Engineering Information: Modeling Synthesis And Rapid Prototyping

The technologies of model syntheses and rapid prototypes allow engineers to create parts on computers, and hold it in their hand hours later.

The Miracle of Rapid Prototyping

Science fiction has come to the factory. The field of Rapid Prototyping (RP) has revolutionized the way that manufactured goods are created. Companies can now create a manufactured item in days, instead of weeks or months, and at far less cost than in the past. But what exactly is Rapid Prototyping?

Rapid Prototyping is the name that is given to a whole suite of new technologies that have been developed within the last 10 years or so. Usually, an RP created part starts out as a CAD (Computer Aided Design) file on a computer. CAD has been around for quite a while, but the new generation of CAD programs produces drawings in three dimensions (3-D), so the entire part can be viewed from any angle. The CAD file contains all the necessary information to create the part. The next step is to convert the CAD file into a file format that can be used by one of several types of Rapid Prototyping machines. The most common method (and file type) is Stereolithography (STL). This is the process of cutting the CAD file into a series of layers, normally about a thousandth of an inch thick. The RP machine then creates each of these layers individually, building up the part from scratch. One of the most common machines starts with a vat of UV sensitive liquid resin. In the vat of resin is a small elevator, with a flat platform on top of it. This platform starts out just a thousandth of an inch below the surface of the resin. Now a UV LASER is used to trace out the bottom layer of the part in the resin on top of the platform. When the light from the LASER hits the resin, it immediately solidifies into hard plastic. Once the LASER has traced out the entire bottom layer, the elevator moves down a thousandth of an inch, and the process is repeated with the next layer. Doing the entire part this way may take several hours, and when it is done, the elevator rises up to the surface, revealing the completed part! Now the part is removed from the machine, cleaned, and is ready to make copies of. Usually fast setting rubbers are used to create a mold, and super fast setting liquid plastic resins are used to create copies out of the rubber mold. This gives the engineers actual working parts to evaluate and test, without the expense, time, and bother of creating steel or aluminum injection molding tooling. Furthermore, if there's something about the part to change, it's a simple matter of changing the 3-D CAD file and making a new Stereolithography master, instead of building new metal tooling.

Another type of Rapid Prototyping machine is called a LOM (Layered Object Manufacturing) machine. This type of machine uses special adhesive paper to create the layers of the part, and uses heat and pressure to bond the layers together. A part made on one of these machines is around the same consistency as wood when it is complete. It can be sanded, finished, and used to create molds and plastic parts. Some LOM machines are capable of creating very large parts, and this method is often used for parts that don't require as much surface detail, although some machines are capable of amazing work. Again, a LASER is used to cut out the layers of paper. It is fascinating to watch one of these machines at work, and the precision with which they cut the paper layers is fantastic.



Another common type of Rapid Prototyping machine is very similar to the inkjet printer you use for your computer. These are known as Fused Deposition Modeling (FDM) machines, and use literally the same technology as your printer. The print head in this case sprays plastic, instead of ink, and builds the part layer by layer, just like the other types mentioned. This plastic is initially softer than many of the other materials used, so the machine normally has a second print head that sprays a support material, usually a wax, around the part as it's being built. This supports the part while the plastic hardens up, and prevents it from sagging. Some of these machines are capable of fantastic accuracy; good enough to produce intricate jewelry and fine surface details simply not attainable by any other RP machine. There are also other machines and technologies arriving all the time, as inventors and industry find new solutions for their need to produce parts quickly.

An exciting new area of Rapid Prototyping is that of Rapid Tooling. Some companies are trying to skip the production of the actual part, and move directly to producing injection-molding tooling using the same technologies already in use for RP parts. Obviously these tools aren't as strong as steel tooling, but they are only designed for limited numbers of parts, so this isn't a problem. This area is rapidly advancing, and may be the future of Rapid Prototyping.

But what other uses can Rapid Prototyping technology be put to? One of the most fascinating is the medical uses of RP that have cropped up. One company produces software that allows the output from a CAT scanner to be sent to a RP machine, creating a 3-D model of a patient's bones or internal organs. This can be incredibly useful for a surgeon who is about to attempt a difficult operation, or who needs to build an appliance or prosthetic for that patient. If that isn't the stuff of science fiction, I don't know what is! Suffice it to say, people will continue to innovate in the exciting field of Rapid Prototyping. The only question is, "What will they think of next?"

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