JPH07252521A - Quenching method by laser beam - Google Patents

Abstract

PURPOSE:To prevent the formation of a softened layer by tempering and to form a uniform quenched layer, at the time of quenching the outer peripheral surface of a tubulous or a columnar material by using laser beam. CONSTITUTION:The laser beam 2 is emitted from a CO2 laser beam oscillator 1 and irradiates the tubulous or the columnar material 3 through a concave cylindrical mirror 5 and a flat integration mirror 6. As the irradiating shape of the laser beam 2, a diameter in the rotating direction of the tubulous or the columnar material 3 is made to be larger than a diameter in the longitudinal direction. By this method, the quenched layer is formed on the wide area in the surface of the tubulous or the columnar material 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quenching method using a laser beam on the outer peripheral surface of a tubular or cylindrical object such as various rotary shafts.

[0002]

2. Description of the Related Art When quenching the surface of a tubular or cylindrical object, the surface of the tubular or cylindrical object rotating about its axis is irradiated with a focused laser beam to obtain a quench-hardened layer having a width equal to the diameter of the laser beam. Methods are commonly used. Alternatively, a method of obtaining a spiral quenching layer on the surface layer of a tubular or columnar object by sequentially irradiating with a laser beam that is scanned in the longitudinal direction at the same time while rotating the tubular or columnar object at low speed with respect to the axis Has been. FIG. 4 shows the configuration of an optical system for obtaining the spiral quenching layer.

[0003]

According to the conventional methods, the laser beam is once radiated on both sides, and the laser beam is radiated again on the hardened or hardened part or its vicinity, so that the tempering is effected by the thermal effect of reheating. As a result, a softened layer is formed, and a quenching layer that is uniform and continuous in the longitudinal direction cannot be obtained. FIG. 2 (a) shows the temperature transition of the surface of the steel material to be processed in the conventional method in which the spiral quenching layer is generated.
As described above, in the conventional method, after the transformation point T _{Ac1 is} reached by heating and temperature rise by the laser beam, the material is not cooled at a cooling rate higher than the critical cooling rate, and is reheated before reaching T _Ms to form a tempered layer. It is the cause.

[0004]

According to the present invention, in a quenching method using a laser on the outer peripheral surface of a tubular or cylindrical object, the diameter of the laser beam with which the tubular or cylindrical object is irradiated in the rotational direction is the longitudinal direction. It is a laser hardening method characterized by being larger. The ratio of the diameter in the rotation direction to the diameter in the longitudinal direction is preferably 2 or more.

[0005]

In the present invention, reheating is performed while the temperature of the tubular or columnar object stays at the transformation point T _Ac1 or higher, and the cause of the tempered layer is eliminated.

The laser beam is focused so as to have a high energy density of 103 W / cm ² or more required for quenching. The beam diameter in the rotation direction is set to a length that allows the outer peripheral surface of the tubular or cylindrical object to uniformly reach T _Ac1 or more while maintaining the increased temperature due to heat input of laser beam irradiation after several rotations. The beam diameter in the longitudinal direction holds the rising temperature due to the heat input of the laser beam irradiation after one rotation, and when the heating portion by laser irradiation is displaced in the longitudinal direction by the rotation pitch, the adjacent heating portions are not interrupted by T _{Hold Ac1} or higher and make the length such that this temperature range is continuous.

FIG. 3 shows the thermal history of the surface of a tubular or cylindrical object in the rotational direction and the longitudinal direction. The laser irradiation part keeps the rising temperature due to the heat input of the laser beam irradiation before one rotation,
By rotating at a relatively high speed so that the total integrated temperature rises to T _Ac1 or more after several revolutions, the outer peripheral surface of the tubular material is artificially simultaneously irradiated with the laser beam from all directions. Further, a laser beam is relatively sent to the tubular or cylindrical object in the longitudinal direction, and T _Ms is cooled at a cooling rate higher than the critical cooling rate by self-cooling or forced cooling from the outside.
The quenching is performed by irradiating a large area with a laser beam by giving a feed rate such that it is rapidly cooled down to control the thermal history of the surface layer of the tubular or cylindrical object. As a result, a uniform hardened layer is formed on the surface layer of the tubular or columnar object without a softening layer due to tempering.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the apparatus used in the embodiment. 15k
A φ 70 mm ring mode laser beam 2 emitted from a CO ₂ laser oscillator 1 of W is incident on an optical system composed of a concave cylindrical mirror 5 and a plane integration mirror 6 of f = 1240 mm, and the concave cylindrical mirror 5 unidirectionally directs it. And a linear beam having a length of 50 mm was obtained at the focal position. The plane integration mirror 6 can freely change and fix the reflection direction of the laser beam by tilting each segment mirror in an arbitrary direction, smoothing the energy intensity distribution of the laser beam on the workpiece, and hardening layer. It is used to control the depth and shape of the.

The focused beam size thus obtained was 3 mm × 50 mm, and a linear beam focused at a high energy density of 104 W / cm ² at a laser output of 15 kW could be obtained. As shown in FIG. 3, the longitudinal direction of the focused laser beam 2 and the longitudinal direction of the tubular or columnar object 3 were arranged to be perpendicular to each other. An antireflection material was applied in advance on the surface of the tubular or columnar object 3 in order to suppress reflection of the laser beam 2 and to prevent a decrease in heat input to the tubular or columnar object 3. At this position, the semicircular surface of the tubular or cylindrical object 3 was irradiated with the linear beam having the above-mentioned shape while rotating the tubular or cylindrical object 3 with φ50 mm and length l = 200 mm at a high speed of 280 rpm or more. When the tubular or cylindrical object 3 is rotated, it is scanned in the longitudinal direction at a feed rate of 1.5 m / min or more at the same time as the rotation, and if cooling is required to obtain a cooling rate of a critical cooling rate or more immediately after laser irradiation, a cooling material. The amount of heat input to the tubular or cylindrical object 3 and the thermal history were controlled by spraying. In this way, regarding the temperature distribution of the heated portion and the non-heated portion by laser irradiation, the target quenching portion is uniformly heated by rotating the tubular or cylindrical object 3 at high speed, and after reaching the predetermined transformation temperature, the longitudinal direction is reached. The tubular or cylindrical object 3 is fed to the inside of the tubular or cylindrical object 3, and the tubular or cylindrical object 3 is self-cooled due to a temperature difference between the inside and the inside of the tubular or cylindrical object 3, or is sprayed with a coolant from the outside, so that the tubular or cylindrical object 3 has a uniform infinite length A hardened layer with a large surface was obtained.

[0011]

According to the present invention, a quenching layer can be formed in a wider area on the surface of a tubular or cylindrical object than in the conventional case. Alternatively, a uniform hardened layer without a softening layer due to tempering caused by reheating due to multiple irradiation with a laser beam can be efficiently processed over a wider range than in the past. This has the effect of improving the wear resistance of the rotary shaft or the reciprocating sliding portion.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus used to carry out the present invention.

FIG. 2 is a diagram showing a comparison of temperature transitions on the surface of a tubular or cylindrical object in the conventional method and the method of the present invention.

FIG. 3 is a diagram showing a temperature distribution on the surface of a tubular or cylindrical object during laser irradiation.

FIG. 4 is a diagram showing a conventional laser irradiation method for a tubular or cylindrical object.

[Explanation of symbols]

1 CO ₂ Laser Oscillator 2 Laser Beam 3 Tubular or Cylindrical Object 4 Bend Mirror 5 Concave Cylindrical Mirror 6 Planar Integration Mirror

Claims (2)

[Claims] 1. A quenching method using a laser on the outer peripheral surface of a tubular or cylindrical object, wherein the diameter of the laser beam with which the tubular or cylindrical object is irradiated in the rotational direction is larger than the diameter in the longitudinal direction. Quenching method. 2. The laser hardening method according to claim 1, wherein the ratio of the diameter in the rotating direction to the diameter in the longitudinal direction is 2 or more.