What determines the accuracy of CNC machining parts

  • In CNC machining Parts programming, the correct use of methods and skills can effectively ensure and improve the accuracy of CNC machine processing. So, what determines the accuracy of CNC machining? Let's learn more about it!



    CNC machine tool processing accuracy is determined by the position detection element, position detection element by the detection element (sensor), and signal processing device, which is an integral part of the CNC machine tool closed-loop servo system.


    Its role is to detect the actual value of the table position and speed and the feedback signal back to the CNC device or servo device, thus forming a closed-loop control. The detection element is generally the use of light or magnetic principles to complete the position or speed detection.


    According to the detection method, position detection elements are divided into direct measurement elements and indirect measurement elements. When measuring the linear motion of the machine tool, the linear detection element is generally used, called direct measurement, and the position closed-loop control is called complete closed-loop control. The measurement accuracy mainly depends on the accuracy of the measuring element and is not affected by the accuracy of the machine tool drive.


    Since the linear displacement of the machine table is proportional to the rotation angle of the drive motor, it can measure the distance of the table movement indirectly by driving the rotation angle of the detection motor or screw. This method is called indirect measurement, and the position closed-loop control is called semi-closed-loop control.


    The measurement accuracy of CNC machining depends on the accuracy of the detection element and the machine feed drive chain. The machining accuracy of the closed-loop CNC machine tool depends mainly on the accuracy of the position detection device. CNC machine tools have very stringent requirements for position detection elements, typically with 0.001-0.01 mm or less resolution.


    The probability of damage to the detection element is higher than damage to the cable assembly. If the detection element fails, the first step is to check the wireless cable for broken wires, soiling, deformation, etc. The detection element can be judged by measuring its output. However, it is required to master the operating principle and the output signal of the detection element. For example: What to do when detecting equipment failure and mechanical oscillation (acceleration/deceleration)?


    1) Pulse encoder failure. Then is the time to check if the voltage of the feedback line terminal on the speed unit drops to a certain point. If the voltage drops, the pulse encoder is defective and should replace the encoder.


    2) The pulse encoder cross-coupling may be damaged, causing the shaft speed to be out of sync with the detected speed, and should replace the coupling.