Analysis of Nine Causes of Unstable Workpieces on CNC Machine Tools

1, the workpiece size is accurate, poor surface finish

The cause of the defect is that the tool tip is damaged and not sharp; the machine tool is in resonance and the placement is not smooth; the machine tool is defective; the machining process is poor.

Solution: If the tool wears or is not sharp after being damaged, re-sharpening or picking a better tool to re-set the knife; the machine tool will resonate or be placed unevenly, adjust the level, lay the bottom, stable and stable; Friction plate guide rails are fierce, screw ball wear or loose, machine tools should pay attention to maintenance, should clean the wire after work, and add lubricants in a timely manner to reduce the conflict; select the right workpiece processing coolant, can reach other processes processing requirements In the case, try to use a higher spindle speed.

2, the workpiece occurs taper head phenomenon

The cause of the problem is that the level of the machine tool has not been adjusted properly. A high and low level has caused the placement to be unstable. When turning the long axis, the dedication information is relatively hard. The tool has a relatively deep knife to form a knife; the tailstock ejector pin is different from the spindle.

Solution: Use the level meter to adjust the level of the machine, lay a solid foundation, and fix the machine to improve its resistance; select a reasonable process and the appropriate cutting feed to prevent the knife from being forced by the knife; adjust the tailstock.

3, the driver phase lamp is normal, and the processed workpiece scale is large and small

The cause of the problem is that the machine tool is running at a high speed for a long time, which leads to wear of the screw rod and the bearing. The error in the repeated positioning accuracy of the tool holder occurs at a long time; the carriage can accurately return to the processing starting point each time, but the dimensions of the workpiece are still changed. . This phenomenon is generally caused by the spindle. The high-speed rolling of the spindle makes the bearing wear harsh, resulting in changes in the processing scale. Metal processing WeChat, content is good, it is worth paying attention to.

Solution: Use the dial indicator to rest on the bottom of the knife holder, through a fixed cycle program corrected by the system, check the repeat positioning accuracy of the carriage, adjust the screw gap, replace the bearing, and use the dial indicator to check the repeat positioning accuracy of the knife holder. Adjust the machine or replace the tool holder; use the dial indicator to check whether the machining workpiece is accurately returned to the starting point of the program. If it can, repair the spindle and replace the bearing.

4, the workpiece size and the actual size of a few millimeters difference, or an axial change

The cause of the problem is that the fast positioning speed is too fast, and the drive and motor response is not enough; after a long period of time, the mechanical dragging screw and the bearing are too tight; the tool rest is too loose after the tool change, and the lock is not tight; If the program is faulty, there is no response to the head or tail or if the tool compensation is not revoked; the electronic gear ratio or the step angle of the system is set to fault.

Solution: If the fast positioning speed is too fast, adjust GO speed properly, cutting acceleration/deceleration and timing to make the drive and the motor work normally at the extra operating frequency; the carriage and the screw crane bearing are too tight after the machine wear is presented. If it is stuck, it is necessary to re-adjust the correction. If the knife holder is too loose, check whether the knife reversal moment is satisfactory. Check whether the turbine worm inside the knife holder wears, whether the clearance is too large, the device is too loose, etc.; if it is If the cause of the program is formed, it is necessary to amend the program, improve according to the requirements of the workpiece drawing, select a reasonable processing technology, and write the correct program according to the requirements of the instruction manual; if it is found that the scale error is too large, check whether the system parameters are set properly, especially the electronics. Whether the parameters such as gears and step angles are damaged, this phenomenon can be measured by dial gauges.

5, processing circular arc is not aspiration, the scale is not in place

Causes: Resonance caused by overlapping of vibration frequency; Processing process; Unreasonable parameter setting, excessive feed rate, out-of-step arc machining; Looseness caused by large screw hole or out-of-step caused by tight screw shaft; Wear.

Solution: Find out the components that have resonance, change their frequency, and prevent resonance; consider the processing technology of the workpiece data, and reasonably program; on the stepper motor, the processing speed F can not be set too large; the machine tool is strong, stable, drag Whether the plate is too tight after being worn, the gap is increased or the tool rest is loose, etc.; replace the timing belt. Metal processing WeChat, content is good, it is worth paying attention to.

6, in the batch production, accidentally present the workpiece

The cause of the problem is that it is necessary to carefully check fixtures, and taking into account the operator's operating methods and the reliability of the fixtures, due to the scale changes caused by the fixtures, it is necessary to improve the tooling to prevent workers from making erroneous judgement by human negligence; The system may be subject to fluctuations in the external power supply or be disturbed and disturbed and then actively generate disturbing pulses, which are transmitted to the drive so that the drive receives the remaining pulses to drive the motor to take away or to walk away.

Solution: Understand its rules, and try to use some anti-disturbance methods. For example, the strong electric cable disturbed by the strong electric field is blocked from the signal line of the weak signal, and the anti-disturbance absorbing capacitor and the shielded cable are used to block the connection. Whether the interface is solid, the grounding contact is closest, and all anti-disturbance measures are adopted to prevent the system from being disturbed.

7. The process of a part of the workpiece has been changed, and the accuracy of other process steps

Cause: The parameters of the program segment program are reasonable, whether it is within the reserved orbit, and whether the programming pattern meets the requirements of the specification

Solution: When threads are presented with chaotic teeth and the pitch is not correct, the peripheral equipment (encoder) that processes the thread and the objective factors of the function are immediately associated.

8, each process of the workpiece has the phenomenon of increasing or decreasing

The cause of the problem is that the program has been programmed incorrectly; the system parameters have been set irrationally; the equipment is not set up properly; there are regular periodic changes to the mechanical transmission components.

Solution: Check whether the instructions used by the program are performed on the track according to the requirements specified in the specification. After dialing the dial indicator, the dial indicator is positioned at the starting point of the program. After the program is completed, the carriage returns to the starting position and the performance is repeated. Even after investigating the results, grasp its 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 accounting coupling parameters and whether the pulse equivalent is accurate; see if the machine tool transmission part is damaged or not. Whether the coupling is even or not, check whether there are periodical and regular defects, and if so, check the key parts and give it a sweep.

9. The scale changes caused by the system are not stable

The cause of the problem is that the system parameters are set unreasonably; the operating voltage is not stable; the system is disturbed by the outside and the system is out of step; the capacitor is added, but the impedance between the system and the driver does not match, resulting in loss of the useful signal; signal between the system and the driver. Transmission is abnormal; system damage or internal defects.

Solution: speed, speedup time is too large, spindle speed, cutting speed is reasonable, whether the operator's parameter correction leads to system function changes; install the voltage regulator equipment; ground wire and determine that has been firmly connected, in the driver pulse output contact Add anti-disturbance absorbing capacitors at the office; select the appropriate capacitor type; check whether the signal connection between the system and the driver is shielded; check whether the connection is firm; check if the system pulse signal is lost or added; send the factory to repair or replace the motherboard.