2011 test07 endsem with answers

8/12/2019 2011 Test07 EndSem With Answers

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8. Which solid representation is suitable to represent gradient objects?

Spatial Decomposition. Specific representations like voxel, octree etc. are also correctanswers.

9. Distinguish between Geometric Modeling and Reverse Engineering .

Geometric Modeling creates the object from scratch whereas Reverse Engineering createsthe Geometric Model of the physical object (through digitizing) . The ultimate goal in bothis the creation of the geometric model, i.e., virtual object.

10. Distinguish between an Expert System and an Expert System Shell .

Expert System Shell is the frame work or package that consists of the facilities to add theknowledge base (in the form of predicate logic), input of data (say, the symptoms) andsearch engine to output the results (say, diagnosis and prescription). nExpert was a

popular Expert System Shell. An expert System is an Expert System Shell along with theknowledge base for a given domain. Mycin was a popular Expert System used fordiagnosis of diseases.

Give full weightage even for expert System = Expert System Shell + knowledge base

11. Distinguish between a surface model and B-Rep.

No point is duplicated. This results in proper stitching or water tight model; i.e., nooverlaps or gaps.

B-Rep has the additional topology of outward normal.

12. Tick the correct statement. Storage of redundancy in B-Rep causes:

(a) increase in space complexity and decrease in time complexity(b) increase in space complexity and increase in time complexity(c) decrease in space complexity and decrease in time complexity(d) decrease in space complexity and increase in time complexity.

13. Tick the correct statement. The memory occupied by

(a) B-Rep is proportional to the sum of the areas of all its surface patches.(b) Exhaustive enumeration is constant.(c) Octree is proportional to the volume of the object.(d) CSG is very high.

14. Tick the correct statement:

(a) Octree is the most accurate solid representation.(b) Octree cannot handle non-manifold objects.(c) Feature details are lost in Octree.(d) Octree can handle self-intersecting objects.

15. Which type of solid is Klein bottle?


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(a) Manifold solid(b) Non-manifold solid(c) Self-intersecting solid(d) Virtual solid

16. A CNC machine is a

(a) Scalar device (b) Vector device (c) Tensor device(d) Raster device (e) Voxel device

17. The most popular display today is:

a. Storage tube with vector graphics b. Storage tube with raster graphicsc. Refresh tube with vector graphics d. Refresh tube with raster graphics

18. Tick two correct answers. Double buffering is required for:

a. Storage tube with vector type monochrome displays b. Refresh tube with raster type monochrome displaysc. Storage tube with vector type color displaysd. Storage tube with raster type color displayse. LCD displays

19. Tick the correct statement in the context of CRT:

(a) Creating any color involves suitable proportion of Red, Green and Blue inconjunction with Yellow. This process involves optical addition of the basic colorsand their subtraction from Yellow.

(b) The three electron guns corresponding to Red, Green and Blue emit electrons atdifferent velocities so as to create different excitements on the phosphor coating. Thisdifferential excitement results in the phosphor coating emitting the desired color.

(c) The electron guns for all the three colors are identical.(d) None of the above is correct.

20. Tick the correct statement to compare two float numbers a and b where eps is the required precision:

a. if (a == b) b. if ((a-b) < eps) c. if ((b-a) < eps) d. if (fabs(a-b) < eps) e. if ((a-b) < eps) && (b-a) < eps))

21. The approximate values of human latencies for touch is:

a. 1 ms b. 10 ms c. 100 ms d. 1000 ms

22. Give two reasons for fixing redundant optical markers on the objects to be tracked.

i. When some markers of an object may be covered by the user or other objects,redundant markers help in identifying them in spite of this.


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ii. More number of markers help in the unique identification.

23. The maximum number of degrees of freedom of an end mill is 5 and the same for the wireof an EDM process is 4.

24. The three types of data required to convert CL file into NC program are

i. Process ii. Kinematics iii. Format or syntax of the controller

25. A VolSim system has two modules, viz., [i] Geometric simulation and [ii] processmodeling. Identify the two correct answers:

a. [i] only is required for verification b. [ii] only is required for verificationc. [i] and [ii] are required for verification d. [i] only is required for optimizatione. [ii] only is required for optimizationf. [i] and [ii] are required for optimization

26. While optimizing end milling path by maintaining constant MRR, the correction factor isrequired

a. only when the tool goes uphill b. only when the tool goes downhillc. when either of these happens.

27. There are two correct answers. Identify both:

a. When volumetric NC simulation using image-space representation is in progress, itcan be viewed from any direction dynamically.

b. When volumetric NC simulation using general stick-like voxel representation is in progress, it can be viewed from any direction dynamically.

c. Image-space representation is the fastest for volumetric NC simulation.d. General voxel representation is the fastest for volumetric NC simulation.e. Octree representation is the fastest for volumetric NC simulation.f. Object is represented in the form of a bundle of sticks in octree representation.

28. The two significant steps in automation are:

i. Automation of the processii. Automation of the process planning

29. What are the three most significant considerations in the selection of a RP machine?

i. Material optionsii. Minimum slice thicknessiii. Support mechanism


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30. What are the two reasons for poor surface finish in RP?

i. Stair-step error due to layered manufacturingii. Uprooting or leftover material at the interface of model and support when the support

is removed.

31. Circle the two RP processes that are capable of making quasi-hollow objects. You will receivezero marks even if you miss one of them.

3DP FDM LOM Object Perfactory SGC SLA SLS SolidDimension

32. Circle the five RP processes that can make transparent objects. You will receive zeromarks even if you miss one of them.

3DP FDM LOM Objet Perfactory SGC SLA SLS SolidDimension

33. Circle the liquid based process has the most efficient use of the photo-polymer?


34. Circle the commercial RP machine that can make color prototypes.


35. Circle the RP machine having single axis. How are the other two axes replaced orcompensated?


Explanation: Using a photo-mask.

36. Circle the two RP processes that use raster writing during layer creation.


37. How is Z accuracy ensured in each of SGC and Model Maker II?

By levelling the surface using milling. (Additional information: SGC uses face millingand Model Maker II uses slab milling)

38. Circle the RP process that benefits the least from nesting ? Why?

3DP FDM LOM Object Perfactory SGC SLA SLS SolidDimension

Reason: When the overhead between layers is high, nesting helps in amortizing overnested parts. The overhead between layers is very small in FDM compared to the timetaken to create the layer through a single nozzle deposition. So, nesting does not help

FDM.

39. The other name of Silicon Rubber Molding is Vacuum Casting .


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40. What are the three types of Investment Casting processes?

i. Shell casting or traditional investment castingii. Flask casting or Plaster casting or Precision castingiii. Evaporative Pattern Casting (EPC) or Lost Foam Casting (LFC)


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Part B(Weightage is mentioned against each question)

1. Expand the following acronyms (You will receive zero marks even if one expansion iswrong): [4]

a. STL : STereo-Lithograpgy Language b. 3DP : Three Dimensional Printing c. FDM : Fused Deposition Modeling d. LOM : Laminated Object Manufacturing e. SGC : Solid Ground Curing f. SLA : Stereo-Lithography Apparatus g. SLS : Selective Laser Sintering h. FGM : Functionally Gradient Material

2. Present the characteristics of the industrial scenario in the past and presently in thefollowing table: [3]

Feature Past Present Economy based on thetype of Govt. protection

Protected economy Open economy

Type of Competition Local Globalarket is dictated by Seller Buyer

n(Profit, Price, Cost) Price = (Cost + Profit) Cost Profit = Price Cost Definition of quality Conformance to design Customer delightOne word to define the

attitude

Complacence Competition

3. Give a binary (i.e., in terms of high/low) comparison of the following RP machines: [2]

Cost Speed Precision Laser-based RP machines excluding LOM High High High Non-laser-based RP machines Low Low Low

4. Which surface is the most cumbersome to build in LOM? Why? What is the solutiongiven by Helisys and what is practised by the users? [2]

Surface: Horizontal planar surface. [0.5 mark] Reason: Only the boundary is cut in LOM. So, horizontal surfaces get stuck with thestock. [0.5 mark] Solution of Helisys: Fine grid cutting to burn the horizontal zones. [0.5 mark]

Practised by users: As fine grid cutting is inefficient, the users tilt the object by a suitableangle so as to avoid horizontal surfaces. [0.5 mark]


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5. Present the comparison between powder-bed and deposition technologies in the form of atable. When options are given, circle the appropriate choice. [5]

Feature Powder-Bed Technologies Deposition Technologies Principle Pre-Laid / Co-Laid Pre-Laid/ Co-Laid

Raw material form Powder / Wire/ Both Powder/ Wire/ Both Particle size when powder is rawmaterial

Coarse / fine Coarse/ fine

Dispensing methodwhen metal powderis raw material

Spread by a viper /Fluidized feeding

Spread by a viper/Fluidized feeding

Support mechanism for non-metals

Inherent /Sacrificial material dispensing/

None

Inherent/Sacrificial material dispensing /

None Support mechanism

for metalsInherent /

Sacrificial material dispensing/ None

Inherent/Sacrificial material dispensing/

None Amenability for FGM

Yes/ No Yes / No

Two examples fornon-metal

i. 3DPii. SLS

i. FDMii. Objet

Choose from [3DP, FDM, LOM, Object, Perfactory, SGC, SLA,SLS, SolidDimension, LENS, POM, SDM, LAM, EBM]

Two examples formetal

i. 3DPii. SLS

iii. EBM

i. LENSii. POM

iii. SDMiv. LAMChoose from [3DP, FDM, LOM, Object, Perfactory, SGC, SLA,SLS, SolidDimension, LENS, POM, SDM, LAM, EBM]

6. Present the comparison of contact and non-contact scanning systems in the followingtable. When options are given, circle the appropriate choice. [2]

Feature Contact type Non-contact type Accuracy High / Low High/ Low Speed High/ Low High / LowThreeexamples

i. CMM using probesii. Manual measurementsiii. Touch probe on a CNC machine

i. White light scanningii. HandiScaniii. Photogrammetryiv. Laser scanningv. Industrial CT scanvi. ...

7. What is time-delivery drug? Which RP process is suitable to produce these drugs andwhy? Briefly explain the procedure of producing it additively. [3]

Time delivery drug has a controlled dissolving rate which is very essential for treatingvery chronic diseases like psychiatric disorders. [0.5 marks]

3DP is suitable. This is because this is the only process that dispenses materials from two


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different sources. Therics, USA, is the pharmaceutical company which produces thesedrugs this way. However, in principle, any deposition process with ability to control flowrate of multiple materials can be used. [1 marks]

Procedure: (1,5 marks)

The rate of dissolving is proportional to the surface area of the tablet. So, theconcentration of the drug shall be distributed such that the specified rate of drug is

proportional to the conformal area. Based on this consideration, the concentration atconformal layers in close intervals is decided.

The resulting gradient geometry is sliced into this horizontal layers retaining theinformation of the relative concentration of the drug and matrix.

The drug is dispensed from top on the surface of the matrix layer every time. In everylayer, while the drug is dispensed, its flow rate is controlled so as to get the desiredconcentration.

8. Distinguish between White Light Scanning and Handiscan . When options are given,circle the appropriate choice. [2]

Feature White Light Scanning Handiscan Nature of light(source and

pattern)

Visible white light. Strips ofwhite and dark light. The widthof these strips narrow downevery time.

Laser. It also projects a visiblered cross to indicate the place

being scanned.

Relative ease ofuse

High/ Low High / Low

Relative size ofobject scanned

Large / Small Large/ Small

Ability to scanobjects alongwith their color

Yes/ No Yes / No

9. Explain the lacuna in todays geometric representation schemes for the design of FGMobjects. How is it to be overcome? [3]

The tools to manufacture GM objects are reasonably matured but the technology torepresent gradient objects is still not mature enough. Existing geometric models representonly the boundary of the objects and they assume the interior filled with the samehomogeneous material.

Existing geometric models use a user-friendly representation to create the model and asystem friendly representation during its usage. The former is FBM or CSG and the latteris B-Rep generally. In addition to these two which address only the boundary, we need athird representation for denoting the interior with affordable precision. The possiblecandidates are voxel and octree.

10. Present the six groups of RM for metals in the form of an inverted tree. [3]


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11. Ignoring the time taken in support building and removal, interlayer overheads and gainsdue to nesting multiple objects in the working envelope, the build time of an object in RPmachines is proportional to one of the following of the object: [a] volume, [b] surfacearea and [c] height. Tick the appropriate cells in the following table in this regard. [3]

LOM FDM SLA SGC Objet PerfactoryVolume

Surface area Height

12. Why are the acrylic patterns used in QuickCast quasi-hollow? Name the RP machine thatcan build these patterns. [2]

The acrylic pattern and the ceramic shell around it have different thermal coefficients. Inorder to reduce the thermal stresses arising out of their differential expansion, the patternis made quasi-hollow.

SLA. QuickCast is a build style.

13. What is visible slicing? Name at least two processes capable of this. [3]

Visible slicing splits the object into segments that can be fully seen from either fromeither top or bottom. Such a segment can be machined completely in two settings. [2marks]

The processes making use of visible slicing are: (1 mark)

i. Shape Deposition Manufacturing (SDM)ii. Segmented Object Manufacturing (SOM)

14. Present the comparison of laminated tools for blanking and stamping. When options aregiven, circle the appropriate choice. [2]


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n = [402, 446].

17. An object has a planar surface slant at 30 from horizontal. When it is built in layers of0.1 mm, what is will be the average roughness (R a ) on this plane? [4]

Ra = [0.1 cos(30)]/2 = 0.0433.

2011 test07 endsem with answers

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