DD286311A5 - METHOD FOR PRODUCING SHAPED PARTS FROM SINTERED MATERIALS BY INJECTION MOLDING - Google Patents

Abstract

The invention relates to a method for producing molded parts from sintered materials by injection molding. The method is used in the production of complicated parts. According to the invention, a metal powder is dried, mixed-milled and mixed with a defined binder mixture. This mixture is supplied as a plasticized mass of a Niederdruckspritzgieszform and processed there at an injection pressure 30 MPa. This is followed by a defined expulsion of the binder mixture and sintering of the resulting molding. {Injection molding; Moldings; Sintered materials; Metal powder, mixed grinding; Binder mixture; Niederdruckspritzgieszform; Injection pressure; expulsion; sintering}

Description

Field of application of the invention

The invention relates to the field of powder metallurgy. It relates to a method for producing molded parts from sintered materials by injection molding. In this case, a mixture of a metal powder and an organic binder mixture is processed to a plasticized mass and then molded in an injection molding process. The moldings are subjected, after being released from the mold, to an extraction process for the binder and a sintering process.

Characteristic of the known state of the art It is known powdery starting materials for mold-complicated parts by mixing with plasticizers and

to produce surfactants (DE 3120501). The sprayed mass obtained in this way is pressed into the mold in special shaping machines, whereby different working pressures are used depending on the method used. The so-formed moldings are immediately demoldable and must prior to sintering a thermal process for expelling the

Binder be subjected. Furthermore, it is known that according to the different working pressures of the forming machines also different Plasticizers (binders) are used. When using injection molding machines with a pressure build-up by Kolbensysten; or screw conveyors that are both

for ceramic and metallic powders and mixtures of these substances are suitable for. As polystyrene, polyethylene and

Polypropylene (OE 2904707, DE 3120501, DE 3120501, DE 3101328) for use. The heating and the pressure build up

160MPa provide a sufficient viscosity of the spray mass and allow the filling of the mold.

In injection molding with a very low, pneumatically or hydraulically generated working pressure up to 30MPa, the

exclusively for finely dispersed ceramics; «Powder having a defined surface anactivity in admixture with the

Plasticizers paraffin and wax (DD 23a i 17, DD 233118, DD 233119) is suitable, the already present low viscosity Sprayed into the mold. The application of this low working pressure is used in particular to secure the Filling from the sprinkling point of relatively fine-structured partial forms. A disadvantage when working with higher pressures up to 1600MPa is in addition to the high plant engineering effort and the high Tool wear, in particular a limit in the degree of complexity and the minimum wall thickness of small

Moldings, as well as the relatively high compressive stresses in the machine system, which have an inhomogeneous (anisotropic) distribution of residual stresses in the erstarten component effect.

Working with a low pressure of up to 30 MPa has the disadvantage that, as soon as special molded part designs are required, the spraying masses produced for this shaping process have to be thin, and when they are processed, segregation phenomena occur which, in particular, occur with metals having a significantly higher specific gravity than, for example Ceramic materials in the way have a negative effect that no dimensionally stable moldings with homogeneous (isotropic) particle and residual stress distribution can be produced.

Object of the invention

The aim of the invention is to realize a method for producing molded parts from sintered materials by injection molding, which is inexpensive and secures the necessary utility of the metal moldings.

Explanation of the essence of the invention

The object of the invention is to provide a method for producing molded parts from sintered materials by injection molding, which allows to produce dimensionally stable moldings with homogeneous particle and residual stress distribution by demixing processes and reactions of the powder, especially with oxygen through the design of the method and by Compliance with defined conditions is counteracted. The aim of the invention is to achieve this. To realize the method, a mixture of a pretreated metal powder and an organic binder is prepared to a plasticized mass and then molded in an injection molding process. After the parts have been removed from the mold, they are subjected to a stripper removal process and a sintering process. According to the invention, the method is characterized by the following method steps:

- Drying of the metal powder having a particle size <25pm with spherical grain shape, at temperatures near 200 ⁰ C.

- Cooling of the powder to 100 to 16O ⁰ C.

- Mixing and activating the powder in vacuum or Nj atmosphere for 1 to 2h

- Mixing of paraffin and polyethylene wax to a binder in the ratio 1: 0.5 ... 5 for 0.5 h at 15O ⁰ C.

- Gradual mixing of up to 10Ma .-% of the powder weight equivalent binder mixture to the metal powder over a period <24 h, at a pressure <10 "'MPa and a temperature between 80 and 100 ⁰ C.

- Melt this mixture in a vacuum

- Supplying this plasticized mass in a low-pressure injection mold and working the mass in this form at an injection pressure OOMPa, at a temperature <150 ⁰ C.

- Stripping of the binder mixture for 30 to 72 hours, wherein the temperature at a rate of 0.1 to 0.2 ° C / min up to 550 ⁰ C is increased

- Sintering of the molding, in particular in a vacuum, for 2.5 to 3 h at 0.8 to 0.95 times the melting temperature of the material.

In an embodiment of the invention, the expulsion of the binder mixture takes place in a closed container in which the molded body is embedded in an alumina hydrate powder.

Expediently, when the binder mixture is expelled, the molding may be arranged on an absorbent substrate, the entire assembly being in particular purged with nitrogen or being worked in vacuo.

embodiments The invention will be described below with reference to two examples. example 1 A powder of a rust and acid resistant steel (FeNi 2) with a specific surface of approx. 2m '/ g, a spherical one

(spherical) grain shape and a particle size of <25 μπι is first dried at 200 ⁰ C for 6h and then after a

Cooling to a temperature in the range of 100 to 15O ⁰ C mixed ground. This mixing in vacuum takes 2 h and

activates the powder. In parallel, a binder mixture of polyethylene wax and hard paraffin Vollraffinat in

1: 1 ratio prepared by mixing for 0.5 h at 150X. Subsequently, this binder mixture with 7.5Ma .-%, based on the powder weight, stepwise to the metal powder

mixed and mixed over a period of 16h. In this case, a temperature between 80 and 100 ° C, maintained at a pressure <10 ' ² MPa. After melting this mixture in vacuo, this low viscosity moldable mass is fed directly to the reservoir of a low pressure injection molding machine. After closing and evacuating this container (10 ' ¹ MPa), the spray mass is conveyed pneumatically directly via a riser into the mold, the viscosity of the

Spray mass, which is crucial for the full behavior of the Sprifzform, übar the delivery pressure can be controlled. At a temperature of 110 "C and an injection pressure of 0.6MPa, for example, in the production of a

thick-walled part filled the mold with a laminar mass flow (higher viscosity by low pressure) and the

Production of a thin-walled part via a turbulent mass flow (low viscosity filled by higher pressure)

and thus counteract the segregation phenomena.

The subsequent Ag driving of the binder mixture takes place in a reducing Nj atmosphere or in a vacuum, at Increase of the temperature in 45h to 200 * C and in 15h to 500 ⁰ C. The moldings are on an absorbent pad

(Porosity> 25%) arranged.

Finally, the molded part is sintered under vacuum at 0.9 times the melting point of the steel (1220 ° C.) for about 3 hours. Example 2

The powder of a hard material mixture (HG 960) with a specific surface of about 3.5 mVg, a spherical (spherical) grain shape and a particle size <15pm is first also dried as described in Example 1, and after cooling, by the mixing in Nj atmosphere, at 150 ⁰ C for 2h, activated.

In addition, the binder mixture of polyethylene wax and hard paraffin Vollraffinat in the ratio 1: 2 is prepared.

Subsequently, this binder mixture with 10Ma .-% based on the powder weight to the hard powder powder is gradually added and mixed over a period of 18h with this. The temperature / pressure ratios are maintained as in Example 1.

This is followed by the Niederdruckspritzgießvorgang also described in Example 1.

The expulsion of the binder mixture geschinht in reducing Ar atmosphere, with an increase in the temperature in 60 h to 26O ⁰ C and in another 12 h at 550 ° C. The moldings are housed in a closed container in which they are completely embedded in Tonerdehydratpulver.

The final sintering in vacuum at 1410 "C for 2.5h completes the process.

With this processing technology, the oxidation process on the powder surface is avoidable and thus a sinking of the molded powder composite is possible.

The first-time application of less expensive low-pressure injection molding on metal powder in conjunction with the steps and conditions according to the invention leads to the production of dimensionally stable molded parts with homogeneous particle and residual stress distribution. Surface-active substances are not used in comparison to ceramic technology.

Claims (4)

1. A method for producing molded parts from sintered materials by injection molding, wherein a mixture of a pretreated metal powder and an organic binder is prepared to a plasticized mass and then formed in an injection molding, wherein the moldings after the release from the mold a Austreibeptozeß for the binder and a sintering process, characterized by the following method steps - Drying of the metal powder, which has a particle size <25 \ xm with spherical grain shape, at temperatures near 200 ⁰ C. - Cooling of the powder to 100 to 15O ⁰ C. - Mixing and activation of the powder in a vacuum or N ₂ atmosphere for 1 to 2 h - Mixing of paraffin and polyethylene wax to a binder in the ratio 1: 0.5 ... 5 for 0.5 h at 150 ⁰ C. - Gradual mixing of up to 10Ma .-% of the powder weight equivalent binder mixture to the metal powder over a period <24 h, at a pressure <10 " ² MPa and a temperature between 80 and 100 ⁰ C. - Melt this mixture in a vacuum - Feed this plasticized mass in a low-pressure injection mold and edit the mass in this form at an injection pressure <30 MPa, at a temperature <15O ⁰ C. - Stripping of the binder mixture for 30 to 72 h, wherein the temperature at a rate of 0.1 to 0.2 ° C7min up to 55O ⁰ C is increased - Sintering of the molding, in particular in a vacuum, for 2.5 to 3 h at 0.8 to 0.95 times the melting temperature of the material. 2. The method according to claim 1, characterized in that the expulsion of the binder mixture takes place in a closed container in which the shaped body is embedded in a Tonerdehydratpulver. 3. Method according to claim 1, characterized in that when expelling the binder mixture of the molding is placed on an absorbent pad, wherein the entire assembly is purged in particular with nitrogen. 4. The method according to claim 3, characterized in that it is carried out in vacuo.