From the discussion of the first two articles, the problem of how thick the plate can be cut by the air compressor equipped with the laser cutting machine mainly depends on the laser power, but has little to do with the pressure of the compressed air.
If the laser power is large enough, the pressure of compressed air can also be cut; If the laser power is not big enough, the compressed air pressure can not be cut.
So how much air compressor should be equipped for laser cutting machine with compressed air as auxiliary gas? What do manufacturer need to pay attention to ?
1. Selection of air compressor
6.1. Selection of air compressor pressure and displacement
As long as the laser power is large enough, the higher the pressure of compressed air, the better the laser cutting quality and the higher the cutting efficiency.
With the development of laser cutting machine power from small power to medium power, then to high power and even super power.
The pressure requirement of the air compressor supporting the laser cutting machine has also increased from the initial 8 bar to 13 bar two years ago, and then to 16 bar now, and it is still developing to 20-30 bar.
The pressure requirement of the air compressor supporting the laser cutting machine has also increased from the initial 8 bar to 13 bar two years ago, and then to 16 bar now, and it is still developing to 20-30 bar.
The proportion of cutting gas is about 80-90% of the total consumption of compressed air.
For the laser cutting machine which does not use compressed air but uses nitrogen or oxygen as auxiliary gas, it still needs a small air compressor to provide cylinder power supply with a 6-7 bar atmospheric air source.
How much air compressor should be equipped for laser cutting machine with compressed air as auxiliary gas?
As auxiliary gas, compressed air is sprayed out of the nozzle coaxially with laser beam to assist laser cutting.
Calculating the compressed airflow through the nozzle can determine how much air compressor needs to be equipped.
The absolute pressure of air before and after the nozzle is set as P and P0 respectively.
According to the nozzle theory, when P0/P ≤ 0.528, the flow rate of compressed air passing through the nozzle in the standard state is as follows:
Where,
- Q – air flow, L/min
- S – effective area of nozzle, m2
- μ – flow coefficient, μ < 1, generally taken as 0.92-0.94
- A – nozzle area
- d – nozzle diameter, m
- p – absolute pressure in front of nozzle, Pa
- T – stagnation temperature of gas in front of nozzle, K
- p – absolute pressure in front of nozzle, Pa
- T – stagnation temperature of gas in front of nozzle, K
In the calculation of the air compressor discharge, it is necessary to consider the laser cutting machine free travel time, the actual working time is between 50-70%.
The actual required displacement QN is calculated as follows:
According to the power of the laser cutting machine, the common seven nozzle specifications are: 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 mm.
Fig. 12 shows the auxiliary gas flow rate of nozzles with different cutting pressure.
Example 1:
Question:
A user’s laser cutting machine uses a 2.0 mm nozzle, and the cutting pressure is expected to reach 1.6 MPa absolute pressure.
How should an air compressor be equipped?
Answer:
As shown in Figure 12, a compressed air flow of 0.491 m3/min is required for 2.0 mm nozzle to maintain 1.6 Mpa absolute pressure;
If the actual outgassing time is 70% and 90% of the air displacement of the compressor is used for auxiliary cutting calculation, the required gas volume is: 0.491 * 0.7/0.9 = 0.382 m3/min, and that of two compressors is not less than 0.764 m3/min.
The nominal discharge capacity of a Baode11TK/16 compressor is 0.97 m3/min, which can be equipped with two laser cutting machines with 2.0 mm nozzle (one driven two), or a laser cutting machine with 2.5mm nozzle.
Example 2:
Question:
How can a Baode15TK/16 laser cutting integrated air compressor be equipped with a laser cutting machine?
Answer:
The nominal discharge capacity of Baode15TK/16 compressor is 1.27 m3/min, which can be converted into: 1.27 * 0.9/0.7 = 1.633 m3/min
According to Fig. 12, one Baode15TK/16 integrated air compressor for laser cutting can be equipped with one laser cutting machine equipped with 3.5 mm nozzle or two laser cutting machines with 2.5mm nozzle (one driven two).
6.2. Selection of air compressor type and system
The quality of compressed air has a direct impact on the quality of laser cutting, and the laser cutting machine generally needs to work continuously, so the air compressor is generally placed near the laser cutting machine.
Therefore, the air compressor must be equipped with a good dryer to remove the moisture in the compressed air as much as possible, and the high precision filter group with enough precision must be configured after the dryer to fully filter oil and dust particles.
After the post-treatment, the pressure dew point of the compressed air reaches 2-5 ℃, the residual oil content is less than 0.001 ppm, and the particle content is less than 0.01 μM,
After the compressed air is dried, the temperature is returned to close to normal temperature, which can effectively avoid condensation again,
Such high-quality compressed air can meet the long-term stable operation of the laser cutting machine, without frequent wiping the protective lens.
The piston air compressor is easy to obtain high pressure, but the piston air compressor is noisy, has many vulnerable parts, and the exhaust oil is not handled well.
Therefore, it is not recommended to use piston air compressor below 1.6 Mpa.
It is generally recommended to select screw-type air compressor with suitable cold dryer and precision filter below 1.6 Mpa.
The compressor should adopt permanent magnet variable frequency motor, which can maintain the stability of air supply pressure and ensure the best cutting effect.
Because most users do not have the knowledge of air compressor and compressed air purification treatment, if the users purchase the air compressor, air storage tank, cold dryer and filter one by one, and then install them by themselves, it is not only troublesome, but also likely that the whole system can not meet the required compressed air quality requirements.
Integrated air compressor integrates compressor, air storage tank, water separator, cold dryer and filter into one, which saves the trouble of user’s self-provided gas tank, cold dryer and filter, the trouble of user’s on-site installation and connection, and the trouble of service provided by multiple suppliers.
It can provide continuous, stable and clean compressed air, which is an ideal choice for supporting high-power laser cutting machine.
At present, the laser cutting machine which needs more than 1.6Mpa compressed air mainly adopts piston compressor, but its development is relatively slow due to the restriction of reliability and quality of piston compressor.
With the popularization of high-power laser cutting machine, the demand for thick plate cutting is increasing.
It is necessary to develop a small flow high-pressure screw air compressor with rated discharge pressure ≥ 2.0 MPa.
7. Problems needing attention
7.1 Over–consideration of the purchase cost
When purchasing the air compressor used for laser cutting, if the purchase cost is excessively considered, it is likely to buy a pile of rotten goods in the end.
Because the air compressor supplier also wants to make money, if he sells the compressor system with high quality compressed air to you at the lowest price in the market, he will not be profitable.
For the sake of business and profit, he can only replace the inferior with the good, and replace the small with the big.
For example, for the sake of competition and profit, the cooling dryers with a nominal treatment flow of 1 m3/min are now on the market, none of them can reach the nominal pressure dew point temperature of 2-8 ℃, and the actual pressure dew point is above 12-16 ℃.
If the air compressor for laser cutting is equipped with such a cold drying machine, the protective lens must be wiped many times a day, and the quality of laser cutting cannot be guaranteed.
Similarly, the oil and gas separation core and its own value is not high precision filter is not cheap.
7.2 Greedy psychology
In the choice of air compressor, the user will generally choose the air compressor with larger displacement than the actual demand, and the sales personnel are also willing to sell the air compressor with large displacement.
However, if the air compressor displacement is too large, much larger than the actual demand.
Even if the air compressor has frequency conversion regulation, it may also cause the air compressor to run at the lowest frequency, the air supply is still excessive, and the machine has to enter the shutdown sleep state.
In order to maintain the stable gas supply pressure, once the gas continues, the air compressor has to start operation.
Such frequent “start-run-sleep-start-run-sleep” will not only shorten the service life of the air compressor, but also cause the lubricating oil in the oil-gas separator to bubble and increase the oil content in the exhaust.
When “the air compressor is too large” has become a reality, it is necessary to modify the controller parameters to try to reduce the number of automatic start and stop of the air compressor, such as changing the normal 10 s no-load delay to 180 s no-load delay.
7.3 Good operating habits
If the air compressor is started first and then the cold dryer is started, it is possible that the exhaust can not reach the required pressure dew point for a long time.
At this time, if the laser cutting machine is operated, it is possible that the water in the compressed air will be fogged on the protective lens of the laser cutting head.
The correct operation habit is to start the cold dryer first, and then start the air compressor when the refrigerant temperature drops to about 5 ℃.
7.4 Operating temperature setting
The exhaust temperature of the general air compressor with 7-8bar exhaust pressure is not more than 90 ℃ under normal use conditions.
The manufacturer generally sets the exhaust temperature at 78-85 ℃.
However, for air compressors with exhaust pressure of more than 1.6Mpa, if such a low exhaust temperature is required, it will be a disaster if it is used on laser cutting machine.
Because the high-pressure air compressor runs in summer and only about 80 ℃ exhaust temperature, the exhaust will be very easy to separate water, resulting in the emulsified foam of lubricating oil to cause the sharp increase of oil content in the exhaust.
As a result, it is impossible to cut or cut out waste products, and even damage the focusing lens.
The exhaust temperature should be set according to different places and seasons according to Figure 14.
7.5 pay attention to daily maintenance
1) Before the formal work every day, the condensate in the air tank should be drained and the oil stain of the condensate water should be observed.
2) It is necessary to observe the oil return condition of the oil return pipe from the oil-gas separator to the main engine of the compressor through the sight glass (Fig. 15) to judge whether the oil content in the exhaust gas is high or low, and whether the lubricating oil or oil separation core needs to be replaced.
a. High-speed airflow carrying a small amount of lubricating oil through the mirror – normal;
b. The sight glass is full of lubricating oil and moves slowly – the pipeline is blocked and needs to be cleaned up;
c. The high-speed airflow carries a large amount of lubricating oil through the sight glass- the oil separation effect is poor and the oil content in the exhaust gas is high, which needs to be solved immediately.
3) Replace the filter element of the precision filter within the time specified by the manufacturer
4) Replace the air filter element, oil separator, oil filter and lubricating oil within the time specified by the manufacturer.
Conclusion:
Compressed air is widely used as auxiliary gas in the laser cutting machine.
It can replace oxygen to cut carbon steel sheet and nitrogen to cut stainless steel, galvanized sheet, aluminum alloy and copper alloy.
The correct selection and use of air compressor can not only guarantee the quality of laser cutting, but also obtain good cutting efficiency and obvious cost-saving.
