JPH04362116A - Laser hardening method for inside surface of cylindrical body - Google Patents

Abstract

PURPOSE:To obviate the generation of a level difference between the 1st round and 2nd round of a hardened part and to allow the continuous execution of hardening operations. CONSTITUTION:A laser beam is moved by one pitch (P2) in the axial line direction of a cylindrical body 6 during the time from just before the laser beam rotates one turn in the circumferential direction of the cylindrical body 6 and right thereafter. A light shielding body is maintained in the state of shielding the laser beam with light shielding parts 8a and is moved circumferentially by nearly 1/2 pitch (1/2 P1) of the light shielding parts, by which the hardened part of nearly the perfect checker patterns having no level difference between the 1st round and the 2nd round is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hardening the inner surface of a cylindrical body, such as a cylinder of an internal combustion engine, in a substantially checkerboard pattern using a laser beam.

0002

2. Description of the Related Art It is known that the wear resistance of the inner surface of the cylinder of an internal combustion engine is improved by laser hardening the inner surface of the cylinder in a substantially checkerboard pattern.

An example of such a conventional method of laser hardening the inner surface of a cylinder is shown in FIG. 3. In this method, a laser beam 2 emitted from a laser oscillator 1 is guided into a cylindrical body 6 to be hardened by an irradiation optical system 5 including a reflecting mirror 3 and a focusing lens 4. It is reflected again toward the inner surface 6a of the cylinder 6 by the disposed reflection mirror 7, and the reflection mirror 7 is rotated around an axis parallel to the central axis L of the cylinder 6 and moved in the direction of the central axis L. The laser beam 2 is scanned in a spiral direction along the inner surface of the cylindrical body 6, and n light-shielding parts 8a and light-transmitting parts 8b are respectively arranged alternately in the circumferential direction.
A light shielding body 8 is rotatably disposed within the cylindrical body 6 so that one side of the laser beam 2 is located in the irradiation optical path of the laser beam 2.
By rotating the light shielding body 8 by a half pitch equal to n in the same direction or in the opposite direction to the rotation of the laser beam 2, a pseudo checkered pattern as shown in FIG. 2 is formed on the inner surface 6a of the cylinder body 6. A patterned hardened portion 9 is formed.

0004

[Problems to be Solved by the Invention] According to the conventional laser hardening method as described above, since the laser beam 2 is scanned spirally along the inner surface of the cylinder 6, the hardening start point on the inner surface of the cylinder 6 is There is a problem that a step of height H occurs at the point where the piston makes one turn from St and enters the second turn, and the piston cannot be smoothly guided in a portion with such a step. In particular, the helical pitch P0 in the direction of the central axis L of the cylinder 6
When is large, the difference in level becomes noticeable and the above-mentioned problem becomes serious. For this reason, if the hardening is performed at least one turn more than the required hardening range, the work efficiency will deteriorate.

[0005] In view of the above-mentioned problems of the conventional technology, the present invention has been developed to eliminate the above-mentioned level difference.
Moreover, it is an object of the present invention to provide a method for laser hardening the inner surface of a cylindrical body, which allows the hardening work to be carried out continuously and efficiently without interrupting the work.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the method of laser hardening the inner surface of a cylindrical body according to the present invention provides a method for laser hardening the inner surface of a cylindrical body. By moving the laser light inside the cylinder in the circumferential direction and axial direction of the cylinder through light shielding bodies arranged alternately in the circumferential direction, the inner surface of the cylinder is intermittently irradiated. In the method of laser hardening the inner surface of a cylinder in a substantially checkerboard pattern, the laser beam is rotated continuously at a uniform speed in the circumferential direction of the cylinder, and immediately before the laser beam makes one rotation in the circumferential direction, From the time when the light shielding body is shielded by one light shielding part, the light shielding body is rotated in the scanning direction of the laser beam by approximately 1/2 pitch of the light shielding part, and when the laser light is shielded by the light shielding part. It is characterized in that the laser beam is moved by a predetermined pitch in the axial direction of the cylindrical body until it leaves the light shielding body.

[0007]

[Operation] When the laser beam makes one rotation in the circumferential direction of the cylindrical body through the light shield, intermittent hardened portions are formed on the inner surface of the cylindrical body during the first round. Between just before and after the laser beam makes one rotation, the laser beam rotates in the circumferential direction and is moved by one pitch in the axial direction of the cylinder, but during this period, the laser beam is blocked by the light shielding part of the light shielding body. Since it is shielded, no spiral hardened portion is formed on the inner surface of the cylinder.

Moreover, during this time, the light shielding body is moved in the circumferential direction by approximately 1/2 pitch of the light shielding part with the laser beam being shielded by the light shielding part, and then the second round of hardening is performed. Because of this, there is no difference in level between the first and second rounds of the hardened part, and it is not possible to tell where the switch was made from the first round to the second round just by looking at the hardened part. It is possible to form an almost perfect checkered pattern of quenched parts that are so beautiful that they are almost invisible.

[0009] Even after the second round, by performing the hardening work in the same manner as from the first round to the second round, the same work and effect can be obtained.

0010

EXAMPLE Hereinafter, one embodiment of the method of the present invention will be explained with reference to FIG.

As the laser hardening device, the same device as shown in FIG. 3 can be used. In addition, the reflecting mirror 7
The rotation means, the means for moving it in the direction of the central axis L, and the means for rotating the light shielding body 8 are preferably controlled by numerical control according to a preset program.

To carry out the method of the present invention using this apparatus, first, the laser beam 2 reflected by the reflecting mirror 3 is heated at the hardening start point St of the inner surface 6a of the cylinder 6.
The entire irradiation optical system 5 is lowered. Also, at this time, the light shielding body 8
An appropriate light shielding portion 8a is positioned at position A shown in FIG.

From this state, the rotating means for the reflecting mirror 7 is activated, and thereafter the reflecting mirror 7 is continuously rotated at a constant speed. During one rotation of the laser beam 2, only the portion of the inner surface 6a of the cylindrical body 6 where the laser beam 2 passes through the light-transmitting portion 8b of the light-shielding body 8 and is irradiated is hardened, and the light-shielding portion of the light-shielding body 8 is hardened. The light-shielded portion 8a remains in an unhardened state, and an intermittent first round hardened portion 10 as shown in FIG. 1 is formed.

[0014] Immediately before the laser beam 2 makes one rotation in the circumferential direction from the hardening start point St, it is blocked by the light shielding part 8a of the light shielding body 8 located at the above-mentioned position A. Until the light shielding body 8 is separated from the
1 in the traveling direction of the laser beam 2 and stopped at position B shown in FIG.

Furthermore, since the laser beam 2 is blocked by the light shielding part 8a at the A position, the light shielding part 8a has moved to the B position.
While rotating the reflecting mirror 7 in the circumferential direction, the reflecting mirror 7 and the entire irradiation optical system 5 are lowered in the direction of the central axis L of the cylinder 6 by a predetermined pitch P2. , the laser beam 2 is moved momentarily to the position of the second round so as to draw a spiral trajectory as shown by the imaginary line in FIG.

Note that in order to prevent the laser beam 2 from being irradiated onto the inner surface of the cylinder 6 while the laser beam 2 is scanning along the spiral trajectory, a light shielding body 8 is provided to prevent the laser beam 2 from irradiating the inner surface of the cylinder 6.
The laser beam 2 is rotated at an angular velocity close to the rotational angular velocity of
It is better to ensure that it can be shielded with a.

[0017] By doing this, there is no difference in level between the first round and the second round, and moreover, just by looking at the quenched part, you can tell where the switch was made from the first round to the second round. It is possible to form a hardened part 10 so beautiful that it cannot be recognized.

After that, the laser beam 2 passes through the light shielding part 8a at position B.
The hardened part 10 of the second round as shown in FIG. is formed.

[0019] From the second round to the third round, and from the nth round to the (n+1)th round thereafter, the process is similar to the case from the first round to the second round described above. By doing so, it is possible to continuously form the hardened portions 10 in a substantially perfect checkered pattern in which the pitch in the circumferential direction is shifted by half a pitch every round.

In the last round, the laser beam 2 is blocked by the light shielding portion 8a of the light shielding member 8 immediately before making one revolution, and then
Emission of the laser beam 2 from the laser oscillator 1 is stopped, or the laser beam is shielded by appropriate means.

[0021]

[Effects of the Invention] According to the present invention, the following effects can be achieved. (a) There is no level difference between the first and second round of the hardened part, or between the other round and the adjacent round, and a beautiful checkered pattern is created. It is possible to form an entrance. (b) Since there is no step at the start of quenching, there is no need to perform extra quenching beyond the desired quenching area.
It's advantageous. (c) Since work can be performed continuously without stopping or interrupting the start of the laser beam in the circumferential direction, workability and work efficiency are good.

[Brief explanation of drawings]

FIG. 1 is a developed view showing an example of a hardened portion on the inner surface of a cylinder that has been laser hardened by the method of the present invention.

FIG. 2 is a developed view showing an example of a hardened portion on the inner surface of a cylinder that has been laser hardened by a conventional method.

FIG. 3 is a schematic perspective view showing an example of a laser hardening apparatus used for carrying out the conventional method and the method of the present invention.

[Explanation of symbols]

1 Laser oscillator 2 Laser light 3 Reflector 4 Focusing lens 5 Irradiation optical system 6 Cylindrical body 6a　Inner surface 7 Reflector 8. Light shielding body 8a　Light shielding part 8b Translucent part 10 Quenching section L Center axis St Quenching start point P1, P2 Pitch

Claims (1)

[Claims] Claim 1: Laser light is transmitted from the inside of the cylinder to the cylinder through a light shielding body which is rotatably disposed inside the cylinder and has a plurality of light shielding parts and transparent parts arranged alternately in the circumferential direction. In a method for laser hardening the inner surface of a cylinder in a substantially checkerboard pattern by moving the laser beam in the circumferential direction and axial direction of the cylinder and intermittently irradiating the inner surface of the cylinder, the laser beam is applied to the cylinder. The laser beam is rotated continuously at a constant speed in the circumferential direction of the laser beam, and from the time when the laser beam is shielded by one light shielding part of the light shielding body just before making one rotation in the circumferential direction, the light shielding body is rotated approximately half the length of the light shielding part. The laser beam is rotated by one pitch in the scanning direction of the laser beam, and the laser beam is preset in the axial direction of the cylindrical body between the time when the laser beam is blocked by the light shielding part and the time when it leaves the light shielding body. A method for laser hardening the inner surface of a cylindrical body, which is characterized by moving only the pitch.