EP-4737597-A1 - METHOD AND PRODUCTION LINE FOR HOT FORMING AND PRESS HARDENING A STRUCTURAL COMPONENT

Abstract

Examples of methods of hot forming structural components are provided. The methods include heating a blank made from a press hardenable boron steel and forming the heated blank in a production line or multi-step apparatus. Examples of the present disclosure provide hot forming and cutting of a blank with a cycle time of 10 seconds or less for each of the tools.

Inventors

• FERNÁNDEZ HERNÁNDEZ, Borja
• CASTILLA MORENO, Jordi
• LÓPEZ LAGE, Manuel
• CASTRILLO AMEZUA, Idoia
• ROMERO RUIZ, Laura

Assignees

• AUTOTECH ENGINEERING, S.L.

Dates

Publication Date

20260506

Application Date

20241030

Claims (15)

1. A method for hot forming and press hardening a structural component in a production line comprising: a furnace; a press tool configured to deform blanks, and the press tool having an upper press die and a lower press die; a cutting tool arranged downstream from the press tool and configured to perform a cutting and restriking operation, and having an upper cutting tool die and a lower cutting tool die; a transfer system to transfer blanks from the furnace to the press tool and from the press tool to the cutting tool, and the method comprising: providing a press hardenable boron steel blank; heating the blank to above an austenization temperature in the furnace; actively cooling at least a selected portion of the blank; deforming and cooling the blank in the press tool; transferring the formed blank from the press tool to the cutting tool; cutting one or more areas of the formed blank and cooling the formed blank in the cutting tool, wherein a temperature of the blank before forming the blank is 600°C - 850°C, wherein a temperature of the formed blank is cooled down to 400 - 600°C in the press tool; and wherein the formed blank is cooled down to 275°C in the cutting tool.
2. The method according to claim 1, wherein the active cooling of at least the selected portion of the blank comprises active cooling in the furnace and/or active cooling of at least the selected portion of the blank comprises active cooling during a transfer from the furnace to the press tool.
3. The method according to claim 1 or 2, wherein the active cooling of at least the selected portion of the blank comprises active cooling in the press tool prior to the deforming of the blank.
4. The method according to any of claims 1-3, wherein the whole blank is heated to above an Ac3 temperature in the furnace.
5. The method according to any of claims 1 - 4, wherein the press hardenable boron steel blank has a content by weight of 0.32 - 0.45%, a manganese content of 0.6 - 1.5%, and a boron content of 0.003 - 0.006%.
6. The method according to any of claims 1-5, wherein the press hardenable boron steel blank is coated.
7. The method according to any of claims 1-6, wherein a cycle time from the moment of extracting a blank from the furnace to extracting the blank from the cutting tool is 12 seconds or less, specifically 10 seconds or less.
8. The method according to any of claims 1-7, wherein the press hardenable boron steel blank includes a first portion with a first thickness, and a second portion with a second thickness, wherein the second thickness is higher than the first thickness.
9. The method according to claim 8, wherein the second portion is more actively cooled than the first portion prior to deforming.
10. The method according to claim 8 or 9, wherein the first portion is actively heated in the press tool and/or cutting tool.
11. The method according to any of claims 1 - 10, wherein the press hardenable boron steel blank is made by joining two or more sub-blanks.
12. The method according to claim 11, wherein the press hardenable boron steel blank is a Tailor Welded Blank, or wherein the press hardenable boron steel blank is made by welding two or more sub-blanks which partially overlap with each other.
13. The method according to any of claims 1 - 12, further comprising cutting at least a portion of the press hardenable boron steel blank in the forming tool.
14. The method according to any of claims 1 - 13, further comprising later cutting the structural component in a laser cutting station.
15. A production line for hot forming and press hardening a structural component comprising: a furnace configured to heat a press hardenable boron steel blank to above an Ac1 temperature, particularly to above an Ac3 temperature; a press tool arranged downstream from the furnace and configured to deform the heated blanks, and the press tool having an upper press die and a lower press die; a first transfer system to transfer blanks from the furnace to the press tool; a cutting tool arranged downstream from the press tool and configured to perform a cutting and restriking operation, and having an upper cutting tool die and a lower cutting tool die; a second transfer system to transfer blanks from the press tool to the cutting tool, wherein the furnace and/or the first transfer system and/or the press tool comprises cooling elements for actively cooling at least a selected portion of the heated blank.

Description

The present disclosure relates to methods for manufacturing hot formed structural components and uses of ultra-high strength steels in hot forming processes. More particularly the present disclosure relates to fast methods for hot forming and cutting structural components. BACKGROUND In the field of vehicle construction, the development and implementation of lightweight materials or components is becoming more and more important in order to satisfy criteria for lightweight construction. The demand for weight reduction is especially driven by the goal of reduction of CO2 emissions. The growing concern for occupant safety also leads to the adoption of materials which improve the integrity of the vehicle during a crash while also improving the energy absorption. A process known as Hot Forming Die Quenching (HFDQ) (also known as hot stamping or press hardening) uses e.g. boron steel sheets to create stamped components with Ultra High Strength Steel (UHSS) properties, with tensile strengths of e.g. 1.500 MPa or more. The increase in strength as compared to other material allows for a thinner gauge material to be used, which results in weight savings over conventionally cold stamped mild steel components. In order to improve corrosion protection before, during or after a hot stamping process, coatings may be applied. For example the use of AI-Si coatings or Zn coatings is known. Depending on the composition of the base steel material, blanks may need to be quenched (i.e. be cooled down rapidly) to achieve the high tensile strengths. In a well-known process, a blank that has been heated to e.g. 900°C or more is transferred to a press, in which it is deformed. At the same time, the blank is rapidly quenched to e.g. a temperature of around 200°C. The rapid quenching is done to obtain a fully martensitic microstructure which leads to high stiffness and strength. Examples of steel materials which can harden by leaving them to cool to room temperature by air cooling with relatively low cooling speed are also known. These steels may be referred to as "air hardenable" steels. The hot stamping process may be performed in a manner such that a blank to be hot formed is heated to a predetermined temperature e.g. to or above an austenization temperature by, for example, a furnace system so as to decrease the strength of the blank i.e. to facilitate the hot stamping process. The heated blank may be formed by, for example, a press system having a low temperature compared to the blank (e.g. room temperature) and a temperature control, thus a shaping process and a heat treatment using the temperature difference may be performed. A hot stamping process may include a conveyor or a transferring device which transfers the heated blank from the furnace to a press tool which is configured to press the blank. Upstream from the furnace system, a cutting system for cutting blanks directly from a steel coil can be provided. The use of multistep press apparatus for manufacturing hot formed elements is known. The multistep press apparatus may comprise a plurality of tools configured to perform different operations on different blanks simultaneously. With such arrangements, a plurality of blanks can undergo different manufacturing steps simultaneously during each stroke of the press apparatus. The efficiency and performance of a multistep apparatus may be higher than systems employing a plurality of different machines or apparatuses for different manufacturing steps, such as, laser trimming or hard cutting. When zinc coated steel blanks are used, the blanks may need to be cooled down to a certain temperature before a hot forming process to reduce or minimize problems such as microcracks. Once the blank is cooled down, it is transferred from the external pre-cooling tool to the multistep press apparatus. US 2022/0258223 discloses press apparatus and methods for manufacturing hot formed structural components. The apparatus comprises a fixed lower body, and a mobile upper body. The apparatus comprises a cooling tool and a press tool which is arranged downstream from the cooling tool, and a blank transfer mechanism to transfer the blank from the cooling tool to the press tool. The cooling tool has an upper gas cooling tool connected to the mobile upper body and/or a lower gas cooling tool connected to the fixed lower body. The press tool comprises an upper pressing die connected to the upper body and a lower pressing die is connected to the lower body. EP3437750 A1 discloses examples of methods of hot forming structural components. The methods include heating a blank made of an Ultra High Strength Steel with an aluminum coating and forming the heated blank in a multi-step apparatus. EP3067129 A1 discloses press systems for manufacturing hot formed structural components. The system comprises a fixed lower body, a mobile upper body and a mechanism configured to provide upwards and downwards press progression of the mobile upper body with respect to