Transcript A finite element study of the deformability of steel

A Finite Element Study of
the Deformability of Steel
Jingyi Wang
Qi Rui
Jiadi Fan
Background
 A real-life problem
 Use finite element analysis software
to simulate the stamping process of
bakeware
punch
holder
die
Background
Improper forming condition will lead to defect.
The wrinkling and fracture defect during deep drawing process
Manufacturing and fixing stamping mold is expensive
Simulation needed to test whether certain mold and
forming condition is reasonable before manufacturing
Method
Experimental and Empirical Analysis
3D model with different parts under dynamic loading– Use
ABAQUS
Different forming conditions
Temperatures
Strain rates
Holding force
Compare, design and optimize forming condition to avoid
possible defect
ABAQUS
Wrinkling
Why wrinkling happens?
 During the deep drawing process, metal flows
inside. From large perimeter area to small
perimeter area.
 Under minimum principal stress, the blank will
be thickened. Uneven thickening will lead to
wrinkling.
 We need a reasonable holding force to provide a
restriction.
Fracture
Why fracture happens?
 The friction between holder and blank, die and
blank will block metal from flowing.
 If the friction is too big, the metal at the
corner will fracture because of over-thinning.
 If the thickness after deformation reduces to
70% of the original thickness or less, we treat
it as fracture.
Temperature effect
As temperature rises, the deformability
However, good deformability may lead
to the over-thinning at the corner.
Higher temperature is also more energy
expensive. So, forming temperature is a
parameter that need to be balanced.
Suggested temperature (dependent on
holding force, material, etc): 550-850 ℃
Maximum stretch depth (mm)
of metal will improve.
Simulation
Experiment
Temperature ℃
Strain rate effect
Under large strain rate, the deformability of
metal is poor. It will be more likely to
generate fracture.
Small strain rate decreases the productivity.
In industrial process, strain rate is also a
design parameter.
Holding force effect
Oversize holding force can lead to fracture
defect
wrinkling defect
Dependent on details of the object
Maximum stretch depth (mm)
An undersize holding force can lead to
Simulation
Experiment
Holding Force (MPa)
Element type
 S4R: 4-node general-purpose shell, reduced integration with
hourglass control, finite membrane strains
 Membrane theory
Target geometry after deep drawing
A realistic geometry
2D and 3D model
Animation
Simulation model
One quarter of the entire model
holder
punch
die
Material property
42CrMo high-strength steel
 Young’s moldus: 210Gpa
 Poison's ratio: 0.31
 Density: 7,830 kg/m^3
 True stress-strain curve
Result—different temperatures
Strain rate: 1, holding force: 10,000N
Temperature: 600 ℃ and 650 ℃
T=600 ℃
T=650 ℃
The thickness at the corner is smaller under higher temperature. As the
thickness ratio are both lower than 70%. It’s unnecessary to simulate a
higher temperature.
Result—different strain rates
Temperature: 600 ℃, holding force:10,000N
Compare strain rate 𝜀: 0.1 and 1
𝜀=0.1
𝜀=1
The thickness at the corner is smaller under higher strain rate
Result–different holding forces
F=5000N
F=10,000N
Reasonable holding force range: 7,000~13,000N
F= 30,000N
Refine the size of blank
After the deep drawing process, the extra blank
needs to be cut off.
The former blank is 400*400mm, it will cause a
huge waste of material.
Refine it to 300*300mm and 240*240mm.
Result–size of the blank
400*400mm
300*300mm
240*240mm good enough for our bakeware
240*240mm
Conclusion
In our particular case, the best forming conditions are
Temperature: T=600℃
Strain rate: 𝜀=0.1
Holding load: F=7,000-13,000N
Original Blank size: 240*240mm
This is just a simple FE application. ABAQUS is able to do very
complicated problems. In our case, the geometry of production is simple.
However, in more complicated cases, we need to consider much more.
Thank you for your listening