Stretch Forming Process Modeling: The Role of Modern Stretch Forming Machinery Design and Performance
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Abstract Extrusion stretch forming is used extensively in the aerospace and architectural industries to add contour to extrusions and roll formed sections. Frame members, stringers, wing spars, curtain tracks and many other important aircraft parts are formed with this process. Forming is achieved by pulling an initially straight part in the tensile direction above the material’s yield point and then wrapping the section around a die to add contour. Local buckling and wrinkling that might appear in a pure bending operation can be avoided. There is current interest in improving the process for greater repeatability and less part rework to reduce cost while achieving tighter tolerances (e.g. [1,2]). The stretch forming die plays a significant role in the process. To this end researchers are interested in quicker die development techniques using non-linear beam theory and non-linear finite element modeling of the forming process. For a complete analytical picture of the process, a close look at the stretch forming machine’s performance must be included in the process model. Two major areas of machine performance are important; machine deflections and hydraulic control system performance. This paper provides a brief overview of the extrusion stretch forming process and then focuses on the structural and control system design of the modern stretch forming machine. Analytical models of the machine deflection as well as its hydraulic control system are developed. A short discussion concerning the difference between traditional “pressure forming” and modern CNC position forming is also included. Insight into the limitations of traditional PID control for the stretch forming machine can be seen from the analysis. It is evident that these machine models must be used to complete the process model to effectively create die designs for close tolerance and highly repetitive part production.Keywords:
Roll forming
The sheet metal multiple-step air-bending forming is a common and effective manufacturing process. It is suitable for forming large workpiece without requiring time-consuming setup operations. Most researches on incremental air-bending forming are mainly based on experiments, and on trial and error basis, the forming processes are described through macroscopic metal deformation. ABAQUS finite element model based on Hill’s anisotropic yield criterion under plane strain conditions is proposed in this paper for studying multi-step incremental air-bending forming process. The numerical simulation for workpiece forming of sheet metal is performed by ABAQUS/Explicit and Standard solvers. ABAQUS/Explicit module is used to simulate the sheet metal forming process, and ABAQUS/Standard module is utilised to simulate the springback process. The researches show that the results predicted with simulation are very close to the experimental data. It can be taken as a valuable tool for process design of multi-step incremental air-bending forming of sheet metal.
Roll forming
Plane stress
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The conventional sheet metal forming processes, such as deep drawing and stretch forming, are used to produce large batches of parts, however they incur in higher initial manufacturing costs attributed to the use of a large amount of tooling. The application of conventional and incremental forming processes combined in the same metal sheet is called hybrid forming. This hybrid process is enacted by pre-forming the sheet through the stretch forming process followed by the final manufacture using the incremental process. The objective of this work is to analyze the influence of the pre-strain imposed during the conventional process on the DC04 steel relative to the maximum strain obtained. A numerical simulation was used to define the parameters for the conventional process and to evaluate the experimental results. The higher major true strains are inversely proportional to the pre-strain in both experimental and simulated results.
Incremental sheet forming
Deep drawing
Strain (injury)
Roll forming
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Roll forming
Tola
Incremental sheet forming
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Roll forming
Radius of curvature
Bend radius
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The high-pressure sheet metal forming of tailor rolled blanks allows the production of optimized components specially developed for their future function, which cannot be made from conventionally rolled sheet metal. The research aims at showing that the two processes, i.e. flexible rolling and high-pressure sheet metal forming, can be well represented in finite element simulations. By linking the finite element models with a combinatory optimization tool it is possible to simulate and optimize the entire process chain and/or the product itself. Within this paper the forming restrictions of the high pressure sheet metal forming of tailor rolled blanks are presented. Furthermore, two optimizations, considering not only the process chain but also the behavior under loading conditions, are shown.
Roll forming
Chain (unit)
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Stretch-forming based on discretely loading is a new process for manufacturing three-dimensional sheet metal part, the stretching load is applied at discrete points on the two ends of sheet metal, by controlling the loading trajectory at each discrete point, an optimal stretch-forming process can be realized, and the formed surface with the strains and stresses more uniformly distributed are obtained so that the forming defect can be avoided. The numerically investigated results on the stretch-forming process of spherical sheet metal part show that, comparing with the traditional stretch-forming, the equivalent strain in the new process is reduced by approximately 30% and equivalent stress reduced by 10%, the range of the strain and stress distributions are reduced by approximately 30%.
Roll forming
Stress–strain curve
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Roll forming is an effective and economical sheet forming process that is well‐established in industry for the manufacturing of large quantities of profile‐shaped products. In cold‐roll forming, a metal sheet is fed through successive pairs of forming rolls until it is formed into the desired cross‐sectional profile. The deformation of the sheet is complex. For this reason, the theoretical analysis is very difficult, especially, if the strain distribution and the occurring forces are to be determined [1]. The design of roll forming processes depends upon a large number of variables, which mainly relies upon experience based knowledge [2]. In order to overcome the challenges and to optimize these processes, FE‐simulations are used. The simulation of these processes is time‐consuming. The main objective of this work is to accelerate the simulation of roll forming processes by taking advantage of their steady state properties. These properties allow the transformation of points on the sheet metal according to a mathematical function. This transformation function is determined with the help of the finite element method and then the next forming steps are computed, based on the generated function. With the aid of this developed method, the computational time can be reduced effectively.
Roll forming
Metal forming
Incremental sheet forming
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Sheet-bulk metal forming is a manufacturing technology, which allows to produce a solid metal component out of a flat sheet. This paper focuses on numerical and experimental investigations of a new multistage forming process with compound press tools. The complete process sequence for the production of this solid metal component consists of three forming stages, which include a total of six production techniques. The first forming stage includes deep drawing, simultaneous cutting and following wall upsetting. In the second forming stage, flange forming combined with cup bottom ironing takes place. In the last stage of the process sequence, the component is sized. To investigate and to improve process parameters such as plastic strain distribution, resulting dimensions and process forces, FEA is performed. Based on these results the developed process is designed.
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Roll forming
Deep drawing
Component (thermodynamics)
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Deep drawing
Roll forming
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Tola
Metal forming
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Springback control is a key issue of the sheet-metal-forming process. In this paper, the mechanism of sheet-metal-forming along the folding trajectory of the computer numerical control (CNC) four-side automatic panel bender was studied, based on the bend-forming springback compensation theory of the power function material model. Firstly, the mechanical property of AZM120 sheet metal standard samples was tested. Then, a theoretical model of springback compensation under plane strain conditions was built, based on the constitutive relationship of the elastic or the elastic-plastic power hardening material. In addition, a sheet-metal-forming trajectory model was designed for sheet metal bending using the vector method. Finally, a laser tracker was used to acquire the folding trajectory, and then the reliability of the trajectory model was verified. On this basis, the influences of geometric and process parameters, such as sheet thickness, forming angle, and bending radius in springback control, were studied according to the theoretical formula and verified by experiments. The proposed method is generally applicable to operation conditions where the bending radius ranges between 1.5 and 6.0 mm and plate thickness ranges from 0.8 to 2.5 mm, and the achieved overall accuracy was more than 89%.
Roll forming
Hardening (computing)
Strain hardening exponent
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