Among the various factors that affect the processing quality and processing capacity of laser cutting machines, the focus position is the most influential. Laser cutting is to focus the high-power laser beam through the focusing mirror to form a small focus, and use the high energy of the focus to melt and vaporize the steel plate to achieve cutting. The positioning of the laser focus is a very critical step. Only when the focus is fixed can a good quality of steel plate cutting be guaranteed.

Relative to the surface of the processed material, after the laser beam is focused, the position of the focus is called the focus position. The focus position will affect almost all processing parameters such as the width of the slit, the slope, the roughness of the cutting surface, the adhesion state of the slag, and the cutting speed.

This is because the change of the focus position will cause changes in the diameter of the beam irradiated on the surface of the processed material and the incident angle of the incident material, which will affect the formation state of the slit and the multiple reflection state of the beam in the slit. These cutting phenomena will affect the flow state of auxiliary gas and molten metal in the slit.

The figure shows the relationship between the focus position Z of the laser cutting machine and the slit width W on the surface of the processed material.

Set the state of the focus on the surface of the processed material as z=o "zero". When the focus position moves upward, it is represented by "+", when it moves downward, it is represented by "-", and the moving amount is represented by mm. The width W of the upper slit at the focus position z=o is the smallest. Regardless of whether the focus position is moved up or down, the upper slit width W will become wider.

This variation also has the same tendency when using processed lenses with different focal lengths. The smaller the beam diameter at the focus position and the shorter the focal length of the lens is, the greater the variation of the upper slit with the change of the focus position will be.

The picture above shows the best focus position of the metal laser cutting machine when processing various processing materials.

(1) is the case when the minimum beam diameter z=0 can be obtained on the surface of the processed material. At this time, the maximum energy density can be obtained on the surface of the processed material, and the melting range is relatively narrow, which determines the processing characteristics.

(2) When the focus position is on the "+" side (Z>O), the irradiation range of the laser beam on the surface of the processed material becomes wider, and the beam in the slit has a diverging angle, which enlarges the slit width.

(3) When the focus position is on the "-" side (Z<0), the range of the laser beam irradiated on the surface of the processed material becomes wider, and the closer to the focus position in the thickness direction, the greater the melting ability, and then a reverse slope occurs.