Major causes of geometric errors in power turret CNC lathes

There are two main methods to improve machine tool accuracy. One method is to eliminate potential error sources by advancing the level of component design, manufacturing, and assembly; this is called the Error Prevention Method. This approach, however, is primarily constrained by the precision of the machine tools used for manufacturing the components themselves. Furthermore, improvements in component quality often lead to increased processing costs, which imposes certain limitations on the application of this method.

The other method is called the Error Compensation Method. This typically involves modifying the machine tool's machining instructions to compensate for errors, thereby achieving the desired motion trajectory and realizing a software-based enhancement of the machine tool's accuracy. Research indicates that geometric errors and errors caused by temperature account for approximately 70% of the total error in a machine tool. Among these, geometric errors are relatively stable and easier to compensate for. Compensating for geometric errors in CNC automatic machine tools can elevate the overall machining level of the entire mechanical industry. This holds significant importance for promoting scientific and technological progress, enhancing China's national defense capabilities, and ultimately strengthening the country's comprehensive national power.

Causes of geometric errors.

It is generally accepted that the geometric errors of CNC automatic machine tools arise from the following reasons:

1. Machine Tool's Original Manufacturing Errors.
   This refers to the motion errors caused by the geometric shape, surface quality, and mutual positional errors of the working surfaces of the components constituting the machine tool. This is the primary cause of geometric errors in CNC automatic machine tools.
2. Machine tool control system errors.
   Includes servo errors of the machine tool axes (contour following errors) and CNC interpolation algorithm errors.
3. 3.Thermal deformation errors.
   Errors caused by structural thermal deformation of the machine tool due to internal heat sources and environmental thermal disturbances.
4. 4.Errors caused by cutting load-induced deformation of the process system.
   Includes errors caused by deformation of the machine tool, tool, workpiece, and fixture. This error is also known as "tool deflection" or "machining deflection." It causes shape distortion of the machined part and is particularly severe when machining thin-walled workpieces or using slender tools.
5. 5.Machine tool vibration errors.
   During cutting operations, CNC automatic machine tools, due to the flexibility of the process and the variability of operations, have a higher probability of operating in unstable regions, which can excite strong chatter vibration. This leads to deterioration of the workpiece surface quality and geometric shape errors.
6. 6.Measurement system errors
   Includes the following aspects:
   (1) Errors inherent to the measurement sensor feedback system itself, caused by manufacturing errors of the measurement sensor and its installation errors on the machine tool.
   (2) Errors arising in the measurement sensor due to component and structural errors of the machine tool, as well as deformation during use.
7. 7.External interference errors
   Random errors caused by changes in the environment and operating conditions.
8. 8.Other errors
   Such as errors introduced by programming and operational mistakes.

The above errors can be classified into two major categories based on their characteristics and nature: Systematic Errors and Random Errors.

The systematic errors of a CNC automatic machine tool are inherent to the machine itself and are repeatable. Geometric errors constitute a major part of these and are also repeatable. Leveraging this characteristic, they can be measured "offline." Techniques employing "offline detection - open-loop compensation" can be used to correct and compensate for them, thereby reducing their impact and achieving the goal of enhancing machine tool precision.

Random errors are stochastic. Eliminating their influence on machining accuracy requires the "online detection - closed-loop compensation" method. This method imposes strict requirements on measuring instruments and the measurement environment, making it difficult to popularize.