Bulk Deformation Processes in Metalworking

1
Bulk Deformation Processesin Metalworking
2
Rolling

• Rolling - deformation process with thickness
  reduced by compressive forces exerted by two
  opposing rolls.

3
Rolling Analysis

• Conservation of material
• Continuity of volume flow rate
• Forward slip
• Rolling force, F

4
Rolling Analysis

• Where the deformation strain
• and the average flow stress
• The torque required for the deformation process
• The power required by the process is

5
Rolling Mechanics

• The rolling process is governed by the frictional
  force between the rollers and the workpiece. The
  frictional force at the entrance side is higher
  than that at the exit side. This allows the
  roller to pull the workpiece towards the exit end.

6
Friction

• voltvrltvf
• Maximum draft, which is the thickness reduction,
  is given as ?2R.
• Coefficient of friction depends on lubrication,
  typically
• cold working 0.1
• warm working 0.2
• hot working 0.4

7
Material and Process Parameters

• Material Parameters
• ductility
• coefficient of friction
• strength, modulus and Poissons ratio
• Process Parameters
• roller speed
• power
• draft
• lubrication

8
Shape Rolling

• In addition to the material and process
  parameters, the rollers will acts as a set of
  dies and have to be pre-formed to take the
  negative shape of the cross-section.
• There may be more than one set of rollers
  required to reduce the workpiece to the
  appropriate shape.

9
Rolling Mill Configurations

• a) two high b) three high c) four high
• d) cluster mill e) tandem rolling mill

10
Ring Rolling

• To make a larger and thinner ring from the
  original ring
• Usually a hot rolling process for large rings and
  cold rolling for small rings
• Typical applications bearing races, steel tires,
  rings for pressure vessel.

11
Thread Rolling

• Production of external thread
• Cold rolling
• High and competitive production rate (up to 8
  parts per second)

12
Gear Rolling

• Similar to the screw thread.
• Typically for helical gears
• Shares the same advantages
• better material usage
• smoother surface
• stronger thread due to work hardening
• better fatigue resistance due to compression

13
Roll Piercing

• Hot working process
• Production of Seamless thick-wall tubes

14
Forging
Open-die forging
Flashless forging
Impression-die forging
15
Mechanics of Forging

• Under ideal condition

Where F forging force Yf flow stress A
cross-section of part
16
Forging

• In open-die forging, barreling occurs.
• But with hot forging, the issue is complicated by
  the thermal distribution within the workpiece and
  the associated flow of metal.

17
Shape factor

• The actual forging force is greater than the
  ideal case.
• The shape factor is to cover the effect of
  barreling and the friction effect.
• Open-die forging is not a net-shape process and
  will require subsequent machining to dimension.

Load-stroke curve
18
Open-die Forging
Fullering
Edging
Cogging
19
Open-die Forging

• Fullering
• Reducing workpiece cross section to prepare for
  subsequent shaping action. Dies with convex
  surface cavity are used.
• Edging
• Similar to Fullering, but the dies have concave
  surface cavitiy.
• Cogging
• Open dies with flat or slightly contoured
  surfaces to reduce cross-section and to increase
  length.

20
Impression-die Forging

• Dies containing the inverse of the shape of the
  part. Flash is allowed on the parting surface.
  The flash serves as a constraint for metal flow
  in the die and help to fill the intricate details
  of the cavity.
• Higher forging forces are required in this
  process than open-die forging. The shape factor
  generally will have a higher value.

21
Impression-die Forging

• The forces are largest at the end of the process
  when the projected area of the blank and the
  friction is largest.
• Again, progressive dies are needed to transform
  the starting blank into a final desired geometry.
• Machining is needed to produce the fine tolerance
  needed.

22
Impression-die Forging

• Pros
• high production rate
• conservation of metal
• greater strength
• favorable grain orientation

Forging Machining
23
Shape Factor
24
Flashless Forging

• Conventional forging part Precision
  forging part

25
Flashless Forging

• The volume control is important and the outcome
  is precision re-production of inverse of cavity
  geometry. Typically for aluminum and magnesium
  alloy.

26
Corning
27
Drop Hammer and Dies
Webs - Thin section parallel to parting
line. Ribs - thin section perpendicular to
parting line Gutter - area for containing flash

• Dies are normally made from tool steel with high
  impact strength and high wear resistance.

28
Upsetting and Heading

• Upsetting and Heading
• The leading section of the stock is forged to
  form a head section using closed-die forging.

29
Upsetting and Heading

• Upsetting is used to form heads of screw and bolt
  with different geometric forms.

30
Swaging

• Swaging used to reduce the cross-sections of
  forged rods or tubes using a set of rotating
  dies. A mandrel is sometimes used to control the
  internal form of the tube.
• Radial forging rotates the stock rather than the
  die.

31
Roll Forging
32
Orbital Forging

• Small contact area reduce the forging force
  required substantially.

33
Hobbing

• To press the die against the softer blank to form
  the final shape.

34
Trimming

• Trimming is a shearing process to remove the
  flash from the workpiece.

35
Design Considerations

• Material
• Die design
• Machine
• Machine processing range
• Machine process setting

36
Design Considerations

• Material
• Ductility
• Strength
• Plastic deformation law (constitutive
  relationship)
• Coefficient (Die/workpiece)
• Variation of properties at processing temperature
  range

37
Design Considerations

• Die Design
• Number of die stations (progressive die)
• Geometric complexity of the part
• Die geometric details
• Draft angle, fillet, radii
• Webs and ribs
• Flash
• Parting surface and parting direction
• Die material
• Die life

38
Design Considerations

• Machine processing range
• Maximum forging force
• Maximum power
• Maximum speed
• Maximum die size

39
Design Considerations

• Machine process setting
• No. of stations
• Velocity profile
• Temperature / time profile
• Force