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Machining

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The most common type of milling machine is the knee and column type. The spindle is fixed in the column or main body and the table is mounted on a knee. – PowerPoint PPT presentation

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Title: Machining


1
Machining
  • Q7

2
Introduction.
  • Topics Machines
  • Drill
  • Lathe
  • Grinder
  • Milling machine
  • Shaping machine
  • CNC machines.
  • Robotics

3
Introduction.
  • Associated Terms.
  • Cutting fluids.
  • Surface finish
  • Forces
  • Measurement's.
  • Tool geometry.
  • Work holding.
  • Chip formation

4
1. PARTS OF DRILL BIT
  • A Body. This section of the drill contains the
    drill flutes.
  • B Parallel shanks. This section of the drill bit
    is held by the chuck.
  • C Flank This determines the cutting lip length
  • D Flute. These provide the passageway for swarf
    to escape up the drill
  • E. Land. This is the thickness of the cutting
    lip
  • F Web this is the edge between both flanks

5
Parts of Drill Cont.
6
Reaming.
  • Reamers are used to accurately finish holes
    drilled by drill bits.
  • Reamers contain more flutes than a drill.
  • Drill bit Reamer

7
Terms.
  • Countersinking is the enlarging of the mouth of
    a drilled hole to accommodate countersunk head
    screws and rivets.

8
Pilot Hole
  • A pilot hole is drilled prior to drilling a large
    hole.

9
Counterboring
  • It is the increasing of the hole diameter to a
    certain depth to accommodate cheese head screws

10
The Centre Lathe.
11
Lathe Processes.
  • Parallel turning.
  • Facing off.

12
Lathe Processes Cont.
  • Taper turning
  • Parting off/Undercut

13
Lathe Processes Cont
  • Radius nose turning.
  • Drilling.

14
More Lathe Processes
15
Cutting Tools.
  • The tool used in a lathe is known as a single
    point cutting tool. It has one cutting edge or
    point whereas a drill has two cutting edges and a
    file has numerous points or teeth.

16
Lathe Tool Shears Workpiece.
  • The lathe tool shear the metal rather than cuts.
    It can only do so if there is relative motion
    between the tool and the work piece.
  • For example the work is rotation and the tool is
    moved into its path such that it forms an
    obstruction and shearing takes place.

17
Lathe Tool Shears Workpiece
18
Screw Cutting.
  • It is slightly more difficult task than plain
    turning.
  • It involves more accurate setting up of the tool
    and exact setting of feed in relation to the work
    rotation.
  • Once this is done however, the process is easy.

19
Screw Cutting
20
Bench Grinder.
21
Grinder
  • A bench grinder or pedestal grinder is a machine
    used to drive an abrasive wheel (or wheels).

22
Grinding Wheels.
  • The wheel can be fitted to the spindle of the
    grinding machine.
  • The wheel rotates at high speed and the work is
    brought into contact with it.

23
Parts of the Grinding Wheel.
  • There are two main constituents in a grinding
    wheel
  • 1 The abrasive (this is the grit)
  • 2. The bond. (this holds the abrasive in a rigid
    shape.

24
The Abrasive.
  • The abrasive forms the cutting edges.
  • Usually, a particular abrasive type is selected
    to suit the materials being ground.
  • The surface finish required on the work
    influences the size of the abrasive grains
    chosen.

25
The Bond
  • The bond, while designed to hold the abrasive in
    the form of a wheel, also must release the grains
    when they become worn.
  • There will be greater pressure on grain from the
    work if it has lost its cutting ability so it
    well become dislodged exposing sharper grains
    underneath.

26
Dressing the Grinding Wheel.
  • In the grinding process, wheel dressing is used
    to restore the cutting surface of any
    irregularities. Grinding wheels are designed to
    have a selfdressing action in which grains should
    break free and expose sharp edges.
  • Wheel dressing will renew a sharp cutting face
    and correct irregularities such as wheel
    concentricity.
  • The process can remove any undulations from the
    wheel.

27
Loading Grinding Wheel
  • Loading of a grinding wheel occurs when small
    particles of the metal being machined clog up the
    spaces between the abrasive grains in the
    grinding wheel

28
Loaded Grinding Wheel.
29
Glazed Grinding Wheel.
  • Glazing occurs when abrasive particles which have
    lost their edge remain trapped in the grinding
    wheel.

30
DIAMOND STICK WHEEL DRESSER
http//its.fvtc.edu/machshop1/Bench/grinder/video/
dresssideLG.mov
31
The Wheel Grit
  • Coarse Grit Fine Grit

32
Surface Grinding
  • A metal cutting process in which flat and
    extremely smooth surfaces are produced. The
    grinding wheel rotates and the workpiece, usually
    held in a magnetic chuck, is fed to and fro
    continuously.
  • At the end of each stroke, the table is moved
    across the wheel by a small amount.
  • The grinding wheel can be lowered to take a new
    cut

33
Surface Grinding Cont
34
Work holding for the Surface Grinding.
  • The magnetic chuck is used to hold work on the
    surface grinder. It consists of a top plate,
    which contains magnetic inserts, a casing which
    contains permanent magnets.
  • To turn the chuck on the magnets are moved on
    line with the inserts, which creates a magnetic
    force through the work piece.
  • The force is strong enough to hold the work piece
    securely in position.

35
Other Workholding methods for Surface Grinding.
  • Adaptor plates, sine chuck, chuck plates,
    universal plates and magnetic chucks

36
Cylindrical Grinding
  • This is used to produce cylindrical objects. The
    workpiece is held in a chuck, or between centres,
    and set to rotate.
  • Then a grinding wheel, when brought into contact
    with the workpiece, will produce a smooth
    accurate cylinder.
  • Long workpieces can be ground as the table can
    reciprocate and the wheel head can move towards
    the workpiece.
  • Tapered work can also be carried out.

37
Cylindrical Grinding Cont.
38
  • Machining processes used to produce cylindrical
    surfaces include
  • Parallel turning, Cylindrical grinding, Drilling,
    Reaming, Boring, Milling.

39
Safety features on a Pedestal Grinder
  • A face guard is supplied with the machine to
    protect against grinding debris.
  • Easily accessible switches allow the machine to
    be turned off quickly.
  • Modern machines are designed to stop quickly.
  • The machine should be firmly attached to the
    ground.

40
Milling - Industrial Applications
  • Milling machines are widely used in the tool and
    die making industry and are commonly used in the
    manufacturing industry for the production of a
    wide range of components.
  • Typical examples are the milling of flat
    surfaces, indexing, gear cutting, as well as the
    cutting of slots and key ways.

41
Typical Applications.
42
Milling Processes.
  • Milling is a metal removal process by means of
    using a rotating cutter having one or more
    cutting teeth.

43
Milling Processes Cont.
  • Cutting action is carried out by feeding the
    workpiece against the rotating cutter.
  • Thus the spindle speed the table feed the depth
    of cut and rotation direction of the cutter
    become the main parameters of the process.

44
Milling
  • Milling is the machining of a surface using a
    cutter which has a number of teeth. A flat
    surface may be produced or special cutters can be
    used to form profiled surfaces.
  • The most common type of milling machine is the
    knee and column type.
  • The spindle is fixed in the column or main body
    and the table is mounted on a knee.

45
Main Parts
  • Base cast iron base houses the cutting-fluid
    reservoir and has a rigid construction to prevent
    vibration.
  • Column mounted on the base, the column contains
    the spindle.
  • Knee allows for vertical movement of the table.
  • Saddle provides transverse movement of the
    table.
  • Table work pieces and work holding equipment are
    located and clamped.
  • Spindle provides the drive for the milling
    cutters

46
Types of Milling Machines.
  • Most of the milling machine are constructed of a
    column and knee type structure and they are
    classified into two main types namely Horizontal
    milling machine and Vertical milling machine.

47
Horizontal Type
Milling cutters are mounted on the arbour.
48
  • The main spindle is mounted horizontally near the
    top of the column.
  • The machine capacity is determined by the maximum
    distance from the table to the spindle as well as
    working surface size and travel in all
    directions.
  • The milling cutters have a hole in them in order
    to be mounted on an arbour.
  • The cutters are usually large in diameter and are
    found in a range of types including slab, side
    and face, saw, angle and form cutters

49
Vertical Type
Variety of cutters can be used
50
  • The spindle is mounted vertically in a head at
    the top of the column.
  • The milling cutters are generally mounted in a
    chuck.
  • There are a range of end mills, slot drills and
    profiled cutters (angle, ball-nose, dovetail,
    tee-slot, corner-rounding, etc.)

51
Milling Cutters
  • Milling tools are highly diverse.
  • An end mill is the term used for the tools shown
    below.
  • These are the most common types of milling
    cutters and they are used for cutting horizontal
    as well as vertical surfaces.

52
Cutting Tools
  • Cutting tools for horizontal milling.
  • Slab mills.
  • For heavy cutting of large and flat surfaces.

53
Side and Face Cutters
  • Side and face cutters.
  • This type of cutting edges on the periphery an
    sides of the teeth for cutting shoulder and
    slots.

54
Slitting Saws
  • Slitting saws.
  • For cutting deep slots or for parting off.

55
Cutting tools for vertical milling.
  • End mills
  • Commonly used for facing, slotting and profile
    milling.

56
Rough Cut End Mills
  • Rough cut end mills.
  • For rapid metal removal.

57
Face Milling Cutters
  • Face milling cutters.
  • For heavy cutting.

58
CHUCK MOUNTED CUTTERS
59
Milling Arbor Cutters
60
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61
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62
Up Cut Milling
  • The conventional milling method. In this process
    the milling cutter is rotating against the
    direction of the workpiece.
  • There is a danger of the workpiece lifting out of
    the vice, therefore effective clamping is
    necessary.
  • A smoother cuttingaction is achieved.

63
Up Cut Milling
64
DOWN CUT MILLING
  • The milling cutter rotates in the same direction
    as the workpiece movement, it is also known as
    climb milling.
  • A blacklash eliminator should be fitted to the
    machine for this type of milling to allow heavier
    cuts to be taken without the tendency to lift.
  • It produces a finish with less defined cuter
    marks.

65
Down Cut Milling
66
Typical Milling Operations.
  • Face Milling This is using the cutter at right
    angles to the cutting surface. The face or end of
    the cutter generates the desired surface on the
    piece. Many of these cutters are chuck mounted.

67
End Milling.
  • End milling is the milling of a flat surface
    with the axis of the cutter perpendicular to th
    machining surface.

68
Gang millilng.
  • Gang milling is a horizontal milling operation
    that utilises three or more milling cutters
    grouped together for the milling of a complex
    surface in one pass.

69
Straddle Milling
  • Straddle milling When the cutters are mounted on
    the arbour and are separated by spacing collars
    this is known as straddle milling.

70
Milling
  • These machines are capable of movement in the
    longitudinal, transverse and vertical directions

71
Milling set up.
  • Correct use of holding devices and a good set up
    are crucial importance in achieving a safe
    accurate and efficient operation of the machine .
  • Large workpiece can be mounted directly onto the
    machine table by means of tenons and screws while
    small workpieces are usually held by a machine
    vice.

72
Milling Safety.
  • Emphasize should be given that the eyes of the
    machine operator must be protected by wearing a
    face shield to prevent accident that may be
    caused by chips, cutting fluid, and tool
    breakage.
  • Machine operators must also take care of their
    body such as fingers which should be kept out of
    any moving parts, especially the rotating cutter
    of the machine, to prevent any unnecessary
    accidents or hurt.

73
  • Peripheral Milling is producing a finished
    surface from the cutting action of the teeth on
    the periphery of the cutter. Up cut and down cut
    milling are examples of peripheral milling

74
Climb vs. Conventional Milling
  • When milling, one should be aware of the
    difference between conventional,and climb
    milling.
  • In conventional milling, the workpiece is fed
    into the rotation of the cutter. This type of cut
    requires lower forces and is preferred for
    roughing cuts.
  • In climb milling, the work moves with the
    rotation of the cutter. This produces a better
    finish. It is not recommended if the workpiece
    cannot be held securely or cannot support high
    forces.

75
CLIMB V CONVENTIONAL
  • CLIMB V CONVENTIONAL

76
MOUNTING MILLING CUTTERS
  • The two main ways to mount milling cutters are
  • (1) Chuck mounted cutters
  • (2) Arbour mounted cuters

77
Milling Cutter Collets
  • The collet of a mill is critical for holding the
    work piece and for easily releasing it. Below are
    shown three types of collets and a cut-away of a
    collet.

78
THE DIVIDING HEAD
  • Dividing head This is used to hold work so that
    it can be rotated accurately for machining
    specific increments(indexing) e.g splines on
    shafts.

79
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81
The Shaping Machine
  • The diagram shows details of a quick return
    mechanism as used on the shaping machine.
  • The slotted link mechanism allows the ram to
    return on its idle stroke quicker than it takes
    to complete a cutting stroke.
  • The length of stroke is altered by moving the
    crankpin location relative to the centre of the
    slotted wheel.

82
Shaping Machine Cont.
  • The maximum stroke is set by locating the pin at
    the farthest point from the centre
  • The angle through which the bull wheel rotates on
    the cutting stroke is larger than the angle of
    the return stroke.
  • The ram will therefore move slower on the cutting
    stroke and faster on the return stroke.

83
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84
Shaping Machine Operations.
85
How the Shaping Machine Works.
86
Quick Return Mechanism.
  • A quick return mechanism such as the one seen
    opposite is used where there is a need to convert
    rotary motion into reciprocating motion.
  • As the disk rotates the black slide moves
    forwards and backwards.
  • Many machines have this type of mechanism.

87
CNC MACHINING
88
CNC MACHINING
  • Safety features incorporated in CNC lathes
  • Machine will not operated without gaurds in place
  • Emergency stop button
  • Allows for pre machining simulation
  • Clear machine guard.

89
C.N.C. Terms.
  • Time dwell This is the code entered if the
    operation requires a time period to execute a
    tool change. (G04)
  • A canned cycle enables a required number of
    repetitive operations to be carried out by a
    single programmed line (block) e.g (G80)

90
C.N.C. Terms Cont.
  • G-Codes control the cutting movement of the tool.
    M-Codes control operation functions. E.g. M04
    starts the spindle in
  • Linear interpolation is the movement of the
    cutting tool while cutting in a straight line.
    E,g GO I

91
C.N.C. Terms Cont.
  • Stepper motor This is a special motor that runs
    on electrical pulses andturns a fraction of a
    revolution for each pulse, it is used on CNC
    machines.
  • A canned cycle is a cnc programme cycle that will
    repeat a process at required amount of times.

92
C.N.C. Terms Cont.
  • The X-axis is the horizontal axis running
    perpendicular with the machine axis. The cross
    slide movement.
  • The z-axis is the vertical axis running parallel
    with the machine axis
  • G-codes are programme codes for cnc machining
    that control the movement of the cutting tool.
    Examples would be GOO, GO 1, G99.

93
C.N.C. Terms Cont.
  • Computer numerical control machining is suitable
    for large quantities of the same part. The
    operator has little involvement. High quality is
    produced
  • Conventional machine requires large levels of
    operator input. The operator moves the tool
    manually. This can lead to Inaccuracies in mass
    production.

94
C.N.C. Terms Cont
  • CAD Computer Aided Design/Drawing/Drafting is
    the process of inputting design data in a system
    with a graphical output.
  • CAM Computer Aided Manufacture uses the CAD
    output to produce components in a variety of
    computerised machines including lathe, milling
    machines, etc.

95
C.N.C. Terms Cont
  • Tool park position is the place where the tool is
    set in order to start a machining operation.
  • G00 is a code to inform to move as quickly as
    possible as the machine is not involved in a
    cutting operation.

96
Areas of Manufacturing where Robots Are Used
  • Aerospace
  • Automotive manufacturing and supply
  • Chemical, rubber and plastics manufacturing
  • Electrical and electronics
  • Entertainment-movie making
  • Food stuff and beverage manufacturing
  • Glass, ceramics and mineral production
  • Printing
  • Wood and furniture manufacturing

97
Specific Robotic Tasks In Manufacturing
  • Assembling products
  • Handling dangerous materials
  • Spraying finishes
  • Inspecting parts, produce, and livestock
  • Cutting and polishing
  • Welding

98
Advantages of Robotics
  • Competitive Advantage
  • Robots can do some things more efficiently and
    quicker than humans.
  • Mechanical
  • Robots never get sick or need to rest, so they
    can work 24 hours a day, 7 days a week.
  • Greater output per hour with consistent quality
  • Continuous precision in repetitive operation
  • Robots don't get bored, so work that is
    repetitive and unrewarding is no problem.

99
Limitations of Robotics
  • Today's robots
  • Are not creative or innovative
  • Can not think independently
  • Can not make complicated decisions
  • Can not learn from mistakes
  • Can not adapt quickly to changes in their
    surroundings
  • Every successful business must depend on real
    people for these abilities.

100
WORKING ENVELOPE OF ROBOT
  • A robot's work envelope is its range of movement.
  •  It is the shape created when a manipulator
    reaches forward, backward, up and down.
  • These distances are determined by the length of a
    robot's arm and the design of its axes.
  • Each axis contributes its own range of motion.

101
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102
Factors that influence surface finish when
parallel turning.
  • Use of cutting fluids or coolant
  • Workpiece material
  • Cutting speed
  • Sharp and well supported cutting tool.

103
Types of Screw Threads.
104
Thread Terminology Cont.
105
ACME Screw Thread Profile Used in Lathe Laed Screw
106
Square Thread Used in Linear Jacks and Clamps
107
BUTTRESS THREAD
108
Cutting Fluids.
  • Cutting Fluids are important in metal cutting
    because they reduce friction, cool the work and
    flush away the chips cut by the tool.

109
ADVANTAGES OF CUTTING FLUID
  • Cutting fluids have the following benefits
  • 1. They cool the cutting tool and work
  • 2. They reduce friction by lubricating the tool
    and chip
  • 3. They wash away swarf
  • These benefits prolong tool and machine life as
    well as reducing power consumption.

110
Cutting fluids in common use.
  • Water
  • It has a high specific heat but is poor in
    lubrication and also encourages rusting. It is
    use as a cooling agent during tool grinding.
  • Soluble oils.
  • Oil will not dissolve in water but can be made to
    form an intimate mixture or emulsion by adding
    emulsifying agents. The oil is then suspended in
    the water in the form of tiny droplets. These
    fluids have average lubrication abilities and
    good cooling properties.

111
  • Mineral oils.
  • They are used for heavier cutting operations
    because of their good lubrication properties and
    are commonly found in production machines where
    high rates of metal removal are employed. Mineral
    oils are very suitable for steels but should not
    be used on copper or its alloy since it has a
    corrosive effect.
  • Vegetable oils.
  • They are good lubricants but are of little used
    since they are liable to decompose and smells
    badly.

112
Effects of Cutting Fluids when Machining.
  • The primary functions of cutting fluids in
    machining are
  • Lubricating the cutting process primarily at low
    cutting speeds
  • Cooling the workpiece primarily at high cutting
    speeds
  • Flushing chips away from the cutting zone

113
  • Secondary functions include
  • Corossion protection of the machined surface
  • enabling part handling by cooling the hot surface
  • Process effects of using cutting fluids in
    machining include
  • Longer Tool Life
  • Reduced Thermal Deformation of Workpiece
  • Better Surface Finish (in some applications)
  • Ease of Chip and Swarf handling

114
Safety Hazards associated with Cutting Fluids.
  • Skin irritation or dermatitis.
  • Staining of work especially aluminium
  • Some give off hazards i.e. rancid smells.
  • Some create a mist or smoke making work area
    hazardous with toxic fumes.
  • Some leave an oily film on work needing extensive
    cleaning by solvents.

115
Safety Hazards associated with Cutting Fluids
Cont.
  • Irritant effects are caused from contact with
    toxic materials. This can cause industrial
    dermatitis, cracking and soreness of the skin.
    Oils, cutting fluids and fluxes are common
    causes.
  • Example - Dermatitis Cracking Skin

116
Factors that influence surface finish when
parallel turning.
  • Use of cutting fluids or coolant
  • Workpiece material
  • Cutting speed
  • Sharp and well supported cutting tool.

117
Types of Screw Threads.
118
Thread Terminology Cont.
119
ACME Screw Thread Profile Used in Lathe Laed Screw
120
Square Thread Used in Linear Jacks and Clamps
121
BUTTRESS THREAD
122
Surface Finish.
  • Factors which influence surface finish
  • The material being machined
  • The cutting speeds used.
  • The sharpness of the cutting tool

123
Machinability.
  • Machinability is a measure of how easy or
    difficult it is to cut a material.
  • The following can be used to determine
    machinability.
  • Tool life weak materials long tool life
    good machinability.
  • Cutting forces low cutting forces good
    merchantability.
  • Surface finish good surface finish good
    machinability.

124
MEASURING METHODS
  • Direct measurements are determined using a
    measuring instrument such as a ruler and the
    scale on the ruler is matched with the component

125
INDIRECT MEASURMENT
126
Measuring Methods Cont.
  • Comparative measurement is when gauges are used
    to compare the size of the component with that of
    the gauge
  • Absolute dimensions. All dimensions are taken
    from the outside end of work piece,
  • Incremental Dimensions. All dimensions are taken
    from the previous Position and not from a fixed
    datum.

127
Reasons why imprecise measurements may be taken
from measuring tools.
  • Burrs or scratching on precision equipment.
  • Human error.
  • Staining or rough use of equipment.
  • Damaged precision equipment.

128
Interference and Clearance Fits
  • Interference Fit.
  • If the limits of the shaft are always larger than
    the limits of the hole an interference fit
    occurs.
  • Clearance Fit.
  • If the limits of the shaft are always smaller
    than the limits of the hole a clearance fit
    occurs.

129
Interference and clearance
130
Gauging
  • Gauging is where specific precision gauges are
    used to check and compare dimensional accuracy.
  • Examples include no go and go Plug and gap
    gauges, telescopic gauges, and screw pitch
    Gauges.
  • Direct measurement requires more skill in setting
    and directly reading, micrometers and precision
    vernier callipers would be examples

131
MEASURING GAUGES
  • The gauge is a PLUG gauge. It accurately
    determines if a hole is drilled to within its
    tolerance.

132
Gap Gauge
  • The gauge is a Gap gauge. Its function is to
    check if the size of a component is within it
    tolerance
  • Spark plug using gap gauge

133
SCREW PITCH GAUGE
  • Screw pitch gauge. This gauge is used to check
    the pitch of screw by placing the blade that fits
    the best on a screw to determine the pitch size.

134
SINE BAR
  • This is used to set up and measure angles
    accurately.

135
THE SINE BAR
  • The sine bar is a precision measuring instrument
    used to measure angles accurately.
  • By using trigonometry, Gauge blocks and knowing
    the centre distances, (usually they come in
    distances of 100mm, 200mm, 250mm and 300mm )
    between the rollers which are of a set diameter.

136
SLIP GAUGES
  • Slip Gauges have very accurate measuring faces,
    flat and parallel to each other. They are usually
    rectangular in shape. They have two very flat
    parallel surfaces at opposite ends.

137
TELESCOPIC GAUGES
There are a range of gauges that are used to
measure a bore's size, by transferring the
internal dimension to a remote measuring tool.
They are a direct equivalent of inside calipers
and require the user to develop the correct feel
to obtain repeatable results
138
TELESCOPIC GAUGES
Telescoping gages need to be rocked over center
to size and center the telescoping gage
139
VERNIER CALLIPERS
140
HOW TO USE VERNIER CALLIPERS?
141
COMPARATORS
  • Comparators are used to compare the sizes of
    components. A simple comparator could consist of
    a dial gauge fixed to a stand.
  • Comparisons can be made quickly if the dial gauge
    is first set to zero using slip gauges to the
    required height.

142
PRECISION BALLS
  • Precision Balls make it possible to take linear
    measurement across angles, in order to calculate
    the angle.

143
  • SCREW CUTTING GAUGE
  • This is used when grinding screw cutting tools to
    ensure that the tool angles recorrect for the
    type of thread being cut. E.g. I.S.0 thread 60
    degrees.

144
Height gauge
  • Provides an accurate method of marking out
    metals and plastics.
  • Relatively easy to use once reading a vernier
    scale is mastered.
  • Can be used with vee blocks on round materials.
  • Can have a digital readout for increased accuracy.

145
CUTTING TOOL GEOMETRY
  • The shear plane will affect the depth of cut and
    hence the amount of power used in the cutting
    process.
  • A large shear plane will give a large depth of
    cut or chip thickness while a small shear plane
    will give a small depth of cut.

146
CUTTING TOOL FORCES
  • Orthogonal cutting has two forces. The tangential
    force and the axial force acting on the tool
    during cutting
  • Oblique cutting has three forces acting on the
    cutting tool. The tangential force, the axial
    force and the radial force. This force is caused
    by the plan approach angle on the cutting tool.
    The axial forces decrease as the radial forces
    increase.

147
Orthogonal Cutting
148
  • Oblique Cutting has three forces acting on the
    cutting tool.
  • The tangential force, the axial force and the
    radial force.
  • This force is caused by the plan approach angle
    on the cutting tool.
  • The axial forces decrease as the radial forces
    increase

149
Oblique Cutting
150
TOOL GEOMETRY CONT.
  • A large rake angle gives a small shear area hence
    easy to cut
  • A small rake angle gives a large shear area and
    therefore more difficult to cut.

151
DYNAMOMETER
  • Used for measuring tool cutting forces

152
Workholding Methods
  • The four-jaw independent chuck has four
    independent jaws that are adjusted individually
    from each other, they are also reversible.The
    four jaw is used to hold square, rectangular and
    irregular shapedWork pieces that cannot be used
    in a self-centring chuck.

153
Workholding Cont.
  • The Three Jaw operates differently by means of a
    pinion engaging with a gear. Each jaw is numbered
    and must be inserted in the correct order All
    three jaws moved simultaneously and automatically
    centre up the work. It is used for circular or
    hexagonal pieces.

154
The Magnetic Chuck.
155
Collets
  • Collets are very precise but must be used on work
    which is the same diametere as the inside of the
    collect.
  • A set of different size collets is normally
    required.

156
Holding Long Work.
  • The Fixed Steady
  • The fixed steady is clamped in the lathe bed and
    supports the work close to where the tool is
    cutting.

157
The Travel Steady
  • The travailing steady is clamped to the saddle
    and supports the work close to where the tool is
    cutting.

158
Mandrel
  • Use to hold long bars

159
FORMING AND GENERATING SURFACES
  • Forming, When the surface produced is a copy of
    the tool producing it, it is referred to as
    forming.. e.g. Screw cutting, u-cutting and
    contour work. Forming uses a specially designed
    cutting tool, which is in the shape of the shape
    to be cut. The tool is then forced directly into
    the work.
  • EG Parting Off Tool

160
Generating a Surface
  • Generating. By moving the tool in various
    directions until the required surface is
    machined. In generating the cutting tool is a
    single point cutter, which follows the path of
    the shape to be cut. ego facing, surfacing. taper
    turning.
  • e.g. taper-turning using the compound slide.

161
Basic Metal Cutting.
  • The usual conception of cutting suggests clearing
    the substance apart with a thin knife or wedge.
  • When metal is cut the action is rather different
    and although the tool will always be wedge shaped
    in the cutting area and the cutting edge should
    always be sharp the wedge angle will be far too
    great for it to be considered a knife shape.
  • Consequently a shearing action takes place when
    the work moves against the tool.

162
Tool Angles.
  • There are three important angle in her
    construction of a cutting tool rake angle,
    clearance angle and plan approach angle.

163
Rake Angle.
  • Rake angle is the angle between the top face of
    the tool and the normal to the work surface at
    the cutting edge. In general, the larger the rake
    and the smaller the cutting force on the tool
    since for a given depth of cut the shear plane.
  • A large rake angle will improve cutting action
    but would lead to early too failure, since the
    tool wedge angle is relatively weak. A compromise
    must therefore be made between adequate strength
    and good cutting action.

164
Clearance Angle.
  • Clearance angle is the angle between the flank or
    front face of the tool and a tangent to the work
    surface origination at the cutting edge.
  • All cutting tools must have clearance to allow
    cutting to take place.
  • Clearance should be kept to a minimum, as
    excessive clearance angle will not improve
    cutting efficiency and will merely weaken the
    tool.
  • Typical value for front clearance angel is 6
    degrees in external cutting.

165
RAKE CLEARANCE ANGLE
166
Cutting Tool Materials.
  • Hot hardness. This means the ability to retain
    its hardness at high temperatures. All cutting
    operations generate heat, which will affect the
    tools hardness and eventually its ability to cut.
  • Strength and resistance to shock. At the start of
    a cut the first bite of the tool into the work
    results in a considerable shock loading on the
    tool. It must obviously be strong enough to
    withstand it.

167
CHIP FORMATION
  • Continuous chip,
  • Discontinuous chip,
  • Discontinuous chip with built up edge.

168
CONTINUOUS CHIP
  • A continuous chip is formed when a ductile metal
    such as aluminium or steel is machined. A
    discontinuous chip is formed when brittle
    materials such as brass or cast iron are machined.

169
Discontinuous Chip
  • The chip leaves the tool as small segments of
    metal resulted from cutting brittle metals such
    as cast irons and cast brass with tools having a
    small rake angle
  • There is nothing wrong with this type of chip in
    these circumstances.

170
Built Up Edge
  • Chip with built up edge Very rough surface on
    the underside of the chip and also on the
    machined surface of the work. Caused by
    continuous chip and can be prohibited by the use
    of coolant to prevent particles of the work being
    welded to the tool face. .

171
Chip Breaker
  • A chip breaker is used to break the continuous
    chip into sections so that the chip cannot tangle
    around the cutting tool. The simplest form of
    chip breaker is made by grinding a groove on the
    cutting tool face a few millimeters behind the
    cutting edge.

172
Cutting Speed Feed.
  • The relative speed of work piece rotation and
    feed rates of the cutting tool coupled to the
    material to be cut are very important.

173
Spindle Speed
  • Spindle speed in revolutions per minute (R.P.M.)
    for the cutter can be calculated from the
    equation.
  • CS X 1000
  • N d
  • Where N R.P.M.
  • Cs

174
Low Coefficient of Friction.
  • Value which describes the ratio of the force of
    friction between two bodies and the force
    pressing them together.
  • The coefficient of friction depends on the
    materials used for example, ice on steel has a
    low coefficient of friction, while rubber on
    pavement has a high coefficient of friction.
    Coefficients of friction range from near zero to
    greater than one under good conditions

175
Tool Materials in Common use.
  • High carbon steel.
  • Contains 1 1.4 carbon with some addition of
    chromium and tungsten to improve wear resistance.
    The steel begins to lose its hardness at about
    250degrees and is not favored for modern
    machining operations where high speeds and heavy
    cuts are usually employed.

176
High Speed Steel.
  • Steel, which has a hot hardness value of about
    600dc possesses good strength and shock resistant
    properties. It is commonly used for single point
    lathe cutting tools and multi point cutting tools
    such as drills, reamers and milling cutters.

177
Cemented Carbides.
  • An extremely hard material from tungsten powder.
  • Carbide tools are usually used in the form of
    brazed or clamped tips.
  • High cutting speeds may be used and material
    difficult to cut with HSS may be readily
    machined using carbide tipped tools.

178
Tool Life.
  • As a general the the relationship between the
    tool life and cutting speed is
  • VTn C
  • Where V Cutting speed in r/min
  • T Tool life in minutes.
  • C Constant.
  • For high speed steels tools are value of C ranges
    from 0.14 to 0.1 and for carbide bits the value
    would be 0.2.

179
Prolonging Tool Life
  • Use cutting fluids when machining.
  • Choose suitable cutting tools for each machining
    process.
  • Run the machine at the correct speed to prevent
    heat build-up.
  • Ensure that the machine is in good condition and
    not prone to excessive vibration.
  • Use the correct cutting speed and cutting feed
    for the material.

180
Feed.
  • The term feed is used to describe the distance
    the tool moves per revolution of the work piece
    and depends largely on the surface finish
    required.
  • For a roughing out a soft material a feed of up
    to 0.25mm per revolution may be used.
  • With tougher material this should be reduced to a
    maximum of 0.1mm/rev.
  • Finishing requires a finer feed than what is
    recommended.

181
Safety Hazards When Machining Mild Steel.
  • Excessive heat may cause deformation of cutting
    tool.
  • The hardness of mild steel may cause tool wear.
  • Discontinues chips may be excessively sharp and
    hot.

182
Factors that influence heat in machining
  • Factors that influence heat in machining
  • Use of coolants help to reduce heat generated
  • Type of material
  • Machining operation
  • Condition of machine and cutting tool.
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