JPH0514001B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical field The present invention relates to an improvement in a sizing method for improving the inner diameter accuracy of a sintered metal gear. (b) Prior art and its problems When the inner diameter or gear accuracy of a sintered metal gear is critical, sizing is generally performed. For this method, the outer mold (die)
A method of making it circular and applying pressure with upper and lower punches,
There are three methods: making the die tooth-shaped and passing a ball through the inner diameter for inner diameter sizing. When these methods are applied to helical gears, various problems arise because the teeth are twisted. These methods will be explained in detail using FIGS. 1 and 2. 1st
In the figure, 1 is a die, 2 is a lower punch, 3 is a core rod, 4 is a tooth of a helical gear, 5 is a sintered metal, and 6 is an upper punch. When the above method is used for helical gears, it is difficult to align the product and the mold, so it is not generally used. If the other method is used, the pressure applied by the upper punch and the lower punch increases tooth profile errors and tooth trace errors, resulting in poor yield. Moreover, this tendency becomes more pronounced as the helix angle of the helical gear increases. The reason for this is that the tooth profile portion is not supported by the mold die, and in order to further improve this, the method shown in FIG. 2 is being considered. This method improves the dimensional accuracy of the center diameter by passing the ball 7 through the center hole of the sintered metal 5. When using this method, even if the product is the same, it is necessary to determine the diameter of the sphere to be passed depending on the dimensional variation during sintering.
For this reason, when the inner diameter tolerance is strict, a huge variety of balls can be used. More specifically, it is necessary to make a selection that takes into account the spring back of the inner diameter after the ball has passed, depending on the dimensional variation during sintering. Sizing methods to solve these problems have been studied in many fields, but no good method has yet been developed. (C) Disclosure of the Invention The present invention is proposed to improve these problems, and will be explained in detail with reference to FIGS. 3, 4, and 5. The numbers in the figure are the same as those shown in FIG. The contact surfaces of the upper punch 6 and the lower punch 2 shown in FIG. By pressurizing the sintered metal, it is possible to improve the dimensional accuracy of the center diameter and at the same time obtain a sintered metal helical gear with small tooth line errors and tooth profile errors in the tooth portion. FIG. 4 shows another application example of the present application. In this case,
By providing a protrusion near the center hole of the sintered metal itself, the same effect as the method shown in FIG. 3 can be obtained. That is, the gist of the present invention is that, as shown in FIG. 5, in the sizing method for a sintered metal helical gear, the contact portion 9 between the upper and lower punches and the sintered metal is separated by 0.5 mm or more from the tooth bottom diameter 8. The present invention provides a sizing method characterized in that the sizing method is carried out in the following manner. In this case, the cross-sectional shape of the die may be circular, oval, rectangular, or a combination thereof, as long as there is no tooth profile and the end is 0.5 mm or more away from the tooth bottom diameter. Moreover, the tooth portion may be located on the outer circumferential surface or the inner circumferential surface. Such a method makes it easy to put in and take out the helical gear, and it is possible to provide a highly accurate sizing method. (d) Example A powder consisting of Cu: 2% by weight, C: 0.8% by weight, and the balance Fe was adjusted to a pressing density of 6.8 kg/cm ³ and molded into a helical gear having the gear specifications shown in Table 1. 1150℃ in an endothermic modified gas (raw material butane) atmosphere
Sizing was performed after 1H sintering. Two sizing methods were used: the conventional method in which the upper and lower punches were made flat, and the method shown in FIG. 3 in which the upper and lower punches were provided with convexities as in the present invention. FIG. 6 shows the tooth profile error and tooth trace error of the sintered metal helical gear obtained as a result. In Fig. 6, A and B show the tooth trace and tooth profile errors by the conventional method,
C and D show tooth trace and tooth profile errors obtained by the method of the present invention. Comparing the conventional method and the method of the present invention, it can be seen that although the tooth profile error does not change much, the tooth trace error is significantly different. In other words, in the conventional method, the pressure applied by the upper and lower punches affects the tooth part, resulting in a tooth trace error of 0.016 to 0.030 mm and a tooth profile error of 0.008 mm, whereas the method of the present invention applies pressure by the upper and lower punches. Pressure does not affect the tooth area, resulting in tooth trace error
Good gear accuracy is shown with 0.002 to 0.003 mm and tooth profile error of 0.006 to 0.008 mm. In this manner, the present invention can provide a method for sizing a sintered metal helical gear that is highly accurate, inexpensive, and highly suitable for mass production. 【table】

[Brief explanation of the drawing]

1 and 2 show a conventional method for sizing sintered metal. 3, 4, and 5 show a method for sizing a helical gear according to the present invention. 6th
The figure shows the accuracy of tooth trace and tooth profile errors obtained according to the present invention and a comparative example. The meaning of each number in the figure is as follows. 1...Die, 2...Lower punch, 3...Core rod, 4...Helical gear teeth, 5...Sintered metal, 6...Upper punch, A...Tooth trace error by conventional method, B... ...Tooth profile error by conventional method, C... Tooth track error by the present invention, D... Tooth profile error by the present invention.

Claims (1)

[Claims] 1. In the sizing method for sintered metal helical gears, the inner surface of the die or the outer surface of the core rod of the sizing mold has a simple cross-sectional shape with no tooth profile, and the shape of the contact surface between the upper and lower punches of the mold and the product is Due to the combination, the contact part is 0.5mm from the tooth root diameter.
A sizing method for helical gears, characterized in that high gear tooth profile accuracy can be obtained by pressure forming the gears in a state where they are spaced apart from each other.