Workpiece processing method

Abstract

To reduce the cost for machining a spline.SOLUTION: A machining method for a work piece W includes a pre-machining step S1 of forming a through-hole 2 in the work piece W and forming a spline 3 on an inner surface of the through-hole 2; a heat treatment step S2 of performing heat treatment on the work piece W on which the spline 3 is formed; and a finish machining step S3 of removing a deformed portion D of the spline 3 generated by the heat treatment step S2, by using a broaching tool 4 made of high-speed steel and having a cutting edge with an obtuse rake angle θ.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for machining a workpiece. [Background technology]

[0002] Patent Document 1 discloses an internal broaching method for machining an involute spline gear on the inner surface of a workpiece using a broach tool.

[0003] In the processing method disclosed in Patent Document 1, first, a broach tool is used to pre-machine the involute spline tooth flanks of a workpiece while leaving a finishing allowance. The pre-machined workpiece is then carburized and quenched, and then a broach tool made of cemented carbide is used to perform finish machining, cutting off the finishing allowance from the involute spline tooth flanks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-230937 Summary of the Invention [Problem to be solved by the invention]

[0005] Broaching tools made of cemented carbide are useful for cutting high-hardness materials such as hardened workpieces. However, cemented carbide broaching tools are significantly more expensive than broaching tools made of high-speed steel, which increases the product cost. For this reason, there has been a demand for reducing the cost involved in machining splines.

[0006] The present invention has been made in view of the above problems, and has an object to reduce the cost involved in machining splines. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a method for machining a workpiece, comprising a pre-machining step of forming a hole in the workpiece and forming a spline on the inner surface of the hole, a heat treatment step of heat treating the workpiece on which the spline has been formed, and a finish machining step of removing a deformed portion of the spline caused by the heat treatment step using a broach tool made of high-speed steel and having an obtuse rake angle on the cutting edge. In the pre-processing step, the spline is processed to a final finished size. A method for machining a workpiece is provided. [Effects of the Invention]

[0008] According to this aspect, since the deformation portion generated in the spline by the heat treatment process is removed, the broaching can be performed using a broaching tool made of high-speed steel, which is less expensive than a broaching tool made of cemented carbide, thereby reducing the cost associated with machining the spline. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a workpiece according to this embodiment. [Figure 2] FIG. 2 is a flowchart showing the flow of the workpiece machining method according to this embodiment. [Figure 3] FIG. 3 is an external view of a broaching tool used for broaching a workpiece according to this embodiment. [Figure 4] FIG. 4 is a partially enlarged view of a broaching tool used for broaching a workpiece according to this embodiment. [Figure 5] FIG. 5 is a diagram for explaining a deformed portion that occurs in the workpiece after the heat treatment process according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] 1 is a cross-sectional view in the axial direction of a workpiece W according to this embodiment. The workpiece W in this embodiment is, for example, a gear that constitutes a power transmission of a reducer mounted on a vehicle.

[0012] 1, the workpiece W has a main body 1 having a gear 11 formed on its outer periphery, a through hole 2 formed to penetrate the main body 1, and a spline 3 formed in the through hole 2. The workpiece W is made of, for example, alloy steel for mechanical structures (such as SCR420H).

[0013] A rotating shaft (not shown) to which output from a motor that drives a vehicle is transmitted is inserted into the through hole 2. A spline that is spline-coupled with the spline 3 formed in the through hole 2 is provided at the tip of this rotating shaft.

[0014] Gear 11 is a helical gear. Gear 11 is engaged with another gear (not shown). These gears form a speed reduction mechanism, which reduces the rotation output from the motor. Note that gear 11 is not limited to a helical gear and may have any shape.

[0015] Next, a method for machining the workpiece W will be described with reference to FIG.

[0016] As shown in FIG. 2, the workpiece W is manufactured through a pre-processing step S1, a heat treatment step S2, a finish processing step S3, and a cleaning step S4.

[0017] In the pre-processing step S1, mainly cutting (step S11), hole drilling (step S12), and broaching (step S13) are performed. Specifically, in the pre-processing step S1, first, in step S11, a metal material is cut to form the outer shape of the main body 1 of the workpiece W. At this time, the gear 11 is also formed.

[0018] Next, in step S12, the main body 1 is drilled to form the through-holes 2.

[0019] Thereafter, in step S13, splines 3 are formed by broaching. Specifically, a broaching tool 4 made of high-speed steel as shown in FIG. 3 is used to form a plurality of spline grooves 3a on the inner surface of the through hole 2. Note that, as shown in FIG. 1, in this embodiment, the splines 3 are provided across a first main body portion 1a on which a gear 11 is formed on the outer periphery of the main body 1, and a second main body portion 1b having a thinner wall thickness than the first main body portion 1a.

[0020] In this embodiment, in step S13, the spline 3 is machined to have a final finished dimension. In other words, in the broaching in step S13 of this embodiment, the spline 3 is formed without providing a finish machining allowance (a machining allowance for machining in the finish machining step S3).

[0021] After the pre-processing step S1 is completed, the process proceeds to the heat treatment step S2. In the heat treatment step S2, the workpiece W, which has been formed with the outer shape (main body 1), through holes 2, and splines 3 in the pre-processing step S1, is subjected to heat treatment. Specific heat treatment techniques include, for example, carburizing and induction hardening.

[0022] After the heat treatment step S2 is completed, the process proceeds to the finishing step S3. The finishing step S3 mainly includes shot peening (step S31), hard turning (step S32), grinding (step S33), broaching (step S34), and gear grinding (step S35). Specifically, in the finishing step S3, first, shot peening is performed in step S31. This imparts residual compressive stress to the workpiece W, improving fatigue strength and the like.

[0023] Next, in step S32, the portion of the workpiece W excluding the gear 11 and the spline 3 is subjected to hard turning.

[0024] Next, in step S33, grinding is performed to finish the workpiece W except for the gear 11 and the spline 3 to the final finishing dimensions.

[0025] Next, in step S34, broaching is performed on the spline 3. In the broaching in step S34, a broaching tool 4 made of high-speed steel is used.

[0026] Here, the broaching in the finishing process S3 (step S34) in this embodiment will be described in detail.

[0027] The workpiece W has a higher hardness than before the heat treatment due to the heat treatment in the heat treatment step S2. For this reason, broaching (finishing of the spline 3) of the workpiece W after such heat treatment is usually performed using a broaching tool made of cemented carbide. Note that the cemented carbide referred to here is an alloy obtained by mixing powder of a hard metal such as tungsten carbide or titanium carbide with powder of a light iron metal such as cobalt or nickel as a binder, and sintering the mixture.

[0028] Such cemented carbide broaching tools are useful for cutting high-hardness materials. However, cemented carbide broaching tools are much more expensive than high-speed steel broaching tools. This increases the product cost (cost related to machining the spline 3).

[0029] Therefore, in this embodiment, broaching is performed using a broaching tool 4 made of high-speed steel. In this embodiment, in order to perform broaching in the finishing machining step S3 (step S34) using a broaching tool 4 made of high-speed steel, the spline 3 is machined to the final finished dimensions in the pre-machining step S1 without providing a finishing allowance. As a result, in the broaching in the finishing machining step S3 (step S34), it is necessary to machine only the deformed portion D (see FIG. 5) that has occurred in the spline 3 during the heat treatment in the heat treatment step S2.

[0030] Here, the deformation portion D will be described.

[0031] As described above, the splines 3 are formed across the first body portion 1a and the second body portion 1b, which is thinner than the first body portion 1a. As shown in Fig. 5, the amount of deformation of the splines 3 formed in the second body portion 1b by the heat treatment in the heat treatment step S2 is greater than the amount of deformation of the splines 3 formed in the first body portion 1a. Therefore, the deformed portion D formed in the splines 3 by the heat treatment in the heat treatment step S2 has a tapered shape whose diameter decreases from the first body portion 1a toward the second body portion 1b.

[0032] Therefore, the areas that require machining in step S34, in other words, deformations that would cause the spline 3 to deviate from the tolerances of the finished dimensions, occur mainly in the areas formed in the second main body portion 1b. In the broaching process (step S34) in the finishing process S3, it is only necessary to process the deformations that occur in these areas, and therefore, the broaching can be performed using a broaching tool 4 made of high-speed steel.

[0033] The height of the deformed portion D generated in the spline 3 by the heat treatment in the heat treatment step S2 is about several μm to several tens of μm. In the broaching in the finishing step S3 (step S34), it is only necessary to remove such a small amount of deformation, so that the broaching can be performed using a broaching tool made of high-speed steel.

[0034] In this embodiment, the rake angle θ of the broaching tool 4 is set to an obtuse angle (for example, approximately −15 degrees) as shown in Fig. 4. By setting the rake angle θ to an obtuse angle in this manner, the rigidity of the cutting edge of the broaching tool 4 can be increased, thereby preventing damage to the broaching tool 4.

[0035] Furthermore, since a high-speed steel broaching tool 4 is used in the broaching in step S34, a normal broaching machine can be used. The cutting speed in the broaching in the finishing process step S3 (step S34) is set to approximately the same as a normal cutting speed using a high-speed steel broaching tool, specifically, within the range of approximately 1 to 14 m / min.

[0036] When the broaching in step S34 is completed in this manner, the process proceeds to step S35.

[0037] In step S35, grinding is performed on the gear 11. Since gear grinding is a common technique, a description thereof will be omitted.

[0038] Finally, in step S4, the workpiece W is cleaned, thereby completing the processing of the workpiece W.

[0039] In this way, in the method for processing the workpiece W of this embodiment, in the finishing processing step S3 (step S34), only the deformed portion D that has occurred in the spline 3 due to the heat treatment step S2 is removed, so that a broaching tool 4 made of high-speed steel can be used.

[0040] For example, in the pre-processing step S1, if the spline 3 is formed with a finishing allowance, and then heat treatment is performed and finish processing is performed, it is necessary to remove the finishing allowance previously provided on the spline 3 and the deformation caused by the heat treatment. In this case, since the processing allowance for the spline 3 portion of the hardened workpiece W becomes large during finish processing, it is not possible to process it with a broach tool 4 made of high-speed steel, and it is necessary to use a broach tool made of cemented carbide.

[0041] In contrast, in the method for machining the workpiece W of this embodiment, the splines 3 are machined to the final finished dimensions in the pre-machining step S1, so that in the finishing machining step S3 (step S34), it is only necessary to machine the deformed portions D of the splines 3 (portions that deviate from the finished dimensions) that have occurred in the heat treatment step S2. Therefore, in the finishing machining step S3 (step S34), broaching can be performed using a broaching tool 4 made of high-speed steel, which is cheaper than a broaching tool made of cemented carbide. This allows the cost associated with machining the splines 3 to be reduced.

[0042] Furthermore, the broaching machine used for broaching in the finishing process S3 (step S34) can be the same as the broaching machine using the high-speed steel broaching tool used in step S13. This eliminates the need to prepare a separate broaching machine for using a broaching tool made of cemented carbide. This reduces the cost of machining the spline 3.

[0043] In the above embodiment, the spline 3 is machined to the final finished dimensions in the pre-machining step S1 without providing a finishing allowance. However, for example, the spline 3 may be machined in the pre-machining step S1 to dimensions that take into account deformation caused by the heat treatment step S2. In this case, the amount of deformed portion D that deviates from the tolerance of the finished dimensions caused by the heat treatment step S2 is reduced in step S34. This allows the amount of cutting in the broaching in the finishing step S3 (step S34) to be reduced, thereby extending the life of the broaching tool 4.

[0044] The configuration, operation, and effects of the embodiment of the present invention configured as above will be described below.

[0045] (1) The method for machining the workpiece W includes a pre-machining step S1 in which a through hole 2 (hole) is formed in the workpiece W and a spline 3 is formed on the inner surface of the through hole 2 (hole), a heat treatment step S2 in which the workpiece W with the spline 3 formed therein is heat treated, and a finishing machining step S3 in which a deformed portion D of the spline 3 caused by the heat treatment step S2 is removed using a broach tool 4 made of high-speed steel and having an obtuse rake angle θ of the cutting edge.

[0046] In this configuration, the deformed portion D generated in the spline 3 by the heat treatment step S2 is removed in the finishing step S3, so that the broaching can be performed using a broaching tool 4 made of high-speed steel, which is less expensive than a broaching tool made of cemented carbide. This reduces the cost of machining the spline 3.

[0047] In addition, in this configuration, the rake angle θ of the cutting edge of the broach tool 4 is set to an obtuse angle, which increases the rigidity of the cutting edge and improves the durability of the broach tool 4. This reduces the cost associated with machining the spline 3.

[0048] Furthermore, while it is difficult to manufacture a broaching tool 4 made of cemented carbide that can accommodate small hole diameters, it is relatively easy to manufacture a broaching tool 4 made of high-speed steel that can accommodate small hole diameters. Therefore, by using a broaching tool 4 made of high-speed steel, the degree of freedom in designing the spline 3 is improved.

[0049] (2) In the method for machining the workpiece W, in the pre-machining step S1, the spline 3 is machined to the final finishing dimensions.

[0050] According to this configuration, by machining the spline 3 to the final finishing dimensions in the pre-machining step S1, it is only necessary to machine the amount of the spline 3 that deviates from the finishing dimensions in the finishing machining step S3. This reduces the load on the broach tool 4.

[0051] (3) In the method for machining the workpiece W, the spline 3 is formed across a first body portion 1a having a predetermined thickness in the workpiece W and a second body portion 1b having a thickness thinner than that of the first body portion 1a. The deformation portion D is a tapered deformation that reduces in diameter from the first body portion 1a toward the second body portion 1b.

[0052] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0053] In the above embodiment, the workpiece W is described as a gear that constitutes the power transmission of a reducer mounted on a vehicle, but this is not limited to this, and the processing method of the above embodiment can be applied to parts for any purpose.

[0054] Furthermore, in the above embodiment, the spline 3 is formed in the through hole 2 as an example, but the spline 3 may also be formed in a non-through hole (a hole with one end closed). [Explanation of symbols]

[0055] 1 Main unit 1a First main body part 1b Second body part 2 through holes 3 Splines 4 Broaching tools 11 Gears

Claims

1. A method for machining a workpiece, comprising: a pre-processing step of providing a hole in the workpiece and forming a spline on the inner surface of the hole; a heat treatment step of subjecting the workpiece on which the spline is formed to a heat treatment; The deformed portion of the spline caused by the heat treatment process is made of high-speed steel, a finishing process step of removing the cutting edge using a broach tool having an obtuse rake angle; In the pre-machining step, the spline is machined to a final finishing dimension.

2. 2. The method for machining a workpiece according to claim 1, the spline is formed across a first body portion having a predetermined thickness in the workpiece and a second body portion having a thickness thinner than that of the first body portion, A method for machining a workpiece, wherein the deformation portion is a tapered deformation that reduces in diameter from the first main body portion toward the second main body portion.

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