Introduction
The quality of the machine itself directly affects the quality of the machine being built. Measuring the quality of a machine tool is multi-faceted, but mainly requires good processability, serialization, generalization, high degree of standardization, simple structure, light weight, reliable work, and high productivity. The specific indicators are as follows:
Process possibility
The possibility of a process is the ability of the machine to adapt to different production requirements. The universal machine tool can complete multi-process machining of various parts within a certain size range, and the process is more likely, so the structure is relatively complicated, and it is suitable for single-piece small batch production. Special machine tools can only complete a specific process of one or several parts, and the process possibilities are narrow. It is suitable for mass production, which can improve productivity, ensure processing quality, simplify machine structure and reduce machine tool cost.
2. Precision and surface roughness
To ensure the accuracy and surface roughness of the machined parts, the machine tool itself must have certain geometric accuracy, motion accuracy, transmission accuracy and dynamic accuracy.
(1) Geometric accuracy, motion accuracy, and transmission accuracy are static accuracy
Geometric accuracy refers to the positional accuracy between components and the shape accuracy and positional accuracy of the main parts when the machine is not in operation. The geometric accuracy of the machine tool has an important influence on the machining accuracy, so it is the main indicator for evaluating the accuracy of the machine tool.
The motion accuracy refers to the geometric position accuracy of the main components when the machine is running at the working speed. The greater the variation of the geometric position, the lower the motion accuracy.
Transmission accuracy refers to the coordination and uniformity of motion between actuators at each end of the machine drive chain.
The above three kinds of precision indicators are all tested under no-load conditions. In order to fully reflect the performance of the machine tool, the machine tool must have certain dynamic precision and shape and position accuracy of the main components under temperature rise. The main factors affecting the dynamic accuracy are the rigidity, vibration resistance and thermal deformation of the machine tool.
The rigidity of the machine tool refers to the ability of the machine tool to resist deformation under the action of external force. The greater the rigidity of the machine tool, the higher the dynamic precision. The stiffness of the machine tool includes the stiffness of the machine tool component itself and the contact stiffness between the components. The stiffness of the machine tool component itself depends mainly on the material properties, cross-sectional shape, size, etc. of the component itself. The contact stiffness between the components is not only related to the contact material, the geometry and hardness of the contact surface, but also related to the surface roughness, geometric accuracy, processing method, contact surface medium, pre-stress and other factors of the contact surface.
The vibrations appearing on the machine tool can be divided into forced vibration and self-excited vibration. Self-excited vibration is a continuous vibration generated inside the cutting process without being disturbed by any external force or exciting force. Under the continuous action of the exciting force, the vibration forced by the system is forced vibration.
The seismic resistance of the machine tool is related to the stiffness, damping characteristics and quality of the machine tool. Due to the different thermal expansion coefficients of the various parts of the machine tool, different deformations and relative displacements 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 precision of the machine tool, there is no uniform standard at present, and the dynamic precision of the machine tool is indirectly evaluated by the precision achieved by cutting typical parts.
3. Serialization and other levels
The serialization, generalization and standardization of machine tools are closely related. Variety serialization is the basis for component generalization and component standardization, and the generalization of components and the standardization of components promote and promote the serialization of varieties.
4. Machine life
The reliability and wear resistance of machine tool structures are the main indicators for measuring the life of machine tools.
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