NOT ALL CO2 LASERS ARE THE SAME
Learn more about a CO2 Laser
A CO2 laser is otherwise known as a gas laser. As the name suggests it is created by harnessing the reaction of a mixture of gases within a sealed tube under vacuum. These gasses are known collectively as the gain medium. The wavelength of this laser is from 9.3µm to typically 10.6µm, which reacts well with most organic materials such as wood and leather, many forms of plastic, paper and card, stone, glass and rubber to name but a few.
Despite what some may claim the 10.6µm laser is not a good wavelength to mark metals but at high power (>600w) and coupled with a gas assist it is suitable for cutting some metals.
At Lotus we supply systems incorporating low power CO2 lasers from 30w up to 400w
G GGGGlass or Metal?
For almost all low power CO2 lasers the tube, or cartridge as it is otherwise known, is sealed and does not consume any gas from an external source. It can be made of glass or metal.
Glass tubes are designed for cutting applications. Metal tubes are suitable for cutting, marking or engraving applications primarily because they are able to be pulsed with higher frequency than glass tubes.
Glass tubes require frequent monitoring for performance fluctuations and often user hardware adjustment (voltage fluctuation) during operation whereas metal tubes do not.
Replacement of a glass tube can be required as often as every 3 months with average useage. Metal tubes can perform consistently for many years even when operated 24/7 and we have experience of some designs of metal tubes working perfectly well even after 9 years of constant operation.
The glass tube is excited by very high levels of DC voltage, typically 20kV for a laser outputting around 40w. Radio Frequency (RF) is used to excite the metal CO2 laser.
Glass tubes can only be cooled by recirculating water. Metal tubes can be cooled by air or water.
Glass tubes by their very nature are fragile and being connected by a hard wire solder joint they are somewhat high risk during replacement. Metal tubes use quick release connectors and are low risk to exchange.
Glass lasers offer little in the way of any performance benefit as in short they are unreliable and are very unstable. Their only advantage is one of very low cost. Typically, comparing an almost like for like power, the glass laser will cost approximately 1/30th the price of an alternative metal RF CO2 laser.
The initial cost differences are somewhat misleading. Considering all factors, using a glass tube will ultimately be more costly for most installations
We have extensively tested both forms of CO2 laser and, as explained above, have found without any doubt that metal tubes offer greater efficiency, performance, stability and have a significantly longer working lifetime.
Therefore, the entire range of CO2 laser systems supplied by Lotus use all-metal tube technology.
What's happening inside the tube?
LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.
The process starts by applying electricity to creat RF, which is used to excite the gas molecules and so create the laser.
The main gas within the tube is CO2 hence the title; CO2 laser. Other gases are Helium, Xenon and Nitrogen. Each of these gases plays a specific role during the creation of the beam for which the process is called population inversion.
Within the tube are a number of optical elements. At one end of the tube is a 100% reflector. At the other end is a partial reflector through which some energy reflects and some escapes. With some designs of tube there are additional internal mirrors. Upon excitation by RF the gas molecules are Stimulated and react to create a population inversion.The optical elements are used to pass the resulting stimilated Light through the gain medium over and over again, Amplifying it with each pass until the desired wavelength is achieved and so allowed to pass through the partial reflector as an Emission of Radiation.
Cooling
Modern RF metal lasers are relatively efficient, however, as a byproduct of the process heat is generated.
It is vital to remove this heat effectively before it has time to alter the structure and state of the laser tube. Inadequate cooling of of a laser is the single biggest factor that influences stable operation and longevity of working life
There are two methods of cooling a laser:
1) By flowing air across cooling veins
2) By flowing chilled water around cooling channels
Water-cooling the laser offers the best form of heat removal from the tube, however, water-cooling adds significantly to the price, overall footprint and running costs of the system.
Water-cooling is best suited to:
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harsh, industrial environments
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where the system will be operated at a high duty cycle for long periods of time
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where the ambient room temperature varies significantly
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where highly consistent results are critical
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where minimising the noise level of the equipment is a significant consideration
Air-cooling is well suited to:
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stable, office type environments
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where the system will be operated with a medium to low duty cycle
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where the ambient room temperature is relatively stable
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where higher noise levels can be tollerated in the work environment
For most installations air-cooling the laser is adequately efficient and offers significant savings in terms of system cost and footprint.
How is the laser power controlled?
Laser power is controlled via the software as a percentage of maximum potential output (0-100%). To increase effective power the laser is pulsed. Pulsing is controlled by frequency in kHz (how many pulses are fired per second). For most common applications this is typically between 500Hz and 10kHz.
Laser power and frequency as well as motion control settings can be varied to provide for a wide variety of cutting and marking applications.
The beam exits the laser tube with a diameter of approximately 2.5mm (depending on model) where optical components further enhance and deliver its effective energy at the workpiece.
Where are our CO2 lasers made?
The majority of our CO2 systems incorporate a laser that is manufactured by Synrad (USA). Synrad was one of the originators of all-metal sealed tube technology and have made tens of thousands of lasers
Some of our higher powered CO2 systems incorporate a laser that is manufactured by Rofin (UK). Rofin has an enviable pedegree for high-performance CO2 lasers
Both companies have a reputation for outstanding products that are more than proven over 20 years of of manufacturing sealed tube all metal RF laser technology.
NOT ALL SOLID STATE LASERS ARE THE SAME
Learn more about Solid State lasers
There are no gasses used in creating these lasers, therefore, collectively this category of laser are known as Solid State lasers.
Within the Solid State category are several sub categories where the names of the lasers are derived from the source that they are generated from. These sub categories can be identified by a scientific name (example Nd:YAG) to describe the rare Earth materials used in the make-up of the laser medium or by the collective acronyms such as DPSS (Diode Pumped Solid State)
The wavelength of Solid State lasers is variable. For marking lasers there are a multitude of differeng wavelengths but the most common types are:
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532nm Nd:YAG This is otherwise known as a 'frequency doubled' YAG or 'green laser'
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1064nm Nd:YAG This is commonly called a YAG laser
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1064nm Nd:YVO4 This is commonly called a Vanadate laser
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1060-1070nm Yb:Fiber This is commonly called a Fiber laser
While differing dramatically in make-up in many ways, all of the above forms of laser are created using the same basic principles: Light (the source) is directed through an active medium which by population inversion generates the laser.
Both the source and the active medium can be a variety of different elements.
The laser source - older technologies
In system incorporating older technology, for the 532nm to 1070nm laser wavelength there are two main types of source used:
Both are used to pump the laser medium giving rise to the terms 'lamp-pumped' laser and 'diode-pumped' laser.
When compared to the alternatives lamp-pumped laser technology is very old, inefficient, unstable and high in terms of maintenance and running costs. Such machines are large in footprint, consume large amounts of energy (often 3-phase) and generate a lot of heat as a by-product. As a consequence, large water-cooling chillers are required for this type of machine. The lamp is a consumable item that in some cases requires replacement as often as every 400 hours of use. The only real advantage of a lamp-pumped laser is its high power output, which is not necessary for most marking applications. Therefore, lamp-pumped YAG lasers are rarely supplied as new machines to manufacturing facilities in the Developed Countries.
The alternative to using a lamp as the source to pump the active medium is to use laser diodes. Most systems use several diodes arranged as bars, stacks or in an array. The benefits of this type of source are significantly increased efficiency, stability and beam quality. System footprint and energy consumption are lower by comparison to a lamp-pumped system. Power input for a diode pumped machine is single phase. Heat output from this type of machine is significantly lower than a lamp-pumped laser but sometimes still requires the use of a closed loop water chiller, albeit normally quite small in size. Running costs are relatively low. In a DPSS system the diode array, or pack as it is sometimes known, is considered a wear item but often has a working life of several thousand hours, so it's not really a consumable in the same sense that a lamp would be.
The laser source - modern technologies
In the most recent form of technology (Fiber laser) the source is always from highly efficient laser diodes.The diodes of a Fiber laser should not be confused with those of the DPSS laser as diodes for the Fiber laser are significantly more efficient, reliable and therefore longer in working life (expected >100k hours)
The laser medium - older technologies
Systems incorporating older technology use a laser medium that is called a 'rod'. The rod is effectively a crystal that is man-made from rare Earth materials. For example an Nd:YAG rod; YAG is an acronym for Yttrium Aluminium Garnet and Nd relates to Neodymium Doping. The rod is ground to a specific size and shape.
Another form of laser rod is Yttrium OrthoVanadate (Nd:YVO4) - commonly called a Vanadate laser. Vanadate lasers are useful for plastics marking applications that require very low power but they are not suitable for annealing or ablation of metals, so they are less commonly used than other forms of YAG laser
The rod is placed within a chamber to work as the active laser medium. At one end of the chamber is a total reflector (mirror) and at the other end is a partial reflector that is otherwise known as the output coupler.
The laser source illuminates, or pumps, the rod to cause the population inversion, which creates the laser beam.
The light energy passes back and fourth through the gain medium with each pass amplifying it until a stimulated emmission passes through the output coupler at the desired laser wavelength.
Lamp Pumped and Diode Pumped lasers are very similar in their make-up.The efficiency of these two technologies can be quantified by the amount of power (electricity) consumed and the degree of heat generated as a by-product of the process. Typical marking lasers that are lamp pumped consume around 30 amps of current and output around 100w of laser power. Much of this power cannot be used primarily because of beam quality issues so use of an aperture is required, which improves beam quality but wastes laser power.
An equivalent DPSS laser will consume around 14 amps of power. Again, because of beam quality issues an aperture is required and laser power is lost, although less power is lost than a lamp pumped machine
Both technologies produce considerable heat as a by-product of inefficiency that has to be removed by water cooling
The laser medium - modern technologies
During the last few years major technological breakthroughs have enabled a doped optical fiber to be used as the gain medium instead of a rod. The process works similary to above but the efficiencies are much higher.
YAG rods are known to deteriorate with use and can be costly to replace, whereas the optical fiber alternative is expected to last for the life of the machine.
Fiber lasers generate a much higher beam quality and do not require the use of an aperture. Therefore they are very efficient and produce a more stable beam with hardly any heat being generated as a by-product of the process, so no chiller is required and simple air-cooling is sufficient.
Energy consumption is exceptionally low at typically just a few amps and because of the improvements in beam quality and efficiency, a well designed Fiber laser at 20w laser output will commonly outperform an equivalent 50w DPSS alternative.
System maintenance of a Fiber source is nigh on non-existent and unlike older technologies Fiber laser technology does not have any consumable parts.
The source of a Fibre Laser is expected to last for tens of thousands of hours with World leading manufacturers such as IPG claiming expected working lifetimes of 100k hours.
So given all of the above, it's no surprise that Fibre lasers quickly became the default technology for most marking applications requiring a laser with a wavelength 1060-1070nm and it's exceptionally rare these days for us to install anything other than a Fiber laser source to any of the marking systems that we supply.
More recently we've even seen the introduction frequency doubled Fiber lasers at 532nm, which will open up a whole new realm of opportunities
Where are our Fiber lasers made?
Fiber laser technology was pioneered by IPG Photonics, who are recognised World leaders in this technology sector. In our evaluation, there are few alternative suppliers that can match the performance, reliability and affordability that's delivered by IPG products. We have installed marking systems that incorporate IPG lasers that are now as old as 7 years and despite heavy use, sometimes 24/7, these machines are still working as well as the day that they were initially installed.
Therefore, we have made a policy decision to use IPG fiber lasers exclusively in all of the Fiber laser marking systems that we manufacture within the 1060-1070nm wavelength.
We offer output powers of 10w, 20w, 30w and 50w all of which are pulsed at 1mJ max Pulse Energy with Pulse Repetition Rates (PRR) of 20-200kHz depending on the model. All versions enjoy exceptional wall-plug efficiency, fast rise/fall times and excellent beam quality, which makes these laser source ideal for marking/engraving applications.
After determining which wavelength and output power of laser source is best suited to your core applications the next decision is choosing a configuration of the motion system for beam delivery.
There are basically three configurations of motion control to deliver a laser
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Via a scan head
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Via a plotter mechanism
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Via a combination of the above two
SCAN HEAD
This type of system is a high speed marking device
The beam exits the laser to arrive at the first mirror. The first mirror deflects the beam onto the second mirror. Both of these mirrors are mounted to galvanometers (galvos), which are essentially motors that can rotate clockwise or counter-clockwise at very high speed and with great accuracy. One of these galvos operates through the X-axis and the other through the Y-axis.
The beam is steered by the galvos and projected on to the top of the lens. All of the scan head systems that we supply incorporate an F-Theta lens, which means that no matter what angle the beam entry, the lens compensates to deliver a consitent focal point with minimal aberration and so produces a consitent result throughout the marking field.
The make-up of the lens is dependent on several factors such as;
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Focal length - this is the distance from the bottom of the lens to the focal point
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Focal point - this is the smallest spot that the lens can focus the laser down to
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Scan area - this is the maximum area of the marking field that the lens can achieve
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Depth of focus - this is the effective working distance in the Z axis measured either side of the focal point where for most applications a decent marking result is achieved. Beyond this distance the laser would be too far out of focus and undesireable results are likely to occur.
Physically, scan head lenses vary in size, material structure and number of optical layers according to the wavelength of the laser.
Lenses for Fiber lasers (1064nm) commonly consist of multiple layers including a protective lower layer. Lenses for CO2 lasers (10.6µm) are commonly single layer without any protective element. Of course, exceptions do occur.
Lens attributes vary considerably and using the correct configuration is critical to maximising quality and productivity of the mark. A parallel can be drawn against choosing the correct lens for a camera or even glasses for a person.
Typically, lenses for scan heads are described by the scan area that they cover. The scan area is always ultimately circular as that is the shape of the lens, however some suppliers quote scan areas as a square measurement.
Lenses with a short focal length will deliver a smaller focal point and they have a smaller scan area, however, they will deliver a higher power density (a more concentrated pulse), which means higher resolution as well as sometimes faster marking results where laser power is a limitation. Lenses with a longer focal length deliver the opposite. Correct selection of the lens is critical for many applications and bigger is not always better.
Fortunately, lenses are easily interchangeable to allow systems to be applied to a wide range of applications
This type of motion system is essentially a vector device and because of the very few and lightweight moving parts systems like this can work at breathtaking speed.
Therefore, for most marking/engraving applications this type of beam delivery is unbeatable.
Flying Optic Laser
This type of system is a cutting and/or low speed engraving device
The beam is directed by reflection off of mirrors, which are attached to a plotter type device. Because several of these optical elements are continually moving these types of machine are collectively called 'Flying Optic Lasers'.There are approximately 4 mirrors in a typical system and each mirror is strategically placed to deliver the beam from the laser source through the lens and onto the material.
Some of the mirrors are attached to the axis of the plotter and are moved through the X and Y planes. Each of the mirrors will be identified by a number according to how they sit in order of receiving the beam from the laser. For example, Mirror #1 would be the first mirror after the beam exits the laser and Mirror #4 would be the last mirror that sits above the lens.
The final mirror will sit just above the lens with both optic elements being housed within what is called the Focus Carriage.
For well designed machines the Focus Carriage will be pressurised with a gas or more commonly cleaned/dried air to minimise the ingress of debris and so reduce contamination of the optics. Even better systems will deliver gas/air by a nosecone sitting just above the material, which can significantly improve the feed rate and edge/surface quality when cutting.
Flying Optic Lenses
The lens truncates the beam to the smallest possible focused spot, which is called the Focal Point.
There are several types of lens but the most commonly used is called a Plano-convex lens, meaning that it's flat on the bottom (plano) and curved on the top (convex).
Lenses for flying optic machines are usually very small, basic and somewhat low in cost, especially when compared to a lens within a Scan Head galvo type marking machine.
Flying optic laser system lenses have very short focal lengths, typically from 1.5" (38mm) to 5" (127mm). Lenses are selected according to the application. With a short focal length the beam profile is very wide but the focal point is very small. Such a lens is good for higher resolution engraving and for cutting of very thin sheet materials but it's not good at all for much else.
A lens with a longer focal length provides for a beam that is narrower in profile but delivers a larger focal point. Such a lens is better for cutting of thicker materials and so not suitable for cutting thin materials or high resolution marking/engraving.
Because of their very short focal lengths the lens within a flying optic system is positioned very close to the material, which for some applications can mean that contamination is a very high risk. Therefore, the lens and even the last mirror of a flying optic system should be considered as consumable parts that will require frequent maintenance (cleaning) and from time to time even replacement.
Flying Optic Motion System
The motion system itself is essentially an XYZ plotter mechanism consisting of two guide rails in the Y axis and a single guide rail in the X axis to form the shape of the letter H. The Y-axis is mounted to the machine chassis and the X axis is mounted on to the Y-axis. The X axis holds the focus carriage
The Z axis can be motorised, manually adjusted or both and is used to bring the material into the focal range of the lens. For some systems the table moves the material into range. For other systems the table is static and the focus carriage is moved to the material. There are some machines that combine both methods.
This design of system delivers the beam over a rectangular area that can cover as much as several meters in size. It is ideal for working on sheet materials or large objects.
Stepper or Servomotors?
Some people get very blinkered, some quite passionate and most quite confused about the the eternal debate: which is the best type of motor to use in a small format flying optic laser system - stepper or servomotor?
The simple truth is that both are appropriate. From a technological perspective stepper motors are the more simple of the two but that doesn't mean they can't be used. For most basic applications a good quality stepper motor will deliver sufficient speed, accuracy and working lifetime with the benefit that when the time comes to change the motor the process is quick, simple and low in cost
Servomotors have advanatges insofar as speed and accuracy are concerned, however, they are typically several times the cost of a good quality stepper alternative.
So in our opinion, for smaller systems in particular the ideal motor is specific to the demands of the user and that is why we have different models that will use both stepper and servomotors.
Larger systems will always incorporate servomotors.
Encoders
A point that's usually missed in the debate about motors is the type of encoder used in a system incorporating servomotors. An encoder is a device to measure the precise location of the motion system. In poorly designed machines, the encoders of a servomotor are radial (a disc) and fixed to the axle of the motor itself, therefore, all readings are measured at the motor and not actually where the focus carriage is located, which can be several meters away from the motor. Better designed machines use linear encoders that provide for greater accuracy by reading the exact location of the focus carrage wherever it may be within the work area of the machine.
Linear encoders are higher cost but then if cost is a big issue why use servomotors at all?
Motion modes - Raster and Vector
There are two modes that a plotter device can be driven in: Raster or Vector.
Raster mode is used to engrave. Vector mode is used to cut or to score (vector engrave)
In Raster mode the focus carriage scans from left to right in the X-axis applying focused laser energy as a series of dots. By stepping the Y-axis at the end of the X-axis travel an image is built up by a combination of these dotted lines. The principle works similar to that of a common office desktop printer. The spacing of Y-axis steps is variable to provide for faster processing times or higher resolution.
In this mode it is quite easy to produce images to photographic detail over the entire work area although unlike a system with a scan head the angle of engraving can only be in one plane (zero degrees)
Vector Mode
This mode is always used when the system is cutting but can also be used to add some interesting effects to engraving, like highlighting the outside edge of text characters or lightly scoring the surface of the material to produced lined engraving results.
Vector mode drives the plotter in a simple X-Y manner to guide the laser beam along the cutting path.
Combination Galvo/Plotting System
There are some specialist systems that use a combination of the above two motion control examples. Such machines are marking only lasers whose main benefits are high speed, high detail marking (using the galvo mechanism) applied over a large field work area (using the plotter mechanism).
The extent of the overall work area is defined by the limits of the XY plotter mechanism, which can cover several square metres for some machines.
These systems mark the overall working area using a ‘tile’ formation. In other words, the galvo marks a square area then moves on to the next adjacent square area to repeat the process until the entire work area has been covered.
Well made systems like this are able to mark the overall work area without obvious joins between the tiles.
Typically these machines will have a very high resolution lens with a 5 axis motion system (XY+XY+Z)
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XY worktable to allow for a large overall work area
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XY galvo head for the beam delivery
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Z to focus the galvo head
Such machines are expensive to manufacture and difficult to maintain but do have a use for specialist, high value applications.
