Reasons why five-axis machining center affects machining accuracy

Five-axis machining CNC center CNC machine tool is a high-speed, high-efficiency, and cost-effective production equipment. It is easy to operate, has a simple process, and greatly reduces labor waste. However, sometimes failures such as unstable processing accuracy may occur under internal or external conditions.

 

The reasons for the unstable processing accuracy of CNC machine tools are as follows:

1. The workpiece size of five-axis CNC machining is accurate, but the surface finish is poor

Reasons for the failure: The tool tip is damaged and not sharp; the machine tool resonates and is unstable; the machine tool crawls; the five-axis machining process is poor.

Solution: If the five-axis machining tool is worn or damaged and is not sharp, re-sharpen the tool or choose a better tool and recalibrate it; the machine tool resonates or is not placed smoothly, adjust the level, lay the foundation, and fix it stably; the machine crawls The reason is that the carriage guide rail is severely worn and the screw ball is worn or loose. The machine tool should pay attention to maintenance, clean the iron wire in time and add lubricating oil to reduce friction; choose a coolant suitable for workpiece processing, if it can meet the processing requirements of other processes. , try to use a higher spindle speed.

                                                                                2. Five-axis machining of CNC workpieces produces the phenomenon of tapered and large heads.

Reason for the failure: The level of the five-axis machine tool was not adjusted properly, one was higher and the other was lower, resulting in unstable placement; when turning the long axis, the material was relatively hard and the tool cut deeper, causing the tool to give way; the tailstock thimble was not concentric with the spindle. .

Solution: Use a spirit level to adjust the level of the machine tool, lay a solid foundation, and fix the five-axis machining CNC center CNC machine tool to improve its toughness; choose a reasonable process and appropriate cutting feed to avoid the tool being forced to give way; adjust the tail seat.

 

3. The driver phase light is normal, but the size of the workpiece processed by the five-axis is sometimes large and sometimes small.

Cause of the failure: The carriage of the CNC machine tool in the five-axis machining center has been running at high speed for a long time, resulting in wear of the screw and bearings; the repetitive positioning accuracy of the tool holder has deviated during long-term use; the carriage can accurately return to the starting point of processing every time, but the processing Workpiece dimensions still vary. This phenomenon is generally caused by the spindle. The high-speed rotation of the spindle causes serious wear of the bearings, resulting in changes in the machining dimensions.

Solution: Use a dial indicator against the bottom of the tool holder, and edit a fixed cycle program through the system to check the repetitive positioning accuracy of the carriage, adjust the screw rod gap, and replace the bearings; use a dial indicator to check the repetitive positioning accuracy of the tool holder. Adjust the machine or replace the tool holder; use a dial indicator to check whether it accurately returns to the starting point of the program after processing the workpiece. If possible, inspect the spindle and replace the bearing.

 

4. The size of the five-axis workpiece differs by a few millimeters from the actual size, or there is a large change in a certain axis.

Cause of the failure: The speed of rapid positioning is too fast, and the drive and motor cannot respond; after long-term friction loss, the screw rod and bearing of the mechanical carriage are too tight and stuck; the tool holder is too loose after tool change and cannot be locked; the edited program Error, the head and tail do not respond or the tool compensation ends without canceling; the electronic gear ratio or step angle setting of the system is wrong.

Solution: If the rapid positioning speed is too fast, adjust the speed of GO, cutting acceleration and deceleration and time appropriately so that the driver and motor can work normally at the rated operating frequency; after the machine tool is worn, the carriage, screw and bearings will be too tight. If it is stuck, it must be readjusted and repaired; if the tool holder is too loose after changing the tool, check whether the reversal time of the tool holder is sufficient, check whether the turbine 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 it is caused by reasons, you must modify the program, improve it according to the requirements of the workpiece drawing, choose a reasonable processing technology, and write the correct program according to the instructions in the instruction manual; if the dimensional deviation is found to be too large, check whether the system parameters are set appropriately, especially the electronic gear and Whether parameters such as step angle are damaged, this phenomenon can be measured by using a dial indicator.

 

5. The arc processing effect is not ideal and the size is not in place for small and medium-sized CNC lathes.

Cause of the failure: Overlapping of vibration frequencies leads to resonance; processing technology; unreasonable parameter settings and excessive feed speed, causing arc processing to lose synchronization; looseness caused by large screw clearance or synchronization caused by too tight screw; timing belt wear and tear.

Solution: Find the components that produce resonance, change their frequency, and avoid resonance; consider the processing technology of the workpiece material and compile the program reasonably; for stepper motors, the processing rate F cannot be set too high; whether the five-axis machining CNC center CNC machine tool is installed Firm and stable, check whether the carriage is too tight after wear, the gap is increased, or the tool holder is loose, etc.; replace the timing belt.

 

6. In mass production, workpieces may occasionally be out of tolerance.

Cause of failure: The tooling fixture must be carefully checked, and the operator’s operating method and the reliability of the clamping must be taken into consideration. Due to the dimensional changes caused by the clamping, the tooling must be improved to prevent workers from making misjudgments due to human negligence; the CNC system may After being affected by fluctuations in the external power supply or interference, interference pulses are automatically generated and transmitted to the drive, causing the drive to accept excess pulses and drive the motor away or less.

Solution: Understand the rules and try to adopt some anti-interference measures, such as: isolating strong electric cables with strong electric field interference from signal lines of weak electric signals, adding anti-interference absorbing capacitors and using shielded wires for isolation. In addition, check the ground wire. Make sure the connection is firm, the ground contact is the closest, and all anti-interference measures are taken to avoid interference to the system.

 

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

Cause of the failure: Whether the parameters of this program segment are reasonable, whether they are within the predetermined trajectory, and whether the programming format meets the requirements of the instruction manual.

Solution: If there are random threads or incorrect pitch during the thread program, it will immediately be associated with the peripheral configuration (encoder) of thread processing and the objective factors of this function.

 

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

Reasons for the failure: programming errors; unreasonable system parameter settings; improper configuration settings; regular and periodic changes in mechanical transmission components.

Solution: Check whether the instructions used by the program are executed according to the required trajectory specified in the instruction manual. You can judge by using the dial indicator. Position the dial indicator at the starting point of the program and let the carriage return to the starting position after the program ends. Repeat the execution. Even if you observe the results and grasp the rules; check whether the system parameters are set reasonably or are considered to have been changed; whether the relevant machine tool configuration meets the requirements in the single calculation of the connection calculation coupling parameters, and whether the pulse equivalent is accurate; check whether the transmission part of the machine tool is damaged, whether the gear Check whether the coupling is uniform, check whether there are periodic and regular fault phenomena, and if so, check the key parts and eliminate them.

 

9. Unstable dimensional changes caused by five-axis machining CNC center CNC machine tool system

Reasons for the failure: Unreasonable system parameter settings; unstable operating voltage; external interference to the system, causing the system to lose synchronization; capacitors have been added, but the impedance between the system and the driver does not match, resulting in loss of useful signals; signals between the system and the driver Abnormal transmission; system damage or internal failure.

Solution: Whether the speed and acceleration time are too large, whether the spindle speed and cutting speed are reasonable, whether the operator’s parameter modification causes a change in system performance; install voltage stabilizing equipment; make sure the grounding wire is reliably connected, and connect the pulse output contacts of the driver Add an anti-interference absorption capacitor; select an appropriate capacitor model; check whether the signal connection line between the system and the driver is shielded and whether the connection is reliable; check whether the system pulse signal is lost or increased; send it to the factory for repair or replace the motherboard.

 

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