Laser Cutting Tips: Optimizing Laser Oxygen Positive-Focus Cutting

Positive-focus cutting refers to positioning the laser focal point on the top surface of the workpiece. This results in a larger beam spot at the bottom of the material, enhancing oxygen participation in the oxidation reaction and improving slag removal. It is primarily used for oxygen-assisted cutting of carbon steel, especially medium-to-thick plates (over 25mm). Oxygen as an auxiliary gas accelerates oxidation reactions, increases cutting speed, and reduces slag adhesion. 

Achieving high-quality cuts depends significantly on three core parameters: focal position, auxiliary gas pressure, and cutting speed. This guide explains how these factors impact cut quality and provides practical solutions for common issues.

1. Impact and Adjustment of Focal Position 

Focal position too high: Uneven energy distribution occurs. The upper section receives concentrated energy, resulting in a smooth upper cut, while insufficient energy at the bottom leaves slag residues and roughness.

Focal position lagging: Reduces heat absorption at the lower edge of the material, causing incomplete melting and sharp residue sticking.

Common Issues:

• Rough lower portion of the cut with slag residue.
• Inconsistent cutting slopes and incomplete penetration.

2. Auxiliary Gas Pressure: Influence and Optimization

Pressure too low: Insufficient gas flow into the cutting slot fails to effectively remove molten slag, leading to rough cut surfaces or cutting failures.

Pressure too high: Excessive gas pressure can create turbulent flows or shockwaves, disturbing the laser focus and reducing melting efficiency, possibly causing wider or burnt cuts.

Gas purity: Oxygen purity should be at least 99.6%; impurities hinder proper oxidation and reduce cutting quality.

Common Issues:

• Excessive slag buildup and rough surfaces at high pressures.
• Sticky residues due to low pressure.

3. Cutting Speed: Controlling Quality and Efficiency

Speed too fast: Insufficient laser energy input leads to incomplete penetration of the lower part, slag cannot be discharged in time, and the incision is rough.

Speed too slow: Excess heat accumulates, causing wider cuts and possible material deformation or burns.

Common Issues:

• Rippled or jagged edges on cutting surfaces.
• Incomplete cuts or re-solidified slag.

Comprehensive Problem-Solving Tips

1. Regular, rough stripes: Significantly increase cutting speed or slightly decrease laser power.

2. Rough upper surface with slag underneath: Increase focal length, select smaller nozzles, and lower gas pressure.

3. Clear top texture with rough bottom: Raise focal position and cutting height.

4. Persistent slag adhesion: Increase focal length, use a larger nozzle, and raise gas pressure.

Final Recommendations

Consistent, high-quality laser oxygen positive-focus cutting requires balanced adjustments of focal position, gas pressure, and cutting speed. Always perform preliminary tests tailored to specific materials and maintain your equipment regularly. If problems persist, consult your equipment supplier or refer to detailed process manuals for further troubleshooting.