Choosing the Focus Position for Laser Cutting of Different Metals

In the laser cutting process, accurately selecting the focus position based on the type of material is key to ensuring cutting quality and efficiency. This technical aspect has gained significant attention across the industry.

1. Carbon Steel Cutting

Thin Plate Cutting: For cutting thinner plates (such as 1-3mm), zero focus, where the focus is positioned on the surface of the material, is commonly used. This helps to improve cutting precision, reduce the heat-affected zone, and achieve smoother cut edges.

Medium and Thick Plate Cutting: When cutting medium-thick carbon steel plates (6-16mm), positive focus is usually the preferred choice. With the focus placed above the material, the laser beam spreads more upon reaching the material's surface, which helps with slag removal and results in a brighter, smoother cut surface.

Thick Plate Cutting: For plates thicker than 16mm, negative focus is typically used to enhance cutting speed, although this may slightly reduce the quality of the cut edge.

2. Stainless Steel Cutting

Thin Plate Cutting: For cutting thin plates, continuous lasers typically employ zero focus to ensure the cutting surface is smooth, with the upper surface near the focus receiving the cleanest cut.

Medium and Thick Plate Cutting: For medium-thick plates, to ensure good edge quality, negative focus is usually adopted. The focus is set deeper within the material to widen the cut and improve gas and molten material flow, ensuring that sufficient energy density is applied to the cutting area.

3. Aluminum Cutting

Thin Plate Cutting: When cutting thin plates, both zero focus and slight positive focus can be used. Zero focus provides better precision and surface quality, while positive focus is suitable when verticality is a critical requirement. It ensures the cut is slightly wider at the top than at the bottom, facilitating slag removal and maintaining verticality.

Medium and Thick Plate Cutting: For medium-thick plates, both positive focus and negative focus can be used. Positive focus requires sufficient laser power and auxiliary gas pressure. When using negative focus, the focus is typically positioned at 1/3 to 1/2 of the plate's thickness, providing more stable cutting and reducing roughness on the cut surface.

4. Copper Cutting

Negative Focus (focus below the surface): For copper, negative focus is the optimal choice, particularly for thicker copper plates (6mm and above). Negative focus increases laser penetration, compensating for the high reflectivity of copper, and allows the laser beam to focus more effectively. This enhances the heat concentration and improves cutting depth and efficiency.

Zero Focus (focus at the surface): For thin copper plates (1-3mm), zero focus is also a feasible option, providing better cutting precision and minimizing the heat-affected zone, which reduces edge deformation during cutting.

By selecting the appropriate focus position, laser cutting efficiency and quality can be significantly improved for different metal materials. The choice of positive focus, negative focus, or zero focus is primarily determined by the thickness, thermal conductivity, and reflectivity of the material. In practice, the correct focus position ensures smooth cutting edges, controlled cutting depth, and minimized heat-affected zones, resulting in optimal processing performance.