Fiber Laser Systems, LLC
940-231-5752
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Fiber Laser Systems, LLC
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Laser
Choices-Zero in on Your Laser Specifications before Buying It will save a lot of time and effort if you determine the type of laser you need for your application before shopping around. This article will lead you through the “mysteries” of lasers to your final selection. We will not go through the technical theories of how a laser works, but what lasers are used for what applications. We will determine the proper choices for Marking, Engraving, Cutting, Welding, and Scribing. There are many types of lasers, each having different characteristics and differing interactions with various materials. We need to know the lasers output wavelength, average power, peak power, pulse rate, beam quality, and beam size. It will also help us to understand the conversion efficiency and consumable requirements of a particular laser to evaluate the operating cost. The following are the various types of lasers we will be considering for the applications I mentioned above: The CO2 Laser, with a wavelength of 10,600 nm (nanometers), reacts best with organic materials, wood, plastic, paper, glass and fabrics but can be used for metal applications at the higher power levels. With output power levels from 10-Watts to 25-Kilowatts, these lasers can be used for marking, engraving, cutting, welding and scribing. Metals are very reflective to the wavelength of CO2 Lasers and they do not work well for marking metals due to the lower power levels required for marking. CO2 Lasers can operate in the continuous wave (CW) mode or a pulsed mode. However, the peak power in the pulse mode generally never exceeds twice the CW power. The latest CO2 lasers, 10-watts to 500-watts are generally RF excited diffusion cooled and sealed units. 10-100-watt CO2 lasers are air cooled and water cooled at power levels above 100-watts. With the water cooling requirement, a refrigerated water chiller is generally necessary. A CO2 laser is approximately 10% efficient, so 90% of the input power is dissipated in heat that needs to be removed from the laser by either air or water cooling, thus further decreasing the wall plug efficiency. At power levels over 500-watts, CO2 lasers need to be provided with a laser make-up gas (the lasing medium) to maintain the output power level of the laser. This make-up gas is a consumable and adds to the operating cost. The sealed lower power CO2 lasers generally can last 3 to 5 years before needing to be recharged with gas. The “Q” Switched Nd:YAG or Vanadate Laser with a wavelength of 1,060 nm is best used for marking and scribing applications. These lasers react well with metals, ceramics, and plastics for marking applications. The average output power levels of these lasers generally range from 5-watts to 100-watts, and the newer units are diode pumped (excited) rather than flash lamp pumped. The unique feature of this Nd:YAG laser is the “Q” Switch which turns the laser beam on and off at frequencies from 1 kHz to 50 kHz. On the off cycle, the diodes continue to pump energy into the laser crystal so that when the beam is turned on again it releases a very high peak power pulse in the multi-kilowatt range. This high peak power pulse quickly breaks down the surface of the material being marked and virtually vaporizes it. These higher power pulses also help in producing a contrasting color when marking plastics. The Diode Pumped Nd:YAG lasers are generally water cooled via small refrigerated chillers to maintain laser output power stability and cool the diodes and laser rod. The solid state Nd:YAG or Vanadate laser rod (crystal) is the lasing medium and will last indefinitely if cared for properly. The laser pumping diodes will generally last from 10,000 to 20,000 hours before replacement is required. The most frequent maintenance required is a change of water, water filter, and anti-algae compound in the closed loop refrigerated chiller’s water circuit every 3 months. Laser optics will also have to be cleaned periodically. The “Q” Switched Nd:YAG and Vanadate lasers can also be frequency doubled to 532 nm (green), frequency tripled to 355 nm (ultraviolet), and frequency quadrupled to 266 nm (deep ultraviolet). The shorter the wavelength the smaller the spot size that the laser beam can be focused to. However, for each conversion to a shorter wavelength, the laser power is significantly decreased and the laser price tag is significantly increased. These shorter wavelengths are generally needed when processing micro-electronic devices that require the finest detail or resolution that can be achieved. The Pulsed Nd:YAG Laser with a wavelength of 1,060 nm is suited to intricate metal welding, cutting, and drilling applications. The average power level of these lasers range from 15-watts to 600-watts and are flash lamp pumped. The pulse rates are generally 1 to 25 pulses per second for lasers with power levels up to 50-watts and 1 to 1000 pulses per second for the highest power lasers. The main feature of the Pulsed Nd:YAG laser is its high energy per pulse which can be up to 80 joules for the highest power laser. This laser functions by using overlapping precisely controlled laser pulses to control the progression of the cut or weld, and in the case of drilling several pulses can be delivered in the same location. For cutting and drilling applications, a high pressure small orifice coaxial gas assist nozzle is used to help remove the molten material from the cut path or drill hole. In the case of welding, a larger orifice lower pressure coaxial nozzle is used to deliver a blanket of inert gas cover to the molten weld area to prevent oxidation. Because the Pulsed Nd:YAG laser uses a broad spectrum flash lamp for laser pumping (excitation), it is fairly inefficient at converting the electrical input power to laser power. It has an efficiency of approximately 3%. These lasers are water cooled at the low end via air/water heat exchangers and at the higher power levels by refrigerated chillers. The flash lamps require changing every 500 to 1000 hours of operation. Higher maintenance costs are associated with changing flash lamps, aligning and cleaning optics, and maintaining the water purity in the closed loop chiller systems. All of this said, it is still the only laser that can be used for certain applications. The Fiber Laser, with a wavelength of 1,060 nm, is the newest laser on the block. It is diode pumped and has power output levels from 5-watts to 10 plus kilowatts. From 5 to 20-watts, it can be “Q” switched for marking and scribing applications including plastics. At the higher power CW mode of operation, it can be used very effectively for metal cutting and welding applications. The beam quality of the Fiber laser is generally better than other 1,060 nm lasers so it will process parts faster for any given power level. The laser beam is delivered to the work piece via small diameter fiber cable with a focusing head so it is very flexible when trying to fit it into tight quarters or moving the laser beam at high speeds on an X-Y-Z Axis Gantry System. One laser can also share its laser beam with several workstations by switching the beam from one fiber optic cable to another. The Fiber laser has a wall plug efficiency of nearly 30%. This means it will take the least amount of electrical power to operate for any given power level. Pump diode lifetimes in excess of 100,000 hours are projected. This is truly a maintenance free laser. Fiber lasers from 5-watts to 100-watts are air cooled and over 100-watts are water cooled. Because of the higher efficiency of the fiber laser, the refrigerated chiller size can be smaller than other types of lasers operating at similar power levels. Cutting, Welding and Marking capabilities of the several laser types mentioned above:
There are many other applications that these lasers can be used for other than the ones listed above. You should now be prepared to approach either a laser manufacturer or laser systems manufacturer that produces the laser type you feel would be required for your application. Most all manufacturers will process evaluation samples at no charge to verify the results you are looking for. Other information that they will need is your desired production rate, your part handling preferences, and automation required.
Lasers – The Second High Power
Density Welding Systems The first high power density welding systems were electron beam. The generation of a high power electron beam in a vacuum environment, accelerating this stream of electrons via high voltage applied between the cathode and anode, and then electromagnetically focusing that total power to a very small spot on the piece to be welded. The power density (power per unit area) was so intense that it immediately vaporized the metal being welded, which then solidified behind the progression of the weld as the aligned weld joint of the part was being moved at a constant velocity under the focused beam. The welding parameters were power, speed, and focus which provided the weld penetration and weld properties desired. The characteristics of an electron beam weld are excellent because the welding takes place in a vacuum environment and oxidation of the weld area is not a problem since any significant oxygen is absent. Other considerations which detract from electron beam welding are that the part or the electron beam gun has to be manipulated in a large vacuum chamber in order for the part to be welded. These large vacuum chambers require large mechanical and oil vapor diffusion pumps to draw down the vacuum to the high vacuum operating level required. Pump down times can be 20 minutes to a few hours for large systems. In the case of welding the large titanium wing box for the Grumman F15 Fighter the vacuum chamber was extremely large and the vacuum pumps were also large and numerous. A second consideration is the fact that electron beam welders produce intense X-Rays. The high voltage electron beam welders (150,000 volts) with stationary electron beam guns produced the highest penetrating X-Rays and thus the vacuum chambers and guns had to be lined with 1/8” thick lead. The lower voltage (60,000 volts) movable gun systems had to use 1 ¼ inch thick steel in the construction of the vacuum chamber to attenuate the X-Rays. Both types of electron beam welders had to use thick leaded glass for the viewing ports. The next iteration of electron beam welders where called non-vacuum welders. With this process the electron beam was generated in a small high vacuum chamber around the electron beam gun only and the electron beam was passed through a small pressure differential orifice into normal atmospheric pressure. The electron beam immediately collided with air molecules and dispersed rapidly. The weld joint needed to be extremely close to the exit orifice (1/8” to 3/8”) or the electron beam spot diameter was too large to do any effective work. Even at a close distance from the exit orifice the weld characteristics lost the deep depth to width ratios associated with high vacuum electron beam welding. The exit orifices were expensive and eroded fairly quickly. The non-vacuum electron beam welder was also a large X-Ray producer and any automation or production material handling equipment had to be baffled and placed in a lead room. Several electron beam in air systems were produced but this technology did not last long. Electron Beam Welding then progressed into the production welding environment with the advent of “Soft-Vacuum” electron beam welding. With this technology the electron beam is generated in a small high vacuum chamber, directed through a small pressure differential orifice and into a partial vacuum generated by only mechanical displacement vacuum pumps. The electron beam still maintains its deep penetrating narrow weld characteristics, while a smaller vacuum chamber closely sized to the parts to be welded, can be evacuated to the operating vacuum level in a matter of seconds rather than minutes. Many automotive and other parts i.e. flywheels, transmission planet carriers, catalytic converters, hydraulic pistons, hacksaw blades, band saw blades, commutator blanks, torque converters, and spark plugs etc. have been produced on a production basis with “Soft Vacuum” electron beam welding equipment. With some of these systems a unique dial feed table with a sliding vacuum seal was incorporated which allowed the part to be pre-evacuated in the station before the weld station. This set up, totally eliminated the vacuum pump down time from the machine cycle time. Production rates up to 3,000 parts per hour have been achieved using this welding technique. With the advent of higher power lasers many of the applications that were accomplished by electron beam are now being processed by laser systems. However, many of the close tolerance high value aircraft engine and aerospace components that require deep penetrating non contaminated welds are still being processed by electron beam. The laser is also a much more versatile tool. The various wave lengths available with lasers can offer some very selective results depending on the interaction of that wavelength with the material being processed. For instants, a Nd:YAG laser with a wavelength 1,060 nm can weld a clear piece of plastic to an opaque piece of plastic by passing directly through the clear piece without affecting it and then impinging on the opaque piece heating and melting its surface and effectively producing a leak-tight weld at the interface of the two materials. Pulsed Nd:YAG lasers are used for intricate highly controlled low penetration welding. This would be the welding of heart pacemakers, heart valves, medical instruments, orthopedic implants, small hermetically sealed electronic enclosures, spot welding razor blades, jewelry welding applications etc. These lasers produce high energy pulses of short duration so a seam weld needs to be produced by overlapping these pulses approximately 75%. High Power CO2 Lasers have been used for numerous welding applications, many of which have replaced electron beam welding for the same applications. However, the future for narrow deep penetrating electron beam type welds will fall to the new High Power Fiber Lasers. These lasers are extremely efficient, have a long expected solid state pumping diode lifetimes of over 100,000 hours, are virtually maintenance free, and can deliver this laser power through a small flexible fiber optic cable. Manufacturers can use robots to manipulate the fiber optic delivery system to weld a wide variety of large production parts or incorporate it into high speed automated production lines. The laser beam quality of the fiber laser (ability to focus to the smallest spot diameter) is superior to other high power lasers and provides faster welding speeds for a given power level or increased production rates. Also because of the better beam quality the stand-off distances of the focusing optics to the work piece can be extended to two to four feet for some applications. Great strides in the number of new laser welding applications can be expected in the near future. The high power fiber laser can be an expensive commodity but should be able to greatly increase productivity and equipment up time and easily justify their cost. Remember; automation, robots, and reliable lasers level the playing field with low labor costs when competing on the world stage.
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Fiber Laser Systems, LLC |
