JPS62104660A - Production of hollow cam shaft - Google Patents

Abstract

PURPOSE:To improve a strength of product and to reduce a production cost by casting molten metal as casting therein a pipe which is previously arranged in a mold after shot-blasting. CONSTITUTION:A pipe 5 such as carbon steel pipe, etc., which is previously shot-blasted, is arranged in a cavity for a cam shaft in the mold. At this time, the pipe 5 is arranged at a corresponding position to an axial center position of the cam shaft 1 in the cavity, and expansion parts 6, 7 of the pipe are formed previously by bulging work at corresponding positions of a cam piece part 2 and sprocket fitting part 4 of the cam shaft. next, he hollow cam shaft is formed by casting the molten metal as casting therein the pipe in the mold. A satin finished pattern surface of the pipe 5 increases the joining area with the casting metal, and the strength of the shaft is improved because of large Young's modulus of the pipe 5. As the core is unnecessary in this casting, the production coat is reduced so much.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a hollow camshaft used in valve train systems of motorcycles and automobiles.

(Prior art) In order to reduce the cost and weight of camshafts used in the valve train systems of motorcycles, automobiles, etc., so-called hollow camshafts, in which the axial center of the camshaft is hollow, have been put into practical use. ing.

A conventional example of the method for manufacturing the hollow camshaft as described above includes, for example, the casting method described in "Nikkei Mechanical" published on May 6, 1985, pages 101 to 105. In this method, a mold is manufactured using the ■ process, and a long sand core (shell core) is placed at the axial center of the camshaft in the mold cavity, and the core is removed by shot blasting etc. after casting. This is a manufacturing method that removes

(Problems to be Solved by the Invention) The conventional hollow camshaft manufacturing method described above has the following 21 drawbacks. First, it is necessary to use a long sand core, which requires a lot of cost to manufacture, and on top of that, the yield rate is reduced due to bending, breakage, etc. of the core. This also means that a large amount of cost is required. Second, after casting, it is necessary to shot blast the hollow part using a small-diameter nozzle, and since a sand core is used, it is necessary to take into account the possibility of sand baking and pinholes caused by gas. The need for inspection requires a lot of effort and also causes quality problems due to the above-mentioned defects.

Therefore, it is possible to manufacture a hollow camshaft by placing a pipe at the center of the camshaft axis in this mold and casting this pipe, but in this case, the molten metal and pipe may be There is a need to improve the weldability of For this reason, a method of plating the outer circumference of the pipe in advance may be considered, but this plating process requires a great deal of effort and expense, so if this method is adopted,
This will lead to a significant increase in the cost of the hollow camshaft.

This invention was made in order to solve the above-mentioned drawbacks of the conventional method, and its purpose is to provide a method for manufacturing a hollow camshaft that can manufacture a high-quality hollow camshaft at low cost. There is a particular thing.

(Means for Solving the Problems) Therefore, in the method for manufacturing a hollow camshaft of the present invention, when casting the camshaft 1 in which the journal part 3 and the cam piece part 2 are connected in the axial direction, A shot-blasted pipe 5 is previously placed approximately at the axial center of the camshaft 1, and the pipe is cast.

(Function) According to the above method, the outer peripheral part of the pipe 5 is integrally welded to the molten metal, while the previously formed hollow part remains inside, making it possible to manufacture a hollow camshaft. Become. At this time, in the above method, since SR does not use a long sand core, it is possible to manufacture a hollow camshaft at low cost, and it is also possible to improve quality by preventing sand burning and pinholes. It is. Furthermore, since the pipe 5 has been shot blasted in advance,
Since deposits such as oil and fat on the surface of the pipe 5 are removed, the occurrence of gas defects can be prevented, and by making the surface of the pipe 5 satin-like, the joint area between the cast material and the surface of the pipe 5 is increased. It becomes possible to improve the weldability of both.

(Example) Next, a specific example of the method for manufacturing a hollow camshaft of the present invention will be described in detail.

FIG. 1 shows a cross-sectional view of a camshaft 1 manufactured by the method of the present invention after casting.
are cam piece parts, and these cam piece parts 2...2
Journal portions 3...3 are arranged in series at appropriate locations between them. Further, reference numeral 4 denotes a sprocket mounting portion, and this sprocket mounting portion 4 may be provided at the end of the camshaft 1, instead of being provided at the center of the camshaft 1 as shown in the figure. A pipe 5, which has been shot blasted in advance, is arranged at the axial center of the camshaft 1, and this pipe 5 is inserted into the cavity for the camshaft 1 formed in the mold before casting. , is placed at the central axis of the camshaft 1, and is cast with /8 hot water. As for the pipe 5, the outer diameter of the journal part 3 is 25 fins,
When the wall thickness is about 61 mm, use one with a wall thickness of about 0.5 to 2.0 mm, preferably about 1.0 to 1.6 mm, and as for the material, the molten metal is cast iron (FC or FCD).
), carbon steel pipes for machine structures (STKM II
Although it is preferable to use A)-, it is not particularly limited thereto.

The pipe 5 is formed with enlarged tube portions 6, . . . , 6 and 7 by bulging or the like at positions corresponding to the cam piece portions 2 . . . 2 and the sprocket mounting portion 4, respectively. The expanded pipe parts 6...6 and 7 are provided to further reduce the weight of the cam piece part 2 and the sprocket mounting part 4, and an example of the above dimensions is a pipe 5 with an inner diameter of 13mm and a wall thickness of 1fi. In practice, it is preferable to expand the diameter by about 5 W, but the diameter is not limited to this. In addition, when performing the above-mentioned diameter expansion, for example, when the diameter is expanded uniformly at any point on the entire circumference of the expanded tube portion 6, or when the top portion 2a of the cam piece is greatly expanded (indicated by X in the figure) as shown in FIG. On the other hand, various methods can be considered, such as a case where the bottom portion 2b is expanded to a small size (indicated by y in the figure), and any of these methods can be implemented. In addition, when performing the above-mentioned casting, a chiller (chilling metal) is placed in the mold at a position corresponding to the top of the cam piece parts 2...2, and the top of the cam piece parts 2...2 is It is preferable that the cam piece parts 2...2 be rapidly cooled to have a chilled structure to increase the hardness of the top part of the cam piece part 2 to improve wear resistance.

In the camshaft manufactured by the method described above, the outer circumferential portion of the pipe 5 is integrally welded to the molten metal, while the pre-formed hollow portion remains inside. It is possible to manufacture a hollow camshaft with the desired hollow section. The hollow camshaft manufactured above was observed with an optical microscope, and the results showed that the casting material and the pipe were completely joined at the joint surface, and that they were mutually diffused and had continuity in terms of metallographic structure. It was confirmed that it has. Since this method does not use a long sand core, it is possible to reduce the cost associated with using a core, and there is no risk of sand burning or pinholes, and the camshaft It is also possible to improve the quality. Moreover, in this case, since the pipe is a forged material manufactured by plastic working, it has the effect of sufficiently reinforcing the cast material with low toughness in terms of strength, and in this respect, the quality of the hollow camshaft is also improved. Is possible. In addition, since the pipe 5 is shot-blasted in advance, deposits such as oil and fat on the surface of the pipe 5 are removed, thereby preventing the occurrence of gas defects.Furthermore, the surface of the pipe 5 is made into a satin-like finish. Since the joint area with the cast material is increased, the joint state between the cast material and the pipe 5 becomes even better.

In addition, a comparative test was conducted between a hollow camshaft manufactured by a conventional manufacturing method (hereinafter referred to as a comparative example) and a hollow camshaft manufactured by the manufacturing method of the present invention (hereinafter referred to as an example). The dimensions of the example are as follows: the journal part 3 has an outer diameter of 25 m, the pipe 5 (carbon steel pipe for mechanical structure) has an outer diameter of 17.31 m, and an inner diameter of 14.111 m; The outer diameter of the journal portion 3 was 25 mm, and the inner diameter was 12 mm.

First, in the static bending test, approximately 2
The specimens taken by cutting the ends from the comparative example and the example were placed on support stands 8.8 arranged at intervals of 501111, and a load was applied to the bottom part 2b of each cam piece.
Deflection was measured. The measurement results are shown in FIG. 4, and as shown in the figure, it is clear that the example has sufficient rigidity and strength. In addition, at the maximum load, only a crank occurred in the example, but a fracture occurred in the comparative example.

In addition, a bending fatigue test was conducted, as shown in Fig. 3, in which both ends of a specimen obtained by cutting the end of the camshaft 1 were placed on a support stand 8.8 similar to the above. The test was carried out by applying a sinusoidal oscillating repetitive load to the bottom portion 2b at 10 cycles/second with a load ratio=minimum load/maximum load ratio value of 0.1. The results are shown in FIG. 5, and as shown in the figure, it is clear that the fatigue strength of the example is better than that of the comparative example.

In addition, hardness comparisons were made between the above examples and comparative examples. Regarding the mass cam piece part 2, the hardness was measured at a position 1.5 mm inside from the surface in the vicinity of the top part 2a. As a result, in the example, the average HRC was 52.4 (n
= 10), whereas in the comparative example, the average HRC was 49
, 9 (n = 10), and the example showed high hardness. On the other hand, regarding the surface of the journal part 3, the average HRC was 17.5 (n = 5) in the example, whereas
In the comparative example, the average HRC was 12.5 (n = 5), and the example showed high hardness.

As described above, the examples are superior to the conventional ones in terms of static strength, fatigue strength, and hardness, which is thought to be due to the following reasons. First of all
In addition, in the example, since the pipe 5 is arranged inside and the casting part is relatively thin, the solidification rate of the /8 molten metal becomes faster, and as a result, the flaky graphite becomes finer. This means that the total flexion tissue is improved. Second, when considering the embodiment as a combination beam, the pipe 5
Since the Young's modulus of steel is about twice that of cast iron, even if its inner diameter is made larger than that of conventional examples, the bending stiffness will increase, and as a result, the amount of deflection and maximum bending stress for the same moment will decrease. This means that

On the other hand, the above method only requires an inexpensive expanded diameter steel tube, and is therefore less expensive than manufacturing methods in which a solid camshaft is manufactured by casting and then the shaft center is drilled by machining. The cost required for the material of the shaft center portion removed by drilling and the machining cost required for drilling a deep hole are eliminated, making it possible to significantly reduce the cost of the hollow camshaft. In addition, with the above machining method, it is difficult to make the hole diameter at the position corresponding to the cam piece part 2 and the sprocket mounting part 4 larger than the hole diameter corresponding to the journal part 3, etc., or if it can be made larger, However, according to the above method, the diameter of the hole at the desired position can be easily increased as described above, and the weight of the camshaft can be reduced.

<Effects of the Invention> In the method for manufacturing a hollow camshaft of the present invention, the hollow part of the camshaft is constructed by casting a pipe, so unlike the conventional method, a long sand core is used. Therefore, it is possible to reduce the cost associated with the use of a core and the labor associated with sand removal and inspection.

Moreover, since there is no sand burning or pinholes caused by the sand core, it is possible to improve the quality of the camshaft. In addition, by subjecting the pipe to shot blasting in advance, it is possible to prevent the occurrence of gas defects due to deposits on the pipe surface, and the surface of the pipe is made satin-like to increase the bonding area between the pipe and the cast material. The joint state between the cast material and the pipe becomes even better.

Furthermore, if the expanded pipe part is formed in the pipe at a position corresponding to the cam piece part etc. as in the above embodiment, the weight of the camshaft can be further reduced, and if a similar weight reduction is achieved by using a sand core. This has the effect of omitting a large amount of effort required to remove sand from the inner surface of the cam piece.

[Brief explanation of drawings]

Fig. 1 is a central vertical cross-sectional view of an example of a hollow camshaft manufactured by the method of the present invention, Fig. 2 is a central vertical cross-sectional view showing a modified example thereof, and Fig. 3 is a static bending and bending fatigue of the hollow camshaft. FIG. 4 is a graph showing the bending test results of Comparative Examples and Examples, and FIG. 5 is a graph showing the fatigue test results of Comparative Examples and Examples. 1...Camshaft, 2...Cam piece part, 3...
・Journal part, 4...Sprocket installation 1.5...
- Pipe, 6... Expanded pipe part of cam piece part, 7... Expanded pipe part of sprocket mounting part.

Claims (1)

[Claims] 1. When casting a camshaft in which a journal part and a cam piece part are connected in the axial direction, a shot-blasted pipe is placed in advance at a position approximately at the axial center of the camshaft in the mold, A method for manufacturing a hollow camshaft, characterized by casting the above-mentioned pipe.