Method for laser welding a workpiece

Abstract

Conventionally there has been a problem wherein a coating material interposed between base materials vaporizes when heated by laser light and mixes into the melted base materials, generating air bubbles within the base materials.　In this method for laser welding workpieces W1 and W2, a laser light LB is generated and a workpiece W1 is irradiated therewith, and an irradiation point P of the laser light LB is oscillated within a predetermined heating region on the workpiece W1 so as to include a welding location where laser welding is to be executed, thereby heating the mating-surfaces region of the workpieces W1 and W2 corresponding to the heating region to a temperature higher than or equal to the boiling point of the coating material of the workpiece W1 and lower than the melting point of the base material of the workpiece W1, forming a gap between the workpieces W1 and W2 by vaporization of the coating material due to heating, discharging the coating material through the gap to the outside of the mating-surfaces region, and melting and welding together the welding location of the base materials of the workpieces W1 and W2.

Description

Technical Field

[0001] The present disclosure relates to a method for laser welding workpieces.

Background Art

[0002] A method is known for laser welding a pair of workpieces (zinc-coated steel sheets) that are overlapped with a coating material (zinc plating) interposed therebetween (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, there has been a problem that the coating material interposed between the base materials vaporizes due to the heating of the laser beam, mixes into the molten base material, and causes bubbles to form inside the base material.

Means for Solving the Problems

[0005] In one aspect of the present disclosure, a method for laser welding a first workpiece and a second workpiece that are overlapped so as to be in surface contact with each other is such that each of the first workpiece and the second workpiece has a base material, and at least one of the first workpiece and the second workpiece has a coating material inserted between the base materials of the first workpiece and the second workpiece. Laser light is generated by a laser oscillator and irradiated onto the first workpiece, and the irradiation point of the laser light is oscillated within a heating region defined on the first workpiece so as to include a welding portion where laser welding is to be performed, whereby the mating surface region of the first workpiece and the second workpiece corresponding to the heating region is heated to a temperature equal to or higher than the boiling point of the coating material and lower than the melting point of the base material of the first workpiece. By vaporizing the coating material by heating in the mating surface region, a gap is formed between the first workpiece and the second workpiece, the coating material is discharged to the outside of the mating surface region through the gap, and after discharging the coating material to the outside of the mating surface region, the welding portion is irradiated with laser light to melt the base materials of the first workpiece and the second workpiece at the welding portion and weld them to each other.

Advantages of the Invention

[0006] According to the present disclosure, since the coating material can be discharged from the mating surface region through the gap, the coating material can be surely removed from the region where the base material is melted. Therefore, when the base material is melted at the welding portion, it is possible to prevent bubbles due to the vapor of the coating material from being mixed into the base material. In addition, since it is not necessary to form through-holes in the base material for discharging the vapor of the coating material to the outside, the process of the welding flow can be simplified.

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the various embodiments described below, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. In the following description, the orthogonal coordinate system C1 in the drawing is used as a reference for directions, and for convenience, the positive x-axis direction of the coordinate system C1 is referred to as the right direction, the positive y-axis direction as the front direction, and the positive z-axis direction as the upward direction.

[0009] Referring to FIGS. 1 and 2, a laser welding system 10 according to an embodiment will be described. The laser welding system 10 is a system for welding a pair of workpieces W1 and W2 by laser light. The laser welding system 10 includes a laser oscillator 12, a light guide member 14, a laser irradiation device 16, an irradiation device moving mechanism 18, an irradiation point moving mechanism 20, and a control device 22.

[0010] The laser oscillator 12 is a solid-state laser oscillator (for example, a YAG laser oscillator or a fiber laser oscillator), or a gas laser oscillator (for example, a carbon dioxide laser oscillator), etc. It generates laser light LB inside by optical resonance in response to a command from the control device 22 and emits it to the light guide member 14.

[0011] The light guide member 14 has optical elements such as an optical fiber, an optical path made of a hollow or light-transmitting material, a mirror, or an optical lens, and guides the laser light LB generated by the laser oscillator 12 to the laser irradiation device 16. The laser irradiation device 16 is a laser scanner or a laser processing head, etc. It condenses the laser light LB incident from the light guide member 14 and irradiates the workpiece W1.

[0012] The irradiation device moving mechanism 18 relatively moves the laser irradiation device 16 with respect to the workpieces W1 and W2. For example, the irradiation device moving mechanism 18 is a vertical articulated robot capable of moving the laser irradiation device 16 to an arbitrary position in the coordinate system C1. Alternatively, the irradiation device moving mechanism 18 may have a plurality of ball screw mechanisms that move the laser irradiation device 16 along the x-y plane of the coordinate system C1 and move it in the z-axis direction of the coordinate system C1.

[0013] The coordinate system C1 is, for example, a world coordinate system that defines the three-dimensional space of the work cell, a movement mechanism coordinate system (e.g., a robot coordinate system) for controlling the operation of the irradiation device movement mechanism 18, or a work coordinate system that defines the coordinates of the workpieces W1 and W2, etc., and is a control coordinate system for automatically controlling the operations of each movable component of the laser welding system 10 (i.e., the irradiation device movement mechanism 18 and the irradiation point movement mechanism 20).

[0014] The irradiation point movement mechanism 20 relatively moves the irradiation point P on the workpiece W1 when the laser irradiation device 16 irradiates the workpiece W1 with the laser beam LB with respect to the workpiece W1. Specifically, the irradiation point movement mechanism 20 includes optical elements such as mirrors or optical lenses, a driving device that drives the optical elements, or a work table that moves the workpieces W1 and W2, etc., and relatively moves the irradiation point P with respect to the workpiece W1 by operating these components.

[0015] The control device 22 controls the operations of the laser oscillator 12, the laser irradiation device 16, the irradiation device movement mechanism 18, and the irradiation point movement mechanism 20. Specifically, the control device 22 is a computer having a processor 50, a memory 52, and an I / O interface 54. The processor 50 has a CPU or a GPU, etc., and is communicably connected to the memory 52 and the I / O interface 54 via a bus 56. The processor 50 performs arithmetic processing for realizing various functions described later while communicating with the memory 52 and the I / O interface 54.

[0016] The memory 52 has a RAM or a ROM, etc., and stores various data temporarily or permanently. The I / O interface 54 has, for example, an Ethernet (registered trademark) port, a USB port, an optical fiber connector, or an HDMI (registered trademark) terminal, and communicates data with an external device wiredly or wirelessly under the command of the processor 50.

[0017] The control device 22 is provided with an input device 58 and a display device 60. The input device 58 has a keyboard, a mouse, a touch panel, or the like, and receives data input from an operator. The display device 60 has a liquid crystal display, an organic EL display, or the like, and displays various data. The laser oscillator 12, the laser irradiation device 16, the irradiation device moving mechanism 18, the irradiation point moving mechanism 20, the input device 58, and the display device 60 are communicably connected to the I / O interface 54 by wire or wirelessly.

[0018] Next, with reference to FIG. 3, the laser irradiation device 16 and the irradiation point moving mechanism 20 according to an embodiment will be described. The laser irradiation device 16 shown in FIG. 3 is a laser scanner and includes a main body portion 24, a light receiving portion 26, an optical lens 28, a lens driving device 30, and an emitting portion 32. The main body portion 24 is hollow and defines a propagation path of the laser beam LB inside thereof. The light receiving portion 26 is provided in the main body portion 24 and receives the laser beam LB that has propagated through the light guiding member 14.

[0019] The optical lens 28 has a focus lens or the like and condenses the laser beam LB. In the present embodiment, the optical lens 28 is supported inside the main body portion 24 so as to be movable in the direction of the optical axis O of the laser beam LB incident on the optical lens 28. The lens driving device 30 has a piezoelectric element, an ultrasonic vibrator, an ultrasonic motor, or the like, and displaces the optical lens 28 in the direction of the optical axis O in response to a command from the control device 22, thereby displacing the focus of the laser beam LB irradiated on the workpiece W1 in the direction of the optical axis O. The emitting portion 32 emits the laser beam LB condensed by the optical lens 28 to the outside of the main body portion 24.

[0020] Inside the main body portion 24, a mirror 34 and 36, and mirror driving devices 38 and 40 are further accommodated. The mirror 34 (first mirror) is supported inside the main body portion 24 so as to be rotatable around the axis A1. The mirror 34 is disposed on the optical path O of the laser beam LB incident inside the main body portion 24 through the light receiving portion 26, and reflects the laser beam LB toward the mirror 36.

[0021] The mirror driving device 38 is, for example, a servo motor, and rotates the mirror 34 around the axis A1 in response to a command from the control device 22. Thus, the mirror driving device 38 can change the orientation of the mirror 34 by rotating it, thereby changing the reflection direction of the laser beam LB by the mirror 34.

[0022] On the other hand, the mirror 36 (second mirror) is supported inside the main body 24 so as to be rotatable around the axis A2. The axis A2 is substantially orthogonal to the axis A1. The mirror 36 is disposed on the optical path O of the laser beam LB reflected by the mirror 34, and reflects the laser beam LB toward the optical lens 28.

[0023] The mirror driving device 40 is, for example, a servo motor, and rotates the mirror 36 around the axis A2 in response to a command from the control device 22. Thus, the mirror driving device 40 can change the orientation of the mirror 36 by rotating it, thereby changing the reflection direction of the laser beam LB by the mirror 36. Generally, the mirrors 34 and 36 are referred to as galvanometer mirrors, and the mirror driving devices 38 and 40 are referred to as galvanometer motors.

[0024] As described above, the laser beam LB incident from the light receiving unit 26 into the main body 24 is reflected by the mirrors 34 and 36, then condensed by the optical lens 28, and emitted to the outside through the emitting unit 32 to irradiate the workpiece W1. The control device 22 operates the mirror driving devices 38 and 40 to change the orientations of the mirrors 34 and 36 respectively, thereby moving the irradiation point P of the laser beam LB irradiated on the workpiece W1 relative to the workpiece W1. That is, in the present embodiment, the mirrors 34 and 36 and the mirror driving devices 38 and 40 constitute the irradiation point moving mechanism 20.

[0025] Next, a method of laser welding the workpieces W1 and W2 using the laser welding system 10 will be described. As shown in FIGS. 1 and 4, the workpieces W1 and W2 are flat members that are overlapped so as to be in surface contact with each other and fixed by a jig (not shown) or the like. In the present embodiment, each of the workpieces W1 and W2 is positioned at a known position in the coordinate system C1 so as to be substantially parallel to the x-y plane of the coordinate system C1.

[0026] The workpiece W1 has a base material 100 and a coating material 102 laminated on the surface of the base material 100. The base material 100 is a flat member made of metal (for example, iron), and has an upper surface 104 and a lower surface 106 opposite to the upper surface 104. In the present embodiment, the coating material 102 is laminated on the surface so as to cover all the surfaces of the base material 100, and has a first layer 102a covering the upper surface 104 of the base material 100 and a second layer 102b covering the lower surface 106 of the base material 100. The coating material 102 is a different type of metal (for example, zinc) from the base material 100.

[0027] Similarly, the workpiece W2 has a base material 110 and a coating material 112 laminated on the surface of the base material 110. The base material 110 is a flat member made of metal (for example, iron), and has an upper surface 114 and a lower surface 116 opposite to the upper surface 114. In the present embodiment, the coating material 112 is laminated on the surface so as to cover all the surfaces of the base material 110, and has a first layer 112a covering the upper surface 114 of the base material 110 and the base 110 material's lower surface 116 and a second layer 112b covering the lower surface 116 of the base material. The coating material 112 is a different type of metal (for example, zinc) from the base material 110.

[0028] In the present embodiment, it is assumed that the base materials 100 and 110 are the same type of metal (iron) as each other, and the coating materials 102 and 112 are the same type of metal (zinc) as each other (for example, the workpieces W1 and W2 are both galvanized steel sheets). The boiling points T1 of the coating materials 102 and 112 (in the case of zinc, about 900°C) are lower than the melting points T2 of the base materials 100 and 110 (in the case of iron, about 1500°C).

[0029] The workpieces W1 and W2 are overlapped and fixed such that the second layer 102b of the coating material 102 and the first layer 112a of the coating material 112 are in surface contact with each other. When the workpieces W1 and W2 are fixed, as shown in FIG. 4, the second layer 102b of the coating material 102 and the first layer 112a of the coating material 112 are inserted between the base materials 100 and 110.

[0030] As a preparation process PP for welding the workpieces W1 and W2, the operator sets working conditions CD for performing the work of welding the workpieces W1 and W2. The working conditions CD include data of the welding location WL where laser welding is to be performed in the present welding process WP described later, and data of the heating region HA where the workpiece W1 is to be heated in the heating process HP described later. Hereinafter, with reference to FIGS. 5 to 9, a method for setting the welding location WL and the heating region HA will be described.

[0031] First, the operator sets the welding location WL for the workpiece W1 in the coordinate system C1. In the example shown in FIG. 5, the welding location WL is defined by two teaching points TP1 and TP2 set on the first layer 102a of the coating material 102 of the workpiece W1 and a welding line LN connecting the teaching points TP1 and TP2. The teaching points TP1 and TP2 are target positions where the irradiation point P of the laser beam LB should be positioned in the present welding process WP described later, and the welding line LN defines the target path for moving the irradiation point P from the teaching point TP1 to the teaching point TP2.

[0032] For example, while visually recognizing the drawing data (CAD data) of the workpieces W1 and W2 displayed on the display device 60, the operator operates the input device 58 to specify the teaching points TP1 and TP2 on the first layer 102a of the workpiece W1. The processor 50 sets the teaching points TP1 and TP2 and the welding line LN in the coordinate system C1 according to the input data from the operator.

[0033] Next, the operator operates the input device 58 to set the heating area HA in the first layer 102a so as to include the welding location WL. In the example shown in FIG. 5, the heating area HA is set as a rectangular area that encloses the entire welding location WL inside it, with its longitudinal direction parallel to the x-axis of the coordinate system C1 and its short-side direction parallel to the y-axis of the coordinate system C1.

[0034] More specifically, the heating area HA has a length x1 in its longitudinal direction and a width y1 in its short-side direction. As an example, the length x1 of the heating area HA is such that the left side SD1 of the heating area HA is arranged at a position separated by a distance x2 (for example, 1 [mm] to 2 [mm]) to the left of the teaching point TP1, while the right side SD2 of the heating area HA is arranged at a position separated by a distance x3 (for example, 1 [mm] to 2 [mm]) to the right of the teaching point TP2. Thus, in this case, the length x1 of the heating area HA is longer than the length of the welding line LN in the x-axis direction of the coordinate system C1.

[0035] Also, the width y1 of the heating area HA can be set to be three times or more the width in the y-axis direction of the bead formed on the welding line LN when the base materials 100 and 110 are welded along the welding line LN in the present welding process WP (or the width of the irradiation point P of the laser beam LB during the present welding process WP or heating process HP). Each vertex and each side of the heating area HA can be represented as coordinates of the coordinate system C1. In this way, the heating area HA is set in the first layer 102a so as to include the welding location WL.

[0036] Next, the operator sets the teaching point TPn and the irradiation point movement path MP for the heating process HP in the heating area HA. The teaching point TPn for the heating process HP is the target position at which the irradiation point P of the laser beam LB should be positioned in the heating process HP described later, and the irradiation point movement path MP defines the target path for moving the irradiation point P from the teaching point TPn to the teaching point TPn+1. An example of the setting of the teaching point TPn is shown in FIG. 6.

[0037] The operator operates the input device 58 to set teaching points TP11, TP12, TP13, TP14, TP15, and TP16 in the heating area HA. In FIG. 6, for ease of understanding, the welding location WL is omitted. In the example shown in FIG. 6, the teaching points TP11, TP12, TP15, and TP16 are respectively arranged at the vertices of the heating area HA, and the teaching points TP14 and TP13 are respectively arranged at the midpoints of the sides SD1 and SD2 of the heating area HA.

[0038] Next, the operator operates the input device 58 to set the forward path of the irradiation point movement path MP based on the teaching point TPn as shown in FIG. 7. In the example shown in FIG. 7, the forward path of the irradiation point movement path MP is set as the path of teaching point TP11 → TP12 → TP13 → TP14 → TP15.

[0039] Next, the operator operates the input device 58 to set the return path of the irradiation point movement path MP as shown in FIG. 8. In the example shown in FIG. 8, the return path of the irradiation point movement path MP is set as the path of teaching point TP15 → TP16 → TP13 → TP14 → TP11. Thus, as shown in FIG. 9, the irradiation point movement path MP is set in the heating area HA as the path of teaching point TP11 → TP12 → TP13 → TP14 → TP15 → TP16 → TP13 → TP14 → TP11.

[0040] The teaching points TP11 to TP16 and the irradiation point movement path MP are represented as the coordinates of the coordinate system C1. The position of the heating area HA in the coordinate system C1 can be represented as the coordinates of the teaching points TP11 to TP16 and the irradiation point movement path MP. Therefore, the heating area HA can be regarded as the area defined by the teaching points TP11 to TP16 and the irradiation point movement path MP.

[0041] As described above, the operator sets the welding location WL (teaching points TP1 and TP2, welding line LN) and the heating area HA (teaching points TP11 to TP16, irradiation point movement path MP) for the workpiece W1. Note that the operator may set a plurality of welding locations WL and heating areas HA at different positions on the workpiece W1 respectively.

[0042] The position data of the welded portion WL set in this way (specifically, the teaching points TP1 and TP2 in the coordinate system C1 and the coordinates of the welding line LN), and the position data of the heating area HA (specifically, the teaching points TP11 to TP16 in the coordinate system C1 and the coordinates of the irradiation point movement path MP) are stored in the memory 52 as the working conditions CD.

[0043] In addition, the working conditions CD include the oscillation speed V1 (first speed) of the irradiation point P in the heating process HP and the laser power LP1 of the laser beam LB, the time t for executing the heating process HP HP , the forward speed V2 (second speed) of the irradiation point P in the present welding process WP and the laser power LP2 of the laser beam LB, the focal position FP of the laser beam LB in the heating process HP and the present welding process WP, and further include data such as the operation mode OM of the laser oscillator 12 in the heating process HP and the present welding process WP.

[0044] The operation mode OM of the laser oscillator 12 includes, for example, a first operation mode OM1 for causing the laser oscillator 12 to generate a first type of laser beam LB1 and a second operation mode OM2 for causing the laser oscillator 12 to generate a second type of laser beam LB2 different from the first type. For example, the first type of laser beam LB1 is a pulsed oscillation laser beam, while the second type of laser beam LB2 is a continuous oscillation laser beam.

[0045] In the preparation process PP, the operator operates the input device 58 to set the speeds V1 and V2, the laser powers LP1 and LP2, the time t HP , the coordinates of the focal position FP in the coordinate system C1, and the operation mode OM as the working conditions CD. Then, the operator creates a welding program PG based on the set working conditions CD (welded portion WL, heating area HA, speeds V1 and V2, laser powers LP1 and LP2, time t HP , focal position FP, operation mode OM).

[0046] This welding program PG is a computer program that causes the processor 50 to execute a welding flow (FIG. 10) described later. Each parameter of the working condition CD is defined in the welding program PG. The created welding program PG is stored in the memory 52 of the control device 22. In this way, in the preparation process PP, the setting of the working condition CD and the creation of the welding program PG are performed.

[0047] Next, with reference to FIG. 10, the welding flow of the laser welding system 10 will be described. The welding flow shown in FIG. 10 starts when the processor 50 receives a welding start command from an operator, a host controller, or a computer program (for example, the welding program PG). The processor 50 executes the welding flow shown in FIG. 10 according to the welding program PG stored in advance in the memory 52.

[0048] In step S1, the processor 50 operates the irradiation device moving mechanism 18 to place the laser irradiation device 16 at a predetermined welding position P with respect to the workpieces W1 and W2. W at which the laser irradiation device 16 is disposed, the entire heating area HA set for one welding location WL to be welded is within the movement range of the irradiation point P on the workpiece W1 by the irradiation point moving mechanism 20. W When the laser irradiation device 16 is disposed at this welding position P, the entire heating area HA set for one welding location WL to be welded is within the movement range of the irradiation point P on the workpiece W1 by the irradiation point moving mechanism 20.

[0049] In step S2, the processor 50 executes the heating process HP. Specifically, the processor 50 first switches the operation mode OM of the laser oscillator 12 to the first operation mode OM1 and transmits a command to the laser oscillator 12 to generate the first type of laser beam LB1 having the laser power LP1. In response to the command, the laser oscillator 12 generates the laser beam LB1 with the laser power LP1 by pulse oscillation and emits it to the laser irradiation device 16 through the light guide member 14.

[0050] At the same time, the processor 50 operates the lens driving device 30 (FIG. 3) of the laser irradiation device 16 to adjust the position of the optical lens 28, thereby controlling the focal point of the laser beam LB1 emitted from the laser irradiation device 16 to the focal position FP1. In the present embodiment, this focal position FP1 is set at a position slightly above (or below) the upper surface of the workpiece W1 (that is, the upper surface of the first layer 102a of the coating material 102).

[0051] In this way, the laser beam LB1 with the laser power LP1 is irradiated onto the workpiece W1. The irradiation point P1 of the laser beam LB1 at this time has an area E1. This area E1 is proportional to the deviation amount of the focal position FP1 from the upper surface of the workpiece W1. At this point, the irradiation point P1 may be arranged at the teaching point TP11 of the heating region HA.

[0052] Next, the processor 50 operates the irradiation point moving mechanism 20 to swing the irradiation point P1 of the laser beam LB1 within the heating region HA at a speed V1. Specifically, the processor 50 changes the orientations of the mirrors 34 and 36 by operating the mirror driving devices 38 and 40, thereby moving the irradiation point P1 relative to the workpiece W1 at a speed V1.

[0053] For example, when the laser irradiation device 16 is arranged at the welding position P W one of the mirrors 34 and 36 can displace the irradiation point P 1 along the x-axis of the coordinate system C1 within the heating region HA by changing its orientation, and the other of the mirrors 34 and 36 can displace the irradiation point P1 along the y-axis of the coordinate system C1 within the heating region HA by changing its orientation.

[0054] The processor 50 repeatedly reciprocates the irradiation point P1 along the above-described irradiation point movement path MP (the path of teaching point TP11 → TP12 → TP13 → TP14 → TP15 → TP16 → TP13 → TP14 → TP11) at a speed V1 by changing the orientations of the mirrors 34 and 36 respectively, thereby swinging the irradiation point P1 within the heating region HA. The speed V1 at this time is set to, for example, 200 [m / min].

[0055] When the irradiation point P1 is rapidly oscillated within the heating region HA in this way, the entire heating region HA is heated by the laser beam LB1, and the heat generated in the heating region HA propagates through the base material 100 to the mating surface region SE of the workpieces W1 and W2, and the mating surface region SE is also heated.

[0056] Note that the mating surface region SE is a region including the lower surface of the second layer 102b of the coating material 102 and the upper surface of the first layer 112a of the coating material 112 that are in surface contact with each other, and can be defined, for example, as a region between the lower surface 106 of the base material 100 and the upper surface 114 of the base material 110 (or the occupied region of the second layer 102b and the first layer 112a).

[0057] Here, in the present embodiment, the processor 50 causes the irradiation point P1 to be at a temperature T (T1 ≤ T < T2) that is equal to or higher than the boiling point T1 of the coating material 102 (i.e., the coating material 112) and lower than the melting point T2 of the base material 100 (i.e., the base material 110) in the mating surface region SE' corresponding to the heating region HA within the heating region HA for a time t HP and continuously oscillates it over time.

[0058] The mating surface region SE' can be defined, for example, as a region obtained by projecting the heating region HA onto the mating surface region SE in the z-axis direction of the coordinate system C1 (in other words, a region within the mating surface region SE where the position and area in the x-y plane of the coordinate system C1 are substantially the same as those of the heating region HA). An example of the mating surface region SE' is schematically shown as a gray region in FIG. 11.

[0059] FIG. 12 shows an example of a graph of the temperature distribution in the y-axis direction of the mating surface region SE' heated in this step S2. The y-coordinate in FIG. 12: y α corresponds to the position in the y-axis direction of the teaching points TP15 and T16 (FIG. 9) in the coordinate system C1, and the y-coordinate: y β corresponds to the position in the y-axis direction of the teaching points TP13 and T14 in the coordinate system C1, and the y-coordinate: y γ corresponds to the position in the y-axis direction of the teaching points TP11 and TP It corresponds to the position in the y-axis direction of 12.

[0060] In step S2, the temperature T of the joint surface region SE’ is controlled so as to fall within a temperature range (T1 ≤ T < T2) that is equal to or higher than the boiling point T1 of the coating material 102 and lower than the melting point T2 of the base material 100, as shown in FIG. 12. In the present embodiment, while the irradiation point P1 makes a round trip along the forward path (FIG. 7) and the return path (FIG. 8) of the irradiation point movement path MP, the irradiation point P1 passes through the path between the teaching points TP13 and T14 in the irradiation point movement path MP twice, while passing through the other paths only once.

[0061] In other words, according to the irradiation point movement path MP, the irradiation point P1 passes more through the central part in the y-axis direction of the coordinate system C1 in the heating region HA in step S2. As a result, the temperature of the central part of the heating region HA becomes the highest, and as a result, also in the joint surface region SE’, as shown in FIG. 12, the temperature of the central part (the part where y = y β ) becomes the highest.

[0062] When the joint surface region SE’ is heated to a temperature T that is equal to or higher than the boiling point T1 and lower than the melting point T2, the second layer 102b of the coating material 102 and the first layer 112a of the coating material 112 existing in the joint surface region SE’ vaporize. The expansion pressure of the gas generated by the vaporization of the coating materials 102 and 112 at this time becomes extremely high.

[0063] Therefore, due to the expansion pressure of the coating materials 102 and 112 generated in the joint surface region SE’, the upper surface 114 of the base material 110 is pushed downward, and the lower surface 106 of the base material 100 is pushed upward. As a result, the base materials 100 and 110 that are at a high temperature elastically deform slightly. The elastic deformation of the base materials 100 and 110 at this time is reversible, and they return to their original shapes when the base materials 100 and 110 are cooled.

[0064] Due to the vaporization of such coating materials 102 and 112, the elastic deformation of the base materials 100 and 110 caused by the vaporization, and the thermal expansion of the base materials 100 and 110 due to heating, as shown in FIG. 13, a gap G is formed between the pair of workpieces W1 and W2. Note that in FIG. 13, the gap G is emphasized for easy understanding, but in reality, it should be understood that the gap G is on the micron order of dimensions.

[0065] The vapor of the coating materials 102 and 112 generated in the mating surface region SE’ is radially blown out to the outside of the mating surface region SE’ through this gap G. As a result, the second layer 102b of the coating material 102 and the first layer 112a of the coating material 112 that were present in the mating surface region SE’ are discharged to the outside of the mating surface region SE’.

[0066] In this way, in this step S2, by heating the mating surface region SE’ to a temperature T that is equal to or higher than the boiling point T1 and lower than the melting point T2, the coating materials 102 and 112 can be discharged from the mating surface region SE’ while keeping the base materials 100 and 110 in a solid state. In other words, the working conditions CD (speed V1, laser power LP1, time t HP , focal position FP1, and operation mode OM1) used in step S2 are set so that the temperature T of the mating surface region SE’ can be controlled within a temperature range that is equal to or higher than the boiling point T1 and lower than the melting point T2.

[0067] The inventor conducted an experiment in which step S2 was executed under the following working conditions CD for workpieces W1 and W2 that are zinc-plated steel sheets each having a thickness of 0.7 [mm]. [Working Conditions CD] Heating Area HA Length x1 = 50 [mm] × Width y1 = 2 [mm] Speed V1 200 [m / min] Laser Power LP1 5 [kW] Time t HP 400 [msec] Focal Position FP1 Position 10 [mm] above the upper surface of workpiece W1 Operation Mode OM1 Pulse Oscillation Mode

[0068] As a result of this experiment, it was confirmed that the coating materials 102 and 112 were discharged from a rectangular area with a length x ≈ 55 [mm] × width y ≈ 3 [ mm ] that entirely included the entire mating surface area SE' inside. That is, this experimental result shows that by appropriately setting the working conditions CD, the coating materials 102 and 112 can be discharged not only from the mating surface area SE' but also from the area around the mating surface area SE'.

[0069] When the time t HP set as the working condition CD has elapsed since the processor 50 started the oscillation of the irradiation point P1 in step S2, the processor 50 sends a command to the laser oscillator 12 to stop the emission of the laser beam LB1, thereby ending the heating process HP in step S2. For example, the processor 50 may stop the emission of the laser beam LB1 by stopping the laser beam generation operation by the laser oscillator 12. Alternatively, the laser oscillator 12 further has a shutter for opening and closing the optical path of the emitted laser beam LB1, and the processor 50 may stop the emission of the laser beam LB1 by closing the shutter.

[0070] Referring to FIG. 10 again, in step S3, the processor 50 determines whether or not the base materials 100 and 110 have been cooled to a temperature equal to or lower than a predetermined threshold value T3. This threshold value T3 may be set, for example, to the melting point of the coating materials 102 and 112, or may be set to the normal temperature of the atmosphere.

[0071] As an example, the processor 50 measures the elapsed time t1 since the end of the heating process HP in step S2, and when the elapsed time t1 reaches a predetermined time t th , it may be determined that the base materials 100 and 110 have been cooled to a temperature equal to or lower than the threshold value T3 (that is, YES).

[0072] This time t this set in advance by the operator (for example, t th = 20 [msec]) as a time sufficient for the base materials 100 and 110 heated in step S2 to be cooled to a temperature equal to or lower than the threshold value T3, and is stored in the memory 52. When the processor 50 determines YES, it proceeds to step S4, while when it determines NO, it loops step S3.

[0073] In step S4, the processor 50 executes the present welding process WP. Specifically, the processor 50 first switches the operation mode OM of the laser oscillator 12 to the second operation mode OM2, and transmits a command to the laser oscillator 12 to generate the second type of laser beam LB2 having the laser power LP2.

[0074] In response to the command, the laser oscillator 12 generates the laser beam LB2 with the laser power LP2 by continuous oscillation, and emits it to the laser irradiation device 16 through the light guide member 14. In the present embodiment, the laser power LP2 is set to a value smaller than the laser power LP1 in step S2 (LP2 < LP1).

[0075] At the same time, the processor 50 operates the lens driving device 30 of the laser irradiation device 16 to adjust the position of the optical lens 28, thereby controlling the focal point of the laser beam LB2 emitted from the laser irradiation device 16 to the focal position FP2. In the present embodiment, this focal position FP2 is set to a position closer to the upper surface of the work W1 (that is, the upper surface of the first layer 102a of the covering material 102) than the above-described focal position FP1 (for example, the position of the upper surface of the first layer 102a).

[0076] Thus, the laser beam LB2 with the laser power LP2 is irradiated onto the work W1. The irradiation point P2 of the laser beam LB2 at this time has an area E2 (< E1) corresponding to the focal position FP2. Note that at this point, the irradiation point P2 may be arranged at the teaching point TP1 of the welding portion WL.

[0077] Next, the processor 50 operates the irradiation point moving mechanism 20 to move the irradiation point P2 of the laser beam LB2 irradiated on the welding portion WL. Specifically, the processor 50 changes the orientations of the mirrors 34 and 36 by operating the mirror driving devices 38 and 40, thereby moving the irradiation point P2 from the teaching point TP1 to the teaching point TP2 and advancing it rightward along the welding line LN at a speed V2. This speed V2 can be set to, for example, 3 [m / min] (i.e., V2 ≪ V1).

[0078] Note that in this step S4, the processor 50 may advance the irradiation point P2 rightward along the welding line LN while oscillating the irradiation point P2. Specifically, the processor 50 changes the orientations of the mirrors 34 and 36 to advance the irradiation point P2 rightward while oscillating it in the y-axis direction of the coordinate system C1. According to this configuration, when the base materials 100 and 110 are melted by the laser beam LB2, generation of spatter can be suppressed.

[0079] When the irradiation point P2 reaches the teaching point TP2, the processor 50 sends a command to the laser oscillator 12 to stop the emission of the laser beam LB2, thereby ending the main welding process WP of step S4. By the main welding process WP of step S4, the base materials 100 and 110 are melted along the welding line LN by the laser beam LB2 and welded to each other at the welding portion WL.

[0080] In step S5, the processor 50 determines whether welding for all the welding portions WL has been completed. For example, the processor 50 can determine whether welding for all the welding portions WL has been completed by analyzing the welding program PG. If the processor 50 determines YES, it ends the flow shown in FIG. 10. On the other hand, if the processor 50 determines NO, it returns to step S1 and executes steps S1 to S5 for the next welding portion WL.

[0081] As described above, in the present embodiment, in step S2, the processor 50 swings the irradiation point P1 of the laser beam LB1 within the heating region HA, thereby heating the mating surface region SE' to a temperature T that is equal to or higher than the boiling point T1 of the covering materials 102 and 112 and lower than the melting point T2 of the base materials 100 and 110, and discharging the covering materials 102 and 112 to the outside of the mating surface region SE' through the gap G formed between the workpieces W1 and W2.

[0082] Then, in step S4, the processor 50 irradiates the welding portion WL with the laser beam LB2 to melt the base materials 100 and 110 at the welding portion WL and weld them to each other. According to the present embodiment, from the region where the base materials 100 and 110 are melted in step S4, the second layer 102b of the covering material 102 and the first layer 112a of the covering material 112 can be removed by step S2. Therefore, when the base materials 100 and 110 are melted at the welding portion WL in step S4, it is possible to prevent bubbles due to the vapor of the covering materials 102 and 112 from being mixed into the interiors of the base materials 100 and 110.

[0083] Further, in the present embodiment, the vaporization of the covering materials 102 and 112 forms the gap G in the mating surface region SE', and the vapor of the covering materials 102 and 112 is discharged to the outside of the mating surface region SE' through the gap G. Therefore, it is not necessary to form through-holes in the base material 100 or 110 for allowing the vapor of the second layer 102b and the first layer 112a generated in step S4 to escape to the outside as in the prior art. Thus, the process of the welding flow can be simplified.

[0084] Further, in the present embodiment, the irradiation point P1 is swung within the heating region HA by changing the orientations of the mirrors 34 and 36. According to this configuration, the irradiation point P1 can be swung at a high speed (speed V1) with respect to the workpiece W1 (that is, the speed V1 can be set to a large value). According to this configuration, in step S2, the entire mating surface region SE' can be heated relatively uniformly.

[0085] Also, in the present embodiment, the speed V2 as the working condition CD in step S4 is set to be much lower than the speed V1 as the working condition CD in step S2 (V2≪V1). According to this configuration, while the entire surface area SE’ of the mating surface can be heated relatively uniformly in step S2, the base materials 100 and 110 can be surely melted in step S4.

[0086] Also, in the present embodiment, the area E1 of the irradiation point P1 in step S2 is larger than the area E2 of the irradiation point P2 in step S4 (E1>E2). According to this configuration, since the heating area by the laser beam LB1 in step S2 becomes larger, the expansion pressure of the coating materials 102 and 112 generated in the mating surface area SE’ can be increased, and the effect of discharging the coating materials 102 and 112 can be enhanced. On the other hand, in step S4, since the laser power per unit area at the irradiation point P2 can be increased, the base materials 100 and 110 can be surely melted.

[0087] Also, in the present embodiment, the laser power LP1 as the working condition CD in step S2 is larger than the laser power LP2 as the working condition CD in step S4 (LP1>LP2). According to this configuration, in step S2, the mating surface area SE’ can be rapidly heated to a temperature T that is not lower than the boiling point T1 of the coating materials 102 and 112 and lower than the melting point T2 of the base materials 100 and 110.

[0088] Also, in the present embodiment, in step S2, the first type of laser beam LB1 (pulsed oscillation laser beam) is irradiated onto the heating area HA, while in step S4, the second type of laser beam LB2 (continuous oscillation laser beam) is irradiated onto the welding location WL. According to this configuration, in step S2, while preventing the temperature of the upper surface of the workpiece W1 from rising excessively, the mating surface area SE’ can be efficiently heated, and in step S4, the base materials 100 and 110 can be efficiently melted.

[0089] In addition, in the present embodiment, in step S2, the irradiation point P1 is oscillated within the heating region HA so that the temperature T' at the center of the heating region HA becomes the highest. By forming a temperature gradient in the temperature distribution of the heating region HA in this way, a temperature gradient as shown in FIG. 12 is also formed in the temperature distribution of the mating surface region SE', and thus, the effect of radially blowing the vapors of the coating materials 102 and 112 to the outside of the mating surface region SE' in step S2 can be enhanced.

[0090] Note that, in order to form a temperature gradient as shown in FIG. 12, in step S2, while the irradiation point P1 passes through the path between the teaching points TP13 and T14 in the irradiation point movement path MP, the processor 50 controls the laser power LP1 to the laser power LP1 _1 while controlling the laser power LP1 to the laser power LP1 _2 (<LP1 _1 ) while it passes through other paths. By increasing the laser power LP1 while the irradiation point P1 passes through the path between the teaching points TP13 and T14 in this way, a temperature gradient can be effectively formed such that the temperature at the center of the heating region HA (i.e., the mating surface region SE') becomes higher.

[0091] In addition, in the present embodiment, after step S2, when the base materials 100 of the workpiece W1 are cooled to a temperature equal to or lower than the threshold value T3 (i.e., when it is determined as YES in step S3), step S4 is executed. By heating and then cooling the base materials 100 and 110 in this way, the material structures of the base materials 100 and 110 are refined, and thus, the strength of the base materials 100 and 110 can be increased. However, the processor 50 may omit the above-described step S3 and execute step S4 immediately after the end of step S2.

[0092] Note that, in the above-described embodiment, the memory 52 stores the materials MT (or thermal conductivities) of the workpieces W1 and W2, the thicknesses f of the workpieces W1 and W2, and the parameters of the working conditions CD (welding location WL, heating region HA, speeds V1 and V2, laser powers LP1 and LP2, time t HP, a data table DT1 in which the focus position FP and the operation mode OM are stored in association with each other may be stored in advance.

[0093] As an example, the data table DT1 includes the materials MT A (or thermal conductivity) of the base materials 100 and 110, the materials MT B (or thermal conductivity) of the coating materials 102 and 112, and the thickness f of the workpieces W1 and W2 (or the thickness of the base material and the thickness of the coating material), and the parameters of the working conditions CD used in step S2 (heating process HP) (for example, the length of the welding line LN, the length x1 and width y1 of the heating area HA, the speed V1, the laser power LP1, the time t HP , the focus position FP1, and the operation mode OM1) may be created so as to be stored in association with each other.

[0094] Then, the processor 50 may display the data table DT1 on the display device 60. In this case, the operator refers to the data table DT1 and can search for the optimal working conditions CD used in step S2 from the materials MT A of the base materials 100 and 110 of the workpieces W1 and W2 to be worked on, the materials MT B of the coating materials 102 and 112, and the thickness f of the workpieces W1 and W2 from the data table DT1.

[0095] Alternatively, the processor 50 may generate an input screen on which the material MT A , the material MT B , and the thickness f can be input and display it on the display device 60. Then, while visually recognizing the input screen displayed on the display device 60, the operator operates the input device 58 to input information on the material MT A , the material MT B , and the thickness f into the input screen.

[0096] Then, the processor 50 inputs the input materials MT A and MT B、and search for the working condition CD corresponding to the thickness f from the data table DT1, and automatically set it as the working condition CD to be used in step S2. According to this configuration, since the setting work of the working condition CD can be automated, the preparation process PP can be facilitated.

[0097] Note that the data table DT1 stores the material MT A and MT B , as well as the thickness f and the parameters of the working condition CD used in step S4 (this welding process WP) (for example, the length of the welding line LN, the length x1 and width y1 of the heating area HA, the speed V2, the laser power LP2, the focal position FP2, and the operation mode OM2), may be created so as to be associated with each other. The data table DT1 can be created by collecting data through an experimental method or simulation.

[0098] Next, with reference to FIGS. 14 and 15, a laser welding system 70 according to another embodiment will be described. The laser welding system 70 is different in that it further includes a temperature sensor 72 from the above-described laser welding system 10. The temperature sensor 72 has, for example, a thermocouple, a platinum resistance thermometer, or an infrared detection type temperature measuring device (such as a thermography camera), and measures the temperature T' of the heating area HA on the workpiece W1 in a contact or non-contact manner.

[0099] Next, with reference to FIG. 16, the welding flow of the laser Welding system 70 will be described. The welding flow in this embodiment is different from the flow shown in FIG. 10 in step S2' (heating process HP). Hereinafter, step S2' will be described with reference to FIG. 17.

[0100] Step S2 ’After the start, in step S11, the processor 50 starts generating the laser beam LB1. Specifically, the processor 50 switches the operation mode OM of the laser oscillator 12 to the first operation mode OM1, as in step S2 described above, and causes the laser oscillator 12 to generate the first type of laser beam LB1 (pulsed oscillation laser beam) having the laser power LP1. At the same time, the processor 50 operates the lens driving device 30 to adjust the position of the optical lens 28 and controls the focal point of the laser beam LB1 to the focal position FP1.

[0101] In step S12, the processor 50 starts the operation of swinging the irradiation point P1 of the laser beam LB1 within the heating region HA. Specifically, the processor 50 operates the irradiation point moving mechanism 20, as in step S2 described above, and starts the operation of swinging the irradiation point P1 of the laser beam LB1 within the heating region HA along the irradiation point moving path MP at the speed V1.

[0102] In step S13, the processor 50 estimates the temperature T of the mating surface region SE'. Specifically, the processor 50 acquires the temperature T' of the heating region HA measured by the temperature sensor 72 at this time and estimates the temperature T of the mating surface region SE' based on the temperature T'. As an example, the memory 52 stores in advance a data table DT2 in which the temperature T' of the heating region HA and the temperature T of the mating surface region SE' are stored in association with each other.

[0103] This data table DT2 can be created through an experimental method, a thermodynamic simulation, or the like. The processor 50 searches the data table DT2 for the temperature T corresponding to the acquired temperature T'. In this way, the processor 50 can estimate the temperature T of the mating surface region SE' at this time from the temperature T' of the heating region HA measured by the temperature sensor 72. As another example, the temperature T of the mating surface region SE' may be estimated by applying the temperature T' of the heating region HA measured by the temperature sensor 72 to a known thermodynamic equation.

[0104] Note that the temperature sensor 72 may be arranged to measure the temperature T' at the center of the heating region HA. In this case, the temperature sensor 72 will measure the maximum temperature T' of the heating region HA, and the processor 50 will estimate the temperature T (maximum temperature) at the center of the mating surface region SE' from this maximum temperature T' in this step S13. Alternatively, the temperature sensor 72 may be arranged to measure the temperature T' at any position within the heating region HA (for example, at any of the positions of the teaching points TP11 to TP16).

[0105] In step S14, the processor 50 determines whether the temperature T estimated in the most recent step S13 is lower than a predetermined threshold value T th1 (T < T th1 ). This threshold value T th1 is predetermined by the operator and stored in the memory 52. For example, the threshold value T th1 may be set to the boiling point T1 (or a temperature below it) of the coating materials 102, 112, or may be set to a temperature higher than the boiling point T1 and lower than the melting point T2 of the base materials 100, 110 (T1 < T th1 < T2). The processor 50 determines YES in the case of T < T th1 and proceeds to step S17, while determining NO in the case of T ≥ T th1 and proceeding to step S15.

[0106] In step S15, the processor 50 determines whether the temperature T estimated in the most recent step S13 is higher than a predetermined threshold value T th2 (T > T th2 ). This threshold value T th2 is predetermined by the operator as a value higher than the above-described threshold value T th1 and stored in the memory 52.

[0107] For example, the threshold value T th2 may be set to the melting point T2 (or a temperature above it) of the base materials 100, 110, or may be set to a temperature higher than the boiling point T1 of the coating materials 102, 112 and lower than the melting point T2 (for example, T1 < T th1 < T th2<T2)として設定されてもよい。プロセッサ50は、T>T th2 If T≦T, the determination is YES and the process proceeds to step S17. th2 If so, the result is NO, and the process proceeds to step S16.

[0108] In step S16, the processor 50 performs the following from the start of step S12: Operation Time t specified in condition CD HP Specifically, the processor 50 measures the elapsed time t2 from the start of step S12, and determines whether the elapsed time t2 is equal to or exceeds the time t HP The processor 50 determines whether the elapsed time t2 reaches the time t HP If the elapsed time t2 reaches the time t HP If it has not been reached, the result is NO, and the process returns to step S13.

[0109] On the other hand, if the determination in step S14 or S15 is YES, in step S17, the processor 50 changes the working condition CD. Specifically, in step S17 after the determination in step S14 is YES, the processor 50, for example, reduces the speed V1, increases the laser power LP1, and HP or the working condition CD is changed so as to bring the focal position FP1 closer to the upper surface of the workpiece W1.

[0110] Here, the speed V1 is decreased, the laser power LP1 is increased, and the time t HP The increase in the temperature T and the approach of the focal position FP1 to the top surface of the workpiece W1 both lead to an increase in the temperature of the heating area HA (i.e., the mating surface area SE'). Therefore, by changing the working conditions CD in this way, the temperature T of the mating surface area SE' is increased by the threshold T th1 It can be increased to or greater.

[0111] On the other hand, in step S17 after determining YES in step S15, the processor 50 increases, for example, the speed V1, decreases the laser power LP1, reduces the time t HP and changes the working conditions CD so as to reduce the time t or separate the focal position FP1 from the upper surface of the workpiece W1.

[0112] Here, the increase in the speed V1, the decrease in the laser power LP1, the reduction of the time t HP and the separation of the focal position FP1 from the upper surface of the workpiece W1 all lead to a decrease in the temperature of the heating region HA (i.e., the bonding surface region SE'). Therefore, by changing the working conditions CD in this way, the temperature T of the bonding surface region SE' of can be reduced to be equal to or lower than the threshold value T. After executing step S17, the processor 50 continues step S2' according to the changed working conditions CD and proceeds to step S16. th2 As described above, in the present embodiment, the processor 50 estimates the temperature T of the bonding surface region SE' from the temperature T' of the heating region HA measured by the temperature sensor 72 and changes the working conditions CD according to the temperature T. According to this configuration, during the execution of step S2', the temperature T of the bonding surface region SE' can be precisely controlled, thereby enhancing the effect of discharging the coating materials 102 and 112 existing in the bonding surface region SE' to the outside. Also, the working conditions CD (for example, the time t

[0113] for executing the heating process HP) can be optimized. HP )

[0114] Note that the laser irradiation device 16 and the irradiation point moving mechanism 20 are not limited to the form shown in FIG. 3. For example, one of the mirrors 34 and 36 may be omitted from the irradiation point moving mechanism 20 shown in FIG. 3. In this case, the irradiation point moving mechanism 20 may be configured to reciprocate the irradiation point P on the workpiece W1 in the x-axis direction of the coordinate system C1 by a length x1 with respect to the workpiece W 1 .

[0115] On the other hand, the irradiation point moving mechanism 20 may further include a work table on which the workpieces W1 and W2 are fixed, and a table driving device (for example, a piezoelectric element, an ultrasonic vibrator, or an ultrasonic motor) that reciprocates the work table in the y-axis direction of the coordinate system C1 with a width y1 (both not shown).

[0116] In this case, the irradiation point moving mechanism 20 swings the workpieces W1 and W2 in the y-axis direction of the coordinate system C1 by the table driving device, and swings the irradiation point P with respect to the workpiece W1 in the x-axis direction of the coordinate system C1 by the other of the mirrors 34 and 36, so that the entire heating region HA can be heated. The heating region HA at this time becomes a substantially rectangular region with a length x1 × width y1, and is defined from the relative movement path of the irradiation point P with respect to the workpiece W1.

[0117] Further, the laser irradiation device 16 is not limited to the laser scanner as shown in FIG. 3, and may be, for example, a laser processing head having a mirror that reflects the received laser light and an optical lens that condenses the laser light reflected by the mirror. In this case, the irradiation point moving mechanism 20 may have a rotating lens rotatably disposed inside the laser processing head.

[0118] This rotating lens is supported on the optical path of the laser light reflected by the mirror of the laser processing head so as to be rotatable around an axis parallel to the optical path, and has a laser light incident surface inclined with respect to the optical path. The irradiation point moving mechanism 20 can displace the irradiation point P on the workpiece W1 by rotating this rotating lens.

[0119] In the above-described embodiment, in the preparation process PP, the case where the operator sets the teaching points TP11 to TP16 and the irradiation point movement path MP after setting the heating region HA with respect to the workpiece W1 has been described (FIGS. 5 to 9). However, the process of setting the heating region HA can be omitted from the preparation process PP.

[0120] For example, after the operator sets the welding location WL for the workpiece W1, the teaching points TP11 to TP16 may be set so as to surround the welding location WL, and then, based on the teaching points TP11 to TP16, the irradiation point movement path MP may be set. In this case, the heating region HA is uniquely determined by the set teaching points TP11 to TP16 and the irradiation point movement path MP, as shown in, for example, FIG. 9.

[0121] Also, in the preparation process PP, after the operator sets the welding location WL, the processor 50 may automatically set the heating region HA so as to include the welding location WL based on the position data of the welding location WL. In this case, the operator may input in advance information such as the length x1, width y1, distance x2, distance x3, etc. shown in FIG. 5 through the input device 58, and the processor 50 may automatically set the heating region HA according to the input data from the operator.

[0122] Note that at least one of the distance x2 and the distance x3 shown in FIG. 5 may be zero. In this case, the teaching point TP1 will be arranged on the left side SD1 of the heating region HA, or the teaching point TP2 will be arranged on the right side SD2 of the heating region HA. Also, the teaching point TP1 may be arranged to the left of the left side SD1 of the heating region HA.

[0123] Alternatively, the teaching point TP2 may be arranged to the right of the right side SD2 of the heating region HA. In this case, while most of the welding location WL is included in the heating region HA, both end portions of the welding location WL will be arranged outside the heating region HA. Here, as described above, as a result of the experiments by the present inventor, it has been found that not only the mating surface region SE' but also the coating materials 102 and 112 can be discharged from the region around the mating surface region SE' by the heating process HP. Therefore, even if a part of the welding location WL is arranged outside the heating region HA, the coating materials 102 and 112 can be discharged from the region where the welding location WL exists.

[0124] Note that the irradiation point movement path MP shown in FIG. 9 is an example, and various other irradiation point movement paths can be considered. FIG. 18 shows another example of the irradiation point movement path MP. In the example shown in FIG. 18, four teaching points TP11, TP12, TP15, and TP16 are set at each vertex of the heating region HA, and the irradiation point movement path MP is set, for example, as the path of teaching point TP11 → TP12 → TP15 → TP16 → TP11. Further, the irradiation point movement path MP can be set as a path that uniformly raises the temperature T of the joint surface region SE' without forming a temperature gradient as shown in FIG. 12 when the heating process HP is executed.

[0125] FIG. 19 shows still another example of the irradiation point movement path MP. In the example shown in FIG. 19, two teaching points TP21 and TP22 are set in the heating region HA, and the irradiation point movement path MP is set as a path that reciprocates between the teaching points TP21 and TP22. The teaching points TP21 and TP22 can be set at the same positions in the y-axis direction of the coordinate system C1 as the teaching points TP1 and TP2. Even in such an irradiation point movement path MP, by appropriately setting the working conditions CD, the entire heating region HA and the joint surface region SE' can be heated.

[0126] Note that in the above-mentioned step S2, as the irradiation point P1 is moved along the irradiation point movement path MP from one teaching point TP α to the next teaching point TP α of the teaching point TP γ , the laser power LP1 may be changed together with the speed V1. Hereinafter, such control will be described with reference to FIG. 20.

[0127] In FIG. 20, the horizontal axis represents two consecutive teaching points TP α and TP γ on the irradiation point movement path MP, and a point (for example, the midpoint) TP α and TP γ between the teaching points TP β , and the vertical axis represents the speed V1 and the laser power LP1. Also, the solid line in the graph of FIG. 20 represents the laser power LP1, while the dashed line represents the speed V1.

[0128] In the example shown in FIG. 20, in step S2, when moving the irradiation point P1 from the teaching point TP α to the teaching point TP γ , while moving from the teaching point TP α to the point TP β , the irradiation point P1 is gradually accelerated and the speed V1 increases, while after passing through the point TP β and until reaching the teaching point TP γ , the irradiation point P1 is gradually decelerated and the speed V1 decreases.

[0129] Thus, assuming that the laser power LP1 is controlled to be constant when the speed V1 changes while moving the irradiation point P1 from the teaching point TP α to the teaching point TP γ , in the heating region HA, the temperature in the vicinity of the teaching points TP α and TP γ where the speed V1 is low can become excessively higher than the temperature in the vicinity of the point TP β . In this case, the temperature T at the edges (for example, sides SD1 and SD2) of the heating region HA may become excessively larger than that at the central part.

[0130] Therefore, as shown in FIG. 20, the processor 50, in step S2, increases the laser power LP1 together with the speed V1 as the irradiation point P1 is moved from the teaching point TP α to the point TP β , and decreases the laser power LP1 together with the speed V1 as the irradiation point P1 is moved from the point TP β to the teaching point TP γ . By changing the laser power LP1 together with the speed V1 in this way, the entire heating region HA (that is, the joint surface region SE) can be heated relatively uniformly.

[0131] Note that in the form shown in FIG. 9, the teaching points TP shown in FIG. 20 α from the teaching point TP γThe irradiation point movement path MP up to, for example, can be the path of TP11 → TP12, the path up to TP13 → TP14, and the path of TP15 → TP16. In this case, the processor 50 controls the value (maximum value, minimum value, or average value) of the laser power LP1 in the path of TP13 → TP14 to LP1 _1 while controlling the value of the laser power LP1 to LP1 _2 (<LP1 _1 ) when passing through other paths.

[0132] On the other hand, the processor 50 may control the laser power LP1 to be constant while the irradiation point P1 passes through the paths of TP12 → TP13, TP14 → TP15, TP16 → TP13, and TP14 → TP11. That is, in this case, the processor 50 changes the laser power LP1 when the irradiation point movement path MP between the two teaching points TP α and TP γ is relatively long, while controlling the laser power LP1 to be constant when the irradiation point movement path MP between the teaching points TP α and TP γ is relatively short.

[0133] Also, in the form shown in FIG. 18, the irradiation point movement path MP from the teaching point TP α to the teaching point TP γ can be the path of TP11 → TP12, the path up to TP12 → TP15, the path of TP15 → TP16, and the path of TP16 → TP11. Further, in the form shown in FIG. 19, the irradiation point movement path MP from the teaching point TP α to the teaching point TP γ can be the path of TP11 → TP12 and the path up to TP12 → TP11.

[0134] In addition, in the above-described working conditions CD, instead of (or in addition to) the laser power LP1 and the focal position FP1, the condensing density ρ1 of the laser beam LB1 irradiated on the heating region HA in step S2 may be determined. The condensing density ρ1 can be defined, for example, as the laser power LP1 per unit area of the irradiation point P1 on the workpiece W1 (that is, ρ1 = LP1 / E1).

[0135] Also, in the above-described working conditions CD, instead of (or in addition to) the laser power LP2 and the focal position FP2, the condensing density ρ2 of the laser beam LB2 irradiated on the welding portion WL in step S4 may be determined. The condensing density ρ2 can be defined, for example, as the laser power LP2 per unit area of the irradiation point P2 on the workpiece W1 (that is, ρ2 = LP2 / E2). Here, the area E of the irradiation point P on the workpiece W1 depends on the focal position FP of the laser beam LB as described above. Therefore, the condensing density ρ can be controlled by appropriately selecting the laser power LP of the laser beam LB and the focal position FP of the laser beam LB.

[0136] Here, in the working conditions CD, the condensing density ρ1 of the laser beam LB1 in step S2 may be set to a value smaller than the condensing density ρ2 of the laser beam LB2 in step S4 (ρ1 < ρ2). For example, in step S2, the processor 50 controls the laser power LP1 to 5 [kW] and controls the focal position FP1 to a position 10 [mm] above the upper surface of the workpiece W1. In this case, the diameter of the irradiation point P1 becomes about 0.9 [mm], and the area E1 is about 0.64 [mm 2 . Therefore, in this case, the condensing density ρ1 can be controlled to ρ1 ≒ 8 [kW / mm 2 .

[0137] On the other hand, in step S4, the processor 50 controls the laser power LP2 to 2 [kW] and controls the focal position FP2 to the position of the upper surface of the workpiece W1. In this case, the diameter of the irradiation point P2 becomes about 0.4 [mm], and thus the area E2 is about 0.13 [mm 2 . Therefore, in this case, the condensing density ρ2 can be controlled to ρ2 ≒ 15.4 [kW / mm 2It can be controlled to >ρ1.

[0138] Note that the memory 52 may store in advance a data table DT3 that stores the condensing density ρ in association with the laser power LP and the focal position FP. Then, when executing step S2 or S4, the processor 50 searches the data table DT3 for the laser power LP and the focal position FP corresponding to the condensing density ρ set in the working condition CD, and irradiates the workpiece W1 with the searched laser power LP and focal position FP, thereby controlling the condensing density ρ.

[0139] Also, in the above-described working condition CD, instead of (or in addition to) the speed V1, the time t required for the irradiation point P1 to make a round trip along the irradiation point movement path MP when the irradiation point movement mechanism 20 swings the irradiation point P1 in the heating process HP MP may be determined. Also, the same operation mode OM (OM1 or OM2) may be adopted in the heating process HP (step S2 or S2') and the main welding process WP (S4). In this case, the same type of laser beam LB (LB1 or LB2) is irradiated onto the workpiece W1 in the heating process HP and the main welding process WP.

[0140] Also, the focal position FP may be the same in the heating process HP and the main welding process WP. In this case, the area E1 of the irradiation point P1 in the heating process HP and the area E2 of the irradiation point P2 in the main welding process WP are substantially the same. Also, the laser power LP may be the same in the heating process HP and the main welding process WP (LP1 = LP2).

[0141] Also, the laser welding system 10 may include a plurality of control devices 22 that individually control the laser oscillator 12, the laser irradiation device 16, the irradiation device movement mechanism 18, and the irradiation point movement mechanism 20. Also, the heating region HA (teaching point TPn, irradiation point movement path MP) may be set not only for the first layer 102a of the covering material 102 but also for the base material 100.

[0142] Alternatively, while setting the heating region HA on the workpiece W1 (the first layer 102a of the coating material 102), the welding location WL may be set on the workpiece W2 (the second layer 112b of the coating material 112). In this case, in the heating process HP, the processor 50 may irradiate the workpiece W1 with the laser beam LB1 from above, while in the main welding process WP, the laser beam LB2 may be irradiated onto the workpiece W2 from below.

[0143] In this case, the laser welding systems 10, 70 may further include a second laser irradiation device 18B capable of irradiating the laser beam LB2 onto the workpiece W2 from below, and a second irradiation point moving mechanism 20B for moving the irradiation point P2 on the workpiece W2. While setting the heating region HA on the workpiece W1 and the welding location WL on the workpiece W2, the heating region HA and the welding location WL are separated in the z-axis direction of the coordinate system C1. However, as shown in FIG. 5, when viewed from the z-axis direction, the welding location WL can be regarded as being included within the heating region HA.

[0144] Also, one of the workpieces W1 and W2 may not have the coating material 102 or 112. For example, when the workpiece W1 does not have the coating material 102, the workpiece W1 is made of the base material 100, and the workpieces W1 and W2 are overlapped such that the lower surface 106 of the base material 100 is in surface contact with the upper surface (the upper surface of the first layer 112a of the coating material 112) of the workpiece W2. In this case, the first layer 112a of the coating material 112 is inserted between the base materials 100 and 110.

[0145] Note that the base materials 100 and 110 may be made of different types of metals. Also, the coating materials 102 and 112 may be made of different types of metals. In this case, in the heating process HP, the mating surface region SE' may be heated to a temperature equal to or higher than the boiling points of the coating materials 102 and 112 and lower than the melting points of the base material 100 (and the base material 110). Also, the coating materials 102 and 112 may be made of materials other than metals (for example, resins).

[0146] Although the present disclosure has been described through the embodiments above, the above embodiments do not limit the invention according to the claims.

Description of Symbols

[0147] 10, 70 Laser Welding System 12 Laser Oscillator 14 Light Guide Member 16 Laser Irradiation Device 18 Irradiation Device Moving Mechanism 20 Irradiation Point Moving Mechanism 22 Control Device 50 Processor 72 Temperature Sensor

Claims

1. A method for laser welding a first workpiece and a second workpiece that are overlapped so as to be in surface contact with each other, comprising: each of the first workpiece and the second workpiece has a base material, and at least one of the first workpiece and the second workpiece has a coating material inserted between the base materials of the first workpiece and the second workpiece; generating laser light by a laser oscillator and irradiating the first workpiece with the laser light; oscillating the irradiation point of the laser light in a heating region defined on the first workpiece so as to include a welding portion where the laser welding is to be performed, by repeatedly reciprocating the irradiation point along a forward path and a return path defined in the heating region, thereby heating a mating surface region of the first workpiece and the second workpiece corresponding to the heating region to a temperature equal to or higher than the boiling point of the coating material and lower than the melting point of the base material of the first workpiece; vaporizing the coating material by heating in the mating surface region to form a gap between the first workpiece and the second workpiece, and discharging the coating material to the outside of the mating surface region through the gap; after discharging the coating material to the outside of the mating surface region, irradiating the welding portion with the laser light to melt the base materials of the first workpiece and the second workpiece at the welding portion and weld them to each other; wherein the forward path is defined to pass through a first vertex, a second vertex, and a third vertex of the rectangular heating region, while the return path is defined to pass through the third vertex, a fourth vertex, and the first vertex of the heating region.

2. reflecting the laser light by a mirror disposed on the optical path of the laser light generated by the laser oscillator to irradiate the first workpiece with the laser light; The method according to claim 1, wherein the irradiation point is oscillated in the heating region by changing the orientation of the mirror.

3. The mirror is: a first mirror disposed on the optical path and displaceable along a first axis in the heating region for displacing the irradiation point; and a second mirror disposed on the optical path of the laser light reflected by the first mirror and displaceable along a second axis orthogonal to the first axis in the heating region for displacing the irradiation point. The method according to claim 2.

4. When heating the mating surface region, the irradiation point is oscillated at a first speed in the heating region. When melting the base materials of the first workpiece and the second workpiece, moving the irradiation point of the laser beam irradiated on the welding portion forward at a second speed lower than the first speed along the welding portion, the method according to any one of claims 1 to 3.

5. The area of the irradiation point of the laser beam irradiated on the heating region when heating the mating surface region is larger than the area of the irradiation point of the laser beam irradiated on the welding portion when melting the base materials of the first workpiece and the second workpiece, the method according to any one of claims 1 to 4.

6. The laser power of the laser beam irradiated on the heating region when heating the mating surface region is larger than the laser power of the laser beam irradiated on the welding portion when melting the base materials of the first workpiece and the second workpiece, the method according to any one of claims 1 to 5.

7. The condensing density of the laser beam irradiated on the heating region when heating the mating surface region is smaller than the condensing density of the laser beam irradiated on the welding portion when melting the base materials of the first workpiece and the second workpiece, the method according to any one of claims 1 to 6.

8. When heating the mating surface region, changing the laser power of the laser beam irradiated on the heating region together with the speed at which the irradiation point swings within the heating region, the method according to any one of claims 1 to 7.

9. When melting the base materials of the first workpiece and the second workpiece, moving the irradiation point of the laser beam irradiated on the welding portion forward along the welding portion while swinging the irradiation point, the method according to any one of claims 1 to 8.

10. When heating the mating surface region, irradiating the heating region with the laser beam of the first type, When melting the base materials of the first workpiece and the second workpiece, irradiating the welding portion with the laser beam of the second type different from the first type, the method according to any one of claims 1 to 9.

11. The laser beam of the first type is a pulsed oscillation laser beam, while the laser beam of the second type is a continuous oscillation laser beam, the method according to claim 10.

12. The method according to any one of claims 1 to 11, wherein when heating the mating surface region, the irradiation point is oscillated within the heating region so that the temperature at the center of the heating region becomes the highest.

13. The method according to any one of claims 1 to 12, wherein after discharging the coating material to the outside of the mating surface region, when the base material of the first workpiece is cooled to a temperature equal to or lower than a predetermined threshold value, the laser beam is irradiated onto the welded portion to melt the base materials of the first workpiece and the second workpiece.

14. The method according to claim 13, wherein the threshold value is the melting point of the coating material.

15. While heating the mating surface region, the temperature of the heating region is measured by a temperature sensor, Based on the temperature measured by the temperature sensor, the temperature of the mating surface region is estimated, The method according to any one of claims 1 to 14, wherein the working conditions for heating the mating surface region are changed according to the estimated temperature of the mating surface region.

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