Design and Simulation of Hydraulic Integrated Valve based on SLM Technology

Intelligent robots put forward the need for miniaturization and integration of hydraulic systems. Based on SLM technology, this paper designs a hydraulic integrated valve, integrates flow channels, adapters and other facilities on the valve body, replaces the original linear movement scheme with a rotating spool scheme, studies parameters such as runner diameter and minimum wall thickness, and simulates and analyzes the flow performance of liquid when the main control runner and a single valve work. The results show that the integrated valve has the advantages of light weight, small size and good performance.


Introduction
The hydraulic system has the advantages of good controllability and high power, and has been widely used in industry [1,2].With the advancement of intelligent robot technology, the hydraulic system has been driven to the direction of miniaturization and integration [3,4].
Hydraulic integrated valve blocks are a common method of hydraulic system integration [5], but their design is limited by traditional processing techniques.As a kind of additive manufacturing [6], SLM (Selective laser melting) technology greatly reduces the limitations of integration in structural design and shows an irreplaceable role [7,8].Similarly, applying SLM technology to the design and manufacture of hydraulic integrated valves can reduce weight and achieve efficiency [9,10].
Based on 3D printing rapid prototyping technology, this paper designs a new type of hydraulic integrated valve block, and simulates and analyzes the flow resistance of hydraulic integrated valve.Compared with the original hydraulic system, the new hydraulic integrated valve has complete functions, small size and light weight, and realizes the pipeless connection to working device.

Formulation of design requirements
In the intelligent manipulator, the functional principle of the hydraulic system currently used is shown in Figure 1.The hydraulic system mainly includes four two-way control valves, each valve has independent two working states.So the system as a whole has a total of 16 working modes, according to the working needs to switch different working mode.As can be seen from the table, the shortcomings of the original hydraulic system include: (1) large weight, reduced payload, and delayed response speed; (2) Large size and takes up a lot of space; (3) Poor effect, subject to traditional processing methods, so that the flow resistance in the valve is high.In order to meet the manipulator's demand for light weight and high performance of hydraulic system, the unique advantages of SLM technology can be used to integrate the hydraulic system, and the structural function improvement is expected to be shown in Table 2.
Table 2. Improvement goals Improvement Method Goal SLM technology Channels of any orientation can be manufactured, which improvs flow performance of the value.

Integrated design
By combining, integrating, and improving the execution mode of the spool movement, the valve body size can be reduced by at least 50%.Reduce the overall weight of the valve body by more than 75%.

Hydraulic integrated valve structure design
In view of the shortcomings of the original hydraulic valve, combined with the process characteristics of SLM technology, the new hydraulic integrated valve is designed as shown in Figure 3.The main components of hydraulic valves include value core, valve sleeve and valve body.

Valve Core and Valve Sleeve
The valve core and the valve sleeve are assembly as shown in Figure 4, and the on-off state with the external oil channel is changed through the rotation of the valve core to complete the required function.
Here, the rotary valve scheme is selected instead of the linear scheme of the original hydraulic valve, which can reduce the axial size of the valve body.

Figure 4.
Assembly of the value spool and the value sleeve The valve core is cylindrical with 3 grooves on it as the hydraulic oil passages.There is an annular oil groove in the middle of the valve core, which is always connected with the external oil hole, as shown Figure 5.At both sides of the annular groove, oil grooves that can be connected to the oil inlet channel and the oil outlet channel are arranged separately in the direction of the busbar, and the two types of oil grooves differ by 90º in the circumferential direction, and each type of oil groove is arranged evenly (180º apart) along the outer circumference.As the valve core rotates, the round head oil groove on one side alternates with the oil inlet hole to form on or off status, while the round head oil groove on the other side forms on or off status with the oil outlet hole.A motor shaft mounting slot is provided at one end of the valve core.

Figure 5. The value core
In order to ensure the rotation accuracy of the valve body and valve core, and achieve a good sealing effect, a valve sleeve is arranged between the working cavity and the valve sleeve to connect the valve body and the valve core, as shown Figure 6.Since the annular oil groove on the valve core is in a constant connection state with the external oil hole, with the rotation of the valve core, the external oil hole is alternately connected with the oil outlet hole and the oil inlet hole to form different working states.
The two working modes of the integrated valve are, through the valve core rotation to control the external oil circuit and the oil inlet or with the oil outlet, the specific working mode is shown in Figure 7, which makes the whole integrated valve a total of 16 working states.

Valve Body
The valve body is the embodiment of the integration of this hydraulic system, which is used to arrange the flow path and provide working space for the rest of the parts, as shown Figure 8.
Let Q = 100ml/s, u=10m/s, then d ≥3.5mm.Calculated according to the pressure drop, Let μ = 0.0085, l = 6mm, m = 0.75, ΔP = 0.02MPa, then d ≥3.2mm.Rounding d is 4mm, which can meet the conditions of use.Therefore, the external working oil channel is the minimum bore runoff channel 4mm.At the same time, since the oil inlet and outlet channel needs to provide the inlet and outlet oil volume of 4 valves, its flow area should be twice the minimum aperture, so its diameter is 8mm, and the interface is slightly larger set to 9mm.
(2) Minimum wall thickness The minimum wall thickness is calculated based on the tensile strength Let py = 1.5pn(pn=16MPa), σb= 200 MPa(The tensile strength of ordinary alloys is greater than 200MPa), d=4mm, so δ ≥ 0.5mm [12].Considering corrosion and protection, taking the minimum wall thickness in the integrated external oil circuit is 2mm.
After design, the comparison with the original hydraulic system is shown in the table 3.

Simulation of valve body flow performance
Since the liquid flow resistance performance is one of the most important indicators for hydraulic valves, numerical simulation of the flow performance of the integrated valve is required.
Figure 11 shows the velocity distribution at egress flows of 100ml and 900ml.It can be seen from the analysis results that with the increase of flow, the trend of pressure drop is obvious, and the liquid resistance of the overall flow channel gradually increases with the increasing flow rate, which is consistent with intuitive understanding.In the case of flow less than 500ml/s, the overall level of pressure loss is low, the maximum is only to the level of 0.8MPa, the influence of liquid resistance is below 5%, and the flow rate of 500ml/s under high pressure of 16MPa, has been able to meet the vast majority of drive requirements, for the caliber of 4mm hydraulic pipeline its flow performance has been relatively excellent.

Single valve simulation
Each valve has two modes, one is to connect the working circuit with the oil inlet pipeline, and the other is to connect the working circuit to the oil outlet line.
(1) Simulation when connected to the inlet line The calculated channel area is shown in Figure 13.
Figure 13.The simulated channel area.Using the standard k-ε model analysis, the inlet 1 and 2 are set to be at both ends of the oil inlet pipeline, and the setting is 16MPa; The outlet is the speed exit, which is 120ml/s and 500ml/s respectively.In order to facilitate comparative observation, the three typical sections as shown in the figure are selected and analyzed as shown in the Figure 14.It can be seen from the speed distribution chart that under different flow rates, the speed distribution is generally consistent, the distribution of the inlet and outlet channels is relatively uniform, the liquid flow resistance is small, and the main pressure loss comes from the spool part, especially under the working conditions of large flow, its speed gradient is more obvious.
(2) Simulation when connected to the outlet line The analysis method is similar to 1.The working conditions are set to:120ml/s(inflow rate), 6MPa(pressure at outlet 1 and outlet 2).
The boundary conditions explain that since the simulation is a reverse flow situation, its condition settings will be adjusted accordingly, outlets 1 and 2 correspond to the two oil outlets of the model, and the inlet corresponds to the original external working oil circuit interface, as shown Fig16.The liquid flow resistance of the flow channel is the same in the two main working modes, and the difference is mainly due to the different distribution of the liquid flow when the flow direction is different; Under normal working conditions, the liquid resistance level of the flow channel is low, can be controlled at about 0.3MPa, in the large flow of 500ml/s liquid resistance is about 3.5MPa, because the pressure drop is related to the speed, according to the results of simulation analysis 2, to control the pressure drop within 1MPa, the flow should be controlled within 250ml/s.

Conclusion
Based on the process characteristics of SLM technology, the paper redesigns the hydraulic integrated valve applied to the intelligent manipulator, and achieves the purpose of reducing the mass by more than 90% and the volume by more than 60%.The work done for the thesis includes: (1) Based on SLM technology, the valve body flow is rearranged, the valve core working mode is improved, and the structure of the hydraulic valve is improved by combining the characteristics of 3D printing to manufacture complex structures.
(2) The simulation analysis test of the improved integrated valve was carried out, and the flow performance of the whole and key parts was tested according to different flow and pressure conditions.
At present, physical tests of this hydraulic valve are being carried out, as shown in Figure18.

Figure 1 .
Figure 1.Hydraulic system in intelligent manipulator The hydraulic system contains two main functional parts: first, the hydraulic drive valve body part shown in Figure 2 (a), a total of 8 oil circuit interfaces; the second is the external oil channel part and the adapter part as shown in Figure 2 (b).

Figure 2 .
Figure 2. Original hydraulic system.(a) the hydraulic drive valve body part;(b) the external oil channel part and the adapter part Structural parameters of the original hydraulic system are shown in Table1.Table1.Structural parameters of the original hydraulic system

Figure 3 .
Figure 3. Hydraulically integrated valves based on SLM technology

Figure 6 .
Figure 6.The value sleeveThe valve sleeve is a ring cylinder, which has 3 holes, an oil inlet hole, an external oil hole and an oil outlet hole.The external oil hole and the ring oil groove on the valve core are always connected.With the rotation of the valve core, the oil inlet hole and the oil outlet hole are connected or isolated with the oil inlet groove and the oil outlet groove on the valve core.The outer surface of the valve sleeve has four O-ring mounting slots, and the inner surface has two glei ring mounting slots near the two ends.Since the annular oil groove on the valve core is in a constant connection state with the external oil hole, with the rotation of the valve core, the external oil hole is alternately connected with the oil outlet hole and the oil inlet hole to form different working states.The two working modes of the integrated valve are, through the valve core rotation to control the external oil circuit and the oil inlet or with the oil outlet, the specific working mode is shown in Figure7, which makes the whole integrated valve a total of 16 working states.

Figure 8 .
Figure 8. Value body The valve body has four cylindrical holes for installing rotary switch valves, and the bottom of each cylindrical hole is opened with oil holes corresponding to the oil holes on the rotary switch valve, and the four rotary switch valves are installed on the block in parallel and work independently of each other.The four rotary on-off valves share the inlet and return channels, and their external oil holes are connected to the external actuator by four curved external oil channels.The valve body is designed with

Figure 10 .
Figure 10.Control piping (mainstream) simulation area ICEM CFD software was used to mesh the fluid, and Fluent software was used to simulate the analysis.The main condition analyzed is the resistance of the liquid flow at different flow rates.According to the working condition of the valve, the inlet pressure is set to 16MPa, and the outlet flow is set to20, 40, 60, 80, 100, 120, 140, 160, 180, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500ml/s.Figure11shows the velocity distribution at egress flows of 100ml and 900ml.

Figure 11 .Figure12.
Figure 11.External oil duct velocity distributionAccording to the simulation results, the flow rate was divided into two groups of 20~180 ml (Group A) and 300~1500 ml (Group B) for easy viewing, and the flow-pressure diagram was made as shown in Fig.

Figure 14 .
Figure 14.Cross-section for the flow analysis Figure 15 shows the velocity distribution of three sections at an outlet velocity of 120ml/s.

Figure 15 .
Figure 15.The velocity distribution of three sectionsThe resistance performance of a single valve when working is shown in TableTable 5. Pressure drop of the value

Figure 16 .
Figure 16.Illustrative diagram of boundary conditions for simulation The velocity distribution is shown in the figure 17.

Figure 17 .
Figure 17.Speed distribution diagramThe resistance properties are as follows in Table5.

Figure 18 .
Figure 18.Hydraulic valves ready for test trials

Table 1 .
Structural parameters of the original hydraulic system 1.Valves Solenoid, sliding valve core, main valve body, oil inlet line, oil outlet line.

Table 3 .
Parameters Comparison of old and new valve

Table 4 .
Amplitude of pressure drop

Table 5 .
Pressure drop of the value

Table 6 .
Pressure drop of the value