Created on:2021-06-23 15:50

Early hydraulic fault diagnosis and maintenance of horizontal machining center

Early hydraulic fault diagnosis and maintenance of horizontal machining center

(1) Statistical analysis of early failure of horizontal machining center

Based on the original records, the early faults of a horizontal machining center are statistically analyzed. The results show that 73% of the machine tool body faults, 5% of the CNC system faults and 22% of the accessory faults. Among the accessory devices, the cooling system failure accounts for 25%, the overall protection system failure accounts for 27%, the hydraulic system failure accounts for 41%, and the lubrication system and pneumatic system failure accounts for 7%.

The failure rate of hydraulic system is the highest, which indicates that the hydraulic system of horizontal machining center is the weak link in the reliability of accessory devices. Therefore, the reliability level of hydraulic components should be considered in the selection. In the early fault statistics of the hydraulic system, it is found that the early fault modes of the hydraulic system are mainly oil leakage, parts damage and excessive noise. There are nine kinds of fault phenomena, as shown in the table below.


Early failure mode and phenomenon of hydraulic system

Failure mode















(2) Analysis of three modes of early failure causes

There are three early failure modes in the hydraulic system of horizontal machining center: oil leakage, parts damage and excessive noise. The main reasons for these three failure modes are as follows.

① Oil leakage a. the quality of oil pipe and pipe joint is unqualified. The oil pipe and pipe joint are purchased from outside. Due to the lack of strict inspection and control before entering the factory and before assembly, the unqualified oil pipe and pipe joint are installed into the main engine. b. Poor assembly quality. The main reason is that the pipe joint is not tightened and the sealant at the pipe joint is not evenly applied.

② The damaged tubing and pressure gauge are easy to be damaged in the early use of machining center. The main reason for the damage is the unqualified quality of tubing and pressure gauge. Tubing and pressure gauge are purchased parts, and their quality is not up to standard, which further indicates the lack of optimization of purchased parts and strict inspection before assembly.

③ The noise exceeds the standard a. the oil filter is blocked. Due to the insufficient design of oil filter capacity, it causes premature blockage, resulting in excessive noise of hydraulic pump. b. Air leakage. Due to the poor assembly, the pipe joint leaks air, so that the air enters the oil suction side, resulting in excessive noise of the hydraulic pump.

(3) Preventive measures

According to the analysis results of the early fault location and the severity of each fault mode of the machining center, the manipulator and spindle box are prone to faults, and the main fault modes are oil leakage, parts damage and excessive noise. Therefore, in addition to the routine maintenance of the machining center, such as refueling, grease change, spot inspection, cleaning, adjustment, calibration, etc, Preventive maintenance should also be carried out for the main failure modes.

① Measures to prevent the leakage of hydraulic cylinder of manipulator A. check the aging and wear of the seal ring to prevent it from being squeezed into the seal gap when it works under high pressure, resulting in bite and leakage. b. Check whether there is micro dust at the cylinder port and shaft head, and wipe it with a soft and clean cloth to prevent scratching the surface of parts, resulting in leakage at the scratch. c. The regular tightening, cleaning, filtering and replacement system shall be strictly implemented. The quenched parts and oil tank shall be cleaned and maintained regularly. The oil and sealing parts shall be replaced regularly. It shall be noted that the new oil added to the oil tank must be carefully filtered and moisture removed.

② Check the flow rate of one-way throttle valve to prevent excessive flow rate leading to high speed of main shaft fork pulling, resulting in excessive impact and noise of manipulator tool taking. b. Check the smoothness of gear transmission to avoid excessive noise caused by unstable gear transmission. c. The dynamic balance test of headstock should be carried out strictly. d. Check the dynamic balance of the spindle.

In addition, the quality of purchased parts should be strictly controlled.

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