Created on:2021-04-29 11:03

Manufacturing technology of single acting radial piston motor

Manufacturing technology of single acting radial piston motor

There are two types of hydraulic motors: high-speed small torque motor and low-speed large torque motor. The structure of high-speed small torque motor (gear motor, vane motor and axial piston motor) is basically the same as that of similar hydraulic pumps, so the material and technology are also basically the same. This paper mainly introduces the material and technology of radial piston type low speed high torque hydraulic motor.

This paper introduces the crankshaft connecting rod type five star wheel hydraulic motor (NHM type hydraulic motor) which is produced by introducing Italian technology.

(1) Structure and technical requirements NHM hydraulic motor is mainly composed of crankshaft 1, shell 2, port plate 4, plunger cylinder 6, plunger 7 and connecting rod 8 (Fig. q). When the high-pressure oil passing through the port plate 4 enters the piston cylinder 6, a hydraulic thrust is generated on the piston 7. The thrust acts on the center of the eccentric crankshaft 1 through the connecting rod 8 to make the output shaft rotate. At the same time, the port plate 4 rotates together. When the position of the piston reaches the bottom dead center, the piston cylinder 6 is connected to the oil discharge port of the motor by the port plate, and the piston is pushed upward by the crankshaft. At this time, the oil after work is discharged Return to the tank through the port plate. Each plunger is connected with high and low pressure hydraulic oil in turn, and the driving torque generated by each plunger to the center of the output shaft is added in the same direction, so that the motor output shaft can obtain continuous and stable torque. Changing the direction of hydraulic oil supply can make the hydraulic motor rotate in reverse direction; if the valve plate is turned to 1800, the motor can also rotate in reverse direction. This kind of motor has the characteristics of low noise, high efficiency and good reliability, which is the preferred product in domestic injection molding machine industry.

In order to ensure the performance and service life of the motor, there are high requirements for the material and machining accuracy of the crankshaft, shell, connecting rod and other key parts.

(2) Material and process requirements of key parts

① The crankshaft is the torque output mechanism of this type of hydraulic motor. It not only needs to have enough strength, but also its eccentric crank is the inner ring of the bearing, which must have high hardness. Therefore, carburized steel combined with surface carburizing and quenching process is selected to make it have strong toughness in the crankshaft core on the basis of ensuring enough surface hardness. When machining, we must pay attention to the shape and size of the crank surface and the coaxiality and parallelism of the bearing rings at both ends.

Because the crankshaft is carburized and quenched with carburized steel, the deformation and high hardness after quenching bring some difficulties to finish machining: the protruding parts on both sides of the crank are thin, which is easy to crack; the crank is eccentric, which is easy to produce quenching deformation. In addition, high machining accuracy is required. The solution is: normalizing after rough turning to eliminate cutting stress, reduce deformation and prepare for carburizing; increasing grinding allowance appropriately to increase carburizing depth to avoid quenching deformation; coating protective layer on thin wall during carburizing to reduce carburizing amount and avoid quenching crack; using spline grinder and electric pulse processing to finally correct the position and size of spline and flat keyway.

The technological process of crankshaft machining is as follows: Die Forging → flat head → marking and drilling center hole → rough turning and setting allowance of 2mm → normalizing and eliminating internal stress → fine axle block excircle with allowance of 0.6 ~ 0.5 8mm - finish turning crank with allowance of 0.6-0.8mm → milling end groove → milling sealing block notch → matching sealing block → milling keyway with allowance of 0.2-0.3mm → drilling inner center hole of end groove → deburring → carburizing and quenching → grinding outer circle → grinding crank → electric pulse machining flat keyway → cleaning and drying → inspection.

② The connecting rod plays the role of force transmission in the motor. It contacts with the cambered surface of the bearing outer ring outside the crankshaft to form a friction pair and play a sealing role; it also contacts with the spherical surface of the plunger inner hole to form a friction pair and play a sealing role, in addition, it also plays a role of universal joint. This requires that the circular surface and spherical surface of the connecting rod should be smooth, wear-resistant and accurate. Moreover, it is a force transmission mechanism, which requires sufficient strength and rigidity.

One end of the connecting rod is an inner arc surface, and the other end is a spherical surface, which is an irregular special-shaped part. In order to facilitate processing, five or six parts should be cast together in casting, and then cut after processing, which can not only improve work efficiency, but also ensure processing accuracy. During machining, in order to reduce the deformation of the internal arc surface after cutting and the deformation during heat treatment, and reduce the cutting stress as much as possible, the precision casting method should be adopted as far as possible to reduce the machining allowance of the blank. Machining spherical surface on CNC lathe and then fine grinding on spherical grinder can ensure machining accuracy and improve work efficiency.

The processing process of connecting rod is as follows: precision casting → normalizing (230 ~ 260hb) → turning inner and outer circle, inner hole grinding amount 0.3 ~ 0.4mm → turning spherical surface, grinding amount 0.3 ~ 0.4mm → drilling through oil hole → grinding inner hole to meet drawing requirements → cutting → deburring and chamfering → surface treatment nitriding → grinding → cleaning and drying → inspection.

③ The shell is the base of the hydraulic motor, all parts are installed on the shell, and it is also the key part of the flow distribution. Not only the flow distribution hole on the back plane must be equal to the flow distributor, but also the five piston cylinders must be on the same indexing plane with the flow distribution hole. Otherwise, the flow distribution is not smooth, which will affect the stability and efficiency of the hydraulic motor. Secondly, it is the crankshaft mounting base, two bearing mounting holes must be on the same axis, so the machining accuracy and coaxiality is the key to the machining of the part. In addition, the rotary friction between the valve distributor and the back surface of the shell and the installation and connection of the five piston cylinders also require the shell to have a high degree of wear resistance and rigidity, so the ductile iron QT600 or alloy steel castings are selected, and the heat treatment hardness is required to be about 230 ~ 260hb.

The machining difficulties of the shell are: axial dimension tolerance; angle control of the five plug holes and the port holes; indexing angle control of the five port holes and the two locating pin holes; accuracy of the two bearing seats.

Adopting a horizontal machining center and a vertical machining center, adopting the process method of one-time positioning on the machining center to complete all processes, and combining with the precision casting process, the above process problems can be met, and the work efficiency can be greatly improved.

The processing process of the shell is as follows: precision casting → normalizing (230 ~ 260hb) → turning the small end positioning excircle → machining two bearing blocks of the inner hole and drilling tapping thread → machining five column plug holes and holes on the plane valve plate, drilling positioning holes and tapping thread → drilling five inclined oil holes → grinding the small end valve plane → deburring all processed burr → cleaning and drying → inspection.

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