TWI571342B - Laser welding device - Google Patents

Description

Laser welding device

This invention relates to a laser welding technique and, more particularly, to a laser welding apparatus.

Laser processing has been flourishing in the past two decades. Among them, laser processing has been widely replaced by traditional machining because of its high precision, high speed and low thermal effect. Since the processing mechanism uses a laser source, and different materials have different absorption rates for the laser wavelength, for example, some metals (such as copper or aluminum) have high reflectivity to the laser source and have fast heat conduction, which is not easy to process. Moreover, because such a material absorption rate is low, a large amount of laser energy is reflected, and it is easy to reflect and damage the laser processing head.

Therefore, many methods of assisting laser welding have been derived, such as tungsten inert gas (TIG)-assisted laser welding technology or green laser-assisted IR laser (1064 nm) welding technology, and the auxiliary heat source is mainly Functions include (1) increasing the temperature of the material itself to increase the absorption rate of the processed laser source, and (2) providing additional energy to the material absorption to aid in processing efficiency.

Taking the green laser-assisted IR laser welding technology as an example, the copper plate welding process is performed with an IR 1064nm 1000W laser source, supplemented by a 70W green laser. The light source, because the absorption rate of copper to IR 1064nm is very low, only about 3% at normal temperature, so the use of high-absorption green laser as an aid, although the temperature of the copper plate can be increased, thereby enhancing the copper plate to IR 1064nm Absorption rate. However, such an architecture requires two kinds of laser sources, which increases the cost burden, and a large amount of laser energy is wasted, and a large amount of laser reflection is also likely to cause work safety problems.

The present invention provides a laser welding apparatus capable of recovering laser scattered reflected light and then incident on a workpiece to fully utilize the laser source energy.

The laser welding apparatus of the present invention includes a laser processing head and a light collecting means. The incident spot of the laser processing head has an angle with the normal to the illuminated portion of the workpiece, and the workpiece has a reflectivity greater than 20% for the incident spot. The light collecting device is disposed on the same side of the laser processing head as the workpiece, and collects the laser scattered reflected light reflected from the irradiated portion of the workpiece, and is incident again at a re-incidence angle greater than the angle The irradiated portion of the workpiece.

Based on the above, the present invention can improve the absorption rate of the material by using a laser source that is wasted by reflection during processing, and recovering the laser-scattered reflected light by the light collecting device, thereby increasing the absorption rate of the material, thereby improving the overall laser energy. The absorption ratio can make full use of the energy of the laser source, and it can also reduce the safety of the work.

The above described features and advantages of the invention will be apparent from the following description.

100‧‧‧Laser welding device

102‧‧‧Laser processing head

104‧‧‧Light collecting device

106‧‧‧ incident spot

108‧‧‧Workpiece

108a, 402‧‧‧ irradiated parts

110‧‧‧ normal

112‧‧‧Laser scattered reflected light

114, 116, 202, 214, 400, 404, 406, 408‧‧‧ spherical mirrors

200, 206, 208, 212‧‧ ‧ flat mirrors

204, 210, 216‧‧ ‧ focusing lens

θ ‧‧‧ angle

Γ‧‧‧re-incidence angle

1 is a schematic view of a laser welding apparatus in accordance with an embodiment of the present invention.

2A to 2F are schematic views of a modification of various light collecting devices of the laser welding apparatus of Fig. 1.

Fig. 3A is a simulation diagram of the angle between the incident spot of the laser welding apparatus of the embodiment and the normal of the irradiated portion of the workpiece.

Fig. 3B is a simulation diagram showing an angle between the incident spot of the laser welding apparatus of the embodiment and the normal line of the irradiated portion of the workpiece.

4A is a schematic view showing the relationship between the position of the light collecting means of FIG. 3A and the radius of curvature.

4B is a schematic view showing the relationship between the position of the light collecting means of FIG. 3B and the radius of curvature.

Figure 5 is a graph plotting the variation of the percentage of collected light on a curved surface simulated by laser incident light.

Fig. 6 is a graph showing the re-incidence power and the welding width of Experimental Example 1.

Fig. 7 is a graph showing re-incidence power and weld width of Experimental Example 2.

1 is a schematic view of a laser welding apparatus in accordance with an embodiment of the present invention.

Referring to FIG. 1, the laser welding apparatus 100 of the present embodiment includes at least a laser processing head 102 and a light collecting device 104. The incident spot 106 of the laser processing head 102 has an angle θ with the normal 110 of the illuminated portion 108a of the workpiece 108, wherein the workpiece 108 has a reflectivity greater than 20% for the incident spot 106, such as a high reflectivity metal such as copper or aluminum. Materials, but the invention is not limited thereto. The light collecting device 104 is disposed on the same side of the laser processing head 102 as the workpiece 108 for collecting the laser scattered reflected light 112 reflected from the irradiated portion 108a of the workpiece 108, and at a re-incidence angle larger than the angle θ . γ is again incident on the irradiated portion 108a of the workpiece 108. Although only one light collecting device 104 is illustrated in FIG. 1, it is contemplated that an additional light collecting device may be provided on the same side of the laser processing head 102 to collect reflected light as indicated by the dashed arrows in the figure. Moreover, by design, the number of collections caused by the light collecting means 104 can be one or more times.

In FIG. 1, light collecting device 104 includes a plurality of light collecting elements, such as two spherical mirrors 114 and 116. Therefore, when the incident spot 106 of the laser processing head 102 is incident on the workpiece 108, the spherical mirror 114 can first converge the reflected laser scattered reflected light 112 into a parallel beam and then reflect at an angle to the other spherical mirror 116. The spherical mirror 116 is incident on the workpiece 108 at a re-incidence angle γ greater than the angle θ to be absorbed by the workpiece 108 again, so that the material absorption rate is improved and the overall laser energy is increased by the absorption ratio.

According to the design requirements, the light collecting device 104 can also have various modifications. Please refer to FIG. 2A to FIG. 2F.

In FIGS. 2A and 2B, the light collecting element includes at least one planar mirror 200 and at least one spherical mirror 202. The spherical mirror 202 of FIG. 2A is the laser-scattered reflected light 112 that receives the incident spot 106 from the workpiece 108, and FIG. 2B is the laser-reflected reflected light that the planar mirror 200 receives from the workpiece 108 by the incident spot 106. 112.

In Figures 2C and 2D, the light collecting element includes at least one focusing lens 204 and a plurality of planar mirrors 206 and 208. The light collecting element of FIG. 2C has a single focusing lens 204 that cooperates with the dual plane mirrors 206 and 208. The focusing lens 204 is placed slightly away from the workpiece 108, allowing the reflected laser scattered reflected light 112 to pass through the focusing lens 204. The focus condition is converged, and the plane mirrors 206 and 208 are again guided to overlap the illuminated portion 108a of the workpiece 108. The light collecting element of Fig. 2D has a large-diameter single-piece focusing lens 204, and a part of the reflected light is collected on the left and right sides, and the two-sided conjugated plane mirrors 206 and 208 are divided into two re-incident light to illuminate the irradiated portion 108a.

The light collecting element shown in FIG. 2E then includes a combination of dual focusing lenses 204, 210 and biplanar mirrors 206, 208, which utilizes focusing lens 204 to concentrate the laser scattered reflected light 112 into parallel light and via biplanar mirror 206 and After returning to the angle of re-injection 208, the irradiated portion 108a is focused by the focusing lens 210.

In FIG. 2F, the light collecting element includes a plane mirror 212, a spherical mirror 214, and a focusing lens 216. The laser scattered reflected light 112 is first collected into parallel light by a single focusing lens 216, and reflected by a spherical surface. The mirror 214 is focused and re-incident.

In the present embodiment, the light collecting means 104 may have various combinations of structures as long as it can collect the scattered reflected light and achieve refocusing incidence, and is not limited to the above description. A plurality of metal spherical mirrors can be employed from the viewpoint of reducing the volume and suppressing the thermal lens effect.

Further, the angle θ between the incident spot 106 of the laser processing head 102 and the normal 110 of the irradiated portion 108a of the workpiece 108 is simulated by ZEMAX, preferably between 15 and 30 degrees. 3A and 3B are simulation diagrams of the incident spot and the normal angle of the irradiated portion of the workpiece at 15 degrees and 30 degrees, respectively. Shown in Figure 3A is the path of the focused spot after re-incidence by the concentrating device (two spherical mirrors 114, 116); and the size and energy distribution of the focused spot are optically simulated by ZEMAX, and it is observed that the light is collected. The spot that is incident on the workpiece 108 by the device 104 can reach an approximately the same size as the initial incident spot, and the light intensity is not lowered due to the expansion of the spot, resulting in a poor effect.

Shown in Figure 3B is the simulated path of the focused spot with an angle θ of 30 degrees, and the ZEMAX optical simulation can observe that the spot size incident on the workpiece 108 through the light collecting device 104 is larger than the initial incident spot, and the shape is slightly Flat long. Therefore, the re-incidence angle γ incident again is preferably 45 degrees or less.

As for the radius of curvature of the light collecting elements of the light collecting device (such as the two spherical mirrors shown in FIGS. 3A and 3B), the spherical reflection is known according to the relationship between the scattered light angle and the intensity distribution, that is, the energy is proportional to cos(θ). The size of the mirror and its distance from the scattered light source determine how much energy is collected. That is, the size of the focusing mirror (such as a spherical mirror) and the distance from the scattered light source determine the percentage of the collected light energy; for example, the radius of curvature of the spherical mirror is twice the distance between the center of the spherical mirror and the illuminated portion.

For example, FIG. 4A is a schematic diagram showing the relationship between the position of the light collecting device of FIG. 3A and the radius of curvature. In FIG. 4A, the distance between the center of the spherical mirror 400 and the portion to be irradiated 402 is 50 mm, so that the first spherical mirror 400 provided may have a radius of curvature of 100 mm and a size of, for example, 2 inches. Spherical mirror 400 is calculated Approximately ±20 degrees of scattered light can be received. If the first spherical mirror 400 is rotated clockwise, the scattering angle of the received scattered light can be increased, but the angle of re-incidence is also increased, and the data can be scaled up according to the data. Then, when the light is incident on the irradiated portion 402 through the second spherical mirror 404, the distance between the center and the irradiated portion 402 is 103 mm, so the radius of curvature of the second spherical mirror 404 can be 206 mm, and the size is, for example, 2 miles.

4B is a schematic view showing the relationship between the position of the light collecting device of FIG. 4A and the radius of curvature. In FIG. 4B, the distance between the center of the first face spherical mirror 406 and the portion to be irradiated 402 is 50 mm, so that the first face spherical mirror 406 provided may have a radius of curvature of 100 mm and a size of, for example, 1 inch. Because the spherical mirror has an angle with the optical axis, it is calculated that it can receive about ±25 degrees of scattered light. If the first spherical mirror 406 is rotated clockwise, the scattering angle of the received scattered light can be increased, but the angle of re-incidence is also increased, and the data can be scaled up according to the data. When the light is incident on the illuminated portion 402 through the second spherical mirror 408, the distance between the center and the illuminated portion 402 is 46 mm, so the radius of curvature of the second spherical mirror 408 can be 92 mm, and the size is, for example, 1 inch. Inches.

In the above double spherical mirror architecture, each incident angle corresponds to a suitable structural parameter, including a radius of curvature, a spherical mirror size, a spherical mirror spacing, a re-incidence angle, and the like. The larger the angle of incidence (ie, the angle θ of Figure 1), the larger the size of the spherical mirror used, and the larger the angle of re-injection (ie, the re-incidence angle γ of Figure 1), the spacing between the two spherical mirrors. The larger the size, the larger the module size. Amplification can increase the distance between the module and the workpiece, and is beneficial for adding other devices such as a blower or a height measuring module.

In addition, if the light collecting elements of the light collecting device are the structures of a plane mirror and a spherical mirror as shown in FIGS. 2A and 2B, the radius of curvature of the spherical mirror can be modified according to an imaging formula to satisfy the following formula:

Where p is the distance between the center of the spherical mirror and the illuminated portion, q is the distance between the center of the planar mirror and the illuminated portion, and the radius of curvature R of the spherical mirror is twice, where f is the focal length.

The above embodiments all assume that the surface of the workpiece is a flat surface, but the present invention is not limited thereto. The graph of Figure 5 can be obtained by simulating incident light on a curved surface using ZEMAX and observing the change in the ratio of the surface to the collected light. Thus, if the surface of the workpiece 108 of Figure 1 has a radius of curvature greater than 30 mm, a high collection efficiency can still be maintained.

The experiments are enumerated below to verify the efficacy of the present invention, but the scope of the present invention is not limited to the following experiments.

Experimental example one

Taking a copper test piece as a workpiece, the input laser power of 137W and the heating rate of 200mm/min were used to illuminate. It was found that the device with only the laser processing head without the light collecting device had no obvious bead on the surface of the copper test piece. . On the contrary, the laser welding device with the light collecting device of Fig. 2D and the incident angle (i.e., the angle θ ) is about 30 degrees, which will leave a clear bead on the surface of the copper test piece and be used as a high power optical power meter. The brand Ophir, Detector: Thmeral sensor-L1500W; Powermeter: NOVA II) records its re-incident laser power, and can obtain the graph of re-incidence power and welding width as shown in Fig. 6.

In Fig. 6, since the copper test piece itself conducts heat quickly, it causes temperature instability, so the change is recorded from the laser-welded 10 mm weld bead. It can be seen from Fig. 6 that the rate of change of the welding width is between -7% and 9%, and the rate of change of the re-incident laser power is between -5% and 8%. The average value of the re-incident laser power is divided by the input laser power to obtain a re-incident laser power ratio of approximately 38%.

Experimental example 2

An aluminum test piece was taken as a workpiece, and the input laser power was 405 W and 426 W, respectively, and the heating rate was 200 mm/min. It was found that the device using only the laser processing head without the light collecting device had no surface on the aluminum test piece. Obvious weld bead. Conversely, a laser welding device having a light collecting device as shown in FIG. 4B, regardless of the energy of 405 W and 426 W, will leave an obvious weld bead on the surface of the aluminum test piece, and the device can record its re-incident laser power. A graph of re-incidence power and weld width shown in FIG.

It can be seen from Fig. 7 that the rate of change of the welding width is between -5% and 5%, and the rate of change of the re-incident laser power is between -4% and 5%. The ratio of the re-incident laser power of the average of the re-incident laser power divided by the input laser power is 61%.

It can be proved from the above experimental examples that the light collecting device can collect about 38% (copper) and 61% (aluminum) of the scattered reflection light source, and can effectively generate the melting zone as compared with the non-light collecting device. The re-incidence power and the welding width are both stable, low in cost, simple in structure, and easy to integrate with the laser processing head.

Experimental example three

In order to compare the invention with green laser assisted IR laser welding, the total absorbed energy of the green laser assisted IR laser welding is first estimated.

First, the incident energy of the IR laser is assumed to be 1000 W. Since the absorption rate of copper to the IR laser is only 13%, the absorbed energy is only (1000 × 13% =) 130 W. The green laser provides 70W of incident energy, while the copper absorbs 40% of the green laser, so the absorbed energy is (70 × 40% =) 28W. Therefore, the total absorbed energy of the green laser-assisted IR laser welding is 158W.

If the light is collected and incident again in the first embodiment, the absorbed energy incident using the IR laser is also 130 W. However, the laser energy collected by the light collecting device is about (1000-130=) 870 W, and the ratio of re-incident laser power is 38% (see Example 1), so the absorbed energy incident on the copper test piece is (870 × 38% × 13% =) 43W, so the total absorbed energy can be increased to 173W, which is 9.5% higher than the total absorbed energy of green-light assisted welding.

In summary, the present invention can recover the laser source scattered and reflected during processing by the light collecting device and then inject it into the workpiece to improve the absorption rate of the material, thereby improving the absorption ratio of the overall laser energy, and not only fully utilizing the lightning. The source energy can also reduce the safety of the work.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧Laser welding device

102‧‧‧Laser processing head

104‧‧‧Light collecting device

106‧‧‧ incident spot

108‧‧‧Workpiece

108a‧‧‧Immediated area

110‧‧‧ normal

112‧‧‧Laser scattered reflected light

114, 116‧‧‧ spherical mirror

θ ‧‧‧ angle

Γ‧‧‧re-incidence angle

Claims (13)

A laser welding apparatus comprising: a laser processing head having an incident spot at an angle to a normal of a portion to be irradiated of the workpiece, the workpiece having a reflectance greater than 20% of the incident spot; and a light collecting device corresponding to the workpiece And disposed on the same side of the laser processing head for collecting the laser scattered reflected light reflected from the irradiated portion of the workpiece, and incident on the irradiated portion of the workpiece again at a re-incidence angle greater than the angle . The laser welding apparatus of claim 1, wherein the angle is between 15 degrees and 30 degrees. The laser welding apparatus of claim 1, wherein the re-incidence angle is 45 degrees or less. The laser welding apparatus of claim 1, wherein the collecting means causes the number of collections to be at least one. The laser welding apparatus of claim 1, wherein the light collecting means comprises a plurality of light collecting elements. The laser welding apparatus of claim 5, wherein the light collecting elements comprise a plurality of spherical mirrors. The laser welding apparatus of claim 6, wherein each of the spherical mirrors has a radius of curvature that is twice the distance between a center of the spherical mirror and the irradiated portion. The laser welding apparatus of claim 5, wherein the light collecting elements comprise at least one planar mirror and at least one spherical mirror. The laser welding apparatus of claim 8, wherein the radius of curvature of the spherical mirror satisfies the following formula: Where p is the distance between the center of the spherical mirror and the illuminated portion, and q is the distance between the center of the planar mirror and the illuminated portion, and the radius of curvature of the spherical mirror is twice the f. The laser welding apparatus of claim 5, wherein the light collecting elements comprise a plurality of planar mirrors and at least one focusing lens. The laser welding apparatus of claim 5, wherein the light collecting elements comprise at least one planar mirror, at least one spherical mirror, and at least one focusing lens. The laser welding apparatus of claim 1, wherein the surface of the workpiece has a radius of curvature greater than 30 mm. The laser welding apparatus of claim 1, wherein the surface of the workpiece is a flat surface.