Plasma cutting or plasma arc cutting is a process that can process conductive materials using a jet of ionized gas. Here we are going to focus on the equipment. What is a CNC plasma cutting machine and how to use it properly? We’ll also discuss plasma cutter gases.
Some plasma cutter machines have CNC cutting tables, and some are directly built into the table. When using the CNC plasma cutting machine, the cutting quality is unstable, , to use the cutter correctly and ensure the part quality, here are some tips for daily use of the plasma cutters.
1. Cut from the edge
Cut as far as possible from the edges, not through holes. Using the edge as the starting point will prolong the life of the consumable parts. The correct method is to directly align the nozzle with the edge of the workpiece and then start the plasma arc.
2. Reduce unnecessary arcing time
The consumption of the nozzle and electrode is very fast when arcing. Before starting, the cutting torch should be placed within the walking distance of the cutting metal.
3. Do not overload the nozzle
Overloading the nozzle or exceeding the working current of the nozzle will quickly damage the nozzle. The current intensity should be 95% of the working current of the nozzle.
4. Adopt reasonable tangent distance
According to the requirements of the instruction manual, adopt a reasonable cutting distance, which is the distance between the cutting nozzle and the workpiece surface. When piercing, try to use the distance twice the normal cutting distance or the maximum height that can be transmitted by plasma arc.
5. The perforation thickness should be within the allowable range
The cutting machine will not be able to make a hole in the steel plate because it is thicker than the working thickness. The typical thickness of perforation is equal to only half of the standard thickness of a cut.
The gas is very important when machining with a CNC plasma cutting machine. The selection of gas will seriously affect the cutting accuracy, slag hanging, and other phenomena. How to choose the right gas to obtain faster-cutting speed and better cutting quality?
1. Hydrogen is combined with other gases as a supplementary gas. For instance, H35 (hydrogen volume fraction of 35%, argon volume fraction of the remainder) is one of the gases with the best plasma arc cutting power, which is mostly due to the presence of hydrogen. Since hydrogen can greatly enhance the arc voltage, the enthalpy of the hydrogen plasma jet is considerable. When combined with argon, the plasma jet’s cutting ability is substantially enhanced.
2. Oxygen can increase the cutting speed of materials made from low-carbon steel. When cutting with oxygen, the mode of operation closely resembles that of a CNC flame-cutting machine. The high temperature and high energy of the plasma arc accelerate the cutting process. The spiral air duct machine, however, must be compatible with high-temperature oxidation-resistant electrodes. In addition, the electrodes must be shielded from impact during arcing in order to prolong their lifespan.
3. Air includes around 78% nitrogen by volume, therefore it is quite creative to employ the slag hanging created by air cutting as opposed to nitrogen cutting; the air also contains approximately 21% oxygen by volume. Due to the presence of oxygen, the cutting speed of low-carbon steel materials with air is also quite high; therefore, air is the most cost-effective working gas. However, when air cutting is used alone, there will be issues such as slag hanging, notch oxidation, and nitrogen growth. Additionally, the poor life of the electrode and nozzle will impact the operating efficiency and cost of cutting. Due to the fact that plasma arc cutting typically employs power supplies with constant current or steep drop external characteristics, the current changes little when the nozzle height is increased, but the arc length and arc voltage will increase, thereby increasing the arc power. However, the arc length exposed to the environment will also increase, as will the energy loss of the arc column.
4. Nitrogen is a frequently employed working gas. Under conditions of high power supply voltage, the nitrogen plasma arc is more stable and has greater jet energy than the argon plasma arc. Even when cutting materials with a high liquid metal viscosity, such as stainless steel and nickel-base alloy, the amount of slag dangling from the incision’s lower edge is minimal. Nitrogen can be used alone or in combination with other gases for plasma cutting. As an example, nitrogen or air are frequently utilized as working gases in mechanized cutting. These two gases have become the norm for high-velocity carbon steel cutting. Nitrogen is occasionally utilized as the starting gas for oxygen plasma arc cutting.
5. Argon hardly interacts with any metals at high temperatures. The CNC plasma cutter from Argon is extremely stable. The nozzle and electrode employed have a lengthy lifespan. However, argon plasma arc voltage is modest, enthalpy is not high, and cutting ability is limited. In comparison to air cutting, the cutting thickness will be approximately 25% thinner. Moreover, in the argon protection environment, the surface tension of molten metal is relatively high, which is roughly 30 percent greater than in the nitrogen environment; thus, there will be more slag-hanging issues. Even if the mixture of argon and other gases is utilized for cutting, slag is likely to adhere. Therefore, using pure argon alone for plasma cutting is uncommon.