Method for manufacturing metal parts and related metal parts

Abstract

A press working method and related metal parts for forming a metal part (1) of a geometric shape such that several regions need to be deformed in opposite directions during press working. The press working method includes the step of preparing a flexible metal blank (10) having at least two subblanks (101, 102) corresponding to subparts (11, 12) of a metal part, the flexible blank further comprising overlapping regions (100) in which the blanks are superimposed on each other, the overlapping regions (100) corresponding to a critical transition region 11T12 between the two subparts, and the overlapping regions comprising a pre-assembly region (1002) and a sliding region (1001). The punch used in the press working operation has gaps between the regions of the punch corresponding to the first subpart (11) and the second subpart (12).

Description

Technical Field

[0001] The present invention relates to a process for manufacturing metal parts and related metal parts. In particular, the present invention relates to the manufacture of complex metal parts formed by pressing.

Background Art

[0002] In the metal part manufacturing industry, particularly in the automotive part manufacturing industry, there is an increasing demand for manufacturing parts with more complex shapes than ever. This makes it possible, for example, to integrate several individual parts into a single unitary part. This simplifies the manufacturing process, replacing a combination of several separate forming operations for manufacturing the individual sub-parts and corresponding joining processes for assembling those individual sub-parts with just one forming operation. This also makes it possible to improve the performance of the part, since the assembly parts between the individual sub-parts are often weak points that can malfunction under load, for example during a collision in the case of automotive parts. Furthermore, the simplification of the manufacturing process has additional positive effects such as reducing greenhouse gas emissions during forming and reducing costs.

[0003] Pressing is a well-known sheet metal forming technique that generally consists of pressing a flat metal sheet between an upper die and a lower die having the shape of the metal part after forming. These dies move relative to each other in a direction called the pressing direction.

[0004] During pressing, the pressed metal flows under the joining forces applied by the upper die and the lower die. Generally, it is impossible to press a part if there are sharp transitions in the direction in which the metal flows. In fact, in the regions where these sharp transitions occur, the sheet metal has to flow in two different directions, which leads to a very high deformation rate, excessive thinning, and ultimately the occurrence of cracks. In some cases, it can also lead to wrinkles in the part.

[0005] This limits the diversity of shapes that can be obtained by conventional press working processes. Japanese Patent Publication No. 2007-29966 provides a first solution for manufacturing complex metal parts by press working. The proposed solution is to provide a metal blank which is an assembly of several subblanks that partially overlap each other, and the subblanks can move relative to each other in the overlapping region during press working. Thus, in a region where the metal blank needs to flow in two distinct directions, each of the two overlapping subblanks can move freely in the said distinct direction, and at first glance, the problems of excessive thinning, cracking, and wrinkling appear to be solved.

[0006] However, when the inventors of the present invention attempted to actually apply the teachings of Japanese Patent Application Publication No. 2007-29966, as demonstrated in the embodiments described below, they encountered serious problems of excessive thinning, cracking, and creasing. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-29966 [Overview of the project] [Problems that the invention aims to solve]

[0008] An object of the present invention is to provide a metal part forming process that enables the press forming of complex shapes in which a thin metal sheet needs to flow in several different directions without causing excessive thinning, cracking, or creasing. A further object of the present invention is to provide a part manufactured according to the method of the present invention that has a complex shape that cannot be achieved using conventional press forming techniques. [Means for solving the problem]

[0009] The object of the present invention is achieved by applying a part manufacturing process according to claim 1, which optionally includes the features of claims 2 to 14 individually or in any possible combination. Furthermore, the present invention relates to a metal part according to claim 15, which optionally includes the features of claim 16 or 17 individually or in any possible combination. Furthermore, the present invention relates to an automobile according to claim 18.

[0010] Other aspects and advantages of the present invention will become apparent by considering the following description, which is given by example and made with reference to the accompanying drawings. The accompanying drawings are not intended to limit the scope of the invention. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view of a specific embodiment of a metal part for which the present invention provides a manufacturing process. [Figure 2] This is a top view of the flexible blank according to the present invention. [Figure 3A] This is a top view of the punch and binder of a press working tool based on prior art. [Figure 3B] This is a top view of the punch and binder of a press working tool according to the present invention. [Figure 4] This is a perspective view of the press working operation at the start of the press working process according to the present invention. For clarity, the upper die is not shown in this figure. [Figure 5] This is a perspective view of the same press working process as Figure 4, but here it shows the end of the press working process. [Figure 6A] This is a top view of the punch and binder of a press working tool according to the present invention. [Figure 6B] This is a top view of a conforming tool according to a specific embodiment of the present invention. [Figure 7] This is a perspective view of a further embodiment of a metal part for which the present invention provides a manufacturing process. [Figure 8]Perspective view of a further embodiment of a metal part for which the present invention provides a manufacturing process. [Figure 9A] Perspective view of a metal part formed by prior art technology. [Figure 9B] Perspective view of a metal part formed by prior art technology. [Figure 9C] Perspective view of a metal part formed in accordance with the present invention. [Figure 10] Perspective view of a specific embodiment of a metal part for which the present invention provides a manufacturing process.

Mode for Carrying Out the Invention

[0012] In the following figures and descriptions, all references to orientation and space are made using the X, Y, Z coordinates associated with the following directions. -X is the longitudinal direction in the horizontal plane, and the X-axis is oriented such that the X coordinate increases in the direction from the front to the rear, that is, a position located at the rear has a larger X coordinate than a position located at the front. -Y is the lateral direction in the horizontal plane. -Z is the height direction, and the Z-axis is oriented such that the Z coordinate increases from a lower position to an upper position, that is, a first position located below a second position has a smaller Z coordinate value.

[0013] A coordinate system is represented in each figure. When the figure is a 2D planar representation, the axis outside the figure is represented by a dot within a circle when it faces the reader according to established convention, and by a cross within a circle when it faces away from the reader.

[0014] In particular, terms such as "top", "up", "upper", "above", "bottom", "low", "lower", "below" are defined according to the height direction. Terms such as "front", "back", "rear", "forward", "backward" are defined according to the longitudinal direction. Terms such as "left", "right", "sideways" are defined according to the lateral direction. The term "horizontal" refers to the orientation of a plane including the longitudinal and lateral directions. The term "vertical" refers to any orientation including the height direction.

[0015] "Substantially parallel" or "substantially perpendicular" means that there may be a deviation of 15° or less from the parallel or perpendicular direction for that direction.

[0016] The metal sheet refers to a flat steel plate. It has an upper surface and a lower surface, which are also called the upper side and the lower side or the upper and lower surfaces. The distance between these surfaces is referred to as the thickness of the sheet. The thickness can be measured, for example, using a micrometer, with its spindle and anvil placed on the upper and lower surfaces. Similarly, the thickness can also be measured for the formed part.

[0017] The average thickness of a part or a portion of a part means the overall average thickness of the material constituting the part after being formed from an initial flat sheet into a three-dimensional part.

[0018] Tailored weld blanks are manufactured by assembling several sheets or cut blanks of steel, known as subblanks, together, for example by laser welding, to optimize the performance of the part in its different areas, reduce the overall weight of the part, reduce the overall cost of the part, and reduce waste. The subblanks forming the tailored weld blank may be assembled with or without overlap, for example, by laser butt welding (no overlap) or by spot welding (with overlap) to each other.

[0019] A flexible blank is a combination of several sub-blanks that include overlapping regions that allow the sub-blanks to move in different directions during the molding process.

[0020] In contrast to tailored weld blanks, monolithic blanks refer to blanks that consist of a single sub-blank rather than several sub-blanks combined with each other.

[0021] Tailored rolled blanks are blanks with multiple thicknesses obtained by varying the rolling process during the steel sheet manufacturing process.

[0022] Ultimate tensile strength, yield strength, and elongation are measured according to ISO standard ISO 6892-1, published in October 2009. Tensile test specimens are cut from a flat area. If necessary, smaller tensile test samples are taken to cover the entire available flat area on the part.

[0023] The bending angle is measured according to the VDA-238 bending standard. For the same material, the bending angle depends on the thickness. For simplicity, the bending angle values ​​in this invention relate to a thickness of 1.5 mm. If the thickness is not 1.5 mm, the bending angle values ​​must be normalized to 1.5 mm by the following calculation, where α1.5 is the bending angle normalized to 1.5 mm, t is the thickness, and αt is the bending angle at thickness t. α1.5 = (αt × √t) / √1.5

[0024] Cold pressing is a metal forming technique that involves shaping a metal sheet into a molded part by pressing it between an upper die and a lower die called a cold pressing tool. For example, a cold pressing tool has a blank holder that allows the metal sheet to be held in place laterally. For example, a cold pressing tool consists of several steps, each of which requires an upper die and a lower die to create a complex shape and / or to punch holes in or trim the sides of a part.

[0025] Hot pressing is a steel forming technique that involves heating a steel blank, or a preform made from a steel blank, to a temperature at which the steel's microstructure transforms at least partially into austenite, and simultaneously forming the high-temperature blank or preform by pressing while rapidly cooling the formed product to obtain a microstructure with extremely high strength, and may sometimes involve additional partitioning or tempering steps in the heat treatment.

[0026] A multi-stage hot press working process is a specific type of hot press working process comprising at least one press working step and at least two processing steps performed at a high temperature exceeding 300°C. For example, a multi-stage process may include a first press working operation and a subsequent hot trimming operation, thus eliminating the need for further trimming of the finished product at the exit of the hot press working process. For example, a multi-stage process may include several consecutive press working steps to manufacture a part having a shape more complex than that which can be achieved using a single press working operation. For example, the part may be automatically transferred from one operation to another in the multi-stage process, for example, using a transfer press. For example, the part may remain within the same tool, which is a multi-purpose tool capable of performing different operations such as a first press working operation and a subsequent in-tool trimming operation.

[0027] A partial hardening hot pressing process is a hot pressing process in which a blank is subjected to a thermal profile that is intentionally adjusted so that different regions of the blank have different material properties at the end of the hot pressing process. For example, this makes it possible to manufacture a hot-pressed part using a single metal blank made from a single material, where different regions of the final part have varying degrees of hardness and elongation. For example, this enables the manufacture of a part having a soft zone and a hard zone, where the soft zone can deform to absorb energy under impact load, while the hard zone resists penetration by resisting deformation. Several different techniques exist for carrying out partial hardening. For example, the material can be heated to different temperatures in different regions of the blank, where the higher temperature region is fully austenitized at the exit of the austenitizing furnace, resulting in an extremely hard microstructure after hot pressing, while the lower temperature region has a critical ferrite / austenite microstructure at the exit of the austenitizing furnace, resulting in a less hard microstructure after hot pressing. For example, in the hot press working process itself, the material can be rapidly cooled at different quenching rates in different areas of the blank, and the areas rapidly cooled at a higher rate will have higher hardness than the areas rapidly cooled at a lower rate.

[0028] Referring to Figures 1 and 11, an object of the present invention is to manufacture a metal part 1 comprising at least the following sub-parts: - A first sub-part 11 extending substantially along a first direction D1. In the following description, this first direction is conventionally selected as the longitudinal direction. The first direction is perpendicular to the press working direction S, which is conventionally selected herein as the height direction, and comprises at least one first side wall 111 (in Figure 1, there are two side walls 111 and 112) substantially parallel to the press working direction, and a first upper part 113 connecting to at least one of the first side walls 111 and extending substantially in a plane perpendicular to the press working direction S. - A second sub-part 12 connected to the first sub-part 11, generally also perpendicular to the press working direction, and extending along a second direction D2 that forms an angle α with the first direction that is strictly greater than 0°, and comprising at least two vertical walls 121 and 122 substantially parallel to the press working direction, and a second upper part 123 connecting the two vertical walls 121 and 122 and extending substantially in a plane perpendicular to the press working direction.

[0029] The metal part 1 shown in Figure 1 is a particular embodiment in which the sub-part has an omega shape with a generally straight vertical wall and a straight and flat top. However, this is not limiting to the present invention, and the sub-part may have, for example, a curved inverted U-shaped cross-section, i.e., a curved vertical wall and a top defined by a two-dimensional line. This is the case, for example, with the first sub-part 11 of the metal part 1 shown in Figure 10.

[0030] In certain embodiments, the angle α between the two main directions D1 and D2 of the sub-components 11 and 12 is in the range of 30° to 90°, more specifically 60° to 90°, and even more specifically 80° to 90°.

[0031] When a metal part 1 is formed by press-working a flat metal blank along the press-working direction S, the first vertical wall 111 is formed by the flow of material in direction F1 across D1, as shown in Figure 1. If the first subpart 11 also includes a second vertical wall 112, it is formed by the flow of material in direction F1'. Simultaneously, the material flows in opposing directions F2 and F2', both of which are across D2, to form the vertical walls 121 and 122 of the second subpart 12. In the transition region 11T12 between subparts 11 and 12, the material needs to flow simultaneously in directions F1 and F2 or directions F1 and F2'. Since the angle between the directions is α or the complementary angle of α to 180°, and α is strictly greater than 0°, this results in simultaneous flow of material in different directions, causing the material to be overstretched, leading to excessive thinning and eventual cracking in the transition region.

[0032] This is illustrated by Figure 9A, an example of a press working simulation of a metal part corresponding to the above explanation, where crack 6 appears in the transition region 11T12 due to the competing deformation directions described above.

[0033] A first part of the solution for manufacturing metal parts according to the present invention is to use a flexible blank 10, as shown in Figure 2. The flexible blank 10 comprises at least, -Two subblanks 101, 102, each substantially corresponding to the first and second subparts 11, 12, respectively. - The subblanks 101 and 102 overlap each other in at least one overlapping region 100 Equipped with, - The overlapping region 100 comprises at least a sliding region 1001 in which the subblanks 101 and 102 are simply superimposed on each other without being further assembled in the blanking stage and can slide freely against each other during the press working operation, and a pre-assembly region 1002 in which the subblanks cannot move relative to each other when handled in blank form, but can slide under the force applied during the press working operation.

[0034] During press working, the region of the flexible blank corresponding to the transition region 11T12 where cracks would normally occur is now a double layer thanks to the presence of the overlapping region 100, and both layers have the freedom to slide against each other, thus preventing the aforementioned problems of excessive thinning and cracking caused by the opposing directions of material flow. For example, in the configuration of Figure 1, the material of the sub-blank 101 corresponding to the vertical wall 111 can move freely in direction F1, while the material of the sub-blank 102 corresponding to the vertical walls 121 and 122 can move freely in directions F2 and F2'.

[0035] The inventors of the present invention surprisingly found that simply providing the flexible blank described above was not sufficient to manufacture a metal part free from press-forming defects in the transition region 11T12. Figure 9B is an exploded view of the results of performing a press-forming operation on the flexible blank as described above. Subparts 11 and 12 are disassembled to highlight the forming challenges encountered. As can be seen, cracks 6 are present in both the first subpart 11 and the second subpart 12.

[0036] The inventors of the present invention have discovered that it is possible to press-form the metal parts according to the present invention by modifying the press-forming process.

[0037] Pressing tools generally consist of a punch and a die. While the die can be understood as the mold in which the part is formed, the punch is used to transfer the shape of the part onto the blank by pushing the blank into the die in the pressing direction. Pressing tools may optionally further consist of a binder, also known as a blank holder, which is used to hold the blank in place during pressing and thus control the flow of the material to achieve a good quality shape.

[0038] Figure 3A is a top view of a punch 2 and binder 3 according to the prior art. Referring to Figure 3B, the inventors of the present invention have surprisingly discovered that the problem of cracking in the transition region when using a flexible blank can be solved by providing a punch 2 having a gap 4 between the regions of the punch corresponding to the first sub-component 11 and the second sub-component 12.

[0039] Figure 9C shows an example of a simulation of press working a flexible blank according to the present invention using a press working tool according to the present invention, namely a press working tool having a gap 4 between the regions of the punch 3 corresponding to the first sub-part and the second sub-part. In this final simulation, no cracks were observed in the transition region 11T12.

[0040] In certain embodiments, the inventors of the present invention have found that the required gap length 4 (i.e., distance g shown in Figure 3B) is related to the height of the vertical walls of two adjacent sub-components in the corresponding transition region 11T12. In fact, the reason cracks occur when no gap is provided is related to the flow of material to form the vertical wall, and the amount of material flow itself is related to the height of the vertical wall. Pressing a component with a higher wall means that more material needs to flow to form the wall. Therefore, the higher the vertical wall, the greater the required gap length. On the other hand, the required gap length g never exceeds the maximum height of the vertical wall, because as you move away from the connection between two adjacent sub-components, the influence of the transition region on the flow of material decreases, and becomes almost zero when the distance from the connection region begins to exceed the height of the vertical wall.

[0041] In a particular embodiment, the length g of the gap 4 is expressed in mm and is 30% or more, preferably 50% or more, preferably 70% or more, of the height of the highest vertical wall of the transition region 11T12, and is less than or equal to the same height of the highest vertical wall of the transition region 11T12.

[0042] In summary, the inventors of the present invention have discovered that it is possible to manufacture a metal part having the above-mentioned properties without excessive thinning or cracking in the transition region by applying the following manufacturing process: - Prepare at least two metal subblanks 101 and 102 corresponding to two subparts 11 and 12 of metal part 1, -A flexible metal blank 10 is formed by pre-assembling at least two metal subblanks in a pre-assembly area and having at least one overlapping area 100 in which the subblanks are superimposed on each other, wherein the overlapping area 100 comprises at least a sliding area 1001 in which the subblanks 101 and 102 are simply superimposed on each other without being further assembled in the blanking stage and can slide freely on each other during the press working operation, and a pre-assembly area 1002 in which the subblanks cannot move relative to each other when handled in blank form but can slide under the force applied during the press working operation. - A punch 2 and a die that move relative to each other in the pressing direction S, wherein the punch 2 has at least one gap 4 between the regions corresponding to the first and second sub-parts 11 and 12, and the press working operation is performed by pressing the flexible metal blank between the punch 2 and the die.

[0043] The press working of a flexible blank according to the present invention is shown in Figures 4 and 5. Figure 4 shows the start of the press working operation at the point when the flexible blank 10 is supplied to the press working tool. In Figure 4, the punch 2 and binder 3 are shown, but the die is not shown for clarity. The punch and die close together in the press working direction S to form a metal part at the end of the press working operation, as shown in Figure 5.

[0044] In certain embodiments, the press working operation is cold forming press working. In certain embodiments, the press working operation is hot pressing, optionally multi-stage hot pressing, optionally partial hardening hot pressing.

[0045] The subblanks 101 and 102 are assembled together in the pre-assembly area 1002, facilitating handling before press working. Meanwhile, sliding movement between the blanks is possible under the forces applied during press working, thereby providing maximum flexibility of movement during the press working stage.

[0046] For example, the blanks are spot-welded to each other in the pre-assembly area 1002 using spot welds 1003, as shown in Figure 2, and the spot welds are strong enough to hold the blanks together during the blank handling stage, but weak enough to be sheared by the forces applied by the blanks during the press working operation.

[0047] For example, the blanks are bonded together in the pre-assembly area 1002 using an adhesive bond that is strong enough to hold the blanks together during the blank handling stage, but allows the blanks to slide against each other under the force applied by the blanks during the press working operation. For example, the adhesive bond is a pressure-sensitive adhesive, which loses its adhesive strength when the assembly is placed under pressure. Conveniently, since the press working operation applies pressure to the pre-assembly area 1002 through the closing motion of the punch and die relative to each other, the pressure-sensitive adhesive naturally loses its adhesive strength during the press working operation, allowing the subblanks to slide against each other more easily under the force applied by the press working operation. For example, the pressure-sensitive adhesive may be an acrylic emulsion adhesive. For example, the pressure-sensitive adhesive may be a double-sided tape adhesive.

[0048] In further possible embodiments, the blanks are mechanically joined to one another in pre-assembly. For example, the blanks are assembled to one another using a clinch assembly that is strong enough to hold them in place during blank handling operations and weak enough to allow the blanks to slide against each other during press working operations.

[0049] In certain embodiments, the pre-assembly region 1002 has a shear resistance strength RS expressed in MPa. The shear resistance strength RS of the pre-assembly region 1002 is defined as the stress required to initiate sliding movement between two subblanks 101 and 102 when stress is applied to one side of subblank 101 and the other side of subblank 102 in the direction of the force generated during the press working operation, and is measured in MPa. In certain embodiments, the shear strength RS is less than the maximum force generated in the direction during the press working operation, which conveniently allows sliding movement between subblanks 101 and 102 to be initiated during the press working operation.

[0050] To successfully design the pre-assembly region 1002, a set of iterative press working simulations can be performed. For example, in the first iteration, a first pre-assembly region 1002 having a first shear resistance strength RS1 is provided. A press working operation is simulated, and the shear force generated between the subblanks 101 and 102 during the press working operation is estimated from the simulation. If the shear force is less than the shear strength RS1, the pre-assembly region 1002 needs to be reconfigured to reduce its shear strength. For example, if the assembly is performed using spot welds, the number of spots used can be reduced, or a different set of spot welding parameters can be used, for example, by reducing the diameter to reduce the strength of the spot welds. For example, if the assembly is performed using adhesive, the area of ​​adhesive application can be reduced, or the amount of adhesive used per surface can be reduced. This results in a redesigned pre-assembly region 1002 having a lower shear strength RS2. A second press working simulation is then performed, and the shear force generated in the pre-assembly region is compared to RS2. If RS2 is less than the shear force generated during press working, this iteration method can be stopped; otherwise, further steps are performed in the reconfigured pre-assembly region having a shear strength RS3, and the process is repeated until a pre-assembly region with a shear strength RSn less than the resulting shear force is finally reached.

[0051] For example, if spot welds are used to assemble subblanks 101 and 102 in a pre-assembly area 1002, the mechanical behavior of the spot welds can be simulated in the following way by applying the method developed in the Fosta 806 project "P 806 - Characterization and simplified modeling of the fracture behavior of spot welds from ultra-high strength steels for crash simulation with consideration of the effects of the joints on component behavior" (Fosta stands for "Forschungsvereinigung Stahlanwendung," i.e., "The Research Association for Steel Application"). The calculation of fracture behavior and associated deletion elements can be simulated using material cards MAT123 and MAT_ADD_EROSION. Further explanation of this method can be found, for example, in "Simulation of Spot Welds and Weld Seams of Press-Hardened Steel (PHS) Assemblies," Stanislaw Klimek, International Automotive Body Congress 2008.

[0052] While the above method of adjusting the configuration of the pre-assembly area can also be performed using a physical press tool to adjust the design, this method, which requires actual physical testing and iterative manufacturing of the adjusted actual physical flexible blanks, may prove to be more time-consuming and expensive than numerical simulation methods.

[0053] After the forming process, the sub-components are no longer fixedly assembled to one another, which can lead to structural weakness in the metal part. To ensure the structural strength of the final part, it is interesting to further assemble the formed sub-components. In a particular embodiment, as shown in Figure 2, the sliding region 1001 of the overlapping region 100 of the sub-blank further comprises at least one post-assembly region 1004 in which the first sub-component 11 and the second sub-component 12 remain overlapping to one another after the pressing process. In this particular embodiment, the manufacturing process further includes a post-assembly step after the pressing process in which at least the first sub-component and the second sub-component are joined to one another in the post-assembly region 1004. For example, the sub-components are joined to one another by spot welding them to each other to form a spot weld 7, as shown in Figure 8. For example, the sub-components are laser welded and optionally remotely laser welded to each other.

[0054] For example, when the present invention is applied to metal parts of an automobile, it becomes possible to integrate both longitudinal and transverse structural elements into a single metal part. For example, it becomes possible to integrate the longitudinal member of the front lateral side and the transverse member of the dash panel into a single part. For example, it becomes possible to integrate the side sill and the seat transverse member into a single part. For example, it becomes possible to integrate the roof rail and the roof transverse member into a single part. For example, it becomes possible to integrate the rear lateral member and the rear transverse member into a single part. By combining various structural elements into a single part, the manufacturing process is simplified, and the part becomes more robust because its longitudinal and transverse components are integrated into the same part and therefore cooperate in an optimal manner.

[0055] In certain embodiments, a conforming process follows the press working process in which the shape of the metal part is further adjusted in the transition region 11T12. In fact, because a gap 4 exists within the punch 2 of the press working tool, the blank material in the transition region 11T12 corresponding to the gap in the punch is not pressed against the die. Therefore, the shape of the metal part in this region does not perfectly reproduce the shape of the die. In certain embodiments, a conforming tool is used which has a punch 21 with a smaller gap 41 between the regions corresponding to the first and second sub-parts, as shown in Figures 6A and 6B. Figure 6A shows a press working punch 2 according to the present invention with a gap 4, and Figure 6B shows a conforming punch 21 according to the present invention with a smaller conforming punch gap 41. By reducing the gap 41 in the conforming tool, the material is pressed more closely against the die and therefore better matches the desired shape in the transition region 11T12. Since the part has already been formed by press working, and the force applied to the rest of the part by the conforming process is much smaller than the force applied during press working, and does not cause cracks in the transition region, it is possible to reduce the gap 41 of the conforming tool. In any case, it is still necessary to have a conforming gap 41 greater than 0 mm. In certain embodiments, the length of the conforming gap 41 is in the range of 10% to 80%, preferably 10% to 70%, preferably 10% to 50%, preferably 20% to 70%, and preferably 20% to 50% of the length of the punch gap 4 for the initial press working.

[0056] In certain embodiments, the press working and conforming operations are performed as two consecutive stages of a transfer press. For example, they are performed as two consecutive stages of a cold press transfer press. For example, they are performed as two consecutive stages of a hot press multi-stage process using a transfer press.

[0057] In certain embodiments, the pressing and conforming operations are performed sequentially using an adjustable punch that can reduce the gap 4 in the pressing stage to a gap 41 in the conforming stage by sliding, for example, a punch element corresponding to sub-part 2 closer to a punch element corresponding to sub-part 11.

[0058] The above configuration of a metal part comprising at least a first sub-part 11 and a second sub-part 12 should be understood as the most basic possible configuration for a metal part according to the present invention. Referring to Figure 7, the metal part 1 may comprise, for example, at least two first sub-parts 11 extending substantially along the first direction D1, each of which is connected to the at least one second sub-part 12 extending substantially along the second direction D2. In this case, the flexible metal blank 10 comprises at least three sub-blanks substantially corresponding to each of the sub-parts, the flexible blank further comprising at least two overlapping regions where each sub-blank extending in the first direction overlaps with a sub-blank extending in the second direction, and each of the overlapping regions comprises at least a pre-assembly region and a sliding region. Furthermore, the press working tool used to manufacture the metal part comprises, in this case, a punch 2 having at least two gaps 4 corresponding to the regions between the first sub-part 11 and the second sub-part 12, respectively.

[0059] According to the present invention, any other combination between the first and second sub-components extending along directions D1 and D2 is also possible. In fact, the gist of the present invention is to provide a manufacturing process that enables the formation of a blank material in the transition region 11T12 without causing cracks.

[0060] In fact, the present invention can be generalized to the configuration of metal parts having three or more principal directions D1 and D2. In fact, the press working problems solved by the present invention occur locally in each transition region 11T12, and each set of transition regions is actually independent of the others.

[0061] Furthermore, the present invention includes metal parts corresponding to the features listed above, which are employed individually or in any possible combination, and which are manufactured by a process that includes all possible combinations of the features of the process detailed above.

[0062] One important advantage of the metal part manufactured according to the process described above is that, in a particular embodiment, it is possible to manufacture a metal part having at least one pair of adjacent subparts, wherein the at least one pair of adjacent subparts has at least one pair of two adjacent vertical walls, such as vertical walls 112 and 121, and the radius of curvature measured in the transition region 11T12 between the two adjacent vertical walls is extremely small. This is not possible with prior art press working techniques that do not use flexible blanks, because the shape of the transition region must be smooth, i.e., have a large radius of curvature, in order to gradually change the flow direction of the material constituting the adjacent vertical walls. For example, in a particular embodiment, the radius of curvature measured in the transition region 11T12 between the two adjacent vertical walls is 20 times or less, more specifically less than 10 times, and even more specifically less than 5 times, the minimum thickness of the metal sheets of the two subparts. In certain embodiments, the radius of curvature is less than 100 mm, more specifically less than 50 mm, more specifically less than 20 mm, more specifically less than 10 mm, and more specifically less than 5 mm. In certain embodiments, the radius of curvature is 0 mm, i.e., the sub-components form acute angles with each other. By providing metal structural components with small or no radius of curvature between adjacent sidewalls, optimal resistance of the component becomes possible, for example, in the case of compressive stress where different sub-components extending in different directions need to cooperate with each other to withstand compression. For example, in the case of automotive structural components, this is advantageous for the same component to withstand lateral and longitudinal impacts.

[0063] In a particular embodiment, the metal part 1 is manufactured by cold-pressing a flexible blank 10 which comprises one of the following materials in the form of a monolithic blank or a tailor-rolled blank, or a combination of materials in the form of a tailor-welded blank.

[0064] - By weight, 0.13% < C < 0.25%, 2.0% < Mn < 3.0%, 1.2% < Si < 2.5%, 0.02% < Al < 1.0%, 1.22% < Si + Al < 2.5%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, Ti < 0.05%, with the balance being Fe and inevitable impurities, having a chemical composition, containing 8% to 15% retained austenite, the balance being ferrite, martensite, and bainite, and having a microstructure in which the total of the martensite and bainite portions is included from 70% to 92%. With this composition, the steel sheet has a yield strength included in the range of 600 MPa to 750 MPa and an ultimate tensile strength included in the range of 980 MPa to 1300 MPa while maintaining an elongation over 19% measured in the rolling direction.

[0065] - By weight, 0.15% < C < 0.25%, 1.4% < Mn < 2.6%, 0.6% < Si < 1.5%, 0.02% < Al < 1.0%, 1.0% < Si + Al < 2.4%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, with the balance being Fe and inevitable impurities, having a chemical composition, containing 10% to 20% retained austenite, the balance being ferrite, martensite, and bainite, and having a microstructure. With this composition, the steel sheet has a yield strength included in the range of 850 MPa to 1060 MPa and an ultimate tensile strength included in the range of 1180 MPa to 1330 MPa while maintaining an elongation over 13% measured in the rolling direction.

[0066] - A fully martensitic steel with a composition containing 0.15% ≤ C ≤ 0.5% by weight.

[0067] - A two-phase steel having a microstructure containing at least martensite and ferrite and having a UTS of at least 590 MPa.

[0068] - A two-phase steel having a microstructure containing at least martensite and ferrite and having a UTS of at least 780 MPa.

[0069] - A duplex steel having a microstructure containing at least martensite and ferrite, and having a UTS of at least 980 MPa.

[0070] In a particular embodiment, the metal part is manufactured by hot-pressing a flexible blank 10 which comprises one of the following materials in the form of a monolithic blank or a tailor-rolled blank, or a combination of materials in the form of a tailor-welded blank.

[0071] - A steel having a composition in weight percent of 0.06% ≤ C ≤ 0.1%, 1% ≤ Mn ≤ 2%, Si ≤ 0.5%, Al ≤ 0.1%, 0.02% ≤ Cr ≤ 0.1%, 0.02% ≤ Nb ≤ 0.1%, 0.0003% ≤ B ≤ 0.01%, N ≤ 0.01%, S ≤ 0.003%, P ≤ 0.020%, containing less than 0.1% Cu, Ni, and Mo, with the remainder being iron and unavoidable impurities resulting from refining. Within this composition range, the yield strength of the corresponding region after hot pressing falls within the range of 700 to 950 MPa, the tensile strength is within the range of 950 MPa to 1200 MPa, and the bending angle exceeds 75°.

[0072] Steel having an ultimate tensile strength after hot pressing in the range of -1300 MPa to 1650 MPa and a yield strength in the range of -950 MPa to 1250 MPa.

[0073] Steel with an ultimate tensile strength after hot pressing ranging from -1300 MPa to 1650 MPa, a yield strength ranging from 950 MPa to 1250 MPa, and a bending angle greater than 75°.

[0074] - A steel having a composition in weight percent containing 0.20%≦C≦0.25%, 1.1%≦Mn≦1.4%, 0.15%≦Si≦0.35%, Cr≦0.30%, 0.020%≦Ti≦0.060%, 0.020%≦Al≦0.060%, S≦0.005%, P≦0.025%, 0.002%≦B≦0.004%, with the remainder being iron and unavoidable impurities resulting from refining. Within this composition range, the ultimate tensile strength of the corresponding area of ​​the hot-pressed part falls within the range of 1300 MPa to 1650 MPa, and the yield strength falls within the range of 950 MPa to 1250 MPa.

[0075] - Steel with a tensile strength higher than 1800 MPa after press hardening.

[0076] - A steel having a composition in weight percent containing 0.24%≦C≦0.38%, 0.40%≦Mn≦3%, 0.10%≦Si≦0.70%, 0.015%≦Al≦0.070%, Cr≦2%, 0.25%≦Ni≦2%, 0.015%≦Ti≦0.10%, Nb≦0.060%, 0.0005%≦B≦0.0040%, 0.003%≦N≦0.010%, S≦0.005%, P≦0.025%, with the remainder being iron and unavoidable impurities resulting from refining. Within this composition range, the tensile strength of the corresponding region after hot pressing is higher than 1800 MPa.

[0077] - Steel having a composition in weight percent of C: 0.15 to 0.25%, Mn: 0.5 to 1.8%, Si: 0.1 to 1.25%, Al: 0.01 to 0.1%, Cr: 0.1 to 1.0%, Ti: 0.01 to 0.1%, B: 0.001 to 0.004%, P ≤ 0.020%, S ≤ 0.010%, N ≤ 0.010%, and optionally, in weight percent of one or more of the following elements, namely Mo ≤ 0.40%, Nb ≤ 0.08%, Ca ≤ 0.1%, with the remainder of the composition being iron and unavoidable impurities resulting from refining.

[0078] - Steel having a composition in weight percent of C: 0.26 to 0.40%, Mn: 0.5 to 1.8%, Si: 0.1 to 1.25%, Al: 0.01 to 0.1%, Cr: 0.1 to 1.0%, Ti: 0.01 to 0.1%, B: 0.001 to 0.004%, P ≤ 0.020%, S ≤ 0.010%, N ≤ 0.010%, and optionally containing in weight percent one or more of the following elements, namely Ni ≤ 0.5%, Mo ≤ 0.40%, Nb ≤ 0.08%, Ca ≤ 0.1%, with the remainder of the composition being iron and unavoidable impurities resulting from refining. Within this composition range, the tensile strength of the corresponding region after hot pressing is greater than 1350 MPa and the bending angle is greater than 70°.

[0079] - A steel having a composition in weight percent of C: 0.2 to 0.34%, Mn: 0.50 to 1.24%, Si: 0.5 to 2%, P ≤ 0.020%, S ≤ 0.010%, N ≤ 0.010%, and optionally containing in weight percent one or more of the following elements, namely Al: ≤ 0.2%, Cr ≤ 0.8%, Nb ≤ 0.06%, Ti ≤ 0.06%, B ≤ 0.005%, Mo ≤ 0.35%, with the remainder of the composition being iron and unavoidable impurities resulting from refining. Within this composition range, the tensile strength of the corresponding region after hot pressing is ≥ 1000 MPa, and the bending angle is greater than 55°.

[0080] -A steel containing, in weight percent, C: 0.13 to 0.4%, Mn: 0.4 to 4.2%, Si: 0.1 to 2.5%, Cr≦2%, Mo≦0.65%, Nb≦0.1%, Al≦3.0%, Ti≦0.1%, B≦0.005%, P≦0.025%, S≦0.01%, N≦0.01%, Ni≦2.0%, Ca≦0.1%, W≦0.30%, V≦0.1%, Cu≦0.2%, and having a composition that satisfies the following combination, namely 114-68*C-18*Mn+20*Si-56*Cr-60*Ni-36*Al+38*Mo+79*Nb-17691*B<20, where the remainder of the composition is iron and unavoidable impurities resulting from refining. For example, this composition is used when hot-pressing parts using a multi-stage process.

[0081] - Steel coated with an aluminum-based metal coating. "Aluminum-based" means a coating containing at least 50% aluminum by weight. For example, the metal coating is an aluminum-based coating containing 8 to 12% Si by weight. For example, the metal coating is applied by immersing the substrate in a molten metal bath. Conveniently, applying an aluminum-based metal coating avoids the formation of surface scale during the heating process of the hot press working process, thereby enabling the manufacture of parts by hot press working without the need for subsequent sandblasting. Furthermore, aluminum-based coatings also provide corrosion protection to metal parts during use, for example, in automobiles.

[0082] Steel coated with an aluminum-based metal coating containing -2.0 to 24.0 wt% zinc, 1.1 to 12.0 wt% silicon, optionally 0 to 8.0 wt% magnesium, and optionally additional elements selected from Pb, Ni, Zr, or Hf, with each additional element having a weight content of less than 0.3 wt%, the remainder being aluminum and optionally unavoidable impurities. Conveniently, this type of metal coating provides the parts with excellent corrosion resistance and a good surface appearance after hot pressing.

[0083] In certain embodiments, at least one element of the rear structure is manufactured by hot-pressing a laser-welded blank including at least one subblank having an aluminum-based metal coating, the aluminum-coated subblank being pre-prepared by ablating at least a portion of the metal coating on the edges to be welded. Conveniently, this removes some of the aluminum present in the coating that would contaminate the weld seam and degrade its mechanical properties.

[0084] In certain embodiments, at least one subblank of the flexible blank 10 comprises at least one region where at least one side is covered with an emissivity-enhancing top layer. The emissivity-enhancing top layer is applied to the outermost surface of the subblank. The emissivity-enhancing top layer allows the surface of the subblank to have a higher emissivity compared to the same subblank that is not coated with the emissivity-enhancing top layer. The emissivity-enhancing top layer can be applied to either the top or bottom surface of the subblank. Furthermore, the emissivity-enhancing top layer can be applied to both sides of the subblank. If the subblank has a metal coating as described above, the emissivity-enhancing top layer is applied over the metal coating. In practice, to increase the surface emissivity with the emissivity-enhancing top layer, it is necessary to cover the outermost surface of the subblank. Conveniently, the emissivity-enhancing top layer allows for an increased heating rate of the subblank and thus improves the productivity of the heating process in the hot press working process. When using several subblanks of different thicknesses, the emissivity-increasing top layer is conveniently applied to the thickest subblank in order to reduce the difference in heating time between the different subblanks, thus increasing productivity, widening the hot press working process window, and enabling the acquisition of a final part with uniform surface properties overall.

[0085] Furthermore, the present invention includes metal parts for automobile bodies corresponding to the features listed above, which can be employed individually or in any possible combination, and which are manufactured by a process that includes all possible combinations of the features of the process detailed above.

[0086] Furthermore, the present invention encompasses the use of such metal parts for assembling the body of an automobile.

[0087] Furthermore, the present invention encompasses automobiles having at least one such metal part.

Claims

1. A manufacturing process for producing a metal part (1) by press-forming a flexible metal blank (10) in a press-forming direction (S), The aforementioned metal part (1) is at least, - A first sub-part (11) extending generally along a first direction (D1) perpendicular to the press working direction (S), and having at least one first side wall (111) substantially parallel to the press working direction (S) connected to a first upper part (113) extending generally in a plane perpendicular to the press working direction (S), - A second sub-part (12) connected to the first sub-part (11), extending generally along a second direction (D2) perpendicular to the press working direction (S) and forming an angle α with the first direction (D1) that is strictly greater than 0°, and comprising at least two vertical walls (121, 122) substantially parallel to the press working direction (S), and a second upper part (123) extending generally in a plane perpendicular to the press working direction (S) and connecting the two vertical walls (121, 122) Equipped with, The flexible metal blank (10) comprises at least, - Two subblanks (101, 102) each substantially corresponding to the first subpart (11) and the second subpart (12), - The subblanks (101, 102) overlap each other in at least one overlapping region (100) Equipped with, - The overlapping region (100) comprises at least one sliding region (1001) in which the subblanks (101, 102) can slide freely relative to each other, and a pre-assembly region (1002) in which the subblanks (101, 102) cannot move relative to each other when handled in blank form, but can slide under the force applied during the press working operation. The aforementioned manufacturing process includes at least, - The step of preparing at least two metal subblanks (101, 102), - The steps of pre-assembling the at least two metal subblanks (101, 102) in the pre-assembly area (1002) to form the flat flexible metal blank (10), - The step of performing the press working operation by pressing the flexible metal blank (10) between a punch (2) and a die that move relative to each other in the press working direction (S), Includes, A manufacturing process in which the punch (2) has at least one gap (4) between the regions corresponding to the first sub-component (101) and the second sub-component (102).

2. The manufacturing process according to claim 1, wherein the first direction (D1) and the second direction (D2) in which the first sub-component and the second sub-component extend form an angle α with respect to each other that is between 30° and 90°.

3. The manufacturing process according to claim 2, wherein the first direction (D1) and the second direction (D2) in which the first sub-component and the second sub-component extend form an angle α with respect to each other that is between 60° and 90°.

4. The manufacturing process according to claim 3, wherein the first direction (D1) and the second direction (D2) in which the first sub-component and the second sub-component extend form an angle α with respect to each other that is between 80° and 90°.

5. The manufacturing process according to any one of claims 1 to 4, wherein the subblanks (101, 102) are assembled to each other in the pre-assembly region (1002) by spot welding.

6. The manufacturing process according to any one of claims 1 to 4, wherein the subblanks (101, 102) are assembled to each other in the pre-assembly region (1002) by adhesive bonding.

7. The manufacturing process according to any one of claims 1 to 6, wherein the pressing operation is performed by hot pressing.

8. The manufacturing process according to any one of claims 1 to 6, wherein the pressing operation is performed by cold pressing.

9. The manufacturing process according to any one of claims 1 to 8, wherein the sliding region (1001) of the overlap region (100) further comprises at least one post-assembly region (1004) in which the first sub-component (11) and the second sub-component (12) remain overlapping each other after the press working is performed, and the manufacturing process further comprises a post-assembly step after the press working in which at least the first sub-component (11) and the second sub-component (12) are joined together in the at least one post-assembly region (1004).

10. The manufacturing process according to claim 9, wherein the post-assembly step is performed by spot welding.

11. The manufacturing process according to claim 9, wherein the post-assembly step is performed by laser welding.

12. The manufacturing process according to any one of claims 1 to 11, wherein after the press working operation, a conforming operation is performed using a conforming punch (21) having a conforming gap (41) between the regions corresponding to the first sub-component and the second sub-component, wherein the conforming gap (41) is smaller than the gap (4) of the initial press working tool (2).

13. The manufacturing process according to any one of claims 1 to 12, wherein the metal part (1) comprises at least two sub-parts (11) extending substantially along the first direction (D1), each of the at least two sub-parts (11) being connected to at least one second sub-part (12) extending substantially along the second direction (D2), the flexible metal blank (10) comprises at least three sub-blanks substantially corresponding to each of the sub-parts, the flexible blank further comprises at least two overlapping regions (100) where each sub-blank (101) extending in the first direction (D1) overlaps with the sub-blank (102) extending in the second direction (D2), and each of the overlapping regions (100) comprises at least a pre-assembly region (1002) and a slide region (1001).

14. The manufacturing process according to any one of claims 1 to 13, wherein the pre-assembly region (1002) has a shear resistance strength RS, expressed in MPa, defined as the stress required to initiate sliding movement between the two subblanks (101, 102) when stress is applied to one side of the subblank (101) and the other side of the subblank (102) in the direction of the force generated during the press working operation, and the shear strength RS is lower than the maximum force generated in the direction during the press working operation.

15. A metal part (1) manufactured according to any one of claims 1 to 14.

16. A metal part (1) according to claim 15, comprising at least one pair of adjacent sub-parts (11, 12) having at least one set of two adjacent vertical walls (111, 121), wherein the radius of curvature measured in the transition region (11T12) between the two adjacent vertical walls is 20 times or less the minimum thickness of the two sub-parts.

17. A metal part (1) according to claim 15 or 16, designed for use in the body of an automobile.

18. An automobile comprising at least one metal part (1) as described in claim 17.

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