What is the reason for sticking slag and blocking the nozzle during laser cutting?

It is a common problem to block the nozzle with slag when laser cutting, which is usually caused by a combination of many factors. The following are the main reasons and systematic analysis:

Core reason analysis

1. Auxiliary gas problem

• Insufficient air pressure: The gas pressure is not enough to effectively blow away the slag, causing the slag to splash upward and adhere to the inner wall of the nozzle.
• Gas impure/wrong type: When cutting stainless steel or aluminum with compressed air containing moisture or impurities, it is easy to produce oxidation reaction and form viscous slag. No oxygen is used when cutting carbon steel (combustion support), or high-purity nitrogen is not used when cutting stainless steel/aluminum (oxidation protection).
• The gas flow is unstable: the gas supply system leaks, the pipeline is too long, or the gas pressure regulating valve fails.

2. Material and process parameters do not match

Material issues:

• The surface is coated, rusted or greasy.
• Uneven material composition (e. g. high silicon content in aluminum alloys).
• The plate is too thick and exceeds the equipment limit.

Improper parameter setting:

• Power too low/speed too slow: insufficient energy input, incomplete vaporization of material, formation of viscous slag.
• Focus position offset: The focus is too high or too low, resulting in insufficient energy density and insufficient cutting.
• Wrong perforation parameters: slag splashes seriously during perforation, progressive perforation or delay protection is not adopted.

3. Equipment and nozzle status

• Nozzle damage or wear: the nozzle aperture becomes larger, deformed or the inner wall is rough, causing airflow disorder.
• Improper distance between the nozzle and the plate: the distance is too large (gas diffusion) or too small (easy to collide and splash slag).
• Optical system pollution: focusing lens pollution causes beam divergence and energy density decrease.
• Cooling system failure: The laser head is overheated, affecting the beam quality and gas stability.

4. Environmental and operational factors

• Ambient dust: poor air quality in the workshop, and dust enters the nozzle with the airflow.
• Unreasonable cutting sequence: continuous cutting of small holes, sharp corners and other parts, heat accumulation.

Systematic investigation and solution

Step 1: Check the gas system

• Use a pressure gauge to check whether the air pressure at the nozzle outlet meets the material requirements (for example, 1.2-1.5Bar is required for cutting 8mm carbon steel).
• Check the purity of the gas source: the purity of nitrogen shall be ≥ 99.99 (cutting stainless steel), and the purity of oxygen shall be ≥ 99.95 (cutting carbon steel).
• Check whether the air pipe is bent or leaking, and whether the filter needs to be replaced.

Step 2: Optimize process parameters

• Adjust the power and speed: refer to the material thickness parameter table for trial cutting and calibration. For example: cutting 2mm stainless steel, the recommended power is 1500W, the speed is 25 m/min, and the nitrogen pressure is 1.5Bar.
• Calibrated focus: Use a focus coupon test to find the best focus position (usually 1/3 thickness below the surface of the material).
• Optimized perforation: the thick plate adopts progressive perforation, and the delay blowing of 0.5-1 second is set.

Step 3: Equipment Maintenance

• Replace the nozzle: check whether the nozzle aperture is round, it is recommended to clean before each shift, and replace the standard nozzle every 40 hours.
• Clean the optical system: Wipe the lenses regularly with absolute ethanol (check daily).
• Calibrate the height sensor: ensure that the distance between the nozzle and the plate is constant (usually 0.8-1.5mm).

Step 4: Materials and Operations Management

• Clean sheet surface before cutting.
• Add leads when programming to avoid arcing directly from inside the material.
• Use anti-reflective coatings or special cutting heads for highly reflective materials (such as copper and aluminum).

List of preventive measures

1. Daily check: gas pressure, lens cleanliness, nozzle wear.

2. Weekly maintenance: clean the air filter and calibrate the height of the cutting head.

3. Parameter management: establish material parameter database, and do trial cutting verification before thick plate cutting.

4. Environmental control: The workshop is equipped with dust removal equipment to maintain stable temperature and humidity (temperature 25±5 ℃, humidity <60%).

Rapid emergency treatment

If a gag has occurred:

• 1. Immediately pause cutting and clean the nozzle.
• 2. Check the quality of the slit: if the section is rough and there is slag, adjust the parameters before continuing.
• 3. A short time can be used for special needle cleaning, serious when the replacement nozzle and check the lens.

Through the above systematic investigation, more than 90% of the problem of sticking slag and plugging can be solved. The key is to maintain equipment stability, gas purity and parameter matching. It is recommended to establish a preventive maintenance record to reduce failures from the source.