In the laser cutting process of general materials, due to the fast cutting speed, the thermal deformation of the parts is small, the dimensional precision of the cutting parts mainly depends on the mechanical precision and control precision of the working table of the laser cutting machine.In the pulse laser cutting process, high-precision cutting device and control technology are adopted, and the dimensional accuracy can reach um level.
There is no uniform standard for the quality evaluation of laser cutting in the world.Up to now, there are no relevant standards for laser cutting quality in China. The main basis for testing the quality of laser cutting is JIS and WES (welding specifications).There are issues regarding the standardization of laser cutting in the CEN (European standardization body) and ISO (international standardization body).The ISO9000 series quality assurance method mainly provided by EU has studied the laser cutting standard and the standard sample specification, which includes: cutting quality grade, setting and processing sample standard, optical system, machine type and beam characteristics of price sample, etc.
For laser cutting processing, the evaluation of its processing quality mainly includes the following principles:
1. The cutting is smooth, without striations and brittle fracture;
2. Narrow slit width, which is mainly related to the laser beam spot diameter;
3. Good slit perpendicularity, small heat-affected zone;
4. No material combustion, no melting layer formation, no large slag;
5. Notch surface roughness, the size of the surface roughness is the key to measure the surface quality of laser cutting.
In addition to the above principles, the state and final shape of the melting layer in the processing process directly affect the above processing quality evaluation indexes.
The surface roughness of laser cutting mainly depends on the following three aspects:
1. Inherent parameters of the cutting system, such as spot mode and focal length;
2. Adjustable process parameters in the cutting process, such as power, cutting speed, type of auxiliary gas and pressure, etc.;
3. Physical parameters of the processed material, such as absorption rate of laser, melting point, viscosity coefficient of molten metal oxide, surface tension of metal oxide, etc.In addition, the thickness of the workpiece also has a great influence on the surface quality of laser cutting.Relatively speaking, the smaller the thickness of the metal workpiece, the higher the roughness grade of the cutting surface.
In order to obtain a better surface quality level, the process parameters such as laser power and cutting speed must be optimized several times.In general, for materials with the same characteristics and thickness, there is an optimal set of cutting process parameters, and different incision surface quality will be obtained.The melting point of metal material is low, the thermal conductivity is big, the melt viscosity coefficient is small, the metal oxide surface tension is small, the laser cutting is easy to obtain the high surface quality.When laser cutting flat plate, it is easy to measure the surface quality, but when carrying out fine machining or cutting some complex patterns, it is difficult to directly measure the surface quality, which can only be controlled by optimizing the test parameters.Therefore, in order to realize automatic cutting, the corresponding relationship between external optimization parameters and surface quality level should be established.