Welcome to the world of lasers. Most people I encounter have mixed reactions when I let them know I work in the laser industry. Their immediate thoughts range from laser pointers to highly scientific research labs and they do not realize lasers are used in many different applications and everyday devices. Optical disk drives, printers, barcode scanners, medical instruments, devices for measuring range and speed, lighting displays and, of course, engraving and cutting systems are common in the laser processing industry. Our focus, of course, will be on engraving and cutting systems that utilize CO2 laser sources.
Laser is an acronym for Light Amplification by the Stimulated Emission of Radiation. When light is referred to, it is based on a term called wavelength from the electromagnetic spectrum. There is visible light ranging from 380nm (nanometers) to 780nm, and for CO2 lasers there is infrared light ranging from 9,400nm to 10,600nm. By comparison, the popular fiber laser source operates at a wavelength of 1,064nm. It’s the wavelength of the laser light that determines which materials you can cut, mark or engrave with your laser.
Why are some lasers called CO2 lasers? Quite simply, it is referring to creating the laser beam by stimulating a gas mixture made up of helium (He), nitrogen (N2), hydrogen (H2), xenon (Xe) and carbon dioxide (CO2). A CO2 laser operates by stimulating the gas mixture with either direct current (DC) voltage or radio frequency (RF) waves. The stimulated gas mixture produces ultra tiny “photons” and when enough are produced, they are released from the laser as a usable laser beam. Currently there are three primary types of CO2 laser sources which describe how the gas mixture is held: glass, metal and ceramic. In laser engraving jargon, the term “laser source” is commonly called the laser “tube,” e.g. a glass tube or a metal tube.
The glass CO2 laser source is the only source that is stimulated by DC voltage. The design of the glass laser tubes has pretty much stayed the same since their introduction in the 1960s. Currently, the production of glass tubes is based almost solely in China whereas most metal and ceramic tubes are manufactured in the USA. The manufacture of glass laser tubes requires a skilled glass blower to form the tube properly so that the tube will stay fully sealed during operation, even when it’s filled with water. Due to the ease of glass conducting heat along with the use of high voltage DC current to stimulate the gas mixture, all glass laser tubes must be cooled using water or a water-based coolant mixture. This continuing supply of liquid coolant during usage is very important; otherwise a glass tube will self-destruct from the high temperatures produced by the laser.
In order to properly cool a glass tube, a water chiller system must be used to continuously recirculate a temperature controlled flow of cold water through the tube during operation. Several years ago I recall many glass tube laser systems that used a cooling system comprised of a bucket of water with a fish aquarium pump that was used to cycle the water through the tube. This is in no way a proper water cooling system for a glass laser tube. A proper water chiller system that will not only recirculate the water through the tube but also stabilize the water temperature is best for a glass tube type laser system. It is one thing to recirculate the water; however, as the water absorbs heat from the tube, the chiller needs to bring the water temperature back down to optimum levels so cooling is generally required.
By charging the laser source with DC voltage there is high energy consumption as the glass tubes require anywhere from 15kV (kilovolts) to 26kV, depending on the wattage of the tube. There is a positively charged lead from the power supply source that attaches to the laser tube directly to provide the necessary voltage to actuate the laser. It is important from a safety perspective to ensure that this positive lead has an insulated rubber boot cover to help contain the high voltage and provide safety to the system and operators.
Metal laser tubes use a metal core/tube to contain the gas mixture as opposed to a glass tube. Ceramic laser tubes use a ceramic core to hold the gas. Instead of using high voltage DC, the metal and ceramic laser tubes use a technique called “radio frequency” to stimulate the gasses to produce the beam. Using radio frequency has advantages over DC voltage, including less energy consumption, better control of the engraving process and a longer lifetime resulting in a higher quality laser beam output over a longer period of time. Metal and ceramic laser sources can be air cooled or water cooled depending on the wattage of the laser. Most wattages ranging from 30-120 watts are air cooled.
Now that we know how it works from the technical aspect, another area to focus on is the quality of the laser beam being produced. Many technical aspects contribute to the glass laser source outputting a large diameter laser beam, typically around 5mm or less depending on the wattage and manufacturer. Also, due to using high voltage DC to generate the beam in the glass laser tube, it is difficult to control the glass tube’s output for “pulsing.” A pulse is essentially clipping the beam into small intermittent bursts of power instead of a continuous flow of laser energy. It is difficult to rapidly adjust DC voltage so pulses can be emitted. This means that a glass laser tube will not produce the best raster engraving quality, especially for engraving photo images. It also means that engraving jobs have to be run at slower speeds in order to achieve better quality.
Because metal and ceramic sources use radio frequency to generate the beam, the radio waves can be cycled on and off very quickly resulting in excellent pulsing, thus rendering excellent raster engraving quality, a characteristic which is very important for photo engraving and fine detail work. The metal laser source has electrodes that generate the radio frequency mounted on the inside of the metal core. Ceramic sources have electrodes mounted on the outside of the source due to the fact that RF can pass through the ceramic. Having electrodes outside of the gas mixture can yield a better quality laser beam and less contamination of the gasses.
The metal core of an RF laser is simply a metal box that is created by welding the pieces of metal together. Having the electrodes on the inside of the metal core can cause scrubbing over time which will weaken the welds. As the welds weaken, you may notice outgassing from the laser source. Outgassing occurs when the gas “leaks” out of the tube resulting in a gradual loss of laser power over time. This means your metal tube laser rated at 60 watts might only output 55 watts after a few years of use.
A ceramic core is manufactured by fusing two halves of the ceramic core together at 800°C. This process not only produces a single core clear of any contaminants due to the extreme heat used, but also provides a solid, uniform core without any welds, eliminating outgassing effects. The purity of the gas directly contributes to not only the beam quality but the lifetime of the laser tube. The quality advantage of the ceramic core is the increased beam quality resulting in finer details along with faster pulses which means highly detailed work can be processed at high speeds.
As you can see, there is a lot of information to consider concerning the laser source, which often is referred to as the “engine” of a laser system. Choosing the laser source that is best for you comes down to your end applications. The simplest way to determine the best choice is to break down your work based on raster engraving and vector cutting.
If you simply want to cut shapes out of various materials either the DC charged or RF charged sources will all produce excellent quality. This is due to the fact that no matter which source is used, the material being cut requires more continuous energy to blast its way through thick materials. If we would like to get particular on details, the RF source may be able to process the cuts slightly faster than the DC charged source simply from the better range of control.
Another factor to consider is the power stability between the sources for low power applications such as cutting paper or thin films. DC charged (glass tube) lasers have difficulty controlling power settings below 10% of maximum power, so a lower power laser tube may be required for sensitive applications. In other words, if you’re using a relatively high wattage laser, say one rated at 100 watts, and you’re trying to cut paper where about 3 watts of power is optimum, you might experience problems trying to fine tune the power of a DC laser. When cutting paper, a high power DC laser will typically result in burning due to the limited amount of power control. The power stability is improved greatly by using an RF laser source.
If you are constantly engraving graphics, photos, text and logos on various materials then the RF charged sources are clearly the best pick. While the DC charged source can produce satisfactory quality engraving, the RF charged source will provide both much higher engraving quality and faster processing speeds. Since the DC charged source pulses at a slower rate, this means you have to run the motion system slower so usually you will not achieve the same quality compared to an RF source.
If you do significant amounts of both engraving and cutting, one option would be to compare results between both laser sources in order to determine your particular needs. Perhaps the DC source engraves your products fine and cutting is no issue or perhaps the RF laser gives you the quality you are looking for and cutting is also no issue.
The cost of ownership and ROI of the laser system are important factors as well. Lifetime of the laser source plays a huge part in both cost of ownership and your ROI. The DC charged (glass tube) laser sources are typically rated by the manufacturers for 1,000-2,000 hours (operating a 40 hour week) or approximately 1-2 years depending on the wattage and manufacturer of the laser source. Due to the numerous manufacturers of DC laser sources, not to mention that virtually all of the glass laser source manufacturers are in China, it is important to seek a quality manufacturer to ensure the longest lifetime. Average cost of a glass tube replacement ranges from $180-$2,000 depending on wattage and manufacturer. As mentioned, virtually all of the glass tube lasers and the replacement tubes come from China and there is a great amount of variability in price, performance and availability.
As for the lifetime of the RF charged sources, there is a slight difference between metal and ceramic core lasers based on their unique properties. The metal tube RF source can last 4-6 years depending on wattage and other variables, while the ceramic RF source can achieve slightly longer lifetimes ranging from 5-7 years. The average cost for refurbishing or refilling the RF laser source is $1,000-$5,000 depending on wattage and manufacturer. In some cases, higher power sources have higher prices than those mentioned.
Choosing a laser source is only one part of fulfilling your laser system needs. Keep in mind there are numerous factors that can affect the overall laser system performance other than the source. The mechanical design and operation of the motion system plays a huge part in delivering not only the laser to your work but also the quality of your work. Does the motion system provide the detail and accuracy necessary for your application? Do you prefer a system utilizing stepper motors or servo motors? Also, the quality and type of optics can influence the desired output. Lastly, keep in mind that the software and electronics tell the laser what to do and how to do it. This is important for operation and performance.
In the ever-growing world, businesses have to adapt constantly to stay up with consumer demands. One factor for laser systems is the footprint of the system. Many shops are full of equipment and perhaps the space available determines what system you can focus in on. DC laser systems typically have a larger footprint due to the size of the glass laser source. The average size for a 60-80 watt glass source is somewhere around 47”-49” in length, meaning the system will be at least that wide. Compared to a RF source measuring in at around 20”, the system’s overall size of the laser unit can be smaller.
As far as maintenance of the sources goes, there is little for both sources. All water cooled lasers using a chiller system require properly maintaining the chiller. Maintaining the chiller can be as simple as draining and refilling the system every six months to one year. Replacement of the laser tube will be more frequent on the DC sources which can add to the down time of the system. While the RF source does not require as many replacements, it is a higher cost component to refurb or recharge whereas with glass tube lasers most users consider the tube to be a “throw-away” that they plan to replace every one or two years.
In summary, DC sources provide the lowest cost solution for a laser on the market. While saving a substantial amount of money the only sacrifice is maintenance, processing speed and engraving quality. The biggest sacrifice on purchasing or owning a RF source is the cost of the source both initially and for refurbishing or replacing the unit. While cutting quality will be similar to a DC source, the engraving quality will be the best available. The right choice is simply a balancing act based on budget, application needs and quality of work.