Laser Cutting Quality Control & Troubleshooting (User’s Guide)

When using a laser cutting machine to process metal materials, the final laser cutting quality is the first concern. For the metal fabricators, if the laser cutting edge quality cannot reach their standard, it will waste the material, reduce the production efficiency and increase the production cost. For individuals who take laser cutting as a hobby or who make a living with laser cutting, they also need to focus on the laser cutting quality so that they can make good products. Laser cutting machine plays an excellent role in the metal fabricating industry. It has high cutting efficiency and good cutting precision. Users need to master the basic skills of laser cutting quality control and laser cutting troubleshooting so that they can truly exert the excellent processing performance of the laser cutting machine.

This article summarizes all the information about laser cutting quality control and laser cutting troubleshooting. And hope it can help users smoothly control laser cutting quality in actual operations and achieve high-quality laser cutting results.

In order to better understand how the laser cutting machine cuts metal, we can look at this picture to learn the working principle of laser cutting metal.

The laser cutting metal process mainly includes the following four steps:

1. The laser source emits a high-energy laser beam. And the laser beam reflects on the reflective lens and focuses on a spot through the focusing lens.
2. The laser beam goes through the nozzle. And at the same time, the auxiliary gas coaxial with the laser beam is also released through the nozzle.
3. The laser beam focuses on the workpiece. And the highly concentrated energy exceeds the melting point and vaporizing point of the metal, making it instantly melt, vaporize and form a hole.
4. The laser cutting head carries the laser beam to move according to the pre-set path and makes the holes continuous, thus forming a cutting seam.

Laser cutting is a process in which laser beam, auxiliary gas and nozzle work together. If the laser power, gas, nozzle and feed rate are set correctly, we can achieve smooth kerf on the workpiece. However, users often do not know how to evaluate the quality of their laser cutting and what causes it. Therefore, in the following section, let us get familiar with how to check the laser cutting quality.

Checking and evaluating laser cutting quality is the premise of laser cutting quality control. Users can check the laser cutting quality according to the following aspects.

In most cases, at the beginning of the laser cutting process, the laser cutting head needs to punch a small hole on the surface of the workpiece and then continue the linear movement. And that punching process is also known as piercing. Piercing quality is one of the essential aspects to test whether the laser cutting parameters are right. If there are abnormal sparks, abnormal noises, or a large piercing gap during the piercing process, that is a manifestation of improper laser cutting parameters.

Generally, most of the metal workpieces cut by laser cutting machines are mechanical parts, so the cutting size must be correct for smooth assembly. Use calipers to measure whether the cutting size of the workpiece meets the requirements and does not exceed the tolerance of the laser cutting machine. In addition, you need to check whether the final laser cutting effect is the same as the preset cutting path. Sometimes the light path is incorrect due to improper settings or nozzle problems. Here is an example of circle laser cutting. If the settings are incorrect or the nozzle is not aligned, you will not get a complete round product.

The kerf (you can also call it cutting slit) in laser cutting is formed by partial melting of metal after laser irradiation. The size of the kerf is a reflection of laser cutting quality. If the kerf is too large, it proves that the laser power is too large or the cutting speed is too slow, resulting in excessive melting of the metal.

The roughness of the cutting slit can be checked according to the depth of the vertical lines formed on the cutting surface. If the vertical lines are clear and deep, it means high roughness and bad cutting quality. If the vertical lines are very shallow, it means low roughness and good cutting quality.

The taper is the angle from the top to the bottom of the laser cutting slit. When the laser cutting parameters are set reasonably, the taper produced by laser cutting of metal plates within 10mm is extremely small and can be ignored. However, if you need to cut thicker workpieces, the cutting position of the laser beam will gradually move away from the laser focus and diverge, which will expand the cutting seam and produce a certain taper. The taper can be controlled within a reasonable range. But if it’s too large, it is generally caused by unreasonable parameter settings.

Burrs directly reflect the laser cutting quality and it is also a problem often encountered in various metal laser cutting occasions. A normal laser cutting process has almost no burrs. If there are any burrs on the cutting edge, it means that the laser cutting parameters are not correct. There are many ways to solve different burr problems for different metals. And we will share the detailed solutions in the last part of the article.

Deformation is also a common concern in the metal processing industry. And it generally occurs when cutting thin metal sheets or performing fine processing on small metal parts. If the laser cutting parameters are incorrect, and the heat from laser irradiation is too high, it will distort the material and cause thermal deformation.  Therefore, we need to prevent the material from overheating and deformation by controlling the laser power, feed rate and other laser cutting parameters.

The laser cutting machine achieves the cutting effect by melting or vaporizing the material. The material around the cutting slit will also be heated by the laser and change the molecular structure. And the area where the molecular structure changes due to laser irradiation is called HAZ (heat-affected zone). Laser cutting will cause a certain heat-affected zone, which is inevitable. However, we can take appropriate measures to control the scope of the heat-affected zone within a reasonable range.

Through the previous section, we learned how to check and evaluate the quality of laser cutting metals. In the following part, we will take you to analyze the seven main factors that affect laser cutting quality. You can start from these seven aspects to better achieve laser cutting quality control.

The factors that affect the laser cutting quality mainly include the laser source, laser power, laser cutting speed, laser focus, auxiliary gas, gas pressure and nozzle.

The laser source is the energy source of a laser cutting machine. And the quality of the laser source will affect the final laser cutting quality to a certain extent. At present, there are many reliable laser source brands on the market, such as IPG, Raycus, Max, JPT, and so on. When choosing a laser cutting machine, you must choose a laser source with stable performance and long life to better control the laser cutting quality.

The laser power represents the cutting capacity of a laser cutting machine. Greater laser power means stronger cutting force. Different types of materials need different laser powers. Moreover, the laser power suitable for different thicknesses of the same metal material is also different. Unsuitable laser power will affect the laser cutting quality in a negative way. For example, if the laser power is too large, the cutting surface will be rough and have burrs. If the laser power is too small, the machine cannot cut through the workpiece.

The cutting speed is an important parameter that cooperates with laser power to control the cutting process. And it will affect the final cutting quality. If the cutting speed is too fast, the workpiece cannot get enough heat to be completely cut through. If the cutting speed is too slow, the workpiece will be overheated and the cutting slit will be large and rough.

The focused point of the laser beam has the highest energy density. The smaller the light spot, the better the cutting result. The focus position of the laser beam directly affects the laser cutting quality, including the slit size, slit roughness and taper. Before operating a laser cutting machine, users need to make sure that the laser beam is focused on the right position. For carbon steel laser cutting, the focus position is on the surface of the workpiece, and the thicker the workpiece, the higher the focus position. For stainless steel laser cutting, the focus position is below the surface of the workpiece, and the thicker the workpiece, the lower the focus position.

The auxiliary gas can assist the laser beam to cut the workpiece with better quality, and quickly blow away the slag at the same time. The commonly used auxiliary gases include oxygen, nitrogen and air. Oxygen is mainly used for processing tool steel, mild steel and thick carbon steel. Nitrogen is mainly used for cutting stainless steel, mild steel and galvanized steel. And the air is mainly used for processing aluminum. The purity of auxiliary gas will affect the final laser cutting result. For example, the minimum purity requirement of nitrogen gas is 99.5%.

The pressure of auxiliary gas will affect the blowing effect of the slag and thus affect the final laser cutting quality. Different metal materials need different optimal gas pressures. If the gas pressure is too low, the molten material cannot be blown off in time and will adhere to the back of the cutting edge. If the gas pressure is too high, it will weaken the cutting ability of the laser beam, making the cutting slit larger and rougher.

The function of the nozzle is to control the injection area of auxiliary gas to control the laser cutting quality. So the structure, size and height of the nozzle will affect the final cutting quality. If the nozzle is partially damaged, it will cause uneven airflow and negatively affect the cutting quality. Different cutting thicknesses are suitable for different nozzle diameters. For example, 1-6mm stainless steel plates are suitable for Φ1.2 nozzle. And 6-10mm stainless steel plates are suitable for Φ2.0 nozzle. In terms of laser cutting quality control, users need to protect the nozzle from collision, deformation, or partial melting. Moreover, the nozzle needs to be coaxial with the laser beam to achieve the best laser cutting quality. In addition, the distance between the nozzle and the workpiece will also affect the laser cutting quality.

There are many factors that affect the laser cutting quality, but this does not mean that it is difficult to obtain high laser cutting quality. Users can analyze which factors may affect the cutting quality according to the processing effect to adjust the parameters. Next, we will share the common laser cutting problems and solutions so that you can solve your laser cutting quality problems in time.

Laser Cutting Quality Problems	Possible Reasons	Solutions
There are small drip-shaped regular burrs on the cutting seam	1.    The laser focus position is too low. 2.    The cutting speed is too high. 3.    The laser power is too low.	1.    Raise the laser focus position. 2.    Reduce the cutting speed. 3.    Increase the laser power.
There are long irregular burrs on both sides of the cutting seam, and there is discoloration on the metal surface	1.    The cutting speed is too slow. 2.    The laser focus position is too high. 3.    The air pressure is too low. 4.    The material is too hot. 5.    The transmission system is not stable.	1.    Increase the cutting speed. 2.    Lower the laser focus position. 3.    Increase the air pressure. 4.    Cool the material. 5.    Check and adjust the transmission system.
There are long irregular burrs on one side of the cutting seam	1.    The nozzle is not aligned. 2.    The laser focus position is too high. 3.    The air pressure is too low. 4.    The cutting speed is too slow. 5.    The center position of the laser focusing lens is offset. 6.    The nozzle is partially blocked or damaged. 7.    The lens is polluted or damaged.	1.    Check and adjust the nozzle. 2.    Lower the laser focus position. 3.    Increase the air pressure. 4.    Increase the cutting speed. 5.    Check and adjust the center position of the laser focusing lens. 6.    Clean or replace the nozzle. 7.    Clean or replace the lens.
The molten material is discharged from the upper side of the material	1.    The laser power is too low. 2.    The cutting speed is too high. 3.    The air pressure is too high.	1.    Increase the laser power. 2.    Reduce the cutting speed. 3.    Reduce the air pressure. Note: Be sure to check if the laser focusing lens is damaged or not, and replace it with a new one if needed.
The cutting edge becomes yellow	1.    The auxiliary gas is not pure. 2.    There are some oxygen gases or air in the air tube.	1.    Check the purity of nitrogen, use nitrogen gas with high purity. 2.    Increase delay to clean the air tube.
The cutting seam is rough	1.    The nozzle is damaged. 2.    The lens is polluted.	1.    Check or replace the nozzle. 2.    Clean or replace the lens.

Laser Cutting Quality Problems	Possible Reasons	Solutions
When cutting a round shape, the finished workpiece is not round	1.    The center position of the lens is not correct. 2.    The nozzle is blocked or damaged. 3.    The laser path is not correct.	1.    Check and adjust the center position of the lens. 2.    Check or replace the nozzle. 3.    Check and adjust the laser path.
The finished workpiece has a gap at the cutting introduction position	1.    The piercing process is too long. 2.    The heat is too high during the cutting.	1.    Shorten the piercing time. 2.    Reduce the duty cycle and cool the material.
The traction line at the bottom is offset, and the bottom cutting slit is wider	1.    The cutting speed is too high. 2.    The laser power is too low. 3.    The air pressure is too low. 4.    The laser focus position is too high.	1.    Reduce the cutting speed. 2.    Increase the laser power. 3.    Increase the air pressure. 4.    Lower the laser focus position.
There are drip-shaped burrs that are similar to slag and are easy to remove	1.    The cutting speed is too high. 2.    The air pressure is too low. 3.    The laser focus position is too high.	1.    Reduce the cutting speed. 2.    Increase the air pressure. 3.    Lower the laser focus position.
The burrs are connected and can be removed as a whole piece	The laser focus position is too high.	Lower the laser focus position.
The burrs on the bottom of the cutting seam are hard to remove	1.    The cutting speed is too high. 2.    The air pressure is too low. 3.    The auxiliary gas is not pure. 4.    The laser focus position is too high.	1.    Reduce the cutting speed. 2.    Increase the air pressure. 3.    Use the auxiliary gas with higher purity. 4.    Lower the laser focus position.
There are burrs on one side of the cutting seam	1.    The center position of the nozzle is not correct. 2.    The nozzle is damaged.	1.    Check and adjust the center position of the nozzle. 2.    Check or replace the nozzle.
The cutting edge is not precise	1.    The air pressure is too high. 2.    The nozzle is damaged. 3.    The diameter of the nozzle is too large.	1.    Reduce the air pressure. 2.    Check or replace the nozzle. 3.    Install a nozzle with proper diameter.
The texture on the cutting is very rough	1.    The laser focus position is too high. 2.    The air pressure is too high. 3.    The cutting speed is too slow. 4.    The material is too hot.	1.    Lower the laser focus position. 2.    Reduce the air pressure. 3.    Increase the cutting speed. 4.    Cool the material.
The molten material is discharged from the upper side of the material	1.    The laser power is too low. 2.    The cutting speed is too high.	1.    Increase the laser power. 2.    Reduce the cutting speed. Note: Be sure to check if the laser focusing lens is damaged. And replace with a new one if needed.
There are abnormal sparks during the cutting	1.    The thread at the connection between the nozzle and laser head is loose. 2.    The nozzle is damaged. 3.    The air pressure is too low.	1.    Tighten the thread. 2.    Check or replace the nozzle. 3.    Increase the air pressure.
The laser cannot cut through the material	1.    The laser power is too low. 2.    The cutting speed is too high. 3.    The laser focus position is too low. 4.    The diameter of the nozzle does not match with the cutting thickness of the metal.	1.    Increase the laser power. 2.    Reduce the cutting speed. 3.    Raise the laser focus position. 4.    Check and replace the nozzle.
The laser beam has breaks	1.    The cutting speed is too high. 2.    The laser power is too low. 3.    The laser focus position is too low.	1.    Reduce the cutting speed. 2.    Increase the laser power. 3.    Raise the laser focus position.

Laser cutting quality is affected by many factors. First of all, improper parameter settings will affect the cutting result, such as laser power, cutting speed, air pressure, etc. In addition, sometimes there will be problems even if the parameters are set correctly. And this is usually because the gas purity is not enough, or the nozzle and lens are contaminated or damaged. Therefore, users need to check the nozzle before cutting, whether the laser head is working properly, and then set the appropriate parameters. Then, analyze the causes according to the specific laser cutting effect, and adjust parameters and check machine parts to achieve the best laser cutting quality.