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Rapid Prototyping Essay, Research Paper
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Today many companies are under pressure to reduce lead time for new product introductions. This is especially true in a market such as computer parts where the lifetime of a product is short. Companies are always searching for a way to create products faster and more efficiently. One tool that allows companies to cut the time between a product concept to launching the product is rapid prototyping.
The rapid prototyping (RP) process generally consists of seven steps. These steps are listed below:
1. The RP equipment imports model data from a CAD/CAM file
2. The RP equipment creates a cross-section of the model using different techniques
3. The RP equipment uses the cross-section to build up the model layer-by-layer
4. The process is repeated until the model is complete
5. The model is removed from the RP equipment
6. Depending on the technology used, some models need to cure in ultraviolet ovens
7. Models are then machined to their final finish
Rapid prototyping allows models to be created within hours. The hand carved models of the past could take weeks, even months to complete. Currently RP is only used for prototyping. Many people hope that someday it will replace the traditional production line.
The declining cost of computers has changed the way a factory works. An increase in use of computers has aided in the advancement of computer-related areas such as computer-aided design (CAD), computer-aided Manufacturing (CAM) and Computer Numerical Control (CNC). Rapid Prototyping would not have been possible with out the existence of these areas.
Over the years, prototyping has gone through three phases. The first phase is manual prototyping. In this phase, prototypes are not very complex and fabrication of prototypes take on average about four weeks. The second phase is virtual prototyping. This phase is when computer models can be stressed, tested, analyzed and modeled as if they were physical prototypes. The third phase is rapid prototyping (RP). This is the creation of 3D objects directly from CAD files. A CAD file is inputted and within a few hours a model is produced. Unlike CNC machines, the model is created by adding material instead or cutting it away from a solid block. This makes producing complex shapes quite simple.
Prototypes are an important part of the design cycle. They are an aesthetic visualization. This is especially important for a consumer item that must look appealing when painted and packaged. They are also a type of form-fit-and function testing. They are used to make sure the part fits into and works with the other parts it is intended to be attached. They can also be used as casting models.
If test of the model leads to design changes, then a new model is needed for further tests. Conventional model-making methods can require weeks or months. With RP, the turnaround for the model-making step can be cut to days. The model can be made within hours. Another advantage of RP is that users report they have been able to cut out a step in the product design cycle. They can skip soft tooling and go directly to hard tooling or they can make cast models from the RP model.
Rapid Prototyping is changing manufacturing. Today, product life cycles are shortening dramatically. Traditional production lines cannot re-tool fast enough for small batch sizes. They are not economically efficient either. Though RP, cheap custom manufacturing is possible. It replaces hand-carved prototype models and patterns. The limitation of RP is that these models have no moving parts and are made out of one medium.
Today’s automated, tool less, pattern less RP systems can directly produce functional parts in limited production quantities. If RP could move beyond the model-making into production, firms would be able to produce any item on demand, from any machine located anywhere. The concept of inventory would become obsolete.
Right now the RP industry is tiny. The major RP companies are small. All RP makers want a business model that similar to the computer printer. They want to reduce upfront costs by generating most profits from the media used in the machine. The machines themselves are expensive. The low-end products start around $70,000 and reach as high as $800,0001. The typical lifespan for a rapid prototyping machine is three and a half years2. Last year 1,195 units were sold worldwide3.
Although few people realize it, rapid prototyping benefits many people. They benefit product designers by allowing them to increase part complexity with little effect on the lead time and cost. Organic, sculptured shapes for aesthetic reasons can be accommodated. There are also fewer constraints with regard to draft angles, parting lines or other such constraints. Tool designers and manufacturing engineers also benefit from RP. The main savings for them are costs4. The manufacturing engineer can reduce design, manufacturing and verification of tooling. Even the marketer and consumer can benefit from RP.
Rapid prototyping systems can be categorized into three types of systems. The first is a liquid-based system. Liquid-based RP systems begin with its material in a liquid state. Through a process known as curing, the liquid is converted into a solid state. The next RP system is the solid-based system. Solid-based systems are meant to include all forms of material, except powder, in the solid state. The solid form can include materials in the form of a wire, roll, laminate or pellet. The third RP system is the powder-based system. Although powder is technically a solid, it is meant as a grain like form.
Most liquid-based rapid prototyping systems build parts in a vat of photo-curable liquid resin, which is an organic resin that solidifies under exposure to laser radiation. The laser cures the resin near the surface which forms a hard layer. When that layer is formed, it is lowered by an elevation control system to allow the next layer of resin to be similarly formed over it. This continues until the entire part is completed. There are some variations to technique depending on the various vendors and laser method.
The next system, solid-based RP systems, are very different than the liquid-based photo-curing systems. They also are different from one another. The common feature between these systems is that they all use solids, in one form or another, as the primary medium to create the prototype. Some of these solid-based systems do use lasers in the prototyping process.
Powder-based RP systems are a special type of solid-based RP systems. These systems primarily use powder as the basic medium for prototyping. Some of the powder-based systems resemble the liquid-based RP systems since they generally have a laser “draw” the part layer by layer. Other powder-based systems such as the three-dimensional printing and the multiphase jet solidification have similarities with the solid-based RP systems. The 3D printer adds the extra dimension simply by printing layer after layer until you have a real, 3D object.
A RP system isn’t necessarily ideal for everyone though. When using a RP system there are three things that need to be taken into consideration when creating a model. These are the tolerances, model size, and materials used.
Tolerances on parts produced in RP machines are around five-thousands of an inch5. Whether such a tolerance is good or bad depends on what the users are doing with the prototypes. Those only interested in aesthetic visualization are quite pleased with that tolerance. Those interested in form-to-fit-and-function testing report that have had to machine critical surfaces and that some models are more durable than others. Those who use the RP system to create casting tools have said they have to do post finishing. Depending on your tolerance requirements, the RP system may not be ideal for you.
Another important factor is the model size. Model size is a constant concern with management. Most engineers feel that the working envelope in the RP machines is big enough for most of the parts that they make. The average envelope size is about a cubic foot6. Larger parts can be made in sections and then glued together.
Although tolerances and model sizes are expected to improve in the future, improved material use is not certain. The current problem is that a model can only be made of a single material, such as metal or plastic. If you’re going to put different materials inside the solid, you need to know exactly where each material should be deposited which creates a huge data handling problem. A solution to this problem would be to avoid putting dissimilar materials together in the first place. Research groups are currently trying to create new materials with previously unknown properties7.
The abilities of the RP systems are bound to change the manufacturing industry. Someday you may be able to design a component using a CAD program in your office and then send the design straight to a 3D printer. Then out pops a carefully constructed component. The RP companies even hope that someday the shopping public can cut out both the manufacturer and the delivery firm from the retail process.
Unfortunately RP machines are currently very expensive. Some have said that rapid prototyping field is in the same position that the microcomputer field was in about 1979. In 1981, when IBM came out with a model which all others standardized, the market grew and prices fell8. Today businesses are built around microcomputers. Although it doesn’t appear that the rate of change for rapid prototyping is likely to be as fast as the microcomputers, the parallel is still there. This is encouraging to the RP companies who are always searching for ways to decrease the cost of RP systems.
However, if these practicality issues are not resolved, rapid prototyping may become a niche technology only used by design engineers as a fancy toy. It is impossible to say which way RP will move and at what speed. They are very practical systems and often benefit the user. As technology moves forward, larger and more complex parts are being created. With each improvement there is hope that someday RP will play a major role in all design and manufacturing processes.
This technology may soon be available for ordinary consumers too. Although commercial 3D ink-jet machines are clearly out of the range of most casual buyers, there are a number of companies who are looking at mass-producing 3D printers for an affordable selling price.
1Robert Daly, “Rapid Prototyping Molds the Future of Manufacturing” (Technology Investor Magazine, August 2000) 38.
4Chee Kia Chua and Leong Kah Fai, Rapid Prototyping: Principles and Applications in Manufacturing (New York, New York: John Wiley and Sons, Inc., 1997) 9.
5Lamont Wood, Rapid Automated Prototyping: An Introduction, (New York, New York: Industrial Press, Inc., 1993) 4.
7Michael Brooks, “Whatever You Want” (New Scientist Magazine, September 30, 2000)
Bennett, Graham. Rapid Prototyping and Tooling Research. Wiltshire,UK: Mechanical Engineering Publications Limited, 1995.
Brooks, Michael. “Whatever You Want.” New Scientist Magazine, September 30, 2000.
Chua, Chee Kia and Leong Kah Fai. Rapid Prototyping: Principles and Applications in Manufacturing. New York, New York: John Wiley and Sons, Inc., 1997.
Daly, Robert. “Rapid Prototyping Molds the Future of Manufacturing”. Technology Investor Magazine, August 2000.
Syan, Cahana S. and Unny Menon. Concurrent Engineering: Concepts, implementation and Practice. London: Chapman and Hall, 1994.
Wood, Lamont. Rapid Automated Prototyping: An Introduction. New York, New York: Industrial Press, Inc., 1993.
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