Fault Analysis and Solutions of 16m CNC Vertical Lathe

(1) Fault phenomenon

If a CNC vertical lathe wants to move the column during operation, it is necessary to start the column moving hydraulic pump. At this time, the hydraulic pump emits a harsh squeal noise. With regard to severe tremor, the column cannot move. If the column lasts for a long time (more than 3min), the oil pipe is often cracked, causing oil blowout. The oil pipe is cracked no less than 5 times per vehicle, especially in winter.

According to the mechanism of static pressure formation and the theory of fluid mechanics, the squeal noise of hydraulic pump and the tubing crack are caused by hydraulic shock and cavitation. That is to say, at the moment of starting the hydraulic pump, the oil inlet pipe is emptied, and the oil cannot keep up with it, resulting in a local vacuum. Then, the oil in the pipe will generate bubbles (cavitation) and subsequent pressure shocks due to sudden changes in flow rate, resulting in huge noise and vibration. This pressure peak will sometimes reach the point where the hydraulic components can be damaged, which will cause the tubing to crack. In winter, due to the lower temperature, the oil fluidity is worse, which further aggravates the suction of the oil inlet pipe and the sudden change of pressure, thus increasing the frequency of failures.

(2) Failure analysis

1. The height difference between the relative position of the hydraulic pump and the oil pool is too large. The oil pool is located at the lower outer side of the bed guide rail. The height difference of the hydraulic pump installed on the sliding seat plate in the column is more than 1m. When it is stopped, all the hydraulic oil in the oil inlet pipe is easy to drain back to the oil pool.

2. The oil suction pipe is restricted by the sliding seat plate and spacer plate in the column, and it turns through three 90 ° angles from the pump end to the oil pool, thus increasing the pressure loss and lengthening the length of the oil pipe.

3. The oil inlet pipe is too thin（ φ 10mm) increases the oil absorption resistance.

(3) Solutions

1. A one-way valve is added between the oil suction port of the hydraulic pump and the primary oil filter to solve the problem of oil leakage during the shutdown period caused by the large relative height difference between the pump and the oil pool, and to eliminate the hydraulic impact and cavitation.

2. Replace the oil suction pipe and improve the pipeline layout. The original 10mm copper pipe was replaced with 24mm galvanized pipe, which expanded the flow diameter and changed the third corner of the original pipe. The original design has disadvantages such as excessive pressure loss along the way and long pipeline due to one-sided pursuit of process installation effect. By drilling through the pipe hole, the Z short path is pursued, and corners are avoided as much as possible. Hard bending is unavoidable and should not be used, and small curvature slow bending is adopted to eliminate the disadvantages of excessive pressure loss along the pipeline and long pipeline.