Laser cutting technology has revolutionized the manufacturing industry, allowing for precise and efficient cutting of various materials.
However, the success of the laser cutting process is highly dependent on several critical factors that must be carefully controlled.
In this article, we explore the key process parameters that play a crucial role in laser cutting, including laser mode, laser power, focus position, nozzle height, nozzle diameter, and auxiliary gases.
We delve into the intricacies of each parameter, examining their impact on the cutting process and the resulting quality of the cut. From the distribution of light intensity in the laser beam to the size of the nozzle aperture, we leave no stone unturned in our quest to provide a comprehensive understanding of laser cutting technology.
Whether you are a seasoned professional or a curious novice, this article is sure to captivate and intrigue, providing valuable insights into the world of laser cutting.
So, sit back, relax, and prepare to be amazed by the wonders of laser cutting technology.
The following factors play a critical role in the laser cutting process:
- Laser mode
- Laser power
- Focus position
- Nozzle height
- Nozzle diameter
- Auxiliary gases
- Auxiliary gas purity
- Auxiliary gas flow
- Auxiliary gas pressure
- Cutting speed
- Sheet material
- Sheet surface quality (e.g., rust, debris, etc.)
The process parameters associated with laser cutting are shown in the figure below.
Fig. 1 Cutting process parameters
I. Laser Mode
The laser mode greatly impacts the cutting process and produces better results when cutting steel plates. This is closely linked to the laser mode and the quality of the external optical lens.
The distribution of light intensity across the cross-section of the laser beam is referred to as the laser transverse mode. The transverse mode is generally considered the laser mode.
Various transverse modes are represented by the symbol TEMmn, where TEM stands for transverse electromagnetic wave and M and N are positive integers that represent the ordinal numbers of points with zero light intensity in the X-axis and Y-axis directions, respectively, known as the mode ordinal.
The following figure displays the foci of several different transverse modes of the laser beam. TEM00 mode, also known as the basic mode, has no points with zero light intensity. TEM10 mode has a zero intensity point in the X direction, and TEM01 mode has a zero intensity point in the Y direction. The larger the mode ordinals M and N, the more points with zero light intensity in the focus.
Laser beams with various transverse modes are referred to as multimode.
Fig. 2 Mode Spot
In the figure mentioned above, the TEM00 mode is referred to as the fundamental mode.
The TEM*01 mode is a single ring mode and is also known as the quasi-fundamental mode. An asterisk * is added to distinguish it from TEM01.
In reality, TEM01 mode and TEM10 mode can be considered the same mode, as the X and Y axes are artificially divided. The stereograms of several modes are depicted below.
Figure 3: Stereogram of TEM00 mode
Figure 4: Stereogram of TEM20 mode
Figure 5: Stereogram of TEM23 mode
Figure 6: Stereogram of Multimode.
II. Focal position
The focus position is a crucial parameter and must be properly adjusted.
1. The relationship between focus position and cutting surface
|Focal position||Schematic diagram||Features|
|Zero focal length: |
The focus is on workpiece surface.
|It is suitable for thin carbon steel below 5mm. |
When the focus is on the upper surface of the workpiece, the cutting result is smooth on the upper surface, but the lower surface is not smooth.
|Negative focal length: |
The focus is under the surface of the workpiece.
|Aluminum, stainless steel and other workpieces adopt this method. |
The focus is located in the center and lower part, resulting in a larger area of smooth surface. The results indicate that the cutting width is wider and the cutting gas flow is greater with a focus at this location, compared to a focus at zero focal length. Additionally, the perforation time is longer at this focus position.
|Positive focal length: |
The focus is on the workpiece surface
|When cutting thick steel plates, oxygen is utilized. The oxidation of the oxygen used for cutting must occur from top to bottom.|
To accommodate the thickness of the plate, a wider cutting width is necessary, which can be achieved by adjusting the settings.
The cutting section resembles that of gas cutting, with oxygen blowing and producing a rough section.
2. The influence of focus position on cutting section
|1.5mm above the surface||0.5mm above the surface||2.5mm above the surface|
3. Focus seek
The basic concept is to use masking glue to block the nozzle and adjust the focus distance. Then, the size of the punctured holes is checked. The position with the smallest hole is the focus. Finally, the best focus for cutting is determined based on the cutting process after the focus has been found.
The shape of the nozzle, the diameter of the nozzle, and the height of the nozzle (the distance between the nozzle outlet and the surface of the workpiece) will impact the cutting outcome.
Fig. 7 Nozzle
1. Function of the nozzle
- It helps to prevent impurities like melting residue from bouncing upward, going through the nozzle, and contaminating the focusing lens.
- It regulates the area and size of gas diffusion to control the cutting quality.
Fig. 8 Gas ejection without nozzle
Fig. 9 Gas ejection with nozzle
2. The relationship between nozzle and cutting quality
The coaxiality between the center of the nozzle outlet hole and the laser beam is one of the important factors affecting the cutting quality. The thicker the workpiece, the greater the influence. Coaxiality will be directly affected when the nozzle deforms or there is a melt stain.
Therefore, the nozzle should be carefully stored to avoid damage and deformation. The shape and size of the nozzle have a high manufacturing accuracy, and the correct installation method should be given attention.
If the nozzle’s condition is poor, cutting conditions may need to be changed, and it is better to replace it with a new one. If the nozzle is not aligned with the laser axis, it will affect the cutting quality as follows.
1) Influence on cutting section
As depicted in the figure, when auxiliary gas is expelled from the nozzle, the gas volume becomes uneven, with molten stain on one side but not on the other. The uneven gas volume has little impact on cutting thin plates less than 3mm, but it becomes more serious when cutting thicker plates, sometimes even preventing a successful cut.
Fig. 10 Influence of coaxiality on cutting section
2) Impact on sharp corners
If the workpiece has sharp or small angles, it is prone to over-melting, which may prevent thick plates from being cut.
3) Impact on perforation
Perforation instability, difficulties in controlling timing, over-melting of thick plates, and difficulty in mastering penetration conditions can occur. However, these issues have little effect on cutting thin plates.
3. Adjustment of coaxiality between nozzle hole and laser beam
The steps to adjust the coaxiality between the nozzle hole and laser beam are as follows:
(1) Apply ink to the outlet end face of the nozzle (usually in red) and attach adhesive tape to the nozzle outlet end face, as shown in the figure.
Fig. 11 Step 1 of adjusting coaxial
(2) Use a power of 10-20 watts for manual drilling.
(3) Remove the self-adhesive paper, being careful to maintain its orientation for comparison with the nozzle.
Under normal conditions, the laser will burn a black spot on the self-adhesive paper. However, if the center of the nozzle deviates too much from the center of the laser beam, the black spot will not be visible (as the laser beam will hit the wall of the nozzle).
Fig. 12 Nozzle deviation too large
(4) If the center point is too large or small, check to ensure that the conditions are consistent and that the focusing lens is secure.
Fig. 13 Loose focusing mirror
(5) Observe the direction of the black spot in relation to the center of the nozzle and adjust the nozzle’s position accordingly.
Fig. 14 Adjusting the position of the coaxial laser beam
4. Nozzle diameter
The size of the aperture has a crucial impact on cutting and perforation quality. If the nozzle aperture is too large, molten material may splash around during cutting and pass through the nozzle hole, potentially damaging the lens. The larger the aperture, the greater the likelihood of this occurring, leading to decreased protection of the focusing lens and shorter lens lifespan.
Comparison of the nozzle aperture
|Nozzle aperture||Gas flow rate||Melt removal capacity|
The difference between φ1 and φ1.5 nozzle
|Nozzle diameter||Thin plate (less than 3mm)||Thick plate (over 3mm) |
High cutting power, longer cooling time and longer cutting time
|φ1||The cutting surface is fine.||The gas diffusion area is small and unstable, but it is basically available.|
|φ1.5||The cutting surface will be thicker, and the corner is easy to have solution stains||The gas diffusion area is large, the gas velocity is slow, and the cutting is stable.|
5. Adjustment of nozzle height
The nozzle height refers to the distance between the nozzle outlet and the workpiece surface. The range for setting this height is between 0.5mm and 4.0mm, with a typical setting of 0.7mm-1.2mm for cutting.
If the height is set too low, the nozzle may collide with the workpiece surface. On the other hand, if it is set too high, the auxiliary gas pressure and concentration will decrease, leading to a decline in cutting quality. During drilling, the height should be slightly higher, around 3.5mm-4mm, to prevent the focus lens from being contaminated by drilling splashes.
Fig. 15 Nozzle height
Capacitive sensor control box
As shown in the figure , the nozzle height adjustment item is shown.
IV. Cutting speed
The cutting speed has a direct impact on the width and roughness of the incision. There is an optimal value for cutting speed that varies with the thickness of the material and the pressure of the cutting gas. This value is typically around 80% of the maximum cutting speed.
1. Too fast speed
If the cutting speed is too high, it can lead to the following problems:
- Incomplete cuts with random sparks.
- Inconsistent cuts with some areas cut through and others not.
- A thick cut section without a solution.
The cut section will have inclined striations and solution stains at the bottom.
Fig. 18 Too fast speed
2. Too slow speed
(1) Overmelting leads to a rough cutting surface.
(2) The slit widens and sharp corners become melted.
(3) This impacts the cutting efficiency.
3. Determine the appropriate cutting speed
Determining whether to increase or decrease the feed speed based on the cutting sparks.
1) Sparks spread from top to bottom
Fig. 19 Normal cutting speed
2) If the spark is inclined, the cutting speed is too fast.
Fig. 20 Too fast cutting speed
3) If the sparks are not diffused and few, and they gather together, the speed is too slow.
Fig. 21 Too slow cutting speed
The feed speed is suitable.
As depicted in the figure, the cutting surface displays a relatively smooth line and there is no melting on the lower half.
Fig. 22 Normal cutting speed
V. Cutting auxiliary gas
Consider the following factors when selecting the type and pressure of the cutting auxiliary gas:
- Oxygen is typically used for cutting ordinary carbon steel with low-pressure drilling and low-pressure cutting.
- Air cutting is commonly used for non-metal cutting.
- Nitrogen is usually used for cutting stainless steel.
- The cutting quality improves with higher gas purity.
- For cutting low carbon steel plates, the gas purity should be at least 99.6%, and for cutting carbon steel plates thicker than 12mm, the oxygen purity should be above 99.9%.
- The nitrogen purity for cutting stainless steel plates should be above 99.6%.
- A higher nitrogen purity results in better quality cuts.
- Poor gas purity not only affects the cutting quality but also causes lens contamination.
1. The influence of auxiliary gas on cutting quality
(1) The gas contributes to heat dissipation and combustion, removes the solution, and enhances the cutting surface quality.
(2) The effects of low gas pressure on cutting.
a. The cutting surface has melted.
b. The cutting speed cannot be increased, affecting efficiency.
(3) The influence of high gas pressure on cutting quality
a. If the airflow is too high, the cutting surface will be thicker and the seam will be wider.
b. If the airflow is excessive, the cut-off piece will melt and a good cutting quality cannot be achieved.
2. The effect of auxiliary gas on perforation
(1) When the gas pressure is too low, it becomes difficult to penetrate and the time increases.
(2) When the gas pressure is too high, the penetration point melts and a large melting area is formed.
As a result, the perforation pressure for thin plates is higher than that for thick plates.
3. Auxiliary gas for cutting plexiglass
Plexiglass is flammable. To achieve a transparent and bright cutting surface, nitrogen or air is chosen as a flame retardant. If oxygen is selected, the cutting quality will not be good enough. Therefore, it is necessary to select the appropriate pressure based on the actual situation when cutting.
The smaller the gas pressure, the higher the brightness of the cutting light and the narrower the hair section. However, if the gas pressure is too low, it will result in slow cutting speed and flame under the plate surface, which can negatively impact the quality of the lower surface.
VI. Laser power
The laser power required for laser cutting mainly depends on the type of cutting and the properties of the material being cut. The largest laser power requirement is for vaporization cutting, followed by melting cutting and oxygen cutting.
The laser power has a significant impact on the cutting thickness, speed, and incision width. As the laser power increases, the thickness of the material that can be cut increases, the cutting speed accelerates, and the width of the incision also increases.
Laser power plays a crucial role in determining the cutting process and quality.
1. The power is too small to cut
Fig. 26 Too low power
2. If the power is too high, the whole cutting surface will melt.
Fig. 27 Excessive power
3. The power is insufficient, resulting in molten stains after cutting.
Fig. 28 Power deficiency
4. The power is appropriate, the cutting surface is good without molten stains.
Fig. 29 Proper power
Summary of cutting parameters
The main parameters of laser cutting
Given the laser power density and material, the cutting speed follows an empirical formula. As long as it is above the threshold, the cutting speed of the material is proportional to the laser power, meaning that increasing the power density can increase the cutting speed.
The cutting speed is also inversely proportional to the density and thickness of the material being cut. There are several ways to improve cutting speed:
(1) Increase power (in the range of 500-3000W);
(2) Change the beam mode;
(3) Reduce the focus spot size (for example, by using a short focal length lens).
For metal materials, if other process variables are kept unchanged, the laser cutting speed can be adjusted within a range while still maintaining a satisfactory cutting quality. This range appears to be relatively wide when cutting thin metals.
After the laser beam is focused, the spot size is proportional to the focal length of the lens. A short focal length lens results in a small spot size and high power density at the focal point, making it ideal for material cutting. However, its disadvantages are a very short depth of focus and limited adjustment margin, making it typically suitable for high-speed cutting of thin materials.
For thicker workpieces, a telephoto lens with a wider focal depth is more suitable for cutting, as long as it has sufficient power density.
In most cases, the highest power density is at the focal point, which is usually just at the surface or slightly below the surface of the workpiece during cutting. Maintaining a constant relative position between the focal point and the workpiece is crucial for obtaining stable cutting quality.
It is important to note that during operation, the lens may heat up due to poor cooling, causing the focal length to change. In such cases, it is necessary to adjust the focal position in a timely manner.
The auxiliary gas is sprayed along the same axis as the laser beam to protect the lens from contamination and remove the molten slag at the bottom of the cutting area. For non-metallic and some metallic materials, compressed air or an inert gas is used to remove the molten and evaporated materials and prevent excessive combustion in the cutting area.
Auxiliary gas pressure
Most metal laser cutting uses a reactive gas (oxygen) to create an oxidative exothermic reaction with the hot metal. This additional heat can increase the cutting speed by 1/3 to 1/2.
When cutting thin plates at high speeds, a higher gas pressure is necessary to prevent the back of the cut from adhering to the slag. When cutting thicker material or at slower speeds, the gas pressure can be reduced as appropriate.
Laser output power
The laser power and the quality of the mode will have a significant impact on the cutting. In actual operation, the maximum power is often set to achieve a high cutting speed or to cut thick materials.
Wrap it up
The above paragraph outlines most of the factors that can impact the parameters of the cutting effect. The following table lists typical values for cutting parameters. These values are not specific to any particular case, but they can be used as a reference to determine the correct starting parameters.
Typical values of DC030 stainless steel cutting parameters
|Distance from nozzle to plate|
Typical values of DC030 low carbon steel cutting parameters
|Distance from nozzle to plate|
Typical values of DC025A1Mg3N2 steel cutting parameters
|Distance from nozzle to plate|
The following pictures show the cutting of 15mm carbon steel and 8mm stainless steel sheets at different focal lengths.