What are the reasons for the unstable size of CNC machine tools?

With the continuous development of the modern machinery industry, CNC machine tools are more and more widely used due to its unique flexible technology characteristics, and its role is also becoming more and more significant, but whether it is a simple CNC machine tool or a full-function CNC machine. Machine tools, or machining centers, have more or less phenomena such as machine lost steps and dimensional instability during machining, which is confusing for operators. Especially in the process of simple CNC lathe processing, the problem is more prominent.

1. The workpiece size is accurate and the surface finish is poor. The cause of the failure is that the tool tip is damaged and not sharp; the machine tool generates resonance and the placement is not stable; the machine tool has crawling phenomenon; the processing technology is not good.

Solution: If the tool is not sharp after being worn or damaged, re-grind the knife or choose a better tool to re-align the tool; the machine will generate resonance or place it is not stable, adjust the level, lay the foundation, and fix it smoothly; the reason for the mechanical creep is drag The plate guide rail is very worn, the lead Screw ball is worn or loose, the machine tool should pay attention to maintenance, the wire should be cleaned after work, and the lubricating oil should be added in time to reduce the friction; the coolant suitable for the workpiece processing can be selected to meet the processing requirements of other processes. In the case, try to use a higher spindle speed.

2, the workpiece produces taper size head phenomenon. The cause of the failure: the level of the machine tool is not adjusted well, one high and one low, resulting in uneven placement; when turning the long axis, the contribution material is relatively hard, the tool is relatively deep, causing the knife phenomenon; The tailstock thimble is not concentric with the spindle.

Solution: Use the level to adjust the level of the machine, lay a solid foundation, fix the machine to improve its toughness; choose a reasonable process and appropriate cutting feed to avoid the tool force to make the knife; adjust the tailstock.

3. The driver phase lamp is normal, and the size of the processed workpiece is large and small. The cause of the failure is that the machine tool carriage is running at a high speed for a long time, resulting in wear of the screw and the bearing; the repeated positioning accuracy of the tool holder is deviated in the long-term use; The number of times can be accurately returned to the starting point of the machining, 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. Metal processing WeChat, the content is good, it is worthy of attention.

Solution: 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, replace the bearing; check the repeat positioning accuracy of the tool holder with the dial indicator. Adjust the machine or replace the tool holder; use a dial indicator to check whether the workpiece is accurately returned to the starting point of the program. If possible, repair the spindle and replace the bearing.

4. The workpiece size differs from the actual size by a few millimeters, or a certain axial direction changes greatly. Cause: The speed of rapid positioning is too fast, and the drive and motor do not react; after the long-term friction loss, the mechanical lead screw and bearing The card is too tight; the tool holder is too loose after the tool change, the lock is not tight; the editing program is wrong, the head and tail are not echoed or the tool is not canceled; the system's electronic gear ratio or step angle setting is wrong.

Solution: If the rapid positioning speed is too fast, the speed of the GO will be adjusted appropriately. The cutting acceleration and deceleration and time will make the drive and the motor work normally at the rated operating frequency. After the machine wear occurs, the carriage and the screw crane bearing are too tight. If the card is dead, it must be re-adjusted. If the tool holder is too loose after the tool change, check whether the tool holder reversal time is satisfied, check whether the worm gear inside the tool holder is worn, whether the clearance is too large, whether the installation is too loose, etc.; If the cause is caused, 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; if it is found that the dimensional deviation is too large, check whether the system parameters are set properly, especially the electronic gear and Whether the parameters such as the step angle are destroyed, this phenomenon can be measured by dialing a dial indicator.

5, the processing arc effect is not ideal, the size is not in place. The cause of the failure: the overlap of the vibration frequency leads to resonance; the processing technology; the parameter setting is unreasonable, the feed speed is too large, the arc machining is out of step; the screw gap is large and loose Or out of step caused by over-tightening of the screw; the belt is worn.

Solution: Find the parts that generate resonance, change their frequency, avoid resonance; consider the processing technology of the workpiece material, and make the program reasonably; for stepper motor, the processing rate F can't be set too large; whether the machine is installed firmly, placed smoothly, drag Whether the board is too tight after wear, the gap is increased or the tool holder is loose; etc.; replace the timing belt. Metal processing WeChat, the content is good, it is worthy of attention.

6. In batch production, occasionally the workpiece is out of tolerance. Cause: The fixture must be carefully checked, and the operator's operation method and the reliability of the clamping must be taken into account. Due to the dimensional changes caused by the clamping, the tooling must be improved to make the worker try to Avoid human error and make false judgments; the CNC 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 take away or less.

Solution: Understand the rules, try to use some anti-interference measures, such as: strong electric cable interference strong signal and weak electric signal signal line isolation, add anti-interference absorption capacitor and shielded line isolation, in addition, check the ground Whether the connection is firm, the grounding contact is closest, and all anti-interference measures are taken to avoid system interference.

7. There is a change in the processing of one part of the workpiece, and the other process steps are accurate. Cause: The parameters of the program are reasonable, whether it is within the predetermined track, whether the programming format meets the requirements of the manual. Solution: There is chaos in the thread block. If the tooth has a wrong pitch, it immediately associates with the peripheral configuration (encoder) of the machined thread and the objective factors of the function.

8. Each process of the workpiece has an increasing or decreasing phenomenon. The cause of the failure: programming error; unreasonable system parameter setting; improper configuration setting; mechanical transmission components have regular periodic changes. Solution: Check whether the instructions used by the program are correct. According to the required trajectory specified in the manual, it can be judged by dialing the dial indicator. Position the dial indicator at the starting point of the program to let the board return to the starting position after the end of the program, and then repeat the execution even if the result is observed, master the law; Check whether the system parameters are set properly or are considered to be changed; the relevant machine configuration is calculated on the connection calculation coupling parameters to meet the requirements, whether the pulse equivalent is accurate; check whether the transmission part of the machine tool is damaged, the gear coupling is uniform, check whether there is periodicity Regular phenomenon of failure, if any, check its key parts and give them exclusion.

9, the dimensional change caused by the system is unstable. Cause: The system parameter setting is unreasonable; the working voltage is unstable; the system is subject to external interference, causing the system to lose synchronization; the capacitor is added, but the impedance between the system and the driver does not match, resulting in useful Loss of signal; signal transmission between the system and the drive is not normal; system damage or internal failure.

Solution: speed, acceleration time is too large, spindle speed, cutting speed is reasonable, whether the operator's parameter modification causes system performance change; install voltage regulator equipment; ground wire and determine that the connection is reliable, the driver pulse output contact Add anti-interference absorption capacitor; select the appropriate capacitor model; check whether the signal connection between the system and the driver is shielded, whether the connection is reliable, check whether the system pulse signal is lost or increased; send the factory for repair or replace the motherboard.

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