Pressing method for steel and use of steel

Abstract

Examples of a method of thermoforming a structural component are provided. The method includes heating a blank made of ultra-high strength steel having an aluminum coating, and shaping the heated blank in a multi-step production line or equipment.

Description

Technical Field

[0001] This application claims the benefit of application No. 23382824.3, filed on August 7, 2023.

[0002] This disclosure relates to methods for manufacturing hot-formed structural components and the use of ultra-high strength steel in hot-forming processes. Background Technology

[0003] In the field of vehicle construction, the development and implementation of lightweight materials and components are becoming increasingly important to meet lightweight construction standards. The need for weight reduction is particularly driven by the goal of reducing CO2 emissions. The growing concern for passenger safety has also led to the adoption of materials that improve vehicle integrity during a collision while also enhancing energy absorption.

[0004] A process known as Hot Forming Hardening (HFDQ) (also called Hot Stamping or Press Hardening) uses, for example, boron steel sheet to produce stamped parts with the properties of ultra-high strength steel (UHSS), having tensile strengths of, for example, 1,500 MPa or higher. This increased strength compared to other materials allows for the use of thinner gauge materials, resulting in a reduction in weight compared to conventional cold-stamped low-carbon steel parts.

[0005] To improve corrosion protection before, during, or after hot stamping processes, coatings can be applied. For example, the use of Al-Si coatings or Zn coatings is known.

[0006] Depending on the composition of the steel base material, the blank may need to be quenched (i.e., rapidly cooled) to obtain high tensile strength. Examples of steel materials that can be hardened by cooling to room temperature with air at a relatively low cooling rate are also known. These steels may be referred to as "air-hardenable" steels.

[0007] Hot stamping can be performed by heating a blank to be hot-formed to a predetermined temperature, such as to or above the austenitizing temperature, via a furnace system, to reduce the strength of the blank, thus enabling the hot stamping process. The heated blank can be formed, for example, by a pressing system having a lower temperature (e.g., room temperature) and temperature control compared to the blank, thus allowing the forming process and heat treatment using the temperature difference to be performed.

[0008] The hot stamping process may include a conveying or transporting device that transfers heated blanks from the furnace to a pressing tool configured to press the blanks. Upstream of the furnace system, a cutting system may be provided for cutting blanks directly from the steel coils.

[0009] The use of multi-step pressing equipment for manufacturing thermoformed components is known. This multi-step pressing equipment may include multiple tools configured to perform different operations on different blanks simultaneously. With such an arrangement, multiple blanks can undergo different manufacturing steps simultaneously during each stroke of the pressing equipment. The efficiency and performance of multi-step equipment can be superior to systems employing multiple different machines or devices for different manufacturing steps (e.g., laser trimming or hard cutting).

[0010] When using zinc-coated steel blanks, the blanks need to be cooled to a certain temperature before the hot forming process to reduce or minimize problems such as microcracks. Once the blanks have cooled down, they are transferred from an external pre-cooling tool to a multi-step pressing device.

[0011] US 2022 / 0258223 discloses a pressing apparatus and method for manufacturing thermoformed structural parts. The apparatus includes a fixed lower body and a movable upper body. The apparatus includes a cooling tool and a pressing tool disposed downstream of the cooling tool, as well as a blank transfer mechanism for transferring a blank from the cooling tool to the pressing tool. The cooling tool has an upper gas cooling tool connected to the movable upper body and / or a lower gas cooling tool connected to the fixed lower body. The pressing tool includes an upper pressing die connected to the upper body and a lower pressing die connected to the lower body.

[0012] EP 3 437 750 A1 discloses an example of a method for hot-forming structural components. The method involves heating a blank made of ultra-high strength steel with an aluminum coating and forming the heated blank in a multi-step apparatus.

[0013] EP3067129 A1 discloses a pressing system for manufacturing thermoformed structural components. The system includes a fixed lower body, a movable upper body, and a mechanism configured to provide an upward and downward pressing process of the movable upper body relative to the fixed lower body. The system further includes a cooling / heating tool configured to cool and / or heat a previously heated blank having locally different microstructures and mechanical properties. The cooling / heating tool includes: upper and lower mating dies, and the upper and lower dies include two or more die blocks and a pressing tool. The two or more die blocks are adapted to operate at different temperatures corresponding to regions of the blank having locally different microstructures and mechanical properties. The pressing tool is configured to stretch the blank, and the pressing tool is arranged downstream of the cooling / heating tool. This system is particularly designed to create "soft zones" to improve ductility and energy absorption in specific regions of components made of Usibor® 1500 (2MnB5). Using 22MnB5 boron steel requires specific temperature control between different die blocks of the cooling / heating tool and downstream post-treatment tools to obtain different microstructures and corresponding different properties.

[0014] EP3067128 A1 discloses a multi-step pressing system for manufacturing thermoformed structural components. The system includes a fixed lower body, a movable upper body, and a mechanism configured to provide an upward and downward pressing process of the movable upper body relative to the fixed lower body. The system further includes a cooling tool configured to cool a pre-heated blank. The cooling tool includes: upper and lower mating dies, and the lower die is connected to the lower body by one or more lower biasing elements and / or the upper die is connected to the upper body by one or more upper biasing elements. The system further includes a pressing tool configured to stretch the blank, and the pressing tool is arranged downstream of the cooling tool. This system is particularly designed for use with zinc-coated ultra-high-strength steel.

[0015] One disadvantage associated with using galvanized steel is that a zinc oxide layer may form on the blank. In many applications, the zinc oxide layer needs to be removed or reduced after the manufacturing process. For example, shot peening can be used to partially or completely remove the zinc oxide layer. Also, components with an AlSi coating can generally be welded better than those with a Zn coating.

[0016] The most commonly used steel in press hardening processes is coated 22MnB5 or similar materials. For example, Usibor® 1500 is commercially available from ArcelorMittal™, MBW-W® 1500 from ThyssenKrupp, and other steel manufacturers offer other steels. After heating to above Ac3 temperature (e.g., after heating to about 900°C), the heated blank can be formed and quenched. Quenching can be performed above the critical cooling rate of about 27°C / s to obtain a substantially fully martensitic microstructure and an ultimate tensile strength of about 1,500 MPa.

[0017] Recently, in-depth research has been conducted on hot stamping of even higher grades of steel. Specifically, 37MnB5 steel or similar steels have a higher carbon content than 22MnB5 and can achieve an ultimate tensile strength of 2,000 MPa or even higher after hot stamping. Usibor® 2000, commercially available from ArcelorMittal™, and MBW-K® 1900 (34MnB4 steel), commercially available from ThyssenKrupp™, are two examples of this type of steel.

[0018] Such steels can be referred to as "second-generation" pressure-hardening steels. This new generation of pressure-hardening steels can be considered, in this context, as boron-manganese steels suitable for hot stamping, with a higher carbon content than 22MnB5, and achieving an ultimate tensile strength greater than 1.500 MPa, specifically at least 1.700 MPa, when fully martensitized after pressure hardening. The silicon content is typically lower than that of first-generation pressure-hardening steels. Examples include 20MnCr, 28MnB5 steels (e.g., Docol PHS1800), 30MnB5 (e.g., SQ1800), 34MnB5 or 34MnB4 (e.g., MBW 1900), and 37MnB5 or 37MnB4 (e.g., Usibor2000 HPF 2000, Docol PHS2000, phs ultraform 2000). The new generation of steel can also be described as PHS 1.700 or higher, namely PHS 1.700, PHS 1.800, PHS 1.900 or PHS 2.000, more specifically PHS 1.900 or higher.

[0019] However, another characteristic of this steel is its brittleness after hot stamping and its very low ductility. This means that post-processing operations, including, for example, joining, are more complex, and energy absorption is limited in the event of impact or collision. This is one of the reasons why, despite their high tensile strength and even the potential to further reduce the weight of automotive structures, these steels have had virtually no practical application in automotive structures to date.

[0020] This disclosure seeks to provide improvements to the hot stamping process for high-grade steel, specifically improvements in multi-step processes and equipment. Summary of the Invention

[0021] In a first aspect, a method is provided for thermoforming structural parts in a multi-step production line. The multi-step production line includes a pressing tool configured for stretching a blank, wherein the pressing tool includes an upper pressing die and a lower pressing die. The production line also includes a first post-pressing tool disposed downstream of the pressing tool and configured to perform a first post-pressing operation, and the first post-pressing tool includes an upper first post-pressing die and a lower first post-pressing die. The upper pressing die and the upper first post-pressing die are configured to operate concurrently. The production line also includes a conveying system for transferring the blank from the pressing tool to the first post-pressing tool.

[0022] The method includes providing a pressable hardenable boron steel blank, preferably having a carbon content of 0.32-0.45 wt%, a manganese content of 0.6-1.5 wt%, and a boron content of 0.003-0.006 wt%, and further includes heating the blank to above an austenitizing temperature. The method also includes stretching the heated blank in a pressing tool and transferring the formed blank from the pressing tool to a first post-pressing tool. The temperature of the blank before stretching is at least 600°C, and the temperature of the formed blank before the first post-pressing operation is 500°C to 650°C, and the temperature at the end of the first post-pressing operation is 400°C to 550°C.

[0023] Based on this aspect, an efficient method for manufacturing structural steel components with increased carbon content is provided, in which one or more post-processing steps can be combined. Production line output can be increased or maximized. Furthermore, structural components with desired mechanical properties can be obtained: combined with an A50 elongation of 5% or higher, specifically 5-6%, an ultimate tensile strength greater than 1.600 MPa, for example 1.700 MPa-1.900 MPa, can be achieved. The high ultimate tensile strength provides the possibility of reducing the thickness of the components and thus their weight. Compared to conventional pressure hardening of this steel, the increased ductility can improve behavior under impact / collision conditions and facilitate further post-processing.

[0024] Yield strength, ultimate tensile strength, and A50 elongation can be measured according to the standard tensile strength test of a metallic specimen as defined, for example, in ISO 6892-1. A50 elongation refers to the elongation at break of a test specimen with an initial length of 50 mm (as opposed to, for example, A80).

[0025] In any of the examples disclosed herein, the pressable hardenable boron steel blank may be coated with an aluminum-silicon (AlSi) coating. Because ultra-high strength steel blanks with an AlSi coating can be used, shot peening to partially or completely remove the zinc oxide layer is not required.

[0026] Here, a multi-step production line can be considered as a line in which several processes are performed simultaneously on different blanks / parts. The operations of these different steps are coordinated: the movement of different tools is coordinated because the cycle time of each stroke is the same. In particular, the movement of different tools can be synchronized. In some examples, different processes and tools can be integrated into a single pressing device, or into a separate device.

[0027] This article refers to pressure-hardening boron steels with a carbon content of 0.32-0.45 wt%, specifically 0.32-0.4 wt%, more specifically 0.32-0.38 wt%, a manganese content of 0.6-1.5 wt%, specifically 0.6-1.4 wt%, and a boron content of 0.003-0.006 wt%, specifically 0.004-0.005 wt%. In reality, even when manufactured by the same steel supplier using the same manufacturing process, slight variations may exist between different steel coils. In fact, even slight variations may exist between blanks cut from the same steel coil. Suitable steels include, for example, 37MnB5 steel, 38MnB5 steel, 34MnB5 steel, and 34MnB4 steel.

[0028] A typical composition of the tested 34MnB4 steel is summarized as follows by weight percentage (the balance being iron (Fe) and impurities): Carbon (C) (%) 0.35 Silicon (Si) (%) 0.8 Manganese (Mn) (%) 0.96 Chromium (Cr) (%) 0.19 Molybdenum (Mb) (%) 0.18 Phosphor (P) 0.012% Sulfur (S) (%) 0.0002 Titanium (Ti) + Niobium (Nb) 0.055% Aluminum (Al) 0.03% Boron (B) (%) 0.002% Nitrogen (N) 0.003% Nickel (Ni) 0.01% Usibor ® 2000 can typically be described as 37MnB5 steel. (Usibor) ®The composition of 2000 is summarized as follows by weight percentage (the balance being iron (Fe) and impurities): Maximum carbon (C) (%): 0.36 Maximum silicon (Si) (%): 0.8 Maximum manganese (Mn) (%): 0.8 Maximum phosphorus (P) (%): 0.03 Maximum sulfur (S) (%): 0.01 Aluminum (Al) (%): 0.01-0.06 Maximum titanium (Ti) (%): 0.07 Maximum niobium (Nb) (%): 0.07 Maximum copper (Cu) (%): 0.20 Maximum boron (B) (%): 0.005 Maximum chromium (Cr) (%): 0.50 Maximum molybdenum (Mb) (%): 0.50 MBW-K® 1900 is generally described as 34MnB4 steel. The composition of MBW-K® 1900 is summarized as follows by weight percentage (balance: iron (Fe) and impurities): Maximum carbon (C) (%): 0.38 Maximum silicon (Si) (%): 0.4 Maximum manganese (Mn) (%): 1.4 Maximum phosphorus (P) (%): 0.025 Maximum sulfur (S) (%): 0.01 Minimum aluminum (Al) (%): 0.015 Maximum titanium (Ti) (%): 0.05 Maximum niobium (Nb) (%): 0.07 Maximum boron (B) (%): 0.005 Maximum chromium (Cr) + molybdenum (Mb) (%): 0.50 MBW ® 1900 is another manganese-boron steel from ThyssenKrupp™, which can achieve an ultimate tensile strength of 1900 MPa. It is commercially available, has an aluminum-silicon coating, and is suitable for hot stamping and the methods disclosed herein. MBW ® The chemical composition of 1900 is summarized as follows by weight percentage (the balance being iron (Fe) and impurities): Maximum carbon (C) (%): 0.38 Maximum silicon (Si) (%): 0.40 Maximum manganese (Mn) (%): 1.40 Maximum phosphorescence (P) (%): 0.025 Maximum sulfur (S) (%): 0.010 Minimum aluminum (Al) (%): 0.1 Maximum niobium (Nb) (%): 0.05 Maximum titanium (Ti) (%): 0.05 Maximum chromium and molybdenum (Cr+Mo) (%): 0.50 Maximum boron (B) (%): 0.005 B1800HS is another boron steel that can achieve an ultimate tensile strength of approximately 1800 MPa and is suitable for hot stamping and the methods disclosed herein. The chemical composition of B1800HS is summarized as follows in weight percentage (balance: iron (Fe) and impurities): Carbon (C) (%): 0.28-0.35 Maximum silicon (Si) (%): 0.5 Manganese (Mn) (%): 1.0-1.8 Maximum phosphorescence (P) (%): 0.025 Maximum sulfur (S) (%): 0.010 Aluminum (Al) (%): 0.01-0.06 Maximum titanium (Ti) (%): 0.05 Maximum boron (B) (%): 0.0050 Maximum chromium, molybdenum, and niobium (Cr + Mo + Nb) (%): 0.80 Another suitable steel is CR1900T-MB-DS. Its chemical composition, summarized by weight percentage, is as follows (balance: Fe and impurities): Carbon (C) (%): 0.30-0.38 Maximum silicon (Si) (%): 0.8 Manganese (Mn) (%): 2.0 Maximum chromium (Cr): 0.25% Maximum phosphorescence (P) (%): 0.03 Maximum molybdenum (Mo): 0.25 Maximum sulfur (S) (%): 0.005 Aluminum (Al) (%): 0.01-0.08 Maximum titanium (Ti) + niobium (%): 0.20 Boron (B) (%): 0.0010-0.0050 Maximum nickel (Ni): 0.10 Maximum nitrogen (N): 0.01 In the example, the blank can be heated above the Ac3 temperature, specifically to 870°C-930°C, and more specifically to 900°C-930°C. Heating can be carried out, in particular, in a furnace located upstream of a multi-step production line.

[0029] In some examples, the multi-step production line also includes a second post-pressing tool disposed downstream of the first post-pressing tool and configured to perform a second post-pressing operation. This second post-pressing tool includes an upper second post-pressing die and a lower second post-pressing die, wherein the upper second post-pressing die is configured to operate in conjunction with the upper die and the upper first post-pressing die. The conveying system is further configured to transfer the formed blank from the first post-pressing tool to the second post-pressing tool. In several examples, the blank temperature at the end of the second post-pressing operation can be between 350°C and 450°C. The second post-pressing tool may include a temperature control system comprising, for example, thermocouples and heaters and / or cooling channels within the tool, to control the blank temperature, particularly ensuring that the blank temperature does not drop too much or too quickly. Further operations can also be performed at temperatures between 350°C and 450°C.

[0030] In some examples, the multi-step production line also includes one or more additional tools disposed downstream of the second post-pressing operation tool, which are configured to operate in conjunction with the pressing tool and the first and second post-pressing tools. Several different tools may be provided in the multi-step production line, including one or more tools for trimming, one or more tools for creating holes, one or more tools for cutting, etc. In some examples, the additional tools may include tools for re-pressing, i.e., tools that perform further steps to form the already deformed blank.

[0031] In some examples, the final additional tooling can be a re-stamping tool. The temperature of the formed blank before re-stamping can be, for example, 250°C to 350°C. The temperature of the formed blank can be high enough to maintain the forgeability of the material and avoid unnecessary tool wear.

[0032] In the example, the operating cycle of the pressing tool can be from 2 to 5 seconds, specifically from 2.5 to 4 seconds, and more specifically approximately 4 seconds. An operating cycle of approximately 4 seconds maintains high throughput and allows for a shutdown time of, for example, 0.5 seconds at the bottom dead center of the press. Such a shutdown time allows for increased temperature control during the process.

[0033] In the example, the transfer time between the pressing tool and the first post-pressing tool can be from 1 to 3 seconds, specifically from 1.5 to 2.5 seconds, and more specifically approximately 2 seconds. The transfer of blanks can take place or at least begin before the upper dies reach their upper positions.

[0034] In some examples, the resulting components can be further subjected to a bake-hardening process. That is, the structural components can be subjected to a temperature of approximately 180°C over a period of approximately 20 minutes. The bake-hardening process can further improve the yield strength of the resulting components, while the ultimate tensile strength remains substantially the same.

[0035] In some examples, the multi-step production line includes a multi-step tool comprising a fixed lower body, a movable upper body, and mechanisms configured to provide an upward and downward pressing process of the movable upper body relative to the lower body. An upper pressing die is connected to the movable upper body, a lower pressing die is connected to the fixed lower body, a first upper post-pressing die is connected to the movable upper body, and a first lower post-pressing die is connected to the fixed lower body. The multi-step production line can be incorporated into a multi-step device that includes a pressing tool in a single pressing device and additional post-pressing tools.

[0036] By integrating the pressing tool and the upper mold of the auxiliary tool into a movable upper body, the transfer time between the pressing tool and the auxiliary tool can be reduced, thereby optimizing the process and increasing productivity. Furthermore, the temperature of the blank can be increased in different steps of the process.

[0037] In some examples, the mold for the cooling tool may include channels for guiding cooling water. The mold for the cooling tool may alternatively or additionally include channels for guiding air.

[0038] In some examples, a blank can be heated to an austenitizing temperature of Ac3, and cooling the fully heated blank includes cooling the blank to a temperature of 600°C-800°C, specifically 650°C-700°C.

[0039] In some examples, the multi-step apparatus may also include a first post-operation tool downstream of the pressing tool, the first post-operation tool including upper and lower first post-operation dies, the upper and lower first post-operation dies including one or more working surfaces facing the formed blank in use, and the lower first post-operation die being connected to the lower body and the upper first post-operation die being connected to the upper body.

[0040] In some examples, the first post-pressing tool may include a temperature control system for controlling the temperature of the formed blank during the first post-operation, the temperature control system optionally including thermocouples in the upper and lower first post-operation dies.

[0041] In some examples, the mold of the first post-pressing tool may include channels for guiding cooling water or cooling air. In some examples, the mold of the first post-pressing tool may include one or more heaters or channels for conducting heat with a liquid or for conducting heat.

[0042] In another aspect, components are provided that can be obtained by any method disclosed herein. Attached Figure Description

[0043] Non-limiting examples of this disclosure will now be described with reference to the accompanying drawings, in which: Figure 1 This schematically illustrates a multi-step production line based on an example. Figure 2 An example of the temperature of a blank during the production process according to an example of this disclosure is schematically shown; and Figure 3 A multi-step apparatus that can be used in an example of the method according to this disclosure is illustrated schematically. Detailed Implementation

[0044] Figure 1 This schematically illustrates a multi-step production line based on an example. Figure 1 The diagram schematically illustrates an example of a method for thermoforming structural components in a multi-step production line.

[0045] A pressure-hardening boron steel coil 10. The pressure-hardening boron steel can be used, having a composition of 0.32-0.45% by weight, 0.6-1.5% by weight manganese, and 0.003-0.006% by weight boron. A punching device 20 can cut blanks of suitable size from the coil 100. The steel has an aluminum-silicon coating.

[0046] The blank may preferably have a thickness of 0.8 mm to 2 mm, specifically 1 mm to 1.6 mm. In some examples, the steel may be 34MnB4 or 37MnB5 steel.

[0047] In specific examples, the steel may have 0.34-0.4% by weight of carbon, specifically 0.34-0.39% by weight, and more specifically 0.34-0.38% by weight. The steel may also have 0.8-1.4% by weight of manganese. The steel may have 0.003-0.005% by weight, specifically 0.004-0.005% by weight of boron. In specific examples, the steel may have 0.3-0.9% by weight, specifically 0.4-0.8% by weight of silicon.

[0048] The blank can be supplied to furnace 30. The blank can be heated above the austenitizing temperature, particularly above the Ac3 temperature. In a specific example, the blank can be heated in the furnace for 5 to 10 minutes and can be heated to about 870-930°C, specifically 900-930°C.

[0049] After leaving furnace 30, the heated blank can be transferred to production line 100. Figure 1 The example production line 100 includes a pressing tool 50 configured for stretching blanks.

[0050] The pressing tool 50 includes an upper pressing die 52 and a lower pressing die 54. The blank can be positioned between the upper pressing die 52 and the lower pressing die 54. The upper pressing die 52 can be processed upward and downward relative to the lower pressing die 54 to deform the previously heated blank.

[0051] Production line 100 also includes a first post-pressing tool 60, which is arranged downstream of pressing tool 50 and configured to perform a first post-pressing operation on the formed blank (the blank that has already undergone a stretching process in the pressing tool). The first post-pressing tool includes an upper first post-pressing die 62 and a lower first post-pressing die 64. The upper pressing die 52 and the upper first post-pressing die 62 are configured to operate in unison. In particular, the upward-downward movement of the upper first post-pressing die 62 can be synchronized with the upward-downward movement of the upper pressing die 52.

[0052] Production line 100 also includes a conveying system for transferring the formed blank from pressing tool 50 to a first post-pressing tool 60. In this particular example, multiple conveying robots with grippers or suction units are provided. The conveying robot 44 can grip the deformed blank after it has been stretched in pressing tool 50 and place it in the first post-pressing tool 60.

[0053] The terms "post-pressing tool" and "post-pressing operation" refer to any tool or operation located downstream of the pressing tool, respectively. The first post-pressing tool 60 may be, for example, a trimming tool for trimming one or more edges of a deformed blank.

[0054] The example production line 100 also includes a second post-pressing tool 70, which includes a second upper post-pressing die 72 and a second lower post-pressing die 74. The upper post-pressing die 72 is configured to operate in conjunction with the first upper post-pressing die 62 and the upper pressing die 52; in particular, the movement of the upper die can be synchronized.

[0055] Another transfer robot 46 can clamp the blank after the first post-pressing operation and place it in the next post-pressing tool. Examples of the second post-pressing tool could be a tool for cutting or a tool for piercing or creating holes.

[0056] In this particular example, an auxiliary tool 80 is provided, comprising an upper die 82 and a lower die 84. The upper die 82 can be configured to operate uniformly and, specifically, in synchronization with other upper dies. A transfer robot 48 can transfer the blank from the second post-pressing tool 70 to the auxiliary tool 80. After final operation at tool 80, the blank can be transferred and stacked by a suitable robot 49.

[0057] It should be clear that in other examples, different tools and different numbers of tools may be provided. In a specific example, the production line may include six tools, including a pressing tool. The last tool in the production line may be a re-stamping tool to provide the final shape of the part.

[0058] Figure 1 The production line shown can be used to manufacture various structural components. In a specific example, structural components with a length and width greater than 1 meter can be manufactured in such a production line. In some examples, integral door rings (door rings made of a single, integrally formed body) can be manufactured in such a production line. Integral door rings can be, for example, single door rings (extending from post A to post B, or from post B to post C) or double door rings (extending from post A to post C).

[0059] It can be based on Figure 1 Other large structural components manufactured in production line 100 include, for example, an integral roof ring, a buffer beam assembly including a buffer beam and a pedestrian beam, an integral ring surrounding the battery box, a rear frame structure including a rear guide rail and crossbeam as an integral structure, and others.

[0060] These large structural components can be efficiently manufactured using hot stamping processes. Due to the size of these components, it is difficult to integrate different tools into a single pressing device. However, this method and system can also be used for other pressable components, such as B-pillars, A-pillars, hinge pillars, bumper beams, etc.

[0061] In some examples, the blank may consist of multiple smaller blanks or sub-blanks. Some sub-blanks may be joined to other sub-blanks in a butt joint of a weld bar (TWB). Alternatively, or additionally, these sub-blanks may partially overlap each other to form an overlapping region with increased thickness compared to other regions. The region with increased thickness may be selected to locally reinforce the structural component. The increased thickness in these regions can cause increased heating time in the furnace. During the stretching operation, and in subsequent processes, the overlapping region may cool more slowly unless specific measures are taken.

[0062] In some examples, biasing elements (such as springs) can be integrated into these upper and / or lower pressing dies, such that certain matching die blocks of the pressing tool (a pair of die blocks of the upper pressing tool and the die blocks of the lower pressing tool facing each other) enter contact with the blank before the other die blocks enter contact. In other words, the selection of these die blocks can close earlier than other die blocks.

[0063] In mold blocks that were established earlier, cooling can begin earlier and can be faster than in other mold blocks. If overlapping areas need to be cooled more quickly, offset mold blocks can be used for those areas. Additionally or optionally, one or more mold blocks can be integrated with heating devices to prevent cooling from being too rapid.

[0064] A method for hot-formed structural components includes heating a blank to a temperature above the austenitizing temperature, such as 900-920°C. The method also includes stretching the heated blank in a pressing tool 50 and transferring the blank from the pressing tool 50 to a first post-pressing tool 60.

[0065] Before stretching the blank, the blank temperature is at least 600°C, specifically at least 650°C. At temperatures below 600°C, stripes form in the coating for stretching. At temperatures of 600°C or higher, the coating is satisfactory after the thermoforming process.

[0066] Before stretching the blank, the blank temperature can specifically be between 700°C and 800°C. The blanks can begin cooling from the moment they leave the furnace and during the transfer from the furnace to the pressing tool. In one example, the transfer from the furnace to the pressing tool may take approximately 4 seconds.

[0067] The temperature of the blank before the first post-pressing operation can be 500°C to 600°C, for example, about 550°C. And the temperature of the blank at the end of the first post-pressing operation can be 400°C to 500°C, for example, about 450°C.

[0068] In the example shown, the temperature of the blank is 350°C to 450°C at the end of the second post-pressing operation.

[0069] The operation cycle of the compression tool (and other tools) can be 2 to 5 seconds, specifically 2.5 to 4.5 seconds, and more specifically approximately 4 seconds. The transfer time between the compression tool and the first subsequent compression tool (and between other tools) can be 1 to 3 seconds, specifically 1.5 to 2.5 seconds, and more specifically approximately 2 seconds.

[0070] It has been found that more gradual cooling of steel, as illustrated in this paper, provides high ultimate tensile strength, combined with increased ductility. Simultaneously, the manufacturing process is highly efficient. In these examples, the average cooling rate from the initial pressing step to the Ms temperature (e.g., approximately 350°C) can be less than 20°C / s, specifically 15°C / s or lower. The final cooling from the Ms temperature to the Mf temperature can be even lower, for example, 10°C / s or lower.

[0071] The final tool 80 can be a re-stamping tool. The temperature of the blank before re-stamping can be between 250°C and 350°C. In the re-stamping tool, the blank can be cooled to below 200°C. Re-stamping can be used to avoid or reduce tolerances and geometric deviations from the intended design and to provide structural parts with precisely defined geometries. Suitable temperature control systems, including heaters and / or cooling systems, can be provided in the pressing tool and all other tools. Such systems can be set in the upper and / or lower dies.

[0072] In particular, any of these tools may include channels for conducting heat transfer media. Specifically, such channels may be cooling channels for conducting cold water. After cooling the corresponding mold, the heated water can be cooled again via a heat exchanger. Any of these tools may alternatively or additionally include a heater, such as an electric heater, to ensure that the blank does not cool down too quickly.

[0073] Figure 2 The temperature distribution of the blank as it leaves the furnace and passes through different tools on the production line is schematically shown. Figure 2 In the example, the temperature of the blank can be reduced from approximately 920°C-930°C to approximately 750°C before the stretching operation in the pressing tool 50.

[0074] Prior to the first post-pressing operation in tool 60, the temperature is reduced to approximately 550°C. The cooling rate for the pressing operation can be approximately 50°C / s.

[0075] The temperature can then be reduced to approximately 450°C during the first post-pressing operation and before the second post-pressing operation. The cooling rate in this particular section can be approximately 25°C / s.

[0076] In the second post-pressing tool 70 and before the additional tool 80, the temperature can be reduced to approximately 400°C at a cooling rate of approximately 12.5°C / s. In the additional tool 110, the temperature can be further reduced to 350°C at a cooling rate of approximately 12.5°C / s.

[0077] In this particular example, the last tool 120 can be a re-stamping tool. The temperature of the blank can be further cooled in the re-stamping tool.

[0078] Experimental results for steels including 37MnB5 and 34MnB4 steels yielded the following: Structural components obtained by this method can have an ultimate tensile strength greater than 1.600 MPa, specifically 1.600 MPa–1.900 MPa, more specifically 1.600 MPa–1.800 MPa, more specifically 1.700–1.800 MPa, or approximately 1.700 MPa. Simultaneously, an A50 elongation of 5% or greater can be obtained. The obtained structural components can have a yield strength of 1.000 MPa or greater, specifically 1.100–1.400 MPa or 1.100–1.300 MPa. In three-point bending tests, bending angles of 40–55°, specifically approximately 50°, can be observed in two directions.

[0079] In some examples, the resulting structural components can be further subjected to a bake-hardening process. The bake-hardening temperature can be between 170°C and 200°C, and the bake-hardening time can be between 15 and 25 minutes. Under bake-hardening conditions, the yield strength of the structural components can increase to 1.050 MPa or greater, specifically 1.200 MPa or greater. This increases the material's energy absorption and toughness. These results have been experimentally confirmed for the aforementioned steel.

[0080] Figure 3 A multi-step apparatus that can be used in an example of a method according to this disclosure is schematically illustrated. The multi-step tool 90 includes a fixed lower body 88, a movable upper body 86, and a mechanism (not shown) configured to provide an upward and downward pressing process of the movable upper body 86 relative to the lower body 88.

[0081] The upper pressing mold 52 is connected to the movable upper body 86, the lower pressing mold 54 is connected to the fixed lower body 88, the first upper rear pressing mold 62 is connected to the movable upper body 86, and the first lower rear pressing mold 64 is connected to the fixed lower body 88.

[0082] Similarly, in this example, the upper mold 72 of the second rear pressing tool is connected to the movable upper body 86, and the lower mold 74 of the second rear pressing tool is connected to the fixed lower body 88.

[0083] Similarly, the upper mold 82 of the auxiliary tool can be connected to the movable upper body 86, and the lower mold 84 of the auxiliary tool can be connected to the fixed lower body 88. Therefore, all the upper molds 52, 62, 72 and 82 move in unison toward and away from the lower molds 54, 64, 74 and 84, respectively.

[0084] The fixed lower body 88 can be a large piece of metal. In this particular example, the fixed lower body 88 can be stationary. In some examples, a mold buffer pad (not shown) may be provided integrated into the fixed lower body 88. The buffer pad may be configured to receive and control the force of the blank holder. The movable upper body 86 can also be a solid sheet of metal. The movable upper body 86 provides stroke cycles (up and down movement).

[0085] The pressing system can be configured to perform approximately 15 strokes per minute, so each stroke cycle can be approximately 4 seconds. In other examples, the stroke cycles can be different. In a multi-step pressing system, all operations forming on the blank need to have the same cycle time. Note that a 4-second stroke cycle may mean that the blank or formed blank undergoes several operations during a cycle of approximately 2 or 2.5 seconds, and transferring the blank between stations may take approximately 1.5-2 seconds.

[0086] The press mechanism can be driven mechanically, hydraulically, or servo-mechanically. The movement of the movable upper body 86 relative to the fixed lower body 88 can be determined by this mechanism. In this particular example, the press can be a servo-mechanical press, thus providing constant pressure during the stroke. Servo-mechanical presses can have unlimited sliding (plunger) speed and position control. Servo-mechanical presses can also provide a good range of available pressure at any sliding position, thus enabling great flexibility in the press. Servo-driven presses have the ability to improve process conditions and productivity in metal forming. The press can have pressures such as 2000 Tn.

[0087] In some examples, the press can be a mechanical press, so the pressure process toward the fixed lower body 88 can depend on the drive and hinge system. Therefore, mechanical pressure can achieve a higher number of cycles per unit time. Alternatively, a hydraulic press can also be used.

[0088] In some examples, one or more of the lower molds 54, 64, 74, and 84 may be connected to the lower body 88 via a lower biasing element configured to bias the lower mold at a position relative to the lower body 88 at a predetermined first distance. In some examples, a single lower biasing element may be provided, or more than two lower biasing elements may be provided. The biasing element may include, for example, a spring, such as a mechanical spring or a gas spring, although some other biasing elements are also possible, such as a hydraulic mechanism.

[0089] In some examples, one or more of the upper molds 52, 62, 72 and 82 may also be connected to the upper body 86 via one or more upper biasing elements configured to bias the upper molds at a predetermined second distance from the upper body.

[0090] With the insertion of the upper and / or lower biasing elements, the contact time between the upper and lower dies can be adjusted and increased during the stroke cycle (the upward and downward movement of the movable upper body 86 relative to the lower body 88).

[0091] The use of such a biasing element allows the cooling tool to have a different cycle time than other tools integrated in the same device. This is explained in more detail in EP3067128. However, within the scope of this disclosure, the use of a biasing element is merely optional. Depending on the steel of the blank and their coating, a biasing element may not be necessary at all. As mentioned herein, such a biasing element can be used to close a complete tool or "die". In the example, the biasing element may be used only for the selection of the die block.

[0092] The pressing tool configured to form or stretch a blank is also integrated into the same pressing device. The upper pressing die 52 may include an upper working surface that faces the blank to be thermoformed during use. The lower die 54 may include a lower working surface that faces the blank to be thermoformed during use. The side of the upper die opposite to the upper working surface can be fastened to the upper body 86, and the side of the lower die opposite to the lower working surface can be fastened to the lower body 88.

[0093] The upper mold 52 and the lower mold 54 may include channels through which cold fluids, such as water and / or cold air, are disposed within the molds. In the water channels, the water may circulate at a higher velocity, thus preventing evaporation. A control system may also be provided, which can control the fluid temperature and flow rate based on temperature measurements, thereby controlling the temperature of the mold.

[0094] In the example, the pressing tool may be equipped with a blank holder configured to hold and position the blank on the lower mold 54. The blank holder may also be provided with, for example, a spring to bias the blank holder to a position at a predetermined distance from the lower mold 22.

[0095] In this example, a first post-pressing tool configured to perform trimming and / or piercing operations is disposed within the same multi-pressing apparatus. This first post-pressing tool is arranged downstream of the pressing tool. The first post-pressing tool includes an upper mating die 62 and a lower mating die 64. The upper mating die 62 may include an upper working surface, and the lower mating die 64 may include a lower working surface. In use, both working surfaces face the workpiece. The side of the upper die 62 opposite to the upper working surface is fastened to an upper body 86, and the side of the lower die 64 opposite to the lower working surface is fastened to a lower body 88. The dies may include one or more blades or cutting blades (not shown) disposed on the working surfaces.

[0096] The first post-pressing tool may also include one or more electric heaters or channels for conducting heat to a fluid, and a temperature sensor for controlling the mold temperature. The sensor may be a thermocouple. In some examples, the upper mating mold 62 and the lower mating mold 64 may include channels through which cold fluids such as water and / or cold air pass.

[0097] In the example, the first post-pressing tool may be provided with a blank holder (not shown) configured to hold and position the blank on the lower die 62. The blank holder may also be provided with one or more biasing elements configured to bias the blank holder at a predetermined distance from the lower die.

[0098] In this example, a second post-pressing tool and an additional tool with upper and lower mating dies are provided. The description of the pressing tool and the dies of the first post-pressing tool generally also applies to these tools. The second post-pressing tool 40 can be configured to perform further trimming and / or piercing operations.

[0099] A mold may include one or more blades or cutting blades arranged on a working surface.

[0100] It should be understood that although the accompanying drawings depict molds with a generally square or rectangular shape, these blocks can have any other shape, even a partially circular shape.

[0101] Automated conveying devices (not shown), such as multiple industrial robots or conveyors, or beams with clamping elements, can also be provided to transfer blanks between tools. Because the conveying devices can be integrated into the same pressing system, conveying time is shorter and temperature control is better.

[0102] In all examples, temperature sensors and control systems can be provided in any tool or in the conveying system to control the temperature. These tools may also be equipped with additional cooling systems, blank holders, etc.

[0103] In some examples, centering elements, such as pins and / or guides, can be provided upstream of the cooling tool to allow for proper centering of the blank.

[0104] For the sake of completeness, all aspects of this disclosure are set forth in the following numbered clauses: Clause 1. A method for thermoforming structural components in a multi-step production line, the method comprising: A pressing tool configured for stretching a blank, wherein the pressing tool includes an upper pressing die and a lower pressing die. A first post-pressing tool, disposed downstream of the pressing tool and configured to perform a first post-pressing operation, includes an upper first post-pressing die and a lower first post-pressing die, the upper and lower first post-pressing dies being configured to operate in concert; and A conveying system for conveying a formed blank from the pressing tool to the first post-pressing tool, and the method comprising: Provide pressable hardened boron steel blanks The blank is heated to a temperature above the austenitizing temperature; and The heated blank is stretched in the pressing tool and the blank is transferred from the pressing tool to the first post-pressing tool. Prior to stretching the blank, the blank temperature is at least 600°C, specifically at least 650°C, and The temperature of the blank prior to the first post-pressing operation is 500°C to 650°C, and wherein... The temperature at the end of the first post-pressing operation is 400°C to 550°C.

[0105] Clause 2. The method according to Clause 1, wherein the temperature of the blank is 700°C to 800°C before stretching the blank.

[0106] Clause 3. The method according to Clause 1 or 2, wherein the blank is heated to 870°C-930°C, specifically 900°C-930°C.

[0107] Clause 4. The method according to any one of Clauses 1-3, wherein the temperature of the formed blank prior to the first post-pressing operation is 500°C to 600°C.

[0108] Clause 5. The method according to any one of Clauses 1-4, wherein the temperature at the end of the first post-pressing operation is 400°C to 500°C.

[0109] Clause 6. The method according to any one of Clauses 1-5, wherein the compressible hardening boron steel blank has a content of 0.32-0.45% by weight, a manganese content of 0.6-1.5% by weight, and a boron content of 0.003-0.006% by weight.

[0110] Clause 7. The method according to Clause 6, wherein the compressible hardening boron steel blank has a content of 0.32-0.4% by weight, a manganese content of 0.6-1.4% by weight, and a boron content of 0.004-0.005% by weight.

[0111] Clause 8. The method according to any one of Clauses 1-7, wherein the steel blank is made of PHS 1.900 or PHS 2.000.

[0112] Clause 9. The method according to any one of Clauses 1-8, wherein the compressible hardenable boron steel blank is coated.

[0113] Clause 10. The method according to Clause 9, wherein the pressable hardenable boron steel blank has an AlSi coating.

[0114] Clause 11. The method according to any one of Clauses 1-10, wherein the multi-step production line further includes a second post-pressing tool disposed downstream of the first post-pressing tool and configured to perform a second post-pressing operation, and includes an upper second post-pressing die and a lower second post-pressing die, the upper second post-pressing die being configured to operate in accordance with the upper pressing die and the upper first post-pressing die, and wherein the conveying system is further configured to convey the blank from the first post-pressing tool to the second post-pressing tool.

[0115] Clause 12. The method according to Clause 11, wherein the temperature of the blank is 350°C to 450°C at the end of the second post-pressing operation.

[0116] Clause 13. The method according to Clause 11 or 12, wherein the multi-step production line further includes one or more additional tools arranged downstream of the second post-pressing operation tool, the additional tools being configured to operate in accordance with the pressing tool and the first and second post-pressing tools.

[0117] Clause 14. The method described in Clause 13, wherein the last additional tool is a re-stamping tool.

[0118] Clause 15. The method according to Clause 14, wherein the temperature of the blank prior to re-stamping is 250°C to 350°C.

[0119] Clause 16. The method according to any one of Clauses 1-15, wherein the operation cycle of the pressing tool is 2 to 5 seconds, specifically 2.5 seconds and 4.5 seconds, and more specifically approximately 4 seconds.

[0120] Clause 17. The method according to any one of Clauses 1-16, wherein the transmission time between the pressing tool and the first post-pressing tool is 1 to 3 seconds, specifically 1.5 to 2.5 seconds, more specifically about 2 seconds.

[0121] Clause 18. The method according to any one of Clauses 1-17, wherein the first post-pressing tool is a tool for cutting, trimming, or making holes.

[0122] Clause 19. The method according to any one of Clauses 1-18, wherein the obtained structural component has an ultimate tensile strength greater than 1.600 MPa, specifically 1.600 MPa-1.800 MPa, more specifically 1.700 MPa-1.800 MPa.

[0123] Clause 20. The method according to any one of Clauses 1-19, wherein the obtained structural component has an A50 elongation of 5% or greater.

[0124] Clause 21. The method according to any one of Clauses 1-20, wherein the obtained structural component has a yield strength of 1,000 MPa or greater, specifically 1,100-1,300 MPa.

[0125] Clause 22. The method according to any one of Clauses 1-21 further includes baking hardening of the structural component obtained, wherein the baking hardening temperature is 170°C to 200°C, and wherein the baking hardening time is 15 minutes to 25 minutes.

[0126] Clause 23. The method according to Clause 22, wherein the yield strength of the obtained structural component is 1.050 MPa or greater, specifically 1.200 MPa or greater.

[0127] Clause 24. The method according to any one of Clauses 1-23, wherein the structural component, after forming, has a length of at least 1 meter, specifically 1-2 meters, and the structural component, after forming, has a width of at least 1 meter, specifically 1-2 meters.

[0128] Clause 25. The method according to Clause 24, wherein the structural component is an integral door ring, and wherein the integral door ring is one of a front door ring extending from the hinge post and A-post to the B-post, a rear door ring extending from the B-post to the C-post, or a double door ring extending from the hinge post and A-post to the C-post.

[0129] Clause 26. The method described in Clause 24, wherein the structural component is an integral roof ring, a buffer beam assembly including a buffer beam and a pedestrian beam, or an integral reinforcing ring surrounding the battery box, or a rear frame structure including a rear guide rail and a crossbeam as an integral structure.

[0130] Clause 27. The method according to any one of Clauses 1-26, wherein the blank has a thickness of 0.8 mm to 2 mm, specifically 1 mm to 1.6 mm.

[0131] Clause 28. The method according to any one of Clauses 1-27, wherein the blank is made of 34MnB4 or 34MnB5 steel.

[0132] Clause 29. The method according to any one of Clauses 1-27, wherein the blank is made of 37MnB5 or 37MnB4 steel.

[0133] Clause 30. The method according to any one of Clauses 1-29, wherein the steel billet has a carbon content of 0.34-0.38% by weight and a manganese content of 0.8-1.4% by weight.

[0134] Clause 31. The method according to Clause 30, wherein the steel billet has a boron content of 0.004 to 0.005% by weight.

[0135] Clause 32. The method according to Clause 30 or 31, wherein the steel billet has a silicon content of 0.3-0.9% by weight, specifically 0.4-0.8% by weight.

[0136] Clause 33. The method according to any one of Clauses 1-32, wherein the multi-step production line includes a multi-step tool comprising a fixed lower body, a movable upper body, and a mechanism configured to provide an upward and downward pressing process of the movable upper body relative to the lower body, and wherein the upper pressing die is connected to the movable upper body, and the lower pressing die is connected to the fixed lower body, and the first upper rear pressing die is connected to the movable upper body, and the first lower rear pressing die is connected to the fixed lower body.

[0137] Clause 34. A structural component which can be obtained by any one of the methods according to any one of Clauses 1-33.

[0138] Although only a few examples are disclosed herein, other substitutions, modifications, uses, and / or equivalents are possible. Furthermore, all possible combinations of the described examples are covered. Therefore, the scope of this disclosure should not be limited to the specific examples but should be determined only by a reasonable reading of the appended claims.

Claims

1. A method for thermoforming structural components in a multi-step production line, the method comprising: A pressing tool configured for stretching a blank, wherein the pressing tool includes an upper pressing die and a lower pressing die. A first post-pressing tool is arranged downstream of the pressing tool and configured to perform a first post-pressing operation, and includes an upper first post-pressing die and a lower first post-pressing die, the upper pressing die and the upper first post-pressing die being configured to operate in a consistent manner. as well as A conveying system for conveying a blank from the pressing tool to the first post-pressing tool, and the method comprising: A pressable hardening boron steel blank is provided, wherein the pressable hardening boron steel blank preferably has a carbon content of 0.32-0.45% by weight, a manganese content of 0.6-1.5% by weight and a boron content of 0.003-0.006% by weight, and wherein the pressable hardening boron steel blank optionally has an AlSi coating. The blank is heated to a temperature above the austenitizing temperature; as well as The heated blank is stretched in the pressing tool and the formed blank is transferred from the pressing tool to the first post-pressing tool. Prior to stretching the blank, the temperature of the blank is at least 600°C, specifically at least 650°C, and The temperature of the blank formed before the first post-pressing operation is 500°C to 650°C, and wherein... The temperature of the blank formed at the end of the first post-pressing operation is 400°C to 550°C.

2. The method according to claim 1, wherein the compressible hardening boron steel blank has a content of 0.32-0.38% by weight, a manganese content of 0.6-1.4% by weight, and a boron content of 0.004-0.005% by weight.

3. The method according to claim 1 or 2, wherein the temperature of the blank is 650°C to 900°C, specifically 700°C to 800°C, before stretching the blank.

4. The method according to any one of claims 1-3, wherein the blank is heated to 870°C-930°C, specifically wherein the blank is heated to 900°C-930°C, and optionally wherein the blank is heated in a furnace.

5. The method according to any one of claims 1-4, wherein the multi-step production line further comprises a second post-pressing tool disposed downstream of the first post-pressing tool and configured to perform a second post-pressing operation, and includes an upper second post-pressing die and a lower second post-pressing die, the upper second post-pressing die being configured to operate in accordance with the upper pressing die and the upper first post-pressing, and wherein the conveying system is further configured to convey the formed blank from the first post-pressing tool to the second post-pressing tool.

6. The method according to claim 5, wherein at the end of the second post-pressing operation, the temperature of the formed blank is 350°C to 450°C.

7. The method of claim 5 or 6, wherein the multi-step production line further comprises one or more additional tools disposed downstream of the second post-pressing operation tool, the additional tools being configured to operate in accordance with the pressing tool and the first and second post-pressing tools.

8. The method of claim 7, wherein the last additional tool is a re-stamping tool, and wherein the temperature of the formed blank prior to re-stamping is 250°C to 350°C.

9. The method according to any one of claims 1-8, wherein the operation cycle of the pressing tool is 2 to 5 seconds, specifically 2.5 to 4.5 seconds, and more specifically approximately 4 seconds, and The transfer time between the pressing tool and the first rear pressing tool is 1 to 3 seconds, specifically 1.5 to 2.5 seconds, more specifically about 2 seconds, and optionally the transfer of the blank occurs before the upper molds have reached their highest positions.

10. The method according to any one of claims 1-9, wherein the obtained structural component has an ultimate tensile strength greater than 1.600 MPa, specifically 1.600 MPa-1.800 MPa, more specifically about 1.700 MPa, and The resulting structural components have a yield strength of 1,000 MPa or greater, specifically 1,100–1,300 MPa.

11. The method according to any one of claims 1-10, wherein the obtained structural component has an A50 elongation of 5% or greater.

12. The method according to any one of claims 1 to 11, further comprising baking hardening of the obtained structural component, wherein the baking hardening temperature is 170°C to 200°C, and wherein the baking hardening time is 15 minutes to 25 minutes, particularly wherein the yield strength of the obtained structural component is 1.050 MPa or greater, specifically 1.200 MPa or greater.

13. The method according to any one of claims 1-12, wherein the structural member has a length of at least 1 meter, specifically 1-2 meters, after forming, and the structural member has a width of at least 1 meter, specifically 1-2 meters, after forming, and particularly, wherein the structural member is an integral door ring.

14. The method according to any one of claims 1-13, wherein the pressable hardenable boron steel blank is made of 34MnB4 steel or 37MnB5 steel.

15. The method according to any one of claims 1-14, wherein the multi-step production line comprises a multi-step tool, the multi-step tool comprising a fixed lower body, a movable upper body, and a mechanism configured to provide an upward and downward pressing process of the movable upper body relative to the lower body, wherein the upper pressing die is connected to the movable upper body, and the lower pressing die is connected to the fixed lower body, and the first upper rear pressing die is connected to the movable upper body, and the first lower rear pressing die is connected to the fixed lower body.

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