How To Solve The Problem Of CNC Machining Accuracy

- May 13, 2019-

1. The workpiece size is accurate and the surface finish is poor.

Fault causes: tool tip damage, not sharp; machine tool resonance, unstable placement; machine tool crawling phenomenon; poor processing technology.


Solution: If the tool is not sharp after wear or damage, the tool will be grinded again or better tool will be selected to re-align the tool; the machine tool will resonate or place unevenly, adjust the level, lay the foundation and fix smoothly; the reason of mechanical crawling is that the trawler guide rail is worn badly, the ball screw is worn or loosened, the machine tool should be maintained, the wire should be cleaned after work and lubricated in time. Oil to reduce friction; select suitable cooling fluid for workpiece processing, in order to meet the processing requirements of other processes, try to choose a higher spindle speed.


2. Workpiece produces taper size head phenomenon

Failure reasons: the level of machine tool placement is not adjusted well, one high and one low, resulting in unstable placement; when turning long axle, the contribution material is hard, the tool is deep, resulting in knife-letting phenomenon; tailstock pin and spindle are not concentric.


Solution: Use level instrument to adjust the level of machine tool, lay a solid foundation, fix the machine tool well and improve its toughness; choose reasonable technology and appropriate cutting feed to avoid tool force concession; adjust tailstock.


3. The driver phase lamp is normal, but the size of the workpiece processed is large or small.

Causes of failure: the long-term high-speed operation of the machine tool Trailer leads to wear of the screw and bearing; the repetitive positioning accuracy of the tool holder deviates in the long-term use; the trailer can accurately return to the starting point of processing each time, but the size of the workpiece is still changing. This phenomenon is generally caused by the spindle. The high speed rotation of the spindle causes serious wear of the bearing, which leads to the change of processing size.


Solution: Depend on the bottom of the tool holder with the dial indicator, and edit a fixed cycle program through the system to check the repetitive positioning accuracy of the trailer, adjust the clearance of the screw and replace the bearing; check the repetitive positioning accuracy of the tool holder with dial indicator, adjust the machine or replace the tool holder; check whether the workpiece is accurately returned to the starting point of the program after processing with dial indicator, and if possible, repair the spindle and replace it. Bearing.


4. The effect of processing arc is not ideal and the dimension is not in place.

Fault causes: resonance caused by overlap of vibration frequency; processing technology; unreasonable parameter setting, excessive feed speed, making arc processing out of step; loosening caused by large clearance of screw rod or out of step caused by excessive tightness of screw rod; wear of synchronous belt.


Solution: Find out the parts that produce resonance, change their frequency, avoid resonance; Consider the processing technology of workpiece materials, and make reasonable program; For stepping motors, the processing rate F should not be set too large; Whether the machine tool is firmly installed, placed smoothly, whether the trawler is too tight after wear, gap increase or tool holder loosening; Replace the synchronous belt.


5. Occasionally, workpiece overshoots occur in batch production.

Reasons for failure: Tools and fixtures must be carefully checked, and considering the operator's operation method and the reliability of clamping, due to the size change caused by clamping, tooling must be improved so that workers can avoid the phenomenon of human negligence to make misjudgments as far as possible; if you want to learn UG programming, you can add a small-scale center QQQ1139746274 (Weixin identical number) numerical control system may be subject to external power fluctuations or interference. The interference pulse is generated automatically and transmitted to the driver, which causes the driver to take away or take less of the surplus pulse-driven motor.


Solution: Understand and grasp its law, try to use some anti-interference measures, such as: strong electric cable with strong electric field interference and signal line isolation of weak electric signal, adding anti-interference absorption capacitance and shielding line isolation, in addition, check whether the ground wire is firmly connected, the earthing contact is nearest, take all anti-interference measures to avoid system interference.


6. Workpiece processing changes in one process, and other processes are accurate in size.

Cause of failure: whether the parameters of the program are reasonable, whether the programming format meets the requirements of the specification or not in the predetermined trajectory.


Solution: When screw thread program period appears chaotic teeth and pitch is not right, it immediately associates with the peripheral configuration (encoder) of thread processing and objective factors of this function.


7. Instability of Size Variation Caused by System

Fault causes: unreasonable system parameter setting; unstable working voltage; system out of step caused by external interference; capacitor has been added, but the impedance between the system and the driver does not match, resulting in loss of useful signals; abnormal signal transmission between the system and the driver; system damage or internal failure.


Solution: speed, acceleration time is too large, spindle speed, cutting speed is reasonable, whether the operator's parameter modification results in system performance change; install voltage stabilization equipment; grounding wire and determine reliable connection, add anti-interference absorption capacitor at the driver pulse output contact; select appropriate capacitor type; check whether the signal connection line between the system and the driver has screen. Shield, whether the connection is reliable, check whether the system pulse signal is lost or increased; send to the factory for maintenance or replacement of the motherboard.