What are the operations that are conducted in sheet forming?
shearing
Bending
stretch forming
deep drawing
What is superplastic forming (SPF)?
A forming process that exploits ultra-fine grains to allow extreme elongation of the material under low stress.
Name the components
Describe the wear behaviour over the amount of strokes of the die.
Name the componenets portrayed here and how the strain is calculated by them.
d_0= initial diameter
1= major strain direction
2= minor strain direction
How is the component beta defined in sheet deformation? Name the different strain states for different betas.
How is the deep drawing force calculated?
How is the component alpha defined in sheet deformation? Name the different strain states for different alphas.
What is the stress state at the tip of the punch?
equiaxial
What are the main parameters affecting sheet formability?
n= strain hardening coefficient
m= strain rate sensitvity index
R= Lankford parameter
What is the difference between diffused and localized necking?
Diffuse necking=”normal” necking in tensile test
localized necking=necking in local plane => limiting problem
Describe the tensile test and the Parameter R (lankford Parameter)
R=the ratio between elongation of thickness and width
for isotropic materials R=1
Why is clearance important in the shearing process?
So the top and bottom crack can meet precisely:
What is a bake hardened steel? What is the increase in hardness? What are they used for?
A steel that is warme to 170°C (baked) and resultingly increases its hardnes throught the formation of correl clouds after deformation.
The bake hardening can increase the hardness by roughly 50 MPa
Bake steels are used for chassis parts due to their good press deformability
What is a trip steel?
Transformation induced plasticity steel:
Stress induced foramtion of Martensite from austenite.
Very good strain hardening coeff. n in addition to hardening from transformation
What happens if clearance is too small in shearing?
Excessive wear on punch and die.
Secondary cracking in the sheared edge.
What is the bending failure criterion in terms of the R/h ratio?
If R/h is too small, fracture occurs due to excessive tensile strain.
List the primary cold-working operations in sheet metal forming.
Shearing – Produces blanks or parts by cutting.
Bending – Deforms sheets into curves or angles.
Stretch Forming – Expands metal without cutting.
Deep Drawing – Forms cylindrical or box-like components.
Differentiate between hot-rolled and cold-rolled sheet metal.
Hot-Rolled Plates: Thicker sheets formed at elevated temperatures, resulting in a rougher surface.
Cold-Rolled Sheets: Thinner sheets formed at room temperature with improved surface finish and dimensional accuracy.
What are the steps of producing a drawn productß
Ironing
Doming
Necking
Seaming
How can one obtain the minimum bending radius to height ratio?
Describe the flexform process.
a flexible rubber diaphragma replaces the solid punch. The metal is deformed by the pressure of the oil.
What is the importance of the rolling direction for the finished piece?
If the grains are alligned parralel to the bending direction, fracture is more likely.
Describe the hydroforming process.
What stress state applies in sheet forming?
Plane stress:
What is the difference between deep drawing and stretch forming?
deep drawing: the blank is free to slide
stretch forming: the blank is gripped
How can the punch force be calculated?
C=empirical constant
UTS=ultimate tensile strength
b=width
h=height
What test are there for the formability of sheet metals?
measurements of basic properties
tensile test
hydraulic expansion test
technological test
bending test
swift test
Nakajima test
How is the thickness change calculated in sheet forming?
Describe the strain hardening coefficient over temperature for BCC and FCC
SFE=stacking fault energy
How are hydraulic expansion tests conducted?
expansion and simultanious pressure measurement.
equiaxial conditions
Which methods can improve sheet formability?
cryogenic forming
High-velocity forming
hot stamping
superplastic forming
How are Martensitic steels formed?
They are not. The austenitized steel is formed and then quenched.
How is a Nakajima test conducted?
Deforming until localized necking or cracking.
Circles are printed on top and considered afterwards.
epsilon one and two are obtained through measuring.
Forming limit diagramms are derived for the different betas.
How is a swift test conducted?
Measurement of the largest diameter that can be drawn without fracture.
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