CNC Machining · 2021年5月7日 0

Three major factors and countermeasures affecting the machining accuracy of CNC machine tools

Numerical control machine tools will inevitably be affected by various factors in the processing process, which will cause certain deviations in their processing accuracy and bring some inconvenience to production and life.

 

1. The precision problem in the machining of CNC machine tools

1.1 The influence of position error in CNC machining on machining accuracy

Position error refers to the variation or deviation degree of the mutual position between the actual surface, axis or symmetry plane of the processed part from its ideal position, such as perpendicularity, position, symmetry, etc. The position error in CNC machine tool processing usually refers to the dead zone error. The cause of the position error is mainly due to the gap and elastic deformation generated during the transmission of the machine tool parts during the processing of the machine tool, and the tool head of the machine tool needs to overcome the friction force during processing. Factors such as lead to position error. In the open-loop system, the position accuracy is greatly affected, while in the closed-loop follow-up system, it mainly depends on the accuracy of the displacement detection device and the speed amplification factor of the system, and the effect is generally small.

1.2 Machining accuracy errors caused by geometric errors in CNC machine tool processing

In CNC machine tool processing, the geometric accuracy of the machine tool is affected by external forces and heat generated by the tool and fixture under the influence of external factors such as the heat generated during processing. According to research, the main reasons for the geometric errors of CNC machine tools are nothing more than the following two: internal factors and external factors. The internal factors of the machine tool’s geometric errors refer to the geometric errors caused by the machine’s own factors, such as the levelness of the machine table, the levelness and straightness of the machine tool rails, and the geometric accuracy of the machine tools and fixtures. External factors mainly refer to the geometric errors generated under the influence of factors such as the external environment and thermal deformation during processing. For example, during the cutting process of tools or parts, due to thermal expansion and deformation, geometric errors occur, which affect the processing of machine tools. Precision and machining precision of parts.

1.3 Machining accuracy error due to machine positioning in CNC machine tool processing

Through long-term data analysis and practical operation of parts processing, it can be seen that machine tool positioning has a greater impact on the machining accuracy of CNC machine tools. From the structural point of view, the machining errors of CNC training tools are mostly caused by positioning accuracy. Among them, the feed system of the machine tool is the main link that affects the positioning accuracy. The feed system of a CNC machine tool usually consists of two parts: a mechanical transmission system and an electrical control system. The positioning accuracy is related to the mechanical transmission system in the structural design. In the closed-loop system, the CNC machine tool can usually prevent the position deviation of the main components in the feed system, such as the ball screw and other components, through the positioning detection device. As for the open-loop system, due to many influencing factors and complicated conditions, positioning monitoring cannot be carried out, so it has a greater impact on the machining accuracy of CNC machine tools.

2. Countermeasures to improve the machining accuracy of CNC machine tools

In the machining process of CNC machine tools, the accuracy of the parts processed directly affects the quality of the product. Some mechanical parts and parts of precision equipment have very high requirements for machining accuracy. Improving the machining accuracy of CNC machine tools is to solve the problem. The point is. Through extensive research and analysis, there are roughly the following methods to improve the machining accuracy of CNC machine tools:

2.1 Improve machining accuracy by controlling the original error of CNC machine tools

In the process of CNC machine tool processing, the error itself is inevitable. There is a certain error between the processed part and the CNC machine tool. This kind of certain error is called the original error.

Therefore, to improve the machining accuracy of CNC machine tools, controlling the original error of CNC milling tools is one of the important countermeasures. A systematic analysis should be carried out for the possibility of the original error, and corresponding improvement measures should be formulated according to the cause of the error and the error type. In the machining process of mechanical parts, the position accuracy and geometric accuracy of CNC machine tools have an important influence on the machining accuracy of parts. Position control and geometric accuracy control should be used to reduce the influence of position and geometric errors on parts. At the same time, air cooling, water cooling and other methods should be used to control the thermal deformation during the processing to reduce the impact of the processing accuracy caused by the thermal deformation error. At the same time, for the position error, it is necessary to reasonably select the tool suitable for the material of the part to avoid tool deformation. At the same time, select a reasonable fixture according to the blank shape of the processed part. If necessary, specially design the fixture for the shape and size of the part to avoid Position error.

2.2 Reasonably design the core components of the machine tool to avoid positioning errors

The positioning accuracy of the machine tool has an important influence on the accuracy of the parts, and the core components that affect the positioning accuracy of the machine tool, such as the straightness and levelness of the feed system, guide rail, and table surface, etc. When designing a CNC bending tool, it is necessary to select core components reasonably. For example, when selecting a ball screw widely used in machine tools, the accuracy of the ball screw should be fully considered, and the more mature ball screw technology should be selected and installed. The support of the ball screw cannot be ignored. The support of the ball screw is closely related to the transmission accuracy of the system. The support of the ball screw is mainly determined by the axial load and the rotation speed, which has an important influence on the machining accuracy of the CNC lathe. Accurate fixing and support methods. In addition, the bearing capacity of the ball screw should be strictly checked during the design process.

 

The drag chain, as a part of the external protection of the machine tool, is now indispensable for the machine tool. Due to its chain link structure, a certain vibration will also be generated when following the movement of the tool post. This vibration will be directly transmitted to the tool, which will eventually affect the machining accuracy to a certain extent.

 

2.3 Improve the machining accuracy of CNC machine tools through real-time monitoring technology

With the continuous improvement of CNC technology, the CNC machine tools are monitored in real time throughout the CNC machining process, the error links in the machining process are adjusted in time, and the error data of each link in the machining process is collected, and fed back to the control terminal, and passed The error data adopts the corresponding error compensation mechanism to carry out timely error compensation, which can effectively improve the machining accuracy of the parts.