How to solve the objective cause of error in CNC machining?

Error is inevitable in CNC processing, but there are subjective and objective reasons for error in CNC processing. Next, we will briefly discuss the objective reasons and solutions.

The error caused by objective reasons can be divided into three parts: numerical control operating system error, mechanical error and tooling error.

1, numerical control system error. According to the control mode of servo system, CNC machining system can be divided into open loop control system, closed loop control system and half closed loop control system. The closed-loop control system can detect the actual position of the tool in real time, and feed back the results to the numerical control system, and compare the feedback value with the instruction value in the system, until the difference is eliminated, the movement will stop, so the control precision is very high. However, there are many unstable factors in the closed-loop position detection feedback, so the debugging work is difficult. If the various parameters do not match, the system will oscillate, resulting in unstable operation of the machine tool. The error of the closed-loop control system is mainly the installation error of the feedback system during the installation process.

The main method to reduce the above error is to improve the installation accuracy of the feedback system and choose the feedback system with higher accuracy as far as possible. There is no feedback link in the semi-closed loop control system, and the tool position accuracy is still affected by the no feedback link. Transmission chain error refers to the relative motion error between the first and the last transmission components 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. Because there is no feedback detection device in the feed system, the error generated by the feed line can not be compensated by feedback information, which leads to the actual position error. For example, the main error of the stepper motor is the step error, the dynamic error and the start - stop error. In view of the above errors, you can choose to meet the step Angle requirements of the motor or subdivision circuit drive motor to improve.

2, mechanical error. CNC machining center mechanical part includes reduction gear, supporting bearings, ball screw pair and coupling, etc. There is reverse clearance of the drive screw. When the worktable moves in reverse, this clearance will cause the motor to idle while the worktable does not move, resulting in errors. The method to eliminate the clearance between ball screw and nut is to apply pretightening force. The extension of cutting and cutting direction is introduced in the open-loop system to prevent undercutting or overcutting from affecting the machining quality of parts. Clearance values in closed loop and semi-closed loop systems can be set as reverse pitch error compensation parameters. For the errors caused by mechanical transmission chain deformation and thermal deformation, we can improve the quality of machine parts (machining accuracy, stiffness and thermal characteristics, etc.), reduce the heat of the internal heat source and strictly control the processing environment and use conditions to solve the problem.

3, Error of tooling and fixture. The positioning error of the fixture will directly affect the dimensional accuracy and position accuracy of the workpiece, so it is required that the fixture should have good positioning accuracy, rigidity and structural manufacturability. Reasonable selection of fixture fulcrum, anchor point and clamping point, to ensure that the deformation of clamping parts in a reasonable range, otherwise too large deformation will affect the processing accuracy of parts. If the corresponding measures are still unable to control the deformation of the parts, the necessary process measures should be considered, such as heat treatment of the parts, to eliminate stress and reduce deformation; For the deformation problem that cannot be solved by heat treatment method, the method of separating coarse and fine milling can be used, and different clamping force can be used for coarse and fine milling.

To sum up, machining parts on CNC machining center is the result of the comprehensive action of the whole process system and processing environment, the error source is very complex, and the machining accuracy of parts depends on various factors of the system. Therefore, it is necessary to consider each link comprehensively, analyze and find out the error sources that affect the precision of parts, so as to take corresponding measures.

Shenzhen Manners Technology Co.,Ltd is the supplier of some of the world’s famous international companies like Blum Novotest, Komet, Geneva Lab, BTL, etc... We specialize in telescoping parts, needle manufacturing, multi-axis CNC machining, Die casting mold, plastic injection mold, stamping mold, Swiss-type turning, laser cut tubing, tube processing, laser welding and automated assemblies for the medical, endoscopic, arthroscopic, orthopedic, firearms, defense, automotive, and specialty industrial markets.

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