Cold Rolling Flashcards
elastic deformation
it is temporary change in the the shape of a material when a load is applied. the object return to its original shape on removal of the load
plastic deformation
this type of deformation is not reversible. in this case the material retains the deformed shape even after the removal of the load
anisotropic
a material not possessing the same properties in all directions
isotropic
a material possessing the the same properties in all directions
the microstructural and mechanical characteristics of a _________plastically deformed metal specimen may be restored to their predeformed states by appropriate heat treatment, during which ____ processes are allowed to occurr
plastically deformed metal specimen……. recovery, recrystallization and grain growth
during_____ there is a reduction in dislocation density and alterations in dislocation configurations
recovery
define recrystallization
is the formation of a new set of grains that are stain free, in addition the material becomes softer and more ductile
grain growth
is the increase in average size of polycrystalline materials, which proceeds by grain boundary motion
work hardening/strain hardening
an increase in hardness and strength caused by plastic deformation at temperature below the plastic deformation range
define metal forming
large group of manufacturing processes in which plastic deformation is used to change the shape of metal work-pieces
what is the tool usually used in metal forming?
die
give examples of stresses that plastically deform a metal
rolling, forging, extrusion
the plastic deformation of metals _____ ; its important to note, however, that the recrystallization temperature varies greatly with different materials
above their recrystallization temperature
elevated temperatures bring about a ______ in the yield strength of a metal and an ___ in ductility
decrease yield strength, increase in ductility
at the temperatures of hot working
recrystallization eliminates the effects of strain hardening
elevated temperature promotes diffusion
hot rolling
a material is passed trough two rolls that rotate opposite directions and the gap is smaller than the material
forging
is mechanically working or deforming a single piece of metal this may be accomplished by the application of successive blows or by continuous squeezing
extrusion
a bar of metal is forced through a die orifice by a compressive force that is applied to a ram; the extruded piece that emerges has the desired shape and reduced cross-sectional area
drawing
is the pulling of a metal piece through a die having a tapered bore by means of a tensile force that is applied on the exict side. a reduction in cross section results, with a corresponding increase in length
name hot working advantages over cold working
work-piece shape can be significantly altered
lower forces and power required
metals that usually fracture in cold working can be hot formed
strength properties of product are generally isotropic
no strengthening of part occurs from work hardening
name hot working disadvantages
lower dimensional accuracy
higher total energy required
work surface oxidation, poorer surface finish
shorter tool life
plastic deformation of metals
below the recrystallizations temperature
Name and define 4 cold working processes
Squeezing/Cold Rolling
Pin a material between to solid objects and cause plastic deformation.
Bending
Is the plastic deformation of materials about a linear axis with little or no change in the surface area.
Shearing/Blanking
Is the mechanical cutting of materials without the formation of chips or the use of burning or melting.
Drawing
Sheet metal
The forming of parts where plastic flow occurs over a curved axis.
Wire/Rod/Tubing
A process of reducing the cross section of the material by pulling it through a die.`
cold working advantages over hot working
no heat required
strength, fatigue, and wear properties are improved, superior dimensional control is achieved, better surface finished
directional properties can be imparted
contamination is minimized
What are cold working disadvantages
high force are required to initiate and complete deformation
less ductility is available
heavier and more powerful equipment is required
metal surfaces mus be clean and scale- free
undesirable residual stresses may be produced
imparted directional proerties are detrimental
in som cases, metal may not be ductile enough to do cold working
intermediate anneals may be required to compensate for the loss of dcutility ath accompanies strain hardening
A materials become more ____ as it is cold worked.
brittle
deformation produced at temperatures ____
intermediate to hot and cold working
compared to hot forming, the lower temperatures of warm working produce _____ an enable production of products with _____
produce less scaling……. better dimensional precision and smoother surfaces
compared to cold working, it offers the advantages of
reduced loads
warm working
tools last longer
The warm regime generally requires less energy than hot working due to the decreased energy in heating the workpiece, ______ through high precision and the possible elimination of postforming heat treatments
energy saved
when _____ a piece of cold rolled material the ___-
blanking/cutting
orientation of the cold rolled direction should be noted
