TED (10)-4028 Reg. No. ..........................

(REVISION-2010) Signature. .......................

SIXTH SEMESTER DIPLOMA EXAMINATION IN MECHANICAL

ENGINEERING—MARCH,2013

ADVANCED PRODUCTION PROCESS

(Maximum marks : 100) [Time : 3 hours]

PART—A

(Maximum marks : 10)

I. Answer all qustions in one or two sentences. Each qustion carries two marks. 1. State four applications of automation.

Material handling. Machine loading application. Assembly of parts. Inspection purposes.

1. Define drawing operation.

Ans: Drawing is the process of producing hollow shapes such as cups and dishes from a flat sheet metal.

2. Differentiate thermo plastics and thermo setting plastics.

Ans: Thermo plastics:

They are formed by addition plymarisation.

Softening is possible on reheating.

Thermo setting plastics:

They are formed by condensation polymarisation.

Softaning is not possible on reheatening. 3. Name two natural Abrasives.

Ans: 1) Sand stone.

2)Corundum.

4. Nme two different types of conveyors.

Ans:

1) Belt conveyor system. 2) Linked conveyor system.

PART—B

(Maximum marks : 30)

II. Answer Any five qustions. Each qustion carries 6 marks. 1. Explain turret head indexing mechanism with the help of suitable

figure.

Ans:

Turret head indexing mechanism

The turret can be indexed along, with its to and fro motion. Mechanisam for automatic indexing of turret shown in figure.

The plunger locks the index plate by spring pressure and prevents rotary movement when the turret is moving forward. During this advance-ment the tool held in the turret performs its operation. Now indexing of turret is done during backward motion of the turret. At backward position of turret, the actuating cam lifts the plunger out of the groove and unlocks index plate. This is due to riding of the pin on the bevel surface of the cam. By this time, the spring loaded pawl engages with a groove of the ratchet plate causes the ratchet to rotate as the turret moves backward. When the index plate rotate through one sixth revolution, the pin and plunger drops out of the cam and plunger locks the index plate in the next groove. Thus the turret is indexed and locked in new position. The next tool is now fed forward and the pawl is released from the plate by the spring pressure.

2. Explain the principle of Gear hobing.

Ans:

Gear hobing:

Hobing is one of the most fascinating generating processes by using special cutter, called hob on a Gear hobing machine.

In gear hobing machine the hob is mounted on a spindle which is carried in the hob slide. Hob slide can be traversed vertically in either direction. The spindle head can be tilted about its axis and set at any desired angle for cutting helical gears.

The hob ratates and fed into the gear blank which is in rotation. The hob and blank are geared togather so that they are worm and worm wheel in mesh. The hob, in rotationfeeds across blank face and generates involute teeth form.

3. Enumarate the advantages and disadvantages of broaching.

Ans:

Advantages

Fast and simple process. High degree of accuracyand finishis possible. Any shape of profile can be easily machined. Machining process is completed with one stroke of broach. Life of broach tool is high. Cutting temperature and tool wear is low. Does not require a highly skilled operator.

Disadvantages:

Not economical for small quantity productions. Cost of broach is high. Tool grinding is difficult and expensive. Not suitable to machine a surface having obstruction. The work must be strong enough to withstand cutting forcess. Very high and delicate jobs cannot broached easily.

4. Interept the influence of grain size in grinding process.

Ans:

Grinding is probably the oldest surface processing method. It has been utilised since the early days of civilisation. In these early days, it was observed that some natural materials scratched the others and resulted in wear in these other materials when they were slid against each other under pressure. These hard materials used by mechanic action were called “abrasives” and parallel to the developments in technology, these abrasives and abrasive processes also developed.In grinding terminology, increasing grain number means decreasing grain size.

Grinding wheel grain size was found to have great influence on surface roughness and grinding force values. Increasing grinding wheel grain size increased the surface roughness values and the grinding forces.

At 0.04-0.05 mm depth of cuts, the surface quality (in terms of Ra) obtained by 80 grain wheel was better by 30%, 80% and 400% than those for 60, 46 and 36 grain wheels, respectively.

Grinding wheel grains were found to penetrate the ground surface at higher depth of cuts of 0.04, 0.05 and 0.06 mm when the grinding wheel of 80 grain was used.

At higher depth of cuts, some burns and cracks were observed on the ground surface by the naked eye for the grinding wheel of 80 grain.

Grooves, burns and waviness can be decreased if depth of cut is reduced when using grinding wheels with small grains.

5. Discuss about the metal spraying operation.

Ans: Metal spraying or metallising is used to furnish a protective coating on base metal. In this method the surfaceof metal is coated with finely divided particles of metals. For spraying, the surface is prepared and then the molten metal is sprayed on the work surface. The work surface is finished with suitable techniques. Mainly two methods are used for metal spraying, are,

Wire method. Powder method

Wire method:The coating material is in the form of wire. It is melted by means of oxy-acetylene flame.

The molten metal is fully atomised by using compressed air and atomised molten metal spray is projected on to a prepared work surface to form adherent coating.

Powder method: The coating metal is in the powder form and is fed from the container through a rubber hose to spray-gun. The powder spray method uses an oxyacetylene welding torch with modified tip which permits the powdered metals to be sprayed through the flame. A gas or compressed air convy the powder metal to the torch tip. Fuel gas can be acetylene or hydrogen.

6. Explain the different types of joints used in robots with the help of neat sketch.

Ans:

i. Linear joint(L-JOINT) :

Permit linear sliding motion between two links whose arms are parallel.

ii. Orthagonal joint (O-joint) :

Permit linear sliding motion between two links which are perpendicularto each other.

iii. Rotational joint (R-joint) :

Provide rotational relative motion of the joint, with the axis of rotation being parallal to the axis of the two links.

iv. Twisting joint (T-joint) :

Permits rotary motion between two links, the axis of rotation being parallel to the axes of the two links.

v. Revolving joint (V-joint) :

Provides rotary motion; the axis of the input link is parallal to the axis of rotation, and the axis of out put link is perpendicular to the axis of rotation.

7. How does flexibility is achieved in manufacturing system.

Ans:

The flexibility in the system can be achieved through job-flexibility and machine-flexibility.

Job-flexibility:

Job flexibility is the ability of the system to cope with the changes in the specification of jobs to be proceed by the system. It can be achieved by increasing the capabilities of machine by providing with more sophisticated controls. It can also be achieved at system level by distributing the required tasks among the work station which are specialised to perform such operations.

Machine-flexibility:

It is the ability of the system to cope with changes and disturbances at the machine and work centers. It is achieved by providing in-process inventories so that break down of one machine does not keep the other machine idle.

PART—C (Maximum marks : 60)

Answer one full qustion from each unit . Each qustion carries 15marks.

UNIT – 1

III. (a) Explain automatic cutting off machine with the help of simple sketch.

Ans:

Automatic cutting off machine

Automatic cutting off machines are designed to produce small parts from bar stock in mass production. They are primerly used for cutting, turning, and facing operation. Special operations such as form-turning, drilling, and threading can also be performed by using attachments.

The required length of stock is fed out with a cam mechanism upto stock stop and is held in collet chuck of the rotating spindle. Stock stop is automatically advanced in line with the spindle axis at the end of each cycle. The tools on the front cross-slide perform operations of turning or forming where as tools on rear cross slide perform the facing, chamfering and the cutting-off operation.

(b) Illustrate the construction and working of a turret lathe with the help of simple figure.

Ans:

Turret lathe

Turret lathe is a saddle type lathe in which hexagonal turret is mounted on a saddle which slides directly on the guide ways of the bed. It is of heavier construction with rigid design. These features makes ut nsuitable for long turning and boring operation. The saddle is moved by hand or power, and feed the tool to the work. The carriage of turret lathe does not extend across the entire bed and thus no rear tool post is on the cross-slide. This allows to accomodate larger work piece.

The main parts of turret lathe shown in figure.The maun parts of cturret lathe are, Bed, Head stock, Turret, Turret sadle, Crosslide and Carrage.

OR

IV. (a) Explain pantograph copying system with the help of necessory sketch.

Ans:

Pantograph copying system

The working of mechanical type copying machine is based upon the principle of the pantograph and is used to copy the form of an involute gear tooth space on to the grinding wheel of a gear tooth grinding machine. It will be noted that the follower, fulcrum and tracer must all lie on a stright line. Also the type of pantograph shown produces a reverse image of the template form on the wheel and hence template must be arranged accordingly. The pantograph ratio L1/L2 varies usually 5:1 to 10:1.

(b) Illustrate the tool layout sequence to manufacture a hexagonal bolt.

Ans:

Tooling layout of operation to be done for the manufacturer of hexagonal bolt is illustrated in below figure.

The sequence of operation to be done for the manufacture of hexagonal bolt by refering the figure, given below.

1) Hexagonal bar stock is used. In the turret faces, bar stop, box turning tool, end forming tool and self opening die head are mounted.

2) For each tool position, the length of travel of the turret is set by feed stop screws.

3) Chamfering tool is held in the front tool post and the parting of tool is held in the rear tool post.

4) Bar stop in the turret face brought to position. 5) The collet opens and the bar stock is pulled out by the bar feeding mechanism after

feeding the bar stop collet closes. 6) The turret goes back and is indexed. Box turning tool come to position. The turret

move towards headstock. The bar is turned down to 16mm diameter for the length of 50mm by the box turning tool.

7) The turret returns to the starting positionand is indexed.End forming tool comes into the position. The turret move forward. The end forming tool machines the bolt end.

8) The turret returns to starting position’s and is indexed. The self opening die head comes into position. The turret moves forward. The end forming thread is cut for 37mm length.The die opens out. The turret goes back the starting position.

9) The chamfering tool in the front slide moves forward and chamfering is done. 10) The front slide is withdrawn to orginal position. 11) The parting off tool post moves forward and cuts off the component. The cycle is

repeated.

UNIT – 11

V. (a) Illustrate the nomenclature of a pull broach with necessary sketch.

Ans:

Broaching tool is made upof a series of cutting edge, which are gradually increases in size along its length.The length of broach is depends on the amount of metal removal, length of stroke, amount of accuracy and the degree of finish.

Three types of teeth are provided on broach tool

Roughning teeth.

Semi-finished teeth, and

Finishing teeth.

The first roughning tooth is the smallest tooth on the broach. Rough teeth are designed to cut the heaviest metal. The next portion has semifinished teeth which are prograssively increase in size upto and including first finishing tooth. Finishing tooth are designed for lighter cuts, and last few finishing teeth are made of same size to attain high degree of accuracy and surface finish.In some broaches last few teeth edges are rounded for burnishing action.

(b) Describe the hole location procedure on a jig boring machine.

Ans:

The accuracy of a hole involves both size and location. For locating the position of a hole exactly on workpiece, the following methods may be used

1)Layout method 2)Transfer method

3)Button method. 4)Coordinate method

1. Layout method :

Layout method consist of drawing lines on a work piece, and marking the centers of hole with a punch. The drill is started in center punch mark. The layout of drilling a hole is shown in figure.

2. Transfer method :

The transfer method consist of drilling or reaming through a hole already exists in a mastar plate. The master plate is used as a jig and is clamped with the work piece. This method is employed in production work where the relative positions of hole location are known.

3. Button method :

The button method or buttoning is a common method of locating the position of hole. In this method tool makerbuttons are used. These are accurately sized hollow cylinders and are available in 7.5, 10, 12.5, 25mm in diameter and about 12.5mm height. Flat washers and machine screw are supplied with the set.

4. Coordinate method :

In this method the position of location is achieved by moving the work piece from a referance point through measured distance along perpendicular axes. Movements are commonly made through cross-slide screw or lead-screw and graduated dials.

OR VI. (a) Illustrate with the help of simple figure the shearing action in the die cutting

operation.

Ans:

Shear action in die cutting operation

In press working, the strip is positioned on the die, and the punch is moved down by the ram. The sharp edges of punch force the metal against the sharp edges of the die opening, and the

blank is sheared out clean it proper clearence is maintained between the cutting edges of punch and die. This shear action starts with slight plastic deformation of the metal as the punch first makes contact with the metal. The cracks will then generated between the edges of punch and die and further prograss with down ward motion of the punch, finallyresults in the seperation of the blank from the strip.

(b) Explain the principle of working of the compound die with the help of simple sketch.

Ans:

Compound die

In compound die two or more cutting operations are performed at single station in a single stroke of the ram. When the ram descends, the blanking and piercing operations are performed simultaniously. For blanking and piercing operation, the punch is used for piercing becomes a die, blanking is done in opposite direction to that of piercing as shown in figure. This die is very economical. It leads to savings in floor space and power, and the accuracy of the parts produced is higher.

UNIT – 111

VII. (a) Explain the different types of bonding processes in the manufacture of grinding wheel.

Ans:

Types of Bonds used in grinding wheels : The various bonds used in grinding wheels or bonded abrasives are Vitrified, Resinoid, Rubber, Silicate, Shellac, Magnesite and Metal bonds. Besides holding the grains together, these bonds also help in defining the type and character of the grinding wheel.

Vitrified (V) or ceramic bonds : These are made from clays, feldspar and other fusible materials in a carefully monitored process. Wheels which use this bond have a porous structure and are fired in kilns with

temperatures exceeding 1000o C. Vitrified wheels are unaffected by water, acids, oils or normal temperature variation. The porosity and strength of these wheels make them ideal for high stock removal operations. Added to this, vitrified bonded wheels have a high modulus of elasticity and this rigidity makes them suitable for precision grinding applications.

Resinoid or Organic (B) bonds : Resinoid or Organic bonds are made from phenolic type plastics or resins and cured in ovens under carefully controlled conditions of temperature ranging between 150oto 200o C. Resinoid wheels are tougher and less rigid than vitrified wheels and are ideally suited for high operating speeds and also for heavy duty operations, often with the aid of fabric or steel ring reinforcement. Their lower modulus of elasticity helps in achieving finer finishes. Unlike vitrified wheels, resinoid bonded wheels are affected by alkalis, humidity or extremes of climatic conditions and tend to deteriorate over a period of time.

Rubber (R) bonds : These are made of both natural and synthetic rubber in a varied range of formulations. Used mainly in centreless and control wheels, these are ideally suited for grinding operations that require a high degree of precision and fine surface finish. In wet grinding operations, thin cut-off wheels used to produce burr and burn free cuts are also made of rubber.

Silicate (S) bond : Releases abrasive grains rather readily and thus gives the wheels a comparatively mild and cool cutting action ideal for operations that require minimum heat and for sharpening edged tools.

Shellac (E) bonds : Denoted by the letter “E” these are made of both natural and synthetic shellac. Wheels made from these bonds have exceptionally cool cutting properties and are particularly suited for grinding very soft materials such as copper. Shellac bonded wheels are highly recommended for very special grinding applications that require high surface finish such as razor blade and roll grinding.

Magnesite (O) Bond : Magnesium Oxychloride denoted by the letter “O” is once again used in a very limited range of wheels. It is cool cutting even without a coolant and is greatly favoured in disc grinders. Being a cold setting bond this is also used for grinding heavy stocks like spring grinding, file grinding etc.

Metal Bonds : Compared to vitrified and organic bonds, the use of metal bonds is very limited. The major use of metal bonds is with diamond abrasive for grinding under harsh conditions. The metal bonded diamond wheel removes material slowly and frequently with high heat generation, but in many applications such as certain glass grinding, abrasive wheel shaping and concrete or stone sawing, the long life outweighs these disadvantages. Metal bonds are also used with aluminium oxide or diamond abrasive to provide conductive wheels for electrolytic grinding.

(b) Explain ultrasonic machining with the help of neat sketch.

Ans:

Ultrasonic machining

Ultra sonic machining remove the material in the form of chips, and has the advantage that it is suitable for conducting as well as non-conducting materials. Also it provides a method for machining hard and brittle material.

Principle: In ultrasonic machining metal removal is effected with the help of abbrasive grains which are made to impinge repeatedly upon the workpiece by a tool vibrating at ultra sonic freequency in the range of 15-30kHz. The abrasive grains are mixed with fluid to form slury and are carried to the gap between work piece and tool. The slury agaitated by the vibrating action of the tool causes the removal of work material by abrasive grains and produce the desired cavity in the work piece. During the machining process the tool is continusly fed forward at the rate consistant with the material removed from the work piece.The circulation of slurry also takes away the warm out grains.

OR

VIII. (a) What are the criteria for selecting a grinding wheel.

Ans:

When selecting a grinding wheel the following factors should be considerd.

1) Constant factors :

Material to be removed

Amount of material to be removed.

Wheel contact.

Type of grinding machine. 2) Variable factors :

Wheel speed.

Work speed.

Condition of the machine.

Skill of operator.

Material to be ground:

The softer grade wheels are required for grinding harder materials. Aluminium oxide wheels are used for grinding metals of high tensile strength and silicon carbide wheels for metals of low tensile strength.

Amount of material to be removed.

Course grains, open structure wheels are recomended for the rapid removal of the material where the surface finish is unimportanjt.

Wheel contact.

The greater the area of contact between the wheel and the work softer the wheel required.

Type of grinding machine.

The more rigid machine requires soft grinding wheel.

Wheel speed.

Harder wheels are recommented for grinding wheels which are running slowly with relation to work. It is advisable to run the wheel at the speed recomended by the manufacture.

Work speed

The harder wheels are used at the higher work speed with relation to the wheel speed.

Condition of the machine.

Machine with good condition requires the softer wheels. Machines with loose spindle or shaky foundation require the use of harder wheels.

(b) Enumerate the uses of powder compact components.

Ans:

Powder metallurgy techniques are used for making large nomber of components.

1. Self lubricating Bearing and Filters :

Porous bronze bearings are made by mixing copper and tin powder in correct proportions, cold pressed to the desired shape and then sintered. These bearings soak up considrable quantity of oil. Hence during service, these bearings produce a constant supplay of lubricant to the surface due to capillary action.

2. Friction Material :

Theae are made by powder metallurgy. Clutch liners and brake bands are the example of friction material.

3. Gears and Pump Rotors :

Gears and pump nrotors for automobile oil pumps are manufactured by powder metallurgy. Iron powder is mixed with graphite, Compacted under a pressure of 40kg/cm and sintered in an electric furnace with an atmosphere and hydrocarbon gas. These are impregnated with oil.

UNIT – 1V

IX. (a)State the application of robot.

Ans:

Material handling. Robort move the work piece from one locations to another.

Machine loading applications. Robort loads the machines with work piece and unloads the finished part.

Spray painting applications. Welding applications. Machining operations. Assembly of parts. Inspection purposes. Aotomotive and Air space industry.

(b) Explain flexible machining cell with the help of block diagram.

Ans:

Flexible machining cell

The flexible machining cell (FMC) has more than one machine tool with some form of pallet changing equipment, such as a robort or other specialised material handling device. The FMC generally has a fixed process, and parts flow sequentially between operations. The cell locks central computer control with real time routing, load balancing, and production scheduling logic.

The use of machining cells reduce the cycle time of the parts produced and subsequently minimise in-process inventory.

OR X. (a) Explain the constructional details of a robot with the help of simple

sketch.

Ans: Although industrial roborts may very widely, they are all made up of the following components,

1) Manipulator. 2) Controller. 3) Sensors. 4) End effector. 5) Power source.

These components may be assembled in one integral unit or separated into individual components connected by pneumatic, hydraulic or electrical umbilical cords.

1) Manipulator :

The manipulator is an assembly of axes capable of motion in various directions. The wrist located at the end of the robort armhas three degree of freedom. These degree of freedom are termed as pitch, yaw and roll. Besides these, the arm has three basic motions.

a. Shoulder swivel – allow vertical motion. b. Elbon extension - allows in / out motion. c. Arm sweap – provides rotational motion.

2) Controller :

The robort controller commands and manipulates the robort arm to perform desired tasks. The robort controller houses the computer system, the motor drive system and the integrated peripherals.

3) Sensors :

Sensors are feed back device that sence the measure the position and, in some cases, the velocity of the each of the various axes of motion and send this information to the control systems for use in coordinating the robort motion.

4) End effector :

The end effector is the end of arm tooling which is mounted on the face plate of the robot arm. End effectors are specially designed for special applications such as grippers, weld torch etc.

5) Power source :

The power supplay is the source of energy to move the regulate the robot’s drive mechanism. The power supplay may be electric hydraulic and pneumatic.

(b) State the advantages of NC and CNC machines over conventional machine tools.

Ans:

S.NO Conventional system NC system CNC system

1 It requires more manual works.

It requires less manual works.

It requires less manual works.

2 Skilled labour is needed. Less skill is enough. Less skill is enough.

3 Less accuracy is obtained More accuracy is obtained More accuracy is obtained

4 The system is less flexible. The system is medium flexible.

The system is more flexible.

5 Part programming is not required.

Part programming is used. Re-programming is easy.

6 Machining is done every time.

Programming and punched tape are read each time.

Only one time,the tap is read and storing is possible.

7 Simulation cannot be done. Simulation is also possible. Simulation is also possible.

8 It is more suitable for less production rate.

It is more suitable for medium production rate.

More suitable formass production rate.