sheet metal forming Flashcards
What is and Why do we have anisotropy?
The ”deformation restistance” in the plate material varies depending on direction of deformation, i.e Anisotropy
Single grains and oxides are elongated in the rolling direction. Thus resulting in a ”mechanical fibre-texture”
The crystallographic direction is rotated within each single grain in the rolling direction resulting in a ”crystal-texture”
Normal Anisotropy effect on ldr?
More or less linear increase in ldr the higher normal anisotropy we have.
How does planar anisotropy affect in deep drawin?
higher \delta r gives more earing
How does n affect the formability?
Higher n gives bette rformability, however increasing strenght of a material reduces n
Which are the Important factors in bending?
Springback Crack initiation Minimum bend radius Workpiece length Bending near holes
Why do we do bottoming?
To recieve full plastic deformation in the bottom to minimize springback.
Why do we avoid bending close to holes.
Holes deform if they are at a insuffictient distance from the bend.
How do we avoid crack initiation while bending?
Avoid bendinglines in rolling direction.
Avoid burrs on the tensile side.
Explain hydroforming
Take a tube between 2 die halves. inser 3 punches of which one fills the part with water. increase pressure to form component.
Hydroforming economic benefits?
Elimination of welding operations
Diminished number of parts
Lower tooling costs
Hydroforming design aspects?
Relatively high flexibility/freedom of design
Good for narrow spaces, “packaging” of complex parts
More uniform (less localised) wall thinning
Strain is more uniform more uniform work-hardening
Hydroforming other benefits?
Q= Geometrical tolerance (outher surface fits tightly to the die.
Weightreduction:
No weld flanges, optimised design
Disadvantages of hydroforming?
Further joining of hydroformed parts may be more difficult
Uses dry lubricants which are costly
Dry lubricants can be difficult to remove
Relatively long cycle time for the hydroforming
Handling time relatively long
Still –there are restrictions in size and shape
Failures in hydroforming?
Buckling Wrinkling Folding back Bursting Necking
geometrical issues with roll forming?
Speingback will occur.
Overbending is necessary for compensating.
End (Flare) difference in between ends and center part of beam
Aplications often requiere subsequent mounting, welding etc.
nonstraight in lower strength materials
