Spiral outer conductor radio frequency coaxial assembly and method of making same

Abstract

The application discloses a spiral outer conductor radio frequency coaxial assembly, which comprises a shell, an inner conductor, an insulator, a cable protection sleeve and a cable; the cable comprises a cable inner conductor, a cable insulator, a cable spiral outer conductor and a cable sheath; the cable protection sleeve is provided with a sheath first positioning surface and a sheath outer surface, and is internally provided with an internal thread and a sheath second positioning surface connected with the internal thread; the cable sheath is inserted into the sheath second positioning surface; the cable spiral outer conductor is connected with the internal thread, so that the cable protection sleeve is connected with the cable; the sheath outer surface is connected with a second inner surface of the shell; the cable inner conductor is electrically connected with the inner conductor arranged in the second insulator through a connector by penetrating through the first insulator, so as to form the spiral outer conductor radio frequency coaxial assembly. The product has reasonable structure design, stable structure, good signal shielding property, and the quality problems existing in tin soldering are overcome through the laser welding mode, the production efficiency is improved, and the quality of the product is ensured.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and in particular to a helical outer conductor radio frequency coaxial assembly and its manufacturing method. Background Technology

[0002] RF coaxial patch cord assemblies are prefabricated communication components, primarily consisting of an RF coaxial cable and RF coaxial connectors at both ends. They are mainly used to connect base station antennas and operator main equipment for transmitting RF signals. Currently, this type of cable assembly on the market suffers from poor installation stability, leading to poor contact in harsh environments, and inadequate shielding, affecting signal transmission. Furthermore, existing RF coaxial patch cord assemblies generally use soldering, which requires solder wire to be melted by high-frequency induction heating between the connector and the cable's outer conductor. However, this process often results in solder bleed-in short circuits due to manufacturing defects, affecting product yield and quality. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a spiral outer conductor radio frequency coaxial assembly and its manufacturing method.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention provides a helical outer conductor radio frequency coaxial assembly, including a housing, an inner conductor, a first insulator, a cable protective sleeve, a second insulator, a cable, and a connector. The cable includes an inner conductor, a cable insulator, a helical outer conductor, and a cable sheath. The cable, from the inside out, consists of the inner conductor, the insulator, the helical outer conductor, and the sheath. The cable protective sleeve has a first positioning surface and an outer surface, and internal threads and a second positioning surface connected to the internal threads. The housing, from its end face inwards, has a third inner surface, a second inner surface, a first positioning surface, and a third inner surface. The cable sheath is inserted into the second positioning surface. The helical outer conductor connects to the internal threads, connecting the cable protective sleeve to the cable. The outer surface of the sheath connects to the second inner surface of the housing. The first inner surface of the housing contains a first insulator and a second insulator arranged sequentially along the cable insertion direction. The inner conductor passes through the first insulator and is electrically connected to the inner conductor located in the second insulator via a connector, forming the helical outer conductor radio frequency coaxial assembly.

[0006] Furthermore, a third insulator is provided outside the inner conductor; the third insulator is disposed inside the housing, and the inner conductor passes through the third insulator and is electrically connected to the inner conductor of the cable; a connector is provided outside the housing.

[0007] Furthermore, the cable sheath cross-section of the cable sheath is in contact with the second positioning surface of the sheath; the cable spiral outer conductor is squeezed and attached to the inner thread end face of the cable protective sleeve by the tooling, forming an irregularly shaped and folded structure of the crimped cable outer conductor, while exposing a section of the crimped protruding insulation.

[0008] Furthermore, the outer surface of the sheath is provided with surface grooves; a sheath punching groove is provided on the outer surface between the surface grooves and the first positioning surface of the sheath; a housing punching groove is provided on the outer surface of the housing corresponding to the second inner surface of the housing; after the cable protection sheath is assembled with the housing, the positions of the sheath punching groove and the housing punching groove correspond to each other.

[0009] Furthermore, a housing guide slope is provided at the connection between the third inner surface of the housing and the second inner surface of the housing; the outer surface of the protective sleeve is pre-installed onto the third inner surface of the housing until the rear end of the outer surface of the protective sleeve reaches the housing guide slope to complete the installation.

[0010] Furthermore, the end of the inner conductor connected to the inner conductor of the cable is provided with an inner conductor end face and an inclined outer diameter of the inner conductor; the first insulator is provided with a first positioning surface of the insulator, a second positioning surface of the insulator, an outer surface of the insulator, an inner hole of the insulator, and an insulator cavity; the first positioning surface of the insulator is in contact with the end face of the inner conductor; the first positioning surface of the sheath is connected to the second positioning surface of the insulator; the inner conductor of the cable passes through the inner hole of the insulator, so that after crimping, it protrudes from the insulator and is located in the cavity of the insulator; and the outer surface of the insulator is interference-fitted with the first inner surface of the shell.

[0011] Furthermore, the inner surface of the second insulator is interference-fitted with the inclined outer diameter of the inner conductor.

[0012] Furthermore, the cable protective sleeve adopts a metal armor structure, and both the cable protective sleeve and the cable spiral outer conductor are made of the same T2 copper material.

[0013] This invention also provides a method for manufacturing a helical outer conductor radio frequency coaxial assembly, the steps of which are as follows:

[0014] Step 1: Pre-install the inner conductor. Insert the second insulator into the first inner surface of the housing, then install the third insulator into the housing. Then, pass the inner conductor end face through the third insulator and the second insulator in sequence, and install the inner conductor with an interference fit between the inclined outer diameter and the inner surface of the insulator.

[0015] Step 2: Install the first insulator into the housing by inserting the outer surface of the first insulator into the first inner surface of the housing, and by making an interference fit between the outer surface of the insulator and the first inner surface of the housing.

[0016] Step 3: Installation of the cable protective sleeve and cable. The outer surface of the protective sleeve is electroplated or coated with a color different from the cable's outer conductor; ternary or silver are recommended for good intermodulation performance. The cable protective sleeve is screwed into the cable, with the sheath's cross-section contacting the second positioning surface. Using a tooling fixture, the cable's spiral outer conductor is pressed and adhered to the inner thread end face of the cable protective sleeve, forming an irregularly shaped, folded structure of the crimped outer conductor, while exposing a section of the crimped insulation. After the outer conductor is crimped, it enters the laser welding equipment platform. After the cable protective sleeve is fixed, the camera captures images and programs the irregular structure of the crimped outer conductor based on the color difference between the spiral outer conductor and the cable protective sleeve, generating a laser welding trajectory. The laser welding uses a specific amplitude to fix the spiral outer conductor and the cable protective sleeve together.

[0017] Step 4: Crimping and installing the spiral outer conductor RF coaxial assembly. Install the connector in the inner hole of the inner conductor. Pre-install the outer surface of the protective sleeve onto the third inner surface of the housing until the rear end of the outer surface of the protective sleeve reaches the guide slope of the housing. Crimping is performed using a press device, ensuring an interference fit between the second inner surface of the housing and the outer surface of the protective sleeve, achieving excellent structural strength. During crimping, the first positioning surface of the sheath moves forward to the second positioning surface of the insulator, pushing the first insulator to move. Simultaneously, the first positioning surface of the insulator pushes the end face of the inner conductor to move, causing the first positioning surface of the sheath to contact and fix with the first positioning surface of the housing, forming a closed internal magnetic field. The inner conductor of the cable is electrically connected to the inner conductor through the connector.

[0018] Step 5: Punching and crimping fixation. After crimping, punch the holes in the punching groove of the housing using a punching tool. During the punching process, the housing is squeezed to form a protrusion on the second inner surface of the housing, which is embedded in the punching groove of the sheath to prevent axial displacement of the cable protection sheath and improve structural strength and reliability. Then, install the connector on the housing to complete the installation of the entire spiral outer conductor RF coaxial assembly.

[0019] Furthermore, in step five, the striking points are evenly distributed around the circumference and number at least four.

[0020] The product structure of this invention is reasonably designed, structurally stable, and has good signal shielding. At the same time, the laser welding method overcomes the quality problems of tin soldering, achieves a high degree of assembly automation, improves production efficiency, and ensures product quality. Attached Figure Description

[0021] Figure 1 This is a cross-sectional view of the radio frequency coaxial assembly with a spiral outer conductor according to the present invention.

[0022] Figure 2This is a schematic diagram of a half-section of the shell structure.

[0023] Figure 3 This is a schematic diagram of a half-section of the first insulator.

[0024] Figure 4 This is a schematic diagram of the half-section and side view of the cable protection sleeve.

[0025] Figure 5 A schematic diagram showing the state when the inner conductor is installed.

[0026] Figure 6 This is a schematic diagram showing the state during cable crimping.

[0027] Figure 7 This is a schematic diagram of the irregular structure and laser welding trajectory after the outer conductor is crimped.

[0028] Figure 8 This is a schematic diagram showing the state during the crimping installation of a spiral outer conductor RF coaxial assembly.

[0029] Wherein: 1. Housing; 2. Inner conductor; 3. First insulator; 4. Cable protective sleeve; 5. Second insulator; 6. Cable; 8. Connector; 9. Third insulator; 10. Connector head; 71. Irregular structure after crimping of outer conductor; 72. Laser welding trajectory; 101. First inner surface of housing; 102. Second inner surface of housing; 103. First positioning surface of housing; 104. Punch groove of housing; 105. Third inner surface of housing; 106. Guide slope of housing; 201. End face of inner conductor; 202. Inclined outer diameter of inner conductor; 301. First positioning surface of insulator; 302. Second positioning surface of insulator; 303. Surface 302; outer surface of insulator 303; inner hole of insulator 304; cavity of insulator 305; straight surface grooves 401; punched groove of sheath 402; first positioning surface of sheath 403; internal thread end face 404; internal thread 405; second positioning surface of sheath 406; outer surface of sheath 407; inner surface of insulator 501; inner conductor of cable 601; cable insulator 602; cross-section of cable sheath 603; spiral outer conductor of cable 604; outer conductor of cable after crimping 605; protruding insulator after crimping 606; cable sheath 607. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 6 and Figure 8As shown, the spiral outer conductor radio frequency coaxial assembly includes a housing 1, an inner conductor 2, a first insulator 3, a cable protective sleeve 4, a second insulator 5, a cable 6, and a connector 8. The cable 6 includes an inner conductor 601, a cable insulator 602, a spiral outer conductor 604, and a cable sheath 607. The cable 6 is arranged sequentially from the inside to the outside with the inner conductor 601, the insulator 602, the spiral outer conductor 604, and the sheath 607. The cable protective sleeve 4 is provided with a first positioning surface 403 and an outer surface 407, and internally has an internal thread 405 and a second positioning surface 406 connected to the internal thread 405. The housing 1 is arranged sequentially from the end face inward. The housing is provided with a third inner surface 105, a second inner surface 102, a first positioning surface 103, and a first inner surface 101. The cable sheath 607 is inserted into the second positioning surface 406 of the sheath. The cable spiral outer conductor 604 is connected to the internal thread 405, so that the cable protective sleeve 4 is connected to the cable 6. The outer surface 407 of the sheath is connected to the second inner surface 102 of the housing. A first insulator 3 and a second insulator 5 are arranged sequentially in the first inner surface 101 of the housing along the insertion direction of the cable 6. The inner conductor 601 of the cable passes through the first insulator 3 and is electrically connected to the inner conductor 2 arranged in the second insulator 5 through a connector 8 to form a spiral outer conductor radio frequency coaxial assembly.

[0032] As a preferred embodiment, such as Figure 1 As shown, a third insulator 9 is provided outside the inner conductor 2; the third insulator 9 is provided inside the housing 1, and the inner conductor 2 passes through the third insulator 9 and is electrically connected to the inner conductor 601 of the cable; a connector 10 is provided outside the housing 1.

[0033] As preferred embodiments, such as 6 and Figure 8 As shown, the cable sheath cut surface 603 of the cable sheath 607 is in contact with the second positioning surface 406 of the sheath; the cable spiral outer conductor 604 is pressed and attached to the inner thread end face 404 of the cable protective sleeve 4 by the tooling, forming an irregularly shaped and folded structure of the crimped cable outer conductor 605, while exposing a section of the crimped protruding insulator 606.

[0034] As a preferred embodiment, such as Figure 4 As shown, the outer surface 407 of the sheath is provided with surface grooves 401; a sheath punching groove 402 is provided on the outer surface between the surface grooves 401 and the first positioning surface 403 of the sheath; a housing punching groove 104 is provided on the outer surface of the housing 1 corresponding to the second inner surface 102 of the housing; after the cable protective sleeve 4 is assembled with the housing 1, the positions of the sheath punching groove 402 and the housing punching groove 104 correspond to each other. The designed surface grooves 401 and punching groove structure prevent the cable from rotating or falling off during fixing, improving structural strength and stability.

[0035] As a preferred embodiment, such as Figure 2 As shown, a housing guide slope 106 is provided at the connection between the third inner surface 105 of the housing and the second inner surface 102 of the housing; the outer surface 407 of the protective sleeve is pre-installed onto the third inner surface 105 of the housing until the rear end of the outer surface 407 of the protective sleeve reaches the housing guide slope 106 to complete the installation.

[0036] As a preferred embodiment, such as Figure 8 As shown, the inner conductor 2 is connected to the inner conductor 601 of the cable at one end, which is provided with an inner conductor end face 201 and an inclined outer diameter 202; the first insulator 3 is provided with an insulator first positioning surface 301, an insulator second positioning surface 302, an insulator outer surface 303, an insulator inner hole 304, and an insulator cavity 305; the insulator first positioning surface 301 is in contact with the inner conductor end face 201; the sheath first positioning surface 403 is connected to the insulator second positioning surface 302; the cable inner conductor 601 passes through the insulator inner hole 304, so that after crimping, the protruding insulator 606 is located in the insulator cavity 305; and the insulator outer surface 303 is interference-fitted with the first inner surface 101 of the shell.

[0037] As a preferred embodiment, the inner surface 501 of the second insulator 5 is interference-fitted with the inclined outer diameter 202 of the inner conductor.

[0038] As a preferred embodiment, the cable protective sleeve 4 adopts a metal armor structure. Both the cable protective sleeve 4 and the cable spiral outer conductor 604 are made of the same T2 copper material. Through the cable protective sleeve 4 structure made of T2 copper material, a good shielding effect is achieved at a low cost, and the anti-interference performance is good.

[0039] This invention also provides a method for manufacturing a helical outer conductor radio frequency coaxial assembly, the steps of which are as follows:

[0040] Step 1: As Figure 5 As shown, the inner conductor 2 is pre-installed, the second insulator 5 is installed into the first inner surface 101 of the housing, and then the third insulator 9 is installed into the housing 1. Then, the inner conductor end face 201 of the inner conductor 2 passes through the third insulator 9 and the second insulator 5 in sequence, so that the inclined outer diameter 202 of the inner conductor is installed with the inner surface 501 of the insulator through an interference fit.

[0041] Step 2: Install the first insulator 3 into the housing 1 by inserting the outer surface 303 of the first insulator 3 into the first inner surface 101 of the housing, and by making an interference fit between the outer surface 303 of the insulator and the first inner surface 101 of the housing.

[0042] Step 3: As Figure 6As shown, the cable protective sleeve 4 and cable 6 are installed with the outer surface 407 of the protective sleeve being electroplated or coated with a color different from the color of the cable outer conductor 604. Ternary or silver coatings are recommended to achieve good intermodulation performance, but the color is not limited to these. The cable protective sleeve 4 is screwed into the cable 6 by rotation, and the cable sheath cut surface 603 of the cable sheath 607 contacts and connects with the second positioning surface 406 of the sheath. Using a tooling fixture, the spiral outer conductor 604 of the cable is pressed and adhered to the inner thread end face 404 of the cable protective sleeve 4, forming an irregularly shaped and folded structure of the crimped cable outer conductor 605, while exposing a section of... After crimping, the insulator 606 protrudes; after the outer conductor is crimped, it enters the laser welding equipment platform. After the cable protective sleeve 4 is fixed, the color information is collected by the camera on the laser welding equipment based on the color difference between the cable spiral outer conductor 604 and the cable protective sleeve 4, the edge of the cable outer conductor 604 is analyzed, the irregular structure 71 after the outer conductor is crimped is identified and a laser welding trajectory 72 is generated. Then, the laser welding path of the cable outer conductor 604 is programmed. The laser welding fixes the cable spiral outer conductor 604 and the cable protective sleeve 4 by laser welding with a certain amplitude.

[0043] Step Four: As Figure 8 As shown, the crimping installation of the spiral outer conductor RF coaxial assembly involves installing the connector 8 in the inner hole of the inner conductor 2, pre-installing the outer surface 407 of the protective sleeve onto the third inner surface 105 of the housing, until the rear end of the outer surface 407 of the protective sleeve reaches the guide slope 106 of the housing, and then crimping it using a press device to achieve an interference fit between the second inner surface 102 of the housing and the outer surface 407 of the protective sleeve, thus achieving good structural strength. During the crimping process, the first positioning surface 403 of the sheath moves forward to the second positioning surface 302 of the insulator, pushing the first insulator 3 to move. At the same time, the first positioning surface 301 of the insulator pushes the end face 201 of the inner conductor to move, so that the first positioning surface 403 of the sheath contacts and fixes itself to the first positioning surface 103 of the housing, forming a closed internal magnetic field. The inner conductor 601 of the cable is electrically connected to the inner conductor 2 through the connector 8.

[0044] Step 5: Punching and crimping fixation. After crimping, punching is performed on the punching groove 104 of the housing using a punching tool. During the punching process, the housing is squeezed to form a protrusion on the second inner surface 102 of the housing, which is embedded in the punching groove 402 of the sheath to prevent axial displacement of the cable protection sleeve 4, thereby improving structural strength and reliability. Then, the connector 10 is installed on the housing 1 to complete the installation of the entire spiral outer conductor radio frequency coaxial assembly.

[0045] In a preferred embodiment, in step five, the punching points are evenly distributed around the circumference, and the number is 4, 6 or other quantities.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A helical outer conductor radio frequency coaxial assembly, comprising a housing, an inner conductor, a first insulator, a cable protective sheath, a second insulator, a cable, and a connector; characterized in that: The cable is provided with an inner conductor, an insulator, a spiral outer conductor, and a sheath from the inside out; the cable sheath is provided with a first positioning surface and an outer surface, and has an internal thread and a second positioning surface connected to the internal thread; the housing is provided with a third inner surface, a second inner surface, a first positioning surface, and a first inner surface from the end face inwards. The cable sheath is inserted into the second positioning surface of the sheath; the spiral outer conductor of the cable is connected to the internal thread, so that the cable protective sheath is connected to the cable; The outer surface of the sheath is connected to the second inner surface of the housing; a first insulator and a second insulator are sequentially arranged in the first inner surface of the housing along the cable insertion direction; the inner conductor of the cable passes through the first insulator and is electrically connected to the inner conductor arranged in the second insulator through a connector to form a spiral outer conductor radio frequency coaxial assembly; The cable sheath cross-section is in contact with the second positioning surface of the sheath; the cable spiral outer conductor is squeezed and attached to the inner thread end face of the cable protective sleeve by the tooling, forming an irregularly shaped and folded structure of the crimped cable outer conductor, while exposing a section of the crimped protruding insulation.

2. The helical outer conductor radio frequency coaxial assembly according to claim 1, characterized in that: A third insulator is provided outside the inner conductor; the third insulator is disposed inside the housing, and the inner conductor passes through the third insulator and is electrically connected to the inner conductor of the cable; a connector is provided outside the housing.

3. The helical outer conductor radio frequency coaxial assembly according to claim 1, characterized in that: The outer surface of the sheath is provided with surface grooves; a sheath punching groove is provided on the outer surface between the surface grooves and the first positioning surface of the sheath; a housing punching groove is provided on the outer surface of the housing corresponding to the second inner surface of the housing; after the cable protection sheath is assembled with the housing, the positions of the sheath punching groove and the housing punching groove correspond to each other.

4. The helical outer conductor radio frequency coaxial assembly according to claim 1, characterized in that: A housing guide slope is provided at the connection between the third inner surface of the housing and the second inner surface of the housing; the outer surface of the protective sleeve is pre-installed onto the third inner surface of the housing until the rear end of the outer surface of the protective sleeve reaches the housing guide slope to complete the installation.

5. The helical outer conductor radio frequency coaxial assembly according to claim 1, characterized in that: The inner conductor is provided with an inner conductor end face and an inclined outer diameter at one end of the inner conductor connected to the inner conductor of the cable; the first insulator is provided with a first positioning surface, a second positioning surface, an outer surface of the insulator, an inner hole of the insulator, and an insulator cavity; the first positioning surface of the insulator is in contact with the end face of the inner conductor; the first positioning surface of the sheath is connected to the second positioning surface of the insulator; the inner conductor of the cable passes through the inner hole of the insulator, so that after crimping, it protrudes from the insulator and is located in the cavity of the insulator; and the outer surface of the insulator is interference-fitted with the first inner surface of the shell.

6. The helical outer conductor radio frequency coaxial assembly according to claim 5, characterized in that: The inner surface of the second insulator is interference-fitted with the inclined outer diameter of the inner conductor.

7. The helical outer conductor radio frequency coaxial assembly according to claim 1, characterized in that: The cable protective sleeve adopts a metal armor structure, and both the cable protective sleeve and the spiral outer conductor of the cable are made of the same T2 copper material.

8. A method for manufacturing a helical outer conductor radio frequency coaxial assembly as claimed in any one of claims 1 to 7, characterized in that: The steps are as follows: Step 1: Pre-install the inner conductor. Insert the second insulator into the first inner surface of the housing, then install the third insulator into the housing. Then, pass the inner conductor end face through the third insulator and the second insulator in sequence, and install the inner conductor with an interference fit between the inclined outer diameter and the inner surface of the insulator. Step 2: Install the first insulator into the housing by inserting the outer surface of the first insulator into the first inner surface of the housing, and by making an interference fit between the outer surface of the insulator and the first inner surface of the housing. Step 3: Installation of the cable protective sleeve and the cable. The outer surface of the protective sleeve is electroplated or coated with a color different from the color of the cable's outer conductor. The cable sheath is screwed into the cable by rotation, and the cable sheath cut surface contacts and connects with the second positioning surface of the sheath; the cable spiral outer conductor is squeezed and attached to the inner thread end face of the cable sheath by the tooling, forming an irregularly shaped and folded structure of the crimped cable outer conductor, while exposing a section of the crimped protruding insulation. After the outer conductor is crimped, it enters the laser welding equipment platform. After the cable protective sleeve is fixed, the irregular structure after the outer conductor is crimped is identified by the color difference between the outer conductor with spiral pattern and the cable protective sleeve through camera shooting and programming design, and a laser welding trajectory is generated. The laser welding fixes the outer conductor with spiral pattern and the cable protective sleeve by laser welding with a certain amplitude. Step 4: Crimping and installing the spiral outer conductor RF coaxial assembly. Install the connector in the inner hole of the inner conductor. Pre-install the outer surface of the protective sleeve onto the third inner surface of the housing until the rear end of the outer surface of the protective sleeve reaches the guide slope of the housing. Crimping is performed using a press device, ensuring an interference fit between the second inner surface of the housing and the outer surface of the protective sleeve, achieving excellent structural strength. During crimping, the first positioning surface of the sheath moves forward to the second positioning surface of the insulator, pushing the first insulator to move. Simultaneously, the first positioning surface of the insulator pushes the end face of the inner conductor to move, causing the first positioning surface of the sheath to contact and fix with the first positioning surface of the housing, forming a closed internal magnetic field. The inner conductor of the cable is electrically connected to the inner conductor through the connector. Step 5: Punching and crimping fixation. After crimping, punch the holes in the punching groove of the housing using a punching tool. During the punching process, the housing is squeezed to form a protrusion on the second inner surface of the housing, which is embedded in the punching groove of the sheath to prevent axial displacement of the cable protection sheath and improve structural strength and reliability. Then, install the connector on the housing to complete the installation of the entire spiral outer conductor RF coaxial assembly.

9. The method for manufacturing the helical outer conductor radio frequency coaxial assembly according to claim 8, characterized in that: In step five, the punching points are evenly distributed around the circumference and there are at least four of them.

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