Hydraulic Automatic Drilling Equipment for Valve Bodies

Jan 25, 2022

1. Overview
A flange is the most commonly used connection in fluid pipelines, which is convenient for installation, maintenance, and replacement of the pipeline. Flanges are generally used for gate valves, globe valves, check valves, ball valves and plug valves under medium and low pressure. The valve body connected by flanges generally has three parts, two flange ends and one middle flange. For small-diameter valves (DN50 and below), 4 to 8 bolt holes need to be provided on each flange surface. There are not only requirements for dimensional tolerance for bolt holes, but also geometric tolerances such as position and coaxiality. Therefore, for the valve body, controlling the machining accuracy of flange bolt holes is one of the difficulties in quality assurance.

Problems such as too large sizes, inaccurate positions, and piping flanges not being able to be connected often occur when the flange bolt hole is processed. With the popularization of CNC drilling machines and machining centers, simple structured process equipment can realize the programming and processing of multiple bolt holes on each flange surface, which improves work efficiency and product quality. However, each valve body needs to be processed with different fixtures 3 times. The hydraulic automatic drilling process equipment of the valve body assembly utilizes the V-50L vertical machining center to realize the multi-station hydraulic clamping and automatic rotation processing of the valve body. This tooling can clamp 3 valve bodies at the same time (Figure 1), and the bolt holes on the 3 flange faces of each valve body can be machined. The dimensional tolerances of the products processed by the new tooling as well as geometric tolerances such as coaxiality and positions all meet the requirements. The clamping time is saved, and the work efficiency is improved by more than 3 times.

1. High-pressure hoses 2. Drill bits 3. Metal oil pipes 4. The object for clamping
5. Button boxes 6. Machine tool chucks 7. Hoses 8. Cables
Figure 1 The structure of the tooling

2. Structural characteristics
2.1 Clamping processes
For valve bodies with DN50 and below, the drilling tooling can clamp 3 pieces at a time, and two valve bodies with DN65 and DN80 can be clamped once. The middle flange is upward, and there is a semi-circular ring positioning step on the tooling cover in the clamping process, which is positioned on the plane of the middle flange and the outer circle. The end flange is supported by two semi-circular rods installed on the bottom plate, which is equivalent to the support of a V-shaped block (Figure 2). The left and right hydraulic cylinders below the lifting plate push the piston rod to move to both sides, and then the piston rod pushes the adjusting seat to both sides. There is an inclined surface with an angle of 16.5° at the upper end of each adjusting seat that fits the inclined surface below the lifting plate. As the adjusting seat moves to both sides, the lifting plate can be pushed upward, and the valve body can be pushed up and pressed tightly at the same time. If the hydraulic cylinder is directly used to push the valve body upward, when the drilling pressure is too high, the working stability of the oil cylinder will be affected. The force direction of the piston of the oil cylinder is perpendicular to that of the drill bit during drilling, and there is slope friction control. Therefore, it is stable.

1. Brackets 2. Rolling bearing seats 3. Oil inlet rings 4. Connecting shafts 5. Shaft connecting plates 6. Top plates 7. Oil inlet plates 8. Bottom plates 9. Adjusting seats 10. Piston rods 11. Left hydraulic oil cylinders 12. Middle hydraulic cylinders 13. Right hydraulic cylinders 14. Lifting plates
Figure 2 The fixture

2.2 Principles of changing positions
After all the bolt holes of the middle flange in the valve body are processed, the spindle of the machine tool is driven by the servo stepper motor to rotate the drilling tool at an angle of 90 to process the bolt holes of the end flange. After the flange hole at one end is processed, the machine tool spindle returns again and rotates 180° to process the flange hole at the other end. After all the flange holes at both ends are processed, the main shaft of the machine tool returns to the initial state, and the 3 sets of hydraulic cylinders under the lifting plate of the tooling are started; the piston rod moves to the middle, and the lifting plate drops. The valve body can be completely removed.

2.3 Working principles of piston rods
The front end of the hydraulic drilling tool is equipped with a connecting shaft. The connecting shaft is supported by a bracket and a bearing seat, and can be driven by the main shaft of the machine tool to rotate. An oil inlet ring is provided on the front end of the connecting shaft, and two Rc1/8 pipe joints M and N are installed on the oil inlet ring. The outside of the pipe joint is directly connected to the hydraulic station of the machine tool through a high-pressure hose. The pressure oil of the hydraulic station enters the oil inlet ring through the solenoid valve, and then enters the oil hole with φ9.5 mm under the connecting shaft through the M pipe joint of the oil inlet ring; it flows to the Rc1/8 pipe joint at K2, and then connects to the Rc1/8 pipe joint of the baseplate end through a metal pipe; it enters the welded oil inlet plate in the middle of the baseplate.

The pressure oil enters the middle hydraulic cylinder oil hole L2 of the compression cylinder through the three oil holes with φ3.2 mm on the bottom plate. Meanwhile, push the left and right piston rods to both sides, and the oil in the left and right cylinders flows into the welded oil inlet plate on both sides through oil holes L1 and L3. The pressure oil flows from the P1 and P3 pipe joints at the end into the K1 and K3 pipe joints through the metal pipe, enters the connecting shaft; and finally flows into the solenoid valve and the oil tank from the outlet N. After the valve body is drilled, only the solenoid valve needs to be reversed. The oil path passes through the above-mentioned reverse circuit; the piston rod in the oil cylinder moves closer to the middle, and the lifting plate that presses the valve body falls; the valve body can be taken out.

2.4 Working principles of hydraulics
The hydraulic principle is shown in Figure 3. The pump motor unit sucks oil from the hydraulic tank through the oil suction filter at the oil inlet, and supplies oil to the control oil circuit through the check valve at the oil outlet. The control oil circuit is divided into a compression or release circuit and a dividing circuit. The compression or release circuit is used to control the compression and release of the compression cylinder, while the dividing circuit is used to control the dividing of the dividing chuck.

(1) The compression or release circuit
When the electromagnet 3DT of the electromagnetic directional valve is energized, the pressure oil is decompressed by the superimposed pressure reducing valve, and then enters the connecting shaft through the electromagnetic directional valve, pressure relay and high-pressure hose as well as the middle hydrocylinder at the bottom of the lifting plate through the oil pipe of the tooling bottom plate. The two piston rods extend outward to realize the lifting of the lifting plate and compress the workpiece. When the electromagnet 4DT of the electromagnetic directional valve is energized, the pressure oil enters the left and right hydraulic cylinders, causing the two compression piston rods to contract inward to release the workpiece. The pressure relay is connected to the oil return and cannot send out a signal. Therefore, the machine tool numerical control system will lock the drilling motion program to ensure safe processing.

1. Suction oil filters 2. Pump motor units 3. One-way valves 4. Pressure gauges 5. Superposed pressure reducing valves 6. Pressure relays 7. Electromagnetic directional valves 8. Superposed directional valves 9. Check valves 10. Check valve switches 11. Accumulators 12. Globe valves 13. Level gauges 14. Hydraulic oil tanks 15. Air filters 16. Oil return filters
Figure 3 Principles of hydraulic control

(2) Dividing circuit
A dividing circuit is a machine tool spindle control circuit that controls the drilling of the three flange faces of the valve body. This set of drilling tooling only uses its dividing function to control the dividing of the dividing chuck.

3. A Comparison of quality and efficiency
Compare the quality and efficiency of drilling at different stages. The first stage is a single piece processed by ordinary machines; the second stage is a single piece processed by CNC machine tools, and the third stage is a multi-piece processed by vertical machining centers. Take a gate valve body with DN50 and CL300 as an example, the comparison of quality and efficiency data is shown in Table 1.

Table 1 The comparison of quality and efficiency

Comparison content	The first stage	The second stage	The third stage
Clamping methods	Bench pliers, clamping single piece three times	Pneumatic compression, clamping single piece three times	Hydraulic automatic compression, clamping multiple pieces at one time
Auxiliary working hours/min	15	3	0.5
Cutting speeds/(r/min)	250	From 1600 to 1800	From 1800 to 2000
Feeding/mm	0.25	0.05	0.05
Knives	High-speed steel and twist drills	Tungsten-cobalt-titanium-niobium carbide blades, standard drill stems	Tungsten-cobalt-titanium-niobium carbide blades, standard drill stems
Surface roughness of inner holes RA/μm	50 to 25	6.4 to 3.2	3.2 to 1.6
Accuracy of inner holes	H14	H12	H11
Machining hole position degrees/mm	Φ0.8	Φ0.3	Φ0.2
Coaxiality of end flange holes/mm	Φ0.8	Φ0.2	Φ0.05
Center flange hole position degrees/mm	Φ1.0	Φ0.4	Φ0.05
Completion time for the single piece/min	40	12	6