What factors affect the quality of laser cutting?
For the application of metal laser cutting machine, cutting quality is the primary condition to be considered. Metal laser cutting machines have good cutting quality and can create value for metal manufacturers. Therefore, it is necessary to grasp the factors that affect the cutting quality. So what factors affect the cutting quality of a metal laser cutter? Let's delve into the details.
The effect of cutting speed on the quality of metal laser cutting
The cutting speed is inversely proportional to the density (specific gravity) and thickness of the material being cut.
Proper cutting speed ensures a smooth cutting line, a smooth transition of the cut section, and melting of the lower part of the workpiece.
The effect of too fast speed on the quality of metal laser cutting
1. May cause cut failure with sparks, see Figure 1.
2. Some areas can be cut off while others cannot.
Partially cut, part not cut
Too fast cutting effect (workpiece retracts)
1. The cut portion is rough.
2. The cutting segment has a diagonal streak path and produces excessive dross on the lower half of the workpiece.
Influence of too low speed on the quality of metal laser cutting
1. May cause excessive sheet metal melting and rough cut surfaces.
2. The kerf will become wider, which may result in lower cutting accuracy, and small rounded or sharp corners may melt.
3. Low cutting efficiency will affect production capacity.
Proper Metal Laser Cutting Speed Selection
The feed rate can be judged from the cutting spark. When cutting normally, the sparks will spread downward, and when the speed is too high, the sparks will accumulate; if the sparks do not spread but gather together, it indicates that the feed rate is too low.
Influence of Nozzle on Metal Laser Cutting Quality
Depending on the nozzle design, airflow conditions will vary, which will directly affect the cut quality.
The main function of the nozzle
The role of the cutting nozzle is
1. To prevent debris (such as molten material) from bouncing up and into the nozzle and damaging the lens.
2. In order to control the area and size of gas diffusion, it plays a role in controlling the cutting quality.
Effect of Nozzle Height on Metal Cutting Quality
During normal cutting, the following height of the nozzle (the distance between the nozzle and the workpiece) should usually be kept at 0.8mm-1.2mm.
A height that is too low can cause the sheet metal part to collide with the nozzle, while a height that is too high can cause the gas to spread out, creating a lot of residue on the bottom surface of the cut.
Furthermore, in order to ensure high quality cuts during the use of a metal laser cutting machine, the height of the cutting nozzle relative to the surface of the workpiece being cut must remain substantially the same.
Modern laser cutters are equipped with inductive or capacitive sensor feedback devices that automatically adjust the distance between the two to a predetermined height range.
Influence of Nozzle Diameter on Metal Laser Cutting Quality
Due to the difference in metal plate, power and auxiliary gas, the selection of nozzle holes will also change accordingly.
The diameter of the nozzle is φ1.0mm, φ1.5mm, φ2.0mm, φ2.5mm, φ3.0mm, etc. Currently, nozzle holes are often used in two sizes: φ1.5mm and φ2mm.
Generally, when the nozzle diameter is small, the gas velocity is high and the molten material removal capability is strong. It is suitable for thin plate cutting and can achieve fine cutting.
When the nozzle diameter is large, the gas velocity is low and the removal ability of the molten material is poor. Suitable for cutting thick plates at low speed.
If a nozzle with a larger aperture is used to quickly cut the flakes, the resulting residue may fly upwards and damage the protective lens.
Influence of Nozzle Deformation on Metal Laser Cutting Quality
During the cutting process, when the nozzle collides or rubs against the workpiece, the nozzle is easily deformed. A deformed nozzle will affect the concentricity of the nozzle center to the laser beam.
When the center of the nozzle and the laser beam are on different axes, the following adverse effects will occur:
· It will affect the quality of the cut part. The volume of assist gas blown from the deformed or melted nozzle is not uniform, causing the cut part to burn or melt on one side. The situation can be even worse when cutting sheet metal thicker than 3mm. Sometimes, it cannot penetrate.
· It will affect the quality of sharp corners. When cutting sharp corners, localized excessive melting may occur. When cutting thick plates, it may not be possible to cut.
· It will affect piercing. The perforation is unstable and the time is not easy to control. Infiltration of thick plates can result in excessive melting and infiltration conditions are difficult to control. The perforation of the sheet is less affected.
Therefore, the nozzle should be placed carefully and not damaged to avoid deformation; the melt on the nozzle should be cleaned in time. At the same time, the nozzle should be highly accurate when manufactured and properly installed. If the conditions are changed during the cutting process due to poor nozzle quality, the nozzle should be replaced in time.
Influence of ceramic ring on the quality of metal laser cutting
The ceramic ring is an important part of the cutting head of the metal laser cutting machine. Its main function is to transmit the electrical signal collected by the nozzle of the laser head, which plays an important role in the normal and stable operation of the laser cutting machine.
The laser ceramic ring structure is mainly composed of a ceramic body, stainless steel parts and copper needles. The ceramic body is mainly used to maintain the insulation of the laser head body. Stainless steel pieces are used to ensure adequate contact with the nozzle to transmit the electrical signal to the copper needle, which then transmits the electrical signal to the transmission line, which is then sent by the internal circuitry to the controller laser head.
We often experience equipment failures, laser heads hitting work surfaces, and other failures for no apparent reason. In fact, this is due to instability or loss of electrical signal caused by a poor laser ceramic ring.
So how to choose a ceramic ring?
· Choose from ceramic rings and gold-plated copper pins. In order to reduce losses during signal transmission, pure gold is plated on the copper pins of the high-quality ceramic ring due to its best conductivity.
· Check the quality of the ceramic body. The upper and lower surfaces of the ceramic body should have a high degree of parallelism. At the same time, the conical surface of the upper part of the ceramic body should have a high degree of smoothness, and there should be no bumps or scratches, otherwise eddy currents may be easily generated and the cutting effect may be affected.
· Check assembly quality. The stainless steel parts should be firmly fixed to the ceramic body and there should be no lifting, deformation or gaps.
Although ceramic rings, nozzles and protective mirrors are small, they are important consumables for laser cutting machines. Choosing the right product is not necessarily the best, but the quality must be ensured to protect the laser cutting
Influence of laser power on the quality of metal laser cutting
The laser power has a decisive influence on the cutting process and quality.
Choose the right cutting power for cutting, the cut part will be smooth and not melted.
1. If the laser power is too small, the heat is insufficient, the temperature of the molten product near the lower edge is lower, and the viscosity is higher, so the high-pressure airflow cannot completely blow it away and stay on the lower edge of the cutting surface, resulting in slag. In severe cases, it may not even be possible to cut and make an incision.
Too little power causes frosting
1. If the laser power is too large, the heat input is too large, so the melting range of the workpiece is larger than the range that the high-pressure airflow can drive away, and the molten metal cannot be completely blown away. Airflow produces excessive combustion.
Excessive power leads to overburning and wide cuts
Influence of lens focal length and focal position on the quality of metal laser cutting
Short focal length lenses are suitable for cutting thin materials at high speed, while long focal length lenses are suitable for cutting thicker workpieces.
We define the focus position as 0 on the top surface of the workpiece. The focus is positive above the top surface of the workpiece, and the focus is negative below the top surface.
The thicker the workpiece, the higher the focus, but the height of the focus should be kept within a certain range. If it is out of range, it will not be cut or even cut through.
When cutting 16mm carbon steel with positive focus, if the focus is too high, the lower surface of the part will be covered with melt; if the focus is too low, the lower surface of the part will be covered with oxide scale
Positive Focus 16mm Carbon Steel Cutting Section
When cutting 8mm stainless steel, a negative focus cut is suitable. The focal position is below the flat plate surface, the cutting surface is uniform, and the cutting part is good. However, when cutting right angles, blue light is easily reflected and cutting ability is limited.
Negative focus 8mm stainless steel cut section
Customers can choose the correct focusing cutting method according to the difference of positive and negative focusing effects when cutting stainless steel and carbon steel, and combine their own processing needs to maximize production efficiency.
Influence of auxiliary gas on the quality of metal laser cutting
The auxiliary gas can not only blow away the slag in time, but also can cool the workpiece and clean the lens. Different assist gases can be used to change the cutting speed and the surface quality of the kerf. This is of great significance for cutting special metals.
Selection of auxiliary gas
Generally, compressed air is suitable for cutting aluminum, non-metallic and galvanized steel sheets, which can reduce oxide film and save costs to a certain extent. Used when the cutting board is not very thick and the requirements for cutting the end face are not too high, such as some sheet metal chassis, cabinets and other product industries.
Nitrogen is an inert gas that prevents oxidation of the cut end face of the product during the cutting process and prevents burning (which can easily occur when the sheet is thicker. Nitrogen can be selected for untreated products that require a high cut end face. For example, some decorative industries , aerospace and other special parts;
Oxygen mainly acts as a combustion accelerant, which enables the laser cutting machine to increase the speed and increase the cutting thickness during the cutting process. Oxygen is suitable for thick plate cutting, high speed cutting and very thin plate cutting, such as some large carbon steel plates and some thicker carbon steel structural parts, oxygen can be used.
Influence of auxiliary gas purity on the quality of metal laser cutting
The purity of nitrogen affects the quality of the cut. Water can damage the laser, so the gas level should be at least 4.5.
Practice has shown that a 2% reduction in oxygen purity will reduce the cutting speed by 50% and lead to a significant decrease in cutting quality.
Influence of auxiliary air pressure on the quality of metal laser cutting
1) When the cutting gas pressure is too high, the cutting surface is rough and the gap becomes wider; at the same time, the cutting part is partially melted, and a good cutting part cannot be formed.
2) When the pressure of the cutting gas is insufficient, a melt will be produced during the cutting process, and the cutting speed cannot meet the production efficiency.
Influence of processing materials on the quality of metal laser cutting
Laser cutting can be negatively affected by treatments that treat the surface of the material, such as galvanized, painted, anodized or covered with multiple layers of plastic film, etc. Zinc treated sheets may develop dross on the edges.
Plates with rust, grease, embroidery spots should be cleaned first and then cut; if it cannot be cleaned, the power and pressure of auxiliary gas should be increased to avoid incomplete cutting.
If there are rusted areas or oxide layers on the surface, the profile of the cut will be irregular and many breakpoints will appear.
