HOT FORMING TOOL WITH INFRARED LIGHT SOURCE

Abstract

The method includes the step of preparing a die assembly and proceeds with the step of heating a blank that is made of metal. The method continues with the step of inserting the heated blank into the die assembly. The method proceeds with the step of closing the die assembly to deform the blank into a structural component. With the die assembly closed, the method continues with the step of simultaneously cooling at least one first portion of the structural component that is in contact with the first and second forming surfaces and directing infrared light directly onto at least one second portion of the structural component through the at least one opening to maintain the at least one second portion at an elevated temperature compared to the at least one first portion.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to tailored structural components with varying microstructures and more particularly to tailored structural components for automotive vehicles and to methods of manufacturing the same.

2. Related Art

High strength structural components formed of steel for automotive vehicles, such as B-pillars, are oftentimes designed with tailored material properties to meet crash standards set by the automotive industry and to meet other requirements. A steel blank can be hot formed and quenched to create hard zones providing the required strength, and soft zones providing an increased ductility in select areas of the blank. Various tailored tempering properties (TTP) technologies can be used to form the soft zones. For example, the soft zones can be formed by heating sections of the dies while forming the blank to a desired shape between the dies. The soft zones can also be formed during a post shaping, annealing process. However, there is a continuing desire for a more efficient method to create soft zones into hot formed components.

SUMMARY OF THE INVENTION AND ADVANTAGES

One aspect of the present invention is related to a method of making a shaped structural component. The method includes the step of preparing a die assembly which includes a first die with a first forming surface and a second die with a second forming surface and wherein at least one of the first and second dies has an opening which extends to a respective one of the first and second forming surfaces. The method proceeds with the step of heating a blank that is made of metal. The method continues with the step of inserting the heated blank into the die assembly between the first and second forming surfaces. The method proceeds with the step of closing the die assembly to deform the blank into a structural component. With the die assembly closed, the method continues with the step of simultaneously cooling at least one first portion of the structural component that is in contact with the first and second forming surfaces and directing infrared light directly onto at least one second portion of the structural component through the at least one opening to maintain the at least one second portion at an elevated temperature compared to the at least one first portion.

The method allows for structural components with tailored tempered properties to be produced in a die assembly with extremely quick cycle times and without the need for any post formation heat treating operations. The method also requires minimal tool costs and energy input, and the die assembly may be quickly modified at little to no additional cost to alter the metallurgical properties of the resulting structural components.

According to another aspect of the present invention, the method further includes the steps of opening the die assembly and removing the structural component from the die assembly and wherein the at least one second portion of the structural component is at a higher temperature than the at least one first portion when the structural component is removed from the die assembly.

According to yet another aspect of the present invention, the heated blank is above 650 degrees Celsius before the step of closing the die assembly.

According to still another aspect of the present invention, the at least one first portion of the structural component has a temperature that is less than 200 degrees Celsius and the at least one second portion of the structural component has a temperature that is greater than 300 degrees Celsius when the structural component is removed from the die assembly.

According to a further aspect of the present invention, the metal of the at least one first portion of the structural component is at least substantially entirely martensite after the structural component is removed from the die assembly.

According to yet a further aspect of the present invention, the step of directing infrared light directly onto the at least one second portion of the structural component occurs for less than an entire time that the die assembly is closed.

According to still a further aspect of the present invention, each of the first and second forming surfaces is provided with at least one opening, and the openings in the first and second dies are aligned with one another.

According to another aspect of the present invention, the step of directing light directly at the at least one second portion of the structural component is further defined as directing light directly at the at least one second portion through both of the aligned openings in the first and second dies.

According to yet another aspect of the present invention, the blank is made of 22MnB5 steel.

According to still another aspect of the present invention, the step of closing the die assembly is further defined as moving one of the first and second dies towards the other of the first and second dies to sandwich the blank between the first and second forming surfaces.

Another aspect of the present invention is related to a die assembly for making tailored structural components. The die assembly includes a first die that has a first forming surface and a second die that has a second forming surface. At least one of the first and second dies is movable relative to the other of the first and second dies to open and close the die assembly. The first and second dies have cooling channels for conveying a coolant through the first and second dies to cool the structural component. At least one of the first and second dies has at least one opening that extends to the respective forming surface. At least one infrared lamp is disposed in the at least one opening for directing infrared light directly onto the structural component when the die assembly is closed.

According to another aspect of the present invention, each of the first and second dies has at least one opening, and the openings in the first and second dies are aligned with one another.

According to yet another aspect of the present invention, the at least one infrared lamp is disposed in the opening of one of the first and second dies and the aligned opening of the other of the first and second dies is free of infrared lamps.

According to still another aspect of the present invention, infrared lamps are disposed in both of the aligned openings in the first and second dies.

According to a further aspect of the present invention, each of the first and second dies has a plurality of the openings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and 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:

FIG. 1 is a perspective elevation view of a structural component produced according to one aspect of the present invention;

FIG. 2 is an enlarged view of a portion of the structural component of FIG. 1 and illustrating a plurality of soft zones that are formed into the structural component;

FIG. 3 is a cross-sectional view of the structural component of FIG. 1 and taken through one of the soft zones shown in FIG. 2;

FIG. 4 is a cross-sectional view of a first exemplary embodiment of a die assembly for making the structural component with a blank being loaded onto the die assembly and the die assembly being in an open condition;

FIG. 5 is another cross-sectional view of the first exemplary embodiment of the die assembly and with the die assembly being in a closed condition and having shaped the blank into a structural component;

FIG. 6 is a cross-sectional view of a second exemplary embodiment of the die assembly with the die assembly being in a closed condition and having shaped the blank into the structural component; and

FIG. 7 is a cross-sectional view of a second exemplary embodiment of the die assembly with the die assembly being in a closed condition and having shaped the blank into the structural component.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENTS

Referring to FIGS. 1-3, a structural component 20, which is made with a method according to one aspect of the present invention, is generally shown. The structural component 20 has tailored material properties because, though it is made of a single, monolithic piece, it has quenched areas with increased hardness and tempered areas with increased ductility. In the exemplary embodiment, the structural component 20 is a B-pillar for an automotive vehicle body. However, it should be appreciated that the method could be employed to make a range of different automotive and non-automotive components including, for example, pillars, beams, bumpers, and rails.

Referring now to FIGS. 4 and 5, the exemplary method includes with the step of preparing a die assembly 22 which includes an upper die 24 and a lower die 26. In a first exemplary embodiment, the upper die 24 is movable in a vertical direction to open (shown in FIG. 4) and close (shown in FIG. 5) the die assembly 22. The upper die 24 has an upper forming surface 28 which faces towards the lower die 26, and the lower die 26 has a lower forming surface 30 which faces towards the upper die 24. The upper and lower forming surfaces 28, 30 are shaped such that when the die assembly 22 in the closed position, a gap between the upper and lower forming surfaces 28, 30 defines a cavity which is shaped generally similarly to the structural component 20.

Each of the dies 24, 26 also includes a plurality of cooling channels 32 for conveying a cooling fluid (such as water) through the dies 24, 26 to cool the upper and lower forming surfaces 28, 30 and thereby quench the structural component 20 during operation of the die assembly 22. The upper and lower dies 24, 26 also include a plurality of sets of aligned openings 34 (one set of aligned openings 34 being shown in FIGS. 4 and 5) which extend from inside the dies 24, 26 to the respective forming surfaces 28, 30 such that the upper and lower forming surfaces 28, 30 are non-continuous. Therefore, during quenching, heat is not extracted from the areas of the structural component 20 that are aligned with the openings 34 as quickly as it is extracted from the surrounding areas. The openings 34 may have any suitable shapes and sizes.

The die assembly 22 also includes a heat source in the form of a plurality of infrared lamps 36 (one being shown in FIGS. 4 and 5) which are disposed in at least some of the openings 34 of the upper die 24 and are aimed to emit infrared light downwardly towards the lower die 26. In the first exemplary embodiment of the die assembly 20, the openings in the lower die 26 are free of infrared lamps 24 or other heat sources and may be empty or may be filled with an insulating material. Alternately, as discussed in further detail below, the infrared lamps 36 may only be disposed in the openings 34 of the lower die 26 or may be disposed in the openings 34 of both of the upper and lower dies 24, 26.

The method proceeds with the step of heating a metal blank 38 in an oven. Preferably, the blank 38 is provided in the form of a sheet of metal and is entirely heated to a generally uniform temperature that is greater than 900 degrees Celsius. The metal of the blank 38 is preferably steel or a steel alloy, such as 22MbB5 steel. However, it should be appreciated that any suitable metal.

The method continues with the step of inserting the heated blank 38 into the die assembly 22 between the upper and lower forming surfaces 28, 30 and into the position shown in FIG. 4. At this point, the blank 36 may be supported by one or more spacers to keep the blank out of contact with or in minimal contact with the lower die 26.

The method proceeds with the step of closing the die assembly 22 to deform the blank 36 between the upper and lower forming surfaces 28, 30 to conform the blank 38 to the shape of the cavity and thereby shape the blank 38 into the structural component 20. The entire blank 38 is preferably at a generally constant temperature of approximately 700 degrees Celsius at the time that the die assembly 22 begins closing. The elevated temperature of the blank 38 allows the metal to very easily conform to the shape of the cavity as the die assembly 22 without overly stressing the metal in a process sometimes known as “hot forming”.

With the die assembly 20 closed, the method continues with the step of quenching a first portion 40 of the structural component 20 that is in direct contact with the upper and lower forming surfaces 28, 30 of the upper and lower dies 24, 26. More specifically, heat is rapidly extracted from the metal of the first portion 40, through the upper and lower forming surfaces 28, 30 and to the cooling fluid in the cooling channels 32 of the upper and lower dies 24, 26. The rapid cooling of the metal of the first portion 40 results in the formation of martensite such that the first portion 40 of the structural component 20 has a very high hardness.

Simultaneous to the quenching of the first portion 40 of the structural component 20 within the die assembly 20, the infrared lamps 36 are operated to direct infrared light through the openings 34 in the upper die 24 and directly onto a plurality of second portions 42 of the structural component 20. The infrared light injects heat into the metal of the second portions 42 to maintain the second portions 42 at elevated temperatures while the first portion 40 rapidly cools during quenching.

When the die assembly 22 is opened and the structural component 20 is removed therefrom, the second portions 42 are preferably still at elevated temperatures relative to the first portion 40. In the exemplary embodiment, when the structural component 20 is removed from the die assembly, the first portion 40 has a temperature that is less than 125 degrees Celsius and the second portions are at a temperature that is greater than 300 degrees Celsius. The relatively slower cooling of the second portions 42 relative to the first portion 40 tempers the metal in the second portions 42 to prevent, or at least reduces, the formation of martensite in the second portions 42 of the structural component 20 and may promote the formation of at least one of tempered martensite, ferrite, pearlite, bainite, austenite, and cementite. As such, the martensitic first portion 40 (referred to hereinafter as the “hard zone 40”) of the structural component 20 has an increased hardness relative to the second portions 42 (referred to hereinafter as “soft zones 42”), and the soft zones 42 have a reduced hardness and increased ductility as compared to the hard zone 40.

As shown in FIG. 3, the structural component 20 also includes transition zones 44 between the soft zones 42 and the hard zone 40. Within the transition zones 44, the ductility of the metal increases from the hard zone 40 to the respective soft zone 42, and the hardness increases from the respective soft zone 42 to the hard zone 40.

The power of the infrared lamps 36, the distance between the infrared lamps 36 and the structural component 20 in the cavity of the die assembly 22 and the time that the infrared lamps 36 are operated may all be specifically chosen in order to provide the soft zones 42 of the resulting structural component 20 with the desired microstructures and material properties. These variables can be different for the different infrared lamps 36 such that the multiple soft zones 42 in the structural component 20 can have different microstructures and different metallurgical properties.

The entire cycle time of the die assembly 22 from inserting the blank 38 between the upper and lower forming surfaces 28, 30 to removing the shaped structural component 20 from the die assembly preferably takes less than twenty seconds. The rapid speed with which the infrared lamp 36 is able to get up to operating temperature has been found to allow for such a quick cycle time, thereby allowing the die assembly 22 to produce a very large number of structural components 20 in minimal time.

To achieve for quick cycle times for the die assembly 22 while still tempering the soft zones 42, when the structural component 20 is removed from the die assembly 22, the soft zones 42 are preferably still at an elevated temperature as compared to the hard zone 40. The hard and soft zones 40, 42 then finish cooling to room temperature outside of the die assembly 22. No post formation heat treating operations are required.

Because the openings 34 of the upper and lower dies 24, 26 extend all the way to the forming surfaces 28, 30, the metal in the soft zones 42 of the structural component 20 cannot be deformed as the die assembly 22 is closed. That is, the soft zones 42 can only be formed into underformed, or flat, areas of the structural component 20.

The soft zones 42 are preferably located in areas of the structural component 20 where increased ductility and/or reduced hardness is desirable. For example, the soft zones 42 can be located in places where mechanical elements, such as self-piercing rivets or flow screws, are to penetrate the structural component 20, thereby allowing for easier penetration of the structural component 20. The soft zones 42 can also be placed in areas of the structural component 20 that are subject to localized forces to reduce local stresses by absorbing energy and prevent, or at least reduce, the formation of cracks in those areas.

Referring now to FIG. 6, a second exemplary embodiment of the die assembly 122 is generally shown with like numerals, separated by a prefix of “1”, indicating corresponding parts with the first exemplary embodiment described above. In the second exemplary embodiment, infrared lamps 136 are provided in the openings 134 of both of the upper and lower dies 124, 126. Accordingly, when the die assembly 122 is closed, infrared light is guided directly onto both a top surface and a bottom surface of the structural component 120 to warm the soft zones 142.

Referring now to FIG. 7, a third exemplary embodiment of the die assembly 222 is generally shown with like numerals, separated by a prefix of “2”, indicating corresponding parts with the first and second exemplary embodiments described above. In the third exemplary embodiment, the lower die 226 lacks openings 234, and therefore, when the die assembly 222 heat is closed, heat is injected into soft zones 242 from the infrared light and heat is extracted from the soft zones 242 through the lower forming surface 230 of the lower die 226. This may allow for some deformation of the metal in the soft zones 242. The rate that the heat is extracted from the soft zones 242 may be controlled by spacing the cooling channels 232 in the lower die 226 further from this area of the lower forming surface 230.

Many modifications and variations of the present disclosure are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the invention.

Claims

1. A method of making a structural component that has tailored properties, comprising the steps of: preparing a die assembly which includes a first die with a first forming surface and a second die with a second forming surface and wherein at least one of the first and second dies presents at least one opening which extends to a respective one of the first and second forming surfaces;heating a blank that is made of metal;inserting the heated blank into the die assembly between the first and second forming surfaces;closing the die assembly to deform the blank into a structural component; andwith the die assembly closed, simultaneously cooling at least one first portion of the structural component that is in contact with the first and second forming surfaces and directing infrared light directly onto at least one second portion of the structural component through the at least one opening to maintain the at least one second portion of the structural component at an elevated temperature compared to the at least one first portion.

2. The method as set forth in claim 1 further including the steps of opening the die assembly and removing the structural component from the die assembly and wherein the at least one second portion of the structural component is at a higher temperature than the at least one first portion of the structural component when the structural component is removed from the die assembly.

3. The method as set forth in claim 2 wherein the heated blank is above 650 degrees Celsius before the step of closing the die assembly.

4. The method as set forth in claim 3 wherein the at least one first portion of the structural component has a temperature that is less than 200 degrees Celsius and the at least one second portion of the structural component has a temperature that is greater than 300 Celsius when the structural component is removed from the die assembly.

5. The method as set forth in claim 4 wherein the metal of the at least one first portion of the structural component is at least substantially entirely martensite after the structural component is removed from the die assembly.

6. The method as set forth in claim 2 wherein the step of directing infrared light directly onto the at least one second portion of the structural component occurs for less than an entire time that the die assembly is closed.

7. The method as set forth in claim 1 wherein each of the first and second forming surfaces is provided with at least one opening and wherein the openings in the first and second forming surfaces are aligned with one another.

8. The method as set forth in claim 1 wherein the first and second dies have openings that are aligned with one another and wherein the step of directing light directly at the at least one second portion of the structural component is further defined as directing light directly at the second portion through both of the aligned openings in the first and second dies.

9. The method as set forth in claim 1 wherein the blank is made of 22MnB5 steel.

10. The method as set forth in claim 1 wherein the step of closing the die assembly is further defined as moving one of the first and second dies towards the other of the first and second dies to sandwich the blank between the first and second forming surfaces.

11. A die assembly for making a structural component, comprising: a first die that has a first forming surface and a second die that has a second forming surface and wherein at least one of said first and second dies is movable relative to the other of said first and second dies to open and close said die assembly;said first and second dies having cooling channels for conveying a coolant through said first and second dies to cool the structural component;at least one of said first and second dies having at least one opening that extends to the respective forming surface; andat least one infrared lamp disposed in said at least one opening for directing infrared light directly onto the structural component when said die assembly is closed.

12. The die assembly as set forth in claim 11 wherein each of said first and second dies has at least one opening and wherein said openings in said first and second dies are aligned with one another.

13. The die assembly as set forth in claim 12 wherein said at least one infrared lamp is disposed in said opening of one of said first and second dies and said aligned opening in the other of said first and second dies is free of infrared lamps.

14. The die assembly as set forth in claim 12 wherein infrared lamps are disposed in both of said aligned openings in said first and second dies.

15. The die assembly as set forth in claim 11 wherein each of said first and second dies has a plurality of said openings.

16. The method as set forth in claim 1 wherein during the step of closing the die assembly to deform the blank into a structural component, the first and second forming surfaces directly contact the blank.

17. The method as set forth in claim 1 wherein the first and second dies have openings that are aligned with one another and wherein the infrared light is directed onto the at least one second portion of the structural portion through only either the opening of the first die or the opening of the second die.