by Chris Woodford. Last updated: January 20, 2016.
Even the best artists struggle to show us what real-world objects look like in all their three-dimensional (3D) glory. Most of the time that doesn't matter—looking at a photo or sketch gives us a good-enough idea. But if you're in the business of developing new products and you need to show them off to clients or customers, nothing beats having a prototype: a model you can touch, hold, and feel. Only trouble is, models take ages to make by hand and machines that can make "rapid prototypes" cost a fortune (up to a half million dollars). Hurrah, then for 3D printers, which work a bit like inkjets and build up 3D models layer by layer at up to 10 times the speed and a fifth the cost. How exactly do they work? Let's take a closer look!
Photo: A B9Creator™—a typical low-cost, DIY 3D printer. Other popular 3D printer makes include Z Corporation, Stratasys, Objet Geometries, and Dimension uPrint. Photo by courtesy of Windell H. Oskay, www.evilmadscientist.com, published on Flickr in 2012 under a Creative Commons Licence.
From hand-made prototypes to rapid prototyping
Before there were such things as computer-aided design (CAD) and lasers, models and prototypes were laboriously carved from wood or stuck together from little pieces of card or plastic. They could take days or even weeks to make and typically cost a fortune. Getting changes or alterations made was difficult and time-consuming, especially if an outside model-making company was being used, and that could discourage designers from making improvements or taking last-minute comments onboard: "It's too late!"
With the arrival of better technology, an idea called rapid prototyping (RP) grew up during the 1980s as a solution to this problem: it means developing models and prototypes by more automated methods, usually in hours or days rather than the weeks that traditional prototyping used to take. 3D printing is a logical extension of this idea in which product designers make their own rapid prototypes, in hours, using sophisticated machines similar to inkjet printers.
Photo: A high-quality rapid prototype of a space plane made in wax from a CAD drawing by NASA. Photo courtesy of NASA Langley Research Center (NASA-LaRC).
How does a 3D printer work?
Imagine building a conventional wooden prototype of a car. You'd start off with a block of solid wood and carve inward, like a sculptor, gradually revealing the object "hidden" inside. Or if you wanted to make an architect's model of a house, you'd construct it like a real, prefabricated house, probably by cutting miniature replicas of the walls out of card and gluing them together. Now a laser could easily carve wood into shape and it's not beyond the realms of possibility to train a robot to stick cardboard together—but 3D printers don't work in either of these ways!
A typical 3D printer is very much like an inkjet printer operated from a computer. It builds up a 3D model one layer at a time, from the bottom upward, by repeatedly printing over the same area in a method known as fused depositional modeling (FDM). Working entirely automatically, the printer creates a model over a period of hours by turning a 3D CAD drawing into lots of two-dimensional, cross-sectional layers—effectively separate 2D prints that sit one on top of another, but without the paper in between. Instead of using ink, which would never build up to much volume, the printer deposits layers of molten plastic or powder and fuses them together (and to the existing structure) with adhesive or ultraviolet light.
Artwork: One of the world's first three-dimensional FDM printers, developed by S. Scott Crump in the 1980s. In this design, the model (pink, 40) is printed on a baseplate (dark blue, 10) that moves in the horizontal (X–Y) directions, while the print head and nozzle (2 and 4, orange) move in the vertical (Z) direction. The raw material for printing comes from a plastic rod (yellow, 46), melted by the print head. The heating process is carefully regulated by a thermocouple (electrical heat sensor) connected to a temperature controller (purple, 86). The rod is extruded using compressed air from the large tank and compressor on the right (green, 60/62). Things have changed a bit since then, but the basic principle (of building up an object by melting and depositing plastic under three-dimensional control) remains the same. Artwork from US Patent 5,121,329: Apparatus and method for creating three-dimensional objects by S. Scott Crump, Stratasys Ltd, June 9, 1992, courtesy of US Patent and Trademark Office.