Errors in CNC Machining are inevitable for Precision Machining Parts processing, but there are subjective and objective reasons for CNC machining errors. Next, we will briefly discuss the objective reasons and solutions. The errors caused by objective reasons are mainly divided into three parts: CNC operating system errors, mechanical errors and tooling errors.

1. CNC system error: CNC machining system can be divided into open-loop control system, closed-loop control system and semi-closed-loop control system according to the control mode of servo system. Among them, the closed-loop control system can detect the actual position of the tool in real time, and feed the result back to the numerical control system, and compare the feedback value with the command value in the system. However, there are many unstable factors in the closed-loop position detection feedback, so debugging is difficult. If the various parameters do not match, the system will oscillate and the machine tool will be unstable. The main error of the closed-loop control system is the installation error generated by the feedback system during the installation process.

The main method to reduce the above errors is to improve the installation accuracy of the feedback system, and try to choose a feedback system with higher precision. There is a non-feedback link in the semi-closed-loop control system, and the position accuracy of the tool will still be affected by the non-feedback link. The error of the transmission chain refers to the error of the relative motion between the first and last transmission elements in the transmission chain, which is the main factor affecting the machining accuracy and can be compensated by modifying the parameters of the numerical control system. The open loop control system has no position detection device and no feedback circuit. Since there is no feedback detection device in the feed system, the error generated by the feed line cannot be compensated by the feedback information, which leads to the actual position error. For example, the main errors of using stepper motors are step error, dynamic error and start-stop error. For the above various errors, you can choose a motor or a subdivision circuit drive motor that can meet the step angle requirements to improve.

2. Mechanical error: The mechanical part of the CNC machining center includes reduction gears, support bearings, ball screw pairs and couplings. There is a backlash in the drive screw. When the worktable moves in the opposite direction, this clearance will cause the motor to idle and the worktable to not move, resulting in errors. For the transmission backlash, the method to eliminate the gap between the ball screw and the nut is to apply a pre-tightening force; introduce the extension of the cut-in and cut-out directions in the open-loop system to prevent undercutting or overcutting and affect the processing quality of the parts; The gap value in closed-loop and semi-closed-loop systems can be set as a parameter for compensation of the reverse pitch error. For errors caused by mechanical deformation and thermal deformation of the mechanical transmission chain, it can be solved by improving the quality of machine parts (machining accuracy, stiffness and thermal characteristics, etc.), reducing the amount of heat generated by the internal heat source, and strictly controlling the processing environment and use conditions.

3. Tooling fixture error: The positioning error of the fixture will directly affect the dimensional accuracy and positional accuracy of the workpiece, so the fixture is required to have good positioning accuracy, rigidity and structural manufacturability. Reasonably select the fulcrum, positioning point and clamping point of the fixture to ensure that the deformation of the part is within a reasonable range when clamping, otherwise the excessive deformation will affect the machining accuracy of the part. If the deformation of the parts cannot be controlled by the corresponding measures, necessary process measures should be considered, such as heat treatment of the parts to eliminate stress and reduce deformation; for deformation problems that cannot be solved by heat treatment, rough and fine milling can be used separately. The method of rough and fine milling uses different clamping forces.

To sum up, the machining of parts on the CNC machining center is the result of the combined action of the entire process system and the machining environment. The source of errors is very complex, and the machining accuracy of the parts depends on various factors of the system. Therefore, it is necessary to comprehensively consider all aspects, analyze and find out the source of errors affecting the accuracy of parts, so as to take corresponding measures.