METHOD FOR THE MANUFACTURING HIGH-TEMPERATURE RESISTANT ENGINE COMPONENTS

Abstract

For near net shape manufacturing of high-temperature resistant engine components of geometrically complex design consisting of an intermetallic phase, a low melting-point metallic phase in the molten state or in a temperature range near the molten state is mixed with a high melting-point metallic phase provided as a metal powder, and the mixture is mechanically treated under the effect of kneading and shear forces, thereby heating it up and reducing its viscosity. In a subsequent injection moulding process the engine component substantially matching the final contour is formed and mechanically finish-machined, if required, and afterwards subjected to a heat treatment for creating an intermetallic phase.

Description

This invention relates to a method for near net shape manufacturing of engine components of geometrically complex design consisting of an intermetallic phase.

It is generally known to manufacture components of geometrically complex design in a few working steps and in near net shape by metal injection moulding. In metal injection moulding (MIM), first a metal powder is mixed with a binder including thermoplastics and waxes to form a flowing material (feedstock). The material in granulate form is injected into a mould using an extruder in a conventional injection moulding process. After cooling, solidification and demoulding, a so-called green compact is initially created, from which the binder is then removed chemically, thermally or catalytically. The porous brown compact resulting from debindering is compacted into its final form in a subsequent sintering process and has, due to its minor residual porosity, mechanical properties substantially matching the properties of the solid material.

For near net shape production of high-temperature resistant components, super-alloys provided in powder form are processed in the MIM method, as is well known. Furthermore, the proposal has already been made to produce a metal powder consisting of an intermetallic phase and to manufacture from this, on the basis of metal injection moulding, high-temperature resistant engine components near to their final dimensions and with a metal-cutting expenditure that is reduced when compared with conventional manufacturing methods. Conventional manufacture of intermetallic phases and of a metal powder made therefrom for metal injection moulding involves high effort and costs in addition, near net shape and dimensionally accurate production of the component presents problems due to the shrinkage of the brown compact as a result of the sintering process following debindering.

The object underlying the present invention is to provide a method for cost-efficient near net shape manufacturing of high-temperature resistant engine components of geometrically complex structure consisting of an intermetallic phase.

It is a particular object of the present invention to provide solution to the above problematics by a method in accordance with the features of patent claim 1.

Advantageous developments of the present invention become apparent from the sub-claims.

The basic idea of the invention is to use metal injection moulding to manufacture engine components consisting of an intermetallic phase, where however a low melting-point metallic phase in the molten or near-molten state is used as the binder and the metal powder is made from a higher melting-point metallic phase, and the moulded part obtained as the result of an injection moulding process and substantially matching the final contour does not have the binder removed, but instead is subjected to a heat treatment for creating an intermetallic phase. As a result, it is possible with a low production effort and low cost expenditure to manufacture near net shape and high-temperature resistant engine components consisting of an intermetallic phase and having a geometrically complex structure. With the same method, three or more metallic phases can also be used to manufacture high-temperature resistant engine components consisting of an intermetallic phase.

Mixing of the low melting-point phase in the molten or near-molten state with the metal powder consisting of the high melting-point phase is performed in an extruder under the effect of kneading and shear forces generated by an extruder screw. The result is very thorough mixing and a temperature increase, plus a reduction in the viscosity of the metal powder/melt mixture for performance of the injection moulding process.

In a further embodiment of the invention, the metal powder/melt mixture can be additionally heated in the extruder by heating means.

The engine component demoulded after solidification can be subjected to a finish-machining process before the heat treatment.

An exemplary embodiment of the invention is explained in more detail on the basis of the drawing, the sole figure of which shows schematically a metal injection moulding device, and on the basis of a processing flow chart.

In step I of the method for near net shape manufacture of a geometrically complex and high-temperature resistant engine component consisting of an intermetallic phase, for example of a turbine blade, a first low melting-point phase, for example aluminum, is provided in the molten state, and a second high melting-point metallic phase, for example iron, is provided as the metal powder. The first low melting-point metallic phase can also be provided in a not completely molten state, in the case of the aluminum used here, in a temperature range between 400° C. and 600° C. below its melting point. Compared with a metal powder consisting of an intermetallic compound, the metal powder made from a metallic phase (in this case iron) can be manufactured with low expenditure.

In the subsequent step II, the molten low melting-point metallic phase (aluminum) and the high melting-point metallic phase (iron) provided as a metal powder are filled into an extruder 3 using a first and second hopper 1, 2 respectively. In step III, which takes place inside the extruder 3, the two metallic phases are intensively mixed with one another. Due to the shear and kneading forces exerted by the extruder screw 4 onto the mixture, the viscosity of the mixture further decreases. Due to the mechanical force effect and possibly the extruder heater, the mixture is also heated.

The mixture of a powdery high melting-point metallic phase and a low melting-point molten metallic phase (Fe, Al), previously transformed into a low-viscosity and injectable state, is now introduced by injection moulding into a mould 5 in step IV. Unlike in a conventional metal injection moulding method, the binder necessary for the injection moulding process does not consist of thermoplastics and waxes, but is formed by the molten low melting-point metallic phase acting as the binder. The metal powder/binder mixture can be injected either directly out of the extruder 4 into the mould 5 or, as shown in the drawing, first placed inside a cylinder 6 and then pressed into the cavity 8 of the mould 5 by means of a plunger 7.

In the following step V, a moulded part matching or substantially matching the final shape of the engine component is demoulded after cooling and solidification, and can be machined with a low amount of metal-cutting in a further step VI. The low melting-point metallic phase acting as the binder in the metal injection moulding process in step IV remains in the moulded part, meaning that unlike in conventional metal injection moulding the moulded part created in the injection moulding process does not have the binder removed.

In a subsequent step VII, the moulded part is subjected to a specific heat treatment matched to the two metallic phases, in this case iron and aluminum, in order to create a high-temperature resistant intermetallic phase. Since a compact (non-porous) moulded part is already available after demoulding, unlike in the known metal injection moulding process that uses a thermoplastic binder, there is no hard-to-control shrinkage of the component during the heat treatment intended to create the intermetallic compound.

As a result of the previously described process steps I to VII, an engine component consisting of an intermetallic compound, being high-temperature resistant and also low in weight due to the use of lightweight components is provided, which can be manufactured cost-efficiently and with a comparatively low production effort in a structure of almost any complexity. Besides the material combination of iron and aluminum mentioned above as an example, a plurality of other high melting-point and low melting-point metallic phases, for example titanium and aluminum, can be used.

LIST OF REFERENCE NUMERALS

First hopper of 3 (Fe powder)

Second hopper of 3 (Al melt)

Extruder

Extruder screw

Mould

Cylinder

Plunger

Cavity of 5

Claims

1. Method for near net shape manufacturing of high-temperature resistant engine components of geometrically complex design consisting of an intermetallic phase, characterized in that at least one low melting-point metallic phase in the molten state or in a temperature range near the molten state is mixed with at least one high melting-point metallic phase provided as a metal powder, that the mixture is mechanically treated, thereby heating it up and reducing its viscosity, and that subsequently in an injection moulding process the engine component substantially matching the final contour is formed and afterwards subjected to a heat treatment for creating an intermetallic phase.

2. Method in accordance with claim 1, characterized in that mixing of the low melting-point phase and the high melting-point phase is performed in an extruder under the effect of kneading and shear forces.

3. in accordance with claim 1, characterized in that the metal powder/ melt mixture is additionally heated by heating means.

4. in accordance with claim 1, characterized in that the engine component demoulded after solidification is subjected to a finish-machining process before the heat treatment.