Continuous stamping forming method for metal valve housing

Abstract

The present invention provides a continuous stamping method for a metal valve housing, comprising the following steps: a positioning hole punching step: processing at least one positioning hole on a metal sheet; a deep drawing step: deep drawing the metal sheet to obtain a revolving wall; a side hole forming step: dividing each side hole on the metal valve housing into two half holes separated by a clamping foot, and forming each half hole in a different process step; a top hole forming step: punching and forming the top hole on the top surface of the metal valve housing, and correspondingly obtaining a top hook; and a blanking step: punching the formed metal valve housing from the metal sheet. The continuous stamping method for the metal valve housing splits a single side hole into two half holes separated by a clamping foot. The separate punching and forming can cause excessive impact, leading to deformation of the revolving wall after shaping. Simultaneously, due to the separate punching and forming, it is convenient to design a lower die to support the clamping foot from the inside, thereby increasing the structural strength and stability of the inner die.

Description

Technical Field

[0001] The invention relates to the technical field of metal stamping and forming, and in particular to a continuous stamping and forming method for a metal valve shell. Background Art

[0002] New energy vehicles (NEVs) use electricity stored in their batteries to power their vehicles, replacing the fuel in traditional fuel-powered vehicles. The battery cell / battery pack is enclosed in a housing, which provides waterproofing, protection, and flame retardancy. The housing also requires timely venting of internal gases during operation to prevent excessive internal pressure in the housing, which could create potential safety hazards.

[0003] This is usually achieved by providing a pressure relief valve on the battery casing. The pressure relief valve generally includes a casing and a valve core that affects the internal pressure to open. The casing of the pressure relief valve can be made of plastic or metal. When the casing is made of metal, the metal casing generally has a gas channel from the inside to the outside, and a valve core is provided in the gas channel. In order to achieve the installation and fixation of the pressure relief valve, gas circulation and valve core positioning. The metal casing needs to be formed with claw-shaped features for installation and fixation, channels for gas circulation, etc., which means that a large number of characteristic structural features need to be provided on the small casing, which brings difficulties to the molding process design of the casing. Summary of the Invention

[0004] Aiming at the problem that the existing metal valve housing has a small structure and a special shape and is difficult to be manufactured using the existing forming process, the present invention provides a continuous stamping forming method for the metal valve housing.

[0005] The technical solution of the present invention provides a continuous stamping method for a metal valve housing, comprising the following steps:

[0006] Punching positioning holes: processing at least one positioning hole on the metal sheet (M);

[0007] Deep drawing step: deep drawing the metal sheet (M) to obtain a revolving wall (W3);

[0008] Side hole forming step: each side hole (W1) on the metal valve housing (W) is divided into two half holes (W1S) separated by a clamping foot (W2), and each half hole (W1S) is formed in a different process step;

[0009] Blanking step: Punch out the formed metal valve housing (W) from the metal sheet (M).

[0010] Preferably, in the side hole forming step, a left punch (PL) for profiling a half hole (W1S) is used to punch out a single half hole (W1S) radially, and then a right punch (PR) for profiling the half hole (W1S) on the other side is used to punch out the half hole (W1S) on the other side radially. The two punched half holes (W1S) together form a side hole (W1), and the punching ranges of the left punch (PL) and the right punch (PR) overlap.

[0011] Preferably, in the side hole forming step, the intersection point where the left punch (PL) overlaps with the right punch (PR) is located at the corner transition of the side hole (W1).

[0012] Preferably, in the side hole forming step, the punching operation steps for the two half holes (W1S) of the same side hole (W1) are staggered by at least one station.

[0013] Preferably, in the step of punching the positioning holes, two positioning holes are processed in a single process, and are respectively located on the two side edges of the metal sheet (M).

[0014] Preferably, in the deep drawing step, the metal valve housing (W) is formed by multiple deep drawing operations, and the range of the drawing coefficient l of a single deep drawing operation is 0.75≤l<1.

[0015] Preferably, in the deep drawing step, the metal valve housing (W) is formed by four deep drawing steps, and the drawing coefficient of a single deep drawing step is not less than 0.8.

[0016] Preferably, in the drawing step, at least one shaping step is provided after the last drawing to adjust the shape and size of the rotating wall (W3) after drawing.

[0017] Preferably, a claw expansion step is further provided after the side hole forming step, and the claw expansion step includes a step of expanding each clamping foot (W2). In each expansion step, the upper mold (PV) and the transverse top block (PH) slide through the inclined contact, and the end of the transverse top block (PH) extends into the interior of the metal valve shell (W) and points to the clamping foot (W2). The upper mold (PV) is lowered to push the transverse top block (PH) to slide horizontally, so that the end of the transverse top block (PH) pushes the clamping foot (W2) to deform outward and maintain plasticity.

[0018] Preferably, the top hole forming step includes at least a top hole punching step, in which the top hole (W6) located at the top of the metal valve housing (W) is punched out by an upper die that matches the expected size and shape of the top hole (W6), leaving the top hook (W5).

[0019] Preferably, the top hole forming step also includes a boss forming step and a bending step, the boss forming step is arranged before the top hole punching step, and the bending step is arranged after the top hole punching step; the boss forming step is used to form a full-circle boss on the top surface of the metal valve shell (W), and the bending step is used to bend the end of the top hook (W5) obtained.

[0020] The metal valve shell of the continuous stamping forming method of the metal valve shell of the present invention has a large aspect ratio. If the metal valve shell is formed by a single deep drawing, the revolving wall and the rounded corners will be broken, and the normal forming of the metal valve shell cannot be completed. The main revolving part of the metal valve shell is formed by multiple deep drawing and shaping. Since multiple deep drawing processes are adopted, the drawing coefficient of a single deep drawing can be effectively controlled to avoid the metal valve shell from breaking during the deep drawing process. On the other hand, each step of the deep drawing process is based on the previous deep drawing process. The forming parameters of the metal valve shell can be gradually controlled by implementing each step of the deep drawing process in sequence, thereby ensuring that the forming process of the metal valve shell is stable and the forming size is uniform, especially ensuring that the wall thickness of the revolving wall after deep drawing is consistent from top to bottom.

[0021] The continuous stamping forming method of the metal valve shell of the present invention splits a single side hole into two half holes separated by a clamping foot and punches and forms them separately, avoiding the problem of excessive impact on the rotating wall when punching the side hole at one time, resulting in deformation of the rotating wall after shaping; at the same time, due to the separate punching and forming, it is convenient to design the lower mold to support the clamping foot from the inside, that is, the outer mold only punches from one side of the clamping foot at a time, and the inner mold can be extended to the other side of the clamping foot to form a complete support for the clamping foot and increase the structural strength and stability of the inner mold; in addition, the separate forming of the side holes has a smaller punching force on the incision, which can make the burrs at the incision lower and softer, which is beneficial to subsequent processing; finally, because the length of a single incision is only about half of that of the one-time forming process, the incision of the upper mold is not easy to wear, which can increase the service life of the upper mold and reduce the frequency of maintenance and replacement of the upper mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the metal valve housing W of the present invention;

[0023] Figure 2 Schematic top view of the metal valve housing W of the present invention;

[0024] Figure 3 Schematic side view of the metal valve housing W of the present invention;

[0025] Figure 4 This is a general flow chart of the continuous stamping method for a metal valve housing of the present invention;

[0026] Figure 5 Schematic diagram of the layout of the continuous stamping method of the metal valve housing of the present invention on the mold;

[0027] Figure 6 Schematic diagram of the step of punching positioning holes in the continuous stamping method of the metal valve housing of the present invention;

[0028] Figure 7 A schematic diagram of the arrangement of positioning holes in the continuous stamping method of the metal valve housing of the present invention;

[0029] Figure 8 It is an overall schematic diagram of the deep drawing step of the continuous stamping method for a metal valve housing of the present invention;

[0030] Figure 9 Schematic diagram of the mold layout of the continuous stamping method of the metal valve housing of the present invention;

[0031] Figure 10 Schematic diagram of the punching position of the continuous stamping method of the metal valve housing of the present invention;

[0032] Figure 11 A schematic diagram of a punching process in a continuous stamping method for a metal valve housing according to the present invention;

[0033] Figure 12 Schematic diagram of the mold layout for the claw expansion step of the continuous stamping method for forming a metal valve housing of the present invention;

[0034] Figure 13 It is a structural schematic diagram of an outward expansion die in the claw outward expansion step of the continuous stamping forming method of the metal valve housing of the present invention;

[0035] Figure 14 Schematic diagram of the mold layout for the top hole forming step of the continuous stamping method for the metal valve housing of the present invention;

[0036] Figure 15 It is a schematic cross-sectional view of the metal valve housing W after being formed in the top hole forming step of the continuous stamping forming method of the metal valve housing of the present invention.

[0037] In the figure,

[0038] W: Metal valve housing W1: Side hole W2: Clamping foot W3: Rotating wall W4: Housing top W5: Top hook W6: Top hole W8: Bottom cover W1S: Half hole F: Step feed direction M: Metal sheet H: Positioning hole D: Die movement direction PL: Left punch PR: Right punch PH: Horizontal top block PV: Upper die DETAILED DESCRIPTION

[0039] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. In this specification, the size ratios in the drawings do not represent the actual size ratios, but are only used to reflect the relative positional relationship and connection relationship between the various components. Components with the same name or the same number represent similar or identical structures and are only for illustrative purposes.

[0040] Figure 1 is a three-dimensional schematic diagram of the metal valve housing W of the present invention, Figure 2 Schematic top view of the metal valve housing W of the present invention, Figure 3 It is a side view schematic diagram of the metal valve shell W of the present invention. The metal valve shell W is made of metal, and in actual application, it is preferably made of stainless steel. The metal valve shell W includes a rotating wall W3 in the form of a rotating body. The rotating wall W3 is the main body of the metal valve shell W. The fluid flows through its internal cavity. The corresponding valve core assembly is arranged in the metal valve shell W. Side holes W1 are evenly distributed on the rotating wall W3. Each side hole W1 has a clamping foot W2 formed therein and opened toward the circumferential outside of the metal valve shell W, wherein the side hole W1 provides a channel for the fluid to enter and exit. At the bottom of the rotating wall W3 is a bottom cover W8, which has a circumferential depression toward the bottom, which is used to accommodate a sealing gasket during installation. The clamping foot W2 cooperates with the bottom cover W8 to fix the metal valve shell W on the installation wall. The top of the rotating wall W3 is the shell top W4. A top hole W6 and a top hook W5 complementary to the top hole W6 are formed in the central recess of the shell top W4. The top hole W6 is used for fluid inlet and outlet, and the top hook W5 is used to suspend the valve core assembly.

[0041] The above-mentioned metal valve shell W is formed by stamping from a metal plate, but the aspect ratio of the revolving wall W3 of the metal valve shell W is approximately 1, and the ductility of the metal plate is limited. During the process of forming the revolving wall W3, cracks will occur at the fillet, and the product will be scrapped. In addition, the overall size of the metal valve shell W is less than 30mm*30mm*20mm. Due to the small size of the metal valve shell W, the movement and layout space of the mold are limited, which brings difficulties to the stamping design. Finally, there are many holes on the metal valve shell W, the distance between the holes is small, and the area occupied by the hollow part is large. During the process of punching the holes, the surface of the already formed metal valve shell W is easily deformed, resulting in unqualified products. The size of the metal valve shell W is small, which is suitable for designing a continuous mold to complete the various processes of the metal valve shell W on a single stamping machine / stamping die, thereby realizing efficient utilization of the production line. For this reason, the present invention designs a continuous stamping forming method for the continuous forming of the metal valve shell W.

[0042] Figure 4 The overall flow chart of the continuous stamping method for metal valve housing is as follows: Figure 5This diagram illustrates the layout of the progressive die used in the continuous stamping process for metal valve housings. A metal strip of suitable width is continuously fed along the illustrated stepwise feed direction F. The die is equipped with multiple stations along this direction to complete a single pass of the strip. These steps along this direction include punching the positioning holes, deep drawing, forming the side holes, forming the top hole, and finally blanking.

[0043] S1. Step of punching positioning holes. Since the metal strip is formed sequentially on each step of the continuous die, in order to ensure that each die processing can accurately fit the area of the previous molding, positioning holes need to be processed on the metal strip to achieve continuous positioning of the metal strip during the stamping process.

[0044] S2. Deep drawing step. As previously mentioned, the metal valve housing W is made of metal, preferably stainless steel. However, stainless steel has low ductility and a high elastic modulus, making it unsuitable for deep drawing. Furthermore, the aspect ratio of the revolving wall W3 of the metal valve housing W is 15:14, slightly greater than 1. This aspect ratio makes it impossible to complete the revolving wall W3 in a single forming step; instead, multiple forming steps are required using reasonable process parameter design. Preferably, after multiple forming steps, the revolving wall W3's shape is precisely adjusted.

[0045] S3, side hole forming step. After completing the deep drawing forming step, in order to avoid deformation caused by excessive impact on the rotating wall W3 and to facilitate the dispersed arrangement of the mold, the side holes on the rotating wall W3 are punched out at each station. Figure 1-3 The foot W2 is located in the middle of the side hole W1, connecting the two parts of the side hole W1 below the foot W2. Due to the small area of the foot W2, it is impossible to arrange an internal support mold accordingly. If it is directly punched, the foot W2 will inevitably collapse and fold toward the inside of the rotating wall W3, accompanied by severe burrs on its edge due to the lack of effective support. Therefore, the two parts of the side hole W1 are punched and formed in two steps. When forming one side of the side hole W1, the space on the other side of the side hole W1 can also be used to accommodate the support mold of the foot W2.

[0046] S4, top hole forming step. Figure 2 The top of the metal valve housing W consists of a metal top hook W5 and a corresponding top hole W6. The top hook W5 is used to hook the elastic component during use. The top hook W5 is supported by a bottom die within the rotating wall W3, while the top hole W6 is punched and formed by a die outside the top hook W5.

[0047] S5, blanking step. After all the forming processes of the metal valve housing W are completed, the metal valve housing W is still grown on the metal plate. The metal valve housing W is punched out from the metal plate along the outer edge of its bottom cover W8 through the blanking step.

[0048] The following is the specific implementation of each step.

[0049] S1, step of punching positioning holes.

[0050] Figure 6 The following is a forming diagram of the step of punching positioning holes. After the rolled metal sheet M is gradually released from the feeder in the front process, it enters the forming space of the mold along the stepping feed direction F. During each stepping process, at least one positioning hole is formed on the metal sheet M. The positioning hole H is used to accurately position the metal sheet M in the next step and subsequent steps. That is, when the next step stops, the positioning hole H enters the corresponding positioning pin on the mold to realize the positioning of the metal sheet M, and accordingly determines the position of the positioning hole H formed on the metal sheet M next time, so as to realize the uniform discharge of the positioning hole H and the metal valve shell W on the metal sheet M, thereby improving the utilization rate of the metal sheet M. It is preferred to set two positioning holes H, that is, one is set on each of the two edges of the metal sheet M in the stepping feed direction F to achieve better positioning. Although the metal valve housing W of the present invention is relatively small in size, it has more total process steps. The single-sided positioning hole H may cause slight distortion in the metal sheet M during transportation, causing it to deviate to one side, resulting in the positioning hole H in the subsequent process being unable to enter the positioning pin and the finished product being unable to be formed. A positioning hole H is provided on each side to avoid such a situation. The relative positions of the positioning holes H on both sides along the step feed direction F do not need to be consistent, and they can be staggered by a certain distance, for example, Figure 7 As shown, the positioning holes H on both sides can be staggered by half the distance L between the positioning holes H on one side, which is equivalent to doubling the positioning density in the step feed direction F and also limiting the distortion of the metal sheet M.

[0051] S2, deep drawing step.

[0052] Figure 8This is a schematic diagram of the deep-drawing process. To ensure that the revolving wall W3 does not crack during the forming process of the metal valve housing W, particularly at the upper and lower fillets, the revolving wall W3 cannot be formed in a single deep-drawing process. Instead, a multiple-drawing process is required, controlling the single-drawing coefficient l of the metal valve housing W to be within 0.75≤l<1. The specific drawing process parameters employed in this continuous stamping method for the metal valve housing are shown in Table 1. Four deep-drawing processes achieve the target drawing diameter and height while minimizing the stress on the material and preventing cracking, ensuring the processability of the metal valve housing W. After completing the deep drawing of the basic shape of the revolving wall W3, it is also necessary to set up a corresponding shaping step, and further adjust and shape the size obtained by the final deep drawing to roughly reach the shape of the blank of the revolving wall W3, so that its size is completely consistent with the revolving wall W3, and trim the fillet of the transition position between the upper and lower parts of the revolving wall W3, and adjust the process fillet formed during the deep drawing process to the shape defined when the revolving wall W3 was designed. In the continuous stamping forming method of this metal valve shell, two shaping steps, namely the initial shaping step S28 and the final shaping step S29, are set up in sequence to achieve the shape finishing of the revolving wall W3 after deep drawing. The position after the deep drawing forming step S2 can also be set for forming the metal valve shell W, and the specific position in the process can be adjusted as needed.

[0053]

[0054] Table 1: Drawing process parameters

[0055] S3, side hole forming step.

[0056] Figure 9 This is a schematic diagram of the side hole forming step. In this step, each side hole W1 is divided into two half holes W1S, which are separated by the clamping foot W2 and punched separately. Specifically, the half-hole punching process is divided into the following steps: side hole one left punching step S31A, side hole two left punching step S31B, side hole three left punching step S31C, side hole one right punching step S32A, side hole two right punching step S32B, and side hole three right punching step S32C, each performing a half-hole punching operation. Figure 10 The solid arrow in the middle is the mold movement direction D of the mold in each step, and the corresponding black-filled part in the front view along the mold movement direction D is the part that is punched in each step. Figure 9 and Figure 10The order of the various steps is specified in the figure. This order is not mandatory and can be varied arbitrarily. The figure only illustrates one implementation. However, the punching operations for the two half-holes W1S of the same side hole W1 are preferably staggered at at least one station, rather than arranged at adjacent stations. This is primarily due to mold setup considerations. Because the metal valve housing W is relatively small, the mounting spacing on the mold is correspondingly reduced. If the two stations for the same side hole W1 are arranged adjacently, a set of upper die punches, each facing the same direction relative to the metal valve housing W, would be required. This is insufficient in the available space.

[0057] Now we will take the punching process of a side hole W1 as an example to explain in detail. Figure 11 As the corresponding schematic diagram, before entering, the rotating wall W3 is approximately a smooth cylinder. In the process, a half hole W1S is punched out radially from a single half hole W1S, and then another half hole W1S is punched out radially from the right punch PR. The two half holes W1S punched out together form the side hole W1. In this process, Figure 11 As shown, within the punching range of the left punch PL and the right punch PR, there is a certain overlap at the junction of the two, which can ensure stable cutting at the connection without generating unnecessary burrs and uncut conditions. The connection point between the left punch PL and the right punch PR is usually selected at the angle position on the side hole W1 to facilitate mold design and ensure that the connection is smooth and without discontinuities.

[0058] S9, claw expansion step.

[0059] The clamping foot W2 of the metal valve housing W obtained by the side hole forming step S3 is on the same circumferential surface as the rotating wall W3, which is consistent with the Figure 1-3 The requirements for the clamping pin W2 that is extended relative to the rotating wall W3 shown in FIG are different. It should be noted that the clamping pin W2 plays a key fixing role in the assembly process. It uses its own metal elasticity to elastically clamp the mounting surface (such as the battery pack shell) between the end of the clamping pin W2 and the mounting surface. Therefore, it is necessary to open the clamping pin W2. Figure 12 As shown, the and are used to squeeze the three clamping feet W2, causing them to deform radially outward. Specifically, in one of the steps, the schematic diagram is as follows Figure 13 As shown, the upper mold PV and the transverse top block PH slide in contact via an inclined surface. The distal end of the transverse top block PH extends into the metal valve housing W and points toward the latch pin W2. As the upper mold PV descends, it pushes the transverse top block PH horizontally. The distal end of the transverse top block PH pushes the latch pin W2 outward, deforming it and maintaining its plasticity, completing the outward expansion. The claw expansion step should be performed after the side hole forming step, but it does not need to be immediately adjacent to it. It can be interspersed between subsequent steps as needed.

[0060] S4, top hole forming step.

[0061] The above steps only complete the overall shape of the metal valve housing W and the forming of the side holes. Next, the top hole forming step S4 needs to be performed. The top hole punching step of the top hole forming step uses an upper mold corresponding to the expected top hole size and shape to punch out the top hole W6 located at the top of the metal valve housing W, retaining the top hook W5.

[0062] Figure 14 The top hole forming step and the blanking step are shown in FIG. The top hole forming step includes at least the top hole punching step, the boss forming step and the bending step, wherein the boss forming step S41 is provided before the top hole punching step S42, and the bending step S43 is provided after the top hole punching step S42. Figure 15 As shown, the boss forming step is first used to form the entire circumferential boss details at position A1 in the figure, and is used to bend the end of the top hook W5 obtained by the forming, and the end is bent into an upward inclination angle to prevent it from sliding after the elastic component is hooked on it.

[0063] S5, blanking step

[0064] The blanking step S5 is to blank the metal valve housing W, that is, to punch the formed metal valve housing W from the metal sheet M along the outer edge of the metal valve housing W and collect it in the receiving area. This is the last step of the whole process.

[0065] The above content only describes the preferred embodiments of the present invention and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solution of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A continuous stamping method for a metal valve housing, characterized in that: The steps include: Punching positioning holes: processing at least one positioning hole on the metal sheet (M); Deep drawing step: deep drawing the metal sheet (M) to obtain a revolving wall (W3); Side hole forming step: each side hole (W1) on the metal valve housing (W) is divided into two half holes (W1S) separated by a clamping foot (W2), and each half hole (W1S) is formed in a different process step; Blanking step: punching out the formed metal valve housing (W) from the metal sheet (M); In the side hole forming step, a left punch (PL) for profiling a half hole (W1S) is used to punch out a single half hole (W1S) radially, and then a right punch (PR) for profiling the other half hole (W1S) is used to punch out the other half hole (W1S) radially. The two punched half holes (W1S) together form the side hole (W1), and the punching ranges of the left punch (PL) and the right punch (PR) overlap. A claw expansion step is further provided after the side hole forming step, and the claw expansion step includes a step of expanding each clamping foot (W2). In each expansion step, the upper mold (PV) and the transverse top block (PH) slide through the inclined contact, and the end of the transverse top block (PH) extends into the interior of the metal valve housing (W) and points to the clamping foot (W2). The upper mold (PV) is lowered to push the transverse top block (PH) to slide horizontally, so that the end of the transverse top block (PH) pushes the clamping foot (W2) to deform outward and maintain plasticity.

2. The continuous stamping method for a metal valve housing according to claim 1, wherein: In the side hole forming step, the intersection point where the left punch (PL) and the right punch (PR) overlap is located at the corner transition of the side hole (W1).

3. The continuous stamping method for a metal valve housing according to claim 2, wherein: In the side hole forming step, the punching operation steps of the two half holes (W1S) of the same side hole (W1) are staggered by at least one station.

4. The continuous stamping method for a metal valve housing according to claim 1, wherein: In the step of punching the positioning holes, two positioning holes are processed in a single process, and are respectively located at the two side edges of the metal sheet (M).

5. The continuous stamping method for a metal valve housing according to claim 1, wherein: In the deep drawing step, the metal valve housing (W) is formed by multiple deep drawing steps, and the range of the drawing coefficient l of a single deep drawing step is 0.75≤l<1.

6. The continuous stamping method for a metal valve housing according to claim 5, wherein: In the deep drawing step, the metal valve housing (W) is formed by deep drawing four times, and the drawing coefficient of a single deep drawing is not less than 0.

8.

7. The continuous stamping method for a metal valve housing according to claim 5, wherein: In the drawing forming step, at least one shaping step is provided after the last drawing to adjust the shape and size of the rotating wall (W3) after drawing.

8. The continuous stamping method for a metal valve housing according to claim 1, wherein: The method further includes a top hole forming step, which is located between the side hole forming step and the blanking step. The top hole forming step at least includes a top hole punching step, in which the top hole (W6) located at the top of the metal valve housing (W) is punched out by an upper die that matches the expected size and shape of the top hole (W6), while retaining the top hook (W5).

9. The continuous stamping method for a metal valve housing according to claim 8, wherein: The top hole forming step also includes a boss forming step and a bending step, wherein the boss forming step is arranged before the top hole punching step, and the bending step is arranged after the top hole punching step; the boss forming step is used to form a boss around the entire perimeter of the top surface of the metal valve housing (W), and the bending step is used to bend the end of the top hook (W5) obtained by the forming.

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