Design for Engineering

Unit 6- Research and Development

Rapid Prototyping Systems

Rapid prototyping

, is the automatic construction of physical objects using solid freeform fabrication . The first techniques for rapid prototyping became available in the 1980s and were used to produce models and prototype parts. Today, they are used for a much wider range of applications and are even used to manufacture production quality parts in relatively small numbers. Some sculptors use the technology to produce complex shapes for fine art exhibitions.

In brief, rapid prototyping takes virtual designs (from computer aided design (CAD) or from animation modeling software), transforms them into cross sections, still virtual, and then create each cross section in physical space, one after the next until the model is finished. It is a WYSIWYG process where the virtual model and the physical model correspond almost identically.

Stereolithography example

Stereolithography is one "flavor" of a technology called Rapid Prototyping. This gives one the ability to "print" out a CAD/CAM computer model in three dimensions. Just as you can currently print out a drawing in 2-D right now, rapid prototyping allows you to print an OBJECT.

It works by taking a computer model and "slicing" it into thousands of very thin layers. Each of these layers can be laid down, one at a time, by a device printing with plastic (which is often called "Fused-Deposition Modeling", or FDM), or with thin layers of paper, or metal foil, or ceramic, or various other materials. Stereolithography uses lasers to photochemically harden special liquid chemicals into a solid plastic form. Whichever method is used, over time, each layer builds up, until you have a completed model

Laser cutting example

This is a custom laser-cut pterosaur puzzle as an example of how you can use two-dimensional pieces to build a three-dimensional part

Fused Deposition Modeling

FDM is a rapid prototyping process used to produce functional ABS thermoplastic models directly from CAD data. The system utilizes a CNC controlled extruder-head which squeezes a fine filament of melted thermoplastic through a nozzle. The nozzle deposits the heated plastic layer-by-layer to form the desired shape. The liquid material hardens immediately on contact in the cooler environment.

Laminated Object Manufacture

In this technique, developed by Helisys of Torrance, CA, layers of adhesive-coated sheet material are bonded together to form a prototype. The original material consists of paper laminated with heat activated glue and rolled up on spools. As shown in the figure below, 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 post-processing. During the build, the excess material provides excellent support for overhangs and thin-walled sections. After the first layer is cut, the platform lowers out of the way and fresh material is advanced. The platform rises to slightly below the previous height, the roller bonds the 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.

Sources

http://en.wikipedia.org/wiki/Rapid_prototyping http://www.pololu.com/lsrproj/lsrprj03/ http://www.sculptors.com/stereolithography.html

http://metals.about.com/library/weekly/aa-rp-fdm.htm

http://www.mne.psu.edu/lamancusa/rapidpro/primer/chapter2.ht

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Standards covered

Standard #2:

Students will develop an understanding of the characteristics and scope of technology. Benchmarks AA. Requirements involve the identification of the criteria and constraints of a product or system and the determination of how they affect the final design and development.

BB. Optimization is an ongoing process or methodology of designing or making a product and is dependent on criteria and constraints.

Standard #10:

Students will develop an understanding of the role of troubleshooting, research and development, invention and innovation, and experimentation in problem solving.

Benchmarks I. Research and development is a specific problem-solving approach that is used intensively in business and industry to prepare devices and systems for the marketplace.

J. Technological problems must be researched before they can be solved.

Standard #13:

Students will develop abilities to assess the impact of products and systems.

Benchmarks J. Collect information and evaluate its quality.

K. Synthesize data, analyze trends, and draw conclusions regarding the effect of technology on the individual, society, and the environment.