By 3DPrinthuset (Denmark) The building on demand (BOD)
printer developed by COBOD International
(formerly known as 3DPrinthuset, now its sister company)
 , CC BY-SA 4.0

  This week we are going to review some advanced manufacturing techniques. A majority of parts manufacturing is done with a process known as subtractive manufacturing. This is the process of taking a piece of metal, plastic, wood or other material and removing portions of it in a controlled fashion, resulting in a finished part. This method is used to make parts like gears, screws, engine blocks and crankshafts.   There has been a lot of talk in recent years of additive manufacturing techniques. This is where you start with nothing and build a part by adding material in a controlled fashion. The most popular additive manufacturing process is called 3-D printing.
  The very first 3-D printers used chemical compounds that harden when exposed to ultraviolet (UV) radiation. This is the invisible light that causes sunburns. It was in 1987 that stereolithography (SL) techniques were developed to create acrylic components. A UV laser is aimed at the reactive resin which instantly hardens. The object is then lowered layer by layer into the liquid and the final part is pulled from the vat of liquid. This technique produces the highest level of detail in the parts, but is the most complex process.
  The second method of additive manufacturing is called jetting and is similar to how an inkjet printer works. The same reactive resin is now sprayed from a nozzle onto a surface and exposed to the UV light, hardening it, before another layer is sprayed. There are also similar methods using powder and spraying an adhesive to create the layers. This is heavily used in industrial manufacturing facilities.

By Bre Pettis – Flickr:
 A Makerbot three-dimensional printer
 using PLA extrusion methods.
CC BY 2.0

  A very similar method to jetting and SL is Selective Laser Sintering (SLS). A powered material that can be rapidly fused by laser heat, such as polymides and thermoplastic elastomers, is placed in thin layers on a metal surface. A powerful laser then fuses (not melts) the powders into layers forming a very durable object. These were used in the manufacturing of custom hearing aids molded to fit the individual’s ear canal perfectly.
The final method of readily available 3-D printing technologies is definitely the cheapest method and the most popular among home users. It is called extrusion printing. This method uses strands of PLA or ABS plastics that are run through a temperature controlled nozzle which melts the plastic and creates the objects layer by layer. This extrusion method has been used not only with plastics, but with concrete, metal, ceramics, and even food, such as chocolate.
  Over the last two decades Missouri University of Science and Technology has been involved in bleeding edge research in the field of additive manufacturing. Among their claims to fame is the Freeze Form Extrusion machine. This machine uses extremely low temperatures (-16 to -40 degrees Celsius) to freeze ceramic pastes consisting of Boron, and Aluminum Tri-Oxide to form ceramic components capable of withstanding extreme heat greater than 2400 degrees Celsius. The process is a two-step process where the part is first frozen together and then baked at a very high temperature to rapidly fuse the ceramics.  Their latest research is in extending this process to fabricate titanium alloy components.
Additive manufacturing can be used today to make everything from key-chains to houses and even human skin grafts and organs. We have come a long way in the last 30-years in manufacturing technologies.

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