For the application of metal laser cutting machine, cutting quality is the first condition to be considered. The metal laser cutting machine has good cutting quality and can create value for metal manufacturers. Therefore, it is necessary to master the factors that affect the cutting quality. What factors will affect the cutting quality of metal laser cutting machine? Let's delve into the details.
Influence of cutting speed on metal laser cutting quality
The cutting speed is inversely proportional to the density (specific gravity) and thickness of the material to be cut.
Proper cutting speed can ensure smooth cutting line, smooth transition of cutting part and melting of lower part of workpiece.
The influence of too fast speed on the quality of metal laser cutting
1. The cutting may fail with sparks, see Figure 1.
2. Some areas can be cut off, while others cannot.
Partially cut off, partially not cut off
Cutting effect with too fast speed (workpiece retreating)
1. The cutting part is rough.
2. The cutting section has diagonal stripe path, and excessive slag is generated in the lower part of the workpiece.
Influence of low speed on the quality of metal laser cutting
1. It may cause excessive melting of sheet metal and rough cutting surface.
2. The cut will become wider, which may lead to lower cutting accuracy, and small fillets or sharp corners may melt.
3. Low cutting efficiency will affect production capacity.
Selection of appropriate metal laser cutting speed
The feed rate can be determined according to the cutting spark. During normal cutting, sparks will diffuse downward, and when the speed is too high, sparks will accumulate; If the sparks do not spread but gather together, the feed speed is too low.
Influence of nozzle on metal laser cutting quality
According to different nozzle design, the air flow conditions will be different, which will directly affect the cutting quality.
Main functions of nozzle
The function of the cutting nozzle is
1. To prevent debris (such as melted material) from bouncing up and entering the nozzle and damaging the lens.
2. In order to control the area and size of gas diffusion, it plays a role in controlling cutting quality.
Influence 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 generally be kept at 0.8mm-1.2mm.
Too low a height may cause the sheet metal part to collide with the nozzle, while too high a height may cause the gas to diffuse, resulting in a large number of residues on the cutting bottom surface.
In addition, in order to ensure high-quality cutting in the process of using the metal laser cutting machine, the height of the cutting nozzle relative to the surface of the workpiece to be cut must be basically the same.
Modern laser cutting machines are equipped with inductive or capacitive sensor feedback equipment, which can 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 of metal plate, power and auxiliary gas, the selection of nozzle hole will change accordingly.
The diameter of the nozzle is φ 1.0mm， φ 1.5mm， φ 2.0mm， φ 2.5mm， φ 3.0mm, etc. Currently, nozzle holes are often used in two sizes: φ 1.5mm and φ 2mm。
Generally, when the nozzle diameter is small, the gas velocity is high and the molten material removal capacity is strong. It is suitable for thin plate cutting and can realize fine cutting.
When the nozzle diameter is large, the gas velocity is low and the removal ability of molten material is poor. Suitable for cutting thick plates at low speed.
If a nozzle with a large aperture is used to cut the flakes quickly, the resulting residue may splash upward and damage the protective mirror.
Influence of nozzle deformation on metal laser cutting quality
In the cutting process, when the nozzle collides or rubs with the workpiece, the nozzle is easily deformed. The deformed nozzle will affect the concentricity between the nozzle center and 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 auxiliary gas blown from the deformed or melted nozzle is uneven, which causes the cutting part to burn or melt on one side. The situation may be worse when cutting metal plates with a thickness of more than 3 mm. Sometimes, it cannot penetrate.
·It will affect the quality of the sharp corners. Local over melting may occur when cutting sharp corners. When cutting thick plates, it may not be possible to cut.
·It will affect perforation. The perforation is unstable and the time is not easy to control. The penetration of thick plates may lead to excessive melting, and the penetration conditions are difficult to control. The perforation of the sheet is less affected.
Therefore, the nozzle shall be placed carefully and shall not be damaged to avoid deformation; The melt on the nozzle shall be cleaned in time. At the same time, the nozzle shall be highly accurate during manufacturing and correct installation. If the conditions are changed due to poor nozzle quality during cutting, the nozzle shall be replaced in time.
Influence of ceramic ring on the quality of metal laser cutting
Ceramic ring is an important part of the cutting head of metal laser cutting machine. Its main function is to transmit the electrical signals collected by the laser head nozzle, 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 ceramic body, stainless steel parts and copper needles. The ceramic body is mainly used to maintain the insulation of the laser head body. The stainless steel part is used to ensure full contact with the nozzle, so as to transmit the electrical signal to the copper needle, which then transmits the electrical signal to the transmission line, and the signal is sent to the laser head of the controller by the internal circuit.
We often encounter equipment failures, laser head hitting the working surface and other failures for no reason. In fact, this is due to the instability or loss of electrical signals caused by poor laser ceramic rings.
How to choose ceramic ring?
·Choose ceramic rings and gold-plated copper needles. In order to reduce the loss in the signal transmission process, because gold has the best conductivity, pure gold is plated on the copper needle of the high-quality ceramic ring.
·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 easily occur and the cutting effect may be affected.
·Check the assembly quality. Stainless steel parts shall be firmly fixed on the ceramic body without lifting, deformation or clearance.
Although the ceramic ring, nozzle and protective mirror are very small, they are important consumables of the laser cutting machine. 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 metal laser cutting quality
Laser power has a decisive influence on cutting process and quality.
Select appropriate cutting power for cutting, and the cutting part will be smooth and will not melt.
1. If the laser power is too small, the heat is insufficient, the temperature of the molten product near the lower edge is low, and the viscosity is high, so the high-pressure air flow cannot completely blow it away and stay at the lower edge of the cutting surface, which will produce slag. In severe cases, it is not even possible to cut and form a cut.
Too low power causes frost
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 can be expelled by the high-pressure air flow, and the molten metal cannot be completely blown away. The airflow produces excessive combustion.
Excessive power leads to excessive combustion and wide cuts
Influence of Lens Focal Length and Focus Position on Metal Laser Cutting Quality
Short focal length lens is suitable for high-speed cutting thin materials, while long focal length lens is suitable for cutting thicker workpieces.
We define the focus position as 0 on the top surface of the workpiece. The focus above the top surface of the workpiece is positive, and the focus below the top surface is negative.
The thicker the workpiece, the higher the focus, but the height of the focus should be kept within a certain range. If it exceeds the 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 this part will be covered by molten materials; If the focus is too low, the lower surface of this part will be covered by oxide skin
Positive focus 16mm carbon steel cutting section
When cutting 8mm stainless steel, it is suitable to use negative focus cutting. The focal point is below the flat surface, the cutting surface is uniform, and the cutting part is good. However, when cutting right angles, it is easy to reflect blue light and the cutting ability is limited.
Negative focus 8mm stainless steel cutting part
Customers can choose the right focusing cutting method according to the different 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 metal laser cutting quality
The auxiliary gas can not only blow away the slag in time, but also cool the workpiece and clean the lens. Different auxiliary 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 plates, which can reduce oxide film and save costs to some extent. It is used when the cutting plate is not very thick and the requirements for cutting end face are not too high, such as some sheet metal chassis, cabinets and other product industries.
Nitrogen is an inert gas, which can prevent the oxidation and combustion of the cutting end face of the product during the cutting process (it is easy to happen when the plate is thick. Nitrogen can be selected for products that need high cutting end face and are not treated. For example, some special parts such as decoration industry, aerospace, etc;
Oxygen mainly acts as a combustion supporting agent to increase the speed and thickness of the laser cutting machine during the cutting process. Oxygen is suitable for thick plate cutting, high-speed cutting and very thin plate cutting. For example, some large carbon steel plates and some thicker carbon steel structures can use oxygen.
Influence of Auxiliary Gas Purity on Metal Laser Cutting Quality
The purity of nitrogen affects the quality of cutting. Water will damage the laser, so the gas level should be at least 4.5.
Practice shows that the cutting speed will be reduced by 50% and the cutting quality will be significantly reduced if the oxygen purity is reduced by 2%.
Influence of auxiliary air pressure on metal laser cutting quality
1) When the cutting air 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 cannot form a good cutting part.
2) When the cutting gas pressure is insufficient, the 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
The surface treatment of the treated material will have a negative impact on laser cutting, such as galvanizing, painting, anodizing or covering with multi-layer plastic film. Zinc treated sheets may produce slag at the edges.
The plates with rust, grease and embroidery spots should be cleaned first and then cut; If it is impossible to clean, the power and pressure of auxiliary gas shall be increased to avoid incomplete cut-off.
If there are rusty areas or oxide layers on the surface, the profile of the cut will be irregular and many breakpoints will appear.