JP2523372B2 - Constant velocity joint outer ring manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an outer ring of a constant velocity joint used for driving a wheel of an automobile, etc., in particular, a method for manufacturing a molding die with less wear. Regarding

(Prior Art) The outer ring of a constant velocity joint has a cup shape and has a vertical track groove on the inner periphery thereof, and the track groove is used as a rolling surface of a ball or a roller. The outer ring is molded through a plurality of forging steps, and is hardened to reduce wear of the rolling surface.

Conventionally, as a method of this hardening treatment, a method of hardening by carburizing using a material such as SCR420 has been widely used, but in addition to the cup part, it is necessary to increase the strength of the entire outer ring such as the spindle part and the heat treatment process. Due to the need for in-line production, the method is being replaced by a method of induction hardening using induction hardened steel such as S48C, S55C.

However, since induction hardened steel is a high carbon steel, it is inferior in cold forgeability or formability. Therefore, in order to improve this, for example, in JP-A-63-216952 and 60-230960, cold forgeability is used. A material has been proposed that can achieve both the induction hardening and the induction hardening.

(Problems to be Solved by the Invention) When molding a cup-shaped component such as an outer ring for a constant velocity joint, so-called backward extrusion is performed using a punch having the same shape as the inner surface of the cup. The stress is likely to be concentrated on a part and cracking easily occurs, and the occurrence of the cracking is sensitive to the magnitude of the molding load, and the mold life is greatly influenced by a slight difference in stress value.

For example, P in FIG. 2 is a punch for forming a tripod type outer ring, but stress is concentrated at the corner portion where the cross-sectional shape suddenly changes like the boundary C between the central portion A and the groove forming portion B and cracks occur. It is apt to occur, and therefore a large load cannot be applied to the punch.

On the other hand, for the material to be molded, even in the case of backward extrusion having a large hydrostatic effect at the portion where the change in the cross-sectional shape changes abruptly, tensile stress may act on the sudden change portion and cracks may occur.

In particular, when the rear extrusion molding of the cup is performed by cold or warm forging, or when the upsetting and extrusion are continuously performed by cold or warm forging, punch life and material cracking become more problems, There is a limitation only by specifying the material as in the above-mentioned JP-A-63-216952 and 60-230960, and the mold life and the crack prevention rate of the material are the same as the carburizing material such as the SCR420 used so far. There was a drawback that it could not be obtained.

That is, it is considered that it is not enough to use the conventionally known material as the carbonization becomes higher and the shape becomes more complicated, and further improvement of the material and review of the molding process are considered necessary.

Moreover, the constant velocity joint outer ring integrally includes a shaft portion having a diameter smaller than the diameter of the outer ring, and the step of forming the shaft portion by front extrusion and then upsetting the cup portion is further performed. Therefore, if a material with a large diameter is used to reduce the molding rate so that it is convenient for upsetting and molding of the cup section, the molding rate at the time of molding the shaft section becomes large, and Problems such as insufficient die strength and seizure occur.

Therefore, in the past, the process design was carried out depending on the relatively small elongation limit of the material, so that the degree of freedom in design was poor.

The present invention has been made in view of these points, and particularly for the main purpose of reducing the punch load in the cup forming step, it is possible to provide a constant velocity joint outer ring having a formability superior to that of a carburized material (SCR420) or more. The subject is to obtain a processing means.

(Means for Solving the Problems) Therefore, the present invention, by modifying the components of the conventional induction hardened steel, to satisfy the hardenability, in particular, improve the elongation limit to improve the formability, In addition, by adopting an appropriate molding rate, cold or warm molding is possible. And the means uses induction hardened material,
In a method for manufacturing a constant velocity joint outer ring, which comprises at least a shaft extruding step, an upsetting step of expanding the raw material, and an extruding step of a cup whose thickness is not constant, the components of the induction hardened material are in a weight ratio. , C; 0.45 to 0.58% Si; 0.15% or less, Mn; 0.15 to 0.35% Cr; 0.5% or less, B; 0.0005 to 0.0035% Ti; 0.050% or less Al; 0.015 to 0.050% Mn + Cr; 0.30 to 0.70% As Fe and impurities, and the forming rate εh = in the upsetting process
60 to 80%, molding rate in cup extrusion process is εA = 50 to 70
It is characterized in that molding is performed in the range of%.

Therefore, the above component ratios are based on the following ideas (1) to (4) based on carbon steel.

(1) C, Si, Mn, C to reduce deformation resistance and forming load
The upper limits of r, P, Mn + Cr are specified.

(2) To prevent cracking (deformability), the upper limits of Ti and S are specified.

(3) The lower limits of C, Mn, and Mn + Cr have been specified to ensure induction hardenability.

(4) The upper and lower limits of B are defined to reduce the variation in induction hardenability.

Regarding the above ratio, C is necessary to secure the hardness, but if it is less than 0.45%, the hardenability is poor, and if it exceeds 0.58%, the cold forgeability is impaired. Si acts as a deoxidizing agent at the time of melting, but since it deteriorates the forgeability, considering warm forging, 0.
It was set to 15% or less. However, 0.10% or less is desirable in cold forging.

Mn is effective in improving the hardenability, but if it is less than 0.15%, the hardenability is poor, and if it exceeds 0.35%, the cold forgeability is impaired.

Cr is also effective in improving hardenability, but if it is too much, it impairs cold forgeability. Therefore, it is set to 0.5% or less in consideration of warm forging, but 0.3% or less is preferable in cold forging.

B is also effective for hardenability, but if it is less than 0.0005%, the effect is poor, and if it exceeds 0.0035%, the effect of improving hardenability decreases and the toughness also decreases, so the range was made 0.0005 to 0.0035%. FIG. 4 shows the effect of B on the induction hardenability. In induction hardening, the quenching depth within the above range of B is large. This data was obtained for a specimen with a diameter of 25 mm and a length of 100 mm under the quenching conditions of frequency 100 KHz, voltage 9.5 KV, and moving speed 3 mm / S.

Although Ti is 0.05% or less, preferably 0.01 to 0.05% and Al is 0.015 to 0.05%, these Ti and Al effectively harden the B by ensuring the hardenability, and N in,
It is effective because O is fixed as a compound, but if it is less than the respective lower limit values, the improvement effect is insufficient, while if it is excessive, the toughness of the material deteriorates.

Furthermore, Mn and Cr are defined as Mn + Cr, and the total amount is 0.3
Although it was set to ~ 0.70%, 0.30 to 0.50% is desirable in the case of cold forging.

The above-mentioned components are particularly different from the conventional examples of JP-A-60-230960, 63-216952 and the like in that the conventional Mn is set to 0.15 to 0.35% when the Mn is 0.6% or less to improve the cold forgeability, and B is 0.0005
~ 0.0050% is reduced to 0.0005 to 0.0035 and the upper limit is lowered, and only the range of good hardenability shown in Fig. 4 is adopted.
Similarly, the lower limit of Cr was specified to maintain the hardenability.

The amount of P, S, O, N, etc. is not a requirement of the present invention, but P
Is 0.015% or less, S is 0.020% or less, O is 0.0015% or less,
It is desirable to keep N to 0.010% or less. When the content is more than this range, the cold forgeability deteriorates.

(Working) Since the above-mentioned means was used, it is possible to perform low-load forming with the same number of steps as the carburized material throughout the entire process, despite the fact that it is a high carbon steel. Is low, the punch life is long, and the cross-section forming ratio εA is low. Therefore, the difference in wall thickness is alleviated even at a sudden change in cross-section, and material cracking does not occur in combination with stress reduction.

 The induction hardenability is equivalent to the conventional one.

(Example) Hereinafter, an example of the present invention and a drawing are described. FIG. 1 shows a forming process of an outer ring of a tripod type constant velocity joint, in which a shaft 2b having a diameter d ₁ is extruded from a die 1 by a front extrusion process from a material 1 having a diameter D ₀ to form an unprocessed portion 2a having a height H _0. The work piece 2 having the above is formed, and the unprocessed portion 2a is upset by an upsetting process to have a diameter D ₁ (cross-sectional area A ₁ ) and a height H _1.
Form the workpiece 3 having 3a. In next backward extrusion process by converting the upset 3a extrusion, and the circular hole cylindrical portion 4a having an outer diameter of D ₁ ≒ D ₂ (cross-sectional area A ₂₎ using a punch P and the die of FIG. 2 work 4 with holes 4b of the average inner diameter D ₃ (cross-sectional area a ₃₎ is molded. Finally, ironing is performed using a die similar to the above process, and the cylindrical portion 5a with an outer diameter D ₄ (cross-sectional area
Outer ring 5 with A ₄₎ and the average inner diameter D ₅ ≒ D the shaft portion and the hole 5b of ₃ is molded.

As shown in FIG. 3, the outer ring 5 has a tubular portion 6 and a shaft portion 7, and a central hole 8 and three track grooves 9 are formed on the inner surface of the tubular portion 6.

The molding rate in the above steps (1) to (3) will be as follows if the sectional reduction rate εA or the upsetting rate εh is added to the step number and shown.

First, in the forward extrusion step, ε _A = 1-a ₁ / A 0 = 1-d ₁ ² / D ₀ ² (× 100%) In the upsetting step, ε _h = 1-H ₁ / H ₀ (× 100%) %) In the backward extrusion process, ε _A = A ₃ / A ₁ = D ₃ ² / D ₂ ² ≈D ₃ ² / D ₁ ² (× 100%) In the ironing process Becomes

The ingredients of the materials used in this example are described in the second section below.
Mn: 0.25%, Cr: 0.20%, B: 0.0015% shown in the table, and this material was molded at the molding rate shown in Table 1 in the process of FIG. The conventional example shown in the table is the molding rate when the above-mentioned conventional material is used.

In Table 1, the forming ratio of the conventional example is a range empirically performed by the manufacturing process based on the elongation limit and upsetting limit of the material and the shape of the outer ring of the constant velocity joint.
On the other hand, in the present invention, about 10 in the second step and the fourth step.
%, It is possible to increase the molding rate in the third step by about 10%.
% Is set low.

More specifically, in the first step, ε _A = 60-80%
The reason is that the ratio of the shaft diameter to the cup diameter is almost constant,
If it is less than 60%, the second step will be burdened, and if it exceeds 80%, the burden in the first step will be excessive and seizure, galling, etc. will easily occur on the die. It was a little too high.

If the molding rate in the second step is less than 60%, the load of the first step must be heavy, and if the conventional material is 70% or more, cracks may occur during upsetting. However, when the material of the present invention was used, the upsetting limit was improved by 10% to 80%, and ε _h = 60 to 80%.

If the molding rate exceeds 70% in the third step, the load increases rapidly, which is not preferable, and the ironing allowance in the fourth step cannot be secured. On the contrary, if the molding rate here is small, the molding rate of the second step (upsetting step) must be increased, and the load of the second step becomes excessive. Therefore, the lower limit is conventionally set to less than 60%. Although it was not possible, the lower limit could be set to 50% in the third step because the molding rate in the second step was improved by 10% as described above. If the lower limit is set to less than 50%, the burden on the fourth step will be excessive. Therefore, ε _A = 50 to 70%.

In the fourth step, if the ironing allowance is less than 10%, the copying accuracy is low, and the accuracy of the inner track groove 9 cannot be ensured. If it exceeds 25%, the material may be broken.
In the present invention, improvement of the elongation limit enables up to 30%,
The copying accuracy is improved, and the accuracy of the track groove can be improved.

The steel material proposed in the practice of the present invention is characterized by having a small amount of Mn and a large amount of B as shown in Table 2, and the crack occurrence rate when upsetting is performed on each steel material in the table is shown in FIG. As shown in. In Fig. 5, the upper limit of the cracking upset rate is 68% for the base steel (general induction hardened steel material).
It is 73.5% for 0960 steel and 80% for the proposed steel.

If a material with a large upsetting limit is used,
The upsetting forming rate ε _h of the process can be made large and the forming rate ε _A of the next third step can be lowered, and the load of the punch and the work in the third step can be reduced.

As is clear from Table 3, the proposed steel in column 3 has the same forming ratio of 65% in the second step as compared to the conventional steel in columns 1 and 2.
However, the forming load is low, and even if the forming ratio is 70% as shown in column 4, the forming load does not increase much compared to the conventional steel. Then, in the third step of cup extrusion, at the same molding rate of 60%, a load reduction of 10% as compared to the first column and 3% as compared to the second column was observed. Again 4
As shown in the column, the forming ratio of the second step was 70%, while the forming ratio of the third step was 55%, which resulted in a further load reduction of 10%.

In the 4th column, ε _h = 70% is set, but since the upsetting limit of the proposed steel is ε _h = 80% from FIG. 5, no cracks occur and there is still room.

On the other hand, in the base steel, cracks may occur at ε _h = 68% and a sufficient margin cannot be secured.
The molding rate in the process cannot be lowered. Especially for a workpiece with a large cup depth, the upsetting rate must be increased by the volume increase, but with the base steel, ε _h = 70
%, It is difficult to load the third step, and ε _A
= 70 to 80%, the load increased rapidly and the punch life was reduced.

Thus, by using the steel material of the present proposal, the range of formability is expanded and the degree of freedom in process design is increased. Therefore, it is possible to reduce the molding load in the third step in which the molding load is particularly large and the stress is likely to be concentrated on the local parts of the punch and the work.

Generally, the punch load lowering the molding rate and is known to decrease significantly, molding rate as Table 3, column 4 epsilon _A
That is, when the cross-section reduction rate is reduced, the load is also reduced. FIG. 6 is a graph showing the relationship, and shows a state in which the extrusion force changes when the recess is extruded into the cylindrical material W ₁ to form W ₂ . As shown in column 4 of Table 3, the forming ratio ε _A of the third step is
When it is reduced to 55%, the forming load also decreases in proportion to this.

On the other hand, as shown in FIG. 7, the durability of the mold is greatly increased by a slight decrease in the stress amplitude value. Fig. 7 shows the fatigue characteristic curve of die steel SKH51. The cyclic strength is 3 × 10 ⁴ times when the stress at P ₁ is 780 MPa, but it is 8 × 10 at 725 MPa at P ₂ where the stress decreases by 7%. ⁴ times,
Stress becomes 1.03 × 10 ⁵ times 702MPa at P ₃ points to 10% reduction, significant growth in durability.

Therefore, as shown in columns 3 and 4 of Table 3, when the forming load is reduced in the third step, the punch life is extended.

During the forming step, the steel material is formed while being subjected to an appropriate heat treatment during the processing as shown in FIGS. 8 and 9.
FIG. 8 shows an example of cold forging in which spheroidizing annealing SA is first performed, and low temperature annealing LA is performed after the second step and the third step. Ninth
The figure shows an example of warm forging. In this case, low temperature annealing LA is performed only after the third step.

Then, induction hardening is carried out after forming and cutting, and the hardness and the hardening depth are as shown in FIG. 10, and compared with the base steel of a and the Japanese Patent Laid-Open No. 60-230960 of b, c.
The proposed steel of (1) exhibits substantially the same values in hardness, quenching depth, etc.

Although the tripod type outer ring has been described above, the same can be applied to the Banfield type outer ring 10 shown in FIG.

(Effects of the Invention) The present invention devises a steel material having a good formability and a component ratio suitable for induction hardening as described above, and performs upsetting at a molding rate that is possible for the steel material. It is possible to reduce the molding rate in the next cup extrusion step in which a load is applied, extend the life of the punch which is most easily damaged during the molding step, and prevent the work from cracking.

[Brief description of drawings]

FIG. 1 is a molding process diagram of the present invention, FIG. 2 is a perspective view of a punch, FIGS. 3 (a) and 3 (b) are longitudinal sectional views and lateral views of a product, and FIG. Graph of penetration depth, Fig. 5 is graph of upset plan and crack occurrence, Fig. 6 is graph of extrusion pressure and cross-section reduction rate, Fig. 7 is graph of fatigue property of die steel,
Fig. 8 is a process drawing during cold forging, Fig. 9 is a process drawing during warm forging, and Figs. 10 (a) and (b) are graphs of hardness and depth of hardening of roller groove and shaft, Figure 11 is a vertical cross-sectional view and slope view of another product. …… 1st process (forward extrusion) …… 2nd process (installation) …… 3rd process (rear extrusion) …… 4th process (ironing) P …… Punch 5 …… Outer ring 7 …… Shaft

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-34644 (JP, A) JP 61-282625 (JP, A) JP 1-104440 (JP, A) JP 56- 23337 (JP, A) JP-A-53-81861 (JP, A)

Claims (1)

(57) [Claims] 1. Production of a constant velocity joint outer ring using an induction hardened material and having at least a shaft extruding step, an upsetting step for expanding the diameter of the material, and an extruding step for a cup whose thickness is not constant. In the method, the components of the induction hardened material are in a weight ratio, C; 0.45 to 0.58% Si; 0.15% or less, Mn; 0.15 to 0.35% Cr; 0.5% or less, B; 0.0005 to 0.0035% Ti; 0.050% or less Al; 0.015 to 0.050% Mn + Cr; 0.30 to 0.70% The balance is Fe and impurities, and the forming rate in the upsetting process is εh = 60.
~ 80%, molding rate in cup extrusion process is εA = 50-70%
A method for manufacturing a constant velocity joint outer ring, characterized in that the molding process is performed within the range of.