KR19980069741A - High strength spline structure and manufacturing method - Google Patents

Abstract

The spline structure of the present invention has a plurality of teeth for transmitting a rotational force, each of which is molded so that at least the portion except the tip has a continuous curve on the arc. In the manufacturing method, the surface hardening treatment is performed on this part of the spline structure from the tip to at least the root. Surface hardening is performed by surface hardening such as high frequency quenching or flame hardening, or by diffusion treatment such as nitriding. As a result, it is possible to prevent the stress from concentrating on the roots and to prevent cracking during the surface hardening treatment. In addition, when the strength of this part is increased by the surface hardening treatment, the fatigue strength of the spline structure is remarkably improved.

Description

High strength spline structure and manufacturing method

The present invention relates to a high-strength spline structure for transmitting rotational force and a method for manufacturing the same, and more particularly, to a spline structure with high fatigue strength.

Conventionally, when a rotating element having a hole corresponding to a rotating shaft is fitted to the rotating shaft to transmit the rotating force, for example, when forming a screw of a plastic molding machine, a groove provided on the rotating shaft and a screw element fitted to the rotating shaft are installed. A key is sandwiched between the provided grooves and used.

However, this key method has a problem in that a large rotational force cannot be transmitted because stress concentration occurs in the groove part of the key. To solve this problem, a spline having a plurality of teeth provided around the axis and a hole matching the spline shape are provided. It is contemplated to use a combination of bosses having.

The spline structure of a straight edge having a polygonal tooth is disadvantageous in terms of strength because a gap groove must be formed in both corners of each root.

On the other hand, in the involute spline structure, it is not necessary to form the above-described gap grooves and the width of the root can be increased, so that the average strength can be improved, but there is a problem that stress concentration in the corner of the root cannot be eliminated.

In order to solve this problem of stress concentration, US patent application Ser. No. 08 / 653,835 proposes an arcuate spline structure having a plurality of arcuate teeth.

It is an object of the present invention to provide an arc-shaped high strength spline structure which does not generate stress concentration and which is excellent in strength, in particular, fatigue strength against repeated loads in the rotational direction which may cause problems.

The object of the present invention described above is provided with a plurality of teeth formed around the axis to transmit rotational force, which is formed along a contour consisting of a continuous curve of an arc at least a portion other than the tip, and at least a portion extending from the tip to the root It can be achieved by the spline structure characterized in that the surface hardening treatment.

According to such a spline structure, stress concentration can be avoided at the corners of the roots and cracks can be prevented from occurring during the surface hardening treatment. In addition, as the strength of this part increases by the surface hardening treatment, the fatigue strength of the spline structure is greatly improved.

On the other hand, according to the present invention, in the manufacturing method of the spline structure having a plurality of teeth formed around the shaft to transmit the rotational force, forming the tooth so that at least the portion except the tip has a contour consisting of a continuous arc-shaped curve, from the tip There is provided a method for producing a spline structure, characterized in that surface hardening is carried out at least at the root portion.

In the present invention, the forming step is preferably a step of rolling the material so that it has a metal structure flowing along its contour. In the cold reduction process, the material is cold pressed to reduce its diameter. The precursor material may be subjected to the cold reduction step in advance.

In this case, the machining rate and the compressive residual stress of the material are increased by the cold reduction process. When the material is rolled into an arc-shaped spline structure, the metal structure changes to form a long fiber flow along the contour of the spline structure. Therefore, it can withstand the repeated load applied to the tip, and the fatigue strength is improved by increasing the residual stress and the surface hardness.

In the method of the present invention, the surface hardening treatment is preferably surface quenching such as high frequency quenching, flame quenching and the like. Alternatively, the surface hardening treatment may be a diffusion treatment such as nitriding treatment or the like.

The surface hardening treatment is more preferably a combination of surface quenching such as high frequency quenching and flame quenching and shot peening performed after the surface quenching. In this case, the fatigue strength is further improved as compared with only the surface quenching treatment described above.

Alternatively, the surface hardening treatment may be a combination of diffusion treatment such as nitriding treatment and shot peening performed after the diffusion treatment. In this case, the fatigue strength is further improved as compared with only the above-described diffusion treatment.

The above object and features of the present invention will be clearly understood from the following description and claims taken in conjunction with the accompanying drawings.

1 is a schematic plan view of an arc-shaped spline shaft constituting a high strength spline structure according to the present invention.

Figure 2 is a schematic plan view showing an involute spline shaft as compared to the arcuate spline shaft of the present invention.

3 is a comparative test showing the fatigue strength of an arc-shaped spline shaft subjected to high frequency quenching treatment and another arc-shaped spline shaft and involute spline shaft not subjected to high frequency quenching treatment.

4 is a comparative test showing fatigue strength between an arc-shaped spline shaft subjected to nitriding treatment and another arc-shaped spline shaft not subjected to nitriding treatment.

Fig. 5 is a comparative test showing the fatigue strength of arc-shaped spline shafts which have undergone shot peening after high-frequency quenching and arc-shaped spline shafts which do not do short peening.

Fig. 6 is a comparative test showing the fatigue strength of the arc-shaped spline shaft subjected to short peening after soft nitriding and the arc-shaped spline shaft not subjected to short peening.

7 is a view showing a cold reduction process for round steel.

8 shows a subsequent rolling process for forming an arcuate spline shaft.

FIG. 9 is a test result diagram showing changes in fatigue strength and residual stress of arc-shaped spline shafts and involute spline shafts manufactured according to a series of processes including high frequency quenching.

10 is a view showing a part of the cross-sectional structure of the rolled spline shaft.

11 is a view showing a part of the cross-sectional structure of the hobbing machined spline shaft.

12 is a test result diagram showing changes in fatigue strength and residual stress of arc-shaped spline shafts and involute spline shafts manufactured through a series of processes including gas soft nitriding.

♣ Explanation of symbols for the main parts of the drawing

1: arc spline shaft 3: tooth

3A: End 3B: Root

5: involute spline shaft 7: tooth

7A: End 7B: Root

An embodiment of the present invention will be described with reference to the drawings.

1 shows an arced spline shaft 1 as an example of a spline structure. This arc-shaped spline shaft 1 has a plurality of teeth 3 formed around the axis S, each tooth 3 having a tooth root formed in a continuous curve of tooth tips 3A and an approximately arc shape. (3B). In other words, a series of semicircles are reversed and connected in sequence to form a wavy curve. You can use a semi-ellipse instead of a semi-circle. This end 3A can be formed to extend along an arc centered on the centerline of the axis S. As shown in FIG.

2 shows the involute spline shaft 5 as a comparison object. In this involute spline shaft 5, the tooth 7 is formed to draw an involute curve about the centerline of the axis S. As shown in FIG. That is, the contour of the tooth (7) is determined using the trajectory (involute curve) drawn by the end of the thread when the thread is wound around the circle and pulled at the end thereof.

Example 1

Referring to Fig. 3, the surface-curing treatment is not to be performed as the arc-shaped spline shaft 1 shown in Fig. 1, in the portion extending from the end 3A to the tooth root 3B of the arc-shaped spline shaft 1. Test samples of the spline shaft were made of each material of S55C, SCM440, and SNCM630 for the three cases of high frequency quenching and involute spline shaft 5 shown in FIG. The torsion fatigue strength (million break strength) was measured and compared for these samples. Here, in the involute spline shaft 5, cracking occurs in the corner portion of the tooth root 7B when the quenching is performed, so that the involute spline shaft subjected to the high frequency quenching treatment is not used as a comparison target.

As shown in FIG. 3, it can be seen that the torsional fatigue strength of the arc-shaped spline shaft 1 subjected to the high-frequency quenching treatment for all the materials of S55C, SCM440, and SNCM630 is the highest. In addition, hardening crack did not generate | occur | produce also about SCM440 and SNCM630 which are conventionally known to be easy to produce a hardening crack.

From the above results, it can be seen that the fatigue strength is increased by performing the high frequency quenching treatment on any material. In the arc-shaped spline shaft 1, no cracking occurs when the high frequency quenching treatment is performed. It can be seen that it is a suitable shape. Also, SCM440 and SNCM630, which are known to be easy to cause quenching cracks, can also improve the properties of alloy steel without causing quenching cracks.

In this way, when the fatigue strength is increased, even if excessive torque acts on the arcuate spline shaft 1, plastic deformation is suppressed to a minimum, so that an element, for example, a screw, inserted in the arcuate spline shaft 1 can be easily replaced. I can do it.

Example 2

Referring to FIG. 4, nitriding treatment (550 ^° C., 60 hours) is a kind of surface diffusion treatment for the arc-shaped spline shaft 1 of FIG. 1 and the involute spline shaft 5 of FIG. 2 made of a material SACM645. Fatigue strength (million breaking strength) was measured and compared.

As shown in FIG. 4, it can be seen that the fatigue strength of the nitrided arc-shaped spline shaft 1 is about 3.5% larger than the fatigue strength of the nitrided involute spline shaft 5.

As described above, the surface hardening treatment such as high-frequency quenching or nitriding treatment was performed on the arc-shaped spline shaft 1 to significantly improve the fatigue strength against rotational load.

Moreover, it turned out that the arc-shaped spline shaft 1 is a shape suitable for surface hardening processes, such as a high frequency quenching.

In the above embodiment, the spline shaft on the axial side has been described, but the present invention can be applied to a spline bore in which the spline shaft is fitted.

Example 3

In this example, a screw shaft (32 mm in diameter and 4 m in total length) for a twin screw extruder (screw diameter 58 mm) is used for a commercially available corrosion-resistant material (e.g., a SUS420J2 round steel in which the hardness of HRC30 is adjusted). An arc-shaped spline shaft 1 as shown in 1 was produced. The cross-sectional shape of this arc-shaped spline shaft 1 is similar to that used in the first and second embodiments.

In this way, and the portion leading to tooth root (3B) in the tooth (3A) of a machining arcuate spline shaft (1) by induction hardening hardness HS65, followed by tempering at 400-450 ^O C a hardness HRC48.

Then, the spline shaft 1 was corrected so that the bending strain might be within 0.2 mm with respect to the full length, and shot peening was performed from the tooth root 3B to the tooth tip 3A using a steel ball.

Fatigue strengths were measured for high-frequency quenching, tempering and short peening at 400-450 ^° C. and for other arc-shaped spline shafts without short peening. As in Example 1, the involute spline shaft 5 is excluded from the comparison.

In addition to the spline shaft made of SUS420J2, Fig. 5 shows fatigue strength measurements for the spline shaft of SUS431 subjected to high frequency quenching and tempering at the hardness of HRC43 and the spline shaft of SUS440M subjected to high frequency quenching and tempering at the hardness of HRC49. As is apparent from Fig. 5, for any material, the fatigue strength of the spline shaft subjected to shot peening was increased by about 9% compared to the spline shaft not subjected to shot peening.

As described above, when the short peening is performed after the quenching on the arc-shaped spline shaft 1, the fatigue strength against rotational load can be significantly improved as compared with the case where the short peening is not performed.

In addition, by using 13-C _r martensitic stainless steel such as SUS420J2, it has high corrosion resistance and high temperature strength, and hardening structure does not change even when used at high temperature up to 400 ^o C, and compressive residual stress is added by shot peening. Thus, the fatigue strength can be prevented from being lowered, and a high temperature, high corrosion resistance high strength spline shaft having a 9-12% improvement in fatigue strength can be obtained.

Example 4

A gas soft nitriding treatment (oil quenching after holding for 5 hours at 550-600 ^° C.) was performed on the entire outer circumferential surface of the arc-shaped spline shaft 1 having the same material and shape as in Example 3 above, The spline shaft was corrected to be within 0.2 mm, and shot peening was performed from the roots 3B and 7B to the ends 3A and 7A using steel balls.

For the arc-shaped spline shaft 1, fatigue strength was compared between the case of performing the soft nitriding treatment and the case of short peening and no short peening.

Referring to FIG. 6, it can be seen that the fatigue strength of the arc-shaped spline shaft 1 which has undergone shot peening is improved by about 18% compared with the case where it is not done.

As described above, by performing the short peening after the soft nitriding treatment in the arc-shaped spline shaft 1, the fatigue strength against rotational load can be significantly improved as compared with the case without the short peening.

In addition, since the weak compound layer on the surface can be removed by shot peening, it is possible to stabilize the strength by preventing cracks in the weak nitride layer during the correction of bending deformation or the action of torque.

Example 5

A commercially available round steel shaft of SUS420J2 is formed with a hardness of HRC23 to form a screw shaft (32 mm in diameter and a total length of 4 m) for a twin screw extruder (screw diameter 58 mm), and as shown in FIG. To reduce the diameter. After completion of the cold reduction step, the shaft was rolled to obtain an arc-shaped spline shaft as shown in FIG.

After rolling, the high frequency quenching on the tooth of the spline shaft the entire circumference up to a hardness of HS65 Rie tooth root, and the mixture was then tempered at a temperature of 400-450 C ^O. Next, using the steel ball of the particle size # 150-300 (diameter about 100-50 micrometers), it was short peening to the tooth root to the pressure of 4-6 kgf / cm <^2> .

9 shows the residual stress and fatigue strength of the arcuate spline shaft as well as the involute spline shaft manufactured by the same manufacturing process. 10 shows the cross-sectional structure of the rolled spline shaft, and FIG. 11 shows the cross-sectional structure of the hobbing machined spline shaft, where the cross-sectional structure of the rolled spline shaft is shown in FIG. You can see the appearance. Metallic structures characteristic of such fiber flows are known to withstand repeated torsional loads and rotational loads well.

In this way, when 13-C _r martensitic stainless steel such as SUS420J2 is used, the fatigue strength is sufficiently maintained at high temperature (below 400-450 ^° C) by tempering at a temperature of 400-450 ^° C after temper and high-frequency quenching. A spline shaft of high corrosion resistance and excellent hardness can be obtained.

Example 6

A commercially available round shaft of SUS420J2 is formed with a hardness of HRC30 to form a screw shaft (32 mm in diameter and a total length of 4 m) for a twin-screw extruder (screw diameter 58 mm) and cold reduction is performed to reduce the diameter as shown in FIG. It was. After the end of the cold reduction process, the shaft was rolled to obtain an arc-shaped spline shaft as shown in FIG.

After rolling, gas soft nitriding treatment (550-600 ^° C., 5 hours, oil quenching) was performed on the entire outer circumferential surface of the spline shaft, and then the bending deformation of the spline shaft was corrected.

Next, shot peening was performed from the root to the tip using a steel ball with a particle size # 150-300 (diameter about 100-50 μm).

FIG. 12 shows the variation of the residual stress and fatigue strength of the arcuate spline shaft as well as the involute spline shaft manufactured by the same process.

As can be seen from this figure, it is possible to sufficiently improve the fatigue strength of the spline shaft by using 13 _C-r-based martensitic stainless steel SUS420J2. In addition, by performing short peening after gas soft nitriding, the compressive residual stress of the spline shaft can be increased to maintain fatigue strength.

In any of the above-described embodiments 5 and 6, since the machining portion of the round shaft is restricted by the surrounding structure during shaping the spline by the cold reduction process and the rolling process, a high processing rate can be realized and the generation of chips As a result, the yield can be increased. Furthermore, by burnishing the spline shaft, the machining surface of the spline shaft can be smoothed and the fatigue strength can be improved.

Since the above description illustrates a preferred embodiment of the high-strength spline structure according to the present invention, those skilled in the art that the present invention can be modified in various forms without departing from the spirit and scope of the invention. Anyone can understand.

Claims (8)

It has a plurality of teeth formed around the axis to transmit the rotational force, which is formed along the contour consisting of a continuous curve of arc-shaped at least a portion except the tip, and surface hardening treatment at the portion from the tip to at least the root Splined structure implemented. A method of manufacturing a spline structure that transmits a rotational force by means of a plurality of teeth formed around an axis, comprising the steps of: shaping the tooth along a contour consisting of an arc-shaped continuous curve at least a portion except the tip, and from the tip to the root A method of manufacturing a spline structure, comprising performing a surface hardening treatment on a portion of the portion. The method of manufacturing a spline structure according to claim 2, wherein the forming step is a rolling step of rolling a material to have a metal structure flowing along the contour. The method for producing a spline structure according to claim 2, wherein said surface hardening treatment is surface quenching. The method for producing a spline structure according to claim 2, wherein said surface hardening treatment is a diffusion treatment. The method for producing a spline structure according to claim 2, wherein the surface hardening treatment is a surface quenching and shot peening performed sequentially. The method for producing a spline structure according to claim 2, wherein the surface hardening treatment is a diffusion treatment and shot peening performed sequentially. The method of manufacturing a spline structure according to claim 2, wherein the precursor material undergoes a cold reduction process for cold reducing the diameter of the material.