Quality evaluation standards for laser cutting machine processing

In the laser cutting process of general materials, due to the fast cutting speed, the thermal deformation generated by the parts is very small. The dimensional accuracy of the cut parts mainly depends on the mechanical accuracy and control accuracy of the laser cutting machine's workbench. In pulse laser cutting processing, high-precision cutting devices and control technologies are used, and dimensional accuracy can reach the um level.

There is currently no unified international standard for the quality evaluation of laser cutting. So far, there is no standard for laser cutting quality in China, and the main basis for testing laser cutting quality is JIS and WES (welding specifications). There are standardization issues regarding laser cutting in CEN (European Organization for Standardization) and ISO (International Organization for Standardization). We have conducted research on the ISO 9000 series quality assurance methods mainly provided by the EU, including laser cutting standards and standard sample regulations. The content includes: classification of cutting quality levels, standards for setting and processing samples, optical systems, models of price samples, and beam characteristics.

For laser cutting processing, the evaluation of its processing quality mainly includes the following principles:

1. Smooth cutting, no stripes, and no brittle fractures;

2. The cutting seam width is narrow, which is mainly related to the diameter of the laser beam spot;

3. Good verticality of the cutting seam and small heat affected zone;

4. No material combustion, no molten layer formation, no large slag;

5. The surface roughness of the incision is the key to measuring the surface quality of laser cutting.

In addition to the above principles, the state of the melted layer during the processing and its final shape directly affect the above processing quality evaluation indicators.

The surface roughness of laser cutting mainly depends on the following three aspects:

1. The inherent parameters of the cutting system, such as spot mode, focal length, etc;

2. Adjustable process parameters during the cutting process, such as power size, cutting speed, auxiliary gas type and pressure, etc;

3. The physical parameters of the processed material, such as laser absorption rate, melting point, viscosity coefficient of molten metal oxide, surface tension of metal oxide, etc. In addition, the thickness of the workpiece also has a significant impact on the surface quality of laser cutting. Relatively speaking, the smaller the thickness of the metal workpiece, the higher the roughness level of the cutting surface.

To achieve a good surface quality level, it is necessary to optimize the process parameters such as laser power and cutting speed multiple times. Generally speaking, for materials with the same characteristics and thickness, a set of cutting process parameters will also result in different surface quality of the cut. Metal materials have low melting points, high thermal conductivity, low viscosity of molten materials, and low surface tension of metal oxides, making it easy to achieve high surface quality during laser cutting. When laser cutting flat plates, it is easy to measure the surface quality, but it is difficult to directly measure them when performing fine machining or cutting some complex patterns. Only by optimizing experimental parameters can the surface quality be controlled. Therefore, in order to facilitate automated cutting, a corresponding relationship between external optimization parameters and surface quality level should be established.