At present, the classification of CNC machine tools mainly includes collection precision, positional accuracy and machining accuracy. The rigidity of CNC machine materials and the temperature at work
1. Precision analysis of CNC machine
At present, the classification of CNC machine tools mainly includes collection precision, positional accuracy and machining accuracy. The rigidity of the CNC machine tool and the temperature during operation will have different effects on the accuracy of the machine tool. The geometric accuracy of the CNC lathe can be further subdivided into spindle geometric accuracy and linear motion accuracy.
In the process of CNC machine tool operation, the relative position between the drive shaft and the rotary shaft should be relatively fixed. In the actual production process, the design is not exactly the same, and the relative spatial position between the two shafts is also It is not fixed, because the bearing components that make up the main shaft will have different degrees of error in the manufacturing process, and will be affected by temperature, work intensity, lubrication and other conditions during use. The bearing accuracy of the drive shaft and the quality of the headstock in the assembly will cause the spindle and its rotating parts to be unbalanced during operation. In addition, the support journal of the drive shaft will have roundness error during the manufacturing process, and the front and rear coaxiality will also be There will be a certain degree of error, and in addition, the spindle will be deformed by heat during the operation, and these factors all have an impact on the geometric accuracy of the spindle of the CNC machine tool.
In addition to the geometric accuracy caused by the drive shaft of the CNC machine tool, the guide rail may have an influence on the positional accuracy of the machine tool due to the friction force and the servo motor used in the machine tool. In CNC machine tools, some components that require uninterrupted operation, such as cylinder oil pumps, electric motors, hydraulic presses, etc., require long-term continuous operation. In the process of their operation, because friction will generate a certain amount of heat, the internal parts will be deformed by thermal expansion, resulting in the actual size and design size of the components, and the structure of the parts will be asymmetrical due to the internal heat. The deformation of the component occurs, so that the deformation of the running parts of the CNC machine tool will have an important influence on the positional accuracy of the machine tool.
The machining accuracy of CNC machine tools is different from the above two precisions. It is the result of the comprehensive influence of various factors on the whole machine tool. It is closely related to the geometric accuracy and positional accuracy of the machine tool. It is related to the transmission system error of the machine tool and the inspection and correction system. Errors, no parts of the fixed part of the part, errors in the position of the tool, etc. are all related. Moreover, the correct editing of the CNC machine tool and the reasonable production process have an impact on the stable production of the machine tool. Therefore, in actual production, in order to improve the machining accuracy of CNC machine tools, it is necessary to improve the geometric accuracy and positional accuracy of the machine tool.
2, detection of CNC machine tool accuracy
CNC machine tools are the same as all other electrical and mechanical equipment. After using for a period of time, they will face aging of electronic components, rusting parts, and wear of mechanical parts. Therefore, in order to keep the machine tool in a good state, the machine tool should be periodically maintained periodically to detect and compensate the accuracy of the CNC machine tool.
2.1 Detection of geometric accuracy
Generally, in the geometric accuracy inspection project of the machining center machine tool, the tool selected for the straightness detection item of the linear motion axis is a flat ruler and a dial gauge, and generally the other two axes perpendicular to the motion axis of the test moving component are tested. Linear deviation on. In a common ordinary vertical CNC machining center, the detection content of the assembly precision mainly includes the flatness of the working surface of the machine tool and the mutual perpendicularity of the movement axis in all directions of the space coordinate. The radial runout of the main shaft in the center hole, the perpendicularity of the spindle and rotary shaft axis and the machine table. The parallelism of the work surface when the machine motion axis moves in the X and Y coordinate directions; the parallelism of the T-slot side of the work surface when the X coordinate direction moves; the straightness of the spindle box when moving in the coordinate direction of the Z axis and the spindle The parallelism of the axis, the axial movement of the spindle, etc.
2.2 Detection position accuracy
The positioning accuracy required for CNC machine tools can be divided into positioning accuracy, reverse deviation accuracy and repeat positioning accuracy. The main content of the positioning accuracy refers to the working surface of the CNC machine tool or other moving parts of the machine tool. The actual movement position in the production is consistent with the position of the program command; the difference of the degree of inconsistency is the positioning error. In the various systems of the machine tool, the errors of the servo system, the detection system, the feed system, and the geometrical errors of the moving parts guide rail are all important factors that cause the positioning error. The positioning error has a direct impact on the dimensional accuracy of the machined parts.
3. Measures to improve the accuracy of machine tools
3.1 Improve the design level
At present, the CNC machine tools we use a lot are mainly domestic machine tools. The machine tool manufacturers basically have some independent research and development capabilities. They can design, manufacture and improve the main parts of the products. Some of the functional parts of the machine tools need to be purchased. . The closed-eye machine is partially deformed due to excessive force, which affects the machining accuracy.
The machine tool drive shaft is affected by wear resistance and temperature rise during use, so the optimized design of its temperature characteristics can effectively maintain the machining accuracy of the machine tool. Usually designed for the spindle system, components that have a greater impact on the machining accuracy of the machine are mounted to a mounting surface that intersects the center of the drive shaft and that is perpendicular to the base of the machine, and then symmetrical on both sides of the headstock. The installation of other components can effectively improve the machining accuracy of the machine due to heat.
3.2 Improve machine tool geometry accuracy
The geometric accuracy of CNC machine tools can play a decisive role in the production precision of machine tools. Therefore, in the design of machine tool manufacturers, it is necessary to reasonably set the working accuracy of the machine tool and select the appropriate processing load. In the process of machine tool machining parts, the friction between the spindle journal and the bearing will increase its temperature. If there is a large error in the spatial position of the box hole of the headstock, it will cause the bearing to roll and deform, seriously affecting The accuracy of the rotation to the bearing. Therefore, it is necessary to strictly control the matching clearance of the spindle bearings.
CNC machine tools are in high-load operation for a long time when machining parts. Usually, machine tool manufacturers use the steel sliding guide sub-structure to improve the rigidity and precision of the machine. This structure allows the CNC machine to have the best geometric accuracy.
3.3 Comprehensively improve machining accuracy
CNC machine tools from design to manufacturing, assembly, and use of a complex process, the control of its machining accuracy is also a comprehensive system problem, can not rely solely on the control of a certain amount or a certain amount to obtain higher machining accuracy. In the production and manufacturing environment, factors that affect the accuracy of the machine tool in the manufacturing process should be fully considered, and the geometric precision caused by casting and machining on the machine tool components should be eliminated. Then, by setting the compensation value of the numerical control system of the numerical control machine tool, the machining accuracy of the machine tool can be effectively improved.
4, the conclusion
At present, the use of CNC machine tools in China has higher processing precision than traditional machine tools, but there is still a big gap with the world's most advanced CNC equipment. In the existing conditions, in order to improve the processing quality of the machine tool and maintain higher processing precision, it is necessary to improve the production process and continuously improve the design and production capabilities.
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