JP2002301583A - Laser welding method and equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize laser welding equipment which is high in reproducibility regardless of the form of material surfaces and is capable of stably performing lap welding of sheets over each other. SOLUTION: The output laser from a main laser oscillator 2 is condensed across a dichroic mirror 81 and galvanomirrors 30 and 31 of a galvanoscanner by a condenser lens 4 onto a work 1. A sub-laser having an irradiation area wider than the irradiation area of the main laser is outputted from a sub-laser oscillator 6 before the pulses of the main laser attain a specified level L1 just once during the pulse widths of the main laser. The sub-laser is transmitted to the galvanoscanner 3 and the condenser lens 4 coaxially with the main laser across a bending mirror 80, beam-condensing position regulating means 9 and the dichroic mirror 81 and is condensed onto the work 1. The work is irradiated with the main laser in the state where the object to be welded is put into a molten state by the sub-laser and the absorptivity to the laser is increased, and therefore the stable lap welding of the sheets over each other can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser welding method and apparatus used for lap welding of at least one thin plate having a thickness of 0.1 mm or less.

[0002]

2. Description of the Related Art As electronic devices become smaller and lighter, for example, a plate material represented by a lead frame of an IC package, a head of a hard disk and the like tends to become thinner year by year. In addition, these plate members are often used by joining a plurality of plate members due to electrical conduction or mechanical characteristics. For this reason, lap welding of two upper and lower plate materials is performed using a pulse laser.

[0003] In particular, when each joint needs to be electrically insulated like a lead frame, or when it is necessary to reduce the amount of heat input to suppress deformation of a plate material like a hard disk head, Spot welding is used.

Here, a conventional spot welding method using a laser will be described with reference to FIGS.

[0005] In the prior art, spot welding using a laser is performed by a laser welding apparatus as shown in FIG.

That is, in FIG. 6, a laser welding apparatus includes a laser oscillator 2 having a laser head 20 and a laser controller 21, an X-axis galvanometer mirror 30 and a Y-axis.
A galvano scanner 3 having an axial galvanometer mirror 31 and transmitting a laser beam output from the laser oscillator 2 and scanning in the XY directions is provided.

The laser welding apparatus also includes a condensing lens 4 for condensing a laser beam on the work 1 and a command for an arbitrary irradiation position to the galvano scanner 3 and a command for the laser irradiation timing to the laser controller 21 at the same time. And a controller 5.

In the laser welding apparatus having the above configuration, the laser output from the laser head 20 is applied to the X-axis galvanomirror 30 in the X-axis direction by the Y-axis galvanomirror 3.
At 1, the respective directions can be changed in the Y-axis direction.

When the laser beams from the galvanometer mirrors 30 and 31 pass through the lens 4 and are condensed on the work 1, the laser condensing position is moved by the galvanometer scanner 3 in the X and Y directions. Is done.

When spot welding is performed at a predetermined position of the workpiece 1, first, the irradiation position and the order are prepared in advance by the main controller 5, and based on the irradiation position and the order, the galvano scanner 3 is positioned by the main controller 5 and the positioning is completed. The timing of the subsequent laser irradiation is instructed to the laser controller 21 respectively.

FIG. 7 is an explanatory view of welding performed by a conventional laser welding apparatus, and is a diagram showing a cross section of the workpiece 1 on which two plate materials are overlapped during and after spot welding.

As shown in FIG. 7A, laser welding basically starts melting from the portion of the plate 1a on the workpiece 1 where the laser is irradiated, and the laser pulse width (irradiation time). The area that is melted by heat conduction according to ()) expands to the lower plate 1b.

For example, when the thickness of each of the upper and lower plate members 1a and 1b is 0.1 mm, a pulse width of 1 to 2 ms is selected. If the pulse width is longer than this, the melting zone penetrates the upper and lower plate members 1a and 1b, but has an excessive heat conduction time. Therefore, as shown in FIG. Are enlarged and the amount of deformation increases.

Conversely, if the pulse width is shorter than 1-2 ms, the area that is melted by heat conduction is reduced, and the upper and lower plate members 1a, 1a
The bonding area of b is reduced.

The power density of the laser depends on the characteristics of the material.
It depends, but 10^Five-10⁶W / cm ^TwoDegree is selected
You. If the power density is higher than this,
Increases the amount of evaporation and plasma, and penetrates the plate materials 1a and 1b.
A through hole is formed. Conversely, when the power density is low
Only heating is performed, and the plate members 1a and 1b do not melt.

At present, as a laser oscillator capable of selecting an appropriate pulse width and power density from the above-described laser processing phenomenon, a pulse-excitation type YAG laser (wavelength 1.
064 μm) is used.

In this laser oscillator, a flash lamp for excitation is turned on with a pulse width of 0.1 to 20 ms, and a pulsed laser corresponding to the pulse width is output. Generally, the absorptivity of a metal to a wavelength of 1.064 μm of a YAG laser is low, and from the viewpoint of the absorptivity alone, the visible light or ultraviolet light has a higher absorptivity, but is suitable for spot welding.
At present, there is no laser capable of outputting visible light and ultraviolet light with a pulse width on the order of s.

Other examples of the prior art include, as summarized in the National Meeting of the Japan Welding Society, Lecture No. 67 (2000-9), “Welding characteristics of various metal materials by different wavelength superimposed laser (2nd report)”, 86, 87. As described on the page, the wavelength 1.064
Research has been conducted on combining a μm YAG laser with a 0.532 μm wavelength Q-switched YAG laser to perform deeper welding than a 1.064 μm wavelength YAG laser alone.

In the case of this prior art, the wavelength is 1.064 μm.
During irradiation with YAG laser of m, Q of wavelength 0.532 μm
The purpose is to perform deep welding by irradiating the pulse of the switch YAG laser many times to form a deeper keyhole, which is an appropriate technique when a thick plate material is used as an object.

[0020]

However, according to the above-mentioned prior art, when a thin metal used for an IC package or a hard disk is spot-welded by using a YAG laser, the metal has a low absorptivity. Problems arise.

FIG. 8A shows a change in laser output (power) with respect to time, FIG. 8B shows a change in absorptivity of the metal material with respect to time, and FIG. 8C shows a power absorbed with respect to time. FIG. 4 is a diagram schematically illustrating the change of the data.

As shown in FIG. 8A, the laser pulse requires a certain period of time from the rise due to the reactance in the power supply circuit to reach the peak value, and has a waveform as shown in the figure.

As shown in FIG. 8B, if the target material is an iron-based metal, the absorption at room temperature with respect to the YAG laser is about 30%. As the temperature rises, the absorptivity increases, and when it melts, the absorptivity rises sharply.

As shown in FIG. 8C, the absorption power, which is the product of the change in the laser output and the absorptivity, is small in the first half of the pulse and rapidly increases in the second half of the melting. In spot welding that is actually performed by melting a material, the duration of a portion having a high absorption in the latter half greatly contributes because it depends on the expansion time of the melting region due to heat conduction and the absorption power.

Here, when the target material becomes thin, the melting depth may be small, so that the pulse width of the laser is short.
Regarding the power density, too much power evaporation at the surface with an excessive power density increases the possibility that a thin melted portion blows off at that pressure. Therefore, the power density is set smaller as the plate thickness becomes thinner.

In the laser output waveform shown in FIG. 8, the pulse width is short and the peak power is also low. For this reason, the duration in the high absorption rate in the latter half, which contributes to melting, is further reduced.

Accordingly, for the same laser power waveform as shown in FIG. 9A, a slight time change (t) from the time when the material surface reaches the melting point and the time when the material surface begins to be rapidly absorbed is started.
a, tb, tc), as shown in FIG. 9 (b), the duration at high absorption changes significantly.

The slight time change (ta, tb, tc) until the start of the rapid absorption is caused particularly by the surface condition. For example, it changes depending on the oxidation state of the material surface, surface roughness, etc.In extreme cases, it only heats the surface without leading to sudden power absorption, or holes are easily formed only in thin plate thickness due to excessive absorption. There are problems, such as danger. Further, the joint area between the upper and lower plates also changes depending on the amount of power absorption that tends to fluctuate.

Therefore, at least one of the plate thicknesses is 0.1
There has been a demand for a method and apparatus for joining thin plates having a thickness of less than 1 mm, which has high reproducibility and can perform stable lap welding regardless of the state of the material surface.

An object of the present invention is to realize a laser welding method and apparatus capable of performing stable superposition welding of thin plates with high reproducibility regardless of the state of the material surface.

[0031]

In order to achieve the above object, the present invention is configured as follows. (1) In a laser welding apparatus having a laser oscillator that oscillates a pulsed laser and a processing optical system that guides a laser output from the laser oscillator to a processing position of a workpiece, a first pulse width and a first pulse width are set. A main laser oscillator for outputting a main laser having a wavelength of 1; a second laser having a second pulse width shorter than the first pulse width of the main laser; and a second laser having a second wavelength shorter than the first wavelength. A sub-laser, and the main laser and the sub-laser are substantially coaxial,
A light condensing means for irradiating the welding target and a trigger controller for controlling the rising timing of each pulse output of the main laser and the sub-laser so that the sub-laser rises after the main laser rises.

(2) Preferably, in the above (1),
The trigger controller controls a rise time so that the sub-laser rises before the power level of the main laser reaches a maximum value.

(3) In the laser welding method for irradiating a thin plate to be welded with a laser to weld the welded object, a main laser having a first pulse width and a first wavelength; The second pulse width shorter than the first pulse width and the first
Using a secondary laser having a second wavelength shorter than the wavelength of the main laser, and irradiating the welding target with the main laser in time advance, and then, during a pulse width period of the main laser, on the welding target, The sub-laser is irradiated to a region including the portion irradiated with the main laser, the pulse width period of the sub-laser is ended before the end of the pulse width period of the main laser, and the welding target is laser-welded.

(4) Preferably, in the above (3),
Before the power level of the main laser reaches the maximum value, the rising timing of the sub-laser is controlled.

In the present invention as described above, a sub-laser having a wavelength with a high absorptivity to the object to be welded and a short pulse width is irradiated on the surface of the object to be welded prior to the maximum power level of the main laser.

Thus, a very shallow portion of the surface to be welded is melted by the auxiliary laser, and the maximum power level portion of the main laser is irradiated before the melted portion solidifies, that is, while the absorptance is high. become. Therefore,
The main laser is absorbed by the welding object with a high absorption rate over the entire pulse width regardless of the surface condition of the welding object,
The welding target is melted by heat conduction to a predetermined depth according to the input energy and the pulse width, and stable welding with high reproducibility, suppressed deformation, can be performed.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a laser welding method and apparatus according to the present invention will be described below with reference to FIGS. FIG. 1 is a schematic configuration diagram of a laser spot welding apparatus according to one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a work to be welded, 2 denotes a main laser oscillator having a pulse width and power for achieving a predetermined welding depth, and the main laser oscillator 2 includes a laser head 20 and a laser controller 21. And

Reference numeral 3 denotes a galvano scanner. The galvano scanner 3 includes an X-axis galvanometer mirror 30 and a Y-axis galvanometer mirror 30.
And an axial galvanometer mirror 31. Reference numeral 4 denotes a condenser lens, and reference numeral 5 denotes a main controller.

Reference numeral 6 denotes a sub-laser oscillator having a pulse width shorter than that of the main laser oscillator 2 and a wavelength having a high absorptivity for the work 1. The sub-laser oscillator 6 includes a laser head 60 and a laser controller 61. And

Reference numeral 7 denotes a trigger controller, reference numeral 80 denotes a bending mirror, and reference numeral 9 denotes condensing position adjusting means. The condensing position adjusting means 9 adjusts the condensing position of the laser output from the sub-laser oscillator 6.

Reference numeral 81 denotes a dichroic mirror. The dichroic mirror 81 transmits the laser beam from the main laser oscillator 2 and reflects the laser beam from the sub laser oscillator 6 to the galvano mirror 31.

Here, the laser used is a YAG laser of a pulse excitation type which is output from the main laser oscillator 2 and has a pulse width of the order of ms.
The wavelength is 1.064 μm.

On the other hand, the laser output from the sub-laser oscillator 6 generally has a higher absorptivity for metal as the wavelength is shorter, and can output a pulse width sufficiently shorter than the ms order. .532 μm or 0.353 μm, and the pulse width is several tens to several hundreds n
An s Q-switched YAG laser is desirable.

In the laser spot welding apparatus having the above configuration, the laser beam output from the main laser oscillator 2 passes through the dichroic mirror 81 and
Reflected by the galvanomirrors 30 and 31 of the condenser lens 4
Is focused on the work 1.

The mirror 30 of the galvano scanner 3
The light condensing position moves in the X direction and the Y direction on the work 1 by the rotation of 31.

On the other hand, the laser beam emitted from the sub-laser oscillator 6 has its direction changed by the bending mirror 80, passes through the condensing position adjusting means 9, is reflected by the dichroic mirror 81, and from here the main beam. The beam is transmitted coaxially with the laser beam from the laser oscillator 2 to the galvano scanner 3 and the condenser lens 4, and is focused on the work 1.

The focusing position of the condenser lens 4 changes depending on the wavelength of the transmitted laser beam. In one embodiment of the present invention, the focusing position is adjusted according to the wavelength of the laser output from the main laser oscillator 2.

Therefore, the wavelength of the laser output from the sub-laser oscillator 6 is different from the wavelength of the laser output from the main laser oscillator 2. If the light is transmitted through the condenser lens 4 without passing through the lens, the focal position is shifted from the work 1.

Therefore, the laser output from the auxiliary laser oscillator 6 needs to be transmitted through the condenser lens 4 via the condenser position adjusting means 9 and focused on the work 1.

FIG. 2 is a schematic structural view of an example of the condensing position adjusting means 9. In FIG. 2, the focusing position adjusting means 9
The sub-laser oscillator 6 includes two lenses 9a and 9b.
It is assumed that the laser beam having the divergence angle θo output from the laser beam passes through the first concave lens 9a, spreads at an angle θ, and is incident on the second convex lens 9b. In this case, the divergence angle θ1 of the laser beam that has passed through the second convex lens 9b is
The following equation (1) is obtained.

Θ ₁ = tan ⁻¹ {(r ₀ + Ltan θ) / f ₁ −tan θ} (1) where r ₀ is the beam radius at the first lens 9 a, and L is the two lenses 9a, the distance between 9b, f ₁ is a convex lens 9b
Is the focal length.

From the above equation (1), the two lenses 9a, 9
By changing the distance L between b, the divergence angle θ ₁ changes. The laser beam having the divergence angle θ ₁ is focused by the focusing lens 4, and the focusing position d is expressed by the following equation (2).

D = f ₄ r ₄ / (r ₄ −f ₄ tan θ ₁ ) (2) where f ₄ is the focal length of the condenser lens 4, and r ₄ is the beam radius of the condenser lens 4 And the incident angle θ to the condenser lens 4
_The light condensing position d changes according to 1.

As described above, the position at which light is condensed by the condensing lens 4 can be varied by the light condensing position adjusting means 9, and the laser from the sub-laser oscillator 6 can be condensed on the work 1. it can.

FIG. 3 is an internal configuration diagram of the trigger controller 7. In FIG. 3, the trigger controller 7
The delay circuits 70 and 71 are provided.

A delay time of t0 is provided by the delay circuit 70 and a delay time of t1 is provided by the delay circuit 71 in response to the laser irradiation command TP from the main controller 5, so that the laser controller 21 for the main laser and the laser controller 61 for the sub-laser are provided. Trigger signals TP0 and TP1 for laser output are output.

By the trigger signals TP0 and TP1,
The main laser oscillator 2 and the sub-laser oscillator 6 emit laser only one pulse for one trigger signal TP.

With the above configuration and function, the lasers output from the main laser oscillator 2 and the sub-laser oscillator 6 are spatially the same optical axis and temporally respond to one trigger signal TP. After the delay time, the work 1 is irradiated one pulse at a time.

Next, a laser spot welding phenomenon using the laser welding apparatus according to one embodiment of the present invention will be described.

FIG. 4 shows the power density distribution of the laser radiated onto the work 1. The maximum power of the main laser is larger than that of the sub laser. If the dotted line in FIG. 4 is the threshold level Th of the power density for melting the surface of the workpiece 1, the light-condensing position adjusting means 9 is adjusted so that the spot diameter of the threshold level Th becomes larger for the sub-laser. Is set by

FIG. 5 is a diagram showing a pulse waveform of the laser output based on the trigger signals TP0 and TP1 output from the trigger controller 7.

As shown in FIG. 5A, first, a delay time t is applied to a command TP from the main controller 5.
The delay time t1 is set so that the output of the main laser starts at 0 and the sub-laser is output during the rise. For example, t1−t0 = 10 μs.

The delay time t1 is shorter than the time required for the power level of the main laser to reach, for example, 10 ⁵ W / cm ² . Further, preferably, assuming that the time from the rise of the main laser to the start of the fall is T, t1-t0 is about T / 10.

In other words, the delay times t0, t0, t0,
1. The beam diameter and power level of the main laser and the sub-laser are determined.

When the work 1 is irradiated with laser with the pulse waveform and the spatial distribution as described above, first, the surface of the work 1 is extremely irradiated by irradiating the sub-laser over a wide area earlier than the main laser rises to a certain level. A shallow range becomes a molten state. Then, within the time that this molten state is maintained, the main laser is irradiated in that area,
It is started up to a predetermined level.

Since the absorptivity with respect to the main laser is increased in a state where the work to be welded is molten, the main laser is efficiently absorbed over the entire time of the pulse of the main laser, and heat conduction is performed according to the pulse width. , The welding depth is determined, and welding having a predetermined joining area can be performed.

Here, the work 1
Since the absorption rate is high and the pulse width is short even if the power is somewhat excessive, the depth of melting by heat conduction and the region to be evaporated are extremely small, and do not pose a problem.

Therefore, only the vicinity of the surface can be reliably brought into the molten state without being influenced by the surface condition of the work 1.

When a reliable melting state can be realized, the power incident on the main laser surely contributes to the expansion of the melting of the work 1 and can be reproduced in accordance with the accuracy of the laser power and the pulse width without being influenced by the surface state. High deformation, reduced deformation,
Stable welding can be performed.

Assuming that the sub-laser pulse is irradiated a plurality of times during the long pulse width of the main laser, the sub-laser pulse during the rising of the main laser pulse only contributes to the melting of the surface of the work 1. Subsequent pulses of the sub-laser are applied to the work 1 already in the molten state, and serve as an energy source from the molten state to the evaporation.
The possibility that a through hole is formed in the work 1 increases.

Similarly, the pulse of the sub-laser is irradiated only once. However, assuming that the pulse of the main laser is irradiated after rising to the above-mentioned constant level, the pulse of the work 1 is influenced by the surface condition of the work 1. In this case, the sub-laser is applied to a portion that has just been overheated or has already been melted.

For this reason, in the former state, that is, in the overheated state, the absorption rate increases, and in the latter state, that is, in the molten state, it contributes to the formation of holes (through holes), and the welding becomes unstable.

When the irradiation area of the sub-laser is smaller than that of the main laser, only the central part of the irradiation area of the main laser contributes to the improvement of the absorptivity, and the power density distribution of the laser is high near the center. In addition, evaporation near the center advances, and the possibility of puncturing increases.

Therefore, as described above, the sub-laser has an irradiation area wider than the irradiation area of the main laser, and the pulse of the main laser is changed to a fixed level L1 (for example, once) during the pulse width of the main laser. It is necessary to irradiate before reaching 10 ⁵ W / cm ² ).

In the above-described example, the light-condensing position adjusting means 9 is used. However, the light-condensing position adjusting means 9 is not used, and the two lasers of the main laser and the sub-laser are equivalent. The condensing lens 4 may be configured so as to be at a suitable condensing position.

Although the above-described example is an example in which the present invention is applied to spot welding, the present invention can be applied not only to spot welding but also to continuous welding.

[0077]

According to the present invention, it is possible to realize a laser welding method and apparatus capable of performing stable superposition welding of thin plates with high reproducibility regardless of the state of the material surface.

That is, the laser emitted from the main laser is absorbed by the material at a high absorption rate over the entire pulse width without being influenced by the surface condition of the material, and the laser is emitted at a predetermined rate according to the input energy and the pulse width. The work is melted by heat conduction to a depth of, and stable welding can be performed with high reproducibility and with suppressed deformation.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laser spot welding apparatus according to one embodiment of the present invention.

FIG. 2 is an internal configuration diagram of a light-condensing position adjusting means in the example shown in FIG.

FIG. 3 is an internal configuration diagram of a trigger controller in the example shown in FIG.

FIG. 4 is an explanatory diagram of irradiation distributions of a main laser and a sub-laser in one embodiment of the present invention.

FIG. 5 is an explanatory diagram of a pulse waveform and an absorptivity change of a main laser and a sub laser.

FIG. 6 is a schematic configuration diagram of an example of a laser pulse welding apparatus according to the related art.

FIG. 7 is an explanatory view of a cross section of a work on which laser pulse welding has been performed in a conventional technique.

FIG. 8 is an explanatory diagram of a laser pulse waveform and a change in absorptance;

FIG. 9 is an explanatory diagram of a variation example of laser power absorption.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Work 2 Main laser oscillator 3 Galvano scanner 3a, 3b Galvano mirror 4 Condensing lens 5 Main controller 6 Sub-laser oscillator 7 Trigger controller 9 Condensing position adjusting means 9a Concave lens 9b Convex lens 20, 60 Laser head 21, 61 Laser controller 70, 71 Delay circuit 80 Bending mirror 81 Dichroic mirror

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshiya Nagano 650 Kandamachi, Tsuchiura-shi, Ibaraki F-term in Hitachi Construction Machinery Finetech Co., Ltd. (Reference) 4E068 BF01 CA02 CA03 CD02 DA14 DB01

Claims (4)

[Claims] 1. A laser welding apparatus comprising: a laser oscillator that oscillates a pulsed laser; and a processing optical system that guides a laser output from the laser oscillator to a processing position of a workpiece. And a main laser oscillator for outputting a main laser having a first wavelength; a second laser having a second pulse width shorter than the first pulse width of the main laser; and a second laser having a second wavelength shorter than the first wavelength. A sub-laser oscillator for outputting a laser beam; a condensing means for irradiating the main laser and the sub-laser substantially coaxially to a welding object; and a main laser and a sub-laser so that the sub-laser rises after the main laser rises. And a trigger controller for controlling a rise time of each pulse output of the laser. 2. The laser welding apparatus according to claim 1, wherein
The laser welding apparatus, wherein the trigger controller controls a rising time so that the sub-laser rises before the power level of the main laser reaches a maximum value. 3. A laser welding method for welding a welding target by irradiating a thin plate to be welded with a laser, comprising: a main laser having a first pulse width and a first wavelength;
Using a sub-laser having a second pulse width shorter than the first pulse width and a second wavelength shorter than the first wavelength, irradiating the welding target with the main laser in time advance, and thereafter, the main laser During the pulse width period, the sub-laser is irradiated to a region on the welding target including the portion irradiated with the main laser, and before the end of the pulse width period of the main laser, the pulse width period of the sub-laser And a laser welding method for laser welding the object to be welded. 4. The laser welding method according to claim 3, wherein
A laser welding method characterized in that a rise timing is controlled so that the sub-laser rises before the power level of the main laser reaches a maximum value.