UNIT 3- MACHINING OPERATIONS

UNIT 3- MACHINING OPERATIONSMachining

It is a metal removing operation from the work piece with the help of machine tools and cutting tools. Metal is removed in the form of chip from the workpiece.

Names of commonly used machine tools:

1. Lathe machines, 6. Milling Machines2. Drilling machines, 7. Boring Machines3. Grinders, 8. Metal Cutting Saws4. Shaping machines, 9. Slotting machines etc.5. Planning Machines,

Lathe Machines

Lathe machine

Basic principle of a lathe machine :Lathe machines are normally used to produce cylindrical surfaces. The job is held in the chuck attached to the head stock or between the centers provided at the head stock or tail stock. The tool is held on the compound rest. Job is rotated at the predetermined speed by the head stock. The tool is moved relative to the workpiece with the help of carriage, cross slide or compound rest. Desired quantity of metal is removed in the form of chip from the work piece.

Specification of a lathe machine A lathe machine is specified by the followingHeight of the centers measured from the lathe bed. Swing diameter over bed. This the largest diameter of work piece which will revolve without touching the bed. It is equal twice the height of centers from the bed.Swing diameter over carriage. It is the largest diameter that can revolve over the cross-slide. This always less than the swing diameter over the bed.Maximum bar diameter. This is the maximum diameter that will pass through the head stock spindle.Length of the bed.

Fig.- Specifications of lathe machine

Classification of Lathe machines

Lathes can be classified into following three typesEngine Lathes Light weight bench engine lathePrecision Tool Room lathesGap lathesTurret LathesSpecial Purpose lathes

Basic Operations Performed on a Lathe Machine :

Turning Plain turning , Step turningFacingTaper Turning Drilling :Boring : Reaming : Knurling :Forming : Chamfering : Parting Off:Threading or thread cutting Turning

Plain turning on lathe machine

Fig.- step turning on lathe machine

Fig.- Facing on lathe machine

Turning on lathe machine

FIG.- TAPER TURNING BY COMPOUND REST METHOD

Taper turning by set over method

Taper turning by swiveling the compound rest

Taper turning by form tool

Eccentric turning on lathe machine

FIG.- KNURLING

Knurling on lathe machine

Knurling on lathe using knurling tool

Knurling tool

FIG.- DRILLING AND BORING

Drilling on lathe machine

Boring on lathe machine

Drilling on lathe

Boring on lathe

Reaming on lathe machine

Reaming on lathe using reamer tool

Reamers

FIGURE GROOVING AND PARTING

Parting on lathe machine

Grooving on lathe

Forming on lathe machine

Chamfering on lathe machine

Threading on lathe

Threading on lathe machine

Shaping Machines

A shaper is used for producing relatively small flat surfaces. A single point tool is mounted on a tool box fitted to a reciprocating ram. The job is clamped in a vice. There is a cutting action in the forward motion of the tool while the return stroke is idle. Job is given indexed feed.

FIG.- SHAPER

Shaper machine

Shaper operations

Horizontal cuttingVertical cuttingInclined cuttingIrregular cutting

HORIZONTAL AND VERTICAL CUTTING ON SHAPER

INCLINED CUTTING ON SHAPER

PLANNING MACHINE OR PLANNERPlanning machines are used for generating large flat surfaces. These flat surfaces may be horizontal, vertical or inclined. Planing machines also perform all the functions that a shaping machine does. The planning machines handle larger and heavy jobs.In planning machines the job is mounted on a table which moves forward and backward. The tool is held firmly on the cross rails in the middle of the machine.

FIGURE- PLANNER

Planer machine

FIG.- MACHINING BED ON PLANNER

Diff. between shaper and planerPlaning MachineShaping Machine1. Machine is heavy and is used for producing large surfaces2. Cutting takes place by reciprocating the work piece3. Heavier cuts can be given4. Several tools can be mounted and employed at a time5. Several jobs requiring similar operations can be machined at a time6. Indexed feed is given to the tool during idle stroke of the work table. 1. Machine is light and only small job can be produced.2. Cutting takes place by reciprocating the tool.3. Only light cuts can be given.4. Only one tool is used at a time.5. Only one job can be taken up at a time.6. Indexed feed is given to the job during idle stroke of the ram.Milling Machine

In milling machine , milling operation is done. Milling is a metal removing process by the help of a multitooth (multi edge) revolving cutting tool. The cutting tool is held on a spindle called arbour and the work piece is fixed on a table. The table reciprocates past the cutting tool and metal removal takes place. Feed for the next cut and the depth of the cut are given by the movement of the table. Each tooth has the same profile. Each tooth after taking a cut comes in operation after some interval. This allows the tool to cool down before the next cut takes place.

FIG.- UP MIILNG AND DOWN MILLING

FIG.- HORIZONTAL MILLING MACHINE

FIG.- VERTICAL MILLING MACHINE

Milling machine

Horizontal milling machine

Vertical milling machine

MILLING OPERATIONSPlain or Slab MillingFace MillingAngular MillingForm MillingStraddle MillingGang Milling

Drilling Machine

Drilling is an operation through which a drilled hole is produced in a job. The machine tool used in this case is called drilling machine and the cutting tool used is called a drill bit or drill.

FIG.- DRILLING

FIG.- TWIST DRILL

Hand drill, drill bit

Hand drill

Bench drilling machine

Fig.- Radial drilling machine

FIG.- RADIAL DRILLING MACHINE

Radial drilling machine

Radial milling machine

Operation performed on a drill machine

Drilling : Operation of producing a cylindrical hole in a solid body by means of a drill.Reaming : Operation of finishing the drilled hole (that is achieving the closer tolerances and desired surface finish) by means of a reamer.Boring : A drilled hole can be enlarged also by means of boring tool on the drill machine.Counter Boring : Enlarging the diameter of the drilled hole only upto certain depth. For this counter boring tool is used. Counter Sinking : It is enlarging the top end of a drilled hole and giving it a conical shape by the help of a counter sinking tool. Spot Facing : Squaring the surface at the top end of a hole to provide a true seat for the bolt head or collar.Tapping : A tap can be rotated inside an already drilled hole to produce internal threads.

FIG.- DRILLING OPERATIONS

Grinding

It is the process of removing material by the abrasive action of a revolving wheel from the surface of a work piece, in order to achieve required dimension and surface finish of the work piece. The wheel used for this purpose is called grinding wheel. Grinding wheel consists of sharp crystals called abrasives held together by a bonding material.

Types of grinding machines

Grinding machines are normally put in two categories :Roughing Grinders Bench , pedestral or floor grindersSwing frame grindersPortable and flexible shaft grindersBelt grinder

Precision Grinders Cylindrical Grinders (three types)Surface GrindersHorizontal spindle, reciprocating table surface grinders Vertical spindle , reciprocating table surface grindersInternal Grinders

Common Grinding Operations :-

FIG.- INTERNAL GRINDING AND CENTERLESS GRINDING

FIG.-GRINDING OPERATIONS

FIG.- SURFACE GRINDING

Hand grinder

Bench grinder

Bench grinder or pedestal grinder

Surface grinder

Cylindrical grinder

Center less grinding machine