Reasons for the heating of the cutting head nozzle during laser cutting

Laser cutting head nozzle fever serious, even burning red, usually not a single cause, but the result of a variety of factors. The following will explain in detail from the main reasons, secondary reasons and solutions.

Main reason

These are the most direct and common problems that cause nozzle overheating.

1. Plasma/reflected heat

• Generation mechanism: When the laser beam is focused on the surface of the metal material, it will instantly melt or even vaporize the metal. An auxiliary gas, such as oxygen or nitrogen, is blown toward this high temperature region. If the energy density is too high or the gas parameters are inappropriate, the vaporized metal and the gas itself will be ionized to form a high-temperature plasma cloud (an electrically neutral gas group with extremely high temperature).
• Heat transfer process: This plasma will not only absorb and scatter laser energy, reduce cutting efficiency, but also return upward to the inside of the nozzle. The huge amount of heat carried by the plasma will be directly transferred to the copper inner wall of the nozzle, causing its temperature to rise sharply., Even burned red and melted.

2. Cooling system failure

Modern high-performance laser cutting heads are designed with water-cooled channels inside, which are specially used to take away the heat absorbed by the nozzles, protective mirror seats and other components.

Frequently Asked Questions:

• Insufficient cooling water flow: failure of cooling water pump, bending of water pipe, clogging of filter, etc.
• The cooling water temperature is too high: the cooling effect of the chiller is not good or the selection is too small.
• Blockage or leakage of cooling water circuit: internal scale or impurities block the flow passage.
• The cooling system is not turned on: forget to turn on the chiller before starting the laser.

Secondary and other causes

These causes, while less direct than the above two, can exacerbate the fever or cause problems individually.

3. Contaminated or damaged lenses

• If the focusing mirror or protective mirror is contaminated (oil, dust) or damaged, its light transmittance and focusing ability will decrease.
• Part of the laser energy is absorbed by the lens itself and converted into heat. This heat is transferred to the mirror base, which in turn heats the surrounding air and the nozzle base.
• In severe cases, excessive lens temperature may cause bursting.

4. Improper setting of process parameters

• Gas type and pressure:
• When using oxygen to cut carbon steel, it is an exothermic reaction that itself generates a lot of heat. If the gas pressure is not appropriate, it is easier to form a strong plasma.
• When using nitrogen to cut stainless steel, if the air pressure is too low to blow away the melt in time, the slag will splash upward, adhere to the inner wall of the nozzle and continue to heat it; if the air pressure is too high, it may cause airflow disorder, which is conducive to plasma formation.
• Cutting speed: The speed is too slow, the laser stays at the same position for too long, and the heat accumulates too much, which is easy to generate plasma and burn the nozzle. If the speed is too fast, it may not cut through, resulting in enhanced reflected light.
• Laser power: When the power is too high and other parameters (such as speed and air pressure) do not match, the energy is excessive and plasma is easily generated.
• Focus position: Incorrect focus position will affect the energy density and cut shape, thereby affecting the discharge of melt and the formation of plasma.

5. The problem of the nozzle itself

• Model mismatch: the nozzle aperture does not match the thickness of the cut plate and the gas pressure. For example, fine cutting with a large aperture nozzle may cause the airflow to diverge and the protection effect is poor.
• Poor quality/damage: The center hole of the nozzle is not round, there are burrs, and the inner wall is not smooth, which will cause unstable airflow and easily form eddy currents, which is not conducive to heat dissipation and slag blowing. Slight deformation of the nozzle after collision with the sheet may also cause this problem.
• Improper installation: The nozzle is not tightened, or the sealing ring is damaged, causing gas leakage and destroying the stable gas curtain protection.

6. External environment and collision

• The surface reflectivity of the plate is too high: when cutting highly reflective materials such as aluminum and copper, a large amount of laser energy is reflected back to the inside of the cutting head and absorbed by the nozzle and mirror seat.
• Collision: The cutting head collides with the plate or fixture, causing the nozzle to deform and the internal parts to shift, destroying the original coaxiality and sealing of the light, gas, and waterway.

Summary and Solution Checklist

When the nozzle heating problem is encountered, it is recommended to check in the following order:

1. Immediately stop the machine for inspection: to prevent further damage to the equipment.

2. Check the cooling system (top priority):

• Confirm that the chiller is on and operating normally.
• Check whether the cooling water flow and pressure meet the equipment requirements.
• Touch the inlet and outlet pipes and feel the temperature difference. If the temperature difference is small, it means that the heat exchange efficiency is low or the flow is insufficient.
• Check the water quality to ensure that there are no impurities.

3. Check and replace optical components:

• Remove the protective lens and inspect it for contamination, burns, or cracks. Always keep the lenses clean.
• Check whether the focusing mirror is in good condition.

4. Check and replace the nozzle:

• Check whether the nozzle aperture currently in use is suitable for the cutting task in progress.
• Check whether the inner hole of the nozzle is smooth and round, and whether there is any melting damage or blockage. Replaced with a brand new, high quality nozzle test.

5. Optimization of cutting process parameters:

• Consult the equipment supplier or experienced process engineer to recalibrate the laser power, cutting speed, gas type and pressure, focus position, etc. according to the material type and thickness. This is the core of solving the problem of plasma overheating.

6. Check the coaxiality and installation:

• Use the alignment tester to check whether the coaxiality of laser, nozzle and gas is accurate.
• Make sure that the nozzle is correctly installed and tightened, and the sealing ring is intact.

7. Observe the cutting process:

• Under the premise of safety, observe the sparks during cutting. A normal spark should be downward and backward. If the spark splashes upward, diverges or is too coarse and bright, it usually means that the parameters are not appropriate and a large amount of plasma is generated.

Through systematic investigation, the vast majority of nozzle heating problems can be effectively solved. If the above steps cannot be solved, it may be that there is a more serious mechanical or optical problem inside the cutting head, and it is necessary to contact the equipment manufacturer for professional maintenance.