How To Solve The Problem Of CNC Machining Accuracy?

- Mar 09, 2019-


How to solve the problem of CNC machining accuracy?


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


   The cause of the failure: the tool tip is damaged, not sharp; the machine tool generates resonance, the placement is not stable; the machine tool has crawling phenomenon; the processing technology is not good.


   Solution: If the tool is not sharp after being worn or damaged, re-grind the knife or choose a better tool to re-align the tool; the machine will generate resonance or place it is not stable, adjust the level, lay the foundation, and fix it smoothly; the reason for the mechanical creep is drag The guide rail of the plate is very worn, the screw of the lead screw is worn or loose, and the machine should pay attention to maintenance. After the work, the wire should be cleaned and the lubricant should be added in time to reduce the friction. The coolant suitable for the workpiece processing can be selected to meet the processing requirements of other processes. In the case, try to use a higher spindle speed.


2. The workpiece produces a taper size


   The cause of the fault: the level of the machine tool is not adjusted well, one high and one low, the placement is not stable; when turning the long axis, the contribution material is relatively hard, the tool eats the knife deeper, causing the knife phenomenon; the tailstock thimble is not concentric with the main shaft.


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


3. The driver phase lamp is normal, and the processed workpiece size is large and small.


   The cause of the failure: the long-term high-speed operation of the machine tool carriage causes the lead screw and the bearing to wear out; the repeated positioning accuracy of the tool holder is deviated in the long-term use; the carriage can accurately return to the machining starting point every time, but the size of the processed workpiece still changes. This phenomenon is generally caused by the main shaft, and the high-speed rotation of the main shaft causes the bearing to wear seriously, resulting in a change in the machining size.


  Solution: Use the dial gauge to lean against the bottom of the tool holder, and edit a fixed cycle program through the system, check the repeat positioning accuracy of the carriage, adjust the screw clearance, replace the bearing; check the repeat positioning accuracy of the tool holder with the dial gauge. Adjust the machine or replace the tool holder; use a dial indicator to check whether the workpiece is accurately returned to the starting point of the program. If possible, repair the spindle and replace the bearing.


4. The workpiece size differs from the actual size by a few millimeters, or a certain axial change


   The cause of the fault: the speed of rapid positioning is too fast, the drive and the motor do not react; after long-term friction loss, the mechanical lead screw and the bearing are too tightly stuck; the tool post is too loose after the tool change, the lock is not tight; the editing procedure Error, the head and tail did not respond or did not cancel the tool to complete; the system's electronic gear ratio or step angle setting is wrong.


   Solution: If the rapid positioning speed is too fast, the speed of the GO will be adjusted appropriately. The cutting acceleration and deceleration and time will make the drive and the motor work normally at the rated operating frequency. After the machine wear occurs, the carriage and the screw crane bearing are too tight. If the card is stuck, the repair must be re-adjusted. If the tool holder is too loose after the tool change, check whether the tool holder reversal time is satisfied, check whether the worm gear inside the tool holder is worn, whether the gap is too large, whether the installation is too loose, etc.; If the cause is caused, it is necessary to modify the program, improve according to the requirements of the workpiece drawing, select a reasonable processing technology, and write the correct program according to the instructions of the manual; if it is found that the dimensional deviation is too large, check whether the system parameters are set properly, especially the electronic gear and Whether the parameters such as the step angle are destroyed, this phenomenon can be measured by dialing a dial indicator.


5. The processing arc effect is not ideal, the size is not in place


   The cause of the fault: the overlap of the vibration frequency causes resonance; the processing technology; the parameter setting is unreasonable, the feed speed is too large, the arc machining is out of step; the looseness caused by the screw gap is large or the screw is too tight; abrasion.


  Solution: Find the parts that generate resonance, change their frequency, avoid resonance; consider the processing technology of the workpiece material, and make the program reasonably; for stepper motor, the processing rate F can't be set too large; whether the machine is installed firmly, placed smoothly, drag Whether the board is too tight after wear, the gap is increased or the tool holder is loose; etc.; replace the timing belt.


6. Occasionally, the workpiece is out of tolerance in mass production.


   The cause of the failure: the fixture must be carefully checked, and the operator's operation method and the reliability of the clamping must be taken into account. Due to the dimensional changes caused by the clamping, the tooling must be improved so that the worker can avoid the misjudgment of human negligence as much as possible; Programming can add a small degree of heart QQ1139746274 (WeChat same number) CNC system may be subject to fluctuations or interference of external power supply automatically generate interference pulses, which are transmitted to the drive to cause the drive to accept excess pulse drive motor to take away or less.


  Solution: Understand the rules, try to use some anti-interference measures, such as: strong electric cable interference strong signal and weak electric signal signal line isolation, add anti-interference absorption capacitor and shielded line isolation, in addition, check the ground Whether the connection is firm, the grounding contact is nearest, and all anti-interference measures are taken to avoid system interference.


7. There is a change in the processing of one part of the workpiece, and the dimensions of other processes are accurate.


  Fault reason: Whether the parameters of the program block program are reasonable, whether it is within the predetermined track, and whether the programming format meets the requirements of the manual.


  Solution: If there is a chaotic tooth in the thread block, if the pitch is wrong, it immediately associates with the peripheral configuration (encoder) of the machining thread and the objective factor of the function.


8. Each process of the workpiece has an increasing or decreasing phenomenon


   Fault reason: programming error; unreasonable system parameter setting; improper configuration setting; mechanical transmission components have regular periodic changes.


   Solution: Check whether the instructions used by the program are executed according to the required trajectory specified in the manual. You can judge by dialing the dial indicator. Position the dial indicator at the beginning of the program to let the board return to the starting position after the program ends, and then repeat the execution. Even if you observe the results, master the rules; check whether the system parameters are set properly or are considered to be changed; the relevant machine configuration is calculated on the connection calculation coupling parameters to meet the requirements, whether the pulse equivalent is accurate; check the machine transmission part for damage, gear Whether the coupling is uniform, check for periodicity, regular failure phenomena, and if so, check the key parts and give them exclusion.


9. The dimensional change caused by the system is unstable


    The cause of the fault: the system parameter setting is unreasonable; the working voltage is unstable; the system is subject to external interference, causing the system to lose synchronization; the capacitor is added, but the impedance between the system and the driver does not match, resulting in loss of useful signal; signal between the system and the driver The transmission is not normal; the system is damaged or internal.


   Solution: speed, acceleration time is too large, spindle speed, cutting speed is reasonable, whether the operator's parameter modification causes system performance change; install voltage regulator equipment; ground wire and determine that the connection is reliable, the driver pulse output contact Add anti-interference absorption capacitor; select the appropriate capacitor model; check whether the signal connection between the system and the driver is shielded, whether the connection is reliable, check whether the system pulse signal is lost or increased; send the factory for repair or replace the motherboard.


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