With the expansion of the economy, the application fields for stainless steel medium and thick plates have expanded. Its products are now widely used in industries such as construction engineering, machinery manufacturing, container manufacturing, shipbuilding, bridge construction, and others. Laser cutting is now the primary method for cutting stainless steel thick plates, and certain process skills are required to achieve high-quality cutting results.
In general, a medium plate is a steel plate with a thickness of 10.0-25.0mm, while a thick plate has a thickness of 25.0-60.0mm. A plate with a thickness greater than 60.0mm is considered extra-thick.
1.Standards for the advantages and disadvantages of laser cutting thick plates
1. Ruggedness
The vertical lines formed by the laser cutting section determine the roughness of the cut surface; the shallower the lines, the smoother the cut section; the deeper the lines, the rougher the section. The higher the cutting quality, the shallower the grain.
2. Elevation
The verticality of the cutting edge is critical for thick sheet metal. When it is moved away from the focus, the laser beam becomes divergent, which may result in inconsistencies in the upper and lower width of the slit; the cutting edge deviates too much from the vertical line, causing the workpiece to be substandard and difficult to use; the more vertical the edge, the higher the cutting quality.
3. Width of cutting
The inner diameter of the contour is determined by the cutting width. In order to ensure that the workpiece is the correct size, the parameters must be adjusted during the cutting process to compensate for the cut material.
4. Grain
When cutting thick plates at high speeds, the molten metal is ejected at the rear of the laser beam rather than from the incision below the vertical laser beam. This will result in a curved line along the cutting edge. To address this issue, reduce the feed rate at the end of the cutting process, which can greatly reduce the formation of lines.
5. Burrs
The presence and amount of burrs is a critical factor in determining laser cutting quality. Burr removal necessitates additional work, which will be calculated in terms of time and labor costs. As a result, the presence of burrs is the primary criterion for determining whether laser cutting is qualified.
6. Heat Affected Area
The depth of the area where the internal structure changes is referred to as the heat-affected zone. The metal area near the cut is heated during laser cutting, which may cause changes in the metal’s structure. Some metals, for example, will harden.
7. Deformation
The part will deform if the cutting heats it sharply, which is especially important in fine processing. Controlling the laser power and using short laser pulses can help to keep parts cool and avoid deformation.
2. Laser cutting of thick stainless steel plates requires specific process requirements.
1. Selection of Nozzles
The nozzle diameter determines the shape of the gas flow entering the incision, the gas diffusion area, and the gas flow rate, all of which affect melt removal and cutting stability. The greater the air flow into the incision, the faster the speed, and the appropriate position of the workpiece in the air flow, the greater the jetting ability to remove the molten material. The thicker the stainless steel, the larger the nozzle, the larger the proportional valve setting, and the higher the flow rate, the higher the pressure and the lower the normal section effect.
The nozzle specifications here primarily refer to the end aperture. Consider Precitec’s cutting nozzle, which has an aperture ranging from 1.5mm to 5.0mm. The choice of aperture is primarily determined by the cutting power. The greater the power, the more heat is generated and the greater the required air volume. When cutting sheets less than 3mm thick, we typically use nozzles with a 2.0mm aperture; when cutting sheets 3mm to 10mm thick, we use 3.0mm nozzles; and when cutting sheets larger than 10mm thick, we use nozzles with a 3.5mm aperture or higher.
Single and double-layer nozzles: Double-layer nozzles are typically used for oxidative cutting (the auxiliary gas is oxygen), whereas single-layer nozzles are typically used for fusion cutting (the auxiliary gas is nitrogen). Some lasers, however, have special instructions; in this case, whether to use a single layer or a double layer, please follow the laser instructions.
2.Auxiliary gas and its purity
Various auxiliary gases, such as oxygen, nitrogen, and air, are frequently used in stainless steel laser cutting processing. Different types of gas are used, and the effect of cutting sections varies. Oxygen has a black section, air has a light yellow section, and nitrogen can keep the original color of oxidized stainless steel. Nitrogen is the preferred auxiliary gas for cutting stainless steel.
3. Focus position
The focus is different, as are the thickness, material, and quality that can be cut. Different materials and thicknesses must be adjusted to achieve a specific focus. Before cutting, the actual zero focus is measured, and the cutting process parameters can be tested and analyzed using the zero focus as the benchmark. The primary process selection direction for stainless steel cutting is negative defocusing.
4.The effect of laser frequency and pulse duty cycle adjustment on cutting quality
The effect of frequency change on the cutting of stainless steel thick plates:
When the frequency is reduced from 500 to 100 Hz, the cutting section effect becomes finer, and the layering gradually fades away. When set to 100Hz, the frequency cannot be cut and the blue light is reversed. Find the best frequency range by changing the frequency. The number of pulses must be perfectly matched with the energy of a single pulse to ensure the best cutting section.
The effect of changing the pulse duty cycle on stainless steel thick plate cutting:
The critical value is 45 percent for the pulse duty cycle. If the duty cycle is reduced further, there will be traces of incomplete cutting on the lower surface. The duty cycle rises to 60%, the section becomes rough, the hierarchy becomes clear, and the cut surface turns yellow.
The pulse duty cycle is the percentage of beam irradiation time in each pulse. The frequency of a pulse is the number of times the peak power appears in it, and the duty cycle is the ratio of peak power to trough power in a pulse.
