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Machine Tools and Machining

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Machining: A SubtractiveType Manufacturing Process which Imparts DesiredShape, Size, and Finish to the Product by Removing Material in the Form ofChipsby a Suitable Cutting Tooland by Providing Suitable Relative Motion

Between the Work piece and Cutting Tool

Cutting Tool: Removes Excess Material through Direct Mechanical Contact Tool

Machine Tool: Provides Necessary Relative Motion Between the Work pieceand Tool

Conventional and Non-Conventional Machining

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Generatrix and Directrix

Generation of Various Surfaces in a Machining Operation

Generatrix Directrix Process SurfaceObtained

MachiningProcess

Straight Line Straight Line Tracing Planar Surface Shaping,

PlaningCircular Straight Line Tracing Cylindrical TurningCircular Straight Line Generation Planar Surface Milling

Plain Curve Circular Tracing Surface ofRevolution

ContourTurning,

Boring,

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DESIGN and TERMINOLOGY of the ENGINE LATHE

The Essential Components of an Engine Lathe are

1. Bed2. Headstock Assembly

3. Tailstock Assembly

4. Carriage Assembly

5. Feed Rod

6. Leadscrew

7. Quick Change Gearbox

Tailstock

Bed

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Rib

Lathe Bed

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Headstock assembly

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Tailstock assembly

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Carriage assembly

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Rack and Pinion

S ifi i f L h

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Specification of Lathe

Size of a Lathe is Designated by Two Dimensions:

1. Swing: This is the maximum diameter of work piece that can be rotatedon a lathe.

2. Maximum distance between headstock and tailstock centres:Indicates the Maximum Length of work piece that can be mountedbetween centers.

3. Length of Bed

Example: 360 X 760 X 1830

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Machining parameters

Cutting Velocity

FeedDepth of cut

Surface roughness 1000

DNV

Cutting Velocity (m/min)

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Different types of Lathes

1. ENGINE Lathe: Suitable for individual part production or modification, notsuitable for repetitive production

2. SPEED Lathe: High spindle speeds are available, usually have only aheadstock, a tailstock, and a simple tool post mounted on a light bed, mainlyused for wood turning, polishing or metal spinning

3. TOOLROOM Lathe: Most-accurate version, versatile to meet therequirements of tool and die work, suitable for smaller parts

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4. GAP-BED Lathe: section of the bed adjacent to headstock is removed topermit larger swing

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5. WHEEL Lathe: Designed for turning railway-car wheels

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6. TURRET Lathe

A longitudinally feedable hexagon turret replaces the tailstock

Ordinary turret lathes use the 11 station tooling setups for completemachining of a piece and minimize machine controlling time.

SIX tools can be mounted on the hexagon turret

Turret can be rotated about the vertical axis to bring each tool into theoperating position and the entire unit can be translated parallel to theways either manually or by power

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7. VERTICAL Lathe

8. AUTOMATIC or SCREW CUTTING Lathe: Mechanical automation

9. NUMERICAL CONTROL (NC) or Computer NC TURNING CENTERS

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TYPICAL OPERATIONS PERFORMED on a LATHE

STRAIGHT or CYLINDRICAL or PLAIN TURNINGFACINGTAPER TURNING

Three Methods for turning External & Internal Tapers on a LatheSwiveling the Compound RestSetting over the tailstockUsing a taper turning attachment

CHAMFERINGPARTING or CUTTING-OFF and NECKING

CONTOUR TURNINGFORM TURNINGDRILLINGBORING

REAMINGTHREAD CUTTING

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Cutting tools

Geometry, cutting temperature, chip breaker,coolant, Shear plane, Shear angle, throw away typetool,

Drill bit geometry,

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Joining takes place without fusion at the interface

No liquid or molten phase is present at the joint

Two surfaces brought together under pressure

For strong bond, both surfaces must be clean:

No oxide films

No residues No metalworking fluids No adsorbed layers of gas No other contaminants

Solid-State Welding Processes

Interatomic bonds between two surfaces

Adhesion Proximity between surfaces

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TYPICAL OPERATIONS PERFORMED on a LATHE

STRAIGHT or CYLINDRICAL or PLAIN TURNINGFACINGTAPER TURNING

CHAMFERINGPARTING or CUTTING-OFF and NECKING

CONTOUR TURNINGFORM TURNINGDRILLING

BORINGREAMINGTHREAD CUTTING

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The point angle, or the angle formed atthe tip of the drill, is determined by the

material the drill will be operating in.Harder materials require a larger pointangle, and softer materials require asharper angle.

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Workholding in Lathe

1. Holding in chuck

2. Holding between centers

3. Holding in a collet

4. Mounting on the faceplate

5. Mounting on the carriage

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Holding between centers

Live center Dead center

Face plate

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Lathe dog

Half center

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Holding in a collet

Advantages:

Forms a collar around the object to be held and exerts astrong clamping force

1. Strong clamping force

2. Speed of chucking is less

3. Self-centering

4. Resistance against being untightened

5. Considerably high level of precision

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Holding in a Mandrel

Solid mandrel

Types:

1. Solid mandrel

2. Gang mandrel

3. Cone mandrel

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Mounting on the carriage

Internal turning / Boring

Steady and follow rest

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Work holding in a drilling machine

1. Vice

2. Jig

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Slideways

Different types of slideways used in machine tools

1. Load carrying capacity2. ease of manufacturing

3. ease of chip disposal4. effective lubrication5. position of slideways

Shape of the slideway depends on

Milli

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Milling

Milling is the process of machining flat, curved, or irregular

surfaces by feeding the workpiece against a rotating cuttercontaining a number of cutting edges.

The milling machine consists basically of a motor drivenspindle, which mounts and revolves the milling cutter, and

a reciprocating adjustable worktable, which mounts andfeeds the workpiece.

Classification of milling machines:Vertical |

Horizontal __

Generally milling machines have self-contained electricdrive motors, coolant systems, variable spindle speeds, and

power-operated table feeds

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Milling Machine1. Column

and kneetype

2. Bed type

3. Planer

type

Column and knee type

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Slab milling Face milling End milling

Types of milling operations(Depending upon the type of milling cutter being used)

Milli C tt N l t

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Milling Cutter Nomenclature

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Tooth, Cutting edge, Tooth face, Rake surface, Clearancesurface, Rake angle, Clearance angle (Primary andsecondary), Flute, Land, Heel, Keyways, Hole diameter,Outside diameter, Width, Pitch of teeth

U illi d D illi

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Up milling and Down milling

1. Milling cutter,2. Work piece,

3. Direction of rotation of cutter (primary motion),4. Feed direction of work piece (secondary motion)

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Milling cutters are usually made of high-speed steel The pitch refers to the angular distance between like or

adjacent teeth.

The pitch is determined by the number of teeth. The tooth faceis the forward facing surface of the tooth that forms the cuttingedge.

The land is the narrow surface behind the cutting edge on each

tooth. The rake angle is the angle formed between the face of the

tooth and the centerline of the cutter. The primary clearance angle is the angle of the land of each

tooth measured from a line tangent to the centerline of the

cutter at the cutting edge. This angle defines the land of each tooth and provides

additional clearance for passage of cutting oil and chips. The hole diameter determines the size of the arbor necessary

to mount the milling cutter.

D illi hi

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Drilling machine

Bench type drilling machine

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Radial drilling machine

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Gang drilling machine