Analysis of nine reasons for "dimensional instability" of CNC machine tools

1. The size of the workpiece is accurate and the surface roughness is poor

Cause of failure: the cutters of the cutters are damaged and not sharp; the machine tools produce resonance, the placement is not smooth; the machine tools have crawl phenomenon; the processing technology is not good.

Solution: tool wear or damage is not sharp, the cutting knife or better to choose to knife; machine resonance or place is not stable, adjust the level, to lay the foundation, the fixation is stable; the reason of causing creeping for carriage rail wear machine, screw rolling beads worn or loose, the machine should pay attention to maintenance, on after work should clean the wire, and promptly add lubricant to reduce friction; choose the coolant for machining, can achieve the processing requirement in other circumstances, try to use high speed spindle.

2. A large taper phenomenon is produced by the workpiece

Fault: the placement machine level did not adjust well, have placed one high and one low, not smooth; turning axis, with relatively hard materials, cutting depth is deep, which make the knife phenomenon; the tailstock spindle is not concentric with the thimble.

The solution is to use leveling machine to adjust the levelness of machine tool, lay a solid foundation, fix the machine tool and improve its toughness, choose reasonable process and proper cutting feed to avoid tool force, and adjust tailstock.

3, the driver phase lamp is normal, while the processed workpiece is small when the size is large.

The cause of the failure is that the machine tool trailing board runs for a long time, resulting in the wear of the screw rod and the bearing. The repeated positioning accuracy of the tool carrier is biased in long term use, and the carriage can be accurately returned to the starting point at any time, but the size of the workpiece is still changing. This phenomenon is usually caused by the spindle. The high speed rotation of the spindle makes the bearing wear seriously and causes the change of the machining dimension. Metal processing WeChat, the content is good, it is worth paying attention to.

Solution: the indicator on the bottom of the turret, and edit a fixed cycle through the system, repetitive positioning accuracy check carriage, adjustment screw gap, replacement of bearings; with repeated positioning precision dial indicator check tool, adjust or replace the mechanical knife; 100 meter detection of workpiece is accurate after return to the program starting point. If you can, then repair the spindle, bearing replacement.

4. The difference between the size of the workpiece and the actual size is a few millimeters, or there is a great change in a certain axial direction.

Fault: fast positioning speed is too fast, drive and motor react; in the long-term mechanical friction loss after the carriage wire rod and bearing tight clamping; cutter replacement after the lock is too loose, not tight; editing program error, head and tail no echo or no cancellation of cutter compensation on the end of the electronic gear; the ratio or the step angle setting error.

Solution: fast positioning speed is too fast, it is appropriate to adjust the speed of the GO, the cutting speed and time and make the driver and motor to work normally in operation under the rated frequency; in the machine tool wear after carriage, screw crane bearing tight clamping, it must be re adjusted after repair; too loose check tool inversion time meets the knife the knife knife inside the worm to check whether the wear gap is too big, the installation is too loose; if the program is the cause, you must modify the program in accordance with the requirements of the drawings, workpiece machining process improvement, selection of reasonable selection, in accordance with the instructions of the instruction of writing correct programs; if found the size deviation is too large to check whether the system parameter setting is reasonable, especially electronic gear and the step angle and other parameters is broken, this phenomenon can be through a dial indicator To measure.

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

The cause of failure is: overlap of vibration frequency leads to resonance; processing technology, parameter setting is not reasonable, feed speed is too large, circular machining is out of step, looseness caused by screw rod clearance or excessive loss of wire rod, wear of synchronous belt.

Solution: find resonance components, change its frequency to avoid resonance; considering the machining process of the workpiece material, reasonable programming; for stepper motor, the processing rate of F can not be set too high; if the machine is installed firmly, placed smoothly, whether the carriage wear too tight or loose knife gap increases; replacement of synchronization belt. Metal processing WeChat, the content is good, it is worth paying attention to.

6. In batch production, occasional workpieces exceed the difference

Fault: must carefully check the fixture, and taking into account the operation of operators, reliability and clamping, clamping due to size change caused by the need to improve the tooling to make workers avoid negligence misjudging phenomenon; NC system may be affected by external power fluctuations or interference automatically after the interference pulse, resulting in the driving pulse drive motor accept excess away or drive to walk less phenomenon,

Solution: to understand and grasp the rules and try to use some anti-jamming measures, such as: power cable and signal line weak signal strong electric field interference isolation, adding anti interference absorption capacitance and use the shielded wire isolation, check the ground is firmly connected to ground contact, recently, to take all measures to avoid anti jamming system interference.

7. There is a change in the processing of a working procedure of the work piece, and the exact size of the other processes.

The cause of the failure: whether the parameters of the program are reasonable, or not in the predetermined trajectory, whether the programming format is in accordance with the requirements of the specification.

Solution: the screw program section is disorderly, the pitch is wrong, it is immediately associated with the processing thread peripheral configuration (encoder) and the objective factors of the function.

8. There is an increasing or decreasing phenomenon in each process of the work piece.

The cause of the failure: the error of program writing, the unreasonable setting of the system parameters, the improper configuration and the regular periodic change of the mechanical transmission parts

Solution: check whether the program uses the instruction execution according to the requirement of trajectory specification, judging by the call dial indicator, dial indicator positioned at the starting point of the program after the end of the program will return to the starting point position, then repeat even observe the results, grasp the rules; check the system parameters are reasonable or considered changes the machine configuration in connection; coupled calculation of single parameter calculation is in accordance with the requirements, the pulse equivalent is accurate; check the machine transmission part is not broken, the gear coupling is uniform, the existence of periodic inspection, fault phenomena, if there is to check the key part and give out.

9. The size changes caused by the system are unstable

Fault: system parameter setting is not reasonable; the working voltage is not stable; systems affected by external disturbances, causing the system out of step; have added capacitance, but the impedance between the system and the driver does not match, resulting in loss of useful signal; signal transmission between the system and the driver is not normal; the system damage or internal fault.

Solution: speed, acceleration time is too large, the spindle speed, cutting speed is reasonable, whether the operator parameters modification leads to system performance change with voltage; equipment; grounding wire and determine the reliable connection in the drive pulse output contacts with interference absorbing capacitor; capacitance models appropriate; signal inspection system with the drive cable is shielded, the connection is reliable, the signal is lost or increasing the pulse check system; send factory repair or replace the motherboard.