JPH0790326A - Manufacture of shim for adjusting clearance of valve of internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the dimensional precision, to simplify the manufacturing processes, and to reduce the manufacturing cost of a shim. CONSTITUTION:A green compact 8 compacted in the compacting process is drawn from a die 5 in the condition where the upper and lower faces of the green compact 8 is pressed in the thickness direction by upper and lower punches 6, 7. This constitution prevents generation of warp in the green compact 8. Thus, the warp or the like is unlikely generated in the shim in the next sintering process or after sintering, and the shim of excellent dimensional precision can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a valve clearance adjusting shim used in a valve operating mechanism of an internal combustion engine, and more particularly,
The present invention relates to a method of manufacturing a shim by a powder metallurgy method.

[0002]

2. Description of the Related Art A tappet (valve lifter) used for a direct-acting type valve operating mechanism in an internal combustion engine has a cylindrical shape with an upper surface closed, and has a circular recess formed in the upper surface for adjusting a valve clearance. The disc-shaped shim is inserted and configured.

Since the shim comes into contact with the rotating cam above it and is subjected to cyclically large repetitive compressive loads, high strength and high wear resistance are required. So the conventional shim
Chromium molybdenum steel or its case-hardened steel (for example, SCM415
(H) and other plate materials are punched into a circle with a cold press,
After that, it is generally manufactured by heat treatment such as carburizing and tempering in order to enhance strength and wear resistance, and then machining the outer peripheral surface etc. to improve dimensional accuracy. is there.

[0004]

In the above-described conventional method for manufacturing a shim, cold punching (shearing) causes burrs, fine irregularities, etc. on the outer peripheral surface of the shim, and also results in a rough surface. Machining on the outer peripheral surface is indispensable, and there is a problem that the number of manufacturing processes increases and the cost increases. There is also a drawback that the yield of the material is poor.

In order to deal with this problem, it is conceivable to form the shim by the powder metallurgy method, that is, the sintering method, which has good yield and dimensional accuracy and does not require post-processing.

However, when a shim is manufactured by a normal powder metallurgy method, since the shim has a relatively thin plate thickness, a warp occurs in the thickness direction when the mold is removed after compacting, and the subsequent sintering is performed. The warpage is expected to increase. for that reason,
It is necessary to perform post-processing such as sizing and coining on the shim after sintering, and to correct the warp by grinding (polishing) the surface and outer peripheral surface, and like the conventional cold punching method, the manufacturing cost Will increase.

The present invention has been made in view of the above problems, and is a method for manufacturing a valve clearance adjusting shim in an internal combustion engine, in which the dimensional accuracy is improved and the manufacturing process is simplified so that the cost can be reduced. Is intended to provide.

[0008]

[Means for Solving the Problems] The object is to compress a powder metallurgy material to form a disk-shaped green compact, and to press both surfaces of the green compact appropriately in the plate thickness direction. However, it is achieved by including a step of demolding and a step of sintering the demolded green compact at a predetermined temperature.

[0009]

[Operation] When the compression-molded compact is demolded in the molding process, the compact is released while pressing both sides in the plate thickness direction, so that the compact does not warp. To be done. Therefore, even in the subsequent sintering step, there is no fear that the warp will increase, and a shim with high dimensional accuracy can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, (1) shows a tappet to which the present invention is applied, and has a cylindrical shape whose upper surface is closed. Disc-shaped recess (1a) formed on the upper surface of the tappet (1)
A shim (2) for adjusting the valve clearance, which is manufactured by the method described in detail below, is removably fitted in the housing.

Reference numeral (3) is a rotary cam that comes into contact with the upper surface of the shim (2). 2A to 2E schematically show the present invention in the order of steps.

The powder metallurgy material used in the present invention, that is, the raw material powder is, for example, a relatively inexpensive Fe (pure iron) -based material, Fe-
C system, Fe-C-Cu system, Fe-C-Cu-Ni system, Fe-Ni-Cu-
Mo type and the like are preferable. Further, the particle size is suitably in the range of 10 to 200 μm.

First, the above-mentioned raw material powder having an appropriate structure is mixed for a predetermined time by adding a mold oil lubricant such as zinc stearate in a mixing step (not shown). Next, in the step shown in FIG. 2 (A), the raw material powder (4) which has been weighed and mixed is inserted into the compression molding die (5) and placed on the lower punch (6).

Next, in the compression molding step shown in FIG. 2 (B), the upper punch (7) is lowered, and the raw material powder (4) in the previous step is strongly pressed at a pressure of 4 to 6 tf / cm ² to manufacture it. A green compact (8) having almost the same shape as the shim (2) is molded.

In the demolding step of FIG. 2C, the green compact (8) molded in the previous step is pressed by the upper and lower punches (6) and (7), that is, the green compact (8) is molded. The upper punch (7) moves the green compact (8) downward (in the plate thickness direction) with a force that does not cause collapse.
The lower punch (6) is raised to the upper end surface of the die (5) while being pressed against, and then the upper punch (7) is raised until it is separated from the green compact (8). ) Is removed and removed.

Next, in the sintering step of FIG. 2 (D), the green compact (8) is housed in a sintering furnace (9) and first preheated at about 500 ° C. to lubricate the mold with zinc stearate or the like. After volatilizing the agent, while supplying atmospheric gas such as argon gas, 11
Heat and sinter at 00-1200 ℃ for a certain period of time. Through the above steps, the sintered metal, that is, the shim (2) as shown in FIG.
Is obtained.

The shim (2) manufactured according to the present invention has the upper and lower punches (6) in the step of demolding the green compact (8).
Since it is released from the mold while pressing it by (7), there is almost no occurrence of warpage even with a relatively small plate thickness.
Therefore, there is no fear of warping in the subsequent sintering process,
It has extremely high dimensional accuracy.

As a result, post-processing such as sizing, coining, or grinding (polishing) of the outer diameter or the surface is unnecessary.

The shims (2) after sintering are infiltrated, impregnated, and surface treated to improve strength, wear resistance and surface hardness.
(Plating), heat treatment, carburizing, nitriding, etc., and in order to enhance the rust preventive effect, oil impregnation treatment, steam treatment, chemical conversion treatment, permeation treatment, etc. may be performed respectively.

In the above-mentioned embodiment, an example is shown in which the green compact (8) is demolded while being pressed by the upper and lower punches (6) and (7) in the demolding step of FIG. 2C. You may use the means of.

That is, the compression molding die (5) has a split mold structure capable of being divided into a plurality of pieces in the radial direction orthogonal to the axis,
Immediately after molding the green compact (8) in the molding process of FIG. 2 (B), the die (5) is divided and at the same time the upper punch (7) is raised,
The green compact (8) may be taken out.

At this time, after the green compact (8) is formed, at the moment when the split molds are separated from the green compact (8), the upper punch is pressed.
The load of (7) is reduced to a region where the green compact (8) does not lose its shape, and then the split mold is completely separated from the green compact (8).
It is better to raise the upper punch (7). Also,
In the case of a mold having a split mold structure, since it is not necessary to raise the lower punch (6), a simple fixed die may be used. Needless to say, the powder metallurgy material used in the present invention is not limited to the above-mentioned Fe system.

[0024]

According to the present invention, the following effects can be obtained. (a) As a result of solving the warp, which is a drawback of the conventional powder metallurgy method, it is possible to manufacture the shim by sintering instead of punching, omitting machining which is indispensable in the punching method, As the yield of materials is improved,
Manufacturing cost is greatly reduced.

(B) As a result of obtaining a shim with high dimensional accuracy, post-processing for correcting warpage or the like after sintering is unnecessary, and the process is simplified and the productivity is improved.

[Brief description of drawings]

FIG. 1 is a central longitudinal front view of a shim obtained according to the present invention and a tappet to which the shim is applied.

FIG. 2 is a schematic view showing the present invention in process order.

[Explanation of symbols]

(1) Tappet (1a) Recess (2) Shim (3) Rotating cam (4) Raw material powder (powder metallurgy material) (5) Mold (6) Lower punch (7) Upper punch (8) Green compact ( 9) Sintering furnace

Claims (2)

[Claims] 1. A step of compacting a powder metallurgy material to form a disk-shaped green compact, a step of demolding the green compact while appropriately pressing both surfaces thereof in the plate thickness direction, And a step of sintering the molded green compact at a predetermined temperature. 2. The green compact is molded in a mold that can be divided in the radial direction, and then the mold is divided in the radial direction while appropriately pressing both surfaces of the green compact. Item 2. A method for manufacturing a valve clearance adjusting shim in an internal combustion engine according to Item 1.