Created on:2021-07-01 09:21

Maintenance of hydraulic sliding table -- technical transformation

Maintenance of hydraulic sliding table -- technical transformation

Sliding table is the main power component of modular machine tool and its automatic line. The accuracy, structural rigidity and technical performance of sliding table have a decisive influence on the technical and economic indexes of modular machine tool and its automatic line, such as working ability, work content, machining accuracy and productivity. The hydraulic slide table is a power component used to complete the feed movement. According to the technological requirements of the parts to be processed, the power box (with multi axle box) and various cutting heads can be installed on it, and matched with the supporting parts to form different forms of modular machine tools, which are used to complete drilling, reaming, boring, countersinking, scraping end face, chamfering, turning end face Milling and tapping. The detection device is installed on the sliding table to complete the feeding action of the automatic detection process.

The HY32B type hydraulic sliding table of horizontal fine boring modular machine tool for thrust surface of cylinder block crankshaft hole is technically reformed and equipped with electro-hydraulic servo control system.

(1) Composition and working principle of hydraulic slide

The hydraulic sliding table is composed of sliding table, sliding seat and hydraulic cylinder. The hydraulic cylinder is fixed on the sliding seat, and the piston rod is fixed under the sliding table. When the pressure oil enters the hydraulic cylinder, the sliding table can move along the guide rail of the sliding seat.

The hydraulic system of the hydraulic sliding table to achieve two feed working cycles, as shown in Figure J, the completed working cycle is as follows: sliding table fast forward one by one, work forward one by two, work forward one by one, stop and fast back.

In the hydraulic system of power sliding table shown in Fig. J, a pressure limiting variable vane pump and a volume throttling speed regulating circuit composed of two speed regulating valves are used in the oil inlet circuit, and a back pressure valve is set in the oil return circuit to stabilize the sliding table

At the same time, the motion stability of the slide is improved. Fast forward and work into the replacement of the use of stroke valve and hydraulic control sequence valve, the speed of the replacement is more stable. At the end of the work, the dead block iron is used to control the rest position of the worktable.

(2) Requirements of machining accuracy for hydraulic position servo system

The depth control of the thrust surface of the cylinder block crankshaft hole is realized by controlling the movement of the sliding table, and the precise control of the sliding table movement depends on the positioning accuracy and repeated positioning accuracy of the servo cylinder. Therefore, in order to ensure the stability of the depth of the hole, higher requirements are put forward for the positioning accuracy of the hydraulic position servo system. In addition, the thrust surface processing needs to feed for many times, and each feed depth is controlled by the position of the servo cylinder. In order to improve the processing efficiency, the servo cylinder is required to reach a stable state in as short a time as possible when changing the position each time. In a word, the requirement of machining accuracy for hydraulic position servo system is to have fast dynamic response and high steady-state accuracy at the same time.

(3) The control principle of electro-hydraulic servo system is developed

As shown in Figure K, the electro-hydraulic servo system of hydraulic sliding table is mainly composed of electro-hydraulic servo valve 2, hydraulic cylinder 1, sliding table driven by piston rod, potentiometer 4, stepping motor, rack and pinion mechanism 5 and proportional amplifier 3. When the moving contact of the potentiometer is in the middle position, there is no voltage output on the contact; When it deviates from this position, it will output the corresponding voltage. The weak voltage produced by the moving contact of the potentiometer needs to be amplified by the proportional amplifier before the electro-hydraulic servo valve can be controlled. The moving contact is driven to rotate by the stepping motor, and the angular displacement and angular velocity of the stepping motor are controlled by the pulse and pulse frequency from the digital control device. The rack is fixed on the sliding table, and the potentiometer is fixed on the gear, so when the sliding table drives the gear to rotate, the potentiometer rotates with the gear to realize negative feedback.

K.jpg

A certain number of pulses sent by the digital control device make the moving contact of the stepping motor drive the potentiometer to turn a certain angle (clockwise rotation), and the moving contact deviates from the middle position of the potentiometer, generating a weak voltage U1, which is amplified into U2 by the amplifier and then input into the control coil of the electro-hydraulic servo valve, so as to make the servo valve produce a certain amount of opening. At this time, the pressure oil enters into the left chamber of the hydraulic cylinder through the opening of the slide valve, pushes the piston and the worktable to move to the right, and the oil in the right chamber of the hydraulic cylinder flows back to the oil tank through the servo valve. As the gear of the potentiometer is meshed with the rack on the sliding table, the potentiometer rotates clockwise when the sliding table moves to the right. When the potentiometer turns around θ At 0, the carbon film middle position of the potentiometer coincides with the moving contact, the output voltage of the moving contact is zero, the signal of the electro-hydraulic servo valve is lost, the valve port is closed, and the sliding table stops moving. The distance of sliding table movement depends on the number of pulses, and the speed depends on the frequency of pulses. When the digital control sends out a pulse in the reverse direction, the stepping motor rotates counterclockwise, and the sliding table moves to the left.

(4) Test results and conclusions

The developed electro-hydraulic servo system is equipped on the reformed HY32B hydraulic sliding table. The test results show that the reliability and accuracy of action sequence control, the repeated positioning accuracy and dynamic characteristics of hydraulic servo cylinder reach or exceed the original technical indexes of the equipment.

The electro-hydraulic servo system has the characteristics of fast dynamic response, high steady-state precision, simple structure and convenient adjustment.

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