EP0701875B1 - Process for preparing metallic articles by injection moulding - Google Patents

Description

The present invention relates to an improved method for Manufacture of metallic molded parts by processing a Injection molding compound, where a.) The injection molding compound to the molded part processed and b.) part of the contained in the molded part Binder removed and c.) Sinters the molded part thus obtained.

For the production of metallic molded parts by powder metal injection molding Various methods are already known. In the EP-A 413 231 describes a process for the production of inorganic Sintered parts described. In a first stage, the sinterable powder and polyoxymethylene as binders a deformable Mass made in the form of granules. From these deformable masses are then so-called by injection molding Green body made. The granules are used in injection molding machines melted and the melt into the corresponding Molds are injected, where they cool down while lowering the temperature and by falling below the glass softening temperature and / or the crystallite melting point of the binder solidify and then removed from the mold (page 1, line 38 to Page 2, line 2). The green bodies obtained in this way become subsequent debinding step from most of the binder exempted, with an acid catalytic debinding the The advantage of this is the gentle removal of the binder to prevent the risk of cracking (page 2, lines 3 to 32). The porous parts thus obtained are then at Temperatures of about 1100 to 1500 ° C sintered, possibly still small amounts of residual binder escape (page 2, Lines 33 to 34).

The process is used to manufacture inorganic sintered molded parts generally very suitable, but it can be, for example in the case of large parts, which may have complicated shapes and / or have thin walls, undesirable during sintering Deformations come. The sintering process requires high temperatures, to set the desired structure in the molded body. Usually the temperatures are around 1100 to 1500 ° C. At these high temperatures can, however, soften the to be sintered molded body can not be excluded. This can For example, with cutlery parts, which during the sintering process plan documents are only very incomplete, too undesirable Deform because the molded body already his own weight experiences a considerable load.

In DE-C 4124393 cutlery parts are disclosed, which by powder metallurgical injection molding. Here too A method is described in which the shaped body essentially through the injection molding process steps, removal of the Binder and subsequent sintering of the molded body (column 2, lines 58 to 64). Here also results the disadvantage that it is in the sintering of the cutlery parts, which have been produced by powder metallurgical injection molding, undesirable deformation can occur.

It was therefore the task of an economic and inexpensive method to find that the disadvantages mentioned remedies and which also in the case of thin-walled or complicated shaped moldings to products of high and uniform Quality leads.

a. die Spritzgießmasse zu dem Formteil verarbeitet und

b. einen Teil des im Formteil enthaltenen Bindemittels bei einer Temperatur von 90 bis 600°C entfernt und

c. das so erhaltene Formteil sintert,

indem man das Formteil auf einer Unterlage sintert, welche annähernd die Kontur des fertigen Formteils aufweist, wobei die Kontur der Unterlage beim Sinterprozeß im wesentlichen erhalten bleibt.Accordingly, a process for the production of a metallic molded part by processing an injection molding compound has been found, whereby

a. the injection molding compound processed into the molded part and

b. removed a part of the binder contained in the molding at a temperature of 90 to 600 ° C and

c. the molded part thus obtained sinters,

by sintering the molded part on a base which has approximately the contour of the finished molded part, the contour of the base essentially being retained during the sintering process.

The invention further relates to those obtainable with the method Molded parts.

The documents used in the method according to the invention ensure good dimensional stability during the sintering process of the molded part. Documents that are particularly suitable advantageously approximately the contour of the finished molded part have a higher creep resistance than that Molded parts or in the sintering temperature range under the influence of Do not crawl the contact forces measurably.

Different materials can be used for the documents become. When using metallic materials, please note that it does not become an undesirable during the sintering process Sintering between the molded part and the base comes. However, this can be done by various measures, such as coating the base with inert powders such as boron carbide, Boron nitride or α-alumina can be avoided. Particularly good ceramic materials such as sintered are suitable Aluminum oxide, zirconium dioxide, silicon carbide, aluminum nitride, Boron carbide or boron nitride.

The production of the base can be preferred for some molded parts directly using the mold for the metallic molding respectively. This is, for example, the case for the production of spoons the case. Here you can use the Form a base by injection molding, which later than Base for the metallic moldings. You can advantageously the dimension of the sintered base set slightly larger than the later molded part so that the Pad has an excellent fit for the molded parts. It is recommended that the underlay be about 1 to 20% larger to dimension as the molded part, particularly preferably 2 to 10%. The measures necessary to set the dimension are known to the person skilled in the art. For example, the shrinkage of the shaped body depends on the composition of the starting materials and can be varied accordingly. Furthermore can influenced by the sintering temperature on the shrinkage become, with increasing the sintering temperature becomes a stronger one Shrinkage of the molded part observed.

The following is the process for making metallic Moldings described schematically in more detail.

In a known manner, sinterable metal powder, flowable binder and any auxiliary materials that may be added a granulate made. There are numerous flowable binders Known fabrics. It is essential that when the temperature rises provide as little residual carbon as possible. For example polyoxymethylene, polystyrene, polymethyl methacrylate, Polypropylene, polyethylene, ethylene-vinyl acetate copolymers as well as their mixtures.

The polyoxymethylene homo- or copolymers are known to the person skilled in the art known per se and described in the literature.

The homopolymers are generally polymerized by Formaldehyde or trioxane produced, preferably in the presence of suitable catalysts.

wobei R¹ bis R⁴ unabhängig voneinander ein Wasserstoffatom, eine C₁-C₄-Alkylgruppe oder eine halogensubstituierte Alkylgruppe mit 1-4 C-Atomen und R⁵ eine -CH₂-, -CH₂O-, eine durch C₁-C₄-Alkyl- oder C₁-C₄-Haloalkyl substituierte Methylengruppe oder eine entsprechende Oxymethylengruppe darstellen und n einen Wert im Bereich von 0-3 hat. Vorteilhafterweise können diese Gruppen durch Ringöffnung von cyclischen Ethern in die Copolymere eingeführt werden. Bevorzugte cyclische Ether sind solche der Formel

wobei R¹-R⁵ und n die oben genannte Bedeutung haben. Nur beispielsweise seien Ethylenoxid, 1,2-Propylenoxid, 1,2-Butylenoxid, 1,3-Butylenoxid, 1,3-Dioxan, 1,3-Dioxolan und Dioxepan als cyclische Ether genannt sowie lineare Oligoformale als Comonomere genannt.Polyoxymethylene copolymers preferred in the context of the invention contain, in addition to the repeating units -OCH ₂ - up to 50, preferably 0.1-20 and in particular 0.3-10 mol% of repeating units.

where R ¹ to R ⁴ independently of one another are a hydrogen atom, a C ₁ -C ₄ alkyl group or a halogen-substituted alkyl group with 1-4 C atoms and R ^{5 is} a -CH ₂ -, -CH ₂ O-, a by C ₁ - C ₄ alkyl or C ₁ -C ₄ haloalkyl substituted methylene group or a corresponding oxymethylene group and n has a value in the range 0-3. These groups can advantageously be introduced into the copolymers by ring opening of cyclic ethers. Preferred cyclic ethers are those of the formula

where R ¹ -R ⁵ and n have the meaning given above. Only examples include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane and dioxepane as cyclic ethers and linear oligoformals as comonomers.

wobei Z eine chemische Bindung, -O- oder -ORO- (R = C₁-C₈-Alkylen oder C₃-C₈-Cycloalkylen) ist, hergestellt wird.Also suitable are oxymethylene terpolymers, for example by reacting trioxane, one of the cyclic ethers described above and a third monomer, preferably a bifunctional compound of the formula

where Z is a chemical bond, -O- or -ORO- (R = C ₁ -C ₈ alkylene or C ₃ -C ₈ cycloalkylene) is produced.

Preferred monomers of this type are ethylene diglycide, diglycidyl ether and Diether from glycidylene and formaldehyde, dioxane or Trioxane in a molar ratio of 2: 1 and diether from 2 mol of glycidyl compound and 1 mol of an aliphatic diol with 2-8 C atoms such as the diglyidyl ethers of ethylene glycol, 1,4-butanediol, 1,3-butanediol, cyclobutane-1,3-diol, 1,2-propanediol and cyclohexane-1,4-diol to name just a few examples.

In addition to the polyoxymethylene homo- and copolymers Poly-1,3-oxiolan and poly-1,3-dioxepan such as in the EP-A-44 475 described, suitable. Process for the preparation of the Homopolymers and copolymers described above are known to the person skilled in the art known and described in the literature, so here there is no need for further details.

The preferred polyoxymethylene homo- or copolymers Melting points of at least 150 ° C and molecular weights (Weight average) in the range of 5000 to 15000, preferably from 7000 to 60000.

Metals that can be contained in powder form are only for example called iron, cobalt, nickel and silicon; Alloys are e.g. iron-based alloys such as low and high alloys Steels, light metal alloys based on Aluminum and titanium as well as alloys with copper or bronze. Finally, there are also hard metals such as tungsten carbide and boron carbide or titanium nitride in combination with metals such as cobalt and Nickel into consideration. The latter can be used in the manufacture of metal-bound hard cutting tools (so-called cermets) become.

Flow aids, stabilizers, for example, are used as auxiliaries or mold release agents used.

The granulate is injection-molded in a known manner Green body made. For this, the granulate is in Injection molding machines at temperatures of about 120 to 220 ° C, preferred 170 to 200 ° C melted and the melt in the appropriate Mold injected where it is under temperature cools down and falls below the glass softening temperature and / or the crystallite melting point of the binder solidifies and then removed from the mold.

The green bodies obtained in this way are used in the subsequent debinding step at temperatures of around 90 to 600 ° C from one large part of the binder contained exempted. This can debinding in the presence of an acid is also recommended, whereby lower when acidic catalytic cleavage of the binder Temperatures during debinding are made possible. Suitable Acids are, for example, nitric acid, oxalic acid or Boron trifluoride; the temperatures are during the debinding here usually at about 110 to 150 ° C.

It can be particularly recommended at the very beginning of the process add another permanent binder in small amounts, which does not remove during acid catalytic delivery becomes.

The remaining residues of the binder ensure one good strength of the molded body even at the beginning of the sintering process, before solidification via the sintering of the metal particle starts.

Polyethylene, for example, are suitable as permanent binders, Polypropylene, polystyrene, polymethyl methacrylate or Polyvinyl pyrrolidone.

The proportions of the permanent binder are preferably about 0.5 to 20% by weight, particularly preferably 2 to 10% by weight, based on the total binder used.

The molded part becomes strong in the subsequent sintering process heated, which changes the structure in the desired manner and any remaining residues of the binder can be driven out. This is what is to be sintered Molded part on a base stabilizing the contours of the molded part brought. The temperatures during the sintering process are usually about 600 to 1600 ° C, preferably 800 to 1400 ° C, the duration usually extends from about 0.5 to 10, preferably 1 to 2 hours without heating and cooling times.

The document should preferably be such that the The molded part to be sintered not only rests at a few points, but also is in extensive contact with the base, so that one good stabilization is ensured during sintering. Here it should be noted that the base itself at the sintering temperatures has sufficient creep stability.

The method according to the invention is particularly suitable for production thin-walled or large or complex shaped components, which already without such support by you Dead weight tends to deform once the creep resistance of the material is reduced. It opens up the possibility also to produce such molded parts by powder injection molding, which so far this method because of the undesirable deformation were not accessible. This is in addition to those already listed Moldings are generally relevant where there is high dimensional accuracy is required. Usually you can with the help of method according to the invention a dimensional accuracy in the finished Shaped parts, which achieve about 0.5%, in special cases Not exceed 0.3% based on the specified value.

Cutlery items such as knives, forks, Spoons as well as moldings with protruding parts that are otherwise under slightly bend their own weight.

The method according to the invention offers a simple possibility To produce molded parts economically and inexpensively, whereby a high dimensional accuracy of even complex shaped components with a total high property level can be achieved. It can the method advantageously already without major effort existing injection molding process for the production of metallic molded parts be involved.

Examples

In an evacuable kneader heated to 185 ° C, 10,080 g of a 316 L stainless steel powder atomized in argon, with a average grain size of 22 microns with 886.5 g of a polyoxymethylene the melt index 50 g / 10 min at 190 ° C, 98.5 g of a polyethylene with a melt index of 42 g / 10 min at 190 ° C and 500 g Butyl glycol mixed as a solvent for the binder component. After a homogeneous mixture was obtained, the kneader became evacuated and the solvent distilled off with further kneading. The kneader was then cooled to 100 ° C., where the mass solidified and was thereby granulated. The so Injection molding compound obtained contained 63 vol .-% of the stainless steel powder.

An injection molding machine was made with a mold for a spoon equipped. The sintered spoon is identified by the Dimensions total length 204 mm, stick length 140 mm, bucket width 44 mm, curvature of the spoon 9 mm, curvature of the handle when resting on a flat surface 12 mm, with wall thicknesses of 1 mm on the spoon part and 3 mm on the stem. Due to the expected linear sintering shrinkage of 14.5% the shape is 14.5% larger in all dimensions than the sintered spoon. The injection molding compound was at one Melt temperature of 190 ° C melted and into the temperature of 110 ° C Mold injected. After a cooling time of approx. 20 sec the green parts were removed from the mold.

In the same shape was used to manufacture the sintered base a mass injected to 56 vol .-% of aluminum oxide powder with an average grain size around 1.2 µm and 44 vol .-% from one Binder consisted of 88 wt .-% of a polyoxymethylene, Melt index 50 g / 10 min at 190 ° C and 12 wt .-% from one Polybutanediol formal with an average molecular weight of around 60,000.

The spoon green containing metal powder was placed in a nitrogen atmosphere, which contained about 1.5% concentrated nitric acid, debinded at a temperature of 120 ° C within 1 h.

The sinter pad was in the same device in a Nitrogen atmosphere, which is also about 1.5% concentrated nitric acid contained, at a temperature of 130 ° C within Debinded for 2.5 hours. Thereupon the unbound sinter pad heated in air at a rate of 3 ° C / min to 1.540 ° C, Maintained at 1.540 ° C for 2 hours and then cooled at 5 ° C / min.

The dimensions of the non-dense sintered base thus obtained are 4% larger than that of the finished sintered metal spoon.

The spoon green part containing the binderless metal powder was opened laid the sinter pad and in one with molybdenum heating elements equipped sintering furnace under hydrogen, which has a dew point of less than -80 ° C at a speed of 5 ° C / min heated to 1,300 ° C, sintered 120 min at 1,300 ° C and the Sinter furnace then cooled. The product was an exactly true to size Get spoons.

Comparative example

The green parts obtained according to Example 1 were from the binder component freed by the parts at a speed of 1 ° C / min from 160 ° C to 210 ° C, with 0.5 ° C / min from 210 ° C to 250 ° C and were heated from 250 ° C to 600 ° C at 2 ° C without the parts on to place the sintered base in a spoon shape. After opening the Entbinderungsofen was found to be spherical Parts of the spoon and stick according to the influence of gravity had set and the bulges partially collapsed become.

The green parts were placed on standard flat aluminum oxide substrates placed and then in the sintering furnace under hydrogen as in the previous one Example heated to 1,300 ° C at a rate of 5 ° C / min and kept at 1,300 ° C for a further 120 min. After that the oven cooled and opened. The curved contours of the spoons had flattened even further.

Claims (4)

1. A process for producing a metallic shaped part by processing an injection-molding composition, where

   a) the injection-molding composition is processed to give the shaped part and

   b) a part of the binder present in the shaped part is removed at from 90 to 600°C and

   c) the shaped part thus obtained is sintered,

   wherein the shaped part is sintered on a support which has approximately the contour of the finished shaped part, with the contour of the support being essentially maintained during the sintering process.
2. A process as claimed in claim 1, wherein the support is built up of ceramic materials.
3. A process as claimed in claim 1 or 2, wherein the support is produced by injection molding using the mold for the metal parts.
4. A shaped part, in particular a cutlery part, obtainable by the process claimed in any of claims 1 to 3.