Bulk Deformation Processes Review Questions Flashcards
What are reasons why bulk deformation processes are important commercially and technologically?
- Capable of significant shape change when hot working is used
- Positive effect on part shape
- Produce little material waste
- Some are net shape processes
Name all basic bulk deformation processes
- rolling
- forging
- extrusion
- wire and bar drawing
What is rolling basic bulk deformation processes
Deformation process in which the thickness of the workpiece is reduced by compressive forces exerted by two opposing rolls
Rolls rotate, thus pulling and simultaneously squeezing the workpiece between them
What is a two-high rolling mill
COnsists of 2 opposing rolls between which the work is compressed
What is a reversing mill in rolling
Two high rolling mill in which the direction of rotating rolls can be reversed to allow the work to pass through either side
what is forging
deformation process in which work is compressed between two dies using either impact or gradual pressure to form part
One way to classify forging ops is the degree to which the work is constrained in a die; by this classification, name three basic types
open die forging
closed die forging
flashless forging
Why is flash desirable in impression die forging
As flash begins to from, friction resists continued flow of metal into gap, constraining bulk of the work material to remain in the die cavity
fwhat are two basic types of forging equipment
forging hammers
forging presses
what is isothermal forging
hot forging operation in which the workpart is maintained at or near its starting elevated temperature during deformation, usually by heating the forging dies to same elevated temperature
metal flows more readily and the force required to perform process is reduced
what is extrusion
compression process in which work material is forced to flow through a die opening to produce desired cross sectional shape
distinguish between direct and indirect extrusion
Direct extrusion / forward extrusion
metal billet loaded onto a container and a ram compresses the material, forcing it to flow through one or more openings in a die at the opposing end of the container
Indirect Extrusion
Die is located on the ram
List some products produced on a rolling mill
- flat sheet and plate stock
- round bar and rod stock
- railroad track rails
- I Beams
- Channels
- C-Channel
- L-Channel
what is draft in a rolling op
Difference between the starting thickness and the final thickness as the workpiece passes between the 2 rolls
what is sticking in a hot rolling operation
COndition in hot rolling in which the surface of the workpiece adheres to the rolls as the piece passes between them, causing severe deformation of the metal below the surface in order to allow passage through roll gap
Identify some of the ways in which force in flat rolling can be reduced
- Use hot rolling
- reduce draft in each pass
- use smaller diameter rolls
Name some products made by extrusion
tubes
bars
why is friction a factor in determining ram force in direct extrusion but not a factor in indirect extrusion
Problem with direct extrusion is the friction that exists between the work surface and the walls of the container as the billet is forced to slide towards the die opening on the other side of the container
Not present in indirect where die is on the ram
what are wire and bar drawing
drawing
operation where cross section of a bar, rod, wire achieved by pulling it through a die opening
bar drawing
large diamater bar and rod stock
Wire drawing
Small diamatere stock
although workpiece in a wire drawing is obviously subjected to tensile strength, how do compressive stresse also play a role in the process
Compressive stresses are present in wire drawing because the starting metal is compressed as it is forced through the approach of the die opening
In a wire drawing drawing operation, why must the drawing stress never exceed yield strength of the work
Because if the drawing stress exceeded the yield strength, the metal on the exit side of the draw die would stretch rather than force metal to be pulled through the die opening.
