The feeding accuracy of automatic feeding CNC lathes directly determines the consistency of workpiece machining dimensions. If there are problems such as feeding too long, too short, or unstable deviation, it can lead to workpiece deviation, rework, and even cause tool collision accidents. The faults of inaccurate feeding are often related to the three major links of "feeding power transmission", "detection feedback", and "mechanical cooperation". It is necessary to investigate the causes one by one and deal with them targetedly in order to efficiently restore equipment accuracy.
1、 Abnormal power transmission of feeding mechanism: deviation tracing from driving to execution
If there is a problem with the power transmission chain of the feeding mechanism (such as the motor, transmission wheel, and feeding roller), it will directly lead to unstable feeding force or speed, causing accuracy deviation.
1. Fault in drive motor and speed control system
If the speed of the feeding drive motor (usually a servo motor or stepper motor) fluctuates and the torque is insufficient, it will cause uneven feeding speed. Common reasons include: unstable motor power supply voltage (need to check the power supply circuit, replace damaged voltage regulators or circuits); Motor encoder malfunction (abnormal feedback signal from the encoder causing deviation in speed control, requiring cleaning or replacement of the encoder); Deviation of speed control system parameters (if servo drive parameters are mistakenly modified, default parameters need to be reloaded to calibrate the matching relationship between motor speed and feed quantity). When processing, it is necessary to first check the motor operating parameters (such as speed and current) through the numerical control system to determine if there are any abnormal fluctuations.
2. Wear or looseness of transmission components
Wear or looseness of transmission wheels, gears, synchronous belts and other components of the feeding mechanism can cause excessive power transmission clearance. For example, the surface of the feeding roller may experience wear due to long-term friction, leading to a decrease in friction between the roller and the workpiece, resulting in a "slip" phenomenon and a shorter feeding length; The synchronous belt is loose (which can be judged by pressing the belt, and if the deflection is too large, the tension wheel needs to be adjusted) or the gear mesh clearance exceeds the standard (the gear needs to be disassembled, cleaned of impurities, and the mesh clearance needs to be recalibrated, and the gear needs to be replaced if it is severely worn). When handling, it is necessary to disassemble the transmission components and check the degree of wear. For slightly worn parts, they can be repaired by grinding, and in severe cases, the same model of accessories need to be replaced.
2、 Detection feedback system failure: "perception bias" in precision control
The detection feedback system (such as displacement sensors and workpiece positioning switches) is responsible for real-time monitoring of the feeding progress. If the system fails, it will cause the CNC system to be unable to accurately control the feeding amount.
1. Displacement sensor malfunction
If displacement sensors (such as grating rulers and linear sensors) experience signal drift or no feedback, it can lead to measurement deviation in the feeding length. Common reasons include: the sensing surface of the sensor is covered with oil stains and iron filings (it needs to be wiped with a dust-free cloth dipped in a special cleaning agent); Poor contact of sensor cables (loose or oxidized wiring terminals, requiring re plugging and polishing of terminals); Sensor zero offset (requires entering the system's "calibration mode" to reset the sensor zero point and ensure accurate measurement starting point). If the sensor itself is damaged (such as cracked casing or signal loss), it needs to be replaced with a sensor of the same model and recalibrated.
2. Abnormal workpiece positioning switch
If the workpiece positioning switch (such as proximity switch, photoelectric switch) is not triggered accurately, it will cause a deviation in the feeding stop position. For example, the installation position of the positioning switch is offset (the position needs to be adjusted according to the original mark to ensure that the switch can be accurately triggered when the workpiece is in place); The sensing distance of the switch is too large (the proximity switch needs to be adjusted to an effective sensing range of 5-10mm from the workpiece); Internal malfunction of the switch (use a multimeter to check the on/off status of the switch and replace it if it fails). When processing, it is necessary to manually push the workpiece and observe whether the switch is triggered at the set position to ensure that the signal is synchronized and fed back to the CNC system.
3、 Mechanical coordination and workpiece factors: the influence of deviations in non dynamic links
In addition to power and detection systems, mechanical fit deviations and workpiece characteristics may also lead to inaccurate feeding.
1. Deviation between feeding channel and guiding components
If the guide plate and limit block of the feeding channel are installed incorrectly, it will cause the workpiece to deviate during feeding. Check the parallelism between the guide plate and the feeding roller (measure the gap with a ruler to ensure even gaps on both sides); Adjust the position of the limit block to avoid the workpiece shifting left and right during the feeding process; If the guiding components are worn (such as scratches on the surface of the guiding plate), they need to be polished, repaired or replaced to reduce the frictional resistance between the workpiece and the guiding components.
2. The influence of the workpiece's own characteristics
If the material of the workpiece is too soft (such as aluminum profiles) or the surface is uneven, it is easy to deform or slip during feeding. The impact of workpiece characteristics on feeding accuracy can be reduced by adjusting the pressure of the feeding roller (increasing pressure appropriately to increase friction), installing wear-resistant pads in the feeding channel (reducing workpiece deformation), or optimizing the workpiece clamping method (such as adding positioning pins).
In summary, to deal with inaccurate feeding faults in automatic feeding CNC lathes, it is necessary to investigate the causes from three dimensions: power transmission, detection feedback, and mechanical cooperation. Combined with the precise positioning of fault manifestations, the problem can be solved through component repair, parameter calibration, or replacement of parts. Regular cleaning of transmission and inspection components, as well as checking of mechanical clearances, are necessary for daily maintenance to ensure stable feeding accuracy in the long term.