Manufacturing method for hollow shaft component

Abstract

To provide a manufacturing method for a hollow shaft component that can reduce manufacturing costs.SOLUTION: A manufacturing method for a hollow shaft component according to the present invention comprises: a heading step of forming a large-diameter hole part 3 from one end side of a raw material 1a; and a heading step of forming a small-diameter hole part 4' positioned concentrically with the large-diameter hole part 3 and separated by a bulkhead part 7 with a predetermined thickness from the large-diameter hole part 3, from the other end side of the raw material 1a, which cuts the bulkhead part 7 in a cutting step to obtain a hollow shaft component. This manufacturing method enables a comparatively inexpensive heading device having a comparatively low capability to perform the heading step. Further, a flank part 5 extended coaxially with the large-diameter hole part 3 and having the same diameter as the diameter of the small-diameter hole part is formed on a bottom part of the large-diameter hole part 3 during heading, which can suppress occurrence of burrs in a subsequent cutting step.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a hollow shaft component having through holes with different diameters in the axial direction.

Background Art

[0002] Conventionally, as a method for manufacturing a hollow shaft component, a method by cold extrusion as shown in Patent Document 1 is known. According to this Patent Document 1, while forming a cylindrical portion by pushing a drilling punch from one end side of a raw material having a flange portion formed at one end in advance, it is clear that the shaft portion pushed forward is formed into a hollow shaft portion by guiding it along a backup punch. Further, Patent Document 2 discloses a method for manufacturing a hollow shaft component in which the outer diameter and the inner diameter are each configured to have different diameters at both ends, and the hollow hole is a through hole. According to this Patent Document 2, it is clear that a hollow hole is formed at one end of the material by preliminary forming by backward extrusion, and then the hollow hole is punched by core deburring to form a through hole having a diameter smaller than that of the hollow hole.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When further processing the hole of the hollow shaft component obtained in Patent Document 1 to form a through hole, it is necessary to punch out the partition wall portion as in the core flash removal process as in Patent Document 2. However, there were problems such as the need for an expensive forging device with considerable capabilities for forming a through hole by forging. Further, when performing a process of penetrating holes with different diameters as in Patent Document 1, burrs are likely to be formed at the penetrated portion, that is, at the stepped portion that is the boundary between the large-diameter hole and the small-diameter hole, and a separate process for removing this is required. In this case, since burrs are generated at the stepped portion in the middle of the through hole, it also takes time to remove them. Furthermore, among metal hollow shaft components, there are many components that cannot be hardened by heat treatment despite the need for a certain degree of hardness. In such cases, a material with high hardness in the as-material state is selected. However, when attempting to obtain a long hollow shaft component having a through hole and made of a material with high hardness by forging, a large forging device with considerable capabilities is also required in this case, and there were problems such as the manufacturing cost of the hollow shaft component becoming high.

Means for Solving the Problems

[0005] The present invention was created in view of the above problems, and an object thereof is to provide a method for manufacturing a hollow shaft component that suppresses manufacturing costs.

[0006] To achieve the above object, the present invention includes a forging step of forming a large-diameter hole portion from one end side of a material, a forging step of forming a small-diameter hole portion that is located coaxially with the large-diameter hole portion and separated from the large-diameter hole portion by a partition wall portion having a predetermined thickness from the other end side of the material, and a cutting step of cutting the partition wall portion from the small-diameter hole portion side to penetrate the small-diameter hole portion into the large-diameter hole portion. Thereby, it becomes possible to perform the forging step by a relatively inexpensive forging device with low capabilities.

[0007] The present invention also relates to a method for manufacturing a hollow shaft component, comprising a forging step of forming a large-diameter hole portion from one end side of a material, and a forging step of forming a small-diameter hole portion that is located coaxially with the large-diameter hole portion from the other end side of the material and is separated from the large-diameter hole portion by a partition wall portion having a predetermined thickness. The method is characterized by having a forging step of forming a relief portion that is continuous coaxially with the large-diameter hole portion and has the same diameter as the small-diameter hole portion at the bottom of the large-diameter hole portion. By forming a relief portion having the same diameter as the small-diameter hole portion at the bottom of the large-diameter hole portion in this way, when performing a cutting process of penetrating the small-diameter hole portion through to the large-diameter hole portion from the small-diameter hole portion side in a subsequent cutting process, burrs are less likely to occur at the penetrated portion.

[0008] Preferably, the material is a cold-forging carbon steel that becomes a desired hardness through work hardening. By selecting and using a cold-forging carbon steel that becomes a desired hardness through work hardening as the material in this way, the workability such as forging and cutting is high, and it is possible to obtain a hollow shaft component having a desired hardness only by the forging pressure and cutting pressure without going through heat treatment.

Effects of the Invention

[0009] According to the present invention, in order to press-form a relief portion having the same diameter as the small-diameter hole portion at the bottom of the large-diameter hole portion, when performing a process of penetrating the small-diameter hole portion from the small-diameter hole portion side into the large-diameter hole portion in a subsequent process, burrs are less likely to occur in the penetrating portion. Therefore, there is an advantage that the process of removing burrs becomes unnecessary and the number of processing steps can be reduced. Further, by using a cold-heading carbon steel that becomes the desired hardness due to work hardening as a material, both cold heading and cutting are easy, and it is possible to obtain a hollow shaft component having the desired hardness only by the processing pressure of cold heading or cutting without heat treatment. In particular, in the cold-heading process, a process of not penetrating the large-diameter hole portion and the small-diameter hole portion formed from both ends respectively is performed, and then these are penetrated by cutting. Therefore, work hardening of the portion to be cut off by cutting can be suppressed as much as possible, and the high workability of the cold-heading carbon steel can be utilized to perform up to the cutting process. Moreover, since a through hole is not formed in the cold-heading process, there is also an advantage that processing can be performed even by a relatively low-capability cold-heading device. Thus, according to the manufacturing method of the hollow shaft component of the present invention, it is possible to measure reduction of the number of processing steps, improvement of workability, suppression of processing equipment costs, etc., and it is possible to reduce the manufacturing cost of the hollow shaft component.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of a method for manufacturing a hollow shaft component according to the present invention will be described. In FIG. 1, reference numeral 1 denotes a hollow shaft component made of carbon steel SWCH6A for cold forging, and is formed in a cylindrical shape by a through hole 2 penetrating the axis. The through hole 2 is configured such that holes with different diameters (a large-diameter hole portion 3 and a small-diameter hole portion 4) communicate with each other inside the shaft component 1 at both ends. That is, the through hole 2 is configured to have steps inside the hollow shaft component 1. Further, the outer diameter of this hollow shaft component 1 is configured such that the diameter for the length of about the small-diameter hole portion 4 of the through hole 2 is larger than the others.

[0012] This hollow shaft component 1 is formed by a forging process and a cutting process. The forging process is composed of forward extrusion, upsetting, and backward extrusion. Specifically, in the forward extrusion, the material 1a shown in FIG. 2(a) is pressed by a punch (not shown) and extruded forward to form a large-diameter hole portion 3 on one end side of the material 1a as shown in FIG. 2(b). Thereby, this portion is formed into a thin cylindrical shape. The tip of the punch used for this forward extrusion is configured to have the same diameter as the diameter of the small-diameter hole portion 4 and to project coaxially and slightly from another main body portion having the same diameter as the large-diameter hole portion 3. Therefore, a relief portion 5 that is continuous coaxially with the large-diameter hole portion 3 and has the same diameter as the small-diameter hole portion 4 is formed at the bottom of the large-diameter hole portion 3.

[0013] Following the forward extrusion, the other end of the material 1a is upset by the upsetting process, and a large-diameter shaft portion 6 is formed here as shown in FIG. 2(c). Next, the large-diameter shaft portion 6 of the material 1a is pressed by a punch (not shown) and extruded backward by the backward extrusion process to form a small-diameter hole portion 4' on the other end side of the material 1a as shown in FIG. 2(d). At this time, the small-diameter hole portion 4' is formed to have a diameter slightly smaller than the diameter of the final small-diameter hole portion 4. By performing the backward extrusion process in this way, the large-diameter shaft portion 6 is formed into a cylindrical shape as the small-diameter hole portion 4' is formed and extends to a predetermined length.

[0014] By the above forging process, a bottomed large-diameter hole portion 3 and a small-diameter hole portion 4' are formed at both ends of the material 1a respectively, but these are not made to penetrate in the forging process. The forging process is completed while leaving the thickness that will become the partition portion 7 between the two. In forging, the capabilities required of the forging device are very different between forming a through hole 2 and forming a bottomed hole. If it is only forming a bottomed hole as in this example, forging can be performed even with a relatively low-capability, small and inexpensive forging device.

[0015] In the cutting process following the aforementioned forging process, the non-penetrating large-diameter hole portion 3 and small-diameter hole portion 4' are made to penetrate. In this cutting process, cutting is performed from the small-diameter hole portion 4' side. While finishing the small-diameter hole portion 4' to a predetermined diameter, it is made to penetrate the large-diameter hole portion 3 to form the through hole 2. The forming dimensions of the small-diameter hole portion 4' in the forging process are determined in advance so that it becomes a predetermined diameter to the extent that its wall surface is shaved in this cutting process. Note that the shaded portion in Fig. 3 is the portion removed by cutting.

[0016] In the cutting process, if the dimensional accuracy of the small-diameter hole portion 4 to be finished does not have to be high, it can be dealt with by drilling (hole-making) with a drill. If high dimensional accuracy is required, it can be dealt with by reaming after drilling or boring with a lathe. In any case, the partition portion 7 separating the large-diameter hole portion 3 and the small-diameter hole portion 4' is removed by cutting. At this time, since a relief portion 5 having the same diameter as the finished diameter of the small-diameter hole portion 4 is formed at the bottom of the large-diameter hole portion 3, the generation of burrs can be suppressed when penetrating by cutting from the small-diameter hole portion 4' side. Even if burrs are generated, since these are not generated at the stepped portion that becomes the boundary with the large-diameter hole portion 3 but in the middle of the small-diameter hole portion 4, it is possible to easily remove the burrs by shaving with a drill or a reamer.

[0017] Further, as described above, since the large-diameter hole portion 3 is forged by forward extrusion and the small-diameter hole portion 4' is forged by backward extrusion, the processing pressure applied to the partition portion 7 in this forging process can be minimized, and work hardening of this portion can be suppressed. Therefore, the machinability in subsequent cutting can be improved, and the life of the tool used for cutting can also be kept long. In particular, by using cold-heading carbon steel as the material, both forging and cutting become easier.

[0018] Also, by going through the forging process and the cutting process, processing pressure is applied to at least the entire surface of the hollow shaft component 1, and the entire surface can be work hardened to increase the hardness. In the case of SWCH6A used in this example, the hardness of the raw material state is about HV100 - 110, but it can be increased to about HV170 - 230. By using cold-heading carbon steel that becomes the desired hardness by work hardening in this way, it is possible to easily perform forging and cutting and obtain the hollow shaft component 1 having the desired hardness without going through heat treatment.

[0019] Note that the manufacturing method of the hollow shaft component according to the present invention is not limited to the above method, and various modifications are possible without departing from the gist thereof. For example, the relief portion 5 does not necessarily have to be formed during forward extrusion, and it may be formed during subsequent drilling or backward extrusion. Also, although the small-diameter hole portion 4' is forged and formed to have a diameter slightly smaller than that of the small-diameter hole portion 4, it may be formed to have the same diameter as the small-diameter hole portion 4 during forging.

Explanation of Reference Numerals

[0020] 1 Hollow shaft component 1a Material 2 Through hole 3 Large-diameter hole portion 4 Small-diameter hole portion 5 Relief portion 6 Large-diameter shaft portion 7 Partition portion

Claims

1. A forging process of forming a large-diameter hole portion from one end side of a material, a forging process of forming a small-diameter hole portion that is coaxially positioned with the large-diameter hole portion from the other end side of the material and is separated from the large-diameter hole portion by a partition wall portion having a predetermined thickness, and a cutting process of cutting the partition wall portion from the small-diameter hole portion side to penetrate the small-diameter hole portion into the large-diameter hole portion, characterized in that it comprises a manufacturing method of a hollow shaft component.

2. A manufacturing method of a hollow shaft component, comprising a forging process of forming a large-diameter hole portion from one end side of a material, and a forging process of forming a small-diameter hole portion that is coaxially positioned with the large-diameter hole portion from the other end side of the material and is separated from the large-diameter hole portion by a partition wall portion having a predetermined thickness, characterized in that it has a forging process of forming a relief portion that is continuous coaxially with the large-diameter hole portion and has the same diameter as the small-diameter hole portion at the bottom of the large-diameter hole portion.

3. The manufacturing method of the hollow shaft component according to claim 1 or claim 2, characterized in that the material is a cold forging carbon steel that becomes a desired hardness by work hardening.

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