CN111195685A

CN111195685A - Thermally assisted roll bending of multiple sheet materials

Info

Publication number: CN111195685A
Application number: CN201910430168.9A
Authority: CN
Inventors: A·K·萨契戴夫; J·E·卡斯利; R·N·萨热
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2018-11-20
Filing date: 2019-05-22
Publication date: 2020-05-26
Also published as: DE102019115988A1; US20200156134A1

Abstract

A heat assist method deforms a sheet metal assembly having constrained ends. The focal flexure region between the constrained ends is heated. The focal bending region is bent when the sheet metal assembly is within the elevated bending temperature range. A metal blank assembly may be formed by the present method and includes an outer metal blank and an inner metal blank secured together with the outer metal blank to form a constrained end. The sheet metal assembly has a bend formed between first and second constrained ends, wherein each sheet metal is bent at the bend with the bend having a maximum gap between the inner sheet metal and the outer sheet metal. The maximum gap is no greater than five times a thickness of one of the inner and outer sheet metal materials, and the radius of the bend is less than three times the thickness of one of the inner and outer sheet metal materials.

Description

Thermally assisted roll bending of multiple sheet materials

Technical Field

The present disclosure relates generally to metal forming and, more particularly, to a heat assisted multi-sheet roll forming process for constraining a metal sheet assembly.

Background

Roll-forming at a production facility is typically accomplished by bending a single sheet of material and plastically deforming it into the desired shape at room temperature using a series of progressively different rolls. The process is continuous and high speed, the result of which is to bend the sheet into a specific profile for a specific purpose.

However, future products are being designed with higher strength materials and complex computer analysis complicates the design of sheet materials that typically require high strength sharp corners. When bending a high strength material, these two factors oppose each other and the region that is subjected to large strain breaks.

To increase the difficulty, the entire sheet metal assembly must be moved as a unit when welding two sheets at their edges. If an attempt is made to bend two metal sheets that may not have a neutral axis on their mating surfaces, the two metal sheets will tend to separate at the bend due to compressive stresses inside the neutral axis and tensile stresses outside the neutral axis. As a result, the inner sheet is pushed inward and the two sheets do not remain together at the bend.

Disclosure of Invention

The present disclosure provides a system and method of deforming a sheet metal assembly having a restrained end attached around a tight bend where the sheet metal does not separate, and another sheet metal assembly having a flip-over bend where the sheet metal pieces are substantially held together.

In one form, which may be combined with or separate from other forms disclosed herein, a method of forming a metal sheet assembly is provided. The method includes providing a metal blank assembly including at least an outer metal blank and an inner metal blank, wherein the outer metal blank is secured to the inner metal blank to form a first restraining end and a second restraining end. The sheet metal assembly has an initial temperature. The method also includes heating a focal bending area (focus bending area) of the sheet metal assembly to a bending temperature range that is at least greater than the initial temperature. The focal flexure zone is located between the first and second constrained ends of the sheet metal assembly. Additionally, the method includes bending the focal bending region of the sheet metal assembly while the sheet metal assembly is within the bending temperature range.

In another form, which may be combined with or separate from other forms disclosed herein, there is provided a sheet metal assembly comprising an outer sheet metal material and an inner sheet metal material. The outer and inner sheet metal materials are secured together to form first and second constrained ends. The sheet metal assembly has a bend formed between first and second constrained ends. Each sheet metal material is bent at a bend, and the bend has a maximum gap between the inner sheet metal material and the outer sheet metal material. The maximum gap is not more than five times the thickness of one of the inner and outer metal sheets. The bend radius is less than three times the thickness of one of the inner and outer metal sheets.

Additional features may be provided, including but not limited to the following: wherein the bending step comprises rolling a roller tool against the sheet metal assembly to form a bend having an outer side and an inner side in the focal bend region; before the heating step, arranging a heat source near the outer plate and/or the inner plate at the focus bending area; heating the focal point bending region by a heat source; wherein the heating step comprises applying laser light to the curved region of the focal spot; providing an inner sheet metal material formed of a first material; providing an outer metal sheet formed of a second material; the first and second materials are different from or the same as each other; providing at least one of the inner and outer metal sheets as being formed of an aluminum alloy; providing at least one of the inner and outer metal sheets as being made of steel; providing an inner sheet metal material having a first thickness; providing the outer metal sheet to have a second thickness; the first and second thicknesses are not equal; the first and second thicknesses are substantially equal to each other; maintaining a maximum gap between the inner and outer metal sheets in the focal bending zone; the maximum gap is not more than five times the thickness of one of the inner and outer metal sheets; the maximum gap is not more than half the thickness of one of the inner and outer metal sheets; after bending, rapidly quenching the sheet metal assembly to maintain a high temperature phase structure at room temperature, or to obtain a different phase structure based on a controlled cooling rate of equilibrium phase transformation; wherein bending the sheet metal assembly further comprises forming the bend with a radius less than three times a thickness of one of the inner and outer sheet metal materials; providing a mold or opposing roller tool having a bend formed therein; wherein the bending step comprises pressing the sheet metal component against the die bend with the roller tool to form a partial bend in the sheet metal component; and/or at least one of the inner and outer metal sheets maintains a high temperature phase structure at room temperature.

Further features and advantages of the present disclosure, as well as various example structures and operations of the present disclosure, are described in detail below with reference to the accompanying drawings. It should be noted that this disclosure is not limited to the specific examples described herein. These examples are presented herein for illustrative purposes only. Other examples will be apparent to persons skilled in the relevant art(s) in light of the teachings contained herein.

Drawings

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic cross-sectional view of an unbent sheet metal assembly in a first step of a method of forming the sheet metal assembly according to the principles of the present disclosure;

FIG. 2 is a schematic cross-sectional view of the unbent sheet metal assembly of FIG. 1 along with a tool for forming the sheet metal assembly according to the principles of the present disclosure;

FIG. 3 is a schematic cross-sectional view of the sheet metal assembly of FIGS. 1 and 2 in a partially bent configuration according to the principles of the present disclosure;

fig. 4 is a schematic cross-sectional view of the metal blank assembly of fig. 1-3 with a bend formed in the metal blank assembly in accordance with the principles of the present disclosure.

FIG. 5 is a schematic cross-sectional view of a bent sheet metal assembly after performing the steps shown in FIGS. 1-4, according to the principles of the present disclosure; and

fig. 5A is a schematic cross-sectional view of another variation of a bent sheet metal assembly after performing the steps shown in fig. 1-4, according to the principles of the present disclosure.

Detailed Description

While the disclosure is described herein using illustrative examples of specific applications, it is to be understood that the disclosure is not so limited. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and examples within the scope thereof and additional fields in which the disclosure finds significant utility.

The present disclosure discloses a heat-assisted method for plastically deforming a metal sheet component. Accordingly, the method involves forming a sheet metal assembly having a bend therein.

A metal blank assembly 10 is provided that includes at least an "outer" metal blank 12 and an "inner" metal blank 14. Since it will be described below that the metal plate material 12 is located outside the bent portion and the metal plate material 14 is located inside the bent portion, the metal plate material 12 is referred to as an "outer plate material" and the metal plate material 14 is referred to as an "inner plate material". Additional sheet metal may also be included in the sheet metal assembly 10 if desired. Thus, the metal blank assembly 10 may have two, three, four, five or any desired number of metal blanks.

The outer and inner

sheet metal materials

12 and 14 are secured together to form a first restraining end 16 and a second restraining end 18. For example, the outer and

inner metal sheets

12, 14 may be secured together by welding, brazing, riveting, or in any other desired manner. In the illustrated example, the weld head 20 joins the outer and inner

sheet metal materials

12, 14 together at the first and second

constrained ends

16, 18.

The sheet metal assembly 10 has a certain temperature, referred to as the initial temperature, prior to bending. For example, the initial temperature may be room temperature.

All of the

metal sheets

12, 14 may be formed of the same or different materials. For example, the two

metal sheets

12, 14 may be formed of steel, or one of the

metal sheets

12, 14 may be formed of steel and the other may be formed of aluminum or an aluminum alloy. All of the

metal sheets

12, 14 may be coated metal sheets or uncoated metal sheets.

If alloyed, the aluminum alloy may include at least 85 wt.% aluminum. Some notable aluminum alloys that may constitute coated or uncoated aluminum substrates are aluminum-magnesium alloys, aluminum-silicon alloys, aluminum-magnesium-silicon alloys, and aluminum-zinc alloys. If coated, the aluminum sheet metal may include a surface layer of refractory oxide material (natural and/or manufactured at high temperatures, such as mill scale) composed of an alumina compound and other possible oxidizing compounds, such as magnesium oxide if the aluminum substrate contains magnesium. Aluminum sheet metal may also be coated with a zinc, tin or metal oxide conversion coating comprised of titanium, zirconium, chromium or silicon oxides as described in U.S. patent No. 9,987,705. The aluminum sheet metal may be provided in forged or cast or extruded form. For example, the metal sheet may consist of a layer of a 2xxx, 3xxx, 4xxx, 5xxx, 6xxx or 7xxx series wrought aluminium alloy sheet, an extruded article, a forged article or other fabricated article. Alternatively, the metal sheet may consist of a 4xx.x, 5xx.x, 6xx.x or 7xx.x series aluminium alloy casting. Other aluminum alloys that may be used include, but are not limited to, AA5754 and AA5182 aluminum magnesium alloys, AA6111 and AA6022 aluminum magnesium silicon alloys, AA7003 and AA7055 aluminum zinc alloys, and Al-10Si-Mg aluminum die cast alloys. The aluminum sheet metal material may also be used in various states including an annealed state (O), a strain hardened state (H), an unstable state (W), and a solution heat treated state (T), if desired. When more than one aluminum metal sheet is used in the metal sheet assembly 10, the composition, thickness, and/or form (e.g., forged or cast) of the aluminum metal sheets may be the same or different.

One or both of the

metal sheets

12, 14 may be made of coated or uncoated steel having various strengths and grades. The steel sheet may be hot rolled or cold rolled, and may be composed of steels, such as low carbon steels, interstitial free steels, bake hardenable steels, High Strength Low Alloy (HSLA) steels, Dual Phase (DP) steels, Composite Phase (CP) steels, Martensite (MART) steels, transformation induced plasticity (TRIP) steels, quench distribution steels (Q & P), twinning induced plasticity (TWIP) steels, and boron steels (e.g., when the steel sheet comprises Press Hardened Steel (PHS)). If coated, the steel sheet may comprise a surface layer of zinc (e.g. hot dip galvanized or electro-galvanized), a zinc-iron alloy (e.g. galvanized or electro-galvanized), a zinc-nickel alloy, nickel, aluminum, an aluminum-magnesium alloy, an aluminum-zinc alloy or an aluminum-silicon alloy.

Either of the metal sheets 12, 14 (and additional sheets, if included) may be cold rolled metal sheets, such as aluminum having a strength greater than 300 megapascals (MPa), preferably greater than 500MPa, or steel having a strength greater than 1000MPa, preferably greater than 1500 MPa.

The method disclosed herein is used to ultimately form the sheet metal component 10 into a component having a bend therein. All of the

sheet metal materials

12, 14 may have unequal thicknesses t1, t2, respectively, or the thicknesses t1, t2 may be substantially equal to each other. By way of example, the thicknesses t1, t2 may be in the range of 0.2-4.0 mm. In the case where t1 and t2 are not equal, the neutral axis N is not located at the interface between the

metal blank

12, 14, but rather the neutral axis N extends through one of the metal blanks 12, 14 (in this case, the blank 12). Thus, when the sheet metal assembly 10 is bent, the entire inner sheet 14 will be in compression, and when the sheet metal assembly 10 is bent, the outer sheet 12 will have a portion 13 in compression and a portion 15 in tension.

To ultimately form the sheet metal assembly 10 into an assembly having a bend therein, the method includes heating the focal bend region 22 of the sheet metal assembly 10 to a bend temperature range that is at least greater than the initial temperature. The focal bending region 22 may be heated by, for example, a heat source 24 disposed adjacent the outer metal sheet 12 such that the outer metal sheet 12 of the focal bending region 22 becomes malleable and may extend around the bend. Prior to the heating step, a heat source 24 is positioned adjacent the outer sheet 12 at the focal point bending region 22. The focal flexure zone 22 is located between the first and second constrained ends 16, 18 of the sheet metal assembly 10. In the alternative, a heat source 24 may be provided adjacent the inner sheet 14 at the focal bend region 22 to apply heat from the interior of the resulting bend.

By way of example, the heat source 24 may be a laser heat source, such as a laser scanning beam. Thus, the step of heating the focal point bending region 22 may be achieved by applying the laser beam 25 to the focal point bending region 22. Other examples of heating may be induction heating, flame heating, polyhalogen heating, high intensity infrared source heating, conductive heating or resistance heating, wherein an electric current will be passed through the thickness of the sheet from a roller tool in contact with one side of the sheet to a second roller in contact with the other side of the sheet. In resistive heating, the resistance of the material to the current is responsible for the heating effect. Heating is then used to assist in bending the sheet. In conductive heating, one or more rollers may be heated by an external source (not shown) such that the material is heated by contact and bends as it passes through the roller dies.

Once the focal bending region 22 reaches the bending temperature range, a bend is formed within the metal blank assembly 10 by bending the focal bending region 22 of the metal blank assembly 10. Bending is completed when the sheet metal assembly 10 is within the bending temperature range. In some examples, the bending temperature range is within or above the two-phase subcritical temperature region, but preferably above the critical temperature. The actual bending temperature range is therefore dependent on the material used for the

metal sheets

12, 14. In some examples, the

metal sheets

12, 14 are heated to the solution temperature or austenitizing temperature using a heat source 24, preferably a laser.

Referring now to fig. 2 and 3, in some examples, to bend the sheet metal assembly 10 over a bending temperature range, a roller tool 26 is rolled against the sheet metal assembly 10 to form a bend 28 in the focal bend region 22. The sheet metal assembly 10 may be pressed by a roller tool 26 against a die 30, the die 30 having a die bend 32 formed therein. In this example, the sheet metal assembly 10 is bent by pressing the sheet metal assembly 10 against the die bend 32 with the roller tool 26 to form the bend 28 in the sheet metal assembly 10. Preferably, the heat source 24 is positioned directly adjacent to the roller tool 26 such that the focal bending region 22 is maintained within a bending temperature range while the sheet metal assembly 10 is bent with the roller tool 26.

Accordingly, as shown in fig. 4 and 5, a kick-out bend 28 is formed in the sheet metal assembly 10, which is formed in both the outer sheet metal material 12 and the inner sheet metal material 14. The bight portion 28 has an outer side 34 formed in the outer sheet 12 and an inner side 36 formed in the inner sheet 14. Thus, the bend 28 includes an outer bend 38 in the outer sheet 12 and an inner bend 40 in the inner sheet 14. The outer bend 38 and the inner bend 40 fit closely together to form the bend 28 in the sheet metal assembly 10. In some examples, the outer and

inner flexures

38, 40 have no gap between them and are in contact with each other, as shown in fig. 5. Heating the focal point bending region 22 reduces the force on the portion 15 of the outer panel 12 that is subjected to the pulling force and helps to balance the forces in the inner bend 40 and the outer bend 38.

Referring now to fig. 5A, in other examples, there is a gap between the outer bend 38 and the inner bend 40; in other words, a gap g exists between the outer sheet metal 12 and the inner sheet metal 14 at the bend 28 of the sheet metal assembly 10. For example, the gap g may be no greater than five times the thickness t2, t1 of one of the inner and outer

sheet metal plates

14, 12. Thus, in this example, the outer panel 12 is thicker than the inner panel 14, so the gap g is no greater than five times t 1. In other examples, the gap g may be much smaller, such as no more than half the thickness t1, t2 of one of the outer and

inner sheets

12, 14, or zero as shown in FIG. 5.

Due to the high intensity heating according to the present disclosure, the metal sheet assembly 10 may be bent to a small radius that is one to three times the thickness of the assembly 10 or one of the

individual sheets

12, 14. Thus, the bend 28 may be a abrupt bend having a radius of curvature r that is less than three times the thickness t1, t2 of one of the outer and inner

sheet metal panels

12, 14, or less than three times the thickness of the assembly 10 as a whole. Thus, in one example, if the outer sheet 12 is thicker than the inner sheet 14, the bend 28 may have a radius of curvature r that is no greater than three times t1, where the radius of curvature r is measured from the bend center C of the bend 28 to the neutral axis N of the sheet metal assembly 10. In other examples, the radius r is no greater than the thickness t1, t2 of one of the inner and

outer sheet materials

12, 14, or no greater than twice the thickness t1, t2 of one of the inner and

outer sheet materials

12, 14.

Cold rolled sheet metal shows elasticity and tends to spring back after bending, resulting in a radius of curvature greater than the initial bend radius. With the intense laser heating of the present disclosure, the spring back effect of the sheet material can be substantially eliminated or greatly reduced, as spring back is strength dependent and the strength during high temperature bending is greatly reduced. Thus, the radius of curvature r is substantially similar to the radius of curvature provided by the

tool systems

26, 30 without any post-processing. Therefore, the radius r produced with the present disclosure may be smaller, such as one to three times the thickness t1, t2, or t1+ t 2.

Although a single roller 26 is shown pressing the metal sheet assembly 10 against the die 30, it should be understood that when the metal sheet assembly 10 is within the bending temperature range, the bending may be accomplished using any other bending process, such as a bending process using multiple rollers. For example, the sheet metal assembly 10 may be continuously fed through parallel rolls on a roll-forming line. In some examples, the sheet metal assembly 10 may be bent into a desired shape through several bending steps, and the bending steps are performed using a plurality of roller dies. Prior to each rolling step, the metal blank assembly 10 may be heated using an additional heat source placed just prior to each set of rollers.

After forming the bend 28 in the metal blank assembly 10, the method may include rapid quenching. Rapid quenching can be accomplished by multiple cold air jets, liquid (water, oil, etc.) jets, contact quenching (e.g., using a rolling tool), self-quenching from the quality of the cold rolled sheet metal, gas jets, or a combination of these quenching methods. The rapid quenching avoids precipitation or any phase change in the sheet metal assembly 10. Rapid quenching enables subsequent precipitation hardening alloys (e.g., aluminum or magnesium) to maintain a high temperature phase structure at room temperature; upon reaching room temperature, the high temperature phase will transform to other higher strength phases, such as retained austenite, martensite, and/or bainite in the presence of steel. After heating and quenching, roll-forming may be continued with another set of roll dies, if desired.

The detailed description and drawings are a support and description for various aspects of the present disclosure. Elements described herein may be combined or exchanged between various examples. While certain aspects have been described in detail, there are various alternative aspects for practicing the invention as defined in the appended claims. The present disclosure is to be considered as illustrative only, and the invention is to be limited only by the following claims.

Claims

1. A method of forming a metal blank assembly comprising:

providing a metal sheet assembly comprising at least an outer metal sheet and an inner metal sheet, securing the outer metal sheet and the inner metal sheet together to form a first constrained end and a second constrained end, the metal sheet assembly having an initial temperature;

heating a focal bend region of the metal blank assembly to a bend temperature range at least greater than the initial temperature, the focal bend region being located between a first constrained end and a second constrained end of the metal blank assembly; and

bending a focal bending region of the sheet metal assembly when the sheet metal assembly is within the bending temperature range.

2. The method of claim 1, wherein the bending step includes rolling a roller tool against the sheet metal assembly to form a bend in the focal bend region, the bend having an outer side and an inner side.

3. The method of any preceding claim, further comprising:

before the heating step, disposing a laser near one of the inner and outer sheets at the focal point bending region; and

heating the focus bending region by applying a laser beam to the focus bending region.

4. The method of any preceding claim, further comprising:

providing an inner sheet metal material formed of a first material; and

the outer metal blank is provided to be formed of a second material, and the first and second materials are different from each other.

5. The method of any preceding claim, further comprising:

providing one of the inner and outer metal sheets as being formed of an aluminum alloy; and

providing the other of the inner and outer sheet metal plates as being formed of steel.

6. The method of any preceding claim, further comprising: wherein the bending step includes forming a bend at the focal bending region, the method further including maintaining a maximum gap between the inner sheet metal material and the outer sheet metal material at the bend, the maximum gap being no greater than five times the thickness of one of the inner and outer sheet metal materials or preferably no greater than half the thickness of one of the inner and outer sheet metal materials, wherein the bending step includes forming a bend at the focal bending region having a radius less than three times the thickness of one of the inner and outer sheet metal materials.

7. The method of any preceding claim, further comprising:

after a high-temperature phase structure is kept at room temperature through bending, rapidly quenching the metal plate assembly; and

providing a die having a die bend formed therein, wherein the bending step comprises bending the sheet metal component against the die with the roller tool to form a partial bend in the sheet metal component.

8. A sheet metal assembly comprising:

an outer metal sheet; and

an inner sheet metal material securing the outer and inner sheet metal materials together to form first and second constrained ends, a bend formed in the sheet metal assembly between the first and second constrained ends, wherein each sheet metal material is bent at the bend, wherein a maximum gap between the inner and outer sheet metal materials is no greater than five times a thickness of one of the inner and outer sheet metal materials or, preferably, no greater than half the thickness of one of the inner and outer sheet metal materials, and the bend has a radius less than three times the thickness of one of the inner and outer sheet metal materials.

9. The metal blank assembly of claim 8, wherein the inner metal blank is formed of a first material, the outer metal blank is formed of a second material, and the first and second materials are different from one another.

10. The metal blank assembly according to claim 8 or 9, wherein at least one of the inner metal blank and the outer metal blank maintains a high temperature phase structure at room temperature.