Manufacturing Rounded Shapes II

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ManufacturingRounded Shapes II

• Manufacturing Processes

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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

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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 gt60000 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

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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

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UltraprecisionMachining

• 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

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UltraprecisionMachining

• 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

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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

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Hard TurningProcedure
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Hard TurningStatistics
Heat dissipated by chips
Tool forces radial force is greatest
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Hard TurningChip Formation
Brittle materials form segmented chips, which
cause a large force against the cutting edge
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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

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Hard TurningSurface Finish
NO YES
A hard journal bearing surface should have a
surface with deep valleys and low peaks
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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

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Cutting Screw Threads
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Cutting Screw Threads
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Die-Head Chasers and Solid Threading Dies

• Straight chaser cutting die (top)
• Circular chaser cutting die (bottom left)
• Solid threading die (bottom right)

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Screw Machine
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Screw Machine
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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

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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

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Knurling Results
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Knurling Operation
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Boring andBoring Machines

• Boring produces circular internal profiles
• Small pieces can be bored on a lathe boring
  mills are used for larger workpieces

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Boring Operation
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Boring Operation
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Boring andBoring 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

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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

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Types of Drillsand Drilling Operations
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Drill Terminology
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Drill Point Angle
Point Angle
118 Standard
135 Harder Materials stainless steel,
titanium Minimizes burring
90 Softer Materials plastic
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Trepanners
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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

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Drills and Drilling

• Small Holes
• Small drills
• .0059-.04 in
• Microdrilling
• .0001-.02 in

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Microdrills
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Pilot Holes
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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

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Drill Feedand Speed

• V pDN/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.

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Drill Feedand Speed
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Drill Feedand 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/pD
• N12(200-300)/(p.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

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Drilling MaterialRemoval Rate

• Material Removal Rate
• MRR (pD2/4)f N
• D drill diameter
• f feed, in/rev or mm/rev
• N RPM

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Drilling MaterialRemoval Rate

• Example
• Drill Diameter .5 in
• Feed .006 in/rev
• RPM 1528 RPM
• MRR (pD2/4)f N
• (p(.5)2/4).0061528
• 1.8 in3/min

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Drilling Operation
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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

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Types of Reamers
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Reamer Terminology
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Tapping and Taps

• Used to make internal threads in workpiece holes
• Types of taps
• Tapered taps
• Bottoming taps
• Collapsible taps

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Tap Terminology
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Drilling, Reamingand 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

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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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T h e
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