As a metal material processing equipment, the air plasma cutting machine used to be used for cutting stainless steel and copper, aluminum, and other non-ferrous metal materials. Now it can also be widely used in the processing of low carbon steel, alloy steel, and other materials. Compared with other processing methods, it is more efficient and easy to operate.
Welded structural parts have been widely used in the industrial field. Sheet cutting is the first step in the process of welding finished products, and it is also an important process to ensure welding quality. The use of advanced modern cutting technology can not only ensure the welding quality of the products, improve labor productivity, but also greatly reduce the manufacturing cost of the company's products and shorten the product production cycle. During production and processing, it is often necessary to cut and weld the workpiece, and the air plasma cutting machine is cutting equipment used to cut various metal materials. It has the advantages of good cutting quality, small thermal deformation, fast cutting speed, and smooth surface. Especially in the processing of medium and thin sheets of non-ferrous metals and low carbon steel, its advantages are more obvious.
The difference between oxy-fuel flame cutting and plasma cutting
The oxy-fuel flame cutting method was invented at the beginning of the last century. In the past century, the oxy-fuel cutting materials used for cutting low-carbon steel and alloy steel have been very mature and still occupy an important position in the market. Because oxy-fuel cutting is limited by its internal structure and gas physical characteristics, its cutting speed cannot be further increased. In order to meet the needs of the rapid increase in the amount of metal cutting, scientists have worked hard to find ways to increase the cutting speed. In the mid-1960s, a high-speed oxy-fuel cutting nozzle was invented, which increased the gas cutting speed by 30% to 50%, but it still could not meet the production needs. Therefore, plasma cutting technology has begun to be applied in this field. Due to the high speed and unique advantages of plasma cutting of low carbon steel and alloy steel, it has been highly valued by shipbuilding and automobile manufacturing industries and has been actively promoted. In recent years, various types of plasma cutting have replaced high-speed oxy-fuel cutting for low-carbon steel and alloy steel. In many developed countries, the processing volume of medium and thin plates using plasma cutting machines is close to 50%. With the development of the economy, it is imperative to use air plasma cutting machines to replace flame cutting in the processing of medium and thin plates.
Energy Density
Compared with gas cutting, plasma arc has a higher heat source energy density, as shown in Table 1.
| Heat source energy density comparison | |||
|---|---|---|---|
| Cutting method | Heat source | Energy density kW/cm² | Temperature t/K |
| Oxyfuel cutting | Oxyfuel flame | 1~3 | 3200 |
| Plasma cutting | Plasma arc | 500~800 | Arc column 16000 Arc column center 32000 |
Cutting speed
Compared with gas cutting, plasma arc has a faster cutting speed, as shown in Figure 1. It can be seen from Figure 1 that when the sheet thickness b=5, the plasma arc cutting is 3 to 4 times the oxy-fuel cutting speed; when b=15, the speed ratio drops to about two times. This provides a reference for us to choose the cutting method, not only to achieve the desired efficiency but also not to cause equipment waste.
Cutting performance
Plasma has good cutting performance, as shown in Table 2.
| Cutting performance comparison table | ||
|---|---|---|
| Project | Oxyfuel cutting | Plasma cutting |
| Heat affected zone | Big | Small |
| Thermal energy | Oxyfuel flame | Electricity |
| Thermal deformation | Large (the thin plate is particularly large) | Small |
| Cut surface finish | General | Good |
| Verticality of the cut surface | Good | Slightly worse |
| Cutting range | Low carbon steel, low alloy steel | All conductive metal materials |
| Cutting size error | 1~2mm | 0.5~1mm |
| Slit width | 1~2mm | 1~3mm |
| Operation form | Complex | Simple |
The principle of oxy-fuel flame cutting and plasma cutting
The plasma arc is also called compressed arc, which is an arc with a relatively small contraction of conductive cross-section and concentrated energy density. Under normal circumstances, gas is a good insulator. It is composed of neutral atoms and molecules. The gas in the arc undergoes a qualitative change. Some of the neutral atoms emit negatively charged electrons and become positively charged. The positive ion is ionized. With these two charged particles, it has the ability to conduct electricity. In the ionized gas, the charges carried by the positive and negative charged particles are equal in number but opposite in direction. Therefore, each of its macroscopic regions exhibits electrical neutrality. The gas in this state in the arc is called plasma. Air plasma arc uses cheap air as the ionization medium. After the gas is ionized, under the action of mechanical compression effect, thermal shrinkage effect, and magnetic shrinkage effect, a high temperature, and high-speed plasma arc are formed to blow the metal material away from the matrix, thereby realizing rapid cutting.
In oxy-fuel cutting, the metal is heated by flame, and then oxygen is blown into the heating zone. Oxygen and the hot metal produce a violent oxidation reaction, which generates heat to melt and blow the metal away. This continuous process is oxy-fuel cutting. Cutting is only possible when the heat released during oxidation is large enough to melt the metal. If the amount of heat released during oxidation is small and the metal cannot be melted, cutting cannot be performed. Theory and practice have proved that, except for carbon steel, almost all metal elements cannot melt themselves by the heat released during oxidation, so other materials cannot be cut with oxy-fuel flame. Therefore, the oxyacetylene flame can only cut medium and low-carbon steel, although it can also cut high-carbon steel and cast iron, as the carbon content in the alloy increases, the oxidation heat release decreases and the cut quality is poor.
Benefit analysis of oxy-fuel flame cutting and plasma cutting
Most people think that oxy-fuel cutting is more economical than plasma arc cutting. In fact, it is not. Air plasma cutting machine is used for cutting. As long as the equipment is selected and operated properly, it is also very economical to cut medium and low thickness plates. Of course, the air plasma cutting machine has a large one-time investment, but the use cost is about 30% less than that of oxyacetylene cutting. Take the LG-80K air plasma cutting machine to process A3 plates with a thickness of 15mm as an example for analysis and comparison, as shown in Table 3.
| Cutting cost comparison | ||
|---|---|---|
| Form | Oxyfuel cutting | Plasma cutting |
| Speed (m/min) | 0.5 | 2.0 |
| Cutting capacity (m/h) | 30 | 120 |
| Power consumption | 250L/h 8.5L/h |
24kW/h 0.2kW/h |
Based on the above, whether it is cutting quality or cutting benefit, the use of air plasma cutting machine for the processing of medium and thin plates is better than oxy-fuel flame cutting. It can be foreseen that as the economy grows stronger, people's thinking changes and the technological transformation of enterprises increases, the proportion of plasma arcs that replace oxy-fuel flame cutting will further increase.
