The quality of the machine tool itself directly affects the quality of the machine. Measuring the quality of a machine tool is multi-faceted, but it mainly requires good processability, serialization, generalization, high degree of standardization, simple structure, light weight, reliable work, and high productivity. Specific indicators are as follows:
Possibility of process
The possibility of the process refers to the ability of the machine tool to adapt to different production requirements. General machine tools can complete multi-step processing of various parts within a certain size range, and the possibility of the process is relatively wide. Therefore, the structure is relatively complex and is suitable for single-piece and small-batch production. Special machine tools can only complete one or a few parts of the specific process, the process is less likely, suitable for mass production, can increase productivity, ensure processing quality, simplify the machine tool structure, reduce machine tool costs.
Accuracy and surface roughness
To ensure the precision and surface roughness of the machined parts, the machine itself must have a certain geometric accuracy, movement accuracy, transmission accuracy and dynamic accuracy.
(1) Geometric accuracy, movement accuracy, and transmission accuracy are static accuracy
Geometric accuracy refers to the positional accuracy of parts and the accuracy and positional accuracy of the main parts when the machine tool is not in operation. The geometric accuracy of the machine tool has an important influence on the machining accuracy. Therefore, it is the main index for evaluating the accuracy of the machine tool.
Motion accuracy refers to the geometrical position accuracy of the main components when the machine tool is running at the working speed. The greater the change in the geometric position, the lower the motion accuracy.
Transmission accuracy refers to the coordination and uniformity of the movement between the end-effectors of the machine tool drive chain.
The above three kinds of accuracy indicators are tested under no-load conditions. To fully reflect the performance of the machine tool, the machine tool must have certain dynamic accuracy and the shape and position accuracy of the main components under the temperature increase. The main factors affecting the dynamic accuracy are the stiffness, vibration resistance, and thermal deformation of the machine tool.
The stiffness of a machine tool refers to the ability of the machine tool to resist deformation under external forces. The greater the rigidity of the machine tool, the higher the dynamic accuracy. The stiffness of the machine tool includes the rigidity of the machine tool component itself and the contact stiffness between the components. The rigidity of the machine tool itself depends mainly on the material properties, cross-sectional shape, and size of the component itself. The contact stiffness between components is not only related to the contact materials, the contact surface geometry and hardness, but also related to the surface roughness of the contact surface, geometric accuracy, processing methods, contact surface media, pre-stress and other factors.
The vibrations appearing on the machine tool can be divided into forced vibration and self-excited vibration. Self-excited vibration is the continuous vibration generated internally by the cutting process without any external force or excitation force. Under the continuous action of the exciting force, the forced vibration of the system is forced vibration.
The seismic resistance of the machine tool is related to the rigidity, damping characteristics and quality of the machine tool. Because the thermal expansion coefficients of the various parts of the machine tool are different, the different deformation and relative displacement of various parts of the machine tool are caused. This phenomenon is called thermal deformation of the machine tool. The error due to thermal deformation can account for up to 70% of the total error.
For the dynamic accuracy of the machine tool, there is no uniform standard at present, and the comprehensive evaluation of the machine tool dynamic accuracy is made indirectly through the precision achieved by cutting the typical parts.
The serialization, generalization and standardization of machine tools are closely linked. The serialization of varieties is the basis for the generalization of parts and the standardization of parts. The generalization of parts and the standardization of parts promote and promote the serialization of varieties.
Machine tool life
The reliability and wear resistance of the machine tool structure are the main indicators for measuring the life of the machine tool.