A plate joining machine tool based on hot melt self-tapping

Abstract

The present invention discloses a plate connection machine tool based on hot-melt self-tapping, which relates to the technical field of hot-melt self-tapping equipment, comprising: a base, on which a processing table is fixedly arranged for fixing a workpiece; a column, fixedly arranged on the base, and a mounting plate is fixedly arranged on the front side of the base; a slide plate, slidably arranged on the front side of the mounting plate, and driven to move laterally by a second telescopic rod on the mounting plate; a hot-melt tapping mechanism and a drilling mechanism, which are arranged in parallel on the front side of the slide plate; a mounting frame, slidably arranged on the front side of the column and located above the mounting plate, and driven to move up and down by a first telescopic rod on the column; a servo motor, fixedly arranged on the mounting frame, and a coupling female joint is provided at its power output end; the present invention uses a drilling mechanism to accurately drill holes in the upper thick plate / hard plate in advance, so that the screws directly pass through the upper plate and perform hot-melt tapping on the lower plate, which completely solves the problems of screw deflection and lower plate tearing caused by hardness / thickness differences in traditional processes.

Description

Technical Field

[0001] The invention relates to the technical field of hot-melt self-tapping equipment, in particular to a plate connecting machine tool based on hot-melt self-tapping. Background Art

[0002] The FDS process utilizes frictional heat generated by the high-speed rotation of the screw to locally melt and soften the base material. Simultaneously, under axial thrust, the screw penetrates the sheet and simultaneously forms a matching thread, ultimately achieving a secure mechanical bond between the materials. This technology, combining friction thermoplastic forming with thread locking mechanisms, is particularly well-suited for joining dissimilar materials, such as the aluminum-steel composite structures widely used in lightweight automotive applications.

[0003] However, current FDS technology typically follows a specific operating sequence when connecting dissimilar materials: the screw should be screwed from the thinner or softer material side to the thicker or harder material side (which can be simply described as a "thin to thick" or "soft to hard" sequence). The core reason for this is that FDS is a one-sided force application process. If the operating sequence is reversed (i.e., screwing from the thick / hard side to the thin / soft side), the thin / soft material on the other side of the joint interface is very likely to displace, plastically deform, or suffer structural damage during the screw penetration process, ultimately reducing the strength of the threaded connection.

[0004] Therefore, providing a special machine tool that can connect screws from "thick to thin" or "hard to soft" is a technical problem that technical personnel in this field urgently need to solve. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a plate connection machine based on hot-melt self-tapping to support FDS technology to achieve "thick to thin" or "hard to soft" sequential connection.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: a plate connecting machine based on hot melt self-tapping, comprising:

[0007] A base, on which a processing table is fixedly arranged for fixing the workpiece;

[0008] The column is fixedly arranged on the base, and a mounting plate is fixedly arranged on the front side of the column;

[0009] The slide plate is slidably arranged on the front side of the mounting plate and is driven to move laterally by the telescopic rod 2 on the mounting plate;

[0010] The hot melt tapping mechanism and the drilling mechanism are arranged in parallel on the front side of the slide;

[0011] The mounting frame is slidably arranged on the front side of the column and located above the mounting plate, and is driven up and down by a telescopic rod on the column;

[0012] The servo motor is fixedly mounted on the mounting frame, and a female coupling is provided at its power output end;

[0013] Among them, the power input ends of the hot melt tapping mechanism and the drilling mechanism are both provided with sub-connectors that match the coupling female connector, and the coupling female connector is selectively docked by the lateral movement of the slide plate.

[0014] Preferably, the drilling mechanism comprises:

[0015] The second slide is arranged on the slide in the vertical direction, and the second moving block and the slide cylinder are slidably arranged inside the slide cylinder, and the rotating cylinder is rotatably arranged inside the slide cylinder;

[0016] The second connecting rod is rotatably connected to the second moving block at the top, a sub-joint is fixedly provided on the top, and the bottom is slidably connected to the rotating drum;

[0017] The first spring is arranged in the rotating drum and abuts against the bottom of the second connecting rod;

[0018] A drill chuck is fixedly arranged at the bottom of the rotary drum, and a drill bit is clamped in the drill chuck;

[0019] The limiting cylinder is screwed to the bottom of the slide cylinder through threads and is located outside the drill chuck;

[0020] Spring 2 is installed on the front side of the slide plate and is used to push the moving block 2 to move upward to achieve the reset function and lift the slide cylinder.

[0021] Preferably, an extension frame is fixedly provided on the outside of the slide cylinder, and a threaded rod arranged along the radial direction of the limit cylinder is screwed on its end. One end of the threaded rod is rotatably connected to a pressure plate, and a knob is fixedly provided on the other end. Turning the knob drives the pressure plate to press the limit cylinder to prevent the limit cylinder from rotating loose.

[0022] Preferably, a flat surface is provided at the thread of the sliding cylinder for screwing onto the limiting cylinder, and engraved lines are provided on the flat surface.

[0023] Preferably, the hot melt tapping mechanism comprises:

[0024] Slideway 1 is arranged on the slide plate in a vertical direction, and a moving block 1 and a nail barrel are slidably arranged therein;

[0025] The connecting rod 1 is rotatably connected to the moving block 1 at the top, a sub-joint is fixedly provided on the top, and a screw sleeve is inserted into the nail barrel at the bottom;

[0026] A pair of positioning clips, hinged to the bottom of the nail barrel in a mirrored manner;

[0027] Spring 2 is installed on the front side of the slide plate and is used to push the moving block 1 to move upward to achieve the reset function and lift the nail barrel.

[0028] Preferably, a movable ring is slidably provided on the outside of the nail barrel, and a top block is fixedly provided on the outer side of the upper part of a pair of positioning clamps, the top block abuts against the lower surface of the movable ring, and a spring three is provided on the outside of the nail barrel to push the movable ring to move downward.

[0029] Preferably, a first T-shaped opening is provided in the mounting plate, a second T-shaped opening is provided in the slide plate, and a third T-shaped opening is provided on the side wall of the nail barrel. When the power input end of the drilling mechanism is vertically aligned with the coupling female joint, the second T-shaped opening is aligned with the first T-shaped opening. When the nail barrel is in a reset state, the third T-shaped opening is aligned with the second T-shaped opening.

[0030] Beneficial effects

[0031] The present invention provides a plate connection machine tool based on hot-melt self-tapping, which has the following beneficial effects: the upper thick plate / hard plate is accurately drilled in advance through the drilling mechanism, so that the screws pass directly through the upper plate and the lower plate is hot-melt tapped, which completely solves the problems of screw deflection and lower plate tearing caused by hardness / thickness differences in traditional processes; the limiting cylinder can be used to control the drilling depth with the upper surface of the plate as the reference plane during drilling, avoiding inconsistent drilling depth due to overall height differences between different workpieces, and ensuring the drilling depth accuracy; a pair of positioning clamps can be used to keep the screws vertical to the plate before hot-melt tapping, thereby improving the hot-melt tapping accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a three-dimensional Figure 1 ;

[0033] Figure 2 The present invention is a three-dimensional Figure 2 ;

[0034] Figure 3 It is a stereoscopic diagram of the hot melt tapping mechanism and the drilling mechanism;

[0035] Figure 4 A three-dimensional diagram of the internal structure of the hot melt tapping mechanism and the drilling mechanism;

[0036] Figure 5 This is the state diagram during drilling processing;

[0037] Figure 6 This is the state diagram during hot melt tapping processing;

[0038] Figure 7 It is a cross-sectional view when the first T-shaped opening, the second T-shaped opening, and the third T-shaped opening are aligned;

[0039] Figure 8 It is a three-dimensional diagram of the slide;

[0040] Figure 9 A three-dimensional diagram of a nail barrel and a positioning clip.

[0041] Figure: 1. Base; 2. Column; 3. Mounting plate; 4. Slide plate; 5. Hot melt tapping mechanism; 6. Drilling mechanism; 7. Mounting frame; 8. Servo motor; 9. Coupling female joint; 10. Slideway 1; 11. Connecting rod 1; 12. Moving block 1; 13. Nail cylinder; 14. Screw sleeve; 15. Sub-joint; 16. Positioning clamp; 17. Moving ring; 18. Spring 3; 19. Top block; 20. Slideway 2; 21. Connecting Rod 2; 22. Moving block 2; 23. Slide; 24. Rotating cylinder; 25. Drill chuck; 26. Drill bit; 27. Spring 1; 28. Limiting cylinder; 29. ​​Extension frame; 30. Threaded rod; 31. Pressing piece; 32. Knob; 33. Spring 2; 34. First T-shaped opening; 35. Second T-shaped opening; 36. Third T-shaped opening; 37. Processing table; 38. Telescopic rod 1; 39. Telescopic rod 2; 40. Plane; 41. Engraved line. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0043] See also Figures 1-9 The present invention provides a technical solution: a plate connecting machine based on hot melt self-tapping, comprising a base 1, a column 2 fixedly provided on the base 1, a mounting plate 3 fixedly provided on the front side of the column 2, a slide plate 4 slidably provided on the front side of the mounting plate 3, a hot melt tapping mechanism 5 and a drilling mechanism 6 provided on the front side of the slide plate 4. When connecting "thick to thin" or "hard to soft" plates, the drilling mechanism 6 first drills a hole in the upper plate (thick plate / hard plate), and then the screw passes through the upper plate to directly perform hot melt tapping on the lower plate, thereby achieving effective connection of "thick to thin" or "hard to soft" plates through hot melt self-tapping;

[0044] See also Figure 3 、 Figure 4 、 Figure 6The hot melt tapping mechanism 5 includes a slide 10 and a connecting rod 11. The slide 10 is arranged on the slide plate 4 in the vertical direction. A moving block 12 and a nail barrel 13 are slidingly arranged in the slide 10. The nail barrel 13 is used to temporarily store screws prepared for hot melt tapping. The top of the connecting rod 11 is rotatably connected to the moving block 12, and the connecting rod 11 can move up and down with the moving block 12. The bottom of the connecting rod 11 is inserted into the nail barrel 13 and is provided with a screw sleeve 14 that matches the nut on the screw. The screw sleeve 14 can move freely downward in the nail barrel 13 and can rotate freely. The diameter of the screw sleeve 14 is larger than the connecting rod 11. When the screw sleeve 14 contacts the top of the nail barrel 13, the nail barrel 13 can be lifted. The bottom of the nail barrel 13 is hinged with a pair of mirrors The positioning clips 16 are provided. When a pair of positioning clips 16 are closed, a bucket-shaped structure can be formed. In addition, when the pair of positioning clips 16 are closed, a through hole is provided at the bottom thereof. The tip of the bottom of the screw can be inserted into the through hole but cannot pass through the through hole. The bottom of the screw can be radially limited by the through hole. When the bottom of the screw is inserted into the through hole, the nut of the screw is in the nail barrel 13. The nut can be radially limited by the nail barrel 13 to ensure that the screw in the nail barrel 13 can be in a vertical state before hot-melt tapping. After the screw sleeve 14 is docked with the nut on the screw, hot-melt tapping is performed by driving the connecting rod 11 to rotate and applying a downward force thereto. When the screw is tapped into the plate and moves downward, the pair of positioning clips 16 can be pushed to open, ensuring that the screw can be completely removed from the nail barrel 13.

[0045] See also Figure 3 、 Figure 4 、 Figure 5 The drilling mechanism 6 includes a slideway 20 and a connecting rod 21. The slideway 20 is arranged on the slide plate 4 in the vertical direction. A moving block 22 and a slide cylinder 23 are slidingly arranged in the slideway 20. The upper part of the connecting rod 21 is rotatably connected to the moving block 22, and the connecting rod 21 can move up and down with the moving block 22. A rotating cylinder 24 is rotatably arranged in the slide cylinder 23. The bottom of the connecting rod 21 is slidably connected to the rotating cylinder 24. The rotating cylinder 24 is connected to the connecting rod 21 through a sliding key. The connecting rod 21 can drive the rotating cylinder 24 to rotate. A spring 27 is provided in the rotating cylinder 24. The first 27 abuts against the bottom of the second connecting rod 21. The bottom of the rotary cylinder 24 is fixedly connected to a drill chuck 25, and a drill bit 26 is clamped in the drill chuck 25. The bottom of the slide cylinder 23 and the outside of the drill chuck 25 are screwed with a limiting cylinder 28. The drill bit 26 can be protruded from the limiting cylinder 28. By rotating the limiting cylinder 28, the drill bit 26 can be moved axially, thereby adjusting the protrusion length of the drill bit 26. When drilling a hole in a plate, the limiting cylinder 28 contacts the upper surface of the plate to limit the drilling depth, thereby realizing the control of the drilling depth with the upper surface of the plate as the reference plane, avoiding inconsistent drilling depths due to overall height differences between different workpieces;

[0046] See also Figure 1, a mounting bracket 7 is slidingly provided on the front side of the column 2 and above the mounting plate 3, a servo motor 8 is fixedly provided on the mounting bracket 7, and a coupling female joint 9 is provided at the power output end of the servo motor 8. The tops of the connecting rod 11 and the connecting rod 2 21 are fixedly provided with sub-joints 15 that match the coupling female joint 9. By controlling the lateral movement of the slide plate 4, the sub-joint 15 at the upper end of the connecting rod 11 or the connecting rod 2 21 can be selected to be vertically aligned with the coupling female joint 9. When the mounting bracket 7 moves downward, the coupling female joint 9 can be docked with the sub-joint 15, and the connecting rod 11 or the connecting rod 2 21 can be driven to rotate by the servo motor 8. A telescopic rod 1 38 for driving the mounting bracket 7 to move up and down is fixedly provided on the column 2, and a telescopic rod 2 39 for driving the slide plate 4 to move laterally is fixedly provided on the mounting plate 3;

[0047] See also Figure 1 、 3 , 4, 5, 6, two springs 2 33 are provided on the slide 4 for pushing the moving block 12 and the moving block 2 22 to move upward. When the coupling female joint 9 is not in contact with the sub-joint 15, the spring 2 33 can push the moving block 12 or the moving block 2 22 to reset, and the nail cylinder 13 can be pulled upward through the connecting rod 11, and the slide cylinder 23 can be pulled upward through the connecting rod 21.

[0048] See also Figure 9 A moving ring 17 is slidingly provided on the outside of the nail barrel 13, and a top block 19 is fixedly provided on the outside of the upper part of a pair of positioning clamps 16. The top block 19 abuts against the lower surface of the moving ring 17. A spring three 18 is provided on the outside of the nail barrel 13 to push the moving ring 17 to move downward. In the natural state, the moving ring 17 can be pushed downward by the spring three 18, so that the pair of positioning clamps 16 are in a closed state. When the screw pushes the pair of positioning clamps 16 to open, the moving ring 17 can be pushed upward by the top block 19. At this time, the spring three 18 can be compressed. Since the top blocks 19 on the pair of positioning clamps 16 are in contact with the moving ring 17 at the same time, it can be ensured that the angles of the pair of positioning clamps 16 are consistent when they are opened.

[0049] See also Figure 8 An extension frame 29 is fixedly provided on the outside of the slide cylinder 23, and a threaded rod 30 is screwed on the end of the extension frame 29. The threaded rod 30 is arranged along the radial direction of the limiting cylinder 28. One end of the threaded rod 30 is rotatably connected to a pressing piece 31, and a knob 32 is fixedly provided on the other end of the threaded rod 30. By turning the knob 32, the threaded rod 30 can be rotated and moved axially, and the pressing piece 31 is pressed against the outer surface of the limiting cylinder 28 to prevent the limiting cylinder 28 from rotating loose.

[0050] See also Figure 8 The slide cylinder 23 is provided with a plane 40 at the thread where the limit cylinder 28 is screwed, and a scale line 41 is provided on the plane 40. The scale line 41 can be used to facilitate observation of the position of the limit cylinder 28.

[0051] See also Figure 2 、 7 A first T-shaped opening 34 is provided in the mounting plate 3, a second T-shaped opening 35 is provided in the slide plate 4, and a third T-shaped opening 36 is provided on the side wall of the nail barrel 13. When the connecting rod 21 is vertically aligned with the coupling female joint 9, the second T-shaped opening 35 is aligned with the first T-shaped opening 34. When the nail barrel 13 is in the reset state, the third T-shaped opening 36 is aligned with the second T-shaped opening 35. The screw can enter the nail barrel 13 through the inclined third T-shaped opening 36, the second T-shaped opening 35, and the first T-shaped opening 34, which is convenient for loading the nail barrel 13. The first T-shaped opening 34, the second T-shaped opening 35, and the third T-shaped opening 36 are all designed according to the screw profiling. The screw can only slide but cannot roll in the T-shaped opening.

[0052] See also Figure 1 、 2 A processing table 37 for fixing the plate is provided on the base 1.

[0053] The working principle and use process of the present invention are as follows: when in use, the workpiece is placed on the processing table 37 and fixed, and the protrusion length of the drill bit 26 is adjusted according to the thickness of the upper plate of the workpiece to control the drilling depth; the slide plate 4 is pulled by the telescopic rod 29 to align the sub-joint 15 on the connecting rod 21 with the coupling female joint 9 vertically, and the mounting bracket 7 is pushed downward by the telescopic rod 1 38. When the coupling female joint 9 is docked with the sub-joint 15 on the connecting rod 21, the servo motor 8 is started. By starting the servo motor 8, the connecting rod 21 can be driven to rotate. The thrust output by the telescopic rod 1 38 can apply a downward force to the connecting rod 21. At this time, the spring 2 33 connected to the moving block 22 is compressed. When the connecting rod 21 moves downward, the slide 23 will drop at the same time (please refer to Figure 5) When the drill bit 26 contacts the workpiece, the spring 1 27 is compressed under the push of the connecting rod 21, and the axial force is transmitted and buffered by the spring 1 27. When the limit cylinder 28 contacts the surface of the workpiece, the slide 23 stops moving downward, and the rotating cylinder 24 and the drill bit 26 also stop moving downward. At this time, a hole with a depth matching the length of the drill bit 26 is drilled in the upper plate of the workpiece. After the drilling is completed, the mounting bracket 7 is pulled up by the telescopic rod 1 38. Under the push of the spring 2 33, the connecting rod 21 can be raised and reset. The slide 23 can be pulled up by the connecting rod 21, so that the drill bit 26 can be pulled out of the drilled hole; put the screw into the first T-shaped opening 34. At this time, the first T-shaped opening 34, the second T-shaped opening 35, and the third T-shaped opening 36 are all in the same position. The T-shaped opening 36 is in a connected state and forms an inclined channel. The screw can slide in the inclined channel and enter the nail barrel 13 by its own weight. The telescopic rod 2 39 is started to push the slide plate 4 to move, so that the sub-joint 15 on the connecting rod 11 is vertically aligned with the coupling female joint 9. The telescopic rod 1 38 is started again to push the mounting bracket 7 to move downward. When the coupling female joint 9 is docked with the sub-joint 15 on the connecting rod 11, the servo motor 8 is started. The servo motor 8 can drive the connecting rod 11 to rotate. The thrust output by the telescopic rod 1 38 can apply a downward force to the connecting rod 11. At this time, the spring 2 33 connected to the moving block 12 is compressed. When the connecting rod 11 moves downward, the nail barrel 13 also drops. (Please refer to Figure 6 ) When the bottom of the positioning clamp 16 contacts the workpiece, the nail barrel 13 stops descending, and the screw in the nail barrel 13 is in a vertical state. The screw sleeve 14 continues to descend to dock with the nut of the screw. Under the push of the connecting rod 11, the screw can push a pair of positioning clamps 16 to open and contact the lower layer of the workpiece, and hot melt tapping is performed on the lower layer (the detailed process of hot melt tapping is existing technology and will not be described in detail here). After the hot melt tapping is completed, the mounting frame 7 is pulled up by the telescopic rod 38, and the connecting rod 11 can be lifted up and reset under the push of the spring 2 33. The screw sleeve 14 can be pulled up by the connecting rod 11 to make the pair of positioning clamps 16 away from the workpiece.

[0054] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A plate connecting machine based on hot melt self-tapping, characterized in that: include: A base (1) is provided with a processing table (37) fixedly disposed on top thereof for fixing a workpiece; A column (2) is fixedly mounted on the base (1), and a mounting plate (3) is fixedly mounted on the front side of the column; The slide plate (4) is slidably arranged on the front side of the mounting plate (3) and is driven to move laterally by the second telescopic rod (39) on the mounting plate (3); A hot melt tapping mechanism (5) and a drilling mechanism (6) are arranged in parallel on the front side of the slide plate (4); A mounting frame (7) is slidably arranged on the front side of the column (2) and located above the mounting plate (3), and is driven to move up and down by a telescopic rod (38) on the column (2); A servo motor (8) is fixedly mounted on the mounting frame (7), and a coupling female connector (9) is provided at the power output end of the servo motor; The power input ends of the hot melt tapping mechanism (5) and the drilling mechanism (6) are both provided with sub-connectors (15) matching the coupling female connector (9), and the sliding plate (4) is moved laterally to selectively connect with the coupling female connector (9); The hot melt tapping mechanism (5) comprises: A slideway (10) is vertically arranged on the slide plate (4), and a moving block (12) and a nail barrel (13) are slidably arranged therein; A connecting rod (11) is rotatably connected to a moving block (12) at the top, a sub-joint (15) is fixedly provided on the top, and a screw sleeve (14) is inserted into the nail barrel (13) at the bottom; A pair of positioning clips (16) are hinged to the bottom of the nail barrel (13) in a mirror-image manner; Spring 2 (33), installed on the front side of the slide (4), is used to push the moving block 1 (12) to move upward to achieve the reset function and lift the nail barrel (13) A movable ring (17) is slidably provided on the outside of the nail barrel (13), and a top block (19) is fixedly provided on the outside of the upper side of a pair of positioning clamps (16). The top block (19) abuts against the lower surface of the movable ring (17), and a spring (18) for pushing the movable ring (17) to move downward is provided on the outside of the nail barrel (13).

2. A plate joining machine tool based on hot melt self-tapping according to claim 1, characterized in that: The drilling mechanism (6) comprises: The second slideway (20) is arranged on the slide plate (4) in a vertical direction, and a second moving block (22) and a slide cylinder (23) are slidably arranged inside the slide cylinder (23), and a rotating cylinder (24) is rotatably arranged inside the slide cylinder (23); The second connecting rod (21) is rotatably connected to the second moving block (22) at the top, a sub-joint (15) is fixedly provided on the top, and the bottom is slidably connected to the rotating drum (24); Spring 1 (27) is arranged in the rotating drum (24) and abuts against the bottom of connecting rod 2 (21); A drill chuck (25) is fixedly arranged at the bottom of the rotary drum (24), and a drill bit (26) is clamped in the drill chuck (25); A limiting cylinder (28) is screwed to the bottom of the slide cylinder (23) through a thread and is located outside the drill chuck (25); Spring 2 (33) is installed on the front side of the slide plate (4) and is used to push the moving block 2 (22) to move upward to achieve the reset function and lift the slide cylinder (23).

3. A plate joining machine tool based on hot melt self-tapping according to claim 2, characterized in that: An extension frame (29) is fixedly provided on the outside of the slide cylinder (23), and a threaded rod (30) is screwed on the end thereof and arranged along the radial direction of the limiting cylinder (28). One end of the threaded rod (30) is rotatably connected to a pressing piece (31), and a knob (32) is fixedly provided on the other end thereof. Turning the knob (32) drives the pressing piece (31) to press the limiting cylinder (28) tightly to prevent the limiting cylinder (28) from rotating and loosening.

4. A plate joining machine tool based on hot melt self-tapping according to claim 2, characterized in that: The thread of the slide cylinder (23) for screwing the limiting cylinder (28) is provided with a plane (40), and a scale line (41) is provided on the plane (40).

5. A plate joining machine tool based on hot melt self-tapping according to claim 1, characterized in that: A first T-shaped opening (34) is provided in the mounting plate (3), a second T-shaped opening (35) is provided in the slide plate (4), and a third T-shaped opening (36) is provided on the side wall of the nail barrel (13). When the power input end of the drilling mechanism (6) is vertically aligned with the coupling female joint (9), the second T-shaped opening (35) is aligned with the first T-shaped opening (34); when the nail barrel (13) is in a reset state, the third T-shaped opening (36) is aligned with the second T-shaped opening (35).

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