The reason for the mechanical creep is that the carriage guide is worn out and the screw balls are worn or loose. The machine tool should pay attention to maintenance. After work, clean the wire and add lubricating oil in time to reduce friction. The problem of unstable size of CNC machining can be said to be very painful. Xiaobian has summarized ten common situations and corresponding solutions for you.
1, the workpiece size is accurate, the surface finish is poor
cause of issue:
1) The tool tip is damaged and not sharp.
2) The machine tool generates resonance and the placement is not stable.
3) The machine has a crawling phenomenon.
4) The processing technology is not good.
Solution (with comparison):
1) If the tool is not sharp after being worn or damaged, re-grind the knife or select a better tool to re-align the tool.
2) The machine tool generates resonance or is not placed smoothly, adjusts the level, lays the foundation, and fixes it smoothly.
3) The reason why the machine generates crawling is that the carriage guide rail is worn hard, and the screw ball is worn or loose. The machine tool should pay attention to maintenance. After work, clean the wire and add lubricating oil in time to reduce friction.
4) Select the coolant suitable for the machining of the workpiece; if it can meet the processing requirements of other processes, try to use a higher spindle speed.
2, the workpiece produces a taper size head phenomenon
cause of issue:
1) The level of machine tool placement is not adjusted well, one high and one low, resulting in uneven placement.
2) When turning the long axis, the workpiece material is relatively hard, and the tool is relatively deep, causing the knife phenomenon.
3) The tailstock thimble is not concentric with the spindle.
solution
1) Use the level to adjust the level of the machine, lay a solid foundation, and fix the machine to improve its toughness.
2) Choose a reasonable process and proper cutting feed to avoid the tool being forced to make the knife.
3) Adjust the tailstock.
3. The driver phase lamp is normal, but the workpiece size is different.
cause of issue
1) The long-term high-speed operation of the machine tool carriage causes the screw and bearing to wear.
2) The repeat positioning accuracy of the tool holder is deviated in long-term use.
3) The carriage can return to the machining starting point accurately every time, but the size of the machined 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 (with comparison)
1) 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, and replace the bearing.
2) Check the repeatability of the tool holder with a dial indicator, adjust the machine or replace the tool holder.
3) Use a dial indicator to check whether the workpiece can be accurately returned to the starting point of the program after machining; if possible, repair the spindle and replace the bearing.
4, the workpiece size changes, or axial changes
cause of issue
1) The speed of rapid positioning is too fast, and the reaction between the drive and the motor does not occur.
2) After long-term friction and wear, the mechanical lead screw and the bearing are too tightly stuck.
3) The knife holder is too loose to lock after the tool change.
4) The edited program is wrong, and the head and tail do not respond or end without canceling the tool.
5) The electronic gear ratio or step angle of the system is set incorrectly.
Solution (with comparison)
1) If the rapid positioning speed is too fast, adjust the speed of G0, cutting acceleration and deceleration and time to make the drive and motor operate normally at the rated operating frequency.
2) After the machine wear occurs, the carriage, the screw and the bearing are too tightly stuck, and the repair must be re-adjusted.
3) If the tool holder is too loose after the tool change, check whether the tool holder reversal time is satisfied, check whether the turbine vortex inside the tool holder is worn, whether the gap is too large, and whether the installation is too loose.
4) If it is caused by the program, 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.
5) If the dimensional deviation is too large, check whether the system parameters are set properly, especially if the parameters such as the electronic gear ratio and the step angle are damaged. This phenomenon can be measured by playing a hundred tables.
5, the processing arc effect is not ideal, the size is not in place
cause of issue
1) The overlap of the vibration frequencies causes resonance.
2) Processing technology.
3) The parameter setting is unreasonable, the feed rate is too large, and the arc machining is out of step.
4) Looseness caused by large screw clearance or out of step caused by excessive screw tightening.
5) The timing belt is worn.
solution
1) Find the part that produces resonance, change its frequency, and avoid resonance.
2) Consider the processing technology of the workpiece material and make a reasonable program.
3) For stepper motors, the machining rate F cannot be set too large.
4) Whether the machine tool is installed firmly, placed stably, the pallet is too tight after wear, the gap is increased or the tool holder is loose.
5) Replace the timing belt.
6, in the mass production, occasionally the workpiece is out of tolerance
1) Occasionally, there is a change in the size of the mass production, and then the processing is resumed without modifying any parameters.
2) Occasionally, a size is inaccurate in mass production, and then the processing size is still unsatisfactory, and the tool is re-aligned and accurate.
solution
1) The fixture must be carefully inspected, taking into account the operator's method of operation, and the reliability of the clamping; due to dimensional changes caused by the clamping, the tooling must be improved to minimize the misjudgment of the worker.
2) The numerical control system may be subject to fluctuations or interference from external power sources, and automatically generate interference pulses, which are transmitted to the drive to cause the drive to accept excess pulse-driven motor to walk more or less; understand the rules and try to use some anti-interference measures. For example, a strong electric cable with strong electric field interference is isolated from a signal line of a weak electric signal, and an anti-interference absorption capacitor is added and isolated by a shielded wire. In addition, check whether the ground wire is firmly connected, the grounding contact is the closest, and take all anti-interference measures to avoid system interference.
7. Each process of the workpiece has an increasing or decreasing phenomenon.
cause of issue
1) Program writing error.
2) The system parameter setting is unreasonable.
3) Improper configuration settings.
4) The mechanical transmission components have regular periodic changes.
solution
1) 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 hundred tables. Position the dial indicator at the starting point of the program to let the board return to the starting position after the program ends, and then repeat the execution. Observe the results and master the rules.
2) Check if the system parameters are set properly or artificially changed.
3) Whether the calculation of the relevant machine configuration on the connection calculation coupling parameters meets the requirements, and whether the pulse equivalent is accurate.
4) Check whether the transmission part of the machine tool is damaged or not, and whether the gear coupling is uniform, check whether there is periodicity or regular failure. If there are, check the key parts and give them exclusion.
8, the workpiece size and actual size are only a few differences
cause of issue
1) The machine tool is rubbed and worn during long-term use. As the gap of the screw increases, the backlash of the machine tool is too large, so that the size of the machining process floats, so the error of the workpiece always changes within the gap.
2) The tool used for machining the workpiece is incorrectly selected, vulnerable, and the tool is not clamped or not tight.
3) The process selects a reasonable spindle speed, cutting feed rate and cutting amount according to the workpiece material.
4) It is related to the balance and stability of the machine tool placement.
5) When the numerical control system generates out-of-step or drive selection, the power is insufficient, and the torque is small.
6) Whether the lock is locked after the tool holder is changed.
7) Whether there is a phenomenon that the main shaft has a beating motion and a poor coaxiality of the tailstock.
8) In some special machining situations, the backlash cannot be replenished, resulting in a deviation in the machining.
Solution (with comparison)
1) After the machine tool wear screw gap becomes larger, reduce the gap by adjusting the screw nut and tightening the middle carriage line, or obtain the gap value by the dialing table (the general clearance is within 0.15 mm), which can be replenished into the computer. The gap compensation function of the computer is used to replace the gap so that the workpiece size meets the requirements.
2) Since the tool material changes the size of the machined workpiece, the tool is selected reasonably according to the requirements, and the tool angle and tooling fixture are reasonably selected according to the process requirements of the workpiece due to improper tool clamping.
3) When it is suspected that it is a process problem in processing, according to the nature of the material, the machining process is reasonably programmed to select the appropriate spindle speed, cutting feed rate and cutting amount.
4) Due to the resonance of the machine tool, the machine tool is placed stably, the level is adjusted, the foundation is laid down if necessary, and the installation is stable.
5) The dimensional change produced by the CNC system, first determine whether the program is compiled according to the size requirements of the paper, and then check whether the set parameters are reasonable according to the selected configuration (such as: G0 fast positioning speed and acceleration/deceleration time constant during cutting, etc.). Whether someone deliberately changes, and secondly, consider whether the selected driver power is reasonable. By judging the phase lamp, observe whether the pulse sent by the computer is out of step.
6) Check that the tool holder has a reversal time after the tool change. Do you have enough time for the tool holder to lock, check the positioning of the tool holder and loosen the locking screws.
7) Check whether the coaxiality of the main shaft and the tailstock are bouncing or striking.
8) Use programming techniques to eliminate gaps.
9, the dimensional change caused by the system is unstable
cause of issue
1) System parameter settings are unreasonable.
2) The operating voltage is unstable.
3) The system is subject to external interference, causing the system to lose synchronization.
4) The capacitor has been added, but the impedance between the system and the driver does not match, resulting in loss of useful signal.
5) The signal transmission between the system and the drive is incorrect.
6) System damage or internal failure.
Solution (with comparison)
1) Whether the speed is fast, the acceleration time is too large, the spindle speed, the cutting speed is reasonable, and whether the system performance changes due to the operator's parameter modification.
2) Install voltage regulator equipment.
3) Grounding wire and make sure that it is connected reliably. Add anti-interference absorption capacitor at the pulse output contact of the driver. Under normal circumstances, the interference of the inverter is large. Please judge with load, because the larger the load will be The larger the load current of the inverter, the greater the interference.
4) Select the appropriate capacitor model.
5) Check whether the signal connection between the system and the driver is shielded, whether the connection is reliable, and check whether the pulse signal of the system is lost or increased.
6) Send the factory for repair or replace the motherboard.
10. Mechanically unstable processing dimensions
cause of issue
1) Is the stepper motor damping plate too tight or too loose?
2) The insulation of the motor plug is reduced and the motor is damaged.
3) The size of the machined workpiece is not properly clamped.
4) The workpiece has an ellipse.
5) The screw backlash is too large.
6) The mechanical screw is installed too tightly.
Solution (with comparison)
1) Adjust the damping disc so that the motor is in a non-resonant state.
2) Replace the motor plug, protect it, or replace the motor.
3) Check if the feed amount is too large or too fast, and check the workpiece clamping. The chuck should not extend too long to avoid the knife.
4) Check the spindle's runout, overhaul the spindle, and replace the bearing.
5) Check the backlash of the screw by dialing the dial indicator, whether the gap has been filled in from the system, and whether the gap is too large after the filling.
6) Check if the screw is crawling and there is a slow response.
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