How to solve the problem of burrs in laser cutting of thin plates

The appearance of burrs in laser cutting of thin plates is a very common issue. This is usually not caused by a single factor but is the result of the combined effect of multiple factors such as equipment, parameters, materials, and gases. To systematically solve this problem, we can follow a troubleshooting process from easy to difficult and from software to hardware. Next, we will elaborate on the specific operations and solutions for each step in detail:

Step 1: Core parameter check and adjustment (the most common problem area)

1. Focus position

• The focus position is one of the most critical parameters affecting cutting quality. An incorrect focus will lead to energy not being concentrated, making it impossible to effectively blow away the slag.
• Symptoms: Both a focus that is too high or too low will cause slag to adhere to the bottom (burrs).

Solution:

• Perform focus calibration: First, ensure that the focus of your equipment is accurate. Use a focus gauge or an automatic calibration function.
• Perform focus testing: On a scrap piece, cut a straight line or a circle at different focus positions (for example, from -1mm to +1mm, with an interval of 0.2mm), and observe which position has the least burrs. For thin plates, it is usually recommended to use negative defocusing (i.e., the focus is below the surface of the plate, at a distance of about 1/3 to 1/2 of the plate thickness), which can form a wider cut and facilitate the downward blowing away of slag by the gas flow.

2. Auxiliary gas

Gas type and purity:

• Cutting carbon steel: Must use oxygen. Oxygen participates in the combustion reaction, providing additional energy and forming low-melting-point iron oxide, which is easily blown away by the gas flow. If air or nitrogen is used, a large amount of black slag burrs will be produced.
• Cutting stainless steel, aluminum alloy: Must use high-purity nitrogen. The role of nitrogen is to blow away the molten metal and prevent oxidation. If the purity of nitrogen is insufficient (suggested to be above 99.9%) or the pressure is too low, burrs will form at the bottom of the material due to oxidation and insufficient cooling.

Gas pressure:

• Too low pressure: Unable to effectively blow away the slag, resulting in burrs piling up at the bottom.
• Too high pressure: For thin plates, excessive pressure may create vortices at the cut, weakening the slag-blowing effect and possibly causing rough cut surfaces and even difficult-to-remove molten lumps.

Solution: Refer to the recommended parameters from the equipment manufacturer based on the material type and thickness, and make fine adjustments accordingly. For example, when cutting 1mm carbon steel, the oxygen pressure is usually between 0.8-1.2Bar.

3. Cutting speed and laser power

• These two need to be perfectly matched.
• Too fast speed: Insufficient energy input, the material is not completely melted and cut, leaving continuous, sticky burrs at the bottom.
• Too slow speed: Excessive energy input, causing the material to over-melt, resulting in a rough cut surface and even the formation of difficult-to-remove molten lumps.
• Power mismatch: Power that is too low is equivalent to a too fast speed, and power that is too high is equivalent to a too slow speed.

Solution:

• Perform parameter testing: Fix other parameters and adjust the cutting speed and power to find the best “speed-power” combination. The ideal cutting state is a flower-like pattern that scatters downward uniformly.

Step 2: Hardware and equipment status check

If parameter adjustments are ineffective, the equipment itself needs to be checked.

1. Nozzle

• Nozzle selection: Using a nozzle with a diameter that is too large (such as φ2.0 or above) is not conducive to gas flow concentration. For thin plates, it is recommended to use a small-diameter nozzle (such as φ1.0 or φ1.5), which can generate a higher-speed gas flow and have a better slag-blowing effect.
• Nozzle condition: Check if there is slag splashing, wear, or deformation at the nozzle opening. A damaged nozzle will disrupt the concentricity and stability of the gas flow and must be replaced in a timely manner.
• Nozzle height: The distance between the nozzle and the surface of the plate (usually 0.5-1.5mm) is very important. Too high will cause the gas flow to disperse, and the slag-blowing effect will be weak; too low will easily collide with the plate and damage the nozzle.

2.Optical lenses

• Cleanliness: If the protective mirror and focusing mirror are contaminated, it will reduce the laser power, resulting in a decrease in cutting ability and the formation of burrs. Regularly clean the mirrors with anhydrous ethanol and lens paper.
• Quality: Check for any microscopic damage or aging of the coating on the mirrors that may not be visible to the naked eye. Replace them if necessary.

3. Laser Beam

• Beam concentricity: The center of the nozzle hole must be exactly aligned with the center of the laser beam. If they are not concentric, it will cause asymmetrical cuts, with one side smooth and the other side with burrs.
• Calibration method: Stick a layer of masking tape on the front of the nozzle, fire a pulse, and observe whether the hole is at the center of the nozzle. If it is off-center, calibration should be performed according to the equipment manual.
• Equipment stability: Check for mechanical vibrations or looseness in the equipment, as these can affect the stability of the cutting.

Step 3: Materials and Other Factors

Material itself

• Surface quality: Oil, rust, and coatings on the surface of the sheet can increase the difficulty of cutting and cause burrs. Clean the sheet before cutting.
• Material type: Different brands and batches of materials have different alloy compositions and surface treatments, which can affect the cutting performance. If you cannot cut well consistently, try a different batch or brand of material.
• Material thickness: Confirm that your laser’s power is sufficient to cut the thickness. Insufficient power will directly result in incomplete cutting and burrs.

Summary and Quick Troubleshooting Checklist

When encountering burr problems, follow this sequence for quick troubleshooting:

1. First, check the gas!

• For cutting carbon steel: Use oxygen and check if the pressure is sufficient.
• For cutting stainless steel/aluminum: Use high-purity nitrogen and check the purity and pressure.

2. Next, adjust the focus!

• Perform a focus test to find the optimal focus position. For thin plates, try negative defocusing.

3. Then, optimize speed and power!

• Perform parameter tests to find the “speed-power” combination without burrs.

4. After that, check the nozzle and optical path!

• Replace a small-diameter nozzle that feels and looks good.
• Check and clean the mirrors.
• Calibrate the concentricity of the nozzle and the laser beam.

5. Finally, consider material issues!

• Clean the surface of the sheet or try another sheet for testing.

By following this systematic troubleshooting process, most burr problems in thin plate laser cutting can be effectively resolved.