Ways to Determine Laser Cutting Parameters

1. Working principle of laser cutting

Laser cutting processing is to replace the traditional mechanical knife with an invisible beam. It has the characteristics of high precision, fast cutting, no limitation to the cutting pattern, automatic typesetting, material saving, smooth cutting, and low processing cost. The mechanical part of the laser cutter head has no contact with the workpiece, and will not scratch the surface of the workpiece during operation. Laser cutting speed is fast with smooth and flat cuts, which generally does not require subsequent processing. Cutting heat affected zone is small, so the plate deformation is small. The incision has no mechanical stress, no shearing burrs, with high processing accuracy, good repeatability, and no damage to the surface of the material. CNC programming can process any patterns and can cut large-format whole plates without opening mould, which is economical and time-saving.

2. Laser cutting equipment composition

Laser cutting equipment is mainly composed of laser source, laser cutting head, numerical control motion system, working platform and high pressure gas compressor. Many parameters affect the laser cutting process, some of which depend on the technical performance of the laser and machine tool, while other parameters are variable.

3. Main parameters of laser cutting

1) Beam mode

Fundamental mode, also known as Gaussian mode, is the most ideal mode for cutting, mainly in low-power lasers with power less than 1kW. Multi-mode is a mixture of higher-order modes. Under the same power, multi-mode has poor focus and low cutting ability. The cutting ability and cutting quality of single-mode laser are better than that of multi-mode.

2) Laser power

The laser power required for laser cutting mainly depends on the cutting material, material thickness and cutting speed requirements. The laser power has a great influence on the cutting thickness, cutting speed, incision width, etc. Generally, the higher the laser power, the thicker it can be cut, the higher speed it can be achieved.

3) Focus position

The focal position has a greater influence on the width of the incision. Generally, the focus is located at about 1/3 of the thickness of the material below the surface. In this position, we can achieve the largest cutting depth and smallest cutting width.

4) Focal distance

When cutting thick steel plates, a beam with a longer focal distance should be used to obtain a cutting surface with good verticality. The focal depth is large with a increased diameter of the spot, which leads to the decrease of power density and reduction of cutting speed. To maintain a certain cutting speed, it is necessary to increase the laser power. It is advisable to use a beam with a smaller focal length for cutting thin plates, so that the spot diameter is small, so that the power density is large to achieve fast cutting speed.

5) Auxiliary gas

The cutting of carbon steel mostly uses oxygen as the cutting gas. The heat generated from iron-oxygen combustion reaction promotes the cutting process, making cutting speed fast and the cut quality good, and obtaining a slag-free cut. The cutting air pressure is determined by the factors of material, sheet thickness, cutting speed and cutting surface quality.

6) Nozzle structure

The structure and shape of the nozzle and the size of the light outlet also affect the quality and efficiency of laser cutting. Different nozzles are used for different cutting requirements. Commonly used nozzle shapes are: cylindrical, cone, square and other shapes. Laser cutting generally adopts a coaxial (air flow and optical axis concentric) blowing method, if the air flow and the optical axis are not coaxial, then a lot of splashes are likely to be produced during cutting. In order to ensure the stability of the cutting process, it is usually necessary to control the distance between the nozzle end the surface of the workpiece, generally 0.5 to 2.0 mm, so that the cutting can proceed smoothly.

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