Mad About Science: Fused deposition modeling

By Brenden Bobby
Reader Columnist

You may have seen the 3-D printers at the library. Ever wondered how they worked?

Last week, we learned about photopolymer resin and its applications in dentistry and 3-D printing, but the library’s 3-D printer doesn’t use resin. It uses a spool of thin plastic that is somehow transformed into an object designed on a computer through the magic of whirring gears and motors.

Courtesy photo.

Printers that use spools of plastic filament are called “fused deposition modeling” printers, or FDM printers. Compared to the intense levels of chemistry involved with photopolymer resin, the method in which an FDM printer transforms spool into cool is really simple.

The filament is fed into a metal nozzle by a motorized gear. The nozzle is then heated to a temperature exceeding 200 degrees Celsius or 392 degrees Fahrenheit, which causes the plastic to melt. The motorized gear that’s pulling the filament into the machine is simultaneously pushing out the molten filament onto the print bed, while other motors direct the print head unit around the bed in whatever pattern was programmed in by the slicing software. Depending on the model, sometimes the print bed will also raise and lower so that the print head doesn’t have to.

The print head will trace an outline of the object with deposited filament and then fill in the interior with something called infill, often hexagonal or triangular patterns that give the item structural stability without expending a huge amount of filament. This keeps the printed item lightweight and inexpensive to produce.

The print head will deposit material over and over again while also blasting the deposition with cool air from a fan to rapidly cool it down and allow it to fuse to the plastic layers below. This is a lot like making a sandwich — the printer is adding layer upon layer, stacking it up until the job is done. Unlike a sandwich, you really don’t want to eat this stuff or it will make you incredibly sick.

FDM printers are very different from resin printers in a lot of respects, but each has its own strengths and weaknesses. FDM printers aren’t able to capture the level of detail that a resin printer can produce, but require considerably less maintenance and precaution than their ultraviolet counterparts.

As an example, with an FDM printer, you can simply pop your print off the build plate as soon as it’s done. A resin printer would require you to remove the build plate, clean the print and build plate in a bath of isopropyl alcohol, then cure the print with ultraviolet light before your print is ready to be used. Additionally, you would need to wait for the alcohol to evaporate from the build plate before you started another resin print — all while wearing gloves, a mask and goggles.

FDM printers aren’t invincible, however. They sport many more mechanical parts than a resin printer, which consists mostly of electrical components.

One large benefit to FDM printers is the huge variety of materials you can print with. While they are all plastic products at heart, there are filaments available that sport wood grain and contain real bits of wood, metallic filaments that will show a patina effect over time, as well as carbon fiber and even food safe plastics.

There are a number of other really interesting 3-D printers on the market, including material jetting, or MJ, printers that operate much like a traditional inkjet printer. The printhead has a section with many perforations aligned in rows and columns. These perforations release droplets of photopolymer resin in very specific patterns based on the item programmed into the printer. A UV lamp is attached to the other side of the print head, allowing the printer to cure the model as it prints it.

This method of 3-D printing is extremely fast and detailed, but it is also very expensive, ranging anywhere from $6,000 to $750,000 per printer. You likely won’t see an MJ printer anywhere outside of a research and development lab for prototyping a company’s products.

One more method of 3-D printing is called selective laser sintering, or SLS. This utilizes a chamber filled with plastic powder that is heated to just below the powder’s melting point. A computer-guided laser then targets specific layers of the powder, pushing it just over the melting point and mechanically fusing the particles. It will do this layer by layer until a sturdy, precise item is seemingly pulled from thin air. This is great for prototyping or creating custom and durable items like chassis for power tools, ski-wear and more heavy-use items. The quality is on par with injection molded items you’d find at just about any store.

3-D printing is incredible technology. Using just a few basic measurements, you can build a model on your computer and print it out over the course of a few hours to replace all manner of things from tool handles to device cases and covers. You can even bring completely new objects into existence that help personalize your living space or your organization. Why conform to what some company overseas thinks your office should look like? Really make it your own!

If you fancy yourself a skilled designer and entrepreneur, you can even make some serious money by starting up your own manufacturing business. Companies will pay top dollar for great designs, and I’d be willing to bet they’d much rather pay to have it shipped six streets down than across the ocean.

Stay curious, 7B.