Laser cutting was first used in the 1970s. In modern industrial production, it is widely used to cut sheet metal, plastics, glass, ceramics, semiconductors, as well as materials such as textiles, wood and paper.
In the coming years, laser cutting is expected to gain substantial growth in precision machining and micromachining applications. First, let's take a look at how laser cutting works.
When the focused laser beam hits the workpiece, the irradiated area heats up quickly, causing the material to melt or vaporize. As soon as the laser beam penetrates the part, the cutting process begins: the beam moves along the contour, melting the material. A jet stream is typically used to blow the molten material away from the incision, leaving a narrow space between the cut part and the structure. These narrow seams are almost as wide as the focused laser beam.
Flame Cut
Flame cutting is a standard technique used to cut low carbon steel where oxygen is used as the cutting gas. Pressurized oxygen is increased to 6 bars before being blown into the incision.
There, the heated metal reacts with oxygen, causing it to burn and oxidize. This chemical reaction releases a large amount of energy (five times the amount of laser energy) that assists the laser beam in the cutting process.
Fig.1 The laser beam melts the part while the cutting gas blows the molten material and slag into the incision
Fusion cutting
Fusion cutting is another standard process used in metal cutting and can also be used to cut other fusible materials such as ceramics. Nitrogen or argon gas is used as cutting gas and air with a pressure of 2 to 20 bar is blown through the incision.
Argon and nitrogen are inert gases, which means they do not react with the molten metal in the incision, but rather blow it to the bottom. The inert gas also protects the cutting edge from oxidation in the air.
Compressed air cutoff
Compressed air can also be used to cut thin sheets. Air pressure increased to 5-6 bar is sufficient to remove molten metal from the incision.
Since almost 80% of air is nitrogen, compressed air cutting is essentially a thermal cutting method.
Plasma assisted cutting
If the parameters are selected correctly, plasma clouds will appear in the incision during plasma-assisted fusion cutting.
The plasma cloud consists of ionized metal vapor and ionized cutting gas.
The plasma cloud absorbs the CO2 laser energy and converts it to heat in the part, allowing more energy to be coupled to the part, which results in faster metal melting and faster cutting.
Therefore, the cutting process is also known as high-speed plasma cutting.
The plasma cloud is transparent to the solid laser, so plasma-assisted fusion cutting can only be used with CO2 laser cutting.
Gasified Cut
Gasified cutting vaporizes the material and minimizes the thermal effect on the surrounding material.
Continuous CO2 laser processing can achieve this effect by evaporating low-heat, high-absorption materials such as thin plastic film and non-melting materials such as wood, paper and foam.
Ultrashort pulse lasers allow this technique to be applied to other materials.
The free electrons in the metal absorb the laser and heat up significantly.
The laser pulse does not react with molten particles and plasma, and the material sublimates directly without transferring energy to the surrounding material in the form of heat.
There is no apparent thermal effect in picosecond pulse ablation of the material and no melting or burr formation occurs.
Fig.3 Cutting by gasification: the laser makes the material evaporate and burn. Steam pressure exhausts the slag from the incision
Several parameters affect the laser cutting process, with some being dependent on the technical performance of the laser generator and the laser cutting machine, while others are adjustable.
Degree of polarization
The degree of polarization indicates the percentage of the laser that is converted.
Typically, the degree of polarization is around 90%, which is enough to obtain a high-quality cut.
Focus diameter
The diameter of the focus affects the width of the incision and can be modified by changing the focal length of the focusing lens. A smaller focus diameter results in narrower incisions.
Focus position
The focal position determines the beam diameter, power density and the shape of the incision on the part surface.
Fi.4 Focus position: inside, surface and top side of the workpiece.
Laser Power
The laser power must correspond to the type of machining, type of material and thickness.
The power must be high enough so that the power density in the part exceeds the processing limit.
Fig.5 Higher laser power can cut thicker materials
Working mode
Continuous mode is mainly used to cut pattern contours in metals and plastics with thicknesses ranging from millimeters to centimeters.
To fuse holes or produce precise contours, low-frequency pulsed lasers are used.
Cutting speed
The laser power and cutting speed must match. Cutting speed that is too fast or too slow can lead to increased roughness and burr formation.
Fig.6 Cutting speed decreases with plate thickness
The diameter of the nozzle
The diameter of the nozzle determines the gas flow and the shape of the airflow leaving the nozzle.
The thicker the material, the larger the diameter of the gas jet and therefore the larger the diameter of the nozzle opening.
Gas purity and pressure
Oxygen and nitrogen are commonly used as cutting gases. Gas purity and pressure have an impact on cutting effectiveness. When cutting with an oxygen flame, the gas purity must be 99.95%.
The thicker the steel plate, the lower the gas pressure required.
When cutting with nitrogen, gas purity should be 99.995% (ideally 99.999%), which requires higher pressure when melting and cutting thicker steel sheets.
Technical parameter
During the initial steps of laser cutting, the user must determine the machining parameters through test operations.
Today, mature processing parameters are stored in the cutting system control device, with corresponding data for each material type and thickness.
Technical parameters allow individuals who are not well versed in technology to operate laser cutting equipment without any problems.
Cut quality judgment
Several criteria determine the quality of laser cutting edges.
For example, the pattern of burr formation, sagging and graining can be assessed with the naked eye.
The straightness, roughness and width of the incision require measurement with specialized instruments.
Material deposition, corrosion, thermal influence region and deformation are also critical factors to be considered when evaluating laser cutting quality.
You can also check the 9 patterns to check the laser cutting quality.
Fig.7 Good cut, bad cut
Broad perspective
The continued success of laser cutting is unmatched by most other techniques, and this trend persists to this day. In the future, laser cutting applications will become more and more promising.
