A special machine tool for C-section segments

Abstract

The present invention discloses a special machine tool for C standard sections, which has a vertical system and a horizontal system for simultaneously machining workpieces. A fixture base for placing the workpiece is provided on the base between the vertical system and the horizontal system. A clamping mechanism for positioning and clamping the workpiece is provided on the fixture base, and the clamping mechanism has the function of maintaining the straightness of a workpiece with a certain length during machining. Through different vertical systems and horizontal systems, different surfaces of the workpiece are simultaneously machined, and machining methods such as milling the surface and drilling and boring holes of the workpiece can be completed simultaneously in one clamping without mutual interference, thus solving the tediousness of multiple clamps and multiple adjustments during the machining process of the workpiece, greatly improving the machining accuracy and machining efficiency of the workpiece, and being particularly suitable for mass production requirements. The automatic loading and unloading mechanism completes the grasping of the finished workpiece and the workpiece to be machined within one stroke, saves the empty running stroke of the grasping mechanism, and saves the waiting time for continuous machining of the machine tool.

Description

Technical Field

[0001] The invention relates to the technical field of machine tool processing, and in particular to a special machine tool for C-sections. Background Art

[0002] The existing machine tools are mostly separated into vertical and horizontal types. The horizontal lathe is a machine tool that mainly uses a turning tool to turn the rotating workpiece. It is the most widely used type of machine tool in machinery manufacturing and repair factories. The milling machine is a machine tool that uses a milling cutter to mill the workpiece. In addition to milling planes, grooves, gear teeth, threads and spline shafts, the vertical milling machine can also process more complex surfaces. It is more efficient than a planer and is widely used in machinery manufacturing and repair departments. For complex workpieces, it is necessary to use a lathe and a milling machine to process them separately, resulting in a large number of clamping times, multiple adjustments and multiple processing of the workpiece. The entire processing process is time-consuming and laborious, resulting in extremely low processing efficiency, and the processing accuracy cannot be guaranteed, which cannot meet the needs of large-scale production. On the basis of this problem, the lengthened workpiece needs to be clamped multiple times on a separate lathe or milling machine, which further increases the cumulative error of the processing, making it difficult to process workpieces with a certain length and complex processing. Summary of the invention

[0003] In view of the above-mentioned problems, the present invention aims to provide a special machine tool for C-sections, which can process different surfaces of a workpiece simultaneously through different vertical systems and horizontal systems. One clamping can simultaneously complete milling, drilling and boring and other processing methods of the workpiece without mutual interference, thereby solving the tedious problems of multiple clamping and multiple adjustments during the workpiece processing, greatly improving the processing accuracy and efficiency of the workpiece, and is particularly suitable for large-scale production needs.

[0004] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a special machine tool for C-sections, having a vertical system and a horizontal system for simultaneously processing workpieces; the vertical system includes a sub-base, a cross slide and a column which are arranged in sequence upward on one side of the base, the column is located on one side inside the base and is provided with a vertically sliding rotary slide, a tool clamping part facing downward is provided on the rotary slide, and a tool magazine equipped with a plurality of tools for tool clamping part tool change is provided on the side wall of the column adjacent to the rotary slide, the horizontal system structure is similar to the vertical system structure, and the difference between it and the vertical system structure is that the tool clamping part of the horizontal system is horizontally arranged on one side of the rotary slide and is directed toward the vertical system, wherein a fixture base for placing the workpiece is provided on the base between the vertical system and the horizontal system, and a clamping mechanism for positioning and clamping the workpiece is provided on the fixture base, and the clamping mechanism has the function of maintaining the straightness of a workpiece of a certain length when being processed.

[0005] Preferably, the clamping mechanism includes a left clamping device and a right clamping device arranged at both ends of the fixture base. A first auxiliary support device, a second auxiliary support device, and a middle clamping device that slides horizontally are arranged between them in a transverse and longitudinal direction. The fixture base is also provided with a positioning device for the workpiece. The first auxiliary support device and the second auxiliary support device are both provided with an adjustable support mechanism for the tool processing position.

[0006] Preferably, both the first auxiliary support device and the second auxiliary support device have a lifting base. The adjustable support mechanism includes an annular "concave" groove opened on the top surface of the lifting base. At least two top blocks that rotate horizontally and annularly along the annular "concave" groove are nested in the annular "concave" groove. The top surface of the top block exceeds the surface of the lifting base by a certain height and abuts against the bottom surface of the workpiece.

[0007] Preferably, an automatic loading and unloading mechanism is arranged on one side of the special machine tool along the length direction of the base. It includes a support frame. A moving table that slides horizontally along its length direction and towards the fixture base is arranged on the support frame. A gripper mechanism that vertically lifts and is used to simultaneously grip the finished workpiece and the workpiece to be processed is arranged at the bottom of the moving table.

[0008] Preferably, the gripper mechanism includes a rectangular frame that is perpendicular to the moving table and rotates along the vertical plane at the bottom of the moving table. Grippers are symmetrically arranged at intervals on both sides of the rectangular frame in the same length direction as the fixture base. A self-locking device is arranged on each gripper.

[0009] Preferably, the gripper is composed of a number of conical blocks arranged at circumferential intervals. The self-locking device includes an elastic sliding locking mechanism arranged on the inner side of the bottom of the conical block. The elastic sliding locking mechanism includes a groove opened on the inner side of the bottom of the conical block. A rectangular block and a spring are sequentially arranged in the groove from top to bottom. The outer side surface of the rectangular block exceeds the inner wall surface of the conical block and fits against the surface of the workpiece.

[0010] Preferably, the tool clamping part has a clamping hole at one end for clamping the tool. A balance positioning device for precisely clamping the tool is arranged in the clamping hole.

[0011] Preferably, the balance positioning device is an annular spring plate group that is evenly distributed along the axial direction in the clamping hole and is used for elastic balance of the tool shank.

[0012] The beneficial effects of the present invention are:

[0013] 1. By means of different vertical systems and horizontal systems, different surfaces of the workpiece are machined simultaneously. Machining methods such as milling the surface of the workpiece and drilling and boring holes can be completed simultaneously in one clamping, and there will be no mutual interference, thus solving the cumbersome problems of multiple clampings and multiple adjustments during the machining process of the workpiece, greatly improving the machining accuracy and machining efficiency of the workpiece, and being particularly suitable for mass production requirements.

[0014] 2. The automatic loading and unloading mechanism completes the grasping of the finished workpiece and the workpiece to be machined within one stroke, saving the empty running stroke of the grasping mechanism and the waiting time for continuous machining of the machine tool.

[0015] 3. The clamping mechanism has the function of clamping the whole workpiece and specifically supporting the machining position to prevent the problem that the workpiece is bent by the external force of the tool.

[0016] 4. The annular spring plate group balances the deflection of the tool shank, making the whole tool coaxial with the clamping hole, and improving the clamping accuracy of the tool and the machining accuracy of the workpiece. Description of the Drawings

[0017] Figure 1 This is the front view of the machine tool of the present invention.

[0018] Figure 2 This is the right view of the machine tool of the present invention.

[0019] Figure 3 This is the top view of the machine tool of the present invention.

[0020] Figure 4 This is the front view of the clamping mechanism of the machine tool of the present invention.

[0021] Figure 5 This is the top view of the clamping mechanism of the machine tool of the present invention.

[0022] Figure 6 This is the top view structure diagram of the first auxiliary support device and the second auxiliary support device of the present invention.

[0023] Figure 7 This is the front view structure diagram of the automatic loading and unloading mechanism of the present invention.

[0024] Figure 8 This is the top view structure diagram of the rectangular frame of the present invention.

[0025] Figure 9 This is the front view structure diagram of the gripper of the present invention.

[0026] Figure 10 This is the balance state diagram of the annular spring plate group for the tool of the present invention. Detailed Description of the Invention

[0027] To enable those of ordinary skill in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] Refer to the attached Figures 1-10 Shown is a special machine tool for C standard sections, which has a vertical system (shown as I in the attached drawings) and a horizontal system (shown as II in the attached drawings) for simultaneously machining a workpiece 100. The machine tool also includes a numerical control system 24, a hydraulic system 25, a cooling system 26, and a chip removal system 27. The vertical system includes a sub-base 2, a cross slide 3, and a column 4 that are sequentially arranged upward on one side of the base 1. A rotary slide 5 that slides vertically is provided on the inner side of the column 4 located in the base 1. A tool clamping part 6 with a downward direction is provided on the rotary slide 5. On the side wall of the column 4 adjacent to the rotary slide 5, there is a tool magazine 17 for tool change of the tool clamping part 6 and equipped with several tools 18. Through the sliding and rotation of the rotary slide 5, the tool change action is completed corresponding to the tool magazine 17. By horizontally and longitudinally moving the column 4 and the rotary slide 5 and the tool clamping part 6 provided thereon through the cross slide 3 on the sub-base 2, the tool clamped on the tool clamping part 6 is moved and positioned to the coordinate points where the workpiece 100 needs to be machined for precise machining. The tool magazine 17 can complete the replacement of the tool clamped by the tool clamping part 6. This vertical system completes the vertical machining mode of the workpiece 100.

[0029] The structure of the horizontal system is similar to that of the vertical system. The difference between its structure and that of the vertical system is that: the tool clamping part 6 of the horizontal system is horizontally arranged on one side of the rotary slide 5 and faces the vertical system. This horizontal system completes the horizontal machining mode of the workpiece 100. Since the machining surfaces of the vertical system and the horizontal system are different and do not interfere with each other, the horizontal system and the vertical system with two different machining directions and simultaneous machining solve the cumbersome problems of multiple clamping and multiple adjustments during the machining process of the workpiece 100, greatly improving the machining accuracy and machining efficiency of the workpiece 100, and are especially suitable for mass production requirements.

[0030] In order to enable this special machine tool to overcome the problem of bending of the workpiece 100 during the machining of a longer workpiece 100 and improve the machining forming accuracy of the workpiece 100, a fixture base 7 for placing the workpiece 100 is provided on the base 1 between the vertical system and the horizontal system. A clamping mechanism for positioning and clamping the workpiece 100 is provided on the fixture base 7. This clamping mechanism has the function of maintaining the straightness of a workpiece 100 with a certain length during machining. The workpiece 100 is clamped and fixed by this clamping mechanism, and the problem that the workpiece 100 is prone to bending when being contacted by the external force of the tool can be overcome, improving the machining accuracy of the longer workpiece 100.

[0031] Specifically, the clamping mechanism includes a left-end clamping device 71 and a right clamping device 72 arranged at both ends of the fixture base 7. A first auxiliary support device 73, a second auxiliary support device 75, and a middle clamping device 74 that slides horizontally are arranged between them in a transverse and longitudinal sliding manner. The specific structure is as Figures 4-5 shown. A linear guide rail 19 is provided on the fixture base 7 for the first auxiliary support device 73, the middle clamping device 74, and the second auxiliary support device 75 to slide horizontally, and a slide plate 20 is longitudinally arranged on the linear guide rail 19 for the first auxiliary support device 73 and the second auxiliary support device 75 to slide longitudinally. The fixture base 7 is also provided with a positioning device for the workpiece 100. The specific structure includes side positioning reference devices symmetrically arranged on both sides of the fixture base 7 and an end positioning device arranged at one end of one side of the fixture base 7. Among them, the side positioning reference device has an oil cylinder push rod 21 and a reference block 22 correspondingly arranged along the width on both sides of the fixture base 7, and the end positioning device includes an end oil cylinder push rod 23.

[0032] During clamping, first place the workpiece 100 between the oil cylinder push rod 21 and the reference block 22 of the side positioning reference device, and push the workpiece 100 to the set position through the end oil cylinder push rod 23 to complete the end face positioning of the workpiece 100. Then, longitudinally push the workpiece 100 through the oil cylinder push rod 21 of the side positioning reference device to contact the reference block to complete the lateral positioning. After positioning, clamp both ends of the workpiece 100 through the left-end clamping device 71 and the right clamping device 72. Then, fix and clamp the middle position of the workpiece 100 by sliding the middle clamping device 74. The clamping devices at both ends and in the middle are all cooperated with the reference block 22 and clamped through the oil cylinder push rod 21. Finally, horizontally and longitudinally move the first auxiliary support device 73 and the second auxiliary support device 75 according to the specific processing position of the workpiece 100 to support both sides of the bottom at the processing position of the workpiece 100 to overcome the external force of the tool on the workpiece 100. The movable first auxiliary support device 73 and the second auxiliary support device 75 can be accurately adjusted according to the processing position on the horizontal plane, and can be more effectively attached to the processing position to support the workpiece 100. The support for the processing position on the side wall of the workpiece 100 is completed through the cooperation of the sliding of the middle clamping device 74 and the left-end clamping device 71 and the right clamping device 72 on both sides.

[0033] Since the horizontal surface of the workpiece 100 may have the need for precise machining at any coordinate position, in order to suit the complex machining method of the surface of the workpiece 100 and prevent interference with the cutting tool caused by the first auxiliary support device 73 and the second auxiliary support device 75, an adjusting support mechanism for the machining position of the cutting tool 18 is provided on both the first auxiliary support device 73 and the second auxiliary support device 75. This adjusting support mechanism can make small-distance adjustments to the support points of the workpiece 100 in the horizontal plane without changing the positions of the first auxiliary support device 73 and the second auxiliary support device 75. While improving the support effect on the workpiece 100, it can avoid the interference problem with the cutting tool 18 at the same time.

[0034] Specifically, both the first auxiliary support device 73 and the second auxiliary support device 75 are provided with a lifting base 8 so as to be able to support according to the clamping height of the workpiece 100 or provide targeted support for the surface of the irregular workpiece 100. The adjusting support mechanism includes an annular "concave" groove 8a opened on the top surface of the lifting base 8. At least two top blocks 9 that are horizontally and annularly rotatable along the annular "concave" groove 8a are nested in the annular "concave" groove 8a. The top surface of the top block 9 protrudes from the surface of the lifting base 8 by a certain height and abuts against the bottom surface of the workpiece 100. According to the change of the actual machining position, the top block 9 is rotated in the annular "concave" groove 8a and has lateral and longitudinal position movements in the horizontal plane, which can firmly support the workpiece 100 while closely adhering to and avoiding the machining position of the cutting tool, effectively preventing the workpiece 100 from bending during machining.

[0035] In order to further improve the automation degree of the special machine tool, an automatic loading and unloading mechanism is arranged on one side of the special machine tool along the length direction of the base 1. It includes a support frame 10. A moving table 11 that horizontally slides along its length direction and towards the fixture base 7 is provided on the support frame 10. A gripper mechanism that vertically lifts and is used to simultaneously grip the finished workpiece 100 and the workpiece 100 to be machined is provided at the bottom of the moving table 11. This gripper mechanism can grip the finished workpiece 100 and the workpiece 100 to be machined in one stroke, saving the empty travel of the gripping mechanism and the waiting time for continuous machining of the machine tool.

[0036] Specifically, the gripper mechanism includes a rectangular frame 12 perpendicular to the moving platform 11 and rotatably arranged at the bottom of the moving platform 11 along the vertical plane. The gripper 13 is symmetrically arranged at both sides of the rectangular frame 12 along the length direction of the fixture base 7 with a certain spacing. Preferably, the automatic grasping of the gripper 13 adopts a hydraulic or pneumatic method. When grasping, first, the gripper on one side of the rectangular frame 12 grasps the workpiece 100 to be processed in the storage area, and then through the lateral and longitudinal movement of the moving platform 11, the workpiece 100 to be processed is moved near the clamping mechanism. Then, the gripper 13 on the rectangular frame 12 on the side where the workpiece 100 is to be grasped clamps the finished workpiece 100 on the clamping mechanism. Then, the rectangular frame 12 is rotated to make the finished workpiece 100 away from the clamping mechanism, and at the same time, the workpiece 100 to be processed is close to the clamping mechanism, and finally, it is placed on the clamping mechanism for clamping to perform the next processing operation. This kind of loading and unloading method can effectively avoid the empty travel of the gripper and reduce the waiting time for continuous machining of the machine tool.

[0037] In order to avoid the problem that the workpiece 100 tilts or drops due to the failure of the gripper and the loss of grasping force, a self-locking device is provided on each gripper 13. Specifically, the gripper 13 is composed of a number of conical blocks 13a arranged at circumferential intervals. The self-locking device includes an elastic sliding locking mechanism arranged inside the bottom of the conical block 13a. The elastic sliding locking mechanism includes a groove 13b opened inside the bottom of the conical block 13a. A rectangular block 14 and a spring 15 are sequentially arranged in the groove 13b from top to bottom, and the outer side surface of the rectangular block 14 extends beyond the inner wall surface of the conical block 13a and fits with the surface of the workpiece 100. First, the workpiece 100 is clamped by the gripper 13 with an external force. At the same time, the rectangular block 14 is closely attached to the side wall of the workpiece 100. When the workpiece 100 is lifted after clamping, the workpiece 100 moves downward due to its own gravity. Through the friction force with the rectangular block 14, the rectangular block 14 compresses the spring and moves downward. At the same time, since the lower opening formed by the multiple conical blocks 13a of the gripper 13 is smaller than the upper opening, when the rectangular block 14 moves downward, it gradually converges towards the middle inside the gripper 13, and then presses tightly on the surface of the workpiece 100. The lower the workpiece 100 moves, the greater the clamping force it receives from the rectangular block 14, thus realizing the self-locking effect on the workpiece 100. This solves the problem that the workpiece 100 tilts or drops due to the failure of the gripper 13, improves the safety of the machine tool operation, and at the same time can avoid the damage caused by the dropping of the workpiece 100. In order to adapt to the clamping operation of workpieces 100 with different specifications, preferably, the surface of the rectangular block 14 in contact with the workpiece 100 is set as an arc surface structure 14a, which can solve the problem that the rectangular block 14 cannot be closely attached to the surface of the workpiece 100 due to the change of the workpiece 100 specifications.

[0038] During the tool change process, there is a positional error between the tool magazine 17 and the clamping hole 601, and there is a fit clearance between the tool and the clamping hole 601. Therefore, after the tool change is completed, there is a clamping deviation between the machining tool 18 and the clamping hole 601, resulting in a decrease in the machining accuracy of the machine tool. To solve this problem, the tool clamping portion 6 that clamps one end of the tool 18 has a clamping hole 601, and a balance positioning device for accurately clamping the tool 18 is provided in the clamping hole 601. It can balance the above errors and fit clearances, improve the coaxiality between the tool 18 and the clamping hole 601, and thus improve the machining accuracy of the machine tool.

[0039] Specifically, the balance positioning device is a set of annular spring plates 16 that are evenly distributed along the axial distance in the clamping hole 601 and are used for elastic balancing of the tool shank 18a of the tool 18. Each set of annular spring plates is composed of spring plates 161 that are spaced apart in the circumferential direction (as Figure 10 shown). When changing the tool 18, the tool shank 18a of the tool 18 enters the clamping hole 601 and passes through the center of the set of annular spring plates 16. The deflection of the tool shank 18a is balanced by the elastic action of multiple circumferentially arranged spring plates 161, making the whole tool 18 coaxial with the clamping hole 601. And the spring plate 161 facilitates the quick clamping and removal of the tool 18 without excessive restrictions. To more quickly remove the tool 18 for replacement, preferably, one end of the spring plate 161 close to the bottom side of the clamping hole 601 is set as an arc surface to facilitate the withdrawal of the tool 18, as Figure 10 shown at A.

[0040] The principle of the present invention is as follows: The automatic loading and unloading mechanism completes the grasping of the finished workpiece 100 and the workpiece to be processed 100 within one stroke, saving the empty running stroke of the grasping mechanism and the waiting time for continuous machining of the machine tool. The workpiece to be processed 100 is placed on the clamping mechanism, and its two ends are respectively clamped and fixed at the left clamping device 71 and the right clamping device 72, and the middle position of the workpiece 100 is fixedly clamped and supported by sliding the middle clamping device 74. Finally, the first auxiliary support device 73 and the second auxiliary support device 75 are moved according to the specific machining position of the workpiece 100 to support both sides of the machining position of the workpiece 100 to overcome the external force of the tool on the workpiece 100. The movable first auxiliary support device 73 and the second auxiliary support device 75 can be accurately adjusted according to the machining position on the horizontal plane, and can be more effectively attached to the machining position to support the workpiece 100, including rotating the top block 9 in the annular "concave" groove 8a according to the change of the actual machining position, closely adhering to and avoiding the machining position of the tool to strongly support the workpiece 100, effectively preventing the workpiece 100 from bending during machining. The supporting effect on the machining position of the side wall of the workpiece 100 is completed by the cooperation of the sliding of the middle clamping device 74 and the left clamping device 71 and the right clamping device 72 on both sides. After clamping and fastening, machining is started. Through different vertical systems and horizontal systems, different surfaces of the workpiece 100 are machined simultaneously without mutual interference, thus solving the cumbersome problems of multiple clamping and multiple adjustments during the machining process of the workpiece 100, greatly improving the machining accuracy and machining efficiency of the workpiece 100, and being particularly suitable for mass production requirements.

[0041] The above shows and describes the basic principle, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A special machine tool for C standard sections, having a vertical system and a horizontal system for simultaneously machining workpieces; the vertical system includes a sub-base (2), a cross slide (3), and a column (4) sequentially arranged upward on one side of the base (1). A rotary slide (5) that slides vertically is provided on one side inside the base (1) of the column (4). A tool clamping portion (6) with a downward direction is provided on the rotary slide (5). On the side wall of the column (4) adjacent to the rotary slide (5), a tool magazine (17) for tool change of the tool clamping portion (6) and equipped with a number of tools (18) is provided. The structure of the horizontal system is similar to that of the vertical system. The difference between its structure and that of the vertical system is that the tool clamping portion (6) of the horizontal system is horizontally arranged on one side of the rotary slide (5) and faces the vertical system. Among them, On the base (1) between the vertical system and the horizontal system, there is a fixture base (7) for placing the workpiece (100). The fixture base (7) is provided with a clamping mechanism for positioning and clamping the workpiece (100), and this clamping mechanism has the function of maintaining the straightness of the workpiece (100) with a certain length during machining. The clamping mechanism includes a left-end clamping device (71) and a right clamping device (72) arranged at both ends of the fixture base (7). Between them, a first auxiliary support device (73), a second auxiliary support device (75), and a middle clamping device (74) that slides horizontally are arranged in a transverse and longitudinal manner. The fixture base (7) is also provided with a positioning device for the workpiece. The first auxiliary support device (73) and the second auxiliary support device (75) are both provided with an adjustable support mechanism for the machining position of the tool (18). On one side of the special machine tool along the length direction of the base (1), there is an automatic loading and unloading mechanism, which includes a support frame (10). On the support frame (10), there is a moving table (11) that slides horizontally along its length direction and towards the fixture base (7). At the bottom of the moving table (11), there is a gripper mechanism that moves vertically and is used for simultaneously gripping the finished workpiece and the workpiece to be machined. The gripper mechanism includes a rectangular frame (12) perpendicular to the moving table (11) and rotatably arranged along the vertical plane at the bottom of the moving table (11). The gripper (13) is symmetrically arranged at intervals on both sides of the rectangular frame (12) in the same length direction as the fixture base (7). Each gripper (13) is provided with a self-locking device. The gripper (13) is composed of a number of conical blocks (13a) arranged at circumferential intervals. The self-locking device includes an elastic sliding locking mechanism arranged inside the bottom of the conical block (13a). This elastic sliding locking mechanism includes a groove (13b) opened inside the bottom of the conical block (13a). In the groove (13b), a rectangular block (14) and a spring (15) are arranged in sequence from top to bottom. And the outer side surface of the rectangular block (14) extends beyond the inner wall surface of the conical block (13a) and fits with the surface of the workpiece (100), and the surface of the rectangular block (14) that fits with the workpiece (100) is set as an arc surface structure (14a). One end of the tool (18) clamped by the tool clamping part (6) has a clamping hole (601), and a balance positioning device for precisely clamping the tool (18) is arranged in this clamping hole (601). The balance positioning device is an annular spring plate group (16) that is evenly distributed along the axial direction at intervals in the clamping hole (601) and is used for the elastic balance of the tool shank (18a) of the tool (18). Both the first auxiliary support device (73) and the second auxiliary support device (75) are provided with a lifting base (8). The adjusting support mechanism includes an annular "concave"-shaped groove (8a) formed on the top surface of the lifting base (8). At least two top blocks (9) that rotate horizontally and annularly along the annular "concave"-shaped groove (8a) are nested in the annular "concave"-shaped groove (8a). The top surface of the top block (9) protrudes a certain height beyond the surface of the lifting base (8) and abuts against the bottom surface of the workpiece (100).

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