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Three techniques for clamping workpieces on CNC lathes

Posted by: Chris Na 2021-05-26 Comments Off on Three techniques for clamping workpieces on CNC lathes

Clamping is an important part of the workpiece clamping process. After the workpiece is positioned, the clamping force must be generated by a certain mechanism to press the workpiece on the positioning element to maintain an accurate positioning position. It will not be generated due to the cutting force, the gravity of the workpiece, the centrifugal force or inertial force of the CNC lathe, etc. Position changes and vibration to ensure machining accuracy and safe operation. This mechanism that generates clamping force is called a clamping device.

(1) The basic requirements of the clamping device (1) The clamping process is reliable and does not change the correct position occupied by the workpiece after positioning. (2) The size of the clamping force is appropriate to ensure that the position of the workpiece is stable and the vibration is small during the processing process, and the workpiece does not produce excessive clamping deformation. (3) The operation is simple, convenient, labor-saving and safe. (4) The structure is good, and the structure of the clamping device is simple, compact, and easy to manufacture and maintain. (2) The direction of clamping force and the selection of point of application (1) The clamping force should be toward the main positioning datum. The workpiece being bored has a requirement for perpendicularity to the /4 surface, so the A surface is the main positioning base surface during processing, and the direction of the clamping force F, should be toward the /4 surface. If the clamping force is changed to the B side, due to the angle error between the side/4 and the bottom B of the CNC lathe, the positioning position of the workpiece will be destroyed during clamping, which will affect the perpendicularity requirements of the hole and the/4 surface. CNC lathe factory (2) The point of action of the clamping force should fall within the support range of the positioning element and be close to the geometric center of the support element. The clamping force acts on the outside of the supporting surface, causing the workpiece to tilt and move, and destroy the positioning of the workpiece. (3) The direction of the clamping force should be conducive to reducing the size of the clamping force. When drilling A hole, the clamping force J and the axial cutting force F. , The direction of the gravity C of the workpiece is the same, and the clamping force required for the machining process is the smallest. (4) The direction and point of clamping force should be applied to the direction and position of the CNC lathe with better rigidity. The axial rigidity of the thin-walled sleeve workpiece is better than the radial attachment, and the clamping force should be applied along the axial direction; when the thin-walled box is clamped, it should act on the flange with good factory performance of the rigid CNC lathe; When there is no convex edge, single-point clamping can be changed to three-point clamping. (5) The point of clamping force should be as close as possible to the workpiece surface. In order to improve the rigidity of the processing part of the workpiece and prevent or reduce the vibration of the workpiece, the point of application of the clamping force should be as close as possible to the processing surface. When the shift fork is clamped, the main clamping force F: Acts vertically on the main positioning base surface, and an auxiliary support is set near the processing surface. Appropriate auxiliary clamping force can be applied to improve the installation rigidity of the workpiece. (3) Estimation of the size of the clamping force The size of the clamping force has a great relationship with the reliability of the workpiece installation, the deformation of the workpiece and the fixture CNC lathe, and the complexity of the clamping mechanism. During the machining process, the workpiece is subjected to cutting force, centrifugal force, inertial force and the weight of the workpiece itself. In general, when machining small and medium-sized workpieces in a CNC lathe factory, the cutting force (moment) plays a decisive role. When processing heavy and large workpieces, the gravity of the workpiece must be considered. When the workpiece is processed under the condition of high-speed motion, the influence of centrifugal force or inertial force on the clamping action cannot be ignored. In addition, the cutting force itself is a dynamic load, which also changes during the machining process. The size of the clamping force is also related to factors such as the rigidity of the process system and the transmission efficiency of the clamping mechanism. Therefore, the calculation of the clamping force is a very complicated problem, and generally only a rough estimate can be made. For the sake of simplicity, when determining the clamping force in low-speed machining, only the influence of the cutting force (moment) on the clamping can be considered, and it is assumed that the CNC lathe process system is rigid and the cutting process is stable. To tighten the most unfavorable instantaneous state, calculate the clamping force according to the principle of static balance, and then multiply it by the safety factor as the actual clamping force required by the CNC lathe, that is, Fj=kF where Fj——actual clamping required Tightening force; F-clamping force calculated according to static balance under certain conditions; k-safety factor, taking into account factors such as changes in cutting force and deformation of the process system, generally take A2 1.5-3. In practical applications, not all CNC lathes need to calculate the clamping force when there is a CNC lathe factory. Manual clamping mechanisms generally determine the clamping force based on experience or analogy. If you really need to calculate the clamping force more accurately, the above method can be used to calculate the clamping force.

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