Working Principle of Spindle Tool - Loosening and Clamping in CNC Machining Centers

Working Principle of Spindle Tool - Loosening and Clamping in CNC Machining Centers

Abstract: This paper elaborates in detail on the basic structure and working principle of the spindle tool-loosening and clamping mechanism in CNC machining centers, including the composition of various components, the working process, and key parameters. It aims to deeply analyze the internal mechanism of this crucial function, provide theoretical references for relevant technical personnel, help them better understand and maintain the spindle system of CNC machining centers, and ensure the high efficiency and precision of the machining process.

I. Introduction

The function of spindle tool-loosening and clamping in machining centers is an important foundation for CNC machining centers to achieve automated machining. Although there are certain differences in its structure and working principle among different models, the basic framework is similar. In-depth research on its working principle is of great significance for improving the performance of machining centers, ensuring machining quality, and optimizing equipment maintenance.

II. Basic Structure

The spindle tool-loosening and clamping mechanism in CNC machining centers mainly consists of the following components:

Pull Stud: Installed at the tail of the tool's tapered shank, it is a key connecting component for the pull rod to tighten the tool. It cooperates with the steel balls at the head of the pull rod to achieve the positioning and clamping of the tool.

Pull Rod: Through the interaction with the pull stud via steel balls, it transmits tensile and thrust forces to realize the clamping and loosening actions of the tool. Its movement is controlled by the piston and springs.

Pulley: Usually serving as an intermediate component for power transmission, in the spindle tool-loosening and clamping mechanism, it may be involved in the transmission links that drive the movement of related components. For example, it may be connected to the hydraulic system or other driving devices to drive the movement of components such as the piston.

Belleville Spring: Composed of multiple pairs of spring leaves, it is a key component for generating the tensioning force of the tool. Its powerful elastic force can ensure that the tool is stably fixed within the tapered hole of the spindle during the machining process, guaranteeing machining accuracy.

Lock Nut: Used to fix components such as the Belleville spring to prevent them from loosening during the working process and ensure the stability and reliability of the entire tool-loosening and clamping mechanism.

Adjusting Shim: By grinding the adjusting shim, the contact state between the pull rod and the pull stud at the end of the piston's stroke can be precisely controlled, ensuring the smooth loosening and tightening of the tool. It plays a crucial role in the precision adjustment of the entire tool-loosening and clamping mechanism.

Coil Spring: It plays a role in the process of tool loosening and assists the movement of the piston. For example, when the piston moves downward to push the pull rod to loosen the tool, the coil spring provides a certain elastic force to ensure the smoothness and reliability of the action.

Piston: It is the power-executing component in the tool-loosening and clamping mechanism. Driven by hydraulic pressure, it moves up and down, and then drives the pull rod to realize the clamping and loosening actions of the tool. The precise control of its stroke and thrust is crucial for the entire tool-loosening and clamping process.

Limit Switches 9 and 10: They are respectively used to send signals for tool clamping and loosening. These signals are fed back to the CNC system so that the system can precisely control the machining process, ensure the coordinated progress of each process, and avoid machining accidents caused by misjudgment of the tool clamping state.

Pulley: Similar to the pulley mentioned in item 3 above, it participates in the transmission system together to ensure the stable transmission of power and enable all components of the tool-loosening and clamping mechanism to work cooperatively according to the predetermined program.

End Cover: It plays the role of protecting and sealing the internal structure of the spindle, preventing impurities such as dust and chips from entering the interior of the spindle and affecting the normal operation of the tool-loosening and clamping mechanism. At the same time, it also provides a relatively stable working environment for the internal components.

Adjusting Screw: It can be used to make fine adjustments to the positions or clearances of some components to further optimize the performance of the tool-loosening and clamping mechanism and ensure that it maintains a high-precision working state during long-term use.

III. Working Principle

(I) Tool Clamping ProcessWhen the machining center is in the normal machining state, there is no hydraulic oil pressure at the upper end of piston 8. At this time, the coil spring 7 is in a naturally extended state, and its elastic force makes the piston 8 move upward to a specific position. Meanwhile, the Belleville spring 4 also plays a role. Due to its own elastic characteristics, the Belleville spring 4 pushes the pull rod 2 to move upward, so that the 4 steel balls at the head of the pull rod 2 enter the annular groove at the tail of the tool shank's pull stud 1. With the embedding of the steel balls, the tensioning force of the Belleville spring 4 is transmitted to the pull stud 1 through the pull rod 2 and the steel balls, thereby tightly holding the tool shank and realizing the precise positioning and firm clamping of the tool within the tapered hole of the spindle. This clamping method utilizes the powerful elastic potential energy of the Belleville spring and can provide sufficient tensioning force to ensure that the tool will not loosen under the action of high-speed rotation and cutting forces, guaranteeing the machining accuracy and stability.

(II) Tool Loosening ProcessWhen it is necessary to change the tool, the hydraulic system is activated, and hydraulic oil enters the lower end of piston 8, generating an upward thrust. Under the action of the hydraulic thrust, the piston 8 overcomes the elastic force of the coil spring 7 and starts to move downward. The downward movement of the piston 8 pushes the pull rod 2 to move downward synchronously. As the pull rod 2 moves downward, the steel balls are disengaged from the annular groove at the tail of the tool shank's pull stud 1 and enter the annular groove in the upper part of the rear tapered hole of the spindle. At this time, the steel balls no longer have a restraining effect on the pull stud 1, and the tool is loosened. When the manipulator pulls the tool shank out of the spindle, compressed air will blow out through the central holes of the piston and the pull rod to clean up impurities such as chips and dust in the tapered hole of the spindle, preparing for the next tool installation.

(III) The Role of Limit SwitchesLimit switches 9 and 10 play a crucial role in signal feedback throughout the tool-loosening and clamping process. When the tool is clamped in place, the position change of relevant components triggers limit switch 9, and limit switch 9 immediately sends a tool clamping signal to the CNC system. After receiving this signal, the CNC system confirms that the tool is in a stable clamping state and can then start subsequent machining operations, such as spindle rotation and tool feed. Similarly, when the tool loosening action is completed, limit switch 10 is triggered, and it sends a tool loosening signal to the CNC system. At this time, the CNC system can control the manipulator to carry out the tool changing operation to ensure the automation and precision of the entire tool changing process.

(IV) Key Parameters and Design Points

Tensioning Force: The CNC machining center uses a total of 34 pairs (68 pieces) of Belleville springs, which can generate a powerful tensioning force. Under normal circumstances, the tensioning force for tightening the tool is 10 kN, and it can reach a maximum of 13 kN. Such a tensioning force design is sufficient to cope with various cutting forces and centrifugal forces acting on the tool during the machining process, ensuring the stable fixation of the tool within the tapered hole of the spindle, preventing the tool from displacement or falling off during the machining process, and thus guaranteeing machining accuracy and surface quality.

Piston Stroke: When changing the tool, the stroke of piston 8 is 12 mm. During this 12-mm stroke, the movement of the piston is divided into two stages. First, after the piston advances about 4 mm, it starts to push the pull rod 2 to move until the steel balls enter the 37-mm annular groove in the upper part of the spindle's tapered hole. At this time, the tool begins to loosen. Subsequently, the pull rod continues to descend until the surface "a" of the pull rod contacts the top of the pull stud, completely pushing the tool out of the spindle's tapered hole so that the manipulator can smoothly remove the tool. By precisely controlling the piston's stroke, the loosening and clamping actions of the tool can be completed accurately, avoiding problems such as insufficient or excessive stroke that may lead to loose clamping or inability to loosen the tool.

Contact Stress and Material Requirements: Since the 4 steel balls, the conical surface of the pull stud, the surface of the spindle hole, and the holes where the steel balls are located bear considerable contact stress during the working process, high requirements are placed on the materials and surface hardness of these parts. To ensure the consistency of the force on the steel balls, the holes where the 4 steel balls are located should be strictly ensured to be in the same plane. Usually, these key parts will adopt high-strength, high-hardness, and wear-resistant materials and undergo precise machining and heat treatment processes to improve their surface hardness and wear resistance, ensuring that the contact surfaces of various components can maintain a good working state during long-term and frequent use, reducing wear and deformation, and prolonging the service life of the tool-loosening and clamping mechanism.

IV. Conclusion

The basic structure and working principle of the spindle tool-loosening and clamping mechanism in CNC machining centers form a complex and sophisticated system. Each component cooperates and closely coordinates with each other. Through precise mechanical design and ingenious mechanical structures, rapid and accurate clamping and loosening of tools are achieved, providing a powerful guarantee for the efficient and automated machining of CNC machining centers. In-depth understanding of its working principle and key technical points is of great guiding significance for the design, manufacturing, use, and maintenance of CNC machining centers. In the future development, with the continuous progress of CNC machining technology, the spindle tool-loosening and clamping mechanism will also be continuously optimized and improved, moving towards higher precision, faster speed, and more reliable performance to meet the growing demands of the high-end manufacturing industry.

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Company Name: Qingdao Taizheng Precision Machinery Co., Ltd.
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