For the past several years, 3D printing technology has been garnering quite a few headlines. Unfortunately, as is common for the main-stream media, many of the interesting science elements are left out of these stories. So I figured it was time for a Common Science treatment of this fascinating technology. This week I will discuss what 3D printing is, and next week I will speculate on its potential.
The printing process starts by creating a digital 3D model of the object to be assembled in computer code. Next, you decide what material you want to build your object from. This choice leads me to the first key element that the mass media usually leaves out. Most stories which one encounters about 3D printers exude boundless optimism about them being able to make just about anything. While 3D printing is quite amazing, there are some limits which are important to understand.
Generally speaking, there are three classes of starting materials which can be used by 3D printers: metal powders, plastic powders, or liquids which rapidly polymerize. Once the material is selected, the computer model guides an extremely precise nozzle to spray successive layers, each approximately 20-100 microns thick. For reference, 100 microns is about the thickness of a human hair. Each layer needs to be fused together using one of the following techniques:
• Plastic powders are melted with a laser beam such that they fuse together when they cool down.
• Metal powders can be joined together in one of two ways. You can shine a laser beam on them such that just the edges melt and then fuse together upon cooling. This process is called sintering and results in an object which is still porous. This makes sintered metals quite useful as very precise filters. Alternatively, the metal powders can be melted with an electron beam, such that they form a solid when cooled.
• Liquids can also be used if they polymerize quickly into a plastic when you shine a laser beam on them.
The limitations in the variety of possible starting materials results in limitations on what can be produced by 3D printers. For example, you can use a 3D printer to make a violin; you just have to make it out of plastic. Apparently, they don’t sound very good.
The basic science behind 3D printing was developed during the late 1970s, and the first 3D printer was constructed in 1984. Over the next three decades, parallel developments in the printer technology, material science, and computer programming resulted in the development of commercially-viable 3D printing processes by 2010. This time lag of 30 years or so between the basic research and the commercial payout is quite typical of many inventions. Therefore, a society with a long-term plan for continued technological advancement and economic development is well-served to invest in basic research.
Writing this column reminded me of my own Ph.D. research which I carried out from 1989 to 1993 in the area of chemical vapor deposition (CVD). In CVD, you are trying to build up successive layers which are only one molecule thick, a layer approximately 1,000 times thinner than what is used in 3D printing. Therefore, you can consider CVD as sort of a next-generation 3D printing technology. If everything stays on schedule, CVD should become a successful commercial technology sometime in the next decade.
Now that we have covered what 3D printing is and how it works, we can move on next week to some of its more interesting applications and possibilities.
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