RU2752359C1 - Method for manufacturing parts of complex shape by hybrid casting-additive method - Google Patents

Abstract

FIELD: mechanical engineering.SUBSTANCE: method relates to mechanical engineering and engine construction and can be used for the manufacture of parts of complex spatial shape from hard-to-process metals and alloys. A method for manufacturing parts of complex shape by a hybrid casting-additive method, including selective laser surfacing using heat-resistant nickel powders, according to the invention is characterized by the fact that initially the linear dimensions of the workpiece of the part are set with an allowance for the value of its thermal deformation, then the workpiece of the part is made by selective powder laser surfacing using a control program, a shell blank with green powder inside is obtained, which is covered with a layer of gasified material by dipping into a bath with a coating thickness exceeding the value of thermal deformation, the coated workpiece is processed after cooling on a high-precision machine with numerical control to the size and required surface roughness of the finished part, the resulting workpiece is covered with a heat-resistant ceramic suspension 6-8 mm thick by dipping 8-9 times into the bath, the suspension layer is dried by an air-ammonia method at a temperature of 20-25°C at a humidity of 60-70%, then the blank with a ceramic coating is calcined at a temperature of 950-1000°C for at least 4 hours, after which the blank in a ceramic form is placed in an induction melting complex, the green powder is melted at a temperature of 1200-1440°C for at least 4 hours, a part with the specified dimensions is obtained, which is cooled in air for 3-4 hours and freed from the ceramic coating.EFFECT: invention achieves ensuring accuracy and quality of the obtained parts of a complex spatial shape made of heat-resistant materials, reducing production costs during manufacturing.1 cl, 3 dwg

Description

The method relates to mechanical engineering and engine building and can be used to manufacture parts of complex spatial shape from difficult-to-machine metals and alloys. The method can be used, for example, for the manufacture of impellers used in gas turbine engines.

Known methods of manufacturing parts of complex shapes using casting technologies. Currently, there are many methods of casting metals that allow you to get workpieces of different shapes, sizes, accuracy and made from different materials.

The existing methods of obtaining the above-mentioned parts of a complex spatial shape, for example, impellers of gas turbine engines, have a number of disadvantages, primarily including the high cost and complexity of machining the surface of the blades, and the disadvantages of these methods are the relatively high cost of molding materials and the complexity of the model. snap.

The known casting method is described in the application for invention No. 94028834, publ. 06/27/1996, in which, in the manufacture of molds, aluminum powder is also used as a filler for a refractory suspension in an amount of 7% by weight of the filler, the molds are made with precision, ensuring the production of castings without mechanical processing. The disadvantages of these methods are the complexity of the manufacture of this form and the relative high cost of the materials used.

Also known is a method of manufacturing a turbine blade from a titanium-based alloy, including the formation of a protective layer located in the zone of the tip of the blade airfoil, covering its leading edge and having a greater erosion resistance than the feather material, by processing the feather with an energy source, and the protective layer is obtained by alloying by remelting a titanium-based alloy, alloying is carried out in a gas atmosphere that forms borides, carbides and / or nitrides with the alloy, and the thickness of the protective layer is 0.1 ... 0.7 mm (Patent RF No. 2033526, publ. 20.04.1995).

The disadvantage of this method is the great complexity, and most importantly, the difficulty in writing a control program for guiding the laser along the processed edge.

The technical objective of the invention is to ensure the accuracy and quality of the resulting parts of complex spatial shape from heat-resistant materials used in gas turbine engines while reducing the complexity of manufacturing.

The technical result is achieved due to the fact that the method for manufacturing parts of complex shapes by the hybrid casting-additive method, according to the invention, includes selective laser surfacing using heat-resistant nickel powders, characterized by the fact that initially the linear dimensions of the workpiece are set with an allowance for the amount of its thermal deformation, Then, according to the specified dimensions, a blank of a part is made by selective powder laser surfacing using a control program, a shell blank with unsintered powder inside is obtained, which is coated with a layer of gasified material by dipping into a bath with a coating thickness exceeding the thermal deformation value, the coated blank after cooling is processed at a high-precision machine with numerical control to the size and required surface roughness of the finished part, the resulting workpiece is coated with a heat-resistant ceramic suspension 6-8 mm thick by dipping 8-9 times into a bath, a layer of sus the pensions are dried by the air-ammonia method at a temperature of 20-25 ° C and a humidity of 60-70%, then the workpiece with a ceramic coating is calcined at a temperature of 950-1000 ° C for at least 4 hours, after which the workpiece in a ceramic mold is placed in an induction melting complex, the unsintered powder is remelted at a temperature of 1200-1440 ° C for at least 4 hours, a part with specified dimensions is obtained, which is cooled in air for 3-4 hours. Then the ceramic coating is removed.

The invention is illustrated by the following drawings:

FIG. 1, view A, B - shows an industrial installation for the additive production of metal products by selective laser fusion, SLM 500 HL.

FIG. 2 shows a workpiece blank 1 with a layer of gasified material (paraffin) 2, obtained using a selective laser fusion operation.

FIG. 3 shows a blank of part 1 with a schematically indicated layer of paraffin 2 and a ceramic suspension 3.

The method is carried out as follows.

To implement the invention, a part profile is made - an impeller (Figs. 1, 2, 3), for example, from a heat-resistant nickel powder using SLM technologies (Selective Laser Melting) - modeling by layer-by-layer deposition of a part from a metal powder.

Obtaining the profile of the impeller is carried out on a selective melting unit SLM 500HL (Fig. 1), which has a large chamber that allows you to create large-sized models with dimensions of 500x280x325mm. Melting is carried out with two lasers with a power of 400W or 1000W each, the minimum thickness of the applied layer is 20 microns. Powders from titanium, aluminum, steel and other metals and alloys are used as consumables. The printer is equipped with a control module with Ethernet interface for connecting to a local network. View A is a general view of the unit with the part being manufactured; View B shows an enlarged image of the working table of the unit with a laser head and a part (impeller). The control of the direction of the laser beam, the determination of its profile, as well as the determination of the required number of layers, according to the operating parameters of the machine used, is carried out using the built-in SG + generator support module. The control program is written in the SLM®Build Processor software environment, which is specifically designed to interact with SLM Solutions machines.

The process of obtaining the profile of the impeller shell blank consists in successive layer-by-layer melting of heat-resistant nickel powder by means of high-power laser radiation. As consumables used, for example, nickel powder grade PNK or similar.

As a result of the selective laser melting operation, the resulting workpiece - the impeller is a shell shape, the outer profile completely repeating the profile of the given part. When obtaining a part by a simple method of selective laser melting, the powder is applied layer by layer with a given discretization along the layer thickness. The powder is applied evenly due to its leveling with a roller built into the configuration of the selective melting unit for a given thickness. The peculiarity of the proposed method consists in leaving, during selective melting, unsintered nickel powder in the inner part of the workpiece, which significantly saves production costs. This is achieved due to the fact that the direction of the laser does not affect the central part of the resulting workpiece, but only the surface part is baked. This is achieved using a specially developed control program that sets the trajectory of the laser.

When receiving a billet with unsintered powder inside, the geometric outer dimensions are set less than the dimensions of the finished part by the amount of thermal deformation that occurs at the stage of subsequent remelting of the nickel powder inside the billet.

The calculation of the dimensions of the linear increase of the part is carried out before the SLM melting operation, based on the data presented in the reference books and taking into account the dimensions of the part in question. It is known that the average coefficient of linear expansion of nickel alloys in the temperature range of 27 ... 1473 ° C is 16.2⋅10 ^-6 deg ^-1 . The calculation of the linear increase in dimensions was carried out for an impeller made of nickel powder PNK with an outer diameter of ∅100 _-0.25 with an increase in its temperature from 27 to 1473 ° C [Landsberg G.S. Elementary physics textbook. Vol. 1. Mechanics. Heat. Molecular physics. - M .: Nauka, 1985. - 606 p.].

The amount of linear expansion is calculated by the formula (1):

α _Т - coefficient of linear expansion for nickel alloys, Т ₂ - upper limit of heating temperature, Т ₁ - initial temperature , L - considered impeller size.

For a given diameter, the total linear expansion is 2.34 mm, which is 1.17 mm of the contour allowance.

Taking into account the size of the allowance determined by formula (1), the geometrical dimensions of the workpiece are set, for example, the impeller (Figs. 2, 3), and according to the corresponding program, SLM surfacing is carried out and a shell workpiece with green powder inside is obtained.

Then the surface of the obtained workpiece 1 (figure 2) is covered with a layer of gasified material (paraffin) 2 with a thickness exceeding the amount of thermal deformation (in the example, 2.34 mm). A layer of paraffin is applied to the workpiece by dipping it into a paraffin bath.

The applied paraffin layer 2 is then processed on a high-precision computer numerical control (CNC) machine to obtain a blank with the required dimensions for the finished part specified in the design documentation (excluding the reduction by the amount of thermal expansion of -2.34 mm) while maintaining the required roughness. For this purpose, a high-precision CNC machine is used, which allows for five-axis machining, which ensures the dimensional accuracy and roughness of the manufactured model. As technological equipment, you can use, for example, a five-axis milling and machining center (FOTS) Mikron UCP600. The thickness of the wax layer after processing should be equal to the value of the thermal expansion of the metal. Providing the roughness parameters is necessary to ensure the roughness parameter on the finished part.

For example, for the manufacture of a billet from a heat-resistant nickel powder, the increment in dimensions is 2.34 mm for an impeller diameter of ∅100 _-0.25.

After processing on the machine, the resulting shell blank (Fig. 2, 3), which was pre-coated with a layer of gasified material (paraffin) 2 and processed on the FOC with CNC, is covered with a special heat-resistant ceramic suspension 3 by dipping the blank into a bath with a ceramic composition, which, when solidification forms the exact mold of the considered part (Fig. 3). For coating, it is necessary to apply at least 8-9 layers of coating, the thickness of the ceramic mold in this case is from 6 to 8 mm. The number of applied layers of ceramic material is due to the fact that when applying less than 8 layers, cracking of the mold is possible during calcination, and the application of 10 or more applied layers increases the material consumption.

After that, the slurry layer must be dried using an air-ammonia method with a humidity control of 60-70% and a temperature in the working room of 20-25 ° C. Such drying with the use of ammonia is used for molds based on ethyl silicate, since ammonia is a strong catalyst for the hydrolysis of ethyl silicate. At a lower moisture content, the hydrolysis process cannot be completed, since a binder is not formed and a shell is not formed. If this indicator is exceeded, the drying process can be significantly delayed.

Then the coating is calcined at an operating temperature of 950-1000 ° C for at least 4 hours. Calcination is carried out in order to dehydrate the coating and the appearance of substances that are a binder for the shells. Higher temperatures and longer heating times can lead to softening of the shell, lower temperatures will not allow the shell to completely harden.

The next step is to directly remelt the model made by the SLM method inside a ceramic mold together with unsintered metal powder using a crucible furnace at temperatures in the range 1200-1500 ° C. This mode is used when remelting heat-resistant nickel alloys, a lower temperature will not allow the material to reach a liquid state, further heating is inappropriate. As a result of this process, a better homogeneity of the structure is achieved, the porosity of the material is reduced, which, having reached the yield point, fills the pores and cracks remaining after the SLM operation. After remelting in a crucible furnace, a finished part of a complex spatial shape is obtained in the form of a casting with precise geometric dimensions and the desired shape.

An example of a specific implementation of the method.

Consider an example of manufacturing a gas turbine engine impeller with overall dimensions according to design documentation: diameter D = 100 _-0.25 mm, height h = 75 _-0.3 mm from PNK-UT1 grade powder. Before carrying out the SLM melting operation, the linear dimensions of the workpiece are determined according to the formula (1): along the contour of the blades (-0.1 mm), for the impeller diameter D (-2.34 mm).

With the help of the control program by the method of selective powder laser surfacing, a shell blank with unsintered nickel powder inside with the above linear dimensions is produced. Surfacing is carried out with a 400 W laser with a thickness of 20 µm, these characteristics are indicated in the control program.

The powder is fed to the platform into the chamber of the selective melting unit, where it is leveled with a special roller to a predetermined layer thickness.

The resulting shell blank must be left in the installation chamber until it cools down, then it is covered with a paraffin layer by immersion in a bath at a temperature of 50-65 ° C for minutes, the layer thickness is equal to a thickness exceeding the thermal deformation value for a diameter of D = 100 _-0.25 mm (t = 2.34 mm) and along the contour of the blades l = 2.5 _-0.06 mm (-0.1 mm).

After the paraffin layer has dried, the workpiece is fed to the Mikron UCP600 milling and machining center, where the coating is processed to the dimensions indicated in the design documentation: l = 2.5 _-0.06 mm - wall thickness and D = 100 _-0.25 mm - impeller diameter, surface roughness corresponds to the finished part roughness equal to Ra = 3.2 μm.

After processing the workpiece at the FOC with CNC, the shell workpiece is coated with a heat-resistant ceramic suspension based on a solution of hydrolyzed ethyl silicate by immersion in a special container for a time not exceeding 5 minutes. This procedure is repeated 8-9 times to obtain a coating thickness of 6-8 mm. After that, the slurry layer is dried by the air-ammonia method with a humidity control of 60-70% and a temperature in the working room of 20-25 ° C. Then the coated workpiece is calcined at an operating temperature of 950-1000 ° C for at least 4 hours in an induction technological complex.

As a result, a casting mold is obtained with linear dimensions of the impeller blade thickness equal to l = 2.5 _-0.06 mm and the impeller diameter - D = 100 _-0.25 mm.

The resulting workpiece in a ceramic mold is placed in an induction technological complex for ferrous and non-ferrous alloys, the unsintered powder is remelted at a temperature of 1200-1500 ° C. The resulting part is cooled in air for 3-4 hours. After solidification and cooling of the casting to a predetermined temperature, the mold is knocked out, the castings are cleaned of ceramic residues and the sprues are cut off from them.

As a result, a finished impeller is obtained with exact dimensions and roughness corresponding to those specified in the design documentation.

By using the proposed method, the dimensional accuracy and quality of the surface layer of the manufactured parts is ensured. The parts obtained by this method practically do not require further finishing. Due to this, as well as due to the rational use of the Selective Laser Melting (SLM) installation, a decrease in the labor intensity of their manufacture is achieved.

Thus, in the end, a casting of the required part of a complex shape was obtained, which is as close as possible in geometric characteristics to the performance of an ideal part, which practically does not require further mechanical processing, and allows to reduce production costs during manufacturing.

Claims (1)

A method for manufacturing parts of complex shape by a hybrid casting-additive method, including selective laser surfacing using heat-resistant nickel powders, characterized by the fact that initially the linear dimensions of the part blank are set with an allowance for the amount of its thermal deformation, then the part blank is made according to the specified dimensions by selective powder laser surfacing using a control program, a shell blank with unsintered powder inside is obtained, which is coated with a layer of gasified material by dipping into a bath with a coating thickness exceeding the thermal deformation, the coated blank after cooling is processed on a high-precision machine with numerical control to the size and required surface roughness the finished part, the resulting workpiece is covered with a heat-resistant ceramic suspension 6-8 mm thick by dipping 8-9 times in a bath, the suspension layer is dried by air-ammonia method at a temperature of 20-25 ° C at 60-70%, then the workpiece with a ceramic coating is calcined at a temperature of 950-1000 ° C for at least 4 hours, after which the workpiece in a ceramic mold is placed in an induction melting complex, the green powder is remelted at a temperature of 1200-1440 ° C in for at least 4 hours, a part with specified dimensions is obtained, which is cooled in air for 3-4 hours and freed from the ceramic coating.

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