new winter 18 examination subject name: advance … · 2019. 1. 28. · 2. extremely hard and...

MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous)

(ISO/IEC - 27001 - 2005 Certified)

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WINTER– 18 EXAMINATION Subject Name: Advance Manufacturing Process Model Answer Subject Code: ___________________________________________________________________________________

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17556 Important Instructions to examiners: 1) The answers should be examined by key words and not as word-to-word as given in the model answer scheme. 2) The model answer and the answer written by candidate may vary but the examiner may try to assess the understanding level of the candidate. 3) The language errors such as grammatical, spelling errors should not be given more importance. (Not applicable for subject English and Communication Skills) 4) While assessing figures, examiner may give credit for principal components indicated in the figure. The figures drawn by candidate and model answer may vary. The examiner may give credit for any equivalent figure drawn. 5) Credits may be given step wise for numerical problems. In some cases, the assumed constant values may vary and there may be some difference in the candidate’s answers and model answer. 6) In case of some questions credit may be given by judgment on part of examiner of relevant answer based on candidate’s understanding. 7) For programming language papers, credit may be given to any other program based on equivalent concept.



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17556 Q.

NO. MODEL ANSWER

MARK

S TOTAL MARKS

1 Attempt any Five 5X4 20

a) Advantages 1. Good Surface finish with accurate profile can be obtained. 2. Extremely hard and brittle material can be easily machine. 3. Conducting as well as non - conducting material can be machined. 4.Any complicated shape can be produced. Disadvantages:- 1. Its overall efficiency is extremely low 2. The process is limited to thin sheets 3. It has very low material removal rate 4. Cost is high

2m merit 2m

demerit

4m

b)

4m 4m

c) Boring machine is a device for enlarging a hole that has already

been drilled (or cast) by means of a single-point cutting tool (or of a boring

head containing several such tools), such as in boring a gun barrel or

an engine cylinder. Boring is used to achieve greater accuracy of the

diameter of a hole, and can be used to cut a tapered hole. Boring can be

viewed as the internal-diameter counterpart to turning, which cuts external

diameters. Boring machines come in a large variety of sizes and styles.

Boring operations on small workpieces can be carried out on a lathe while larger workpieces are machined on boring mills.

3m for exp 1 m for

diag

4m

https://en.wikipedia.org/wiki/Drill

https://en.wikipedia.org/wiki/Casting

https://en.wikipedia.org/wiki/Tool_bit

https://en.wikipedia.org/wiki/Gun_barrel

https://en.wikipedia.org/wiki/Cylinder_(engine)

https://en.wikipedia.org/wiki/Turning



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d) The axis identification in CNC machines are divided into two types.

(i) Linear axes: X, Y and Z axes are identified as linear axes (ii) Rotary axes: A, Band C axes are identified as rotary axes Z-axis: First the Z-axis is fixed for the machine tool. It is the main spindle axis. In a vertical milling machine, the vertical axis of the machine spindle is set as the Z axis. The positive Z-axis is taken in the direction that causes the cutting tool to move away from the work piece. (i.e. it increases the distance between the work piece and the tool. It means that movement of the cutter in upward direction is positive Z-axis. The movement of the tool in downward direction i.e. towards the work piece is set as negative Z-axis X-axis: It is always horizontal and parallel to the work piece holding surface. It indicates the longitudinal travel of the work table. Y-axis: It is perpendicular to both X and Z-axes. It is also horizontal and indicates the cross travel of the table A-axis: It is the axis of-rotary motion of a tool along -axis. Clockwise rotation is considered as positive movement looking in +X direction. B-axis: It is the axis of rotary motion of a tool along Y-axis. Clockwise rotation is considered as positive movement looking in +Y direction.

1m per

point

4m



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17556 C-axis: It is the axis of rotary motion of a tool along Z-axis. Clockwise rotation considered as positive movement looking in +Z direction.

e)

1m per

point

4m

f)

2m per

sketch

4m



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17556 T slot milling cutter

g) It increases the efficiency and speed of the equipment.

It helps to avoid the replacing of the parts of equipment before the scheduled time.

It reduces the cost when the work is done is faster and the machine dosent breakdown in the middle of the work schedule.

It is better because it saves from spending too much when the machine breaks down completely and requires big time repair.

1m per

point

4m

2 Attempt any four 4 x 4 16

a)

WJM process- As shown in figure, water from reservoir is pumped to the intensifier using a hydraulic pump. The intensifier accepts the water at low pressure and pressurizes it to around 400Mpa. Pressurized water is then sent to the accumulator. The accumulator stores the water during idle period and given out during cutting. Pressurized water then enters nozzle by passing through control valve and flow regulator. Control valve controls the direction of water and limits the pressure of water under permissible limits. Flow regulator regulates and controls the flow rate of water Water finally enters the nozzle , the jet steam coming out of nozzle strikes the workpiece and induces stresses. These stresses are used to cut the workpiece.

2m for

diag 2m for exp

4m



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17556 b) Process parameters:

1.Supply voltage: It is the voltage which is provided by the power supply system. It ranges from 50V to 400V DC supply. 2.Break down voltage: It is the voltage at which the dielectric breakdown. Increase in breakdown voltage results in increase of spark energy. 3. Resistance and Capacitance: Increase in capacitance will result in increase of metal removal rate. Decrease in resistance will result in increase of metal removal rate. 4. Spark plug setting: Decrease in spark gap results in lower metal removal rate. This results in better surface finish and high accuracy. 5.Pulse duration The pulse duration ranges from 2 to 2000microseconds. Decrease in pulse duration will result in high tool wear 6.Spark frequency: It is about 1000sparks/sec The increase in spark frequency results in improved surface finish.

1m per

point

4m

c) 1. To machine the exotic material those were difficult to machine by conventional machining process. 2. To fulfil the requirements of new age like innovative design, tighter tolerances, micromachining and economy. 3. To obtain intricate shapes. For example, a square blind hole of 15mm x 15mm x 30mm. 4. Overcome difficulty to machine the material. For example Inconel, Ti alloy, Carbide, Ceramics. 5. To fulfil the requirements of low stress grinding. (If done by conventional then it reduces productivity). 6. Drilling deep hole with small hole diameter (for example 15 mm diameter holes with length / diameter ratio of 20). 7. Machining of composites.

1m per

point

4m

d) G71 - Input in Metric G90 - Absolute Positioning G91 - Incremental Positioning G03 - Circular Interpolation CCW

1m per

point

4m

e) safety procedures in CNC Machines are:- 1. Always keep the area around the machine clear of obstacles. 2. Always stack material where you can reach it but where it is clear of the moving parts of the machine. 3. Always check that tools are sharp and set correctly. 4. Always check that the correct tool data is entered into the CNC program. 5. Always make sure that all guards are in position while the machine is in operation.

1m per

point

4m



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17556 6. Always make sure spindle direction is correct for right-hand or left-hand operation. 7. Always conduct a dry run to ensure the program is correct. 8. Do not use compressed air to blow chips from the parts of the machine, machine surfaces, cabinets, controls or floor around the machine.

f) Parts to be machined on broaching machine Bearing caps Bearing bodies Cylinder block Connecting rods Gears and turbines Keyways Splines (note: any other part that can be manufactured in broaching machine can be considered)

Im for per part

4m

3 Attempt any two 2 x 8 16

a) i AJM WJM

Abrasives are used for removing metal

Water is used as a tool to remove metals

More heat is produced as compared to WJM

Less heat is produced as compared to AJM

There is a possibility of abrasive particles getting embedded in the work material hence cleaning is necessary after every operation

Here cleaning process is not required after every operation

Can cut ductile materials as compared to WJM

Cannot cut ductile materials

1m per

point

8M a) ii EDM W EDM

A tool has a reverse profile of what has to be produced

A tool does not have a reverse profile of what has to be produced

EDM uses an electrode for cutting Wire EDM utilizes, as the name indicates, a wire to discharge the electric current sent into the electrically conductive metal workpiece

Here the tool is not required to be kept in tension

The wire ( tool) has always to be kept in tension

Very Small holes cannot be produced as compared to WEDM

Very small holes can be produced

1m per

point

b

12345 N110 G90 G21 G94 G40 EOB N120 M06 TO1 EOB N130 M03 S800 EOB

8M 8M



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N140 G00 Z5 M08 EOB N150 G00 X-2 Y-10 EOB N160 G01 Z-5 F120 EOB N170 Y-2 EOB N180 X-2 Y102 EOB N190 X75 Y102 EOB N200 G02 X95 Y80 I0 J-20 F90 EOB N210 G01 X95 Y-2 F120 EOB N220 X53 Y-2 EOB N230 X53 Y28 EOB N240 X27 Y28 EOB N250 X27 Y-2 EOB N260 X-2 Y-2 EOB N270 G00 Z5 EOB N280 G28 EOB N290 M05 EOB N300 M09 EOB N310 M30 EOB

c) Various parts of a horizontal broaching machine are: 1) Power Head:- it provides arrangement for getting required power to run the system. 2) Machine bed:- it is support to all machine members. It also absorb shock and vibrations as it is made of cast iron. It is used to carry and support other accessories of machine. Bed is the robust casting on which the main units are

mounted. The construction of bed is such so that it can bear the

load/pressure exerted during the operation. 3) Tool holder:- it is a device to hold the tool correctly in position in order to maintain precision and accuracy in all machined work piece. 4) Supporting table:- it gives enough support to the wqork piece. It provides stability to the work piece during operation. It is used for mounting of fixture and workpiece. 5. Broach: It is a multipoint cutting tool used for machining purpose (external and internal) . A broach is a multiple-edged tool that has successively higher cutting edges along the length of the tool.

6. Pulling head: It holds broach and required for pulling purpose for machining. It supports the front end of ram.

7. Tool support: It is used to support other side of broach. Advantages:- 1. The process can be done for both internal and external machining. 2. It is simple operation, hence does not required highly skilled operator. 3. As loading and unloading is rapid, the rate of production is high. 4. As both rough and finishing can be done in one pass, so broaching is fast operation.

2m per part

2m per

merit

2m for

demerit

8m



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17556 5. Broaching is faster than any other machining operation. 6. High accuracy and high surface finish can be obtained. 7. The cutting force of the broach serves to clamp the work piece and hold it firmly in position. 8. Any form that can be produced on a broaching tool can be produced by the tool. Limitiations:- 1. It is a single purpose tool.Tool cost is very high, so the process is justified only for mass production. 2. In some cases, it is not suitable for low production rates. 3. The parts to be broached must be strong enough t o withstand high cutting forces. 4. Surface to be broached must be acessble. 5. Blind hole can not be easily produced. 6. Tool sharpening is difficult and expensive process.

4 Attempt any four 4 x 4 16

a) M04 Spindle Start (Counter Clockwise)

M08 Coolant ON

M18 Air blast off

M39 Door closekk

1m per

code

4m

b) Straddle Milling:- The straddled is the operation of production of vertical flat surface on both side of workpiece by using two side milling cutter mounted on same arbour. The distance between the two cutters is correctly adjusted by using suitable spacing collars. The straddle milling is very commonly used to produce square or hexagonal surface. When cutting a hexagonal head of a bolt, two opposite sides of the head are cut, then the spindle of the indexing fixture or the swivel vice is rotated 60° and other two sides of the work piece are straddle milled, then the spindle is again rotated 60° and remaining two sides of the work piece are straddle milled

3m for exp

and 1 m for sketch

4m



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17556 c)

4m 4m

d) W- Manufacture’s Prefix A -Type of Abrasive (Aluminium Oxide) 46- Grain Size (medium) K- Grade (Medium) 5- Wheel Structure (Dense) V – vitrified Bond B Resinoid bond E Manufacture’s Symbol.

½ m per

point

4m

e) BALANCING OF GRINDING WHEEL: In order to obtain a good surface finish, prevent-vibration and chatter and undue wear of machine parts, it is necessary that grinding wheel has good balance.Thus, the grinding wheel should be properly tested for balance before use. If the wheel becomes out of balance through wear it should be balanced by removing from the machine.The wheel should be trued before balancing. Balancing can be done by three ways:

By filling the lead: Small wheels may be balanced by milling a short recession the inside of the lange and filling it with lead.

By stucking weights: The wheel is mounted at the centre of a perfectly

1m for

diag 3m for exp

4m



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17556 straight and round spindle, the assembly is them rested on a knowledge balancing stand. Any out of balance will result in the wheel coming to test with the heavy side underneath. Correct weight can be then struck on the opposite side to balance the wheel

By using a recessed flanged: The wheel inbalance is tested as in above methods. A recersed flange is used and the weights can be moved over it along the recess to balance the large wheels.

5 Attempt any two 2 x 8 16

a)

4m for

sketch 4m for exp

8



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17556 Bed: A fixed bed is considered as the baase of the machine Table: A table is mounted on the bed. The table has longitudinal movement only. Cross rail: A cross rail is fitted on the column. It may be lowered or raised to suit the height of the workpiece Tool head: Two vertical tool head are fitted on the cross-rail which can move towards each other. Two horizontal tool head are mounted on the column which can move vertical over it.

b) 1. Gear Shaving Process: Gear shaving process can be linear or rotary. In the linear type rack type cutter is used. While rotarymethod employs a pinion cutter. The cutter teeth are serrated to form a series of cutting edges. Toobtained relative sliding action between the tooth profile the work gear and shaving cutter are set up in thegear shavingmachine with cross axes. Due to the sliding action very small amount of material from thegear tooth is removed and finished profile surface is obtained.

2. Gear Grinding: It is a finishing process to remove considerable amount of the metal after heat treatment to obtain predetermined quality gear. There are three general methods of gear grinding Form wheel grinding,Generation grinding ,Threaded wheel grinding .The grinding wheel is dressed to the form that is exactly required on the gear. Need of indexing makes the process slow and less accurate. The wheel or dressing has to be changed with change in module, pressure angle and even number of teeth. Form grinding may be used for finishing straight or single helical spur gears, straight toothed bevel gears as well as worm and worm wheels.

2m diag 2m exp

2m diag 2m exp

8



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c) List of milling operations

Plain milling operation Face milling operation Side milling operation Straddle milling operation Angular milling operation Gang milling operation Form milling operation Profile milling operation End milling operation

Gang Milling:- The gang milling is the operation of machining several surface of a workpiece simultaneously by feeding the table against a number of cutters having same or different diameters mounted on the machine. The distance between the two cutters is adjusted by placing spacer in between them. The method save machining time and widely used in repetitive work.

4m for

enlist 1m diag 3m exp

8m



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17556 6 Attempt any four 4 x 4 16

a) Explain honing process. Honning is abrading process used mainly for finishing round holes by means of bonded abrasive stone called hones. Honning is primary used to correct out of roundness, taper, toll marks and axial distortion. Mostly Honning is done on internal cylindrical surfaces such as automobile cylinder walls. The Honning tool consists of cylindrical body having 6 or 8 abrasive stick which is made up of common abrasive and bonding material. The sticks are equally spaced about the periphery of the honing tool. They are held against the work surface with controlled light pressure, usually exercised by small springs. The commonly used abrasives are silicon carbide and aluminium oxide having grit size of 80 to 600. Coolants are essential for the operation, to flush away small chips and to keep the temperature uniform. Honing is cutting operation and has been used to remove as much as 3mm of stock. When the honing is done manually the tool is rotated and the work piece is passed back and forthover the tool. For precision honing the tool is given a slow reciprocating motion as it rotates.

3m exp 1m diag

4m

b) Polishing Lapping

Polishing produce a shiny surface Lapping does not produce bright shiny surface

Polishing removes negligible amount of metal

Lapping removes metal from the surface to be finished

Polishing consist of producing a kind of plastic flow of the surface crystal so that the high spots are made to fill the low spot.

Lapping involves cutting action

2m per

point

4m

c) There are two major selection criterias for choosing a grinding wheel are 1 Constant Factors

a) Workpiece material b) Amount of stock to be removed c) Area of contact d) Type of grinding machine used

2 Variable Factors a) Wheel speed b) Work speed c) Condition and capacity of machine

2m per

point

4m



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17556 d) Personal factor

d) Importance of maintenance record Prevent expensive repair works from happening Helps you create specialised maintenance programs It increases the safety of operators Necessity To minimize the number of breakdown To keep plant in good working condition To carry out the work of all machines smoothly To improve quality of products and improve productivity Minimize accidents

2m for

importance

2m for

Necessity

4m

e) Explain maintenance procedure for Machine Belts:- a. Keep the belt groove clean and in good condition. b. Check the alignment of belt drive before it is put to use. c. Preserve the belt from conditions injurious to rubber. d. Never use idler pulley on the top side of a V-belt. e. The belt should not be too tight or loose it will wear quickly.

1m per

point

4m

f) 1.Main spindle- Cause Improper Lubrication. Miss handling. Remedies- Proper lubrication of spindle parts will increase overall efficiency and life of spindle.periodic examination is required.Handling should be done only skilled operator 2.Head stock Cause: wear and tear in gear ,improper lubrication,poor foundation,wrong fuel used over loading of machine,lack of knowledge,excessive friction,indifferent attitude towards minor fault,Corrosion of parts

Remedies Lubricate regularly, periodically checking and parts should be replaced if required, overloading should be avoided,Operators should be trained, 3. Feed box Causes improper lubrication excessive friction indifferent attitude towards minor fault.

1m per part

4m



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17556 Corrosion of some parts Remedies. Checking regularyly, Operators should be trained to handle 4. Saddle Causes poor foundation ,excessive friction, indifferent attitude towards minor fault. Improper installation,Corrosion,improper handling by the operator Remedies Checking properly,Lubrication should be done regurlarly,

new winter 18 examination subject name: advance … · 2019. 1. 28. · 2. extremely hard and...

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