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Information Sheets
Auxiliary Equipment
General Considerations for installation
There are many aspects to consider before the installation of the machine, and primarily, a lot of planning will have been made at least 12 months previously. In considering the space requirements for instance, this may involve re-planning or changing areas of the workshop to suit the flow of production parts.
There are also the safe working of the areas around the machine to consider, and in some cases, structural changes have to be made to fit the machine into an existing environment. In more extreme cases, purchasers have moved factory!.
For higher-powered lasers, the standard Electrical connection into the factory comes under close scrutiny. Laser resonators can range from 2kW to 12kW and more these days, and a typical 5kw resonator, will require at least 105kva [152amps/phase @ 400volts] to run the complete installation.
It is very important for the purchaser to have his factory surveyed prior to adding or changing machines of this type, without knowing what it will cost in terms of running large supplies from Sub - Stations nearby.
Pneumatic supplies to laser machines have taken on a more important role, in that compressed air is increasingly used as a cutting gas option for materials up to 3mm. thick. Obviously, one cannot have the air supplies of old, with their oil residues and dirt ingestion. A modern compressor will have dryers and chillers combined to supply dry and clean air at the required pressure.
To take the example of a laser cutting system, the waste products include: fume (fine particles and/or vapour); hot sparks; dust (heavy particles), hot metal parts, slag and dross. Modern machines contain all of these waste products, in one form or another. In particular, the laser generated fume must be removed from the working area, filtered and (depending on the process and the materials) exhausted or recycled. (See fume extraction and safety)
One of the most important factors when considering an installation is the construction of the floor; a factory floor that may have been down for many years may not be suitable. The modern laser machine requires a high specification concrete floor, at least 200mm. deep, and may need to be isolated from the rest of the factory floor, but this will depend on the manufacturers specification for the particular laser base. It is also extremely important for the new floor to be level over the entire area within say 10mm. The modern concrete floor will also be oil resistant.
Gas supplies are an important part of the installation. Consideration has to be given to the pressures, flows and the degree of purity required. Rigid pipework installations, although probably costly, are a better long term solution than flexible pipework.
Chillers for Lasers
Most laser systems require a chiller of some type. The size and type of chiller required depends on the laser type and advice needs to be sought the laser supplier. Some lasers, especially low power diode-pumped solid state lasers either feature an integrated water chiller or can be air/conduction cooled. However, most common industrial lasers (high power diode-pumped solid state, flashlamp pumped solid state and carbon dioxide lasers) require a substantial amount of heat to be dissipated (1 – 20kW).
Many, but not all industrial lasers include a water-water heat exchanger. The laser water circuit (the secondary circuit) may require specific water conditions (eg de-ionized or not, additives or not etc.) This needs to be checked with the laser supplier since the wrong "water" can damage the laser. The primary circuit uses external plant water or water from a stand-alone chiller. Stand-alone chillers can take the form of water-water exchangers, water-air exchangers or solid-state chillers. Especially in the case of water-air and solid-state chillers, consideration must be given the hot air that the chiller will dump into the surroundings and how this is dissipated. It is often better to situate the chiller either in a separate well-ventilated room or outside. Consideration should also be given to the acoustic noise from the chiller. If the chiller is to be installed outdoors then check its suitability for this. Consideration should be given to protecting it from the elements and also frost-protection. The compatibility of the cooling fluid (additives or de-ionized water etc) with the materials used in the chiller and water circuit should also be checked. Incompatible materials/fluids can lead to poor laser performance or damage or build-up of sludge or erosion of components.
When choosing a stand-alone chiller the chilling capacity must be chosen with care. The laser supplier can provide details on the capacity required but in addition the chiller supplier should be consulted with regard to the potential effect of local ambient conditions (air temperature, humidity, plant water temperature) on the chiller performance. Even after this is taken into account, it is usually wise to allow an additional safety margin of at least 20%. The chiller will also require its own electrical supply, generally 3 phase; its current capacity should not be overlooked.
Gas supply for laser processing systems
The gas supply is more than likely to be an important component of your processing system, especially if you are cutting or welding. Not only is the type and quality of gas important but also is the correct supply method. Choosing the wrong supply option will cost you money.
The type of gas supply required depends upon the type of gas, volume consumption, flow rates, pressure and purity required. Most of this information is available from your system supplier although understanding your commercial operation is vital. If you have just purchased your first laser processing system you are unlikely to know what you need, which is why it is worth while getting in contact with your gas supplier who will have a good understanding of your gas supply needs.
Lasing Gases
CO2 and excimer lasers require a mixture of gases to generate the laser energy, which typically requires high purity gas used in small volumes and so is supplied in cylinders. The lasing gas can be supplied as individual components which is blended inside the laser or premixed in a single cylinder.
Assist Gases
Assist or process gases are used at the point where the laser interacts with the material. Usually assist gas is used in large volumes especially when cutting which means that individual cylinders no longer become a viable option.
The supply of gas traditionally falls into three categories; compressed, cryogenic and bulk cryogenic. More recently a fourth option has become available in the form of nitrogen generators.
Making the right choice for your business is critical, so seek help at an early stage. The following is a brief overview of the options, for further information on the capability; pros and cons of the options see nitrogen assist supply options for laser cutting”.
Compressed
For low volume, special or emergency supply, Manifolded Cylinder Pallets (MCPs) are often the best solution. These are typically 15 cylinders packaged together and are available for immediate supply setup when using a special high flow regulator. The MCPs are delivered on the back of a lorry and will need lifting off with a forklift.
Cryogenic
As volumes increase Cryotanks become the preferred supply option, as the product is stored as a cryogenic liquid, which takes up much less space than compressed gases. These tanks can be filled by a road tanker on site or delivered like cylinders, full for empty.
Bulk
For high volume requirements a bulk cryogenic storage vessel is the most economical supply mode. Bulk tanks are filled from larger cryogenic road tankers.
The Trifecta was specifically designed to meet the requirements of the laser cutting market. It provides high pressure supply from medium pressure bulk.
Generator
Increasing volumes still for nitrogen it might be worth considering a nitrogen generator. Nitrogen generators are stand alone units which removes the unwanted oxygen from the air. Nitrogen generators will struggle to give high purity, especially at larger flow rates, which will be apparent from the discoloration of the cut edge. This is especially apparent on thicker stainless steel cuts.
Maintaining gas purity from cylinder supply to laser resonator
Lasers are particularly susceptible to gaseous impurities in the lasing gas. These can have a range of adverse effects from a simple reduction in laser output power to optical element and mechanical/electrical equipment damage. Impurities such as moisture and hydrocarbons can significantly reduce the power of the beam and affect its mode quality and damage internal mirrors and the output coupler. However, should the proportions of the mixture be significantly altered then significant equipment damage can arise. The composition of the mixture can significantly affect the lasing gas viscosity and its impedance. Changes in viscosity can cause undue strain on the turbine or roots blower, which circulates the gas through the laser in the fast axial flow designs. The effect of increased impedance can affect the discharge characteristics and the electrical power supply.
Both of the above conditions can quite easily be caused through poor operational procedures and incorrect gas control and delivery equipment selection.
Regulators
For lasing gases high quality regulators suitable for use with special gases should only be used. These regulators should be of two stage construction to give the best flow control and are normally fitted with a stainless steel diaphragm. Welding regulators with neoprene diaphragms should not be used as they have a significant leak rate which leads to the ingress of atmospheric impurities into the lasing gas stream. The use of changeover manifolds is recommended as these can help ensure continuous operation of the laser such that the laser does not switch off when a lasing gas cylinder is emptied.
Pipelines
The pipeline material should ideally be either stainless steel or copper. However, in the majority of installations polymer or plastic piping is typically used. In fact some laser manufacturers supply their own tubing with their lasers. In general some flexibility is required in these supply lines and some polymer tubing can be accepted provided it is of the right material and of limited length. All polymer materials are permeable to some degree which can lead to low level diffusion through the tube walls. Some materials show higher levels of permeability to moisture and oxygen and these should not be used. High density polyethylene HDPE is considered to be the most suitable material for lasing gases for CO2 lasers.
| Permeability of various hose materials | |||
| Hose Material | Water Vapour (ppm) | Oxygen (ppm) | Nitrogen (ppm) |
| Stainless steel | 1 - 2 | 1 | 2 - 3 |
| Copper | 1 - 2 | 1 | 2 |
| Teflon | 1 - 2 | 16 | 15 |
| Polyethylene | 1 - 2 | 1 | 5 |
| PVC | 6 | 2 | 6 |
| Welding Hose | 15 | 4 | 7 |
| Urethane | 18 | 1 | 2 - 3 |
Purging
When exchanging lasing gas cylinders it is advisable to purge the regulator and line to ensure that there is no ingress of atmospheric gases and contaminants. This requires a more complex gas delivery arrangement which includes 2 cut off valves and a vent line. Such an installation requires that the operator be specially trained in performing the venting procedure correctly, as improperly used this arrangement can cause more impurity ingress than by using a simple pigtail connector with a check valve fitted at the end.
Cylinder hook up
Great care must be taken to ensure that the right gas is hooked up to the right delivery line. If the supply gases are accidentally transposed then the incorrect gas mixture can be introduced into the laser resonator and the associated consequences previously described.
Leak checking of installation
The gas delivery installation should be regularly leak tested to check its integrity because if gas can get out then impurities can also get in. A good rough check is the see if the pressure in the lasing gas lines has dropped over a weekend when the laser has been shut down. However, a regular leak test of the lasing gas supply should be part of the routine maintenance procedure for the system.
Particulate filters
Lasers are very sensitive to particulate debris in the resonator and so great care must be taken to ensure that no particulate is introduced via the lasing gas. Particulate filters are desirable, however, in practice they are rarely fitted.
Excimer lasers
Due to the corrosive and toxic nature of both hydrogen chloride and fluoride based mixtures, panel mounted control systems are recommended. In addition all equipment for F2 service must be suitably passivated. Specialist equipment suppliers should be consulted.
The gas cylinders themselves should be stored in specialised gas cabinets. Due the corrosive and toxic nature of these gases all venting and exhaust must pass through a suitable gas scrubber to eliminate any traces of the halogen.
Maintenance
The gas control equipment and gas delivery lines should be regularly inspected and maintained to the manufacturer’s recommendations. Routine leak testing of the supply should be undertaken to ensure that there is no atmospheric contamination of the lasing gas stream.
Health and Safety
Although lasing gases for CO2 lasers are generally non-toxic, they are inert and therefore do not support life.
In large quantities they can displace air and cause an asphyxiation hazard due to oxygen depletion.
Lasing gases are typically supplied in compressed gas cylinders and all the relevant risks associated with general cylinder handling apply.
Materials Safety Data Sheets should be available from your gas supplier, for all the constituent gases that are used as lasing gases and also for some of the specific lasing gas mixtures. These should be read carefully by all those likely to come into contact with the products and the manufacturer’s recommendations carefully followed.
Excimer lasing gases are on the other hand extremely corrosive and toxic and require extremely careful handling. Specific Materials Safety Data Sheets and instructions regarding their use can be obtained from your gas supplier for the halogen containing gas mixtures.
Fume Extraction
Laser Generated Airborne Contaminants (LGACs) is a term used for the dust and vapour that is generated when a material is processed with a laser. Lasers are increasingly used to mark, etch, cut and weld a wide variety of materials, and coupled with the right fume extraction system they deliver excellent results. Fume extraction is required for most laser operations in order to protect personnel, but it can also have the added benefit of enhancing the performance of the laser process. It is therefore of paramount importance that the correct fume extraction system be specified.
The majority of laser processing involves removal of material. In the case of cutting mild steel, the bulk of laser job shop work, the fume (iron oxide) is innocuous, though the build up of rust deposit in the factory may alone provide an incentive to improve the fume extraction. More generally, depending on the material, LGACs may include a variety of vapours, some of which may be noxious (e.g. benzene, phosgene during the processing of some plastics), together with the solid (small particle) products of complete and partial combustion, which may include some toxic oxides (e.g. chromium and nickel oxides from stainless steel).
In addition to safety concerns, airborne particles can cause problems for the laser if they are allowed to be deposited on the lens or remain in the processing area, causing beam distortion and attenuation. Deposition of particulates within the laser enclosure can contaminate the product and creates the need for regular cleaning of associated equipment. The only practical method of overcoming the above problems is to remove airborne contaminants as quickly and completely as possible by the provision of an efficient fume extraction system.
The first decision to be made is the type of fume extraction equipment to install: either to clean up the fume and return the air to the workplace or to remove the fume to outside the workplace (though the fume should generally still be filtered). In both cases there is the issue of possible leakage of LGACs into the workplace. Also, for air recycled into the workplace the possibility of ineffective removal of hazardous elements of the fume must be considered; for fume exhausted to the atmosphere the issue of environmental pollution has to be considered. And even where the process zone is completely enclosed and fume extraction is complete in normal operation, provision needs to be made for fume-related hazards occurring during maintenance (especially cleaning of the process enclosure) and servicing (especially filter changes).