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What are the reasons why the bulk deformation processes are important commercially and technologically?
What is rolling in the context of the bulk deformation processes?
Rolling is a deformation process in which the thickness of the workpiece is reduced by
compressive forces exerted by two opposing rolls. The rolls rotate, thus pulling and simultaneously
squeezing the workpiece between them.
In rolling of steel, what are the differences between a bloom, a slab, and a billet?
A bloom is a rolled steel workpiece with a square cross section of about 150 mm by 150
mm. The starting work unit for a bloom is an ingot heated in a soaking pit. A slab is rolled from an
ingot or a bloom and has a rectangular cross section of about 250 mm by 40 mm. A billet is rolled
from a bloom and has a square cross section of about 40 mm by 40 mm.
What is draft in a rolling operation?
Draft is the difference between the starting thickness and the final thickness as the
workpiece passes between the two opposing rolls.
What is sticking in a hot rolling operation?
Sticking is a condition in hot rolling in which the surface of the workpiece adheres to the rolls as the piece passes between the rolls, causing severe deformation of the metal below the surface in order to allow passage through the roll gap.
Identify some of the ways in which force in flat rolling can be reduced.
A reversing mill is a two-high rolling mill in which the direction of rotation of the rolls can
be reversed to allow the work to pass through from either side.
Besides flat rolling and shape rolling, identify some additional bulk forming processes that use rolls to effect the deformation.
Some other processes that use rolls are ring rolling, thread rolling, gear rolling, roll piercing, and roll forging.
Forging is a deformation process in which the workpiece is compressed between two dies,
using impact or gradual pressure to form the part.
One way to classify forging operations is by the degree to which the work is constrained in the die. By this classification, name the three basic types.
Because its presence constrains the metal in the die to fill the details of the die cavity.
What is a trimming operation in the context of impression die forging?
Trimming is a shearing operation used to remove the flash on the workpiece after impression die forging.
What are the two basic types of forging equipment?
The two types of forging machines are hammers, which impact the workpart, and presses, which apply a gradual pressure to the work.
What is isothermal forging?
Isothermal forging is a hot forging operation in which the die surfaces are heated to reduce
heat transfer from the work into the tooling.
Extrusion is a compression forming operation in which a workpiece is forced to flow through a die opening, thus taking the cross-sectional shape of the die opening.
Distinguish between direct and indirect extrusion.
In direct extrusion, also known as forward extrusion, a metal billet is loaded into a container, and a ram compresses the material, forcing it to flow through a die opening at the opposite end of the container. In indirect extrusion, also known as backward extrusion, the die is incorporated into the ram, and as the ram compresses into the metal billet, the metal is forced to flow through the die opening in a direction that is opposite (backwards) of the ram motion.
Name some products that are produced by extrusion.
Products produced by continuous extrusion include structural shapes (window frames,
shower stalls, channels), tubes and pipes, and rods of various cross sections. Products made by
discrete extrusion include toothpaste tubes, aluminum beverage cans, and battery cases.
Why is friction a factor in determining the ram force in direct extrusion but not a factor in indirect extrusion?
Friction is a factor in direct extrusion because the work billet is squeezed against the walls of the container so that friction resists the movement of the billet toward the die opening. In indirect extrusion, the billet does not move relative to the container walls, and thus there is no friction.
What does the centerburst defect in extrusion have in common with the roll piercing process?
They are both examples of how compressive stresses applied to the outside surface of a solid cylindrical cross section can create high tensile stresses in the interior of the cylinder.
What is wire drawing and bar drawing?
Wire and bar drawing are bulk deformation processes in which the cross section of a wire or bar is reduced by pulling (drawing) it through a die opening.
Although the workpiece in a wire drawing operation is obviously subjected to tensile stresses, how do compressive stresses 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 operation, why must the drawing stress never exceed the yield strength of the work metal?
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.
The starting workpiece in steel hot rolling of plate and sheet stock is which of the following (one best answer): (a) bar stock, (b) billet, (c) bloom, (d) slab, or (e) wire stock?
The maximum possible draft in a rolling operation depends on which of the following parameters (two correct answers): (a) coefficient of friction between roll and work, (b) roll diameter, (c) roll velocity, (d) stock thickness, (e) strain, and (f) strength coefficient of the work metal?
Which of the following stress or strength parameters is used in the computation of rolling force (one best answer): (a) average flow stress, (b) compression strength, (c) final flow stress, (d) tensile strength, or (e) yield strength?
Which of the following rolling mill types are associated with relatively small diameter rolls in contact with the work (two correct answers): (a) cluster mill, (b) continuous rolling mill, (c) four-high mill, (d) reversing mill, and (e) three-high configuration?
Production of pipes and tubes is associated with which of the following bulk deformation processes (three correct answers): (a) extrusion, (b) hobbing, (c) ring rolling, (d) roll forging, (e) roll piercing, (f) tube sinking, and (g) upsetting?
Which of the following stress or strength parameters is used in the computation of the maximum force in a forging operation (one best answer): (a) average flow stress, (b) compression strength, (c) final flow stress, (d) tensile strength, or (e) yield strength?
Which of the following operations are closely related to open-die forging (three best answers): (a) cogging, (b) flashless forging, (c) fullering, (d) impression-die forging, (e) Mannesmann process, (f) precision forging, (g) soaking, and (h) upsetting?
Flash in impression die forging serves no useful purpose and is undesirable because it must be
trimmed from the part after forming: (a) true or (b) false?
(b). Flash causes build-up of pressure inside the die, which forces the work metal to fill the
Which of the following are classified as forging operations (four correct answers): (a) coining, (b)
fullering, (c) impact extrusion, (d) roll piercing, (e) swaging, (f) thread rolling, (g) trimming, and (h)
(a), (b), (e), and (h). Trimming, answer (g), although associated with forging, is a cutting
Which of the following are alternative names for indirect extrusion (two correct answers): (a) backward extrusion, (b) direct extrusion, (c) forward extrusion, (d) impact extrusion, and (e) reverse extrusion?
The production of tubing is possible in indirect extrusion but not in direct extrusion: (a) true or (b) false?
(b). Tube and pipe cross sections can be produced by either direct or indirect extrusion.
Which of the following stress or strength parameters is used in the computation of the force in an extrusion operation (one best answer): (a) average flow stress, (b) compression strength, (c) final flow stress, (d) tensile strength, or (e) yield strength?
In which of the following extrusion operations is friction a factor in determining the extrusion force (one best answer): (a) direct extrusion or (b) indirect extrusion?
Theoretically, the maximum reduction possible in a wire drawing operation, under the assumptions of a perfectly plastic metal, no friction, and no redundant work, is which of the following (one answer): (a) zero, (b) 0.63, (c) 1.0, or (d) 2.72?
Which of the following bulk deformation processes are involved in the production of nails for lumber construction (three best answers): (a) bar and wire drawing, (b) extrusion, (c) flashless forging, (d) impression die forging, (e) rolling, and (f) upsetting?
(a), (c), and (d). Bar stock is rolled, and then drawn into wire stock. Upset forged is used to form the nail head.
Johnson's formula is associated with which one of the four bulk deformation processes: (a) bar and wire drawing, (b) extrusion, (c) forging, and (d) rolling?
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