DE102016004954A1 - Method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, such as silicon nitride - Google Patents

Abstract

The invention has for its object to develop a method for producing an injection mold that, for example, the dimensional accuracy of the spherical shape of a ball sealing surface (3) without any greening or post-processing after the sintering of a sliding block made of silicon nitride (2), optimally meet the increased demands on the Form accuracy to ensure the sealing associated with the sealing and sliding tasks is fair. The inventive method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, such as silicon nitride, characterized in that first sprayed with this manufactured according to the prior art base injection mold at least 25 pieces basic components, debinded and then sintered, these measured below, the measured results are statistically evaluated and digitized as the actual contour (8), compared with the nominal geometry (7) and mirrored perpendicular to the nominal geometry (7), and the material-specific shrinkage factor is scaled up to the resulting correction surface (s) (9) 10) of the correction surface (s) are "matched" to the nominal geometry (7) by means of interfaces (11) and the correction surface (s) (9) are transferred together with the interfaces (11) as modeling surface (s) to the base injection mold. The invention relates to a method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, such as silicon nitride, to ensure a high dimensional accuracy, based on the design nominal geometry (7).

Description

The invention relates to a method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, such as silicon nitride, to ensure a high dimensional accuracy, based on the design nominal geometry.

In recent decades, new ceramic materials have been developed which, due to their special property profile, are becoming more and more widely used in technology. Main applications of these so-called high-performance ceramics (ies) are mostly where the use of metals or plastics causes problems due to mechanical or chemical wear and / or heat resistance.

High performance ceramics are "advanced, high performance ceramics" made from powders of oxide, nitride, carbide or boride with a defined composition.

The production of the components takes place via the production of a green compact from the respective powder by compacting and / or by the plastic deformation of the liquefied powder, for example very effectively by injection molding. The ceramic with the desired properties is then produced by sintering at temperatures of approx. 1,050 ° C to 2,200 ° C from this green body.

As densification takes place during sintering, this is associated with a material-specific shrinkage process in the order of about 20%.

As a result of the process steps "shaping" and "firing", however, the ceramic components are subject to very high tolerances after firing. In the manufacture of the sliding shoes for in the DE 10 2008 026 218 B4 as well as in the DE 10 2013 011 209 B3 Due to the high wear resistance, the low thermal expansion, the corrosion resistance / insensitivity to almost all pumped media, the high density as well as the low weight, the use of high-performance ceramics, especially silicon nitride, offers itself.

As an effective method for producing the green compacts, the injection molding process offers.

That in the DE 39 42 686 C2 discloses a method for injection molding of ceramics, in which a molding material of a ceramic powder and a binder is plasticized and molded with an injection molding machine, describes a solution for avoiding pores or welds in the ceramic molding.

But even with the consideration in the DE 39 42 686 C2 revealed doctrine, occur on the surfaces of the sintered after injection molding ceramic molding shape deviations from the design nominal geometry.

These shape deviations are, for example in the production of the sliding blocks for axial piston pumps made of silicon nitride by injection molding, in the area of arranged on these sliding ball sealing surfaces so functional critical that such sliding shoes for axial piston pumps, without any reworking of the ball sealing surfaces, can not be produced by injection molding of silicon nitride.

This arranged on each of the sliding shoes ball sealing surface places increased demands on the dimensional accuracy and surface quality, only by the arranged on the shoes ball sealing surfaces can be the sealing of the axial piston connected sealing and sliding tasks (along this functional surface) of the ball sealing surface fair.

Therefore, on the manufactured according to the current state of the art, ball sealing surfaces a machining post-processing of the high-strength ceramic component is mandatory.

Due to the high hardness and high wear resistance and necessary for processing, absolutely necessary expensive tools and aids such reworking a ball sealing surface after sintering is very expensive, because due to the high material hardness for finishing the ball sealing surface only erosive methods such as grinding, honing, cloth or special procedures such as ultrasonic and laser processing come into question.

The invention is therefore based on the object of developing a method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, such as silicon nitride, which ensures high dimensional accuracy for components produced by injection molding with subsequent sintering from injection-moldable materials of high-performance ceramics, such as silicon nitride that, for example, the dimensional accuracy of the spherical shape of a (for example, arranged on a shoe for axial piston pump) ball sealing surface without any greening, as well as without any post-machining the high-strength ceramic spherical surface shape after the sintering of silicon nitride manufactured shoe optimally meets the increased demands on the dimensional accuracy to ensure the sealing associated with the sealing and sliding tasks of these functional surfaces.

According to the invention, this object is achieved by a method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, such as silicon nitride, for example for producing a component from silicon nitride with a ball sealing surface, according to the features of the main claim of the invention.

Advantageous embodiments, details and features of the invention will become apparent from the dependent claims and the following description of the solution according to the invention in conjunction with seven representations of the inventive solution.

It show the:

1 : an axial piston pump 1 in side view in section with a sliding shoe 2 and the ball sealing surface disposed thereon 3 ;

2 : a slide shoe 2 for axial piston pumps 1 in side view in section with the ball sealing surface 3 ;

3 : an injection molded shoe 2 after sintering with sink marks 6 ;

4 : the flow path in the injection molding tool during the production of the green pieces of the sliding shoes 2 ;

5 : a drawing shoe illustrated 2 with the nominal geometry 7 (Nominal contour) of the ball sealing surface 3 , the IS contour 8th after sintering and the representation of the correction surface according to the invention 9 ;

6 : the detail A according to 5 , with the edge region determined according to the invention 10 ;

7 : the detail A according to 5 after scaling up the shrinkage factor and with the determined interface 11 with tangent-continuous curve in the original border area 10 ,

The 1 shows an axial piston pump 1 in the side view, in section with a sliding shoe 2 and the ball sealing surface disposed thereon 3 ,

In the prior art, these sliding shoes for axial piston pumps made of steel with appropriate heat treatment or coatings (eg DLC) are produced.

Currently in the production of these, as an item in the side view in section in the 2 illustrated sliding shoes 2 required work processes are complex and energy-intensive. These are turning, honing, colosting, trovalizing, drying and coating.

Despite these high production costs, the sliding shoes are very susceptible in terms of running time as well as friction losses, as even the smallest deviations in the process or in the operating conditions have a major impact on the final product, especially in the case of coatings.

In the search for alternative solutions, a main objective was to reduce the process steps and thus the logistical effort, since currently the above-described process steps required for the production of the sliding shoes are carried out by four suppliers at four different locations.

With this alternative solution but at the same time a high dimensional stability and insensitivity to all eligible pumped media (media from acidic to basic), as well as a homogeneous, störunanfälliges structure should be ensured, also should in the context of the required development of the currently deploying product the robustness of these shoes significantly increased in terms of their wear and their temperature resistance, while also reducing the power consumption of the axial piston pumps by a significant reduction in friction losses during operation.

The material used in this study was also the ceramic high-conductivity materials.

Components with such geometries for use in such tribological systems, however, can not be made in the current state of the art of ceramic high-conductivity materials in the required quality and with the predetermined / required tolerances economically / cost-effectively in industrial mass production.

This applies to both the non-oxidic ceramics (such as SIC, Si3N4) as well as the oxide ceramics (such as Al2O3) in connection with the industrial processes used in these materials, such as injection molding or pressing.

In the present case, the full interchangeability with respect to the component made of steel "shoe" is a mandatory Basic requirement for the use of a new material, so that the component, the shoe, not in consideration of the material used, ie material-specific, can be redesigned.

In connection with the use of high performance ceramics, preferably silicon nitride, both the very small wall thickness, as well as the exact form of the spherical shape was very critical.

First try these shoes 2 Producing high-performance ceramics by injection molding showed that the quality of the sinter-finished surface and the component-specific tolerances led to sink marks after the sintering process 6 formed on the spherical shape, which when using these sintered sliding shoes 2 too high leakage in the area of the ball sealing surface 3 led.

Further studies revealed the sliding shoes made of silicon nitride 2 in the 3 illustrated geometry after the sintering fire. Characteristic are sink marks 6 in the area of the thin-walled ball sealing surface 3 after the sintering process.

It turned out that these sink marks 6 also related to the flow behavior of high performance ceramics in the injection mold. In the 4 is therefore the flow path 4 in the injection mold, in the manufacture of the green compacts of the sliding shoes 2 , with the position of the injection point 5 shown.

The dimensional and form tolerances of ceramic components produced by injection molding as standard are after the sintering firing at +/- 3% relative to the nominal geometry, here the nominal geometry 7 ie a ball sealing surface 3 with a ball diameter of 10 mm then the achievable with the standard injection molding process dimensional accuracies in the tolerance range of 9.7 mm to 10.3 mm.

According to the state of the art, it is currently possible to reduce these manufacturing tolerances to 1.5%.

To realize this, u. a. changed the sprue system, heated the sprues, but also tested a multi-part sprue system.

In addition, sintering aids were used around the spherical shape of the ball sealing surface 3 to support in sintering and so on.

However, it was confirmed only that it is only possible with the currently customary in the prior art precision method resulting in significantly increased production costs, the manufacturing tolerances of injection molded components, ie concretely the shoes 2 to reduce to a maximum of 1.5% after sintering.

Thus, the dimensional accuracies that can be achieved with significantly increased expenditures were still too high for the given ball diameter of 10 mm after sintering, and were within the tolerance range of 9.85 mm to 10.15 mm.

A desired interchangeability with respect to the component made of steel, here the sliding shoe 2 , but would only be guaranteed if the surface form deviations are within a maximum of 0.04 mm.

These (precision) components should be produced from a high-performance ceramic as inexpensively as possible and, if possible, by injection molding. In this case, a material of high-performance ceramics, preferably silicon nitride, should be used, and the ball sealing surface 3 on the slide shoe 2 should after sintering without an individual post-processing of the ball sealing surface 3 meet the increased demands on the dimensional accuracy to meet the sealing and sliding tasks associated with the sealing of the sliding surfaces.

The method according to the invention for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, using the exemplary embodiment for producing a sliding shoe, will be described below 2 for those in the 1 illustrated axial piston pump 1 , presented.

With the inventive method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, it has been possible to eliminate the disadvantages of the prior art, ie concretely sliding shoes 2 for axial piston pumps 1 produced by injection molding of silicon nitride whose surface shape deviations after sintering in the tolerance range of 0.04 mm, so that the sealing surfaces produced by means of the inventive solution 3 without individual post-processing to meet the increased demands on the dimensional accuracy to ensure the sealing and sliding tasks associated with the seal. The inventive method will be described below with reference to the representations in the 5 . 6 and 7 be explained in more detail.

According to the invention, a standard basic injection molding tool with a base injection mold arranged in this basic injection molding tool was used for this purpose Construction documents of each to be manufactured component, here the shoe 2 predetermined, in the 5 illustrated nominal geometry 7 based on the material-specific shrinkage factor, as well as the usual in the art for such methods and materials tool parameters, was formed.

• A: mit der Basisspritzgussform 80 Stück Basisbauteile abgespritzt, entbindert und danach gesintert werden, und
• B: dass danach diese gesinterten 80 Stück Basisbauteile unter Berücksichtigung Ihrer ursprünglichen Lage in der Basisspritzgussform mittels eines optischen Messverfahrens vollständig vermessen, und diese Messwerte statistisch ausgewertet und zu 100% digitalisiert werden, und
• C: dass danach durch einen Vergleich dieser Messwerte mit der konstruktiv vorgegebenen SOLL-Kontur, der Nominalgeometrie 7, der Kugeldichtfläche 3 die funktionskritischen Formabweichungen ermittelt werden, und
• D: dass nachfolgend die Messwerte der digitalisierten funktionskritischen Formabweichungen, beispielsweise mittels eines Computerprogrammes, wie eines herkömmlichen CAD-Programms, weiterverarbeitet werden, und
• E: dass danach die digitalisierten Formabweichungen, z. B. mittels des CAD-Programms, mit jeweils einer Punktewolke überzogen, und so die in der 5 dargestellte IST-Kontur 8 abgebildet wird, und
• F: dass danach alle erzeugten Punkte der IST-Kontur 8, lotrecht zur, d. h. normal an der konstruktiv vorgegebenen Nominalgeometrie 7 der Kugeldichtfläche 3 (als Spiegeloberfläche) gespiegelt werden, so dass außerhalb der konstruktiv vorgegebenen Nominalgeometrie 7 der Kugeldichtfläche 3 jeweils eine neue Punktewolke entsteht, und
• G: dass danach diese neue Punktewolke/n, z. B. mittels des CAD-Programmes, zu jeweils einer in der 5 dargestellten Korrekturfläche 9 verbunden wird, und
• H: dass danach auf diese Korrekturfläche/n 9 der werkstoffspezifische Schwindungsfaktor aufscaliert wird, und z. B. mittels des CAD-Programmes die Randbereiche 10 der Korrekturfläche/n 9 mittels Grenzfläche/n 11 mit tangentenstetigem Kurvenverlauf an die ”nicht eingefallene Oberfläche” mit der Nominalgeometrie ”angepasst” werden, wodurch so in der Gesamtheit, d. h. aus der jeweiligen Korrekturfläche 9 und der zugeordneten Grenzfläche 11, die Modellierfläche/n entsteht/entstehen, und
• I: dass nachfolgend unter Berücksichtigung Ihrer ”ursprünglichen” Lage diese, wie erläutert ermittelten Modellierfläche/n nun in die Basisspritzform übertragen werden, d. h. dort eingearbeitet werden, wodurch so aus der Basisspritzform eine Revisionsspritzform entsteht, und
• K: dass danach, analog zu Punkt A, anschließend mit der Revisionsspritzform Revisionsbauteile abgespritzt, entbindert und danach gesintert, und diese wie unter Punkt B beschrieben nachfolgend vermessen und ausgewertet werden, und
• L: dass falls dabei erneut funktionskritische Formabweichungen ermittelt werden, d. h. Formabweichungen an Funktionsflächen die noch nicht im Bereich der Oberflächenrauheit des jeweils zu verarbeiteten Werkstoffes nach dem Sinterprozess liegen, werden die Prozessschritte (analog der beschriebenen Abfolge A bis einschließlich K) so lange wiederholt bis die Formabweichungen am Bauteil im Bereich der Oberflächenrauheit des jeweils zu verarbeiteten Werkstoffes nach dem Sinterprozess liegen.

It is essential to the invention that, in connection with the present exemplary embodiment,

• A: with the basic injection mold 80 pieces base components hosed, debinded and then sintered, and
• B: that after that completely measure these sintered 80 piece base components taking into account their original position in the basic injection mold by means of an optical measuring method, and these measured values are statistically evaluated and digitized to 100%, and
• C: that afterwards by a comparison of these measured values with the constructively specified nominal contour, the nominal geometry 7 , the ball sealing surface 3 the functionally critical form deviations are determined, and
• D: that subsequently the measured values of the digitized function-critical form deviations, for example by means of a computer program, such as a conventional CAD program, further processed, and
• E: that then the digitized form deviations, z. B. by means of the CAD program, each covered with a cloud point, and so in the 5 illustrated actual contour 8th is pictured, and
• F: that after that all generated points of the actual contour 8th , perpendicular to, ie normal to the design nominal geometry 7 the ball sealing surface 3 (as a mirror surface) are mirrored, so that outside the constructive nominal geometry 7 the ball sealing surface 3 in each case a new point cloud arises, and
• G: that after this new point cloud / n, z. B. by means of the CAD program, each one in the 5 illustrated correction surface 9 is connected, and
• H: that after this correction area / n 9 the material-specific shrinkage factor is scaled up, and z. B. by means of the CAD program, the edge regions 10 the correction area / n 9 by means of interface / n 11 with tangent-continuous curve to the "non-sunken surface" with the nominal geometry "adjusted", whereby so in the entirety, ie from the respective correction surface 9 and the associated interface 11 , the modeling surface (s) arise / arise, and
• I: that subsequently, taking into account your "original" position, these modeling surface (s) as explained will now be transferred to the basic injection mold, ie incorporated therein, thus producing a revision injection mold from the basic injection mold, and
• K: that then, analogously to point A, then sprayed with the Revisionsspritzform revision components, debinded and then sintered, and these as described under point B subsequently measured and evaluated, and
• L: that if again functionally critical form deviations are determined, ie form deviations on functional surfaces that are not yet in the range of the surface roughness of the respective material to be processed after the sintering process, the process steps (analogous to the described sequence A to K) are repeated until the Shape deviations on the component in the area of the surface roughness of the respective material to be processed after the sintering process are.

To reduce the surface roughness of the sintered components, in the present embodiment, the sliding blocks 2 made of silicon nitride after sintering.

The surface roughness of the sinter rough surfaces of the sliding shoe is reduced from 0.04 mm to 0.02 mm.

After sintering and Trowalisieren is in the present embodiment in the 1 and 2 illustrated, planar pump work surface 12 the sliding shoes 2 , to ensure optimum sealing while minimizing friction losses of the axial piston pump in operating condition, still ground flat. At the same time, the surface roughness of the trowalized pump work surface becomes 12 of the sliding shoe described in the embodiment 2 again significantly reduced to less than 0.006 mm. By means of the method according to the invention for producing an injection mold, it has been possible to achieve a high dimensional accuracy for components produced by injection molding with subsequent sintering from injection-moldable materials of high-performance ceramics, such as silicon nitride, so that, for example, as explained in the exemplary embodiment, the dimensional accuracy of the spherical shape of a (for example a Gleitschuh arranged for axial piston pump) ball sealing surface without any greening, but also without any post-processing of the high-strength ceramic ball surface shape after the sintering of the shoe made of silicon nitride, optimally the increased demands on the dimensional accuracy to ensure the sealing associated with the sealing and sliding tasks this Functional surfaces is fair.

LIST OF REFERENCE NUMBERS

1

axial piston pump

2

shoe

3

Ball sealing surface

4

flow behavior

5

injection point

6

sink mark

7

nominal geometry

8th

IS-contour

9

correction area

10

border area

11

interface

12

Pump working space

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008026218 B4 [0006]
• DE 102013011209 B3 [0006]
• DE 3942686 C2 [0008, 0009]

Claims (3)

Method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics, such as silicon nitride, based on a basic injection molding tool with a base injection mold arranged in this base injection mold, which is based on the nominal geometry specified in the design documents of the respective component to be manufactured ( 7 ), and which is designed taking into account the material-specific shrinkage factor, as well as the usual in the art for such methods and materials tool parameters, characterized in that : first sprayed with this basic injection mold at least 25 pieces of base components, debindered and then sintered and then B: that thereafter fully measure these sintered, at least 25 base components, taking into account their original position in the base injection mold, by means of an optical measurement method, and statistically evaluating and digitizing these measured values to 100%, and C: thereafter by comparing these Measured values with the constructively specified nominal contour, the nominal geometry ( 7 ), the functionally critical form deviations are determined, and D: that subsequently the measured values of the digitized function-critical form deviations are further processed, for example by means of a computer program such as a conventional CAD program, and E: that after that the digitized form deviations / s, e.g. B. by means of the CAD program, with one / more points cloud / n covered and, as the actual contour ( 8th ), and F: that after that all generated points of the actual contour ( 8th ), perpendicular to, ie normal to the design nominal geometry ( 7 ), the target contour, (as a mirror surface) are mirrored, so that outside of the design nominal geometry ( 7 ) each time a new point cloud is created, and G: that after this new / n point cloud / n, z. B. by means of the CAD program, each having a correction surface ( 9 ), and H: that after this correction area / n ( 9 ) the material-specific shrinkage factor is scaled up, and the edge regions ( 10 ) of the correction area / n ( 9 ) by means of interfaces ( 11 ) with a tangent-continuous curve to the "non-sunken surface" with the nominal geometry ( 7 ), z. B. by means of the CAD program, "adjusted", whereby so in the entirety, ie from the respective correction surface ( 9 ) and the associated interface ( 11 ), the modeling surface (s) is / are formed, and I: that subsequently considering their "original" position in the base injection mold, these modeling surface (s) as explained will now be transferred to the base injection mold, ie incorporated therein, thus resulting in the basic spray form a revision injection mold is formed, and K: then, analogously to point A, but then sprayed with the Revisionsspritzform the "revision components" debinded, then sintered and subsequently measured and evaluated as described in point B, and L: that if again Functional deviations in shape are determined, ie form deviations on functional surfaces which are not yet in the range of the surface roughness of the respective material to be processed after the sintering process, the process steps (analogous to the described sequence A to K) are repeated until the deviations in shape on the component in the Surface roughness of the respective material to be processed after the sintering process are. A method for producing an injection mold for components made of injection-moldable materials of high performance ceramics according to claim 1, characterized in that to reduce the surface roughness of the sintered components, they are tumbled after sintering. A method for producing an injection mold for components made of injection-moldable materials of high-performance ceramics according to claim 1 or claim 2, characterized in that to further reduce the surface roughness of special planar functional surfaces after sintering, for example, to ensure a friction loss associated therewith, these planar functional surfaces are ground flat.

Images