Laser welding assembly and method

[0001] This U.S. National Stage Patent Application claims the benefit of International Application Number PCT/CA2012/000366 filed Apr. 13, 2012 entitled “Laser Welding Assembly And Method,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/475,925 filed Apr. 15, 2011, entitled “Laser Welding Assembly And Method,” the entire disclosures of the applications being considered part of the disclosure of this application and hereby incorporated by reference.

[0002] 1. Field of the Invention

[0003] The subject invention is related to welding assemblies and methods. More specifically, the subject invention is related to a laser welding assembly and method.

[0004] 2. Description of the Prior Art

[0005] Two common welding processes for joining two or more metal components are gas metal arc welding (GMAW) and laser beam welding (LBW). During the GMAW process, a wire electrode is fed into a torch, which melts the wire electrode at the intersection of, for example, two plates. The melted wire subsequently cools to join the two plates. A shielding gas is generally used to protect the welding area from atmospheric gasses which could otherwise compromise the integrity of the weld. Typical electrode wires are of silicon, manganese, titanium or aluminum materials, and typical shielding gases are inert gases, such as argon or helium. GMAW is sufficient for many applications, but generally produces a relatively shallow weld profile, which often must be built up to achieve desired structural characteristics of the weld. GMAW is also limited by the speed at which the wire electrode can be melted to form the weld.

[0006] During the LBW process, a laser head produces a continuous or pulsed high power density laser beam to melt the materials being joined. The spot size of the laser beam can be varied by adjusting the power wattage supplied to the laser head or by adjusting the focal point of the laser beam. LBW is advantageous because it can produce a weld with a deep penetration.

[0007] The combination of GMAW and LBW is generally referred to as hybrid laser arc welding (HLAW). The HLAW is advantageous since it results in an increase in both weld penetration depth and welding speed when compared to each process alone. Different joint configurations (e.g. lap joint, butt joint, T-joint, corner joint or edge joint) have different optimum orientations of the torch and laser head. Typical HLAW assemblies are setup in a specific joint configuration and can only be adjusted between welding operations with physical/manual effort, thereby limiting the effectiveness and the efficiency of the HLAW process.

[0008] There remains a significant and continuing need for an improved welding assembly for welding various joint configurations.

[0009] One aspect of the subject invention provides for a laser welding assembly and method for welding various joint configurations with a dynamically adjustable laser head. With the dynamically adjustable laser head, the assembly can efficiently and quickly weld plates of various materials (e.g., steel, aluminum and/or magnesium) into many different joint configurations. Further, the laser head can be moved to different angles on-the-fly during the welding operation to optimize the weld to weld complicated patterns. For example, dynamic adjustments of the laser head can adjust the amount of melt produced by the laser beam and/or the penetration of the laser beam during a single welding operation. Moreover, the laser head can be dynamically moved in a weaving pattern, which further increases the amount of melt produced by the laser beam along a joint.

[0010] The laser welding assembly could also be a hybrid laser arc welding (HLAW) assembly having a dynamically adjustable laser head and a torch which could either be non-adjustable or dynamically adjustable. If the torch is dynamically adjustable, it can either be adjusted along with the laser head or independent of the laser head to optimize the welding process.

[0036] Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an exemplary hybrid laser arc welding (HLAW) assembly 20 for producing a hybrid laser arc weld between at least two work pieces is generally shown in FIG. 1. The HLAW assembly 20 includes a torch 22 for gas-metal arc welding (GMAW) and a laser head 24 for laser beam welding (LBW). As will be discussed in greater detail below, the HLAW assembly 20 is dynamically adjustable to weld plates 26 (or any other types of metallic work pieces) into a variety of different joint configurations, such as lap joints (FIGS. 2-6), butt joints (FIG. 7), T-joints (not shown), corner joints (not shown) or edge joints (not shown). The components being joined can be of any desirable type of metal including, for example, steel, aluminum, magnesium and various alloys.

[0037] In operation, the HLAW assembly 20 is first positioned in front of an intersection between the plates 26 to be welded. The torch 22 and laser head 24 are then activated, and the HLAW assembly 20 is moved in a direction of travel along the interface of the two plates 26 by a robot (not shown). It may be desirable for the laser head 24 to lead the movement along the interface so that it can produce a deep penetrating weld while the torch 22 eliminates any undercutting in the materials. However, the torch 22 could lead the movement if desired.

[0038] The laser wattage and spot size of the laser head 24 are preferably chosen based on the material(s) being welded, the material thickness and the joint configuration. For example, the settings for the laser head 24 could be five kilowatts (5 kw) of power and a spot size of six hundred micrometers (600 μm) to weld one particular joint. Likewise, the shielding gas and the material of the wire electrode for the torch 22 are chosen based on the material of the plates 26 being welded, the plate thickness, the joint configuration, the wire electrode diameter, the wire feed speed, the travel speed, the power source type (direct current or alternating current) and the torch angle.

[0039] In the first embodiment of the HLAW assembly 20, as shown in FIG. 1, the torch 22 is mounted directly on the robot 27 (also shown in FIG. 8), and the laser head 24 is mounted on a table 28, which is attached to the robot 27. The torch 22 and laser head 24 are angled toward one another such that they are aimed at a point on the joint to be welded adjacent to one another. The torch 22 and laser head 24 are preferably angled relative to one another such that they are aimed at targets adjacent one another such that the melted material produced by the torch 22 overlaps with the melted material produced by the laser head 24 to produce a hybrid laser arc weld between the plates 26. Most preferably, the torch 22 and laser head 24 are aimed at targets with approximately a two millimeter (2 mm) pitch, or gap, between one another. This pitch may be beneficial since it allows both the torch 22 and laser head 24 to pass an area of the joint without the metal cooling therebetween. Alternately, the pitch between the torch 22 and laser head 24 could be less than four millimeters (4 mm). Both the torch 22 and laser head 24 are preferably positioned such that the push or drag angles of the torch 22 and laser head 24 are approximately fifteen degrees (15°). The table 28 of the first exemplary embodiment is rotatably coupled to the robot 27 about a first axis A₁, and a first servo motor 30 is operatively connected to the table 28 for rotating the table 28 relative to the robot 27. In the first exemplary embodiment, the first servo motor 30 is configured to rotate the table 28 to any orientation from a zero degree (0°) angle as shown in FIG. 13 to a ninety degree (90°) angle as shown in FIG. 16. A tool centering point (TCP) calibration may be performed each time the table 28 is rotated, between welding operations, or periodically to ensure a proper alignment of the torch 22 and the laser head 24.

[0040] As shown in FIG. 2, both the laser head 24 and the torch 22 are aimed at a lap joint formed between the plates 26 at approximately a forty-five degree (45°) angle. In FIG. 3, the table 28 supporting the laser head 24 has been rotated upwardly and the laser beam is striking the lap joint formed between the plates 26 at an angle greater than forty-five degrees (>45°). In FIG. 4, the table 28 supporting the laser head 24 has been rotated to a ninety degree (90°) degree angle. These are three orientations that are possible with the first exemplary embodiment because the orientation of the table 28 can be quickly and dynamically adjusted with the first servo motor 30, thereby altering the orientation of the laser head 24 relative to the torch 22. These adjustments can be made during a welding process or between welding processes.

[0041] Referring now to FIGS. 5 and 6, three possible programmable angles of the laser head 24 for welding two plates 26 with a lap joint configuration are shown. The letter “A” designates a steep angle, the letter “B” designates a medium angle and the letter “C” designates a shallow angle. When the laser head 24 is oriented at the steep angle position (“A”), the laser beam will strike the upper of the plates 26 and create a volume of melt to help bridge the gap between the plates 26. The torch 22 then joins the melt with the lower of the plates 26 to strengthen the weld joint between the plates 26. When the laser head 24 is oriented at the medium angle position (“B”), the laser beam will strike the lower corner of the upper of the plates 26 and create a melt, which fills the gap between the plates 26. This will also provide for a deeper penetration by the laser beam at the interface of the two plates 26 as compared to the steep angle described above. Simultaneously to the laser beam creating the melt, the torch 22 fills any undercut produced by the laser. When the laser head 24 is oriented at the shallow angle position (“C”), the laser beam will produce a deep penetrating weld into the intersection of the two plates 26. Simultaneously, the torch 22 caps the weld with a bead and eliminates any undercutting. With the servo motor 30, the laser head 24 can quickly and dynamically be moved between positions “A”, “B” and “C” to achieve the desired weld while the torch 22 is held at a constant orientation relative to the plates 26. A camera (not shown) or any type of sensor can be used to monitor the condition of the weld, and the orientation of the laser head 24 can be dynamically adjusted according to the condition of the weld.

[0042] Referring now to FIG. 7, three possible programmable angles of the laser head 24 for welding two plates 26 with a butt joint configuration are shown. Similar to FIGS. 5 and 6, the letter “A” designates a steep angle, the letter “B” designates a medium angle and the letter “C” designates a shallow angle. When the laser head 24 is oriented at the steep angle position (“A”), the laser beam will produce a deep penetrating weld into the intersection of the two plates 26 to be welded. Simultaneously, the torch 22 can be held at a ninety degree (90°) angle to cap the weld with a bead and eliminate any undercutting. When the laser head 24 is oriented at the medium angle position (“B”), the laser beam strikes one of the plates 26 and creates a melt to fill the gap between the plates 26 being welded. Simultaneously to the laser beam creating the melt, the torch 22 fills any undercut produced by the laser beam. When the laser head 24 is oriented at the shallow angle position (“C”), the laser beam strikes one of the plates 26 and creates a volume of melt to help bridge the gap between the two plates 26 being welded.

[0043] The laser head 24 can also be in communication with a controller (not shown) which controls the spot size of the laser beam and the power supplied to the laser head 24. A larger spot size has been found to stabilize the arc of the torch 22, whereas a narrower spot size generally produces a deeper weld penetration. A narrower spot size also tends to allow for higher travel speeds and thus, quicker welds.

[0044] A second exemplary embodiment of the HLAW assembly 120 is generally shown in FIGS. 9 and 10. In this exemplary embodiment, the torch 122 and laser head 124 are mounted on a common table 128. This arrangement allows the torch 122 and the laser beam to maintain a substantially constant pitch and orientation with respect to one another. The table 128 of the second exemplary embodiment is rotatably coupled to the robot 127 about a first axis A₁, and a first servo motor 130 is operatively connected to the table 128 for rotating the table 128. In this configuration, only a single TCP calibration is typically necessary to calibrate both the torch 122 and the laser head 124. The second embodiment is advantageous because it allows the torch 122 and laser head 124 to be quickly and dynamically adjusted together to weld any desirable joint configuration.

[0045] Referring now to FIG. 11, a third exemplary embodiment of the HLAW assembly 220 is generally shown. In this embodiment, the torch 222 and laser head 224 are mounted on separate tables 228, each independently rotatable about the first axis A₁. A first servo motor 230 is operatively coupled to the table 228 supporting the torch 222 for rotating the torch 222, and a second servo motor 230 is operatively coupled to the table 228 supporting the laser head 224 for rotating the laser head 224. A TCP calibration may be performed for each movement of either table 228 in order to calibrate the torch 222 and laser head 224 separately. The third embodiment is advantageous because it allows the torch 222 and laser head 224 to be dynamically adjusted independently of one another to optimize the weld for any desirable joint configuration.

[0046] FIGS. 12-24 show additional features of the second exemplary embodiment, though these features are also applicable to the first and third exemplary embodiments. A trunnion 132, or a lift, could be operatively coupled to the laser head 124 for rotating the laser head 124 about a second axis A₂. A trunnion servo motor 133 is operatively coupled to the trunnion 132 for controlling the amount of rotation of the laser head 124 about the second axis A₂. With the trunnion 132 and the trunnion servo motor 133, the laser head 124 can be swung independently of the torch 122 and can be oriented to heat the plates 26 at an angle independent of the torch 122. The trunnion 132 could be moved to reposition the laser head 124 either after the table 128 is adjusted or simultaneous to the dynamic adjustment of the table 128. Thus, the trunnion 132 and trunnion servo motor 133 provide an additional degree of freedom for adjusting the laser head 124.

[0047] Since the trunnion 132 is coupled to the laser head 124 of the second embodiment (with the torch 122 and laser head 124 mounted on a common table 128), the table 128 could be reciprocated in opposite directions to move the torch 122 in a “weaving” motion and produce a thicker weld. While the common table 128 is being reciprocated, the trunnion servo motor 133 could function to hold the laser head 124 steady, and therefore, the laser head 124 continues to produce a deep weld between the plates 26. In other words, during this process, the torch 122 is weaving while the laser beam moves in a straight line with the trunnion servo motor 133 countering the reciprocation of the common table 128 supporting both the torch 122 and the laser head 124.

[0048] Alternatively, the laser head 124 can be moved in a weaving motion by the trunnion servo motor 133 while the torch 122 remains in a constant orientation. This could be advantageous in creating additional melt with the laser beam without increasing spot size, which would otherwise result in reduced weld penetration. When additional melt is no longer required, the trunnion servo motor 133 could stop the weaving motion. FIGS. 17-19 show the laser head 124 producing such a weaving pattern. Alternately, as shown in FIGS. 20-21, the laser head 124 could be guided to follow a curve or a feature in a part to be welded while the torch 122 is maintained in a stable orientation. Even further, as shown in FIGS. 22-23, the laser head 124 could be moved to perform a stitch operation while the torch 122 is maintained in a stable orientation or vice versa.

[0049] Referring now to FIG. 24, an exemplary laser TCP station 135 for calibrating the laser head 124 is shown. The TCP station 135 includes two spaced alignment plates 134 of a low melting point material, e.g. aluminum. During the initial setup of the TCP station 135, alignment holes are burned into these plates 134 with the laser head 124. A temperature sensor 136 is then aligned with the two alignment holes in the alignment plates 134. During the TCP process, the laser head 124 is moved into the position shown in FIG. 24, and the laser head 124 is activated. If the laser beam passes through both of the alignment holes, then the temperature sensor 136 will report that the laser head 124 is properly aligned. If the temperature sensor 136 does not detect the laser beam, then the laser head 124 is either not functioning properly or is misaligned and must be re-aligned to calibrate the assembly 120.

[0050] The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention.