JPH0215845A - Forming method for cup-shaped part - Google Patents

Abstract

PURPOSE:To reduce the rate of generation of cracks in forming a cup-shaped part by ironing the outer periphery of a blank having an underfill part before extrusion and extruding it backward while filling the underfill part. CONSTITUTION:In forging the cup-shaped part the blank 1 in the final stage of upsetting is formed in a tapered shape so that its upper part becomes large in diameter. On one hand, an ironing land 4 is provided in the inner hole 3 of an extrusion die and the hole diameter of a small diameter part 4 beneath the ironing land 4 is formed to be nearly equal to the small diameter beneath the blank 1. The outer periphery of tapered blank 1 inserted into the inner hole 3 of the extrusion die is ironed by the pressing of an extrusion punch 6 when it passes through the ironing land 4, the underfill part is filled like the blank 1a and the tapered blank is extruded backward as it is. As a result, the rate of generation of the cracks is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming a cup-shaped part that is forged through an upsetting process to an extrusion process.

(Prior art) Conventionally, when forging a cup-shaped part such as the outer ring of a constant velocity joint, the material is first formed to a predetermined outer diameter by upsetting, and then a rear extrusion process is performed to form the cup-shaped part. It is molded. At this time, in the upsetting process, the material is compressed vertically (left and right) in order to form the material to a predetermined outer diameter.
On the pressurizing surface, the material does not spread uniformly due to friction, resulting in a barrel-like shape with the central side protruding, and the material at the outer edge of the pressurizing surface tends to be lacking in thickness. Further, when this material is forged into a cup shape by backward extrusion, the inner peripheral edge of the pressurizing surface also has a characteristic that there is a slight lack of thickness. On the other hand, the present inventor has disclosed a cold continuous forming method that can omit the intermediate annealing step from upsetting to extrusion, as shown in Patent Application No. 62-324515, but in this case, As shown in Figure 4-A, although the underfill 52 at the inner peripheral edge that occurs at the contact surface with the bunch 51 during extrusion is reduced, the underfill 53 at the outer peripheral end that occurs during upsetting still remains. there were.

(Problem to be Solved by the Invention) When attempting to extrude a lid material with a lack of thickness at the peripheral edge as described above, the peripheral edge with the lack of thickness is insufficiently restrained with the inner hole of the extrusion die. Therefore, not only is sufficient hydrostatic pressure not applied to the peripheral edge, but also a tensile stress that exceeds the elongation of the material acts, causing crack C to occur as shown in Figure 5-B, and this deficiency. There was a tendency that the higher the degree of meat, the higher the crack occurrence rate.

Furthermore, when extrusion processing is performed without the intermediate annealing step as in the continuous cold forming method of the present inventors, the above-mentioned under-walled portions are more likely to occur than in the conventional single-shot forming method. The crack occurrence rate is high, and this crack is caused by SCM.
350 compared to relatively stretchy materials like 420H.
It has also been found that carbon steels such as C548C, which are induction hardened and have a high carbon content, are becoming more and more popular.

On the other hand, if an attempt is made to eliminate this missing material during upsetting, a strong compressive load is required during upsetting, which not only reduces the durability of the mold, but also increases the degree of sealing of the mold as it is upset. The load increases at an accelerating rate as the parts are filled, which can eventually lead to mold failure, so some amount of underfilling is inevitable.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention has decided to squeeze the outer periphery of a material having a lack of thickness before extrusion, fill in the lack of thickness, and then process the material.

(Function) At the time of extrusion, the missing part is filled, so there is no unrestricted part with the inner hole of the extrusion die as in the conventional case, and compressive stress acts effectively.

(Example) An example of the method of the present invention will be described based on the attached drawings. Fig. 1 is a longitudinal sectional view showing the shape change of the material in each processing step, Fig. 2 is a longitudinal sectional view showing the shape of the material after upsetting by the method of the present invention, and Fig. 3 is the inner hole of the extrusion die. FIG. 3 is a vertical cross-sectional view showing a change in shape after insertion into the holder. The present invention is applied to continuous cold forming that does not require an intermediate annealing process, that is, forward extrusion and upsetting of lops and 2ops and backward extrusion and ironing processing of 3ops and 4ops shown in Fig. This is carried out during the main period during the molding process. For this reason, as shown in Figure 2, the shape of the material 1 during the final upsetting process is formed into a tapered shape with a larger diameter at the upper part, that is, the larger diameter at the upper part is slightly smaller than the desired outer diameter. The raw material 1 is tapered from approximately the center so that it becomes larger, and is squeezed from the bottom to the top, so that the squeezed excess meat can move to the two missing parts. In the case of this embodiment, the taper angle is 10 degrees. On the other hand, the rear extrusion die is as shown in Figure 3.
In order to iron the material 1, an ironing land 4 is provided in the inner hole 3 of the extrusion die, and the hole diameter of the small diameter portion 5 below the ironing land 4 is formed between the small diameter of the lower part of the material 1 and the path. There is. Therefore, when the tapered material 1 inserted into the inner hole 3 of this extrusion die passes through the ironing land 4 by the pressure of the extrusion punch 6, the outer periphery of the material 1 is squeezed.
As shown in a, the missing part is filled and then pushed out backwards.

(Effects of the Invention) As described above, since the present invention fills the missing thickness at the peripheral edge of the material and extrudes it, the crack occurrence rate is reduced as shown in the following table. In other words, this table shows the crack occurrence rate depending on the size of the underfill, but in the conventional example shown in Table 1, in the case of a material such as 553C, which has a high carbon content, the underfill during upsetting is small. Despite this, single-shot molding (intermediate annealing performed)
2%, and 5 to 10% in continuous molding, but in the case of the present invention shown in Table 2, there was no cracking rate at all despite the large underfill during upsetting. Ta. Moreover, the machining allowance after molding due to underfilling, so-called t in FIG. 4-A, can also be reduced.

table

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view showing the shape change of the material during the forging process.
Fig. 2 is a longitudinal sectional view showing the shape of the material after upsetting by the method of the present invention, Fig. 3 is a longitudinal sectional view showing the change in shape after inserting it into the inner hole of the extrusion die, and Fig. 4-A is the conventional one. Fig. 4-B is a longitudinal cross-sectional view showing the shape change during continuous cold forming, and Fig. 4-B is a plan view showing the occurrence of cracks in the material. In the drawing, 1.18 is the material, 2 is the missing part, 3 is the inner hole, 4 is the iron-formed land, 5 is the small diameter part, 51 is the punch, 52.5
3 indicates a lack of thickness, C indicates a crack, and t indicates a machining allowance. 1st op 0p Figure 2 Figure 3 (B) C

Claims (2)

[Claims] (1) In a forming method in which a material that has been upset formed with its outer periphery constrained is forged into a cup shape by backward extrusion, the outer periphery of the material is strained before backward extrusion, and the lack of thickness at the peripheral edge of the material caused by upsetting. A method for forming a cup-shaped part, which is characterized by filling the part with excess material and then extruding it. (2) Claim 1 characterized in that the process from upsetting to backward extrusion is continuous cold forming without intermediate annealing, and the processed material is carbon steel with a carbon content of 0.3% or more.
The method for forming cup-shaped parts described in .