Adjusting the laser cutting machine's focus position is crucial for ensuring cutting quality. Incorrect focus position can lead to problems such as incomplete cutting, rough cross-sections, and increased dross. The following are detailed adjustment methods and precautions:

I. Impact of Focus Position

Focus above the material surface (positive defocus): Suitable for thick plate cutting, with more concentrated energy, but prone to dross generation.

Focus on the material surface (zero defocus): A general setting suitable for medium-thin plates (1-10mm).

Focus below the material (negative defocus): Suitable for thin plates (<3mm), with finer cuts but less penetrating power.

II. Adjustment Methods

1. Manual Test Cut (Commonly Used)

Steps:

Prepare the test cut material: Select scrap material of the same material and thickness as the final cut.

Set the initial focus (refer to the machine manual, usually on the material surface).

Cut a test pattern (such as a straight line or a small square).

Observe the cutting results:

Incomplete cut → Focus too far (need to lower the nozzle or adjust the defocus to negative).

Rough cross-section/excessive dross → Focus too close (need to raise the nozzle or adjust the defocus).

Make minor adjustments and repeat the test until the cut is smooth and dross-free.

2. Inclined Plate Test Method (More Accurate)

Steps:

Prepare an inclined plate (e.g., a metal plate tilted 10° to 30°).

Cut a straight line along the inclined surface. Due to height variations, the focus position will continuously change.

Observe the position with the best cut quality and record the Z-axis height at that point; this is the optimal focus.

3. Autofocus (devices with height sensors)

Capacitive/laser displacement sensors: Automatically track the material surface and dynamically adjust the focus (suitable for curved or uneven surfaces).

Steps:

Enable the "Autofocus" function in the control system.

Set the focus offset (e.g., +0.5mm or -1mm, depending on the material).

Start cutting. The sensor will compensate for height variations in real time.

III. Focus Setting Reference for Different Materials

IV. Precautions

Nozzle Height: Generally maintain 0.5-2mm (linked to the focus and requires simultaneous adjustment).

Gas Pressure: Increase the pressure (1-2MPa) when cutting thick plates with oxygen; decrease the pressure (0.5-1MPa) when cutting thin plates with nitrogen.

Lens Cleaning: A dirty focusing lens can cause focus shift; check and clean it regularly.

Material Surface Condition: Rust or coatings may affect autofocus and require pre-emptive treatment.

V. Troubleshooting Common Problems

Problem 1: Cutting Edge Tilting

Cause: Focus shift or misaligned beam.

Solution: Recalibrate the optical path and check if the focusing lens is installed upside down.

Problem 2: Severe Bottom Dross

Cause: Focus too low or insufficient gas pressure.

Solution: Raise the focus position and increase the assist gas pressure.

Problem 3: Inability to Cut Through Thick Plates

Cause: Focus too high or insufficient power.

Solution: Lower the focus, switch to oxygen-assisted combustion, or upgrade to a higher-power laser.

Summary

Thin Plates: Negative defocus (-0.5 to -2 mm) → Greater precision.

Thick Plates: Positive defocus (+1 to +3 mm) → Enhanced penetration.

Autofocus equipment: Preferred, especially for curved or uneven surfaces.

After adjustment, be sure to conduct a trial cut to verify and record the optimal parameters for subsequent use.