CNC milling machines are commonly used machining equipment in the CNC machining industry. Their processing accuracy will directly affect the size and shape of the workpiece, thereby affecting the final output quality of the product. The precision of CNC milling machines is that each moving part can achieve accurate positions under the same control of the same system.
Although my country's CNC processing industry is becoming increasingly developed and processing machine tools have gradually moved to the forefront of the world, there are still many problems in practical applications that need to be dealt with in actual operations.
The following editor will briefly describe the factors that directly affect the machining accuracy of CNC milling machines from the following aspects:
1. Backlash error and screw pitch error.
First of all, it must be considered that my country's modern CNC milling machines mainly use servo motors to drive ball screws for positioning control. Therefore, the transmission error of the ball screw during operation will change the precision positioning of the CNC milling machine. Some CNC milling machines use a semi-closed-loop control servo system. When the servo system generates a drive pulse signal to the servo motor, it will ensure that the rotation angle of the servo motor is consistent with the private servo system.
However, since there will be a large or small gap between the gear gap of the transmission reduction box and the screw nut, these gaps are reflected at the moment of reverse transmission. The performance is that the motor has reversely rotated to a certain angle, but the corresponding The moving parts never moved. There will also be differences in the pitch at different positions, which is the screw pitch error.
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2. Structural error of fully closed-loop emergency system
With the fully closed-loop feed system, especially the existence of electrical compensation, theoretically, there should be no backlash error and pitch error. However, in the actual production process, errors caused by these two factors still exist. Mechanical gaps in system transmission will cause feedback equipment such as gratings to reversely move. Errors in the manufacturing of the ball screw lead to inconsistencies between the position required by the servo system and the position detected by the feedback device. The servo system drives the motor to repeatedly search for the comparison position, which will cause the machine tool to shake, which will also affect the customization accuracy of the milling machine. This is also one of the reasons why milling machines vibrate during processing.
3. Influence of guide rail accuracy
The bed guide rails of CNC machine tools are installed on the milling machine bed, and their function is to maintain the accuracy and processing accuracy of each part of the milling machine. Therefore, no matter what time, the bed guide rails should allow each linear motion component to always maintain linear accuracy during movement. When the milling machine spindle maintains stable rotation, other components must also maintain stable feed accuracy.
The accuracy of the guide rail determines the accuracy of each moving part to a large extent, which in turn affects the accuracy of the processed parts. When the machine tool is working, the working parts are fed back and forth, so the friction performance of the guide rail surface and the guide rail straightness error and parallelism error will also directly affect the performance of the moving parts.
4. Interference effects at the production site
There are various interference wave sources, other electrical equipment and various vibrations in the production workshop, which will affect the CNC milling machine during the production process.
In factories, there are many high-frequency power supplies and oscillation circuits. The mutual compatibility of these interferences will produce strong electromagnetic waves. These electromagnetic waves can radiate to a wide range of CNC machine tools, actually affecting the stable operation of the CNC system and the processing accuracy of the milling machine.
CNC milling machines have a limited voltage range. However, in the actual production process, there will be other large-scale electrical equipment in the factory environment. These equipments will produce large voltage fluctuation interference when they are started. When the voltage fluctuation exceeds what the CNC milling machine can withstand, When reaching the limit, the system power supply of the CNC milling machine will issue a warning. On the other hand, vibrations on the factory floor will also cause vibrations in Chuangshen, which will also affect the processing accuracy of the CNC milling machine.
In addition to the above reasons, the processing performance, rigidity, and mechanical vibration tolerance of the CNC milling machine itself will affect the final quality of the processed parts. From this perspective, the quality of the CNC milling machine itself must be guaranteed.
The above talks about the impact of various factors that come with the CNC milling machine itself on the machining accuracy. In fact, the cutting amount will also affect the accuracy of milling machine processing. The rotation speed of the tool, the cutting depth, the feed amount, the milling speed, etc. are all very important parameters. The actual application methods of cutting parameters selected for different parts will also be different. These differences will affect the accuracy, size and roughness of the processed parts.
Therefore, before using a CNC milling machine to process parts, you must comprehensively use the equipment, tools, and drawings marking the dimensions of the parts, etc., to rationally select the necessary parts required for part processing.
Finally, operators of CNC milling machines need to have a clear understanding of the factors that affect the processing accuracy of CNC milling machines on a daily basis, and they must combine a large number of actual processing operations with practical analysis of various reasons, and ultimately improve the actual processing accuracy of parts processed by CNC milling machines as much as possible. .
We have learned about the various causes that actually affect the accuracy of CNC milling parts, so do you know how to avoid these problems?
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2. Overview of solutions
1. Positioning of the reference plane for blank clamping.
CNC milling machines usually process parts of various shapes according to the actual needs of customers, and some are even rough-surfaced rough materials, such as cylinders, squares, spheres or other irregular shapes.
This material itself has large errors. During the processing process, it is necessary to determine the accurate datum customization. This operation will also facilitate the operator to measure the size of the part and further improve the processing accuracy of the part.
2. Control the temperature of the CNC milling machine within a certain range.
During the processing of parts on a CNC milling machine, the associated bearing parts will rub against each other, which will generate a large amount of heat. At the same time, the heat generated by the milling machine itself, the heat generated by the friction between the tool and the blank, and the superposition of various heats will increase the temperature of the blank. Rapid rise. In this case, if the milling machine equipment cannot dissipate heat in time, the parts being processed will deform.
Therefore, CNC milling machines usually need to install appropriate heat dissipation devices to increase the heat dissipation area of the equipment so that the CNC milling machine can dissipate heat on its own during operation.
3. Make error compensation during parts processing.
Method ①: If the operating system of the CNC milling machine has a reverse deviation problem, error compensation is required. Machine tool operators use CNC programming to position certain units at the beginning of processing to achieve error compensation and eliminate reverse deviations.
Method ②: CNC programming can not only achieve accurate positioning during milling, but also realize CNC milling machine interpolation without changing the CNC milling machine body.
The above are all the main reasons that will affect the machining accuracy of CNC milling machines. You can also contact us directly to learn more about CNC machining related information.