A Paper on:
RAPID PROTOTYPING Presented by PUJITHA AHALYA.B
USMAN ALI
III/IV B.TECH
III/IV B.TECH
[email protected]
[email protected]
DEPARTMENT OF MECHANICAL ENGINEERING
KONERU LAKSHMAIAH COLLEGE OF ENGINEERING (Autonomous) Greenfields, Vaddeswaram, Guntur district, Andhra Pradesh.
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Abstract: Prototype refers to the paradigm of the object that has to be fabricated. Of the other techniques available, rapid prototyping stands better. Rapid prototyping is the automatic construction of physical objects using solid free form fabrication. Rapid prototyping takes virtual designs from computer aided design (CAD), transforms them into thin horizontal cross-sections, still virtual and then creates each cross-section in physical space, one after the next until the model is prepared. It is a WYSIWYG (what you see is what you get), process where the virtual model and physical model correspond almost identically. Objects can be made which are extremely accurate, complex, and picturesque, and which no other technology can produce. The design undergoes iterative observation before the final output. Traditional prototyping techniques are over-ridden by RP. Rapid prototyping system reduces construction of complex objects to a manageable, straight forward and relatively fast process. This has resulted in their wide use by engineers as a way to manufacturing, to better understand and communicate product designs and to make rapid tooling to manufacture those products. RP makes use of the techniques such as: stereo-lithography, Laminated Object Manufacturing, Selective laser Sintering, Fused deposition modeling, and 3D-printing, 3D-inkjet printing. The aim of this paper is to demonstrate the application of rapid prototyping (RP) technology as a compelling tool that can provide benefits throughout the process of developing new products. It aims to provide an insight into the way in which RP technologies have been integrated into this strategic design development process that employ to ensure that the products under development are marketable, manufacturable and ultimately profitable. 1.
Introduction:
Prototype: In many fields, there is great uncertainty as to whether a new design will actually do what is desired. New designs often have unexpected problems. A prototype is built to examine the function of the new design before starting production of a product. The gross cost of production is decided in the development phase. Thus, the product development phase plays a vital role in the manufacturing organization. Advanced technologies such as Rapid prototyping and tooling constitute an important part to product design and development. Prototype enables to do desired modifications during development phase of any product. Also, a model or prototype is very much necessary to communicate an idea between product developers and customers. Rapid prototyping refers to the automatic construction of mechanical models with the use of machines , which makes use of computer-aided manufacturing (CAM).The machine reads data from a CAD drawing and lays down successive layers of liquid, powder or sheet material and this way builds up the model from a series of cross sections. These layers, which correspond to the virtual cross section in the CAD model, are joined together or fused automatically to create the final shape. It is able to create almost any shape or geometric feature. The standard data interface between CAD software and the machine is the STL file format. A STL file approximates the shape of a part or assembly using triangular facets tiny facets produces a higher quality surface.
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The word RAPID relative: construction of a model with contemporary methods can take from several hours to several days, depending on the method used and the size and the complexity of model.
2. Need For Prototyping: The extreme usage of complicated shapes and availability of limited resources led the way to development of things field of manufacturing methodology. To increase effective communication. To decrease development time. To decrease costly mistakes. To minimize sustaining engineering changes. To extend product lifetime by adding necessary features and eliminating redundant features early in the design. Takes less time to design and manufacture. Meets customer demand.
3. Methods of Prototyping: There are two main methods of prototyping, which are derived from similar approaches in sculpture. • Subtractive prototyping Additive prototyping Subtractive process:. In this technique the machine starts out with a block of plastic and uses a delicate cutting tool to carve away material, layer by layer to match the digital object. They may start with a block, sheet, or tube of raw material and then, by drilling, cutting, lathing or by grinding; the material is removed, yielding the desired object or product. This is similar to a computer-controlled lathe. This is earlier and less efficient. Additive process: The desired object is built from bottom to top in very thin layers. Whereas subtractive techniques require hard-earned craft skills for the complicated and unique setups that vary with each job, additive techniques require no special knowledge on the part of the prototype fabricator. Rapid prototyping is an additive process . Today's additive technologies offer advantages in many applications compared to classical subtractive fabrication methods such as milling or turning, they are:
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Objects can be formed with any geometric complexity or intricacy without the need for elaborate machine setup or final assembly; Rapid prototyping systems reduce the construction of complex objects to a manageable, straightforward, and relatively fast process.
4. The Basic Process: Although several rapid prototyping techniques exist, all employ the same basic five-step process. The steps are: • •
Create a CAD model of the design Convert the CAD model to STL format
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Slice the STL file into thin cross-sectional layers
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Construct the model one layer atop another
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Clean and finish the model
4.1. 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.
4.2. Conversion to STL Format: The various CAD packages use a number of different algorithms to represent solid objects. To establish consistency, the Stereo lithography format has been adopted as the standard of the rapid prototyping industry. Therefore, the second step is to convert the CAD file into Stereo lithography (.stl) format. This format represents a threedimensional surface as an assembly of planar triangles, "like the facets of a cut jewel."
4.3. Slice the STL File: In the third step, a pre-processing program prepares the STL file to be built. Usually the prototypes are less accurate and weaker in z-directions so placing the shortest dimension of prototype in z-direction increases accuracy and also shorten the building 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.
4.4. Layer-by-Layer Construction: The fourth step is the actual construction of the part. Using one of several techniques RP machines build one layer at a time from polymers, paper, or powdered metal. Most machines are fairly autonomous, needing little human intervention.
4.5. 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.
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5. Rapid Prototyping Techniques: Most commercially available rapid prototyping machines use one of six techniques. The techniques are o Stereo lithography. o Laminated Object Manufacturing o Selective Laser Sintering o Fused Deposition Modeling o
3-D Inkjet Printing
5.1 Stereo lithography: Stereo lithography is the most widely used Rapid prototyping technology. The technique builds three-dimensional models from liquid photosensitive polymers that solidify when exposed to ultraviolet light or laser beam. 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 model’s cross section while leaving excess areas liquid. Next, an elevator incrementally lowers the platform into the liquid polymer. A sweeper recoats the solidified layer with liquid, and the laser traces the second layer atop the first. The process is repeated until the prototype is complete. Later 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 coring. Benefits of Stereo lithography: 1. 2. 3. 4.
Stereo lithography provides greatest accuracy. Good surface finish can be obtained. Low delivery time. Tolerances can be obtained up to 0.1 mm.
5.2 Laminated Object Manufacturing:
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Technique material is usually a paper sheet laminated with adhesive on one side, but plastic and metal laminates are appearing. Layer fabrication starts with sheet being adhered to substrate with the heated roller. The laser then traces out the outline of the layer. Non-part areas are cross-hatched to facilitate removal of waste material. Once the laser cutting is complete, the platform moves down and out of the way so that fresh sheet material can be rolled into position. Once new material is in position, the platform moves back up to one layer below its previous position and the process can now be repeated. The excess material supports overhangs and other weak areas of the part during fabrication. The crosshatching facilitates removal of the excess material. Once completed, the part has a woodlike texture composed of the paper layers. Moisture can be absorbed by the paper, which tends to expand and compromise the dimensional stability. Therefore, most models are sealed with a paint or lacquer to block moisture ingress. Benefits of Laminated object manufacturing: 1. Low cost of operation. 2. The parts can be made quite large. 3. Material used for prototyping is readily available.
5.3 Fused Deposition Modeling: FDM is the most widely used rapid prototyping technology after stereo lithography. A plastic filament is unwound from a coil and supplies material to an extrusion nozzle. The nozzle is heated to melt the plastic and has a mechanism which allows the flow of the melted plastic to be turned on off. The nozzle is mounted to a mechanical stage which can be moved in both horizontal and vertical directions. As the nozzle is moved over the table in the required geometry, it deposits a thin bead of extruded plastic hardens immediately after being squirted from the nozzle and bonds to the layer below. The entire system is contained within a chamber which is held at a temperature just the melting point of the plastic. Benefits of FDM: 1. 2. 3.
The method is office friendly and quiet. These are high precision machines. The parts can be made quite large.
5.4 Selective Laser Sintering:
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Heat fusible powders are used in this technique to make a prototype. 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-fusible 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. This method proves to best as it makes use of metal powders directly. Benefits of Selective Laser Sintering: 1. Metals can be used.
5.5 3-D Ink-Jet Printing: The parts are built upon a platform situted in a bin full of powder material. An inkjet 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, glue, or other sealants to improve durability and surface finish. Typical layer thickness is of the order of 0.1 mm. Two different materials, a starch based powder (not as strong, but can be burned out, for investment casting applications) and ceramic powder are used for this purpose.3D Systems' 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 .If the part is narrow enough, the print head can deposit an entire layer in one pass. Otherwise, the head makes several passes. The machines use two ink-jets. 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.
Benefits3-D Ink-Jet Printing: 1. 2. 3. 4.
This process is very fast, and produces parts with a slightly grainy surface. This yields extremely good accuracy, allowing the machines to be used in the jewellery. Speedy fabrication and low materials cost. It’s probably the fastest of all RP methods.
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6. Advantages: Provides Concept models for better visualization. Provides the proof of concept necessary to attract funding. Early visibility of the prototype gives users an idea of what the final system looks like. Encourages activity interaction among users and producer. Enhance communications between marketing, engineering, manufacturing, and purchasing departments. Assists to identify any problems with the efficacy of earlier design, requirements analysis and coding activities To extend product lifetime by adding necessary features and eliminating redundant features early in the design.
No tools are required hence the problem of tool wear and stopping process for tool change is also absent. The product development cost reduces effectively. Increases system development speed, get products market sooner.
7. Disadvantages: Only limited materials can be used for production. Difficult to produce the larger prototypes.
Stair Step Effect – RP techniques produce a vertical stair step surface finish since parts are built by creating discrete layers. Accuracy – The precision required in a model is another important consideration. Though the required accuracy & repeatability are specified for most generation processes. Quite often the end results depend on operator’s skill & talent in generating CAD Models.
8. Applications: 8.1 Mechanical applications:
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Rapid Prototyping (RP) is a continuously evolving technology. RP models are becoming widely used in many industrial sectors. Adjacent are the some of mechanical components made by RP technique.
This is the prototype of 4-cylinder block. RP technology is able to produce the prototypes of any complicated design. It can be used to prepare the patterns for casting. Thus patterns produced can be used for investment moulding.
Rapid Manufacturing: Rapid prototyping is moving towards tool-less manufacturing applications, known as Rapid manufacturing, as materials and systems improve. Rapid Manufacturing is a process of producing products directly from CAD data. RM is used for short runs and is ideal for producing custom parts tailored to the user’s exact specifications. NASA is also experimenting in using RP machines to produce space suit and gloves. They make use of the delivery of metal powders into a highpower laser beam where they're fused into layers. Robotic or X-Y-Z controlled-platform systems are used to guide the deposition of the material and very large parts and tools can be made These systems produce fully-dense metal parts with good accuracy and metallurgical properties requiring relatively minor secondary finishing operations. Figure shows the valves made with titanium material.
8.2 Medical applications: Rapid prototyping in the field of medicine is making a move with an inclined pace. Surgeons make use of the prototypes made by RP technique for successive planning of complicated operations.
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It is indigestible fact that rapid prototyping in conjunction with some recent medical developments may able to produce organs with great difficulty. Surprisingly they include kidneys, heart. Researchers at the Medical University of South Carolina have been putting the building blocks in place to "print" working and transplantable human kidneys. The figure shows the possible road map for printing the organs.
The fanciful image shows the possibility of printing or fabricating human hearts. This heart here shows the stepping stone to the next Gen extreme complex yet realistic models, which will be a boon to the Medical field.
8.3 Electrical-Electronic applications: Precession processes are also under development for the mass fabrication of small metal parts. Figure shows a tiny transformer, an electronic component made by using SDM.
8.4 Art, Architecture Design: Ra p id prototyping is being used by a number of artists to build a wide variety of sculptural objects. Some of these works are realistic and representational while others are abstract.
Conclusion: Let’s throwing lights on the Advantages which are more profound then the known Disadvantages, it’s evident that though expensive, this technology proves to develop more creative, complex and imaginative objects with the help of high definition machines. At present the process is costlier than other conventional ones yet it assures that in the near future this technology has an authenticated role to play for the development in all known fields of science and technology. To conclude this technology comes with a promise that it will be available with much lower cost, to all Research centers, Universities, and all high schools for better designs. 10
References: § § § §
Applied Manufacturing Technology – Edwards. Fundamentals of Modern Manufacturing- M.P.Groover. www.rapidprototyping.com. www.georgehart.com.
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