JPS6326176B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a remelting hardening treatment method for forming a chilled layer on a cam portion of a camshaft. The camshaft links the opening and closing of the valves with the rotation of the crankshaft, introducing the air-fuel mixture into the combustion chamber at the appropriate timing, and discharging combustion gas from the combustion chamber. The structure is such that it slides into contact with the Therefore, the sliding surface of the cam portion is required to have higher wear resistance and pitting resistance than other parts. Conventionally, therefore, a chilled metal is set in the mold during casting to form a chilled layer on the cam sliding surface. However, forming a chilled layer using a chilled metal is troublesome due to the casting method, and it may not be possible to form the chilled layer at an appropriate location.Furthermore, the obtained chilled layer does not have sufficient wear resistance. It has no hardness or pitting resistance. Therefore, recently, a remelting hardening process has been proposed in which the cam sliding contact surface of a cast camshaft is remelted using a high energy heat source such as a plasma arc, and then rapidly cooled to form a chilled layer. Here, if the remelting and hardening treatment is performed using the high energy heat source without preheating the cam part, volumetric shrinkage will occur when the remelted part is rapidly solidified to form a chilled layer, resulting in cracks. The so-called cold-shut phenomenon occurs in which oxygen separates from oxides in cast iron, combines with carbon to generate carbon dioxide, and solidifies before this carbon dioxide can escape, creating porosity. occurs. To avoid this, the cam portion should be heated and melted very slowly.
This poses a problem in terms of productivity and cannot be put to practical use. Therefore, before remelting,
It is common to preheat the entire camshaft to 250°C to 400°C. On the other hand, the journal part of the camshaft is not required to have as much wear resistance and pitting resistance as the cam part, and it is troublesome to form a chilled layer due to the casting method, so it is not used without any heat treatment. It is common that However, since the journal portion is in sliding contact with the bearing, sufficient wear resistance is required, and for this purpose, it is desirable to perform quenching or remelting hardening treatment. The present invention was created in view of the fact that preheating is necessary to remelt and harden the cam part, and that it is also preferable to apply heat treatment such as quenching or remelt hardening to the journal part. It is an object of the present invention to provide a method for remelting and hardening a cam portion of a camshaft, which can heat treat a journal portion and remelt and harden a cam portion without increasing the number of steps. In order to achieve this object, the present invention first performs heat treatment such as hardening or remelting on the journal part of the camshaft using a high-energy heat source such as plasma arc, TIG, or laser beam, and then uses the heat from this heat treatment to heat the cam part. The gist is that the cam portion is preheated and then remelted and hardened using the high energy heat source. Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawing is a schematic view of the journal part of the camshaft being remelted, and shows the camshaft 1.
has journal parts J1 to J5, an oil seal part 2, and cam parts C1 to C12, and is rotatably supported around a shaft. Further, a torch holder 3 is installed above the camshaft 1 in parallel with the camshaft 1, and a plasma torch 4 is attached to the torch holder 3 so as to be able to reciprocate from side to side. In the present embodiment, each plasma torch 4... is made to face the journal parts J1 to J5 and the oil seal part 2 with a predetermined distance from each other, and then, while rotating the camshaft 1, the plasma torch 4...
... to reciprocate in the left and right direction, plasma arc 4
Scanning so that the locus a traces a meandering locus on the surfaces of the journal parts J1 to J5 and the oil seal part 2,
Let it remelt. Here, the plasma current was 80 A, and the operating time of the plasma torch 4 was 48 seconds. Then, the journal parts J1 to J5 and the oil seal part 2 were remelted, and the temperatures of the cam parts C1 to C12 after 30 seconds were as shown in the table.

[Table] As can be seen from this [Table], the cam part after the journal part was heat-treated was heated to a sufficient preheating temperature. After that, the plasma torch 4...... is moved along the torch holder 3 and the cam parts C1 to C12 are
The cam parts having similar shapes are simultaneously remelted and then rapidly cooled to form a chilled layer on the surface of the cam parts. Here, since the cam parts C1 to C12 are heated to the preheating temperature as described above, no crack or cold shut phenomenon occurs. In addition, in the embodiment, the journal parts J1 to J
5 and the oil seal portion 2 are remelted, but quenching may be performed by heating to the austenitizing temperature without melting. As is clear from the above explanation, according to the present invention, the journal part can be hardened or remelted by heating for preheating when the cam part is remelted and hardened using a high energy heat source such as a plasma arc. As a result, a camshaft with excellent journal characteristics can be obtained without any increase in the number of processes, and work efficiency is also increased because heat treatment of the journal part and remelting hardening treatment of the cam part can be performed in a series of processes. Improving dramatically.

[Brief explanation of the drawing]

The drawing is a schematic view of the journal portion of the camshaft undergoing remelting and hardening treatment. In the figure, 1 is the camshaft, 4 is the plasma torch, J1, J2, J3, J4, J5 are the journal parts, C1, C2, C3, C4, C5, C6, C
7, C8, C9, C10, C11, and C12 are cam parts.

Claims (1)

[Claims] 1. Heat the journal part of the cast camshaft to the quenching temperature using a high-energy heat source such as plasma TIG or laser beam, or re-melt it, use the heat at this time to preheat the cam part of the cast camshaft, and then A method for remelting and hardening a cam portion of a camshaft, characterized in that the cam portion is remelted using the high energy heat source and further rapidly cooled.