rapid prototyping full report
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Rapid Prototyping Technology is a group of manufacturing processes that enable the direct physical realization of 3D computer models. This technology converts the 3D computer data provided by a dedicated file format directly to a physical model, layer by layer with a high degree of accuracy. This technology is fast developing and is more than
competitive to traditional model building techniques considering time and degree of detail. The paper gives an overview on existing major RP techniques and their applications in engineering fields.
3. The basic process
4. Rapid prototyping techniques
6. RPT vs. conventional technologies
7. Future developments
The past decade has witnessed the emergence of new manufacturing technologies that build parts on a layer-by-layer basis. Using these technologies, manufacturing time for parts of virtually any complexity is reduced considerably. In other words, it is rapid.
Rapid Prototyping Technologies and Rapid Manufacturing offer great potential for producing models and unique parts for manufacturing industry. Thus, the reliability of products can be increased; investment of time and money is less risky. Not everything that is thinkable today is already workable or available at a reasonable price, but this technology is fast evolving and the better the challenges, the better for this developing process.
The term Rapid prototyping (RP) refers to a class of technologies that can automatically construct physical models from Computer-Aided Design (CAD) data.
It is a free form fabrication technique by which a total object of prescribed shape, dimension and finish can be directly generated from the CAD based geometrical model stored in a computer, with little human intervention. Rapid prototyping is an "additive" process, combining layers of paper, wax, or plastic to create a solid object. In contrast, most machining processes (milling, drilling, grinding, etc.) are "subtractive" processes that remove material from a solid block. RPâ„¢s additive nature allows it to create objects with complicated internal features that cannot be manufactured by other means.
In addition to prototypes, RP techniques can also be used to make tooling (referred to as rapid tooling) and even production-quality parts (rapid manufacturing). For small production runs and complicated objects, rapid prototyping is often the best manufacturing process available. Of course, "rapid" is a relative term. Most prototypes require from three to seventy-two hours to build, depending on the size and complexity of the object. This may seem slow, but it is much faster than the weeks or months required to make a prototype by traditional means such as machining. These dramatic time savings allow manufacturers to bring products to market faster and more cheaply.
The Basic Process
Although several rapid prototyping techniques exist, all employ the same basic five-step process. The steps are:
1. Create a CAD model of the design
2. Convert the CAD model to STL format
3. Slice the STL file into thin cross-sectional layers
4. Construct the model one layer atop another
5. Clean and finish the model
CAD Model Creation: First, the object to be built is modeled using a Computer-Aided Design (CAD) software package. Solid modelers, such as Pro/ENGINEER, tend to represent 3-D objects more accurately than wire-frame modelers such as AutoCAD, and will therefore yield better results. The designer can use a pre-existing CAD file or may wish to create one expressly for prototyping purposes. This process is identical for all of the RP build techniques.
Conversion to STL Format: The various CAD packages use a number of different algorithms to represent solid objects. To establish consistency, the STL (stereolithography, the first RP technique) format has been adopted as the standard of the rapid prototyping industry. The second step, therefore, is to convert the CAD file into STL format. This format represents a three-dimensional surface as an assembly of planar triangles, "like the facets of a cut jewel." 6 The file contains the coordinates of the vertices and the direction of the outward normal of each triangle. Because STL files use planar elements, they cannot represent curved surfaces exactly. Increasing the number of triangles improves the approximation, but at the cost of bigger file size. Large, complicated files require more time to pre-process and build, so the designer must balance accuracy with manageability to produce a useful STL file. Since the STL format is universal, this process is identical for all of the RP build techniques.
Slice the STL File: In the third step, a pre-processing program prepares the STL file to be built. Several programs are available, and most allow the user to adjust the size, location and orientation of the model. Build orientation is important for several reasons. First, properties of rapid prototypes vary from one coordinate direction to another. For example, prototypes are usually weaker and less accurate in the z (vertical) direction than in the x-y plane. In addition, part orientation partially determines the amount of time required to build the model. Placing the shortest dimension in the z direction reduces the number of layers, thereby shortening build time. The pre-processing software slices the STL model into a number of layers from 0.01 mm to 0.7 mm thick, depending on the build technique. The program may also generate an auxiliary structure to support the model during the build. Supports are useful for delicate features such as overhangs, internal cavities, and thin-walled sections. Each PR machine manufacturer supplies their own proprietary pre-processing software.
Layer by Layer Construction: The fourth step is the actual construction of the part. Using one of several techniques (described in the next section) RP machines build one layer at a time from polymers, paper, or powdered metal. Most machines are fairly autonomous, needing little human intervention.
Clean and Finish: The final step is post-processing. This involves removing the prototype from the machine and detaching any supports. Some photosensitive materials need to be fully cured before use. Prototypes may also require minor cleaning and surface treatment. Sanding, sealing, and/or painting the model will improve its appearance and durability.
Rapid Prototyping Techniques
Most commercially available rapid prototyping machines use one of six techniques. At present, trade restrictions severely limit the import/export of rapid prototyping machines, so this guide only covers systems available in the U.S.
Patented in 1986, stereolithography started the rapid prototyping revolution. The technique builds three-dimensional models from liquid photosensitive polymers that solidify when exposed to ultraviolet light. As shown in the figure below, the model is built upon a platform situated just below the surface in a vat of liquid epoxy or acrylate resin. A low-power highly focused UV laser traces out the first layer, solidifying the modelâ„¢s cross section while leaving excess areas liquid.
Figure 1: Schematic diagram of stereolithography. 7
Next, an elevator incrementally lowers the platform into the liquid polymer. A sweeper re-coats the solidified layer with liquid, and the laser traces the second layer atop the first. This process is repeated until the prototype is complete. Afterwards, the solid part is removed from the vat and rinsed clean of excess liquid. Supports are broken off and the model is then placed in an ultraviolet oven for complete curing.
Stereolithography Apparatus (SLA) machines have been made since 1988 by 3D Systems of Valencia, CA. To this day, 3D Systems is the industry leader, selling more RP machines than any other company. Because it was the first technique, stereolithography is regarded as a benchmark by which other technologies are judged. Early stereolithography prototypes were fairly brittle and prone to curing-induced warpage and distortion, but recent modifications have largely corrected these problems.
3.2 Laminated Object Manufacturing
In this technique, developed by Helisys of Torrance, CA, layers of adhesive-coated sheet material are bonded together to form a prototype. The original material consists of paper laminated with heat-activated glue and rolled up on spools. As shown in the figure below, a feeder/collector mechanism advances the sheet over the build platform, where a base has been constructed from paper and double-sided foam tape. Next, a heated roller applies pressure to bond the paper to the base. A focused laser cuts the outline of the first layer into the paper and then cross-hatches the excess area (the negative space in the prototype). Cross-hatching breaks up the extra material, making it easier to remove during post-processing. During the build, the excess material provides excellent support for overhangs and thin-walled sections. After the first layer is cut, the platform lowers out of the way and fresh material is advanced. The platform rises to slightly below the previous height, the roller bonds the second layer to the first, and the laser cuts the second layer. This process is repeated as needed to build the part, which will have a wood-like texture. Because the models are made of paper, they must be sealed and finished with paint or varnish to prevent moisture damage.
Figure 2: Schematic diagram of laminated object manufacturing. 8
Helisys developed several new sheet materials, including plastic, water-repellent paper, and ceramic and metal powder tapes. The powder tapes produce a "green" part that must be sintered for maximum strength. As of 2001, Helisys is no longer in business.
3.3 Selective Laser Sintering
Developed by Carl Deckard for his masterâ„¢s thesis at the University of Texas, selective laser sintering was patented in 1989. The technique, shown in Figure 3, uses a laser beam to selectively fuse powdered materials, such as nylon, elastomer, and metal, into a solid object. Parts are built upon a platform which sits just below the surface in a bin of the heat-fusable powder. A laser traces the pattern of the first layer, sintering it together. The platform is lowered by the height of the next layer and powder is reapplied. This process continues until the part is complete. Excess powder in each layer helps to support the part during the build. SLS machines are produced by DTM of Austin, TX.
Figure 3: Schematic diagram of selective laser sintering. 9
3.4 Fused Deposition Modeling
In this technique, filaments of heated thermoplastic are extruded from a tip that moves in the x-y plane. Like a baker decorating a cake, the controlled extrusion head deposits very thin beads of material onto the build platform to form the first layer. The platform is maintained at a lower temperature, so that the thermoplastic quickly hardens. After the platform lowers, the extrusion head deposits a second layer upon the first. Supports are built along the way, fastened to the part either with a second, weaker material or with a perforated junction.
Stratasys, of Eden Prairie, MN makes a variety of FDM machines ranging from fast concept modelers to slower, high-precision machines. Materials include ABS (standard and medical grade), elastomer (96 durometer), polycarbonate, polyphenolsulfone, and investment casting wax.
Figure 4: Schematic diagram of fused deposition modeling. 10
3.4 Solid Ground Curing
Developed by Cubital, solid ground curing (SGC) is somewhat similar to stereolithography (SLA) in that both use ultraviolet light to selectively harden photosensitive polymers. Unlike SLA, SGC cures an entire layer at a time. Figure 5 depicts solid ground curing, which is also known as the solider process. First, photosensitive resin is sprayed on the build platform. Next, the machine develops a photomask (like a stencil) of the layer to be built. This photomask is printed on a glass plate above the build platform using an electrostatic process similar to that found in photocopiers. The mask is then exposed to UV light, which only passes through the transparent portions of the mask to selectively harden the shape of the current layer.
Figure 5: Schematic diagram of solid ground curing. 11
After the layer is cured, the machine vacuums up the excess liquid resin and sprays wax in its place to support the model during the build. The top surface is milled flat, and then the process repeats to build the next layer. When the part is complete, it must be de-waxed by immersing it in a solvent bath. SGC machines are distributed in the U.S. by Cubital America Inc. of Troy, MI. The machines are quite big and can produce large models.
3.6 3-D Ink-Jet Printing
Ink-Jet Printing refers to an entire class of machines that employ ink-jet technology. The first was 3D Printing (3DP), developed at MIT and licensed to Soligen Corporation, Extrude Hone, and others. The ZCorp 3D printer, produced by Z Corporation of Burlington, MA is an example of this technology. As shown in Figure 6a, parts are built upon a platform situated in a bin full of powder material. An ink-jet printing head selectively deposits or "prints" a binder fluid to fuse the powder together in the desired areas. Unbound powder remains to support the part. The platform is lowered, more powder added and leveled, and the process repeated. When finished, the green part is then removed from the unbound powder, and excess unbound powder is blown off. Finished parts can be infiltrated with wax, CA glue, or other sealants to improve durability and surface finish. Typical layer thicknesses are on the order of 0.1 mm. This process is very fast, and produces parts with a slightly grainy surface. ZCorp uses two different materials, a starch based powder (not as strong, but can be burned out, for investment casting applications) and a ceramic powder. Machines with 4 color printing capability are available.
3D Systemsâ„¢ version of the ink-jet based system is called the Thermo-Jet or Multi-Jet Printer. It uses a linear array of print heads to rapidly produce thermoplastic models (Figure 6d). If the part is narrow enough, the print head can deposit an entire layer in one pass. Otherwise, the head makes several passes.
Sanders Prototype of Wilton, NH uses a different ink-jet technique in its Model Maker line of concept modelers. The machines use two ink-jets (see Figure 6c). One dispenses low-melt thermoplastic to make the model, while the other prints wax to form supports. After each layer, a cutting tool mills the top surface to uniform height. This yields extremely good accuracy, allowing the machines to be used in the jewelry industry.
Ballistic particle manufacturing, depicted in Figure 6b, was developed by BPM Inc., which has since gone out of business.
Figure 6: Schematic diagrams of ink-jet techniques. 12
Applications of Rapid Prototyping
Rapid prototyping is widely used in the automotive, aerospace, medical, and consumer products industries
The aerospace industry imposes stringent quality demands. Rigorous testing and certification is necessary before it is possible to use materials and processes for the manufacture of aerospace components. Yet, Boeing's Rocketdyne has successfully used RP technology to manufacture hundreds of parts for the International Space Station and
the space shuttle fleet. The company also uses RP to manufacture parts for the military's F-18 fighter jet in glass-filled nylon .Another not yet mature idea is to have a RP machine on board of the International Space Station (ISS) to produce spare parts for repair jobs. Models are widely used in automotive industry for design studies, physical experiments etc. Functional parts have been used for titanium casting have been made by RP techniques for parts in F1 racing cars
The Department of Architecture at the University of Hongkong is applying Rapid Prototyping Technology for teaching students about the new possibilities in testing there draft, e.g. for lighting conditions, mechanical details. One example is the Sidney Opera House.
RPT has created a new market in the world of orthodontics. Appearance conscious adults can now have straighter teeth without the embarrassment of a mouth full of metal. Using stereolithography technology custom-fit, clear plastic aligners can be produced in a customized mass process. The RP world has made its entry into the hearing instrument world too. The result is instrument shells that are stronger, fit better and are biocompatible to a very high degree. The ear impression is scanned and digitized with an extremely accurate 3-D scanner. Software specially developed for this converts the digital image into a virtual hearing instrument shell .Thanks to the accuracy of the process, instrument shells are produced with high precision and reproducibility. This means the hearing instruments fit better and the need for remakes is reduced. In the case of repairs, damage to or loss of the ITE instrument, an absolutely identical shell can be manufactured quickly, since the digital data are stored in the system.
Arts and Archeology
Selective Laser Sintering with marble powders can help to restore or duplicate ancient statues and ornaments, which suffer from environmental influences. The originals are scanned to derive the 3D data, damages can be corrected within the software and the duplicates can be created easily. One application is duplicating a statue . The original statue was digitized and a smaller model was produced to serve a base
for a bronze casting process.
A much-anticipated application of rapid prototyping is rapid tooling, the automatic fabrication of production quality machine tools. Tooling is one of the slowest and most expensive steps in the manufacturing process, because of the extremely high quality required. Tools often have complex geometries, yet must be dimensionally accurate to within a hundredth of a millimeter. In addition, tools must be hard, wear-resistant, and have very low surface roughness (about 0.5 micrometers root mean square). To meet these requirements, molds and dies are traditionally made by CNC-machining, electro-discharge machining, or by hand. All are expensive and time consuming, so manufacturers would like to incorporate rapid prototyping techniques to speed the process.
RPTvs. conventional technologies
RPT does notâ€and will notâ€replace completely conventional technologies such NC and high-speed milling, or even hand-made parts. Rather, one should regard RPT as one more option in the toolkit for manufacturing parts. Figure 14 depicts a rough comparison between RPT and milling regarding the costs and time of manufacturing one part as a function of part complexity10. It is assumed, evidently, that the part can be manufactured by either technology such that the material and tolerance requirements are met.
1. Strength, Elasticity and Temperature Resistance.
2. Typical quantities
3. Standard accuracy
4. Time Savings
5. Surface structure
7. Use any type of model
Rapid prototyping is starting to change the way companies design and build products. On the horizon, though, are several developments that will help to revolutionize manufacturing as we know it.
One such improvement is increased speed. "Rapid" prototyping machines are still slow by some standards. By using faster computers, more complex control systems, and improved materials, RP manufacturers are dramatically reducing build time.
Another future development is improved accuracy and surface finish. Todayâ„¢s commercially available machines are accurate to ~0.08 millimeters in the x-y plane, but less in the z (vertical) direction. Improvements in laser optics and motor control should increase accuracy in all three directions. In addition, RP companies are developing new polymers that will be less prone to curing and temperature-induced warpage.
The introduction of non-polymeric materials, including metals, ceramics, and composites, represents another much anticipated development. These materials would allow RP users to produce functional parts.
Another important development is increased size capacity. Currently most RP machines are limited to objects 0.125 cubic meters or less. Larger parts must be built in sections and joined by hand. To remedy this situation, several "large prototype" techniques are in the works.
One future application is Distance Manufacturing on Demand, a combination of RP and the Internet that will allow designers to remotely submit designs for immediate manufacture.
Finally, the rise of rapid prototyping has spurred progress in traditional subtractive methods as well. Advances in computerized path planning, numeric control, and machine dynamics are increasing the speed and accuracy of machining. Modern CNC machining centers can have spindle speeds of up to 100,000 RPM, with correspondingly fast feed rates. 34 Such high material removal rates translate into short build times. For certain applications, particularly metals, machining will continue to be a useful manufacturing process. Rapid prototyping will not make machining obsolete, but rather complement it.
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• Rapid Prototyping (RP) techniques are methods that allow designers to produce physical prototypes quickly.
• It consists of various manufacturing processes by which a solid physical model of part is made directly from 3D CAD model data without any special tooling.
• The first commercial rapid prototyping process was brought on the market in 1987.
• Nowadays, more than 30 different processes (not all commercialized) with high accuracy and a large choice of materials exist.
• These processes are classified in different ways: by materials used, by energy used, by lighting of photopolymers, or by typical application range
The Rapid Prototyping Technique
• In the Rapid Prototyping process the 3D CAD data is sliced into thin cross sectional planes by a computer.
• The cross sections are sent from the computer to the rapid prototyping machine which build the part layer by layer.
• The first layer geometry is defined by the shape of the first cross sectional plane generated by the computer.
• It is bonded to a starting base and additional layers are bonded on the top of the first shaped according to their respective cross sectional planes.
• This process is repeated until the prototype is complete.
Prototyping- What is it ?
Physical Model of the product
. Degrees of Prototyping
. Full Complete scale Model - functional model
. Scaled Model - functional/ simulated material
. Geometrical configuration
. Partial ….
Design Change (iterations)
Free Form Prototyping (complex object fabrication/ visualization)
Testing Fit/ Packaging
Cost, Time, and resource estimation
First to Market -- Critical for today’s industry
Rapid production (concurrent activities)
JIT concept (0 Inventory)
Rapid tooling / no tooling -- trend in technology
Design for manufacturability
Design for assembly
Design for maintainability
Design for reliability
Design for Quality
Design Parameters (Tolerances/ allowances)
. Reverse Engineering
. Die fabrication
. Tool Path generation
Classification of Prototyping Technology
Subtractive Processes (Material Removal)
Ex : Milling, turning, grinding,-- machining centers .., when used for prototype production
Degree of automation vary
Additive (Material Build-up)
Ex : Stereolithography
Degree of sophistication vary
Ex : Forging, Casting, ..
When used for Prototyping, it is usually manual
Sophistication of Prototyping Technology
Such Technology is known by different terms, such as :
Free form Fabrication (F3)
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postgraduate programmes (Master and Doctoral) with MHRD scholarship/assistantship. The performance of the candidate in GATE will be considered for admission. If the candidate is to be selected through interview for postgraduate programmes, minimum 70% weightage is to be given to the performance in GATE. The remaining weightage (30% maximum) can be given to the candidate’s academic record or performance in interview. The admitting institution could however prescribe minimum passing percentage of marks in the interview. Some colleges/institutes specify GATE qualification as the mandatory requirement even for admission without MHRD scholarship/assistantship.
The performance of the candidate in GATE will be considered for admission. If the candidate is to be selected through interview for postgraduate programmes, minimum 70% weightage is to be given to the performance in GATE. The remaining weightage (30% maximum) can be given to the candidate’s academic record or performance in interview. The admitting institution could however prescribe minimum passing percentage of marks in the interview
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Rapid prototyping is the fabrication of parts from CAD data sources. Several rapid prototyping methods have been created to produce objects of complex geometries in a relatively short amount of time. Rapid prototyping allows design challenges to be determined earlier in the design process, saving time and money. The technology of rapid prototyping is easy to access and simple to understand.
To begin the process, the powder delivery system is moved up a set distance permitting a layer of material powder to be created in the fabrication chamber by the roller. The function of the roller is to distribute and compress the powder evenly in the fabrication chamber. The multi-channel jetting head then creates a layer of liquid adhesive in the geometry of the part in the bed of powder. A layer of the part geometry is created when the powder that containing liquid adhesive bonds and hardens.
When a layer is completed, the fabrication piston will move down in increments. These increments are specified to determine the layer thickness.
• Fast Fabrication
• Low Material Cost
• Variety of Colors
• No external supports are required
• Surface Finish
The fused disposition modeling process uses plastic filament that is 1/16” in diameter and stored on a coil. Material that is fed from a hopper in the form of pellets is an option in some low cost configurations. The entire system is enclosed in an oven chamber to control of the process temperature. The system operates best slightly under the melting point of the plastic.
The nozzle is able to move in the X and Y directions and is mounted to a stage system. Layers are formed by very small beads of plastic being deposited from the nozzle in the shape of the part geometry. The plastic beads begin harden immediately after being extruded from the nozzle in addition to bonding with the layer beneath.
Good layer bonding with ABS materials
Fast small part production
Good for parts with thin walls
Usage of water soluble materials allows support structures to be easily removable.
• Slow production rates for thick sectioned parts.
• Secondary operations are needed to remove support structures.
• Poor surface finishes.
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•Selective Laser Sintering (SLS)
•Wax jet printing (Thermojet)
•Light Engineered Net Shaping (LENS)
•Fused Deposition Modeling (FDM)
•Solid Base Curing
•Laminated Object Modeling (LOM)
–material is added, not removed
•Direct fabrication from a CAD file
•Selective Laser Sintering (SLS)
•Wax jet printing (Thermojet)
•Light Engineered Net Shaping (LENS)
•Fused Deposition Modeling (FDM)
•Solid Base Curing
•Laminated Object Modeling (LOM)