Machining Processes Used to

1
Machining Processes Used to Produce Round Shapes

• Chapter 22

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Various Cutting Operations

• Turing produces straight, conical, curved, or
  grooved workpieces
• Facing produces a flat surface at the end of
  the part
• Boring to enlarge a hole
• Drilling - to produce a hole
• Cutting off to cut off a workpeiece
• Threading to produce threads
• Knurling produces a regularly shaped roughness

3
Cutting Operations

• Fig Various cutting operations that can be
  performed on a late. Not that all parts have
  circular symmetry

4
Tool Geometry

• Rake angle
• controls direction of chip flow
• Strength of the tool
• Side rake angle
• Bake rake angle controls direction of chip flow
• Cutting edges affects surface finish and
  tool-tip strength
• Nose radius affects surface finish
• Material Removal Rate (MRR) is the volume of
  material removed per unit time

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Turning Parameters

• Forces in turning
• Cutting force acts downward on the tool tip
• Thrust force acts in the longitudinal direction
• Radial force acts in the radial direction
• Roughing and Finishing Cuts
• Rough cut high speed cut with little regard for
  dimensional tolerance
• Finishing cut lower feed rate and depth of cut
• Tool Materials, Feeds, and Cutting Speeds
• See table 22.4
• Cutting Fluids
• See table 22.5

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Components of a Lathe

• Fig Components of Lathe

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Lathes and Lathe Operations

• Lathes are the oldest machine tools
• Lathe Components
• Bed supports all major components
• Carriage slides along the ways and consists of
  the cross-slide, tool post, apron
• Headstock Holds the jaws for the work piece,
  supplies power to the jaws and has various drive
  speeds
• Tailstock supports the other end of the
  workpiece
• Feed Rod and Lead Screw Feed rod is powered by
  a set of gears from the headstock

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Lathe Specifications

• A lathe is specified by its
• Swing maximum diameter of the workpiece
• Distance from headstock and tailstock centers
• Length of the bed
• Lathes are available in a variety of styles and
  types of construction power
• Types of lathes
• Bench lathe
• Placed on a bench
• Low power
• Hand feed operated
• Toolroom lathes High precision
• Engine lathes
• Available in a wide variety of sizes
• Used for a variety of turning operations

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Right Hand Cutting Tool

• Fig (a) Designations and symbols for a
  right-hand cutting tool solid high-speed-steel
  tools have a similar designation. Right-hand
  means that the tool travels from right to left.

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Workholding Devices

• Chucks
• usually equipped with 3 or 4 jaws
• 3 jaw chucks generally are self centering. Used
  for round work pieces.
• Can be centered within .025mm independently.
• 4 jaw chucks are for square, rectangular, or
  odd-shaped workpieces
• Can be power actuated

• Fig (a) and (b) Schematic illustrations of a
  draw-in-type collets. The workpiece is placed in
  the collet hole, and the conical surfaces of the
  collet are forced inward by pulling it with a
  draw bar into the sleeve. (c) A push-out type
  collet. (d) Workholding of a part on a face plate.

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Mandrels

• Fig Various types of mandrels to hold
  workpieces for turning. These mandrels are
  usually mounted between centers on a lathe. Note
  that in (a) both the cylindrical and the end
  faces of the workpiece can be machined, whereas
  in (b) and (c) only the cylindrical surfaces can
  be machined.

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• Tracer Lathes
• Machine tools with attachments
• Capable of turning parts with various contours
• A tracer finger follows the template and guides
  the cutting tool
• Automatic Lathes
• Increasingly being automated
• Automatic Lathes are suitable for medium to high
  volume production
• Automatic Bar Machines
• Formerly called automatic screw machines
• Designed for high-production-rate machining of
  screws and other threaded parts
• All operations are preformed automatically
• Equipped with single or multiple spindles

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Turret Lathes

• Capable of performing multiple cutting operations
  on the same workpiece
• Turning
• Boring
• Drilling
• Thread cutting
• Facing
• Turret lathes are very versatile
• Types of turret lathes
• Ram-type ram slides in a separate base on the
  saddle
• Saddle type
• more heavily constructed
• Used to machine large workpeiceces

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Computer Numerically Controlled Lathes

• Computer Numerical Controls (CNC)
• Equipped with one or more turrets
• Each turret is equipped with a variety of tools
• Performs several operations on different surfaces
  of the workpiece

• Fig A computer numerical control lathe. Note
  the two turrets on this machine.

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Turning Process Capabilities

• Production rates
• See Table 22.8
• Surface finish and dimensional accuracy

Fig The range of dimensional tolerances
obtained in various machining processes as a
function of workpiece size. Note that there is an
order of magnitude difference between small and
large workpieces.
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Design Considerations for Turning Operations

• Parts should be designed so that can be fixtured
  and clamped in the work holding devices
• Dimensional accuracy and surface finish specified
  should be as wide as possible
• Avoid sharp corners, tapers, and major
  dimensional variations in the part
• Use near-net-shape forming
• Cutting tools should be able to travel across
  workpiece without obstruction
• Standard cutting tools, inserts, and toolholders
  should be used
• Materials should be selected for their
  machineability

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Guidelines for Turning Operations

• Minimize tool overhang
• Support workpiece rigidly
• Use machine tools with high stiffness and high
  damping capacity
• When tools begin to vibrate and chatter, modify
  one or more of the process parameters, such as
  tool geometry, cutting speed, feed rate, depth of
  cut, or use of cutting fluid
• Chip Collection Systems
• Drop them on a conveyor belt
• Dragging the chips from a setting tank
• Using augers with feed screws
• Magnetic conveyors
• Vacuum methods

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High-Speed Machining, Ultraprecision Machining,
and Hard Turning

• High-Speed Machining
• High speed 600 - 1,800 m/min
• Very high speed 1,800 - 1,800 m/min
• Ultrahigh speed gt 18,000
• Important factors
• Power and stiffness of the tools
• Stiffness of tool holder
• Spindle design
• Inertia of the machine-tool components
• Fast feed drives
• Level of automation
• Selection of appropriate cutting tool
• Ultraprecision Machining uses a single-crystal
  diamond, also known as diamond turning
• Hard turning
• When hardness increases, machinability decreases
• Uses polycrystalline cubic boron nitride, cermit,
  or ceramic cutting tools
• Competes successfully with the grinding process

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Cutting Screw Threads

• Screw-Thread Nomenclature
• Standardization of screw threads began in the
  middle 1880s

• Fig (a) Standard nomenclature for screw
  threads, (b) Unified National thread and
  identification of threads, (c) ISO metric thread
  and identification of threads.

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Cutting Screw Threads

• Design Considerations for Screw-Thread Cutting
• Should allow for the termination of threads
  before they reach a shoulder
• Eliminate shallow, blind tapped hole
• Chamfers should be specified at the ends
• Threaded sections should not be interrupted with
  slots, holes, or other discontinuities
• Use standard tooling for threads
• Operations should be completed in one step

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Cutting Screw Threads

• Fig (a) Cutting screw threads on a lathe with a
  single-point cutting tool. (b) Cutting screw
  threads with a single-point tool in several
  passes, normally utilized for large threads. The
  small arrows in the figures show the direction of
  feed, and the broken lines show the position of
  the cutting tool as time progresses. (c) A
  typical carbide insert and toolholder for cutting
  screw threads. (d) Cutting internal screw threads
  with a carbide insert.

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Types of Screw threads

• Fig Various types of screw threads

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Boring

• Boring produces circular internal profiles in
  hollow workpieces
• Boring mills are used for large workpieces
• Holes can be bored up to 20M if needed
• See fig. 22.20
• Machines are available with a variety of features
• Horizontal boring machines
• Jig borers

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Drilling And Drills

• Drills
• Have high lenth to diameter ratio
• Capable of producing deep holes
• Some what fexable
• Flutes two spiral grooves that run the length of
  the drill and allow the chips to escape
• Small changes in drill geometry can have a
  significant effect on the drills performance

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Drilling And Drills

• Types of drills
• Twist drill most common drill
• Step drill produces holes of two or more
  different diameters
• Core drill used to make an existing hole bigger

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Drilling And Drills

• Drilling operations
• Counterboring countersinking produce
  depressions on the surface to accommodate the
  heads of screws
• Center drill is a short and is used to produce
  the hole at the end of a piece of stock
• Spot drill is used to spot (start) a hole at the
  desired location
• Gun Drilling - used fro drilling gun barrels and
  deep holes
• Thrust Force and Torque
• Thrust force acts perpendicular to the hole axis
• Can cause the drill to bend or break if excessive
• Drilling Practice
• Held in drill chucks
• walking can be a problem when starting a hole
• The drill should be guided
• Used a center drill to start a hole
• Drills can be reconditioned
• Drill life is measured by the number of holes
  drilled.

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Drill point Geometries

• Fig Standard chisel-point drill indicating
  various features. The function of the pair of
  margins is to provide a bearing surface for the
  drill against walls of the hole as it penetrates
  into the workpiece drills with four margins
  (double-margin) are available for improved drill
  guidance and accuracy. Drills with chip-breaker
  features are also available. (b) Crankshaft-point
  drill. (c) Various drill points and their
  manufacturers 1. Four-facet split point, by
  komet of America. 2. SE point, by Hertel. 3.New
  point, by Mitsubishi materials. 4. Hosoipoint, by
  OSG Tap and Die. 5. Helical point.

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Reaming And Reamers

• Operation used to make an existing hole
  dimensionally more accurate than by drilling
  alone
• The hole making sequence is
• Centering
• Drilling
• Boring
• reaming

Fig various types of drilling and reaming
operations.
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Gun Drilling

• Fig (a) A gun drill showing various features.
  (b) method of gun drilling.

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Trepanning

• Fig (a) trepanning tool (b) trepanning with
  drill mounted single cutter.

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Drilling Machines

• Fig Schematic illustration of the components of
  (a) a vertical drill press and (b) a radial
  drilling machine.

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CNC Milling Machine

• Fig A three axis computer numerical control
  drilling machine. The turret holds as much as
  eight different tools, such as drills, taps, and
  reamers.

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Reamers

• Fig Various types of drilling and

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Tapping And Taps

• Internal threads in workpiceces can be produced
  by tapping
• A tap is a chip-producing threading tool
• Tapping may be done by hand or
• Drilling machines
• Lathes
• Automatic screw machines
• Vertical CNC milling machines

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Tapping and Taps

• Fig (a) Terminology for a Tap (b) Tapping of
  steel nuts in production

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THE END