Chapter 16: Bulk Forming Processes

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Chapter 16Bulk Forming Processes

• DeGarmos Materials and Processes in
  Manufacturing
  
• This is an important chapter-read all of it!

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16.1 Introduction

• Metal has been shaped by deformation processes
  for several thousand years
  
• Forging, rolling, and wire drawing were performed
  in the Middle Ages
  
• The Industrial Revolution allowed these processes
  to be done at a higher level
  

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16.2 Classification of Deformation Processes

• Bulk deforming processes can be classified as
  primary or secondary processes
  
• Primary processes reduce a cast material into
  slabs, plates, and billets
  
• Secondary processes reduce shapes into finished
  or semifinished products
  
• Bulk deformation processes are those processes
  where the thickness or cross sections are reduced
  
  
• Sheet-forming operations involve the deformation
  of materials whose thickness and cross section
  remain relatively constant

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16.3 Bulk Deformation Processes

• Rolling
• Forging
• Extrusion
• Wire, rod, and tube drawing
• Cold forming, cold forging, and impact extrusion
• Piercing
• Squeezing processes

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16.4 Rolling

• Rolling operations reduce the thickness or change
  the cross section of a material through
  compressive forces
  
• Often the first process that is used to convert
  material into a finished wrought product
  
• Thick stock can be rolled into blooms, billets,
  or slabs

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Classes of Castings

• Ingots for bulk deformation processing - 85
• Cast to near net shape - 15

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Starting Stock

• Blooms have a square or rectangular cross
  section
  
• Billets are usually smaller than a bloom and can
  have a square or circular cross section
  
• Can be further rolled into structural shapes
• Slabs are a rectangular solid with a width
  greater than twice the thickness
  
• Can be used to produce plates, sheets, or strips

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Rolling

• used to produce flat plates, sheets and foil in
  long lengths, at high speeds and with good
  surface finish in process called flat rolling.
  
• plates rolled materials have a thickness
  greater than .25 inch and used for structural
  applications ship hulls, boilers,bridges,
  girders.
• sheets generally less than .25 inch thick
  supplied in either flat or coil form, used for
  auto bodies, appliances, food and beverage
  containers, kitchen and office equipment
• foil extremely thin sheets of metal less
  than .0003 for wrapping candy and cigarettes
  

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Rolling

• -- high capital investment cost
• -- low to moderate labor cost
• -- moderate operator skill required

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Flowchart of Rolling Operations
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Basic Rolling Process

• Metal is passed between two rolls that rotate in
  opposite directions
  
• Friction acts to propel the material forward
• Metal is squeezed and elongates to compensate for
  the decrease in cross-sectional area
  

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Hot Rolling and Cold Rolling

• In hot rolling, temperature control is required
  for successful forming
  
• Temperature of the material should be uniform
• Rolling is terminated when the temperature falls
  to about 50 to 100 degrees above the
  recrystallization temperature
  
• Ensures the production of a uniform grain size
• Cold rolling products sheet, strip, bar and rod
  products with smooth surfaces and accurate
  dimensions

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Rolling
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Rolling
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Rolling
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Rolling
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Rolling
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Progressive Shape Rolling

• In progressive roll forming, a metal strip is
  cold formed by passing it
  
• through shaped rolls to achieve a desired shape. 
  The stock is fed
  
• longitudinally through successive pairs of
  contoured rolls that
  
• progressively form the workpiece into the desired
  shape.
  
• Used for mass production of long pieces with
  relatively close tolerances
  
• Utilizes ductile workpiece materials Material is
  usually less than 1/8 in. thick and 20 in. wide
  Produces workpieces at a typical forming speed of
  100 fpm Is suitable for decorative and structural
  products

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Progressive Shape Rolling

• Stages in shape rolling of an H-section part.
  Various other structural sections, such as
  channels and I-beams, are also rolled by this
  process.

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Progressive Shape Rolling
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Thread-Rolling Process
Thread Rolling a cold forming process used to
make straight or tapered threads on round rods.
-- doesn't produce any metal scrap -- strain
hardens the threads in the process
-- sets up compressive residual surface stresses
(resistant to fatigue) -- produces smooth surf
ace finish -- better grain structure of threade
d parts, than produced by cutting
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Thread-Rolling
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Thread-Rolling
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Ring Rolling

• One roll is placed through the hole of a
  thick-walled ring and a second roll presses on
  the outside
  
• Produces seamless rings
• Circumferential grain orientation and is used in
  rockets, turbines, airplanes, pressure vessels,
  and pipelines

Figure 16-6 Schematic of horizontal ring rolling
operation. As the thickness of the ring is
reduced, its diameter will increase.
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Forging
Note size of worker!!
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16.5 Forging

• Processes that induce plastic deformation through
  localized compressive forces applied through
  dies
  
• Oldest known metalworking process

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Traditional Forging
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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Open Die Forging

• Ideal deformation of a solid cylindrical specimen
  compressed between flat frictionless dies.
  
• Deformation in upsetting with friction at the
  die-workpiece interfaces.

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Open-Die Forging

• Open-Die Forging-- forging in which the dies are
  relatively flat and allow the material to freely
  deform in directions lateral to the applied load.
  
• -- Upsetting
• -- Cogging
• -- Fullering
• -- Edging
• -- Heading
• -- Piercing

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Upsetting

• UPSET FORGING Upset forging, also called hot
  heading, is a process by which the
  cross-sectional size of a bar is increased,
  either at an end or at some point along its
  length. It is done on specially designed
  upsetting machines, using closed dies to control
  size and shape.
• Typically, dies have several stations, and the
  parts are formed progressively by moving the
  parts from one die station or cavity to another
  until the forging is complete.
• Upset forging machines are made in several sizes,
  the largest capable of handling bars ten inches
  in diameter. Heads of bolts, valves, single and
  cluster gear blanks, artillery shells, and
  cylinders for radial engines are examples of
  parts made by upset forging.

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Upsetting
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Upsetting Examples
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Cogging

• Cogging forging that occurs when the
  deformation is done in by a sequence of steps at
  specific intervals systematically over a larger
  piece. Sometimes called incremental forging

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Fullering

• forging with an angled die that moves material
  laterally toward the center of the load
  

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Edging

• forging with an angled die that moves material
  laterally away from the center of the load
  

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Heading

• an upsetting process used to create head bolts,
  screws or other fasteners.

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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Impression Die Forging
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Impression Die Forging

• Forging in which the material is shaped to fill
  out a die cavity defined by the upper and lower
  die halves. The dies are not fully closed and
  allows some material to escape as flash.
• Usually required a number of
• intermediate forging and
• trimming steps to fully form
• the workpiece.
•  Requires more complex
• (and more expensive) dies than open
  die forging
  

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Impression Die Forging
(1) (2) by upsetting
(3) (4) by impression die
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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Closed-Die Forging

• Closed-Die forging in which the material is fully
  constrained in the cavity created by the upper
  and lower die halves.
  
• Allows more accurately shaped parts to be
  formed.
  
• No flash is formed, therefore little waste
  material
  
• Higher interface pressures required
• Requires very accurate control of material volume
  and proper die design.
  

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Closed-Die Forging
Spark plug base machined with blank and waste
Spark plug base cold formed with blank and waste
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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Roll Forging Operation

• Roll forging (cross-rolling) operation forging
  that is done by using a pair of rollers with
  shaped grooves
  
• Tapered leaf springs and knives can be made by
  this process with specially designed rolls.

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Roll Forging Machine
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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Coining

• Coining- cold squeezing of metal while all of the
  surfaces are confined within a set of dies

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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Orbital Forging Process

• The die is in contact with only a portion of the
  workpiece surface. This process is also called
  rotary forging, swing forging, and rocking-die
  forging and can be used for forming bevel gears,
  wheels, and bearing rings.

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Types of Forging Processes

• Open-Die Forging
• Impression Die Forging
• Closed-Die Forging
• Roll Forging
• Coining
• Orbital Forging
• Swaging or Radial Forging

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Swaging

• Also known as rotary swaging and radial forging
• Uses external hammering to reduce the diameter or
  produce tapers or points on round bars of tubes

Figure 16-20 Schematic of the roll-forging
process showing the two shaped rolls and the
stock being formed. (Courtesy of Forging Industry
Association, Cleveland, OH.)
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Swaging
Figure 16-21 (Below) Tube being reduced in a
rotary swaging machine. (Courtesy of the Timkin
Company, Canton, OH.)
Figure 16-23 (Below) A variety of swaged parts,
some with internal details. (Courtesy of
Cincinnati Milacron, Inc. Cincinnati, OH.)
Figure 16-22 (Right) Basic components and motions
of a rotary swaging machine. (Note The cover
plate has been removed to reveal the interior
workings.) (Courtesy of the Timkin Company,
Canton, OH.)
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Swaging Operation
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The figure shows the principle of operation of a
classical rotary swager. The motorized spindle
(4) is slotted, in order to hold the backers (3)
and the dies (5). The spindle passes the backers
over the rollers (2), thus delivering a blow to
the dies. In rotary swaging process, the head (1)
is fixed.
http//www.torrington-machinery.com/process/rotary
_swaging.html
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With all the factors involved, consider using a
software program to help in anything but simple,
already solved situations
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Finite Element Simulation

• Back of the envelope calculations are not very
  good for practical problems. Use the
  finite-element method of analysis to predict
  
• plastic deformation in forging.

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Forging of a Crankshaft

• Objective
• reduce flash by 30 percent !

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Forging of a Crankshaft
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Forging of a Crankshaft
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Material Cost Savings
The cost of NOT doing it right the first time?
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View forging DVD
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16.6 Extrusion

• Metal is compressed and forced to flow through a
  shaped die to form a product with a constant
  cross section
  
• May be performed hot or cold
• A ram advances from one end of the die and causes
  the metal to flow plastically through the die
  
• Commonly extruded metals aluminum, magnesium,
  copper, and lead

Figure 16-25 Direct extrusion schematic showing
the various equipment components. (Courtesy of
Danieli Wean United, Cranberry Township, PA.)
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Advantages of Extrusion

• Many shapes can be produced that are not possible
  with rolling
  
• No draft is required
• Amount of reduction in a single step is only
  limited by the equipment, not the material or the
  design
  
• Dies are relatively inexpensive
• Small quantities of a desired shape can be
  produced economically

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Extrusion Machine
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Typical Extruded Products
Figure 16-26 Typical shapes produced by
extrusion. (Left) Aluminum products. (Courtesy of
Aluminum Company of America, Pittsburgh, PA.)
(Right) Steel products. (Courtesy of Allegheny
Ludlum Steel Corporation, Pittsburgh, PA.)
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Extrusion Examples
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www.aluminumextrusions.com/ extrusions/
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Extrusion dies
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Extrusion of Seamless Tube

• Extrusion of a seamless tube. The hole in the
  billet may be prepunched or pierced, or it may be
  generated during extrusion.

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Extrusion pushes the material through the die
Drawing pulls the material through the die
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16.7 Wire, Rod, and Tube Drawing

• Reduce the cross section of a material by pulling
  it through a die
  
• Similar to extrusion, but the force is tensile

Figure 16-36 Cold-drawing smaller tubing from
larger tubing. The die sets the outer dimension
while the stationary mandrel sizes the inner
diameter.
Figure 16-34 Schematic drawing of the rod-or
bar-drawing process.
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Drawing
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Drawing Machine
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16.11 Surface Improvement by Deformation
Processing

• Deformation processes can be used to improve or
  alter the surfaces of the metal
  
• Peening- mechanical working of surfaces by
  repeated blows of impelled shot or a round-nose
  tool
  
• Burnishing- rubbing a smooth, hard object under
  pressure over the minute surface irregularities
  
• Roller burnishing- used to improve the size and
  finish of internal and external cylindrical and
  conical surfaces

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Summary

• There are a variety of bulk deformation
  processes
  
• The main processes are rolling, forging,
  extrusion, and drawing
  
• Each has limits and advantages as to its
  capabilities
  
• The correct process depends on the desired shape,
  surface finish, quantity, etc.