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DEPARTMENT OF MECHANICAL ENGINEERINGIV B.Tech 1st Semester

Additive Manufacturing -Unit 1

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UNIT – ITopics to be covered:Introduction: Prototyping fundamentals, historical development, fundamentals of rapid prototyping, advantages and limitations of rapid prototyping, commonly used terms, classification of RP process.Liquid-based rapid prototyping systems: Stereo lithography Apparatus (SLA): models and specifications, process, working principle, photopolymers, photo polymerization, layering technology, laser and laser scanning, applications, advantages and disadvantages, case studies. Solid Ground Curing (SGC): models and specifications, process, working principle, applications, advantages and disadvantages, case studies.Text Book:Rapid Prototyping: Principles and Applications – Chee KaiChua, K FLeong and C S Lim, World Scientific publications.Reference Book:Rapid Manufacturing – D.T. Pham and S.S. Dimov, Springer.Rapid Prototyping & Manufacturing – Paul F.Jacobs, ASME Press.

Day-1

1. What is a Prototype?Ans: Prototype is an early model or sample of a product to be developed. It is built mainly to visualize final product or to test a concept or a process.

2. What are the different types of prototype?Ans: Prototype can be categorized as per three aspects as given below,

- Implementation – depending upon the range of prototyping the complete product or part of it, it can be a full scale prototype or only a component or a subassembly.

- Form of the prototype – depending on the model being tangible or intangible it is either Physical prototype or Virtual prototype.

- Degree of approximation – the prototype can be just a rough representation of the final product or it can be an exact full scale representation of the actual product.

Raghu Engineering College Dept.ofMechEngg . Additive Manufacturing Unit-I

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The below figure represents different types of prototype considering all the three aspects.

Figure 1 Types of prototypes considering all three aspects

3. Explain the need for Rapid Prototyping.Ans:The competition in the manufacturing industry has significantly intensified in recent years. Therefore there has been a demand in reducing the product development cycle. A product development cycle involves four steps design – test – manufacture and market. So, efforts were made to decrease time in each step. The design and testing phase takes maximum time in developing a product that is why this phase needed more squeezing. This phase involves testing of different concepts and processes by developing different prototypes. The researchers then came up with the idea of Rapid Prototyping that is a sufficiently fast process to fabricate prototypes and hence reducing the product development cycle.

4. What is Rapid Prototyping?Ans:Rapid prototyping (RP) is a technique to fabricate three dimensional products directly from the digital data or computer aided design (CAD) data.This concept was developed in 1980s and was mainly intended for fabricationof prototypes or concept models.In this process the parts are built


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by layer by layer material deposition on a moving platform. Therefore it is sometimes known as Layered Manufacturing (LM). Later on this technique was modified to be implemented for direct manufacturing of products. Hence now it is more commonly known as Additive Manufacturing (AM) because in thistechnique part is built by continuous addition of material in contrast to the traditional material removal manufacturing technique.

5. Discuss the evolution of Prototyping.Ans: Prototyping has been into existence since ages when human started developing tools and since then human knew only about manual prototyping. Another two types of prototyping has been developed recently. So, we can say that the prototyping process has gone through three phases as given below.

i. First phase – Manual PrototypingIn this early phase, prototypes were not very sophisticated and complex. Those were made manually and were highly labor intensive. The average time to make one prototype was around four weeks. ii. Second phase – Soft or Virtual PrototypingThis phase of prototyping started in 1980s with the introduction of computer aided design (CAD), computer – aided manufacturing (CAM). Different types of tools became available to test, analyze and modify virtual prototypes effortlessly. iii. Third phase – RapidPrototypingThe third phase started in late 1980s with the introduction of a technique that could directly fabricate real objects from CAD data in just few hours. The best part was highly complicated and difficult to produce parts could also be easily built.NOTE: Even with the advent of RP in many cases still virtual prototyping is preferred over RP due to material limitations of RP and inability to perform endless what – if scenarios in RP.

Home work:Web links:

1. https://www.youtube.com/watch?v=Icj5xhTux9M Important questions:

1. Why rapid prototyping is important in Industries?2. Explain the evolution of Prototyping.


https://www.youtube.com/watch?v=Icj5xhTux9M

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3. What do you mean by prototypes?

Day - 2

1. Explain in detail the process chain of Rapid Prototyping.Ans: Regardless of several RP techniques available today, all of them adopt the same basic process, which can be summarized in five steps as given below.Step – 1: 3D ModelingThis step involves preparation of the 3D CAD model of the final object to be built. It can be done using any Design software. This phase is the most time consuming part of the entire process.If the hard copy of the object is available, sometimes instead of generating a CAD model, the object is 3D scanned to capture point cloud data and surface model of the final object is created. Step – 2: Data conversion & TransmissionThe 3D model now needs to be converted to a machine understandable language. Presently, all the RP system follows a data format known as .STL (Stereolithography or Standard Tessellation Language) file format. This format was developed by 3D systems. In this format,the complete 3D model is converted to a set of data points or coordinates. Now this .STL file is transferred to the computer integrated with the RP system. Representation of .STL file is given below in fig 2.

Figure 2 (a) Representation of STL format of simple shapes


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Figure 2 (b) Representation of STL file of a sphereStep – 3: Checking & SlicingThe next step is checking for if any errors are there in the .STL file and it is done by different software available with the RP machines. If any error is found it is repaired and is prepared for building. Once the STL files are verified to be error free, slicing is done. Slicing is the process of cutting the model into thin layers or cross-sections. The thickness of layers depends upon the selected RP process e.g for SLA the layer thickness is 0.12 mm to 0.50 mm. The thinner the layer more is the accuracy and the better the surface quality. Depending on the RP process selected the support structure is also generated in this step for overhanging parts.

Figure 3 Representation of slicing (a) 3D model (b) sliced model (c) one layer

Step – 4: BuildingFinally the part is built by the automated machine. The model making material is deposited layer by layer on a platform as per the slice data


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generated by the software. The build duration depends on the size and complexity of the object being built. Step – 5: Post-processingAfter the building is complete, the part is taken out of the machine and is cleaned properly to get rid of the excess material. In some RP techniques additional processing is required to give desired surface finish and improve aesthetics. In some liquid based RP processes post curing is also required.

2. What are the key aspects of RPT?Ans: Rapid prototyping has mainly 4 aspects.

i. InputThe input given to a RP machine can be a CAD model or a physical model directly. If it is a physical model, the point cloud data of the same is captured by different machines like coordinate measuring machine (CMM) or laser digitizer. In both the cases the model is finally converted to STL or IGES format and slice data is generated.

ii. MethodThere are numerous vendors available for RP systems with different techniques being applied but they can be classified into following categories: photo-curing, cutting and gluing or joining, melting and solidifying or fusing and joining or binding. Again photo-curing can be single laser beam, double laser beam or masked lamp.

iii. MaterialThe types of material used in RP can be in solid, liquid or powder forms. The solid form material can be wire, laminates or pallets. Currently, the raw material being used in almost all RP machines includes, paper, nylon, wax, resins, metals and ceramics.NOTE: Use of concrete in RP machines is recently developed.

iv. ApplicationsApplication of RP parts can be grouped into design, engineering analysis and planning and manufacturing and tooling. A wide range of industries can benefit from RP and these include aerospace, automotive, biomedical, consumer, electrical and electronics products etc.All these aspects are represented below in the RP wheel (Fig. 4).


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Figure 4 Represenation of a RP wheel

3. List the classification of RP systems. Ans: All the existing RP processes can be categorized in several ways but one of the best ways to categorize is with respect to initial form of model material being used to build the part. So, according to this RP processes can be mainly of three types (i) Liquid based, (ii) Solid based and (iii) Powder based.

i. Liquid based:If the initial form of the raw material being used is in liquid state then it is called liquid based RP process. The main concept used in all liquid based RP processes is photo-curing. Depending on the types of photo-curing implemented there can be different types of processes. The following are some important liquid based RP:

- 3D system’s Stereolithography Apparatus (SLA)- Object Geometries Ltd.’s Polyjet- D-MEC’s Solid Creation System (SCS)- Cubital’s Solid Ground Curing (SGC)- CMET’s Solid Object Ultraviolet-laser Printer (SOUP)ii. Solid based:

All form of material in solid forms is considered under this category. So, the raw material can be in the form of wires, rolls, laminates or pellets. Mainly


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two methods are used in solid based systems, one is Melting & Solidifying or Fusing and the other one is Cutting & Gluing or Joining. Some important solid based RP processes are given below:

- Stratasys’s Fused Deposition Modeling (FDM)- Cubic technologies Laminated Object Manufacturing (LOM)- 3D System’s Multi Jet Modeling (MJM)- Kira’s Paper Lamination Tech (PLT)- Shape Deposition Manufacturing Processiii. Powder based:

Powder based is also a kind of solid based RP process but it is considered to be another category. All these processes use Joining / Binding method using laser beam or binder/ glue. Some powder based RP processes are listed below:

- 3D System’s Selective Laser Sintering (SLS)- Z Corporation’s Three - dimensional Printing (3DP)- EOS’s EOSINT- Optomec’s Laser Engineered Net Shaping (LENS)- Arcam’s Electron Beam Melting (EBM)

4. What are the advantages of Rapid Prototyping?Ans: There are numerous benefits of RP and can be broadly categorized into direct benefits and indirect benefits.

i. Direct benefits:Benefits to companies

- The introduction of RP helped the companies to experiment more with the physical product to give the best output in a short period of time. That made the products more complex in shape and form, aesthetically beautiful.

- The savings in time and cost ranges from 50% to 90% depending on the size of production.

Benefits to designers- Complexity of the product can be increased to impart more functionality

and improve aesthetics with worrying about the difficulty in manufacturing.

- Part count can be reduced making its production easier.- Material can be minimized and optimization of strength can be done.


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- No need to worry about the manufacturing possibilities.Benefits to tooling and manufacturing engineers

- Tooling cost is minimized- Reduced part count will again minimize assembly, purchasing and

inventory expenses.- Reduced labor content and scrap cost- Design misinterpretation can be avoided (what you design is what you

get)- Any quick change in design, dimensions, tolerances can be easily

accommodated.- Higher part repeatability- No spare parts inventory as parts can be made on demandii. Indirect benefits:

Apart from the manufacturing industry, the consumers are also benefitted by the RP.Benefits to market

- Reduction in time-to-market - Reduced risk as no need to project customer needs and market

dynamics several years into the future- Products offering performance / price of latest technology - New products being test marketed economically

Benefits to consumer- Product more closely matches individual needs and wants- Greater diversity of product- On demand customized product possible- Products can be available at lower price as manufacturer’s savings pass

on.5. What are the limitations of Rapid Prototyping?

Ans:Disadvantages:

1. The initial set up cost is very high2. Not suitable for large sized applications3. Low surface finish4. Low part strength

Homework:Watch these videos.Web links:


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https://www.youtube.com/watch?v=WzmCnzA7hnEhttps://www.youtube.com/watch?v=TAp93r_q1FcImportant questions:

1. Explain the process chain of a Rapid prototyping process.2. What are the key aspects of RP?3. What are the advantages and disadvantages of Rapid Prototyping?4. Describe the advantages of RP in terms of in beneficiaries such as the

product designers, tool designer, manufacturing engineer and consumers.

Day – 3

1. Explain the Stereo Lithography Apparatus (SLA) process.Ans:It is a liquid based RP process that builds part from a vat containing photo – curable liquid resin using a laser beam. This process was developed by 3D systems in 1988 as the first ever commercial RP system.

Figure 5 An SLA process

Process:3D systems’ Stereolithography process builds part directly from computer aided design data like any other RP process.


https://www.youtube.com/watch?v=TAp93r_q1Fc

https://www.youtube.com/watch?v=WzmCnzA7hnE

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- The process starts with a vat containing liquid photo-curable resin and a moving platform that is set just below the resin surface.

- The 3D modeled CAD data is transferred to the RP system and converted to STL format.

- Support structures are generated for overhanging parts and finally the control unit slices the model as well as the support structures usually of 0.025 mm to 0.5 mm.

- According to the slice data captured, the optical scanning system directs and focuses the laser beam on the liquid resin. The 2D cross section that was exposed to the laser beam solidifies to a depth greater than one layer.

- The elevator table then moves down by a calculated distance such that a liquid resin of one layer thickness comes over the solidified portion. The next layer is scanned by the laser as per the slice data. The process then continues till the complete part is ready.

- The part is then collected from the vat and is cleaned ofexcess material.2. What are the main components of a SLA system?

Ans:The main component of an SLA system includes:

- Hardware: computer, control panel, laser, optical scanning system and a process chamber.

- Software: 3D Lightyear, MaestroDay – 4

1. What are the main principles of a SLA?Ans:The basic principle underlying the SLA process is based on two principles:

i. Photo-polymerizationii. Layer-by-layer building

Photo-polymerization:2. It is the process of linking small molecules (monomer ‘M’) into chain like

larger molecules called polymer. When chain like polymers are linked further cross-linked polymer is formed.

3. The process is started by a photo – chemical process by the help of photo-initiators (Pi).

4. The photo-initiators absorb some photons and get excited and some of them produce free radicals that act as a catalyst for the polymerization process.


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5. The free radicals then react with the monomer units to form polymerization initiating molecules (PM.). This step is a chain initiation step.

6. After activation these molecules go on reacting with different monomer units to form longer chains. This step is called chain propagation step.

7. If the monomer units have different chemical group cross linking takes place that generates an insoluble continuous network of molecules.

8. The monomers unit are chosen such that crosslinking will be more so that the polymerized molecules don’t re-dissolve back to liquidmonomer also to the polymer formed should be of higher strength to sustain various forces acting upon it during the further processing.

9. The complete polymerization process has been represented in figure 6.

Figure 6 Representation of a photo- polymerization process


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Laser scanning &Layering technology:- The important component of SLA is the laser and the optical scanning

system. The ability of directing a focused radiation of specified power and wavelength to the liquid resin and forming patterns of solidified polymer as per the slice data is the key characteristic of SLA system.

- The laser beam of appropriate power and wavelength is sent through a beam expanding telescope to fill the optical aperture of a pair of cross axis, galvanometer driven and beam scanning mirrors. This forms the optical scanning system of the SLA and focuses the laser beam on the surface of the liquid resin.

- The solidification of the liquid resin depends on the energy per unit areai.e exposure deposited during the motion of the focused spot on the surface of the photopolymer. If the photo-polymer exceeds the threshold exposure required for solidification then the resin solidifies.

- The depth of solidification or curing depends on the duration of exposure which is inversely proportional to the speed of the scanning system.

- So, essential parameters to be controlled for proper curing are accurate exposure (speed of scanning system), focused spot size, power and wavelength of the laser.

Another important factor to be properly controlled is the layer thickness.- The computer software slices the CAD model into layers and data in

each slice is sent to the scanning system to make patterns on the liquid resin.

- To make the next layer the platform must move down by one layer thickness after each curing and this is achieved by precision level mechanism. This distance should be exactly equal to the slice thickness of the computer model and the thickness of the solidified resin layer.

Parameters that influence the performance and functionality of the final parts are:

i. Physical and chemical properties of the resinii. Speed and resolution of optical scanning systemiii. Power, wavelength and type of the laser usediv. Spot size of the laser beamv. Recoating system vi. Post-curing process2. What are the strength and weaknesses of SLA process?


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Ans:The major strengths of SLA are:

i. Round the clock operation – The SLA system can run continuously unattended round the clock.

ii. Build volumes –There are different SLA machines that cover a large range (from 250 × 250 × 250 mm3 to 737 × 635 × 533 mm3)that suits the need of most users.

iii. Good accuracy – The accuracy of SLA is good as compared to other RP processes. So, used for many applications.

iv. Surface finish –The SLA gives one of the best surface finish amongst any RP process.

v. Wide range of material – There is a wide range of materials from general purpose materials to specialty materials for specific applications.

Limitations:Apart from a number of advantages, all RP processes have some disadvantages. Main limitations of SLA are as given below:

i. Requires support structure – The overhangs and under cuts need some support elements before fabrication. After fabrication the supports are removed and scrapped.

ii. Requires post processing –The removal of supports structures and other unwanted material after the fabrication is a tedious job, time consuming and can damage the model.

iii. Requires post curing – All the liquid based RP system needs curing. This is required to impart more strength and integrity to the part.

3. What are the applications of SLA process?Ans:

- Physical Models for Visualization, Conceptualization, Packaging and Presentation

- Prototypes for Design, Analysis, Verification and Functional testing - Parts for Prototype Tooling and Low Volume Production Tooling - Patterns for Investment Casting, Sand Casting and Molding - Tools for Fixture and Tooling Design, and Production Tooling

Note: If the question is – Explain in detail the Stereo Lithography Apparatus.The answer should be written by combining question 1 & 2 from day – 3 and questions 1, 2 and 3 from day – 4.


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Homework:1. Brief about a case study on SLA process.2. Watch SLA process video.

Web Links: https://www.youtube.com/watch?v=sTNUrFzHbxchttps://www.youtube.com/watch?v=yW4EbCWaJHE

Important questions:1. Explain a SLA process.2. List out the advantages and limitations of a SLA process.3. Explain the photo-polymerization process in SLA.

Day – 5

1. Explain the Solid Ground Curing (SGC) process.Ans: This is a high end liquid based RP system providing wider range for various modeling demands. It was developed by Cubital Ltd. and Israelis’ company. It uses liquid resin cured resin as model material and water soluble wax as support material and ionographic solid toner for creating erasable image of the cross section on the glass mask.Process: The building process consists of mainly three steps.

i. Data preparationii. Mask generationiii. Model making

Data preparation- Like any other RP process CAD model is prepared first and is sent to the

RP system in STL format.- Using Cubital’s Solider DFE (Data Front End)searches for any flaws if

present in the CAD file and repairs it.- Slice data is generated and is digitally sent to the mask generator.

Mask Generation- After the slicing data is received, the mask plate is charged through an

“image-wise” ionographic process. - The charged image is then developed with electrostatic toner (refer

picture 1 of figure 7).Model Making

- A thin layer of photo-polymer resin is spread on the work surface (refer picture 2 of figure 7).


https://www.youtube.com/watch?v=yW4EbCWaJHE

https://www.youtube.com/watch?v=sTNUrFzHbxc

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- The photo mask from the mask generator is placed just above the work piece and exposed to collimated UV lamp for a few seconds (refer picture 3, 4 of figure 7).

- The resin layer under the UV light hardens as per the image on the photo mask. The thickness of hardened layer formed is kept more than the required layer thickness.

- The unsolidified resin is then collected from the work piece by vacuum suction (refer picture 5 of figure 7).

- The molten wax is then filled inside the cavities and allowed to solidify by cooling it (refer picture 6 of figure 7).

- The layer is then milled to exact layer thickness required (refer picture 8 of figure 7).

- The next layer is then prepared over this layer by in the same process (refer picture 9 of figure 7). The complete cycle is repeated till the final part is ready.

The complete process is given below in the figure 7,


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Figure 7 A process flow of Solid Ground Curing

Day – 61. What are the main components of a SGC system?

Ans:The main component of SGC system includes:

- Data front end (DFE) work station- Model production machine (MPM) that again includes process engine,

operator’s console and vacuum generator- Automatic Dewaxing machine2. What are the main principles of a SGC system?

Ans: The basic principlesinvolved in the SGC process are given below:

i. Photo-polymerizationRaghu Engineering College Dept.ofMechEngg . Additive Manufacturing Unit-I

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- The chaining process is exactly same as that of SLA process only instead of Laser UV light is used here.

- Again in SLA an optical scanning system was used but here the portion to be solidified by the UV light is generated by a masked plate.

- The mask is prepared by printing the 2D image data of each slice on a transparent plate by nonimpact ionography printing process. This iconography process is similar to Xerography used in photo copiers and laser printers. The image is formed by depositing a black powder or toner on the mask plate. This carbon soot adheres to the substrate electrostatically.

- Once exposed the electrostatic toner is removed from the substrate for reuse

ii. Parallel processingIt is possible to process and build multiple parts in parallel by grouping them into batches.

iii. Layer-by-layer buildingThe layers are formed one over the other by continuous process of resin deposition and masked illumination. The layer thickness achieved after the hardening of the layer is more than the required one. The exact thickness is achieved by milling each layer before building the next layer. This milling process helps in achieving proper dimensional accuracy and also helps in adhesion of the new layer to be built.

iv. Support structureThe SGC system doesn’t need any external support structure as wax is deposited in the cavities after one layer is formed. This solidified wax gives the required support to the overhangs and undercuts.

3. What are the strengths and weaknesses of a SGC process?Strength:

- Parallel processing: Multiple parts can be processed and build.- Low Time and Cost: Speed of the system is very high (about 8 times than

other competitors) as whole cross-sectional area is solidified at a time. Production cost is 20-25% lower

- Self-supporting: Support structure made of wax supports the part in all dimensions so no special support structure is needed.

- Unique part properties: Parts produced are reliable, accurate, sturdy, machinable and can be mechanically finished.

- RP software (DFE) is interactive and user friendly


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- Minimum shrinkage effect: Shrinkage low due to full curing of each layer - High structural strength and stability: Due to curing of each layer before

the next layer internal stress developed are too minimal.- Process is not hazardous (no odors are generated)

Limitations:- Large space requirement: System physical dimensions large in

comparison to the other systems with a similar build volume.- Difficulty in removing wax: At times, wax is difficult to remove as it

might get stuck in corners and crevices.- Wastage of material: Lots of waste material generated due to shavings

produced by the milling process.- Machines are noisy in operation 4. What are the applications of SGC process?

General application- Conceptual Design Presentation- Design Proofing- Engineering Testing, Integration and Fitting- Functional Analysis- Exhibits, Pre-Production Sales, Market Research

Tooling and casting applications- Investment Casting, Sand Casting, fabrication of plastic parts

Mold and Tooling - Silicon Rubber Tooling, Epoxy Tooling, Spray Metal Tooling, Acrylic

Tooling, Plaster Mold CastingMedical imaging

- Diagnostic, Surgical Operation and Reconstruction Planning; Custom Prosthesis Design

Note: If the question is – Explain in detail the Solid Ground Curing (SGC. The answer should be written by combining question 1 from day – 5 and questions 1, 2, 3 and 4 from day – 6.

Homework:1. Brief about a case study on SGC process.2. Watch SGC process video.

Web Links: https://www.youtube.com/watch?v=DiIMMVbTdAc

Important questions:


https://www.youtube.com/watch?v=DiIMMVbTdAc

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1. Explain RP process chain with neat sketch. 2. Distinguish between traditional prototyping and rapid prototyping. 3. List fundamentals of Prototyping and discuss them in detail. 4. Write the historical development of Rapid Prototyping. 5. List fundamentals of Rapid Prototyping and discuss them in detail. 6. Outline the Advantages and Limitations of Rapid Prototyping. 7. Explain the classification of RP Process. 8. Discuss Rapid Prototyping process chain. 9. Explain Fundamental Automated Process chain. 10. List Advantages and Limitations of Rapid Prototyping and discuss each

one of them in detail. 11. Briefly explain the stereo lithography process with neat sketch and

what are the process parameters of SLA system that influence the part quality?

12. List Advantages and Limitations of Stereo Lithography process and discuss each one of them in detail.

13. Write the Applications of Stereo Lithography Apparatus. 14. Explain the working principle and process of Solid Ground Curing with a neat sketch. 15. Outline the Advantages and Limitations of Solid Ground Curing. 16. List Applications of Solid Ground Curing and discuss each one of them in detail. 17. Outline the Advantages and Limitations of Stereo Lithography process. 18. List Applications of Stereo Lithography Apparatus and discuss each one of them in detail.

IV B.Tech Mechanical Engineering Additive Manufacturing First Unit- Assignment - 1Topics covered: Introduction to Rapid Prototyping, Liquid based Rapid Prototyping Systems a) Stereo Lithography (SLA), b) Solid Ground Curing (SGC)1. a) Explain RP process chain with neat sketch. b) Distinguish between traditional prototyping and rapid prototyping.


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2. Briefly explain the stereo lithography process with neat sketch and what are the process parameters of SLA system that influence the part quality? 3. a) What is Rapid Prototyping and explain about different steps involved in Rapid Prototyping technology. b) Describe the benefits and limitations of Rapid Prototyping.4. Describe the working principle, advantages and disadvantages of SLA process with a neat diagram. 5. a) Describe the various stages in the development of rapid prototyping systems with highlighting the advantages and limitations. b) Explain rapid prototyping process chain. 6. a) Write the few applications of stereo lithography system? b) List advantages and disadvantages when rapid prototyping concept is applied to solid ground curing (SGC)? 7. Explain the importance of support structure.8. Describe the working principle, advantages and disadvantages of SLA process with a neat diagram. Generation and the possible design in detail?9. Briefly Explain the following?a) i). Differentiate between digital and Virtual Manufacturing? ii) Classify Additive Manufacturing processes? iii) Define Tessellation?


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