jntu anan 3 2 me cadcam set 1

S.1CAD/CAM (April/May-2012, Set-1) JNTU-Anantapur

B.Tech. III-Year II-Sem. ( JNTU-Anantapur )

Code No: 9A03602/R09

III B.Tech. II Semester Regular Examinations

April/May - 2012

CAD/CAM( Mechanical Engineering )

Time: 3 Hours Max. Marks: 70

Answer any FIVE Questions

All Questions carry equal marks

- - -

1. What is product cycle? Explain it with reference to a CAD/CAM application. (Unit-I, Topic No. 1.2)

2. What are the various co-ordinate systems used in computer graphics? Explain their significance.

(Unit-II, Topic No. 2.1)

3. Explain various curve representation methods used for geometric modeling. (Unit-III, Topic No. 3.2)

4. What are NC elements? Explain the features of NC machining center. (Unit-IV, Topic No. 4.1)

5. What is FMS? Discuss various components of FMS in detail. (Unit-VI, Topic No. 6.1)

6. What do you understand by MRP-I? Explain. (Unit-VII, Topic No. 7.2)

7. What is a part family? Explain various methods of part family formation. (Unit-V, Topic No. 5.1)

8. What is quality control? Explain various contact inspection methods. (Unit-VIII, Topic No. 8.1)

S e t - 1S o l u t i o n s

S.2 Spectrum ALL-IN-ONE Journal for Engineering Students, 2013


SOLUTIONS TO APRIL/MAY-2012, SET-1, QP

Q1. What is product cycle? Explain it withreference to a CAD/CAM application.

Answer : April/May-12, Set-1, Q1

For answer refer Unit-I, Q7.

Q2. What are the various co-ordinate systemsused in computer graphics? Explain theirsignificance.


Co-ordinate Systems

The co-ordinate systems used in computer graphicsare as follows,

(i) World Co-ordinate System (WCS)

(ii) User Co-ordinate System (UCS)

(iii) Screen Co-ordinate System (SCS).

(i) World Co-ordinate System (WCS)

The WCS is the reference space of the model withrespect to which all the inputs of geometrical data is stored.It is an actual coordinate systems used directly as a masterfor the component. Thus, it is also called as model coordinatesystem.

The WCS is used when there is a difficulty inidentifying the desired plane (face). As shown in figure, theWCS is associated with three non-collinear points. The firstindicates the origin and second indicates X-axis. The thirdpoint indicates the xy plane of WCS. The cross product oftwo unit vectors i.e., first and second point (X-axis) and firstand third point determines the Z-axis.

x

y

x

y

Figure: Top View

y

x

z y

x

z

Figure: Isometric View

z

x

z

x

Figure: Front View

z

y

z

y

Figure: Right Side View

Significance

It is an only coordinate system in which softwareidentifies the storing or retrieving geometrical datainformation.

(ii) User Co-ordinate System (UCS)

If the complex geometry is to be modelled with respectto an auxiliary coordinate system instead of WCS. Then, it istermed as user coordinate systems.

As shown in figure, if x', y', z' is user coordinate systemused for modelling the slot. The other UCS also can bedefined depending upon the geometry. Thus, this alternatecoordinate system reduces the modelling complexity.



x

yz

z'

y'

x'

x

yz

z'

y'

x'

Figure: User Coordinate System

Significance

The user coordinate system are oftenly used since itcan be positioned at any position with the orientation ofaxes as per the user needs.

(iii) Screen Coordinate System (SCS)

Graphics packages require the coordinate parametersto be specified with respect to Cartesian reference frames.There are two different types of Cartesian screen referencesystem with respect to its orientation. They are,

(a) Coordinate origin at the lower left screen corner

(b) Coordinate origin at the upper left screen corner.

(a) Coordinate Origin at the Lower Left Screen Corner

The standard coordinate orientation is as shown infigure (1), with the coordinate origin in the lower left cornerof the screen. It is most commonly used reference frame.Raster scan starts from the bottom left corner of the screen,sweeps horizontally across and steps from bottom to topuntil it reaches the top left corner i.e.,

(i) The origin is at the bottom left of the screen.

(ii) The positive direction of the vertical axis willpoints upwards.

(iii) The row is fixed first and the column increaseswithin that row.

y

x

y

x

y

x

y

x

Figure (1) Figure (2)

(b) Coordinate Origin at the Upper Left Screen Corner

Some systems particularly personal computers orientthe Cartesian reference frame as shown in figure (2), with theorigin at the upper left corner. In addition, it is possible insome graphics package to select a position such as centerof the screen for the coordinate origin. For convenience ofinternal processing, the origin at the top left corner isdesignated as follows,

(i) In text mode, as there is no zeroth row or zerothcolumn, the origin is (1, 1)

(ii) In graphic mode, the left most top most pixel isdesignated (0, 0).

The computer counts from left to right horizontally, itcounts from top to bottom vertically. The numbering systemdiffers between character graphics and pixel graphics.

Q3. Explain various curve representationmethods used for geometric modeling.


For answer refer Unit-III, Q14.

Q4. What are NC elements? Explain the featuresof NC machining center.


For answer refer Unit-IV, Q1, Q17.

Q5. What is FMS? Discuss various componentsof FMS in detail.


Flexible Manufacturing System

For answer refer Unit-VI, Q7.

Components of FMS

The various components of FMS equipment are asfollows,

1. Work stations

2. Automated material handling and storage system.

3. Computer control system.

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1. Work Stations

Now-a-days, the workstations are operated by CNCmachine tool to achieve greater efficiency in the field ofproduction. The various workstations,

(i) Machining centers

(ii) Load and unload stations

(iii) Assembly work stations

(iv) Inspection stations

(v) Forging stations

(vi) Sheet metal processing etc.

2. Automated Material Handling and Storage System

Material handling and storage system are veryimportant for the system flexibility. Material handling systemsare used to transport work parts between the two processingstations.

The function of automated material handling andstorage system are as follows,

(i) Transfer of workparts between workstations

(ii) Handling of workparts

(iii) Temporary storage

(iv) Loading and unloading of workparts

(v) Compatible with computer control.

3. Computer Control System

For answer refer Unit-VI, Q8, Topic: Function of FMSComputer Control System.

Q6. What do you understand by MRP-I? Explain.


For answer refer Unit-VII, Q10, Q8.

Q7. What is a part family? Explain variousmethods of part family formation.


Part Family

For answer refer Unit-V, Q5.

Methods of Part Family Formation

There are generally three methods for grouping andall the three methods are time consuming and involve analysisof much data by properly trained personnel. The threemethods are,

(i) Visual inspection

(ii) Production Flow Analysis (PFA)

(iii) Parts classification and coding system.

(i) Visual Inspection

This method is the least sophisticated and leastexpensive method. It involves the classification of parts intofamilies by looking at either the physical parts or photographsand arranging them into similar groups. This method is generallyconsidered to be the least accurate of the three.

(ii) Production Flow Analysis (PFA)

This method is the method of identifying part familiesand associated machine tool groupings by analyzing theroutes sheets for parts produced in a given shop. Thedisadvantage of production flow analysis (PFA) is that itaccepts the validity of existing route sheets, with number ofconsideration given, to whether these process plans arelogical or consistent.

(iii) Parts Classification and Coding System

This method is the most time consuming andcomplicated of the three methods. However, it is the mostfrequently applied method and is generally recognized to bethe most powerful of the three methods.

Q8. What is quality control? Explain variouscontact inspection methods.


Quality Control

For answer refer Unit-VIII, Q1.

Contact Inspection Methods

Contact type inspection methods are classified intotwo types. They are,

1. Coordinate measuring machines

2. Mechanical probes or profilometer.

1. Coordinate Measuring Machines

For answer refer Unit-VIII, Q10.

2. Mechanical Probes or Profilometer

Profilometer is an instrument used to inspect variouscomponents during inspection process.

Construction

It consists of a mechanical probe/stylus, magneticcoil, galvanometer and amplifier. Mechanical probe knownas tracer has a diamond shaped pointed tip of radius 12microns and it is suspended on a spring. A magnetic coil islocated in the magnetic field and is linked to the upper por-tion of tracer. Amplifier is used to amplify the current pro-duced by the coil in magnetic field. The pressure of thetracer point on surface is from 0.5 to 2.5 gms. Galvanometershows the readings as the tracer is moved over the surfaceof workpiece.



��

��

Springs

��

Probe or stylus

Surface to be tested

Induction coil

Magnet

��

��

Springs

��

Probe or stylus

Surface to be tested

Induction coil

Magnet

Figure: Profilometer

WorkingInitially the tracer is moved over the surface of workpiece. As the tracer moves, the irregularities present over

workpiece surface cause the tracer to vibrate. The vibration of tracer is transmitted to the coil, which is responsible to inducecurrent. The current induced is amplified and measured using galvanometer. But, if the surface is uniform, the galvanometershows steady readings without any deflection. Hence, the surface roughness of workpiece may be checked or measured

directly by tracing the mechanical probe on the workpiece.

jntu anan 3 2 me cadcam set 1

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