Lesson 2: 3D Printing


What is 3D Printing?

3D printing is a process of taking a 3D model created on a computer and turning it into a physical object.

There are several 3D printing type. Among the most common are:

  • Fused Deposition Modeling (FDM) / Fused Filament Fabrication (FFF)
  • Stereolithography (SLA)
  • Selective Laser Sintering (SLS) / Direct Metal Laser Sintering (DMLS) - Selective Laser Melting (SLM) / Direct Metal Laser Melting (DMLM)
  • Polyjetting
  • Plaster Based 3D Printing (PP)

They all rely on layer-by-layer fabrication, which means that the material used to create the object is made one layer at a time. The most common 3D printers you will find in homes and offices are based on FDM / FFF or SLA processes. These are the least expensive and easiest to implement methods of 3D printing.

3D printing” can also be referred to as “                                 ” or even “                                  

How Do 3D Printers Work?

The best way to understand how 3D printing works is to understand the technologies. All 3D printers do not use the same base technology.

When we wish to print a 3D model that we have created in our design software, we export our 3D model as a special file (usually with the extension of .stl, .obj, .ply, .3mf). But before the printer can read the file, the file must be converted into G-code.

G-code is a

Fused Deposition Modeling (FDM / Fused Filament Fabrication (FFF)

Fused Deposition Modeling (FDM) was invented by S. Scott Crump. He commercialized the technology in 1990 via StrataSys (www.statasys.com). The name is a trademarked term and as a result, the technology is often referred to as Fused Filament Fabrication (FFF).

Approximately 95% of all desktop 3D printers use FDM / FFF. A thermoplastic such as PLA or ABS material is fed into an extruder and through a hot end. The hot end melts the plastic. The printer then acquires its instructions from a computer via the G-code and deposits the melted plastic layer-by-layer until the entire object is fabricated.

 

Definitions:

Thermoplastic – A plastic that is

PLAPolylactic Acid.

ABSAcrylonitrile Butadiene Styrene.

 

Both PLA and ABS will perform best if sealed and stored to prevent absorption of moisture from the air. Long term exposure to a humid environment can degrade printing performance and quality of the finished parts.

 

PLA versus ABS

PLA

ABS

PLA is derived from sugar and gives off a smell similar to semi-sweet cooking oil

ABS is notable for its smell of hot plastic. Odor can be reduced by using ABS that is pure and free of contaminants and heated to the proper temperature.

PLA has less part warping. It is possible to print without a heated print bed.

ABS needs a heated print bed in order to deter warping or curling of the surface when in direct contact to the print bed.

Created from processing any number of plant products including corn, potatoes or sugar-beets. PLA is considered form Earth-friendly compared to the petroleum-based ABS.

Used in food packaging and can be commercially composted (not in your household backyard compost).

Naturally transparent, but can be colored.

Strong and more rigid than ABS but can be more difficult to work in complicated interlocking assemblies and pin-joints.

Printed objects will have a glossier look and feel

PLA can be sanded and machined.

The lower melting temperature may make it unsuitable for hot environments, such as a hot car on a sunny day.

ABS is a polymer and can be engineered to have many properties.

Strong plastic with mild flexibility compared to PLA.

Flexibility of ABS makes creating interlocking parts or pin connected objects easier to work.

Easy to sand and machine.

Soluble in Acetone allowing welding of parts together with a drop or two, or smooth and created high gloss y brushing or dipping full pieces in Acetone (Acetone is the active ingredient in nail polish remover)

Easier to recycle than PLA

Strength, flexibility, machinability and higher temperature melting point make it a preferred plastic for mechanical uses.

Stereolithography (SLA)

The first 3D printing technology to be invented in 1986. Instead of extruding hot material out of a hot end, the SLA process works with a laser or DLP projector combined with a photosensitive resin. Objects are printed in a vat of the resin as a laser or other lighting source cures the resin layer-by-layer.

SLA machines are able to achieve better accuracy and less of a layered appearance than FDM / FFF technology.

SLA: 3D Printed Miller 91 race car.

SLA process of a prototype part

Selective Laser Sintering (SLS) / Selective Laser Melting (SLM) / Direct Metal Laser Sintering (DMLS) / Direct Metal Laser Melting (DMLM)

All four of the technologies are similar but with marked differences. SLS and DMLS are the same technologies, but the difference is the materials used. DMLS refers to the layer-by-layer fusing of metal powders using a laser beam, while SLS is the same process, but with non-metal materials (plastics, glass, ceramics, etc).

DMLS and SLS do not fully melt the materials, instead fusing them at the molecular level.

SLM is a process that will be used for metals made of a single material (such as titanium) as the laser is able to completely melt the molecules together.

Difference between “fusing” and “melting”

Fusing

Melting

DMLM of an aircraft engine part from General Electric.

DMLS of a liquid oxygen (LOX) hydrogen injector from NASA

DMLS of a manufacturing tool part from EOS

Polyjetting

A Polyjet 3D printer is a resin-based printer functioning similar to inkjet printers. It merges the technologies of inkjet printing and the stereolithography process. The polyjet print head deposits small amounts of photosensitive resin on the build platform, similar to an inkjet printer. An ultraviolet light that it attached to the print head simultaneously cures the material as it is printed. Once a cross section is complete, the build platform is lowered slightly to make room for the next layer. As the object is created, support material is added to supplement the strength of fine parts and down-facing surfaces.

Polyjet technology from Solid Concepts

Plaster Based 3D Printing (PP)

This process requires the use of two different materials: a powder material (gypsum plaster, starch, etc) that sits on a print bed and a binding ink that is ejected from a nozzle similar to an inkjet printer. The binding ink hardens the powder one layer at a time. Once a layer is bound, a rake-like instrument sifts additional powder over that layer and the process continues until the object is complete.

 

Ceramic 3D printing from Medalta