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Manufacturing Rounded Shapes II

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					  Manufacturing
Rounded Shapes II

   Manufacturing
    Processes
           Outline

Specialized Turning Operations
  High-Speed Machining
  Ultraprecision Machining
  Hard Turning
Cutting Screw Threads
Knurling
Boring and Boring Machines
Drilling and Drills
Reaming and Reamers
Tapping and Taps
Chip Collection
 High-Speed Machining
Decreases cutting time by increasing cutting
  speed
Approximate Range of Cutting Speeds:
- High Speed: 2000-6000 ft/min
- Very High Speed: 6000-60000 ft/min
- Ultrahigh Speed: >60000 ft/min

Decreases total energy required:
- Power for high-speed machining ≈ .004
   W/rpm
- Power for normal machining
  ≈ .2-.4 W/rpm

Most important when cutting time is a
  significant part of the manufacturing time
High-Speed Machining

Factors:
- Stiffness of the machine tools
- Stiffness of tool holders and
  workpiece holders
- Proper spindle for high speeds
  and power
- Sufficiently fast feed drives
- Automation
- A proper cutting tool for high
  cutting speeds
- Ability to hold the piece in
  fixtures at high speed
       Ultraprecision
        Machining
Used for very small surface finish
 tolerances in the range of
 .01 µm

The depth of cut is in the range
 of nanometers

Machine tools must be made
 with high stiffness
         Ultraprecision
          Machining
Factors:
- Stiffness, damping, and geometric
  accuracy of machine tools
- Accurate linear and rotational motion
  control
- Proper spindle technology
- Thermal expansion of machine tools,
  compensation thereof, and control of the
  machine tool environment
- Correct selection and application of
  cutting tools
- Machining parameters
- Performance and tool-condition
  monitoring in real time, and control
  thereof
        Hard Turning

Used for relatively hard, brittle
 materials

Produces parts with good
  dimensional accuracy, smooth
  surface finish, and surface
  integrity

May be used as an alternative to
 grinding
Hard Turning
 Procedure
 Hard Turning
  Statistics




     Heat dissipated by chips




Tool forces: radial force is greatest
 Hard Turning
Chip Formation




Brittle materials form segmented
chips, which cause a large force
against the cutting edge
         Hard Turning

Advantages (as an alternative to
  grinding)

- Lower cost of machine tools
- Ability to machine complex parts in
  a single setup
- Ability to create various part styles
  or small part numbers efficiently
- Less industrial waste
- Ability to cut without fluids
  (eliminates grinding sludge)
- Easily automated
   Hard Turning
   Surface Finish



      NO                 YES




A hard journal bearing surface should have a
  surface with deep valleys and low peaks
Cutting Screw Threads

Cutting threads on a lathe is
 slower than newer methods

- Die-Head Chasers
  used to increase production
  rate of threading on a lathe

- Solid Threading Dies
  used for cutting straight or
  tapered threads on the ends of
  pipes or tubing
Cutting Screw Threads
Cutting Screw Threads
 Die-Head Chasers and
  Solid Threading Dies




Straight chaser cutting die (top)
Circular chaser cutting die (bottom left)
Solid threading die (bottom right)
Screw Machine
Screw Machine
 Cutting Screw Threads
Design Considerations:
- Threads should not be required to reach
  a shoulder
- Avoid shallow blind tapped holes
- Chamfer the ends of threaded sections to
  reduce burrs
- Do not interrupt threaded sections with
  slots, holes etc.
- Use standard thread tools and inserts as
  much as possible
- The walls of the part should be thick
  enough to withstand clamping and cutting
  forces
- Design the part so that cutting operations
  can be completed in a single setup
            Knurling

Used to create a uniform roughness
 pattern on cylindrical surfaces

Performed on parts where friction is
  desired (knobs, grip bars etc.)

Types:
- Angular Knurls
  create a pattern of diamond-
  shaped ridges
- Straight Knurls
  create a pattern of straight
  longitudinal ridges
Knurling Results
Knurling Operation
       Boring and
     Boring Machines
Boring produces circular internal
 profiles

Small pieces can be bored on a
 lathe; boring mills are used for
 larger workpieces
Boring Operation
Boring Operation
       Boring and
     Boring Machines
Design Considerations:
- Avoid blind holes when
  possible
- A higher ratio of the length to
  the bore diameter will cause
  more variations in dimensions
  because the boring bar will
  deflect more
- Avoid interrupted internal
  surfaces
     Drilling and Drills

Types of drill
- Twist drill (most common)
- Gun drill
- Trepanner

Pilot Holes
  Sometimes, when drilling
  large-diameter holes, it is
  necessary to drill a smaller
  hole first to guide the large drill
    Types of Drills
and Drilling Operations
Drill Terminology
     Drill Point Angle
                                    Point Angle




                   118° Standard




135° Harder Materials       90° Softer Materials
stainless steel, titanium          plastic
   Minimizes burring
Trepanners
    Drills and Drilling

Deep Holes
 Complications may occur when
 drilling a hole longer than 3
 times the drill diameter

Problems
- Chip removal
- Coolant dispensing to the
  cutting edge
- Tool deflection
    Drills and Drilling

Small Holes
 Small drills
 .0059-.04 in

 Microdrilling
 .0001-.02 in
Microdrills
Pilot Holes
     Drills and Drilling

Forces and Torque

 Thrust force:
 acts perpendicular to the axis of the
 hole; large forces can cause the
 drill to bend or break

 Torque:
 the torque acting to turn the drill

 These values are difficult to
 calculate
            Drill Feed
           and Speed
             V = πDN/12
V = cutting speed in ft/min;
Velocity at which the drill edge moves
  along the workpiece surface
D = diameter of the drill
N = RPM of the drill

Feeds for drills are listed as in/rev or
  m/rev. Multiply these by the RPM to
  obtain the feed in in/min or m/min.
  The feed cannot be controlled
  accurately on a drill press fed by
  hand.
 Drill Feed
and Speed
            Drill Feed
           and Speed
Example:
Work Material:        Aluminum
Tool Material:        High Speed Steel
Drill Diameter:       .5 in
Recommended Cutting Speed: 200-300
  ft/min (from table)

              N = 12V/πD
          N=12*(200-300)/(π*.5)
            =1528-2293 RPM

Recommended Feed for aluminum, .5in =
   .006-.01 in/rev (from table)
 f = (.006-.01)*1528 RPM = 9.2-15.2 in/min
     Drilling Material
     Removal Rate
Material Removal Rate

      MRR = (πD2/4)f N

        D = drill diameter
   f = feed, in/rev or mm/rev
            N = RPM
      Drilling Material
      Removal Rate
Example:
Drill Diameter: .5 in
Feed:           .006 in/rev
RPM:            1528 RPM

        MRR = (πD2/4)f N
      = (π(.5)2/4).006*1528
          = 1.8 in3/min
Drilling Operation
Reaming and Reamers

Used to improve the dimensional
 accuracy or surface finish of an
 existing hole

Types of reamers
- Hand reamers
- Rose reamers
- Fluted reamers
- Shell reamers
- Expansion reamers
- Adjustable reamers
Types of Reamers
Reamer Terminology
    Tapping and Taps

Used to make internal threads in
 workpiece holes

Types of taps
- Tapered taps
- Bottoming taps
- Collapsible taps
Tap Terminology
      Drilling, Reaming
        and Tapping
Design Considerations:
- Holes should be drilled on flat surfaces
  perpendicular to the hole axis to
  prevent drill deflection
- Avoid interrupted hole surfaces
- The bottoms of blind holes should
  match standard drill point angles
- Avoid blind holes when possible; if large
  diameter holes are to be included,
  make a pre-existing hole in fabrication
- Design the workpiece so as to minimize
  fixturing and repositioning during drilling
- Provide extra hole depth for reaming or
  tapping blind or intersecting holes
         Summary

Specialized cutting procedures
 exist for unusual materials and
 requirements

Proper procedure, securing of
  the workpiece, and feeds and
  speeds must be considered to
  prevent damage and injuries
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