Under the conditions of rigidity, a larger depth of cut is used for roughing to reduce the number of passes and improve the productivity of the workpiece; for finishing, a smaller depth of cut is generally used to obtain higher surface quality. Affecting the final machining accuracy and machining efficiency of the workpiece, in addition to the reasons of the CNC machine tool itself, it should also include reasonable machining route settings, tool selection and correct installation, reasonable selection of cutting amount, programming skills, and rapid control of dimensional accuracy. comprehensive consideration.
1. Programming skills
NC programming is the most basic work of NC machining. The pros and cons of the workpiece machining program directly affect the final machining accuracy and machining efficiency of the machine tool. It can start from several aspects, such as clever use of inherent programs, reduction of cumulative errors of CNC system, and flexible use of main programs and subprograms.
1. Flexible use of main program and subprogram
In the processing of complex molds, it is generally processed in the form of one mold and multiple pieces. If there are several identical shapes on the mold, the relationship between the main program and the subprogram should be used flexibly, and the subprogram should be called repeatedly in the main program until the processing is completed. It can not only ensure the consistency of processing dimensions but also improve its processing efficiency.
2. Reduce the cumulative error of the CNC system
Generally, the incremental method is used to program the workpiece, which is based on the previous point. In this way, the continuous execution of multi-segment programs will inevitably generate a certain cumulative error. Therefore, try to use absolute programming when programming, so that each program segment is based on the workpiece. The origin is the benchmark, so that the cumulative error of the CNC system can be reduced and the machining accuracy can be guaranteed.
Machining accuracy is mainly used to produce products, and machining accuracy and machining error are terms used to evaluate the geometric parameters of the machined surface. However, the actual parameters obtained by any machining method will not be absolutely accurate. From the function of the part, as long as the machining error is within the tolerance range required by the part drawing, it is considered that the machining accuracy is guaranteed.
Machining accuracy refers to the actual geometric parameters (size, shape and position) of the part after machining. The difference between them is called machining error. The size of the machining error reflects the level of machining accuracy. The larger the error, the lower the machining accuracy, and the smaller the error, the higher the machining accuracy. The following is a brief introduction to the methods to improve the machining accuracy of workpieces:
1. Adjust the process system
1): The trial cutting method is adjusted by trial cutting - measuring size - adjusting the amount of knife bite of the tool - cutting by cutting - try cutting again, and so on until the desired size is reached. This method has low production efficiency and is mainly used for single-piece small batch production.
2): The adjustment method obtains the required size by pre-adjusting the relative positions of the machine tool, fixture, workpiece and tool. This method has high productivity and is mainly used for mass production.
2. Reduce machine tool error
--The rotation accuracy of the bearing should be improved
①Select high-precision rolling bearings
②Using high-precision multi-oil wedge dynamic pressure bearings
③Using high-precision hydrostatic bearings
--Improve the accuracy of accessories with bearings
①Improve the machining accuracy of box support holes and spindle journals
②Improve the machining accuracy of the mating surface with the bearing
③ Measure and adjust the radial runout range of the corresponding parts to make the error compensation or offset
--Appropriately preload the rolling bearing
①Can eliminate the gap
②Increase bearing stiffness
③ Homogenization of rolling element error
--The spindle rotation accuracy is not reflected on the workpiece
3. Reduce the transmission error of the transmission chain
(1) The number of transmission parts is small, the transmission chain is short, and the transmission precision is high
(2) The use of deceleration transmission is an important principle to ensure the transmission accuracy, and the closer the transmission pair is to the end, the smaller the transmission ratio should be
(3) The precision of the end piece should be higher than that of other transmission parts
Fourth, reduce tool wear
(1) The tool must be re-sharpened before the tool size wear reaches the stage of rapid wear
(2) Select special cutting oil for full lubrication
(3) The tool material should meet the process requirements
5. Reduce the stress and deformation of the process system
(1) Improve the stiffness of the system, especially the stiffness of the weak links in the process system
(2) Reduce the load and its changes
6. 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 a reasonable machine tool component structure and assembly benchmark
(4) Accelerate to achieve heat transfer equilibrium
(5) Control the ambient temperature
Seven, 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 the workpiece, and the reasonable arrangement of the process can effectively improve the accuracy of the workpiece.
More about this source textSource text required for additional translation information
Send feedback
Side panels
History
Saved
Contribute
2. Reasonable setting of processing routes
Reasonable setting of processing route and processing sequence is an important basis for optimizing workpiece processing program. It can be considered from the aspect of the machining path and the method of feeding.
When carrying out CNC milling of the workpiece, it is necessary to select the appropriate feed method according to the technological 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 cut-in and cut-out routes 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, in the milling process, down milling or up milling should be selected according to the condition of the workpiece.
3. Tool selection and correct installation
Whether it is CNC machining or ordinary machining, the tool directly acts on the workpiece, so its selection and installation are the most important factors for the machining accuracy and surface quality of the workpiece. Especially when the workpiece is processed on the CNC machining center, the tools are stored in the tool magazine in advance, and once the processing starts, they cannot be replaced at will. Therefore, the general principle of tool selection is: easy 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 part of the CNC machining process. Its size is an important parameter of the main motion and feed motion of the machine tool, and has an important impact on the machining accuracy, machining efficiency and tool wear of the workpiece. The selection of cutting amount includes cutting speed, back cut amount and feed amount. The basic selection principle is: when the rigidity allows, a larger depth of cut is used for roughing to reduce the number of passes and improve the productivity of the workpiece; a smaller depth of cut is generally used for finishing to obtain a higher surface quality.
Post time: Sep-26-2022
