The MT2V NC Profile Milling Machine is a CNC copy milling machine manufactured by OER LIKON and imported by our factory. It was installed and debugged in July 1997 and put into operation shortly after. From January 1998, the hydraulic lubrication system of the machine began to experience oil leakage at the lower end of the main spindle housing, especially when the temperature dropped. However, the oil leakage gradually stopped after the spindle ran for about 20 minutes. During this time, all the machine tools were operating normally without any alarm signals.
The MT2V CNC profile milling machine is classified as a heavy-duty machine tool, and its isotropic rail lubrication is managed by an independent automatic rail lubrication system. Its hydraulic and spindle lubrication system differs significantly from that of the FB2V and FB3V models produced by Oricon. The hydraulic and spindle lubrication system operates using a shared main oil tank filled with HM68 anti-friction hydraulic oil. Motor M1 drives two gear pumps (1P and 2P) simultaneously. Pump 1P supplies hydraulic oil at 8MPa pressure through check valve 5, direct relief valve 6, and accumulator 8 to the hydraulic system. Each solenoid valve controls functions such as spindle speed, chuck clamping, spindle head loosening, and Z-axis clamping.
Pump 2P provides lubricating oil to the headstock via direct relief valve 2 and chiller 1, then distributes it through oil distribution pipes to lubricate bearings and gears inside the headstock. The used oil returns to the sump at the bottom of the headstock. Pump 3P draws the oil back into the main tank. When the machine's main power switch is turned on, pump 3P starts automatically for 20 seconds to drain the oil in the sump. The hydraulic lubrication system starts, and pump 3P runs accordingly. When the system stops, pump 3P delays for 45 seconds to ensure all remaining oil is withdrawn.
Chiller 1 monitors the temperature of the lubricating oil passing through it. If the oil temperature rises to a set point, the chiller activates to cool the oil. If the temperature drops below the set value, the chiller stops. A schematic diagram of the hydraulic and spindle lubrication system is provided below, along with key components: 1. Chiller, 2. Direct relief valve, 3. Main tank, 4. Oil filter, 5. Check valve, 7. Manual shutoff valve, 8. Accumulator, 9. Hydraulic selector switch, 10. Oil pressure gauge.
During the initial period after installation, the machine experienced oil leakage at low temperatures, but no alarms were triggered, indicating that the issue was not related to high-pressure hydraulic leaks. The fault likely originated in the spindle lubrication system. Since the machine was still under warranty, foreign technicians replaced pump 3P twice without success. As ambient temperatures rose, the oil leakage gradually decreased and eventually disappeared. However, during the winter of 1998, the problem reappeared.
After reviewing the hydraulic lubrication data, we found that when the hydraulic selector switch 9 is set to "2P," the oil pressure should be between 0.5 and 1 MPa. At the lowest ambient temperature of 6°C, the oil pressure during cold start was measured at 1.8 MPa, which dropped as the oil temperature increased. Once the oil reached 25°C, the chiller activated, and the pressure stabilized at 0.7 MPa. As the oil pressure decreased further, the leakage reduced, and the machine returned to normal operation.
The oil temperature fluctuated between 18°C and 26°C, and the oil pressure varied between 0.7 MPa and 1.3 MPa depending on the temperature. This relationship was recorded in Table 1. It became clear that the initial oil pressure adjustment during summer needed to be recalibrated in winter. Lower temperatures increased the oil viscosity, reducing the return flow of the pump and causing excess oil supply to the spindle housing, leading to leakage.
Based on the oil temperature and pressure relationship, the specified oil pressure range of 0.5–1 MPa should not be interpreted as a static value but as a fluctuating range dependent on temperature. Setting the pressure too low could cause insufficient lubrication, while setting it too high might lead to excessive oil supply during cold starts, resulting in oil leakage. After adjusting the oil pressure to a higher value, the system operated smoothly, and the oil pressure and temperature relationship improved, as shown in Table 2.
Since the adjustment, the machine has been running without issues for over two years, and the oil leakage problem has not occurred again. The system now maintains stable performance across varying temperatures.
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