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With the continuous development of the modern machinery industry, CNC machine tools are widely used in various industries due to their safety, high precision, and unique flexible technology. However, whether it is a simple CNC machine tool or a full-function CNC machine tool , Or machining centers, there are more or less phenomena such as lost steps on the machine tool and unstable dimensions during processing, which confuses the operator. Especially in simple CNC machine tools, the problem is more prominent. So what are the reasons for the "dimension instability" of CNC machine tools? Today, IWC will tell you that the main reasons for the "dimension instability" of CNC machine tools are mainly as follows:
1. The size of the workpiece is accurate, and the surface finish is poor
The cause of the failure: the tool tip is damaged and not sharp; the machine tool resonates and the placement is not stable; the machine tool has crawling phenomenon; the processing technology is not good. Solution: After the tool is worn or damaged, it is not sharp, then re-sharpening or selecting a better tool to re-calibrate the tool; the machine has resonance or is not stable, adjust the level, lay the foundation, and fix it smoothly; the cause of mechanical crawling is drag The plate guide rail is severely worn, the ball screw is worn or loose, the machine tool should be maintained, and the iron wire should be cleaned after get off work, and lubricated in time to reduce friction; choose a coolant suitable for workpiece processing, if it can meet the processing requirements of other processes In this case, try to choose a higher spindle speed.
2. The phenomenon of taper and small head on the workpiece
The cause of the failure: the level of the machine is not adjusted properly, one high and one low, resulting in uneven placement; when turning the long axis, the contribution material is harder, and the tool eats deeper, causing the tool to give way; the tailstock thimble is not concentric with the spindle. Solution: Use a level to adjust the level of the machine tool, lay a solid foundation, and fix the machine tool to improve its toughness; choose a reasonable process and appropriate cutting feed to avoid the tool being forced to give it to the knife; adjust the tailstock.
3. The phase light of the driver is normal, but the size of the processed workpiece is sometimes large and sometimes small
The cause of the failure: long-term high-speed operation of the machine tool carriage causes the screw and bearing to wear; the repeated positioning accuracy of the tool post produces deviations during long-term use; the carriage can accurately return to the starting point of processing every time, but the size of the workpiece is still changing. This phenomenon is generally caused by the main shaft. The high-speed rotation of the main shaft causes serious wear of the bearing, leading to changes in machining dimensions. Metal processing WeChat, the content is good and worthy of attention. Solution: Use a dial indicator to lean against the bottom of the tool post, and at the same time edit a canned cycle program through the system to check the repeat positioning accuracy of the carriage, adjust the screw gap, and replace the bearing; use the dial indicator to check the repeat positioning accuracy of the tool post, Adjust the machine or replace the tool post; use the 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 size of the workpiece is different from the actual size by a few millimeters, or a certain axial direction is greatly changed
The cause of the failure: the rapid positioning speed is too fast, the drive and the motor can't react; the mechanical carriage screw and the bearing are too tight after long-term friction loss; the tool post is too loose after tool change, and the lock is not tight; the edited program Error, the head and tail do not respond or the tool compensation is ended; the electronic gear ratio or step angle of the system is set incorrectly. Solution: If the rapid positioning speed is too fast, adjust the GO speed appropriately, and the cutting acceleration and deceleration and time will make the drive and motor work normally at the rated operating frequency; after the machine tool wears out, the carriage, the screw rod and the bearing are too tight If it is stuck, it must be re-adjusted and repaired; if the tool post is too loose after tool change, check whether the reversal time of the tool post is satisfied, check whether the worm gear inside the tool post 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 in accordance with the requirements of the workpiece drawing, a reasonable processing technology is selected, and the correct program is written in accordance with the instructions of the manual; if the size deviation is found to be too large, check whether the system parameters are set properly, especially the electronic gear and Whether the step angle and other parameters are damaged, this phenomenon can be measured by using a dial indicator.
5. The effect of machining arc is not ideal, and the size is not in place
The cause of the failure: the overlap of the vibration frequency causes resonance; the processing technology; the parameter setting is unreasonable, the feed speed is too large, and the arc processing is out of step; the looseness caused by the screw rod gap or the out of step caused by the screw rod is too tight; the timing belt Wear. Solution: Find out the resonant parts, change their frequency to avoid resonance; consider the processing technology of the workpiece material, and make a reasonable program; for the stepper motor, the processing rate F cannot be set too large; whether the machine tool is installed firmly, placed smoothly, and dragged Whether the plate is too tight after being worn, the gap is increased or the tool holder is loose, etc.; replace the timing belt. Metal processing WeChat, the content is good and worthy of attention.
6. In the mass production, the workpiece is out of tolerance occasionally
The cause of the failure: the tooling 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 size change caused by the clamping, the tooling must be improved to avoid the misjudgment by the worker due to human negligence; the CNC system may When the external power supply fluctuates or is disturbed, it will automatically generate interference pulses, which are transmitted to the drive and cause the drive to receive excess pulses. The drive motor takes away or runs less. Solution: Understand and master the law, try to use some anti-interference measures, such as: The strong electric cable interfered by the strong electric field is isolated from the signal wire of the weak electric signal. Add anti-interference absorbing capacitance and use shielded wire to isolate. In addition, check whether the ground wire is firmly connected and the grounding contact is nearest. Take all anti-interference measures to avoid system interference .
7. There is a change in the processing of a certain process of the workpiece, and the size of the other processes is accurate
Cause of failure: Whether the program parameters of the program segment are reasonable, whether they are in the predetermined trajectory, whether the programming format meets the requirements of the manual. Solution: When the thread program segment has messy teeth and the thread pitch is incorrect, it will immediately associate with the peripheral configuration (code器) and the objective factors of the function.