JP2748624B2 - Sizing method for cylindrical sintered parts - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for sizing a cylindrical sintered part capable of improving the sizing accuracy by suppressing an increase in load on a mold.

[Conventional technology]

Sintered parts made by powder metallurgy have higher productivity and are more cost effective than those made by cutting, forging, etc. As a result, the types of sintered parts that require high precision are increasing.

Such parts include internal gears and external gears. There are also similar cylindrical parts provided with splines instead of teeth.

This type of part requires high-precision processing of teeth and splines, but since sintered parts cannot avoid thermal distortion during sintering, the shape and dimensions are corrected by sintering after sintering to correct the accuracy. Enhancements have been made.

FIG. 2 shows a conventional sizing method for a part having a gear or a spline inside. The sintered component 10 in this case has a structure in which a flange 12 is provided at one end of a boss 11 and a stepped helical spline 13 is formed inside the boss. The sizing die includes a die 1 for correcting the outer diameter portion of the boss 11, a core rod 2 for correcting the inner diameter side of the component 10, a lower punch 3 for correcting the lower end surface of the component, An upper punch 4 for correcting the upper end surface.

Now, in this conventional sizing method, FIG.
Δt = 0 to 0.05 mm on both inside and outside of the part 10 as shown in
The part is pressed down by the upper punch 4 and inserted into the die 1 and the core rod 2 as shown in FIG. 2B, and the lower end is received by the lower punch 3 and pressure is applied by the punches 3 and 4 from above and below. Is added. However, this method has the following problems.

[Problems to be solved by the invention]

For a sintered component having a gear or a spline on one of the inner and outer diameter surfaces, the shape accuracy and dimensional accuracy after sizing cannot be sufficiently increased only by providing a radial correction allowance of about 0 to 0.05 mm.

Therefore, in order to increase the accuracy, it is necessary to increase the radial correction allowance or to keep the radial correction allowance small, and to compensate for the shortage of the radial correction allowance by increasing the axial compression allowance. is there. However, as for the sintered parts during sizing, the density of the inner and outer surfaces increases as the pressing by the mold progresses,
Furthermore, with the increase in the density, the frictional resistance between the mold (die and core) also increases. Therefore, the former method of increasing the radial correction allowance increases the end face pressure, and causes the mold (die or die). Punch) is easily damaged.

In addition, the latter method of increasing the axial compression allowance requires a large end face pressure and also increases the amount of deformation of the part,
Accordingly, not only the die and the punch but also the component itself is easily damaged.

An object of the present invention is to provide a sizing method capable of increasing the sizing accuracy of a cylindrical sintered part without causing the above-mentioned problems.

[Means for solving the problem]

In the present invention, as a solution to the above-described problem, a portion where the inside and outside positional relationship is opposite to the portion requiring high processing accuracy of the sintered part (the outside diameter side of the corresponding position if the requested portion is inside is assumed) and this portion The mold surface to be straightened is preferably tapered at an angle corresponding to 1 ° or more, and sizing is performed by increasing the radial straightening allowance of the part on the side where the tapered portion is higher than the high processing accuracy required portion. .

In the case where the portion requiring high machining accuracy is a helical or straight groove or tooth, the radial correction allowance of the portion is set to 0 or 0 or less, which causes a gap between the portion and the die, and the portion is tapered to the tapered side. It is advisable to add a correction fee to compensate for.

It is also preferable to move the core rod relative to the die during compression by the mold for the following reasons.

[Action]

If a taper corresponding to the sintered part and the mold is provided, a wedge effect will occur in the part during compression, so even if the end face pressure applied from above and below is small, uniform and large radial compression can be applied to the part requiring high processing accuracy from inside and outside Force can be exerted,
Even if the radial compression allowance is increased, it is possible to prevent the mold from being damaged by suppressing the increase in the end face pressure, and it is also possible to improve the radial dimensional accuracy of sintered parts by increasing the radial correction allowance. become.

Here, the reason that the radial correction allowance of the portion having a helical or straight groove or tooth is preferably 0 or 0 or less is as follows. That is, as the radial correction allowance is smaller, friction during compression with the mold is less likely to occur, and the front face to be corrected is more likely to follow the mold. On the other hand, the radial correction allowance on the tapered side can be effectively compressed in the radial direction by the wedge effect described above. Therefore, if the portion requiring high machining accuracy eliminates the radial correction allowance and compensates for the necessary correction allowance of the corresponding portion by compression using the wedge effect, the effect of suppressing the increase in the end face pressure is further improved, and the dimensional accuracy is improved. be able to.

In addition, when the core rod is relatively moved with respect to the die during compression by the mold, one of the core rod or the die is moved together with the component, and friction due to the relative movement between the one mold and the component can be eliminated. Therefore, this also contributes to increase in the radial correction allowance by reducing the end face pressure.

〔Example〕

An embodiment of the method of the present invention will be described with reference to FIG.

The sizing target sintered part 10 has a flange on one end of the boss 11.
12 is a flanged cylindrical body having a stepped helical spline 13 formed inside the boss. In the present embodiment, the outer diameter surface 11a of the boss portion of the sintered component 10 is tapered by θ = 2 °. Also, the inner diameter surface 1a of the die 1 has θ = 2 °.
Corresponding to the taper.
The radial correction allowance for the 11a part was 0.3 mm, and the radial correction allowance for the helical spline 13 part was 0 mm.

The sintered part 10 is fitted on the upper part of the core rod 2 as shown in FIG. 2B, and is pushed down together with the core rod 2 by the upper punch 4 and pushed into the die 1 as shown in FIG. As shown in (d), pressure was applied to the upper and lower punches 4 and 3 from above and below.

As a result, despite the extreme increase in the radial correction allowance of the surface 11a to 0.3 mm, it was possible to improve the spline accuracy by performing smooth sizing without damaging the mold.

Sizing was also performed on components having a helical gear in place of the helical spline 13 under the same conditions, but the results were almost the same.

The following table compares the gear accuracy at that time with the accuracy obtained by the conventional sizing method.
It is 1/10.

In the embodiment, a part of the inner diameter side has a helical spline or a cylindrical body with a flange of a helical gear as a sizing target. However, a gear or a spline inside a target part may be straight. In addition, as shown in FIG. 3, there is no flange, as shown in FIG. 4 or 5, a helical or straight spline or gear 13 'is provided from one end to the other end of the component 10, or at one end. The effect of the present invention can be obtained even with a bottomed cylindrical part having a bottom.

Further, the same effect can be obtained by sizing a sintered component having spline grooves and gear teeth on the outer diameter side with a taper corresponding to a mold for correcting the inner diameter side and the portion. .

〔effect〕

As described above, according to the present invention, the radial correction allowance of a part is increased by a simple method of attaching a taper corresponding to a sintered part and a mold to be sized, thereby increasing the load burden on the mold. The sizing accuracy can be improved without inviting, so it is possible to use sintered parts that are advantageous in terms of manufacturing and cost even if adoption of sintered bodies has been refused due to accuracy problems. It can contribute to expanding the use of sintered parts and reducing the cost of various devices and equipment such as automobiles and electric equipment.

[Brief description of the drawings]

1 (a) to 1 (d) are views showing an example of the method of the present invention in the order of steps, FIGS. 2 (a) and 2 (b) are step diagrams of a conventional sizing method, and FIGS. The figure is a sectional view showing another example of the sizing target component. 1 ... die, 1a ... inner diameter surface, 2 ... core rod, 3 ...
Lower punch, 4 Upper punch, 10 Sintered parts, 11 Boss part, 11a Outer diameter surface of boss part, 12 Flange, 13 Helical spline, 13 'Helical or straight Spline or gear.

Claims (3)

(57) [Claims] 1. A method for sizing a cylindrical sintered part having a die, upper and lower punches, and a core as straightening dies and having a part requiring high processing accuracy on an inner diameter side or an outer diameter side. The taper of the angle corresponding to the part where the positional relationship between the inside and the outside is reversed (the outer diameter side of the corresponding position if the requesting part is tentatively inside) and the mold surface that corrects this part is further added. A sizing method for a cylindrical sintered part, wherein the sizing is performed by increasing a radial correction allowance of a part on a taper side than a part requiring high processing accuracy. 2. When the portion requiring high machining accuracy is a helical or straight groove or a tooth, the radial correction allowance of the portion is set to 0 or less than 0 where a gap is formed between the mold and the tapered side. Claim (1) to add a correction fee to make up for it
A sizing method for a cylindrical sintered part according to the above. 3. The method for sizing a cylindrical sintered part according to claim 1, wherein the core rod is moved relative to the die during compression by the mold.