Before cutting any plate, the distance between the focus and the plate must be adjusted.
Different materials and cutting methods require different focus positions, as shown in the figure below. Therefore, laser cutting requires continuous and dynamic adjustment of the focus position.
So how can the focus position be changed?
Methods for adjusting the focus position
It is generally believed that focusing can be achieved by changing the upper and lower positions of the cutting head:
In general, the easiest way to obtain the desired focus position is by adjusting the height position of the cutting head.
For example, if the cutting head is lowered, the focusing position will also be lowered. On the other hand, if the cutting head is raised, the focusing position will be increased accordingly, 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 affects the flow and diffusion of the gas, which subsequently impacts the quality of the cut.
Typically, the distance between the nozzle and the workpiece remains a fixed value within a certain range.
Adjusting the cutting height by moving the cutting head up and down as a whole can also affect the quality of the cut.
Therefore, raising the cutting head to adjust the cutting height is not appropriate as it affects the quality of the cut.
Therefore, the method of adjusting the lens height 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:
When the focus lens drops, the focus position decreases, and when the focus lens rises, the focus position increases. This ensures that the cutting head remains in its original position as a whole and that the distance between the nozzle and the workpiece remains constant, thus avoiding any interference from the airflow mentioned above.
Focus lens adjustment technology moves with the times:
In the beginning, adjusting the up and down movement of the focus lens was done manually using a wrench or directly rotating the independent roller or knob.
As technology has advanced, autofocus has become increasingly prevalent. A motor drives the focusing lens to move up and down.
When focusing manually, individuals must move the cutting head to the edge of the machine tool and then make adjustments.
When using the autofocus method, adjustments can be made by software from anywhere on the machine tool, making it more convenient to use.
How to find the zero focus position
The height of the focus position is relative to the zero focus point.
Therefore, it is essential to determine the position of the focus zero point before adjusting the focus. Then move the focus lens up or down a certain distance to adjust the increase or decrease value of the focus position.
According to the previous analysis, the smallest point occurs at the zero focus position, indicating the smallest crack.
Moving the focus position up or down causes the spot of light to become thicker, resulting in a linear widening of the slit and reduced cut quality.
The zero focus position of the cutting head is generally close to the “0” indication scale.
To locate the focus zero position, start by setting the scale to “0” and placing a flat plate on the bench. Continue making a cut every 1mm in the range of -5mm to +5mm.
Carefully compare the resulting slits and identify the narrowest point as the focus zero position.
When making subsequent cuts, adjust the scale based on the previously found zero focus position (i.e. +1 scale position) to change the corresponding amount of blur.
Common focus positions of low power laser cutting:
In actual cutting applications, it is necessary to select the appropriate focus position based on specific cutting requirements. You can refer to the following post to learn more about choosing laser cutting focus in detail.
How to choose laser cutting focus?
