'Introduction to Commonly Used Clamps for CNC Lathes' Characteristics of Chuck Usage

Introduction to Commonly Used Clamps for CNC Lathes

　　1. Introduction to commonly used fixtures for CNC lathes Lathe fixtures mainly refer to fixtures installed on the lathe spindle. This type of fixture is connected to the machine tool spindle and drives the workpiece to rotate with the spindle. Lathe clamps are mainly divided into two categories: various chucks, which are suitable for processing disc parts and short-axis parts; clamps with center holes and top centering positioning and mounting workpieces, which are suitable for shaft parts with larger lengths or more processing procedures. CNC turning processing requires that the fixture should have high positioning accuracy and rigidity, simple structure, strong versatility, easy installation of the fixture on the machine tool, rapid loading and unloading of workpieces, automation and other features. 1. Various chuck fixtures In most CNC lathe processing, the outer circle of the workpiece or blank is used for positioning. The following fixtures are circumferential positioning fixtures. The three-claw chuck is the most commonly used universal fixture for lathes. The biggest advantage of the three-claw chuck is that it can automatically center and clamp.

　　2. It has a large range and fast clamping speed, but there are errors in the centering accuracy, so it is not suitable for secondary clamping of workpieces with high coaxiality requirements. In order to prevent the deformation and vibration of the workpiece from affecting the processing quality during turning, when the workpiece is clamped in the three-jaw self-centering chuck, its overhang length should not be too long. For example: if the workpiece diameter is 30mm, its overhang length should not be greater than 3 times the diameter; if the workpiece diameter is 30mm, its overhang length should not be greater than 4 times the diameter. At the same time, it can also prevent the workpiece from being bent or dropped by the turning tool, causing cutting accidents. Jaws CNC lathes have two commonly used standard chuck jaws, which are hard jaws and soft jaws. Hard jaws and soft jaws of a three-jaw self-centering chuck. When the jaws are clamped on an unmachined surface, such as a casting or a rough bar surface, and a large clamping force is required, the hard jaws are used; usually to ensure stiffness and wear resistance, the hard jaws need to be heat treated and have a higher hardness. When it is necessary to reduce the diameter runout deviation of two or more parts.

　　3. When the table has been processed and no pinch marks are expected, soft claws should be used. Soft claws are usually made of low carbon steel. Before use, the soft claws must be bored to match the workpiece being processed. The biggest feature of soft claw clamping is that the workpiece can still maintain a certain position accuracy even after being clamped multiple times. The clamping and correction time of the workpiece is greatly shortened. When turning soft claws or loading and unloading parts each time, attention should be paid to using the same square hole of the wrench and the clamping force should be uniform. Using other square holes of the wrench or changing the size of the clamping force will change the movement amount of the chuck's plane thread, thus affecting the positioning accuracy after clamping. 2. Hydraulic power chuck. There are two common types of three-jaw chucks: mechanical and hydraulic. Hydraulic chuck has sensitive action, fast and convenient clamping, can achieve large pressing force, can improve productivity and reduce labor intensity. However, the clamping range changes slightly, and the claw position needs to be readjusted when the size changes greatly. CNC lathes with a high degree of automation often use hydraulic self-centering cards.

　　4. Chuck, especially suitable for batch processing. The clamping force of the hydraulic power chuck can be controlled by adjusting the oil pressure of the hydraulic system to adapt to the clamping of bars, disk parts and thin-walled sleeve parts. The claws on each base card holder can be individually manually adjusted for coarse and fine positions. Each claw can be moved manually to clamp and position the parts. Before processing, the center of the workpiece processing surface must be centered to the center of the chuck (spindle). Adjustable-jaw four-jaw chucks require more time to clamp and align parts than other types of chucks. Therefore, this chuck is rarely used on CNC lathes, which are crucial to improving productivity. Adjustable jaw four-jaw chuck is generally used to position and clamp parts with non-concentric or structurally symmetrical surfaces. When using four-jaw chucks, faceplates, angle irons (bent plates), etc. to clamp irregularly heavy workpieces, a counterweight must be added.

　　5. High-speed power chuck In order to improve the production efficiency of CNC lathes, higher and higher requirements are placed on their spindles to achieve high-speed and even ultra-high-speed cutting. Now some CNC lathes even reach rmin. For such high rotational speeds, ordinary chucks are no longer suitable, and high-speed power chucks must be used to ensure safe and reliable processing. As the rotation speed of the chuck increases, the centrifugal force of the jaw assembly, which is composed of the jaws, the slide seat and the fastening screw, increases sharply, and the clamping force of the jaws on the parts decreases. Type A center hole shape and dimensions Figure 5 Type B center hole high-speed power chuck is often equipped with a centrifugal force compensation device, using the centrifugal force of the compensation device to offset the clamping force loss caused by the centrifugal force of the jaw assembly. Another method is to reduce the mass of the jaw assembly to reduce centrifugal force.

　　6. Install the workpiece between the two tips. For shaft parts with larger lengths or more processing steps, in order to ensure the clamping accuracy during each clamping, two centers can be used for clamping. Center hole The center hole is a common positioning reference for shaft parts. The workpiece is installed between the spindle top and the tailstock top. However, if the axes of the two tops of the lathe do not coincide (front and rear direction), the turned workpiece will become a cone. Therefore, the tailstock of the lathe must be adjusted laterally so that the two center axes coincide. The choice of center hole type cannot be ignored. There are four types of center holes used for support and clamping at both ends of shaft parts. Their structures and uses are different, adapting to different processing accuracy and clamping requirements, and cannot be mixed. Therefore, the following principles should be followed when selecting: For shaft parts with average precision and the center hole does not need to be reused, A-type center holes can be used. For shaft parts with high precision requirements and many processes, the center hole needs to be used multiple times.

　　7. The center hole is to replace the cylindrical hole part of the above two center holes with internal threads. For workpieces that need to fix other parts in the axial direction, this type of central hole with internal threads can be used. The difference between the R-type center hole and the A-type is that the 60-degree conical surface is changed into an arc surface, so the contact with the tip becomes a line contact, which can automatically correct a small amount of position deviation. It is suitable for shaft parts that require high positioning accuracy, but is rarely used. Automatic clamping toggle chuck. When processing shaft parts on a CNC lathe, the blank is installed between the spindle center and the tailstock center, and the workpiece is rotated by the toggle chuck or the toggle tooth center on the spindle. This type of fixture can transmit sufficient torque during rough turning to adapt to the high-speed cutting of the spindle. The workpiece is mounted on the center and tailstock center of the lathe. When rotating the tailstock screw of the lathe towards the spindle.

　　8. When tightening the workpiece, the tip also presses the spring that has an automatic reset function. When the tip moves to the left, the sleeve will also move synchronously with the tip. A lever is installed in the slot of the sleeve. When the sleeve moves with the tip, the left end contact of the lever swings counterclockwise along the slope of the cone ring around the support pin axis, so that the right end contact of the lever clamps the workpiece and transmits the torque of the machine tool spindle to the workpiece. The top of the shifting teeth. The top of the shifting teeth. The housing can be connected to the lathe spindle hole through a standard reducing sleeve or directly. The housing is equipped with a tip for centering the blank. The shifting gear sleeve is connected to the housing through screws. The backstop ring can prevent the screws from loosening. CNC lathes usually use this fixture to process shaft parts with a diameter of 10660mm. Composite chuck and one clamp and one top. Composite chuck is not only suitable for installing workpieces between two centers, but also suitable for installing workpieces with one clamp and one top. In order to ensure good rigidity during processing, the method of clamping one end with the other end and using the rear center is used when turning heavier workpieces. In order to prevent the axial displacement of the workpiece due to the action of cutting force, a limit support must be installed in the chuck, or the step limit of the workpiece must be used, so that it can withstand large axial cutting forces and achieve accurate axial positioning.

　　Some points to note when centering and clamping workpieces with center holes are as follows: When processing shaft workpieces between the centers, the axis of the tailstock center must be adjusted to coincide with the axis of the lathe spindle before turning. When machining a slender shaft between two centers, a tool rest or a steady rest should be used. During the machining process, attention should be paid to adjusting the top tightening force, and the dead center and center frame should be lubricated. When using the tailstock, the sleeve should be extended as short as possible to reduce vibration.

　　The main features of Bedford chucks used in lathes:

　　1. Large low-frequency torque and stable output

　　2. High performance vector control

　　3. Fast dynamic response of torque and high speed stabilization accuracy

　　4. Slow down and stop quickly

　　5. Strong anti-interference ability.