JPS59144587A - Laser welding method - Google Patents

Abstract

PURPOSE:To decrease the thermal influence on a fine wire having high strength and the stress concentration in the end part of welding in laser butt welding of the fine wire and an equal thickness plate by irradiating a laser to the end part of the plate material apart slightly from the fine wire and welding both materials with the power increased at the beginning and end points. CONSTITUTION:A plate material having the thickness roughly equal to the diameter of a fine wire material having high strength is provided apart from the wire at about 1/2 of the plate thickness. The laser light for irradiating both surfaces by a mirror and a half mirror is moved to irradiate the end part of the plate material, thereby melting the end part and welding the same to the fine wire. The power of the irradiation at a beginning point 8a and an end point 8d is increased in this state. The weld zone having substantial curvature is thus obtd. in the end part 16 of welding and a local stress concentration is eliminated. The laser weld zone having high weld strength is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a laser welding method that is effective for performing welding with high welding strength.

[Prior art]

When laser welding butt joints, it is generally necessary to accurately follow the boundary lines with as few gaps as possible.

The reason for this is that because the spot diameter of the laser beam is small, the laser beam passes through the gap and does not effectively input energy to the welding parts, and the heat transfer efficiency deteriorates, making welding defects more likely to occur. . However, the situation is different in the case of butt welding of the above-mentioned thin wire and flat plate.

FIG. 1 is a schematic diagram of a welding location by a conventional laser welding method. As can be seen from this figure, a depression 2 is formed in a part of the thin wire 1, so that the diameter is not small and the welded end cannot have a sufficient curvature. When bending stress is applied to the thin wire 1 in this state,
Since stress is concentrated at the welded end 2', the fatigue strength against repeated loads is reduced. Furthermore, if the material of the thin wire 1 is a high-strength material, the transverse rupture strength of the material may be reduced due to thermal effects associated with melting. These effects combine to often result in the strength of the welded thin wire being significantly lower than that of the base metal.

[Purpose of the invention]

An object of the present invention is to provide a laser welding method that reduces thermal effects on thin wires, forms smooth fillets at weld ends, and obtains welds with high weld strength.

[Summary of the invention]

In general, there are two factors that reduce the nominal fatigue strength of welded parts: One of these is a decrease in the transverse rupture strength of the base metal due to the thermal effect during welding. This can be further divided into two parts: the melting/solidification process and the transformation in the solid phase.

Another factor is the deviation from the nominal value due to stress concentration in the weld.

When welding is performed using a laser, a welded portion with a narrow solid phase transformation layer can be obtained due to its rapid heating and cooling characteristics. However, the materials used in highly integrated mechanical parts, which have been rapidly developed in recent years, are high-strength materials whose thermal history is a serious issue, and there is an increasing need to bond dissimilar metals. If a laser is used for this type of welding, the molten and solidified layer will have a non-uniform composition, resulting in a low-quality alloy υ, and the transverse rupture strength will decrease. This point is an obstacle to the success of laser welding.

On the other hand, since laser welding does not use filler metal,
Another drawback is that sufficient fillet is not formed in the weld.

The present invention was devised in consideration of this situation. The basic idea is to adopt a joint structure that minimizes heat input into materials with poor weldability, and to use a welding method that creates a shape with sufficient curvature at the welded end after welding. It is in.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

Figure 2 shows a welded joint. In the figure, the thin wire 3 is a high-strength material with poor weldability (for example, tool steel, cemented carbide, elbow, alloy, tungsten).

Ti alloy, etc.), and the flat plate 4 is made of stainless steel, which has a thickness comparable to the diameter of the thin wire 3 and has good weldability.

A gap 5 is provided between the thin wire 3 and the flat plate 4.
There is. The width of this gap 5 is set to a sufficiently short distance (1/2 degree of the thickness of the flat plate 4, for example, 0.1 degrees or less) so that the metal melted by laser beam irradiation flows in and stays there due to its own surface tension. do. Then, welding is performed by irradiating the laser beam 7 from both sides of the flat plate 40 at the same time so that the laser beam spot 6 is at a position shifted from the gap 5 by the length of the radius of the spot 6.

Furthermore, as shown in FIG. 3, half of the spot 8 is on the flat plate 9.
Only when this occurs, the pulse width of the laser beam is shortened and the beak power is increased to remove the portions corresponding to both ends of the weld bead. That is, as shown in Fig. 4, the waveforms are those for welding (8b, 8c) and those for removal processing (8a).

8d) Welding is performed with the following changes.

In this case, in order to detect that only half of the spot 8 hits the flat plate 9, a method using an optical system as shown in FIG. 5.6 can be considered. In FIG. 5, the output light from the processing laser 10 is divided into two parts by a bar mirror 13, and after being focused by a condensing mirror 15, it is irradiated onto a flat plate 9 to perform welding.

On the other hand, in FIG. 6, the output light from the aiming laser 11 is split into two parts by the half mirror 13, and after being focused by the condensing mirror 15, it is directed towards the flat plate 9, but it is temporarily separated from the flat plate 9. In this case, the light is returned to parallel light by the condensing mirror 15, reflected by the cold mirror 14, and reaches the photodetector 16. Therefore, the extent to which the laser beam deviates from the flat plate 9 can be quantitatively detected by monitoring the output of the photodetector 16.

By using such an optical system, the laser beam can be irradiated from both sides of the flat plate 9, so welding can be performed with less energy and in a shorter time than when welding one side at a time. Furthermore, a timing pulse is generated when half of the spot 8 hits the flat plate 9, and sequence control is enabled in which seaming and welding are performed by repeated irradiation pulses while changing the pulse width.

〔Effect of the invention〕

As explained above, according to the present invention, most of the laser light is absorbed by the flat plate, and heat transfer occurs only when the molten metal wets the surface of the thin wire and welding is performed, so welding is performed with less thermal influence. As a result, a decrease in transverse rupture strength of the base material can be suppressed.

In addition, by removing both ends of the weld bead, the seventh
As shown in the figure, since a welded portion with a sufficient curvature is obtained at the welded end 16, local stress concentration is eliminated, and a decrease in fatigue strength is suppressed.

[Brief explanation of drawings]

1 to 3 show the shape of a joint between a thin wire and a flat plate, FIG. 4 shows a pulse waveform, FIGS. 5 and 6 are schematic diagrams of a processing optical system, and FIG. 7 shows an example of a good welded part. 1.3... Thin wire, 4,9... Flat plate, 5... Gap,
8a. 8d... Laser irradiation position for removal processing, 10... Laser for processing, 11... Laser for aiming, 12... Total reflection mirror, 13... Half mirror 114... Cold mirror, 15... ...Condenser mirror, 16...Photodetector. 31st ¥] ¥! lJ4 (2) Figure 5
1 Figure 1/511-f)q (2)

Claims (1)

[Claims] 1. In a method of laser welding a belt-shaped flat plate having a thickness similar to the diameter of a part of a thin wire made of a high-strength material by butting each side of the thin wire, there is a gap between the thin wire and the flat plate. A laser welding method characterized by providing a gap and performing welding by irradiating a laser beam parallel to the welding line and shifted toward the flat plate by a certain distance. 2. In the laser welding method according to claim 1, a step of removing a part of the flat plate is added by increasing the peak power of the laser beam only at the start and end points of the welding part. Laser welding method.