Analysis Of 9 Reasons For The Instability Of Workpieces Processed By CNC Machine Tools

1. The size of the workpiece is accurate and the surface finish is poor
Reasons: The tool tip is damaged and not sharp; the machine tool resonates and the placement is not stable; the machine tool has a creeping phenomenon; the processing technology is not good.
Solution: After the tool is worn or damaged, it is not sharp, then re-sharpen the tool or select a better tool to re-calibrate the tool; if the machine tool resonates or the placement is unstable, adjust the level, lay the foundation, and fix it smoothly; the reason for the machine creeping is drag. The plate guide rails are severely worn, and the screw balls are worn or loose. The machine tool should pay attention to maintenance. After going to get off work, the wire should be cleaned and lubricating oil should be added in time to reduce conflicts; select the coolant suitable for workpiece processing, and meet the processing requirements of other processes. In this case, try to use a higher spindle speed.


2. The workpiece has the phenomenon of taper size head
Reason: The level of the machine tool is not adjusted properly, one is high and the other is low, and the placement is not stable; when turning the long axis, the dedication material is relatively hard, and the tool eats the knife deeply, resulting in the phenomenon of letting the knife; the tailstock thimble and the spindle are not concentric.
Solution: Use a spirit level to adjust the level of the machine tool, lay a solid foundation, and fix the machine tool to improve its durability; choose a reasonable process and appropriate cutting feed to prevent the tool from being stressed and let the tool; adjust the tailstock.


3. The phase light of the driver is normal, but the size of the processed workpiece is large and small.
Reasons: The machine tool carriage runs at high speed for a long time, resulting in wear of the screw and bearing; the repeated positioning accuracy of the tool holder is inaccurate in long-term use; the carriage can accurately return to the starting point of processing every time, but the size of the workpiece is still changed. This phenomenon is generally caused by the main shaft, and the high-speed rolling of the main shaft causes serious wear of the bearing, resulting in changes in the processing size. Metal processing WeChat, the content is good, it is worth paying attention to.
Solution: use the dial indicator to lean against the bottom of the tool holder, correct a fixed cycle program through the system, check the repeatability of the carriage, adjust the screw gap, and replace the bearing; use the dial indicator to check the repeatability of the tool holder, Adjust the machine or replace the tool holder; use the dial indicator to check whether the workpiece is accurately returned to the starting point of the program after processing the workpiece. 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 there is a great change in a certain axis
Reason: The speed of fast positioning is too fast, and the drive and motor cannot respond; after a long-term conflict and wear, the mechanical drag plate screw and bearing are too tight and stuck; the tool holder is too loose after changing the tool, and the locking is not tight; the correction procedure If it is wrong, the head and tail do not respond or cancel the tool compensation; the electronic gear ratio or step angle of the system is wrongly set.
Solution: If the fast positioning speed is too fast, adjust the speed of the GO appropriately, and the cutting acceleration and deceleration speed and time make the drive and motor work normally under the extra operating frequency; after the machine tool wears, the carriage and screw crane bearings are too tight If it is stuck, it is necessary to readjust and correct it; if the tool holder is too loose after changing the tool, check whether the reversal time of the tool holder is satisfactory, check whether the turbine worm inside the tool holder is worn, whether the gap is too large, whether the device is too loose, etc.; if it is If it is caused by the program, it is necessary to revise the program, improve it 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; Whether the parameters such as gear and step angle are damaged, this phenomenon can be measured by playing the dial indicator.


5. The effect of the processing arc is not ideal, and the scale is not in place
Reasons: Overlapping of vibration frequencies causes resonance; processing technology; unreasonable parameter settings, excessive feed speed, and out-of-step arc processing; looseness caused by large screw gap or out-of-step caused by over-tightening of the screw; synchronous belt wear .
Solution: find out the parts that have resonance, change their frequency to prevent resonance; consider the processing technology of the workpiece material, and compile the program reasonably; for the stepping motor, the processing rate F should not be set too large; whether the machine tool is firmly installed, placed smoothly, and dragged Whether the plate is too tight after wear, the gap increases or the tool holder is loose, etc.; replace the timing belt. Metal processing WeChat, the content is good, it is worth paying attention to.


6. In mass production, the workpiece is occasionally out of tolerance
Reason: It is necessary to carefully check the tooling fixture, and considering the operator’s operation method and the reliability of the clamping, it is necessary to improve the tooling due to the size change caused by the clamping so that workers can try to prevent misjudgment caused by human negligence; CNC system It may be fluctuated by the external power supply or actively generate disturbance pulses after being disturbed, which will be transmitted to the drive, causing the drive to accept the remaining pulses and drive the motor to take away or lessen the phenomenon.
Solution: Understand and grasp its rules, try to use some anti-interference methods, such as: strong electric cable interference with strong electric field and weak electric signal signal line block, add anti-interference absorption capacitor and use shielded wire to block, in addition, check the ground wire Whether the connection is solid, the ground contact is close, and all anti-interference measures are taken to prevent the system from being disturbed.


7. The processing of a certain process of the workpiece has been changed, and the scale of other processes is accurate
Reason: Whether the parameters of this block program are reasonable, whether they are within the reserved track, and whether the programming format meets the requirements of the manual
Solution: There are random teeth in the thread program segment, and the pitch is wrong, then immediately think of the peripheral equipment (encoder) for processing the thread and the objective factors of this function.


8. Each process of the workpiece has the phenomenon of increasing or decreasing
Reasons: programming errors; unreasonable system parameter settings; improper equipment settings; mechanical transmission components have regular and periodic changes
Solution: Check whether the instructions used by the program are executed according to the requirements specified in the manual. It can be judged by playing the dial indicator. Position the dial indicator at the starting point of the program and let the carriage return to the starting position after the program is completed, and then repeat the execution. Even if you investigate the results and grasp the rules; check whether the system parameters are set reasonably or are considered to be changed; whether the relevant machine tool equipment meets the requirements in the connection calculation coupling parameters, and whether the pulse equivalent is accurate; check whether the transmission part of the machine tool is damaged or not, the gears Check whether the coupling is uniform, check whether there are periodic and regular faults, and if so, check the key parts and remove them.


9. The scale changes caused by the system are unstable
Reason: unreasonable setting of system parameters; unstable operating voltage; system is disturbed by external, causing the system to lose synchronization; capacitors have been added, but the impedance between the system and the driver does not match, resulting in loss of useful signals; signal transmission between the system and the driver Abnormal; system damage or internal fault.
Solution: whether the speed, acceleration time is too large, the spindle speed and cutting speed are reasonable, whether the operator’s parameter correction leads to changes in system performance; install voltage stabilizer equipment; make sure that the ground wire is firmly connected, and the pulse output contact of the drive Add anti-interference absorbing capacitors; select the appropriate capacitor model; check whether the signal connection line between the system and the driver is shielded, whether the connection is reliable, and check whether the system pulse signal is lost or added; send it to the factory for repair or replacement of the motherboard.

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