Forming Processes

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Forming Processes

• General Manufacturing Processes Engr.-20.2710
• Instructor - Sam Chiappone

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Deformation Process

• Permanent (plastic) deformation of a material
  under tension, compression, shear or a
  combination of loads.
• Types of Deformation
• Bulk flow in (3) dimensions
• Simple shearing of material
• Compound to simple bending
• Combination of above

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Deformation Process

• Stresses used to produce change
• Tension
• Compression
• Shear
• Combination in multiple axis
• (2) Classifications
• Bulk Significant change in surface area,
  thickness and cross section reduced, and overall
  geometry changed.
• Sheet Some deforming of material, but initial
  material thickness remains the same

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Deformation Process
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Deformation Process
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Deformation Process
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Deformation Process
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Process Variables

• (3) Classification
• Independent
• Controlled by the engineer
• Dependent
• Process determines outcome
• Independent / Dependent

Figure 15-1 Schematic representation of a
metalforming system showing independent
variables, dependent variables, and the various
means of linking the two.
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Work Ranges

• (2) Types of mechanical work where material
  undergoes plastic deformation
• Hot Working (HW)
• Cold Working (CW)

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Definition of HW vs. CW

• HW is performed above the recrystallization temp
  of the material and CW is done below the
  recryllization temp of the material.
• Recystallization Temp- The approximate minimum
  temp at which complete recyrallization of a cold
  worked metal occurs within a specified time.
• -Heat Treaterss Guide, American Society for
  Metals
• Approximate temperature ranges
• HW- .6 melt temp.
• WW - .3-.6 melt temp.
• CW - less than .3 melt temp.
• Example - CRS 950-1300F

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Definition of HW vs. CW

• Approximate temperature ranges
• HW - .6 melt temp. of the material
• WW - .3 to .6 melt temp of the material
• CW - less than .3 of the material
• Example - 1020 CRS 950 - 1300F

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Hot Working

• When HW a metal is in a plastic state and is
  easily formed. The forces required to deform the
  metal are less than CW. Some mechanical
  properties of the metal are improved due to
  process characteristics.
• At elevated temperatures, metal microstructures
  are rebuilding continually through the
  recrystallization process which allows for much
  higher deformation.

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Advantages to HW

• Porosity in metal is largely eliminated
• Impurities (inclusions) are broken up and
  distributed through the metal
• Course grains are refined
• Due to grain refinement, the physical properties
  are generally improved
• Ductility and resistance to impact are improved
• Strength is increased

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Advantages to HW
Figure 15-3 Cross section of a 4-in.-diameter
case copper bar polished and etched to show the
as-cast grain structure.
Figure 15-4 Flow structure of a hot-forged gear
blank. Note how flow is parallel to all critical
surfaces. (Courtesy of Bethlehem Steel
Corporation, Bethlehem, PA.)
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Advantages to HW

• Amount of energy necessary to change the shape of
  the raw material in a plastic state is far less
  than if the material was cold.
• Economical compared to CW

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Disadvantages to HW

• High working temp. can result in rapid
  oxidation/scaling of surface poor surface
  finish
• Generally, close tolerances are hard to control
• Equipment and tool maintenance costs are high

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Primary HW Processes

• Rolling
• Forging
• Extrusion
• Pipe tube manufacturing
• Drawing

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Rolling

• Heated metal is passed between rotating rolls to
  reduce the cross-section.

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Rolling

• One of the primary first process to convert raw
  material into finished product.
• Starting material (Ingots) are rolled into
  blooms, billets, or slabs by feeding material
  through successive pairs of rolls.
• Bloom - square or rectangular cross section with
  a thickness greater than 6 and a width no
  greater than 2xs the thickness
• Billets - square or circular cross section - -
  smaller than a bloom
• Slabs - rectangular in shape(width is greater
  than 2xs the thickness), slabs are rolled into
  plate, sheet, and strips.

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Forging

• The plastic deformation of metals, typically at
  elevated temperatures, using compressive forces
  exerted through a die to conform the metal to a
  desired shape.
• Process advantages
• Closing of voids in the metal
• Reduced machining time
• Improve the physical properties of the starting
  metal

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Forging

• Process disadvantages
• Possible scale inclusions in forging
• Tooling cost can be high
• Usually not used for short production runs

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Forging Methods

• Open-Die Drop Hammer - heated metal is placed
  between diesa force is delivered with a steam
  hammer.
• Accuracy is not good
• Complicated shapes are difficult to produce

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Forging Methods

• Open-Die Drop Hammer - Steam Hammer

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Forging Methods
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Forging Methods

• Upset forging
• Grip a barheat the endforge into desired shape
• Product examples
• Bolts
• Engine valves

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Forging Methods

• Impression Die Drop Hammer Forging - Hot pliable
  metal is forces into the shape of closed
  impression dies. This process is typically
  performed in a progressive method through a
  series of dies to control the flow.
• 2 Types of drop forge hammers
• Steam
• Gravity

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Forging Methods

• Impression Die Drop Hammer Forging

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Forging Methods
Figure 16-12 Impression drop-forging dies and the
product resulting from each impression. The flash
is trimmed from the finished connecting rod in a
separate trimming die. The sectional view shows
the grain flow resulting from the forging
process. (Courtesy of Forging Industry
Association, Cleveland, OH.)
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Forging Methods

• Press Forging
• Large.thick work
• Slow Squeezing action penetrates entire work
  piece producing uniform deformation
• Dies are typically heated to
• Assist surface flow
• Reduce surface heat loss
• Assist in obtaining close tolerances and surface
  finish
• Two types of presses -- mechanical and hydraulic
• Hydraulic - up to 50,000 tons

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Forging Methods

• Press Forging

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Hot Extrusion

• A plastic deformation process in which metal is
  forces under pressure to flow through a single,
  or series of dies until the desired shape is
  produced.
• Advantages
• Wide variety of shapes
• High production rates
• Improved microstructure and physical properties
• Close tolerances are possible
• Economical
• Design flexibility

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Hot Extrusion
Figure 16-25 Direct extrusion schematic showing
the various equipment components. (Courtesy of
Danieli Wean United, Cranberry Township, PA.)
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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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Pipe, Tube, and Wire Manufacturing

• Tube - Butt or electric welding and Piercing

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Pipe, Tube, and Wire Manufacturing

• Wire Drawing

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Drawing

• Flat sheet or a plate of metal is forced into a
  recess with a depth more than several times the
  starting materials thickness.

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Cold Working

• CW is done below the recrystallization point of
  the material. In CW, greater forces are required
  to transform the raw metal into the desired
  shape.
• One major advantage..as the grain deformation
  proceeds greater resistance to the action is
  building resulting in improved strength and
  hardness (strain hardness).
• CW is a high volume production process.

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Cold Working

• Similar processes as HWmajor differences include
• Forces required
• Temperature range
• Equipment specifications

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Advantages Disadvantages

• Advantages
• No heat required
• Better surface finish
• Superior dimensional control---little or no
  secondary operations
• Strength, fatigue, and wear properties are
  improved
• Improved machinability

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Advantages Disadvantages

• Disadvantages
• Increased stress in materialstrain hardening
• Greater force required to work raw material
• Heavier and more powerful equipment is required
• Undesirable stresses may be produced in final
  product