JPS60204834A - Method for hardening cam part of cam shaft by remelting - Google Patents

Abstract

PURPOSE:To obtain a cam shaft having superior journal characteristics without increasing the number of stages by preheating the cam parts of a cast cam shaft by making use of heat generated during the hardening of the journal parts before the cam parts are hardened by remelting. CONSTITUTION:The journal parts J1-J5 of a cast cam shaft are heated to the hardening temp. or remelted with a high energy heat source such as plasma TIG or laser beams. The cam parts C1-C12 of the cam shaft are preheated by making use of heat generated during the heating or remelting. The cam parts C1-C12 are then remelted with a high energy heat source and quenched to form chilled layers on the surfaces of the cam parts C1-C12.

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. It has a structure that makes sliding contact with the tappet. Therefore, the sliding surface of the cam portion is required to have higher wear resistance and pitting resistance than other parts. For this reason, conventionally, a cooling umbrella 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. Therefore, recently, high-energy heat sources such as plasma arc are used to remelt the cam sliding surface of the cast camshaft.
A remelting hardening process has been proposed in which the material is 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 contraction will occur when the remelted part is rapidly solidified to form a chilled layer. The so-called cold phenomenon occurs when oxygen separates from oxides in the cast iron, combines with carbon to generate carbon dioxide, and solidifies before the carbon dioxide can escape completely, creating porous conditions. A shutting phenomenon occurs. To avoid this, it is possible to heat and melt the cam part very slowly, but 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 used without any heat treatment because it 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. It is common to do so.

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 developed in view of the fact that preheating is necessary to remelt and harden the cam portion, and that it is also preferable to subject the journal portion to heat treatment such as quenching or remelt hardening. An object of the present invention is to provide a method for remelting and hardening a cam portion of a camshaft, which allows heat treatment of a journal portion and remelting hardening of a cam portion without increasing the number of steps.

In order to achieve this objective, the present invention first applies plasma arc and TIG to the journal portion of the camshaft.

Heat treatment such as hardening or remelting is performed using a high energy heat source such as a laser beam, the cam portion is preheated by the heat from this heat treatment, and then the cam portion is remelted and hardened using the high energy heat source. That is the gist of it.

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 undergoing remelting treatment, and the camshaft (1) has journal parts (Jl) to (J5), oil seal part (2), and cam part (C1) to (C12), and is rotatably supported around an axis. Also camshaft (1)
A torch holder (3) is installed above the camshaft (1) in parallel with the camshaft (1), and a plasma torch (4) is attached to this torch holder (3) so as to be able to reciprocate from side to side.

In this embodiment, each plasma torch (4)
... are made to face the journal parts (Jl) to (J5) and the oil seal part (2) at a predetermined interval, and then, while rotating the camshaft (1), the plasma torch (0...) is reciprocated in the left and right direction. Then, the locus of the plasma arc (4a) scans the surfaces of the journal parts (''l) to (J5) and the oil seal part (2) so as to draw a meandering locus, causing them to remelt.Here, the plasma current is 80^ The operating time of the plasma torch (4) was 48 seconds.

Then, the journal parts (Jl) to (j5) and the oil seal part (2) were remelted, and the temperatures of the cam parts (CI) to (012) after 30 seconds were as shown in the table.

[Table] As can be seen from Table E, the cam portion after the journal portion 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 (CI) to (C12) are moved.
), the cam portions having similar shapes are simultaneously remelted and further rapidly cooled to form a chilled layer on the surface of the cam portion.

Here, the cam parts (CI) to (012) are heated to the preheating temperature as described above.

No crack or cold shut phenomenon occurs.

In addition, in the embodiment, the journal part (jl) ~ (''5
) and the oil seal part (2) may be heated to the austenitizing temperature and quenched without being melted.

As is clear from the above description, according to the present invention, the journal portion is hardened or remelted by heating for preheating when the cam portion 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 adding any additional processes, and the heat treatment of the journal part and the remelting hardening treatment of the cam part can be performed in a series of processes, which improves work efficiency. Greatly improved.

[Brief explanation of drawings]

The drawing is a schematic view of the journal portion of the camshaft being remelted and hardened. In the figure, (1) is the camshaft, (4) is the plasma torch, (Jl), (J2), (J3), (J4), (J5
) is the journal part, (CI), (C2), (C3), (
C4), (C5), (CB), (07), (08). (09), IC:lo), (c+1), and (CH) are cam parts. Patent applicant Honda Motor Co., Ltd.

Claims (1)

[Claims] Plasma TIG, the journal part of the cast camshaft
The cam part of the cast camshaft is heated to the quenching temperature using a high-energy heat source such as a laser beam or remelted, and the cam part of the cast camshaft is preheated using the heat generated at this time, and then the cam part is heated using the high-energy heat source. A method for remelting and hardening a cam portion of a camshaft, which method comprises remelting and further rapidly cooling the cam portion of a camshaft.