Tooling fixture of numerical control machining center

Abstract

The present application relates to the field of machining equipment, specifically to a tooling fixture of a numerical control machining center, comprising an electric three-jaw chuck, a clamping block connected to the electric three-jaw chuck through a fan-shaped block arranged thereon, the clamping block being fixedly connected to the corresponding jaw of the electric three-jaw chuck, a surface changing mechanism slidingly arranged on the clamping block, and a contact block fast detachably connected to the surface changing mechanism, the electric three-jaw chuck driving its jaw to drive the clamping block to move, so that the clamping block completely blocks the non-abutting surface of the contact block before abutting against the workpiece, effectively preventing the generated debris from adhering to and contaminating the contact block during machining, and then the clamping block pushes the working surface of the contact block to stably abut against the outer side surface of the bar; when the workpiece is replaced, the surface changing mechanism drives the contact block to rotate half a circle to quickly switch the working surface, realizing efficient continuous clamping, and the non-abutting surface of the contact block is automatically cleaned after surface changing through the cleaning assembly, and the cleaning effect is detected in real time and fed back by the visual assembly.

Description

Technical Field

[0001] This invention relates to the field of machining equipment, specifically a tooling fixture for a CNC machining center. Background Technology

[0002] Tooling fixtures play a crucial role in positioning and clamping workpieces in CNC machining centers. Their performance directly affects machining accuracy, operational safety, and production efficiency. High-precision and high-stability fixtures can effectively reduce workpiece vibration and displacement during machining, thereby ensuring part dimensional consistency, surface quality, and controllability of the machining process. They are indispensable process equipment in modern precision manufacturing.

[0003] Currently, electric three-jaw chucks are widely used for clamping rotating workpieces such as bars and shafts due to their compact structure, uniform clamping force, and high degree of automation. In traditional use, operators usually need to place the workpiece between the jaws first, and then use electric drive to make the three jaws move radially synchronously to achieve centering and clamping of the workpiece.

[0004] When a traditional electric three-jaw chuck clamps a bar stock with an arc-shaped surface, the working surface of the clamping block is flat and cannot fully fit with the curved surface of the workpiece, forming a local gap. During the machining process, cutting chips are easily intruded and adhered to the clamping surface by the coolant, which means that manual cleaning is required every time the workpiece is changed, which seriously affects the efficiency of continuous machining.

[0005] Furthermore, after multiple clamping operations, the surface of the clamping block in contact with the workpiece will develop microscopic indentations or wear due to concentrated pressure. This change is often difficult to detect in time. As the number of clamping operations increases, the actual positioning position of the workpiece will slowly shift, eventually causing the dimensions of the machined workpiece to gradually exceed the standard. Operators usually only discover the problem after a batch of defective products appear. At this time, not only is it necessary to readjust the tool or adjust the machining program, but it may also cause serious losses of materials, time and production capacity. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a tooling fixture for a CNC machining center, including an electric three-jaw chuck, a clamping block connected to the electric three-jaw chuck by a fan-shaped block, the clamping block being fixedly connected to the corresponding jaws of the electric three-jaw chuck, a face-changing mechanism being slidably arranged on the clamping block, and a contact block being quickly connected to the face-changing mechanism.

[0007] The contact block has a cubic structure to provide two sets of four high-precision working surfaces. Each time a workpiece is changed, the face-changing mechanism rotates the contact block half a turn to change the surface, thereby performing high-precision clamping of the workpiece without debris.

[0008] The clamping block is equipped with a cleaning component and a vision component. After the contact block is changed, the cleaning component automatically cleans the non-abutting surface of the contact block and the vision component detects and provides feedback on the cleaning effect. Then, driven by the electric three-jaw chuck, the clamping block moves to completely cover the non-abutting surface of the contact block, maintains the cleaning effect, and pushes the working surface of the contact block to press against the workpiece. During processing, the vision component detects the flatness of the original working surface of the contact block to determine the working surface life and provides wear warning.

[0009] With the help of face-changing clamping, feedback-based automatic cleaning and maintenance, and wear warning, long-term stable operation and automatic continuous machining operation can be completed under high-precision clamping of workpieces.

[0010] Preferably, three sector blocks are provided and are fixedly installed on the upper side of the electric three-jaw chuck along the circumference by bolts. The gap between two adjacent sector blocks forms a slide, and the clamping block is slidably connected in the slide.

[0011] Preferably, the face-changing mechanism includes a slide block that is slidably disposed on the clamping block along its length direction, and a helical spring is disposed between the slide block and the clamping block. The helical spring is used to push the non-abutting surface of the contact block to separate from the clamping block.

[0012] Preferably, the face-changing mechanism further includes a lower plate component rotatably disposed on the upper side of the slide block, and an upper plate component rotatably disposed on the upper side of the lower plate component. The upper plate component is detachably connected to the contact block by a vertical insertion method.

[0013] Preferably, a direct drive motor is fixedly installed inside the slide block, and the output shaft of the direct drive motor is fixedly connected to the corresponding lower plate component.

[0014] Preferably, a limiting groove is fixedly provided on the upper side of the lower plate, and a square rod is provided on the lower side of the upper plate. The upper plate drives the square rod through the limiting groove to drive the lower plate to rotate.

[0015] Preferably, the limiting groove has a groove structure that is wide on the outside and narrow in the middle. The limiting groove pushes the square rod through its groove wall, so that the lower plate can drive the upper plate to rotate, and at the same time, the square rod has a corresponding free rotation angle within the limiting groove.

[0016] Preferably, the cleaning assembly includes a U-shaped frame rotatably mounted on the upper side of the clamping block, with brushes fixedly installed on the two vertical sections of the U-shaped frame that are far apart from each other.

[0017] Preferably, a drive motor is fixedly installed inside the clamping block, and the output shaft of the drive motor is fixedly connected to the U-shaped frame. When the drive motor stops, the horizontal section of the U-shaped frame is located in the direction perpendicular to the length of the clamping block.

[0018] Preferably, the vision component includes a high-definition camera fixedly installed inside the clamping block and taking pictures corresponding to the contact block, and an LED light fixedly installed inside the clamping block for supplementary lighting.

[0019] The beneficial effects of this invention are as follows: First, this invention uses an electric three-jaw chuck to drive its jaws to move the clamping block, so that the clamping block completely covers the non-abutting surface of the contact block before clamping the workpiece, effectively preventing debris generated during processing from adhering and contaminating the contact block. Subsequently, the clamping block pushes the working surface of the contact block to stably clamp the outer side of the bar stock. When changing workpieces, the face-changing mechanism drives the contact block to rotate half a turn to quickly switch the working surface, achieving high-efficiency continuous clamping. At the same time, the cleaning component automatically cleans the non-abutting surface of the contact block after face changing, and the vision component detects and provides feedback on the cleaning effect in real time. During the processing, the vision component also detects the flatness of the original working surface of the contact block, thereby judging the working surface life and issuing a wear warning, so that the operator can intervene in time and avoid batch processing deviations and resource waste caused by the accumulation of wear on the clamping surface.

[0020] Second, the present invention uses a cubic contact block to provide two sets of four high-precision working surfaces, which can be used sequentially through a surface-changing mechanism, greatly extending the effective service life of a single contact block and significantly reducing the frequency of manual replacement of contact blocks due to wear of the working surfaces. At the same time, the contact block and the upper plate adopt a vertical plug-in quick-release connection method, which allows for rapid disassembly and assembly when the whole replacement is required, further reducing maintenance downtime and the frequency of manual intervention, and improving the convenience of fixture use and continuous operation capability.

[0021] Third, this invention adopts a structural design in which the clamping block completely covers the non-abutting surface of the contact block during the clamping process. This completely isolates debris from adhering to the non-abutting surface of the contact block during the processing stage, ensuring that the new working surface of the contact block is clean and usable after each face change and can be directly used for high-precision clamping. At the same time, the vision component performs flatness detection on the original working surface after replacement, accurately judges its wear state, and thus intelligently decides whether to use the next set of working surfaces or prompts to replace the new contact block, ensuring the long-term stability of the contact block's clamping accuracy for the workpiece.

[0022] Fourth, after the face is changed, the drive motor controls the U-shaped frame to rotate, so that the brushes on both sides actively brush the exposed non-abutting surface of the contact block, effectively removing residual dirt. The cleaning effect can also be detected by the vision component. Then the clamping block moves and completely blocks the non-abutting surface of the contact block, maintaining its clean state by physical isolation, providing a reliable guarantee for the next clamping, and realizing the automated operation of cleaning and protection. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a schematic diagram of the overall structure of the present invention when clamping bar stock workpieces.

[0025] Figure 2 This is a schematic diagram of the structure of the electric three-jaw chuck, sector block, clamping block and contact block in this invention.

[0026] Figure 3 This is a schematic diagram of the structure of the clamping block, contact block, slide, and U-shaped frame in this invention.

[0027] Figure 4 This is a partial cross-sectional view of the clamping block, contact block, slide, and U-shaped frame in this invention.

[0028] Figure 5 This is an exploded view of the lower plate, upper plate, direct drive motor, and slide block in this invention.

[0029] Figure 6 This is a structural schematic diagram of the middle rod and the lower plate component of the present invention.

[0030] In the diagram: 1. Electric three-jaw chuck; 2. Sector block; 3. Clamping block; 4. Face-changing mechanism; 5. Contact block; 21. Slide rail; 31. Cleaning component; 32. Vision component; 41. Slide base; 42. Lower plate component; 43. Upper plate component; 44. Direct drive motor; 311. U-shaped frame; 312. Brush; 313. Drive motor; 321. High-definition camera; 322. LED light; 421. Limiting groove; 431. Square rod. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0032] See Figure 1 , Figure 2 and Figure 3 A tooling fixture for a CNC machining center includes an electric three-jaw chuck 1. A clamping block 3 is connected to the electric three-jaw chuck 1 via a fan-shaped block 2. The clamping block 3 is fixedly connected to the corresponding jaws of the electric three-jaw chuck 1. A face-changing mechanism 4 is slidably arranged on the clamping block 3. A contact block 5 is quickly connected to the face-changing mechanism 4. The contact block 5 has a cubic structure to provide two sets of four high-precision working surfaces. Each time a workpiece is changed, the face-changing mechanism 4 rotates the contact block 5 half a turn to change the surface, thereby achieving high-precision clamping of the workpiece without debris inclusion.

[0033] It is worth noting that the two oppositely arranged working surfaces of the contact block 5 form a group, so that when the face-changing mechanism 4 rotates the contact block 5 half a turn, the two working surfaces in the same group alternately face the workpiece for clamping. When the wear of one group of working surfaces exceeds the standard, the clamping is continued by replacing the other group of working surfaces, which greatly extends the service life of the same contact block 5 and reduces the frequency of manual intervention.

[0034] It should be noted that the electric three-jaw chuck 1 can be detachably connected to the platform of the CNC machining center by means of bolts or pressure plates, so that the CNC machining center can process the workpiece held by this tooling fixture.

[0035] See Figure 1 and Figure 2 There are three sector blocks 2, which are fixedly installed on the upper side of the electric three-jaw chuck 1 along the circumference by bolts. The gap between two adjacent sector blocks 2 forms a slide 21. The clamping block 3 is slidably connected in the slide 21. When clamping the bar stock, the bar stock is placed on the upper side of the three sector blocks 2. Then, the electric three-jaw chuck 1 drives its jaws to move synchronously towards the workpiece, so that the jaws drive the clamping block 3 to move synchronously. The clamping block 3 drives the contact block 5 to abut against the workpiece through the face-changing mechanism 4. Then, the clamping block 3 presses against the contact block 5 and transmits the pressing force to the workpiece, thereby quickly clamping the workpiece.

[0036] To ensure clamping efficiency, this invention utilizes the processing time to inspect the side of the working surface of contact block 5 that is not in contact with the workpiece, in order to provide wear warning. The specific structure is as follows: (See attached diagram). Figure 3 and Figure 4 The clamping block 3 is provided with a vision component 32, which includes a high-definition camera 321 fixedly installed in the clamping block 3 and taking pictures corresponding to the contact block 5, and an LED light 322 fixedly installed in the clamping block 3 for supplementary lighting.

[0037] When the contact block 5 presses against the workpiece, the clamping block 3 presses against the working surface of the contact block 5, so that the clamping block 3 completely covers the side of the working surface of the contact block 5 that is not against the workpiece. By pressing against the workpiece, it can prevent the debris during processing from adhering to the working surface, so that after the contact block 5 rotates half a turn to change the surface, the workpiece can be clamped quickly and continuously.

[0038] Subsequently, during the processing, the side of the contact block 5 that is attached to the clamping block 3 is illuminated by LED light 322, and then the working surface is photographed and inspected by high-definition camera 321. The photographic inspection data is then transmitted to the host computer, which analyzes and judges the data to determine whether the flatness and wear of the working surface exceed the standard values. This inspection and judgment process adopts a mature feedback closed-loop vision inspection module in the existing technology, which can quickly and accurately use photographic data to detect the condition of the working surface of the contact block 5.

[0039] When the flatness and wear of one working surface in the same group exceed the standard value, the contact block 5 is rotated a quarter turn by the face-changing mechanism 4, thereby automatically activating another group of working surfaces on the contact block 5 to continue clamping. Without manual intervention, clamping accuracy is guaranteed and clamping efficiency is maintained. When the flatness and wear of one working surface in each group exceed the standard value, the contact block 5 is replaced manually to achieve wear warning, thereby timely detection and avoiding large losses.

[0040] To achieve automatic separation of clamping block 3 and contact block 5 when changing workpieces, the present invention designs the following structure: (See attached diagram) Figure 3 , Figure 4 and Figure 5 The face-changing mechanism 4 includes a slide block 41 that is slidably disposed on the clamping block 3 along its length. A helical spring is disposed between the slide block 41 and the clamping block 3. The helical spring is used to push the non-abutting surface of the contact block 5 to separate from the clamping block 3. A lower plate 42 is rotatably disposed on the upper side of the slide block 41. An upper plate 43 is rotatably disposed on the upper side of the lower plate 42. The upper plate 43 is detachably connected to the contact block 5 by a vertical insertion.

[0041] During clamping, the clamping block 3 moves towards the workpiece under the drive of the jaws, so that the clamping block 3 pushes the slide block 41 to move synchronously through the helical spring. The slide block 41 drives the contact block 5 to move synchronously through the lower plate 42 and the upper plate 43. At this time, the helical spring is in a naturally extended state, that is, the contact block 5 is in a position where it does not contact the clamping block 3.

[0042] When contact block 5 abuts against the workpiece, continue moving clamping block 3. Contact block 5 stops moving due to the obstruction of the workpiece, causing clamping block 3 to gradually approach contact block 5. Finally, clamping block 3 moves until it abuts against contact block 5, transferring the clamping force from contact block 5 to the workpiece, thus completing the clamping of the workpiece. Figure 1 As shown, after processing is completed, the electric three-jaw chuck 1 automatically moves its jaws outward to the processing position, causing the helical spring to push the contact block 5 and the clamping block 3 to automatically separate again.

[0043] To achieve automatic face changing of contact block 5, the present invention designs the following structure: (See attached diagram) Figure 3, Figure 4 , Figure 5 and Figure 6 A direct drive motor 44 is fixedly installed inside the slide block 41. The output shaft of the direct drive motor 44 is fixedly connected to the corresponding lower plate 42. A limit groove 421 is fixedly provided on the upper side of the lower plate 42. A square rod 431 is provided on the lower side of the upper plate 43. When the contact block 5 and the clamping block 3 automatically separate again, the direct drive motor 44 is started to drive the lower plate 42 to rotate half a turn. The lower plate 42 pushes the square rod 431 through the limit groove 421 to drive the upper plate 43 to rotate, so that the upper plate 43 drives the contact block 5 to rotate half a turn synchronously, thereby completing the alternation of the same group of working surfaces.

[0044] It is worth noting that when it is necessary to change to another set of working surfaces for clamping, the output shaft of the direct drive motor 44 rotates 90 degrees, causing the contact block 5 to rotate 90 degrees synchronously, thereby changing to another set of working surfaces that correspond to the workpiece. When clamping again, the direct drive motor 44 rotates the contact block 5 half a turn again, so that the two working surfaces of another set are used alternately, greatly extending the frequency of manual intervention.

[0045] To prevent the working surface of the contact block 5 from not properly aligning with the workpiece due to errors in the rotation angle of the direct drive motor 44, thus causing the contact block 5 to be misaligned when clamping the workpiece, the present invention designs the following structure: (See attached diagram) Figure 4 , Figure 5 and Figure 6 The limiting groove 421 has a groove structure that is wide on the outside and narrow in the middle. The limiting groove 421 pushes the square rod 431 through its groove wall, so that the lower plate 42 drives the upper plate 43 to rotate, and at the same time, the square rod 431 has a corresponding free rotation angle in the limiting groove 421.

[0046] When the lower plate 42 rotates, the lower plate 42 drives the limiting groove 421 on it to rotate synchronously. Only when the groove wall of the limiting groove 421 moves to fit against the square rod 431 can the limiting groove 421 transmit torque to the square rod 431, causing the contact block 5 to rotate. Therefore, when the limiting groove 421 stops after rotating half a revolution, the upper plate 43 can rotate freely with the square rod 431 within the limiting groove 421 at a certain angle, so that when the clamping block 3 abuts against the contact block 5, the contact block 5 can automatically adapt to fit against the clamping block 3, and then automatically adjust the angle to ensure that the workpiece is clamped.

[0047] In this embodiment, the square rod 431 can rotate freely by ten degrees in the limiting groove 421, and the direct drive motor 44 is a high-precision motor in the prior art, whose rotation angle error does not exceed five degrees.

[0048] To automatically clean debris from the working surface of contact block 5 that originally abutted the workpiece after face changing without manual intervention, the present invention designs the following structure: (See attached diagram) Figure 1 , Figure 2 , Figure 3 and Figure 4 A cleaning component 31 is provided on the clamping block 3. The cleaning component 31 includes a U-shaped frame 311 rotatably mounted on the upper side of the clamping block 3. Brushes 312 are fixedly installed on the two vertical sections of the U-shaped frame 311 that are far apart from each other. A drive motor 313 is fixedly installed inside the clamping block 3. The output shaft of the drive motor 313 is fixedly connected to the U-shaped frame 311.

[0049] After the contact block 5 changes surface, the drive motor 313 is started to drive the U-shaped frame 311 to rotate, so that the U-shaped frame 311 drives the brushes 312 on both sides to actively brush the exposed working surface of the contact block 5 that originally abutted the workpiece. Figure 3 As shown, residual dirt is efficiently removed, and then the drive motor 313 is stopped, so that the horizontal section of the U-shaped frame 311 driven by the drive motor 313 is located in the position perpendicular to the length direction of the clamping block 3 when it stops. Figure 1 As shown, the U-shaped frame 311 prevents the clamping block 3 from obstructing the contact between the contact block 5.

[0050] Then, the high-definition camera 321 takes pictures of the cleaned working surface for inspection and sends the picture inspection data back to the host computer. The host computer analyzes the data to determine whether the working surface is clean. If it is, the workpiece is clamped. If not, the host computer starts the drive motor 313 again to clean the working surface again. Then, the high-definition camera 321 takes pictures for inspection again until the working surface is clean.

[0051] The drive motor 313 in this embodiment adopts a high-precision motor in the prior art, which can respond quickly to rotation and can also stop quickly and accurately at a certain angle position. The angle error of the drive motor 313 does not exceed five degrees.

[0052] It should be noted that by using existing automatic loading and unloading devices, such as robotic arms, to replace the workpieces on this tooling fixture, the drive motor 313 drives the brush 312 to clean the contact block 5. Therefore, the necessary steps in the existing processing are fully utilized, and the cleaning operation is handled in parallel without adding extra processing time, thus ensuring processing efficiency.

[0053] Then the electric three-jaw chuck 1 drives the clamping block 3 to move again, and makes the clamping block 3 press against the contact block 5, so that the contact block 5 clamps the new workpiece. The clamping block 3 covers and adheres to the contact block 5 again, which can maintain the cleanliness of the working surface of the contact block 5 by physical isolation, providing a reliable guarantee for the next clamping. Then the above steps are repeated to continuously clamp the workpiece with high precision.

[0054] It should be noted that sealing rings are provided at the rotation positions of the lower plate 42 and the slide 41, and at the rotation positions of the U-shaped frame 311 and the clamping block 3, which can prevent coolant from flowing into the clamping block 3 during workpiece processing. In addition, the clamping block 3 at the position of the drive motor 313 and the slide 41 at the position of the direct drive motor 44 are detachably connected to sealing baffles with heat dissipation vents at the bottom, thereby preventing water from entering the direct drive motor 44 and the drive motor 313.

[0055] In this embodiment, both the contact block 5 and the clamping block 3 are made of high wear-resistant and corrosion-resistant hard alloy. The upper plate 43 consists of a lower plate-shaped structure and an upper square column structure. A square groove matching the shape of the square column is opened on the bottom wall of the contact block 5. The square column is inserted into the interior of the square groove, so that the upper plate 43 and the contact block 5 can be quickly connected together. In this embodiment, the contact block 5 can be stably slid into the square column under the action of gravity to maintain the connection between the upper plate 43 and the contact block 5. In practical applications, a screw can be threaded on the upper side of the contact block 5. The screw is screwed into the interior of the contact block 5 and the square column to achieve a more stable connection.

[0056] Although this invention adds structures such as a face-changing mechanism 4, a clamping block 3, and a contact block 5 to the existing chuck fixture, slightly increasing the manufacturing cost of a single fixture set, the automatic face-changing mechanism of the contact block 5 and the automatic switching mechanism of the working surface group, combined with online visual inspection and automatic cleaning functions during the processing, can achieve cleaning management, wear warning, and continuous maintenance of the working surface of the contact block 5 without human intervention. This effectively solves the problems of decreased accuracy and frequent machine stoppages for adjustment caused by contact surface wear and dirt contamination in traditional clamping, thus ensuring the long-term maintenance of clamping accuracy and stability during large-volume, continuous processing. The comprehensive benefits of increased production efficiency and reduced scrap rate can quickly balance the increased investment in the early stage. For modern CNC machining scenarios that pursue high automation and high reliability, this invention has significant economic benefits and high practicality.

[0057] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0058] Furthermore, the terms "first," "second," "number one," and "number two" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," "number one," or "number two" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0059] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0060] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A tool holder for a numerically controlled machining center comprising an electrically powered three-jaw chuck, characterized in that, The electric three-jaw chuck is connected with clamping blocks through the setting of fan-shaped blocks, the clamping blocks are fixedly connected with corresponding claws of the electric three-jaw chuck, a surface changing mechanism is slidably arranged on the clamping blocks, and a contact block is quickly detachably connected to the surface changing mechanism. The contact block is in a cuboid structure to provide two groups, i.e. four high-precision working surfaces, each time when a workpiece is replaced, the surface changing mechanism rotates the contact block by half a circle to change the surface, so that the workpiece is clamped with high precision without any debris. A cleaning assembly and a visual assembly are arranged on the clamping block, the cleaning assembly automatically cleans the non-abutting surface of the contact block after the surface is changed, the cleaning effect is detected and fed back through the visual assembly, then, under the driving of the electric three-jaw chuck, the clamping block moves to completely block the non-abutting surface of the contact block to maintain the cleaning effect and push the working surface of the contact block against the workpiece; during machining, the visual assembly detects the flatness of the original working surface of the contact block to determine the service life of the working surface and give a wear warning. With the surface changing clamping, feedback type automatic cleaning and maintenance, and wear warning, long-term stable operation and automatic continuous operation of the workpiece with high-precision clamping are completed. The surface changing mechanism comprises a sliding seat slidably arranged on the clamping block along the length direction of the clamping block, a helical spring is arranged between the sliding seat and the clamping block, and the helical spring is used to push the non-abutting surface of the contact block away from the clamping block. The surface changing mechanism further comprises a lower disc rotatably arranged on the upper side of the sliding seat, an upper disc is rotatably arranged on the upper side of the lower disc, and the upper disc is detachably connected with the contact block through vertical insertion.

2. The tool holder according to claim 1, wherein Three fan-shaped blocks are arranged, and are fixedly installed on the upper side of the electric three-jaw chuck through bolts along the circumference of the electric three-jaw chuck, the gap between adjacent two fan-shaped blocks forms a sliding channel, and the clamping block is slidably connected in the sliding channel.

3. The tool holder according to claim 2, wherein A direct drive motor is fixedly installed in the sliding seat, and the output shaft of the direct drive motor is fixedly connected with the corresponding lower disc.

4. The tool holder according to claim 1, wherein A limiting groove is fixedly arranged on the upper side of the lower disc, a square rod is arranged on the lower side of the upper disc, and the lower disc drives the square rod to rotate the upper disc through the limiting groove.

5. The tool holder according to claim 4, wherein The limiting groove is in a groove structure with a wide outer part and a narrow middle part, the square rod is pushed by the groove wall of the limiting groove to realize the rotation of the upper disc driven by the lower disc, and the square rod has a corresponding free rotation angle in the limiting groove.

6. The fixture of claim 1, wherein, The cleaning assembly comprises a U-shaped frame rotatably arranged on the upper side of the clamping block, and brushes are fixedly installed on the sides of the two vertical sections of the U-shaped frame away from each other.

7. A tool holder for a numerically controlled machining center according to claim 6, characterized in that, A driving motor is fixedly installed in the clamping block, the output shaft of the driving motor is fixedly connected with the U-shaped frame, and the horizontal section of the U-shaped frame is located at a position perpendicular to the length direction of the clamping block when the driving motor is stopped.

8. The tool holder according to claim 1, wherein The visual assembly comprises a high-definition camera fixedly installed in the clamping block and used for shooting the contact block, and an LED lamp fixedly installed in the clamping block and used for light supplement.

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