JPH0141685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for remelting camshafts and the like.

(Prior art) Parts of the surface layer of cast iron parts, such as the surface of the cam part of a camshaft and the tip part of a rocker arm, come into sliding contact with other parts, so these parts have better wear resistance than other parts. , excellent properties such as pitting resistance are required. For this reason, the surfaces of these cast iron members are subjected to remelting treatment.

Such remelting treatment is performed, for example, as shown in FIG.
A plasma torch 11 is disposed at a predetermined distance from the camshaft 9 and the plasma torch 11 is reciprocated several times within the width of the cam surface 10a. The cam surface 10a was remelted while drawing.

(Problems to be Solved by the Invention) Conventionally, DC current has been used as the arc current supplied to the plasma torch 11, and therefore the energy of the plasma arc supplied to the surface of the cam portion 10 varies over time. It has become constant.

However, at or near the turning point 13 of the reciprocating vibration of the plasma torch 11, the speed becomes slow due to the inertia of the plasma torch and the limit of the response time of the control speed of the drive system. The steering movement speed of the plasma torch 11 becomes slower. Therefore, at the turning points 13 of the plasma torch and in the vicinity thereof, the energy of the plasma arc given per unit area of the cam part surface 10a is transferred to other parts (for example, the central part
4,...), the remelt layer becomes deeper, and a remelt layer having a uniform depth cannot be obtained.

Figure 3 illustrates the above relationships, respectively.A,
B shows time on the horizontal axis and steering speed and arc current on the vertical axis, respectively. Time T3 is the half-week period of the reciprocating motion of the plasma torch, and T1 is the half-cycle in which the plasma torch is accelerated to a constant speed. From T2 to T3 indicates the time required for the plasma torch to decelerate and reach the turning point. C
is the half-cycle movement of this plasma torch (distance L)
This figure shows a cross section of the remelt layer obtained by
5a, that is, the turning point of the plasma torch and its vicinity are deeper than the others.

As described above, in the conventional remelt treatment method, the depth of the obtained remelt treatment layer is not uniform, and the hardness of the surface thereof is not uniform depending on the location.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a remelt treatment method in which a remelt treatment layer having a uniform depth can be obtained and the hardness of the surface of a remelt treatment member can be uniform.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a torch 1
When performing remelt processing by generating an arc between the torch 1 and the base material 2, when the relative movement speed is small, the relative movement speed is such that the pulse width per cycle is small, corresponding to the relative movement speed of the torch 1 and the base material 2. When is large, a pulse current with a large pulse width per cycle is generated, and this is superimposed on the DC arc current (Fig. 2B). Approximately constant arc energy is given.

(Operation) The above means operates as follows. In other words, the arc energy given to a unit area of the base material is constant regardless of the relative movement speed between the base material and the torch, and the remelt treatment layer 8 with a uniform depth is obtained on the surface of the processing member, which is uniform over the entire area of the processing member. hardness can be obtained.

(Embodiment) A preferred embodiment of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a diagram schematically showing a configuration for implementing the method according to the present invention. In FIG. 1, reference numeral 1 denotes a plasma torch, which is disposed with its nozzle portion 1a facing a cam member 2, which is a base material, and is spaced apart from it by a predetermined gap, and which is rotated in the direction of the arrow by a predetermined drive device. 1 is caused to reciprocate horizontally over a distance L (in the direction of arrows G and H with respect to the base material 2) by a drive device 3.
The nozzle portion 1a of the plasma torch 1 has an electrode (not shown) made of tungsten or the like built-in, and a shield gas such as an inert gas, a working gas such as argon gas, an ejection port for additive metal powder, etc. are provided at appropriate locations. Be prepared.

In such a configuration, when the cam member 2 is used as the other electrode and an arc is generated between the torch electrode and the base material 2 in the shielding gas, and the working gas and additive metal powder are ejected, the working gas becomes plasma and a high-temperature, high-speed plasma arc is generated. The molten metal is sprayed onto the surface layer of the cam member 2, forming a molten pool in this area.
The additive metal powder is melted into this molten pool and chilled, so that the surface of the cam member 2 is subjected to remelt treatment.

Incidentally, reference numeral 4 denotes a DC arc current supply source that supplies a DC arc current to the electrode of the plasma torch 1 to generate an arc between the electrode and the base metal. On the other hand, reference numeral 5 denotes a speed detector (for example, a tacho generator) connected to the drive device 3 of the plasma torch 1 to detect the speed of the plasma torch 1, and its output signal is transmitted to the pulse current generator 6. This pulse current generating device 6 corresponds to the output signal of the speed detector 5, that is, the pulse width per cycle is small when the speed of the plasma torch 1 is small, and the pulse width per cycle is small when the speed is large. Generates a pulse current with a large pulse width. The pulse current from the pulse current generator 6 is superimposed on the DC arc current from the arc current supply source 4 by a superimposer 7 and supplied to the plasma torch 1.

Figure 2 shows the above relationships when the frequency of the pulse current generator is constant, in the same way as Figure 3 (shown in the conventional example). are shown by taking the torch speed and the arc current supplied to torch 1, respectively, at time T3.
represents a half cycle of the reciprocating motion of the plasma torch, T1 represents the time it takes for the plasma torch to accelerate during the half cycle until it reaches a constant speed, and T2 to T3 represents the time it takes for the plasma torch to decelerate and reach the turning point. As is clear from A and B, when the speed of the plasma torch 1 is low, a pulse with a small width is applied, and when the speed of the plasma torch 1 is high, a pulse with a large width is applied so that the arc energy applied per unit area of the cam member 2 becomes approximately constant. It is tatami mated to. C
is the half-cycle movement of this plasma torch (distance L)
This figure shows a cross section of the remelt layer obtained by the method, and the depth of the remelt layer 8 is approximately constant over the distance L thereof.

Furthermore, when the pulse width of the pulse current generator is constant, when the torch speed is low, the pulse frequency is low, and when the torch speed is high, the pulse frequency is low.
A similar effect can be obtained by increasing the pulse frequency.

It should be noted that the present invention is not limited to this embodiment, and for example, a plasma torch may be used for remelting treatment using a Teigue torch, etc., and the configuration shown in FIG. 1 is not limited to this. do not have.

(Effects of the Invention) As is clear from the above explanation, according to the remelt treatment method of the present invention, the arc energy given to the unit area of the base material is constant regardless of the relative movement speed of the base material and the torch, and the treated member A remelt treated layer 8 of uniform depth can be obtained on the surface of the treated member, and uniform hardness can be obtained over the entire area of the treated member.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing the configuration of an embodiment of the present invention, and Fig. 2 A, B, and C show the torch speed, the arc current supplied to the torch, and the remelt layer obtained by these, respectively. FIG. 3 is a diagram showing a conventional example similar to FIG. 2, and FIG. 4 is a diagram showing an example of a conventional remelting process. In the drawing, 1 is a plasma torch (torch), 2 is a cam member that is a base material, 3 is a drive device, 4 is an arc current supply source, 5 is a speed detector, 6 is a pulse generator,
7 is a superimposing device, and 8 is a remelt processing layer.

Claims (1)

[Claims] 1 When performing remelt treatment by generating an arc between the torch and the base material, if the relative movement speed is small, the pulse width per cycle is small, and the relative movement speed is When it is large, a pulse current with a large pulse width per cycle is generated, and this is superimposed on the DC arc current to give approximately constant arc energy per unit area of the base material regardless of the relative movement speed. A remelt processing method characterized by: