Under the condition that the rigidity allows, the rough machining takes a larger depth of cut to reduce the number of passes and improve the productivity of the workpiece; the fine machining generally takes a smaller depth of cut to obtain a higher surface quality. Influencing the final processing accuracy and processing efficiency of the workpiece, in addition to the reasons of the CNC machine tool itself, it should also be based on the reasonable processing route setting, the selection and correct installation of the tool, the reasonable selection of the cutting amount, the programming skills and the rapid control of dimensional accuracy. Comprehensive considerations.
1.Programming Skills
Numerical control programming is the most basic work of numerical control processing. The pros and cons of the programming of workpiece processing directly affect the final processing accuracy and processing efficiency of the machine tool. It can start from several aspects such as clever use of inherent programs, reducing the cumulative error of the CNC system, and flexible use of main programs and subroutines.
1. Adjust the process system
1): Trial cutting method is adjusted by trial cutting-measuring size-adjusting the amount of cutting of the tool-cutting-retry cutting, and so on until it reaches the required size. This method has low production efficiency and is mainly used for single-piece and small-batch production.
2): The adjustment method obtains the required size by adjusting the relative positions of the machine tool, fixture, workpiece and tool in advance. This method has high productivity and is mainly used for mass production.
2. Reduce machine tool error
--Should improve the rotation accuracy of the bearing
①Select high-precision rolling bearings
②Using high-precision multi-oil wedge dynamic pressure bearing
③Using high-precision hydrostatic bearings
--Improve the accuracy of accessories related to the bearing
①Improve the machining accuracy of the box support hole and the spindle journal
②Improve the machining accuracy of the mating surface with the bearing
③Measure and adjust the radial runout range of corresponding parts to compensate or offset the error
--Appropriate pre-tightening of rolling bearings
①Can eliminate the gap
②Increase bearing stiffness
③Equalization of rolling element error
-Make the spindle rotation accuracy not reflected on the workpiece
3.Third, reduce the transmission error of the transmission chain
(1) The number of transmission pieces is small, the transmission chain is short, and the transmission accuracy is high
(2) The use of reduced speed transmission is an important principle to ensure transmission accuracy, and the closer the transmission pair is to the end, the smaller the transmission ratio should be
(3) The accuracy of the end pieces should be higher than other transmission parts
Fourth, reduce tool wear
(1) The tool must be re-sharpened before the tool size wear reaches the sharp wear stage
(2) Use special cutting oil for sufficient lubrication
(3) The material of the tool should meet the process requirements
Fifth, reduce the force deformation of the process system
(1) Improve the rigidity of the system, especially the rigidity of weak links in the process system
(2) Reduce the load and its changes
Sixth, reduce the thermal deformation of the process system
(1) Reduce the heat generation of the heat source and isolate the heat source
(2) Equilibrium temperature field
(3) Adopt reasonable machine tool component structure and assembly benchmark
(4) Accelerate the heat transfer balance
(5) Control the ambient temperature
Seventh, reduce residual stress
(1) Increase the heat treatment process to eliminate internal stress;
(2) Reasonably arrange the technological process.
The above is the method to reduce the error of machining the workpiece, and the reasonable arrangement of the process can effectively improve the accuracy of the workpiece.
2. Reasonable setting of processing route
Reasonable setting of processing route and processing sequence is an important basis for optimizing the programming of workpiece processing. It can be considered from the aspect of processing trajectory and feed method.
When performing CNC milling of workpieces, you can help you choose the appropriate feed method based on the process requirements of the workpiece to ensure the cutting accuracy and processing efficiency of the workpiece. When milling the outer contour of a plane workpiece, the cutting-in and cutting-out route of the tool should be arranged. Try to cut in and out along the extension line of the contour curve to avoid knife marks at the junction. At the same time, down milling or up milling should be selected according to the condition of the workpiece in the milling process.
3. The selection and correct installation of tools
Regardless of whether it is CNC machining or ordinary machining, the tool directly acts on the workpiece, so the machining accuracy and surface quality of the workpiece are the most important factors when it is selected and installed. Especially the workpiece is processed on the CNC machining center, and the tools are stored in the tool magazine in advance, and once the processing is started, it cannot be replaced at will. Therefore, the general principle of tool selection is: convenient installation and adjustment, good rigidity, high durability and high precision.
4.Reasonable choice of cutting amount
The determination of the cutting amount is an important content of the CNC machining process. Its size is an important parameter of the main motion and feed motion of the machine tool. It has an important influence on the machining accuracy, machining efficiency and tool wear of the workpiece. The selection of cutting amount includes cutting speed, back-cutting amount and feed amount. The basic selection principle is: if the rigidity allows, use a larger cutting depth for roughing to reduce the number of passes and increase the productivity of the workpiece; for finishing, a smaller cutting depth is generally used to obtain a higher surface quality.