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Things You Should Know About Laser Cut Kerf

As a piece of common equipment for sheet metal processing, laser cutting machine plays an important role. Efficient cutting and high-precision cutting are deeply rooted in the hearts of the people.

However, after long-term use, the performance of the equipment will also decline, and even the cutting plate will have large kerfs, which will affect the cutting quality.

This needs to be solved in time. Let’s take a look at it together below.

The cutting performance of optical fiber laser cutting machine decreases, on the one hand, because the machine is worn out after working for a long time, on the other hand, because of the lack of maintenance during the operation of the machine.

How big is the kerf of laser cutting

kerf of laser cutting

The cutting methods of different plates are different; the requirements are different, and the equipment used is also different; in addition, the cutting kerfs cut by materials of different thicknesses are also different.

Taking 10mm plate as an example, generally speaking:

(1) Cutting with metal laser cutting machine, cutting accuracy: ± 0.025mm; kerf width: 0.2 ~ 1mm

(2) Cutting with plasma cutting machine, with cutting accuracy of ± 0.3mm; kerf width: 0.5 ~ 1.2mm

(3) If acetylene is used for manual cutting, the cutting accuracy: ± 1mm; kerf width: 1.0 ~ 1.5mm

Materials with a thickness of less than 3.0mm, the kerfs are generally within 0.3 ~ 0.5mm.

The thicker the material, the larger the cutting kerf.

In addition, it is also related to the cutting nozzle and cutting method used.

Factors affecting the cutting kerf

Laser cutting machine has been developed for many years and has gradually become the mainstream processing equipment of metal processing.

There are always some problems in cutting, such as too large cutting kerf.

So what are the factors affecting the kerf width of laser cutting machine? There are four main factors:

1. Quality of laser beam

Quality of laser beam

The laser beam generated by the laser is not emitted vertically but has a scattering angle.

Therefore, when we use the laser cutting machine to cut the workpiece, a certain taper will be formed, so the quality of the laser beam is also very important in cutting.

Generally, the focus shall not be adjusted at will after adjustment.

It only needs to be adjusted when there are obvious problems in the cutting effect.

2. Different cutting materials

Fiber Laser Cutting Effect
Fiber Laser Cutting Effect

According to different cutting materials, the actual effect of cutting is also different.

In laser cutting, the smaller the spot of the laser beam, the better the cutting effect.

In addition to the quality of the laser beam affecting the spot, the material of the workpiece itself will also affect the size of the spot.

For example, copper is a material with high reflectivity, which is not conducive to the formation of light spot, so the requirements of the copper laser cutting machine are relatively high compared with ordinary metals.

3. Thickness of material

Under the cutting conditions of the same material and the same power, the larger the thickness of the material, the cross-section is relatively burr and uneven.

To be exactly the same as the sheet material section, the power of the laser needs to be increased.

4. Cutting speed

The reason why the laser cutting machine is well accepted is because of its fast cutting speed.

When other conditions remain unchanged, the cutting speed of the laser cutting machine is too slow or too fast will not achieve a good cutting effect.

If the speed is too slow, the roughness of the kerf may be very large. If the speed is too fast, the roughness of the kerf may be reduced.

However, if the speed is too fast, it may be impossible to penetrate, so it is very important to control the speed and not blindly pursue high-speed cutting.

Relationship between cutting speed and kerf width

When the laser power and auxiliary gas pressure are constant, the laser cutting speed maintains a nonlinear inverse relationship with the kerf width.

When the cutting speed increases, the kerf width decreases; When the cutting speed decreases, the kerf width will increase.

There is a parabolic relationship between cutting speed and surface roughness of the cutting section.

With the decrease of cutting speed, the surface roughness of the section increases, and with the increase of cutting speed, the surface roughness improves.

When an optimal cutting speed is reached, the surface roughness of the cutting section is small.

When the cutting speed increases to a certain value, the plate cannot be cut through.

Relationship between focus position and kerf width

Among the factors affecting the processing quality and processing capacity of laser cutting machine, the most influential is the focus position, and its specific relationship with processing is as follows.

Relative to the surface of the processed material, the focus position is called the focus position after the laser beam is focused.

The focus position will affect almost all processing parameters, such as the width, slope, roughness of cutting surface, adhesion state of slag, cutting speed and so on.

This is because the change of the focus position will cause the change of the beam diameter on the surface of the processing material and the incident angle into the processing material.

As a result, it will affect the formation state of the kerf and the multiple reflections of the beam in the kerf.

These cutting phenomena will affect the flow state of auxiliary gas and molten metal in the kerf.

Relationship between focus position and kerf width

As shown in the figure, the relationship between the focus position Z of the laser cutting machine and the kerf width W of the machined material surface is shown.

The state of the focus on the surface of the processed material is set to Z = O “zero”, the focus position is represented by “+” when moving upward, “-” when moving downward, and the moving amount is represented by mm.

The focus is at the focus position Z = 0, and the upper kerf width W is the minimum. Whether the focus position is moved up or down, the upper kerf width W will become wider.

This change has the same tendency when processing lenses with different focal lengths are used.

The smaller the beam diameter at the focus position and the shorter the focal depth of the lens, the greater the variation of the upper kerf with the change of the focus position.

Focus positionFeaturesApplication

Focus position Z=0

The kerf is the narrowest and can be processed with high precisionProcessing requiring slope reduction;
Processing with high requirements for surface roughness;
High speed cutting;
Reduce the processing of heat affected zone;
Micro machining

Focus position Z > 0

Widening below the kerf, can improve the flow of gas and the fluidity of meltCW and high frequency pulse processing of thick plate;
Acrylic plate processing;
Tool die processing;
Ceramic tile processing

Focus position Z < 0

Widening above the kerf, can improve the flow of gas and the fluidity of meltAir cutting of aluminum;
Nitrogen cutting of aluminum;
Air cutting of stainless steel;
Nitrogen cutting of stainless steel;
Air cutting of galvanized steel sheet

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

(1) The minimum beam diameter Z = 0 can be obtained by the material surface.

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) The focus position is on the “+” side (Z > o)

At this time, the irradiation range of the laser beam on the surface of the processed material becomes wider, and the beam in the kerf appears a diffusion angle, which expands the kerf width.

(3) The focus position is on the “-” side (Z < 0)

At this time, the range of the laser beam irradiated on the surface of the processed material becomes wider.

The closer to the focus position in the plate thickness direction, the greater the melting capacity, and then the reverse slope occurs.

Three solutions for cutting kerf too wide

Usually, when we use the laser cutting machine to finish the processing, there will be a large cutting kerf occasionally, so the cutting accuracy of the workpiece is low and can not meet our requirements.

What is the reason for this situation? Is there any way to solve it?

Through continuous observation and summary, the technical engineer has obtained three solutions:

1. We need to check whether the focal length of the fiber laser cutting machine is correct

The form of optical fiber focal length adjustment is divided into manual and automatic.

Manual focusing is easy to be forgotten by technicians, especially after replacing or cleaning the lens, the focal length should be adjusted.

2. Lenses are the key reason

Check whether the lens is damaged or dirty, because this will lead to laser scattering and laser beam thickening. Replacing or cleaning the lens is the only way.

3. The placement of laser tube is also a very important aspect

Check the spot quality of the laser.

If there are two points or the light spot is not round, the support point of the laser tube may need to be adjusted.

Many people will ignore this reason, which also needs attention.

Large laser cutting seam is not a big problem, but the equipment needs to be maintained after processing and production for a period of time.

In fact, there will be some small abnormalities in the process of use, which requires us to do a good job in maintenance, so as to ensure the efficient and long-term operation of the laser cutting machine and create maximum value for users.

Experience of ensuring laser cutting kerf quality

The factors affecting the quality of laser cutting kerf are very complex.

From the above contents, we know that in addition to the processing material itself, there are many other factors that determine the kerf width, including beam characteristics, laser power, cutting speed, nozzle type (aperture) and nozzle height, focus position, auxiliary gas type and pressure, etc.

Here are some experiences of using laser cutting machine to ensure the cutting quality (i.e. cutting focus):

  • Good cutting kerf quality (i.e. cutting focus) is very important to the cutting process. At least, it will affect the cutting effect, and the burr is serious. At worst, it will cause serious edge burning and plate explosion.
  • However, after the focus is aligned, it generally does not need to be adjusted repeatedly. Generally, it needs to be adjusted when there are obvious defects in the cutting effect.
  • In addition, the lens needs to be adjusted after maintenance.
  • It also needs to be adjusted when switching thin and thick plates repeatedly.
  • Necessary trial cutting must be carried out before plate replacement to ensure that there are no problems in the processing process.

Note: observe every day and maintain the lens once a week.

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