Stereolithography & Rapid Prototyping

What is it? And why is it important?

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.

A great collection of background info and supporting links can be found by doing a websearch for "rapid prototyping." Here's a link into this fascinating world. There's now even shareware available, so we can begin exploring this tech.

Image
	   of hardcopy version of Happy Buddha statue made by
	   stereolithography.

A particularly excellent example of this can be see in the work of Brian Curless and Marc Levoy at Stanford University. They've developed a way to make a 3-D scan of an object, then transmit that data to a remote site, where an exact duplicate (accurate to several tenths of a millimeter) model is made via stereolithography. You can see their results, as well as images of the original & replicated copy (Buddha image at right). You can even download their 3-D image data, to put into your own stereolithography machine, so that you can have a copy too. (What's that? You don't have one, yet? Well...neither do I. But after you see what they can do, perhaps you'll want one, too. :-) )

Why is this tech important? Well, think about everyone who's getting a Net-link, nowadays. Think about how they can download programs, audio data, animations, info of whatever sort. Now think about being able to download the 3D data for just about ANYTHING, and having your computer "print" you a copy.

New kitchen appliances, plates, cups, statues, candlesticks, lamp bases, bookends, whatever. Right now, people are going out to BUY lots of cheap plastic gizmos. Also right now, people are swapping software, music, images, and videos for free with each other. In a short time, I think people will begin swapping gizmos and models with each other, saying "Look what I just made!" Shortly after that, EVERYONE will be making things, and trading them around. I think that's going to be pretty exciting. :)

When it's not just Brian and his lab-mates at Stanford doing this, but everyone on the internet, and when stereolithography machines are as cheap as a PC, and data files are as plentiful as web-pages, the world is going to work a whole lot differently...

Here's another example, from my own life. In the last few months, I've had to go down to the local Sears Parts Center twice to buy replacement parts for two different applicances. (A new valve-piece for our water softener, to remove minerals from the well-water that feeds our house, and our washing machine, which needed a new water pump.)

In the case of the water-softener part the old one had a metal piece that had corroded away. The new one was made of recycled plastic. I had to drive 20 miles, show the guy the old one, he pulled up the part diagrams ON A COMPUTER SCREEN, and we verified the part I needed. Then he went back and found it on the shelf. It worked like a charm, but if it's already on the computer, it would have been even easier if I could have located the part I needed online, sent a digital payment to Sears for the plans, then had my own machine make up that part out of my own recycled plastics.

In the case of the washing machine's water pump, I called up Sears' toll-free number on the phone, told the woman what model machine I had, and what I needed, and she gave me the part number. I then had to drive 20 miles again, to go back to that same warehouse, and have the guy pull it off the shelf for me. Most of the parts on it were plastic, although there were a few metal pieces. (That's OK. Rapid prototyping machines do metal as well, and there are some out that will now do multiple materials in one model. The best spec I've seen so far was up to 6 different materials at once, including plastic, metal, and ceramic.) Once again, the part was KNOWN by Sears' computer.

We already have digital payments across the net. We already have download capability. We already have CAD/CAM software. We already have plastics lying all over the place. And we already have stereolithography machines.

What's missing? The integration to put all those pieces together. And that integration is rapidly heading our way.

One more example. I have a blender from Betty Crocker. It cost me $12 on sale at a local store. Almost every thing on the blender, except the motor, is made of plastic. One of those parts, the little whirlygig that spins on the motor and turns the blades, has broken, so the blender is currently sitting unused in the cupboard. Has been for several months.

Yes, I could buy another one. Yes, I could throw it away. (Although I'm reluctant to fill up landfills with plastic and be a "disposable" consumer.) Yes, I could bring it to a recycle center. Yes, I could probably get Betty Crocker to send me a replacement, since this was definitely a materials/manufacture issue.

But I could also probably sit down and have the measurements for that piece in about 5 minutes. I could have one of my architect friends whip up a model on CAD/CAM, and could send that data to Brian Curless to have a part made. All the effort would probably cost considerably MORE than $12. But it would keep several pounds of plastic and metal out of our landfills. It's probably the route I'll follow. For now, the blender just sits...waiting. Might as well wait here as out in the ground, someplace. :-)


Addendum: Unfortunately, we moved house in late 1997, and in the interest of lightening our load, lots of ballast was gotten rid of, including the blender. We brought it to a recycle center, but it does seem like a waste.


There are numerous companies actively producing these rapid prototyping systems. One site of note is Stratasys, who makes numerous systems that can produce models in a variety of sizes and materials.

Image of an FDM
	 rapid prototype coffeepot made of heat-tolerant materials.

In a Stratasys electronic newsletter dated June 12, 2003, they announced some recent improvments in their materials and FDM capabilities:

STRATASYS ADDS HIGH-END PPSF PLASTIC AND OTHER INNOVATIONS

-A third high-performance material for the FDM Titan, PPSF, is now available, and two upgrades to the Titan have been added.

-Among rapid prototyping materials, PPSF (or polyphenylsulfone) has the highest strength, heat resistance, and chemical resistance. The aerospace industry will welcome the material's VO flammability rating. Automobile manufacturers can take advantage of its petroleum resistance and its ability to function at over 400 degrees F; and medical-product makers can sterilize PPSF prototypes. This PPSF prototype can handle hot coffee and a warmer plate temperature of 212.

-One beta-test site, Parker Hannifin, installed a PPSF model onto an automotive engine. The part, a filter called a crankcase vapor coalescer, was mounted on a V8 engine and tested for 40 hours to determine filter- medium efficiency. The part collected gasses containing 160-degree F oil, fuel, soot, and other combustion by-products. "The assembly didn't leak, and it appeared to have the same strength and properties as when first assembled," said Parker Hannifin's Russ Jensen, "We're pleased with its performance."

-On the Titan, PPSF was preceded by ABS plastic and polycarbonate.

OTHER TITAN UPGRADES INCLUDE MODEL RESOLUTION INCREASE

-Earlier this year Stratasys announced two other upgrades for the Titan: A resolution improvement via a reduced layer thickness as well as soluble support material (for ABS modeling).

-Resolution has increased to 0.005 inches(0.127mm)--a level previously available only on Stratasys' highest capacity machine. The improved resolution allows design engineers to build models with smoother surface finish and finer feature detail than before. The second upgrade is the addition of Stratasys' automated support-removal process marketed as Waterworks. This process uses water-soluble model-support material, which speeds the modeling process because it is simply dissolved after model completion. "The FDM process requires no post-processing -- only support removal. Automating this removal makes FDM arguably the most effortless rapid prototyping process available," says materials-development director Bill Priedeman.


Patrick Salsbury


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