Sheet Metal Flashcards
Sheetmetal production volumes can be _______(up to ________ units)
High, 10^8
What are the two Sheetmetal production methods?
Bending, Matched Die Forming
_____________ is a sheet metal method that is simple, cheap, single curved parts, small volumes
Bending
_____________ is a sheet metal method that is complex, expensive, produces double curved parts, high volumes
Matched Die Forming
The first step in sheet metal forming is ____________________________
Blanking
In sheet metal forming, you need to exceed the materials ___________ in order to bend the metal
Yield Stress
Sheet metals will typically have some amount of ____________, but here we will assume ________ materials
Anisotropy, isotopic
What are the 4 regions on the stress strain Curve?
Elastic, Plastic, Necking, Unloading
The Yield stress is the critical point of which 2 regions?
Elastic and Plastic
The elastic region is characterized by the stress increasing _________ with strain
Linearly
The slope of the Stress Strain Curve in the elastic region is ____________________
Youngs Modulus
Interatomic bonds act like _______
springs
In the Elastic region, Upon removal of load, the material returns to original __________ and has no __________________ deformation
shape, permeant
At the _________dislocations begin to form in the __________
Yield Stress, Crystal Lattice
Yield stress can sometimes be difficult to determine from test so the ________off-set method is often used
0.2%
In the plastic region, Movement of the dislocations occur along “___________” that cause one portion of the lattice to _____relative to the other.
Slip Planes, slip
_________________ or ________________ is when slip planes begin to hinder each other and it takes more and more stress to continue to deform the material
Strain or work hardening
The ultimate strength (or Maximum _____________ is the ______________ strength a part will see before failure
Maximum stress, tensile strength
What happens after the ultimate strength as the material deforms and stress drops?
Necking
Stress is calculated using the materials __________ area, if it was calculated using ________________ area, stress would continue to increase in necking region
original, instantaneous
Calculating stress using time- varying area is called _________
True Stress
If the load is reduced or removed, the material will follow a linear ________ curve that is _________ to the elastic portion of the curve
Unloading, parallel
The point where the unloading curve ________ the strain axis is the amount of _________ deformation
intersects, permanent
The ______________ is an indication of the amount of material elongation at failure
Strain - Failure
The most, basic sheet metal forming is bending a _______ to some ________, α, with some _______, R
Blank, angle, radius
The ________________________ is the smallest radius a sheet metal bend an have
Minimum Bending Radius (MBR)
The MBR Model Assumptions are:
1. All deformations take place in a _________ defined by α and R
2. The metal deformation has the same behavior in tension as
in compression (i.e., anti-symmetric stress-strain curve)
3. The _________ (NA) does not change in length
4. The metal outside NA becomes _______, inside becomes _____
5. Metal is __________ and homogeneous
Zone, neutral axis, thinner, thicker, isotropic,
As a result of the MBR assumptions, the maximum strains occur at the ________ (R+/-_____/2)
Surfaces, t
The tensile strain-to-failure (εmax) will set the _____________
MBR
In general, we can bend metal with a ______ radius than predicted by the model
Sharper
MBR is inaccurate because there is a transition zone outside of the bend in which material _______ somewhat, meaning that some of the required deformation is ________ by this region
Deforms, taken up
MBR is inaccurate because materials in bending do not experience __________, so can they can deform more than what is suggested by tensile tests. In tensile tests, _________________ is concentrated in a small volume, yet strain-to-failure is calculated using total length.
necking, necking deformation
After bending the sheet metal, there will always be some amount of “___________” associated with the ___________ of the elastic strain
Spring back, unloading
If we can predict the amount of spring back in a part, we can account for it by bending the part
_____________than the desired ending angle
more
The amount of spring back is proportional to the ratio of __________ to ______________energy (______ + ________)
elastic, total, (Elastic, Plastic)
Energy stored in the part is equal to the area under the ______________ curve
Stress-Strain
It is hard to predict spring back exactly, but if it is known in a reference case, we can use the __________ to predict what it will be if we changed the thickness or the bending radius
Energy Ratio
What are the three common methods for sheet metal bending covered?
Air bending, Bottom/V die bending, Wipe Bending
This Sheetmetal bending method deforms part by three point loading
Air Bending
This Sheetmetal bending method sandwiches the part between the die and the punch
Bottoming (or V-die bending)
This Sheetmetal bending method occurs when a part is bent as a cantilever by a moving die
Wipe Bending
In ______________________ sheet metal is passed relatively slowly over turning ___________ while ____________ are moved with each pass to gradually deform the part. This is good form making cylindrical and cone shapes as well as complex profiles
Roll bending, driving rollers, adjustable rolls,
Roll forming has _______ tolerance control and initial investment is _______
Tight, high
Roll forming is usually used with _________, but not _______, which is typically extruded
Steel, aluminum
For sheet metal forming, it is often convenient to consider____________ in which each incremental change in length is divided by the instantaneous length and then summed (i.e., integrated) from the _________ to __________________
True strain, initial length, instantaneous length
When metal is deformed in multiple steps, it is easier to use ___________and add the deformations after each step than it is to find the ___________strain
true strain, final nominal
When tension is applied in one direction, the positive deformation (ε1) is accompanied by ___________ deformation in the other two directions.
negative
Multi-axial deformations are related by ___________, ν
Poisson’s Ratio
Poisson’s ratio typically falls between ______ and ______ for metals
.25, .35
Recall that during plastic deformation, the crystal structure slides against each other, allowing us to assume that the _________ stays constant during ________________
Volume, plastic deformation
For double-curved parts, the applied stress is _______, so uniaxial tensile test data are not sufficient to determine _________ limits
Biaxial, formability
A forming limit diagram (FLD) shows ________combinations of strain in the two axes
Viable
Plotted strains on a FLD are _________ Strains
True
Study The FLD Curve slides
Study The FLD Curve slides
Spring back in double curved parts will occur in ________directions
two
What are the two types of spring back in double curved parts?
Out of plane, in plane
If a part is highly double curved (e.g., hemispherical bowl) then the shape is typically _______ enough to resist spring back
stiff
For shallow shapes, having some sort of _______will help the part and help prevent excessive spring back
flange
What are the five methods for making double curved parts?`
Panel Beating, Deep Drawing, Matched Die Forming, Rubber Forming, Hydroforming
_______________________ involves placing the part on a die or a leather sand bag and __________ it into shape with a rounded mallet and it requires a lot of time
Panel Beating, beating
What Double Curved manufacturing method is this?
o Used for items like pans and cans
o Consists of a die, blank holder and a punch
o The punch draws the blank down, forming the product
o The blank is free below the punch
o Lubricant is used between the blank and the blank holder
o Too much pressure on blank or force behind the punch could rupture part
Deep Drawing
Deep drawing works best if the material has a large ____________
on stress strain curve
plastic region
What Double Curved manufacturing method is this?
o Similar to deep drawing, except the underside of the blank is fully supported by the lower die
o Used extensively in the automotive industry
o Can require significant upfront investment in dies and tools
o Often why different automobile brands will share body styles
o Can be done on a single line with each die doing a portion of the forming called sequential die forming
Matched Die Forming
What Double Curved manufacturing method is this?
Similar to matched die forming, but lower die is a ___________ and cheaper because the lower die does not have to be matched to the upper die
Rubber pad
What Double Curved manufacturing method is this?
o Instead of a punch, water under high pressure forces the sheet into the die
o Often used with tubes, where the pressure causes the to expand outward
o Expensive, but fast and can allow tight tolerances
Hydroforming
