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

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

SIXTH SEMESTER DIPLOMA EXAMINATION IN MECHANICAL

ENGINEERING—OCTOBER,2014

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. List any three work holding devices used on turret and capstan lathes.

Ans:

Collets . Chucks. Fixtures. 2. Define the term automation.

Ans:

Automation or automatic control, is the use of various control systems for operating

equipment such as machinery, processes in factories, boilers and heat treating ovens,

switching in telephone networks, steering and stabilization of ships, aircraft and other

applications with minimal or reduced human intervention. Some processes have been

completely automated.

3. What do you mean by broaching process.

Ans:

Broaching is the fastest machining process by using a special tool (broach) made up of a series of cutting edjes which are gradually increase in size.It is best suited for mas production, and can be produce accurate plane or formed shapes on internal or external surfaces.

4. List any artficial abrasives extensively used.

Ans:

Silicon carbide (SiC). Aluminium oxide (Al2O3). Boron carbide. Cubic carbon nitride. And Manufactured diamond. 5. What is tranfer-line automation.

Ans:

A transfer line is a manufacturing system which consists of a predetermined

sequence of machines connected by an automated material handling system and designed

for working on a very small family of parts. Parts can be moved singularly because there’s

no need for batching when carrying parts between process stations (as opposed to a job

shop for example). The line can synchronous, meaning that all parts advance with the same

speed, or asynchronous, meaning buffers exist between stations where parts wait to be

processed. Not all transfer lines must geometrically be straight lines, for example circular

solutions have been developed which make use rotary tables, however using buffers

becomes almost impossible.

PART—B

(Maximum marks : 30)

II. Answer Any five qustions. Each qustion carries 6 marks. 1. Draw a block diagram of capstan lathe and mark the important parts.

Ans:

2. Explain the principle of gear hobing with a neat sketch.

Ans:

Gear hobing

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

The principle of a gear hobbing as shown in figure. The hob rotates and fed into the gear blank which is in rotation. The hob and blank are geared togather so that they rotate in a correct relation ship as if theyare worm and worm-wheel in mesh. The hob, in rotation, feeds across blank face and generates involute teeth form.

3. List the advantages and disadvantages of jigs and fixtures.

Ans:

The main purpose of jigs and fixtures is to provide proper location and clamping of the job. In addition, jigs also facilitate to guide the tool. The advantages of jigs and fixtures are.

Reduse the operation time, and increase the productivity. Facilitates uniform quality and ensures interchangeability of component. Unskilled operators can do the job; thus, saving in labour cost. Ensure higher accuracy and surface quality, and Reduce the overall cost of production.

The only disadvantage is that jig and fixtures are costly devices and the cost of manufacture increases. But the cost may be offset by produsing a large nomber of components.

4. Describe the principle of cylindrical grinding with a neat sketch.

Ans:

In cylindrical grinders the work is mounted between the centers and rotated against the grinding wheel. The work may also be held in a chuck for certain operations.

The plain cylindrical grinding machine shown in figure. It has the following parts,

1. Bed or Base 2. Table 3. Headstock 4. Tailstock or Foot stock 5. Wheel head

Base:

The base or bed rests on the floor. The top of the base is machined accurately to form ways for the table. It also houses the table drive mechanism.

Table:

The lower table mounted on the ways of the bed. It provides traverse motion to the work past the grinding wheel. It can be operated manualy.

Upper table:

It is mounted on lower table and can be swivelled for grinding tapers and alignment purposes. The head stock and tail stock are mounted on this table.

Head stock:

Head stock supports and drive the work piece with the help of centre and dog or chuck

Tailstock:

Tailstock or foot stock is mounted on the right end of the table. It can be adjusted along the length of the bed to support the right end of the work.

Wheel head:

Wheel head is mounted on a cross-slide at right angle to the table, providing the in-feed movement of the wheel to the work.

Acylindrical centre type grinding machine is specified by the maximum diameter

and the length of the workpiece that can be accomodated between the centers.

5. With the help of a neat sketch explaine the principle of anodizing process.

Ans:

Anodising

Anodising is the process of produsing oxide film on aluminium bars. It is used on aluminium both for decorration and for protection of the base metal. The articles to be anodised are first cleaned properly. The film is produced by Electro-chemical reaction. The aluminium work work piece is made anode, and cathode is made of either lead or graphite. For anodising, sulphuric acid is mostly used as electrolyte and the process may be carried with AC or DC. DC is generally employed as it generates a coating that has deeper penetration. As current is passed through electrolyte, oxygen is liberated at the surface of the work piece and immediately combines with it to form the oxide film. The thickness of the oxide film increases with the current density and with lowering of the temperature of the solution.

At an optimum temperature of 3°c, a very hard film of about 0.15mm thickness is prodused. Above, 30°c no anodising will take place because sulphuric acid will dissolve the oxide as soon as it is produced. At 20°c, an oxide film of 0.01 mm thickness is produced.

6. List the advantages of powder metallurgy.

Ans:

Advantages of powder metallurgy

Although the cost of making powder is no loss of material. The components

produced are clean, bright and ready for use.

Components can be produced with good surface finish and close tolerance.

High production rate.

Complex shapes can be produced.

Wide range of properties such as density, porosity and particle size can be obtained

for particular applications.

There is usually no need for subsequent machining or finishing operations.

This process fecilities mixing of both metallic and nonmetallic powders to give

products of special characteristics.

7. List any six advantages of NC machines.

Ans:

Advantages of NC machines.

NC machines are capable of uninterrupted machining, and does not stop at the end of the cut to plan its next move.

Complex contour shapes can be machined economically. Produce parts with high accuracy and close tolerance without taking any special

precautions. Required less operator skills. Expensive jigs and fixture are not required. Uniformity in duplicating is assured. Programmed tapes can be stored and reused whenever a repeat order is received. Human errors are eliminated and there fore, inspection cost is reduced.

PART—C

(Maximum marks : 60)

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

UNIT – I III. (a) List any five difference between Turret lathe and Capstan lathe.

(b) Explain the working of automatic screw cutting machine with a line sketch.

Ans:

Automatic screw cutting machine

In automatic screw machine the head stock is movable and the tool are fixed in the slides. These machines are employed for mass production of long accurate parts of small diameter bar stock. These machines are chiefly used in the precision industries for manufacture of watches, instruments, radio parts etc.

The swiss type automatic screw machine as shown in figure.

The stock held by a rotating collet in the head stock and is fed through a hard bushing in the centre of the tool head. Five single point tools are placed radialy on the tool head around the bushing. Tools on horizontal slide performs plane turning while other tools on three slides are used for knurling, chamfering, recessing and cutting-off operations. These tools are controlled by cams that brings the tools in as required for different operations. The special operations such as centering, drilling, and reaming are performed by auxiliary slide.

OR

IV. (a) What do you mean by a machining centre? Explain.

Ans: The term “machining centre” describes almost any CNC milling and drilling machine that includes an automatic tool changer and a table that clamps the work piece in place. On a machining centre, the tool rotates, but the work does not. The orientation of the spindle is the most fundamental defining characteristic of a machining centre. Vertical machining centres generally favour precision while horizontal machining centres generally favour production—but these are loose generalizations, and plenty of machining centres break out of them. Another common machining centre type is the five-axis machining centre, which is able to pivot the tool and/or the part in order to mill and drill at various orientations

(b) Explain the bar feeding mechanism of a turret lathe.

Ans:

Bar feeding mechanism of a turret lathe

Bar work in turret lathes can be processed conveniently by incorporating bar-feed mechanism. The purpose of this mechanism is to fed the bar forward through spindle into the bar stop when the collet chuck open after completing the first piece. Bar may be fed by hand, but one has to stop the machine for feeding the bar and it also wastes a lot of time.

Various types of bar feeding mechanism have been designed to fed the bar immediately when the collet opens without stopping the machine.

The bar is passed through the bar chuck, lathe spindle and then through the collet chuck. The bar chuck rotates in a sliding bracket which is mounted on long sliding bar. The weight attached to chain exerts thrust all the time on bar chuck which is holding the bar by means of two sets screws and forces the bar through the spindle when the collet chuck is released. Thus the bar feeding mechanism facilitate to feed the bar without stopping the machine.

UNIT – II

V. (a) List five advantages 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.

(b) Explain the working of a Horizontal Broaching machine with a neat sketch.

Ans:

Horizontal Broaching machine

The horizontal broaching machine is used for surface broaching or internal broaching, the later being most common. The work is held in fixture. In the surface broaching the tool is pulled over the surface while for internal broaching the broach is pulled through the work. These machines are mostly pull type and can be operated at a cutting speed of 3 to 15 m/min. Hydraulic horizontal machine hasan infinitly variable range of cutting speed with return speed much greater.The broach is pulled over the top

surface of the work piece held in fixture. The hydraulic cylinder which pulls the broach is housedin the right end of the machine.

OR

VI. (a) List the difference between jigs and fixtures.

Ans:

Jigs Fixtures

Hold the work piece in position and guide the cutting tool.

Hold the work piece in position, but not guide the cutting tool.

Usually movable on machine table. Clamped in a fixed position on machine table.

Used for drilling, reaming tapping and counter boring

Used for milling, turning, grinding, welding etc.

.Lighter in construction. Heavy in construction.

(b) Briefly explain the working of any two types of drill jigs with simple line sketch.

Ans:

Template jig:

Template is a simplejig and may be used when making plain holes. It consists holes to guides the tool and is used directly over the component.

Channel jig:

The body of channel jig is in the form of standard channel. The component is located in a channel and is clamped by screw. It is used for drilling simple symmetrical shapes.

UNIT – III

VII. (a) What are the factors affecting the selection of grinding wheels.

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) Briefly describe the principle and process of Ultrasonic Machining.

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 do you mean by Chemical Milling.

Ans:

Chemical Milling

Chemical milling (CHM) involves removing the workpiece materials by chemicals. The process details are discussed below.

In chemical milling the part to be machined is immersed in a chemical etchant that removes the desired metal.

In chemical milling the work piece is first thoroughly cleaned. All oil and grease must be completely removed and dried. Portions which are not to be machined are coated or covered with a materials resistant to the chemicals. These chemical resistant materials are called maskants and include materials like vinyl plastics and neoprene rubber with a resin base. After maskant coating is cured, the maskant is cut and stripped off over the portions to be machined with the help of a scribing knife and a template.

The work piece is then dipped completely into a tank containing chemical etchant. This etchant attack exposed surface and dissolve away the metal. After removing the material to a required depth, the workpiece is removed from the bath, demasked and cleaned throughly.

(b) Briefly describe the principle of EDM and explain the working of EDM with simple sketch.

Ans:

Electrical discharge machining

Electrical discharge machining is also known as spark erosion. With this process soft or extremely hard workpieces such as tungsten carbides can be machined. The working principle described below.

Principle :

In this process the metal is removed by intense heat of electric spark. The tool and the work piece are submerged in dielectric fluid. The spark discharges are created by maintaining sufficient potential difference between tool and work piece, seperated by a dielectric in a very small gap. A large nomber of electrons emitted from tool impinges on work material and thus develop a very high temperature. This temperature is sufficient to melt and even vaporise a part of the metal. In this way metal is removed from the workpiece.

UNIT – IV

IX. (a) What do you mean by artificial intelligence.

Ans:

Artificial intelligence uses symbolic processing, knowldge base and special engineering techniques. It fecilitates easy description of various complex relations among various symbolic objects.

AI techniques deal with models. AI models are constructive ones and can solve real problems automatically.

(b) Describe the various types of joints used in robots.

Ans:

A joint permit the relative motion between two links or arms of robot. Various types of mechanical joints are,

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 jint (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.

OR

X. (a) Discuss the advantages of CNC machine.

Ans:

Advantages of CNC machine

CNC are more flexible, and possess storage facilities. CNC machines are faster thanNC machines.The other advantages of CNC are,

Suitable for small batch quantities as well as for complex jobs with multiple operations.

Reduction in time for launching a new product by redusing jigs, fixtures and special toolings.

Requires less inspection and production of better quality products. Editing of programms at floor level is very conveniently done.

(b) Briefly describe the basic elements of a NC machines.

Ans:

Elements of numerical control machine tools

The main elements of a NC machine tool are shown in figure.

1. The control unit (NC Console or Director)

2. The drive unit.

3. Magnetic box.

4. The position feedback package.

5. Manual control, and

6. Machine tool.

The instructions written for manufacturing the components are undergo electronic

processing and the control unit sends command signals to the drive unit and magnetic box

which is electrically controlled.

The command signals sent to drive unit through servomotor control the length of

travel and feed rate, while the command signals to magnetic box controls the function such

as starting or stopping of motor, selecting spindle speed, actuation of tool changes, coolant

supply etc.

The position feedback package sends the information about the actual position

achieved to the control unit. If there is any difference between the position desired and the

actual position achieved, the drive unit is actuated by suitable amplifier from the error

signal.

Manual control helps the operator to perform some function such as motor star-stop, coolant supply control, axes movements, speed change, feed change etc.