What are the methods to ensure and improve the machining accuracy of machine tools

In machining, the error is inevitable, but the error must be within the allowable range. Through error analysis, master the basic law of its change, so as to take corresponding measures to reduce machining errors and improve machining accuracy.

Methods to ensure and improve machining accuracy can be roughly summarized as the following:

1. Reduce the original error, improve the geometric accuracy of the machine tool used for parts processing, improve the accuracy of fixtures, measuring tools and tools themselves, and control the force of the process system, thermal deformation, tool wear, deformation caused by internal stress, and measurement errors Directly reduce the original error. In order to improve the machining accuracy, it is necessary to analyze the original errors that produce the machining errors, and take different measures to solve the main original errors that cause the machining errors according to different situations. For the processing of precision parts, the geometric accuracy and stiffness of the precision machine tools used should be improved as much as possible, and the processing thermal deformation should be controlled; for the processing of parts with a formed surface, the main thing is how to reduce the shape error of the forming tool and the installation error of the tool. This method is a basic method widely used in production. It is to try to eliminate or reduce these factors after identifying the main factors that produce machining errors. For example, the turning of slender shafts now uses the large-pass reverse turning method, which basically eliminates the bending deformation caused by the axial cutting force. If supplemented by a spring top, the effect of thermal elongation caused by thermal deformation can be further eliminated. (Guide: The working principle and main features of self-extruding screws)

2. Compensating the original error The error compensation method is to artificially create a new error to offset the original error in the original process system. When the original error is negative, the man-made error is taken to be positive. Otherwise, take the negative value and try to make the two equal; or use one original error to offset the other original error, and try to make the two equal , The direction is opposite, so as to reduce the processing error and improve the processing accuracy.

3. Transfer the original error The error transfer method is essentially to transfer the geometric error, force deformation and thermal deformation of the process system. There are many examples of error transfer methods. For example, when the accuracy of the machine tool fails to meet the requirements of parts processing, it is often not blindly to improve the accuracy of the machine tool, but to find a way from the technology or the fixture to create conditions to transfer the geometric error of the machine tool to the aspect that does not affect the machining accuracy. For example, grinding the spindle taper hole to ensure its coaxiality with the journal is not guaranteed by the rotation accuracy of the machine tool spindle, but by the fixture. When the machine tool spindle and the workpiece are connected by a floating connection, the original error of the machine tool spindle is transferred.

4. Evenly share the original error. In processing, due to the existence of the blank or the previous process error, the processing error of this process is often caused, or due to the change of the material properties of the workpiece, or the process change of the previous process (such as blank finishing Later, the original cutting process was cancelled), which caused a big change in the original error. To solve this problem, it is best to adopt the method of grouping to adjust the average error. The essence of this method is to divide the original error into n groups according to its size, and reduce the error range of each group to 1/n of the original, and then adjust the processing according to each group.

5. Homogenize the original error. For shafts and holes that require high matching accuracy, grinding technology is often used. The grind tool itself does not require high precision, but it can perform micro-cutting on the workpiece during relative movement with the workpiece, and the high points are gradually ground away (of course, the mold is also partly ground by the workpiece), and finally the workpiece is very high. High precision. This process of friction and wear between surfaces is the process of continuous error reduction, which is the error equalization method. Its essence is to use closely related surfaces to compare each other, check each other to find out the difference from the comparison, and then make mutual correction or mutual reference processing, so that the error of the processed surface of the workpiece is continuously reduced and homogenized. In production, many precision reference parts (such as flat plates, rulers, etc.) are processed by the error averaging method.

6. In-situ processing method. In processing and assembly, some accuracy problems involve the interrelationship between parts or components, which is quite complicated. If you blindly improve the accuracy of parts and components, sometimes it is not only difficult, or even impossible. Using the in-situ machining method (also called self-processing and fitting method), it is possible to easily solve the seemingly difficult precision problem. The in-situ machining method is commonly used in the machining of mechanical parts as an effective measure to ensure the machining accuracy of the parts.