Before cutting any plate, the distance between the focus and the plate must be adjusted.
Different cutting materials and cutting methods will lead to different choice of focus position (as shown in the figure below).
Therefore, laser cutting needs to continuously and dynamically adjust the focus position. So, how to change the focus position?

Methods to adjust focus position

It is generally believed that focusing can be achieved by changing the upper and lower positions of the cutting head.
Generally, the simplest way is to obtain the ideal focus position only by changing the height position of the cutting head.
For example, if the cutting head is lowered as a whole, the focus position will be lowered, and if the cutting head is raised as a whole, the focus position will be raised, as shown in the figure below.

In fact, there are other factors to consider when adjusting the focus position.
A nozzle is installed at the bottom of the cutting head. The distance between the nozzle and the workpiece will affect the flow rate and diffusion of gas, and then affect the cutting quality.

Generally, the distance between the nozzle and the workpiece is a fixed value within a certain range.
Moving the cutting head up and down as a whole will affect the cutting quality.
Therefore, it is not appropriate to adjust the cutting height by lifting the cutting head, which will affect the cutting quality.

So The method of adjusting the height of the lens inside the cutting head is more scientific.

By changing the position of the internal focusing lens, the position of the focusing point can also be changed: the focus lens drops and the focus position decreases; the focus lens rises and the focus position rises.
In this way, the cutting head as a whole remains in its original position, and the distance between the nozzle and the workpiece will not change, so as to avoid the influence of air flow mentioned above.

The technology of adjusting focusing lens keeps pace with the times.

In the early days, the way of adjusting the up and down movement of the focus lens was completed manually, that is, use a wrench or directly rotate the self-contained roller or knob to adjust the up and down movement of the focus lens; Nowadays, with the development of technology, automatic focusing is used more and more: that is, the motor drives the focusing lens to move up and down.
Manual focusing requires moving the cutting head to the edge of the machine tool and then operating by people during each adjustment; Using the automatic focusing method, no matter where the cutting head is on the machine tool, the vast majority can be adjusted by software, which is more convenient to use.

How to find the position of zero focus

The height of the focus position is relative to zero focus. Therefore, before focusing, first determine the position of zero focus, and then move the focus lens up / down a certain distance, so as to adjust the increase / decrease value of the focus position.
According to the previous analysis, at the position of zero focus, the spot is the smallest, that is, the slit is the smallest. Moving the focus position up and down will thicken the light spot, resulting in linear widening of the slit and low cutting quality.

Generally, the zero focus position of the cutting head is near the indication scale of “0”.
First adjust the scale to 0, put a flat plate on the workbench, and then cut a line every 1mm within the range of – 5mm and + 5mm.
Carefully comparing these slits, the narrowest position of the slit is the zero focus position.
In subsequent cutting, based on the zero focus position found above (i.e. + 1 scale position), adjust the scale up or down to change the corresponding defocus amount.