Powder Metallurgy, Forming, Machining, and Grinding

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Chapter 26

• Powder Metallurgy, Forming, Machining, and
  Grinding

Powder Metallurgy Primary Forming Processes
Secondary Forming Processes Machining Grinding
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• Powder metallurgy (P/M) consists of several steps.

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• Compacting consolidates and densifies the
  component for transportation to the sintering
  furnace.

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• Cold isostatic pressing is performed at room
  temperature with liquid as the pressure medium.
  Hot isostatic pressing is performed at elevated
  temperature with gas as the pressure medium.

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• A macroetched section through a forging indicates
  that the grain flow follows the contour of the
  component, which often maximizes strength in the
  direction of greatest operating stress.

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• In impression die forging, the workpiece is
  shaped within the cavities of two dies that come
  together to completely enclose it.

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• Roll forging is used to produce components with
  long, symmetrical sections, often with a slight
  taper, by forcing the workpiece between two
  matched and grooved rolls that rotate in opposite
  directions.

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• Upset forging is used to gather a large amount of
  material at one end of a bar, such as in the
  forming of a wrench socket.

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• Ring rolling is the shaping of seamless rings by
  reducing the cross section and increasing the
  circumference of a donut-shaped blank.

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• Rotary forging requires significantly less force
  compared with other forging processes.

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• Radial forging is used to produce components
  having a circular cross section.

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• Rolling is described by the roll design and roll
  configuration.

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• The primary methods of extrusion are forward
  extrusion and backward extrusion.

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• Fast ram speeds and short strokes are used in
  impact extrusion, and, because of the impulsive
  force applied, high production rates are possible.

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• The neutral axis is the boundary line between
  tensile and compressive stresses in bending.

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• Bending methods include draw bending, compression
  bending, and press bending.

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• Roll bending is used to curve plate, sheet, and
  bars into cylinders or cylindrical segments using
  machines with two or three rolls.

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• Spinning is a process of forcing disks or tubing
  into cones, disk shapes, hollow cylinders, and
  other circular shapes by combined forces of
  rotation and pressure.

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• Stretch forming is a process for forming sheet
  metal by applying tension to it and then wrapping
  it around a die of the desired shape.

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• Superplastic forming enables sheet metal to be
  deformed into complex shapes under relatively low
  pressure.

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• In metal stamping operations, sheet metal is
  formed into the desired shape by the punch and
  the die.

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• Cold heading is used to force metal to cold flow
  into enlarged sections by endwise squeezing.

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• In rotary swaging, tapered dies open and shut
  rapidly, as much as several thousand times a
  minute, as the workpiece is fed in.

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• Sizing, coining, and hobbing are finishing
  operations that change metal thickness and
  configuration by squeezing and working the metal
  beyond its yield point.

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• Thread rolling is the production of threads by
  rolling the workpiece between two grooved die
  plates and is most commonly used for making screw
  threads.

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• Ironing is a process for smoothing and thinning
  the wall of a shell or cup.

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• The cutting tool is characterized by the rake
  angle and the relief angle.

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• A lathe is a basic feature of any machine shop
  and performs a variety of turning functions.

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• Trepanning is a machining process for producing a
  circular hole or groove in solid stock, or a
  disk, cylinder, or tube from solid stock.

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• Milling is the removal of material from a
  workpiece by a rotary tool with teeth that engage
  the workpiece as it moves past the tool.

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• Broaching is cutting with a bar that has a series
  of teeth on one face that is pushed or pulled
  over the surface of the workpiece.

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• Electrical discharge machining is the removal of
  metal by rapid spark discharge between different
  polarity electrodes.

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• Electrochemical machining is the controlled
  removal of metal by anodic dissolution in an
  electrolytic cell in which the workpiece is the
  anode and the tool is the cathode.

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• Chemical milling is the controlled dissolution of
  a workpiece surface by contact with chemical
  reagents varying in type and strength.

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• Grinding wheels are marked with symbols that
  designate their properties.