Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/067—Dividing the beam into multiple beams, e.g. multifocusing
  • B23K26/0676—Dividing the beam into multiple beams, e.g. multifocusing into dependently operating sub-beams, e.g. an array of spots with fixed spatial relationship or for performing simultaneously identical operations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/067—Dividing the beam into multiple beams, e.g. multifocusing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/20—Bonding
  • B23K26/21—Bonding by welding
  • B23K26/22—Spot welding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/20—Bonding
  • B23K26/21—Bonding by welding
  • B23K26/24—Seam welding
  • B23K26/244—Overlap seam welding

Definitions

• This invention relates generally to welding systems, and more specifically to laser welding systems and methods.
• Modem manufacturing processes often require joining of dissimilar materials, such as nickel to brass, stainless steel to copper, stainless steel to brass, or metal to cermet. Attempts to fusion weld dissimilar materials have met with limited success due to intermetallic phases formed in the weld. The different physical properties of the two materials lead to complex problems in weld pool shape, solidification microstructure, and segregation patterns. State of the art laser welding techniques result in hard, brittle microstructure, having low strength and large cracks. Such welds are unreliable and the welding processes unstable.
• Previous laser welding devices using rotating laser beams have employed complex optics and mechanisms.
• a laser beam is passed through spinning optical elements, which divert the laser beam from the optical axis and generate a circular path on the welding target.
• Lenses, mirrors, and prisms used to divert the laser beam are not radially symmetrical or are mounted asymmetrically to the optical axis, limiting rotation speed. This limits the speed and stability of the laser beam at the welding target.
• a slow speed increases the interaction time of the laser beam with the welding target, requiring reduced beam power to avoid spattering and a rough weld.
• the increased interaction time results in bad metallurgical performance for welding of dissimilar metals. Decreased optical stability reduces the accuracy of the weld.
• One aspect of the present invention provides a system for welding a target and having an optical axis including a source of a laser beam, a rotatable diffraction grating converting the laser beam to a pair of laser spots rotating about the optical axis, and a lens focusing the pair of laser spots on the target.
• Another aspect of the present invention provides a method for welding a target including providing a planar rotatable diffraction grating, rotating the rotatable diffraction grating about an optical axis orthogonal to the plane of the rotatable diffraction grating, directing a laser beam along the optical axis onto the rotatable diffraction grating to generate a split beam, and focusing the split beam onto the target.
• Another aspect of the present invention provides a system for welding a target including a planar rotatable diffraction grating, means for rotating the rotatable diffraction grating about an optical axis orthogonal to the plane of the rotatable diffraction grating, means for directing a laser beam along the optical axis onto the rotatable diffraction grating to generate a split beam, and means for focusing the split beam onto the target.
• FIGS. 1 & 2 are a cross section and weld path schematic diagrams, respectively, of a welding system made in accordance with the present invention
• FIGS.3&4 are weld path schematic diagrams for 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 flow chart of a method for welding in accordance with the present invention.
• FIGS. 1 & 2 are a cross section and weld path schematic diagrams, respectively, of a welding system made in accordance with the present invention.
• the welding system diverts a laser beam through a rotatable diffraction grating to generate a pair of rotating laser spots on a target.
• welding system 20 includes a source 22 of a laser beam 24, a rotatable diffraction grating 26, and a lens 28.
• the optics of the welding system 20 are aligned along optical axis 30.
• the rotatable diffraction grating 26 converts the laser beam 24 to a pair of laser spots 32 rotating about the optical axis 30.
• FIG. 2 illustrates the welding process with the laser spots 32 forming welds 50 on the target 34, i.e., the welds 50 do not yet form a complete circle.
• the welding system 20 can also be used to make welds which are less than a complete circle if desired.
• the rotatable diffraction grating 26 is secured in rotatable housing 40, which is carried in fixed housing 42 by high speed bearings 44.
• a speed controlled AC servomotor 46 drives the rotatable housing 40 through a belt 48.
• the arrow at the rotatable diffraction grating 26 illustrates the rotation of the rotatable diffraction grating 26.
• the optical axis 30 is along the direction of gravitational force, so that the rotatable housing 40 hangs from the fixed housing 42.
• the source 22 of the laser beam 24 can be a fiber optic conductor transmitting the laser beam 24 from a laser 21 or the direct output of a laser.
• the laser 21 can be any pulsed or continuous laser source suitable for welding.
• the laser 21 is a neodymium- doped yttrium aluminum garnet (Nd: YAG) laser generating a laser beam at a wavelength of 1064 nm and a pulse power of about 600 to 6000 Watts.
• the laser is an HL204p available from Trumpf Laser GmbH of Schramberg, Germany.
• the laser beam 24 spreads on entering the rotatable housing 40, becoming spreading beam 60.
• the rotatable diffraction grating 26 can be any diffraction grating suitable for dividing the laser beam 24 into at least a pair of laser spots 32, such as a binary phase diffraction grating.
• the rotatable diffraction grating 26 generates split beam 62 from the spreading beam 60, and is secured within the rotatable housing 40, which rotates about the optical axis 30.
• the rotatable diffraction grating 26 is planar and radially symmetric. The plane of the rotatable diffraction grating 26 is orthogonal to the optical axis 30, allowing rotation of the rotatable diffraction grating 26 at high speed about the optical axis 30.
• the rotatable diffraction grating 26 can be a photoresist coated on glass or etched in fused silica as desired for the particular laser used.
• the pattern of the rotatable diffraction grating 26 can be selected to produce more than one pair of laser spots 32, or that a stack of separate rotatable diffraction gratings can be used.
• one rotatable diffraction grating splitting the laser beam into two identical images can be positioned with its pattern at right angles to another rotatable diffraction grating of the same types, generating four split beams and two pairs of laser spots.
• the lens 28 can be any single or group of lenses collimating and focusing the split beam from the rotatable diffraction grating 26 to provide a focused beam 66 on the target 34, - A -
• the lens 28 is stationary relative to the optical axis 30.
• the lens 28 includes a collimating lens 52 and a focusing lens 54, such 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 the focused beam 66 from the collimated beam 64.
• the rotatable diffraction grating 26 can be moved axially within the spreading beam 60 to determine the diameter of the laser spots 32 and the diameter of the weld path 51 on the target 34. Placement of the rotatable diffraction grating 26 within the spreading beam 60 provides the flexibility of adjusting the diameter of the weld path 51 on the target 34, i.e., adjusting the pitch between the laser spots 32 in accordance with the grating constant and position of the rotatable diffraction grating 26. In another embodiment, the rotatable diffraction grating 26 can be disposed between the collimating lens 52 and the focusing lens 54 in the collimated beam 64.
• Placement of the rotatable diffraction grating 26 within in the collimated beam 64 fixes the diameter of the weld path 51 on the target 34, i.e., fixes the pitch between the laser spots 32 in accordance with the grating constant of the rotatable diffraction grating 26.
• the target 34 and workpiece 36 can be any two parts to be joined by welding.
• the target 34 is plate and the workpiece 36 is a hollow cylinder.
• both the target 34 and the workpiece 36 are plates.
• the target 34 is a wire and the workpiece 36 is a plate.
• the target 34 and workpiece 36 can 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 the welding is to seal the ceramic burners of high intensity discharge (HID) lamps.
• HID high intensity discharge
• the target 34 and workpiece 36 can be carried on a stage 38 to hold the target 34 and workpiece 36 in position for welding.
• the plane of the target 34 is orthogonal to the optical axis 30, so the weld path 51 on the target 34 is a circle.
• plane of the target 34 is at an angle relative to the optical axis 30, so the weld path 51 on the target 34 is an ellipse.
• the angle can be any angle for which the laser spots 32 are sufficiently in focus over the whole weld path 51 to provide sufficient power to make the weld, such as an angle between the plane of the target 34 and the optical axis 30 of less than about 20 degrees.
• the stage 38 is stationary with respect to the optical axis 30 during welding.
• a driver 39 moves the stage 38 during welding to make complex weld paths on the target 34, such as cycloids.
• the driver 39 can be programmed to move the target 34 orthogonal to the optical axis 30 in any track desired, such as a linear or two dimensional track.
• a high purity shield gas such as air, nitrogen, argon, and/or oxygen, can be applied at the target 34 to provide cooling and aid plasma formation.
• the shield gas can be selected as desired for the particular materials of the target 34 and the workpiece 36.
• the flow of the shield gas can be cross flow, down flow, and/or box flow, as desired.
• the pair of laser spots 32 rotate about the optical axis 30 on the weld path 51 generating welds 50 on the target 34.
• the diameter of the laser spots 32 is typically in the range of about 0.1 to 0.6 mm, as desired for a particular application.
• the high speed rotation of the rotatable diffraction grating 26 moves the laser spots 32 rapidly across the target 34, limiting the interaction time between the laser spots 32 and the target 34.
• the interaction time is defined as the time required for the laser spot 32 to move one diameter of the laser spot 32 on the target 34.
• the interaction time is also the time that the laser spot 32 is at a certain point along the total weld path 51.
• the interaction time is typically 0.1 to 0.2 ms.
• the limited interaction time produces a sound weld by delivering high energy to both the target 34 and the workpiece 36 in a very short time.
• the high energy forms a plasma plume and a keyhole through the target 34 to the workpiece 36.
• the reflection of the laser light within the keyhole increases energy delivery to the target 34.
• Molten metal around the keyhole flows into the area behind the moving laser spot 32 due to surface tension and solidifies, forming the weld 50.
• the limited interaction time reduces spattering near the weld and results in a smooth weld surface.
• the desired interaction time depends on the materials of the target 34 and the workpiece 36, and is a function of the velocity of the laser spot 32 on the target 34.
• the interaction time is defined as the time required for the laser spot 32 to move one diameter of the laser spot 32 on the target 34.
• the interaction time is also the time that the laser spot 32 is at a certain point along the total weld path 51.
• the velocity of the laser spot 32 is determined by the diameter of the weld path 51, which is typically set by the configuration of the target 34 and the workpiece 36 to be welded, and the rotation speed of the rotatable diffraction grating 26, which is variable.
• the rotation speed of the rotatable diffraction grating 26 is typically between about 1500 and 4500 rpm, and less than 10,000 rpm.
• the speed of the laser spot 32 on the target 34 is typically about 500 mm/sec and can be in the range of about 200 to 800 mm/sec.
• the desired interaction time of the laser spot 32 with the target 34 is typically about 0.2 msec and can 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 varied with time, to produce particular welding results.
• the laser can be on for less than the time required for one of the laser spots 32 to navigate half of the weld path 51 to generate two separate welds along the weld path 51, one path from each laser spot 32.
• the laser can be on for the time required for one of the laser spots 32 to navigate half of the weld path 51 to generate a circular weld along the weld path 51.
• the laser can be on for more than the time required for one of the laser spots 32 to navigate half of the weld path 51 to generate a multipass weld along the weld path 51.
• the power to the laser can also be varied with time during the weld. For example, the power can be turned on sharply at the beginning of the weld, held constant for most of the weld, and tapered off, such as a linear taper, at the end of the weld. Tapering off the power at the end of the weld assures that no hole is left at the end of the weld.
• FIGS.3 & 4 are weld path schematic diagrams for a welding system made in accordance with the present invention.
• FIG.3 illustrates a weld path for a stationary target with two pairs of laser spots.
• FIG. 4 illustrates a weld path for a linearly moving target with one pair of laser spots.
• FIG.3 illustrates the welding process with the laser spots 32a, 32b having formed weld 50 on the target 34, i.e., the weld 50 forms a complete circle.
• the welding system 20 can also be used to make welds which are less than a complete circle if desired.
• the two pairs of laser spots 32a, 32b can be generated by stacking two rotatable diffraction gratings at right angles to each other. Those skilled in the art will appreciate that any number of rotatable diffraction gratings can be stacked to generate the desired number of pairs of laser spots.
• a weld 50 is generated along a complex weld path along a linear track 58 by moving the target 34 along a line in a plane perpendicular to the optical axis of the welding system.
• the speed of the target 34 relative to the rotation speed of the rotatable diffraction grating determines whether loops 56 are formed (prolate cycloids) or whether the weld path is a series of two crossing curves (curtate cycloids).
• a complex weld path along a linear track 58 can be used to attach a linear target to a workpiece or to connect two plates along an edge.
• a driver operably connected to the stage carrying the workpiece and the target 34 drives the linear motion of the target 34.
• the driver can be programmed to drive the target along complex tracks as suited to a particular target shape.
• the driver can be programmed to provide a circular track near the circumference of a large circular target, resulting in a complex weld path along the edge of the circular target.
• FIG. 5, in which like elements share like reference numbers with FIG. 1, is a schematic diagram of another welding system made in accordance with the present invention.
• the rotatable diffraction grating 26 is disposed in the collimated beam 64 rather than the spreading beam 60.
• the welding system 20 includes a source 22 of a laser beam 24, a rotatable diffraction grating 26, and a lens 28 including a collimating lens 52 and a focusing lens 54.
• the optics of the welding system 20 are aligned along optical axis 30.
• the rotatable diffraction grating 26 located between the collimating lens 52 and focusing lens 54 converts the laser beam 24 to a pair of laser spots rotating about the optical axis 30 on the target 34.
• the rotatable housing securing the rotatable diffraction grating 26, the speed controlled AC servomotor driving the rotatable housing, and the fixed housing about the rotatable housing have been omitted from FIG. 5 for clarity of illustration.
• the collimating lens 52 receives the spreading 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.
• the focusing lens 54 receives the split beam 62 and generates a focused beam 66, which provides the focused pair of laser spots on the target 34.
• FIG. 6 is a flow chart of a method for welding in accordance with the present invention.
• the method for welding a target includes providing a planar rotatable diffraction grating 100, rotating the rotatable diffraction grating about an optical axis orthogonal to the plane of the rotatable diffraction grating 102, directing a laser beam along the optical axis onto the rotatable diffraction grating to generate a split beam 104, and focusing the split beam onto the target 106.
• the method further includes moving the target perpendicular to the optical axis, such as moving the target along a line perpendicular to the optical axis.
• the method further includes applying shield gas to the target.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Laser Beam Processing (AREA)

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• 2006
  • 2006-06-26 KR KR1020077030407A patent/KR20080017057A/ko not_active Application Discontinuation
  • 2006-06-26 EP EP06765880A patent/EP1910014A1/de not_active Withdrawn
  • 2006-06-26 JP JP2008519062A patent/JP2008544859A/ja not_active Withdrawn
  • 2006-06-26 WO PCT/IB2006/052100 patent/WO2007000717A1/en not_active Application Discontinuation
  • 2006-06-26 CN CNA2006800237909A patent/CN101291774A/zh active Pending

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