Springback compensation in formed sheet metal parts
Finite element methods for compensating for springback in aircraft parts meet the visual appearance and aerodynamics of complex parts including those made of fabricated sheet metal. The methods can be used to make narrow parts (e.g., leading edge and slats) and double negative curvature parts, and do not need to leave marks on the surface of the sheet so that visual aspects are not adversely affected. The point to point compensation technique uses approach equations with constants adjustable for curves. The constant(s) used depend on geometry and type of forming (e.g., stretch or hydraulic press). Use of mechanical properties of the material is not required.
1. A method of manufacturing a part comprising:
using at least one processor, discretizing a tooling surface using a finite element analysis to determine initial coordinates (x 0 , y 0 , z 0 ) wherein x 0 , y 0 , z 0 represent initial three-dimensional position;
using the at least one processor, compensating for springback by calculating new coordinates (x 1 , y 1 , z 1 ,φ) for the tooling surface point-to-point using interpolation equations that depend on the type of machining to be used to reconfigure and machine a solid to make a new part but which are not dependent on mechanical properties of the part, wherein x 1 , y 1 , z 1 represent three-dimensional position for the tooling surface and φ indicates force direction at that three-dimensional position;
using the at least one processor, reconfiguring and machining the solid based on the calculated new coordinates (x 1 , y 1 , z 1 ,φ) for the tooling surface, to make the new part;
inspecting the part to determine whether a target curved surface is obtained; and
if the target curved surface is not obtained, iterating the above steps.
2. The method of claim 1 wherein the discretizing comprises selecting a cell size based on the variation of the local geometry of the part, and applying a first coefficient indicative of a maximum distance value to be springback compensated and a second coefficient indicative of curve displacement.
3. The method of claim 1 wherein iterating includes determining primary and secondary coefficients in the inspected part.
4. The method of claim 1 wherein the iterating comprises using coefficients based on data sources of conformed parts.
5. The method of claim 1 including providing springback compensation on curved surfaces using finite element analysis to minimize cost, reduce residual stresses and deformations in riveted structures of an aircraft.
6. The method of claim 1 including using approach equations with constants adjustable for curves depending on geometry of the part and type of forming used for machining.
7. The method of claim 1 wherein machining comprises stretch forming and the new positions comprise stretch forming data.
8. The method of claim 7 further including processing the part at room temperature or heating the part for alloyed parts.
9. The method of claim 1 wherein the part is curved and the method performs springback compensation only within the curves of the part.
10. The method of claim 1 wherein the at least one processor defines a mesh for the tooling surface point-to-point, wherein the processor uses a mesh size that varies based on curvature of the tooling surface.
11. The method of claim 1 wherein φ comprises an angle parallel to the tooling surface and indicates the direction of force in main deformation.
12. The method of claim 1 wherein the at least one processor compensates by applying compensation in the direction of main deformation based on a sinusoidal function, and applying compensation perpendicular to the direction of main deformation using a linear function.
13. A system for manufacturing a part while compensating for springback comprising:
a processing system including at least one processor that discretizes a tooling surface using a finite element analysis to determine initial coordinates (x 0 , y 0 , z 0 ), where x 0 , y 0 , z 0 represent initial three-dimensional position, compensates for springback by calculating new coordinates (x 1 , y 1 , z 1 ,φ), wherein x 1 , y 1 , z 1 represents three-dimensional position for the tooling surface and φ indicates force direction at that three-dimensional position, for the tooling surface point-to-point using interpolation equations that depend on the type of machining to be used to reconfigure and machine a solid to make a new springback-compensated part but are not dependent on mechanical properties of the part, and reconfigures a solid based on calculated new positions; and
a machine that uses said type of machining and data relating to the new coordinates to make the new springback-compensated part;
the processing system accepting parameters relating to the new part to determine whether a target curved surface is obtained, and if the target curved surface is not obtained, iterating discretizing a tooling surface using a finite element analysis, calculating new positions point-to-point using interpolation equations, and reconfiguring a solid based on calculated new positions.
14. The system of claim 13 wherein the processing system is configured to discretize by using a cell size based on the variation of the local geometry of the part, and applying a first coefficient indicative of a maximum distance value to be springback compensated and a second coefficient indicative of curve displacement.
15. The system of claim 13 wherein the processing system iterating includes determining primary and secondary coefficients in the inspected part.
16. The system of claim 13 wherein the processing system iterating comprises using coefficients based on data sources of conformed parts.
17. The system of claim 13 wherein the processing system is configured to provide springback compensation on curved surfaces using finite element analysis to minimize cost, reduce residual stresses and deformations in riveted structures of an aircraft.
18. The system of claim 13 wherein the processing system is further configured to use approach equations with constants adjustable for curves depending on geometry of the part and type of forming used for machining.
19. The system of claim 13 wherein the machine comprises a stretch forming machine and the new positions comprise stretch forming data.
20. The system of claim 19 wherein the machine manufactures the part at room temperature or heats the part for alloyed parts.
21. The system of claim 13 wherein the processing system calculates convergence of data dependent on mesh size and angle, wherein the mesh size is variable in the same part, depending on the complexity of the geometry.
22. The system of claim 13 wherein the processing system calculates new coordinates to compensate for springback based on only 4 variables (x, y, z, φ).
23. The system of claim 13 wherein the part is curved and the processing system performs springback compensation only within the curves of the part.
24. A method of manufacturing a part and compensating for springback, comprising:
using at least one processor, discretizing a tooling surface using a finite element analysis to determine initial coordinates (x 0 , y 0 , z 0 ), wherein x 0 , y 0 , z 0 represent initial three-dimensional position;
using the at least one processor, calculating new coordinates (x 1 , y 1 , z 1 , φ) wherein x 1 , y 1 , z 1 represents three-dimensional position for the tooling surface and φ indicates force direction at that three-dimensional position, for the tooling surface point-to-point using interpolation equations that depend on the type of machining to be used to reconfigure and machine a solid to make a new part, to compensate for springback;
using the at least one processor and said type of machining, reconfiguring and machining the solid based on the calculated new coordinates (x 1 , y 1 , z 1 , φ) for the tooling surface, to make the new part while compensating for springback;
inspecting the part to determine whether a target curved surface is obtained; and
if the target curved surface is not obtained, iterating the above steps.