Reasons and solutions for high accuracy deviation of nc machine tools

Reasons and solutions for high accuracy deviation of nc machine tools

Accuracy has always been one of the important standards to measure the quality of a CNC machine tool. However, many friends of the machine tool have lost accuracy after being used for a period of time.

1. Accurate workpiece size and poor surface finish

Fault reason: the tool tip is damaged and not sharp; The machine produces resonance and the placement is not stable. The machine tool has crawl phenomenon; The processing technology is not good.

Solution: if the tool is not sharp after being worn or damaged, re-sharpen it or choose a better tool to re-align it; The machine produces resonance or placement instability, adjustment level, laying foundation, fixed stability; The reason for the mechanical crawling is that the guide rail of the drag plate is badly worn, the ball ball of the lead bar is worn or loose, the machine tool should pay attention to maintenance, clean the iron wire after commuting, and add lubricating oil in time to reduce the friction. Select cooling fluid suitable for workpiece processing, and try to choose higher spindle speed when meeting the requirements of other processes.

2. The workpiece produces taper head phenomenon

Fault reason: the machine placement level is not adjusted well, one high one low, resulting in placement instability; When turning a long shaft, the material contribution is relatively hard, and the cutter eats more deeply, resulting in the phenomenon of the cutter. Tailstock ejector is different from the spindle.

Solution: use the level to adjust the level of the machine tool, lay a solid foundation, and fix the machine tool to improve its toughness; Choose reasonable technology and proper cutting feed to avoid the force of the cutter; Adjust the tailstock.

3. The driver phase lamp is normal, while the size of the processed work piece is large or small

Fault reason: the machine's dragging plate runs at high speed for a long time, resulting in the wear of the screw and bearing; The repeated positioning accuracy of the tool holder produces deviation in the long term use. The pallet can accurately return to the starting point each time, but the size of the workpiece still changes. This phenomenon is generally caused by the spindle, the high-speed rotation of the spindle makes the bearing wear seriously, resulting in the change of machining dimensions. Metal processing WeChat, good content, worthy of attention.

Solution: use the scale to lean against the bottom of the tool holder, and edit a fixed circulation program through the system to check the repeated positioning accuracy of the drag plate, adjust the screw clearance and replace the bearing; Check the repeated positioning accuracy of the tool holder with a dial indicator, adjust the machine or replace the tool holder; Check whether the workpiece is returned to the starting point of the program accurately with a dial indicator. If so, repair the spindle and replace the bearing.

4. The size of the workpiece is a few millimeters away from the actual size, or a big change in axial direction

Fault reason: the speed of fast positioning is too fast, and the drive and motor cannot react. After a long period of friction loss, the mechanical drag rod and bearing are too tight and stuck; The tool holder is too loose after changing, and the lock is not tight; Edit program error, head, end without echo or cancellation of knife patch; The system's electronic gear ratio or step Angle setting error.

Solution: fast positioning speed is too fast, then adjust the GO speed appropriately, cutting plus and minus speed and time to make the driver and motor work normally at rated operating frequency; When the machine tool wear occurs, the drag plate and screw crane bearing become too tight and become stuck, then it must be readjusted and repaired. If the tool holder is too loose after replacing the tool holder, check whether its reverse time is satisfied, check whether the turbine worm inside the tool holder is worn, whether the clearance is too large, and whether the installation is too loose. If it is caused by the program, the program must be modified, improved according to the workpiece drawings, selected reasonable processing technology, and compiled the correct program according to the instruction in the manual; If the size deviation is found to be too large, check whether the system parameters are set properly, especially the parameters such as the electronic gear and step Angle are damaged, and the occurrence of this phenomenon can be measured by using the scale.

5. The arc machining effect is not ideal and the size is not in place

Fault reason: the overlapping vibration frequency leads to resonance; Processing technology; The parameter setting is unreasonable, the feeding speed is too high, and the arc machining is out of step. Loose due to large gap of the screw rod or out-of-step due to too tight of the screw rod; Synchronous belt wear.

Solution: find the resonant parts, change their frequency and avoid resonance. Considering the processing technology of the workpiece material, reasonably compile the program; For stepper motor, the machining rate F cannot be set too high. Whether the machine is installed firmly and stably, whether the drag plate is too tight after wearing, the clearance increases or the tool holder becomes loose, etc. Replace the tape. Metal processing WeChat, good content, worthy of attention.

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

Cause of failure: the jig must be carefully checked, taking into account the operator's operation method, and the reliability of the clamping. Due to the size change caused by clamping, the tooling must be improved to avoid human negligence and misjudgment. The numerical control system may be subject to the fluctuation of external power supply or be interfered by the automatic interference pulse, which will be transmitted to the driver so that the driver receives the redundant pulse-driven motor to take away or leave less.

Solution: grasp the rule, try to use some anti-jamming measures, such as: strong electric field disturbance of high voltage cables and weak current signal of the signal isolation, join the absorption capacity of anti-interference and a shielding wire isolation, in addition, check whether the ground wire connection is firm, grounding contact recently, all anti-interference measures should be taken to prevent the system disturbance.

7. There are changes in one process of the workpiece, and the dimensions of other processes are accurate

Cause of failure: whether the program parameters of the program segment are reasonable, whether the program format meets the specification requirements within the predetermined trajectory

Solution: screw thread segments with random teeth and incorrect pitch, immediately associated with the peripheral configuration (encoder) and the function of objective factors.

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

Fault cause: programming error; Unreasonable system parameter Settings; Improper configuration Settings; Mechanical transmission components have regular periodic changes of fault

Solution: check whether the instructions used by the program are executed in accordance with the required trajectory specified in the instruction manual. You can judge by the percentage table, and position the percentage table at the starting point of the program to make the drag board return to the starting point after the program ends. Repeat the execution even if you observe the results and master the rules. Check whether the system parameters are set reasonably or considered to be changed; The machine tool configuration in connection calculation of the coupling parameters of single calculation is in compliance with the requirements, pulse equivalent is accurate; Check whether the transmission part of the machine tool is damaged, whether the gear coupling is uniform, whether there are periodic and regular failures, if there are, check the key parts and remove them.

9. The size change caused by the system is unstable

Fault reason: unreasonable system parameter setting; Unstable working voltage; Due to external interference, the system is out of step. Capacitance has been added, but the impedance mismatch between the system and the driver leads to the loss of useful signals; Abnormal signal transmission between system and driver; System damage or internal failure.

Solution: whether the speed, acceleration time is too large, the spindle speed, cutting speed is reasonable, and whether the operator's parameter modification leads to system performance change; Installing voltage stabilizing equipment; The grounding line is confirmed to be reliably connected, and the anti-interference absorbing capacitance is added at the driver pulse output contact; Select appropriate capacitance type; Check whether the signal connection line between the system and the driver is shielded, whether the connection is reliable, and whether the system impulse signal is lost or added; Send to factory for repair or replacement of motherboard.