JP6342844B2 - Turbine wheel manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a turbine wheel incorporated in a turbocharger used in an automobile engine or the like, and more particularly, firing with high dimensional accuracy by metal powder injection molding (may be described as MIM method (Metal Injection Molding method)). The present invention relates to a method for manufacturing a sintered product as a turbine wheel, which is a final product (final finished product), without obtaining a sintered product by machining (secondary processing) the sintered product.

  A turbocharger used in an automobile engine or the like amplifies the flow rate of exhaust gas so that the engine can efficiently obtain output even at low speed rotation, and uses this exhaust energy to When the turbine rotates, the intake-side turbine directly connected to the exhaust-side turbine is rotated, so that air is forcibly taken into the engine.

In general, a supercharger mounted on a vehicle or the like is composed of three parts: a high-temperature turbine wheel, a low-temperature compressor wheel, and a rotor shaft that connects the two.
The high temperature side turbine wheel is made of a cast material such as a heat-resistant metal and has a plurality of spiral blades and a rotor shaft connecting portion. The low temperature side compressor wheel is made of a cast material such as an aluminum alloy, and has a spiral shape and a plurality of blades.

In general, each blade is thinner toward the tip.
With regard to this turbine wheel, a method of being manufactured by casting has been adopted, but a method of manufacturing by metal powder injection molding capable of improving dimensional accuracy as compared with the manufacturing by casting has also been developed. Japanese Patent No. 4240512 (Patent Document 1) discloses a method of manufacturing a turbine wheel by this metal powder injection molding. The method for manufacturing a turbine wheel disclosed in Patent Document 1 has a plurality of curved blades extending radially from a central shaft portion and bent at the upper end in a rotational direction. A method of manufacturing a metal turbine wheel to which a rotor shaft serving as a rotating shaft is coupled, and a step of cutting a sintered product having a shape approximate to a desired final product manufactured by a metal powder injection molding method And a step of pressing the blade, the sintered product has a blade tip height within a range of ± 1.0% with respect to a target value of the final product, and a blade pitch of ± 0. In the cutting process, a rotor shaft coupling portion that is centered on the center of rotation of the turbine wheel is provided on the bottom surface of the central shaft portion in the cutting process. Processing In the pressing step, after fixing the sintered product with the rotation center as a midpoint, the central axis of the sintered product is simultaneously synchronized with a plurality of correction pins arranged radially with respect to the fixed sintered product. What is performed by sliding toward the part, the correction pin has a shape corresponding to the space shape between each blade, is arranged at equal intervals according to the number of blades, along each blade surface, Each blade is inserted in the direction of the central axis so as to be sandwiched from both sides. According to this turbine wheel manufacturing method, even a turbine wheel having thin blades can be manufactured with high dimensional accuracy.

Japanese Patent No. 4240512

However, as described in paragraph 0009 of Patent Document 1, in this manufacturing method, a desired final product cannot be obtained directly from the MIM method. That is, a sintered product having a certain relationship with a desired final product is prepared by the MIM method, and then the center position is determined by cutting the rotor shaft connecting portion, and then the space shape between the blades of the final product is determined. By inserting a straightening pin having a shape corresponding to each of the blades while simultaneously synchronizing between the blades, the deformation of the blades and the pitch interval of the blades are adjusted, and the dimensional accuracy of the blades is ± 0.0.
A turbine wheel having a coaxiality and a center balance accuracy higher than that of a conventional cast product can be obtained. For this reason, the sintered product manufactured by the MIM method must be pressed (mechanical processing, secondary processing) using a correction pin. Thus, this manufacturing method has a problem that the manufacturing cost tends to be high because secondary processing after sintering is required.

  The present invention has been developed in view of the above-mentioned problems of the prior art, and its object is to complete a sintered product by the MIM method as a final product without the need for secondary processing after sintering. Another object of the present invention is to provide a method for manufacturing a turbine wheel with a very thin blade tip (for example, 0.3 mm or less) and high dimensional accuracy (for example, a small unbalance amount) while reducing the manufacturing cost.

In order to achieve the above object, the method for manufacturing a turbine wheel according to the present invention employs the following technical means.
That is, the method for manufacturing a turbine wheel according to the present invention has a plurality of curved blades extending radially from the central shaft portion and bent at the upper end in the rotational direction. A metal turbine wheel to which the rotor shaft is connected is manufactured. In this method, an organic binder is added to metal powder, heated and mixed, and then a heat-kneading step for obtaining an injection molding material by crushing or pelletizing, and injection molding the injection molding material into the shape of a turbine wheel to produce a molded body. An injection molding step, a degreasing step for degreasing the produced molded body in a degreasing atmosphere, and a sintering for producing a sintered product by sintering the degreased molded body in a sintering atmosphere after the degreasing step. And after the degreasing step, the compact is placed on a setter and processed to complete a sintered product as a final product.

Preferably, the setter may have an apparent porosity of 15% to 18%.
More preferably, the main components of the setter are alumina and silica, and the weight ratio of silica can be 3% to 10%.
More preferably, the setter may have a flatness of 0.02 mm to 0.1 mm.
The most preferable embodiment of the method for manufacturing a turbine wheel according to the present invention has a plurality of curved blades extending radially from the central shaft portion and bent at the upper end in the rotational direction. A method of manufacturing a metal turbine wheel to which a rotor shaft serving as a rotating shaft is connected to a side, wherein an organic binder is added to a metal powder and heated and mixed, and then pulverized or pelletized to obtain an injection molding material An injection molding step for producing a molded body by injection molding the injection molding material into the shape of the turbine wheel; a degreasing step for degreasing the produced molded body in a degreasing atmosphere; and after the degreasing step In a sintering atmosphere, a sintering step of sintering a degreased molded body to produce a sintered product, and after the degreasing step, By treatment by placing the serial moldings setter, there is to complete the sinter as the final product, to the setter, silica with 3% to 4.8% containing alumina weight ratio formation by being, flatness I 0.02mm~0.1mm der, apparent porosity is characterized by using a those 15% ～16.7%.

  According to the present invention, the sintered product by the MIM method is completed as a final product without the need for secondary processing after sintering, and the blade tip is very thin (for example, 0.3 mm or less) while reducing the manufacturing cost. A turbine wheel with high dimensional accuracy (for example, a small unbalance amount) can be manufactured.

It is a three-view figure and a perspective view of a turbine wheel manufactured by a manufacturing method of a turbine wheel concerning an embodiment of the invention. It is a perspective view of the setter used in the manufacturing method of the turbine wheel concerning an embodiment of the invention. It is the perspective view and top view with which the turbine wheel was mounted in the setter used in the manufacturing method of the turbine wheel which concerns on embodiment of this invention. It is a flowchart of the manufacturing method of the turbine wheel which concerns on embodiment of this invention.

Hereinafter, a method for manufacturing a turbine wheel according to an embodiment of the present invention will be described in detail with reference to the drawings.
A turbocharger is a well-known device for supplying air to an engine inlet at a pressure higher than the atmosphere. The turbocharger essentially comprises an exhaust gas driven turbine wheel 10 mounted on a rotatable shaft (rotor shaft) within a turbine housing. As shown in FIG. 1, the turbine wheel 10 used in this turbocharger is made of a heat-resistant metal and has a spiral shape and has a plurality of blades 20 and a rotor shaft connecting portion 40. In addition, a boss portion 50 having a center of rotation as a midpoint is usually provided at the upper end of the central shaft portion 30.

  The size of the turbine wheel 10, the shape of the blade 20, and the number of blades 20 vary depending on the engine displacement used. FIG. 2 is a perspective view of the setter 100 and the setter 200 used in the turbine wheel manufacturing method according to the present embodiment, and FIG. 3 is a perspective view and a plan view of the setter 100 and the setter 200 on which the turbine wheel 10 is placed. FIG. 4 shows a flowchart of the turbine wheel manufacturing method according to the present embodiment. As shown in FIG. 4, this manufacturing method includes a degreasing step (degreasing step) and a sintering step (degreasing step).

  In the conventional manufacturing method of the turbine wheel 10, a sintered product having a shape approximate to a desired final product is first manufactured, and the sintered product is secondarily processed to manufacture the turbine wheel 10 that is a final product. It was. That is, a final product (final finished product) is manufactured through a secondary processing step after the sintering step S500 of FIG. On the other hand, in the manufacturing method according to the present embodiment, a sintered product having a desired final product shape is manufactured without requiring a secondary processing step of the sintered product. In order to obtain a final product shape in this sintering process (which may include a degreasing process), a high dimensional accuracy is required for the sintered product. For this reason, the degreasing step S400 and later (more specifically, the degreasing step S400 and the firing step). In step S500), the turbine wheel 10 (which is still a molded product here) is placed on the flat setter 100 or setter 200 for processing.

  The setter 100 and the setter 200 are usually used for sintering or heat treatment of non-ferrous alloys such as iron, stainless steel and copper, and tungsten superpolymerized gold, and refractories such as alumina and alumina / silica are used. Refractories such as alumina and alumina / silica used at the time of sintering or heat treatment are widely used because they do not react with the treated body. The setter 100 or the setter 200 is mounted with the molded body obtained in the injection molding step S300, and the setter 100 or the setter 200 in a state where the molded body is mounted is the degreasing step S400 or more (more specifically, the degreasing step S400). And the degreasing step S400 and the sintering step S500 are executed in the processing furnace used in the sintering step S500).

  Since the setter 100 or the setter 200 has the characteristics described later, the sintered product processed in the sintering process (which may include a degreasing process) can realize high dimensional accuracy, and the sintered product can be subjected to secondary processing. The shape of the final product can be made unnecessary. That is, in the method for manufacturing a turbine wheel according to the present embodiment, in the degreasing step S400 and subsequent steps shown in FIG. 4, the molded product is placed on the setter 100 or the setter 200 and processed, whereby the sintered product is used as the final product. It is characterized by being completed. Thus, the setter 100 or the setter 200 for realizing high dimensional accuracy without requiring secondary processing of the sintered product will be described in detail.

  The setter 100 or the setter 200 will be described in detail with reference to a perspective view of the setter 100 and the setter 200 shown in FIG. 2 and a perspective view and a plan view of the setter 100 and the setter 200 shown in FIG. As shown in FIGS. 2 and 3, each of the setter 100 and the setter 200 has a flat plate shape, and the turbine wheel 10 is placed on the upper surface thereof. In contrast to the flat plate-like setter 200 that does not include a chamfered portion, the setter 100 includes a chamfered portion 120 whose four sides of the upper surface (and / or the lower surface) are chamfered and a corner chamfered portion 130 whose four corners are chamfered. Is different. And as shown in FIG. 3, the turbine wheel 10 which is a suitable number of process target objects is mounted in these setters 100 or 200.

The setter 100 or the setter 200 has an apparent porosity (first feature), main component (second feature), and flatness (third feature) as features that are compositionally more prominent than shape features. ).
<First feature>
The apparent porosity of the setter 100 and the setter 200 is 15% to 18%. Here, the apparent porosity means that the setter 100 and the setter 200 have pores therein, and the volume ratio of pores that are open to the outside air in the pores (open pores that are open to the outside). (Ratio of the total volume of open pores to the total volume). The higher the apparent porosity, the more preferable the component of the (organic) binder in the degreasing step S400 (preferably because the component of the binder is easily released as a gas from the molded body and the dimensional accuracy of the sintered product is improved). If this apparent porosity is low, the component of the (organic) binder is difficult to come off in the degreasing step S400 and adheres to the setter 100 or 200, and the molded product adheres to the setter when the molded product is sintered in the sintering step S500. This will reduce the dimensional accuracy of the sintered product. However, when the apparent porosity is too high, the strength of the setter 100 and the setter 200 is lowered, which is not preferable. For this reason, in the present embodiment, the apparent porosity is preferably in the range of 15% to 18%.

<Second feature>
The main components of the setter 100 and the setter 200 are alumina (aluminum oxide, Al ₂ O ₃ ) and silica (silicon dioxide, SiO ₂ ), and the weight ratio of silica is 3% to 10%. . Here, in addition to alumina and silica, which are the main components of the setter 100 and the setter 200, a small amount of ferric oxide (Fe ₂ O ₃ ) and sodium oxide (Na ₂ O) (0.05% to 0.00% by weight). About 1%). As the weight ratio of silica is lower, the generation of impurities can be reduced. As the weight ratio of silica is higher, impurities are generated and the impurities adhere to the setter 100 or setter 200, thereby reducing the dimensional accuracy of the sintered product. End up. However, when the weight ratio of silica is too low, the weight ratio of alumina is relatively increased, and the manufacturing costs of the setter 100 and the setter 200 are increased. For this reason, in the present embodiment, the weight ratio of silica is preferably 3% to 10%.

<Third feature>
The flatness of the setter 100 and the setter 200 is 0.02 mm to 0.1 mm. Here, the flatness represents a space between two parallel planes defined by the JIS standard. For example, the flatness is a reference standard (optical) that is completely flat. The flatter is measured with an interference fringe generated optically by bringing the setter 100 or the setter 200 into contact with the flat and applying a short wavelength light source, or the interference generated on the setter 100 or the setter 200 by reflecting the laser on the optical flat. The fringes are analyzed and measured without contact with the setter 100 and the setter 200, or measured with a contact type three-dimensional measuring device. The higher the flatness of the setter 100 and the setter 200, the higher the dimensional accuracy of the sintered product, and the lower the flatness, the lower the dimensional accuracy of the sintered product. However, if the flatness is too high, the manufacturing costs of the setter 100 and the setter 200 increase, which is not preferable. For this reason, in this Embodiment, it is set as the preferable range that flatness is 0.02 mm-0.1 mm.

Hereinafter, the setter 100 and the setter 200 other than those described above in the turbine wheel manufacturing method according to the present embodiment will be described. In addition, in the following description, while the part overlaps with the content of patent document 1, the content of patent document 1 may be diverted in the part which is not described in the following description.
The turbine wheel 10 is made of powdered metal as a raw material, and a molding material obtained by adding a necessary amount of an organic binder is prepared (S100 in FIG. 4), and the product is sintered in advance. A molded body is formed by molding with a mold considering the later shrinkage rate. In this case, the mold is formed so that the sintered product satisfies the dimensional accuracy of the final product in consideration of the shrinkage rate after sintering of the product (so that the secondary processing step is not required). To form a molded body. For this reason, the sintered product after sintering the molded product becomes the final finished product (S600 in FIG. 4). The mold is provided with a pouring gate for the molding material in the boss portion 50 or the rotor shaft connecting portion 40 in FIG. 1 to inject the molding material. The mold structure of the blade has a shape designed so that each blade does not undercut, and the nesting moves linearly from the center of the boss, thereby enabling continuous molding by the mold.

The metal used in the turbine wheel has corrosion resistance and is made of a heat-resistant steel metal material. Inconel, which is a Ni-based alloy, is mainly used. Among them, Inconel 713C (Ni-12.5Cr-4.2Mo-6.1Al-0.8Ti-2.0Nb) is generally used.
As metal powder made of Inconel metal material, alloy powder manufactured by water atomization or gas atomization method is usually used, but in addition to the alloy powder of powder made by these atomization methods, it is adjusted so that it becomes an alloy component during sintering. Element powders may be added according to the composition. In general, water atomized powder can be produced in a larger amount than gas atomized powder, so the manufacturing cost is also low, but because the powder shape tends to be irregular, the tap density tends to be low, and The amount of oxygen also increases. On the other hand, although the manufacturing cost of the gas atomized powder is increased, it is easy to obtain a spherical powder and the tap density is increased. For this reason, the water atomized powder and the gas atomized powder may be mixed and used in consideration of the cost and the tap density.

In addition, a titanium aluminum alloy that is lightweight and has high heat resistance at high temperatures is used. Using a composition in which the ratio of titanium to aluminum is TiAl, and adding 1 to 5% of the total amount of chromium, vanadium, manganese, and niobium to the titanium aluminum, ductility and workability are improved.
As the metal powder made of titanium aluminum metal material, alloy powder manufactured by plasma arc method, gas atomization method and pulverization method is used, but in addition to the alloy powder of powder made by these, it becomes an alloy component at the time of sintering The element powder may be adjusted and added according to the composition. In general, the pulverized powder can be produced in a larger amount than the plasma arc method and the gas atomized powder, so the manufacturing cost is also low. However, since the powder shape tends to be irregular, the tap density tends to be low. The amount of oxygen in the powder also increases. On the other hand, although the production cost of plasma arc powder and gas atomized powder is high, it is easy to obtain spherical powder and has a feature that the tap density is high. For this reason, in consideration of cost and tap density, pulverized powder may be mixed with plasma arc powder or gas atomized powder.

  As for the average particle diameter of the metal powder in this Embodiment, 1-30 micrometers is preferable. When the average particle size is less than 1 μm, the amount of binder added increases as the surface area of the powder increases, and deformation during degreasing increases. In addition, when the amount of the binder is increased, the shrinkage rate at the time of sintering is increased, the dimensional variation after sintering is increased, and it is difficult to obtain a sintered product with high dimensional accuracy in a subsequent pressing step. When the powder particle size exceeds 30 μm, it becomes difficult to stably obtain a sintered density (relative density) of 95% or more, the strength is remarkably lowered, and it cannot be used as a product. A more preferable average particle diameter is 5 to 12 μm, and more desirably 8 to 10 μm. In the present embodiment, the average particle diameter means an average diameter of 50% cumulative weight measured using a particle size distribution measuring apparatus using a laser diffraction / scattering method. As a particle size distribution measuring apparatus, SALD-2000 model manufactured by Shimadzu Corporation can be used.

As the organic binder, an organic binder containing 5 to 40% by volume of polyacetal and 5 to 40% by volume of polypropylene is used. By using polyacetal and polypropylene in the organic binder, the amount of deformation during degreasing can be suppressed as compared with conventional binders using polyethylene, ethylene vinyl acetate, and acrylic resin.
Polyacetal is indispensable as a substance that increases the strength of the molded body, prevents deformation of the molded body at 600 ° C. or lower during sintering, and does not leave carbides after sintering. Polypropylene imparts toughness to the molded body and prevents cracking of sintering and separation of added low melting point compounds. Polypropylene also has the property that no carbides remain after sintering.

  When the addition amount of polyacetal and polypropylene is less than 5 Vol% with respect to the total amount of the organic binder, deformation at the time of degreasing becomes large, and the prescribed dimensional accuracy after sintering cannot be obtained. On the other hand, if the addition amount of polyacetal and polypropylene exceeds 40% by volume with respect to the total amount of the organic binder, the viscosity at the time of molding increases and the molding material cannot be completely filled in the mold.

A more preferable polyacetal content is 10 to 30% by volume, and a more preferable polypropylene content is 10 to 30% by volume.
As materials other than polyacetal and polypropylene, the following organic materials can be used.
Fatty acid ester, fatty acid amide, phthalic acid ester, paraffin wax, microcrystalline wax, polyethylene wax, polypropylene wax, carnauba wax, montan wax, urethanized wax, maleic anhydride to provide fluidity and improve degreasing Modified waxes and polyglycol compounds are used. Particularly preferred materials include paraffin wax, fatty acid ester, and polypropylene wax.

In addition, polyethylene, amorphous polyolefin, ethylene vinyl acetate copolymer, acrylic resin, polyvinyl butyral resin, glycidyl methacrylate resin, and the like can be used in order to impart fluidity during molding and flexibility in the molded body. Particularly preferred materials include polyethylene and amorphous polyolefin.
In order to improve the fluidity and degreasing property, in order to provide the fluidity and flexibility, the organic binder is 30 to 60% by volume (Vol%) with respect to the total amount of the metal powder and the organic binder. It is preferable to make it 30 to 50% by volume.

The organic binder and metal powder having the above ratio are heated and kneaded at about 160 to 180 ° C. for about 2 hours to completely disperse and mix the metal powder with the organic binder (S200 in FIG. 4). Thereafter, it is taken out and formed into a pellet shape having a diameter of about 5 mm by an extruder or a pulverizer, and is used as a molding material for injection molding (S300 in FIG. 4).
And in shaping | molding, it is necessary to determine a metal mold | die shape in consideration of the dimension of the final finished product after sintering. These dimensions are dimensions obtained after sintering or by the hot isostatic pressing method, and the dimensions differ depending on the sintering density. Therefore, the mold design needs to fully consider the subsequent dimensional changes. For this purpose, it is necessary to design the dimensions of the mold in consideration of the above dimensional accuracy, and it is necessary to calculate the shrinkage ratio from molding to sintering in advance.

  In the conventional organic binder system, deformation occurs during the degreasing process, and it is very difficult to obtain a product within the size range of the sintered product. However, the particle size of the metal powder, the amount of the binder, and the binder component should be used. Thus, a sintered product with higher dimensional accuracy than the conventional one can be manufactured by the MIM method. Furthermore, a sintered product processed using the setter 100 or the setter 200 in the sintering process (which may include a degreasing process) can achieve high dimensional accuracy, and the sintered product is a final product that does not require secondary processing. It can be a shape.

  The mold is attached to an injection molding machine for molding, and the number of molded products obtained is generally one by one mold. The capacity of the injection molding machine is adjusted appropriately according to the size of the product. In general, molding is performed using a molding machine having a clamping force of about 50 to 150 tons. The injection speed and pressure are adjusted so that defects such as bubbles and cracks do not occur in the molded body, and the mold is provided with a gas escape for effectively releasing the air generated in the mold and the gas generated from the molding material. There is a need. When there is no effective gas escape, air or gas generated from the molding material is taken into the molded body, and bubbles are generated in the molded body.

  The obtained molded body is put into a degreasing furnace, and the added organic binder is removed (S400 in FIG. 4). The degreasing furnace for removing the organic binder is performed using any one of a reduced pressure inert gas atmosphere, an atmospheric pressure inert gas atmosphere, and an atmospheric pressure hydrogen gas atmosphere. In the case of a sintering apparatus having a degreasing function, the degreasing sintering is performed. Can be done consistently. As the degreasing furnace, a batch type degreasing furnace or a continuous (belt type, pusher type, walking beam type) degreasing furnace can be used. In particular, it is effective to perform degreasing using a jig having a shape along the shape of the molded body so as to prevent deformation to a minimum in view of the fact that the amount of deformation increases during degreasing. After this degreasing step S400 (degreasing step S400 and sintering step S500), the setter 100 or setter 200 provided with the above-mentioned <first feature>, <second feature>, and <third feature> is formed into a molded product. Is placed and processed.

Inconel and titanium-aluminum alloy (including mixed powder of titanium and aluminum) degrease atmosphere is either vacuum inert gas atmosphere, atmospheric inert gas atmosphere or atmospheric hydrogen atmosphere. In the case of a titanium aluminum alloy, the maximum temperature is 600 ° C. or less.
When the degreasing atmosphere is in the air, the powder is oxidized at 300 ° C. or higher, and the amount of oxygen after sintering increases, which greatly affects the strength of the sintered product. Therefore, a depressurized inert gas atmosphere, an atmospheric pressure inert gas atmosphere, and an atmospheric pressure hydrogen atmosphere are used as the degreasing atmosphere. In the case of Inconel, nitrogen or argon is used as the inert gas, but it is preferable to use nitrogen gas in consideration of cost. In the case of a titanium alloy, it is desirable to carry out with argon or hydrogen in consideration of nitriding of the material. The temperature increase rate during degreasing is preferably 50 ° C./hr or less from room temperature to 400 ° C. in consideration of deformation during degreasing. Moreover, the deformation | transformation at the time of degreasing of a molded object can be suppressed by using the jig | tool which considered the deformation | transformation of a molded object at the time of degreasing.

  The temperature of Inconel degreasing is 800 ° C. or less, and in the case of titanium aluminum alloy, it is 600 ° C. or less. However, at about 300 ° C., about 30% of the organic binder tends to remain, and above 600 ° C., the organic binder is easily removed completely. When moving to the sintering step, the molded body may collapse, and a more preferable degreasing temperature is 400 ° C to 500 ° C. Moreover, it is effective to use a sintering furnace having a degreasing function as a method for preventing the collapse of these molded products, and it is possible to shift to sintering without lowering the temperature even after the degreasing. Also, by connecting a continuous (belt type, pusher type, walking beam type) sintering furnace as well as a continuous type (belt type, pusher type, walking beam type) degreasing furnace, the degreasing step S400 to the sintering step S500 are performed. Processing can be performed continuously without interruption.

Next, the sintering step (S500 in FIG. 4) will be described.
In the inconel sintering process, any one of a reduced pressure inert gas atmosphere, an atmospheric pressure inert gas atmosphere, a pressurized inert gas atmosphere, and a vacuum atmosphere is used as a sintering atmosphere. As the inert gas, a large amount of chromium is used as a material during sintering. Therefore, it is preferable to use argon gas in consideration of nitriding of the material. The sintering temperature is 1000 ° C. or higher and 1500 ° C. or lower. However, if the sintering temperature is lower than 1000 ° C., the sintering is insufficient. In order for the sintered density to be 95% or more, 1200 to 1400 ° C is desirable, and further 1250 to 1380 ° C is desirable. Further, it is desirable to maintain the maximum temperature for about 2 to 4 hours in consideration of the improvement of the sintering density during sintering and the dimensional variation during sintering. As in the degreasing process, deformation occurs at high temperatures in the sintering process, so it is effective to use a jig for preventing deformation of the sintered product.

  In the sintering process of the titanium aluminum alloy, any one of a reduced pressure inert gas atmosphere, an atmospheric pressure inert gas atmosphere, a pressurized inert gas atmosphere, and a vacuum atmosphere is used as a sintering atmosphere. Considering oxidation and nitridation at the time of sintering, it is preferably performed in a vacuum. The sintering temperature is 800 ° C. or higher and 1300 ° C. or lower, but if it is less than 800 ° C., the sintering is insufficient, and if it exceeds 1300 ° C., it melts during sintering. In order for the sintered density to be 95% or more, 900 to 1250 ° C. is desirable, and further 1000 to 1200 ° C. is desirable. Further, it is desirable to maintain the maximum temperature for about 2 to 4 hours in consideration of the improvement of the sintering density during sintering and the dimensional variation during sintering. As in the degreasing process, deformation occurs at high temperatures in the sintering process, so it is effective to use a jig for preventing deformation of the sintered product.

In degreasing and sintering, considering the production volume, batch type degreasing furnaces and sintering furnaces are used for small quantities of various products, and degreasing and sintering are performed by pusher type continuous furnaces and walking when the number increases. By using a continuous process using a beam type continuous furnace and a belt type continuous furnace, the production amount can be dramatically improved.
By setting the density of the sintered product to 95% or more in terms of relative density, the mechanical strength and hardness at high temperatures can be maintained. When the relative density is less than 95%, the mechanical strength at high temperatures, particularly the elongation and hardness, are lowered, and continuous use at high temperatures is difficult.

The relative density of the sintered product can be measured by the Archimedes method.
A ceramic jig that fits in the inner diameter of the shaft coupling inner diameter portion shown in FIG. 1 that has been calculated in advance for the shrinkage rate after sintering in the degreasing process (degreasing step S400) to the sintering process (sintering step S500) for both Inconel and titanium aluminum alloy. By installing the dimensional accuracy of the inner diameter can be improved.

  The obtained sintered product is further subjected to a hot isostatic pressing method (HIP method) in order to further increase the sintered density to improve the mechanical strength and to improve the reliability of the mechanical strength in a high temperature range. It may be processed by. In this case, a sintered product having a relative density of 98% or more without a pinhole inside is stably obtained by processing at a low temperature of about 10 ° C. to 100 ° C. and a high pressure of about 10 MPa to 180 MPa. be able to. Inconel uses a sintered HIP device that can perform a pressure treatment of up to about 6 MPa during the sintering process, so that a sintered product with a relative density of 98% or more can be obtained without using the HIP method in the subsequent process. is there.

  According to the method for manufacturing a turbine wheel according to the present embodiment, in the degreasing step S400 and the sintering step S500, a setter having the above-described <first feature>, <second feature>, and <third feature>. Since the molded product is placed on 100 or the setter 200 for degreasing and sintering, the dimensional accuracy of the sintered product can be increased to the dimensional accuracy required as a final finished product. It can be completed as a final product without further processing.

The turbine wheel 10 was manufactured by the turbine wheel manufacturing method according to the present embodiment without subjecting the sintered product to secondary processing. The molding material, heat-kneading conditions, injection molding conditions, degreasing conditions, sintering conditions, etc. were as follows. 100 turbine wheels 10 were manufactured and evaluated by measuring dimensional variations.
[Example 1]
Metal powder: Inconel 713C Average particle size 9.2 μm
-Organic binder composition: Polyacetal 25 Vol%, Polypropylene 25 Vol%, Amorphous polyolefin 10 Vol%, Paraffin wax 35 Vol%, Fatty acid ester 5 Vol%
・ Metal powder: 67 Vol% Organic binder 33 Vol%
-Heat kneading: 180 ° C for 2 hours-Injection molding conditions: Injection temperature: 190 ° C Mold temperature: 40 ° C
・ Molding machine: Clamping force 100 ton, Mold: 1 piece ・ Degreasing condition: Maximum temperature 600 ° C. (nitrogen) 2 hours hold ・ Sintering condition: Maximum temperature 1350 ° C. (argon, reduced pressure atmosphere) 3 hours hold [Example 2]
・ Metal powder: Titanium aluminum alloy (added 2% vanadium) Average particle size 12.7μm
-Organic binder composition: Polyacetal 25 Vol%, Polypropylene 25 Vol%, Amorphous polyolefin 10 Vol%, Paraffin wax 35 Vol%, Fatty acid ester 5 Vol%
・ Metal powder: 67 Vol% Organic binder 33 Vol%
-Heat kneading: 180 ° C for 2 hours-Injection molding conditions: Injection temperature: 190 ° C Mold temperature: 40 ° C
・ Molding machine: Clamping force 100 ton, Mold: 1 piece ・ Degreasing conditions: Maximum temperature 500 ° C. (argon) held for 2 hours ・ Sintering conditions: Maximum temperature 1170 ° C. (vacuum atmosphere) held for 3 hours Mold for injection molding The turbine wheel made of Inconel of [Example 1] and the titanium aluminum alloy of [Example 2] has the same shape as the turbine wheel 10 shown in FIG. 1 (wheel diameter: 43 mm, Number of blades: 12).

The specifications of the setter 100 and the setter 200 used in the turbine wheel manufacturing method according to the present embodiment are as follows.
-Example setter specifications Apparent porosity: 16.7%
Ingredients: 94.93% by weight of alumina, 4.81% by weight of silica, 0.10% by weight of ferric oxide, 0.16% by weight of sodium oxide
Flatness: 0.05mm
Using the above-described example setter in the degreasing step S400 and the sintering step S500, inconel of [Example 1] and titanium aluminum alloy of [Example 2] are processed according to the manufacturing flowchart of S200 to S500 of FIG. did. In both Inconel of [Example 1] and the titanium aluminum alloy of [Example 2], the dimensions required for the final product can be obtained after sintering, and secondary processing after sintering is required. The product (turbine wheel 10 shown in FIG. 1) within the final product size tolerance could be obtained. The turbine wheel 10 manufactured by the method for manufacturing a turbine wheel according to the present embodiment is not subjected to secondary processing after sintering. For example, the blade thickness is thin (the blade tip is very thin (for example, 0.3 mm) The following :) Flatness of bottom surface, tip height of blade upper end, blade pitch, concentricity of inner diameter of rotor shaft coupling portion, perpendicularity of inner diameter of rotor shaft coupling portion, unbalance amount, etc. are within dimensional tolerance of final product Was able to get the final finished product.
[Comparative example]
The comparative example setter shown below is used in the degreasing step S400 and the sintering step S500, and the same Inconel as in [Example 1] and the same titanium aluminum alloy as in [Example 2] are manufactured according to the manufacturing flowchart of S200 to S500 in FIG. The process was executed. In both Inconel of [Example 1] and the titanium aluminum alloy of [Example 2], the dimensions required for the final product cannot be obtained after sintering, and secondary processing of the sintered product is necessary. Met.
・ Comparative setter specifications Apparent porosity: 13.4%
Ingredients: 88.43% by weight of alumina, 11.42% by weight of silica, 0.05% by weight of ferric oxide, 0.10% by weight of sodium oxide
Flatness: 0.3mm
As described above, according to the method for manufacturing a turbine wheel according to the present embodiment, in the degreasing step S400 and the sintering step S500, the above-described <first feature>, <second feature>, and <third feature> In order to place the molded product on the setter 100 or the setter 200 having the characteristics> and perform the degreasing treatment and the sintering treatment, the dimensional accuracy of the sintered product can be increased to the dimensional accuracy required as a final finished product. The sintered product can be completed as a final product without secondary processing.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICABILITY The present invention is suitable for a method for manufacturing a turbocharger turbine wheel used in an automobile engine or the like, and does not require secondary processing after sintering, and completes a sintered product by the MIM method as a final product, thereby reducing the manufacturing cost. This is particularly preferable in that a turbine wheel with high dimensional accuracy can be manufactured while being lowered.

DESCRIPTION OF SYMBOLS 10 Turbine wheel 20 Blade 30 Center shaft part 40 Rotor shaft coupling part 50 Boss part 100, 200 setter S100 Preparation step (preparation process) of organic binder and metal powder
S200 Heat kneading step (heat kneading process)
S300 Injection molding step (injection molding process)
S400 Degreasing step (degreasing process)
S500 Sintering step (sintering process)
S600 Step of taking out the final product (takeout step)

Claims (1)

A metal turbine wheel having a plurality of curved blades extending radially from the central shaft portion and having an upper end bent in the rotational direction, and a rotor shaft serving as a rotational shaft connected to the bottom surface side of the central shaft portion in use. A method of manufacturing
A heating and kneading step of adding an organic binder to the metal powder and heating and mixing, and then crushing or pelletizing to obtain an injection molding material,
An injection molding step of producing a molded body by injection molding the injection molding material into the shape of the turbine wheel; and
In a degreasing atmosphere, a degreasing step for degreasing the produced molded body,
After the degreasing step, in a sintering atmosphere, sintering the degreased shaped body to produce a sintered product, and
After the degreasing step, the sintered product is completed as a final product by placing and processing the molded body on a setter,
The setter, by being made of alumina containing 3% to 4.8% silica by weight ratio, it flatness 0.02mm~0.1mm der, an apparent porosity of 15% ～16.7 A method for manufacturing a turbine wheel, characterized in that a turbine wheel is used.

Images