Root Cause Analysis & Whole-Life Cycle Optimization Case of 200T Servo Punch Press Abnormal Vibration and Noise Fault

This case targets a 200T servo punch press matched with HCK-600 three-in-one uncoiler, straightener and feeder, supplied to an automotive new energy connector stamping production line. The equipment completed installation, alignment, debugging and acceptance on July 12, 2026. The normal production stamping speed range is 15–35 strokes per minute, processing cold-rolled steel strip with material thickness 0.8–1.2 mm. The main function is forming, punching and trimming of vehicle electrical structural parts. The workshop adopts two-shift continuous production mode, with daily operating duration up to 16 hours. The fault first appeared on October 12, 2026. Operators reported obvious low-frequency vibration transmitted to the workbench, accompanied by continuous rumbling noise during down stroke. When the stamping speed was adjusted above 28 SPM, the vibration became more intense. The online inspection station found that the flatness of stamped parts exceeded the tolerance, and the die protection sensor sent intermittent abnormal signals. The customer stopped the production line for inspection and contacted our after-sales department for technical support. The whole handling process includes remote preliminary diagnosis, on-site measurement and testing, root cause locking, fault elimination, performance verification, technical training and long-term maintenance scheme formulation. This case study systematically sorts out the fault mechanism, detection logic, rectification scheme, risk assessment and standardized preventive measures, which can provide reference for the maintenance of the same series servo punch presses and the improvement of installation and acceptance standards.

We built multi-dimensional data groups including design benchmark, fault state, post-repair state and long-term monitoring data. The detailed comparison table is as follows:

Data analysis shows that multiple parameters deviated from the allowable range synchronously when the fault occurred. The vibration and noise are not isolated single-point abnormalities. The decrease of bolt fastening force weakened the constraint of the frame; the aging damping pad lost vibration isolation performance; the bearing preload clearance increased, which changed the dynamic characteristics of the rotating pair. Under the excitation of periodic stamping impact force, the natural frequency of the whole equipment structure was close to the excitation frequency, resulting in structural resonance. Resonance further amplified the vibration, transmitted the vibration to the die and the material belt, and finally caused the dimensional out-of-tolerance of stamping products. The increase of friction inside the bearing also raised the operating temperature and produced abnormal running noise.

We adopted the 5Why analysis method to trace the fault source layer by layer: Why did the punch vibrate and make abnormal noise? → The overall structure resonated during stamping stroke. Why did resonance occur? → The frame constraint capacity decreased and the damping performance declined, matching the excitation frequency of stamping impact. Why did the constraint and damping decline? → Anchor bolts loosened under alternating impact load, damping rubber pads hardened and aged, main shaft bearing preload clearance increased. Why did these changes happen without being discovered in advance? → The customer’s daily maintenance checklist only focused on oil level and abnormal alarm, lacking regular torque inspection and vibration detection items. Why was there no relevant inspection requirement in the customer’s maintenance system? → In the initial handover training, the customer’s maintenance team paid insufficient attention to the hidden danger of slow structural performance degradation under long-term impact load.

Classify the causes into three categories:

1. Direct physical causes: bolt loosening, damping pad aging, bearing pre-tightening clearance drift.
2. Management cause: incomplete daily maintenance items, lack of regular structural health inspection.
3. System optimization cause: the original equipment handover training material did not emphasize the periodic inspection requirements of foundation and rotating support parts for servo punch under continuous impact working condition.

Step 1: Safety lockout and tagout. Cut off the main power and air source of the punch, release the residual pressure of the hydraulic and lubrication system, lock the operation panel to prevent accidental startup. Step 2: Disconnect the three-in-one feeder linkage signal, remove the die and material belt to create safe operation space. Step 3: Use hydraulic jacks to lift the punch frame evenly at four supporting points, take out the old damping pads, clean the base contact surface and the foundation surface, install new high-damping nitrile rubber pads. Step 4: Re-level the frame with a precision optical level gauge, control the horizontal tolerance within 0.02 mm/m. Step 5: Tighten 8 anchor bolts in diagonal grading sequence according to 430 N·m torque value, mark the bolt position after fastening for subsequent visual inspection. Step 6: Dismantle the front cover of the main shaft bearing housing, clean the bearing raceway and rolling elements, check for pitting and wear, adjust the locking nut to set the preload clearance back to factory standard, fill with high-temperature composite lithium grease. Step 7: Check and dredge all lubrication pipelines, test the lubrication pump outlet pressure to ensure stable oil supply to the bearing position. Step 8: Restore the die and feeder linkage, carry out no-load running test from low speed to rated speed step by step, record vibration, noise and temperature data. Step 9: Load test with the actual production material and die, continuously run for 2 hours, sample products to detect flatness and size.

All parameters must meet the factory acceptance index; no abnormal vibration and rumbling noise under the whole speed range; die protection sensor no longer sends false alarm; product dimensional qualification rate returns to the design level.

This fault belongs to progressive hidden danger. If it continued to run without disposal, the resonance would accelerate the fatigue wear of the main shaft bearing, even lead to bearing locking, main shaft scratch, die chipping and more serious equipment damage, bringing much higher maintenance cost and longer shutdown cycle. Combined with this case, we optimized the supporting service system:

1. Revise the handover training document for servo punch, add the inspection frequency and operation standard of foundation bolts, damping components and main shaft bearing status.
2. Add vibration regular detection item in the cloud maintenance plan. For equipment working in double-shift continuous stamping condition, vibration inspection is required every 30 days.
3. Set up spare parts suggestion list for customers: configure damping pads, main shaft bearing assembly and high-temperature grease as recommended consumables for long-term use.
4. For automotive industry customers with high continuous production requirement, launch quarterly paid equipment health scanning service, including vibration testing, infrared temperature measurement, bolt torque sampling inspection and electrical signal recording.
5. Collect the vibration characteristic data of different models of servo punch under different working conditions, build a fault early warning database, and improve the accuracy of remote abnormal identification in the future.

Servo punch presses have excellent flexibility and precision, but their structural supporting parts are always subjected to cyclic impact load during stamping production. The degradation of damping parts and the relaxation of threaded connection are slow and hidden failure modes, which cannot be identified by simple alarm signals. This fault was successfully handled relying on the two-level service mode of remote pre-diagnosis plus rapid on-site engineering support. After eliminating the fault, we did not stop at simple repair. We supplemented technical training and optimized the customer’s maintenance management system, helping the customer realize the transformation from passive breakdown repair to active predictive maintenance. For our company, this case also promoted the iteration of training materials and after-sales inspection standards, forming replicable standardized disposal process for similar vibration and noise faults of servo punch presses. The whole-life cycle after-sales service is not only troubleshooting when faults occur, but also continuously helping customers identify potential risks, standardize maintenance behaviors and protect the long-term stable operation of stamping production lines.

Q1: What is the difference between vibration fault diagnosis of servo punch and traditional mechanical punch?

A1: The stamping speed of servo punch can be adjusted steplessly. The excitation frequency changes with the stroke speed. It is easier to produce resonance at a certain speed section. Traditional fixed-speed mechanical punch has single excitation frequency, so the resonance risk and vibration law are different. We need to collect vibration data under multiple speed gears for analysis.

Q2: Why adopt diagonal sequence when tightening anchor bolts?

A2: Diagonal graded fastening can avoid unilateral stress on the frame, prevent the punch base from tilting and ensure uniform stress on each damping pad and anchor bolt. Sequential tightening along one side will cause frame distortion and affect the alignment accuracy.

Q3: What kind of damping pad material is suitable for heavy-duty servo punch working under long-time impact?

A3: We recommend high-damping nitrile rubber composite pad with high hardness and anti-fatigue formula. Ordinary rubber pads are easy to harden and lose elasticity quickly under continuous impact and temperature rise, and cannot maintain stable vibration isolation effect.

Q4: How to judge whether the main shaft bearing has suffered irreversible wear after this fault?

A4: We judge comprehensively by checking raceway surface for pitting, peeling and scratch, measuring runout value, monitoring temperature rise and noise change under long-time load operation. If only the clearance drifts without surface damage, adjusting preload can restore performance; if there is pitting corrosion, the bearing assembly must be replaced directly.

Q5: What suggestions can be given to customers to arrange vibration detection work in daily production?

A5: Equip a portable vibration tester, fix the detection points at the four corners of the frame and the bearing housing. Record the amplitude and frequency data regularly. Once the data shows a continuous upward trend, arrange inspection in advance, do not wait for obvious noise or product out-of-tolerance.

Q6: If the same resonance phenomenon occurs again after replacement of damping pads and bolt fastening, what other factors should be checked?

A6: Check the flatness and settlement of the concrete foundation, check whether the die is overweight or unbalanced, check the balance cylinder pressure of the punch, check whether the servo control curve has been modified randomly, and check the vibration transmission from adjacent equipment on the same foundation.