Journal of Engineering Research and Studies E-ISSN 0976-7916

Research Article APPLICATION OF CAD IN RAPID PROTOTYPING TECHNOLOGY 1Mr.Sanjay C. Kumawat, 2Mrs. A.L.Gawali

Address for Correspondence 1Lecturer in mechanical Department, J.T.M.College Of Engg.Faizpur, Jalgaon 2Lecturer in Mechanical. Department, SSGBCOE&T Bhusawal (MH) ABSTRACT Now a day, one of the critical factors in competitive technology is “time to market” along with foolproof design. This critical factor indicates the entire product design cycle from concept to product design to prototype to manufacturing process design to actual implementation. To have command over this critical factor Computer aided designing (CAD) and manufacturing (CAM) is taking hold as a mean of speeding the time to market for new product development. This paper described how CAD approach is used in Rapid Prototyping techniques (RPT) for design and development of new products. Use of this CAD techniques in RPT techniques shorten the time to market and further for research and development of time of new products. KEYWORDS: CAD/CAM, Rapid Prototyping Technology (RPT) 1.0 INTRODUCTION analyzed and modified just considering like physical Computer-Aided-Design (CAD) involves the use of prototype [4]. computers to create product design drawing and 3D 2.3 Third Phase: Rapid Prototyping models. This CAD is associated with interactive Rapid Prototyping of physical parts, also known as, computer graphics. CAD system is powerful tool and desktop manufacturing, free-form fabrication, or layer used in mechanical design, and geometrical modeling manufacturing technology represents the third phase in of products and components. Computer-Aided- the evolution of prototyping [4]. Manufacturing (CAM) involves the use of computer 3.0. Introduction to Rapid Prototyping technology to assist in all the phases of manufacturing Rapid Prototyping is an important recent advancement a product, including process and production planning, in manufacturing. The Rapid Prototyping is a process machining, scheduling, management, and quality by which a solid physical model of a part is made control. These two-system i.e. CAD/CAM are directly form a 3-dimensional CAD drawing. The term combined to get added benefit. The database developed rapid prototyping (RP) also refers to a class of during CAD is stored and then CAM processes it technologies that can automatically construct physical further, into the necessary data and instructions for models from Computer-Aided Design (CAD) data. product quality [2]. Rapid Prototyping Technology This technique was developed in mid-1980s [8]. Rapid (RPT) is developed in 1988. RP enable the prototyping is an "additive" process, combining layers development of a geometrically exact replica of a part of paper, wax, or plastic to create a solid object. In in matter of hours, as compare to days or weeks using contrast, most machining processes (milling, drilling, traditional model-shop techniques. Rapid prototyping grinding, etc.) are "subtractive" processes that remove of physical parts also known as solid free from material from a solid block. RP’s additive nature fabrication, desktop manufacturing or layer allows it to create objects with complicated internal manufacturing technology [1]. features that cannot be manufactured by other means. 2.0 Prototyping Definition These "three dimensional printers" allow designers to A prototyping is the first or original example of quickly create tangible prototypes of their designs, something that has been or will be copied or rather than just two-dimensional pictures. Such models developed; it is a model or preliminary version [4]. have numerous uses. They make excellent visual aids There are three phases of prototyping as described for communicating ideas with co-workers or follows. customers. In addition, prototypes can be used for 2.1 First Phase: Manual (or hard) prototyping design testing. For example, an aerospace engineer The first phase began many centuries ago. In this might mount a model airfoil in a wind tunnel to phase, prototypes are typically not very sophisticated measure lift and drag forces [4]. Of course, "rapid" is a and fabrication of prototype takes on average about relative term. Most prototypes require from three to four weeks. The techniques used in making these seventy-two hours to build, depending on the size and prototypes tend to be craft-based and extremely labour complexity of the object. This may seem slow, but it is intensive [4]. much faster than the weeks or months required to make 2.2 Second Phase: Soft or Virtual prototyping. a prototype by traditional means such as machining. In this phase, computer models were created using These dramatic time savings allow manufacturers to CAD modeling software and can be tested, stressed, bring products to market faster and more cheaply. At

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Journal of Engineering Research and Studies E-ISSN 0976-7916 least six different rapid prototyping techniques are (magnetic resonance imaging) and x-ray data, and laser commercially available, each with unique strengths [7]. and digitizing arm scans. 4.0 Benefits of Rapid Prototype Technique [RPT]. Representation methods used to describe CAD
Helps in complete visualization of the physical geometry vary from one system to another. A standard model. interface is needed to convey geometric descriptions
Communicating desired form, fit, and function. from various CAD packages to RP systems. The STL
Providing feedback about ergonomic and (StereoLithography) file i.e. (. STL file) consists of an aesthetic requirements. unordered list of triangular facets representing the
Providing an example to a vendor for quotation. outside skin of an object. There are two STL file
Facilitating quick changes in a design (especially formats. One is the ASCII format and the other is true for castings). binary format. The size of an ASCII STL file is lager
Reduced cycle times and increased innovation. than that of the binary format but is human readable
we can build mold components directly from the [2]. CAD geometry In an STL file, triangular facets are described by a set 5.0 Applications of Rapid Prototype Technique. of X, Y, and Z co-ordinates for each of the three In design verification vertices and a unit normal vector with x, y, and z to • In product development. indicate which side of facet is an inside the object. An • In engineering Analysis example is shown in Fig. 3. • In Manufacturing Tooling. • Aerospace Industry. • Automotive Industry. • Dental device development. • Biomedical Industry. • Jewelry Industry. • Coin Industry. • Tableware Industry. • Electronic products. 6.0 Limitations of Rapid Prototype Technique. Fig. 1 CAD Approach for Rapid Prototyping • Limitation on maximum size of the model. Large parts usually must be built separately and connected manually. • Larger parts can be quite expensive. • Limited material properties. • Varying accuracy between the x-, y-planes and the z-plane. • Because parts are built in sections, the properties may not be very isotropic. • Initial investment and maintenance cost is high. 7.0 .STL file as a prototype data 3D Systems developed the STL file format to transfer Fig .2 The basic procedure for RP modeling geometry to the SLA machine. STL files are faceted There are several advantages with the STL file. Firstly, representations of data composed of triangles. The data it provides a simple method of representing 3- for the STL file can come from a variety of sources: a dimensional CAD data. Secondly, it is a de facto solid CAD model, a sewn (air-tight) surface quilt, MRI standard, which is used in most of the CAD systems (magnetic resonance imaging) and x-ray data, and laser and RP systems. Finally, it can provide simple files for and digitizing arm scans. data transfer for geometric shapes [3]. Several 7.0 .STL file as a prototype data disadvantage of the STL file exist. Firstly, the STL file 3D Systems developed the STL file format to transfer is many times larger than the original CAD data file for geometry to the SLA machine. STL files are faceted a given accuracy parameter. The STL file carries much representations of data composed of triangles. The data redundant information such as duplicate vertices and for the STL file can come from a variety of sources: a edges. solid CAD model, a sewn (air-tight) surface quilt, MRI

JERS/Vol.II/ Issue IV/October-December, 2011/252-257

Journal of Engineering Research and Studies E-ISSN 0976-7916

Fig. 3 STL file with triangular facets 8.0 The Basic Process for all Rapid Prototype manageability to produce a useful STL file. In the Technique. third step , a pre-processing program prepares the STL Although several rapid prototyping techniques exist, all file to be built. Several programs are available, and employ the same basic five-step process. The steps are most allow the user to adjust the size, location and as described follows. orientation of the model. Build orientation is important 1) Create a CAD model of the design. for several reasons. First, properties of rapid prototypes 2) Convert the CAD model to STL format. vary from one coordinate direction to another. For 3) Slice the STL file into thin cross-sectional layers. example, prototypes are usually weaker and less 4) Construct the model one layer atop another. accurate in the z (vertical) direction than in the x-y 5) Clean and finish the model. plane. In addition, part orientation partially determines First step , the object to be built is modeled using a the amount of time required to build the model. Placing Computer-Aided Design (CAD) software package. the shortest dimension in the z direction reduces the Solid modelers, such as Pro/ENGINEER, Solid Works, number of layers, thereby shortening build time. The Inventor, and Catia tend to represent 3-D objects more preprocessing software slices the STL model into a accurately than wire-frame modelers such as number of layers from 0.01 mm to 0.7 mm thick, AutoCAD, and will therefore yield better results. The depending on the build technique. The program may various CAD packages use a number of different also generate an auxiliary structure to support the algorithms to represent solid objects. To establish model during the build. Supports are useful for delicate consistency, the STL (Stereolithography, the first RP features such as overhangs, internal cavities, and thin- technique) format has been adopted as the standard of walled sections. The fourth step is the actual the rapid prototyping industry. construction of the part. Using one of several The second step , therefore, is to convert the CAD file techniques as described above. RP machines build one into STL format. This format represents a 3D surface layer at a time from polymers, paper, or powdered as an assembly of planar triangles, "like the facets of a metal. Most machines are fairly autonomous, needing cut jewel." The file contains the coordinates of the little human intervention. vertices and the direction of the outward normal of The final step is post-processing. This involves each triangle. Because STL files use planar elements, removing the prototype from the machine and they cannot represent curved surfaces exactly. detaching any supports. Some photosensitive materials Increasing the number of triangles improves the need to be fully cured before use. Prototypes may also approximation, but at the cost of bigger file size. Large, require minor cleaning and surface treatment. Sanding, complicated files require more time to pre-process and sealing, and/or painting the model will improve its build, so the designer must balance accuracy with appearance and durability.

JERS/Vol.II/ Issue IV/October-December, 2011/252-257

Journal of Engineering Research and Studies E-ISSN 0976-7916

9.0 Different Rapid Prototyping Techniques. post-processing. During the build, the excess material 9.1 Stereolithography Technique. provides excellent support for overhangs and thin- Patented in 1986, Stereolithography started the rapid walled sections. After the first layer is cutting is prototyping revolution. The technique builds three- completed, the platform lowers out of the way and dimensional models from liquid photosensitive fresh material is advanced. The platform rises to polymers that solidify when exposed to ultraviolet slightly below the previous height, the roller bonds the light. 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. Fig. 5 Shows the Laminated Object Manufacturing process.

Fig.4 Stereolithography Technique 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 Fig.5 Laminated Object Manufacturing Technique polymer. A sweeper re-coats the solidified layer with 9.3 Selective Laser Sintering Technique. liquid, and the laser traces the second layer atop the Developed by Carl Deckard for his master’s thesis at first. This process is repeated until the prototype is the University of Texas, selective laser sintering was complete. Afterwards, the solid part is removed from patented in 1989. The technique uses a laser beam to the vat and rinsed clean of excess liquid. Supports are selectively fuse powdered materials, such as nylon, broken off and the model is then placed in an elastomer, and metal, into a solid object. Parts are built ultraviolet oven for complete curing. Stereolithography upon a platform, which sits just below the surface in a Apparatus (SLA) machines have been made since 1988 bin of the heat-fusible powder. A laser traces the by 3D Systems of Valencia, CA. To this day, 3D pattern of the first layer, sintering it together. The Systems is the industry leader, selling more RP platform is lowered by the height of the next layer and machines than any other company. Because it was the powder is reapplied. This process continues until the first technique, StereoLithography is regarded as a part is complete. Excess powder in each layer helps to benchmark by which other technologies are judged. support the part during the build. Fig. 4 Shows the Stereolithography process. 9.4 Fused Deposition Modeling Technique. 9.2 Laminated Object Manufacturing Technique. In this technique, filaments (appx. 2.8-mm dia.) of In this technique, developed by Helisys of Torrance, heated thermoplastic are extruded from a tip that CA, layers of adhesive-coated sheet material are moves in the x-y plane. Like a baker decorating a cake, bonded together to form a prototype. The original the controlled extrusion head deposit very thin beads of material consists of paper laminated with heat- material onto the build platform to form the first layer. activated glue and rolled up on spools. 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

JERS/Vol.II/ Issue IV/October-December, 2011/252-257

Journal of Engineering Research and Studies E-ISSN 0976-7916

Fig.6 Selective Laser Sintering Technique Fig.7 Fused Deposition Modeling Technique. 9.5 Solid Ground Curing Technique. 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. 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 photo mask (like a stencil) of the layer to be built. This photo mask is printed on a glass plate above the build platform using an electrostatic The platform is maintained at a lower temperature, so process similar to that found in photocopiers. The mask that the thermoplastic quickly hardens. After the is then exposed to UV light, which only passes through platform lowers, the extrusion head deposits a second the transparent portions of the mask to selectively layer upon the first. Supports are built along the way, harden the shape of the current layer. After the layer is fastened to the part either with a second, weaker cured, the machine vacuums up the excess liquid resin material or with a perforated junction. Materials and sprays wax in its place to support the model during include polyester, polypropylene, ABS, elastomers, & the build. The top surface is milled flat and then the investment casting wax. Fig. 7 Shows the Fused process repeats to build the next layer. When the part is Deposition Modeling Technique. complete, it must be de-waxed by immersing it in a solvent bath.

Figure 8 SGC steps for each layer: 1) Mask preparation, 2) Applying liquid photopolymer layer, 3) Mask positioning and exposure of layer, 4) Uncured polymer removed from surface, 5) wax filling,6) Milling for flatness and thickness.

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Journal of Engineering Research and Studies E-ISSN 0976-7916

Fig. 9 3-D Printing Process.

9.6 3-D Printing Technique. Systems has also developed a 3-D printing based Parts are built upon a platform situated in a bin full of system. Fig. 9 shows the 3-D Printing process. powder material. A 3-D printing head selectively CONCLUSION "prints" binder to fuse the powder together in the Rapid Tooling is enabling art to production of quality desired areas. Unbound powder remains to support the parts and accelerating time to market by concentrating part. The platform is lowered, more powder added and on tool rather than the part. For the same work a leveled, and the process repeated. company might have taken 5-6 months to develop and When finished, the green part is sintered and then implementation of a new product development removed from the unbound powder. 3-D Printing used previously; it is now possible to accomplish the target to produce ceramic molds and cores for investment in as little as 2-3 weeks. So, for achieving this time to casting, also to make powder metal tools and products. market fastly CAD/CAM and RPT technologies are After each layer, a cutting tool mills the top surface to used .This paper highlights the salient features of this uniform height. technology, This yields extremely good accuracy, allowing the REFERENCES machines to be used in the jewelry industry. 3D 1. D. Kochan, et. al, “ Rapid prototyping issues in the 21 st century”, computer in industry, Vol 39 (1999) 3-10

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Journal of Engineering Research and Studies E-ISSN 0976-7916

2. D. Pham, “A comparison of rapid prototyping technologies”, Int. Jou. of machine tools and manufacturing, Vol. 38 (1998) 1257-1287 3. Steven Ashley, “ Rapid prototyping is coming of Age”, Mechanical Engineering, Vol. 117, (1995) 62-68 4. Chua Kai, “Rapid prototyping: principle and applications in manufacturing”, John Wiley and sons, Inc. New York, 1997 5. J. Giannatsis et. al.,“A study of the build-time estimation problem for Stereolithography systems”, Robotics and computer Integrated manufacturing, Vol. 17, (2001) 295- 304 6. Gregory Lee , “Virtual prototyping on personal computers” , Mechanical Engineering , Vol. 117 , (1995) 70-73 7. S. H. Choi, “ A virtual prototyping system for rapid product development” , computer-Aided-Design, (2003) 1-12 8. Steven Ashley, “ From CAD art to rapid metal tools” , Mechanical Engineering, Vol. 119 (1997) 82-87.

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