JPH01310113A - Manufacture of remelted chill cam shaft - Google Patents

Abstract

PURPOSE:To improve durability by irradiating high density energy heat source at a time over whole width of a cam nose part, and turning a raw member of cam shaft in turning direction on operation of the cam. CONSTITUTION:Plural numbers of torches 3 for TIG arc are arranged on a cam part 2 of a raw member of cam shaft 1 in axial direction, and four arcs 5 are generated at the same time between tungsten electrodes 4 of respective torches 3 for TIG arc and the surface of the cam part 2. The raw member of cam shaft 1 is made to turn in the turning direction of cam shaft at the time of operation. Unevenness in hardness is not generated in a remelted and solidified part thereby, and again structural directionality becomes agreeable to the turning direction of the cam shaft on cam operation, therefore wear resistance becomes good and durability is improved.

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a remelted chill camshaft used for manufacturing a camshaft which is a valve train component of an internal combustion engine. (Prior Art) A camshaft, which is a valve train component of an internal combustion engine, is required to have excellent wear resistance on its sliding surface with a cam that is a mating member, especially on the surface of the cam nose portion. Therefore, as a method for manufacturing camshafts with excellent surface wear resistance, a cooling metal is set in the cam nose forming part of the camshaft casting mold, and the surface of the cam nose part that is formed by contacting this cooling metal is There were some that formed a chilled hardened layer (supercooled hardened layer) by supercooling. However, this method has the disadvantage that the process of setting the cold metal is cumbersome and that flash is often generated, which increases the number of steps required to remove it. Therefore, as a means of surface hardening without using a chiller, as shown in FIG.
In some cases, the surface is remelted by irradiation with a high-density energy heat source such as the TIG arc 14 generated between the TIG arc 14, and then a chill hardened layer is formed by self-cooling. trajectory 14a
In this method, the cam part 12 of the camshaft rough material 11 is relatively weaved by an amount corresponding to the entire width of the cam part 12 to form a sheep intestine shape (such a sheep intestine shaped arc axis mark 14a makes it possible to The method of self-cooling the melted book is shown in the drawings of Japanese Patent Application Laid-Open No. 80-184694). (Problem to be Solved by the Invention) However, in such a conventional method for manufacturing a remelted chill camshaft, the tungsten electrode 13 is relatively oscillated in the width direction during remelting so that the beads overlap. Therefore, as shown in FIG. 5, a part of the first re-melted solidified layer 15a of i'G, which was previously re-melted and self-cooled, melted and self-cooled the second re-melted solidified layer 15b. The heating during remelting to form the structure may result in tempering, and a tempered layer (soft layer) 16 may be formed between them.
As shown in Figure 5, the hardness and abrasion resistance may not be constant because they differ considerably, and the direction of rotation of the camshaft rough material during remelting is the same as the direction of rotation of the camshaft during operation. Because the direction of the structure was not always aligned uniformly and in the same direction, the wear resistance such as pitting resistance and scuffing resistance may be inferior. I had an issue. (Purpose of the Invention) The present invention was made to solve the above-mentioned problems of the prior art. It is an object of the present invention to provide a method for manufacturing a remelted chill camshaft that can be aligned in the rotational direction of the camshaft.

[Structure of the invention]

(Means for Solving the Problems) A method for manufacturing a remelted chill camshaft according to the present invention includes:
Re-melting and solidifying at least the surface of the cam nose portion of the camshaft rough material by irradiation with a high-density energy heat source,
When remelting and solidifying the portion into a chilled structure, a high-density energy heat source is irradiated over the entire width of at least the cam nose portion at once to remelt the entire width of at least the cam nose portion at the same time, and the camshaft rough material at the time of remelting is This method is characterized by remelting and solidifying the rotation direction of the camshaft so that it matches the rotation direction of the camshaft during cam operation. It is characterized by being a means to do so. As the material for the remelted chill camshaft according to the present invention, it is preferable to use alloyed cast iron so that a chilled hardened layer is formed by self-cooling by air cooling after remelting. C:3. O~3.5%,
Cr: 0.5-1.0%, Cu: 0.05-0.15
%, Mo: o, i ~0.3%, Ni: 0.1 ~ 0
．． 3%, Mn: 0, 5~l, 0%, P: 0
．． 1% or less, S: 0.1% or less, Si: 1.5 to 2.5
%, the balance being Fe and impurities. The reason why it is preferable to set each component in such a range is that C
If the C content is too low, an incompletely chilled structure tends to occur and the wear resistance decreases, so it is preferably 3.0% or more, and if the C content is too large, the graphitization phenomenon becomes gradually noticeable. It is preferably 3.5% or less, and when the Cr content is low, the tendency to whitening (chilling) is suppressed, the thickness of the chilled structure becomes thinner, and the hardenability of the camshaft rough material decreases. However, the heat-affected zone shows a isothermal transformation curve (
T, T, T, curve) as a result of the pearlite nose having a pearlite base, the amount of wear increases and pitting occurs.
It is preferable to set the content to 0.5% or more.Even if the Cr content is large, not only will there be little improvement in wear resistance, but it will also increase the aggressiveness of the mating material, and even damage the camshaft. When the raw material is cast, the chill gets deep inside, making it difficult to process hollow oil holes, etc.
% or less, and by controlling the Cu content, it is possible to eliminate the occurrence of defects when casting the camshaft rough material, so it is preferably 0.05 to 0.0.
It is preferable to set it in the range of 15%, and if the Mo content is low, the wear resistance will be insufficient or pitting will occur for the same reasons as in the case of Cr, so it should not be more than 0.1%. is preferable, as even if the Mo content is large, not only will there be little improvement in wear resistance, but the attack on the mating material will be greater, and furthermore, when the camshaft rough material is cast, chill will reach the inside. It is preferable to keep it at 0.3% or less because machining of hollow oil holes etc. is difficult due to Nf entering the material.If an appropriate amount of Nf is not included, the wear resistance of the material itself will be poor and the material will be aggressive to the other material. Since it becomes large, 0.1~
The amount of Mn is preferably 0.3%. If the amount of Mn is too small, the graphitization phenomenon becomes noticeable, so it is preferably 0.5% or more. If the amount is too large, graphitization will be inhibited, but the chilled structure will remain after casting. This is because the cracking will increase the overall hardness and reduce workability. The P content is preferably 1.0% or less; if the P content is too high, a brittle steadite phase (Fe-Fe3C-
Fe3F) is precipitated and cracks are likely to form along this, resulting in poor pitting resistance, so it is preferable to keep the S content at 0.1% or less, and if the S content is too high, workability will decrease. This is because the content is preferably 0.1% or less. The method for manufacturing a remelted chill camshaft according to the present invention includes:
More preferably, alloyed cast iron having the above components is used as the material for the camshaft, and it is desirable to perform preheating prior to remelting the camshaft rough material produced by casting. In other words, remelting is performed without preheating. This is because when air cooling is performed together with self-cooling, the cooling rate is too high and the heat-affected zone tends to become a martensite base. Such a camshaft is undesirable because it is not only highly aggressive against mating materials, but also tends to crack or pitch during use. Therefore, in the method for manufacturing a remelted chill camshaft according to the present invention, it is desirable to perform preheating prior to the remelting treatment to prevent the cooling rate after the remelting treatment from becoming excessive.In this case, the preheating temperature If it is too low, it is difficult to obtain the above-mentioned effects, and if it is too high, the cooling rate becomes too slow, forming pearlite and reducing wear resistance, so it is particularly desirable that the preheating temperature is in the range of 200 to 300°C. After the camshaft rough material is preheated in this way, it is remelted by irradiation with a high-density energy heat source at the above-mentioned preferred temperature of 200 to 300°C. It is preferable to use a high-density energy heat source such as a TIG arc, plasma arc, laser beam, or electron beam. Cooling after remelting can be done by air cooling, or if necessary, the cooling rate can be adjusted by furnace cooling, air cooling, etc. It is not impossible to control. FIG. 1 is a perspective view showing an embodiment of the method for manufacturing a remelted chilled camshaft according to the present invention, and more preferably, a camshaft rough material 1 is formed using a camshaft casting mold using a molten alloy cast iron having the above-mentioned components. After casting, and then releasing the mold, the camshaft is made of rough material 1, preferably 200 mm.
Preheat to ~300°C, use, for example, a TIG arc as a high-density energy heat source, and install multiple TIG arc torches 3 in the width direction of the cam portion 2 of the camshaft rough material 1, in the case of the illustrated example, four trees. lined up, four arcs 5 are simultaneously generated between the tungsten electrode 4 of each TIG arc torch 3 and the surface of the cam part 2 in the width direction of the cam part 2,
The camshaft rough material 1 is rotated so that the direction of rotation of the camshaft rough material 1 matches the rotational direction of the camshaft during operation.
While rotating the cam part 2 and adjusting the distance between the cam part 2 and the tungsten electrode 4, in the illustrated example, the entire width of the cam part 2 is simultaneously remelted by four arc trajectories 6, and after being remelted, it is sequentially heated in the atmosphere. The cam portion 2 is cooled in air, and the cooling rate is controlled by furnace cooling, air cooling, etc. as necessary to form a remelted chilled hardened layer on the surface of the cam portion 2. (Example) A camshaft rough material was manufactured by casting alloy cast iron having the composition shown in Nos. 01 to 6 in Table 1 in a camshaft casting mold without using a cooling metal. Holes and cam oil holes were machined, black scales on the cam portion and journal portion were cut, and machining was performed to obtain predetermined dimensions to obtain a camshaft rough material for remelting. Next, each of the camshaft rough materials was preheated to 200 to 300° C. to prevent cracking after solidification. Preheating in this case is preferably performed by resistance heating or heating in a furnace.After that, as shown in the column of forward rotation in Figure 2, the direction of rotation of the camshaft rough material (arrow x1 direction) and the direction of the cam during remelting are determined. While gradually rotating the camshaft rough material in a direction that matches the direction of rotation of the camshaft during operation (arrow x2 direction), slowly weave it using the TIG arc torch 15 as shown in FIG. While heating, the cam sliding surface is heated and remelted by irradiating high-density energy under the conditions shown in Table 2, self-cooled by air cooling in the atmosphere, and then solidified in order to form a bond on the surface of the cam part. A remelted chill cured layer was formed. Subsequently, the cam portion of the remelted and chilled camshaft crude material was polished to obtain a product camshaft. As shown in Table 2 and Table 1, no defects were observed in No. 6, which used alloyed cast iron with a more desirable composition than the above, whereas No.
In the case of 5 to 5, it was found to be defective. and,
In products with such defects, stress was concentrated in the defective portions, resulting in poor wear resistance and durability. Therefore, as an embodiment of the present invention, a first
Cast alloy cast iron having the composition No. 6 in the table is cast into a camshaft casting mold without using a chilled metal to produce a camshaft rough material, and in this state, hollow oil holes and cam oil holes are machined. At the same time, the black scale on the cam portion and journal portion was cut off, and machining was performed to obtain a predetermined size to obtain a camshaft rough material for remelting. Next, after preheating the camshaft rough material to 200 to 300°C to prevent cracking after solidification, four TIG arc torches were arranged in the width direction of the cam part as shown in Figure 1. Then, as shown in the forward rotation column of Figure 2, the direction of rotation of the camshaft rough material during remelting (direction of arrow x1) and the direction of rotation of the camshaft during cam operation (direction of arrow x2) match. While gradually rotating the camshaft rough material in the direction of the camshaft, four arcs are irradiated at once in the width direction of the cam part to remelt the entire width of the cam part at the same time,
Then, by sequentially solidifying by self-cooling, a remelted chill hardened layer was formed on the surface of the cam part. As shown in the photograph substituted for the drawing in Figure 3, this re-melted chill-hardened layer had a uniformly oriented structure, and was confirmed to have a defect-free metal structure. . Subsequently, the cam portion of the remelted and chilled camshaft crude material was polished to obtain a product camshaft, and then a durability test was conducted by motoring under the conditions shown in Table 3. The results are shown in Table 4. Table 3 As a result, pitting occurred for the first time after 8 cycles of durability as shown in Table 4, and it was recognized that the product had good abrasion resistance and durability. this is,
When remelted and solidified by conventional weaving,
In contrast to the tempering-softened layer shown in FIG. 5, which is not formed at all in this example, the hardness distribution is uniform. At the same time, since the direction of rotation of the camshaft rough material during remelting is made to match the direction of rotation of the camshaft during cam operation, the cam follower 8 is This is because the direction in which the cam follower 8 slides is approximately in the forward direction with respect to the direction of the structure shown by the arrow M, and the cam follower 8 slides smoothly on the surface of the chill hardened layer. Next, as Comparative Example 1, in the embodiment of the present invention, four TIG arc torches were used to simultaneously remelt the cam portion in the width direction as shown in FIG. Then, a product camshaft was obtained in the same manner as in the embodiment of the present invention, except that it was remelted by weaving using one TIG arc torch as shown in FIG. Next, when a durability test was conducted by motoring under the conditions shown in Table 3, pitching occurred for the first time after 5 cycles of durability time, and as in the embodiment of the present invention, the cam follower 8 was restarted during cam operation. Since the structure of the melted and solidified part is slid in a substantially forward direction, the sliding properties are good in this respect, but since a tempered softened layer is formed as shown in Figure 5, When the entire width of the cam portion was remelted + 1 solidified at the same time as in the embodiment of the present invention, the wear resistance and durability were better than when the entire width of the cam portion was remelted and solidified by weaving. Furthermore, as Comparative Example 2, as shown in the column of reverse rotation in FIG.
A product camshaft was obtained in the same manner as in Comparative Example 1, except that the direction of force was reversed to the direction of rotation of the camshaft during cam operation (direction of arrow Y2). Next, a durability test by motoring was conducted under the conditions shown in Table 3. As shown in Table 4, the first pitting occurred after 1 cycle of durability, and the wear resistance was poor. The cause of this is that the rotation direction of the camshaft rough material during remelting (arrow Y1 direction in Figure 2) is opposite to the rotation direction of the camshaft during cam operation (arrow Y2 direction in Figure 2). Therefore, as shown in the column of reverse rotation in Fig. 2, the direction of the sliding force with the cam follower 8 is almost the opposite direction to the direction of the structure shown by the arrow N, and the cam follower 8 touches the surface of the chilled hardened layer. This is because it slides by stroking it backwards.

【Effect of the invention】

The method for manufacturing a remelted chill camshaft according to the present invention includes:
Re-melting and solidifying at least the surface of the cam nose portion of the camshaft rough material by irradiation with a high-density energy heat source,
When remelting and solidifying the portion into a chilled structure, a high-density energy heat source is irradiated over the entire width of at least the cam nose portion at once to remelt the entire width of at least the cam nose portion at the same time, and the camshaft rough material at the time of remelting is The rotational direction of the camshaft is matched to the rotational direction of the camshaft during cam operation to re-melt and solidify the camshaft, similar to the method of setting a chilled metal in a camshaft casting mold to form a chilled hardened layer. There is no need for the process of setting a chilled metal, and there is no unevenness in hardness in the remelted/solidified part unlike in conventional remelting/solidification methods, and the directionality of the structure is similar to that during cam operation. The camshafts are aligned in the rotational direction of the camshaft, and a camshaft with good wear resistance and excellent durability can be obtained, which is an extremely excellent effect.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of the method for manufacturing a remelted chill camshaft according to the present invention, and Fig. 2 shows the rotational direction of the camshaft rough material during remelting and the rotational direction of the camshaft during cam operation. Fig. 3 is a photograph (400x magnification) showing the metal structure of the remelted and solidified portion in the embodiment of the present invention, and Fig. 4 shows the production of a conventional remelted chill camshaft. FIG. 5, which is a perspective view showing the method, is an explanatory view showing the state of formation of a soft layer by the conventional method for manufacturing a remelted camshaft. 1... Camshaft rough material, 2... Cam part, 4, 4° 4.4... Electrode, 6, 6, 6.6... Arc locus. Patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] (1) When re-melting and solidifying at least the surface of the cam nose portion of the camshaft rough material by irradiation with a high-density energy heat source and making the re-melted and solidified portion into a chilled structure, the high-density energy heat source covers the entire width of at least the cam nose portion. is irradiated at once to simultaneously remelt at least the entire width of the cam nose portion, and to remelt and solidify the camshaft rough material by aligning the direction of rotation of the camshaft rough material at the time of remelting with the direction of rotation of the camshaft during cam operation. A method for manufacturing a remelted chill camshaft, characterized by: