How to do it with rough and serrated section when laser cutting carbon steel

When laser cutting carbon steel, the cross section is rough and serrated, which is usually not caused by a single reason, but by the mismatch of multiple process parameters. The following will provide you with detailed solutions from two aspects: the main causes and systematic troubleshooting steps.

The main cause analysis.

The rough and serrated section is essentially the result of unstable energy input and poor auxiliary gas slag discharge. Specifically can be summed up in the following categories:

1. Process parameter problems (most common):

· The cutting speed does not match: the speed is too fast, the energy accumulation is insufficient, and the continuous cutting cannot be formed, forming faults and serrations; the speed is too slow, excessive burning, and the section is severely melted, and the same is rough.

Laser power is too low: the power is not enough to completely vaporize or melt the material, resulting in cutting through, hanging slag and forming a rough section.

· Auxiliary gas problems:

· Improper air pressure: The air pressure is too low to blow away the slag in time, and the slag adheres to the lower part of the incision to form serrations and burrs; too high air pressure may cause cooling effect on the cutting seam and affect energy concentration.

Insufficient gas purity: Insufficient oxygen purity (for carbon steel, usually ≥ 99.95%) will reduce the efficiency of the oxidation reaction, resulting in insufficient combustion and the formation of a rough section.

·Incorrect focus position: If the focus is too deep or too shallow, the energy density of the beam will be insufficient to form a smooth cutting line. Focus is one of the most sensitive parameters affecting the quality of the incision.

2. Equipment and hardware status problems:

·Nozzle wear or pollution: nozzle hole deformation, sputtering blockage, will lead to gas flow field disorder, can not effectively blow slag.

·Lens pollution or damage: there are stains or damage on the protective mirror and focusing mirror, which will scatter laser energy, resulting in a decrease in the power actually reaching the workpiece and a deterioration of the beam quality.

· Guide/gear and other mechanical structure loose: the movement system is not stable, will produce jitter, directly reflected in the cutting section to form a zigzag line.

· Poor beam quality: the laser itself output spot mode is not good, the energy distribution is not concentrated.

3. Material and processing environment:

· Rust, paint or coating on the surface of the material: these impurities will absorb and reflect the laser unevenly and interfere with the cutting process.

· The quality of the material itself: the uneven composition of the plate and the large internal stress will also lead to inconsistent cutting effects.

· The plate is not flattened: during the cutting process, the plate undulates, causing the focus position to change continuously.

Systematic investigation and solution (from easy to difficult)

Please follow the following steps to check and adjust, the high probability can solve the problem.

The first step: basic inspection and preparation

1. Check and clean the optical system:

· After shutdown, check and clean the focusing mirror and protective mirror. If there are any scratches or stains that cannot be removed, replace them immediately.

· This is the first step to ensure beam quality and the lowest cost maintenance.

2. Check and replace the nozzle:

· Check whether the nozzle aperture currently used matches the thickness of the plate (usually the thicker the plate, the nozzle aperture can be slightly larger).

· Check whether the nozzle opening is worn (becomes oval) or blocked by slag. If there is a problem, replace it with a new nozzle immediately.

3. Check gas purity and pressure:

· Confirm that the oxygen purity meets the requirements (≥ 99.95%).

· Check the gas path for leaks.

· The air pressure setting refers to the recommended parameters of the equipment manufacturer and makes fine adjustments. For the case of serrations and slag hanging, you can try to increase the air pressure appropriately (for example, increase 0.5-1Bar) to observe the effect.

Step 2: Optimization of core process parameters

When performing the following commissioning, it is strongly recommended to use the “cutting process test chart” (the 1 kind of square chart containing many different parameter combinations) to quickly compare and find the best parameter combination.

1. Adjust the focus position:

· This is the most crucial step. The focus position is usually based on 0 (plate surface) and is negative downward.

· Current phenomenon (coarse and jagged): It is likely that the focus is too deep (too large negative value) or too shallow (positive value).

· Debugging method: Based on the existing parameters, the focus position is systematically changed from low to high (or from high to low) in steps of 0.2mm or 0.5mm for trial cutting. You will find the “best focus position” with the smoothest section and the smallest pan teeth “. Usually when cutting carbon steel, the focus will be about 1/3 of the plate thickness below the surface of the plate.

2. Optimize cutting speed and power:

· Principle: Power and speed need to be coordinated.

· Current Phenomenon (Coarse Jagged): First suspect too fast or too low power.

· Debugging method:

Method A (fixed power): keep the current power unchanged, gradually reduce the cutting speed, observe the change of section. If the sawtooth decreases, the original speed is too fast.

Method B (fixed speed): Keep the current speed unchanged, gradually increase the laser power, and observe the cross-sectional changes. If it is improved, the original power is insufficient. The best state is to find the critical point that “just cuts through and the section is smooth. If the speed is too fast, faults and serrations will occur. If the speed is too slow, it will lead to over-burning of the plate and serious slag hanging at the bottom.

3. Fine tune gas pressure:

· After adjusting the focus, speed and power, fine-tune the air pressure.

· Observe the spark during cutting: the ideal state is that the spark is long and uniform, and it is sprayed downward. If the sparks are sparse, short, and divergent, the air pressure or velocity is inappropriate.

· For serrations and hanging slag, it is usually effective to increase the air pressure appropriately.

Step 3: Advanced Check

If none of the above steps work, there are deeper issues to consider.

1. Check the mechanical structure of the equipment:

· Check whether the beam, gear and rack are loose. Push the cutting head by hand to feel whether there is abnormal gap or shaking.

· When running at low speed, observe whether the machine is running smoothly. Mechanical loosening can directly cause cutting serrations.

2. Check the laser output:

· If possible, use a laser power meter to check whether the actual output power matches the set value.

· The deterioration of the beam mode (such as changing from the basic mode TEM00 to the high-order mode) will also lead to the reduction of cutting ability. In this case, it is necessary to contact the equipment supplier for professional inspection and maintenance.

Summary and Quick Action Checklist

When you encounter this problem, follow this order:

1. Change: Replace with a new, clean protective mirror and nozzle.

2. Adjust: Systematically adjust the focus position, which is the fastest way to get results.

3. Drop: Reduce the cutting speed appropriately.

4. Increase: If the speed reduction is invalid, try to increase the laser power.

5. Check: check whether the oxygen purity and air pressure are accurate, and increase the air pressure appropriately.

6. Test: If the problem persists, conduct a cutting process test to find the best parameter combination for the current plate.

7. Connection: If all methods fail, immediately contact the after-sales service of the equipment to check the mechanical transmission and laser status.

Laser cutting is a “balanced” art, which requires the perfect coordination of the four core elements of power, speed, gas and focus. Patiently systematic debugging is the key to solving such problems.