Causes of problems with CNC machining accuracy

1. System-induced dimensional changes are unstable

Cause of fault: Unreasonable system parameters setting; unstable working voltage; system is disturbed by external interference, causing the system to lose steps; capacitance has been added, but the impedance between the system and the driver does not match, resulting in the loss of useful signals; signal between the system and the driver Unusual transmission; system is damaged or internal malfunction.

Solution: Speed, acceleration time is too large, spindle speed, cutting speed is reasonable, whether the operator's parameters modify it leads to changes in system performance; install voltage stabilization equipment; grounding wire and confirm that it has been reliable to connect, and the driver pulse output contact point Add anti-interference absorption 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, check whether the system pulse signal is lost or increased; send it to the factory for repair or replacement of the motherboard.

2. The workpiece produces a taper head

Cause of the fault: The level of the machine tool is not adjusted properly, one high and one low, resulting in unstable placement; when turning the long shaft, the contribution material is relatively hard, and the tool is deeper, causing the phenomenon of giving way; the tailstock thrust is different from the spindle.

Solution: Use a level to adjust the level of the machine tool, lay a solid foundation, and fix the machine tool well to improve its toughness; choose a reasonable process and appropriate cutting feed to avoid the tool being subjected to stress; adjust the tail seat.

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

Cause of the fault: The machine tool drag plate is running at high speed for a long time, resulting in wear of screw rods and bearings; the repeat positioning accuracy of the tool holder deviates during long-term use; the drag plate can accurately return to the starting point of processing every time, but the size of the processing workpiece still changes. This phenomenon is generally caused by the spindle, which causes severe wear of the bearings and lead to changes in the processing size.

Solution: Use a dial meter to lean against the bottom of the tool holder, and at the same time, edit a fixed cycle program through the system, check the repeat positioning accuracy of the drag plate, adjust the screw gap, and replace the bearing; use a dial meter to check the repeated positioning accuracy of the tool holder, Adjust the machinery or replace the tool holder; use a dial meter to check whether the workpiece is accurately returned to the starting point of the program after processing it. If possible, repair the spindle and replace the bearing.

4. The workpiece size is several millimeters different from the actual size, or there is a great change in a certain axial direction

Cause of the fault: The speed of fast positioning is too fast, and the drive and motor cannot react; the mechanical drag screw and bearing are too tight and stuck after long-term friction loss; the tool holder is too loose after changing the tool, and the lock is not tight; editing program Error, the head and tail do not echo or the knife repair is terminated; the system's electronic gear ratio or step angle settings are wrong.

Solution: if the fast positioning speed is too fast, adjust the speed of the GO appropriately, and the cutting speed and time will make the driver and motor work normally at the rated operating frequency; after the machine tool wear occurs, the drag plate and screw crane bearings are too tight. If the tool holder is stuck, it must be adjusted and repaired; if the tool holder is too loose after changing the tool holder, check whether the reversal time of the tool holder is satisfied, check whether the turbo worm inside the tool holder is worn, whether the gap is too large, whether the installation is too loose, etc. If it is a program If the cause is caused, the program must be modified, improved according to the requirements of the workpiece drawing, selected a reasonable processing technology, and wrote the correct program in accordance with the instructions in the instruction manual; if the dimensional deviation is found to be too large, check whether the system parameters are set reasonably, especially the electronic gears and Whether parameters such as step angle are damaged, this phenomenon can be measured by typing a dial table.

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

Cause of fault: overlapping vibration frequency leads to resonance; processing technology; unreasonable parameter settings, excessive feed speed, resulting in loss of arc processing; looseness caused by large screw gap or loss of step caused by excessive tight screw; synchronous belt Wear.

Solution: Find out the components that generate resonance, change their frequency, and avoid resonance; consider the processing technology of workpiece materials and prepare the program reasonably; for stepper motors, the processing rate F must not be set too large; whether the machine tool is installed firmly and placed smoothly, drag Whether the plate is too tight after wear, the gap is increased or the tool holder is loose, etc.; replace the synchronization belt.

6. During mass production, excessive workpiece errors occur occasionally

Cause of the fault: The tooling and fixtures must be carefully checked, and the operator's operating method and the reliability of the clamping are taken into account. Due to the dimensional changes caused by clamping, the tooling must be improved so that workers can try their best to avoid human negligence and misjudgment; the CNC system may When fluctuations or interference from external power sources are caused, interference pulses are automatically generated, which will cause the driver to accept unnecessary pulses and drive the motor to take away or avoid running.

Solution: Understand and master the rules, try to adopt some anti-interference measures, such as: strong electric cables with strong electric field interference are isolated from the signal lines of weak current signals, add anti-interference absorption capacitors and use shielded wires to isolate them, and check the ground line Whether the connection is firm, the grounding contact is closest, and all anti-interference measures should be taken to avoid interference from the system.

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

Cause of the fault: whether the parameters of the program block are reasonable, whether they are within the predetermined track, and whether the programming format meets the requirements of the manual.

Solution: If there are messy teeth in the thread block and the pitch is incorrect, then the peripheral configuration (encoder) of the thread processing and the objective factors of this function will be immediately associated with.

8. Each process of the workpiece has an increase or decrease

Cause of failure: program writing errors; system parameter settings are unreasonable; configuration settings are improper; mechanical transmission components have regular periodic changes.

Solution: Check whether the instructions used by the program are executed according to the requirements specified in the instructions. You can judge by typing the dial table, position the dial table at the starting point of the program, and let the drag board return to the starting point after the program is finished, and then execute it repeatedly. Even if you observe the results, master the rules; check whether the system parameters are set reasonably or are considered to be changed; whether the relevant machine tool configuration meets the requirements on the connection calculation coupling parameters, and whether the pulse equivalent is accurate; check whether the transmission part of the machine tool is damaged and the gears are Whether the coupling is uniform, check whether there are periodic and regular faults. If so, check its key parts and exclude them.

9. Accurate workpiece size and poor surface finish

Cause of the fault: the tool tip is damaged and not sharp; the machine tool resonates and the placement is unstable; the machine tool has crawling phenomenon; the processing technology is not good.

Solution: If the tool is not sharp after being worn or damaged, then resharpen the knife or choose a better tool to re-fit the knife; the machine tool resonates or is unstable, adjusts the level, lays the foundation, and fixes it smoothly; the reason for the machine crawling is dragging The plate guide rail is severely worn, the lead screw ball is worn or loose, and the machine tool should pay attention to maintenance. After commuting, the wire should be cleaned and lubricated oil should be added in time to reduce friction; choose coolant suitable for workpiece processing to meet the processing requirements of other processes. In the case, try to choose a higher spindle speed.