In laser cutting, the focal point position is the core parameter determining cutting quality, and it has a direct causal relationship with burr (dross) formation. Precisely controlling the laser cutting machine's focal point is the primary technical means to obtain a clean, burr-free cross-section.

How the Focal Point Position Affects Burr Formation

The focal point position determines the distribution of laser energy along the material's thickness. When the laser cutting machine's focal point is set on the material surface (zero focal length) or slightly above it, the area with the most concentrated energy is located at the top of the plate. This leads to sufficient vaporization of the upper material, but insufficient energy at the bottom, preventing the molten material from being completely blown away by the assist gas, thus causing condensation on the cut back to form bottom burrs. Conversely, when the focal point penetrates deep into the material (negative defocus), the energy is more concentrated in the lower and middle layers of the plate, which is beneficial for the complete melting of the bottom material. With appropriate gas pressure, this can effectively reduce dross and obtain a more vertical cross-section.

The Synergistic Effect of Focal Point, Gas Pressure, and Speed

The effect of the focal point must be considered in conjunction with the assist gas pressure and cutting speed. Even with correct focus, insufficient air pressure in the laser cutter will prevent the molten material from being effectively blown away from the kerf, resulting in burrs. Similarly, excessively high cutting speeds will leave insufficient heating time for the material, preventing the molten material from being expelled. Therefore, the optimal process is a balance between precise focus, sufficient air pressure, and matching speed. Typically, when cutting thick plates, using negative defocus combined with higher air pressure is a common and effective method for suppressing burrs.

Practical Adjustment Recommendations: When your laser cutter exhibits persistent burrs, prioritize focus calibration testing. Use plates of varying thicknesses to perform focus step tests (e.g., from +3mm to -3mm in 0.5mm intervals), observing the cross-sectional quality and burr situation at each focus point. Record the best results and store them as standard process parameters for that material in the laser cutter's database. Regularly cleaning and protecting the lens to ensure stable beam quality is fundamental to maintaining focus performance.

Understanding and mastering the intrinsic relationship between focus and burrs can help you solve cutting quality problems from a process principle perspective, fully realizing the performance potential of your laser cutter. If you have any questions, please consult a RITMAN Laser after-sales engineer.