This is my impression of the state of 3D printing technology based on my visit to RAPID 2012 (http://rapid.sme.org/2012/public/enter.aspx) and reading some articles on the industry.  The post includes the applications of additive manufacturing, the additive manufacturing process, a comparison against subtractive manufacturing technologies, and a comparison between the different additive manufacturing technologies.

It is the basis for a talk I will give to set the context for a 3D printer design project at a hackerspace, Pumping Station:  One.  At the event, Jeremy, from TinyWorkshop, will discuss what’s going on in consumer 3D printing.

Applications
The promise of 3D printing is its ability to support general purpose making.  There is already a huge range of applications for which 3D printing has been used, piloted, or envisioned:

• Buildings (http://www.youtube.com/watch?v=JdbJP8Gxqog&feature=player_embedded, http://m.popsci.com/technology/article/2012-08/researcher-aims-print-3-d-print-entire-houses-out-concrete-20-hours),
• Cars (http://techtripper.com/worlds-first-3d-printed-racing-car-can-pace-at-140-kmh/),
• Planes (http://www.forbes.com/sites/parmyolson/2012/07/11/airbus-explores-a-future-where-planes-are-built-with-giant-3d-printers/), plane parts (Boeing now uses 300:  http://printready.co/tech/boeing-making-airplane-parts-using-3d-printing/, http://machiningaustralia.com.au/3d-content-to-print-solutions/)
• After-market parts (http://www.wired.com/design/2012/09/synthesizer-lets-you-3-d-print-your-own-parts/)
• Electronics (http://www.optomec.com/Additive-Manufacturing-Applications/Printed-Electronics-for-3D-Printing, http://www.economist.com/node/21559593),
• Tissue (http://www.gizmag.com/3d-bio-printer/13609/), teeth (http://www.sciencedaily.com/releases/2011/07/110714101509.htm), bones (http://www.universaldesignstyle.com/titanium-bones-made-from-3d-printing/)
• Lights (http://www.disneyresearch.com/research/projects/hci_printedoptics_drp.htm),
• Ceramics (http://uwe.ac.uk/sca/research/cfpr/research/3D/index.html),
• Food (http://www.psfk.com/2012/08/3d-printed-pasta-google-cafeteria.html), and
• Guns (http://www.forbes.com/sites/markgibbs/2012/07/28/the-end-of-gun-control/; http://www.thingiverse.com/thing:11770 and http://animalnewyork.com/2012/3d-printed-guns/)

Manufacturing process
To produce something:

• Draw a 3D model in a CAD program.  Software for doing this includes Solidworks (industry standard), SpaceClaim (capable of holding more data), and SensAble Freeform (allows you to draw with a pen in space).  An example of the resulting file format is IGES.
• Post-process the 3D model.  The result is a texture-less model defined by a lot of small triangles.  Materialise Magics is an example of software used for this.  The resulting file format is STL.
• Use CAM software to translate the STL file into instructions for the machine.  This involves slicing the 3D model into layers and giving instructions for how the machine should move (in gcode).
• The machine follows the instructions to print the part.
• The part undergoes finishing (if necessary).  This could include anything from including an exterior layer of metal (e.g., www.vacucoat.com, www.repliform.com), painting the part, sand-blasting or hand-finishing.

Comparison between additive and subtractive manufacturing technologies
I believe that the benefits that additive manufacturing has over subtractive manufacturing (e.g., drilling, milling, turning, etc.) include:

• It can do complicated geometries.  For example, high performance car companies have used 3D printing to make fuel injectors that would be difficult if not impossible to machine.
• It is faster.  To get a sense, lead times for 3D printed parts at a machine shop, Solid Concepts, are 1-3 days as against 3-9 days for machined parts (http://www.solidconcepts.com/).
• Labor costs are lower than machined parts.
  • 3D printed parts require less assembly.  Less assembly means less labor and weight.  Given the importance of these factors in aerospace, one company used 3D printers to make a duct, because it saved them three sub-assembly steps.  In the long-run, it will also be easier to make objects containing a variety of materials.  Just as sophisticated milling machines have carousels where they can switch their tooling, so too 3D printers might be able to cycle through materials they print.
  • 3D printed parts require less setup.  There is no blank to fixture (though you might need to program in a support structure—a step that most 3D printing CAM software takes care of automatically).
• There is less wasted material.  Because you are adding material instead of removing it, the only waste is the support structure, which can be re-used by some 3D printing technologies.

The downsides of 3D printing relative to subtractive manufacturing include:

• Material variety.  More materials are available if you make something using traditional methods.  This implies a relatively limited range of mechanical, thermal, and electrical properties.  That being said, the range of materials you can 3D print is quickly expanding (it already includes plastic and metal).
• Tolerances.  While most machine tools hold tolerances of .0002”, most 3D printers fall in the 0.004” – 0.013” range (the exception is Polyjet parts which hold tolerances as small as 0.0006”).
• Machine and material costs are higher.  (Cost data is from http://usatoday30.usatoday.com/money/industries/manufacturing/story/2012-07-10/digital-manufacturing/56135298/1)
  • The machines are expensive:  good ones are $100,000 vs. $50,000 for a comparable milling machine.
  • The materials are expensive.  Plastics and metal powders can be 60 times as expensive as traditional equivalents.
  • At higher volumes, the economics don’t make sense.  For example, for Audiovox to make control buttons, it would cost them $0.96 per button to 3D print as against $0.30 to make using a mold.  However, the setup costs for the mold were $4000.  In another example, for Mydea to 3-D print an electrical housing for an infrared camera, it would cost them $40 each as against $5 each to make using traditional methods.  However, the tooling for the traditional method would cost $17,000.

Solid Concepts has funded some wonderful destructive testing research to identify the properties of different 3D printed parts (https://www.solidconcepts.com/resources/brochures/).  To give you a sense of the results, I consolidated the information they have in a number of their brochures into a single table.  Each cell indicates the range of properties available for a given technology.  When they did not specify the results, I filled it in with information from manufacturers’ literature when possible.  Properties of materials made with traditional methods are also included for comparison.  A description of the columns (e.g., what tensile strength is) is available at the end of the post.

Additive manufacturing technologies described
Essentially there are two types of 3D printers.  Both involve building a part layer by layer.   Some make a layer by extruding raw material that will be solidified in a particular pattern.  Others make a layer by solidifying a particular pattern in a bed of raw material.

Technologies involving raw material extrusion

• Heat (Fused deposition modeling).  In these printers, a strand of thermoplastic (filament) is fed through a heated nozzle (extruder).  After the liquefied strand is placed, it solidifies as it cools.  An example of this type of printer is Stratasys’s Dimension 1200ES (http://www.dimensionprinting.com/3d-printers/3d-printing-1200es.aspx).

• Light (Polyjet).  In these printers, a liquid photopolymer is applied using an inkjet printer nozzle.  After it has been applied, light is passed over the whole bed to cure the layer.  An example of this is Objet’s Connex 500 (http://objet.com//3d-printers/connex/objet-connex500).

Technologies involving bed solidification

• Adhesive.  In these printers, a glue (binder) is applied to a sand-like substance.  It bonds the powder in the desired pattern.  An example of this is ZCorporation’s Zprinter 650 (http://www.zcorp.com/en/Products/3D-Printers/ZPrinter-650/spage.aspx).  A different example of this technology is used by Ex One to print metal parts (http://exone.com/materialization/systems/M-Flex).  A large scale example is Voxeljet’s VX4000 (http://www.voxeljet.de/en/systems/vx4000/), which is capable of printing parts 12′ x 6′ x 3′.

• Light (Stereolithography and Digital Light Processing).  In these printers, a light (ultraviolet or visible) is projected on a photopolymer (a resin that solidifies when light of a particular wavelength is shone on it) of the specified shape.  It solidifies (cures) the photopolymer in the desired pattern.  An example of a Digital Light Processing printer is EnvisionTEC’s Perfactory 4 Standard XL (http://www.envisiontec.de/index-page=machines&id=42.php.html).  An example of a Stereolithography printer is 3D Systems’s iPro 9000 XL (http://production3dprinters.com/sla/ipro-9000-xl-sla-production-printer).

• Laser (Selective Laser Sintering).  In these printers, a laser is shone on powdered plastic or metal.  It melts the powder in the desired pattern.  An example of this type of printer is the EOSINT M 280 (http://www.eos.info/en/products/systems-equipment/metal-laser-sintering-systems.html).

Additive manufacturing technologies compared
A couple of observations based on the below table:

• SLS printed nylon has, across the board, superior mechanical properties when compared to the other plastic 3D printing materials.  But, you pay for it in the cost of the machine.
• Of the less expensive machines, Fused Deposition Modeling produces parts with the best mechanical properties, Polyjet machines have the highest resolution, SLA seems to strike a balance between material strength and resolution, and Zprinted parts are suitable for show (due to their superior capacity for color).

The columns in the table can be described as:

• Tensile strength is how hard you can pull on the ends of a rod before it breaks.  The tensile modulus is the relationship between how much force is applied to the ends of the rod and how much the rod will elongate.  This is a video of a tensile strength test:

• Flexural strength is how hard you can push down on the middle of the rod (with the ends supported) before it breaks.  The flexural modulus is the relationship between how much force is applied to the middle of the rod and how much it bends.  This is a video of a flexural strength test:

• Impact strength is the force an object can absorb when struck with an arm on a pendulum.

• Heat deflection is, for a given load, the temperature at which something deforms (http://www.matweb.com/reference/deflection-temperature.aspx).