Investigations on the deformation mechanism of a novel three-sheet incremental forming
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Incremental sheet forming
Ductility (Earth science)
The evaluation of the enhanced formability in incremental sheet forming processes (ISF), and especially in its simplest variant single point incremental forming (SPIF), has been intensively studied within the sheet metal forming community for the last decade. In general, the formability limit in SPIF is defined by means of the fracture forming limit (FFL). This FFL is usually well above the forming limit curve (FLC), which is the limit controlling failure by necking in conventional sheet metal forming operation on ductile metal sheet. However, low ductility sheet metal such as AA2024-T3 presents usually a fracture-controlled mechanism independent to the forming operation considered. In this context, this paper consist in a critical analysis on formability and failure of AA2024-T3 sheets deformed by SPIF. The study is carried out from a double perspective based on an experimental plan including conventional and incremental forming tests, and numerical simulations using the flow formulation finite element tool DEFORM-3D®. The results show the experimental evidence of a formability enhancement in SPIF above the conventional FFL for this kind of material as well as the necessity of calibrating numerical simulations of these incremental forming processes using experimental data obtained from the corresponding experimental SPIF tests. Keywords: Sheet metal forming, incremental sheet forming (ISF), single point incremental forming (SPIF), formability, fracture.
Incremental sheet forming
Necking
Forming limit diagram
Ductility (Earth science)
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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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Incremental sheet forming
Stylus
Deep drawing
Metal forming
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Incremental sheet forming
Material Flow
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Incremental sheet forming
Forming limit diagram
Metal forming
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Incremental sheet forming
Ductility (Earth science)
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Abstract In this work it is assessed the potential of combining conventional and incremental sheet forming processes in a same sheet of metal. This so-called hybrid forming approach is performed through the manufacture of a pre-forming by conventional forming, followed by incremental sheet forming. The main objective is analyzing strain evolution. The pre-forming induced in the conventional forming stage will determine the strain paths, directly influencing the strains produced by the incremental process. To conduct the study, in the conventional processes, strains were imposed in three different ways with distinct true strains. At the incremental stage, the pyramid strategy was adopted with different wall slopes. From the experiments, the true strains and the final geometries were analyzed. Numerical simulation was also employed for the sake of comparison and correlation with the measured data. It could be observed that single-stretch pre-strain was directly proportional to the maximum incremental strains achieved, whereas samples subjected to biaxial pre-strain influenced the formability according to the degree of pre-strain applied. Pre-strain driven by the prior deep-drawing operation did not result, in this particular geometry, in increased formability.
Incremental sheet forming
Deep drawing
Strain (injury)
Pyramid (geometry)
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Deep drawing
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Incremental sheet forming
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Single point
Multi point
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Incremental sheet metal forming is an evolving process, which is suitable for the production of limited quantities of sheet metal components. The main advantages of this process over conventional forming processes are reduced setup cost and manufacturing lead time, as it eliminates the need of special purpose dies, improves formability, reduces forming forces, and provides process flexibility. The objective of this work is to investigate a new hybrid-forming process, which intends to combine incremental sheet metal forming with deep drawing process and has been named as “incremental stretch drawing.” A number of setups and fixtures were developed to carry out experiments to achieve incremental stretch drawing and understand the mechanism of the process. This process addresses some of the challenges of incremental sheet metal forming, that is, limited formability in terms of forming depth, especially at steeper wall angles and subsequent thinning of sheet. It is observed that the proposed process is able to reduce thinning as much as about 300%, considering same forming depth for incremental sheet metal forming and incremental stretch drawing processes. Improvement in formability, in terms of forming depths, also has been observed to be near about 100% in particular cases.
Incremental sheet forming
Deep drawing
Thinning
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