WO2016146120A1

WO2016146120A1 - Method for producing a porous component made from at least one material m and having a foam structure as well as a subsequently fabricated porous component

Info

Publication number: WO2016146120A1
Application number: PCT/DE2016/200125
Authority: WO
Inventors: Heinrich Sauer
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2015-03-17
Filing date: 2016-03-09
Publication date: 2016-09-22
Also published as: DE102015204752A1

Abstract

The invention relates to a method for producing a porous component (1, 1') made from a material (M) and having a foam structure, comprising the following steps: introducing a granulate (6), comprising a first powder containing at least one polymer and further comprising a second powder of the material (M), into an injection moulding machine (2), by means of which the granulate (6) is conveyed and transferred into a moulding compound (6a); gassing of the moulding compound (6a); bringing of the gassed moulding compound (6a´) out of the injection moulding machine (2) into an injection mould (9) by forming a foamed moulding compound and a moulding (10), and solidifying of the moulding (10); debinding of the solidified moulding (10) and sintering of the debinded moulding (10) by forming the porous component (1, 1´), wherein at least one injection-moulded part (12) is inserted in the injection mould (9) and the foamed moulding compound is injected on the at least one injection-moulded part (12), wherein after solidifying of the foamed moulding compound the formed moulding (10c) comprises the at least one injection moulded part (12), and/or at least two moulding compounds (6a) containing different materials (M) are brought simultaneously and/or one after the other into the injection mould (9).

Description

Method for producing a porous component from at least one material M and having a foam structure and a porous component produced thereafter

The invention relates to a method for producing a porous component from at least one material M and having a foam structure and a porous component produced by the method. Porous components having a foam structure formed of different materials, such as metal, metal alloys, ceramics, glass or plastic are already known.

Thus, DE 197 17 894 A1 discloses a process for the production of moldings based on metal foam. In this case, a powder of a metal or a metal alloy with particles of a blowing agent, which splits off a gas at elevated temperatures, compacted to form a green body and heated to a temperature above the decomposition temperature of the blowing agent and the melting temperature of the metallic powder. The forming metallic melt is foamed by the forming gas of the decomposing blowing agent and the formed metal foam solidified by cooling to a shaped body.

As further possibilities for the production of metal foam, the injection of gas into a molten metal is known, which was previously made foamable by adding solid ingredients.

DE 10 2006 053 155 A1 describes a process for the production of open-pore ceramic foam, wherein an open-pore, burn-off foam structure is impregnated with an aqueous suspension containing talc, silica and kaolinite and dried. Subsequently, the impregnated foam structure is calcined at a temperature at which the foam structure burns off and the talc, silica and kaolinite sinter together to form the ceramic foam. DE 44 05 331 A1 also describes a method for producing a

Ceramic member having a ceramic foam structure in which a molded article comprising substantially non-oxide ceramic components is prepared by oxidizing from a surface of the molded article. The foam structure is also provided by impregnating an open-pore plastic foam with a Keramikschiicker.

German Patent No. 634405 discloses a process for the production of foam glass, wherein a non-refined glass containing sulfate radicals is fritted with reducing substances until the melt is swollen.

For the production of plastic foams several methods are known. In physical foaming, a plastic melt is foamed by a physical action, for example, by release of gas in a polymerization reaction. In a chemical foaming, a propellant is added to a plastic granulate and the granules are melted. Due to the heat supply, a volatile constituent of the propellant separates, which leads to foaming of the plastic melt. In the case of mechanical foaming, a gas is pressed into the melt of the plastic to be foamed or a liquid organic mass still to be polymerized.

DE 103 07 736 A1 describes the production of an open-cell foam by melting a thermoplastic or a mixture containing a thermoplastic. The melt thus obtained is mixed under pressure with at least one blowing agent and foamed. The cell opener used is a powdery solid, in particular comprising graphite, or a foreign polymer. As blowing agents inert gases, hydrocarbons, aliphatic alcohols or ketones or esters, chemical blowing agents, etc. are described. These are optionally used in combination with water. The foam is produced, for example, by means of an extruder.

WO 201 1/016718 A1 discloses a process for the production of components by injection molding, wherein a mixture of a powder and binder comprising at least one thermally decomposable polymer and a low molecular weight solvent largewicht, produced and sprayed. This is followed by debindering and sintering to form a component.

US 4,734,237 discloses a method for the production of components of metallic see and / or ceramic powders. The powder is mixed with a gelling agent, in particular agar and / or agarose, and water and sprayed to form a dimensionally stable component. Subsequently, a drying and sintering to form a component made of metal and / or ceramic. JP2003213304 A discloses an injection molding method using pellets formed of metal or ceramic powder and binder kneaded together. Furthermore, a foaming agent is added during injection molding, so that bubbles are formed in the formed component. As foaming agent, a gas of the injection molding compound is abandoned. The formed injection molded part is after the

Demoulding debinded and sintered.

DE 102012202104 A1 describes a production of a roller bearing cage or cage segment by means of metal powder injection molding (MIM = Metal Powder Injection

Molding).

It is an object of the invention to provide a further method for producing a porous component made of a material M and having a foam structure and a porous component produced by this method. The object is achieved for the method for producing a porous component of at least one material M and having a foam structure comprising the following steps:

- introducing a granulate comprising a first powder containing at least one polymer and further comprising a second powder of the at least one material M in an injection molding machine, by means of which the granules are conveyed and converted into a molding material;

- gassing the molding compound;

Discharging the gassed molding material from the injection molding machine into an injection mold to form a foamed molding compound and a molded part, and solidification of the molding;

- Debinding the solidified molding and sintering of the debindered sprue to form the porous member, wherein

at least one injection molded part is inserted in the injection mold and the foamed molding compound is injection molded onto the at least one injection molded part, wherein after solidification of the foamed molding compound the formed injection molding comprises the at least one injection molded part, and / or at least one of the injection mold simultaneously and / or successively two molding compounds are introduced, which contain different materials (M).

Here, high demands are placed on a coordinated shrinkage behavior of the molded part and the solidified, foamed molding compound during debindering and sintering. In particular, it has proven to be useful if the first powder is also used to form the injection-molded part. This facilitates the bonding of the foamed molding compound to the molding in the injection mold. It is possible to produce porous components which have the foam structure only in part of their component volume. Also different materials M in the molding and in the molding compound can be joined together by sintering. If, alternatively or in combination, at least two foamed molding materials containing different materials M are introduced into the injection mold simultaneously and / or in succession, a smooth transition between the molding compounds and thus also the second powder in the produced injection molding and porous component can be produced , This improves the connection and thus the mechanical strength between the areas with different materials M.

The inventive method allows a fast, automated and thus cost-effective production of the molding by means of an already known for the production of plastic foam using an injection molding machine. The foaming of the molding compound takes place at the outlet of the gassed molding compound from the injection molding machine, wherein the required temperatures and pressures can be accurately monitored and adjusted. The molding compound is applied in an injection mold and solidified in the mold. It will the outer shape of the formed, solidified injection molded to the desired final contour of the porous component to be produced.

In this case, a porous component is also understood as meaning that has a foam structure only in a partial region of its component volume. In general, porous components with open or closed porosity can be formed, and in macroscopic partial regions of the porous component as well

a closed porosity next to an open porosity or

a closed porosity next to an area without porosity or

an open porosity next to an area without porosity or

a closed porosity can be formed next to an open porosity and furthermore next to an area without porosity.

In this case, component volumes which have at least a wall thickness of 1 mm are regarded as macroscopic partial regions.

The granules are preferably formed by forming a powder mixture of the first powder and the second powder and converting the powder mixture into the free-flowing granules. The granules are produced in particular in a so-called compounding process, in which the first and the second powder are intimately mixed and a molding compound is produced. From the molding compound a free-flowing granules is produced, with which an injection molding machine can be automatically charged. Alternatively, ready-to-process granules may alternatively be finished. In particular, at least partially, biopolymers are used for the inventive method for the formation of the first powder.

In a particularly preferred embodiment, the method according to the invention comprises the following steps:

Using the granulate comprising the first powder containing at least one thermoplastic polymer and further the second powder of the at least one material M;

- Introducing the granules in the injection molding machine, by means of which the granules are conveyed and heated until the molding material is in the form of a melt; Injecting a supercritical gas into the melt,

- discharging the fumigated melt from the injection molding machine into an injection mold to form a foamed molding compound and a molded part;

- cooling the injection molding to a temperature below the melting range of the first powder with solidification of the injection molding;

- Debinding the solidified molding and sintering the debindered injection molding to form the porous member.

The use of thermoplastic polymers allows a mechanical foaming of the melt, without at the same time chemical reactions take place in the injection molding machine and at the same time have to be controlled or at least monitored. This leads to a simplification of the process and the required system technology. Preferably, the first powder comprising the at least one thermoplastic polymer melts in a temperature range from 50 ° C to 250 ° C, in particular from 80 ° C to 180 ° C, on. The temperature range in which the second powder melts from the material M is significantly higher, so that it does not change its solid state of aggregation during the performance of the process.

In particular, at least one thermoplastic polymer from the group comprising polyacetal (POM), polyolefins and polyamides is used. The first powder preferably comprises the at least one thermoplastic polymer and further at least one substance from the group of alcohols, waxes and Karbonsäu- rederivate. In particular, paraffin wax has proved to be a wax.

Supercritical CO2 or supercritical N ₂ is preferably used as the supercritical gas. In an alternative embodiment of the method according to the invention, this comprises the following steps:

- Introducing the granules in the injection molding machine, by means of which the granules are conveyed and heated until the molding material is in the form of a melt;

- Adding an aggregate to the granules and / or the molding material, which decomposes and releases a propellant gas;

- Applying the fumigated melt from the injection molding machine in an injection mold to form a foamed molding material and a molded part, and solidification of the molded part;

Due to the addition of a solid aggregate to the granules and / or the molding compound simplifies in this process, the structure of the injection molding machine. The solid aggregate can be mixed homogeneously and thus a particularly uniform distribution of the pore structure in the porous component can be achieved.

In a further alternative embodiment of the method according to the invention, this comprises the following steps:

- Using the granules containing the first powder at least one

Hydrocolloid and further comprises the second powder of the at least one material;

- Introducing the granules, optionally with the addition of water, in the injection molding machine, by means of which the granules are conveyed and compacted until the formed molding material is present as a gel;

- injecting a supercritical gas into the gel;

- Applying the gassed gel from the injection molding machine in an injection mold to form a foamed gel and a molded part, and solidification of the molded part;

The term "hydrocolloids" encompasses a large group of polysaccharides and proteins which dissolve in water as colloids and show a high ability to gel, a particularly suitable hydrocolloid being the biopolymer agar can be solidified by drying. In a particularly preferred variant of the method according to the invention, a bonding of a solidified first injection molding with at least one solidified further injection molding takes place. This is followed by a joint debindering of the interconnected injection-molded parts and sintering of the debindered, interconnected injection-molded parts to form the porous component. In particular, porous components are formed which, because of their complex geometry, can not be produced in a single injection molding process or at least can not be readily manufactured. Depending on the first powder used, the injection-molded parts are joined, for example by plastic welding, in which a thermoplastic polymer in the first powder is heated and the heated joining surfaces of the injection-molded parts are pressed against one another. Upon cooling of the bonding surfaces, a solid bond is formed between the moldings, whereby the molding formed therefrom can have a highly complex shape. When using hydrocolloids in the first powder already moistening of the connecting surfaces of the injection moldings and a bringing into contact with this sufficient to make a connection between the

Produce molded parts. After drying, there is also an educated injection molding which can have a highly complex shape.

It is particularly advantageous if the first injection molding and at least one of the further injection molded parts each contain second powder of different materials M. As a result, porous components can be formed, which are formed in partial areas of different foam materials. This makes it possible to achieve a targeted adaptation of the properties of the porous component to the existing application and, in particular, to the local application on the component. In this case, regions of the porous component which are subject to wear, for example, can be formed, for example, from ceramic, while corrosively stressed regions can be formed from metals or metal alloys. However, the production of such a porous component requires special attention to the adaptation of the shrinkage or the temporal shrinkage behavior of the first injection molding and the at least one further injection molding during debindering and subsequent sintering. A deviation in the shrinkage behavior of the first injection molding from the shrinkage behavior of the at least one further injection molding leads to stresses in the transition region of the first injection molding to at least one further injection molding and thus to cracks and / or structural weakening the porous member, if such can be formed dimensionally stable.

It has proved to be particularly useful if, for the formation of the first molded part as material M, a tempering steel and for the formation of the at least one further

Springs as material M a tool steel is used.

The material M is formed in particular from metal, a metal alloy, ceramic or a mixture of at least two of these materials. In particular, the material M is formed of metal, a metal alloy or ceramic. In this case, the melting range for the material M, ie the temperature at which the material M begins to soften, is generally above the melting range or the melting temperature of the first powder. Titanium is to be mentioned as a particularly preferred metal here. Metal alloys of tempered steel, stainless steel, mild steel and tool steel are also preferred. A particularly preferred ceramic material M is Si ₃ N _{4 here} .

In a preferred embodiment of the process, at least 50% by volume and at most 70% by volume of the granules are formed from the second powder. Preferably 55% by volume to 65% by volume of the granules are formed from the second powder. A higher proportion of the second powder in the granules affects the foamability of the melt, while a smaller proportion of the second powder in the granules affects the stability of the sintered framework of the material M, which remains after debindering the molding with stabilizing residues from the first powder.

Debinding of the molded part takes place in particular by means of bakeout, by means of dissolving out by a solvent or by chemical decomposition of the carbon-containing components of the first powder. Not 100% of the first powder is usually removed, but only 80 to 99%, in particular 90 to 95%, to ensure a residual strength of the debindered sprue for the sintering process. When sintering the debindered sprue, the remaining residues of the first powder decomposes and ideally completely removed.

The object is further achieved for the porous component of at least one material M and having a foam structure at least in partial regions of its component volume produced by the method according to the invention, in that the foam structure has a degree of foaming in the range from 2: 5 to 1:50.

The degree of foaming is the ratio of the density of the sintered foam structure to the density of the second powder from which the foam structure is formed. Such porous components have a reduced weight compared to components made of solid material and are inexpensive and automated to produce.

In a particularly preferred embodiment, the porous member is designed in the form of a cage or a cage segment for a roller bearing, wherein the cage or the cage segment is designed for receiving rolling elements. Such a cage in lightweight construction is ideal in particular for rolling bearings in special applications in the field of aerospace engineering. In a further preferred embodiment, the porous component is in the form of a motor element, in particular in the form of a finger lever.

The porous component in the form of a cage, a cage segment or a motor element is preferably formed from a material M made of metal and / or a metal alloy and / or ceramic. However, engine elements are particularly preferably formed from metal or a metal alloy.

Figures 1 to 6 are intended to exemplify a known and in particular inventive method and porous components produced therewith. So shows:

FIG. 1 shows a known process using a first powder comprising a thermoplastic polymer;

FIG. 2 shows a porous component made of a metal alloy;

3 shows a method according to the invention, in which an injection-molded

Form part of a foam structure is molded Figure 4 a from the injection molding according to Figure 3 after debinding and

Sintered porous member according to the invention;

Figure 5 shows a method in which two solidified moldings are connected;

and

6 shows the formed according to Figure 5, joined sprue. and

FIG. 1 shows a known process using a first powder comprising a thermoplastic polymer in the form of polypropylene. As a second powder of the material M tool steel is used, which has a higher melting temperature than the first powder of polypropylene. The first powder and the second powder are mixed together, one not shown here

Compounding process takes place, which provides a flowable granules 6. The granulate 6 is filled via a filling aid 5 in an injection molding machine 2 (both shown here in longitudinal section) and compacted by means of a screw conveyor 4. The injection molding machine 2 has a heating tape 3, which causes heating of the granules 6 in the injection molding machine 2. During the melting of the granules 6, a molding compound 6a in the form of a melt of the thermoplastic polymer is formed, into which the second powder is mixed. Now, an injecting a supercritical gas 8 takes place, here in the form of supercritical N _2, a Gaszuführein- direction 7 into the injection molding machine 2, and thus the melt. An application of the gassed molding compound 6a ^' or fumigated melt from the injection molding machine 2 is carried out to form a foamed molding compound and a molded part 10. The introduced into the melt gas 8 expands upon exiting the fumigated molding compound 6a ^' from the injection molding machine 2 and foams the Melt up. In this case, the foamed melt is injected into a cavity 9c (indicated by dashed lines) of an injection mold 9, which consists of two parts 9a, 9b. In this case, the part 9b is movable (see double arrow) in order to enable removal from the injection mold 9 of the solidified injection molding 10 (shown visibly here in the closed injection mold 9 for the sake of clarity). The solidification of the injection molding 10 takes place by cooling the injection molding 10 to a temperature below the melting temperature of the thermoplastic polymer in the closed injection mold 9. For this purpose, the injection mold 9 is connected to a cooling device, not shown. The solidified injection molded part 10 removed from the injection mold 9 is debinded by baking, with the first powder extending to decomposed to a residue and volatilized. This is followed by sintering of the debinded injection molding to form a porous component 1 (see FIG. 2) from the second powder. FIG. 2 shows a porous component 1 formed from the material M, in this case from the tool steel, according to the known method according to FIG. 1, with a closed pore space 11. In this case, the porous component 1 generally has a foam structure with regard to its component volume. Figure 3 shows a method according to the invention, in which an injection-molded

Molded part 12 a foam structure is molded. The same reference numerals as in Figure 1 denote the same elements. Again, the injection molding machine 2 is shown in longitudinal section. In the injection mold 9, an injection molded part 12 is inserted and the injection mold 9 is closed. Subsequently, the fumigated molding compound 6a ^'is injected into the injection mold 9, wherein the formed foamed molding compound covers the free surfaces of the molding 12 and connects to them. After solidification of the foamed molding compound in the injection mold 9, there is a molded part 10 c, which includes the molded part 12. Alternatively, the molded part 12 can also be formed by injecting an injection molding compound into the injection mold 9 and solidifying it before the foamed molding compound is injected into the same injection mold 9. For this purpose, the injection mold 9 is transported by a first injection molding machine, which is filled to form the molding 12, to a further injection molding machine, which provides the foamed molding compound.

Alternatively, according to the invention, at least two molding compounds 6a, which contain different materials M, can be introduced into the injection mold 9 simultaneously and / or successively. An injection of the injection molding compounds in the injection mold 9 can be carried out simultaneously or immediately successively, with the un solidified injection molding compounds intimately connect and mix in the contact area. But also a solidification of the first injected injection molding compound to form a molding to which the second injection molding compound is injected, is possible. Also, combinations of these approaches, wherein from the first injection molding compound produces a molding and then both injection molding compounds are injected simultaneously is possible. Also, from the two simultaneously injected injection molding compounds, first a solidified molded part can be formed and then a third injection-molding compound can be injection molded, the composition of which differs preferably from the two injection molding compounds used to form the molded article.

In this way, porous components with highly complex outer geometry and internal structure and composition can be produced. FIG. 4 shows the porous component 1 ^' which has been formed from the molded part 10c comprising the molded part 12 (formed in accordance with the method shown in FIG. 5) by subsequent debindering and sintering. In this case, the area of the porous component 1 ^' , which is formed by the sintered shaped part 12 ^' without porosity, and furthermore the area of the porous component 1 ^' , which is formed by the sintered foam structure 10c ^' , are shown separately.

FIG. 5 shows a method in which two injection-molded parts 10a, 10b which have been formed by a method according to the invention are joined. In this case, the solidified injection-molded parts 10a, 10b are heated at their connecting surfaces 100 until the first powder can be softened and deformed. Subsequently, the two injection-molded parts 10a, 10b are pressed against one another with their heated connecting surfaces 100 (see arrows on force F), wherein the connecting surfaces 100 connect to one another. After cooling, there is a molded part 10, see Figure 6, which is composed of the two moldings 10a, 10b. Now debindering and sintering of the molding 10 can take place to form a porous component thereof. In this way, porous components with highly complex outer geometry and internal structure and composition can be produced. LIST OF REFERENCE NUMBERS

1, 1 ^' porous component

2 injection molding machine

3 heating tape

4 screw conveyor

5 filling aid

6 granules

6a molding compound

6a ^' fumigated molding material

7 gas supply device

8 supercritical gas

9 injection mold, divisible

9a, 9b parts of the injection mold 9

9c cavity

10,10a, 10b, 10c injection molding

10c ^' sintered foam structure

100 interface

1 1 pore space

12 molding

12 ^' sintered molding

M material

F force

Claims

claims

1 . Process for producing a porous component (1, 1 ^' ) from at least one material (M) and having a foam structure, comprising the following steps:

- introducing a granulate (6) comprising a first powder containing at least one polymer and further comprising a second powder of the at least one material (M) in an injection molding machine (2), by means of which the granules (6) conveyed and in a molding compound (6a ) is transferred;

- gassing the molding compound (6a);

- applying the gassed molding compound (6a ^' ) from the injection molding machine (2) in an injection mold (9) to form a foamed molding material and a molded part (10), and solidification of the molded part (10);

- Debinding the solidified injection molding (10) and sintering of the debindered injection molding (10) to form the porous member (1, Γ), wherein

in the injection mold (9) at least one injection-molded part (12)

is inserted and the foamed molding compound is injection-molded onto the at least one injection-molded part (12), wherein after solidification of the foamed molding composition of the formed molding (10c) comprises the at least one injection-molded part (12), and / or in the injection mold (9) simultaneously and / or one after the other at least two molding compounds (6a) are introduced which contain different materials (M).

2. The method of claim 1, wherein the granules (6) is formed by a powder mixture of the first powder and the second powder is formed and the powder mixture is transferred into the flowable granules (6).

3. The method according to claim 1 or claim 2, comprising the following steps:

- using the granules (6) comprising the first powder containing at least one thermoplastic polymer and further the second powder of the at least one material (M);

- Introducing the granules (6) in the injection molding machine (2), by means of which the granules (6) is conveyed and heated until the molding material (6a) is in the form of a melt;

- injecting a supercritical gas (8) into the melt ,; - Applying the fumigant melt from the injection molding machine (2) in an injection mold (9) to form a foamed molding material and a

Molded parts (10);

- cooling the injection molding (10) to a temperature below the melting range of the first powder while solidifying the injection molding (10);

- Debinding the solidified molding (10) and sintering the debindered injection molding (10) to form the porous member (1, Γ).

4. The method according to claim 1 or claim 2, comprising the following steps:

- supplying an aggregate to the granules (6) and / or the molding compound (6a), which decomposes and liberates a propellant gas;

- Applying the fumigant melt from the injection molding machine (2) in an injection mold (9) to form a foamed molding material and a

Molded parts (10) and solidification of the molded part (10);

5. The method according to claim 1 or claim 2, comprising the following steps:

- using the granulate (6) comprising the first powder containing at least one hydrocolloid and further the second powder of the at least one material (M);

- Introducing the granules (6), optionally with the addition of water, in the injection molding machine (2), by means of which the granules (6) is conveyed and compacted until the molding compound formed (6a) is present as a gel;

- injecting a supercritical gas (8) into the gel;

- Application of the gassed gel from the injection molding machine (2) in an injection mold (9) to form a foamed gel and a molded part (10), and solidification of the molding (10);

6. The method according to any one of claims 1 to 5, comprising the following further steps:

- bonding a solidified first molded part (10a) to at least one further solidified molded part (10b);

- Common debindering the interconnected injection-molded parts (10a, 10b) and sintering the debindered, interconnected injection-molded parts (10a, 10b) to form the porous member (1, 1 ^' ).

7. The method of claim 6, wherein the first injection molding (10a) and at least one of the further injection moldings (10b) respectively second powder of different materials

(M) included.

8. The method according to claim 7, wherein for forming the first molded part (10a) as material (M) a tempering steel and for forming the at least one further

Moldings (10b) as a material (M) a tool steel is used.

9. The method according to any one of claims 1 to 8, wherein the material (M) is formed of metal, a metal alloy, ceramic or a mixture of at least two of these materials.

10. The method according to any one of claims 1 to 9, wherein at least 50 vol .-% and at most 70 vol .-%, in particular 55 vol .-% to 65 vol .-%, of the granules (6) are formed from the second powder ,

1 1. Porous component (1, 1 ^' ) of at least one material (M) and having a foam structure at least in partial areas of its component volume, produced by a method according to one of claims 1 to 10, wherein the foam structure has a degree of foaming in the range of 2: 5 to 1 : 50.

12. Porous component according to claim 1 1, which is designed in the form of a cage or a cage segment for a rolling bearing, and wherein the cage or the cage segment is designed to receive rolling elements.

13. Porous component according to claim 1 1, which is in the form of a motor element, in particular in the form of a finger lever formed.