3D Printing: 9 Common Processes

 

You’ve already considered the possibilities for 3D printing. You’ve imagined a not-too-distance future where you can download the file for a car part, remote,  appliance , etc., and print a replacement in just a few minutes from the comfort of your home. Engineer something you’ve been toying with in your head for years. Improve something you already use.

Then there’s what a lot of heavy-hitting groups are experimenting with: printing objects to use as prototypes in aerospace, medical orthopedics, and energy industries.

Besides all the imagined possibilities, there’s sheer excitement around 3D printing and all the things we haven’t thought of just yet. Some technology experts are even going so far to call in-home 3D printing the third industrial revolution.

3D printing is a technology that is, for the hobbyist, still young: only in the last few years have truly affordable options for the weekend inventor sprung up. But we’re almost past the early adopter phase, and there’s plenty of things to learn to make sure you’re on the cutting edge of this new technology.

So, what exactly is it?

3D printing is an additive manufacturing process that makes solid, three dimensional objects from a digital file, often a CAD file. It widens the narrow definition of ‘printing’: instead of using ink to put words on paper, we’re now using materials to make objects. It’s a pretty wide definition, and you may already be thinking of several ways this could work. In fact, there are several ways that already do.

Initially invented in the 1980s, 3D printers were large and expensive. As technology and engineering costs have fallen, more inventors have been able to tweak existing processes or create entirely new processes. The main differences among processes are the materials used and the way layers are deposited and/or built. For instance, some methods melt or soften material to create the layers, while other processes cure liquid material.

We’ve put together a primer on the most common types of 3D printing, including pros and cons. As with any rapidly developing technology, this info isn’t all-encompassing; it’s intended to give you a strong starting point as you enter the world of 3D printing.

Before we jump into the nuts and bolts of each process, consider the reasons 3D printing is being hailed so highly:

  • Rapid prototyping: If your product is easy to test out, you can innovate quickly. Concept to prototype time shrinks. Companies and individuals can understand quickly what works, what doesn’t, and whether their business ideas are viable.
  • On-demand creation: Everything is on demand these days, so why not manufacturing? If companies can produce a product on demand, they don’t have to outsource or over-produce, reducing warehouse space and money spent.
  • Less waste: It’s an additive process, so the object is built up, versus a subtractive process where an object is carved out of raw material. (Less waste can often mean less cost, too.)
  • Accessibility: People living in remote areas now have access to products they may not otherwise be able to get.
  • Potential: 3D printing truly has the potential to change the entire nature of manufacturing. Imagine consumers downloading a file to print the latest device instead of running out or waiting in line at a big box store

Enough with the background, let’s jump into common 3D printing processes. First up, the original:

Fused deposition modeling (FDM)

Also known as: fused filament fabrication (FFF), plastic jet printing (PJP)

FDM is one of the original processes, and FDM printers were the first to come to market in the mid-1990s.

How it works: The printer melts a thermoplastic filament, often acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA). A heated extrusion nozzle then deposits the molten filament onto the plate, in X and Y coordinates, as defined by the CAD files. After each layer, the build plate, which serves as the base, lowers down, providing the Z coordinate, for that third dimension.

Depending on the object’s shape, support structures can be inserted during printing, and removed on completion.

  • Pros: At-home options are cheap and easy to find; allows for rapid prototyping for companies and individuals; a huge range of materials can be used.
  • Cons: Structural integrity isn’t the best: small overhangs work, but nothing unsupported.

Stereolithography (SLA)

Also known as: optical fabrication, photo-solidification, or resin printing

SA is one of the oldest 3D processes, invented in 1983 by Chuck Hull.

How it works: Like FDM, this is a bottom-up approach, but the material in this process is photosensitive liquid resin. The printer shines a UV laser onto the resin, solidifying anywhere the laser touches. The machine steps down a layer, and continues the next layer. Once the object is complete, it must be rinsed with a solvent, or baked in a UV oven, to de-activate the photosensitivity.

  • Pros: Creates accurate, minute details, perfect for jewelers or cosmetic dentistry
  • Cons: Its high cost (machines are often over $100k) means it’s likely to stay only in the commercial sector

Digital light processing (DLP)

DLP is used mostly in commercial industries, though some DIYers are building their own printers, and using smartphones to cure the resin.

How it works:  Similar to SA, DLP uses a photosensitive polymer as the material. Instead of using UV beams, however, a special projector projects light that cures the resin. The projector comprises a grid of micro-mirrors, laid out on a semiconductor chip controlled by a computer. The mirrors tilt: one angle produces light and creates a bright pixel; the other angle turns the pixel dark. The projector then hardens the polymer layer by layer. Any remaining liquid polymer is drained away.

  • Pros: The speedy projectors print highly-accurate, layers in just seconds.
  • Cons: Structural integrity can be a little iffy on unsupported structures.

Selective laser sintering (SLS)

SLS dates back to the mid-1980s at University of Texas, and it’s used mostly for prototyping development pieces.

How it works:  This technique uses powerful UV beams, similar to SLA, but the material is powdered. The UV laser sinters, or heats without melting, a layer of powdered granules, binding the material together. As long as the material is powdered, the printer can handle plastic, metal, glass, or ceramic. Once formed, the object must cool in the printer.

  • Pros: Wide range of usable materials; remaining powdered material can be recycled.
  • Cons: The high-powered lasers are expensive, so SLS remains mostly a commercial process.

Selective laser melting (SLM)

Can be considered a subset of SLS

SLM’s ability to handle heavy metals make it perfect for the aerospace and medical industries that are pioneering its use.

How it works:  Unlike SLS, the laser in this process must entirely melt the metallic powders, so SLS is uses for heavy-duty metals like titanium, stainless steel, aluminum, and cobalt chrome.

  • Pros: SLM offers large-scale and detailed structures.
  • Cons: Using these heavy metals is risky, and it’s prohibitively expensive, so it’s resigned to commercial industries like aerospace, energy, and medical orthopedics.

Electron beam melting (EBM)

This technology is being used in the medical implant and energy markets. GE has invested heavily, especially for developing turbine blade.

How it works:  This is a larger, more intense version of SLS. EBM uses metal powders, but the UV beam is replaced by a computer-controlled electron beam and a high vacuum. This metallic melting point can get as hot as 1000° Celsius.

  • Pros: There’s a lot of potential.
  • Cons: It’s expensive and slow.

Laminated objects manufacturing (LOM)

LOM works a bit differently than the ones we’ve talked about so far.

How it works:  The printer starts with layers of adhesive paper, though plastic and metal laminates are possible, too. The printer heats and presses the layers, fusing them together. Then, a computer-controlled laser or knife cuts the object’s shape, piece by piece. Depending on the design, some printers can machine and drill the object, too. Once the excess material is cut away, the object can be sanded or sealed with paint.

  • Pros: Really affordable, especially when using paper; can make larger-scale objects, pretty quickly, too; full-color options are available
  • Cons: Dimensional accuracy isn’t great; the technology is still being developed

Binder jetting (BJ)

Also known as: multi-jet modeling, powder bed printing, inkjet 3D printing, drop-on-powder printing

Chalk this up to the engineers at MIT who invented binder jetting. It’s perfect for prototyping and short-run manufacturing, especially in medical, automotive, and aerospace industries. Keep an eye on this process, as its full potential is still being explored.

How it works:  This process uses two materials: a powder based (often gypsum) and a bonding agent. The bonding agent adheres the layers of powder together. After each layer is complete, the build plate lowers, and the process repeats.

  • Pros: The big pro here is BJ offers full-color printing, just by adding pigments to the binding agent (typically CMYK); there’s a lot of investment in this process, with HP developing ‘multijet fusion’ to improve detailed output
  • Cons: The structural integrity isn’t great (yet), so don’t expect super high-res prints

Material jetting (MJ)

Also known as: wax casting

This is the people’s 3D print technology. There’s no specific inventor, because the casting part of this process has been used by jewelers for centuries to create high-quality, customized jewelry in various metals. Technology has innovated this process by automating the wax casting.

How it works:  The printer melts the wax, then several nozzles sweep back and forth, depositing the wax into an aluminum build plate in layers. As the wax touches the plate, it cools and solidifies. A different wax with a lower melting point serves as structural support, and it is deposited below and of the object’s structural overhangs. When finished, a heated bath melts away the support wax.

  • Pros:  Don’t need to buy a 3D printer to use this technology – companies like Shapeways and Sculpteo offer printing on their machines.
  • Cons: Castable wax is fragile; with only a few degrees separating soft wax from molten wax, you have to work fast.

Today, these are the 9 most common 3D printing processes. Of course, if you’re into experimenting, a lot of people are making their own processes, simply by modifying a standard inkjet printer and using a wide range of materials. You could even use a 3D printer to make modification to your self-styled printer.

References

https://en.wikipedia.org/wiki/3D_printing

http://www.pcmag.com/article2/0,2817,2394720,00.asp

https://all3dp.com/types-of-3d-printer-technology-explained/

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