Root Cause Analysis of NC Servo Feeder Feed Length Deviation & Material Skipping on 200T High-speed Servo Punch Press

Root Cause Analysis of NC Servo Feeder Feed Length Deviation & Material Skipping on 200T High-speed Servo Punch Press, Optimization of Preventive Maintenance and After-sales Service Strategy

This case targets a 200T high-speed servo punch press equipped with NC servo feeder, deployed at a new energy metal stamping enterprise in Zhejiang. The production line manufactures battery shrapnel and automotive connector terminals, which demand ultra-strict feeding precision with design tolerance ±0.02 mm. The customer reported intermittent feeding length drift and random material skipping. The defective stamping parts displayed inconsistent hole pitch, triggering batch rejection and forced line shutdown.

Our after-sales team completed remote pre-diagnosis, spare part scheduling, on-site disassembly, component replacement, precision calibration and operator training. The whole repair cycle took 18 hours, and feeding accuracy recovered to factory specification. This case systematically analyzes fault root causes, evaluates service implementation effect, summarizes technical lessons, and upgrades the customer’s long-term equipment maintenance strategy.

The fault occurred intermittently instead of appearing continuously. At low feed speed, the equipment ran relatively stable; when production switched to rated high-speed mode, material skipping and feeding deviation happened randomly. The servo load curve fluctuated violently on HMI, and occasional abnormal squeaking sound came from the pressure roller assembly. The customer had tried resetting feeding parameters and tightening roller clamping force, but the problem reoccurred after short-time operation.

1. Pressure roller bearing wear: Long-term high-speed rotation generated bearing clearance and radial runout. The clamping force applied to metal coil became unstable during feeding.
2. Aging synchronous belt: Belt tooth wear and elasticity attenuation caused slipping under heavy load. The rotation angle of the feeding roller failed to match the instruction signal sent by servo driver. These two defects worked together, resulting in inconsistent material advance distance and random material skipping. Adjusting parameters or clamping force only temporarily alleviated the symptom rather than solving the mechanical wear issue.

1. The customer’s daily maintenance checklist ignored regular inspection of transmission components including bearings and synchronous belts. Operators only focused on surface cleanliness and lubrication, without checking belt tension and bearing noise periodically.
2. No regular feeding accuracy sampling test was scheduled. The defect was discovered only after finished products were inspected, which meant the fault had already existed for a period before shutdown.

1. Remote pre-diagnosis: Engineers remotely reviewed HMI data, fault videos and defective samples before departure, locked suspected worn parts and reserved spare parts in advance, greatly cutting on-site troubleshooting duration.
2. On-site safe disassembly and component replacement: Follow lockout-tagout safety procedure, replace worn pressure roller bearing and aging synchronous belt. Re-adjust roller gap and clamping force according to official technical manual.
3. Multi-stage precision calibration: Conduct single-step feeding test, low-speed continuous feeding test and punch-feeder linkage full-speed test. Repeated sampling measurement confirms feeding accuracy meets standard.
4. On-site maintenance training: Train operators and maintenance personnel on inspection methods, early fault recognition, parameter backup steps.
5. Long-term tracking: Build dedicated equipment file, add the machine to bi-quarterly proactive inspection plan. Implement follow-up check at 24h,48h and 7 days after repair handover.

After repair, the feeder runs continuously under rated 35 m/min feed speed. Actual feeding accuracy stabilizes at ±0.018 mm, servo average load drops to 62% with smooth curve, no abnormal noise or material skipping appears. Batch product rejection caused by feeding deviation is eliminated. Customer production schedule is back on track. The customer’s maintenance team masters inspection skills for transmission components, which reduces the risk of similar sudden downtime.

1. Intermittent feeding accuracy failure of NC servo feeder is usually caused by mechanical transmission wear rather than parameter error. When accuracy fluctuates randomly, inspect pressure roller bearing and synchronous belt first.
2. For high-precision stamping lines, periodic sampling measurement of feeding length must be included in daily inspection, to capture early wear signals before mass defective parts occur.
3. Synchronous belt and pressure roller bearing belong to consumable parts. Establish fixed replacement cycle according to accumulated feeding length instead of waiting for obvious failure.
4. Regularly back up servo feeder parameters to avoid parameter loss caused by power failure or drive replacement.

Q1: What is the difference between this mechanical wear fault and parameter setting error? A1: Parameter error usually causes consistent, repeatable feeding deviation, and the fault appears every cycle. Mechanical wear like bearing and belt aging leads to intermittent, random deviation. The fault severity changes with feed speed and material thickness. Adjusting parameters cannot eliminate the problem fundamentally.

Q2: How to set the replacement cycle for synchronous belt and pressure roller bearing of NC servo feeder? A2: The cycle depends on accumulated feeding length, operating speed and material type. For high-speed production of thin metal strip under 35 m/min, we recommend inspecting belt tension and bearing noise every 80,000 meters of feeding length, and replace the synchronous belt every 400,000 meters. Bearings should be replaced when obvious runout or abnormal noise is detected.

Q3: What risks will happen if worn synchronous belt continues to work? A3: The belt teeth may shear suddenly in high-speed operation, leading to sudden material skipping, severe dimensional deviation of stamping parts, and potential risk of mould collision. Mould damage will bring far higher repair cost and longer downtime than replacing the belt in advance.

Q4: What is the key point of pressure roller clamping force adjustment after component replacement? A4: The clamping force should be sufficient to prevent material slipping, but excessive force will accelerate roller and bearing wear. Adjust according to material thickness and tensile strength. After adjustment, carry out multiple single-step feeding tests to verify no slipping and stable feeding length.

Q5: Why do we need to perform multi-stage feeding tests after maintenance? A5: Single-step test only verifies static feeding accuracy. Low-speed and full-speed linkage tests can simulate real production load. Some hidden defects only emerge under continuous high-speed operation. Multi-group tests ensure the fault is completely removed before returning to mass production.

Q6: What items will be checked during our bi-quarterly proactive preventive inspection? A6: The inspection covers belt tension and tooth wear, bearing temperature and abnormal noise, guide rail lubrication, encoder dust removal, feeding accuracy sampling calibration, servo drive load check, parameter backup, and assessment of customer’s daily maintenance execution. We will deliver a formal maintenance report with suggested replacement timeline for wearing parts.