When using a 12kW Fiber Laser Cutter it is best to adjust focus positioning, focus & focal adjustment, oxygen pressure and cutting speed for optimal results.

laser cutter nozzle slit width blog

focus position

Changing the focus position in cutting processes has a significant impact on spot size, both on the surface and inside the board. By increasing the focus length, the spot becomes thicker and the slit widens, affecting the heating area, slit size, and slag discharge capacity.

For optimal results in carbon steel oxygen cutting, it is recommended to use a positive focus. This positioning places the cutting focus directly on the workpiece, positioned above the cutting material.

Positive focus is particularly beneficial for carbon steel oxygen cutting (See case study here). It allows for a wider bottom slit on the workpiece compared to the upper surface slit, facilitating effective slag discharge and enabling oxygen to fully participate in the oxidation reaction at the bottom. Within a specific focus range, increasing the positive focus size results in a larger plate surface spot, better preheating, and improved heat distribution around the cutting seam. As a result, the carbon steel cutting surface appears smoother and brighter.

Focus Adjustment

When adjusting the focus from 11 to 12.5, noticeable changes occur. The light spot gradually expands, resulting in an increased cutting gap. The use of auxiliary gas intensifies, effectively blowing away the slag from the bottom of the cutting surface through the widened slit. This process ultimately produces a remarkably smooth cutting surface.

By increasing the focus from 11 to 12.5, several improvements can be observed. The expanding light spot enhances visibility, while the widened cutting gap allows for more precise cutting. The increased flow of auxiliary gas aids in the removal of slag from the bottom of the cutting surface, contributing to the creation of a smooth and refined cutting result.

focal adjustment

When the focal length is increased from 11 to 12.5, significant changes occur in the cutting process. The light spot gradually expands, resulting in an increased cutting gap. However, when the cutting is performed at an appropriate speed, the top texture decreases, ultimately forming a smooth and polished surface.

laser cutting focal adjustment

oxygen pressure


Oxygen plays a crucial role as a combustion supporter in the cutting process. It not only speeds up the cutting speed but also enables the cutting of thicker plates. Oxygen is particularly suitable for various applications, such as cutting thick plates, high-speed cutting, and even very thin plates like larger and thicker carbon steel plates.

Now, when it comes to gas pressure, increasing it can initially boost the cutting speed. However, it’s important to note that there’s a maximum pressure threshold. Beyond that point, further increases in gas pressure can actually lead to a decrease in cutting speed. This happens because the airflow experiences variations in pressure and temperature, resulting in an uneven density across the field. This density gradient causes changes in the refractive index within the field, which in turn affects the focus of the beam energy. This interference can cause beam refocusing or divergence, impacting the melting efficiency and even altering the mode structure, ultimately leading to poor cutting quality.

It’s worth mentioning that if the beam divergence becomes too significant, the beam spot will become too large, making it less effective in effectively cutting the plate. So, finding the right balance in gas pressure is crucial for achieving optimal cutting results.

laser focus 11 low pressure


One major advantage of reducing the auxiliary gas pressure is a decrease in slag formation at the bottom of the cutting surface caused by over-burning. Additionally, this reduction in pressure leads to shallower cuts on the top surface, resulting in a smoother and more refined cutting surface. These advantages contribute to improved cutting quality

laser focus 11.5 low pressure


However, it’s important to be aware of the potential drawbacks. When the air pressure is too low and there is insufficient auxiliary gas entering the slot, it can negatively impact the cutting process. Insufficient cutting power may be experienced, and in some cases, stagnant slag may accumulate within the slot. This can lead to difficulties in achieving proper penetration and hinder the overall cutting effectiveness.

Cutting speed

Laser cutting speed plays a crucial role in determining the quality of the cut. When all other parameters are kept constant, the cutting speed and the density and thickness of the material being cut are inversely proportional. It means that as the cutting speed increases, the density and thickness of the material should decrease for optimal results.

Finding the right cutting speed is key to achieving a smooth cutting surface without any slag production in the lower part. However, if the cutting speed is set too fast, it can lead to incomplete cuts, resulting in sparks flying and slag being generated in the lower part. In some cases, it can even lead to lens damage due to excessive heat. On the other hand, if the cutting speed is too slow, it can cause the material to overmelt, widen the slit beyond desired dimensions, and potentially result in workpiece damage.

laser cutting speed comparisons

When the cutting speed is slow, it can result in a dark cutting surface with visible linear stripes on the upper part. This occurs because the laser beam remains in one position for an extended period of time.

On the other hand, increasing the cutting speed can have a positive impact. The cutting surface becomes brighter, and the undesirable stripes tend to disappear. This is due to the reduced dwell time of the laser beam at any given spot.

laser cutting speed comparison 1

However, it’s important to note that excessively fast cutting speeds can have drawbacks. While it helps in reducing the bottom oxide film (which occurs due to overburning), it also increases the likelihood of producing tumors or irregularities in the material.

Finding the optimal cutting speed is crucial to balance these factors. It ensures a well-lit cutting surface without prominent stripes and minimizes the formation of tumors while managing the oxide film. Achieving the right balance leads to improved cutting quality.

Laser cutting speed comparison 2