Gear machining method

Abstract

The objective is to provide a rolling method that can achieve good rolling accuracy by suppressing deformation of the hollow portion after rolling, even when performing the same processing cycle as for a solid cylindrical workpiece, without adding any prior processes before rolling. [Solution] A gear machining method comprising a first machining step of performing a rolling process to increase tooth height on the outer surface of a workpiece having a hollow portion using a rolling die, and a second machining step of performing only a rolling process to increase tooth thickness on the workpiece using the same rolling die after the first machining step.

Description

Technical Field

[0001] The present invention relates to a method of performing gear machining on the outer peripheral surface of a workpiece using a flat die for rotary forging.

Background Art

[0002] Conventionally, in rotary forging using a flat die for rotary forging, various flat dies for rotary forging and rotary forging methods using the same have been disclosed (see Patent Documents 1 and 2). However, these flat dies are intended for solid cylindrical workpieces, and in rotary forging of hollow cylindrical workpieces, there is a problem that the hollow hole portion is greatly deformed by a large load during rotary forging.

[0003] Therefore, several rotary forging methods for hollow cylindrical workpieces have been disclosed. For example, Patent Document 3 discloses a rotary forging method using a round die. Further, Patent Document 4 discloses a rotary forging method using a mandrel in the hollow portion for a hollow cylindrical workpiece.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the rolling process using a round die as disclosed in Patent Document 1, the rolling machine used had to be large, leading to increased costs and lead times. Also, in the rolling process with a core as disclosed in Patent Document 2, a process of removing the core was required after the processing was completed, which also increased the processing time. At the same time, there was a possibility that the diameter of the hollow portion would widen, and in order to ensure the diameter of the hollow portion, there were certain constraints on the material and thickness of the workpiece.

[0006] Therefore, the object of the present invention is to provide a rolling method using a flat die for rolling that can suppress deformation of the hollow portion after rolling and obtain good rolling accuracy in rolling a workpiece (especially a hollow cylindrical workpiece) without adding a pre-processing step (so-called preparation step) before rolling, and even with the same processing cycle as a solid cylindrical workpiece. [Means for solving the problem]

[0007] The gear machining method of the present invention is a gear machining method using a flat die for rolling, comprising a first machining step of performing a rolling process to increase the tooth height on the outer surface of a workpiece having a hollow portion, and a second machining step of performing only a rolling process to increase the tooth thickness on the workpiece after the first machining step. [Effects of the Invention]

[0008] The gear machining method of the present invention reduces the load on the finishing teeth of the flat die used for rolling by limiting the directionality of the workpiece having a hollow portion to only the circumferential direction (tooth thickness direction in the gear), thereby significantly suppressing deformation of the hollow hole in the workpiece and simultaneously raising the machining accuracy of the workpiece (gear) to the same level as that of a solid workpiece. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the first machining step of the gear machining method of the present invention. [Figure 2]This is a schematic diagram of the second machining step of the gear machining method of the present invention. [Modes for carrying out the invention]

[0010] An embodiment of the rolling die of the present invention will be described with reference to the drawings. Figure 1 shows a schematic cross-sectional view of the first processing step using the cutting portion of the rolling die, which is one embodiment of the present invention, and Figure 2 shows a schematic cross-sectional view of the second processing step using the finishing portion of the rolling die.

[0011] As shown in Figure 1, in the first processing step, the hollow cylindrical workpiece is subjected to rolling by the cutting portion 10 of the rolling die, resulting in a tooth height increase on the outer surface. At this stage, uniform teeth can be formed on the outer surface while minimizing deformation of the hollow portion.

[0012] Next, in the second processing step shown in Figure 2, the workpiece is subjected to a rolling process that increases the tooth thickness using the finishing part 20 of the rolling die. In this step, directionality is imparted to the already formed teeth only in the circumferential direction, and the tooth thickness is made uniform, thereby further improving the strength and precision of the workpiece. As a result, it becomes possible to manufacture high-precision gears while suppressing deformation of the hollow part of the workpiece. It is effective to set the tooth thickness increase to 0.02 mm or less per half rotation of the workpiece.

[0013] As described above, the thread rolling method of the present invention does not require the use of a mandrel as in the conventional method, thus simplifying the processing steps and reducing costs. Furthermore, it avoids the need for larger thread rolling machines, enabling mass production of high-quality gears while keeping equipment investment low.

[0014] Furthermore, the rolling process method of the present invention has fewer conventional restrictions regarding the material and thickness of the workpiece, and can be applied to a wide range of materials. As a result, it can be used as a highly versatile processing technology that can meet diverse needs. [Examples]

[0015] Next, a coining test (hereinafter referred to as “this test”) was conducted using a plurality of flat dies for coining according to the present invention (hereinafter referred to as “the invention products”), and the test results will be described. The invention products used in this test were flat dies for coining having a biting portion provided with a plurality of biting teeth that first perform coining on the workpiece, and a finishing portion that is continuously formed on the biting portion and provided with a plurality of finishing teeth. The total length of the invention products was 24 inches, and the material was high-speed tool steel.

[0016] The specifications of the workpiece (gear) and the coining conditions in this test were as follows. · Material of the workpiece: Carbon steel (S45C) · Diameter of the workpiece: 20.605 mm · Hardness of the workpiece: 180 - 210 HRC · Module: 1 · Number of teeth: 20 · Pressure angle: 30° · Coining width: 32 mm · Coining speed: 10 m / min · Lubricant type: Oil-based lubricant

[0017] First, a coining test was conducted with the tooth thickness increase amount per half rotation (0.5 rotation) of the workpiece set at three levels of 0.02 mm, 0.035 mm, and 0.050 mm, and the cumulative pitch error of the gear as the workpiece was measured for each condition. As a result, the cumulative pitch error when coining was performed with the tooth thickness increase amount set at 0.02 mm was in the range of 15 - 24 μm.

[0018] In contrast, the cumulative pitch error when coining was performed with the tooth thickness increase amount set at 0.035 mm was in the range of 30 - 38 μm, and the cumulative pitch error when coining was performed with the tooth thickness increase amount set at 0.050 mm was in the range of 21 - 45 μm, and all the cumulative pitch errors exceeded 30 μm.

[0019] Next, with the tooth thickness increase per half-rotation (0.5 rotations) of the workpiece set to 0.02 mm, further rolling tests were conducted in two cases: one where the total tooth thickness increase was 2.3 rotations, and another where it was 1.5 rotations.

[0020] As a result, the cumulative pitch error of the workpiece rolled with a total tooth thickness increase of 2.3 rotations was in the range of 16 to 24 μm. In contrast, the cumulative pitch error of the workpiece rolled with a total tooth thickness increase of 1.5 rotations was in the range of 26 to 45 μm.

[0021] Based on the above test results, it was confirmed that setting the tooth thickness increase per half-rotation in the rolling process to 0.02 mm is optimal for minimizing the cumulative pitch error. Specifically, when the tooth thickness increase was 0.02 mm, the cumulative pitch error remained within a stable range of 16 to 24 μm. On the other hand, when the tooth thickness increase was set to 0.035 mm and 0.050 mm, the cumulative pitch error exceeded 30 μm, clearly indicating a decrease in accuracy.

[0022] Furthermore, regarding the total tooth thickness increase, comparative tests of 2.3 rotations and 1.5 rotations showed that 2.3 rotations allowed for a more precise machining process, with the cumulative pitch error reduced to 16-24 μm. Conversely, 1.5 rotations resulted in a larger cumulative pitch error of 26-45 μm, indicating lower precision.

[0023] Therefore, the results of this test revealed that the optimal processing conditions for achieving high-precision rolling of gears are to set the tooth thickness increase per half-rotation to 0.02 mm and the total tooth thickness increase to 2.3 rotations. By setting these conditions, the quality of the rolling process can be improved, and the performance and reliability of the product can be enhanced. [Explanation of Symbols]

[0024] 10 Meal service section 20 Finished part

Claims

1. A gear machining method using a flat die for rolling, characterized by comprising: a first machining step of performing a rolling process on the outer surface of a workpiece to increase the tooth height; and a second machining step of performing only a rolling process on the workpiece to increase the tooth thickness after the first machining step.

2. The gear machining method according to claim 1, characterized in that, in the second machining step, the dimension of the tooth thickness increase is 0.02 mm or less per half rotation of the workpiece.

3. The gear machining method according to claim 2, characterized in that the workpiece has a hollow portion.

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