Tech Thursday: Rapid Proto - Hyping

Permalink 07/08/04  

Over the last ten years, one manufacturing process has gained steam like no other. Rapid prototyping is the darling of the design world, engineering, and the media. But is it really everything they say? The answer, of course is yes, definitely... in the right circumstances.
But don't worry. Your Tech Thursday Angel is here to explain all.
Stereo Lithography

What's a prototype, and why would I want one so fast?
Rapid Prototyping- (RP) is a collective name for all the different technologies that allow a physical model of a computer generated 3d part file to be built in order to evaluate the qualities of that model. RP not only allows for quick models to be made, but also, in many cases, intricate models that would otherwise be impossible with traditional manufacturing. There are lots of different RP processes and each one has advantages and disadvantages. Most often, a rapid prototyping process has three distinct steps. First, model the object in a computer program that can export a file useable by your process of choice. Often, these files are .stl or .obj, but conversion software is available to go between most formats. The file is then sent to the RP machine, sometimes with a simple preparation program, and a 3d reproduction of it is formed in the prototyping medium. Lastly, the part is removed from the machine, and cleaned up, which, depending on the process, can be easy, or slightly labor intensive. Lets go over the processes really quick.

More than one way to skin a (prototype) cat
We don't want to drag you down, if you want more, just click the link.

SLA - Stereolithography uses two UV lasers to cure a model one layer at a time in a vat of UV-sensitive epoxy resin. By building these layers upon one another, a part is formed. The epoxy can have a variety of durometers, from hard to rubbery. Resolution is very high, and the resin can be wet sanded to a high gloss. Requires sacrificial support structure

SLS - Selective Laser Sintering uses one high-powered laser to "Sinter", or fuse a powder of build material into a solid layer, and then fuse another layer on top of that to build an object. The build material can be anything from plastic powder to glass/ceramic powder, and even metals. Resolution is very high, but because of the material, post-finishing is sometimes difficult.

Solid Ground Curing is a photochemical process, which works in a similar way to SLA, but allows for a much faster turnaround for large files. In order to do this, some detail is sacrificed, but it still maintains a good surface finish. The large part sizes make it very appealing.

3DP - 3D Inkjet Printing basically retrofits an inkjet printer for printing wax or cyanoacrylate glue. The wax is simply deposited on itself, but the CA glue method cures a layer of corn-starch powder filler. They print fast, and accurately. The wax printers are favored by jewelers for their ability to print lost wax positives, while the cornstarch machines allow printing in color, for visualization of drugs, and even visualization of stresses in parts in color

FDM - Fused Deposition Modeling prints with an extruded bead of molten plastic. The resolution isn't the highest, but they can print in ABS and even print parts with dissolvable wax pieces for easy clean-up. The build material is also cheaper than SLA.

Laminated Object Manufacturing stacks and glues layers of paper together before cutting a profile in the last-placed sheet. The process repeats until their is a brick of paper with a cut surface extending through it. The outer waste is removed, and a solid paper block part remains. This method is great for sand mold making for casting, since the prototype cannot have undercuts due to the waste removal.

Surface Modeled Prototypes are the cheapest of the lot, because they are cut out of paper or cardboard. A computer algorithm translates the 3d model into a series of planar surfaces and unfolds them to print on a standard printer. The pieces can be cut out using a laser cutter of knife plotter, or just your own two hands. Then, they are stitched, glued, taped, or otherwise joined together to form the surface of the 3d model. These models are often not completely accurate, but they provide good size and feel feedback about things like larger consumer products that would be very expensive to mock up using any other method. Also look at Pepakura, another software package.

If you need more information, check out this process advantages chart to see how they stack up against each other. Now that you know all the different kinds, what about when the heck we're supposed to use them? Well, to everything, there is a season...


Don't Zig when you should Zag
Keep the following in mind when having parts made:

Material Properties - Do you need long life, or rubberyness? Clear plastic? Magnetic? SLA and FDM will work for 99% of your projects, but it's good to know about the other ones so when you want a part that gets up to 600F you know to make it out of ceramic on an SLS.

Accuracy to the model - is this getting painted and passed off as a molded piece? Or are you interested in giving 100 to little old ladies to get a general idea of how they feel in their hands? Surface Modeling is a great way to check out sizing and button placement issues. One big step up is FDM, which doesn't have injection molded finish qualities, but it's believable all the same. SLA is the top of the top for accuracy, and can be painted with a minimum of cleanup.

Cost - Same question as before, what do you need out of this prototype. SLS could run you the most money depending on the options, but you probably won't always need metal or ceramic parts. FDM and SLA are both very economical because of market competition.

Part Size - again, for most projects, the 1 foot cubed to 3 foot cubed build areas in the average commercial machines is more than enough for us. But, if you ever get interested in something bigger, you should check out Solid Ground Curing.


What are people doing with this crud anyway?
Everything from jewellery to Geology Visualization. Bathsheba Grossman makes impossible sculpture with a computer and Rapid prototypes. Freedom of Creation is even experimenting with a 100% RP production strategy for their furniture and lighting.


The Wrap Up
So folks, the basic gist is that if a part is mildly complex, and can be made out of plastic, then Rapid Prototyping is a good option. Simple parts should still be made by machine shops or NC machinery (that's a different kettle of fish for a different Thursday). We hope this helped clear things up for you in the RP department. Next time you have a great idea, see if there's a place for a computer-designed custom part; it might be the solution you're looking for.


I've Got To Have More...
Alright you information hungry crazy person, you asked for it. And if these links aren't enough for you, check out our rapid prototyping sponsors on the right:

Manufacturers
ZCorp 3DP
Stratasys FDM

Services
CFA Design Prototyping Service
Stereolithography.com
Rapid Pro Manufacturing

More Information
Rapid Prototyping Primer
Rapid Proto Resource Center
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