Laser cutting has the advantages of small thermal deformation, high cutting accuracy, and easy to realize unmanned automatic cutting.By using high-power laser source, the cutting speed and surface quality are better than plasma cutting.Therefore, laser cutting technology has developed into a modern cutting tool.Laser cutting machine not only has the complex Mechatronics characteristics of conventional numerical control equipment, but also has its unique structural characteristics, such as optical system, high-pressure system and cooling system.In order to minimize the processing time and reduce the cost, it is necessary to do the equipment maintenance to ensure the highest processing speed of the machine tool, so as to increase the average time without failures and improve the utilization rate of the equipment.

1. C02 laser cutting machine by Bystronic laser AG

Fig.-1-Optical-structure-diagram-of-Bystronic-laser-cutting-machine

1.1 Design structure of Bystronic laser cutting machine

Bystronic’s laser machine can be divided into bed, exchange table, electrical control cabinet, laser generator and laser control cabinet, loading and unloading device, etc.The cutting tool is a laser beam;By fixing the reflector group installed on the moving coordinate axis of the machine, the floating optical system is adopted.The beam is transmitted to the workpiece to ensure the stability of the light path from the laser generator to the cutting head.At present, this technology has become a standard technology widely used in the world. The laser activation medium is a mixture of carbon dioxide, nitrogen and helium. The gas flow direction is consistent with the cavity axis. The axial flow gas can be cooled effectively, so the energy conversion process in the cavity can be optimized.

1.2 Processing principle of Bystronic laser cutting machine

Cutting process is the interaction among laser beam, cutting auxiliary gas and workpiece. This means that the laser acts on the surface of the material, the material is heated and melted by high temperature, and then the hot material is burned or blown away by auxiliary gas to form a slit. Therefore, the laser cutting parameters, such as power and pressure, can be adjusted to achieve the best effect.

2. Maintenance of Bystronic C02 laser cutting machine

According to the structure and processing principle of the equipment, the maintenance can be divided into four parts: peripheral equipment, machine bed and control, laser generator and high pressure part maintenance, and process control.

2.1 Maintenance of peripheral equipment

Most users only consider that the maintenance of the equipment is the equipment itself. In fact, the maintenance of peripheral equipment is quite important.

2.1.1 The quality of the power

Because of the high-voltage system, laser cutting machines generally require the high quality of power supply. .Generally, the allowable grid voltage rangeis- 10 %~ + 5 % of the rated value.If the voltage fluctuation is large, three-phase imbalance, or high-frequency interference, it will cause the malfunction of the machine tool and the damage of high-voltage components. Therefore, it is necessary to monitor the quality of the main power supply frequently.For areas with poor power grid quality, it is recommended to install voltage regulators and use special lines;At the same time, it should also ensure that it works normally.The Bystronic laser machine also requires the equipment to be grounded independently. One is to protect the grounding for safety design, and the other is to ensure the stability of the distance sensing of the cutting nozzle during cutting.Therefore, the equipment grounding resistance should be measured regularly.

2.1.2 The quality of compressed air

In addition to the needs of conventional pneumatic system, the external optical path lens of laser cutting machine is generally protected by compressed air.
The cutting machine of Bystronic laser AG is equipped with multi-stage air filters in the gas unit and laser generator of the machine tool, such as oil-water separator, activated carbon filter, etc, For the protective gas source of the lens, the ultrapac filter is used for secondary filtration to ensure that the gas is dry and clean, and the replacement cycle of the filter element is clearly limited. But it should be emphasized that although the equipment has its own filtering device, there are still requirements for users’ compressed air source.If there is too much water and oil, the life of the filter element will be greatly shortened.Once the lens is polluted, the service life will be greatly shortened, the laser power will be reduced, the cutting speed will be reduced. As a result, the maintenance cost will be increased.Therefore, the maintenance of laser cutting machine must not forget the maintenance of air compressor and dryer.

2.1.3 Laser gas purity

The laser gases of CO2 laser cutting machine are CO2, He and N2.
All manufacturers have strict standards for gas purity, as shown in Table 1:
Table 1 Gas purity index of laser cutting machine

Only when the purity of laser gas is ensured, the best E/N value (characteristic energy of electron) of
discharge can be obtained after mixing, and stable laser can be produced.
If the gas content exceeds the standard, especially the water content exceeds the standard, the energy of
laser beam will be weakened, and the aging of internal components such as discharge tube and discharge
electrode will be accelerated.
Of course, the service life of internal lens of resonator will be shortened.

2.1.4 Maintenance of vacuum cleaner

The process of laser cutting will produce a lot of industrial dust.The function of vacuum cleaner is to remove dust and odor and keep the equipment and environment clean.The cleaning and maintenance of dust removal equipment should be carried out regularly in strict accordance with the regulations to ensure the dust removal effect. If the cutting dust can not be effectively removed, it will adhere to the mechanical and electrical components, accelerate the wear of mechanical components. Electrical components are also easy to short circuit, resulting in failure. When the cutting head adheres too much dust, the detection of nozzle distance will be inaccurate. When cutting stainless steel, aluminum alloy and other materials with high energy focusing requirements, the cutting quality is difficult to guarantee. For the maintenance of the cooling device, the main content is to replace the standard cooling water regularly, clean the water filter, the condenser and air flter, etc. For those with long service life, it is necessary to check the refrigerant quantity when the refrigeration effect decreases. Relevant details should refer to the attached equipment data, and you can contact the technical service department of the manufacturer when necessary.

2.1.5 Maintenance of chiller

The efficiency of CO2 laser is 10% ~ 20%, and most of the input power is used for gas heating, and the gas temperature rises rapidly. When the working gas temperature reaches 300 °C, the particle inversion of the laser upper level does not exist and there is no laser output.In fact, when the temperature exceeds 150 °C, the photoelectric conversion efficiency has been significantly reduced. Therefore, the laser cutting machine has cooling device to keep the laser gas temperature constant and cool the laser lens and other heating parts. In general, if the chiller has a fault alarm, such as temperature alarm and flow alarm, it will automatically cut off the high voltage and turn off the laser. The laser cutting machine can’t start normally before eliminating the trouble of the water chiller. So, the stability of the chillr determines the state of the whole cutting equipment.

2.2 Maintenance of machine bed and control part

Daily transmission parts of the machine, such as chain, rack and guide rail, should be cleaned and lubricated frequently. The oil should change regularly, especially turbine oil and vacuum pump oil. It is noticeable that iregular replacement of turbine oil will greatly shorten the life of the turbine, resulting in huge economic losses. In addition, the cooling and ventilation system of the numerical control device should be cleaned regularly according to the production environment.
It should check whether the cooling fans work normall, whether the air conditioning equipment and drying equipment work normally, and whether there is water and air leakage. Due to the large dust in laser cutting environment, attention should also be paid to the dust prevention of electric cabinet. In addition to maintenance, the door of the electric cabinet should be opened as lttle as possible. Because the dust and metal powder floating in the air fall on the printed circuit board or electrical connector, it is easy to cause the insulation resistance between components to drop, resulting in failure or even damage to components. In addition, it should pay attention to keep the random data, installation software and parameter backup disk. If possible, it is recommended to use cloning software to back up the hard disk data.

2.3 Maintenance of laser generator and high voltage part

For the maintenance of laser generator and high voltage part, it is generally completed by professional and technical personnel of the manufacturer, such as the cleaning and adjustment of the high voltage module, the cleaning of the optical path lens in the laser, and the adjustment of the laser power and mode.
Bystronic laser Ag company will provide tracking service for each laser cutting machine. By signing maintenance contract with customers, the company will carry out comprehensive maintenance and debugging of the equipment according to the “maintenance inspection list”, find out the hidden trouble in time, and effectively ensure the stability and integrity of the equipment.

2.4 Control of machining process

The control range of machining process is very wide, including the optimization of cutting sequence and layout, the optimization of cutting parameters and so on.It is necessary to emphasize the aspects that are easy to ignore in daily maintenance:

2.4.1 Purity of cutting auiliary gas and cleaning of gas pipeline

Due to the impurities in the gas or pipeline, the gas pressure reducing valve will be blocked after a long time of use.Thus, the cutting gas pressure is unstable, which will inevitably lead to the decline of processing quality.

2.4.2 Maintenance of cutting head

Regularly check the status of cutting head lens and cutting nozzle, and clean or replace them in time.If internal leakage is found, replace the sealing ring immediately.Finall, an effective preventive guardianship system should be established.The purpose is to prevent the occurrence of equipment accidents and strictly control the accidents caused by poor equipment lubrication. Operators should strictly abide by the operating procedures, and put an end to the occurrence of equipment failure and precision reduction caused by operating errors and violating the operating procedures. Make fault repair and maintenance records. When every troubleshooting or maintenance work is completed, it is necessary to carefully record the fault phenomenon, troubleshooting method, when and what maintenance has been done, which is helpful for tracking management and brings convenience for future maintenance. For laser cutting machine, it is necessary to stock some spare parts properly. According to the actual situation, it can be equipped with wearing parts such as lens, nozzle, ceramic ring, It can also refer to the manufacturer’s suggestion to equip some circuit boards and high-power modules that are prone to failure. When on-site maintenance, it will bring great convenience to the troubleshooting. Otherwise, it is easy to fall into the embarrassing situation of “making a meal without rice”, resulting in the shutdown of the equipment and prolonging the maintenance cycle.At present, many users implement TPM (total production maintenance) management system, whicheffectively improves the overall efficiency of the equipment. It is worth promoting.

3. Conclusion

The maintenance of laser cutting machine is a necessary measure to ensure the long-term maintenance or comprehensive recovery of equipment processing capacity (efficiency and accuracy) and maintain the use value of the equipment.It is an effective means to reduce the use cost of laser cutting machine and improve the utilization rate of equipment.