixture is placed in the heatable tool 1 and in this example with two opposing presses 2 presses the heated mixture. In the tool 1 further pistons 3 are formed, which, however, are not moved in this case, so that the mold to be produced has 4 undercuts, which are also filled with the powdery starting material, which contains the corresponding proportion of binder, when compacting by flowing.

As indicated by the double arrows on the press rams 3 , their position can be adjusted so that the size of the mold 4 can be changed in these areas. However, they only form lateral stops in the actual manufacturing process of the component and do not actively participate in the compression process.

It should be noted that the two halves of the tool 1 are relatively rigidly connected to one another and the connection used, if at all only slightly, yields elastically in order to avoid cracking when the two tool halves spring back.

With the example shown in FIG. 1, tool 1, the component also shown in Fig. 2 was prepared where different in this component dimensioned undercuts, in particular has at the right and lin ken component edge, which are oriented transversely to the pressing direction of the press ram 2.

The component was made from a metal powder with the Han "Densmix" made by Höganäs, which has no cross flow properties per se. This normal hot press powder becomes more conventional Used wisely, there can be no condensation in edge areas can be reached and the typical Tears on the deflection edges. This is what it is about actually about these cracks and not about Cracks caused by the relief of the tool can stand.

In Figs. 3 and 4 are two micrographs of the T-shaped component of Figure 2 at a magnification of 50:... Corresponding to 1 from the middle region of the component in Figure 3 and the edge portion in Fig 4 in Fig 2. marked local positions.

It can be seen that the density of the component in the marginal areas only slightly smaller than in middle area of the T-shaped component.

In Fig. 5 another cylindrical construction part is shown, the undercuts of 3 mm, 6 mm and 9 mm from the edge of the central cylinder, has. For the production, a mixture of 80 vol .-% of a normal powder and the added fine fraction of 20 vol .-%, consisting of fine carbonyl iron powder, was used. The commercially available starting powder is available from Höganäs under the trade name "Di staloy AE". 3% by mass of binder were added to this powder mixture of normal powder and the fine fraction and the whole was mixed. If necessary, preheating can be carried out so that the binder binds the fine powder to the coarser normal powder and a coating with the binder is achieved.

The component prepared in this way in tool 1 according to FIG. 1 was subsequently sintered at temperatures of approximately 1,250 ° C. Figs. 6 to 8 show the component thus prepared micrographs where marked with B, C and D component with a magnification of 50: 1 is achieved, wherein the component samtdichte a Ge of 7.39 g / cm ^3. In FIG. 7, a relief crack can also be seen at position C, that is to say at an edge of an undercut, which has occurred due to the relief of the tool 1 and which is consequently not a tear as was to be avoided in accordance with the object of the invention.

FIG. 9 schematically shows the density distribution of a component, as is also shown in FIG. 5, but this component was sintered at 1150 ° C.

In the photographic representation of a corresponding component shown in FIG. 10 with undercuts of 3 mm, 6 mm and 9 mm from the edge of the central cylinder, there is also a sectional representation recognizable at the right edge, of a grinding through the T-shaped component recognizable.

In a further example, the ratio of normal, relatively coarse to the fine fraction of the powder was changed and only 10% by volume of fine powder was added to the normal powder. The micrographs shown in FIGS . 12 and 13 again come from positions that are made clear in FIG. 11. It was found that with this ratio of normal to fine powder similarly good results could be achieved and no shear cracks occurred at the edges. If cracks have occurred, they are relief cracks that are caused by the tool structure and that are caused by the elasticity of the connection of the two tool parts being too high.

Another corresponding component was created with a Stainless steel powder mixture made at the 80% by volume of a relatively coarse powder (less than 150 µm) and 20% by volume of a fine powder (less than 22 µm) be used.

In the Fig. 14 is a photographic representation of a component according to the invention with a transverse bore is directed transversely to the pressing direction, recognizable. The example shown shows a cross hole that has been made by a pullable core and through which a screwdriver has been inserted for clarification. This transverse bore, which is obtained without additional machining, can be located almost at any height of the component and thus very different deformations can be produced from above and below. It can be clearly seen that a large part of the transverse bore produced is located in an area which is transverse to the actual pressing direction. Such training could not be achieved with the usual procedure and P. Beiss pointed out, for example, at the NNS conference and the Hagen Symposium that such che cross holes can only be obtained in the neutral zone of such components, since in this Area the deformation from the top and bottom is the same size.

In addition to the cross holes, blind holes can also be made be produced in the same way, but be preferably in the neutral zone already mentioned should, since otherwise the bending moments on the core to be used for this is too large.

With the method according to the invention, however, threads can also be incorporated into the component, likewise without additional machining steps. For this purpose, a core with the corresponding external thread is also used. After the pressing process, the core with the external thread, which must be free of undercuts, is then screwed out of the component. In Fig. 15 different micrographs of a component with the thread are recognizable again. The threaded blind hole was pressed by one of the two press rams 2 in tool 1 , as shown in FIG. 1.

Such a threaded component can be like with powder mixtures that have a fine fraction of 20 or 10 vol .-%, which is 100%  resulting residual portion is a coarse powder, here be put. When working according to the invention ge again binder proportions of a maximum of 4% by mass are sufficient sufficient flow of powder material during to secure the pressing process.

The blind holes already mentioned can be produced without additional movable stamp segments that were used for this purpose according to the prior art. The mold 4 can be filled backwards in the tool 1 and a pin attached to the upper punch 2 , which forms the shape of the blind hole and during the pressing, the powdery starting material flows backwards and forms the blind hole with a uniform density of the material around the Pin on the stamp 2 . Tests with pegs with a length of 8 mm were successfully carried out.

In the manufacture of the components with the method according to the Invention, in particular in the dimensioning of the mold 4 in the tool 1 and again very particularly with the dimensioning of the cores, the shrinkage occurring during the subsequent sintering must be taken into account, but this is smaller than in conventional process, which is metal powder injection molding.

Claims (16)

1. A process for the production of components from powder, by hot flow compacting in the powder or a powder mixture in a tool and pressed, wherein the shape of the component is formed by the pressure and the resulting green body is then sintered, characterized in that the Powder or powder mixture, a thermoplastic binder or a binder mixture is added in an amount which is at least so large that the applied pressure can cause the powder-binder mixture to flow and which is at most so large that the green body does not become during the sintering disintegrates; that the powder mixture is brought into the heated tool; the temperature is set above the softening temperature of the binder; the powder mixture is pressed at least on one side by means of a ram and is also pressed into areas transverse to the pressing direction by viscous flow and the green body obtained in this way is sintered. 2. The method according to claim 1, characterized in that the powder binder with a proportion of 0.5 to 4 mass% added becomes. 3. The method according to claim 1 or 2, characterized in that a powder with a admixed fine fraction between 5 and 40 vol .-% is used. 4. The method according to claim 1 or 2, characterized in that a powder with a wide grain size distribution is used.   5. The method according to any one of claims 1 to 4, characterized in that ceramic powder ver is applied. 6. The method according to any one of claims 1 to 4, characterized in that glass or art fabric powder is used. 7. The method according to any one of claims 1 to 4, characterized in that a metal powder is used. 8. The method according to claim 7, characterized in that fine powder in which Alloy elements are included, used becomes. 9. The method according to any one of claims 1 to 8, characterized in that powder, fine powder and binder mixed at elevated temperature and the binder softens and / or melts, so that with the binder the fine to the coarse powder bound and the particles together with binder are coated before entering the tool to be led. 10. The method according to claim 9, characterized in that powder-binder mixture preheated and then inserted into the tool becomes. 11. The method according to any one of claims 1 to 10, characterized in that a polymer wax Mixture is used as a binder.   12. The method according to any one of claims 1 to 11, characterized in that the powder binder is mixed into a split tool. 13. The method according to any one of claims 1 to 12, characterized in that min at least form an inner contour in the component core inserted into the tool or on one of the tool parts is arranged. 14. The method according to claim 13, characterized in that with the core under construction part of a cross hole is formed. 15. The method according to claim 13, characterized in that with the core under construction partly a hole is formed with a thread. 16. The method according to any one of claims 1 to 15, characterized in that the pressure and the temperature during the shaping and / or the Distribution of the particle size of the powder turned are placed so that a density in the green compact above 70% of the theoretical density to which Related powder, can be achieved.