ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

UNIT-6MILLING AND GRINDING

Milling is a process of removing excess material from the w/p with a rotating cutting tool called milling cutter. The milling cutter is a multipoint cutting tool with cutting teeth formed on the circumference or on the end face or on the both. With suitable speed and multi cutting edges, material can be removed at a faster rate and also fine surface finish can be produced.

Milling process is used for producing flat, contoured or helical surfaces for cutting threads, slots, toothed gears etc.

Principle of milling:Milling works on the principle, that when a w/p is fed slowly against a multi point cutter, revolving at high speed, material can be removed. As the w/p moves against the tool, each tooth of the cutter removes metal from the surface of the w/p to produce the desired shape.

Up Milling or conventional milling:If the w/p is fed in the direction opposite to that of the rotating cutter, the process is called up milling.

Climb milling or down milling:If the w/p is fed in the same direction as that of the rotating cutter, it is called down milling or climb milling.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 1

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

UP MILLING DOWN MILLINGCOMPARISON BETWEEN UP AND DOWN MILLING

UP MILLING DOWN MILLING

The w/p is fed in the direction opposite to that of the rotating cutter.

The w/p is fed in the same direction as that of the rotating cutter.

Thickness of the chip is minimum at the beginning of the cut and reaches maximum when the cut ends.

Thickness of the chip is maximum at the beginning of the cut and reaches to the minimum when the cut ends.

The cutting force is directed upwards and this tends to lift the w/p from the table. Hence greater clamping force is necessary.

The cutting force acts downwards, that keeps the w/p firmly on the table. There by permitting lesser clamping forces.

Chips get accumulated at the cutting zone .These chips interfere with the revolving cutter, thereby impairing the surface finish.

Chips do not interfere with the revolving cutter as they are disposed easily by the cutter .Hence there is no damage to the surface finish.

Difficult for efficient cooling since the cutter rotates in upward direction carrying away the coolant from the cutting zone.

Efficient cooling can be achieved since the coolant can easily reach the cutting zone.

Used for machining hard surfaces such as castings and forging.

Used for finishing operation and small works.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 2

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

CLASSIFICATION OF M.M1. Column and knee type

a. Horizontal or plain M.Mb.Vertical M.Mc.Universal M.M

2. Fixed bed type M.M 3. Planer Type M.M 4. Special purpose M.M

HORIZONTAL M.M

The machine consists of1. Base: The base forms the foundation of the m/c upon which all the other parts are mounted.2. Column: is a vertical hollow casting that houses main drive and the spindle.3. Knee: Knee can slide up and down on the vertical guide ways provided on the front face of the column. Knee is actuated by means of an elevating screw .Knee supports the saddle.4. Saddle: supports the work table and can be moved horizontally on the guide ways provided on the upper face of the knee.5. Spindle: is a hollow shaft supported by the column. The spindle obtains the power from the motor and transmits it to the arbor. The arbor carries the cutter and rotates about a horizontal axis.6. Work table: rests on the saddle and can be moved at right angles to the movement of the saddle. The work table is provided with T-slots for holding the w/p.7. Over arm: is mounted on the column, supports the yoke, which in turn supports the free end of the arbor.OPERATION: In operation, the w/p is raised against the rotating cutter to give the required depth of cut. The table is moved in a horizontal plane to give feed to the w/p.Horizontal M.M are used to obtain grooves,slots,keyways,gear teeth etc.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 3

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

HORIZONTAL M.MVERTICAL M.M

The machine consists of1. Base: The base forms the foundation of the m/c upon which all the other parts are mounted.2. Column: is a vertical hollow casting that houses main drive and the spindle.3. Knee: Knee can slide up and down on the vertical guide ways provided on the front face of the column. Knee is actuated by means of an elevating screw .Knee supports the saddle.4. Saddle: supports the work table and can be moved horizontally on the guide ways provided on the upper face of the knee.5. Work table: rests on the saddle and can be moved at right angles to the movement of the saddle. The work table is provided with T-slots for holding the w/p.6. Spindle: spindle head is fixed to the vertical column. The spindle head may be either fixed, sliding, swivel head type or it may be a combination of the last two.

In sliding type, the spindle can be moved up and down to perform operations like grooving, slotting, facing etc.The swivel head type is used to work on angular surfaces.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 4

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Generally Vertical M.M is used to perform end milling and face milling operations.

VERTICAL M.M

MILLING OPERATIONS:PLAIN MILLING OR SLAB MILLING;It is performed on Horizontal M.M.It is the operation of producing plain horizontal surfaces parallel to the axis of the rotating cutter. Plain or slab milling cutter is used which has straight or helical teeth on the periphery of a cylindrical surface.

End Milling: End milling is used for machining end surfaces, slots, and pockets. Cutter used in end milling is END MILL CUTTER. It has teeth on the bottom face as well as the periphery and may have straight or helical flutes.

Slot Milling: Slot milling is the operation of producing slots in work pieces. The slots can be of varied shapes such as plain, T- slots, Dovetail slots etc.The cutter to be used is chosen according to the shape of the slot to be produced.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 5

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Angular milling: is a process used for milling all types of an angular cuts, grooves and similar work. The faces of angular cutters may be the same or each face may be at different angle.

Form milling: is used to produce curved profiles and also convex, concave and spline etc.They may also be used for cutting gear teeth.

Straddle milling: is a process in which a pair of side milling cutters is used for machining two parallel surfaces of a work piece simultaneously. Two or more cutters are mounted on an arbor with a distance spacer between them.

T-slot milling

Slot milling

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 6

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Specifications of Universal Milling machine Table overall size Power traverse Sped range

GRINDINGGrinding is a process of removing excess of material by the abrasive action of a rotating wheel on the surface of the work piece. It is basically a finishing operation employed to produce a work piece of high accuracy and surface finish.SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 7

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

The Wheel used for grinding operation is known as grinding wheel. It consists of sharp crystals called “abrasives” that are held together by suitable bonding.

Principle of Grinding

Grinding is a process in which the excess material is removed by the rubbing action of the abrasive particles. The process removes very little material in the form of fine chips when compared to that of drilling or milling process and this makes it to be called a finishing process.

Abrasives:Abrasives are mineral crystals that act as cutting edges in a grinding wheel. The hardness of the crystals is much higher than that of the workpiece.Abrasives are of two types.

Natural abrasives Artificial abrasives

Natural abrasives: Are available in nature. They include 1. Diamond2. Emery3. Corundum4. Sand stone5. Garnet

Diamond is a crystalline form of carbon, is the hardest material ever known. Among natural abrasives, diamond is the most commonly used and is used extensively for sharpening carbide and ceramic tools.

Sand stone or solid quartz is used for sharpening wood working tools.SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 8

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Emery and corundum are natural aluminium oxide and have a greater hardness and better abrasive action than quartz.Garnet sand is a good abrasive, and a common replacement for silica sand in sand blasting.

Use of natural abrasives is limited because they contain higher percentage of impurities and posses non – uniform properties.(Hardnss,toughness).

Artificial Abrasives:These are manufactured abrasives that are fre from impurities

and posses properties better than those of natural abrasives. Cubic boron nitride(CBN) Aluminium oxide(Al2O3) Silicon Carbide (SiC) Boron Carbide

CBN: is used for grinding iron, steel alloys of iron and similar materials. Also used as a mineral and a machining insert.

Aluminium oxide (Al2O3): It is used for grinding alloy steel carbon steels etc.It is also useful as refractory in the linings of special furnaces.

Silicon Carbide: is a synthetic abrasive which is harder than aluminium oxide.Caborundum is a type of silicon carbide that is used to grind the surfaces of marble, stones and granite.SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 9

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Boron Carbide: use in tool die fabrication, lapping and ultra sonic machining.

Bonding Materials: is an adhesive substance that holds the abrasive particles together to form a grinding wheel. The most commonly used bonding materials are Vitrified bond Silicate bond Resinoid bond Rubber bond Shellac bond

Vitrified bond: This is the most commonly used bonding material. Vitrified bond is made of clay and feldspar .The bond is strong, rigid, porous and not affected by fluids (water, oil and acids).Generally 80% of the wheel is made up of vitrified bond.

Silicate bond: It is made up of sodium silicate. It is used in operations that generate less heat. Silicate bonds are not strong as vitrified bonds.

Resinoid bond: is made up of synthetic resin or a plastic that becomes hard after heating. This bond has a good strength and is more elastic than vitrified bond but resistance to heat and chemical action is low.Resinoid bond is the most frequently used bond next to vitrified bond.

Rubber Bond: is made up of natural or synthetic rubber. Rubber bonded wheels are denser than retinoid bond but are less heat resistant. Rubber bonds are used where a good surface finish with high dimensional accuracy is a primary requirement. It is the most flexible bond.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 10

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Shellac Bond: This is a organic bond. It has considerable strength and its elasticity is greater than other types of bond. But this bond is not suitable for heavy duty work.

Classification of grinding Machine:

1. Surface grinding Machine Horizontal spindle G.M Vertical Spindle G.M

2. Cylindrical G.M3. Centerless G M4. Special G M 5. Internal G M

Surface grinding Machine: S G M is mainly used for grinding flat surfaces, angular and irregular surfaces can also be finished.

It consists of a horizontal spindle carrying the grinding wheel and a reciprocating work table. The work piece can be directly clamped on the table or by means of a magnetic chuck.

In operation, the rotating grinding wheel is brought in contact with the surface of the work piece removes material in the form of fine grains.

Reciprocating table gives the longitudinal feed to the work piece and vertical downward movement of the wheel gives the required depth of cut.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 11

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Cylindrical Grinding Machine is used for grinding external cylindrical surfaces that may be plain, tapered or contoured.

In operation, the cylindrical work piece is made to rotate between the two centers. Separate motor is used to drive the headstock and the grinding wheel.SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 12

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

The work table is made in two parts.The upper table carries the head stock and tailstock and can be swiveled by a small angle that enables to grind taper surfaces.The lower table mounted on the horizontal guide ways provides longitudinal movement for the upper table.

In operation, both the grinding wheel and the work piece are made to rotate in opposite direction. As the work piece reciprocates the grinding wheel comes in contact with the cylindrical surface of the workpiece.The abrasive action of the wheel removes material from the work piece in the form of fine chips.

Centerless grinding: is used for grinding surfaces of work piece that cannot be held and rotated between centers. This process is primarily useful for grinding long, slender shafts or bars.

Work piece is supported by the grinding wheel, regulating wheel and a work rest. The grinding operation is performed by the grinding wheel only. The function of the regulating wheel is to support the work piece while in operation. Regulating wheel carries a rubber bond and helps in the rotation of the work piece.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 13

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

Both grinding wheel and regulating wheel rotate in the same direction. The work rest supports the work piece from the bottom.

Question Bank

1. Explain with a neat diagram the principle working of a milling machine.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 14

ACHARYA INSTITUTE OF TECHNOLOGY DEPARTMENT AUTOMOBILE ENGINEERING

SUB: ELEMENTS OF MECHANICAL ENGINEERING II SEMESTER ACADEMIC YEAR 2012-13 Sub Code : 10EME24Staff: SRINIVAS Y V

2. What is cylindrical grinding? Explain with a neat sketch.3. What is milling? Classify the different types of milling machines.4. List and explain the various operations that can be performed on

a milling machine.5. Name the various abrasives and binding materials used in

grinding wheel and explain each one of them.6. Explain with a neat sketch working principle of center less

grinding process.7. Explain the principle of milling and draw a schematic sketch of a

horizontal milling machine and label its parts.8. Distinguish between cylindrical grinding and surface grinding.9. Explain the following with sketches

a) Up milling b) down milling c) face milling10.Explain and draw a schematic sketch of a vertical milling

machine and label its parts.11.Explain the different types bonding of grinding wheels and the

materials used.

SRINIVAS Y V. Asst. Prof. Dept. of AUTO. Engg. Ac.IT Page 15