JP2008544859A - Laser welding system and method - Google Patents

Abstract

  A laser welding system and method for welding a target and having an optical axis, a source 22 of a laser beam 24 and a pair of lasers that rotate the laser beam 24 about the optical axis 30 It includes a rotatable diffraction grating 26 that converts to a spot 32 and a lens that focuses the pair of laser spots 32 onto a target 34.

Description

  The present invention relates generally to welding systems, and more particularly to laser welding systems and methods.

  Modern manufacturing processes often require bonding of dissimilar materials, for example, bonding nickel to brass, stainless steel to copper, stainless steel to brass, or metal to cermet. Attempts to fusion weld dissimilar materials are only somewhat successful due to the intermetallic phase formed in the weld. Different physical properties in the two materials lead to complex problems in the weld pool shape, solidification microstructure, and segregation pattern. Current laser welding techniques are hard, brittle microstructures, weak and result in large cracks. Such welding is an unreliable and unstable welding process.

  A conventional laser welding apparatus using a rotating laser beam uses complicated optical systems and mechanisms. Typically, the laser beam is passed through a rotating optical element that deflects the laser beam from the optical axis and creates a circular path on the weld target. The lenses, mirrors, and prisms used to deflect the laser beam are not radial symmetric or are mounted asymmetrically with respect to the optical axis to limit the rotational speed. This limits the stability and speed of the laser beam at the target to be welded. The slow speed increases the interaction time of the laser beam with the welding target and requires a reduction in beam power to avoid sputtering and rough welding. As the interaction time increases, the metallurgical capacity of dissimilar metal welding decreases. As optical stability decreases, so does the accuracy of welding.

  It would be desirable to have a laser welding system and method that overcomes the above disadvantages.

  One aspect of the invention is a rotatable diffraction grating that welds a target and has an optical axis that converts the laser beam into a laser beam source and a pair of laser spots that rotate about the optical axis. And a lens for focusing the pair of laser spots on a target.

  Another aspect of the present invention is a method of welding a target, comprising the step of providing a planar rotatable diffraction grating, and a rotatable diffraction grating around an optical axis orthogonal to the plane of the rotatable diffraction grating. A method of providing a split beam, directing a laser beam along an optical axis to the rotatable diffraction grating, and focusing the split beam on a target to generate a split beam.

  Another aspect of the present invention is a system for welding a target comprising a plane rotatable diffraction grating and means for rotating the rotating grating about an optical axis orthogonal to the plane of the rotating grating; To generate a split beam, a system is provided having means for directing a laser beam along the optical axis to the rotatable diffraction grating and means for focusing the split beam on a target.

  The above and other features and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and the same.

  1 and 2 are a cross-sectional view and a schematic view of a welding path, respectively, of a welding system made in accordance with the present invention. The welding system deflects the laser beam through a rotatable diffraction grating to produce a pair of rotating laser spots at the target.

  With reference to FIGS. 1 and 2, the welding system 20 includes a source 22 of a laser beam 24, a rotatable diffraction grating 26, and a lens 28. The optical system of the welding system 20 is aligned along the optical axis 30. The rotatable diffraction grating 26 converts the laser beam 24 into a pair of laser spots 32 that rotate about the optical axis 30. The stationary lens 28 focuses the pair of laser spots 32 on the target 34 in order to weld the target 34 to the workpiece 36 carried on the stage 38. FIG. 2 illustrates the welding process with the laser spot 32 forming a weld 50 at the target 34, ie, the weld 50 has not yet formed a complete circle. Those skilled in the art will appreciate that the welding system 20 can also be used to make welds that are not perfect circles if desired. The rotatable diffraction grating 26 is attached to a rotatable housing 40 that is carried in a fixed housing 42 by high speed bearings 44. The speed-controlled AC servo motor 46 drives the rotatable housing 40 through a belt 48. The arrows in the rotatable diffraction grating 26 illustrate the rotation of the rotatable diffraction grating 26. In one embodiment, the optical axis 30 is along the direction of gravity so that the rotatable housing 40 hangs from the stationary housing 42.

  The source 22 of the laser beam 24 can be a fiber optic conductor that carries the laser beam 24 from the laser 21 or a direct output of the laser. The laser 21 can be any pulsed or continuous laser source suitable for welding. In one example, laser 21 is a neodymium doped yttrium aluminum garnet (Nd: YAG) laser that produces a laser beam with a wavelength of 1064 nm and a pulse power of about 600 to 6000 watts. In one embodiment, the laser is HL204p, available from Trumpf Laser GmbH of Schramberg, Germany. As the laser beam 24 enters the rotatable housing 40, it diffuses into a diffused beam 60. Those skilled in the art will recognize that various types of lasers and various types of wavelengths suitable for particular applications such as welding, cutting, drilling, and / or ablate can be used if desired. You will understand that.

  The rotatable diffraction grating 26 can be any diffraction grating, such as a two-phase diffraction grating suitable for dividing the laser beam 24 into at least a pair of laser spots 32. The rotatable diffraction grating 26 generates a split beam 62 from the diffuse beam 60, which is mounted in a rotatable housing 40 that rotates about the optical axis 30. The rotatable diffraction grating 26 has plane and radial symmetry. The plane of the rotatable diffraction grating 26 is orthogonal to the optical axis 30 and allows the rotatable diffraction grating 26 to rotate about the optical axis 30 at high speed. The rotatable diffraction grating 26 can be covered with photoresist on glass or etched in fused silica if desired for the particular laser used. Those skilled in the art will appreciate that the pattern of the rotatable grating 26 can be selected to produce more than a pair of laser spots 32, or that a large number of separate rotatable gratings can be used. . For example, one rotatable diffraction grating that splits a laser beam into two identical images can have its pattern on another rotatable diffraction grating of the same type that produces four split beams and two pairs of laser spots. It can be located at right angles to it.

  The lens 28 collimates and focuses the split beam from the rotatable diffraction grating 26 to provide a focused beam 66 on the target 34 that produces the pair of laser spots 32. It can be a lens. The lens 28 is fixed with respect to the optical axis 30. In one embodiment, lens 28 includes a collimating lens 52 and a focusing lens 54 as found in the BEO 30 focusing optics available from Trumpf Laser GmbH of Schramberg, Germany. The collimating lens 52 generates a collimated beam 64 from the split beam 62, and the focusing lens 54 generates a beam 66 that is focused from the collimated beam 64.

  In the illustrated example, the rotatable diffraction grating 26 can be moved axially within the diffusing beam 60 to determine the diameter of the weld path 51 and the diameter of the laser spot 32 at the target 34. Placing the rotatable diffraction grating 26 in the diffused beam 60 is an adjustment of the diameter of the welding path 51 in the target 34, ie, the adjustment of the pitch between the laser spots 32 according to the position of the rotatable diffraction grating 26 and the grating constant. Provide flexibility. In other embodiments, the rotatable diffraction grating 26 may be disposed between the collimating lens 52 and the focusing lens 54 in the collimated beam 64. Positioning the rotatable diffraction grating 26 in the collimated beam 64 fixes the diameter of the welding path 51 in the target 34, ie, fixes the pitch between the laser spots 32 according to the grating constant of the rotatable diffraction grating 26.

  Target 34 and workpiece 36 may also be two parts to be joined by welding. In one example, the target 34 is a plate and the workpiece 36 is a hollow cylinder. In another example, both the target 34 and the workpiece 36 are plate-shaped. In another example, the target 34 is a wire and the workpiece 36 is plate-shaped. Target 34 and workpiece 36 may be dissimilar materials such as nickel and brass, stainless steel and copper, stainless steel and brass, or metal and cermet. The target 34 can be metal and the workpiece 36 can be a delicate material such as metalized plastic, ceramic, and / or metalized glass. One exemplary use of welding is to seal a ceramic burner of a high intensity discharge (HID) lamp.

  Target 34 and workpiece 36 may be carried on stage 38 to secure target 34 and workpiece 36 in a position for welding. Typically, the plane of the target 34 is orthogonal to the optical axis 30 and then the weld path 51 at the target 34 is circular. In other embodiments, the plane of the target 34 is at an angle with respect to the optical axis 30 so that the weld path 51 at the target 34 is elliptical. The angle is such that the laser spot 32 is sufficiently focused throughout the weld path 51, such as less than about 20 degrees, to provide sufficient power to form a weld, such as the plane of the target 34. And the angle between the optical axis 30. In one embodiment, stage 38 is fixed relative to optical axis 30 during welding. In other embodiments, the driver 39 moves the stage 38 during welding to create a complex welding path, such as a cycloid, on the target 34. Those skilled in the art will appreciate that the driver 39 can be programmed to move the target 34 perpendicular to the optical axis 30 in any trajectory as desired, for example, in a linear or two-dimensional trajectory. I will.

  A high purity shielding gas such as air, nitrogen, argon, and / or oxygen may be applied at the target 34 to provide cooling and auxiliary plasma formation. The shielding gas may be selected as desired for a particular material target 34 and workpiece 36. The flow of shielding gas can be crossflow, downflow, and / or boxflow if desired.

  Referring to FIG. 2, a pair of laser spots 32 rotate around the optical axis 30 in a weld path 51 that produces a weld 50 at the target 34. The diameter of the laser spot 32 is typically in the range of about 0.1 to 0.6 mm if desired for a particular application. The high speed rotation of the rotatable diffraction grating 26 causes the laser spot 32 to move rapidly across the target 34 and limits the interaction time between the laser spot 32 and the target 34. Here, the interaction time is defined as the time required for the laser spot 32 to move one laser spot 32 diameter at the target 34. The interaction time is also the time at which the laser spot 32 is at a certain point along the entire welding path 51. For a weld path 51 that traverses in 10-20 ms, the interaction time is typically 0.1-0.2 ms. The limited interaction time produces a reliable weld by providing high energy to both the target 34 and the workpiece 36 in a very short time. The high energy forms a keyhole and plasma plume through the target 34 to the workpiece 36. Reflection of the laser light within the keyhole increases energy transfer to the target 34. The molten metal around the keyhole flows into the area behind the moving laser spot 32 due to surface tension and solidification, forming a weld 50. The limited interaction time reduces sputtering near the weld and results in a smooth weld surface.

  The desired interaction time depends on the material of the target 34 and the workpiece 36 and is a function of the velocity of the laser spot 32 at the target 34. Here, the interaction time is defined as the time required for the laser spot 32 to move one diameter of the laser spot 32 at the target 34. The interaction time is also the time at which the laser spot 32 is at a certain point along the entire welding path 51. The speed of the laser spot 32 is determined by the diameter of the weld path 51 and the rotational speed of the rotatable diffraction grating 26, which are usually set by the configuration of the target 34 and workpiece 36 to be welded. The rotational speed of the rotatable diffraction grating 26 is typically between about 1500 and 4500 rpm and is slower than 10,000 rpm. The speed of the laser spot 32 at the target 34 is typically about 500 mm / second and may be in the range of about 200 to 800 mm / second. The desired interaction time of the laser spot 32 with the target 34 is typically about 0.2 msec and may be in the range of about 0.1 to 0.5 msec.

  The power to the laser can be switched on and off and / or changed over time to produce a specific welding result. The laser is applied for less than the time required to guide half of the weld path 51 for one of the laser spots 32 to produce two separate welds along the weld path 51. obtain. The laser can be applied for the time required to direct half of the weld path to one of the laser spots 32 to produce a circular weld along the weld path 51. The laser can be applied longer than the time required to guide half of the weld path 51 to one of the laser spots 32 to produce a multi-pass weld along the weld path 51. . The power to the laser can be changed over time during welding. For example, power is sharply turned on at the beginning of the weld, remains constant for most of the weld, and gradually turns off so that the line tapers at the end of the weld. At the end of the weld, turning off the power gradually ensures that no holes are left at the end of the weld.

  3 and 4 are schematic views of a welding path for a welding system made in accordance with the present invention. FIG. 3 illustrates the welding path for a fixed target with two pairs of laser spots. FIG. 4 illustrates a welding path for a linear moving target having a pair of laser spots.

  Similar elements share similar reference numbers in FIG. 2, and referring to FIG. 3, a first pair of laser spots 32a and a second pair of laser spots 32b are welded 50 onto the target 34. Rotate around the optical axis 30 on the welding path 51 that generates FIG. 3 illustrates the welding process with the laser spots 32a, 32b forming a weld 50 on the target 34, ie, the weld 50 forms a complete circle. Those skilled in the art will appreciate that the welding system 20 can be used to make fewer than full circle welds if desired. Two pairs of laser spots 32a, 32b can be generated by stacking two rotatable gratings at right angles to each other. One skilled in the art will appreciate that any number of rotatable diffraction gratings can be stacked to produce the desired number of pairs of laser spots.

  Similar elements share the same reference numbers in FIG. 2, and referring to FIG. 4, the weld 50 moves the target 34 along a line in a plane perpendicular to the optical axis of the welding system. , Generated along a complex weld path along a linear trajectory 58. The speed of the target 34 relative to the rotational speed of the rotatable grating determines whether the loop 56 is formed (long cycloid) or the welding path is two consecutive cross curves (short cycloid). Complex welding paths along the linear track 58 can be used to attach a linear target to the workpiece or to connect two plates along the edges. In one embodiment, a driver operably connected to the stage carrying the workpiece and target 34 drives the linear motion of target 34. One skilled in the art will appreciate that the driver can be programmed to drive the target along a complex trajectory to be adapted to a particular target shape. For example, the driver can be programmed to provide a circular trajectory near the circumference of a large circular target, resulting in a complex weld path along the edge of the circular target.

  FIG. 5 is a schematic diagram of another welding system made by the present invention, with similar elements shared with like reference numerals in FIG. In this embodiment, the rotatable diffraction grating 26 is disposed within the collimated beam 64 rather than the diffused beam 60.

  The welding system 20 includes a source 22 of a laser beam 24, a rotatable diffraction grating 26, and a lens 28 that includes a collimating lens 52 and a focusing lens 54. The optical system of the welding system 20 is aligned along the optical axis 30. A rotatable diffraction grating 26 positioned between the collimating lens 52 and the focusing lens 54 converts the laser beam 24 into a pair of laser spots that rotate about the optical axis 30 on the target 34. The rotatable housing to which the rotatable diffraction grating 26 is mounted, the speed controllable AC servo motor that drives the rotatable housing, and the fixed housing relative to the rotatable housing are omitted from FIG. 5 for clarity of explanation.

  The collimating lens 52 receives the diffuse beam 60 from the source 22 and generates a collimated beam 64. The rotatable diffraction grating 26 receives the collimated beam 64 and generates a split beam 62. A focusing lens 54 receives the split beam 62 and generates a focused beam 66 that provides a pair of laser spots focused on the target 34.

  FIG. 6 is a flowchart of a welding method according to the present invention. The method of welding the target includes providing a planar rotatable grating 100, rotating the rotatable grating about an optical axis orthogonal to the plane of the rotatable grating, and generating a split beam. For this purpose, the method includes the step 104 of directing the laser beam along the optical axis to the rotatable diffraction grating and the step 106 of focusing the split beam on the target. In one embodiment, the method further includes moving the target perpendicular to the optical axis, eg, moving the target along a line perpendicular to the optical axis. In other embodiments, the method further comprises applying a shielding gas to the target.

  While the embodiments of the invention disclosed herein are presently preferred, various changes and modifications may be made without departing from the scope of the invention. For example, the welding system described herein can be used to weld, cut, drill, and / or ablate a target. The scope of the invention is indicated in the claims, and all changes that come within the scope of the means and equivalents are intended to be embraced therein.

FIG. 1 is a cross-sectional view of a welding system made in accordance with the present invention. FIG. 2 is a schematic view of the welding path of a welding system made in accordance with the present invention. FIG. 3 is a schematic diagram of the welding path of a welding system made in accordance with the present invention. FIG. 4 is a schematic view of the welding path of a welding system made in accordance with the present invention. FIG. 5 is a schematic diagram of another welding system made in accordance with the present invention. FIG. 6 is a flowchart of the welding method according to the present invention.

Claims (22)

A system for welding a target and having an optical axis,
A laser beam source;
A rotatable diffraction grating that converts the laser beam into a pair of laser spots that rotate about the optical axis;
A lens for focusing the pair of laser spots on a target;
Having a system.   The system of claim 1, wherein the rotatable diffraction grating is located between the source and the lens.   The system of claim 1, wherein the lens comprises a collimating lens and a focusing lens, and the rotatable diffraction grating is located between the collimating lens and the focusing lens.   The system of claim 1, wherein a plane of the rotatable diffraction grating is orthogonal to the optical axis.   The system of claim 1, wherein the lens is fixed relative to the optical axis.   The rotatable diffraction grating is a first rotatable diffraction grating, the pair of laser spots is a first pair of laser spots, and the laser beam is applied to a second pair of laser spots rotating around the optical axis. The system of claim 1, further comprising a second rotatable diffraction grating for converting the lens, wherein the lens focuses the first pair of laser spots and the second pair of laser spots on the target. The described system.   The system of claim 1, wherein a velocity at the target of one of the pair of laser spots is between about 200 mm / sec and about 800 mm / sec.   The system of claim 1, wherein an interaction time between one of the pair of laser spots and the target is between about 0.1 ms and 0.5 ms.   The system of claim 1, wherein the rotational speed of the rotatable diffraction grating is between about 1500 rpm and about 4500 rpm.   The system of claim 1, wherein the rotatable diffraction grating is selected from the group consisting of a photoresist coated glass grating and an etched fused silica grating.   The system of claim 1, wherein an angle between the target and the optical axis is less than about 20 degrees.   The system of claim 1, further comprising a driver operably connected to the target for moving the target perpendicular to the optical axis. A method of welding a target,
Providing a planar rotatable diffraction grating;
Rotating the rotatable diffraction grating about an optical axis orthogonal to a plane of the rotatable diffraction grating;
Directing a laser beam along the optical axis to the rotatable diffraction grating to generate a split beam;
Focusing the split beam on the target;
Having a method.   14. The method of claim 13, wherein focusing the split beam comprises collimating the split beam to a collimated beam and focusing the collimated beam.   The method of claim 13, further comprising moving the target perpendicular to the optical axis.   The method of claim 13, further comprising moving the target along a line perpendicular to the optical axis.   The method of claim 13, further comprising applying a shielding gas to the target. A system for welding a target,
A planar rotatable diffraction grating; and
Means for rotating the rotatable diffraction grating about an optical axis perpendicular to the plane of the rotatable diffraction grating;
Means for directing a laser beam along the optical axis to the rotatable diffraction grating to generate a split beam;
Means for focusing the split beam on the target;
Having a system.   19. The system of claim 18, wherein the means for focusing the split beam comprises means for collimating the split beam to a collimated beam and means for focusing the collimated beam.   The system of claim 18, further comprising means for moving the target perpendicular to the optical axis.   The system of claim 18, further comprising means for moving the target along a line perpendicular to the optical axis.   The system of claim 18, further comprising means for applying a shielding gas to the target.

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