The focus in laser cutting refers to the position where the smallest spot formed by the laser beam is focused. During the working process of the laser cutting machine, the laser beam is focused through a lens or a reflector to form a high energy density spot, which is the focus. Focus plays a vital role in laser cutting, which directly affects the quality, accuracy and efficiency of cutting.

Different focus positions can cause significant differences in cutting results. According to the position of the focus relative to the workpiece surface, the focus position can be roughly divided into the following types:

Focus is on the material surface (zero focus)

The focus is on the upper surface of the material, and the highest energy density of the laser beam is concentrated on the top layer of the material. This setting is suitable for cutting thin materials and provides very fine cutting edges and fast cutting speeds. Suitable for cutting thin metal plates, stainless steel, aluminum alloy, etc.

The focus is inside the material (positive focal length)

The focus position is inside the material, usually set in the middle or deeper of the material's thickness. This focus position can effectively penetrate thicker materials and is suitable for cutting thicker metal sheets. The setting of positive focal length can reduce the heat-affected zone on the upper surface and improve the quality of the cutting edge.

Focus is above the material (negative focal length)

The focus is located above the material, the light spot gradually becomes larger, and the energy density gradually weakens from the surface to the interior of the material. This setup is suitable for piercing and cutting thick materials and is capable of producing larger cutting widths. The negative focal length is suitable for initial perforation and high-energy cutting needs of thick plates.