JPS6253309B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates primarily to a grinding method applied to a valve train cam for an engine, and particularly to a chill cam whose cam crests are chilled.

Conventionally, as a method of this kind, a method is known in which a cam is rotatably prepared on a swinging cradle that responds to the profile of the master cam, and a rotating grindstone is applied to the cam from the side. The general method is to apply the grindstone to the cam in a rotating state to gradually cut the cam, and in order to shorten the machining time, it is necessary to increase the rotation speed of the cam. According to this, since the cam is of a swinging type, followability is poor, resulting in inconveniences such as an inability to obtain an accurate profile and a poor surface finish.

The object of the present invention is to provide a method free of such inconveniences, in which a cam with a hardened cam crest is rotatably prepared on a cradle, and a circular base portion of the cam with low hardness is used. A first grinding step in which a rotating grindstone is advanced to the base circle portion as a grinding starting point and grinding is performed to a predetermined depth, a second grinding step in which the cam is rotated once and rough grinding is performed, and then the cam is and a third grinding step in which spark-out processing is performed by rotating the grinding wheel at least once.

An example of implementing the present invention will be explained with reference to the attached drawings. In the drawings, reference numeral 1 indicates a cam to be machined, and the cam 1 is rotatably provided on a rocking cradle that responds to the profile of a master cam. In the drawings, reference numeral 2 indicates a grindstone, and the grindstone 2 is located on the side of the cam 1 and is rotatably prepared on a grindstone head. Thus, when the grindstone 2 is rotated and the grindstone head is advanced, the cam 1 is ground by its action, and this point is not particularly different from the conventional one. The cam 1 is, for example, a second cam.
As shown in the figure, the cam ridge portion is used as a chill hardened portion 1a, and the internal hardness distribution is as shown in the third figure, for example.

According to the present invention, in such a device, the cam 1 is stopped in advance at a position where the base circular portion 1b becomes the grinding start point as shown in FIG. 1, and the grindstone 2 is rotated in this state. Then, the cam 1 is fed forward and the portion 1b is cut to a predetermined depth.
Rotate in one direction for at least one rotation.
In this way, the cam 1 has undergone rough polishing by removing the shaded portion of its circumferential surface, and the spark-out machining, that is, finish polishing, is then completed by rotating the cam 1 at least once more. This operation is, for example, as shown by line A in FIG. 4, and compared to the conventional type shown by line B in the figure,
Processing time is significantly reduced. To be more detailed,
Especially when considering the case where the cam 1 is the above-mentioned chill cam, the grinding wheel 2 first has a base circular portion 1b with low hardness.
The grindstone 2 has a relatively small amount of wear and tear, and the next time the cam 1 is rotated, the grindstone 2 grinds from the inside of the cam 1, which has low hardness, outward. This prevents the abrasive grains from falling off.
In this case, the number of revolutions of the cam 1 inevitably decreases, and thus the followability of the cradle is good and the profile accuracy is improved. In addition, the whetstone 2
Although a normal grinding wheel may be used, it is preferable to use one having hard abrasive grains such as artificial diamond cubic boron electrodeposited thereon.

In this way, according to the present invention, a cam with a hardened cam crest is rotatably prepared on a cradle, and a rotating grindstone is placed on the base circular portion of the cam, with the base circular portion of the cam having low hardness as the starting point for grinding. Since the first grinding process is provided in which the grinding wheel is advanced and ground to a predetermined depth, the first grinding process shortens the arc of contact between the grinding wheel and the cam to grind areas with low hardness, thereby reducing heat generation. At the same time, the load on the abrasive grains is reduced, allowing for faster grinding without damaging the whetstone.
Next, a second grinding process is provided in which the cam is rotated once to perform rough grinding, so that the second grinding process eliminates grinding cracks on the cam side part where the contact arc between the grindstone and the cam is long and has the highest hardness. The cam crest also shortens the contact arc of the grinding wheel to reduce the amount of wear on the grinding wheel, and then the cam is rotated at least once to perform spark-out processing, so the third grinding step is This has effects such as significantly shortening machining time and improving machining accuracy.

[Brief explanation of the drawing]

Fig. 1 is a plan view explaining one example of the method of the present invention, Fig. 2 is a plan view of an example of a chill cam, Fig. 3 is a diagram of its hardness distribution, and Fig. 4 is a line explaining its operation. It is a diagram. 1...Cam, 2...Whetstone, 1b...Base circle part.

Claims (1)

[Claims] 1. A cam with a hardened cam crest is rotatably prepared on a cradle, and the base circular part of the cam with low hardness is used as the starting point for grinding, and a rotating grindstone is advanced toward the base circular part until it reaches a predetermined depth. A cam grinding method consisting of a first grinding step in which the cam is ground, a second grinding step in which the cam is rotated once to perform rough grinding, and a third grinding step in which the cam is then rotated at least once to perform spark-out processing. .