JPH0349652B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a stepped shaft from steel by forward extrusion. There are several methods to manufacture shafts with large and small diameter parts used in automobile parts, etc., such as cutting, hot forging, cold forging, and cold extrusion, but cold is advantageous in terms of cost and productivity. In many cases, interextrusion is used. Since cold extrusion applies severe processing to the steel material without heating it, breakage of the steel material may occur, which would not be a problem with hot working. The mode of fracture is classified into two types: surface cracking and internal cracking, but the latter type is easily overlooked because it is not comparable to visual inspection during post-processing product inspection, and mechanical parts of this type are If the product is used with a built-in defect, it may cause a serious accident.
In the case of relatively large parts, it is also possible to conduct a complete online inspection using non-destructive testing.
Some factories are implementing this. However, it is difficult to inspect small parts, and in the case of small-volume production, it is often economically impractical to have such non-destructive inspection equipment. In the first place, this type of defect occurs due to severe cold processing of steel materials, so one way to prevent them is to improve the properties of steel materials, and we have already aimed at this. Steel materials have also been recently developed. However, as a steel material processor, whenever such steel materials are used, a demand inevitably arises for the steel materials to be subjected to even more severe processing. Figures 1A, B, C, D, E, and D' are views showing one aspect of the manufacturing process of the stepped shaft, and A→B→C
If the molding is done in the order of →D→E, the shaft diameter will be machined in order from the thickest to the thinnest as d ₀ →d ₁ →d ₂ →d ₃ →d ₄ , which is the conventional processing method. be. However, when such processing is performed, defects such as internal cracks often occur, which limits processing. Therefore,
It is desired to develop a cold extrusion method that does not cause such problems. The present invention has been developed in view of the current situation, and enables a much higher degree of processing than conventional methods. During manufacturing, after extruding the third thinnest shaft, the thinnest shaft is extruded from the third thinnest shaft, and then the second thinnest shaft is extruded from the third thinnest shaft. The cold extrusion method is characterized by: The present invention will be explained in detail below. The method of the present invention is shown in Fig. 1 A, B, C, D, E,
In the step D', after extruding the shaft diameter d ₂ at C, D
Instead, move to D' and first extrude the smallest shaft diameter d ₄ , then return to E and extrude the second smallest shaft diameter d ₃ . The example in Figure 1 is an example of 4-stage extrusion, but in 5-stage extrusion, 6-stage extrusion, etc., the third thinnest shaft is extruded, and then the thinnest part is extruded from the third thinnest shaft. The key point is then to extrude the third thinnest shank from the third thinnest shank. These improvements in forming methods will significantly increase the limits of what can be processed without internal cracking. This is because the occurrence of internal cracks has a strong correlation with the number of extrusions through a die, and the most effective way to prevent cracks is to reduce the number of extrusions. That is, if the steps A→B→C→D→E in FIG. 1 are used, the smallest diameter d ₄ portion will be formed by extruding the material d ₀ four times. In this case, depending on the steel material, there is a risk that internal cracks will occur at the portion with a diameter of _d4 . However, if the same steel material is subjected to the process of the present invention from A→B→C→D'→E, no internal cracks will occur in the portion having a diameter of _d4 in most cases. This is because under this condition, the portion d ₄ is extruded from the material d ₀ only three times. Furthermore, for steel materials with better workability that develop internal cracks at the 5th stage,
If extrusion is completed at each step, no internal cracks will occur.
The same holds true even if the number of stages increases. Note that the present invention is based on the prerequisite that the stepped shaft is manufactured by forward extrusion three or more times, because steel materials subjected to such processing cannot be formed by forward extrusion two or less times. This is because the risk of internal cracks occurring is extremely low. In this way, the method of the present invention increases the machining limit of steel materials, so when it is necessary to fabricate a part with a large dimensional difference between thick and thin parts in one piece, conventionally the thick part is upset. It is now possible to manufacture thin parts by continuous extrusion, which previously had to be done by cutting, resulting in a significant improvement in productivity. Furthermore, the process change required is simply a change in the order of the dice, and there is no cost increase at all. Next, the effects of the present invention will be explained in more detail with reference to Examples. Extrusion was performed 3 to 5 times using normalized carbon steel S ₁₅ C, S ₄₅ C, and S ₅₅ C for mechanical structures. The die used was made of carbide and had a daos half angle of 17°. In either example, the conventional method is to start with the thickest diameter and then extrude the thinnest part. However, in the present invention, the diameter is first extruded starting from the thickest part, and then the second thinnest part is extruded. It is extruded, and the thinnest part is extruded one step before that. Due to this difference in process, internal cracks occurred in the thinnest part in the final process in the conventional method, but in the method of the present invention, all were sound. In these examples, as shown in the right column of the table, the method of the present invention shows an improvement of about 70% or more in area reduction rate compared to the conventional method that allows for sound extrusion. As mentioned above, the present invention does not increase the equipment cost at all compared to the conventional method, significantly increases the machining limit of steel materials, and as a result eliminates the upsetting or cutting process, resulting in significant cost reduction and productivity. It brings about improvements and makes a great contribution to production. 【table】

[Brief explanation of drawings]

FIGS. 1A, B, C, D, E, and D' are schematic diagrams showing an example of the forward extrusion process.

Claims (1)

[Claims] 1. When manufacturing a stepped shaft by forward extrusion three or more times, after extruding the third thinnest shaft, extrude the thinnest shaft from the third thinnest shaft, and then A cold extrusion method that is characterized by extruding a thin shaft from the third thinnest shaft.