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MACHINE
MACHINE T
TOOLS
OOLS
(2015-16)
(2015-16)
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MACHINE TOOLS
MACHINE TOOLS
INTRODUCTION:
• The process of metal cutting in which chip is formed is
effected by a relative movement b/w the work piece and the hard edge of the cutting tool.
• The relative motion is produced by a combination of rotary
and translatory motion of either work piece (or) tool (or) both.
Machine Tool
Machine Tool Relative MotionRelative Motion W
Woorrkk TTooooll L
Laatthhee RR TT
S
Shhaappeerr,, PPllaanneerr TT TT D
Drriilllliinngg FFiixxeedd R R & & TT M
Miilllliinngg TT RR S
Suurrffaaccee GGrriinnddiinngg TT RR C
Cyylliinnddrriiccaall GGrriinnddiinngg R R & & TT RR
The relative motion present between Work
and Tool in various Machine Tools.
• The motion responsible for the cutting action is known as
the primary motion or cutting motion.
• The motion responsible for gradually feeding the uncut
portion is termed as the secondary motion or feed motion.
• Depending on the nature of these relativ e motions, various
types of surfaces can be produced.
• The line generated by the CUTTING MOTION is called
the GENERATRIX and the line generated from the FEED MOTION is called the DIRECTRIX.
• Various geometries can be obtained depending on the
shapes of the Generatrix and the Directrix and their relative directions.
Generation of various surfaces Generation of various surfaces S.
S.NoNo GeGeneneraratrtrix ix (G(G)) DDiirreeccttrriix x ((DD)) SuSurrffaacce e oobbttaaiinneedd PPrroocceessss ((aa)) SttrraS aiigghht t LLiinnee SSttrraaiigghht t LLiinnee PPllaaiin n SSuurrffaaccee TTrraacciinng g oof f GG ((bb)) CiirrccuC ullaarr SSttrraaiigghht t LLiinnee CylindCylindricricalal SurSurfaceface Tracing of GTracing of G
((cc)) CiirrccuC ullaarr SSttrraaiigghht t LLiinnee Plain Surface (Lines)Plain Surface (Lines) Envelope of GEnvelope of G ((dd)) PllaPaiin n CCuurrvvee CCiirrccuullaarr Surface of revolutionSurface of revolution Tracing of GTracing of G
LA
CARRI
CARRIAGE ASS
AGE ASSEMBL
EMBLY
Y
Video 1 6 TOOLPOST (1) COMPOUND SLIDE (2) SWIVEL PLATE (2B)
HANDWHEELS (2A, 3B, 5A) CROSS-SLIDE (3)
SADDLE (4) APRON (5)
SPEC
SPECIFICA
IFICATIONS
TIONS OF LA
OF LATHE
THE
1) Height of centers over bed U.K. spec. 2) Maximum swing over
bed USA spec. 3) Maximum swing over
carriage
4) Maximum swing over Gap
5) Maximum distance b/w centers
6) Length of bed 7) No. of speeds and
EARLY LATHES
EARLY LATHES
EARLY LATHES
EARLY LATHES
EARLY LATHES
EARLY LATHES
EARLY LATHES
EARLY LATHES
TYPES OF LATHES
TYPES OF LATHES
It is a very small lathe mounted on separately prepared bench or cabinet and used for small, precisionworks.
2) Speed lathe: They do not have pr ovision for power feed and have no gear box, carriage, lead screw etc.
Two or three spindle speeds are available by cone pulley arrangement. They are used for wood turning, polishing,
metal
3) Engine lathe: In olden days lathe was driven by a steam engine. Hence the name is still in existence even after modern lathes are provided with motor drive.
4) Tool Room La the: It is nothing but the engine lathe equipped with some extra attachments for accurate and precision work like taper turning attachment, follower
rest, collets, different types of chucks etc. The bed is relatively small.
5) Capstan & Turret lathes: These are sem i automatic type machines very useful for mass production (small lot sizes). Less skill is required for operator and wide range of operations can be performed. They carry special mechanisms for indexing their tool heads. They are provided with a front tool post which can hold 4 turning related tools and rear tool post which can hold 2 to 4 turning related tools. The turrets
can hold onlyonly drilling related tools. The turning tools used in the rear tool post are reverse tools with reverse geometry.
Video 2,3
Turret Indexing Turret Indexing
T
Turret Indexinurret Indexing in g in CapstaCapstan and Tn and Turret Laurret Lathesthes
Just before indexing at the end of the return stroke, the locking pin is withdrawn by the lever which is lifted at its other end by
gradually riding against the hinged wedge as shown.
Further backward travel of the turret slide causes rotation of the free head by the indexing pin and lever as shown.
Rotation of the turret head by exact angle is accomplished by insertion of the locking pin in the next hole of the six equi-spaced holes.
T
T
Capstan Lathe Capstan Lathe
Capstan Lathe Layout Capstan Lathe Layout
T
Tuurrrreet t LLaatthhee CCaappssttaan n llaatthhee 1. Turret head (square (or)
hexagonal) is mounted on saddle
1. Turret head (round (or) square (or) hexagonal) is mounted on auxiliary slide that moves on guide ways provided on saddle 2. The above arrangement gives
rigidity as forces are transferred to bed. Hence capable of ha ndling heavy jobs (up to 200mm) and
severe cutting conditions.
2. Less rigidity, vibrations occur, hence suitable for lighter and smaller jobs (up to 60mm) and precision work.
3 Tool travel is along entire bed length
3. Tool travel is limited because of auxiliary slide traverse limitation. 4. Tool feeding is slow and
causes fatigue to operator hands
4. Tool feeding is fast and causes less fatigue to operator hands. 5. No tail stock 5. No tail stock
6) Automatic lathes: These are designed so that all the working and Job handling movements of the complete Manufacturing process for a job are done automatically. No participation of the operator is required during the
operation. They fall in the category of heavy duty, high speed lathes employed in mass production(large lot sizes). Geneva mechanism is used for indexing the turret.
Types of automatic lathe:
1) According to type of stock material
Bar automatics; Chucking automatics 2) According to No. of spindles
Single spindle; Multiple spindle
3) According to the directions of the axis of m/c spindles
Horizontal; Vertical
Video 4,5,6,7
The general purpose single spindle automatic lathes are widely used for quantity or mass production (by machining) of high quality fasteners; bolts, screws, studs, bushings, pins, shafts, rollers, handles and similar small metallic parts from long bars or tubes of regular section and also often from separate small blanks. Unlike the semiautomatic lathes, single spindle automats are :
• used always for producing jobs of rod, tubular or ring type and
of relatively smaller size.
• run fully automatically, including bar feeding and tool
indexing, and continuously over a long duration repeating the same machining cycle for each product
• provided with up to five radial tool slides which are moved by
cams mounted on a cam shaft
• of relatively smaller size and power but have high er spindle
Swiss type automatic lathe Swiss type automatic lathe
The characteristics and applications of these single spindle automatic lathes are :
In respect of application:
• Used for precision machining of thin slender rod or
tubular jobs, like components of small clocks and wrist watches in mass production.
•
Job size3 to 30 mm.
⎯
Diameter range – 2 to 12 mm;⎯
Length range –• Dimensional accuracy and surface finish – almost as good
as provided by grinding
In respect of configuration and operation:
• There is no tailstock or turret
• High spindle speed (2000 – 10,000 rpm) for small job
• The headstock travels enabling axial feed of the bar stock
against the cutting tools as shown
• The cutting tools (up to five in number including two on
the rocker arm) are fed radially
• Drilling and threading tools, if required, are moved axially
using swivelling device(s)
• The cylindrical blanks are prefinished by grinding and are
moved through a carbide guide bush
Video 8
7) Special – purpose lathes: These are designed to perform certain specified operations only.
Eg: Facing lathe, vertical lathe, crank shaft lathe
Video 9,10,11,12
1) Chucks
----a) 3 Jaw – Self centering, smaller in size, used for round cross sections
b) 4 Jaw – Not self centering, medium in size, used for round, square, rectangular cross sections.
WORK HOLDING DEVICES
WORK HOLDING DEVICES
c) Collets– Fixed size. They are air operated or hand operated. Used in – Tool Room lathes, Bar Automatic Lathes,
d) Pneumatic Chucks – In chucking Automatics
Note: In bar automatics the component is parted of from the bar and in chucking automatics, the component is released from the chuck and another blank is loaded from the magazine.
e) Magnetic – Used for ferrous metals in Lathe, Milling, Surface Grinding machines for light works and also where Distortion is not permitted like in aerospace components. f) Vacuum – Similar to above, used for non ferrous metals
2) Face plate – Used for large size work pieces of round, square, rectangular, and also very complex geometries not possible in any other devices.
3) Carriers, Catch plates or Carrier Dogs –
Used for supporting shafts, mandrels for imparting rotation. They clamp around the work piece and allow the rotary motion of the machine's spindle to be transmitted to the work piece.They are used in Lathes and also Cylindrical grinding operations.
4) Centers – For supporting the rotation a) Live centre – used with face plate b) Dead centre – used in tail stock
Revolving Dead centre (Used for high speeds
and high clamping pressures)
Non-Revolving Dead centre Live centre
5) Mandrel – Used to support the work pieces and also for holding hollow parts to meet concentricity requirements
Live Centre Carrier Dog Mandrel Face Plate Work piece Dead Centre
6) Steady rest – mounted on bed, used for long heavy jobs that deflect centrally by self weight.
7) Follower rest – mounted on carriage and moves with tool, used for long thin jobs that deflect laterally by cutting force.
TOOL POST
TOOL POST
Tool Setting on Lathe
Tool Setting on Lathe
1. Setting the tool below the centre decreases the effective rake angle and increases the effective clearance angle. This increases the cutting forces.
2. Setting the tool above the centre increases the effective rake angle and decreases the effective clearance angle. This increases
rubbing with flank surface.
1) 2)
Effective Rake is the apparent Rake angle w.r.t tool and work position and not the actual rake
HSS Tool Holders
TOOL
TOOL HOLDER
HOLDERS
S
Brazed Carbide tip Tool Holders (Can be grinded)
Box Tool Holders – Used in turret lathes to apply heavy cuts & act as travelling steadies.
OPERATIONS
OPERATIONS
1) Straight turning: Here the work rotating about lathe axis, tool is fed parallel to it, depth of cut is perpendicular to it, thus producing a straight cylindrical surface. Here Diameter is effected but Length is not effected. 2) Shoulder / Step turning:
Same as above except that diameter is reduced only up to certain length.
d
ФDD
3) Facing:- Here the tool is fed perpendicular to the lathe axis
and depth of cut is parallel to the lathe axis and thus producing a flat surface. Here
Length (in Shafts) / thickness (in plates) is effected, but Diameter is not effected.
4) Knurling:- Process of embossing a diamond shaped pattern on work surface which is used for gripping purpose.
Video 13,14
D1
D2
L
θ
5) Taper turning:- Operation of producing tapered surfaces. The following methods are used
1. Swiveling of compound rest – Any Angle, Any Corresponding Taper length.
D1 = Larger Dia D2 = Smaller Dia L = Taper length
θ
= Half Cone Angle 2θ
= Included Angle /2. Tailstock set over – Small Angle, Long Job
S = Set over Distance
L = Total Length of Work Piece
d f
3) Form Tool – Any Angle, Short taper length
4) Combined Feeds – 450Chamfers
The cross slide is delinked from the saddle and is
connected to the attachment fixed on the bed. As the carriage (saddle) moves longitudinally, the cross slide is moved crosswise by the guide block which
moves along the guide bar preset at the desired taper
angle. This action causes the cutting tool to move at an angle to the axis of the work piece to produce a taper.
5) Taper turning attachment
Video 15
( Movement of tool is similar to Movement of tool is similar to combined feed combined feed )
d f
Video 16
6) Metal Spinning:- It is the operation of pressing and forming cup shaped components from sheet metal.
7) Spring winding:- We can wind spring on lathe. Here coiled spring can be made by passing a wire around the mandrel which is rotated in a chuck.
8) Miscellaneous
9) Thread cutting:- There are different thread forms like V, Square, Acme, buttress etc. Here the tool has the shape of thread profile. Zero rake angle is used for form tools like threading tool, parting tool, grooving tool etc.
Majority of screws are right handed threads. They are tightened by clock wise rotation. When cut on lathe, tool advances from right to left. Screws with left handed threads are used in exceptional cases. They are tightened by counter clock wise rotation. When cut on lathe, tool advances from left to right. Spindle rotation is same for both operations but lead screw rotation is opposite. Left hand threads are used on lathe spindles, left hand pedal of bicycle, connections on the acetylene Cylinders (to avoid wrong connections), left-hand grinding wheel on a bench
grinder, in Turnbuckles in
combination with right handed threads to adjust the tensions in
cables, tie rods etc. Left Hand
Thread
Right Hand Thread Helix
Tapered threads are used for water (or) Gas pipes and plumbing supplies, which require a water tight (or) air tight connection. Tapered threads produce a wedging action and hence produces a pressure tight joint.
Thread Terminology: Thread Terminology:
Lead – The distance moved by screw or nut in one revolution.
Pitch (P) – The distance between two successive peaks or valleys.
Lead = P for single start thread Lead = 2P for double start threads
(It has two start points) Lead = 3P for triple start threads
(It has three start points)
Single Single Double Double Triple Triple
V threads are the standard threads used on most threaded fasteners and are by far the most common.
Due to its profile, the square thread is more difficult to machine than a V thread and is only used where strength and wear resistance make it worthwhile.
The Acme and Buttress threads are easier to machine. The Buttress thread can be used only where the applied loading is always in one direction. It is sometimes used in bench vices.
The Lead screw in lathe in combination with split nut uses an Acme thread which can apply load in both directions. Lathe spindle and lead screw must be in same relative position for each cut. A Thread-chasing dial is attached to
carriage for this purpose. It will take care of engagement of thread at the same starting point for every cut.
Thread-Chasing dial Thread-Chasing dial
Video 17,18,19
Half Nut / Split Nut Half Nut / Split Nut
Video 17,18,19
Feed Rod is provided in medium to big size lathes and is engaged for other lathe operations except threading and operates by rack and pinion mechanism operated by change gears and other gears in apron.
Video 20
•“Back gear" is a gear mounted at the back of the headstock
and allows the chuck to rotate slowly with greatly-increased turning power.
•Screw cutting also requires slow speeds.
•With a back gear fitted, the lathe not only becomes capable
of cutting threads but can also tackle heavy-duty drilling, big-hole boring and large-diameter turning and facing; in
other words, it is possible to use it to the very limits of its capacity and strength.
Back Gear Back Gear
TIME ESTIMATION
TIME ESTIMATION
1) Machining Time = T = Length of cut / (feed x rpm) = L / (f x N) min
f = feed in mm/rev
2) Cutting speed= V =
πDN
/ 1000 m/minD = Starting diameter of work in mm, N = RPM of work Note: Some times D is taken as mean diameter also.
3) Combining above two formulae we can write, T =
πDL
/ 1000fV min3) Feed per minute, f m = f x N mm/min
4) Depth of cut = d = (Di – Df ) / 2 Di = Initial dia, Df = Final dia
5) Power or Work done = F x V N-m/min
6) Total Time for Threading = Time per cut x No. of cuts Time per cut = L / (p x N) [For Single Start Thread] p = Pitch = 1 / No. of threads per unit length
L = Length of W.P + Approach Length + Over Travel 7) Time for Drilling =
πDL
/ 1000fVL = Depth of hole, D = Dia of drill 8) Time for Boring =
πDL
/ 1000fVL = Depth to be bored, D = Starting Dia of hole 9) Time for facing = L / (f x N)
L = Radius of W.P
Gear Train Calculation for Thread cutting: 1) Transformation ratio = Gear Ratio
= Lead of Work piece / Lead of Lead screw
= Speed of Lead screw / Speed of Work piece (Spindle)
These relations are true for threads cut in metric or inches units. All lathes are generally provided with set of change gears having teeth from 20 to 120 with a variation of 5 teeth. (20, 25, 30, 35, 40, etc). In addition the set has gear with 127 teeth called translating gear.
For a simple Gear train, Gear Ratio =
No. of teeth on Driver Gear (On Spindle) / No. of teeth on Driven Gear (On Lead Screw)
The number of teeth on The number of teeth on intermediate gear has no effect on the gear ratio. intermediate gear has no effect on the gear ratio.
For a Compound Gear train, Gear Ratio =
(a/b) x (c/d) a, b, c, d = Teeth of
SHAPER
SHAPER
INTRODUCTION: The shaper is a reciprocating type of machine tool intended primarily to produce flat surfaces. These surfaces may be horizontal, vertical or inclined. Here the cutting tool is given a reciprocating motion, and after every cutting stroke, the work is fed (during return stroke) to provide an uncut layer for machining.
Here cutting is not continuous and hence the machining is known as Intermittent cutting operation. This is used for initial rough machining. The cutting tool is a single point tool similar to lathe.
Video 3,4
Bull Gear used in shaper to reduce the speed of rotation obtained from motor
TYPES
TYPES
1. According to the type of mechanisms used for giving reciprocating motion to the ram.
a) Crank Shaper:
Crank and Slotted lever mechanism is used to change rotary motion of the driving gear called bull gear.
b) Geared Shaper: Rack and pinion mechanism is used. Geared shapers have a
reversible electric motor
or any mechanical
mechanism which quickly
returns the ram, in
c) Hydraulic Shaper: By hydraulic power i.e. oil with high pressure is pumped into a cylinder with piston.
Advantages Advantages
1) The cutting speed is constant almost throughout the stroke unlike the other shapers where the speed changes continuously.
2) Power available remains constant through out hence it is possible to utilize the full cutting capacity of the tool.
3) The ram stroke reverses quickly with out any shock as the oil on either side of the piston provides a cushioning effect hence vibrations are minimum. Inertia of moving parts is relatively small.
4) The range and number cutting speeds possible are relatively large and control is simple.
5) More strokes per minute can be obtained by consuming less time for the cutting and return strokes at a given cutting speed.
2. According to the position and travel of ram.
a) Horizontal shaper: Reciprocates in a horizontal axis. b) Vertical shaper: Reciprocates in a vertical axis.
It has a round table that can rotate and also can be fed longitudinally and cross wise. Also the ram can be reciprocated at an angle up to
100 from the vertical position
enabling machining inclined
c) Traveling head shaper: The ram moves cross wise for feed during reciprocation. Used for heavy jobs where table feed is not possible.
3. According to the type of design of the table:
a) Standard Shaper: Table has only 2 movements, to give feed.
b) Universal shaper: In addition to t he 2 movements, the table can be swiveled about
a horizontal axis
parallel to the ram ways and the upper portion of the table can be tilted about a second horizontal axis
SPECIFICATIONS:
1) The max. Length of stroke or cut 2) Table size
3) Return time to cutting time ratio. 4) Number of speeds and feeds. 5) Floor space required
6) Weight of machine etc
OPERATIONS ON HORIZONTAL SHAPERS: 1) Machining Horizontal, Vertical, Angular surfaces 2) Cutting Slots, Grooves, Key ways, Splines, Gears etc
(External Only)
OPERATIONS ON VERTICAL SHAPERS: Similar to Slotters.
SPECIFICATIONS AND OPERATIONS
SPECIFICATIONS AND OPERATIONS
(1) Cutting speed V = NL(1+m)/1000 m/min (This theoretical formula is used in calculations)
L = Length of cutting stroke in mm m = Ratio of return time to cutting time
N = No. of double strokes per min = RPM of bull gear Note:
1. In actual practice, the cutting speed changes during the cutting stroke in the crank type and geared type shapers. Hence the average cutting speed is expressed as:
Vavg = V / 2 = NL(1+m) / 2 x 1000
2. The stopping point of cutting stroke in hydraulic shapers can vary depending on the resistance offered to cutting by the work material.
TIME ESTIMATION
TIME ESTIMATION
(2) Time required by cutting stroke = L / 1000V
(3) Return stroke time = m x cutting stroke time= mL/ 1000V (4) No. of double strokes required to complete the job = W / f
W = Width of W.P.
f = feed in mm (or) mm/Cutting stroke (or) mm/double stroke (5) Total time taken for one complete cut = LW(1+m)/1000fV (6) Metal Removal Rate (MRR) = 1000Vfd mm3 / min,
where d = depth of cut in mm (7) Power consumed = K x MRR hp
where K = constant for calculating horse power consumed (8) Theoretical peak to valley height = R t = 0.5 f / tan
θ
mm Where 2θ
= Angle b/w the two cutting edges in the singlepoint tool f /2
SLOTTER
SLOTTER
INTRODUCTION:
This operates almost on the same principle as that of a shaper. Slotter was invented before shaper. Here the ram reciprocates in a vertical axis. There is no quick return and the mechanism used for ram is Crank and connecting rod mechanism. The slotter is provided with a rotary table that can be moved longitudinally and cross wise. The slotter is us ed for making regular and irregular surfaces both internal and external and also for handling complex work pieces. Slotter is more robust compared to vertical shaper.
Video 1,2
TYPES
TYPES
1) Puncher slotter: A heavy, rigid machine, for removing large amount of metal from large forgings and castings. The length of stroke is very large (1.8 - 2m).2) Precision slotter: It is a lighter machine and is operated at high speeds. Used for accurate finish, using light cuts.
SPECIFICATIONS AND OPERATIONS
SPECIFICATIONS AND OPERATIONS
SPECIFICATION: 1. Length of stroke 2. Diameter of table
3. Amount of cross and longitudinal travel of the table 4. No. of speeds and feeds
5. Floor space required
6. Net weight of the machine etc. OPERATIONS:
1) Machining slots, keyways, grooves of various shapes, both internal and external, Internal machining of blind
holes, machining of dies, punches etc.
2) Machining flat surfaces, Cylindrical surfaces, Cams, internal and external gears.
PLANER
PLANER
INTRODUCTION: The planer like shaper is a m/c tool primarily intended to produce plane and flat surfaces by a single point cutting tool. A planer is very large compared to shaper. In a planer the work which is supported on the table reciprocates past the stationary cutting tool and feed is given by the lateral movement of the tool.
Video 5,6
TYPES
TYPES
1)Double housing planer (or) standard planer: Has two vertical housings connected by a cast iron member on top. Table is mounted on the bed and can reciprocate. The Cross
rail can move up and down on the vertical housings and one or two tool heads provided can travel cross wise for tool feed across the cross rail.
2) Open side planer: Only one side housing and the cross rail is suspended as cantilever. Used for very wide Jobs.
3) Divided Table Planer: Also called Tandem Planer. This type of planer has two tables on the bed which may be reciprocated separately together. This type of design saves much of the idle time while setting large no. of identical pieces on the machine.
TABLES CROSS RAIL
4) Pit planer: It is a massive construction. The table is stationary, the column carrying the cross rail reciprocates on massive horizontal rails mounted on both sides of the table. Suitable for very large works.
5) Edge or plate planer: This is specially intended for squaring and beveling the edges of steel plates used for different pressure vessels and ship building works.
SPECIFICATIONS AND OPERATIONS
SPECIFICATIONS AND OPERATIONS
SPECIFICATIONS:
1.The size of the largest rectangular solid that can reciprocate under the tool.
2. No. of speeds and feeds available, 3. Floor space reqd.
4. Net wt. of machine etc. OPERATIONS:
(1) Planning flat horizontal, vertical, angular surfaces (2) Slots and grooves.
DRILLING
DRILLING
INTRODUCTION: A drilling machine was primarily designed to originate a hole, but it can also perform a No. of similar o perations. In a drilling machine holes may be dri lled quickly and at low cost. The hole is generated by the rotating edge of a cutting tool known as the drill which exerts large force on the work clamped on the table. The cutting motion is provided by rotating the drill and feeding is done by giving rectilinear motion to the drill in the axial direction. Here the dr ill used has two cutting edges called lips.
Video 1
TYPES
TYPES
(1) Portable drilling machine:
This type of D.M. can be operated with ease anywhere in the work shop and is use d for drilling holes in work pieces in any position which cannot be drilled in a standard D.M. The entire D.M. including the motor is compact and small in size. The max. size of the drill that can accommodate is not more than 12 to 18 mm.
(2) Sensitive D.M. It is a small machine designed for drilling small holes at high speed in light and small jobs. The base of the machine may be mounted on a bench or on the floor. There is
no arrangement for the
automatic feed of the drill spindle. High speed and hand feed are necessary
for drilling small holes. As the operator can sense the progress of the drill it is called S.D.M. Drills size is 1.5
to 15.5 mm can be used in this machine. Super sensitive D.M. are designed to drill holes as small as 0.35 mm and can be rotated at a speed of 20,000 rpm or above.
(3) Upright D.M.: This is designed for handling medium sized W.P. It is similar to a S.D.M. but is heavier and l arger t han S .D.M. and i s
supplied with power feed
arrangement.
a) Round Column Section (or) Pillar D.M.: It consists of round column and a round table. The table can be moved up and down on the column for accommodating W.P. of different heights. The table may be rotated 360o about its own centre. The max.
size of the hole that can be drilled is not more than 50mm.
(b) Box Column Section Upright D.M.: The upright
D.M. with box column
section has a square table fitted on the slides at the front face of the machine column. Heavy box column gives the machine strength and rigidity. The table is raised or lowered by an elevating screw that gives additional support to the table.
Heavier W.P. and holes
more than 50 mm dia can be drilled by it.
(4) Radial D.M: It is intended for drilling medium to large and heavy W.P. It consists of a heavy, round vertical column mounted on a large base. The column supports a radial arm which can be raised and lowered to accommodate work pieces of difference heights The arm may be swung around to any position over the work bed. The drill head containing mechanism for rotating and feeding the drill is mounted on the radia l arm and can be moved horizontally on the guide ways and clamped at any desired position. This can be further classified as
(b) Semi Universal RDM:- In addition to the above 3 movements, the drill head can be swung about a horizontal axis to the arm. This 4th movement of the drill
head permits drilling hole at an angle to the H.P. other than normal position.
(c) Universal RDM:- In addition to the above 4 movements the drill
head may be rotated on a
horizontal axis. All these 5 movements enable it to drill on a W.P. at any angle and in any plane.
(5) Gang D.M.: When a No. of single spindle D.M. columns are placed side by si de on a common base and have a common, work table, the machine is known as G.D.M. In a G.D.M. 4 to 6 spindles may be mounted side by side. The speed and feed of spindles are controlled independently.
This type of machine is specially adapted for production work. A series of operations may be performed on the work by simply shifting the work from one position to the other on the work table each. Spindle may be set up properly with difference tools for different operations. Video 2, 3
(6) Multiple spindle D.M.: The function of the multiple spindle D.M. is to drill a No. of holes in a piece of work simultaneously and to reproduce the same pattern of holes in a No. of identical pieces in a mass production work such machines have several spindles driven by a single motor and all the spindles holding drills are fed into the work. Simultaneously. Feeding motion is usually obtained by raising the work table. But the feeding motion may also be secured by lowering the drill heads. The spindles are so constructed that their centre distance may be adjusted in any position as required by various jobs within the capacity of the drill head. For this purpose, the drill spindles are connected to the main drive by universal joints. The spindles are connected by a number of planetary gears so that even different size drills can be loaded.
Video 4,5
7) Deep Hole Drilling machine: Special machine and drills are required for drilling deep holes in rifle barrels, long spindles, oil holes in crank shafts, long shafts etc. The machine is operated at high speed and low feed. A long job is usually supported at several points to prevent any
deflection. The work is usually rotated while the drill is fed into the work. This helps in feeding the drill in a st. path. The machine may be Horizontal type (or) Vertical
type. The drill is withdrawn automatically each time when it penetrates in to the work to a depth equal to its d ia. This process permits the chip to clear out from the work.
Video 6,7,8
There are different types of deep hole drilling processes and are categorized by how the cutting coolant flushes heat and chips from the cutting face. They are:
G
Gunun drdrilillilingng - The cutting tool is a straight fluted solid rod that has a hole bored down the center. Coolant is pumped through a hole in the inside of the drill. It flows back outside the drill, through the flute, bringing the
chips with it. Drilling size (dia) is
BT
BTAA (B(Bororiinngg anandd TTrreepapannnniningg AAssssocociaiatitionon)) - The cutting tool is a tube. Coolant is pumped around the outside of the cutting tool at heavy pressure and carries chips out through the center of the tube. Very high penetration rates can be achieved with this system along with good surface finish. Depth to Diameter ratio is highest.
Because tubes
have minimum
sizes, this is only
an acceptable
technology for holes of diameter over 15 mm and up to 600 mm.
Examples of Deep Hole Drilling Examples of Deep Hole Drilling
Specifications
Specifications
1. Max. size of drill that the machine can operate, 2. Max. spindle travel
3. Table diameter / size
4. Morse taper No. of the drill spindle
5. No. of spindle speeds and feeds available. 6. Floor space required
TERMINOLOGY
TERMINOLOGY
Drills are manufactured as: 1. Straight shank drills (up toϕ
13.5 mm) 2. Taper shank Drills (ϕ
14.0 mm onwards) Tang Shank Neck Body TipDrilling M/c Spindle
Drill Chuck with Chuck key
Drift Sleeve
Morse
Morse taper taper is is provided provided on on all all drilling
drilling accessories, accessories, inside inside drillingdrilling machine
machine spindle, spindle, lathe lathe tail tail stock,stock, lathe turret, and lathe centres
DRILL GEOMETRY
DRILL GEOMETRY
Land / Margin: It maintains the alignment of the drill so that hole is straight and to the right (correct) size.
Helix angle: Angle formed b/w a plane containing drill axis and the leading edge of land. Based on the value of the angle the drills can be classified as
1) Slow spiral series: 12o to 22o - Used for brass, bronze,
CI that produce broken chips (brittle materials). They provide less lifting power, but are stronger, used for
shallow holes. Also used in horizontal applications where drill is not rotating.
2) Regular spiral series: 28oto 32o - most widely used
3) Fast/High spiral series: 34 o to 38o – Used for softer
ferrous and non-ferrous materials producing long string like chips (ductile materials). They provide great lifting power, but are weak, used for deep holes.
Lip angle: Angle formed b/w the cutting edges (lips). Smaller point angles results in lower effective rake. Effect of change in effective rake is negligible on drill performance. Smaller the point angle, longer the lip length. Smaller point angles generate wider and thin chips. Higher point angles generate narrow and thick chips. Higher point angle increases the cutting efficiency of the drill because most materials are cut efficiently in the form of thick chips. Longer lip lengths reduce load per unit length of the lip and helps in resisting the wear caused by abrasive action during machining of metals like C.I.
1) M.S. 1180 (< 180 HB) 2) Steel 1180 (180 - 280 HB) 3) Steel 1350 - 140o(280 – 380 HB) 4) Grey C.I. 900 (< 180 HB) 5) Grey C.I. 1180 (180 - 280 HB) 6) Chilled C.I. 1350 – 1400(> 350 HB) 7) Aluminum 118 0 8) Copper 1180 9) Bronze 1180 10)Brass 1110
Clearance / Lip relief Angle: Angle formed b/w flank and a plane normal to drill axis at the
tip of the drill. Large angles (80 –120) are used for ductile
matls. to compensate elastic recovery. Small angles (60 –80)
OPERATIONS
OPERATIONS
1) Drilling – Process of making hole in solid body.
2) Boring – Enlarging a hole completely with an adjustable tool with only one cutting edge.
3) Counter boring - Enlarging one end of the hole to form a square shoulder with srcinal hole to avoid projections in assemblies.
4) Counter sinking - Making a cone shaped enlargement to provide a recess for a screw head.
5) Reaming – Sizing and finishing a small unhardened hole.
a) b) c)
a) Straight flute reamer is used for through holes in materials that do not form chips like C.I, Bronze, Brass. They form fine powder that will fall by gravity.
b) Left hand spiral flute reamer is used for through holes in other materials and is very effective as they push the chips out of the through hole.
c) Right hand spiral flute reamer is used for blind holes as they pull the chips out of them.
Chucking (M/c) Reamer
M/c Reamers
d) Rose reamers are primarily used for roughing prior to final reaming. The cylindrical part of the reamer has no cutting edges, but merely grooves cut for the full length of the reamer body, providing a way for the chips
to escape and a channel for lubricant to reach the cutting edges. To prevent binding they have a slight back taper. The cutting edges at the end are ground to a 45
0
e) Shell reamers are similar to cutting portion of a chucking reamer. They are supplied without a shank and has a hole through the center. A arbor is used in conjunction with the shell reamer, the slots in the reamer engage lugs on the arbor for driving power.
6) Lapping – Sizing and finishing a hole already hardened. 7)Tapping–Process of making internal threads in small holes.
8) Spot facing – Process of smoothing and squaring the surface around the hole or seat for a nut (or) head of a screw for burr removal.
Machine Tap with holder Manual Tap
Centre Drill used for making a centre impression on surface for locating the drill point, locating the lathe & Grinding centres.
Burr formation
during drilling
9) Trepanning – Operation of producing a hole by removing metal along the circumference of a hollow cutting tool. Used for producing large holes in plates.
Video 9,10,11
TIME ESTIMATION
TIME ESTIMATION
1) Cutting speed, V=
πDN
/ 1000 m/min 2) Machining Time, T = L / (f x N) = L / f m L = L1 + L2 + L3 + L4 (Some times L= L1 + 0.5D) L1 = Depth of hole L2 = Approach length L 3 = Length of tip = 0.5D /tanθ
= 0.29D (For 2θ
= 1180)(where, 2
θ
= Lip angle) L4 = Over Travel3) Depth of cut, d = D / 2 4) MRR =
πD
2fN / 4 =πD
2fMILLING
MILLING
INTRODUCTION:
A milling machine is a machine tool that removes metal as the work is fed against a rotating multi point cutter. The cutter
rotates at a high speed, and because of the multiple cutting edges it removes the metal at a very fast rate. The first milling machine came into existence in about 1770 and was of French srcin.
TYPES
TYPES
1. Column & knee type: Most commonly used for general shop work. The ta ble is mounted on the kn ee casting, which in-turn is mounted on the vertical slides of the main column. The knee is vertically adjustable on the column, so that the table can be moved up and down to accommodate work of various heights. The table can be moved longitudinally and cross wise on the knee
casting. Classification of this type is based on methods of supplying power to the table, diff. movement of the table and diff. axis of rotation of the main spindle.
(a) Hand milling machine Feeding is done by hand and used for light and simple operations like slots, grooves, keyways. This is available in both horizontal & vertical models Table movements are as above.
(b) Plain milling machine This is a
horizontal type
milling m/c. This is more r igid and sturdy, for heavy work, can be fed by
hand or power.
Table can be fed as above.
Video 1,2
(c)Universal milling machine This is also a horizontal type milling m/c. In addition to 3
movements in plain
milling machine the table has a fourth movement i.e. it is fed at an angle to milling cutter. This enable it to perform helical milling. This machine can produce spur, spiral, bevel gears, twist drills, reamers, milling cutters etc.
(d)Omniversal
milling machine This is a horizontal type milling m/c. The extra fifth movement is the table can be tilted in vertical plane by providing aswivel arrangement
at the knee. This enables milling in any plane. Taper
spiral groves in
reamers, bevel gears etc can be done.
(e) Vertical milling machine Here the position of the spindle is vertical and
┴
to the work table. The spindle head is clamped to the vertical column and can be swiveled at an angle . Also the spindle head can be adjusted up / down relativeto work. The table
movements are same as plain milling machine.
Video 3,4
2. Plano Miller:
It resembles a planer. It is having multiple spindle heads both in vertical and horizontal planes. It has a cross rail which can be raised or lowered along with cutters. Hence no. of work surfaces can be machined
simultaneously, thereby
reducing production time. In a plano miller, the table has
feed movement instead of reciprocation. Hence the table movement here is much slower than planning machine.
Video 5
3. Rotary table Machine A modification of vertical milling machine adopted for machining flat surfaces. A No. of work pieces can be mounted on a circular table which rotates about vertical axis. The face milling cutters can be mounted on two (or) more vertical spindles and can be set at diff. heights relative to work so that when one cutter is roughing the other is finishing them. Continuous loading and unloading of work pieces can be done by the operator
4.Planetary milling machine: Here the
work is held
stationary while the revolving cutter / cutters move in a planetary path to
finish a cylindrical
surface on the work either internally / externally /
simultaneously. This
machine is particularly adopted for milling internal / external threads of different pitches.
Video 6,7
5. Pantograph milling machine It can duplicate a job by using a pantograph mechanism which permits the size o
the work piece reproduced to be smaller than, equal to or greater than the size of a template or model used for this purpose. A pantograph is a mechanism that is generally
constructed of fou r bars or links joined in the fo rm of parallelogram. Pantograph machines are available in 2D or
3D models. 2-D models are used for engraving letters or other designs, 3-D models are used for copying any shape and contour of the work piece. The tracing stylus is moved manually on the contour of the model to be duplicated and the milling cutter mounted on the spindle moves in a similar path on the work piece, reproducing the shape of the model.
Video 8
SPECIFICATIONS
SPECIFICATIONS
1. The maximum length of longitudinal, cross and verti cal travel of the table.
2. No. of spindle speeds,
3. No. of table speeds and feeds 4. Floor space required
5. Net weight required
6. Spindle nose taper (for vertical milling machine spindle) and taper on horizontal milling machine arbors
MILLING
MILLING GEOMETR
GEOMETRY
Y
Pe
Peripripherheralal cutcutterter:: As the cutting edges are arranged radially on the periphery the rake angle is called radial rake which is the cutting edges angle w.r.t to the periphery of the cutter. +ve radial rake gives better performance in peripheral milling. Fa
Facece cucutttterer:: Two rake angles are defined here.
(a) Radial rake is the cutting insert’s angle w.r.t the periphery of the cutter
(b) Axial rake is the cutting insert’s angle w.r.t the central axis of the cutter.
Axial Rake has significant effect on axial force and thrust applied to the spindle. Radial rake has major effect on tangential and radial forces. +ve axial rake, - ve radial rake gives best performance.
FACE CUTTER
Side View
METHODS OF MILLING
METHODS OF MILLING
1. Peripheral Milling: It is the operation performed by a milling cutter to produce a machined surface parallel to the axis of rotation of the cutter. Here the cutting force is not uniform throughout the length of cut by each tooth. Due to this reason, a shock is developed in the mechanism of the machine that leads to a vibration. The quality of surface generated and the shape of the chip formed is dependent upon the rotation of the cutter relative to the direction of feed movement of the work. According to the relative movement between the tool and work, the peripheral milling is
(a) Up milling / Conventional milling: The metal is removed by the cutter which is rotated against the travel of the W.P.
The thickness of the chip is min. at the beginning of cut max. when the cut terminates. The cutting force is directed up wards and this tends to lift the work from the fixtures. This is used for roughing operations. The chips accumulate at the cutting zone, and
may be carried over with the cutter, spoiling the work surface. It generates a poor finish. Cutting force and power are more.
(b) Down milling/ Climb milling: The metal is removed by the cutter which is rotated in the same direction of travel of the W.P. The thickness of the chip is max. when the tooth begins its cut and it reduces to the min. when the tooth
leave the work. The cutting force is directed down wards and this tends seat the work firmly in the work holding devices. Hence fixture design is easier. This operation cannot be used on old machine as the ba ck lash error present in the scr ew elements that ma y cause vibration and dam ages the work surface considerably. Hence this operation should be performed on rigid machines provided with back last
eliminator. This is used for finishing operations. The chips are also disposed off easily and do not interfere with the cutting. This results in improved surface finish. Cutting force and power are less.
BACKLASH ELIMINATOR: This eliminates the backlash (play) between nut and table lead screw. Two independent nuts are mounted on lead screw. The nuts engage common crown gear which meshes with rack. The axial movement of rack is controlled by the backlash eliminator, engaging a knob on front of saddle. Turning the knob forces the nuts to move along lead screw in opposite directions.
2. Face Milling: This is performed to produce a flat machined surface to the axis of rotation of the cutter. In this operation both up milling and down milling may be considered to be performed simultaneously on the work surface. When the cutter rotates through half of the revolution the direction of movement of the cutter tooth is opposite to the direction of feed and the condition reverse when the cutter rotates through other half of revolution. The chip thickness is min. at the beginning and at the end of the cut, and it is max. when the work passes through the centre line of cutter. The surface generated in face milling is characterized by the tooth circular marks of the cutter. Face milling gives superior finish than peripheral milling.
Draw Bolt Spindle
Cutter Holder
3. End Milling: It is a combination of peripheral and face milling operations. The cutter has cutting edges both on the end face and on the periphery. The cutting characteristics may be of peripheral or face milling type according to the particular cutter surface used. When end cutting edges are
only used to remove metal, the direction of rotation of the cutter and direction of helix of the cutter should be same. When peripheral cutting edges are used, the direction of rotation of the cutter and direction of helix of the cutter must be opposite to each other.
Draw Bolt Collet Holder
End Mill Collet
TAPER USED IN MILLING MACHINES
TAPER USED IN MILLING MACHINES
American Standard Taper of 3.5” per foot is made standard taper in all milling machines built in U.S.
Brown and Sharpe Taper of 0.5” per foot is also widely used on collets, arbors of horizontal machines, inside of vertical
machine spindles and on
grinding machine spindles. This is used in European and Asian Countries
OPERATIONS
OPERATIONS
1. Plain Milling: Producing plain, flat horizontal surface. This is called slab milling if performed with a peripheral cutter and called face Milling if a face milling cutter is used.
2. Side Milling: Producing flat vertical surface on the side of a work piece by using side milling cutter.
3. Straddle Milling: Producing flat vertical surfaces on both sides of the work piece by us ing two side milling cutter mounted on the same arbor. The distance between the two cutter can be adjusted by using spacing collars.
4. Gang Milling: Machining several surfaces simultaneously using a No. of cutters of same or diff. diameters mounted on the arbor of the machine, used widely for repetitive work
Video 9
5. Form Milling: Producing irregular contours using form cutters like concave, convex or any other shape.
6. End milling: Producing flat surfaces which may be vertical, horizontal or at an angle in reference to the table surface like slots, grooves, key ways, steps etc. A vertical milling machine is most suitable for end milling.
Convex Cutter
Concave Cutter Convex Milling Concave Milling
7. Saw milling: Producing narrow slots or grooves using saw milling cutter. It can also be performed for complete parting off operation.
8. Gear cutting: By using form re lieved cutter having the same profile of the tooth space of the gear.
9. Helical Milling: Producing helical flutes or grooves around the periphery of a cylindrical or conical work piece. 10. Cam Milling: Producing cams by using universal dividing head and a vertical milling attachment.
INDEXING
INDEXING
It is the operation of dividing the periphery of a piece of work into any No. of equal parts. This is adopted for producing hexagonal and square headed bolts cutting
splines on shafts, flutes in milling cutters, drills, taps and reamers, cutting of Gears, cams etc. Indexing is accomplished by using a special attachment known as dividing head or Index head. They are of 3 types
1) Plain / Simple dividing head 2) Universal Dividing head 3) Optical Dividing head
Using these dividing heads, the work can be set in vertical, horizontal or in in clined positions re lative to the table surface. There are several methods of indexing. The choice of any one method depends upon the No. of divisions required and the type of dividing head used.
PLAIN / SIMPLE INDEXING HEAD
PLAIN / SIMPLE INDEXING HEAD UNIVERSAL INDEXING HEADUNIVERSAL INDEXING HEAD
OPTICAL OPTICAL INDEXING INDEXING HEAD HEAD
METHODS OF INDEXING
METHODS OF INDEXING
1) Direct Indexing: Also called rapid indexing, is used making small No. of d ivisions. This can be performed in both plain and universal dividing head. The spindle and index
crank are connected by bevel gears. The required No. of divisions on the work is obtained by means of the rapid index plate generally fitted to the front end of the spindle nose. The plate has 24 equally spaced holes, into any one of which a spring loaded in is pushed to lock the spindle with the frame. While indexing, the pin is first taken out and then the spindle is rotated by hand, and after the required position is reached, it is again locked by pin. when the plate is turned throughout the required part o a revolution, the dividing head spindle and the work are also turned through the same part of the revolution.
With a rapid index plate having 24 holes, it is possible to divided the work into equal divisions of all factors of 24 i.e. 2,3,4,6,8,12,24
Rule:
No. of holes = No. of holes in the direct index plate
to be moved No. of divisions required
Q) Find out the index movement required to mill a hexagonal bolt by direct indexing.
Ans. No. of holes to be moved = 24/6 = 4
After machining one side of the bolt the index plate will have to be moved by 4 holes for 5 times to machining the remaining 5 faces of the bolt.
Video 10
2) Simple Indexing: Also called plain indexing, is more accurate and suitable for numbers beyond the range of rapid indexing. The bevel gears are replaced by a worm and worm wheel. The shaft carrying the crank has a single threaded worm and it meshes with the worm wheel on spindle having 40 teeth. 40 turns of crank are necessary to rotate the spindle thro' one revolution,
i.e one complete turn of the index crank will cause the worm wheel to make 1/40 of a revolution. For indexing fractions of a turn, various index plates are used.
Rule:
Index crank movement = 40/N,
where N = No. of divisions required.
If the crank movement obtained from the formula is a whole No. the index crank should be rotated equal to the whole No. derived. If the crank movement obtained from the above formula is a whole No. and a fraction then, the numerator and denominator of the fraction are multiplied by a suitable common No. which will make the denominator of the fraction equal to No. of holes in the index plate. The new numerator now stands for the No. of holes to be moved by index crank in the hole circle derived from denominator, in addition to the complete turns of crank.
Q) Set the dividing head to mill 30 teeth on a spur wheel blank. Use 21 hole index plate.
Ans.
Index crank movement
= 40/30 = =
=
Thus for indexing, one complete turn and 7 holes
in 21 hole circle of the index plate will have to be moved by the index crank, if 21 hole plate is selected. This can also be performed with 18 hole plate [ ] or 24 hole plate [ ]
also.
Video 11
3) Compound indexing:- The indexing method is called compound due to the two separate movement of the index crank in two diff. hole circles of one (same) index plate to obtain a crank movement not obtainable by plain indexing. 4) Differential Indexing: The differential indexing may be considered as an automatic method (mechanization) of performing compound indexing. Here the Index crank is connected to milling machine feed rod through a set of gears to get continuous rotation for spindle for making helical grooves as shown.
Video 12
TIME ESTIMATION
TIME ESTIMATION
1. Time required per cut = L / (f x N) = L / f m L = L1+ ATT
L1=Length of W.P ; ATT = Added Table Travel
2. Total Milling time= Time per cut x No. of cuts(or) Indexing 3. Cutting speed, V =
πDN
/ 1000; D = Cutter Diameter4. Feed per tooth. f t = f / Z = f m/ NZ, Z = No. of teeth 5. MRR = Wdf m ; d = depth of cut; W= Width of WP
Calculation of ATT: Operations performed on the milling machines are done by peripheral cutters / slab cutters/ side and face cutters (Horizontal M/c) and face cutters or end mills (Vertical M/c).
a) For Peripheral / Slab Cutters / Side and Face Cutters
FRONT VIEW
FRONT VIEW General Case
(v) Maximum uncut chip thickness =
(vi) Average uncut chip thickness =
(vii) Peak to valley height for surface roughness = (viii) Effective no. of teeth cutting at same time = (ix) Mean Tangential Force =Fmt = K d f m W /
π
DNK = Material Constant (x) Mean Cutting Power = Fmt V
i) Tool fully engaged, Roughing Pass – doesn’t require “Full Wipe”
b) For Face Cutters/End Mills
ii) Tool fully engaged, Finishing Pass – requires “Full Wiping ” (Single pass feed) iii) Tool not fully engaged with W<D/2; iv) Tool not fully engaged
but W ≥ D/2;
Offset Cases
Special Cases
W/2 W O A B C OT AL = 0.5 cm OT = 0.5 cm W W/2 L = L1 + OT L1 L1 L = L1 + AL + OT + D (i) (ii) A TOP VIEW TOP VIEW
AL L1 OT W O A B AL L1 OT W AL = OT = D/2 (iii) (iv) TOP VIEW TOP VIEW
