Method for producing a shift finger using metal powder injection molding

Abstract

A method for manufacturing a shift finger (200) using metal powder injection molding, comprising: Mixing a metal powder and a binder to obtain a base material for injection molding; Forming a molded body by injecting the base material for injection molding into a mold formed in a shape of the shift finger (200) using an injection nozzle; Degreasing the molded body; Sintering the degreased molded body to form a sintered body; and Post-processing of the sintered body, wherein the metal powder comprises 0.4 to 0.6 wt% of carbon, 1.5 to 2.5 wt% of nickel and the remaining wt% of iron, and wherein the forming of the molded body is carried out by using the injection nozzle in a temperature range of 100 to 200°C, wherein the base material for injection molding is obtained by mixing 85 to 90 wt.% of the metal powder and 10 to 15 wt.% of the binder, wherein the degreasing of the molded body is carried out by solvent extraction in a temperature range of 35°C to 50°C using a normal hexane solvent, and by performing thermal decomposition in a temperature range of 100°C to 150°C, wherein the formation of the sintered body is carried out by heating in a temperature range of 1250°C to 1350°C, where the binder is paraffin wax.

Description

BACKGROUND 1. Field of the invention

[0001] The present invention relates to a method for manufacturing a shift finger using metal injection molding, and more particularly to a method for manufacturing a shift finger using metal injection molding, which replaces a conventional type casting method with a metal injection molding method excellent in dimensional accuracy, thus reducing costs, and improving physical properties by adjusting powder compositions and precise process conditions. 2. Description of the state of the art

[0002] In general, a manual transmission is a device installed between a clutch and a drive shaft to appropriately change a drive power of an engine in accordance with a change in the running condition of vehicles, and has a handling mechanism for the transmission so that the transmission is operated by the driver's handling.

[0003] Fig.1 is a perspective view of a shift finger mounted on a manual transmission. As shown, the manual transmission typically includes a control mechanism for shifting gears and a synchromesh mechanism meshed with the control mechanism. A shift finger 200 is installed to actuate a shift spool connected to the synchromesh mechanism. The shift finger 200 should be precisely formed and have durability (such as strength, wear resistance, or the like) because the shift finger 200 is consistently used in a harsh environment for a long period of time.

[0004] Typically, the shift finger 200 is manufactured by a casting process using ductile iron (for example, Korean Standard FCD450, FCD500, and FCD600). However, due to the complex shape of the shift finger 200, several additional processes are required to form a final shape after casting.

[0005] Namely, when the shift finger 200 is manufactured by the casting process, the dimensional accuracy deteriorates. Therefore, there is a problem that the product cost is increased due to post-processing, which results in additional processing costs and further loss of materials.

[0006] US 2010 / 0 032 859 A1 provides a method for producing an injection-molding substance and an injection-molding substance. DE 693 07 172 T2 relates to a binder system for use in the injection molding of metal powders, ceramic powders, and metal-ceramic composite powders, as well as molding mixtures containing this binder system. DE 10 2006 030 100 A1 relates to a shift finger for an actuating element, such as a shift shaft or a detent sleeve. US 2007 / 0 246 131 A1 discloses a metal powder production device for producing a metal powder, comprising a feed for supplying a molten metal, a liquid ejection unit, and a course modification unit. US 2010 / 0183471 A1 discloses a method for producing an article by metal injection molding of aluminum or an aluminum alloy.DE 695 14 722 T2 relates to the injection molding of metallic or ceramic powder particles known as powder injection molding (PIM), and in particular to the use of a special binder system. DE 60 2004 008 192 T2 relates to a raw powder for sintering and further to a microparticulate, low-alloy steel for sintering or other such raw powders for sintering that have a high sintering density and are modified to produce uniform properties. DE 10 2005 008 789 A1 relates to a metal powder sintered body using fine powders as the raw material, and to the manufacturing process thereof. SUMMARY

[0007] The present invention has been made in an effort to provide a method of manufacturing a shift finger using metal injection molding, which has the advantages of increased economy by improving the molding accuracy by using a metal injection molding method instead of a conventional molding method, and is applicable even to a harsh or rugged environment such as a manual transmission or the like by setting the optimal powder compositions and process conditions.

[0008] An exemplary embodiment of the present invention provides a method for manufacturing a shift finger using metal powder injection molding, comprising: mixing a metal powder and a binder to obtain a base material for injection molding; forming a molded body by injecting the obtained base material for injection molding into a mold formed in a shape of the shift finger using an injection nozzle; degreasing the molded body; sintering the degreased molded body to form a sintered body; and post-processing the sintered body, wherein the metal powder contains 0.4 to 0.6 wt% of carbon, 1.5 to 2.5 wt% of iron, and 0.5 to 1.5 wt% of tin.-% of nickel and the remaining weight percent of iron, and wherein the forming of the molded body is carried out by using the injection nozzle in a temperature range of 100 to 200°C, wherein the obtaining of the base material for injection molding is carried out by mixing 85 to 90 wt% of the metal powder and 10 to 15 wt% of the binder, wherein the degreasing of the molded body is carried out by solvent extraction in a temperature range of 35°C to 50°C using a normal hexane solvent, and by carrying out thermal decomposition in a temperature range of 100°C to 150°C, wherein the forming of the sintered body is carried out by heating in a temperature range of 1250°C to 1350°C, wherein the binder is paraffin wax.

[0009] Advantageously, the method according to the present invention, which has the above-mentioned configuration, reduces the corresponding manufacturing costs by replacing a conventional casting method with a metal injection molding method, which is excellent in dimensional accuracy, and reduces process costs and material loss due to rework. In addition, the method according to the present invention can ensure applicable physical properties even for harsh and harsh environments by adjusting metal powder compositions and precise process conditions to improve durability, such as strength, material fatigue, or the like. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a shift finger mounted on a manual transmission. Fig. 2 is a flowchart illustrating a method of manufacturing a shift finger using metal injection molding in accordance with an exemplary embodiment of the present invention. Fig. 3 is a picture illustrating the shift finger mounted on a shaft. Fig. Figure 4 is a picture illustrating the shift finger during a twist test. DETAILED DESCRIPTION

[0010] It is to be understood that the terms used in the specification and the appended claims should not be construed as being limited to generic and dictionary meanings, but should be interpreted based on the meanings and concepts corresponding to the technical spirit of the present invention on the basis of the principle that the inventor may determine terms which are suitable for the best possible explanation of the inventor's own invention.Therefore, the configuration illustrated in the description and drawings as proposed herein is merely a preferred example of the present invention for illustrative purposes only, and is not intended to limit the scope of the invention, so it is understood that other equivalents and modifications which can be substituted at the time of filing the present invention can be made thereto without departing from the spirit and scope of the invention.

[0011] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is also to be understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of the recited features, integers, steps, acts, elements, and / or components, but do not preclude the presence or addition of one or more features, integers, steps, acts, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed terms.

[0012] Unless specifically stated or obvious from the context, the term "about," as used herein, is understood to be within a range of normal tolerance in the art, for example, within 2 standard deviations of the mean. "Approximately" may be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clearly evident from the context, all numerical values ​​provided herein are modified by the term "about."

[0013] Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0014] Although the shift finger manufactured using a conventional casting process somewhat meets the physical property requirements for a manual transmission application, these properties are not necessarily dimensionally stable, and thus multiple post-processing processes are required. Therefore, there is the problem of increased cost of the shift finger due to rework, which entails additional processing costs and leads to material waste.

[0015] Therefore, the present invention relates to a manufacturing method for replacing the existing casting method for the shift finger with a metal powder injection molding method, which provides improved dimensional accuracy.

[0016] Metal injection molding (MIM) is a new powder metallurgy molding technology that adapts powder metallurgy technology to injection molding, a mass-production process for forming precision plastic parts. Generally, the MIM process involves mixing a fine metal powder and a binder as a key component for fluidity, injecting the mixture into a mold, removing the binder from the molded body, and finally sintering the powder at a high temperature to produce components.

[0017] Generally, metal injection molding provides improved dimensional accuracy compared to the casting method, but the physical properties of the resulting product are poor. Therefore, post-processing is required to improve the physical properties through surface heat treatment or the like. In addition, when using the conventional casting method, it is difficult to achieve the desired physical properties because it is difficult to control the carbon within the material. Therefore, the casting method is inadequate as a method for manufacturing components that operate in harsh or rugged environments, such as a manual transmission or the like.

[0018] Therefore, it is an object of the present invention to solve the above-mentioned problems and to ensure improved dimensional accuracy so that the resulting product has a shape almost identical to the shape of the final end product by adjusting alloy components and manufacturing process conditions in a metal injection molding method, to reduce the amount of rework and the loss of materials, and thus realize cost reduction.

[0019] Fig. Figure 2 is a flowchart illustrating a method for manufacturing a shift finger using metal injection molding in accordance with the present invention. The following provides a detailed description in the order of the steps. 1. Mixing step (S100)

[0020] First, to obtain base materials for injection molding, a metal powder and a binder are mixed. The binder is added to maintain the fluidity and shape of the metal powder during injection molding. Specifically, 85 to 90 wt.% of the metal powder and 10 to 15 wt.% of the binder are mixed together. Paraffin wax is used as the binder.

[0021] The weight ratio is intended for a homogeneous mixture of the metal powder and the binder. If the metal powder contained therein is less than approximately 85 wt.%, the fluidity for injection molding will be high, while a long time will be required for degreasing. In addition, if the metal powder contained therein is more than 90 wt.%, the molded article will not have a sufficient degree of strength when injection molding is performed. Accordingly, the metal powder and the binder are mixed at the above-mentioned weight ratio.

[0022] In addition, the metal powder is made by mixing individually provided metallic elements, which preferably contain 0.4 to 0.6 wt% of carbon (C), 1.5 to 2.5 wt% of nickel (Ni) and the remaining wt% of iron.

[0023] Specifically, carbon (C) is added to increase the strength and hardness of the material and to allow fine alloying elements to precipitate as carbides. The carbon content is 0.4 wt% or more to achieve the desired mechanical strength. Furthermore, the carbon content is 0.6 wt% or less to reduce the impact value, which leads to brittleness.

[0024] Nickel is added to improve mechanical properties and quenching qualities during heat treatment. The nickel content is 1.5 wt% or more to achieve the desired mechanical strength and quenching qualities. Furthermore, the nickel content is approximately 0.5 wt% or less when considering the cost of nickel relative to its effect. 2nd injection step (S110)

[0025] The resulting injection molding base materials are injected into a mold formed in the shape of the shift finger through an injection nozzle, thus forming a molded article in a shape substantially close to the final finished product (realizing the final shape). The injection nozzle temperature can be set by considering the fluidity of the injection molding base materials and the evaporation of the binder. The injection nozzle temperature is within the range of 100 to 200°C, so that internal gas bubbles in the molded article are completely eliminated. 3rd step of degreasing (S120)

[0026] Since the molded body contains the binder, a degreasing process is performed to remove the binder. The most common method of removing the binder is by slowly heating the molded body to evaporate the binder through thermal decomposition.

[0027] However, when the binder is heated and evaporated, since most of the binder evaporates slowly at low temperatures and quickly when reaching a certain high temperature, deformation of the molded article, such as bending or twisting, may occur. Therefore, it is necessary to minimize the deformation of the molded article step by step when performing solvent extraction and thermal decomposition in the degreasing step.

[0028] In the present case, the binder in the molded body is removed by immersing the molded body in normal hexane (n-hexane) as a solvent and by extracting the solvent in a temperature range of 35°C to 50°C.

[0029] If the temperature is higher than 50°C, the reaction rate for binder removal is so high that the binder is removed before a suitable extraction path is formed in the molded body, resulting in a crack in the molded body due to stress concentration. If the temperature is lower than 35°C, the crack may not form, but it takes a long time to remove the binder, resulting in an increase in process costs. Therefore, the temperature is within the above-mentioned range.

[0030] Next, thermal decomposition is performed to remove a high-melting-point binder remaining in the molded body. In this case, the binder is completely removed by heating within a temperature range of 100°C to 150°C before sintering.

[0031] As described above, the binder is rapidly removed by continuously performing solvent extraction and degreasing during thermal decomposition. This can reduce process costs by shortening the overall processing time and ensure stability during the sintering process. 4th step of sintering (S130)

[0032] A vacuum may be provided by a pump, after generating an ambient pressure by means of a gas, preferably by introducing argon gas, a sintered body may be formed by heating the degreased molded body in a temperature range of 1250°C to 1350°C and sintering is carried out while maintaining the temperature range for a certain period of time.

[0033] The molded body can be strengthened by densification and grain growth during the sintering process. Sintering is carried out in the temperature range mentioned above to obtain the necessary mechanical properties by homogenizing the carbon (C) and nickel (Ni) in the molded body. 5th step of post-processing (S140)

[0034] A post-processing step includes all the additional processes necessary to produce the final product from the sintered body, and the additional processes include methods of dimensioning a required portion, pressing the sintered body to provide exact dimensions, performing high-frequency heat treatment, or the like, as required.

[0035] Preferably, the post-processing may include a final step for manufacturing a product, which includes a heat treatment such as carburizing, a surface polishing process, or the like. [Table 1] Objects Yield strength (MPa) Tensile strength (MPa) Test specification State-of-the-art casting process 390 450 ISO 6892, ISO 2740 An exemplary embodiment of the present invention 482 714 ISO 6892, MPIF Standard 50

[0036] Table 1 presents a comparison in strength between a shift finger in accordance with an exemplary embodiment of the present invention and a shift finger manufactured by a prior art casting method. As shown in the table, the yield strength and tensile strength of the shift finger manufactured in accordance with the exemplary embodiment of the present invention are measured at 482 MPa and 714 MPa, respectively. The yield strength and tensile strength are approximately 24% and 59% greater than the yield strength and tensile strength of the shift finger manufactured by the prior art casting method. [Table 2] Objects Fatigue (test torque 100.4 Nm) Breaking torque (Nm) State-of-the-art casting process 78,000 cycles 228 to 251 An exemplary embodiment of the present invention 547,000 cycles 272 to 310

[0037] Table 2 presents a comparison in material fatigue and fracture torque between a shift finger in accordance with an exemplary embodiment of the present invention and a shift finger manufactured by a conventional casting process. Fig. 3 is a picture illustrating the shift finger mounted on a shaft, and Fig. Figure 4 is a picture illustrating a shift finger during a twist test.

[0038] Material fatigue is measured by applying a twisting torque in an actual operating environment, and fracture torque is measured as a twisting torque when a component is broken due to twisting.

[0039] As shown in the table, the material fatigue and the fracture torque of the shift finger manufactured in accordance with the exemplary embodiment of the present invention are 547,000 cycles and 272-310 Nm, respectively, and the shift finger in accordance with the present invention has improved material fatigue compared with the shift finger manufactured by the conventional casting method.

[0040] As described above, the present invention has the effect of reducing the manufacturing cost by approximately 50% compared to the manufacturing of the shift finger produced by the conventional casting method by employing metal injection molding without any post-processing. In addition, the present invention can provide the shift finger with increased strength by optimizing the powder compositions and processing conditions.

[0041] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will recognize that various changes, additions and substitutions are possible without departing from the scope and spirit of the invention as disclosed in the appended claims.

Claims

[1] A method for producing a shift finger (200) using metal powder injection molding, comprising: Mixing a metal powder and a binder to obtain a base material for injection molding; Forming a molded body by injecting the base material for injection molding into a mold formed in a shape of the shift finger (200) using an injection nozzle; Degreasing the molded body; Sintering the degreased molded body to form a sintered body; and Post-processing of the sintered body, wherein the metal powder comprises 0.4 to 0.6 wt% of carbon, 1.5 to 2.5 wt% of nickel and the remaining wt% of iron, and wherein the forming of the molded body is carried out by using the injection nozzle in a temperature range of 100 to 200°C, wherein the base material for injection molding is obtained by mixing 85 to 90 wt.% of the metal powder and 10 to 15 wt.% of the binder, wherein the degreasing of the molded body is carried out by solvent extraction in a temperature range of 35°C to 50°C using a normal hexane solvent, and by performing thermal decomposition in a temperature range of 100°C to 150°C, wherein the formation of the sintered body is carried out by heating in a temperature range of 1250°C to 1350°C, where the binder is paraffin wax.

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