Metrics for machine tool quality

The quality of the machine tool itself directly affects the quality of the machine being manufactured. There are many aspects to measuring the quality of a machine tool, but it mainly requires good craftsmanship, high degree of serialization, generalization, standardization, simple structure, light weight, reliable operation, and high productivity. The specific indicators are as follows:
1. Possibility of technology
Process possibility refers to the ability of a machine tool to adapt to different production requirements. General-purpose machine tools can complete multi-process processing of various parts within a certain size range. The process possibilities are wide, so the structure is relatively complex, and they are suitable for single-piece and small-batch production. Special-purpose machine tools can only complete specific processes of one or several parts. Their process possibilities are narrow and they are suitable for mass production. They can improve productivity, ensure processing quality, simplify machine tool structures, and reduce machine tool costs.
2. Accuracy and surface roughness
To ensure the accuracy and surface roughness of the parts being processed, the machine tool itself must have certain geometric accuracy, motion accuracy, transmission accuracy and dynamic accuracy.
Geometric accuracy refers to the mutual position accuracy between components and the shape accuracy and position accuracy of main parts when the machine tool is not running. The geometric accuracy of machine tools has an important impact on machining accuracy and is therefore the main indicator for evaluating machine tool accuracy.
Motion accuracy refers to the geometric position accuracy of the main components of the machine tool when it is running at working speed. The greater the change in geometric position, the lower the motion accuracy.
Transmission accuracy refers to the coordination and uniformity of movement between the end-effectors of the machine tool transmission chain.
The above three accuracy indicators are all tested under no-load conditions. In order to fully reflect the performance of the machine tool, the machine tool must have a certain dynamic accuracy and the shape and position accuracy of the main components under the action of temperature rise. The main factors that affect the dynamic accuracy are the stiffness, vibration resistance and thermal deformation of the machine tool.
The stiffness of a machine tool refers to the machine tool's ability to resist deformation under the action of external forces. The greater the stiffness of the machine tool, the higher the dynamic accuracy. The stiffness of the machine tool includes the stiffness of the machine tool components themselves and the contact stiffness between the components. The stiffness of the machine tool component itself mainly depends on the material properties, cross-sectional shape, size, etc. of the component itself. The contact stiffness between components is not only related to the contact material, the geometric size and hardness of the contact surface, but also to the surface roughness, geometric accuracy, processing method, contact surface medium, preload and other factors of the contact surface.
Vibration occurring on machine tools can be divided into forced vibration and self-excited vibration. Self-excited vibration is a continuous vibration generated internally during the cutting process without being interfered by any external force or excitation force. Under the continuous action of the excitation force, the vibration caused by the system is called 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 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 caused by thermal deformation can account for up to 70% of the total error.
There is no unified standard for the dynamic accuracy of machine tools. A comprehensive evaluation of the dynamic accuracy of machine tools is mainly made indirectly through the accuracy achieved by cutting typical parts.
3. Degree of serialization, etc.
The serialization, generalization and standardization of machine tools are closely related. Variety serialization is the basis for component generalization and parts standardization, while the generalization of components and the standardization of parts promote and promote the variety serialization work.
4. The life of machine tools
The reliability and wear resistance of the machine tool structure are the main indicators for measuring the life of the machine tool.