Hot stamping system and method

Abstract

A method for hot stamping a plurality of blanks includes providing a plurality of blanks. The method also includes heating the plurality of blanks concurrently in a batch heating furnace at an intermediate temperature for a first time duration. The method also includes heating at least one of the plurality of blanks in a roller hearth furnace at a stamping temperature for a second predetermined period of time after heating the at least one of the plurality of blanks in the batch heating furnace. The method also includes stamping the at least one of the plurality of blanks in a die after heating the at least one of the plurality of blanks in the roller hearth furnace.

Description

HOT STAMPING SYSTEM AND METHODCROSS-REFERENCE TO RELATED APPLICATION

[0001] This PCT International Patent Application claims the benefit of and priority to U.S. Provisional Patent Application Serial No. 63 / 456,581 filed on April 3, 2023 titled “Hot Stamping System And Method,” the entire disclosure of which is hereby incorporated by reference.FIELD OF THE INVENTION

[0002] The present disclosure relates to a hot stamping system for forming components from blanks of steel.BACKGROUND

[0003] Hot stamping, also known as press hardening or hot press forming, is a process of forming blanks of steels into desired shapes. Hot stamped components are used in various industries, such as the automotive industry, for their lightweight and high rigidity characteristics. According to a conventional hot stamping process, an unformed blank of steel is first heated in a furnace, then shaped in a die while in its hot condition, and finally quenched to provide high strength properties.

[0004] In more detail, hot stamping processes often involves heating a steel blank in a roller hearth furnace to a temperature of approximately 850° C to 950° C until the steel blank obtains an austenite microstructure. Next, the heated blank is transferred from the hearth furnace to a hot forming apparatus which includes a pair of dies. The heated blank is stamped or pressed to a predetermined shape between the dies. The hot formed part is then quenched by being cooled to a temperature low enough to transform the austenite microstructure to a martensic microstructure.

[0005] An issue with conventional hot stamping processes is cycle times are relatively long due to specific heat-up requirements for sheet steel blanks, and particularly a duration of time it takes to heat the individual blanks in the roller hearth furnace in order to satisfy the heatup requirements. More particularly, hot stamping processes are often bottlenecked by a rate at which the blanks can be heated prior to being stamped. Technologies have been developed in attempts to improve overall cycle time of the hot stamping process, but there remains a need for further improvements to hot stamping systems.SUMMARY OF THE INVENTION

[0006] According to an aspect of the disclosure, a method for hot stamping a plurality of blanks includes providing a plurality of blanks. The method also includes heating the plurality of blanks concurrently in a batch heating furnace at an intermediate temperature that is less than a stamping temperature for a first predetermined time duration. The method also includes heating at least one of the plurality of blanks in a roller hearth furnace at the stamping temperature for a second predetermined period of time after heating the at least one of the plurality of blanks in the batch heating furnace. The method also includes stamping the at least one of the plurality of blanks in a die after heating the at least one of the plurality of blanks in the roller hearth furnace.

[0007] According to another aspect of the disclosure, a system for hot stamping a plurality of blanks includes a batch heating furnace that is configured to heat the plurality of blanks concurrently at an intermediate temperature that is less than a stamping temperature for a first predetermined time duration. A roller hearth furnace is configured to heat the plurality of blanks at the stamping temperature for a second predetermined period of time. Furthermore, a die is configured to stamp the plurality of blanks after heating the at least one of the plurality of blanks in the roller hearth furnace.

[0008] By simultaneously preheating a large quantity of blanks at the intermediate temperature which is less than the stamping temperature in the batch furnace, a large portion of the time required for heating can effectively be saved because the blanks may spend minimal time in the roller hearth furnace to obtain an austenite microstructure prior to stamping. This shortens an overall cycle time of the stamping process relative to prior methods. Final mechanical properties are not affected by the dwell time in the batch furnace due to it being treated at less than the stamping temperature. For example, an interdiffusion layer of an AlSi coating may be kept below a predetermined critical thickness while in the batch furnace.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0010] FIG. l is a schematic diagram of a system for hot stamping;

[0011] FIG. 2 is a graph illustrating a temperature of blanks heated in accordance with the subject system over time;

[0012] FIG. 3 is a side, cross-sectional view of a component made with the subject system, illustrating a total thickness of a resulting coating and a thickness of an interdiffusion layer;

[0013] FIG. 4 is a graph presenting a thickness of an interdiffusion layer of a blank as the blank is heated in a furnace over time; and

[0014] FIG. 5 is a schematic diagram of a method of hot stamping with the subject system.DESCRIPTION OF THE ENABLING EMBODIMENT

[0015] Referring to the figures, wherein like numerals indicate corresponding parts throughout the several views, a system 10 for hot stamping steel components is provided. The system 10 may be used to form various types of components of various shapes, such as automotive components like body pillars, roof rails, rockers, bumpers, and door intrusion beams. Generally, according to the subject system 10, an unformed blank 12 of steel is first heated in a batch heating furnace 14, then heated in a roller hearth furnace 16, then shaped in a die 17 while in a hot condition, and then quenched in the die 17 to provide high strength properties.

[0016] The system 10 includes a plurality of the blanks 12 that are ultimately formed into the final component. The term “blank” 12 as used herein may include a single component or more than one blank segments that are connected to one another, e.g., via a weld. The blanks 12 may be of various materials including, but not limited to, ultra-high strength steels such as 22MnB5 boron steel. In one embodiment, the steel material used to form the blank 12 comprises 0.18% to 0.28% carbon, 0.7% to 1.0% silicon, 1.0% to 2.0% manganese, 0.12% to 0.7% chromium, 0.1% to 0.45% molybdenum, 0.025% maximum phosphorus, 0.008% to 0.01% sulfur, 0.02% to 0.05% titanium, 0.01% to 0.06% aluminum, and 0.002% to 0.004% boron, based on the total weight of the steel material. In another embodiment, the steel material comprises a mixture of manganese and boron, for example 22MnB5. According to an embodiment, the blank 12 is initially provided with a coating formed of aluminum and silicon (AlSi). As best shown in FIG. 3, this coating typically ultimately forms an interdiffusion layer 22 along the surface of the resulting hot formed component. The interdiffusion layer 22 is a byproduct of heating steel with an AlSi coating. It is typical that design specifications of resulting products require an interdiffusion layer 22 thickness (a measurement of the specificintermetallic at the boundary of the steel substrate and the AlSi coating) of less than 16 gm, and a total coating thickness (from a surface of the component to the underlying steel substrate) of less than 50 pm. It is recognized that if either of these thicknesses is permitted to grow excessively large, weldability of the steel is impacted.

[0017] Prior to hot forming, the blanks 12 may undergo various cold-forming processes, such as trimming and stamping, and may also be welded. These cold-forming processes may be used to form the blank 12 into various desired initial positions.

[0018] The batch heating furnace 14 simultaneously heats any number of the blanks 12 at an intermediate temperature which is beneath a stamping temperature, and below a critical temperature at which the interdiffusion layer 22 begins to excessively form. According to an embodiment, the critical temperature starts above 800° C, thus the intermediate temperature is at approximately 800° C. The blanks 12 are heated in the batch heating furnace 14 at the intermediate temperature for a first predetermined time duration to sufficiently pre-heat the blanks 12. According to an embodiment, the first predetermined time duration is between approximately five minutes and four hours, but can vary depending on factors like a thickness of the blanks 12 and what temperature is selected for the intermediate temperature. Other intermediate temperatures could be used, but studies show that above 800° C is the upper limit at which the interdiffusion layer 22 begins to excessively develop, and 700° C is the temperature at which an interdiffusion layer does not develop at all. The first predetermined time duration is generally limited only by over-development of the interdiffusion layer 22, thus any timeframe may be used that does not lead to such an over-development. According to another embodiment, the first predetermined timeframe is between approximately five minutes and one hour.

[0019] The use of the batch heating furnace 14 in the above-discussed manner permits large quantities of blanks 12 to be simultaneously heated and maintained at the intermediate temperature for extended periods of time prior to entering the roller hearth furnace 16 without excessively forming the interdiffusion layer 22. This reduces an overall cycle time of the hot stamping process relative to prior systems because the blanks 12 may spend considerably less time in the roller heath furnace 16. The use of the batch heating furnace 14 also prevents contamination of rollers 19 in the hearth furnace 16 and provides uniform patch part heating of the blanks 12. It should be appreciated that a large quantity of blanks 12 may include, for example, batches of ten or more blanks 12 at a time.

[0020] As illustrated in FIG. 1, the roller hearth furnace 16 is configured to heat individual blanks 12 after being pre-heated in the batch heating furnace 14. The roller hearth furnace includes a plurality of rollers 19 along a length of the roller hearth furnace 16 between an entrance 18 and an exit 20 such that the blanks 12 move along the rollers 19 in a conveyor-like manner between the entrance 18 and exit 20. According to an embodiment, the roller hearth furnace 16 heats the blanks 12 at a stamping temperature and for a second period of time which is sufficient to permit the blanks 12 to obtain an austenite microstructure. According to an example embodiment, the stamping temperature is approximately 930° C and the second predetermined period of time is in a range of approximately zero to 300 seconds. This effective heating time is much shorter than a conventional heating process due to the blanks 12 being preheated in the batch heating furnace 14. The second predetermined time can vary depending on factors like a thickness or material of the blank 12. For example, a thicker blank would generally require a longer second predetermined time than a thinner blank. According to another embodiment, the second period of time could be in a range of approximately zero to 60 seconds.

[0021] According to an embodiment, heating the blanks 12 in this manner in the roller hearth furnace 16 causes an austenite microstructure to be formed throughout the steel material. More particularly, during these heating steps, all carbides in the steel material of the blank may dissolve so that there are no residual carbides. After the heating step, the microstructure of the steel material is substantially austenite, for example at least 75% austenite, or entirely austenite (100% austenite).

[0022] After heating in the roller hearth furnace 16 for the second predetermined period of time, the heated blank 12 is quickly transferred from the roller hearth furnace 16 to the die 17 while the blank 12 is still above the austenite temperature and thus still includes the substantially austenite microstructure where it is formed into the desired shape. The die 17 may include an upper component 24 and lower component 26, with one or more of the upper and lower components 24, 26 configured to move relative to one another. During operation, the blank 12 is positioned between the upper and lower components 24, 26 such that they can form the blank when moved against one another. After forming in the die 17, the blank 12 is quenched to provide high strength properties.

[0023] According to the above and with reference to FIG. 23, a method for hot stamping includes the step of 100 providing a plurality of blanks 12. The method also includes 102 heating the plurality of blanks 12 concurrently in the batch heating furnace 14 at the intermediate temperature for a first predetermined period of time. According to an embodiment, as previously noted, the intermediate temperature is approximately 800° C and the first predetermined period of time is between approximately 5 minutes and 4 hours. According to another embodiment, the first predetermined timeframe is between approximately five minutes and one hour.

[0024] The method also includes 104 heating at least one of the plurality of blanks 12 in the roller hearth furnace 16 at the stamping temperature and for the second predetermined period of time after heating the at least one of the plurality of blanks in the batch heating furnace 14. According to an embodiment, the stamping temperature is approximately 930° C and the second predetermined period of time is approximately zero to 300 seconds. The method also includes 106 stamping the at least one of the plurality of blanks 12 in the die 17 after heating the at least one of the plurality of blanks in the roller hearth furnace 16. According to another embodiment, the second period of time could be in a range of approximately zero to 60 seconds. The method may also include 108 quenching the at least one of the plurality of blanks 12.

[0025] By simultaneously preheating a large quantity of blanks at the intermediate temperature in the batch furnace 16, a large portion of the time required for heating can effectively be saved because the components can spend less time in the roller hearth furnace 16 as compared to prior methods, which shortens an overall cycle time of the hot stamping process. Final mechanical properties of the blanks 12 are not affected by the dwell time in the batch furnace 16 due to the blanks 12 being treated at the intermediate temperature, which is less than the critical temperature in the batch furnace 14. As illustrated in FIG. 4, it isn’t until the blanks reach the critical temperature that the interdiffusion layer 22 becomes excessively thick (at approximately 16 pm). FIG. 2 illustrates that the blanks 12 can reach the intermediate temperature in the batch furnace 14 in the first predetermined time duration, and then enter the roller hearth furnace 16 in which they are heated at the stamping temperature for the second predetermined period of time to provide the austenite microstructure. Testing has shown that material properties of the blank 12 are not affected by the length of time spent at the intermediate temperature in the batch furnace 16 according to the embodiments of the present disclosure.

[0026] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in that particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0027] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or later, or intervening element or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0028] Although the terms first, second, third, etc. may be used herein to described various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms may be onlyused to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0029] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0030] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

CLAIMSWhat is claimed is:

1. A method for hot stamping a plurality of blanks, comprising: providing a plurality of blanks; heating the plurality of blanks concurrently in a batch heating furnace at an intermediate temperature being less than a stamping temperature for a first predetermined time duration; heating at least one of the plurality of blanks in a roller hearth furnace at the stamping temperature for a second predetermined period of time after heating the at least one of the plurality of blanks in the batch heating furnace; and stamping the at least one of the plurality of blanks in a die after heating the at least one of the plurality of blanks in the roller hearth furnace.

2. The method as set forth in claim 1, wherein the intermediate temperature is approximately 800° C.

3. The method as set forth in claim 2, wherein the first predetermined time duration is between approximately 5 minutes and 4 hour.

4. The method as set forth in claim 1, wherein the stamping temperature is approximately 930°C.

5. The method as set forth in claim 4, wherein the second predetermined period of time is approximately zero to 300 seconds.

6. The method as set forth in claim 1, wherein each of the plurality of blanks are heated in the roller hearth furnace individually.

7. The method as set forth in claim 1, wherein the roller hearth furnace has an entrance and an exit, and a plurality of rollers positioned along a length of the roller hearth furnace between the entrance and the exit, and wherein heating at least one of the plurality of blanks in the roller hearth furnace includes moving each of the plurality of blanks through the roller hearth furnace along the rollers at the stamping temperature between the entrance and the exit of the roller hearth furnace.

8. The method as set forth in claim 1, wherein heating the at least one of the plurality of blanks in the roller hearth furnace produces an interdiffusion layer thickness on an aluminum silicon coating on the blank of less than 16 pm.

9. A system for hot stamping a plurality of blanks, comprising: a batch heating furnace configured to heat the plurality of blanks concurrently at an intermediate temperature being less than a stamping temperature for a first predetermined time duration; a roller hearth furnace configured to heat the plurality of blanks at the stamping temperature for a second predetermined period of time; and a die configured to stamp the plurality of blanks after heating the at least one of the plurality of blanks in the roller hearth furnace.

10. The system as set forth in claim 9, wherein the intermediate temperature is approximately 800° C.

11. The system as set forth in claim 10, wherein the first predetermined time duration is between approximately 5 minutes and 4 hour.

12. The system as set forth in claim 9, wherein the stamping temperature is approximately 930°C.

13. The system as set forth in claim 12, wherein the second predetermined period of time is approximately zero to 300 seconds.

14. The system as set forth in claim 9, wherein the roller hearth furnace is configured to heat each of the plurality of blanks individually.

15. The system as set forth in claim 9, wherein the roller hearth furnace has an entrance and an exit, and a plurality of rollers positioned along a length of the roller hearth furnace between the entrance and the exit, and wherein the roller hearth furnace is configured to move each of the plurality of blanks through the roller hearth furnace along the rollers at the stamping temperature between the entrance and the exit after the plurality of blanks have been heated at the stamping temperature in the batch heating furnace.

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