In the initial stage of the development of CNC machine tools, the mechanical structure did not change much compared with the general machine tool, but only in the automatic shifting, tool holder and table automatic indexing and handle operation. With the development of numerical control technology, considering its control mode and use characteristics, it puts higher requirements on the productivity, processing precision and life of the machine tool. The main mechanism of CNC machine tools has the following characteristics: 1) Due to the high-performance stepless variable speed spindle and servo drive system, the limit transmission structure of CNC machine tools is greatly simplified, and the transmission chain is greatly shortened; 2) To adapt to continuous automatic processing And improve the processing productivity, CNC machine tool mechanical structure has high static and dynamic stiffness and damping accuracy, as well as high wear resistance, and small thermal deformation; 3) to reduce friction, eliminate transmission gap and obtain higher processing Accuracy, more efficient transmission parts, such as ball screw pair and rolling guide, anti-backlash gear transmission, etc.; 4) In order to improve working conditions, reduce auxiliary time, improve operability, and improve labor productivity, automatic tooling is adopted. Auxiliary devices such as clamping devices, tool magazines, automatic tool changers and automatic chip removal devices. According to the applicable occasions and mechanism characteristics of CNC machine tools, the following requirements are imposed on the structure of CNC machine tools:
First, the high static and dynamic stiffness of the machine tool
The CNC machine tool is automatically processed according to the instructions provided by numerical control programming or manual input data. Due to the geometrical accuracy and deformation of the mechanical structure (such as machine bed, guide rail, table, tool holder and headstock), the positioning error cannot be artificially adjusted and compensated during the machining process. Therefore, mechanical structural components must be used. The resulting elastic deformation is controlled to a minimum to ensure the required machining accuracy and surface quality.
In order to improve the rigidity of the CNC machine tool spindle, not only the three-support structure is often used, but also the double-row short cylindrical roller bearing and the angular contact radial thrust bearing with good rigidity are hinged out to believe that the force bearing is used to reduce the radial direction of the main shaft. And axial deformation. In order to improve the rigidity of the large parts of the machine tool, the bed of the closed interface is adopted, and the hydraulic balance is used to reduce the deformation of the machine tool caused by the positional change of the moving parts. In order to improve the contact stiffness of various parts of the machine tool and increase the load-carrying capacity of the machine tool, the contact point per unit area is increased by scraping, and a sufficient pre-load is applied between the joint surfaces to increase the contact area. These measures can effectively improve the contact stiffness.
In order to give full play to the high-efficiency machining capability of CNC machine tools and to enable stable cutting, dynamic stiffness must be improved while maintaining static stiffness. Commonly used measures include increasing the stiffness of the system, increasing the damping, and adjusting the natural frequency of the member. Tests have shown that increasing the damping coefficient is an effective method to improve vibration resistance. The welded structure of the steel plate can increase the static stiffness, reduce the structural weight, and increase the damping of the component itself. Therefore, in recent years, the bed, the column, the beam and the table of the steel plate welded structure have been used on the numerically controlled machine tool. Sealing sand castings are also beneficial for vibration attenuation and have a good effect on improving vibration resistance.
Second, reduce the thermal deformation of the machine tool
Under the influence of internal and external heat sources, different parts of the machine tool will undergo different degrees of thermal deformation, so that the relative motion relationship between the workpiece and the tool is broken, which is also a quarterly decline of the machine tool. For CNC machine tools, the effect of thermal deformation is even more serious because all machining processes are controlled by calculations. In order to reduce thermal deformation, the following measures are usually adopted in the numerical control machine tool structure.
First, the high static and dynamic stiffness of the machine tool
The CNC machine tool is automatically processed according to the instructions provided by numerical control programming or manual input data. Due to the geometrical accuracy and deformation of the mechanical structure (such as machine bed, guide rail, table, tool holder and headstock), the positioning error cannot be artificially adjusted and compensated during the machining process. Therefore, mechanical structural components must be used. The resulting elastic deformation is controlled to a minimum to ensure the required machining accuracy and surface quality.
In order to improve the rigidity of the CNC machine tool spindle, not only the three-support structure is often used, but also the double-row short cylindrical roller bearing and the angular contact radial thrust bearing with good rigidity are hinged out to believe that the force bearing is used to reduce the radial direction of the main shaft. And axial deformation. In order to improve the rigidity of the large parts of the machine tool, the bed of the closed interface is adopted, and the hydraulic balance is used to reduce the deformation of the machine tool caused by the positional change of the moving parts. In order to improve the contact stiffness of various parts of the machine tool and increase the load-carrying capacity of the machine tool, the contact point per unit area is increased by scraping, and a sufficient pre-load is applied between the joint surfaces to increase the contact area. These measures can effectively improve the contact stiffness.
In order to give full play to the high-efficiency machining capability of CNC machine tools and to enable stable cutting, dynamic stiffness must be improved while maintaining static stiffness. Commonly used measures include increasing the stiffness of the system, increasing the damping, and adjusting the natural frequency of the member. Tests have shown that increasing the damping coefficient is an effective method to improve vibration resistance. The welded structure of the steel plate can increase the static stiffness, reduce the structural weight, and increase the damping of the component itself. Therefore, in recent years, the bed, the column, the beam and the table of the steel plate welded structure have been used on the numerically controlled machine tool. Sealing sand castings are also beneficial for vibration attenuation and have a good effect on improving vibration resistance.
Second, reduce the thermal deformation of the machine tool
Under the influence of internal and external heat sources, different parts of the machine tool will undergo different degrees of thermal deformation, so that the relative motion relationship between the workpiece and the tool is broken, which is also a quarterly decline of the machine tool. For CNC machine tools, the effect of thermal deformation is even more serious because all machining processes are controlled by calculations. In order to reduce thermal deformation, the following measures are usually adopted in the numerical control machine tool structure.
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