Fiber laser cutting quality: most common defects and their solutions

A modern fiber laser can create very precise cuts with a clean cutting edge that do not require further processing. However, even a powerful and high-quality CNC laser does not guarantee a perfect result in all circumstances. The quality of the cut is influenced by a combination of a number of factors - the set power, cutting speed, focal position, nozzle condition, cutting gas pressure and quality, the condition of the protective glass and the material itself.

Do you need advice?

If burrs start to appear on the bottom edge of the cut, the laser does not cut in some places or the appearance of the cutting edge deteriorates significantly, it is not always the right solution to simply increase the laser power.

In this article, we will look at the most common problems in laser cutting of metals, their possible causes and the procedure for finding a defect.

What affects the quality of a laser cut?

The resulting cut quality is always a combination of machine, technology and correct settings. The most important factors include:

  1. Cutting speed
  2. Focus position
  3. Type and pressure of cutting gas
  4. Diameter and type of cutting nozzle
  5. Centering of the laser beam
  6. Cleanliness of the protective glass
  7. Correct function of height sensing
  8. Condition of the cutting head
  9. Material burn-through setting

Parameters suitable for 2mm structural steel, for example, will be completely different from those for cutting 15mm sheet metal. The settings for oxygen, nitrogen or compressed air are also different.

That is why modern CNC fiber lasers have technological tables created for individual materials and thicknesses, which are then further optimized according to the specific production when the machine is put into operation.

Burrs on the lower edge of the cut

Burrs are among the most common problems in laser cutting. They can be almost imperceptible, but they can also create a significant layer of solidified material, which must then be removed mechanically.

The appearance of burrs alone does not yet accurately determine the cause. The following areas most often need to be checked.

Cutting speed

A speed that is too high can cause the laser to not cut the material properly and the molten metal is not sufficiently removed from the cutting gap.

However, the problem can also arise when cutting too slowly, when an unnecessarily large amount of energy is introduced into the material.

The ideal solution is therefore not to simply reduce the speed, but to find the right ratio between:

Power - Speed ​​- Gas pressure

Insufficient or unstable gas pressure

Among other things, the auxiliary gas in laser cutting has the task of removing molten material from the cutting gap.

If the flow or pressure is insufficient, the molten metal can remain on the lower edge of the cut and create burrs or slag.

It is therefore advisable to check not only the set pressure value, but also the actual pressure during cutting.

Sufficient compressor capacity is also important for a compressed air system.

Incorrect focus position

The position of the laser beam focus significantly affects the way in which the energy is distributed in the thickness of the material. An incorrectly adjusted focus can cause:

  • Poorer laser penetration through the material
  • A rougher cutting edge
  • A larger amount of burrs
  • A cutting gap that is too wide

Modern laser heads therefore use automatic focus position changes. However, automatic focusing does not mean that it is not necessary to have the technological parameters set correctly for a specific material.

The laser does not cut the sheet metal

If the laser does not cut the material in places, it is advisable to proceed systematically. Increasing the power should not be the first reaction.

Dirty protective glass

The protective glass protects the optical parts of the laser head from dirt and spatter generated during cutting and burning.

If the glass is dirty or damaged, the passage of laser radiation and thus the quality of the cut may deteriorate.

A typical symptom may be a situation where the machine initially cuts correctly, but the quality gradually deteriorates.

The protective glass is therefore a consumable part of the cutting head and its condition should be checked regularly.

The condition of the cutting nozzle is important

The nozzle costs minimally compared to the price of the laser machine, but its condition has a fundamental impact on the quality of the cut.

The cutting gas flows directly into the cutting gap through the nozzle.

A bad nozzle can result in increased burr formation or even incomplete cutting of the material.

How to recognize a problem with centering?

One possible symptom is a different cut quality depending on the direction.

  1. One side of a square blank is of good quality
  2. The opposite side has a significantly worse edge

In such a case, in addition to the technological parameters, it is appropriate to check the condition of the nozzle and the centering of the laser beam relative to the nozzle opening.

Checking the nozzle should be one of the first things the operator does in the event of a sudden deterioration in quality.

Rough or wavy cutting edge

With well-adjusted cutting, the edge should have an even structure.

If there are noticeable grooves, ripples or changes in the structure in different parts of the burnished piece, the cause may be, for example:

  • Incorrect speed
  • Inappropriate focus position
  • Insufficient power for the given thickness
  • Unstable gas pressure
  • Damaged nozzle
  • Dirty protective glass

The direction of the grooves on the edge is also important. This can help an experienced technician find the cause of the problem.

The influence of cutting gas on edge quality

The choice of cutting gas can change not only the cutting speed and operating costs, but also the final appearance of the cut.

Oxygen

Oxygen is traditionally used mainly in cutting structural steel.

During cutting, it actively participates in the process and allows cutting even thicker material with lower laser power.

The disadvantage is the formation of an oxidized cutting edge. If the product is to be subsequently powder coated or further technologically processed, in some cases it may be necessary to remove the oxide layer.

Nitrogen

Nitrogen is an inert gas and is used where a clean and unoxidized cutting edge is required. Typical applications are:

  • Stainless steel
  • Aluminum
  • Visible parts

When cutting with nitrogen, the entire process power must be supplied by the laser, which is why sufficient power of the laser source is important, especially for thicker materials.

Compressed air

Compressed air is an interesting economic alternative for many applications. However, it must be:

  • Dry
  • Free of oil
  • Clean

For use with powerful fiber lasers, a suitably sized compressor and high-quality compressed air treatment are required.

In practice, compressed air can be very advantageous, for example, when processing some thinner materials, galvanized sheets or aluminum.

Scale and oxidized edge of structural steel

If we cut structural steel with oxygen, oxidation occurs during the process. A certain color and oxide layer are therefore not automatically a sign of incorrect machine settings.

The decisive factor is what result the subsequent technology requires.

If the cut-out goes directly into the structure, for example, the oxidized edge may not be a major problem. However, if painting or welding follows, it may be more appropriate to choose a different cutting technology or to treat the edge before the next operation.

Cutting structural steel with nitrogen or mixed gases is therefore increasingly used with modern high-performance fiber lasers.

Distance of the laser head from the material

The cutting head automatically monitors the surface of the sheet metal during work and maintains the required distance of the nozzle from the material.

If the height sensing does not work properly, the cutting gas flow conditions and the cut quality also change. The problem can be caused by, for example:

  • Damaged ceramic part of the head
  • Dirty nozzle
  • Poor electrical contact
  • Deformed or wavy sheet metal
  • Incorrect height sensing calibration

After the laser head collides with the material, it is therefore advisable to check not only the nozzle itself, but also its mounting and ceramics.

A quality laser needs correct settings

The power of the laser source is important when choosing a CNC laser, but it is certainly not the only parameter that determines the resulting quality of production.

It is therefore important to perform cutting tests on materials that the customer will actually process when installing a new fiber laser.

For GWEIKE laser cutting machines, we provide installation, commissioning, setting of cutting parameters and operator training directly at the customer's site. Our services also include subsequent technical and service support.

When should I contact the service?

If the basic technological parameters, nozzle, protective glass have been checked and the cut quality is still significantly worse than before, it is advisable to consult the service. The technician can then check, for example:

  • The condition of the cutting head
  • The condition of the optical system
  • The height sensing function
  • Gas pressure and flow
  • Control system settings

The more precisely the customer describes the problem, the faster the diagnosis can be.

Frequently asked questions about laser cutting quality

Why do burrs form during laser cutting?
Burrs can form when there is an inappropriate combination of speed, focal position and cutting gas pressure. The cause can also be a damaged or poorly centered nozzle or a dirty protective glass.

How do I recognize a poorly centered nozzle?
One typical symptom can be a different cut quality depending on the direction of movement of the laser head. One cutting direction can be significantly better than another.

Why does the cutting quality gradually deteriorate?
If the quality gradually deteriorates, it is advisable to check the consumable parts of the cutting head, the condition of the protective glass, the nozzle and the stability of the cutting gas supply.

Is it better to cut with oxygen, nitrogen or air?
It depends on the material, thickness and desired edge quality. Oxygen is often used for structural steel, nitrogen where we need a clean, non-oxidized edge, and compressed air can be an economical solution for a number of common applications.

Do you need advice on choosing a CNC laser?

We supply GWEIKE CNC fiber lasers for cutting sheets, pipes and profiles. We provide a complete supply of technology including installation, setting cutting parameters, operator training and warranty and post-warranty service.

If you are considering purchasing a new laser cutting machine or need advice on a suitable configuration for a specific production, we will be happy to discuss your needs with you and propose a suitable solution.

Contact

info@cnc-laser.cz
+420 777 210 149