Pretreatment tool for detecting internal atmosphere of microwave product

Abstract

The utility model provides a microwave product internal atmosphere detection pretreatment tool which comprises a step milling cutter, a transparent pre-tightening limiting plate and pressing plates, the pre-tightening limiting plate is arranged on a cover plate of a to-be-detected piece, the step milling cutter penetrates through a center hole of the pre-tightening limiting plate, the tool comprises two pressing plates, and the two pressing plates are arranged on the two sides of the pre-tightening limiting plate respectively. According to the invention, the tool composed of the stepped milling cutter, the pre-tightening limiting plate and the pressing plate is used for processing the to-be-detected piece before internal atmosphere detection, and before internal atmosphere detection, the to-be-punctured blind hole and the sealing mounting groove are processed on the cover plate of the to-be-detected piece, so that the processing time of the internal atmosphere detection pretreatment of the cover plate is shortened, and the processing efficiency is improved. The volume of the secondary cavity is reduced, the unfavorable conditions of insufficient vacuum degree, even air leakage and the like during internal atmosphere detection are avoided, and the accuracy and reliability of internal atmosphere detection results of microwave products are improved.

Description

Technical Field

[0001] This utility model relates to the field of product testing, specifically to a pretreatment fixture for detecting the internal atmosphere of microwave products. Background Technology

[0002] Currently, to ensure the reliability of internal chips and components during long-term use, hermetic packaging is necessary. High concentrations of water vapor, hydrogen, oxygen, carbon dioxide, and organic gases such as methanol in the internal atmosphere can damage the devices. Under the influence of external factors, these hazards or potential defects can worsen, leading to device malfunction. Therefore, the internal atmosphere content is one of the important indicators for evaluating the reliability of hermetic packaged devices. Internal atmosphere content testing is a destructive test, requiring the use of a piercing steel needle to mechanically penetrate the device's seal and collect the internal atmosphere, which is then sent to an analysis chamber. After testing, the microwave product can be resealed and used with a new cover plate.

[0003] Because internal atmosphere testing requires a high-vacuum, sealed connection to the equipment throughout the entire process, and microwave hybrid integrated circuit products are mostly component-type products with large dimensions, they are more prone to deformation and warping. The cover plate thickness of large-size components is 3-5 times that of small-size devices. The puncture process is done manually, and mastering the puncture force relies heavily on experience; the sample must be punctured without causing significant surface deformation and leakage. In related technologies, testing personnel often use a ball-head grinding head to reduce the thickness of the puncture area. However, the surface processed by the ball-head grinding head is not flat, and because microwave component cover plates are thick, a certain depth of recess needs to be ground to place a sealing ring in this recess to achieve vacuum. The concave surface may exceed the elastic deformation of the sealing ring, which is not conducive to achieving a vacuum. Furthermore, when puncturing the curved surface, the lack of a suitable point of force makes the tip prone to drift, leading to deformation or even breakage of the needle. Once the product is punctured, the inability to achieve an effective vacuum environment results in sample rejection. Utility Model Content

[0004] In view of the shortcomings of the prior art described above, the present invention provides a pretreatment fixture for detecting the internal atmosphere of microwave products, so as to solve at least one of the above-mentioned technical problems.

[0005] To achieve the above and other related objectives, the technical solution provided in this application is as follows.

[0006] This application provides a pretreatment fixture for detecting the internal atmosphere of a microwave product. The fixture includes a stepped end mill, a transparent pre-tightening limiting plate, and two pressure plates. The pre-tightening limiting plate is set on the cover plate of the part to be tested. The stepped end mill passes through the central hole of the pre-tightening limiting plate, and the two pressure plates are respectively set on both sides of the pre-tightening limiting plate.

[0007] In one embodiment of this utility model, the stepped end mill includes a shank and a cutter head. The cutter head is located at the lower part of the shank. The cutter head is provided with a limiting surface, a first stepped cutter head, a second stepped cutter head, and a third stepped cutter head. The first stepped cutter head is located on the side of the limiting surface away from the shank. The third stepped cutter head is located at the center of the cutter head. The second stepped cutter head and the third stepped cutter head are located on the side of the first stepped cutter head away from the limiting surface. The cutting depth of the second stepped cutter head is greater than the cutting depth of the first stepped cutter head, and the cutting depth of the third stepped cutter head is greater than the cutting depth of the second stepped cutter head.

[0008] In one embodiment of the present invention, the first stepped cutter head includes a plurality of first cutter substrates, with a first preset width between two adjacent first cutter substrates, and the included angle between two adjacent first cutter substrates is 90° to 120°. A cutting edge is provided on the side of the first cutter substrate, and a cutting edge is provided on the side of the first cutter substrate opposite to the limiting surface.

[0009] In one embodiment of the present invention, the second stepped blade head is disposed on the side of the first blade substrate away from the limiting surface and at a distance of a second preset width from the side of the first blade substrate. The second stepped blade head is in the shape of an arc protrusion, and the arc surface of the arc protrusion is the blade setting surface.

[0010] In one embodiment of the present invention, the third stepped cutter head includes a plurality of second cutter substrates, each second cutter substrate being disposed on the side of the corresponding first cutter substrate away from the limiting surface, and adjacent two second cutter substrates being spaced apart by a first preset width, the side of the second cutter substrate being arc-shaped and having a cutting edge, the side of the second cutter substrate away from the first cutter substrate having a cutting edge, and the second stepped cutter head and the third stepped cutter head being spaced apart by a third preset width.

[0011] In one embodiment of the present invention, the two sides of the handle are rectangular or circular, and the limiting surface is disposed on one side of the handle.

[0012] In one embodiment of this utility model, the pre-tightening limiting plate is cuboid and a trapezoidal protrusion is provided at the center of the front side of the cuboid. The central hole is located at the center of the trapezoidal protrusion. The side of the pre-tightening limiting plate near the test piece is provided with multiple petal-shaped radial grooves. The multiple grooves are connected by annular grooves. Some of the grooves are closed grooves, and some of the grooves are through grooves that pass through the pre-tightening limiting plate along a first direction, wherein the first direction is perpendicular to the two pressure plates.

[0013] This application provides a pretreatment fixture for internal atmosphere testing of microwave products. The fixture includes a stepped end mill, a transparent pre-tightening limiting plate, and pressure plates. The pre-tightening limiting plate is set on the cover plate of the component to be tested. The stepped end mill passes through the central hole of the pre-tightening limiting plate. The fixture includes two pressure plates, which are respectively set on both sides of the pre-tightening limiting plate. This application uses a fixture composed of a stepped end mill, a pre-tightening limiting plate, and pressure plates to pretreatment the component to be tested for internal atmosphere testing. Before internal atmosphere testing, the flat-bottomed blind hole to be punctured and the sealing ring mounting groove are machined on the cover plate of the component to be tested. This shortens the processing time for pretreatment of the internal atmosphere of the cover plate, reduces the volume of secondary cavities, and avoids adverse situations such as insufficient vacuum or even leakage during internal atmosphere testing, thus helping to improve the accuracy and reliability of the internal atmosphere testing results of microwave products.

[0014] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the present invention. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments conforming to the present invention and, together with the description, serve to explain the principles of the present invention. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0016] Figure 1 This is a schematic diagram of a microwave product internal atmosphere detection pretreatment fixture, illustrating an exemplary embodiment of the present invention.

[0017] Figure 2 This is a three-dimensional exploded view of a microwave product internal atmosphere detection pretreatment fixture, as shown in an exemplary embodiment of this utility model.

[0018] Figure 3 This is a top view of a microwave product internal atmosphere detection pretreatment fixture, as shown in an exemplary embodiment of this utility model.

[0019] Figure 4 This is a schematic diagram illustrating the blade head structure of an exemplary embodiment of the present invention;

[0020] Figure 5 This is an enlarged schematic diagram of the cutter head structure shown in an exemplary embodiment of the present invention;

[0021] Figure 6 This is a schematic diagram of the front of the pre-tightening limiting block, as shown in an exemplary embodiment of the present invention;

[0022] Figure 7This is a schematic diagram of the back of the pre-tightening limiting block shown in an exemplary embodiment of the present invention;

[0023] Figure 8 This is a schematic cross-sectional view of the workpiece after cutting, as shown in an exemplary embodiment of this utility model;

[0024] Figure 9 This is a schematic diagram of the cover plate after processing, as shown in an exemplary embodiment of the present invention.

[0025] Reference numerals: 110-Stepped end mill; 120-Pre-tightening limiting plate; 130-Pressure plate; 140-Workpiece to be inspected; 111-Tool holder; 112-Tool head; 1121-Limiting surface; 1122-First stepped end mill; 1123-Second stepped end mill; 1124-Third stepped end mill; 151-Side wall of the first recess; 152-Bottom of the first recess; 153-Side wall of the second recess; 154-Bottom of the second recess; 155-Annular groove; 156-Cover plate. Detailed Implementation

[0026] The embodiments of this utility model will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. It should be understood that the preferred embodiments are only for illustrating this utility model and not for limiting the scope of protection of this utility model.

[0027] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0028] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the present invention.

[0029] Currently, to ensure the reliability of internal chips and components during long-term service, hermetic packaging is required. High concentrations of internal atmospheres, such as water vapor, hydrogen, oxygen, carbon dioxide, and organic gases like methanol, can damage devices. Under the influence of external factors, these hazards or potential defects can worsen, leading to device malfunction. Therefore, the internal atmosphere content is one of the important indicators for evaluating the reliability of hermetic packaged devices. Internal atmosphere content testing is a destructive test, requiring the use of a piercing steel needle to mechanically penetrate the device's cover plate, collect the internal atmosphere, and send it to an analysis chamber. After testing, the microwave product can be resealed and used with a new cover plate.

[0030] Because internal atmosphere testing requires a high-vacuum, sealed connection to the equipment throughout the entire process, and microwave hybrid integrated circuit products are mostly component-type, they are larger in size and more prone to deformation and warping. Furthermore, component-type products typically use 1-1.5mm thick cover plates for encapsulation, while other types of devices generally use 0.2-0.3mm thin cover plates. The cover plate thickness for large-size components is 3-5 times that of small-size products. The piercing process of the device's cover plate is generally done manually, and mastering the piercing force relies heavily on experience; the force must penetrate the sample without causing significant surface deformation and leakage. Component product cover plates are thick and tough, making it difficult for piercing needles to penetrate directly. Forcing piercing can easily damage the needle and cause severe deformation and leakage on the pierced surface, making internal atmosphere testing impossible. During testing, improper testing procedures and inadequate auxiliary fixture design often lead to significant errors in test results or even make testing impossible. Therefore, the quality of sample pretreatment before puncture directly affects the accuracy of test results. Pretreatment, which has a significant impact on test results, is of great practical significance for improving test accuracy and guiding similar internal atmosphere tests.

[0031] In related technologies, to puncture the cover plate, testing personnel often use a ball mill to grind and reduce the thickness of the puncture area. However, the ball mill does not produce a flat surface. Moreover, because the microwave component cover plate is relatively thick, a 0.7-1.2mm deep pit needs to be ground out, and a sealing ring needs to be placed in this pit to achieve the purpose of vacuuming. The concave curved surface may exceed the elastic deformation of the sealing ring, which is not conducive to achieving a vacuum. When the puncture steel needle pierces the curved surface, the tip may drift due to the lack of a suitable point of force, causing the steel needle to deform or even break. Once the product is punctured, if an effective vacuum environment cannot be achieved, the sample will be scrapped.

[0032] To solve the above problems, such as Figure 1As shown, this application provides a pretreatment fixture for detecting the internal atmosphere of a microwave product. The fixture includes a stepped end mill 110, a transparent pre-tightening limiting plate 120, and two pressure plates 130. The pre-tightening limiting plate 120 is set on the cover plate of the part to be tested 140. The stepped end mill 110 passes through the central hole of the pre-tightening limiting plate 120, and the two pressure plates 130 are respectively set on both sides of the pre-tightening limiting plate 120.

[0033] Specifically, such as Figures 1 to 3 As shown, the pretreatment fixture for internal atmosphere testing of microwave products includes a stepped end mill 110, a pre-tensioning limiting plate 120, and two pressure plates 130. The stepped end mill 110 is used to grind the cover plate of the workpiece 140 to be tested. The pre-tensioning limiting plate 120 is used to fix the stepped end mill 110 and to observe the grinding process through the transparent pre-tensioning limiting plate 120. The two pressure plates 130 are used to fix and align the pre-tensioning limiting plate 120. The pre-tensioning limiting plate 120 is located on the cover plate of the workpiece 140 to be tested. The stepped end mill 110 passes through the central hole of the pre-tensioning limiting plate 120 and contacts the workpiece 140 to be tested. The two pressure plates 130 are respectively set on both sides of the pre-tensioning limiting plate 120 to fix the pre-tensioning limiting plate 120, thereby stabilizing the stepped end mill 110.

[0034] In detail, such as Figure 2 As shown, the step end mill 110 includes a shank 111 and a cutter head 112, with the cutter head 112 located at the lower part of the shank 111, as shown. Figure 4 As shown, the cutting head 112 is provided with a limiting surface 1121, a first stepped cutting head 1122, a second stepped cutting head 1123, and a third stepped cutting head 1124. The first stepped cutting head 1122 is located on the side of the limiting surface 1121 away from the tool holder 111. The third stepped cutting head 1124 is located at the center of the cutting head 112. The second stepped cutting head 1123 and the third stepped cutting head 1124 are located on the side of the first stepped cutting head 1122 away from the limiting surface 1121. The cutting depth of the second stepped cutting head 1123 is greater than the cutting depth of the first stepped cutting head 1122, and the cutting depth of the third stepped cutting head 1124 is greater than the cutting depth of the second stepped cutting head 1123.

[0035] More in detail, such as Figure 4As shown, the first stepped cutter head 1122 includes multiple first cutter substrates. A first preset width d1 is spaced between two adjacent first cutter substrates, and the included angle between two adjacent first cutter substrates is 90° to 120°. That is, the first stepped cutter head 1122 has four first cutter substrates with an included angle of 90° between two adjacent first cutter substrates, or the first stepped cutter head 1122 has three first cutter substrates with an included angle of 120° between two adjacent first cutter substrates. This invention uses a 120° included angle as an example for description. A cutting edge is provided on the side of each first cutter substrate, and a cutting edge is provided on the side of the first cutter substrate facing away from the limiting surface 1121. That is, the first cutter substrate has a bottom cutting edge and a side cutting edge.

[0036] In detail, such as Figure 4 As shown, the second stepped cutter head 1123 is disposed on the side of the first cutter substrate away from the limiting surface 1121 and at a distance of a second preset width d2 from the side of the first cutter substrate. The second stepped cutter head 1123 is in the shape of an arc protrusion, and the arc surface of the arc protrusion is the cutting edge setting surface.

[0037] More in detail, such as Figure 4-5 As shown, the third stepped cutter head 1124 includes multiple second cutter substrates. Each second cutter substrate is disposed on the side of the corresponding first cutter substrate away from the limiting surface 1121, and there is a first preset width d1 between two adjacent second cutter substrates. The side of the second cutter substrate is arc-shaped and is provided with a cutting edge. The side of the second cutter substrate away from the first cutter substrate is provided with a cutting edge, that is, the second cutter substrate is provided with a bottom cutting edge and a side cutting edge. It should be noted that the second stepped cutter head 1123 and the third stepped cutter head 1124 are separated by a third preset width d3.

[0038] More in detail, such as Figure 5 As shown, the handle 111 has rectangular or circular sides, and the limiting surface 1121 is located on one side of the handle.

[0039] In detail, such as Figure 1 , 6 As shown in Figure 7, the pre-tightening limiting plate 120 is cuboid with a trapezoidal protrusion at the center of its front side. A central hole is located at the center of this protrusion. The pre-tightening limiting plate 120 is positioned on the side closest to the workpiece 140 to be inspected. Figure 7 As shown, there are 8 radial grooves in a petal shape. The 8 grooves are connected in the middle of the pre-tightening limiting plate by a circular groove. 4 grooves are closed grooves that are not connected, and 4 grooves are through grooves that pass through the pre-tightening limiting plate along a first direction. The first direction is perpendicular to the two pressure plates. That is, the openings of the 4 grooves are located on the side of the pre-tightening limiting plate. These closed grooves are used to temporarily store the chips generated during the milling process, and these through grooves are used to quickly discharge the high-temperature chips from the milling groove area, thereby ensuring the stable operation of the milling process.

[0040] like Figures 1 to 9 As shown, the working principle of the microwave product internal atmosphere detection pretreatment fixture provided in this application is as follows:

[0041] Determine the puncture point of the part to be tested 140. There must be no partitions or screws below the puncture point, and no components. The area where the air inside the product can be quickly extracted by the vacuum of the equipment after puncture is the puncture point, and the puncture point is the center of the milling circle.

[0042] Place the workpiece 140 to be inspected on the worktable, fix the fixture on the workpiece 140 and adjust the level; fix the stepped milling cutter 110 through the fixing block 130 on the fixture, and use transparent material for the pre-tightening limit block 120 to facilitate observation and avoid milling through during the cutting process.

[0043] Start the internal atmosphere detection pretreatment fixture, and use a stepped end mill 110 to mill a stepped hole in the workpiece 140 to be inspected, combined with... Figure 4 , 5 As can be seen from points 8 and 9, the first recessed cavity is cut by the bottom and side cutting edges of the first stepped cutter head 1112. The side wall 151 of the first recessed cavity is cut by the side cutting edge of the first stepped cutter head 1122, and the bottom 152 of the first recessed cavity is cut by the bottom cutting edge of the first stepped cutter head 1122. However, the limiting surface 1121 on the cutter head 112 is not sharpened. When the limiting surface 1121 contacts the cover plate 156, the stepped milling cutter 110 cannot cut, which can effectively limit and control the cutting depth. The annular groove 155 is cut by the arc-shaped cutting edge of the second stepped cutter head 1123. The second recessed cavity is cut by the bottom and side cutting edges of the third stepped cutter head 1124. The side wall 153 of the second recessed cavity is cut by the side cutting edge of the third stepped cutter head 1124, and the bottom 154 of the second recessed cavity is cut by the bottom cutting edge of the third stepped cutter head 1124. 153 is the sidewall of the puncture blind hole diameter, which must be larger than the puncture needle. The annular groove 155 is used to place the sealing ring. The sealing ring's main function is to prevent sealing failure caused by workpiece warping, thus preventing air leakage. After milling, the thickness of the cover plate at its maximum depth is only about 0.3mm. Simultaneously, the bottom 154 of the second recessed cavity must be flat to prevent displacement or jumping due to warping during needle puncture. The cover plate of the workpiece to be inspected after pre-processing with the tooling is as follows... Figure 9 As shown, after the cutting process before internal atmosphere detection is completed, the pretreatment fixture is removed, the burrs on the part to be tested 140 are cleaned, and the internal atmosphere detection process is carried out.

[0044] It should be noted that the above process of polishing the cover plate of the part to be inspected using pretreatment tooling is a process of using tools and does not involve any improvement to the method.

[0045] This application provides a pretreatment fixture for detecting the internal atmosphere of microwave products. The fixture includes a stepped end mill, a transparent pre-tightening limiting plate, and two pressure plates. The pre-tightening limiting plate is set on the cover plate of the part to be tested. The stepped end mill passes through the central hole of the pre-tightening limiting plate. The two pressure plates are respectively set on both sides of the pre-tightening limiting plate. The stepped end mill includes three stepped cutter heads of different depths to achieve different opening depths. The cutter head of the stepped end mill is also provided with a limiting surface. This application utilizes a tooling system consisting of stepped milling cutters, a pre-tensioning limiting plate, and a pressure plate to pre-treat the internal atmosphere of the workpiece before testing. Three stepped milling cutters of varying depths are used to grind different recesses on the cover plate. Before internal atmosphere testing, the blind hole to be punctured and the sealing ring mounting groove are machined on the cover plate of the workpiece. The first recess provides a suitable point of force during puncture, and the bottom of the puncture recess is flat to protect the puncture needle. The thickness of the cover plate at the puncture point is reduced, thus shortening the processing time for pre-treatment of the internal atmosphere of the cover plate. Furthermore, the processing range and depth are precisely controllable. The sealing ring is installed in the sealing mounting groove to achieve a vacuum effect, preventing air leakage during internal atmosphere testing. This reduces the volume of secondary cavities and avoids insufficient vacuum or even air leakage during internal atmosphere testing, contributing to improved accuracy and reliability of internal atmosphere testing results for microwave products.

[0046] The above embodiments are merely illustrative of the principles and effects of this utility model and are not intended to limit the scope of this utility model. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this utility model. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this utility model should still be covered by the claims of this utility model.

Claims

1. A microwave product internal atmosphere detection pre-treatment tooling characterized by, The tooling includes a stepped end mill, a transparent pre-tightening limiting plate, and two pressure plates. The pre-tightening limiting plate is set on the cover plate of the workpiece to be inspected. The stepped end mill passes through the central hole of the pre-tightening limiting plate, and the two pressure plates are respectively set on both sides of the pre-tightening limiting plate.

2. The microwave product internal atmosphere detection pre-treatment tooling of claim 1, wherein, The stepped end mill includes a shank and a cutter head. The cutter head is located at the lower part of the shank. The cutter head is provided with a limiting surface, a first stepped cutter head, a second stepped cutter head, and a third stepped cutter head. The first stepped cutter head is located on the side of the limiting surface away from the shank. The third stepped cutter head is located at the center of the cutter head. The second and third stepped cutter heads are located on the side of the first stepped cutter head away from the limiting surface. The cutting depth of the second stepped cutter head is greater than the cutting depth of the first stepped cutter head, and the cutting depth of the third stepped cutter head is greater than the cutting depth of the second stepped cutter head.

3. The microwave product internal atmosphere detection pre-treatment tooling of claim 2, wherein, The first stepped cutter head includes a plurality of first cutter substrates, with a first preset width between two adjacent first cutter substrates, and the included angle between two adjacent first cutter substrates is 90° to 120°. A cutting edge is provided on the side of the first cutter substrate, and a cutting edge is provided on the side of the first cutter substrate opposite to the limiting surface.

4. The microwave product internal atmosphere detection pre-treatment tooling of claim 3, wherein, The second stepped cutter head is disposed on the side of the first cutter substrate away from the limiting surface and at a distance of a second preset width from the side of the first cutter substrate. The second stepped cutter head is in the shape of an arc protrusion, and the arc surface of the arc protrusion is the cutting edge setting surface.

5. The microwave product internal atmosphere detection pre-treatment tooling of claim 4, wherein, The third stepped cutter head includes a plurality of second cutter substrates, each of which is disposed on the side of the corresponding first cutter substrate away from the limiting surface, and there is a first preset width between two adjacent second cutter substrates. The side of the second cutter substrate is arc-shaped and is provided with a cutting edge. The side of the second cutter substrate away from the first cutter substrate is provided with a cutting edge. There is a third preset width between the second stepped cutter head and the third stepped cutter head.

6. The microwave product internal atmosphere detection pre-treatment tooling of claim 2, wherein, The two sides of the handle are rectangular or circular, and the limiting surface is located on one side of the handle.

7. The microwave product internal atmosphere detection pre-treatment tooling of claim 1, wherein, The pre-tightening limiting plate is cuboid in shape, and a trapezoidal protrusion is provided at the center of the front side of the cuboid. The central hole is located at the center of the trapezoidal protrusion. The side of the pre-tightening limiting plate near the test piece is provided with multiple petal-shaped radial grooves. The multiple grooves are connected by annular grooves. Some of the grooves are closed grooves, and some of the grooves are through grooves that pass through the pre-tightening limiting plate along a first direction, wherein the first direction is perpendicular to the two pressure plates.

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