As early as the 1970s, lasers were first used for cutting. In modern industrial production, laser cutting is more widely used in sheet metal, plastic, glass, ceramics, semiconductors, textiles, wood, paper and other materials processing. In the next few years, the application of laser cutting in precision machining and micro machining will also achieve substantial growth.

laser cutting 

When the focused laser beam hits the workpiece, the irradiation area will rise sharply to melt or gasify 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 cutting part and the plate frame, which is almost the same width as the focused laser beam.

flame cutting 

Flame cutting is a standard process for cutting low carbon steel, using oxygen as cutting gas. Oxygen is pressurized up to 6 bar and blown into the incision. There, the heated metal reacts with oxygen: combustion and oxidation begin. The chemical reaction releases a large amount of energy (up to five times the laser energy) to assist the laser beam in cutting.

Fig. 1 the laser beam melts the workpiece, and the cutting gas blows away the molten material and slag in the incision

Melt cutting

Melt cutting is another standard process used in 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, and only blow them away to the bottom. At the same time, the inert gas can protect the cutting edge from air oxidation.

Compressed air cutting

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

Plasma assisted cutting

If the parameters are properly selected, plasma clouds will appear in the plasma assisted melting 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 converts it into the workpiece, so that more energy is coupled to the workpiece, and the material will melt faster, thus making the cutting speed faster. Therefore, this cutting process is also called high-speed plasma cutting.

Plasma clouds are in fact transparent to solid-state lasers, so plasma assisted melting and cutting can only use CO2 lasers.

Gasification cutting

Vaporization cutting evaporates the material to minimize the thermal effect on the surrounding materials. 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 non melting materials such as wood, paper and foam.

Ultrashort pulse laser makes this technology applicable to other materials. The free electrons in the metal absorb the laser and heat up sharply. The laser pulse does not react with the molten particles and plasma, and the material sublimates directly. 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.

Parameter: adjust machining process

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

Focal diameter

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

Focal position

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

laser power 

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

Working mode

Continuous mode is mainly used to cut standard profiles of metals and plastics in millimeter to centimeter sizes. In order to melt the perforation or produce a precise contour, a low-frequency pulse laser is used.

Cutting speed

The laser power and the laser cutting speed must match each other. Too fast or too slow cutting speed will lead to the increase of roughness and the formation of burrs.

Fig. 6 cutting speed decreases with the increase of plate thickness

Nozzle diameter

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

Gas purity and pressure

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

When oxygen flame cutting is used, the purity of gas should reach 99.95%. The thicker the steel plate, the lower the gas pressure used.

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

Technical parameter table

In the early stage of laser cutting, the user must decide the setting of processing parameters by trial operation. Now, mature machining 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 enables even those unfamiliar with this technology to operate the laser cutting equipment smoothly.

Evaluation factors of laser cutting quality

There are many standards for judging the edge quality of laser cutting. Standards such as burr form, depression and grain can be judged with naked eyes; Perpendicularity, roughness and notch width need to be measured with special instruments. Material deposition, corrosion, heat affected zone and deformation are also important factors to measure the quality of laser cutting.

The continuous success of laser cu