Manufacturing technology i 1 18 - copy

Machining

Machining• Machining

– A subtractive process used to get desired shape, size, andfinish by removing surplus material in the form of chipsby a cutting tool and by providing suitable relative motionbetween the workpiece and cutting tool

– Process of finishing by which jobs are produced to thedesired dimensions and surface finish by graduallyremoving the excess material from the preformed blank inthe form of chips with the help of cutting tool (s) movedpast the work surface (s).

• Machining requirements

Using SINGLE-Point Cutting Tools

Using MULTI-Point Cutting Tools

Using ABRASIVES as Cutting Tools

Turning Step Turning Taper Turning Form Turning Contour Turing

Facing Necking Parting-Off Boring

Counter-Boring Counter-Sinking

Shaping Planing

Milling Drilling Reaming Knurling Sawing

Grinding Honing Lapping Polishing Buffing

Machining Processes

Unconventional Machining Processes

AJM, USM, WJM

ECM, ECG

CHM

IBM, PAM, EDM, LBM, PAM

Machine tool

• A machine tool is a non-portable power operated andreasonably valued device or system of devices in which energyis expended to produce jobs of desired size, shape and surfacefinish by removing excess material from the preformed blanksin the form of chips with the help of cutting tools moved pastthe work surface (s)

• Physical functions of a Machine Tool in machining are: – firmly holding the blank and the tool – transmit motions to the tool and the blank– provide power to the tool-work pair for the machining

action– control of the machining parameters, i.e., speed, feed and

depth of cut

Basic Machine Tools Centre lathes

– Cylindrical shapes

– Manual lathes or CNC

Basic Machine Tools

Centre lathes

External

Internal

Basic Machine Tools Shaping machine• Ram: it holds and imparts cutting motion to the tool through

reciprocation

• Bed: it holds and imparts feed motions to the job (blank)

• Housing with base: the basic structure and also accommodate the

drive mechanisms

Basic Machine Tools Shaping machine• Power drive with speed and feed change mechanisms

• Shaping machines are generally used for producing flat surfaces, grooving, splitting etc.

Basic Machine Tools

Planing machine• In planing the job reciprocates for cutting motion and the tool

moves slowly for the feed motions unlike in shaping machine.

• Planing machines are usually very large in size and used for

large jobs and heavy duty work.

Basic Machine Tools

Drilling machine

• Drilling (originating or enlarging cylindrical holes)

• Boring, counter boring, counter sinking etc.

• Cutting internal threads in parts like nuts using suitable attachment

Basic Machine Tools

Drilling machine

• Column with base: it is the basic structure to hold the other parts

• Drilling head: this box type structure accommodates the power drive and the speed and feed gear boxes

• Spindle: holds the drill and transmits rotation and axial translation to the tool for providing cutting motion and feed motion

• Pillar drill, column drill, radial drill, micro-drill etc.

Basic Machine ToolsMilling machine• Flat surfaces• Slotting• Slitting• Grooving• Parting• Forming

Classification of Machine Tools

1. Direction of major axis– horizontal center lathe, horizontal boring machine etc. – vertical – vertical lathe, vertical axis milling machine etc. – inclined – special

2. Purpose of use– general purpose – e.g. lathes, milling, drilling machines etc. – single purpose – e.g. facing lathe, roll turning lathe etc. – special purpose – for mass production

3. Number of spindles– single spindle – center lathes, milling machines etc. – multi-spindle – gang drilling machines etc.


4. Degree of automation

– Manual – e.g. lathes, drilling machines etc.

– Semi-automatic – e.g. turret lathe

– Automatic – e.g., CNC Drill, CNC Mill, CNC lathe etc.

5. Type of automation

– fixed automation – e.g., single spindle and multispindle lathes

– flexible automation – e.g., Machining Centers 6. Precision

– Ordinary

– High precision


7. Size – Heavy duty – e.g., heavy duty lathes (e.g. ≥ 55 kW), boring

mills, etc.– Medium duty – e.g., lathes (e.g. – 3.7 ~ 11 kW), column

drilling machines etc. – Small duty – e.g., table top lathes, drilling machines,

milling machines. – Micro duty – e.g., micro-drilling machine etc.

8. Configuration– Stand alone type – most of the conventional machine tools. – Machining system – e.g., machining center, FMS etc.

Cutting Tool

• Removes excess material through direct mechanical contact

• Tool moves along the workpiece at a certain velocity (cutting speed – V)and a depth of cut (to) to produce a chip just ahead of tool by shearing thematerial continuously along the shear plane

Tool material Selection depends on:

• Work material (hardness, chemical and metallurgical state)

• Part features (geometry, accuracy, finish, surface-integrity)

• Machine tool characteristics (rigidity, horsepower, speed, feed , precision)

• Support system (Operator, sensors, controls, method of chip removal,lubrication, maintenance)

Cutting Tool

Tool Selection (material, geometry, cutting conditions)

Cutting Tool

• Tool Material Characteristics

– Hardness

– Toughness

– Wear Resistance

– Chemical Inertness

– Resistance to bulk deformation

– Thermal Properties

– High Stiffness

– Geometry

– Finish

Cutting Tool

Hardness of cutting materials

Hardness—resistance to deforming and flattening

Cutting Tool

Wear resistance—resistance to abrasion and erosion

Toughness—resistance to breakage and chipping

Cutting Tool

Cutting Tool

Cast-cobalt alloys (1915)

Cutting Tool

Cutting Tool

• Tool steels• HSS• Coated HSS• Cast Cobalt Alloys• Carbides / Sintered Carbides• Coated Carbides• Ceramics• Cermets• Diamonds• Polycrystalline CBN’s

– and many more…………..

Cutting ToolTool steels• Carbon and low-/medium-alloy steels• Steel is considered to be carbon steel:

– when no minimum content is specified or required for Cr, Co, molybdenum, Ni, Ti, W, V or zirconium etc.

– when the specified minimum for copper does not exceed 0.40 percent;

– when the maximum content specified is less than Mn - 1.65, Si - 0.60, Copper - 0.60.

– steel which is not stainless steel• 0.9 to 1.3% carbon• With increase in carbon content, steel become harder and

stronger

Cutting ToolTool steels

• With increase in carbon content, steel become lesser ductile and melting point decrease

• Hardness loss at 200 0C

• Mo and Cr increases hardenability

• Mo and W improves wear resistance

• Applications

– Drills, Taps, Dies etc.

– Low speeds

Cutting ToolHSS• Good wear resistance, hardenability and hot hardness• Good toughness and resistance to fracture• Good cutting at 400 0C• Easy fabrication• Types

– Molybdenum (M series)• 10% Mo with Cr, V, W, Cr and Co• High abrasion resistance than t series• Less Distortion than T series• Cheaper than T series

– Tungsten (T series)• 12-18% W, Cr, V and Co (18-4-1 W-Cr-V)

• Used for complex tool geometries

Cutting ToolTiN coated HSS• Film thickness 0.00254 - 0.00508 mm• 10-20% higher cutting speeds than HSS• Gear cutters, drills, bandsaw, circular saw blades, form tools,

inserts etc.• Reduced tool wear• High hardness• PVD

Cutting ToolCast Cobalt Alloys• Cobalt rich, chromium-tungsten-carbon cast alloys • Stellite tools (Deloro Stellite Company)• Non-magnetic and corrosion-resistant cobalt alloy• W or Mo and a small amount of carbon• Retain hardness to much greater temperatures• 25 % higher cutting speeds than HSS• Cast to shape• Used only for single point tools or saw blades

Cutting ToolCarbide or Sintered Carbides• Types:

– Tungsten carbide (WC bonded together in a cobalt matrix)• 1-5 µm WC particles are combined with cobalt in a mixer, then presses and

sintered into the desired insert shapes.• Cemented carbides \ Sintered Carbides• With increase of Co – toughness increases but there is decrease in strength,

hardness and wear resistance• Machining steels, CI, nonferrous and nonmetals

– Titanium Carbide (TiC in Ni-Mo alloy matrix)• Higher wear resistance than WC• Lesser toughness than WC• Machining hard materials like steels, CI • Higher speeds than WC• Finishing and semifinishing ferrous alloys• Auto industry using Ni-Mo binder

Cutting ToolInserts• Individual cutting tools with several cutting points• Sq inserts (8 cutting edges), triangular insert (6 cutting edges)

Cutting Tool

Inserts are clamped on tool shank with various locking mechanisms

• (a) Clamping

• (b) Wing lock pins

• (c) Thread-less lock pins - secured with side

• (d) Brazed on a tool shank

Cutting Tool

Chip Breaker

• Continuous chips are undesirable as they are a potential safety hazard

• Cutting at low speed may lead to welding of chips to tool face

• Ideal chip – Shape of letter “C” or number “9” and fits within 25 mm square block

• Procedure used for breaking chips intermittently is with use of chip breaker

Cutting Tool

Chip Breaker(a) tightly curled chip(b) chip hits workpiece and breaks(c) continuous chip moving away from workpiece(d) chip hits tool shank and breaks off

Cutting Tool

Chip Breaker

• Controlling chip flow

• Eliminating long chips

• Reducing vibration and heat

Cutting Tool

Chip Breaker

• Chip breaking in softer materials like Al include machining at small increments and then pausing.

• In shaping, milling or other such intermittent operations chip breakers are not required

Cutting Tool

• American National Standards Institute (ANSI) – C-1 to C-8

• ISO Standards – P, M and K

Classification of Tungsten Carbides

Cutting Tool

ISO Classification of Carbide Cutting ToolsAccording to Use

Cutting Tool

Coated Carbide tools• Coating increase tool life by 200-300 times

• Coating increase 50-100% in speed of the same tool life

• 80-90 % of carbide tools are coated

• Bulk tool material can be tough, shock resistant carbide that can withstand

high temperature plastic deformation and resist breakage

• Thin chemically stable, hard refractory coating of TiC, TiN, TiCN or

Al2O3, Diamond, TiAlN, CrC, ZrN etc.

• Fine grained coatings

• Free form binders and porosity

• Low coeff. of friction for coating – non adherence of chips on rake face

Cutting Tool

Coated Carbide tools• Single or multiple• Multiple coating provide stronger metallurgical bond between

coating and substrate• For multiple coating:

– Innermost layer should bondwith substrate

– Outermost layer should resistwear

– Intermediate layer shouldbond well and be compatiblewith both layers

Cutting Tool

Cutting Tool

Ceramics (White or cold-presses ceramics)• 1950• Pure Aluminium oxide, Al2O3, or SiC• Pressed into insert shapes

under high pressure• TiC and ZrO may be

added to improve toughness and resistance to thermalshock

Cutting Tool

Ceramics• Particulates or whiskers• 2 to 3 times cutting speed than WC• High hardness and chemical inertness• Hard and brittle – require rigid tool holders and machine tools• Less tendency to adhere to metals during machining – good SF • Used for high speed cutting/finishing of super-alloys and high

strength steels• Not suitable for Al, Ti as they react with alumina based

ceramics

Cutting Tool

Cermets (Ceramics + Metal)

• Black or hot-pressed ceramics

• Mix of 70% aluminium oxide and 30% TiC

• Intermediate performance between ceramics and carbides

Cutting Tool

Polycrystalline CBN• High hardness (Knoop 4700 at 20 oC 4000 at 1000 oC)• Low chemical reactivity• 0.5-1 mm layer of PCBN is bonded to a carbide substrate by

sintering under pressure.• Carbide provides toughness – CBN provides high wear

resistance and cutting edge strength• Used for automotive industry• Used for aerospace materials• Higher cost than ceramics tools or cemented carbides but tool

life is 5-7 times that of a ceramic tool

Difficult-to-machine materials

Cutting Tool

Polycrystalline CBN

PCBN Tips

Solid PCBN

Cutting Tool

Diamond

• High Wear resistance, low tool-chip friction, sharp cutting edges

• Used for fine surface finish and dimensional accuracy

• Brittle - Light and uninterrupted finishing cuts

• High speed machining and fine feeds

• Single-crystal diamond tool – machining optical mirrors

• Polishing is not required after machining

• Polycrystalline diamond tools (compacts or industrial diamonds) – small synthetic crystals, fused by high pressure and temperature to a thickness of .5-1 mm and bonded to a carbide substrate

Tool Geometry

Tool Geometry

• One or more sharp cutting edges

• Connected to cutting edge – two surfaces

– Rake face – directs the flow of newly formed chip and is oriented at an angle α (rake angle – measured relative to plane perpendicular to work surface)

• Positive rake angle – reduces cutting force

– Flank – provides a clearence between tool and newly generated work surface, thus protecting the surface from abrasion (relief angle)

Tool Geometry

• Tool point (nose radius) – The point (rounded to a certain radius) on tool penetrates below the original work surface

Cutting Condition

• Cutting speed ‘v’

• Tool movement (lateral across the work) – feed ‘f’

• Penetration of cutting tool below the original work surface –‘DOC’

RMR = vfd

where, RMR = material removal rate (mm3/min), v = cutting speed (mm/s), d = DOC (mm)

Types of Chips• Chip has two surfaces

Shiny – in contact with rake face (rubbing of chip as it moves up the tool face)

Rough or jagged – no contact with any solid body

• Primary shear Zone – along the shear plane

• Secondary Zone – shearing action after chip has been formed (results from friction between chip and tool along the rake face)

• Continuous

• Continuous with BUE

• Serrated

• Discontinuous

Types of Chips

• Continuous– Good surface

– Steady cutting force

– Undesirable in automated machining

– Formed in ductile materials at high cutting speeds and high rake angles

Tool GeometryContinuous with BUE

• Ductile materials at low-to-medium cutting speeds, friction between tool and chip tends to cause portions of work material to adhere to rake face of tool near the cutting edge

• BUE forms and grow, then becomes unstable and breaks off• Detached BUE sometimes takes away portions of tool rake

face (may lower tool life)• Detached BUE that are not carried off may imbed in newly

created work surface causing roughness• Thin stable edge protects tools

Types of Chips

Serrated (segmented, non-homogeneous)

• Difficult-to machine- materials like Ti, Ni-base super alloys at higher cutting speeds.

• Saw-tooth appearance (semi-continuous)

• Produced by cyclical chip formation of alternating high shear strain followed by low shear strain

Types of Chips

Discontinuous

• Brittle materials (like CI) at low cutting speeds

• Chips forms as separate segments

• Fluctuating cutting forces

• Irregular texture to machined surface

• Desirable for ease of chip disposal

Types of Chips

Type of Chip ?

Orthogonal Cutting

• Cutting edge is perpendicular to direction of cutting speed• Force by tool forms chip in material by shear deformation

along shear plane (angle Ø with work plane)• Cutting edge is positioned at a certain distance below original

work piece (to - chip thickness prior to chip formation• When chip forms along shear plane its thickness increases (tc)• Chip thickness ratio ‘r’

– r = to/tc

LatheLathe

• Oldest Machine Tool invented

• Principal form of surface produces – cylindrical

• Turning - Workpiece is rotated, while single-point cutting tool removes material by traversing in direction parallel (cylindrical jobs) to the axis of rotation

LatheTypes:

– Engine lathe– Tool room lathe– Speed lathe– Turret lathe– Automatic lathe– Numerical control lathe

Centre Lathe • Generally workpiece is clamped by centres in lathe• Also called as Engine lathe (driven by steam engines)

• Heavy duty machine tools with all the components have powerdrive for all tool movements except on compound rest

• Most engine lathes are equipped with chip pans and a built-incoolant circulating system

LatheTool room lathe

• Tool making / smaller parts

• Greater accuracy and usually a wider range of speeds and feeds than engine lathes.

• Designed to have greater versatility to meet the requirementsof tool and die work

• Generally used for machining smaller parts

• High range of sizes

LatheSpeed Lathe

• Speed lathes usually have only a headstock, a tailstock, and a simple tool post

• Usually three or four speeds

• Mainly used for wood turning, polishing, or metal spinning

• Spindle speeds up to 4000 rpm.

LatheTurret Lathe

• Hexagon turret replaces the tailstock

• Turret used for mounting tools and feed into the work piece

• Turret lathes Use the 11 station tooling and so as to increaseproduction rate by reducing tool changing time .

• Six tools can be mounted on the hexagon turret

• Turret can be rotated about the vertical axis to bring each toolinto the operating position

Lathe

• Headstock• Spindle• Live centre• Gear box• Feed Gear box• Tailstock• Carriage• Cross slide• Tool post

Lathe

Lathe Specifications

LatheWork Holding Devices

• Suitable locations

• Effective clamping

• Support

• Face plate: for holding irregular shape w/p

• Lathe centers: for holding long jobs

• Chuck:

– 3 jaw chuck for circular or hexagonal section

– 4 jaw chuck for irregular shapes

– Magnetic chuck for holding soft metal

Lathe

Work Holding Devices

Lathe

Mandrel– for holding hollow disc shape w/p for machining

of side faces

LatheCollet

– for holing small diameter tool and work pieces

Lathe Tool Geometry

• Tool cross-section – square or rectangular

• Shank (supported in tool post of lathe) – part of tool, on one end of which cutting point is formed

+α

α=0 -α

Positive Rake Zero Rake Negative Rake

Positive rake – helps reduce cutting force and thus cutting power requirementNegative rake – to increase edge-strength and life of the toolZero rake – to simplify design and manufacture of the form tools. Clearance angle must be positive (3o ~ 15o)

Lathe Tool GeometryKinds of tools and surface

Lathe

• Right/Left tool

– Tools have primary cutting edge by means of which the direction of the movement of tool for removing of metal is indicated

– Tool is termed as right, right palm is placed on tool, the direction of thumb indicates the direction of tool motion (tool towards the headstock)

Lathe Tool Geometry

• Zero or negative rake are used for better heat conductivity on carbide, ceramic PCD and PCBN tools

• Negative rake angle increase tool forces, it keeps tool in compression and provides added support to cutting edge. This help in making intermittent cuts and in absorbing impact during initial engagement of tool

Lathe Tool Geometry

Systems of description of tool geometry• Tool-in-Hand System

– where only the salient features of the cutting tool point are identified or visualized (no quantitative information)

• Machine Reference System – ASA system

Lathe Tool Geometry

Machine Reference System

• American Standards Association (ASA) system

• Geometry of a cutting tool refers mainly to its several angles

or slope of its salient working surfaces and cutting edges.

Those angles are expressed w.r.t. some planes of reference.

• Machine Reference System (ASA) is based on three planes of

reference and three coordinates of reference. These references

are chosen based on the configuration and axes of the machine

tool concerned.

Lathe Tool Geometry

Lathe Tool Geometry

• Back-rake angle: Angle b/w face of tool and base of shank (measured in a plane through the side cutting edge, and at right angle to base)

• Side-rake angle: Angle b/w face of the tool and the base of shank (measured in a plane perpendicular to the base, to the side cutting edge)The side rake and back rake angle combines to form effective rake angle (true rake or resultant rake)

• End-relief angle: Angle between the portion of the end flank immediately below the end cutting edge, and a line drawn through this cutting edge perpendicular to the base (measured in plane perpendicular to the end flank)

• Side-relief angle: Angle between portions of the end flank immediately below the side-cutting edge and a line drawn through this cutting edge perpendicular to the side flankRelief angles affects tool life and surface quality of workpiece

Lathe

a. 3D views of toolb. Oblique view of tool from cutting edge

Lathe Tool Geometry

• Side and end cutting-edge angles defines nose angle. Side cutting Edge angle controls the width and thickness of chips

• Nose radius has a major influence on surface finish. High nose radius decrease tool wear and improves surface finish.

LatheTurning is the process of machining external cylindrical and

conical surfaces.

– Straight turning: for producing cylindrical shapes

– Taper turning: for producing conical shapes

– Facing: making edges square and clear

– Chamfering: slightly tapering and rounding off of edges

– Threading: for producing threads

– Drilling: for creating /producing hole

– Boring: for enlarging hole and correcting shape

– Parting off or necking: separating or making square groove

– Knurling: making impression for firm gripping

– Reaming: finishing purpose

Lathe - Turning

Turning Cuts

Roughing

– As heavy as proper chip thickness, tool life, machine power and work material properties permit

– Slow speeds for hard workpieces

Finishing

– Light, usually less than (0.015 in)

– Usually same tool is used for roughing and finishing

Lathe - Turning

Lathe - TurningCutting speed – V (fps)

DOC d = (D1-D2)/2

Length of Cut = Distance travelled ‘L’ + Allowance ‘A’

Feed - f

Rpm value of machine tool - N = 12V/πD1

Cutting Time – T = (L+A)/fN

MRR = L(πD12- πD2

2)/4

(L+A)/fNNeglecting A and substituting N

MRR = 12Vfd (d is very small as compared to D1(d = 1))

Lathe – Taper Turning

• Cutting tool is fed at an angle to the axis of rotation producing an external/internal conical surface.

• Tapers generally specified in degrees of included angle between the sides (or rate of change in diameter along the length mm/mm)

Taper tuning can be performed by using:

• Swiveling of compound rest (short and steep tapers)

• Form tools

• Offsetting tail stock

• Taper turning attachment (fine taper-ness)

• NC lathe with programmed movement of tool

Lathe – Taper TurningSwiveling of compound rest (short and steep

tapers)Tool is set

at half of taper angle w.r.t. lathe axis and moved with compound rest

only

Manual Feed (non-uniform)Short and steep tapersLimited movement of comp. restLow productivityPoor surface roughness

Lathe – Taper TurningSwiveling of compound rest (short and steep

tapers)

Lathe – Taper Turning

Form Tools

Feed is given by plunging the tool directly into the work

Short tapers like chamfering

Tool may vibrate excessively on long tapers

Poor surface quality in long tapers

Lathe – Taper TurningOffsetting tail stock

Offsetting results in inclination in job’s axis of rotation by half angle of taper

The feed is given parallel to guide ways

Lathe – Taper TurningOffsetting tail stock

Lathe – Taper TurningTaper turning arrangement

Separate slide way is arrange at rear of cross-slide. This slide can be rotated at angle

The cross-slide is made free by disconnecting it from lead screw

• Crossslide ismade freeand toolis movedwith helpofattachment at anangle

Taper turning attachment

Lathe-BoringBoring

Enlarging of an existing hole

Correction of eccentricity

Holes may be bored straight, tapered or irregular threads

Similar to internal turning while feeding tool parallel to rotation axis of workpiece

Higher clearance angle and lower length to diameter

Boring bar is used

Lathe-BoringBoringCutting Time – T = (L+A)/fN


MRR = L(πD12- πD2

2)/4

(L+A)/fN

MRR = 12Vfd

Lathe-FacingFacing

Producing flat surface

Tool is fed across the end of rotating workpiece

Tool feeds perpendicular to axis of rotating workpiece

Cutting speed is determined from largest diameter on workpiece

Tool point must be set exactly at height of center on workpiece

Length of cut - L = D1/2 (rod)

- L = (D1-D2)/2 (tube)

Lathe-Facing

Lathe-FacingFacing

Producing flat surface

Tool is fed across the end of rotating workpiece

Tool feeds perpendicular to axis of rotating workpiece

Cutting speed is determined from largest diameter on workpiece

Tool point must be set exactly at height of center on workpiece


- L = (D1-D2)/2 (tube)

Lathe-FacingCutting Time – T = (L+A)/fN = (D1/2 + A)/fN


MRR = π D12dfN

substituting N, L=D1/2 MRR = 6Vfd

End facing: facing by tool moving radially

outward from the center

Shoulder facing: facing the stepped

cylindrical work piece

Lathe-Facing

Lathe - Parting

Necking is a making partial cut-off

Lathe - PartingCut-off tool is used

One section of workpiece is severed from remaining

Tool should be set exactly at height of axis of rotation

Tool is fed perpendicular to rotational axis


- L = (D1-D2)/2 (tube)

Cutting Time – T = (L+A)/fN = (D1/2 + A)/fN


MRR = π D12dfN

substituting N, L=D1/2 MRR = 6Vfd

Drilling

Tool (Drill) can be mounted on the tailstock of engine lathes or

turrets of turret lathes

Fed by hand against a rotating work piece along the axis of lathe

Coolant can be used

Occasional withdrawal to clear chips and delivery of coolant to

cutting edge

Lathe - Drilling

Similar to drilling on lathe

It is semi-finishing operation that

enlarges an existing hole

Tool is rotated and fed along

rotational axis.

Lathe - Reaming

Knurling

Roughening the surface of work

piece for better gripping.

Generally a cold-forming process

Process involves pressing of two

hardened rolls against the rotating

work piece with sufficient force to

form impression (the knurl) like

raised diamond pattern.

Lathe - Knurling

Knurling

Lathe - Knurling

Contour turning

The tool follows a contour creating acontoured form on the turned partinstead of parallel to the axis.Cross slide is made free to followthe path of contour.

Form TurningCutting edge of Tool has a Specific Form or Shape and is

fed radially inward towards the axis of rotating workpiece.

Chamfering The tool is fed radially inward

used to cut an angle on thecorner of the cylinder,forming a chamfer to avoidsharp edges.

Drilling

• Drilling is most common single machining operation

• Drilling makes up 25% of machining

• Drilling occurs at the end of a tool

Drilling1. A small hole is formed by the web—chips are not cut here in

the normal sense.

2. Chips are formed by the rotating lips.

3. Chips are removed from the hole by the screw action of the helical flutes.

4. The drill is guided by lands or margins that rub against the walls of the hole.

Twist Drill

Drilling

Twist Drill

Drilling

Drilling

• Rake angle of a drill varies along the cutting edges (lips)– Negative close to point– Equal to helix angle out at lip

• Generally rake angle is 24o

• High speed drilling - rake angle is 30o

• Soft materials (plastics) – rake angle is 0o to 20o

• Cone angle – affects direction of flow of chip across the tool face and into the flute– Generally cone angle of 118°– Brittle materials (gray CI, Mg alloys) 90° to 118°– Ductile materials (Al alloys) 118° - 135°

Drilling

• The most common drills are twist drills

• Twist drills have three parts

– Body: consisting of spiral grooves called flutes, separated by lands

– Point: a wide variety of geometry are used

– Shank: a straight or tapered section where the drill is clamped.

Drilling

(a) straight shank with tang,(b) tapered shank with tang,(c) straight shank with whistle notch,(d) straight shank with flat notch.

Drilling

Intersection of web and cone produces a

straight line chisel end

Cutting Speed at drill center is low (approaching zero)

Cutting speed at outer tips is highest

Drilling• Straight line chisel point causes drills to “walk” along the

surface

• This effect is counter by using centering techniques

– Center punches

– Pre-drilled guide holes for large holes

• Specialized tips are used to produce self centering holes where hole position is critical.

– Helical tips

– Four-facet tips

– Racon

– Bickford

– Center core, or slot drills

Drilling

Drilling

Center Core Drill

Twin carbide tips brazed on steel shank and a slot in center

Drilling

Drilling

• Specialty Drills

– Hole cutters: used for holes in sheet stock

– Step drill – used for two or more diameters

– Subland drills: used for multi diameter holes

– Indexable drills: used for high speed shallow holes in solid stock

– Centre drill bit with internal coolant

– Micro drills (pivot drills): used for holes 0.02 to 0.0001 inch diameter where grain boundaries and inclusion produce non-uniform material properties

Drilling

Hole Cutters

• When cutting large holes in sheet stock, a hole cutter is used

• Hole cutters have a pilot drill in the center used to accurately locate the center

• Also called a hole saw

DrillingStep Drill

Single set of flutes and is ground to two or more diameters

Subland Drill

Separate set of flutes on a single body for each diameter.

DrillingIndexable Drills

Drilling

• Microdrills0.0001 in – 0.125 in

Drilling

Drill Chucks

• Small Drill Press – Chuck is permanantly attached

• Large Drill Press – Chuck has tapered shank that fits into the taper on machine spindle

• Chucks use chuck keys/collet-type holders

Drilling

Drill Chucks

Machine Tools for Drilling

• Drilling can be performed on:– Lathes

– Vertical mills

– Horizontal mills

– Boring machines

– Machine centers

• Specialized machines designed specifically for drilling called “drill presses”

DRILLING MACHINE Drilling is Most Commonly Performed on a Drill Press.

Upright Drill Press.

DRILL PRESS Consistsof Following Parts1. Base, 2. Column 3. Power-Head 4. Spindle 5. WorktableThese may be bench

or floor mounted depending on the size

Drill can be fedmanually orautomatically

TYPES of DRILLING MACHINES

MAIN TYPE Applications

1. BENCH Holes up to 0.5 in. Diameter canbe Drilled. Very High Speed up to30,000 rpm

2. UPRIGHT Speeds Ranges from 60 to 3500RPM

3. RADIAL For Large Workpieces thatCannot Easily be HandledManually.

TYPES of DRILLING MACHINES

MAIN TYPE

Applications

4. GANG Mass Production variety ofpurposes such as Holes ofDifferent Sizes, Reaming,Counterboring, on a Single Part.

TYPES of DRILLING MACHINESMAIN TYPE

Applications, Designation

5. MULTI-SPINDLE

Mass Production Machines with as manyas 50 Spindles Driven by a SinglePower head and Fed Simultaneouslyinto Work.

6. DEEP-HOLE

For Drilling Long (Deep) Holes inRifle Barrels, Connecting Rods, andLong Spindles.

Manufacturing technology i 1 18 - copy

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Transcript of Manufacturing technology i 1 18 - copy