Since the introduction of 3D printers in the 1980s, the devices have been used to build meat, chocolate, human organs, clothing, cars and houses. It’s more mainstream than ever and you can buy a machine for less than $200.
3D printing, also called additive manufacturing or rapid prototyping, has many advantages over more traditional subtractive manufacturing methods, which involve starting with a piece of metal or wood and removing material using milling tools, drills, and other tools. The two main advantages are that 3D printers produce much less waste and are better at creating objects with complex shapes. Instead of a complex assembly process, everything can be manufactured in one place.
“Mass production methods, almost all of them are pretty fixed,” says Diana Haidar, an associate professor of mechanical engineering at Carnegie Mellon University. “You can only make exactly the same parts again and again. But people also want customized pieces. 3D printing has a niche here.”
How exactly does a 3D printer work?
What is 3D printing?
Think about the type of printing that most people are very familiar with: printing with ink on paper. This is 2D printing because there is a region with an x-axis and a y-axis, so two degrees of freedom. There is a third dimension to 3D printing: height. The files you feed into 3D printers are 3D images that a software program then cuts into horizontal layers.
“The idea is that I have a 3D object and I’m going to break it down into many individual layers. We use slicer software for this,” explains Haidar. “Then there is usually a two-axis head that moves and builds a single layer. Then either the head goes up or the bed goes up [that the object is being built on] will fall. But there is a Z-axis change so we can build one layer at a time.”
Popular methods for 3D printing
One of the most common types of 3D printing is Fused Deposition Modeling (FDM). “It is spatially the cleanest,” says Haidar.
This method involves inserting a spool of wound filament (usually plastic or polymer) into the head of the machine. There is a heating unit in the head that melts the polymer. Polylactic acid (a type of plastic) is one of the most commonly printed 3D materials because it is cheap and has a relatively low melting point of around 180 degrees Celsius (350 degrees Fahrenheit). When used as a feed material, engineers typically set the 3D printer at around 200 degrees Celsius (390 Fahrenheit) to ensure that the material is melted as it is extruded from a small nozzle but is then allowed to harden back into shape. The smaller the nozzle, the higher the resolution of the printed object.
The second most popular method for 3D printing is an older technique called stereolithography, or SLA. In this case, photocurable resin is the printing material instead of a solid spool. This technique uses a bath of sticky, sticky resin in a glass tank that has not yet cured. A UV laser beam and several mirrors each harden one layer. Each time a layer cures, it becomes solid, is sheared off the bottom glass in the tank, and then lifted out of the bath – eventually forming a solid, coherent structure.
The third most popular 3D printing method is so-called laser powder bed fusion. This technique works well for printing or pressing metals together. First, there is a large, flat bed of metal powder, and a laser cuts out a shape and fuses the desired shapes. Once a layer is finished, the bed lowers and a roller spreads a new fine layer of powder onto the surface.
Another common 3D printing method is polyjet printing, which allows engineers to work with a variety of nozzles and materials (from hard to soft) in one print.
What types of materials can be 3D printed?
Although 3D printers most commonly print with plastics, they can also be optimized for printing metal-embedded materials, ceramic-embedded materials, and wood-embedded materials. Different types of fibers or particles can be mixed with polymer binders to give objects different properties.
When special machines print organs (e.g. a heart), multiple nozzles can be pre-filled with syringes to inject different types of cells. Instead of a coil, the machine injects a hydrogel.
How much do 3D printers cost?
The cheapest 3D printer on the market costs around $200, and these machines are used by engineering students to quickly create models. But spending less money on such a machine comes with compromises. The cheaper models tend to be more demanding and break more often. They are also not as consistent in producing the same object over and over again. For example, the polymer or plastic building material may warp if the temperature changes too much from the inside of the nozzle to the outside environment. “You don’t see this as often with the large machines because they have clearly enclosed environments that are temperature controlled and may even have a cooling circuit,” explains Haidar.
A mid-range desktop machine for FDM printing typically costs $3,000, and software packages are included in that price. A higher quality machine that can produce larger objects using a more durable base material can cost $200,000. Spending all that money has big benefits down the line. “Your maintenance costs are a lot lower. It’s easier to print materials that the smaller machines would have difficulty with,” says Haidar. “These machines are the closest you can get to a professionally manufactured part.”
The fanciest machines print from metal, such as aluminum. The metal 3D printers can cost up to $1 million as they need to be operated in a space that is very well controlled, ventilated and capable of suppressing explosions (if they occur).
