Created on:2021-05-28 09:24

Manufacturing technology of inclined axial piston pump

Manufacturing technology of inclined axial piston pump

(1) The technical requirements are shown in Figure L. the oblique axial piston pump is mainly composed of cylinder block 1, port plate 2, connecting rod plunger pair 17, transmission spindle 18 and other key parts. This kind of pump is a high power density hydraulic pump. The best plunger pump can work in high pressure (generally 32Mpa, some up to 40MPa and above), high speed (up to 6000r / min), high temperature (continuously working at 80 ℃ oil temperature) and other harsh working conditions for a long time, and has high volumetric efficiency (up to 98% under rated working condition) and total efficiency (up to 93% under rated working condition). This requires that all parts in the shell should not only have enough strength and rigidity, but also have high dimensional accuracy and shape and position accuracy.

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(2) Common materials and process requirements

① The spindle diagram m shows the schematic diagram of the spindle. The spindle plays the role of transmitting torque. At the same time, seven "hemispherical dimples" are evenly distributed along the circumference on the end face of the drive plate of the spindle. There is also a "hemispherical dimple" in the center of the spindle. These dimples form a ball hinge with the ball head on the connecting rod and the ball head on the central rod. One of them is matched with the framework oil seal, so the ball hinge should move flexibly, and the leakage from the gap should not be too large, which requires the ball socket to have high geometric accuracy and low surface roughness. In addition, there are strict requirements for the distribution circle and uniform distribution error of each ball and socket. The dimension tolerance, radial runout and surface roughness of the outer circle matched with the bearing shall meet certain requirements; the surface roughness of the section matched with the framework oil seal shall reach 0.2 μ m, and spiral knife marks are not allowed. So the manufacturing of the spindle is very difficult.

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The spindle materials are mostly nitrided alloy steel, such as 38CrMoAl, 40Cr2MoV, etc. after nitriding treatment, it can obtain high surface hardness, high fatigue strength and good resistance to overheating and deformation. Sometimes the inner wall of the ball socket of the driving disc is covered with a friction reducing layer.

The hemispherical socket on the spindle is mainly processed by forming tool or whirlwind milling. Among them, whirlwind milling can achieve high accuracy (tolerance zone < 0.02mm, surface roughness < 0.8 μ m, sphericity ≤ 0.006mm), high efficiency, suitable for mass production, but the equipment cost is high. The process of whirlwind milling is: firstly, the ball bit is used for rough machining of hemispherical socket, with a difference of 0.3-0.5mm from the final size, and then the special ball socket whirlwind milling is used for finish milling. After nitriding treatment, the hemispherical socket is ground to meet the design size requirements.

② The material of connecting rod piston pair is usually high speed steel.

When the inclination angle is less than or equal to 25 °, the connecting rod is conical and has two ball heads. One of the ball heads and the steel plunger are rolled as a whole after finishing, and then the outer circle and the ball head are ground after heat treatment. The dimension, shape and roughness of the connecting rod and plunger before rolling should meet the design requirements. The dimensional tolerance, axial displacement and swing of the connecting rod in the plunger after heat treatment should meet the design requirements The other end is hinged in the ball socket of the spindle drive plate with a pressing plate.

When the inclination angle is 40 ° as shown in Fig. n, the whole structure without connecting rod with one end of ball head and the other end of conical plunger is adopted (the function of connecting rod is considered in the actual use of conical plunger).

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The machining process of conical plunger is as follows: blanking, sawing single piece → die forging → quenching and tempering heat treatment → milling two end faces → drilling center hole → turning forming → rough grinding → nitriding heat treatment → fine grinding → final inspection and storage.

③ The transmission main shaft of the cylinder oblique shaft pump does not pass through the cylinder, and its cylinder diameter is smaller than that of the straight shaft pump. In addition, the side force has less overturning effect on the cylinder, so the working condition of the valve pair is better than that of the straight shaft pump, and the allowable speed is also higher.

Most inclined shaft pumps use bimetal cylinder block. The outer surface is made of high-quality steel, and the hole matched with the plunger and the spherical surface matched with the valve plate are copper layers, which are cast copper alloys. The process requirements are as follows: the cast copper alloy shall meet the designed chemical composition and mechanical properties; the cast copper layer shall not have defects such as sand holes, porosity and severe segregation; the copper layer shall be firmly combined with the base metal without delamination; the dimension tolerance, cylindricity, surface roughness of the holes matched between the cylinder block and the plunger, as well as the diameter tolerance and equal angle tolerance of the seven hole distribution circle shall meet the design requirements The diameter, sphericity, runout and surface roughness of the spherical surface matched with the valve plate shall meet the design requirements.

The schematic diagram of cylinder block parts is shown in Figure o. The typical machining process of cylinder block is: normalizing → rough turning outer circle and central hole → rough turning: profiling turning R175 spherical surface → drilling seven column plug holes → bimetal casting spherical surface → semi finishing turning outer circle of end face → turning end face, reference outer circle and central hole → expanding seven column plug holes → finishing turning: profiling turning R175 spherical surface → drilling seven inclined holes → gas nitriding → pressing plunger copper sleeve and central shaft sleeve → grinding outer circle The process is as follows: → rough boring seven column plug holes → fine boring seven column plug holes → fine grinding R175 spherical surface → cleaning and deburring → final inspection and warehousing.

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④ The material of valve plate is similar to that of straight shaft pump.

Inclined shaft pump mostly adopts spherical valve plate. The spherical surface of valve plate should have high dimensional accuracy, surface quality and form and position accuracy, that is, the spherical surface and ball diameter, runout and surface roughness should be guaranteed. The arc size, surface roughness and symmetry of both sides of valve plate of variable displacement pump should meet the drawing requirements. After heat treatment, the hardness should meet the design requirements. The parts after grinding shall not be scratched.

The parts diagram of spherical valve plate is shown in Figure P. The typical machining process of spherical valve plate is as follows: quenching and tempering → rough turning both ends and outer circle → semi finish turning outer circle, boring center hole → finish turning: profiling turning r176 spherical surface → drilling four holes of waist groove and locating pin hole → milling waist groove → rough grinding outer circle → rough grinding end face → rough grinding r176 spherical surface → centralized chamfering, deburring and cleaning → gas nitriding → fine grinding end face → pressing center bushing → fine grinding center hole After finishing grinding r176 spherical surface, centralized cleaning, final inspection and storage.

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⑤ The shell and the back cover of the oblique axis pump are the carrier of the core parts and the support of the installation and fixation. Because of the inclination angle, there are accurate requirements for the intersection of the two axes (called intersection degree), as well as the dimensional tolerance and surface roughness of the bearing.

The oil passage of the back cover should withstand extremely high pressure without leakage. The cold processed hole of the variable displacement pump has accurate requirements for dimensional tolerance, roundness, surface roughness, etc., and the arc channel radius, surface roughness, symmetry, etc. matched with the valve plate have higher accuracy requirements.

(3) Explanation

① Inclined shaft piston pump is a precision machining component, although the volume is not large and there are not many parts, it has high requirements for casting quality and appearance, machining dimensions and tolerances of parts, surface roughness, form and position tolerances, etc. Only when the quality of parts meets the design requirements can the performance and reliability of products be guaranteed.

② In the process of machining and before assembly, it is necessary to deburr the parts of the inclined shaft pump to prevent bumps and scratches, and carefully clean them to prevent iron filings, sticky sand, dust, sundries, etc. from mixing into the pump shell, affecting the cleanliness of the pump and causing the performance defects and even damage of the pump.

③ In order to ensure the performance and long service life of the pump, we should pay attention to and ensure the cleanliness of the oil in use, and pay attention to the correct assembly during maintenance and disassembly.

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