The Application of Air as Auxiliary Gas in Laser Cutting

Lasers have been widely used in various fields since the first laser was produced by humans in 1960 by means of vibration, starting with the medical field.

Since the 1970s, laser technology has gradually entered the field of industrial cutting.

To this day, laser cutting equipment has been widely used in enterprises.

However, due to the popularity of laser cutting equipment, the price competition between enterprises is becoming more and more fierce, which leads to the decrease of profitability of laser cutting equipment in enterprises.

How to reduce the cost of laser cutting equipment becomes more and more urgent under the background that the whole processing industry needs to transform and upgrade, enterprises need to focus on more value-added production processes such as process improvement, efficiency improvement and R&D investment.

This article will focus on the use of air as an auxiliary gas in laser cutting process to reduce the cutting cost.

 

The influence of different auxiliary gas on cutting quality

First, let’s look at the process of laser cutting:

The laser generated by the vibrator passes through the lens and is gathered at a point to form tiny spots of light. By precise control of the distance between the lens and the plate, ensure that the laser spot is stable in the direction of material thickness. At this time, due to the convergence of the lens, the light spot gathers the laser energy with very large power density, and the power density usually reaches 106~109W/cm2. The material absorbs the light spot energy and melts instantly, and the molten liquid is blown off by using the auxiliary gas to complete the cutting process.

During the whole cutting process, the main function of the auxiliary gas is to form the driving force and remove the molten metal liquid from the material itself.

In this process, different types of gases have different effects on materials and sections:

⑴ Oxygen

When oxygen is used as an auxiliary gas, it can not only blow away the molten metal liquid, but also has an oxidation reaction which will promote the melting of metal, so as to realize the melting of thicker material.

This process will significantly improve the processing power of the laser.

Meanwhile, due to the presence of oxygen, the cutting surface of the material will be significantly oxidized. Besides, it has a quenching effect on the material around the cutting surface, which improves the hardness of the material and has a certain effect on the subsequent processing.

⑵ Nitrogen

As an auxiliary gas, nitrogen forms a protective atmosphere around the molten metal liquid, preventing the material from being oxidized to ensure the quality of the cut surface.

But at the same time, because nitrogen has no oxidation capacity to increase heat transfer, it does not help to improve cutting ability like oxygen.

In addition, as nitrogen is used as an auxiliary gas, nitrogen consumption is very large, resulting in higher cutting costs than other gases.

⑶ Air

Nitrogen is about 78% of the air, and oxygen is about 21%.

When cutting with air as the auxiliary gas, the cutting section must have an oxidation reaction because of the presence of oxygen.

But at the same time, due to the presence of a large amount of nitrogen, the oxidation reaction is not enough to enhance the heat transfer, and the cutting ability will not be improved.

Therefore, the air cutting effect can be understood as between nitrogen cutting and oxygen cutting.

The advantage is that the cost of air cutting is very low. All costs are the power consumption caused by air compressor to provide air, and the consumption of filter element in the air pipeline.

 

The effect of different auxiliary gas on cutting cost

FIG. 1 shows the cutting section effect of 1.5mm thick 304 stainless steel using nitrogen and air as the auxiliary gas.

As can be seen from fig.1 (scroll down):

When nitrogen is used as the auxiliary gas, the section is silvery bright, and when the air is used as the auxiliary gas, the section is pale yellow.

Next, we will analyze the cutting cost of air and nitrogen respectively as auxiliary gases with 1.5mm thick 304 stainless steel, as shown in table 1.

The model used in the comparison is the latest generation of fiber laser cutting machine, which is equipped with the self-developed fiber laser vibrator.

The above cost analysis shows that:

When using air as an auxiliary gas cutting, cutting costs per hour is 23.7% lower than using nitrogen. Such cutting cost reduction can play a very important role in reducing the overall factory processing cost.

In addition, the power consumption of air compressor is analyzed as follows:

At present many enterprises are using no variable screw air compressor if using a permanent magnet frequency screw air compressor, air compressor alone can save up to 50% electricity. The cutting cost is 36.2% lower when using air as auxiliary gas than using nitrogen.

 

Table 1 Cutting cost comparison

ItemSUS304-1.5SUS304-1.5
Processing Speed (mm/min)3500035000
Auxiliary GasAirNitrogen
Air Pressure (Mpa)0.80.8
Auxiliary Gas Flow (NL/min)296.7296.7
Processing Time Per Meter (sec)1.71.7
Electricity Cost (Yuan/Hr)14.67514.675
Air Compressor Electricity Cost (Yuan/Hr)12.255.25
Auxiliary Gas Cost (Yuan/Hr)015.347
Subtotal (Yuan/Hr)26.92535.272
Electricity Cost (Yuan/m)0.0120.012
Air Compressor Electricity Cost (Yuan/m)0.0060.002
Auxiliary Gas Cost (Yuan/m)00.015
Total (Yuan/m)0.0180.029

Note:

⑴ In the above cost analysis, the Operation Ratio of the machine tool is calculated by 70%, and the electric charge is calculated at 1 yuan/KW. The nitrogen cost is calculated according to the liquid nitrogen 1.5 yuan/kg.

⑵ When cutting with air, the power consumption of the air compressor is calculated according to the no-speed screw air compressor of 17.5kW, 1.26MPa and 2.3m3/min.

⑶ When using nitrogen as the auxiliary gas cutting, the air compressor still needs to supply gas to the machine, so it will also generate electricity cost.

The cutting section when nitrogen as auxiliary gas

(a) The cutting section when nitrogen as the auxiliary gas

The cutting section when air as auxiliary gas

(b) The cutting section when air as the auxiliary gas

Section comparison of two parts (nitrogen on the left and air on the right)

(c) Section comparison of two parts (nitrogen on the left and air on the right)

Fig.1 Cutting section effect when using nitrogen and air as the auxiliary gas

 

The range of application when using air as the auxiliary gas

⑴ Carbon steel plate /Q235 steel plate

After the plate thickness exceeds 1.5mm, the cutting section will produce a certain burr. But the burrs are not sharp enough to scratch the paper.

For different power and different types of vibrators, the maximum thickness that can be cut varies when the air as the auxiliary gas.

⑵ Stainless steel plate /SUS304 steel plate

The cutting section produces a yellow oxide layer.

⑶ Aluminum plate /A1050 plate & Aluminum alloy plate /A5052 plate

The cutting burr will decrease relative to nitrogen.

The cutting range is shown in table 2 when carbon dioxide laser cutting machines and fiber laser cutting machines use air as an auxiliary gas.

Table 2 The maximum thickness of the plate is cut when the air is used as an auxiliary gas

Materials Gas4KW CO2 Laser Cutter4KW Fiber Laser Cutter
Q235 steel plateAir3mm3mm
Oxygen20mm22mm
SUS304 steel plateAir3mm3mm
Nitrogen12mm18mm
A1050 aluminum plateAir6mm2mm
Nitrogen6mm8mm
A5052 aluminum alloy plateAir6mm2mm
Nitrogen10mm16mm

The effect of air as an auxiliary gas on cutting

⑴ For carbon steel plate

When cutting with air as an auxiliary gas, the part section will produce smaller burrs, but the burrs are not sharp and can be applied to parts which have low requirements on the burr.

⑵ For stainless steel plate

Since the air acts as an auxiliary gas, the material will be oxidized after processing. In this way, the oxide will produce the defects such as slag and stoma when welding the cutting section, which will affect the welding seam quality, and thus the strength of the welding position will decrease.

Therefore, it is necessary to polish the oxide layer of the welding section to improve the welding quality after the use of air as the auxiliary gas to complete the cutting of the parts.

In addition, the cut section will oxidize, producing a yellow oxide layer. If it’s an outer part, then there has some influence.

The oxide layer also has an effect on the welding process. It is necessary to polish the oxide layer before the welding operation can be done.

⑶ For aluminum plate and aluminum alloy plate

Using air as an auxiliary gas can reduce the cutting burr. If nitrogen is used, the cutting burr will be larger.

 

Requirements for air supply device when using air as the auxiliary gas

When air is used as an auxiliary gas, air pressure needs 0.9MPa.

Considering the pressure level of the air compressor produced by the manufacturer, the screw type air compressor with rated working pressure reaching 1.26MPa and the flow rate reaching 2.3m3/min should be selected.

Special attention should also be paid to the quality of compressed air, ensuring that the air has a drying rate of 99% and moisture content less than 1/100.

Therefore, the filter elements in the compressed air pipeline must use the brand products with reliable quality, and pay special attention to changing the filter element in time.

Meanwhile, for choosing a dryer, there are two types of regenerative adsorption dryer and freeze dryer, each of which has its own characteristics.

However, when considering a long time using, less maintenance and gas supply stability, it is recommended to choose regenerative adsorption dryer.

Finally, when selecting the diameter of compressed air pipeline and pressure reducer, be sure to satisfy the flow and pressure of the output gas of the compressor so as to ensure the stability of pressure when using compressed air.

In addition, the permanent magnetic frequency converter screw air compressor has been sold in the market. This kind of air compressor can save up to 50% electricity compared with the non-variable speed screw air compressor.

 

Conclusion

In the increasingly fierce competitive environment of the industry, it is one of the means to gain the competitive advantage by improving the product process difficulty and improving the product’s industrial design level and so on.

It is also an effective way to achieve competitive advantage to save processing cost under the existing process.

Using air as an auxiliary gas for cutting materials can reduce cutting costs and bring more profits to enterprises, thus providing more help for the transformation and upgrading of enterprises.

2018-05-17T16:54:34+00:00 Cutting|

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