NEW PRODUCT DEVELOPMENT BY RAPID PROTOTYPING

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1 Proceedings of the National Conference on Trends and Advances in Mechanical Engineering, YMCA Institute of Engineering, Faridabad, Haryana.., Dec 9-10, NEW PRODUCT DEVELOPMENT BY RAPID PROTOTYPING Jolly Shah 1, Ravi K Sharma 2 1,2 Sr. Lecturer, Institute of Technology and Management, Gurgaon, Haryana 1,2 jollyshah80@yahoo.com, ravipvb@rediffmail.com Abstract Rapid prototyping is an automated process that quickly builds physical prototypes from 3D CAD files composed of surface quality or solid models. In the manufacturing arena, productivity is achieved by guiding a product from concept to market quickly and inexpensively. Rapid prototyping technology aids this process. These processes produce objects by addition of material on a layer-by-layer basis while in case of conventional methods which do so by removal of materials. This paper includes the various methods of rapid prototyping processes, their discussion, advantages and areas of application. This paper is intended to provide a means to discern the differences in the many rapid prototyping systems available and emerging today. 1.0 Introduction The past decade has witnessed the emergence of new manufacturing technologies that build parts on a layer-bylayer basis. Using these technologies, manufacturing time for parts of virtually any complexity is measured in hours instead of days, weeks, or months; in other words, it is rapid.. It automates the fabrication of a prototype part from a three-dimensional (3-D) CAD drawing. This physical model conveys more complete information about the product earlier in the development cycle. The turnaround time for a typical rapid prototype part can take a few days. Conventional prototyping may take weeks or even months, depending on the method used. Rapid prototyping can be a quicker, more cost-effective means of building prototypes as opposed to conventional methods. This review will refer to the new technology as "rapid prototyping." "Fabrication processes fall into three categories: subtractive, additive, and compressive. In a subtractive process, a block of material is carved out to produce the desired shape. An additive process builds an object by joining particles or layers of raw material. A compressive process forces a semi-solid or liquid material into the desired shape, in which it is then induced to harden or solidify." Most conventional prototyping processes fall into the subtractive category. These would include machining processes such as milling, turning, and grinding. Machining methods are difficult to use on parts with very small internal cavities or complex geometries. Compressive processes, also conventional, include casting and molding.[1] 2.0 What is Rapid Prototyping? The new rapid prototyping technologies are additive processes. They can be categorized by material: photopolymer, thermoplastic, and adhesives. Photopolymer systems start with a liquid resin, which is then solidified by discriminating exposure to a specific wavelength of light. Thermoplastic systems begin with a solid material, which is then melted and fuses upon cooling. The adhesive systems use a binder to connect the primary construction material. Rapid prototyping systems are capable of creating parts with small internal cavities and complex geometries. Also, the integration of rapid prototyping and compressive processes has resulted in the quicker generation of patterns from which molds are made. The first commercial process was presented at the AUTOFACT show in Detroit (US) in November 1987, by a company called 3D Systems, Inc. At that time, the process was very inaccurate and the choice of materials was limited. Therefore, the parts obtained where considered prototypes. Like in software engineering, a prototype is something to look at, serves as a basis for discussion but cannot be used for anything ``serious'', i.e. in a production environment. Since then, Rapid Prototyping Technologies (RPT) has taken enormous strides. Nowadays, there are over 30 processes some of which are commercial, while others are under development in research laboratories. The accuracy has improved significantly, and the choice of materials is relatively large, to the extent that the term prototype is becoming misleading; the parts are more and more frequently being used for functional testing or to derive tools for pre-production testing. It is very likely that a new term, or one of the numerous other expressions that are floating around, will replace it in the future. It is true that rapid prototyping at the beginning (in the past) can be achieved using conventional methods such as NC milling and hand carving. However, the term RP is normally reserved for the new technologies that build 1

2 parts by adding material instead of removing it. In order to regard RP in the right perspective, one would need to compare it with the conventional methods. Unfortunately, this is beyond the scope of the present work. [2] 3.0 Basic Processes Visualization refers to the utilization of computer graphics and imaging to convert numerical data into pictures. Prototypes can be categorized into two areas: soft and hard. Hard prototypes refer to the actual physical models that can be touched. Soft prototypes are the computer-generated renderings of a design. Visualization tools integrate CAD-based systems with animation to obtain a more detailed view of the model. Its capabilities include production simulation and finite element analysis. Visualization can also be a marketing tool. Soft prototypes generated by visualization tools cannot be touched, but can provide another method of communicating product design specifications. Future developments in the areas of holograms and virtual reality will aid visualization tools in generating three- dimensional renderings.[3] A hard prototype requires the same processes at the beginning of the manufacturing. The basic steps of this process are given below: 1. Create a CAD model of the design 2. Convert the CAD model to STL format 3. Divide the STL file into thin cross-sectional layers 4. Manufacture the model layer to layer 5. Remove the model after finishing 4.0 Types of Rapid Prototyping All the processes described in this Section take as input a 3D model and a set of parameters that are processdependent. The model to be manufactured is sliced by a set of parallel planes. The space between two adjacent slices is called a layer. The component of the process where the part is built is called the workspace. Although the processes described here can differ significantly, e.g. by the use of materials other than photopolymers, the underlying theme is the same; they all build parts on a layer-by-layer basis. Such processes are generally known as Layered Manufacturing Techniques (LMT). These technologies are changing at a quick pace, and the information contained herein may become quickly outdated.[7] 4.1 Stereo lithography In StereoLithography, a laser generates an ultraviolet beam that solidifies focused surface areas of a photopolymer in a vat. This process continues, slice by slice, until the system completes the part. Figure 1 illustrates the concept. 3D Systems offers three models of the SLA. Fig. 1 A Schematic drawing of an SLA The process begins with the vat filled with the photopolymer liquid and the elevator table set just below the surface of the liquid. The operator loads a three-dimensional CAD solid model file into the system. If needed, supports are designed to stabilize the part during building and post-curing. The translator converts the drawing into the.stl file. The control unit slices the model and supports into a series of cross sections from to 0.07 mm. thick. The computer-controlled optical scanning system directs and focuses the laser beam so that it solidifies a two-dimensional cross section on the surface of the photopolymer. The elevator table then drops enough to cover the solid polymer with another layer of the liquid. A leveling wiper moves across the surface of the polymer. The laser then draws the next layer. This process continues, building the part from the bottom up, until the system completes the product. The part is then raised out of the vat and cleaned of excess polymer. It then proceeds to the Post Curing Apparatus for the final cure. 2

3 Proceedings of the National Conference on Trends and Advances in Mechanical Engineering, YMCA Institute of Engineering, Faridabad, Haryana.., Dec 9-10, Scanning time depends on the geometry of the contours, hatch patterns, the speed of the laser, and the recoating time (i.e. the time taken to place a layer of photopolymer over the last solidified layer) Selective laser sintering Selective Laser Sintering (SLS) is a process that employs a powdered material approach to rapid prototyping. The process begins with the deposition of a thin layer of powder, which is heated to just below its melting point. A laser selectively traces the surface of the powder and sinters the material together. This process continues layer by layer until a final product is complete. Carl Deckard developed SLS at the University of Texas at Austin in Fig. 2 a schematic drawing of SLS system The SLS process begins with the atmosphere preparation in the process chamber, which is heated to the operating temperature. One powder feed piston rises to distribute a layer of material. At the same time, the partbuilding cylinder lowers to the desired layer thickness. The other powder feed piston also lowers to accommodate any surplus material, which the leveling roller transfers across the build area. The deposited powder is heated to a temperature just below its melting point. Using a raster scanning pattern, the laser draws one cross section of the desired part to sinter the powder particles. Unsintered powder remains to support the next layer, which is then distributed, leveled, and sintered. A laser sinters selected areas causing the particles to melt and then solidify. Unlike the processes mentioned above where there is only one phase transition, in sintering there are two: from solid to fluid, back to solid again. Processes that behave in this way are generally known as selective laser sintering (SLS) processes. The materials being used or investigated include plastics, wax, metals, and coated ceramics. An advantage to this system is its ability to provide supported building. The unsintered powder surrounding the part in the build cylinder acts as a natural support for the next layer. No elaborate supports need to be built such as in some photopolymer systems. Also, the excess powder material can be returned to the powder feed cartridges for reuse. 4.3 Laminated object manufacturing Laminated Object Manufacturing (LOM) is a system developed In 1989 by Helisys, Inc., Torrance, CA. LOM differs from the systems previously reviewed in that, rather than building up a part by adding materials to a stack through a forming process, layers of sheet materials such as paper, plastics, or composites are attached to a stack, and the laser cuts away the unused portions. Fig. 3 a schematic drawing of LOM 3

4 A winding and an unwinding roll provide a ribbon of the material. A stepper motor positions the material onto the building platform. A heated roller moves across the surface of the material, bonding it to the stack. An x-y positioning table with mirrors and optics reflects and focuses the CO2 laser beam, which cuts a profile of the part. The area of material surrounding the part profile is cut in a crosshatch pattern to facilitate its removal later. The excess material left in the building block acts as a support structure for the next layer. This process can be considerably fast. Because the laser is cutting around the periphery of the object, building a thick-walled part takes no longer than a thin-walled one. A great advantage with this process is that it is not limited by the complexity of the part. Since there are virtually no internal stresses, the part has no deformation or shrinkage commonly associated with photopolymer systems. 4.4 Solid ground curings The SGC method was developed and commercialized by Cubital Ltd. (Israel). The production machine uses these data to cure an entire layer of photopolymer in a solid environment. An ultraviolet light completely cures the material through a photomask. No post-curing is required. The SGC process is illustrated in Figure 4. Fig. 4 a schematic drawing of SGC It begins with the input of the three- dimensional CAD data of the part and selection of layer thickness. The computer then generates the cross-sectional slice data of the model. An image representing the cross- sectional layer is sent to the mask plotter, where a glass plate is charged with ions, and electrostatic toner develops the negative image of the layer. At the same time, the workpiece carriage is at the resin application station. The carriage and mask meet at the exposure cell, where a shutter opens for 3 seconds exposing the resin to ultraviolet light through the transparent areas of the mask. All exposed areas are completely cured. The mask moves back to the plotting station where it is physically and electrostatically erased in preparation for the next layer. The part is again exposed to ultraviolet light without a mask. This solidifies the residual resin that the wiper could not pick up. The carriage then moves to the wax applicator station, which deposits a layer of wax 0.2 mm thick to fill in all voids and cavities. The wax is solidified by a cold plate at the cooling station. The workpiece then moves to the milling station where a fly cutter mills the layer down to the desired thickness. A vacuum collects any chips produced during this process. The workpiece carriage lowers to accommodate the spreading of resin for the next layer, and the process continues until the part is complete. The water-soluble wax is melted in a microwave oven, and the part is cleaned in warm water. This method cures each layer separately as it is built. This minimizes shrinkage and eliminates the need for postcuring. Also, the solid polymer and wax environment eliminates the need for elaborate support structures. This significantly made easier to build parts of geometric complexity. A problem with this method is that it produces a lot of material waste. The resin picked up by the wiper and vacuum during the milling process cannot be used again. Uncured resin is hazardous material. 4.5 Fused deposition modeling The process is less similar to SLA. A polymer filament is fed into the head, melted, and deposited. It cools to form the part. It's similar to MIG (metal inert gas) welding, but on a smaller scale. 4

5 Proceedings of the National Conference on Trends and Advances in Mechanical Engineering, YMCA Institute of Engineering, Faridabad, Haryana.., Dec 9-10, Why Use of Rapid Prototyping? Most people know that using prototypes of product designs can dramatically speed up their design approval and manufacturing processes. Unfortunately, many haven't heard of or used RP. As mentioned earlier, speed is one of the most distinguishing features of RPT when compared to conventional methods. In fact, in many cases, the use of RPT can only be justified if the part can be obtained quickly. Quite often, though, the limiting factor is the time spent preparing the data. Once the data is correct, manufacturing time is known and relatively fast. Using rapid prototyping, we can improve our ability to get the right product to market faster and thus improve our profits through increased revenues. This is made possible by catching mistakes and making changes earlier in the product development cycle. Physical prototypes are helpful to just about everyone involved in developing products. Fig. 6 Engine block castings Figure shows DaimlerChrysler uses stereo-lithography part (right) as a pattern for the tooling of the actual engine block casting (left).[5] 6.0 Application of RPT Rapid prototyping technology is applicable to all industries. The various scenario of it is described below: RPT in manufacturing : RPT can be useful to anyone who manufactures a product or needs a physical object. To illustrate the strategic importance of RPT, we will use, as an example, the manufacturing industries. Fig.7 Changes in the requirement of manufacturing industry One company markets product in 12 countries. The same product family may have 8 different motors and 5 different technical features. The different technical features can be simple such as different materials, processes, or complex such as differences in the internal housing. These differences are needed in order to attend to 5

6 specific needs of users or to differenciate oneself from the competition. In addition, product lifetimes are becoming shorter, forcing a design group to develop new products within a shorter time. [4] This scenario requires changes on how a product is developed. Different groups-design, engineering, marketing, production-must cooperate more closely towards a common goal and work concurrently. RPT can be an effective means for evaluating a design before costly committments are made, commitments that affect manufacturing costs and, ultimately, the final cost of the product. Using RPT, if product is developed then it can saves 60% of cost and 80%of time then convention manufacturing with good dimension accuracy and engineering qualities. 6.1 Other areas of application Audi performance racing used RP to create mold masters that in turn produced turbocharger intakes and exhausts. An architectural project in Phoenix, Arizona, used RP to produce scale versions of 80- to 90-story buildings to demonstrate how the buildings' appearance mimicked the area's mountain ranges. Recent dental devices have met with uncharacteristic wide-ranging acceptance in the medical community partially because RP models enabled better feedback and assistance in production. RP has also been used in forensic analysis. A murder victim's skull was prototyped to preserve the original as evidence.[6] 6.2 RPT in medical application Applying RPT in the medicine is a new and exciting field. Many applications have become possible due to the convergence of three distinct technologies, like Medical Imaging, Computer Graphics and CAD, and RPT. Computer-Assisted Tomography (CT) and Magnetic Resonance Imaging (MRI) provide high resolution images of internal structures of the human body, e.g. bone structures and organs. Once these images have been processed by suitable software tools, it is possible to transfer the result to a RP process and obtain a physical part, called a medical model. These technologies provide doctors and surgeons with new tool-physical models of human internal structures-to better plan and prepare complex surgeries. Thus the process is useful in addition to reduced risks, reduced patient suffering, and improvements in the quality of the results. 7.0 Advantages of RPT The rpt is a technology of future. The technology is leading in all aspects due to following advantages: 1. Reduced lead times and costs 2. Improved quality of product 3. Better visualization of the product 8.0 Disadvantages of RPT There is another side of coin also i.e. it has certain disadvantages which can be described below: 1. Size of the prototype is limited. 2. Limited material properties 3. Varying accuracy in x-y planes & z plane 4. Surface finish 9.0 Conclusion Rapid prototyping technology is impact the industry by its versatile advantages. With wide-ranging benefits and fairly low costs, RP can provide major returns via increased innovation and reduced production costs. Still, RP doesn't fit every application. They have to use their engineering skills to evaluate if the limitations in material properties, part size, and cost are applicable to their project and product. Globalization is demanding the manufacturers for reduction in cost and improvement in quality of the products which can be fulfilled by RPT. References 1. Rapid prototyping & manufacturing by P.F.Jacobs 2. Society Of Manufacturing Engineers(SMA)/Rapid Prototyping Association(RPA) ( 3. The CAD/CAM handbook by Carl Machover 4. CAD/CAM, Robotics And Factories of future