Shell extrusion and necking single-station continuous forming method

Abstract

The invention provides a shell extrusion and necking single-station continuous forming method which comprises the following steps: an extrusion forming step: placing a blank in a female die cavity of a lower female die, and after an extrusion male die is assembled on an upper die plate, controlling an upper die assembly to descend so as to extrude the blank, so that the blank is formed into a blind hole shell with preset wall thickness and bottom thickness; and shell necking, specifically, the upper die assembly is controlled to ascend so that the extrusion male die can be disengaged from a cavity opening of the female die cavity, the extrusion male die can be detached from the upper die plate, the necking die can be assembled on the upper die plate, and the upper die assembly is controlled again to descend till the conical opening and the top end of the blind hole shell are buckled to form a necking shell. High-quality forming of a necking shell component can be achieved by replacing the male die in the upper die assembly and sharing the same set of lower die assembly, die replacement time consumption is effectively reduced, blank heat dissipation is reduced, efficient necking of a shell is ensured, the forming quality of the necking shell is improved, and the die manufacturing cost and the product forming cost are effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of metal forming technology, specifically relating to a single-station continuous forming method for shell extrusion and necking. Background Technology

[0002] Thick-walled, tapered shell components (especially those with high aspect ratios) possess excellent resistance to complex loads, lightweight design, and transport efficiency due to their unique structure. They are widely used in aerospace equipment, weaponry, underwater equipment, and critical load-bearing components of pressure equipment—fields with stringent requirements for serviceability under extreme conditions. To ensure high strength, these components typically utilize high-strength alloy steel and ultra-high-strength aluminum alloys. The structural characteristics, performance requirements, and material selection of these components present a challenge in balancing manufacturing efficiency, component performance, and manufacturing cost. The aforementioned high aspect ratio generally refers to H / D ≥ 3 (where H is the height of the formed shell component and D is the maximum outer diameter of the main body of the formed shell component), and thick wall refers to t / D > 0.1 (where t is the wall thickness of the main body of the formed shell component).

[0003] The main methods for manufacturing thick-walled, tapered shell components with large aspect ratios include machining, spinning-tapering, and extrusion-tapering. Machining eliminates the need for mold development and offers fast response and simple operation. However, it suffers from extremely low material utilization, high production costs, and the inability to improve the internal structure and mechanical properties of the component, making it difficult to meet service requirements. Spinning is another method for manufacturing such parts. Its advantages include high material utilization and convenient tapering, but it requires extrusion to prepare cylindrical blanks, resulting in a long processing cycle. The rotary feed leads to poor uniformity of the component's structure and properties, and obvious texture, affecting the anisotropy of the component's mechanical properties. The manufacturing efficiency is also low. Therefore, spinning is not suitable for the low-cost manufacturing of small-diameter, high aspect ratio conical shells.

[0004] Extrusion-neck forming is a commonly used forming method for thick-walled, necked shell components with large aspect ratios. This method typically involves reverse extrusion-neck forming and reverse extrusion-thinning drawing-neck forming, such as... Figure 1 As shown, the advantage of reverse extrusion forming is that it subjects the metal to a triaxial compressive stress state during the extrusion process, allowing for sufficient plastic deformation and achieving significant improvements in microstructure and properties. However, its disadvantages include a long metal flow path during reverse extrusion, large-area contact between the billet and the die resulting in high frictional resistance and back stress, and the high aspect ratio of the punch making it prone to failure under repeated high forming loads, significantly reducing die life. Failure can only be delayed by sacrificing production efficiency through multiple heating and extrusion passes, which not only increases energy consumption but also poses safety risks. Figure 2As shown, the advantages of reverse extrusion-thinning deep drawing are a smaller contact area between the billet and the die, which reduces the overall forming load. However, its disadvantages are that the amount of deformation per pass is limited by the thinning stretching coefficient, requiring multiple thinning and stretching passes to achieve the required deformation. The forming process often requires multiple heating passes and changing multiple sets of dies to achieve extrusion, thinning, and drawing processes. Furthermore, it is prone to instability for small-diameter, thin-walled shells. Therefore, extrusion-neck forming has become the preferred low-cost manufacturing solution for such components.

[0005] Continuous forming of thick-walled, necked shell components with large aspect ratios typically involves extrusion-spinning equipment, dedicated extrusion-necking equipment, or multi-station extrusion equipment and dies. Its advantages include automation and high production speed, but disadvantages include high equipment and die development costs and complex process development. In related technologies, single-station extrusion-necking methods for thick-walled, necked shell components with large aspect ratios usually require replacing the entire set of dies after the extrusion forming process to achieve the necking process. This method has the advantages of lower equipment and die costs and lower process development costs, but disadvantages include long die replacement time, reduced heat dissipation from the billet leading to a shorter necking window, affecting product quality, and the labor-intensive and time-consuming process of heating the entire set of dies, which shortens die life and increases production costs. Summary of the Invention

[0006] Therefore, the present invention provides a single-station continuous forming method for shell extrusion and necking, which can overcome the shortcomings of the related single-station extrusion-necking forming method, which requires the necking process to be carried out by changing the entire set of molds after the extrusion forming process is completed. The mold change is time-consuming, the heat dissipation of the billet shortens the necking process window, and affects the product quality.

[0007] To address the aforementioned problems, this invention provides a single-station continuous forming method for shell extrusion and necking, employing a shell forming mold. The shell forming mold includes an upper mold assembly and a lower mold assembly. The lower mold assembly includes a lower template and a lower die disposed thereon, the lower die having a cavity. The upper mold assembly includes an upper template and an extrusion punch and a necking die selectively assembled to the side of the upper template facing the lower die. The necking die has a conical opening, smaller at the top and larger at the bottom, formed on its bottom end face. The forming method includes the following steps:

[0008] Extrusion forming step: The blank is placed in the cavity of the lower die, and after the extrusion punch is assembled on the upper die plate, the upper die assembly is controlled to descend to extrude the blank so that the blank is formed into a blind hole shell with a preset wall thickness and bottom thickness.

[0009] Shell narrowing step: Control the upper mold assembly to rise so that the extrusion punch is dislodged from the cavity of the die cavity, remove the extrusion punch from the upper template and assemble the narrowing mold onto the upper template, and control the upper mold assembly to descend again until the conical opening is engaged with the top of the blind hole shell to form a narrowed shell.

[0010] In some embodiments, the following steps are included after the extrusion forming step and before the shell necking step:

[0011] Partial heating of the shell: The top area of ​​the blind hole shell is heated, and the blind hole shell with the heated top area is placed back into the cavity.

[0012] In some embodiments, the extrusion punch includes a forming reverse extrusion punch and a tapered drawing punch, and the lower die assembly further includes a pad that can be positioned at the bottom of the die cavity. The extrusion forming step specifically includes:

[0013] The pad is placed at the bottom of the cavity of the die cavity, and then the blank is placed in the cavity of the die cavity. The upper die assembly with the forming reverse extrusion punch is controlled to descend so that the blank is reverse extruded into an intermediate blank with a central blind hole.

[0014] Remove the intermediate blank and the pad from the cavity of the die, and after removing the forming reverse extrusion punch from the upper template, replace and assemble the tapered drawing punch.

[0015] The upper die assembly is lowered again to draw and extrude the intermediate blank to form the blind hole shell.

[0016] In some embodiments, the lower die includes an inner die body and an outer die body fitted onto the radially outer side wall of the inner die body, the die cavity being formed on the inner die body; and / or, the bottom of the die cavity is a cone shape that is larger at the top and smaller at the bottom, and the longitudinal cross-sectional shape of the pad is a cone shape that matches the bottom of the cavity.

[0017] In some embodiments, a cooling channel is formed within the outer mold body, the cooling channel being constructed on the mating annular surface of the inner mold body and the outer mold body, and the cooling channel having an inflow channel and an outflow channel. During the extrusion molding step, cooling fluid is introduced into the cooling channel to form a circulation; and / or, a lower backing plate is provided between the outer mold body and the lower template, the lower backing plate having a ejector pin through hole communicating with the bottom of the cavity, the ejector pin passing through the lower template and the ejector pin through hole in sequence, and the ejector pin having a limiting ring protruding radially outward, the ejector pin having an ejection position. The ejector rod is capable of being driven to move up and down between the ejector position and the blocking position. When the ejector rod is in the ejector position, the limiting ring abuts against the bottom side of the inner mold body. When the ejector rod is in the blocking position, the limiting ring abuts against the top side of the lower mold plate and the top end of the ejector rod is inserted into the bottom of the cavity. When the intermediate blank, blind hole shell, and narrowed shell are unloaded from the cavity, the ejector rod is controlled to be in the ejector position. When force is applied to the blank, intermediate blank, blind hole shell, and narrowed shell, the ejector rod is controlled to be in the blocking position.

[0018] In some embodiments, an upper concave template is detachably assembled on the top side end face of the outer mold body. The upper concave template has a first central through hole corresponding to the top side cavity opening of the die cavity. The working ends of the forming reverse extrusion punch and the tapered drawing punch can be inserted into the die cavity through the first central through hole. The lower mold assembly also includes a die guide sleeve and a stripper plate. A second central through hole is formed in the die guide sleeve. The upper opening diameter of the second central through hole is equal to the outer diameter of the main body of the forming reverse extrusion punch. When the forming reverse extrusion punch is assembled on the upper template, the die guide sleeve is assembled on the upper concave template and coaxially arranged with the first central through hole. When the tapered drawing punch is assembled on the upper template, the stripper plate is assembled on the upper concave template so that the blank can be removed from the tapered drawing punch during the lifting process of the tapered drawing punch.

[0019] In some embodiments, the upper mold assembly further includes a support core mold optionally assembled to the upper mold plate on the side facing the lower die, the support core mold passing through the conical opening, the support core mold being used to form radial support for the top of the blind hole blank during the housing narrowing step.

[0020] In some embodiments, the upper die assembly further includes a punch seat and a punch retaining ring, which are stacked sequentially along the direction away from the upper die plate and located on the side of the upper die plate closer to the lower die plate. The punch retaining ring is detachably assembled to the bottom end face of the punch seat, and a punch collar with a tapered positioning hole is formed in the central region of the punch retaining ring. The top of the main body of the forming reverse extrusion punch, the tapered drawing punch, and the supporting core die is formed with an inverted tapered ring that mates with the tapered positioning hole. The diameter of the tapered positioning hole decreases from top to bottom. The punch seat has a first insertion hole, and the punch retaining ring has a second insertion hole. The diameter of the first insertion hole is larger than the diameter of the second insertion hole.

[0021] In some embodiments, the punch collar and the punch fixing ring are separately provided; and / or, an upper pad is further provided between the upper template and the punch seat, and the top end face of the main body of the forming reverse extrusion punch, the tapered drawing punch and the supporting core mold can abut against the bottom side end face of the upper pad.

[0022] In some embodiments, prior to the extrusion molding step, the blank is heated to the molding temperature and the lower die, the forming reverse extrusion punch, the tapered drawing punch, and the necking die are preheated and kept warm. Alternatively, the portions of the lower die, the forming reverse extrusion punch, the tapered drawing punch, the necking die, and the ejector pin that contact the blank are uniformly sprayed with lubricant.

[0023] The single-station continuous forming method for shell extrusion and necking provided by this invention has the following beneficial effects:

[0024] The blank is extruded into a shell structure with a central blind hole, i.e., a blind hole shell, by the extrusion punch. The top of the blind hole shell is then extruded towards its central axis by the descending extrusion die to form a narrowed shell. High-quality forming of the narrowed shell component can be achieved by replacing the punch in the upper die assembly and using the same set of lower die assemblies. There is no need to replace the entire set of dies for shell narrowing after the extrusion forming process, which effectively reduces the time spent on die replacement, reduces the heat dissipation of the blank, ensures efficient shell narrowing, improves the forming quality of the narrowed shell, and effectively reduces the die manufacturing cost and product forming cost. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0026] Figure 1This is a schematic diagram of the forming process of the shell using a single reverse extrusion method in the prior art;

[0027] Figure 2 This is a schematic diagram of a forming process in the prior art where a shell is formed by reverse extrusion and then further thinned and drawn by a deep drawing ring.

[0028] Figure 3 This is a longitudinal cross-sectional schematic diagram of the thick-walled shell with a constricted top and an inverted cone bottom that is intended to be formed according to the present invention.

[0029] Figure 4 This is a schematic diagram of the steps of the shell extrusion and necking single-station continuous forming method in an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of the working state of the mold before the material is discharged before the reverse extrusion deformation in an embodiment of the present invention. A forming reverse extrusion punch is used in the figure, and the forming reverse extrusion punch in the figure does not apply force to the blank.

[0031] Figure 6 This is a schematic diagram of the working state of the mold after the reverse extrusion deformation ends in an embodiment of the present invention;

[0032] Figure 7 This is a schematic diagram of the working state of the mold after unloading following the reverse extrusion deformation in an embodiment of the present invention;

[0033] Figure 8 This is a schematic diagram of the working state of the die before deep drawing and extrusion deformation in an embodiment of the present invention. The figure shows a tapered deep drawing punch.

[0034] Figure 9 This is a schematic diagram of the working state of the die after the deep drawing and extrusion deformation is completed in an embodiment of the present invention;

[0035] Figure 10 This is a schematic diagram of the working state of the mold after unloading following the deep drawing and extrusion deformation in an embodiment of the present invention;

[0036] Figure 11 This is a schematic diagram of the working state of the mold before material feeding in the necking deformation embodiment of the present invention. The diagram shows a necking mold and a supporting core mold.

[0037] Figure 12 This is a schematic diagram of the working state of the mold after the necking deformation is completed in an embodiment of the present invention;

[0038] Figure 13 This is a schematic diagram of the working state of the mold after unloading following the shrinkage deformation in an embodiment of the present invention;

[0039] Figure 14 This is a top view of the upper die when the stripper plate is assembled (the stripper plate is in the blocking state) in an embodiment of the present invention.

[0040] Figure 15 This is a top view of the upper die when the stripper plate is assembled (the stripper plate is in a non-blocking state) in an embodiment of the present invention.

[0041] Figure 16 This is a vector diagram of metal flow during a traditional reverse extrusion process, with arrows indicating the direction of metal flow.

[0042] Figure 17 Is adopted Figure 16 The extrusion pressure curve (load prediction diagram) of a high-carbon steel billet during the traditional reverse extrusion process is shown in the figure. It can be clearly seen from the figure that the maximum forming extrusion pressure required is as high as 846t.

[0043] Figure 18 This is a vector diagram of metal flow during the deep drawing process after reverse extrusion in this invention. The arrows in the diagram indicate the direction of metal flow.

[0044] Figure 19 The extrusion molding method of the present invention is used for... Figure 17 The extrusion pressure curve (load prediction diagram) of the same material blanks when performing tapered deep drawing shows that the maximum forming extrusion pressure required is about 422t.

[0045] The attached figures are labeled as follows:

[0046] 11. Lower mold plate; 12. Lower die cavity; 1201. Inner mold body; 1202. Outer mold body; 1203. Cooling channel; 1204. Inflow channel; 1205. Outflow channel; 121. Die cavity; 122. Spacer block; 13. Lower backing plate; 131. Ejector pin through hole; 14. Ejector pin; 141. Limiting ring; 15. Upper die plate; 151. Annular groove; 16. Die opening 17. Guide sleeve; 21. Stripper plate; 22. Upper template; 23. Forming and extrusion punch; 24. Tapered drawing punch; 25. Narrowing die; 26. Conical opening; 27. Supporting core mold; 28. Upper backing plate; 29. ​​Punch seat; 30. Punch retaining ring; 31. Punch collar; 32. Guide post; 33. Guide post pressure plate; 34. Guide sleeve pressure plate; 100. Blank. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0049] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90° or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0050] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0051] See also Figures 3 to 19 As shown in the embodiment of the present invention, a single-station continuous forming method for extruding and necking of a shell is provided. The shell forming mold includes an upper mold assembly (not labeled in the figure) and a lower mold assembly (not labeled in the figure). The lower mold assembly includes a lower template 11 and a lower die 12 disposed thereon. Taking the orientation in a specific usage state as a reference, the lower die 12 is disposed above the top surface of the lower template 11. The lower die 12 has a die cavity 121. The upper mold assembly includes an upper template 21 and an extrusion punch (not labeled in the figure) and a necking die 24 selectively assembled on the side of the upper template 21 facing the lower die 12. A conical opening 241, smaller at the top and larger at the bottom, is formed on the bottom end face of the necking die 24. It is understood that the size of the conical opening 241 matches the necking size of the top of the shell component to be formed. The forming method includes the following steps:

[0052] Extrusion forming step: Place the blank 100 in the cavity 121 of the lower die 12, and after the extrusion punch is assembled on the upper die 21, control the upper die assembly to descend to extrude the blank 100 so that the blank 100 is formed into a blind hole shell with a preset wall thickness and bottom thickness (the specific wall thickness and bottom thickness can be reasonably set according to actual needs).

[0053] Shell narrowing step: Control the upper mold assembly to rise so that the extrusion punch is dislodged from the cavity of the die cavity 121 (i.e., the top opening of the die cavity 121), remove the extrusion punch from the upper template 21 (i.e. disassemble), and assemble the narrowing mold 24 onto the upper template 21. Control the upper mold assembly to fall again until the conical opening 241 engages with the top of the blind hole shell to form a narrowed shell.

[0054] In this technical solution, the blank 100 is extruded into a shell structure with a central blind hole, i.e., a blind hole shell, by the extrusion punch. The top of the blind hole shell is extruded towards its central axis by the descending extrusion of the necking die 24 to form a neck and finally form a necked shell. High-quality forming of the necked shell component can be achieved by replacing the punch in the upper die assembly and sharing the same set of lower die assemblies. There is no need to replace the entire set of dies for shell necking after the extrusion forming process, which effectively reduces the time spent on die replacement, reduces the heat dissipation of the blank, ensures efficient necking of the shell, improves the forming quality of the necked shell, and effectively reduces the die manufacturing cost and product forming cost.

[0055] In some embodiments, the following steps are included after the extrusion forming step and before the shell necking step:

[0056] The shell local heating step is as follows: the top part of the blind hole shell is heated, and the blind hole shell with the heated top part is placed back into the cavity 121. It can be understood that the position of the aforementioned top part is determined based on the starting position of the final shrinkage of the shell.

[0057] In this technical solution, the top area of ​​the blind hole shell is heated selectively before the top of the blind hole shell is narrowed, so as not to heat the blind hole shell as a whole, which can further reduce heat loss.

[0058] In some embodiments, the extrusion punch includes a forming reverse extrusion punch 22 and a tapered drawing punch 23. The lower die assembly also includes a pad 122 that can be positioned at the bottom of the die cavity 121. The pad 122 occupies the bottom space of the die cavity 121, thereby providing downward deformation space for the blank 100 placed in the die cavity 121 to further deform downward. It should be noted that the bottom shape of the tapered drawing punch 23 should be consistent with the bottom shape (blind hole end) of the final formed shell, and the outer wall surface of the main body of the tapered drawing punch 23 should also have a corresponding working ring (not indicated in the figure, also called a working zone). The extrusion forming step specifically includes:

[0059] After the pad 122 is placed at the bottom of the cavity 121, the blank 100 is placed inside the cavity 121. The upper die assembly with the forming reverse extrusion punch 22 is controlled to descend so that the blank 100 is reverse extruded into an intermediate blank with a central blind hole. That is, the intermediate blank is formed by the reverse extrusion of the cavity formed by the forming reverse extrusion punch 22, the cavity 121 and the pad 122. During the reverse extrusion process, the position of the aforementioned pad 122 remains unchanged so as to form a clamping and extrusion of the blank 100 together with the aforementioned forming reverse extrusion punch 22.

[0060] The intermediate blank and the pad 122 are removed from the cavity 121, and the forming reverse extrusion punch 22 is removed from the upper template 21 and then replaced with the tapered drawing punch 23. When the pad 122 is removed from the bottom area of ​​the cavity 121, the pad 122 no longer occupies the bottom space of the cavity 121, thereby forming a blank 100 at the bottom of the intermediate blank to provide downward deformation space for further deformation.

[0061] The upper die assembly is lowered again to draw and extrude the intermediate blank to form the blind hole shell.

[0062] In this technical solution, a pad 122 is selectively placed at the bottom of the cavity 121 of the lower die 12. This allows the pad 122, whose position remains unchanged, to occupy the bottom area of ​​the cavity 121 during the reverse extrusion deformation process of the blank 100 placed in the cavity 121. Consequently, the downward extrusion stroke of the forming reverse extrusion punch 22 in this invention can be shortened, eliminating the need for the forming reverse extrusion punch to descend nearly the entire length of the formed shell as in the reverse extrusion forming shell process of the prior art. This effectively shortens the metal flow path. The length of the die is reduced, decreasing the contact area between the blank and the die, thereby reducing frictional resistance and back stress. Simultaneously, the length of the corresponding forming punch 22 can be reduced to a certain extent (approximately the height of the aforementioned pad 122), improving the die's service life (in the prior art, excessively long punches lead to low die life when forming shells with large aspect ratios). After the blank 100 is back-extruded, the aforementioned pad 122 is removed from the die cavity 121, creating a suspended area below the bottom of the back-extruded blank 100. This allows for better control of the die's life when using the aforementioned... When the extrusion drawing punch 23 is further inserted into the anti-extrusion blind hole formed in the center of the aforementioned blank 100, the outer wall portion of the blank 100 above the working ring of the extrusion drawing punch 23 is subjected to a vertically upward tensile force, while the blank 100 below the working ring continues to be stretched and deformed downward under the extrusion action of the extrusion drawing punch 23, ultimately forming a shell with a top opening. This achieves the distribution of the deformation of the blank 100 between the two processes of anti-extrusion deformation and stretching extrusion deformation, resulting in more labor-saving and efficient forming, saving energy and significantly reducing costs. This invention improves production efficiency. Furthermore, it is worth emphasizing that the shell forming mold of this invention can achieve the final forming of the blank 100 by simply placing and removing the pad 122 in the die cavity 121 and replacing the forming punch 22 and the tapered drawing punch 23. This significantly reduces the types of molds used and the number of parts that need to be replaced, offering the advantage of quick disassembly and replacement. It solves the problem of difficult mold replacement during the extrusion forming of thick-walled shell components with large height-to-diameter ratios, shortens mold replacement time, and further shortens the production cycle. It is particularly suitable for forming thick-walled shell components with large height-to-diameter ratios.

[0063] See details Figure 18 and Figure 19 As shown in the figure, the wall of the component (i.e., the shell) is the main deformation zone. During the entire extrusion process, the metal flow vector in this zone is divided by the working zone of the punch (the area indicated in the figure). Above the working zone is the flow vector opposite to the extrusion direction, and below the working zone is the flow vector in the same direction as the extrusion direction. That is, the shell material is split vertically by the working zone. At this time, part of the frictional resistance is used to provide tensile stress in the deformation zone of the component wall in the same direction as the metal flow. For comparison, see [reference needed]. Figure 15As shown in the figure, the conventional reverse extrusion forming shell method is adopted. During the entire reverse extrusion process, the metal flow vector in this area always maintains a single vector characteristic opposite to the extrusion direction. At this time, the metal in the wall deformation zone is subjected to the extrusion force in the same direction as the metal flow and the friction force in the opposite direction of the metal flow. All the friction force is the deformation resistance that needs to be overcome. This force provides compressive stress in the wall deformation zone of the component in the opposite direction of the metal flow.

[0064] Further comparison Figure 17 and Figure 19 As shown, the maximum extrusion force used in traditional reverse extrusion molding is 846t, while the molding method of the present invention requires about 422t, which means that the molding method of the present invention is more labor-saving.

[0065] Based on the size requirements of the shell forming and taking into account the forming efficiency, the specific height of the aforementioned pad 122, that is, the proportion of the cavity bottom space occupied by the aforementioned die cavity 121, can be reasonably selected. For example, in a specific embodiment, the height of the aforementioned pad 122 is consistent with (i.e. equal to) the height of the bottom cone portion of the finally formed shell.

[0066] It is worth noting that in this technical solution, one of the aforementioned forming reverse extrusion punch 22, extrusion tapered drawing punch 23, and necking die 24 can be switched and assembled on the same upper template 21 according to the actual process requirements. This achieves the continuous process of reverse extrusion-drawing extrusion-necking extrusion using the same set of molds with only a few parts replaced, thereby completing the forming purpose of the shell component with necking. The process is simple, convenient to operate, and has extremely high work efficiency.

[0067] In some embodiments, the lower die 12 includes an inner die body 1201 and an outer die body 1202 fitted onto the radially outer side wall of the inner die body 1201. The die cavity 121 is formed on the inner die body 1201. Specifically, the aforementioned outer die body 1202 is fitted onto the inner die body 1201 with an interference fit. The interference fit applies prestress to the die to improve its load-bearing capacity and increase the die life.

[0068] In this technical solution, the lower die 12 is formed by combining an inner mold body 1201 and an outer mold body 1202 that fit together, and the die cavity 121 is formed on the inner mold body 1201. The lower die 12 with the combined structure can match the inner mold body 1201 with the material corresponding to the forming temperature of the blank 100. At the same time, the material selection of the outer mold body 1202 does not need to consider the high temperature resistance, thus making the material cost of the lower die 12 lower. In addition, the lower die 12 with the combined structure can be replaced separately if one of them, especially the inner mold body 1201, is damaged, without having to replace the outer mold body 1202, which can further reduce the mold manufacturing cost.

[0069] In some embodiments, the bottom of the cavity 121 is a cone shape that is larger at the top and smaller at the bottom. The longitudinal cross-sectional shape of the pad 122 (that is, the cross-section formed by cutting the pad 122 along its center line by a vertical plane) is a cone shape that matches the bottom of the cavity. In this way, the conical fit between the pad 122 and the bottom of the cavity 121 can be used to lock the position of the pad 122, ensuring reliable and stable support of the bottom end of the blank 100 when the blank 100 is reverse extruded, thereby ensuring reliable and stable reverse extrusion forming. Of course, it is understood that the conical shape of the bottom of the cavity 121 should match the bottom conical shape of the shell to be formed.

[0070] In some embodiments, a cooling channel 1203 is formed within the outer mold body 1202. The cooling channel 1203 is constructed on the mating ring surface of the inner mold body 1201 and the outer mold body 1202, and the cooling channel 1203 has an inflow channel 1204 and an outflow channel 1205. It is understood that the aforementioned inflow channel 1204 and outflow channel 1205 are respectively connected to an external cooling source (e.g., a cooling air source or a cooling water source) to form a circulation. In the extrusion molding step, cooling fluid is introduced into the cooling channel 1203 and forms a circulation, thereby achieving temperature control of the outer mold body 1202 and the inner mold body 1201, maintaining a constant molding temperature, preventing high-temperature creep deformation of the lower die 12, avoiding softening and wear of the mold at excessively high temperatures, and improving the service life of the lower die 12.

[0071] In some embodiments, a lower backing plate 13 is provided between the outer mold body 1202 and the lower mold plate 11. The lower backing plate 13 has a push rod through hole 131 communicating with the bottom of the cavity 121. The push rod 14 passes sequentially through the lower mold plate 11 and the push rod through hole 131. The push rod 14 has a limiting ring 141 protruding radially outward. The push rod 14 has an ejector position and a blocking position and can be driven to move up and down between the ejector position and the blocking position. When the push rod 14 is in the ejector position, ... The limiting ring 141 abuts against the bottom side of the inner mold body 1201. When the ejector rod 14 is in the blocking position, the limiting ring 141 abuts against the top side of the lower mold plate 11 and the top end of the ejector rod 14 is inserted into the bottom of the cavity 121. When the intermediate blank, blind hole shell and narrowed shell are unloaded from the cavity 121, the ejector rod 14 is controlled to be in the ejecting position. When force is applied to the blank 100, intermediate blank, blind hole shell and narrowed shell, the ejector rod 14 is controlled to be in the blocking position.

[0072] In this technical solution, a lower pad 13 is further provided between the lower template 11 and the outer mold body 1202. On the one hand, the push rod through hole 131 on the lower pad 13 forms a lifting and lowering movement space for the limiting ring 141 on the push rod 14. The push rod 14 can be driven to lift and lower between the material ejection position and the material blocking position, thereby realizing the limiting and material ejection functions of the bottom end of the blank. On the other hand, it can simplify the structural design of the outer mold body 1202.

[0073] In some embodiments, an upper concave template 15 is detachably assembled on the top side end face of the outer mold body 1202. The upper concave template 15 has a first central through hole (not indicated in the figure) corresponding to the top side cavity opening of the concave mold cavity 121. The working ends of the forming reverse extrusion punch 22 and the tapered drawing punch 23 (i.e., Figure 5 The bottom end (as shown) can be inserted into the cavity 121 through the first central through hole. It is understood that a forming cavity for the shell is formed between the punch and the cavity wall of the cavity. The lower die assembly also includes a die guide sleeve 16 and a stripper plate 17. A second central through hole (not shown in the figure) is formed within the die guide sleeve 16. The diameter of the upper opening of the second central through hole is equal to the outer diameter of the main body of the forming reverse extrusion punch 22. When the forming reverse extrusion punch 22 is assembled onto the upper die plate 21, the... The guide sleeve 16 is assembled on the upper concave template 15 and coaxially arranged with the first central through hole. This not only guides the forming reverse extrusion punch 22, but also supports the main structure of the forming reverse extrusion punch 22 away from the lower concave die 12 during the reverse extrusion process, ensuring reliable and stable axial force application of the forming reverse extrusion punch 22 and preventing large-span bending deformation due to excessive length of the forming reverse extrusion punch 22. When the blank 100 is placed in the aforementioned concave die cavity 121, the top of the blank 100 (e.g., Figure 4 (As shown) The bottom end of the second central through hole of the aforementioned die guide sleeve 16 is in contact with the die to form an alignment. When the extrusion tapered drawing punch 23 is assembled on the upper template 21, the stripper plate 17 is assembled on the upper concave template 15 so that the blank 100 can be removed from the extrusion tapered drawing punch 23 during the lifting process of the extrusion tapered drawing punch 23, that is, the blank is stripped. For details, please refer to [link to relevant documentation]. Figure 14 and Figure 15 As shown.

[0074] The aforementioned lower template 11, lower pad 13, outer mold body 1202, and upper concave template 15 can be connected by bolts from bottom to top.

[0075] In some embodiments, the upper concave template 15 has an annular groove 151 surrounding the first central through hole on one end face of the upper template 21. The bottom end of the die guide sleeve 16 is installed in the annular groove 151. That is, the bottom end of the die guide sleeve 16 is placed in the annular groove 151 from top to bottom. No other structural design is required. The shape matching and positioning of the annular groove 151 and the die guide sleeve 16 are sufficient. The die guide sleeve 16 can be easily removed from the upper concave template 15 when switching deformation processes.

[0076] In some embodiments, the diameter of the second central through hole on the side near the upper concave template 15 is larger than its upper opening diameter and equal to the diameter of the blank 100, so as to match the end size of the blank 100 with a larger diameter, and at the same time, it can form a limiting radial support for the protruding structure at the top of the blank 100 during the reverse extrusion forming process.

[0077] In some implementations, see reference Figure 14 and Figure 15 As shown, the first end of the unloading plate 17 is hinged to the upper concave template 15, and the second end of the unloading plate 17 can be fixedly connected to the upper concave template 15 (e.g., by a detachable positioning component such as bolts). The unloading plate 17 has a semi-circular notch that matches the outer diameter of the main body of the extrusion drawing punch 23. Thus, during the process of the extrusion drawing punch 23 completing the downward drawing and extrusion forming of the blank 100, the semi-circular notch and the main body of the extrusion drawing punch 23 can be contacted and matched through the semi-circular notch to separate the blank that is held tightly on the extrusion drawing punch 23 from top to bottom.

[0078] It is understandable that the mating surface formed by the aforementioned shrinking mold 24 and the top side end face of the inner mold body 1201 is also the parting surface of the shell component opening shrinking deformation.

[0079] In some embodiments, the upper mold assembly further includes a support core mold 25 optionally assembled to the upper mold plate 21 on the side facing the lower die 12, the support core mold 25 passing through the conical opening 241. It is understood that the outer diameter of the main body of the aforementioned support core mold 25 should be equal to the inner diameter of the constriction. In a preferred embodiment, the aforementioned support core mold 25 protrudes beyond the conical opening 241, and the support core mold 25 is used to form radial support for the top of the blind hole blank during the shell constriction step.

[0080] In this technical solution, a support core mold 25 is provided that passes through the conical opening 241, which can limit the inner diameter of the top narrowing of the blank 100 and ensure the quality of the narrowing.

[0081] In some implementation methods, see details. Figure 5As shown, the upper mold assembly also includes a punch seat 27 and a punch retaining ring 28, which are stacked sequentially along the direction away from the upper mold plate 21 and located on the side of the upper mold plate 21 closer to the lower mold plate 11. The punch retaining ring 28 is detachably assembled to the bottom end face of the punch seat 27, and a punch collar 29 with a tapered positioning hole (not indicated in the figure) is formed in the central region of the punch retaining ring 28. The top of the main body of the forming reverse extrusion punch 22, the tapered drawing punch 23, and the supporting core mold 25 forms... There is an inverted conical ring (not labeled in the figure, also called a sizing band) that mates with the conical positioning hole. The diameter of the conical positioning hole decreases from top to bottom. The punch seat 27 has a first insertion hole (not labeled in the figure), and the punch retaining ring 28 has a second insertion hole (not labeled in the figure). The diameter of the first insertion hole is larger than the diameter of the second insertion hole. It should be noted that when the forming punch is the aforementioned support core mold 25, the aforementioned punch retaining ring 28 can be replaced by the aforementioned necking mold 24.

[0082] In this technical solution, the tapered positioning hole and the inverted tapered ring on the punch form an axial positioning, which can have a larger contact area, realize the wedge-type installation between the punch and the mounting component, increase the shear resistance of the corresponding punch, and eliminate the phenomenon of poor connection stability that occurs when using threaded connections.

[0083] In some embodiments, the punch collar 29 and the punch retaining ring 28 are separately configured. The materials of the separately configured punch retaining ring 28 and punch collar 29 can be reasonably selected according to actual conditions. For example, the aforementioned punch collar 29 can be made of a material with a lower hardness than the punch retaining ring 28, which can utilize its softer characteristics to provide dimensional compensation for the punch and other related components. At the same time, if one of them is damaged, it can be replaced separately without replacing the whole, reducing mold maintenance costs. It should be noted that the punch retaining ring 28 and punch collar 29 are in a non-high-temperature state during disassembly and assembly, which can avoid contact with the high-temperature punch and avoid safety hazards during manual disassembly and assembly.

[0084] In some embodiments, an upper pad 26 is provided between the upper template 21 and the punch seat 27. The top end face of the main body of the forming punch 22, the tapered drawing punch 23 and the supporting core die 25 can abut against the bottom side end face of the upper pad 26. In this way, the upper pad 26 can be used to physically protect the upper template 21, prevent the top end of each punch from directly contacting the upper template 21 and causing damage to the upper template 21, and further reduce maintenance costs.

[0085] See details Figure 5As shown, the upper template 21, upper backing plate 26, and punch seat 27 are assembled and connected from top to bottom using multiple long bolts (not marked in the figure, but in a specific embodiment, six bolts are arranged in a ring at intervals). When replacing the punch during use, only the aforementioned punch fixing ring 28, punch collar 29, and the corresponding punch need to be disassembled and assembled. There is no need to disassemble and assemble the upper template 21, upper backing plate 26, and punch seat 27, which greatly reduces the weight of disassembly and assembly, facilitates quick disassembly and assembly of the mold, meets the requirements of rapid switching of process flow, and further shortens the production cycle.

[0086] In some embodiments, a plurality of vertical guide components (not labeled in the figure) are provided at intervals between the upper template 21 and the lower template 11 to guide the linear movement of the upper and lower template components toward and away from each other. In a specific embodiment, four vertical guide components are provided in total, evenly spaced at the four corner areas of the upper template 21 and the lower template 11. Each vertical guide component specifically includes a guide post 31 and a guide sleeve 32 that are fitted inside and out and can slide along their axial direction. The guide post 31 is fixedly connected to the lower template 11 through a guide post pressure plate 33, and the guide sleeve 32 is fixedly connected to the upper template 21 through a guide sleeve pressure plate 34.

[0087] In summary, this invention, through the design of a combination structure, combination method, and parting surface of a set of molds, utilizes the method of orderly metal flow control to rationally allocate the distribution of metal flow and deformation, thereby achieving extrusion-necking labor-saving forming and process coupling of thick-walled constricted shells with large height-to-diameter ratios. This overcomes the shortcomings of existing technologies and achieves the goals of low hydrostatic pressure labor-saving extrusion forming, extrusion-necking process coupling, effectively shortening mold changeover time, increasing mold service life, improving component preparation efficiency, and reducing production costs.

[0088] In some embodiments, prior to the extrusion molding step, the blank 100 is heated to the molding temperature and preheated and kept warm. The lower die 12, the forming reverse extrusion punch 22, the tapered drawing punch 23, and the necking die 24 are then uniformly sprayed with lubricant on the portions of the lower die 12, the forming reverse extrusion punch 22, the tapered drawing punch 23, the necking die 24, and the ejector pin 14 that are in contact with the blank 100.

[0089] See details Figure 5 As shown, the upper template 21, upper backing plate 26, and punch seat 27 are assembled and connected from top to bottom using multiple long bolts (not marked in the figure, but in a specific embodiment, six bolts are arranged in a ring at intervals). When replacing the punch during use, only the aforementioned punch fixing ring 28, punch collar 29, and the corresponding punch need to be disassembled and assembled. There is no need to disassemble and assemble the upper template 21, upper backing plate 26, and punch seat 27, which greatly reduces the weight of disassembly and assembly, facilitates quick disassembly and assembly of the mold, meets the requirements of rapid switching of process flow, and further shortens the production cycle.

[0090] In some embodiments, a plurality of vertical guide components (not labeled in the figure) are provided at intervals between the upper template 21 and the lower template 11 to guide the linear movement of the upper and lower template components toward and away from each other. In a specific embodiment, four vertical guide components are provided in total, evenly spaced at the four corner areas of the upper template 21 and the lower template 11. Each vertical guide component specifically includes a guide post 31 and a guide sleeve 32 that are fitted inside and out and can slide along their axial direction. The guide post 31 is fixedly connected to the lower template 11 through a guide post pressure plate 33, and the guide sleeve 32 is fixedly connected to the upper template 21 through a guide sleeve pressure plate 34.

[0091] In summary, this invention, through the design of a combination structure, combination method, and parting surface of a set of molds, utilizes the method of orderly metal flow control to rationally allocate the distribution of metal flow and deformation, thereby achieving extrusion-necking labor-saving forming and process coupling of thick-walled constricted shells with large height-to-diameter ratios. This overcomes the shortcomings of existing technologies and achieves the goals of low hydrostatic pressure labor-saving extrusion forming, extrusion-necking process coupling, effectively shortening mold changeover time, increasing mold service life, improving component preparation efficiency, and reducing production costs.

[0092] The assembly method and assembly sequence of the aforementioned shell mold are described below:

[0093] 1. The upper template 21 is assembled with the upper worktable of the press (not shown in the figure) by fastening bolts. The upper template 21, the upper pad 26 and the punch seat 27 are assembled by internal hex bolts to form a whole.

[0094] 2. The guide sleeve 32, guide sleeve pressure plate 34 and upper template 21 are assembled by internal hex bolts;

[0095] 3. The forming reverse extrusion punch 22, the tapered drawing punch 23, and the supporting core die 25 are respectively wedged into and assembled with the punch collar 29;

[0096] 4. The punch retaining ring 28 and the constricted die 24 with a conical opening 241 are respectively assembled with the punch seat 27 by internal hex bolts;

[0097] 5. The inner mold body 1201 and the outer mold body 1202 are assembled by heating the outer mold body 1202 or freezing the inner mold body 1201;

[0098] 6. The upper concave template 15 and the outer mold body 1202 are assembled by internal hex bolts;

[0099] 7. The lower template 11 is assembled with the lower worktable of the press using fastening bolts;

[0100] 8. The guide post 31, guide post pressure plate 33, and lower template 11 are assembled by internal hex bolts;

[0101] 9. The top rod 14 is inserted into the center hole of the lower template 11;

[0102] 10. The outer mold body 1202 is assembled with the lower pad plate 13 and the lower template 11 by internal hex bolts;

[0103] 11. The pad 122 is placed into the cavity of the lower die 12 and contacts the upper end face of the ejector pin 14;

[0104] 12. The mold guide sleeve 16 is inserted into the annular groove 151 of the upper concave template 15;

[0105] 13. The unloading plate 17 and the upper concave template 15 are assembled by hexagon socket bolts (one end is hinged and the other end can be fixed).

[0106] The following describes the aforementioned forming method of the present invention with reference to a specific embodiment, for preparing a shell component having a single-end opening with a constricted top and a tapered bottom, specifically including the following steps:

[0107] S1. Pre-forming preparation: Heat the cylindrical blank (i.e., the aforementioned blank 100) to the forming temperature; install the mold on the press according to the above-mentioned combination working method, assembly relationship and assembly steps, and preheat and keep it warm for forming reverse extrusion punch 22, lower die 12, and pad 122; evenly spray oil-based graphite lubricant on the contact parts of the forming reverse extrusion punch 22, upper die plate 15, lower die 12 and pad 122 with the blank 100; turn on the circulating cooling water; place the pad 122 into the die cavity (i.e., the aforementioned die cavity 121); then place the heated blank 100 into the cavity formed by the lower die 12 (specifically the inner mold body 1201) and the upper die plate 15, and install the mold guide sleeve 16 in place, as follows. Figure 5 As shown;

[0108] S2. Reverse extrusion deformation process: such as Figure 5 and Figure 6 As shown, the pad 122 fills the cavity formed by the lower die 12 and the upper die 15 from a "V" shape to a "U" shape. After the extrusion process begins, as the forming reverse extrusion punch 22 moves downward, the blank 100 is gradually filled with the cavity and flows upward to generate reverse extrusion flow. When the forming reverse extrusion punch 22 moves downward to the designated position and stops, the blank 100 is a "U" shape with a designated wall thickness and bottom thickness, and the reverse extrusion deformation process is completed.

[0109] S3. Unloading the "U"-shaped billet: (e.g.) Figure 7 As shown, after the reverse extrusion deformation process is completed, the forming reverse extrusion punch 22 is raised, the die guide sleeve 16 is removed, and then the "U" shaped blank is ejected and taken out by the ejector rod 14.

[0110] S4. Change the mold and place the heated "U"-shaped blank inside: (e.g.) Figure 8 As shown, replace the forming reverse extrusion punch 22 with the tapered drawing punch 23, remove the pad 122 and the die guide sleeve 16, install the stripper plate 17 and rotate it to the non-blocking state (as shown). Figure 15 As shown), the mold replacement is completed. Oil-based graphite lubricant is evenly sprayed onto the contact parts of the extrusion cone drawing punch 23, upper concave template 15 and lower concave template 12 with the "U" shaped blank. The circulating cooling water is turned on, and the heated "U" shaped blank is placed into the cavity formed by the lower concave template 12 and the upper concave template 15.

[0111] S5. Deep drawing and extrusion deformation process: such as... Figure 8 and Figure 9 As shown, the removal of the pad 122 causes the cavity formed by the lower die 12 and the upper die plate 15 to change from a "U" shape to a "V" shape, and the stripper plate 17 is rotated to the stop position (as shown). Figure 13 As shown in the figure, after the extrusion process begins, as the extrusion cone drawing punch 23 descends, the "U"-shaped blank gradually fills the cavity and generates a drawing deformation flow. When the extrusion cone drawing punch 23 descends to the designated position and stops, the blank is a "V" shape with a specified wall thickness, bottom thickness and taper, and the drawing extrusion deformation process is completed.

[0112] S6. Unloading of “V” shaped billets: (e.g., ...) Figure 10 As shown, after the deep drawing and extrusion deformation process is completed, the extrusion cone drawing punch 23 is raised and the "V" shaped blank is separated from the extrusion cone drawing punch 23 under the action of the stripper plate 17. Then the stripper plate 17 is rotated to a non-stopping state, and then the "V" shaped blank is ejected and taken out by the ejector rod 14.

[0113] S7. Change the mold and place the locally heated "V"-shaped blank inside: (e.g.) Figure 11 As shown, the extrusion cone drawing punch 23 is replaced with the support core die 25, the punch retaining ring 28 is replaced with the necking die 24, the stripper plate 17 and the upper concave plate 15 are removed, and the support core die 25, the necking die 24 and the lower concave die 12 are evenly sprayed with oil-based graphite lubricant in contact with the "V" shaped blank. The "V" shaped blank that has been locally heated is placed into the cavity formed by the lower concave die 12.

[0114] S8. Shrinking and deformation process: such as Figure 11 , Figure 12 As shown, after the necking deformation process begins, as the support core mold 25 and the necking mold 24 move down to the designated position, the "V" shaped blank gradually necks and completes the necking deformation process, and the shell extrusion and necking are completed.

[0115] S9. Example of shell unloading: as follows Figure 13As shown, after the necking and deformation process is completed, the support core mold 25 and the necking mold 24 are raised, and then the extruded shell of the embodiment is pushed out and taken out by the push rod 14.

[0116] To improve the shrinking deformation effect, the working part of the shrinking mold 24 can be preheated with waste material after cold installation.

[0117] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0118] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A single-station continuous forming method for shell extrusion and necking, characterized in that, The forming process employs a shell forming mold, which includes an upper mold assembly and a lower mold assembly. The lower mold assembly includes a lower template (11) and a lower die (12) disposed thereon. The lower die (12) has a die cavity (121). The upper mold assembly includes an upper template (21) and an extrusion punch and a necking die (24) selectively assembled on the side of the upper template (21) facing the lower die (12). A conical opening (241) with a smaller top and a larger bottom is formed on the bottom end face of the necking die (24). The forming method includes the following steps: Extrusion forming step: Place the blank (100) in the cavity (121) of the lower die (12), and after the extrusion punch is assembled on the upper die plate (21), control the upper die assembly to descend to extrude the blank (100) so that the blank (100) is formed into a blind hole shell with a preset wall thickness and bottom thickness. Shell narrowing step: control the upper mold assembly to rise so that the extrusion punch is dislodged from the cavity of the die cavity (121), remove the extrusion punch from the upper template (21) and assemble the narrowing die (24) onto the upper template (21), control the upper mold assembly to fall again until the conical opening (241) engages with the top of the blind hole shell to form a narrowed shell.

2. The forming method according to claim 1, characterized in that, The following steps are included after the extrusion forming step and before the shell necking step: Local heating step of the shell: heat the top part of the blind hole shell, and then put the blind hole shell with the heated top part back into the cavity (121).

3. The forming method according to claim 1 or 2, characterized in that, The extrusion punch includes a forming reverse extrusion punch (22) and a tapered drawing punch (23). The lower die assembly also includes a pad (122) that can be positioned at the bottom of the die cavity (121). The extrusion forming step specifically includes: After placing the pad (122) at the bottom of the cavity (121), the blank (100) is placed in the cavity (121), and the upper die assembly with the forming reverse extrusion punch (22) is controlled to descend so that the blank (100) is reverse extruded into an intermediate blank with a central blind hole. The intermediate blank and the pad (122) are removed from the cavity (121), and the forming reverse extrusion punch (22) is removed from the upper template (21) and then the extrusion tapered drawing punch (23) is replaced and assembled. The upper die assembly is lowered again to draw and extrude the intermediate blank to form the blind hole shell.

4. The forming method according to claim 3, characterized in that, The lower die (12) includes an inner die body (1201) and an outer die body (1202) fitted onto the radial outer wall of the inner die body (1201). The die cavity (121) is formed on the inner die body (1201). And / or, the bottom of the die cavity (121) is a cone shape with a larger top and a smaller bottom, and the longitudinal section shape of the pad (122) is a cone shape that matches the bottom of the cavity.

5. The forming method according to claim 4, characterized in that, A cooling channel (1203) is formed inside the outer mold body (1202). The cooling channel (1203) is constructed on the mating ring surface of the inner mold body (1201) and the outer mold body (1202). The cooling channel (1203) has an inflow channel (1204) and an outflow channel (1205). In the extrusion molding step, cooling fluid is introduced into the cooling channel (1203) and a circulation is formed. And / or, a lower pad (13) is provided between the outer mold body (1202) and the lower template (11). A push rod through hole (131) communicating with the bottom of the cavity of the die cavity (121) is formed on the lower pad (13). The push rod (14) passes through the lower template (11) and the push rod through hole (131) in sequence. The push rod (14) has a limit that protrudes outward along its radial direction. Position ring (141), the push rod (14) has a push position and a block position and can be driven to move up and down to switch between the push position and the block position. When the push rod (14) is in the push position, the limit ring (141) abuts against the bottom side of the inner mold body (1201). When the push rod (14) is in the block position, the limit ring (141) abuts against the top side of the lower mold plate (11) and the top end of the push rod (14) is inserted into the bottom of the cavity of the cavity (121). When the intermediate blank, blind hole shell and narrowed shell are unloaded from the cavity of the cavity (121), the push rod (14) is controlled to be in the push position. When force is applied to the blank (100), intermediate blank, blind hole shell and narrowed shell, the push rod (14) is controlled to be in the block position.

6. The forming method according to claim 5, characterized in that, The upper concave template (15) is detachably assembled on the top side end face of the outer mold body (1202). The upper concave template (15) has a first central through hole corresponding to the top side cavity opening of the concave mold cavity (121). The working ends of the forming reverse extrusion punch (22) and the tapered drawing punch (23) can be inserted into the concave mold cavity (121) through the first central through hole. The lower mold assembly also includes a die guide sleeve (16) and a stripper plate (17). A second central through hole is formed in the die guide sleeve (16). The upper opening of the second central through hole is straight. The diameter is equal to the outer diameter of the main body of the forming reverse extrusion punch (22). When the forming reverse extrusion punch (22) is assembled on the upper template (21), the die guide sleeve (16) is assembled on the upper concave template (15) and coaxially arranged with the first central through hole. When the extrusion tapered drawing punch (23) is assembled on the upper template (21), the unloading plate (17) is assembled on the upper concave template (15) so that the blank (100) can be removed from the extrusion tapered drawing punch (23) during the process of the extrusion tapered drawing punch (23) being raised.

7. The forming method according to claim 6, characterized in that, The upper mold assembly also includes a support core mold (25) optionally assembled on the side of the upper mold plate (21) facing the lower die (12), the support core mold (25) passing through the conical opening (241), the support core mold (25) being used to form radial support for the top of the blind hole blank during the shell narrowing step.

8. The forming method according to claim 7, characterized in that, The upper mold assembly also includes a punch seat (27) and a punch retaining ring (28) stacked sequentially along the direction away from the upper mold plate (21) and located on the side of the upper mold plate (21) closer to the lower mold plate (11). The punch retaining ring (28) is detachably assembled on the bottom end face of the punch seat (27), and a punch collar (29) with a tapered positioning hole is formed in the central area of ​​the punch retaining ring (20). The top of the main body of the forming reverse extrusion punch (22), the tapered drawing punch (23) and the support core mold (25) is formed with an inverted tapered ring that cooperates with the tapered positioning hole. The diameter of the tapered positioning hole decreases from top to bottom. The punch seat (27) has a first insertion hole, and the punch retaining ring (28) has a second insertion hole. The diameter of the first insertion hole is larger than the diameter of the second insertion hole.

9. The forming method according to claim 8, characterized in that, The punch collar (29) and the punch fixing ring (28) are separately provided; and / or, an upper pad (26) is also provided between the upper template (21) and the punch seat (27), and the top end face of the main body of the forming reverse extrusion punch (22), the tapered drawing punch (23) and the supporting core mold (25) can abut against the bottom side end face of the upper pad (26).

10. The forming method according to claim 7, characterized in that, Before the extrusion molding step, the blank (100) is heated to the molding temperature and preheated and kept warm. The lower die (12), the forming reverse extrusion punch (22), the tapered drawing punch (23), and the necking die (24) are uniformly sprayed with lubricant on the parts of the lower die (12), the forming reverse extrusion punch (22), the tapered drawing punch (23), the necking die (24), and the ejector pin (14) that are in contact with the blank (100).

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