PES INSTITUTE OF TECHNOLOGY BANGALORE SOUTH CAMPUS Hosur Road, (1K.M. Before Electronic City), Bangalore 560 100 DEPARTMENT OF MECHANICAL ENGINEERING SCHEME AND SOLUTION - I ST INTERNAL TEST Subject : RAPID PROTOTYPING Semester: VIII Sub. Code : 10ME837 Section: A&B Name of the faculty : ASHUTOSH KHANNA Q.No Question Marks 1 Why there is need for time compression in product development? 10 Write brief history of RP Technology. Sol Any new product development has to go through various design and testing phases so that it can become 100% successful in market and remain competitive and sustainable. This is time consuming and hence need is felt in time compression in product development, which is very well done by using Rapid prototyping techniques. The Time Compression in Product is well shown below: 2 Mark s TIME COMPRESSION 5 Marks In time compression in Product development Conceptual Design, Detail design, Engineering Analysis Tooling, Production stages has been modified with use of Rapid Prototyping and Direct Digital Manufacturing Techniques thus substantially compressing the product development time, and thus making companies product quality and competitive in today s ever changing business environment. Brief history of RP Technology 1986: First Patent on Stereo lithography By Charles Hull, Founder of STRATASYS. 1989: Patent on Selective Laser Sintering By Carl Deckard 1992: Fused Deposition Modelling Patent Acquired By STRATYSYS. 2004: Dr Boyers Introduced Open Source REPRAP 2008: Direct Digital Manufacturing and 3D Printing 3 Marks
Que No 2 Question (10 Marks) Write classification of RP Techniques? Explain with help of Flow chart CAD data flow in a RP System. In all commercial RP processes, the part is fabricated by deposition of layers contoured in a (x-y) plane two dimensionally. The third dimension (z) results from single layers being stacked up on top of each other, but not as a continuous z-coordinate. Therefore, the prototypes are very exact on the x-y plane but have stair-stepping effect in z-direction. If model is deposited with very fine layers, i.e., smaller z-stepping, model looks like original. One of the basic way of classifying a RP Technology is based on use of material or type of process, which results in creating a 3D Component, following is simple classification based on Process RAPID PROTOTYPING Flow chart CAD data flow in a RP System
Question 3 (10 Marks) Explain a basic Stereo lithography System? Write various process parameters associated with a SLA System. Give Example of Commonly made Components/Prototypes created by a SLA System. A Basic Stereo lithography System is Composed of 1. Solid State Laser Device 2. A Scanner System 3. An Elevator Platform 4. A Liquid Resin VAT. 5. Computer Hardware And Software A laser beam is directed in the X-Y axes across the surface of the resin according to the 3D data supplied to the machine (the.stl file), whereby the resin hardens precisely where the laser impinges the surface and local solidification in X Y Direction occurs forming a layer of thickness as small as.006 inches. Once the layer is completed, the computer controlled sensor actuated platform within the vat drops down by a fraction (in the Z axis) and the subsequent layer is traced out by the laser. This continues until the entire object is completed and the platform can be raised out of the vat for removal. After each layer is built the Prototype is ready for post-processing and excess resin is removed using a solvent such as alcohol and cured using a uv light source. Various Process parameters for a SLA Process are 1. Laser type, wavelength, 2. power 3. Layer thickness 4. Drawing speed 5. Max part weight 6. Elevator resolution & 7. repeatability 8. Vat capacity 9. Max build envelop 10. Operating system Commonly made Components are Prototypes for concept models, Form-fit for assembly tests and process planning, Models for investment casting, replacement of the wax pattern Patterns for metal spraying, epoxy molding and other soft tooling, and Micro parts.
Ques No 4 Question What is selective laser sintering? Write and explain various component of SLS Equipment? How its different than Stereo lithography System. Laser sintering is a laser based 3D printing process that works with powdered materials. The laser is traced across a powder bed of tightly compacted powdered material, according to the 3D data fed to the machine, in the X-Y axes. As the laser interacts with the surface of the powdered material it sinters, or fuses, the particles to each other forming a solid. As each layer is completed the powder bed drops incrementally and a roller smoothes the powder over the surface of the bed prior to the next pass of the laser for the subsequent layer to be formed and fused with the previous layer, a typical SLS System is Composed of CO2 Laser Device, A Build Chamber, Powder Level Roller, Powder feed, Computer Interface, Sensors and actuators. Before starting CO2 laser scanning for sintering of a slice the temperature of the entire bed is raised just below its melting point by infrared heating in order to minimize thermal distortion (curling) and facilitate fusion to the previous layer Marks (10) Selective laser sintering (SLS) gives the capability of flexible snaps and living hinges as well as high stress and heat tolerance, Wide variety of materials such as flexible and rigid plastics, electrometric materials, fully dense metals and casting patterns Unlike Stereo lithography supports not needed and there is reduced distortion from stresses In SLA Build strategies have been developed to increase build speed and to decrease amount of resin by depositing the parts with a higher proportion of hollow volume. These strategies are devised as these models are used for making cavities for precision castings. Here walls are designed hollow connected by rod-type bridging elements and skin is introduced that close the model at the top and the bottom. These models require openings to drain out uncured resin.
Que 5 What is Fused Deposition Modelling? Explain the role of Extruder is quality of the component created using FDM process. What are the various process parameters in FDM System In Fused Deposition Modelling (FDM) process a movable (x-y movement) nozzle on to a Substrate deposits thread of molten polymeric material. The build material is heated slightly above (approximately 0.5 C) its melting temperature so that it solidifies within a very short time (approximately 0.1 s) after extrusion and cold-welds to the previous layer as shown in figure below: 10 Marks The quality of Extrusion can be understood from the fact that mathematical or physics-based understanding of extrusion processes can quickly become complex, since it can involve many nonlinear terms like nozzle design, material, discharge through nozzle etc. The basic science involves extrusion of highly viscous materials through a nozzle. It is reasonable to assume that the material flows as a Newtonian fluid in most cases. Hence main drawback results 1. Accuracy which is relatively low and further it is 2. Its difficult to build parts with complicated details 3. Poor strength in vertical direction and 4. Slow for building mass parts. 5. Further steady nozzle movement and material extrusion rates, addition of support structures for overhanging features and speed of the nozzle head, which affects the slice thickness. Various Process parameters and their values are as follows a) Liquefier temperature: b) Chamber temperature c) Stand off distance d) Filament feed rate e) Nozzle diameter (0.012 and 0.025 inch) f) Deposition speed g) Material type (The build and support materials come in filament form, about 0.070 inches in diameter and rolled up on spools) i) Fill spacing /Build envelop (10" x 10" X 10" range, whereas the 8000 and the Quantum can build 24" x 20" x 24" parts)
Que 6 What are the various process parameters of a Selective Laser Sintering Equipment? What are the advantages of SLS Technique of 3D Prototyping? In a SLS System a laser beam is traced over the surface of a tightly compacted powder made of thermoplastic material. The powder is spread by a roller over the surface of a build cylinder. A piston moves down one object layer thickness to accommodate the layer of powder. The power supply system is similar in function to the build cylinder. It also comprises a cylinder and piston. In this case the piston moves upward incrementally to supply powder for the process. SLS system contains the following hardware components: 1. Build chamber dimensions (381x330x457mm) 2. Process station (2100x1300x1900mm) 3. Computer cabinet (600x600x1828mm) 4. Chiller (500x800x900mm) 5. The software that comes with the Vanguard TM si2tm SLS System includes the Windows 2000 operating system and other proprietary application software such as the slicing module, automatic part distribution module, and part modification application software. Process parameters can be lumped into four categories: (1) laser-related parameters (laser power, spot size, pulse duration, pulse frequency, etc.) (2) scan-related parameters (scan speed, scan spacing, and scan pattern) (3) powder-related parameters (particle shape, size and distribution, powder bed density, layer thickness, material properties, etc.) (4) temperature-related parameters (powder bed temperature, powder feeder temperature, temperature uniformity, etc.) Various Advantages of SLS RP Techniques are as Follows Parts and/or assemblies that move and work that have a good surface finish and feature detail Selective laser sintering (SLS) gives the capability of flexible snaps and living hinges as well as high stress and heat tolerance Wide variety of materials such as flexible and rigid plastics, electrometric materials, fully dense metals and casting patterns inexpensive materials safe materials supports not needed reduced distortion from stresses produce parts simultaneously
Que 7 Compare the FDM, SLS and SLA RP Technique based on accuracy, surface finish, materials, build time, cost etc. 10 Marks RP is a group of technologies which allow rapid freeform fabrication of 3D objects of limitless geometric complexity through a layered manufacturing process. RP technology has potential to reduce time required from conception to market up to 10-50 percent (Chua and Leong, 2000) as shown in figure 10. It has abilities of enhancing and improving product development while at the same time reducing costs due to major breakthrough in manufacturing (Chua and Leong, 2000). Although poor surface finish, limited strength and accuracy are the limitations of RP models, it can deposit a part of any degree of complexity theoretically. Therefore, RP technologies are successfully used by various industries like aerospace, automotive, jewelry, coin making, tableware, saddletrees, biomedical etc. It is used to fabricate concept models, functional models, patterns for investment and vacuum casting, medical models and models for engineering analysis (Pham and Demov, 2001) A comparative study of various process are tabulated below Parameter SLA SLS FDM Accuracy Best Flexible Process Depends On Extrusion Surface Finish Best Least Depends On Nozzle Material Limited Resins Metallic Materials can be used Large material base Buildtime High High High Cost High Cost of Equipment And Materials High Cost of Equipment Mass Production Under development Under development Functional Components can be created Component Strength Material Best
Que 8 Write Brief Notes of Following: 1. Stair Stepping Effect. 2. Tessellated CAD Model and Slicing 3. Applications of SLS 4. Build Styles STAIR STEPPING EFFECT RP process belong to the generative (or additive) production processes unlike subtractive or forming processes such as lathing, milling, grinding or coining etc. in which form is shaped by material removal or plastic deformation. In all commercial RP processes, the part is fabricated by deposition of layers contoured in a (x-y) plane two dimensionally. The third dimension (z) results from single layers being stacked up on top of each other, but not as a continuous z-coordinate. Therefore, the prototypes are very exact on the x-y plane but have stair-stepping effect in z-direction. If model is deposited with very fine layers, i.e., smaller z-stepping, model looks like original. RP can be classified into two fundamental process steps namely generation of mathematical layer information and generation of physical layer model. Real error on slice plane is much more than that is felt, as shown in figure 12(a). For a spherical model Pham and Demov (2001) proposed that error due to the replacement of a circular arc with stair-steps can be defined as radius of the arc minus length up to the corresponding corner of the staircase, i.e., cusp height (figure 12 (b)). Thus maximum error (cusp height) results along z direction and is equal to slice thickness. Therefore, cusp height approaches to maximum for surfaces, which are almost parallel with the x-y plane. Maximum value of cusp height is equal to slice thickness and can be reduced by reducing it; however this results in drastic improvement in part building time. Therefore, by using slices of variable thicknesses (popularly known as adaptive slicing, as shown in figure 13), cusp height can be controlled below a certain value. TESSALATION In tessellation surfaces of a CAD model are approximated piecewise by using triangles. It is true that by reducing the size of the triangles, the deviation between the actual surfaces and approximated triangles can be reduced. In practice, resolution of the STL file is controlled by a parameter namely chordal error or facet deviation as shown in figure 2. It has also been suggested that a curve with small radius (r) should be tessellated if its radius is below a threshold radius (ro) which can be considered as one tenth of the part size, to achieve a maximum chordal error of (r/ro). Value of can be set equal to 0 for no improvement and 1 for maximum improvement. Here part size is defined as the diagonal of an imaginary box drawn around the part and is angle control value (Williams et al., 1996).
APPLICATIONS OF SLS (1) Concept models. Physical representations of designs used to review design ideas, form and style. (2) Functional models and working prototypes. Parts that can withstand limited functional testing, or fit and operate within an assembly (3) Polycarbonate (Rapid CastingTM) patterns. Patterns produced using polycarbonate, and then cast in the metal of choice through the standard investment casting process. These build faster than wax pattern sand are ideally suited for designs with thin walls and fine features. These patterns are also durable and heat resistant. (4) Metal tools (Rapid ToolTM). Direct rapid prototype of tools of molds for small or short production runs. Selective Laser Sintering Applications: Rapid Manufacturing Aerospace Hardware UAS, UAV, UUV, UGV Hardware Medical and Healthcare Electronics; Packaging, Connectors BUILD STYLES Once part deposition orientation is decided and slice thickness is selected, tessellated model is sliced and the generated data in standard data formats like SLC (stereolithography contour) or CLI (common layer interface) is stored. This information is used to move to step 2, i.e., generation of physical model. The software that operates RP systems generates laser-scanning paths (in processes like Stereolithography, Selective Laser Sintering etc.) or material deposition paths (in processes like Fused Deposition Modeling). This step is different for different processes and depends on the basic deposition principle used in RP machine. Information computed here is used to deposit the part layer-by-layer on RP system platform.