Limitations
o Surface finish and delicate features are inferior to other processes
o The process is slow since the entire contour is to be filled
o The strength is low in the vertical direction
o Accuracy and surface finish is poorer as compared to the other RP processes.
Rapid tooling (RT)
Another important phase of product development is the manufacture of production tooling. Characteristically, all tooling require quite a long time for production and reasonable investment. So, many efforts have been put in to improve this phase to achieve savings in time and cost. Traditional sand casting has limitation of simplistic forms and dimensional accuracy. Investment casting offers better potential in terms of complex form geometry, better dimensional accuracies, and excellent surface finish. Machining processes for metal removal using conventional machine tools or latest NC machines, EDM, wire cutting machine and so on, give very high dimensional accuracies but these machining operations are time consuming and costly.
World over, manufactures and toolmakers are shifting from routine methods to rapid tooling for prototype and production purposes. This not only saves time and money but also gives a competitive edge at the crucial stage of product development. There are two main application areas of rapid tooling: Soft tooling, using silicon RTV moulds, epoxy tools or spray metal tooling for manufacturing 10 to 1000 plastic parts. Using conventional moulding processes, these moulds could also be used for metal parts to be made by investment casting or by centrifugal casting of low melting alloys of zinc and aluminium. Currently many companies are offering systems and technologies for making these soft tools.
The second area related to hard tooling for production purpose is being explored. Using quick cast SLA parts or investment casting frequency division multiplexing (FDM) patterns; one can cast accurate core and cavity tooling by shell investment casting process. The rapid prototyping parts could also be used for electroformed nickel tools or spray nickel shells. One more route exploited is for making electrodes for electrical discharge machine (EDM) of moulds for plastic parts. By using RP model as a pattern, a female abrasive filled epoxy die is made. This is used to grind away the graphite block for preparing graphite electrode for use in EDM of moulds.
The potential rewards of rapid tooling are enormous and newer avenues are being explored everyday.
Benefits of rapid prototyping
To the product designer: The product designers can increase the part complexity with little effect on lead-time and cost. They can optimise part design to meet customer requirements, with little restrictions like material wastage or large thin walls, which are otherwise imposed by machining operations. There is improved design creativity and valuable feedback on the design can be obtained from various sources.
To the manufacturer: The manufacture can avail of the benefits like early realisation of profit, reduction in cost due to reduction in wastage and scrap, reduced labour content, reduced inventory, assembly and inspection costs due to reduction in parts count. All testing and design changes are carried out before spending any money on tooling. Design problems can be solved before they become tooling glitches or manufacturing fiascos. The RP parts act as important communication tools between the designers, engineers, and vendors. Different people interpret 2-D drawings differently and clearing this confusion costs valuable time. When everyone can look at the part itself, inspect it, even touch it - design concepts are clarified and misunderstandings disappear. Design errors like thin walls, misaligned apertures, and inner walls crossing outer walls, etc cannot be identified in 2D drawings or 3D models. RP helps in locating and solving these problems early before costly scrapping or reworking of tools is required. The tooling can be done only when the concept is refined and the data is verified. In short, rapid prototyping and tooling are manufacturing tools that enable industries to optimise information at front end of design and manufacturing process and thereby work smarter and faster.
To the marketer: The market greatly benefits from these techniques because of the advantages like reduced time to market, reduced risk of product failure in the market, manufacturing of products that meet customer requirements and possibility of test-marketing of new products. Limited editions of a variety of conceptual prototypes of the same product can be launched followed by mass production of the most successful ones.
To the consumer: The consumer can buy products, which meet individual needs and wants. There is a much wider diversity of offerings to choose from.
Applications of RP&T
Prototypes made using rapid prototyping & tooling (RP&T) systems find applications as:
Concept models: Designers always prefer to present form ideas in mock-up models or prototype of product, for final presentations. Quick RP models become very handy for this purpose. Though little expensive, the time saved is enormous and one can make very intricate details even like snap-on to demonstrate the working of fitments.
Models for market research: With RP technology, several different variations in design models can be made simultaneously and the best one can be selected. Few accurate copies of the selected one could be produced in a short time to get a feel of the market.
Rapid tooling: Toy manufactures are exploiting rapid tooling methods to make injection moulds to introduce a number of designs in the market in peak season. Final hard tooling is done only for those toys, which perform best in the market.
Tender model: Many automotive companies have started realising the advantages of providing a physical three-dimensional part model to a sub-contractor for a quote. This helps the vendor to decipher the CAD file quickly and assists them in deciding the parting lines, which is a very important step in tool design.
Wind tunnel models: The models of planes, automobiles, trains, buildings, and structures are tested for performance in wind tunnels. Accurate RP models can help in obtaining reasonably good results.
Models for stress analysis: Many RP models are directly used for experimental stress analysis and other analytical methods.
Medical applications: RP parts are being increasingly used to manufacture one-off replicas of bones. The scanned (CT or MRI) data of affected bone areas is used to prototype the part, which in turn is used to create ceramic shells for investment casting of metallic replacement parts.
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| Posted : 10/27/2005 |
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