METHOD OF DESIGNING AND FORMING A SHEET METAL PART
A method of forming a part and a method of designing a part to be formed from a sheet metal blank is disclosed. The part may be formed from lightweight high-strength material to an extent that would normally exceed the forming limits of the material if the part were attempted to be formed in one step in a multi-part die set. Critical areas including deep pockets and sharp radius areas of the final part are formed from a preform or intermediate shape part. The preform is further formed in a fluid pressure forming process to a final part shape wherein broad radius areas of the preform are formed into deep pockets and sharp corners.
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1. Field of the Invention
The present invention relates to a method of forming and a method of designing a part from a sheet metal blank that includes drawing a sheet metal blank to an intermediate shape that is then subsequently formed to a final design shape that includes a critical region.
2. Background Art
Many manufacturing processes are available to form sheet metal blanks into parts in a wide variety of industries. Such manufacturing processes are well suited to form parts having less complex geometries. Some parts may have a critical region that may not be formed by conventional processes without exceeding the formability limits of the material to be formed. Such critical regions may exceed formability limits due to the depth draw required to form the part or due to the need to form tight radii.
To manufacture parts having critical regions, several parts having less complex geometries may be formed and then joined together by welding, riveting or other conventional fastening techniques. Another approach to forming parts having a complex geometry is to form the parts after they are heated to an elevated temperature in a warm forming or super-plastic forming process. Forming parts in an elevated temperature can create issues regarding lubrication and can result in excessive thinning of the walls of the part.
Another approach to forming complex parts having critical regions is to initially form the part, then apply a heat treatment to the part to restore material ductility before reforming the part to the desired final shape. One problem with this approach is that a substantial period of time is required to heat treat the part and the part must be heated treated according to a precise heat treatment schedule to be effective. Another variation of this method is incremental forming in which the part is partially formed and then rapidly heat treated. Any forming method, including heat treating or pre-heating the part, tends to result in excessive thinning of the blank.
Another process which has been proposed is referred to as hydro-mechanical drawing (also down as Amino technology) that provides for friction reduction in localized areas where a material enters the die cavity. The friction reduction allows additional metal to be drawn into the die cavity from the flange area of the blank. Hydro-mechanical drawing processes are not well suited to forming parts where excessive local stretching is required in control areas of a large panel that are located at a substantial distance from the edge of the die because the additional material cannot be drawn from the flange area into the central area.
Part forming processes are also impacted by the type of material that is formed. Aluminum, high-strength steel and advanced high-strength steels tend to be less ductile and have low formability, or forming limits. In particular, forming processes incorporating a heating step or heat treating step are better suited to aluminum alloys and are not generally feasible for high-strength steel and advanced high-strength steels. The need to provide the final parts that offer high-strength properties with reduced weight make it important to use these types of advanced materials for weight reduction. However, the low forming limits of such materials and alloys limit design freedom and the types of parts that may be made with these types of materials.
This development as summarized below solves the above problems and other problems that represent a long-felt need in the field that will allow more complex parts to be made from lightweight, high-strength alloys.
The improvements proposed herein are summarized below.
SUMMARYA method is provided for forming a part into a final design shape that has at least one critical forming region, or area, from a sheet metal blank. The method comprises drawing the blank to form an intermediate shaped part that includes a bulge adjacent to the critical region. The intermediate shaped part is then further formed by forming the bulge into the critical region to form the final design shape.
According to other aspects of this development, the forming step is performed in a fluid pressure forming process. As used herein, the term fluid pressure forming process should be construed to include hydro-forming, gas-forming and electro-hydraulic forming.
The critical regions are areas of the final design shape that require drawing the blank into a sharp corner or drawing the blank to a depth that exceeds the forming limits of the blank. According to the method, in the drawing step, the blank is drawn to a depth that is within the forming limits of the blank. Then, the step of forming the part to the final design shape results in the formation of a final part design that would exceed the forming limits of a single step forming process. The method also involves providing an intermediate shaped part that has at least one bulge that is adjacent an increased radius critical region. The intermediate shaped part has substantially the same surface area compared to the surface area of the final part shape.
According to another characteristic of the method, an intermediate cavity defined by the intermediate part shape is confined within a boundary of a final cavity defined by the final part shape. According to the method, the drawing operation may be performed in a stamping die set that has at least two dies. The forming, or bonding, operation can then be performed in a fluid pressure forming tool after the initial drawing operation is completed.
A method of designing a part to be formed from a sheet metal blank is provided according to the following steps. A final part shape is defined as a computer-aided design model. The final part shape is analyzed using finite element analysis. Critical regions are identified in the final part shape where forming limits of the sheet metal blank may be approached or exceeded. A design shape is simulated to locally reduce the strain applied to the blank in developing an intermediate part shape based upon the shape of the final part. The surface area of the intermediate part shape and the final part shape are substantially the same.
A method of designing a part may further include defining an intermediate cavity within the intermediate part shape that is within a boundary of a final cavity defined by the final part shape.
In the analysis step of the method of designing a part, finite element analysis is used to determine nodal forces in the critical regions of the part. Nodal forces are imposed to transform the final shape into the intermediate shape in the simulating step.
In the step of simulating the design shape, the final part shape is elastically deformed to develop the intermediate part shapes so that the surface area relationship of the intermediate part shape and the final part shape is maintained and the intermediate shape is within the final part shape.
The method of designing a part may further include designing at least one bulge in the blank that is formed in the intermediate part shape and is then reformed to provide material from the bulge to the critical region. The intermediate part shape is designed to be formed and then reformed to allow the bulge to flow into a sharp corner. Development of the intermediate part shape is an iterative process and the final part is tested to verify that the forming limits are not exceeded as the final part is formed.
These and other aspects of the methods will be better understood in view of the attached drawings and the following detailed description of the illustrated embodiments.
The die design method as illustrated in the above drawings and described below facilitates forming complex sheet metal stampings using lightweight material, such as high-strength steels, advanced high-strength steels, and aluminum alloys. Strain distribution tends to be non-uniform in the majority of sheet metal stampings. Strain is greatest where the material is stretched to the greatest extent in sharp corners and in deep pockets. For example, vehicle parts such as license pockets and door handle pockets may have sharp corners and deep pockets that cannot be formed in a single drawing operation to the desired shape.
Referring to
The second step in the process is to determine what forces will be required to deform a simulated elastic blank according to the planned strategy. Structural code capable of simulating contact interaction between the blank and the die is used to simulate the sheet metal forming process. Examples of structural code include MATRAS, LS DYNA, ABAQUS and AUTOFORM, or the like which may be used to simulate sheet metal forming processes. The material is modeled as a thin elastic membrane to develop an equivalent surface.
Numerical analysis is used to calculate and distribute nodal forces that would be required to form the blank from the final shape to a preform shape based upon the FEA data.
Referring to
The distribution of nodal forces for deforming the blank “backwards” from the final shape is defined based upon the numerical analysis. The resulting distribution of nodal forces is illustrated in
The preform shape 18 includes a bulge 24 that is located adjacent to a critical area 20 that is a deep draw pocket or sharp radius area of the part. The preform shape is designed to facilitate forming the final shaped part that is shown in
According to the method, a mathematical tool manipulates the CAD data of the final part by distributing artificial nodal forces required to pull the material out of the sharp corners, assuming that the panel is elastic, to provide a smooth surface preform 18. Also according to the method, in the backwards simulation very high pressure is applied to the flange area to prevent it from moving as the preform shape is calculated to be moving backwards from the final shape data. Metal is drawn from the sharp corners of the final part shape 10 to form the preform part shape 18 with substantially no stretching from the sharp corners into the reserve areas, or bulge 24. In the method, the degree of stretching in the blank 40 as it is formed from the preform shape 18 to the final shape 10 is managed by shrinking the mesh of the final part backwards into the shape of the preform shape 18. When the blank is actually formed from the preform 18 to the final shape 10, the bulge 24 may be formed to a greater extent than the other parts of the preform shape 18.
Referring to
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The procedure illustrated in
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The boundary of the intermediate part shape shown in
By assuming an elastic blank is being formed, the surface area of the preform shape 18 and the final part shape 10 within the cavity may be maintained substantially equal to each other. By keeping the surface area of the preform and the final part shape the same, the preform may be bent, instead of being stretched, to the final part shape.
While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
Claims
1. A method of forming a part from a sheet metal blank, wherein the part has at least one critical region that is formed to a final design shape, the method comprising:
- drawing the blank to form an intermediate shaped part that includes at least one bulge adjacent to the critical region;
- forming the intermediate shaped part to form the at least one bulge into the critical region to form the final design shape.
2. The method of claim 1 wherein the forming step is performed in a fluid pressure forming process.
3. The method of claim 1 wherein the critical regions are areas of the final design shape that require drawing the blank into a sharp corner that exceeds the forming limits of the blank.
4. The method of claim 1 wherein the critical regions are areas of the final design shape that require drawing the blank to a depth that exceeds the forming limits of the blank.
5. The method of claim 1 wherein in the drawing step the blank is drawn to a depth that is within the forming limits of the blank, and wherein the step of forming the part to the final design shape results in forming a part that would exceed the forming limits of a single step process.
6. The method of claim 1 wherein the intermediate shaped part has at least one bulge and an increased radius critical region and wherein the intermediate shaped part has substantially the same surface area compared to the surface area of the final part shape.
7. The method of claim 1 wherein an intermediate cavity defined by the intermediate part shape is within a boundary of a final cavity defined by the final part shape.
8. The method of claim 1 wherein the drawing operation is performed in a stamping die set that has at least two dies.
9. A method of designing a part to be formed from a sheet metal blank comprising:
- defining a final part shape as a computer aided design model;
- analyzing the final part shape using finite element analysis;
- identifying critical regions in the final part shape where forming limits of the sheet metal blank are approached or exceeded;
- simulating a design shape to locally reduce the strain applied to the blank in developing an intermediate part shape based upon the shape of the final part, wherein the surface area of the intermediate part shape and the final part shape are substantially the same.
10. The method of designing a part of claim 9 wherein an intermediate cavity defined by the intermediate part shape is within a boundary of a final cavity defined by the final part shape.
11. The method of designing a part of claim 9 wherein in the analysis step finite element analysis is used to determine nodal forces in the critical regions and imposing the nodal forces required to transform the final design shape into the intermediate shape in the step of simulating the design shape.
12. The method of designing a part of claim 9 wherein in the step of simulating the design shape the final part shape is elastically deformed to develop the intermediate part shape so that the surface area relationship of the intermediate part shape and the final part shape is maintained and the intermediate shape is within the final part shape.
13. The method of designing a part of claim 9 wherein at least one bulge of the blank is designed to be formed in the intermediate part shape that is reformed to form the at least one bulge into a deep cavity.
14. The method of designing a part of claim 9 wherein at least one bulge is designed to be formed in the intermediate part shape that is reformed to form the at least one bulge into a sharp corner.
15. The method of designing a part of claim 9 wherein the intermediate part shape is developed in an iterative process wherein at least one bulge is designed to be added in at least one critical region, and further comprising testing the final part to verify that forming limits are not exceeded to form the final part.
16. A method of designing a part to be formed from a sheet metal blank comprising:
- defining a final part shape as a computer aided design model;
- analyzing the final part shape using finite element analysis;
- identifying critical regions in the final part shape where forming limits of the sheet metal blank are approached or exceeded;
- simulating a design shape to locally reduce the strain applied to the blank in developing an intermediate part shape based upon the shape of the final part, wherein an intermediate cavity defined by the intermediate part shape is within a boundary of a final cavity defined by the final part shape.
17. The method of designing a part of claim 16 wherein the step of simulating the design shape further comprises elastically deforming the final part shape in the simulation to develop the intermediate part shape so that the surface area relationship of the intermediate part shape and the final part shape is maintained.
18. The method of designing a part of claim 16 wherein at least one bulge of the blank is designed to be formed in the intermediate part shape that is reformed to form the at least one bulge, wherein the at least one bulge is formed into the critical region.
19. The method of designing a part of claim 16 wherein the intermediate part shape is developed in an iterative process wherein at least one bulge is designed to be added in at least one critical region, and further comprising testing the final part to verify that forming limits are not exceeded to form the final part.
20. The method of designing a part of claim 16 wherein the forming step is performed in a fluid pressure forming process.
Type: Application
Filed: May 5, 2008
Publication Date: Nov 5, 2009
Applicant: FORD GLOBAL TECHNOLOGIES, LLC (Dearborn, MI)
Inventor: Sergey F. Golovashchenko (Beverly Hills, MI)
Application Number: 12/115,026
International Classification: B21D 22/00 (20060101); B21D 22/21 (20060101);