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This work investigates the relationship between temperature and formability of sheet metal in Electrically Assisted Incremental Sheet Metal Forming (EAISMF). The formability of sheet metal is explored concerning temperature changes induced by a DC power supply. Ductile fracture is a critical factor influencing sheet metal forming, as it is primarily based on plastic deformation. This study establishes an empirical criterion for fracture determination, shedding light on the EAISMF process.
Incremental Sheet Forming (ISF) is a process of plastic deformation of
sheet metal blank. This technique is all about forming sheet metal
using a Computer Numerical Control (CNC) machine with the help of
forming tool for localized deformation. Slight variation is developed
in the ISF process to enhance the formability of sheet metal. When
compared to the conventional sheet metal process this provides ease in
the manufacturing process for generating complex shapes.
Manufacturing of dies is a tedious process and for various shapes and
dimensions, separate dies have to be produced with greater
dimensional accuracy which is time and cost consuming process.
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simple numerical code is generated using Master CAM software. This
code is fed into a CNC machine where the hemispherical forming tool
enhances localized deformation of sheet metal.
Increased focus on design and fabrication of sheet metal blank
fixture is necessary to determine its formability concerning its
dependent parameters. In recent trends requirement of complex
contours of sheet metal is drastically increasing for several
applications such as household interior designs, the body structure of
automobile and aerospace industries.
The disadvantage of incremental
sheet metal forming (ISF) is that it consumes much time when
compared to other conventional forming processes.
The formerly idea on incremental sheet metal processing
techniques are developed by Matsubara [1]. This kind of
manufacturing is particularly recommended when forming brittle
sheet metals and is used in the automobile and aerospace industries.
The predominant advantages of this process are the large amounts of
deformation and the decrease in the required deformation forces that
can be obtained. These benefits are possible because of the minor heat
treatments carried out in between the increments of deformation [5].
The treatments get rid of the effects of cold work or strain hardening
by causing recrystallization to take place all through every process and
therefore resulting in a new, overall weaker material. Manufacturing
industries require flexibility in components processing techniques to
adapt to improving the technology. As a CNC machine can perform
forming process ISF can make a remarkable change in manufacturing
sectors such as in automobile, aerospace industries.
The term failure can be roughly categorized as the onset of plastic
instabilities such as buckling, the formation of localized necking or
the ultimate fracture [8]. From the views of sheet metal forming,
failure can be described with the aid of the formation of localized
necking, wrinkles or macroscopic cracks. To precisely describe the
deformation behaviour of metal sheets, the mathematical fracture
strain equations have to properly signify the material behaviour below
complicated loading conditions and additionally precisely predict the
limit state conditions at the crucial factors at some point of the
deformation process.
Experimental and theoretical determined Forming Limit Diagrams
(FLDs) and Forming Limit Stress diagrams (FLSDs) are both the
failure standards formulated by employing principle strains or
stresses, which outline the failure when the precise criterion is
satisfied [7]. Due to the vulnerable ductility of these high strength
materials, correct prediction of metal forming limits all through
deformation has ended up a huge issue. Researchers have carried out
endless efforts to construct the relationship between the prevalence of
failure and the established engineering concepts. A greater downfall is
that achievable low-dimensional accuracy, because the part must be
constantly eliminated and re-fixed before and after the heat treatments.
The reduced accuracy arises from the fact that the part might also no
longer be fixed in the precise trend every time it is eliminated and re-
installed. This paper shows the relationship between various
parameters that are significantly dependent on the formability of sheet
metal. Optimization of such parameters overcomes drawbacks of the
process and enhances the implementation of the EAISMF process for
several applications. In the future, the ISF process can be modified
and experimented as there is a scope on metal forming of a variety of
materials.
A mathematical model depicting the relation between temperature and formability in Electrically Assisted Incremental Sheet Metal Forming
(EAISMF) process
The Electrically Assisted Incremental Sheet Metal Forming (EAISMF) process begins with the heating of the sheet metal using a DC power supply connected to its ends. The thermal effect of heating enhances formability by reducing the force required for plastic deformation compared to conventional ISF.
The sheet metal is then subjected to a rotating forming tool, typically a hemispherical or parabolic shape, which is operated by the spindle in a CNC machine. Proper clamping of the sheet metal onto the EAISMF fixture is crucial for dimensional accuracy and surface finish. Common factors affecting formability include wall angle, tool radius, tool speed, and sheet thickness, which are consistent with other ISF processes.
The EAISMF process utilizes electric current to heat the sheet metal, minimizing the force needed for deformation. A suitable fixture is required to hold the sheet metal securely. The choice of forming tool size and shape influences surface quality and manufacturing time.
A mathematical model is developed to establish the relationship between temperature and formability in the EAISMF process. The net temperature of the sheet metal is determined as the sum of the preheating temperature due to electric current and the temperature rise during plastic deformation.
The preheating temperature (T1) resulting from electric current is calculated using the Joules heating effect formula:
T1 = J2ρcΔt / (mcp)
Where:
The average temperature rise (T2) during plastic deformation is determined as:
T2 = (work done / vol) * (ρCp / Δt)
The work done per unit volume for plastic deformation is represented by integrating along the effective fracture strain:
(work done / vol) = ∫(dεf / σ)
The effective stress function, following the Von Mises yielding criterion for an isotropic material, is given as:
σ̅ = √(1/2 * ((σ1 - σ2)2 + (σ2 - σ3)2 + (σ3 - σ1)2))
Substituting this into the equation for work done per unit volume, we get:
(work done / vol) = ∫(dεf / σ̅)
The final average temperature rise (T2) due to plastic deformation is calculated as:
T2 = (Kεn√3) / (2rtool(rtool + t0sin(π/2 - ψ))εfρCp)
Combining the contributions from T1 and T2, we obtain the relationship between temperature (T) and formability in the EAISMF process:
T = (J2ρcΔt) / (mcp) + (Kεn√3) / (2rtool(rtool + t0sin(π/2 - ψ))εfρCp)
Thus the obtained equation relates temperature at that point of
forming. The temperature (T) is due to DC current supply along the
sheet metal and rise in temperature by friction between forming tool
and sheet metal.
Further experimentation on the EAISMF process is essential to validate the observations made in this study. Comparisons with numerical models and finite element simulations, taking into account appropriate boundary conditions, can enhance our understanding of this process and its potential applications.
Relationship Between Temperature and Formability in EAISMF Process. (2024, Jan 04). Retrieved from https://studymoose.com/document/relationship-between-temperature-and-formability-in-eaismf-process
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