JP4666901B2 - Laser welding method and laser welding apparatus - Google Patents

Description

  The present invention relates to a laser welding method and a laser welding apparatus applicable to spot welding and the like.

  Aluminum alloys, which are light metals, are excellent in workability, corrosion resistance, weldability, electrical conductivity, and thermal conductivity, and are used in various applications such as heat dissipation materials, aluminum cans, and extruded shapes. In addition, magnesium alloy, which is a light metal, has higher strength than plastic and lighter than aluminum, as well as excellent strength, steel properties, thermal conductivity, vibration absorption, etc., and also excellent recyclability. It is used in many applications such as automotive parts such as steering wheels and electronic equipment casings.

  As a welding method for these metals, there is resistance welding in which a strong welding current is passed for a short time and the metal is welded using heat generated on the welding surface. However, an aluminum alloy or the like has extremely good electrical conductivity. Therefore, it is necessary to pass a larger current to the welding pin serving as the electrode than when welding other metal materials, and the electrode is formed of Cu or the like. In the welding pin, Cu is adhered to the welded material or the workpiece to be welded, and the welded material or the workpiece is adhered. For this reason, when welding aluminum alloy etc., the lifetime of a welding pin tends to become short, and the intensity | strength of a welding part also becomes weak compared with the welding of another metal material.

  As a welding method for light metal materials such as aluminum alloy and magnesium alloy, there is laser welding in addition to resistance welding. Laser welding is performed by a laser beam condensed by an optical system, and a high power density can be obtained. Therefore, since melting can be instantaneously generated, high-speed welding is possible. The inventors have studied laser spot welding of a magnesium alloy using a YAG laser as shown in Non-Patent Document 1 as an example.

  Further, Non-Patent Document 1 reports that when the laser beam is focused on the surface of a magnesium alloy serving as a test material, the welding area is narrowed and the welding strength is reduced.

Hisato Ito, Toshikatsu Asahina, Hikaru Toki: Presentation of the 104th Spring Meeting of the Japan Institute of Light Metals, (2003), 181

  The present invention has been made in view of the background art as described above. The purpose of the present invention is to provide a laser capable of improving the welding strength by using a pressure applied to a test material in combination with laser welding of a light metal material. It is providing the welding method and the laser welding apparatus used for this method.

  Another object of the present invention is to provide a laser welding method capable of expanding the welding area and improving the welding strength by positioning the focal point of the laser beam above the specimen, and a laser welding apparatus used in this method. Is to provide.

The laser welding method according to the present invention is a laser welding method in which a light metal plate is laser-welded to a metal plate, the light metal plate is superimposed on the metal plate, and the metal plate and the light metal superimposed using a pair of jigs. Holding the plate with the first pressure, irradiating the light metal plate with a laser beam for a predetermined time from the light metal plate side, and heating the welded portion of the light metal plate to a temperature lower than the melting point of the light metal plate and higher than the softening temperature The laser irradiation is stopped after a predetermined time, and at the same time the laser irradiation is stopped, the metal plate is pressed against the light metal plate from the metal plate side with a second pressurizing force higher than the first pressurizing force. The jig that supports the plate is provided with a protrusion that presses the metal plate locally. The jig that supports the metal plate applies the second pressing force to the metal plate against the light metal plate. Supports light metal plates and light metal plates when pressed That is deformed to the jig side, when irradiating the laser beam to the light metal plate, the output of the laser beam, stepwise or gradually raised to a predetermined level, the metal plate and light metal plates is magnesium alloy.

In the present invention, for example, after performing laser beam irradiation for a predetermined time, pressurization is performed with the second applied pressure and laser irradiation is stopped, so that the welded portion of the light metal plate is dispersed, that is, thinned and the welding strength is weakened. To prevent.

Further, in the present invention, the focal position of the condensing lens constituting the laser head is set above the light metal plate so that the light metal plate is irradiated, and the light metal plate or the work piece to be welded during welding is obtained. The metal plate may be prevented from evaporating, and the light metal plate to be welded may be heated in a large area to a temperature lower than the melting point of the light metal plate and higher than the softening temperature , thereby increasing the joining area and increasing the welding strength. .

Further, the pressurization can be performed from the metal plate side. Further, the jig may use titanium or a titanium alloy as a material having low thermal conductivity in order to suppress heat radiation from the test material .

According to the present invention, a metal plate and a light metal plate, which are superimposed using a pair of jigs, are held with a first applied pressure, and the light metal plate is irradiated with a laser beam for a predetermined time from the light metal plate side. The welded portion is heated to a temperature lower than the melting point of the light metal plate and higher than the softening temperature , and after a predetermined time, the laser irradiation is stopped, and the laser irradiation is stopped. By pressurizing the metal plate against the light metal plate with pressure from the metal plate side and performing the overlap welding, the welding strength can be improved. That is, instead of applying the second pressing force from the start of laser beam irradiation, the welding positions of the light metal plate are dispersed by shifting the laser irradiation and pressurization with the second pressing force in time, that is, It is possible to prevent the weld strength from becoming thinner. And a welding location can be pressurized reliably by a protrusion. In this welding, since the light metal plate is pressed with the second pressure in a state where the light metal plate is heated to a temperature lower than the melting point of the light metal plate and higher than the softening temperature , the protrusion penetrates the metal plate, and the welding strength is increased. It can prevent weakening. In addition, according to the present invention, when the light metal plate is irradiated with the laser beam, the light metal plate is excessively heated to evaporate by gradually or gradually increasing the output of the laser beam to a predetermined level. Can be prevented.

  Hereinafter, a laser spot welding method and a laser spot welding apparatus to which the present invention is applied will be described with reference to the drawings.

  In the laser welding to which the present invention is applied, a magnesium alloy is used for the work piece and the work piece. Specifically, this magnesium alloy is obtained by machining a magnesium alloy having a thickness of 0.6 mm to a length of 75 mm and a width of 20 mm, polishing the front and back surfaces, and degreasing and washing with butanone. The chemical composition of this magnesium alloy is shown in Table 1, and the mechanical properties are shown in Table 2.

  In addition, this magnesium alloy is MS1 prescribed | regulated by Japanese Industrial Standard (JIS), for example.

  As shown in FIG. 1, a laser spot welding apparatus 10 used for this laser spot welding superimposes a magnesium alloy 1 as a workpiece to be welded and a magnesium alloy 2 as a welded product, and a lower jig 11 and an upper jig 12. And hold it between. Specifically, the lower jig 11 serving as the first jig is a support member that supports the superposed magnesium alloys 1 and 2 from the side of the magnesium alloy 1 serving as the workpiece, and serves as the second jig. The upper jig 12 is in contact with the magnesium alloy 2 to be welded, and holds the magnesium alloys 1 and 2 superimposed on the lower jig 11 so as to be sandwiched therebetween. The lower jig 11 further serves as a pressure member that applies pressure to the upper jig 12 side during laser welding, and the magnesium alloy 1 is locally applied to the contact surface with the magnesium alloy 1 that is the workpiece. For example, a protrusion 11a having a diameter of 6 mm is provided for pressing. Further, the upper jig 12 is formed with a through hole 12a for irradiating the magnesium alloy 2 as a welded product with the laser beam B. The diameter of the through hole 12a is, for example, 10 mm. The upper jig 12 serves as a support member in cooperation with the lower jig 11.

  For the lower jig 11 and the upper jig 12, a material having low thermal conductivity is selected in order to efficiently heat the magnesium alloys 1 and 2, and here, a titanium alloy is used. Therefore, a material having high thermal conductivity such as Cu is not suitable. In addition, as long as it is a material with low heat conductivity, a ceramic etc. may be sufficient besides a titanium alloy.

The lower jig 11 holds the magnesium alloys 1 and 2 by applying a first pressurizing force of 32 N, for example, to the upper jig 12 before laser irradiation. Further, when performing laser welding, the lower jig 11 is heated to a temperature lower than the melting point and higher than the softening temperature by applying a second applied pressure larger than the first applied pressure to the upper jig 12 side. The magnesium alloy 2 that is the work piece is pressed and joined to the magnesium alloy 2 that is the welded material in a wet state.

  Provided above the magnesium alloys 1 and 2 held by the lower jig 11 and the upper jig 12 is a laser head 13 serving as a laser irradiation unit so that the optical axis is perpendicular to the magnesium alloys 1 and 2. It has been. The laser head 13 uses a YAG (Yttrium Aluminum Garnet) laser as a light source. In laser welding, a carbon dioxide laser may be used in addition to a YAG laser. The carbon dioxide laser has a high output and is generally used for welding thick plates. However, since the thermal influence is great, the workpiece is distorted. Therefore, in the laser head 13 for the purpose of welding a thin metal plate, a YAG laser having a low output, little thermal influence on the test material, and easy focusing and output control is used. Further, since the YAG laser can be transmitted by an optical fiber, it can be automatically welded by attaching a laser head to the robot. Of course, when welding thick plates, a carbon dioxide laser may be used. Specifically, here, a pulse YAG laser having a maximum average output of 550 W (maximum pulse energy of 70 J) is used. When the laser beam B is applied, the laser output is increased stepwise or gradually to a predetermined level instead of once, and energy is applied stepwise or gradually. Thereby, it can prevent that the magnesium alloys 1 and 2 are heated too much and evaporate.

  Further, the laser head 13 incorporates an optical system composed of a plurality of lens groups including a condensing lens for condensing the laser beam B emitted from the YAG laser above the magnesium alloy 2 that is a weldment. Yes. For example, a condensing lens having a focal length of 80 mm is used in this optical system. The laser head 13 is further provided with a focus mechanism for adjusting the focal position P of the focus lens. The focus mechanism is, for example, a mechanism that raises and lowers the laser head 13 and can adjust the focal position P of the condenser lens in the optical axis direction by raising and lowering the laser head 13. In this example, the focal position P of the optical system is set to a position 12 mm above the magnesium alloy 2 that is the workpiece.

In this laser welding, the focal position P is set above the magnesium alloy 2 which is a welded product. When the focal position P is set on the surface of the magnesium alloy 2 which is a welded product, excessive heat input occurs, the magnesium alloy 2 is evaporated and removed, and the welding strength may be reduced. Further, when the focal position P is set to the surface of the magnesium alloy 1 which is the lower workpiece, the melting and evaporation of the magnesium alloy 2 which is the welding article proceeds, and further, the magnesium alloy 1 which is the workpiece is evaporated and removed. As a result, the welding strength may decrease. In laser spot welding to which the present invention is applied, the focal position P is set above the magnesium alloy 2 which is a welded product, so that the magnesium alloys 1 and 2 are prevented from evaporating at the time of welding. Is heated to a temperature lower than the melting point of the magnesium alloy 2 and higher than the softening temperature , and the welding area is increased to increase the welding strength.

  Further, the laser spot welding apparatus 10 is provided with a gas supply unit 14 for spraying an assist gas or a back shield gas to a welding location in the chamber. Specifically, the gas supply unit 14 sprays an inert gas such as argon or helium on the welding site so that laser welding is performed in an inert gas atmosphere, thereby preventing oxidation of the welding site. Here, the gas in the chamber is replaced for 20 seconds or longer.

In laser spot welding to which the present invention is applied, the magnesium alloys 1 and 2 are fixed with a pressing force of 32 N (first pressing force) before laser irradiation. Next, the laser beam B is applied to the magnesium alloy 1 as a welded material through the through hole 12a of the upper jig 12. Then, the laser beam B is irradiated for a predetermined time, and at least the welded portion of the magnesium alloy 2 to be a welded product is heated to a temperature lower than the melting point of the magnesium alloy 2 and higher than the softening temperature . For example, the magnesium alloy 2 is heated to about 200 ° C. or higher (for example, about 565 ° C. to 600 ° C.). The magnesium alloy 2 is brought into a state of being easily deformed by being heated to about 200 ° C., and being in a semi-molten state by being heated to about 565 ° C. to about 600 ° C. Then, after irradiating the laser beam B for a predetermined time, the lower jig 11 is moved upward to apply a second pressing force higher than the first pressing force, and at the same time, the irradiation of the laser beam B is stopped and the welding is finished. In this laser spot welding, the second pressurizing force is not applied from the start of the laser beam B irradiation, but the laser irradiation and pressurization with the second pressurizing time are shifted in time to weld the magnesium alloy 2. The locations are prevented from being dispersed, that is, thinned and the welding strength is weakened. Of course, as long as welding is possible, the second pressure may be applied from the start of irradiation with the laser beam B. Further, the irradiation time of the laser beam B is not a state in which the welded portion is melted but a time until it is heated to a temperature lower than the melting point of the magnesium alloy 2 and higher than the softening temperature . In this laser spot welding, since the pressurization is performed by the lower jig 11, if the welded part is completely melted, the protrusion 11 a of the lower jig 11 penetrates the magnesium alloy 1 as the workpiece to be welded. Because it ends up.

  Table 3 shows the welding conditions.

  FIG. 2 shows the welding time and the possibility of welding exerted by the laser output when the second applied pressure is 222N. When the total heat input for heating the magnesium alloys 1 and 2 is the product of laser output (Q), laser irradiation time (T), and frequency (F), welding is performed at 10.4 × 10 3 to 13.8 × 103 J or more. It becomes possible. As the irradiation time becomes longer, welding becomes possible with a slightly lower laser output. Although not shown, when the second applied pressure is 194 N, welding is performed at 13.2 × 103 to 14.4 × 103 J, and when the second applied pressure is 250 N, welding is performed at 10.0 × 103 to 11.0 × 103 J or more. did it. From the above, it can be confirmed that welding is possible with a low heat input as the second applied pressure increases.

  FIG. 3 is an appearance photograph of the laser spot weld. The magnesium alloys 1 and 2 as test materials are deformed into a circular convex shape toward the upper jig 12 because the second pressing force is applied by the protrusion 11 a of the lower jig 11. Moreover, the joint fracture | ruptured to the magnesium alloy 2 which is a weldment located in the upper side can be confirmed. This is because the magnesium alloy 2 as a welded product was not heated to a temperature at which plastic deformation was possible, or because the magnesium alloy 2 evaporated due to excessive heat input. In this example, the fractured joint was confirmed, but this fracture can be prevented by adjusting the intensity of the laser beam B.

  FIG. 4 shows the macroscopic and microscopic structure of the laser spot weld cross-section. The deformation | transformation by the protrusion 11a of the lower jig | tool 11 can be confirmed similarly to the external appearance photograph shown in FIG. Looking at the macroscopic picture, the magnesium alloys 1 and 2 are welded at points A and E where the second pressure is applied. This is because the second pressurizing force is applied not only by the heating by the laser beam B but also by the protrusion 11 a of the lower jig 11. In the structure of the welded portion, the inclusions observed at the grain boundaries of the spot welded joint as shown in Non-Patent Document 1 were not observed. The crystal grain size is about 16.2 μm at the A and E points, about 19.2 μm at the B and D points, and about 21.5 μm at the C point, both of which are about 9.4 μm of the base material. Compared to Further, the crystal grains tend to become coarse as the deformation amount increases. The cracks correspond to the fractured joint in FIG. 3, and are not confirmed at the A point and E point, which are joints, but were confirmed only at the most deformed C point.

  FIG. 5 shows the relationship between welding time and tensile shear load. Although the difference in the tensile shear load due to the difference in the second applied pressure and the laser output was not clearly recognized, the tensile shear load showed a high value at the welding time of 40 seconds and 50 seconds in each condition. With regard to the fracture mode, many shear shapes were observed under welding conditions of a welding time of 30 seconds to 50 seconds, and many plug shapes were recognized at 60 seconds. However, no interface type was recognized. The reason why the low strength was exhibited under the condition of the welding time of 30 seconds was that the amount of indentation was small, and a shear fracture was exhibited. The reason why the low strength was exhibited under the condition of the welding time of 60 seconds was that the amount of indentation was large, the thickness of the joint portion was reduced, and the fracture occurred from that point, and it was a plug-type fracture. Further, as the second pressing force increases, the amount of pushing increases, and there is a tendency to cause a plug-type fracture. The joint showing the highest value is when the second applied pressure is 222 N, the welding time is 50 seconds, and the laser output is 23 J and the tensile shear load is 2.4 kN. A relatively stable strength was obtained under the condition that the second applied pressure was 222N. A value of 1.2 kN or higher, which is the maximum value of the resistance spot welded joints of magnesium alloys 1 and 2, can be obtained under all conditions of welding time of 40 seconds and 50 seconds.

According to the laser spot welding as described above, the welding strength is obtained by irradiating the magnesium alloy 2 that is the welded product with the laser beam B, and pressurizing the magnesium alloys 1 and 2 with the second applied pressure. Can be increased. Specifically, in laser spot welding, the second pressurization force is not applied from the start of laser beam B irradiation, but the laser irradiation and pressurization with the second pressurization time are shifted in time, thereby producing a magnesium alloy. It is possible to prevent the welded portion of 2 from being dispersed, that is, thinned and the welding strength from being weakened.

In laser spot welding, the focal position P is set above the magnesium alloy 2 that is the welded product, so that the magnesium alloys 1 and 2 are prevented from evaporating at the time of welding. Thus, it can be in a state of being heated to a temperature lower than the melting point of the magnesium alloy 2 and higher than the softening temperature , and the joining area can be increased and the welding strength can be increased. When pressurizing with the second pressurizing force, the magnesium alloy 1 as the workpiece is pressed by the protrusion 11a of the lower jig 11 so that the welded portion can be reliably pressed. And since this welding is pressurized in the state heated to the temperature lower than melting | fusing point of the magnesium alloy 2 and higher than a softening temperature , the protrusion 11a of the lower jig | tool 11 penetrates the magnesium alloy 1 which is a to-be-welded object. Therefore, it is possible to prevent the welding strength from becoming weak.

  Next, a further specific example of the laser spot welding apparatus used for laser spot welding as described above will be described with reference to FIG. The laser spot welding apparatus 20 includes a movable plate 21 on which a lower jig 11 is provided and a fixed plate 22 on which an upper jig 12 is provided. The fixed plate 22 is fixed to one end of a guide shaft 23 and is movable. The plate 21 is attached to the guide shaft 23 so as to be movable in an arrow D direction and a counter arrow D direction in FIG. Further, in the laser spot welding apparatus 20, an operation plate 24 for moving the movable plate 21 is attached to the guide shaft 23 so as to be movable. An elastic body 25 such as a coil spring is attached to the guide shaft 23 between the movable plate 21 and the operation plate 24. The movable plate 21 is urged by the elastic body 25 in the direction of arrow D in FIG. Yes. When the feed screw 26 rotates, the operation plate 24 moves along the guide shaft 23 in the direction of arrow D and the direction of the opposite arrow D in FIG. 6, and is pressed by the elastic body 25 in the direction of arrow D in FIG. The movable plate 21 also moves in the same direction.

  Further, the lower jig 11 of the movable plate 21 is formed with a concave portion 11b for holding the thin plates of the magnesium alloys 1 and 2, and the concave portion 11b is formed with the above-described protrusion 11a. The upper jig 12 is formed with a through-hole 12a through which the laser beam B emitted from the laser head 13 provided on the upper side of the fixed plate 22 is passed.

  The laser head 13 is provided with a focus adjustment mechanism 26. The focus adjustment mechanism 26 can adjust the focal position P by moving the laser head 13 up and down. Here, as described above, the focal position P is set to a position 12 mm above the magnesium alloy 2 held by the lower jig 11.

  In the laser spot welding apparatus 10 configured as described above, when the feed screw 25 is rotated, the operation plate 24 and the movable plate 21 move in the direction of arrow D in FIG. The arranged magnesium alloys 1 and 2 are brought close to the upper jig 12 of the fixing plate 22 and fixed and held by the first pressurizing force described above. Next, when the laser head 13 is driven and the laser beam B is irradiated onto the magnesium alloy 2 and the second pressurizing force is applied to the magnesium alloys 1 and 2, the operation plate 24 rotates the feed screw 25. As a result, it is further moved in the direction of arrow D in FIG. As a result, the elastic body 25 contracts, and the movable plate 21 receives the elastic force of the elastic body 25, and the second is applied to the magnesium alloys 1 and 2 fixedly held by the lower jig 11 and the upper jig 12. Apply pressure. That is, in the laser spot welding apparatus 20, the first pressurizing force and the second pressurizing force applied to the magnesium alloys 1 and 2 are adjusted by adjusting the feed amounts of the operation plate 24 and the movable plate 21 by the feed screw 25. can do.

In the above example , spot welding has been described as an example, but it can also be applied to seam welding.

It is a figure explaining laser spot welding to which the present invention is applied. It is a figure which shows the propriety of the welding which the welding time which a 2nd pressurizing force sets to 222N, and a laser output exert. It is an external appearance photograph of a laser spot welding part. It is a photograph which shows the macroscopic and microscopic structure | tissue of a laser spot welding part cross section. It is a figure which shows the relationship between welding time and a tensile shear load. It is a figure explaining the specific example of a laser spot welding apparatus.

1, 2 Magnesium alloy, 10 Laser spot welding device, 11 Lower jig, 11a Protrusion, 12 Upper jig, 12a Through hole, 13 Laser head, 14 Gas supply part

Claims (3)

In a laser welding method for laser welding a light metal plate to a metal plate,
Superimposing the light metal plate on the metal plate,
Holding the superimposed metal plate and light metal plate with a first pressure using a pair of jigs,
The light metal plate is irradiated with a laser beam for a predetermined time from the light metal plate side, the welded portion of the light metal plate is heated to a temperature lower than the melting point of the light metal plate and higher than the softening temperature, and the laser is irradiated after the predetermined time. Stop the irradiation,
At the same time as stopping the laser irradiation, the metal plate is pressed against the light metal plate from the side of the metal plate with a second pressure higher than the first pressure,
The jig for supporting the metal plate is provided with a protrusion that presses the metal plate locally,
When the jig that supports the metal plate presses the metal plate against the light metal plate with the second pressure, the protrusion is configured to attach the light metal plate to the metal plate and the light metal plate. Deform it to the supporting jig side,
When irradiating the light metal plate with the laser beam, the output of the laser beam is increased stepwise or gradually to a predetermined level,
The laser welding method, wherein the metal plate and the light metal plate are magnesium alloys.   The laser welding method according to claim 1, wherein the laser beam is irradiated onto the light metal plate with a focal position set above the light metal plate.   The laser welding method according to claim 1, wherein the jig is titanium or a titanium alloy.

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