1. Geometric error of CNC machine tools
The traditional machining process system is mainly composed of four parts: machine tool, tool, fixture and workpiece. The operation error of each link will affect the machining accuracy. Take the influence of machine tools as an example, which is the carrier of tools and workpieces. Its own accuracy has a great influence on the machining accuracy of the workpiece, especially the three major aspects of the spindle, the guide rail and the transmission chain. Among them, the radial runout, axial runout, angular swing and other errors of the main shaft will reduce the rotation accuracy of the main shaft, which will have a negative impact on the machining accuracy of the parts; the horizontal plane straightness and vertical plane straightness in the production process of the guide rail, the front and rear guide rails There will be a certain error in parallelism, plus some quality effects during the installation process, which will ultimately affect the accuracy of the workpiece. For example, the horizontal straight line error △1 of the rail will cause the diameter δH=2△1 error of the workpiece; the transmission chain controls the speed change of the main movement and feed movement of the machine tool, if the transmission components have manufacturing errors, assembly errors, wear and other problems, It will inevitably have a negative impact on the accuracy of the workpiece, especially the workpiece such as gears and threads. The main motion and the feed motion have strict transmission ratio, and the error of the transmission chain has a great influence on the accuracy.
2. Human error
The errors of human factors are mainly reflected in three aspects: adjustment, clamping and measurement. There are two types of adjustments in machining: trial cut adjustment and adjustment adjustment, but it is difficult to be absolutely accurate, and errors will occur. Taking the trial cutting method as an example, when the feed mechanism is displaced under the action of friction, it is difficult to completely match the actual feed rate with the theoretical total feed rate. For example, the total theoretical feed of the CA6136 lathe requires infeed. A small grid tool holder is moved forward by 0.02mm, but the actual distance that the tool holder moves forward is often less than the theoretical feed. The clamping error mainly includes the hyperbolic error during tool setting, the positioning error of the fixture, the clamping force and clamping direction error, and the shape or size deformation error of the workpiece.
3.CNC machining errors
At present, the application of computer numerical control machine tools in machinery manufacturing is becoming more and more common. Compared with traditional ordinary machine tools, the control of numerical control system is much smaller than the error of human operation. However, computers are not omnipotent, and the programming, numerical control device, servo drive and other technologies used by CNC machine tools will also bring errors. Taking programming as an example, the main sources of errors are mathematical errors and process errors. Let me talk about math errors first, because the coordinate values of each node of a part are usually not rational numbers, and even rational numbers are beyond what a computer can represent. Therefore, when the computer discards part of the data, approximation algorithm error, model error, truncation error, etc. will occur; during processing, if the basic size is not calculated during programming, errors will occur.