Basic Knowledge of Laser Cutting
2021-04-21858

Laser was firstly used for cutting in the 1970s. In modern industrial production line, laser cutting is more widely used in sheet metal, plastics, glass, ceramics, semiconductors, textiles, wood and paper and other materials processing.

 

In the next few years, the application of laser cutting in the field of precision machining and micro-machining will also achieve substantial growth.

 

Laser Cutting

 

When the focused laser beam hits the workpiece, the temperature of irradiated area will rise sharply to melt or vaporize the material. Once the laser beam penetrates the workpiece, the cutting process begins: the laser beam moves along the contour line while melting the material. Usually a jet of air is used to blow the melt away from the incision, leaving a narrow gap between the cut part and the plate frame, which is almost as wide as the focused laser beam.

 

Flame Cutting

 

Flame cutting is a standard process used when cutting mild steel, using oxygen as the cutting gas. Oxygen is pressurized up to 6 bar and then blown into the incision. There, the heated metal reacts with oxygen: it starts to burn and oxidize. The chemical reaction releases a large amount of energy (up to five times the laser energy) to assist the laser beam in cutting.

 

Fusion Cutting

 

Melt cutting is another standard process used when cutting metal. It can also be used to cut other fusible materials, such as ceramics.

 

Nitrogen or argon is used as cutting gas, and gas with a pressure of 2-20 bar is blown through the incision. Argon and nitrogen are inert gases, which means that they do not react with the molten metal in the incision, but only blow them to the bottom. At the same time, inert gas can protect the cutting edge from air oxidation.

 

Compressed Air Cutting

 

Compressed air can also be used to cut thin plates. Air pressure to 5-6 bar is enough to blow away the molten metal in the incision. Since nearly 80% of the air is nitrogen, compressed air cutting is basically a fusion cutting.

 

Plasma Assisted Cutting

 

If the parameters are selected properly, plasma clouds will appear in the plasma-assisted melting and cutting incision. The plasma cloud is composed of ionized metal vapor and ionized cutting gas. The plasma cloud absorbs the energy of the CO2 laser and transforms it into the workpiece, so that more energy is coupled to the workpiece, and the material will melt faster, resulting in faster cutting. Therefore, this cutting process is also called high-speed plasma cutting.

 

The plasma cloud is actually transparent to the solid laser, so the plasma-assisted melting and cutting can only use CO2 laser.

 

Vaporization Cutting

 

Vaporization cutting evaporates the material, minimizing the thermal effect on the surrounding materials as much as possible. The above effect can be achieved by using continuous CO2 laser processing to evaporate materials with low heat and high absorption, such as thin plastic films and infusible materials such as wood, paper, and foam.

 

Ultrashort pulse lasers allow this technology to be applied to other materials. The free electrons in the metal absorb the laser and heat up violently. The laser pulse does not react with the molten particles and plasma, the material directly sublimates, and there is no time to transfer energy to the surrounding materials in the form of heat. When the picosecond pulse ablates the material, there is no obvious thermal effect, no melting and burr formation.

 

Parameters: adjust the processing process

 

Many parameters affect the laser cutting process, some depend on the technical performance of the laser and machine tool, while others are variable.

 

Degree of Polarization

 

The degree of polarization indicates what percentage of the laser light is converted. The typical degree of polarization is generally around 90%. This is sufficient for high-quality cutting.
 

Focus Diameter

 

The focal diameter affects the width of the incision, and the focal diameter can be changed by changing the focal length of the focusing lens. A smaller focal diameter means a narrower incision.

 

Focus Position

 

The focal position determines the diameter of beam and power density on the surface of the workpiece and the shape of the incision.

 

 

Laser Power

 

The laser power should match the processing type, material type and thickness. The power must be high enough that the power density on the workpiece exceeds the processing threshold.

 

Operating Mode

 

The continuous mode is mainly used to cut standard contours of metals and plastics from millimeters to centimeters in size. In order to melt the perforation or produce a precise contour, a low-frequency pulsed laser is used.

 

Cutting Speed

 

The laser power and cutting speed must match each other. Cutting speeds that are too fast or too slow will result in increased roughness and burr formation.

 

Nozzle Diameter

 

The diameter of the nozzle determines the flow and shape of the gas jetted from the nozzle. The thicker the material, the larger the diameter of the gas jet, and correspondingly, the larger the diameter of the nozzle.

 

Gas Purity and Pressure

 

Oxygen and nitrogen are often used as cutting gases. The purity and air pressure affect the cutting effect.

 

When using oxygen flame cutting, the gas purity needs to reach 99.95%. The thicker the steel plate, the lower the gas pressure used.

 

When using nitrogen for melting and cutting, the gas purity needs to reach 99.995% (ideally 99.999%), and higher air pressure is required for melting and cutting thick steel plates.

 

Technical Data Sheet

 

In the early stage of laser cutting, users must decide the setting of processing parameters by themselves through trial operation. Now, mature processing parameters are stored in the control device of the cutting system. For each material type and thickness, there are corresponding data. The technical parameter table allows even those who are not familiar with this technology to operate the laser cutting equipment smoothly.

 

Laser Cutting Quality Evaluation Factors

 

There are many criteria for judging the quality of laser cut edges. Standards such as burr form, depression, and grain can be judged with the naked eye; verticality, roughness and cut width need to be measured with special instruments. Material deposition, corrosion, heat affected area and deformation are also important factors to measure the quality of laser cutting.

 

Broad Prospects

 

The continued success of laser cutting is beyond most other company. This trend continues today. In the future, the application prospects of laser cutting will become more and more broad.