Automatic tool changing systems are critical components in modern CNC machining centers, enabling efficient production processes with minimal human intervention. These sophisticated mechanisms provide the speed, precision, and reliability required in today's manufacturing environments, from traditional machining centers to advanced cnc plasma cutting machine operations.
A well-designed automatic tool changer must minimize tool change time, maintain high repeatability in tool positioning, store an adequate number of tools, and feature a compact, reliable structure. These systems have revolutionized manufacturing processes across industries, including the cnc plasma cutting machine sector where precision and efficiency are paramount.
I. Forms of Automatic Tool Changers
Automatic tool changers store a certain number of tools and perform automatic tool exchanges. They must meet requirements such as short tool change time, high tool repeat positioning accuracy, sufficient tool storage capacity, compact structure, and safety reliability. The basic forms are as follows, each with specific applications in different machining scenarios including cnc plasma cutting machine setups.
1. Turret Tool Changer
The turret tool changer is a simple automatic tool changing device, commonly used in CNC lathes. According to processing requirements, it can be designed as a square, hexagonal turret, or disc-type axially mounted tool turret, capable of installing 4, 6, or more tools. This design is also finding applications in specialized cnc plasma cutting machine configurations for material processing versatility.
Tool Changing Movement:
Figure 5-46 shows a CNC lathe hexagonal turret (i.e., hexagonal tool post), whose action sequence is as follows:
1. Turret Lifting
After the CNC device issues a command, pressure oil enters the lower cavity of the clamping cylinder through hole A, causing piston 1 to rise and turret 2 to lift, disengaging the positioning movable pin 10 from the fixed pin 9. At the same time, the face clutch 5 at the lower end of the piston rod engages with the idle gear 7. This precise movement is crucial for maintaining alignment, whether in traditional machining or cnc plasma cutting machine operations.
2. Turret Indexing
After the turret is lifted, pressure oil enters the left cavity of the indexing cylinder through hole C, and the piston 6 moves to the right, driving the rack 8 to move through the connecting plate 13, causing the idle gear 7 together with the face clutch 5 to rotate 60° counterclockwise to realize turret indexing. The piston stroke should be equal to 1/6 of the pitch circle circumference of gear 7 and is controlled by a limit switch. Similar precision indexing is essential in cnc plasma cutting machine tool changers for accurate material processing.
3. Turret Clamping
After the turret is indexed, pressure oil enters the upper cavity of the clamping cylinder through hole B, and the piston 1 drives the turret 2 to descend. Six cylindrical fixed pins 9 with inclined wedges are precisely installed on the chassis of the gear 3. The movable pin 10 is used to eliminate the gap between the fixed pin and the hole to achieve reverse positioning. When the turret 2 descends, the movable pin clamps with another fixed pin 9. At the same time, the cone surface of gear 3 and ring gear 4 contact, and the turret is positioned and clamped in the new position. At this time, the face clutch is disengaged from the idle gear. This clamping mechanism ensures the stability required for high-precision operations, from milling to cnc plasma cutting machine applications.
4. Indexing Cylinder Reset
After the turret is clamped, pressure oil enters the right cavity of the indexing cylinder through hole D, and the piston 6 drives the rack to reset. Since the face clutch has been disengaged at this time, the rack drives the gear to idle on the shaft. If the positioning and clamping actions are normal, the push rod 11 contacts the corresponding contact 12, sending a signal that the tool change process is completed. This confirmation mechanism is vital for maintaining production efficiency in automated systems, including advanced cnc plasma cutting machine setups.
II. Tool Magazines
The tool magazine is one of the main components in an automatic tool changer. Its function is to store various tools needed in processing cleanly, safely, and stably, and under the control of the CNC system, quickly and accurately send the required tools to the tool change position and receive unused tools from the spindle. Since most machining centers have fixed tool pick-up and delivery positions in the tool magazine, the tool magazine also needs mechanisms to move and position tools to ensure reliable tool changes. This is equally important in specialized equipment like the cnc plasma cutting machine, where tool changes must be precise to maintain cutting quality.
Each tool and guide sleeve that needs to be replaced in the tool magazine must accurately stop at the tool change position. This can be achieved by using a simple position controller or a servo position control system similar to a semi-closed-loop feed system, or by using a combination of electrical and mechanical pin positioning. Generally, the comprehensive positioning accuracy is required to reach 0.1~0.5 mm. These precision standards ensure that even complex operations, whether in milling centers or cnc plasma cutting machine systems, maintain consistent quality.
1. Types of Tool Magazines
According to the number of tools stored and the channel method, tool magazines are usually divided into the following types, each with specific advantages for different applications including cnc plasma cutting machine configurations:
1 Linear Tool Magazine
In a linear tool magazine, tools are arranged in a straight line, so this type of tool magazine is also called a row-type tool magazine. Its structure is simple but can store a limited number of tools (usually 8-12), and it is rarely used now. However, its simplicity makes it suitable for certain specialized applications, including some cnc plasma cutting machine setups where only a few tool types are needed.
2 Disc-type Tool Magazine
Figure 5-58 shows a disc-type tool magazine. This is a more commonly used tool magazine form, which can store up to 50-60 tools, but if the number of stored tools is too large, the structural size becomes huge and incompatible with the machine tool layout.
To further expand the tool storage capacity, disc-type tool magazines can adopt multi-circle distribution, multi-layer distribution, and multi-row distribution forms. To adapt to the layout of the machine tool spindle, the tool axes on the tool magazine can be configured in different directions, such as axial, radial, or oblique directions, as shown in Figure 5-58. Figure 5-58(d) shows a disc tool magazine where tools can be flipped 90°, and this structure can simplify the tool picking action. This versatility makes disc-type magazines popular in various machining environments, including cnc plasma cutting machine systems that require multiple tool configurations.
Disc-type Tool Magazine Configurations:
- (a) Radial tool picking form
- (b) Axial tool picking form
- (c) Tool radially placed
- (d) Tool obliquely placed
These various configurations allow disc-type magazines to be integrated into different machine designs, from vertical machining centers to specialized cnc plasma cutting machine systems.
III. Tool Holding
Tools must be mounted in standard tool holders. China has developed the TSG tool system and formulated tool holder standards, which specify two types of tool holders: straight shank and 7:24 taper shank. They are used for spindles with cylindrical holes and conical holes respectively, and their structures are shown in Figure 5-64. The keyway 1 in the figure is used to transmit cutting torque, and the screw hole 4 is used to install an adjustable pull rod for tightening the tool holder. The axial and radial dimensions of the tool should be adjusted on the tool setting instrument before the tool can be loaded into the tool magazine. This standardization ensures compatibility across different machines, including the cnc plasma cutting machine, where tool consistency is crucial.
Taps and reamers should be installed in floating fixtures first, then into standard tool holders. During the tool change process, the manipulator must rotate quickly after grasping the tool holder, perform tool pulling and inserting actions, and ensure that the angle position of the tool holder keyway is aligned with the drive key on the spindle. Therefore, the gripping part of the manipulator must be very reliable and ensure appropriate clamping force, and its movable claws must have a locking device to prevent the tool from rotating or falling off during the tool change process. These requirements apply equally to all precision machining equipment, from milling machines to the cnc plasma cutting machine.
1. Shank-type Clamping
Shank-type clamping is also known as axial clamping. The front end of the tool holder has a V-shaped groove for manipulator clamping. At present, this clamping method is widely used in CNC machine tools in China, as well as in many cnc plasma cutting machine configurations.
Figure 5-65 shows the manipulator palm structure. It mainly consists of a fixed claw 7 and a movable claw 1. The movable claw 1 can rotate around the shaft 2, and one end is supported against the stop pin 3 under the action of the spring plunger 6. The adjusting bolt 5 is used to keep the palm at an appropriate clamping force.
The locking pin 4 enables the movable claw 1 to firmly clamp the tool holder, preventing the tool from loosening during the exchange process. The locking pin 4 can also move axially to release the movable claw 1, so that the claw can withdraw from the V-shaped groove of the tool holder. This design ensures secure tool handling even in high-vibration environments like the cnc plasma cutting machine.
2. Flange-type Clamping
Flange-type clamping is also known as radial clamping or disc-type clamping. The flange structure on the tool holder is shown in Figure 5-66. 1 is the pull rod, and the front end of the tool holder 2 has a flange 3 for manipulator clamping. The flange adopts a concave shoulder surface.
Figure 5-67 shows flange-type clamping, where Figure 5-67(a) shows the released state and Figure 5-67(b) shows the clamped state.
The outstanding advantage of flange-type clamping is that when using an intermediate handling device, tools can be easily transferred from one manipulator to another auxiliary manipulator. This flexibility makes it suitable for complex automation systems, including integrated manufacturing cells that incorporate cnc plasma cutting machine technology.
Tool Holder Designs
(a) Straight Shank Tool Holder
Designed for spindles with cylindrical holes, featuring precise dimensions for consistent mounting. The straight shank provides stable gripping surface for automatic changers in various machines, including the cnc plasma cutting machine.
- 1 - Keyway for torque transmission
- 2 - Manipulator gripping part
- 3 - Tool holder positioning and clamping part
- 4 - Threaded hole for pull rod
(b) Tapered Shank Tool Holder
Featuring a 7:24 taper for secure fit in conical spindle holes, providing excellent centering accuracy and transmission of both torque and axial forces. This design is common in high-precision machining centers and advanced cnc plasma cutting machine systems.
IV. Example of Automatic Tool Changer with Tool Magazine
THK6370 Type Automatic Tool Changing CNC Horizontal Boring and Milling Machine
The automatic tool changing device of the THK6370 type automatic tool changing CNC horizontal boring and milling machine consists of a chain-type tool magazine and a tool changing device, where the tool magazine is managed by a microcomputer. The machine tool structure is shown in Figure 5-68. This level of automation is now becoming standard in advanced manufacturing, including the cnc plasma cutting machine industry.
The chain-type tool magazine is placed on the left side of the machine tool, with a capacity of 45 tools. The manipulator is installed on the front face of the spindle box and can move up and down along the column guide rail with the spindle box to realize tool changing at any position. This flexibility allows for complex machining operations without manual intervention, similar to how modern cnc plasma cutting machine systems operate.
Machine Component Identification:
#1
Manipulator
#2
Tool magazine
#3
Spindle box
#4
Spindle
#5
Tool magazine column
#6
Upper sprocket
#7
Dovetail guide
#8
Tool seat
#9
Lower sprocket
#10
Gearbox
This configuration demonstrates the integration of various components into a cohesive automatic tool changing system. The chain-type magazine offers greater tool storage capacity than disc-type magazines while maintaining efficient access to tools. Similar principles of component integration apply to other advanced machining systems, including the modern cnc plasma cutting machine, where tool management directly impacts productivity and precision.
Automatic tool changing systems represent a critical advancement in CNC machining technology, enabling unprecedented levels of productivity, precision, and flexibility in manufacturing processes. From simple turret changers to complex chain magazine systems with robotic manipulators, these technologies continue to evolve to meet the demands of modern production environments, including the specialized requirements of the cnc plasma cutting machine industry.
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