CA1210077A - Laser material processing through a fiber optic - Google Patents

Laser material processing through a fiber optic

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Publication number
CA1210077A
CA1210077A CA000441986A CA441986A CA1210077A CA 1210077 A CA1210077 A CA 1210077A CA 000441986 A CA000441986 A CA 000441986A CA 441986 A CA441986 A CA 441986A CA 1210077 A CA1210077 A CA 1210077A
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CA
Canada
Prior art keywords
fiber optic
laser
laser beam
core
cladding
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Expired
Application number
CA000441986A
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French (fr)
Inventor
Marshall G. Jones
Gregory Georgalas
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General Electric Co
Original Assignee
General Electric Co
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Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
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Publication of CA1210077A publication Critical patent/CA1210077A/en
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Abstract

LASER MATERIAL PROCESSING THROUGH A FIBER OPTIC

Abstract of the Disclosure Pulse laser energy in the near infrared and visible spectrum is passed through a single fiber optic at power levels required for material and metal processing.
A neodymium-YAG used in pulsed mode is coupled to the end of a quartz fiber optic which transmits peak powers in the kilowatt range. The beam at the output of the fiber optic is focused to achieve power densities capable of cutting, drilling, etc. The main advantage is greater flexibility of laser beam manipulation.

Description

~ 77 RD-14527 LASER MATE~IAL PROCESSING I'HROUGH A FIBER OPTIC
Background of the Invention This invention relates to a laser beam delivery method and system and more particularly to transmission of laser energy through a fiber optic at power levels high enough for manufacturing purposes.
Typically, laser beam delivery for material processing is accomplished through the use of an ensemble of mirrors and prisms for beam steering. An increase in beam steering flexibility is possible when a laser beam is passed through a fiber optic. This flexibility enhances the access to difficult locations on a workpiece during manufact~re. ~uch material processing as drilling, cutting, welding, and selective heat treating and laser surfacing is possible with the laser remote from the workstation.
Laser energy has been transferred along a fiber optic for the purpose of laser communications and laser surgery in the medical field. In both cases, the laser beam is a continuous wave (CW) and average power levels of 100 watts have not been exceeded. As much as 20 watts of CW power from a CO2 laser, which has a 10~6 micrometer wavelength in the far infrared, have been transmitted through a fiber optic. The 100 watt CW power level was achieved from a laser that has a 1.06 micrometer wavelength in the near infrared. Only the CO2 laser has been used with a fiber optic for material processing with applica-tions such as engraving and cloth cutting. The average or pea~ powers are not sufficient for welding, cutting, drilling, and heat treating metals at cost effective rates. The CO~ laser fiber optic which is composed of thallous bromide and thallous iodide is capable of 55 percent transmittance at 10O6 micrometers, and because of this level of transmissivity ~' ~z~ 7 RD-14527 requires cooling. The neodymiumyttrium alumium garnet laser, a source of 1O06 micrometer wavelength energy, has provided the 100 wat-t CW average power for surgical applications.
Such power levels are adequate for limited metal processing but have not been applied. Peak powers in excess of 1000 watts would be more desirable for metal processing.
Summary of the Invention Laser energy is coupled into a single fiber optic which is used as a lightguide to deliver sufficient pulse energy to a workpiece for material processing. A laser beam generated by a solid state neodymium-YAG laser or other laser which is operated in pulsed mode and has a wavelength in the near infrared and visible spectrum, is focusd onto one end of the fiber optic core, preferably made of quartz.
Energy with a peak power in the kilowatt range is passed through the fiber to the output end. The emerging laser beam is focused onto the workpiece at a power density high enough for manufacturing processes such as drilling, cutting, welding, heat treating, and laser surfacing.
The system has a lens that focuses the laser's beam to a small spot whose diameter is less than the fiber core diameter; the numerical aperture is such that the included angle cf the focused beam is less than about 24. In a specific embodi-ment, coupling takes place through a holding fixture made of copper or gold which reflects laser energy and prevents stray energy from entering the fiber optic cladding and melting it.
The cladding at the fiber end is removed and the fiber isreceived in a hole in the fixture. A second embodiment for average power levels up to 250 watts has another input coupler. The fiber end is stripped of cladding and shielding and only the shielding is removed in the nxt section to allow beam coupling through core-air and core-cladding zones, and the prepared fiber end is mounted in a ~ 7~ RD-14527 glass holder. At the output is a lens system -to recollimate and refocus the laser beam onto the workpiece.
This is a flexible laser beam delivery system with minimum optical losses, and increases the degrees of freedom of laser beam manipulation. It is especially attractive Eor metal processing with robotic control.
Brief Description of the Drawing Fig. 1 is a diagram of the laser coupled fiber optic system used to apply laser energy to a metal workpiece.
Fig. 2 is a longitudinal cross section through the fiber optic and shows passage of the laser beam along the core.
Fig. 3 shows an improved input mechanism to transmi-t higher amounts of average power into the fiber optic.
Detailed Description of the Invention Metal processing and the processing of other materials is accomplished by the laser energy delivery system in the figures. Average power levels on the order of 250 watts and peak powers of se~eral kilowatts have been transmitted through an individual fiber optic. A neodymium-yttrium aluminum garnet laser~ which has a wavelength in the near-infrared, is operated in pulsed mode. Other suitable solid state lasers are the ruby laser with a waveleng~h of 680 nanometers, and the alexandrite laser with a wavelength of ~30-730 nanometers, both in the visible spectrum. All the near infrared and visible wavelengths are transmitted in a quartz fiber optic without melting the quartz. This kind of fiber optic is preferred because the fiber is flexible and quartz can be drawn into long ~ibers and is a pure material; impurities tend to absorb energy. The system includes provision for coupling the laser energy in-to the fiber and focusing th~ beam leaving the fiber to a power density sufficient for material processing.

~2i~Q77 RD-1~527 In Fig. 1, a Nd-YAG laser 10 being used in a pulsed mode is coupled to a 1000 micrometer diameter fused quartz fiber optic 11 by focusing the laser beam 12 down on the end of the fiber with a lens 13. In order for the laser energy to enter the fiber, two conditions are needed. Flrst, the small spot at the focal plane has a diameter less than the diameter of quartz core 14. Second, the numerical aperture of the fiber optic is such that the included angle of the focused beam (like a cone angle) is smaller than 22-24.
For best results the end of core 14 is ground optically flat and has an antireflection coating 15. Coupling takes place through a holding fixture 16 made of copper which has a hole to receive the fiber 11. About one-quarter inch of the transparent silicon cladding 17 is removed from the end of the fiber. The copper fixture 16 helps to protect the fiber cladding from any stray laser energy that does not enter the end of the fiber, and prevents melting of the cladding.
Copper tends to reflect 1.06 micrometer laser energy at moderate power levels. A better material would be gold, a higher reflective material.
Referring to the cross section of fiber optic 11 in Fig. 2, the laser beam travels along quartz core 1~ in a zig-~ag path and is reflected at the interface with silicon cladding 17. The optical fiber has a nylon shielding or jacket 18. If a fused quartz fiber optic with a glass cladding is used, the flexibility of the fiber would be decreased but the power carrying capability may increase, since the 1.06 micrometer wave length is transparent to glass, thus leading to lower risk in potential cladding damage. The fiber has a diameter less than 1 millimeter;
fibers larger than this are less flexible.

Having transmitted laser energy through the fiber optic 11 a lens assembly 19, 20 is used to collimate and focus ~ 77 RD-14527 the laser beam. The emerging beam at the output end of the ~iber optic tends to spread out. The beam is recollimated by lens 19 and refocused by lens 20 onto the me-tal workpiece 21. The power density of the focused beam at the focal plane is sufficient for various metal processes. The laser beam may be passed through a glass plate 22 to protect the lenses from any metal vapor. An antireflection coating on the three lens elements increases the transmissivity.
Average power levels up to 155 watts were transmitted into the fiber. With a pulse width (pulse length) of 0.6 milliseconds and a pulse rate of 30 pulses per second, a peak power range of 4000-6000 watts was achieved. After focusing this beam at the output of the fiber optic, power densities of 106-107 watts/cm2, capable of drilling and cutting, were achieved. The 155 watts of laser pulse energy were transmitted through a 1 millimeter fiber optic without any detectable attenuation with bend radii greater than 8 inches (200 millimeters). With fiber bend radii of 1.5 inches (37.5 millimeters), transmittance at 1.06 micrometers is 87 percent.
The laser beam output from the fiber optic was focused on a 0.30 inch (0.75 millimeters) thick Inconel 718 workpiece resulting in both drilling and cutting the material.
The diameter o~ output lens 19, 20 may be much smaller than illustrated, resulting in an output end that is much easier to move around. The end of the fiber may be ground to be a lens element or part of a lens, or a separate element may be attached to the fiber.
The input mechanism in Fig. 1 allows only up to 155 watts of average laser energy, not enough for all processing tasks; higher powers are prohibited due to thexmal limitatlons at the input coupling. Up to 250 watts of average power were transmitted into the fiber optic with the improved coupler ~ 77 RD-14527 in Fig. 3. The fiber tip is stripped of silicon cladding 17 and shielding 18 for 0.75 inches. In the next section just the shielding is removed for an equal distance. This prepared end is then placed in a Pyrex~ holder 23 and set at the proper focal plane of the laser. The prepared end allows beam coupling through two zones, core-air and core-cladding. The first region permits the highly divergent incident beam to enter the fiber ll through a greater acceptance angle provided by the core-air interface. The second zone will provide additional reflections to insure transmission of the collected light energy. The third zone of core, cladding and shielding provide a rugged housing for fiber handling.
Average power levels up to 250 watts were transmitted into a fiber of approximately five meters in length. With a pulse width of 0.2 millisecond and a pulse rate of 200 pulses per second, a peak power range of 5000-9000 watts was achieved.
After focusing the beam at the output of the fiber optic, power densities (106-107 watts/cm2) capable of drilling and cutting were achieved.
Up to 250 watts of Nd-YAG laser pulse energy can be transmitted through a l millimeter fiber optic without detectable attenuation with fiber bend radii greater than 4 inches (lO0 millimeters). At the 4 inch radii, transmittance at 1.06 micrometers is 90 percent. A 0.060 inch (154 milli-meter) thick titanium 6Al-4V workpiece was both drilled and cut. With the ability to transmit the higher amounts of average power the system is much more versatile to the materials processing industry.
The main advantage of the fiber optic laser delivery system is an increase in beam steering flexibility. The degrees of freedom of laser beam manipulation are increased.

~ D-14527 With the fiber optic basically light in weight, the laser beam is moved in almost any direction at a rapid speed.
Being able to loca-te the laser remotely from the workstation is an additional advantage of transmit-ting a laser beam through a lightguide such as a fiber optic. The flexibility inherent in a fiber optic laser beam delivery system also makes it very attractive for laser material processing with robotic control.
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims (6)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:
1. The method of delivering laser energy to perform manufacturing processes comprising:
generating a near infrared or visible wavelength pulsed laser beam;
providing a single fiber optic, less than 1000 micrometers in diameter, having a clad quartz core from which the cladding is removed for a short distance and whose end is optically flat to enhance coupling of energy;
focusing said laser beam onto the end of said quartz core to a small spot those diameter is less than the core diameter, the numerical aperture of said fiber optic being such that the included angle of said focused beam is less than 24°;
transmitting energy with a peak power in the kilowatt range through said fiber optic; and refocusing the merging beam onto a workpiece at a power density sufficient for material and metal processing.
2. The method of claim 1 wherein average power levels up to 250 watts are transmitted into said fiber optic.
3. An improved industrial laser energy delivery system comprising:
a laser operating in pulsed mode that produces a near infrared or visible wavelength laser beam;
a single fiber optic having a quartz core, a cladding and a shielding;
a holding fixture for one end of said fiber optic from which said cladding and shielding is removed, said holding fixture made of a metal such as copper and gold that reflects said laser beam and prevents stray energy from melting said cladding;

a lens which focuses said laser beam onto one end of said quartz core to a small spot less than the core diameter, the numerical aperture of said fiber optic being such that the included angle of said focused beam is smaller than 24°;
said fiber optic serving as a lightguide that transmits peak powers in the kilowatt range to the output end; and a lens system that collimates and focuses the emerging beam onto a workpiece to perform metal processing.
4. An improved industrial laser energy delivery system comprising:
a laser operating in pulsed mode that produces a near infrared or visible wavelength laser beam;
a single fiber optic having a quartz core, a cladding and a shielding;
a holder for one end of said fiber optic from which said cladding and shielding are removed, and then only said shielding is removed, to allow beam coupling through core-air and core-cladding zones;
means for focusing said laser beam onto one end of said quartz core to a small spot whose diameter is less than the core diameter, the numerical aperture of said fiber optic being such that the included angle of said focused laser beam is less than 24°;
said fiber optic serving as a lightguide that transmits peak powers in the kilowatt range to the output end; and means for collimating and focusing the emerging laser beam onto a workpiece to perform material and metal processing.
5. The system of claim 4 wherein the end of said fiber optic to which said laser beam is coupled is optically flat and has an antireflection coating.
6. The system of claim 5 wherein said laser is selected from the group comprising a neodymium-YAG laser, a ruby laser, and an alexandrite laser.
CA000441986A 1982-12-20 1983-11-25 Laser material processing through a fiber optic Expired CA1210077A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US45095182A 1982-12-20 1982-12-20
US450,951 1982-12-20

Publications (1)

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CA1210077A true CA1210077A (en) 1986-08-19

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5463215A (en) * 1992-11-13 1995-10-31 Commissariat A L'energie Atomique Device for aligning the axis of a light beam with the axis of an optical fiber

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5463215A (en) * 1992-11-13 1995-10-31 Commissariat A L'energie Atomique Device for aligning the axis of a light beam with the axis of an optical fiber

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