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Printing-On-Demand: But, printing what?

The machine consists of several parts. First, there is a build station which houses the vat and platform seen in the above diagram. Residing above the platform is the ultraviolet laser. A computer is next to this build station - when building, the computer monitor provides information on the status of the build, what layer is being built, how much time until the next layer will be built, etc. Additionally, there is a post curing apparatus. This looks almost like a microwave, the part is placed on the turntable inside the PCA, and the part is exposed to additional ultraviolet light as part of the curing process. There are many different machines available from 3D Systems, the manufactures of stereolithography apparatus (SLA). Capacities, speed, and other parameters differ. Different resins are recommended for differnet machines.

A stereolithography machine works as follows:
A controller positions a vertical elevator, housed inside a vat filled with a liquid photosensitive resin, so that it rests just below the liquid surface. An optical scanning system directs UV laser light which "draws" a shape, one layer at a time, onto the surface of the resin. As the laser strikes the surface the resine is solidified: the first layer of the model is built.
After that, the elevator goes down, just submerging the solidified layer. The scanning process is repeated and a second layer is built on top of the first one.
This process of submerging and laser scanning goes on and on until the entire model is built.
The basic principle of creating a 3D structure by piling it up layer by layer is common to all RP techniques. Only the materials and methods used are different.

Computer printers have come a long way: from the massive chain printers that first graced those hermetically-sealed mainframe corporate shrines; to my first terminal that used a long hexagonal die that spun around and then laterally positioned itself to strike just the right character through a ribbon (slow, but the terminal only printed at about 10 characters/second!); to the daisy wheel printers with film ribbons that rivaled the printing of the day's gold standard-the IBM Selectric; to the amazing (but expensive until recenlty) laser printer; and finally to today's ink jets that can rival the quality of professionally-printed pictures.

But other types of printers, using variations on the theme of ink jets as well as other technologies, have been printing far more than pictures- they have been printing solid objects. And as you will shortly see, far more!

The lead-up

The field is called stereolithography. By various means, it takes a 3D CAD-type drawing file as its input and creates the real solid object by 'printing' bits of special material (or hardening just the right areas of a liquid), one layer at a time.

(With inkjet technologies, the heads move across the area to be 'printed', leaving tiny bits of material (instead of ink) where the bottom layer of the object should exist. The 'printer' then moves the platform holding the object down one layer-height and repeats the process, depositing material where it should be in the second layer. Similarly, this process continues to the top layer and, when complete, a real,accurate, 3D object has been created that can be used as a mold for creating more parts (perhaps out of materials that can't (yet) be printed). Or in many cases the parts are used as direct prototypes.

With some 'liquid' systems, a bath of liquid resin is the target of a set of lasers (perhaps three). The lasers converge on just the areas where solid parts of the object should exist, and the combined heat of the three lasres striking that point solidifies the resin.

The table holding the resine bath then moves down one layer-height, and the process repeats until the entire object stands proud.)

Image-a part printed by stereolithography

This process is also known as 'Rapid Prototyping.' Another technique is based on the typical laser printer, which deposits a known amount of material with precise placement. The 'paper tray' moves down a layer, and the process repeats.

Although there are still limitations as to what can be made in this manner, the magic is that today, you can e-mail a CAD file to a company that does this work, and often have the furnished prototype in your hands (via FedEx) within two- days!

(Unless, of course, you happen to have a 'home stereolithography' kit - shall we call this Desktop Manufacturing? But that's perhaps still a (short?) ways into the future, since researchers are exploring how to make such devices affordable. That way, little Jimmy can create his full-color, exactly-as-he-wants-them toy soldiers, and much more...)

The NBIC connection

Now that we have a sense of how 'printing' solid objects is already in widespread use, consider taking the concept a bit farther, as is being done at the Medical University of South Carolina. An article describes how 'Tissue Engineer' Vladimir Mironov has washed the ink out of inkjet printer cartridges and replaced it with a suspension of cells, such as hamster ovary cells, or of other biological material. The second cartridge is loaded with a 'thermo-reversible gel' which remains liquid below 68 degrees but solidifies above 90 degrees.

Image-Printing living tissue

Of course these tissue engineering techniques are in their infancy; there is a long way to go before your surgeon can print up a 'heart on demand.' But between techniques such as these, and other efforts resulting from NBIC, the convergence of Nanotechnology, Biology and medicine, Information sciences, and Cognitive sciences (such as growing complete organs insitu), 'Kidneys To Go' may eventually find its way into the Yellow Pages!
And won't THAT change the rules...

Courtesy : The Hindu