JPS5828677Y2 - Differential pinion cold forming mold - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a mold for cold open molding a differential pinion used in a differential gear, and particularly relates to improving the strength of the mold.

The differential gear uses a differential pinion gear with a special shape in which the end surface on the large diameter side forms a spherical surface, but it is not easy to manufacture this at a low cost.

The inventors of the present invention manufactured a blank for a differential pinion by cold forming, and created a mold with the idea of omitting at least the cutting of the tooth surface.

As shown in FIG. 1, the initially prototyped mold had a cavity in which the lower mold 1 had exactly the same shape as the intended product 2; It was found that the part (corresponding to the root of the product) was easily damaged and was not suitable for practical use.

Considering the purpose of use of the differential pinion gear, it is necessary that the large-diameter side end surface 4 is a spherical surface, and the end surface of the upper toothed portion (in Fig. 1, it coincides with the parting surface 7 of the toothed portion 6) ) 5 must be located inside the spherical surface for convenience of assembly.

If we try to satisfy this strict condition and also make the tooth surface as wide as possible to reduce the contact surface pressure, the end surface 5 of the tooth part should be the first
As shown in the figure, it has to be determined immediately inside the spherical surface including the end surface 4.

Therefore, if the cavity of the lower mold 1 is to have the same shape as the product, as is clear from FIG. However, since the toothed part 6 of the lower mold 1 is a part that protrudes into the cavity and is subjected to extremely severe load conditions during molding, the tip part 3 has an acute angle. It lacks strength and the tip 3 breaks off, making it impossible to obtain sufficient durability.

Therefore, in order to solve this problem, a lower mold 11 was manufactured as a prototype in which the parting surface 1T of the tooth profile portion 16 was perpendicular to the center line CL, as shown in FIG.

However, it was found that this lower mold 11 was also not suitable for practical use.

In this lower mold 11, the angle α between the parting surface 11 of the tooth profile 16 and the ridge line 18 becomes an obtuse angle, increasing the strength of the tip 13, so that this part will not be chipped. The area of the rising surface 19 increases, and the fill-up load acting on this rising surface 19 during molding increases, resulting in cracks in the corner 9 surrounded by the root of the rising surface 19 and the root of the tooth profile 16. It happens and happens all the time.

If the cavity is shaped as shown by the broken line in Figure 2, this cracking can be prevented, but in this case, the amount of cutting required to finish the product 2 in the shape shown by the two-dot chain line increases. This results in increased manufacturing costs and decreased material yield.

Therefore, we further searched for a lower mold that would be suitable for practical use, but in the process, we produced a prototype mold with a special shape, which resulted in chipping and cracking at the tips and corners of the tooth profile. It was found that the mold was sufficiently durable for practical use, and therefore it was possible to cold forge a blank for a differential pinion, and the present invention was developed.

However, the feature of the cold forming die for a differential pinion according to the present invention is that the parting surface of the tooth profile forms an obtuse angle with the ridgeline of the tooth profile and an acute angle with the center line of the die. It is at a determined point.

A more detailed explanation will be given based on the drawings showing the subolinal embodiment.

In FIG. 3, 21 is a lower mold, in which a cavity 20 having a recessed portion having the same shape as the tooth profile of a target differential pinion (product) 22 is formed.

The cutout surface 27 of the tooth profile 26 of the lower die 21 is determined to form an obtuse angle of approximately 9005' with the ridge line 28 of the tooth profile 26 and an acute angle of approximately 65° with the center line CL.

A through hole 31 is formed in the center of the lower mold 21 and is concentric with the cavity 20, and a protruding rod 32 is slidably fitted into the through hole 31.

The protruding rod 32 is in the position shown in FIG. 3 during molding, and its tip surface 33 forms a part of the bottom surface of the cavity 20, and after the molding is completed, it is pushed upward by an actuator (not shown) to complete the molding. It serves to eject the blank from the cavity 20.

Reference numeral 34 denotes an upper mold, which is provided with a recess 35 having a shape that corresponds to the large-diameter end surface (spherical surface) 24 of the differential pinion 22 and the parting surface 27 of the toothed portion 26 with a substantially constant gap therebetween. 21, and is moved toward and away from the lower die 21 by a forging press (not shown).

The mold configured like a nose has a tip 2 of the tooth profile 26.
3 forms an obtuse angle as described above, it has sufficient strength, and the area of the rising surface 29 at the top of the cavity 20 is also relatively small, so the fill-up load is limited and no cracks occur in the corner 39. It is fully usable for practical use.

Therefore, if a material having a volume slightly larger than the volume of the differential pinion 22 is put into the cavity 20 and the upper die 34 is lowered, the material will be molded into a shape that fills the cavity 20, and the excess material will be poured into the lower part. It is pushed out into the gap 36 left between the mating surfaces of the mold 21 and the upper mold 34 and becomes a flash.

After the upper die 34 is raised, the protruding rod 32 is pushed up to eject the molded blank from the cavity 20.

A through hole is formed in the center of the blank formed as above, and the end face on the large diameter side is machined into the shape shown by the two-dot chain line in Fig. 3, and then hardened to form the desired small differential. The gear is completed.

This embodiment is an example of cold forging a differential pinion whose pitch cone has an apex angle of 64°. Good results were obtained when the angle α formed between the parting surface 27 and the center line CL of the lower mold was approximately 65°, but the angle α, Of course, β is not limited to the angle in the above embodiment, but its optimum value also changes depending on the size of the apex angle of the pitch cone of the differential pinion gear.

However, it is generally preferred that the angle α be between 90° and 125°, and particularly preferably between 90° and 100°.

The housing angle β is preferably 90o-65°t'L<75
The car is particularly heavy at the angle of -65°.

As described in detail above, the present invention is practical for cold open molding blanks for differential pinion gears by selecting the parting surfaces of the teeth in the mold to meet specific conditions. The mold was successfully obtained, and it has an excellent effect in making it possible to manufacture differential pinions at a much lower cost than in the past.

[Brief explanation of drawings]

FIGS. 1 and 2 are vertical cross-sectional views showing the main parts of the lower die of a mold that was prototyped in the process of completing the present invention. FIG. 3 is a vertical cross-sectional view of a main part showing an embodiment of the present invention. 20... Cavity, 21... Bent bottom type, 23...
...Tip of the tooth profile, 24...Large diameter side end surface, 26...Curved tooth profile, 27...Parting surface of the tooth profile, 28... Ridgeline of tooth profile, 29...
Rising surface, 32...Protruding rod, 34...
Upper mold, 39...corner.

Claims (1)

[Scope of utility model registration request] A mold for cold-open molding a small gear for a differential device, the parting surface of the tooth profile in the mold forming an obtuse angle with the ridgeline of the tooth profile and an acute angle with the center line of the mold. A cold forming mold for a differential pinion, characterized in that the mold is determined to form a differential pinion.