1 Introduction With the increasing demand for work efficiency, hydraulic chucks have gradually replaced manual chucks and have been widely used. In order to meet the processing requirements of different workpieces, such as rectangular surface, cylindrical surface and other irregular surface parts of the workpiece, and some clamping surface and the workpiece surface eccentricity of the workpiece, usually requires the use of four-jaw hydraulic chuck. Looking at the four-jaw hydraulic chuck produced by hydraulic chuck manufacturers at home and abroad, its structure is that one cylinder drives four clamping jaws and clamps at the same time. The center of the workpiece is difficult to be coaxial with the spindle rotation center, and the center of each clamping is adjusted. All have to be achieved by the claws of the vehicle, which is inconvenient. Even if the adjustment is relatively accurate, due to the deviation of the clamping surface of the workpiece itself, according to the principle of three-point centering, it is still not possible to achieve four-point circle, and the four claws in the four clamping jaws after the three-jaw clamping are virtual clamps. When the cutting force is large, the clamping force may not be enough, resulting in even accidents of waste products, which restricts the application of the four-jaw hydraulic chuck. To this end, our factory developed a four-claw self-centering hydraulic chuck, and successfully applied to the 1.2m CNC vertical lathe. This article focuses on the structure of the chuck, the working principle, the adjustment of the jaws and the calculation of the clamping force.
1. Cylinder I 2. Cylinder II 3. Piston 4. Piston II 5. Pull Block I
6. Pull block II 7. Guide sleeve 8. Lever 9. Horizontal pull block 10. Workbench
11. Adjust the nut 12. Lock nut 13. Slider 14. Gripper four-jaw hydraulic chuck Principle 2 How it works The four-jaw hydraulic chuck schematic is shown on the right. The chuck divides the four jaws into two symmetrical groups, driven by two different cylinders. The two oil cylinders have the same pressure area and are supplied by the same oil line 1, thus ensuring that the output forces of the two oil cylinders are equal. The two piston rods are connected to their respective pull blocks, and through a lever boost mechanism, the slide block and the clamping jaws are pulled to perform corresponding movements to achieve a clamping action. Each jaw travels 12 to 15mm. When the oil line 1 is supplied with oil, the clamping jaws are clamped. Due to the workpiece clamping surface deviation, two pairs of jaws may hold the workpiece in time, but because the two cylinders communicate with each other, and the two cylinders have the same pressure area, when the two pairs of jaws After the workpiece is clamped, the pressure of the hydraulic oil in the two cylinders is always equal, which ensures that the four clamping jaws clamp the workpiece and the clamping force is basically the same. 3 Adjustment of jaws The adjustment of jaws can be divided into coarse and fine adjustment steps. In the coarse adjustment, according to the size of the workpiece clamping diameter, under the premise of fully taking into account the factors such as the jaw stroke and workpiece eccentricity, the four clamping jaws are moved to a suitable position and the screws can be tightened. For most workpieces, only coarse adjustment is required. For some workpieces with high precision, fine tuning is also required. Fine tune the results of the coarse measurement, record the deviation of each jaw, fine-tune each jaw, and the maximum amount of fine adjustment of each jaw is greater than the tooth pitch of one comb. When adjusting, loosen the lock nut 12 with a special wrench. According to the deviation of each claw, turn the adjustment nut 11 to a suitable position with a special wrench, and then tighten the lock nut 12. When mass production, it is generally only necessary to perform a fine adjustment. 4 Calculation of clamping force Each cylinder output force is F-pull=PA=pP[( D1 )2-( d1 )2]=pP[( D2 )2-( d2 )2] 2 2 2 2 (1) Medium: P - Pressure oil pressure A - Effective pressure area D1, D2 - Diameter of cylinder I, II d1, d2 - Diameter of piston rod I, II Pressure of each pair of jaws F clamp is F clamp = F Pull L1 h L2 (2) Where: L1, L2 - length of the two levers of the lever mechanism h - transmission efficiency total clamping force F is always F total = 2F clips (3) by equations (1), (2) (3) It can be seen that the clamp clamping force can be changed by adjusting the input oil pressure. 5 Conclusion The actual use of the proof, we developed the four-jaw hydraulic chuck has a compact structure, easy maintenance, clamping range, easy adjustment, adjustable clamping force, etc., can be used to clamp rectangular workpiece, round workpiece, Some irregular workpieces and eccentric workpieces are rotated.
