2009-test07-chap04 rp (liquid, sls, 3dp, appn and issues)

8/12/2019 2009-Test07-Chap04 RP (Liquid, SLS, 3DP, Appn and Issues)

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INDIAN INSTITUTE OF TECHNOLOGY, BOMBAYDepartment of Mechanical Engineering

Course : ME-617 Rapid Product DevelopmentInstructor : K.P. KarunakaranDate : October 30, 2009 (Friday) 5:00PM

L-T-P-C : 3-0-0-6I Semester 2008-09

Duration : 75 min.Instructions:Answer all the questions; answer as briefly as possible.

Roll NoMarks /50

TEST 7: RP Photo-polymer processes, SLS, 3DP, Applications and Issues

Part A(1 mark each)

1. Which make and model of RP machine is the most popular in Indian jewelryindustry? SLA

2. Name the two RP technologies that can make metallic and ceramic prototypes.3D printing & SLS

3. Which commercial RP machine can make color prototypes?Z corp

4. Give the expansions of LOM, FDM, SLA, SLS, SGC and 3DP.Laminated Object Manufacturing, Fused Deposition Modeling, Selective LaserSintering, Stereo-Lithography Apparatus, Solid Ground Curing, 3D printing.

5. Name the RP machine that has only a single axis. What compensates for the other twoaxes?

Solid Ground Curing, Perfactory

6. How is Z accuracy ensured in each of SGC and Model Maker II?The z accuracy is maintained by the milling step which carried out after the wax

coating.

7. Mention at least two RP processes that use multiple tools for depositing material.FDM, Objet, Z-Corp.

8. Nesting is the method of building more than one prototype simultaneously within theworking volume. Which of [LOM, SGC, FDM, SLA] has the least advantage ofnesting? Why?FDM and SLA has the least advantage of nesting.

9. Which RP process was related to the story of the thirsty crow and in what context?SLA, for maintaining low level of raw material exposing to the environment.

10. List at least three most popular approaches to micro-RP machines?SLA, SGC, MoldSDM.

11. Mention at least two significant features/advantages of the Perfectory RP machinedeveloped by Envisiontec, Germany over SLA?


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- Inverted part buliduing and hence less raw material inventory.- No laser and hence cheaper.- Part building time is proportional to only height.- Only one moving axis.

Part B(Weightage is mentioned against each question)

1. List the various physical forms of raw materials used in the popular RP processes anddiscuss their influence on the characteristics of the prototype produced.[3]

Liquid (Photopolymer): Most accurate as it can be spread to any thickness. Transparentparts and hence the prototype can be used for photo-elasticity.

Sheet: Any material can be produced in the form of the sheet therefore excellent materialvariety. but the limitations on the thickness of the paper that can be used. Hencesurface finish is not good compared to other processes.

Powder: Any material can be produced in the form of the powder form therefore excellentmaterial variety. The final product has high strength compared to the others. Thesurface finish is governed by the powder size. Starch or Plaster based powder Heredifferent binders can be used where the final product can have different colours andthe surface finish is governed by the powder particle size.

2. Name the four photo-polymer-based RP processes and compare them in the form of atable.[4]

Light Liquid Light Source Special Feature

SLA Sharp Wide Laser - CAD to be modifiedfor Support

- Most accurate, fastestand costiest

SGC(Photomasking)

Wide Wide Flood Light -Optical Mask-Wax Support-Time Area

Object Wide Sharp Flood Light -Multiple Jets-Jelly(Support)

Envisiontek Selectively wide Wide Flood Light -Building From The top-Mirror Display

3. What is the support mechanism used in each of [LOM, FDM, SLA, SLS, SGC, 3DP].[3] LOM: Remaining sheet stock acts as support. Grid cutting is done on this stock toenable part extraction.FDM: There is a separate nozzle from which a support material is deposited.SLA: support structures are automatically added to the CAD model wherever requiredand after all the layers are made the support structures are carefully cut.SLS: Remaining uncured power layer acts as the support, so explicit support structuresare not required.


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SGC: this is achieved simply by pouring wax in the regions not affected by the light; noneed for computing the region requiring support and modify the CAD model.3DP: the power layer acts as the support structure so it does not require any explicitsupport structure.

4. Compare the features of die/mold and component vis-a-vis Layered Manufacturing

[2]

Metallic Components Metallic Tools

Components may have overhangsand interior features (re-entrants).Therefore, a support mechanism isrequired.

Tools are always converging towards the otherhalf. In other words, any layer is contained byits previous layer and hence no need for asupport mechanism. Even conformal coolingducts/ channels can be made without supportalthough their shape will not be uniform.

Stringent requirement on materialproperties as they affect theperformance.

Variations in material properties do not affectthe performance of the parts produced; only thelife of the tool only is compromised.

Use of RP for regular production iscalled Rapid Manufacturing.However, this proves to beexpensive. Rapid Nanotechnologyis the key for this issue.

Tools made by conventional methods are veryexpensive and hence can be justified only forlarge volume production. As they take longtime to make, they are major bottlenecks inproduct launch. So improvement in toolmaking contributes to fast product launch.

5. What is meant by time-release drug delivery? Which RP technology is suitable formanufacturing tablets used for this purpose and which feature of it makes this

possible? Name the company using this approach. Why or why not can SLS bedeployed for this application?[3]

Time release drug delivery means adding the drug into the blood stream at acontrolled rate over time. This is used in chronic patients such as the ones withneurotic disorders.

3DP is suitable for manufacturing tablets used for this purpose. This is possiblebecause of material addition from 2 sources.

This is used by Therics, USA.

SLS cannot be used because it has only one material. If one can change the materialcomposition every layer, one may achieve quasi-gradience. This too may not satisfyas the tablet dissolves conformally.

6. What is photo-elasticity? List any two commercial RP processes whose prototypescan be used for this analysis.

[2]It is a physical testing using a transparent model. When the model is stressed, itsoptical characteristics at different points correspond to the stresses. These can becaptured using polarized light in the form of fringe patterns.


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SLA, Objet, SGC & Perfactory

7. Why are deep dipping and doctor blade required in SLA?[3]Both are required for maintaining the liquid level accuracy. Directly moving down to

the desired z level will not guaranty flow of the viscous liquid (surface tension) andhence it goes down more and comes back to the desired level. But then the excessliquid does not flow down readily. Therefore doctor blade is used to remove the extralevel of liquid.

8. What does the laser do in each of [LOM, SLA, SLS, Laser printer]?[2]LOM Cutting in each layer, grid cutting.SLA Curing the photopolymer.SLS To fuse the power particles together, i.e. sinteringLaser printing Charging/Discharging the roller

9. Bring out at least three differences between the SLS processes of 3D Systems andEoS.[2] Separate machines for each material in EOS. Complete sintering of the raw metal powder in EOS whereas plastic coated metal

powder in 3DS. Furnace processing for full sintering and copper impregnation is required in 3DS.

10. What do you understand by Functionally Gradient Materials? What is the state-of-the-arts in the manufacture of gradient components? What are the issues related to itsdesign? [4]

Functionally gradient materials are the materials whose properties are designed to vary indifferent parts of the product such that the localproperties of the material in a part are suitable for the designed function of the part.

11. Which was the first RP machine in India and which company bought it? Why is thisprocess not popular any more?[2]

SGC is the first RP machine to reach india and Datar Switch Gears had purchased it. It isnot popular for the following reasons:

The process is more complex with two cycles and many sub-systems (maskingcycle, polymer spreader, polymer cleaner, wax spreader, wax cooling plate,milling head, vacuum suction of chips); hence, less reliable. Furthermore, thisrequires a full time operator attention.

Dewaxing is time-consuming. Creates a lot of waste of wax.

12. Classify the 6 RP processes [LOM, FDM, SLA, SGC, SLS, 3DP] under each of thefollowing three categories giving reason for the same in one line each:[3]a. RP process whose cycle time is proportional to the surface area of the objectb. RP processes whose cycle time is proportional to the volume of the objectc. RP process whose cycle time is in between both these types


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LOM c because the laser has to do the profile as well as grid cutting hence it is greaterthan the surface area but less then the volume of the object.FDM b becauseSLA b because of complete deposition of the volume in each layerSGC c. In fact, it is proportional to only part height.SLS b because the laser has to scan the complete area of each layer to fuse the material.

3DP b because for each layer complete area has to be scanned for spraying the bindingmaterial.

13. Name at least three ways of transporting laser beam to the required position giving anexample of a RP process for each. Mention their relative merits and demerits.[3]

1. Using a series of mirrors one on each slide LOM2. Using a galvanometer (a single mirror deflected in 2 directions) - SLS & SLA3. Using piping (optical fiber cables) Not in the std. RP machines but in metal RPmachines of higher capacity.

14. Match the following:[3](A) LOM - (a) SLS(B) FDM - (b) grid cutting(C) SLA - (c) Easy support(D) ObJet - (d) Color prototyping(E) EoS - (e) Curtain technology(F) ZCorp - (f) Strong parts

(A) LOM - (b) grid cutting(B) FDM - (f) Strong parts(C) SLA - (e) Curtain technology

(D) ObJet - (c) Easy support(E) EoS - (a) SLS(F) ZCorp - (d) Color prototyping

2009-test07-chap04 rp (liquid, sls, 3dp, appn and issues)

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