Double-Side Oil Feeder Uneven Lubrication and Nozzle Blockage Fault Matched to 160T Servo Punch Press

Case Study of Double-Side Oil Feeder Uneven Lubrication and Nozzle Blockage Fault Matched to 160T Servo Punch Press: Root Cause Analysis, Systematic Cleaning Scheme and Lubrication Preventive Maintenance Standard

This case is derived from the actual after-sales maintenance record of a 160T servo precision punch press production line equipped with double-side automatic oil feeder and NC servo feeder. The production line is used for continuous blanking and forming of 1.2 mm cold-rolled steel automotive structural brackets. The stamping speed is 40–45 strokes per minute, adopting two-shift continuous production mode. The double-side oil feeder is responsible for applying uniform lubricating oil film on both upper and lower surfaces of the steel strip before entering the forming die, to control friction and heat. The oil feeder was installed and put into operation together with the punch press, with a total running time of 14 months before the fault occurred.

The equipment ran stably in the early stage. The workshop maintenance team only supplemented stamping oil according to the liquid level and never carried out deep maintenance for the oil circuit, filter and nozzle group. In the recent one month, the customer replenished lubricating oil twice, and mistakenly mixed two different brands of stamping oil. After mixing, the oil gradually turned dark brown, and fine suspended sludge appeared. At first, individual nozzles occasionally stopped spraying, and the operator increased the atomization air pressure to compensate. The adjustment temporarily improved the oil output, but accelerated oil splashing and sludge accumulation. After a period of time, the number of blocked nozzles increased, oil flow difference between left and right sides expanded, the product non-conforming rate rose sharply, and the die polishing frequency increased significantly. The customer’s internal maintenance team only cleaned the surface of individual nozzles, but could not solve the repeated blockage problem, so they submitted an emergency service application.

The core equipment configuration parameters are as follows: Punch press model: 160T servo punch press; supporting feeder: NC servo feeder; auxiliary equipment: double-side oil feeder with 12 atomizing nozzles; rated oil flow per side: 12 ml/min; standard atomization air pressure: 0.20–0.25 MPa; processing material: 1.2 mm cold-rolled steel strip; production stroke rate: 40–45 SPM; lubricant type: low-viscosity stamping oil for cold forming.

Before on-site service, the remote engineer connected with the customer’s maintenance supervisor. The engineer guided the customer to record HMI flow and pressure data, shoot nozzle working video, check oil color and tank sediment, and confirm the oil replenishment record. According to the customer’s description of mixed oil filling and the phenomenon of gradually worsening blockage, the remote team judged that the fault belonged to composite oil circuit pollution fault, rather than electrical control failure or oil pump damage. The remote engineer issued operation restrictions: do not continue to increase air pressure and oil pressure at will, do not disassemble the flow regulating valve without authorization, to prevent valve core scratch and seal leakage. The work order was generated, spare parts were reserved, and the on-site engineer was dispatched.

After arriving at the workshop and completing safety locking, the engineer first read the historical operation log of the oil feeder. The left oil circuit flow fluctuated between 2–6 ml/min, the right side was 7–10 ml/min, and the atomization air pressure was adjusted to 0.32 MPa, exceeding the upper limit of the standard range. When observing the nozzle group, 4 nozzles had obvious sludge blockage at the orifice, the sprayed oil was in the form of large drops instead of uniform mist, and 3 nozzle joints had oil dripping traces. The oil liquid in the oil tank was dark brown, with a large amount of fine suspended impurities, which was obviously deteriorated after mixing.

The engineer closed the oil pump, relieved the pipeline residual pressure, and took out the oil suction filter inside the oil tank and the precision filter before the oil distribution manifold. The filter screen was covered with thick oil sludge mixed with iron powder. The clogging reduced the effective flow area of the oil circuit, resulting in insufficient oil supply pressure and unstable outlet flow. Since the equipment was put into use, the filter elements had never been replaced, only simple surface wiping was carried out.

The engineer inspected the oil hoses and manifold. Several hoses were bent for a long time, the inner wall was deformed, and sludge accumulated at the bottom dead angle of the horizontal manifold. The oil pressure regulating valve had been adjusted many times, the internal return spring suffered fatigue, and the pressure stability became poor. When the oil temperature rose after continuous operation, the oil viscosity decreased, and dripping became serious. When the machine just started with low oil temperature, the oil flow was insufficient. The compressed air quality test found that the air contained water vapor and compressor oil pollution. Without terminal filtering, the moisture entered the oil tank and accelerated oil oxidation and sludge generation.

By checking the customer’s oil purchase and filling records, the engineer confirmed that two different brands of stamping oil were mixed. The incompatibility of additives produced colloidal precipitate, which was the main source of sticky sludge. This explained why the blockage recurred quickly after simple nozzle cleaning.

Through systematic inspection and verification, the fault was confirmed as a composite fault caused by the superposition of management, liquid, mechanical and air source factors. The root causes are sorted as follows:

1. Lubricating oil management defect: The customer mixed two incompatible stamping oils, and chemical reaction produced colloidal sediment, which was the source of oil sludge. The oil liquid deteriorated, the lubricating performance decreased, and the impurity content increased greatly.
2. Maintenance cycle missing: The filter elements were not replaced for 14 months. The filter lost the interception function of iron powder and sludge, and the impurities entered the rear pipeline and nozzle group continuously, causing blockage.
3. Improper parameter adjustment: After the nozzle was blocked, the operator blindly increased the atomization air pressure to compensate for insufficient oil output. High pressure aggravated oil splashing, accelerated sludge accumulation, and formed a vicious cycle.
4. Pipeline layout defect: Part of the oil hose was bent sharply, and dead corners existed in the manifold, which were easy to deposit sludge. The sealing rings of individual nozzle joints were aging, leading to dripping.
5. Unpurified compressed air: The air inlet lacked water-oil separation filter, moisture and compressor oil entered the lubrication system continuously, accelerating oil oxidation and deterioration.
6. Lack of patrol judgment standard: The daily inspection only paid attention to whether the oil feeder was running, without checking the atomization state, flow data and oil liquid condition. Early abnormal signals were ignored until quality defects broke out on a large scale.

It should be emphasized that the oil feeder pump body, control circuit and flow sensor itself had no damage. If only cleaning the nozzle without replacing deteriorated oil and clogged filters, the fault will reappear in a short time.

The rectification work was designed to eliminate all root causes, and the implementation steps were standardized and recorded:

1. Discharge deteriorated oil and clean the oil tank. All mixed deteriorated oil was drained. The inner wall of the oil tank was soaked and cleaned with special lubrication system cleaning agent, and oil sludge and sediment were completely wiped. After the tank was fully dried, the same model of qualified stamping oil specified in the manual was refilled to the marked standard liquid level. The engineer marked the oil model on the tank body and posted a warning label prohibiting mixed filling.
2. Replace all filter components. The built-in suction filter of the oil tank and the fine filter before the manifold were replaced with new stainless steel filter elements. The old filters were reserved as samples for the customer’s maintenance team to understand the impurity accumulation situation.
3. Disassemble, ultrasonically clean and reassemble all nozzles. All 12 atomizing nozzles were disassembled. The nozzle core and orifice were soaked in cleaning solvent, and ultrasonic cleaning was used to remove sticky sludge. After cleaning, each nozzle was tested one by one to confirm fine atomization. The aging O-rings at the nozzle installation interface were replaced to eliminate dripping risk.
4. Optimize pipeline and recalibrate pressure parameters. Deformed oil hoses were replaced, the pipeline layout was adjusted to avoid sharp bending and dead corners. The oil pressure regulating valve and atomization air pressure valve were reset to the factory recommended value of 0.22 MPa for atomization air pressure. The adjusted valve position was marked with paint to prevent random adjustment by operators.
5. Add air-water separator and precision air filter. A terminal purification filter was installed at the air inlet of the oil feeder to remove water vapor and oil impurities in compressed air, reduce the oxidation rate of stamping oil and slow down sludge formation.
6. Technical training and document handover. Train operators and maintenance personnel on oil selection, filling specification, daily patrol points, filter replacement operation, nozzle cleaning method and abnormal emergency handling. Hand over the customized preventive maintenance checklist and record form.

Q1: Why is it easy for maintenance personnel to fall into the misunderstanding of only cleaning the nozzle when dealing with oil feeder blockage fault? A1: Because the blocked nozzle is the most intuitive visible fault point. When the nozzle is cleaned, the oil output can recover temporarily, which makes people think the problem is solved. However, if the oil liquid has deteriorated and the filter is severely clogged, a large number of impurities still exist in the oil tank and pipeline. These impurities will flow to the nozzle again with the oil circulation, and the blockage will recur quickly. This is the essential difference between temporary symptomatic treatment and root cause rectification.

Q2: What harm will excessive atomization air pressure cause to the whole stamping process besides oil dripping? A2: Excessive air pressure will break the oil film into scattered large oil drops, which cannot form a continuous and uniform lubricating layer on the strip surface. Local oil film is too thick while some areas are lack of oil. The splashing oil mist will diffuse into the punch press guide rail and servo slide block, polluting the original lubricating grease of the punch press. Long-term high-pressure air impact will also accelerate the wear of the nozzle core and shorten the service life of the nozzle assembly.

Q3: What is the difference between the sludge formed by oil mixing and the ordinary iron powder sludge produced in normal production? A3: Ordinary sludge under normal working conditions is mainly the mixture of iron powder, dust and a small amount of oil oxidation products, with relatively loose texture. The precipitate produced by incompatible mixed oil is colloidal, sticky and adhesive. It is easy to stick firmly on the filter screen, pipeline inner wall and nozzle orifice. Ordinary blowing and simple wiping cannot remove it, and ultrasonic cleaning and full oil change are required.

Q4: What is the correct operation sequence when carrying out full oil circuit maintenance of double-side oil feeder? A4: The standardized sequence is: 1. Shut down the punch press and oil feeder, cut off air source and power, implement lockout-tagout; 2. Release residual pressure of oil circuit and air circuit; 3. Drain the old oil; 4. Clean the oil tank; 5. Replace filter elements; 6. Disassemble, clean and inspect nozzles and sealing rings; 7. Inspect and replace deformed pipelines; 8. Refill qualified lubricating oil; 9. Reset and calibrate pressure parameters; 10. Run the machine for atomization test and sample stamping verification. Do not reverse the order to avoid secondary pollution of the clean oil circuit.

Q5: How to choose the matching stamping oil for double-side oil feeder? A5: It should be selected according to the stamping material, material thickness, forming difficulty and production speed specified in the equipment manual. Different materials such as cold-rolled steel, stainless steel, aluminum alloy and copper correspond to different viscosity and additive systems. After determining the oil model, it is necessary to fix the supplier and avoid mixing oil of different brands and models. When replacing the oil type, the whole oil circuit must be cleaned thoroughly.

Q6: What is the logical relationship between the lubrication system maintenance of the oil feeder and the die life management of the 160T servo punch press? A6: The oil feeder is the front-end guarantee of die lubrication. Stable and uniform oil film reduces the friction coefficient between material and die cutting edge and forming surface, controls instantaneous high temperature, reduces adhesive wear and thermal fatigue of the die. If the lubrication system is unstable, the die will bear alternating dry friction and boundary friction. The wear speed will increase exponentially, the frequency of die polishing and repair will rise, and the service life will be greatly shortened. Therefore, regular maintenance of the oil feeder is an important part of die cost control.

Combined with this composite fault case, we form the following standardized preventive maintenance specification, which can be applied to the oil feeder matched with servo punch press production line:

1. Daily maintenance (before each shift): Check whether the oil liquid level of the oil tank is within the normal range, supplement the same model of stamping oil when insufficient; observe the atomization effect of each nozzle, check for dripping, oil leakage or no oil output; check whether the oil liquid has abnormal color and peculiar smell; record abnormal phenomena in the equipment log.
2. Weekly maintenance: Check the indication of oil pressure and atomization air pressure on HMI, confirm that the parameters are within the standard range; check whether the oil pipeline is squeezed, bent and deformed; drain the water accumulated in the air-water separator of the air inlet.
3. Monthly maintenance: Inspect the pollution degree of the filter element; test the oil flow balance of left and right oil circuits; clean the surface of the nozzle group; check the tightness of each joint for oil seepage.
4. Bi-monthly maintenance: Replace the oil suction filter inside the oil tank and the precision filter before the manifold; clean the bottom sediment of the oil tank. If the workshop dust is heavy and the iron powder output is large, shorten the replacement cycle to one month.
5. Quarterly maintenance: Disassemble all nozzles for deep cleaning; check the aging degree of sealing rings and oil hoses; calibrate oil pressure and air pressure valves; check the working state of the flow sensor.
6. Semi-annual maintenance: Carry out full oil circuit cleaning and oil liquid replacement, even if there is no obvious blockage fault; comprehensively inspect the oil distribution manifold and remove accumulated sludge.
7. Spare part stocking suggestion: It is recommended to stock a set of filter elements, 2–4 spare atomizing nozzles, matching sealing O-rings and cleaning agent kits on site, so as to shorten the maintenance time when blockage and leakage occur.

This case shows that the fault of uneven lubrication and nozzle blockage of double-side oil feeder is often not an independent mechanical failure of nozzles. It is usually the result of the superposition of non-standard oil management, missing maintenance cycle, blind parameter adjustment and unpurified air source. The fault develops gradually and hidden. In the early stage, only individual nozzles are blocked, which is easy to be ignored. As the impurities accumulate continuously, the lubrication balance of the whole oil circuit is destroyed, which finally triggers large-scale quality defects and increases die wear loss.

Our service team adopted the layered isolation diagnosis method, found all root causes, and implemented a complete rectification plan including oil change, tank cleaning, filter replacement, nozzle ultrasonic cleaning, pipeline optimization and air source purification. After maintenance, the oil feeder realized stable bilateral uniform atomization, the product qualification rate returned to the normal level, and the die loss risk was eliminated. On the basis of this case, the formed preventive maintenance specification helps customers build a long-term lubrication management system, avoid repeated similar faults, stabilize the stamping quality of the 160T servo punch press production line, and control the comprehensive production cost.