Additive Manufacturing: Production on Demand

September 2011
Topics: Technological Innovations
Additive manufacturing is a technique for building parts on demand out of layers of rawmaterial such as plastic or metal.
Manufacturing plant

3-D Printing

Beside a sun-baked road, members of a military bomb disposal unit cool their heels. A hundred yards behind them, a convoy of armored vehicles idles. A hundred yards ahead of them squats the burned out hull of an automobile, the perfect place to hide a roadside bomb. At their feet sits the robot employed by the unit to remotely investigate suspected bomb sites. One of its treads is detached, the victim of a broken fastener.

It's been a chronic problem for the unit, so they have no more replacement parts on hand. The next shipment of parts isn't scheduled for four days. Just as the convoy commander walks up to discuss choosing a new route, a Humvee races around the stalled convoy. On the passenger seat is the tread fastener, built from scratch on demand—courtesy of additive manufacturing.

Additive manufacturing, sometimes called 3-D printing, is a technique where a product is built up layer by layer from raw material, such as a liquid plastic or powder metal, following a computer-aided design blueprint. The technique was created in the late 1980s to cheaply produce custom parts for prototypes.

Additive Manufacturing: Production on Demand

Rapid and Flexible Resupplying

With our enemies forced to innovate rapidly to survive, it's become increasingly important for the U.S. military to improve its own agility and flexibility. That means looking for ways to overcome a burdensome acquisition cycle requiring a great amount of cost, time, security, and storage space. With additive manufacturing, parts could be produced where they're needed,when they're needed.

Using additive manufacturing would allow for rapid replacement of parts in the field and allow deployed units to remain mission-ready. The technology could be installed and operated at or near deployment locations. Through the use of secure satellite data links or a local parts database, warfighters could access CAD designs for replacement parts, allowing them to repair equipment without the need to establish supply chains or wait for shipments. It could even allow operators to modify a part's design based on its performance in the field.

MITRE is pursuing a research project, called MakeOne, which investigates how to bring additive manufacturing capabilities to the field. MITRE is also designing a data model that helps designers understand all the relationships and attributes of additive manufacturing equipment and materials.

Layer by Layer

A common form of additive manufacturing uses a machine similar to an ink jet printer. The printer deposits a layer of resin on a support table according to a computer-directed design. An ultraviolet light cures the resin into a thin solid layer about as thick as copy paper. Successive layers are added by lowering the support table and printing a new cross-section layer until the part is complete in three dimensions.

Other types of additive manufacturing include:

  • Sintering—heating powdered metal below its melting point until it forms a solid mass
  • Melting—fusing particles together with heat
  • Spray deposition—building solid objects with layers of finely sprayed molten metal
  • Stereo lithography—three-dimensional printing process that makes a solid object from a computer image by using a computer-controlled laser to draw the shape of the object onto the surface of liquid plastic
  • Lamination—bonding solid layers together, as with plywood

Spare Tires

The safety of using parts produced with additive manufacturing techniques is the government's biggest concern in adopting the technology. But industry already uses additive manufacturing in high-performance environments such as airplane manufacturing and race car engine construction. Materials research has led to durable and flame-retardant plastics and high-grade titanium alloys that work well in the process.

When dealing with safety concerns, it's also important to consider additive manufacturing as a supplier of temporary parts rather than final replacement parts. If a part breaks in the field, vital equipment may be down until the replacement part can be secured. This can sometimes require great time, great money, or both.

But with additive manufacturing supplying a temporary part,equipment can remain operational until the actual replacement arrives. Because the temporary part is not intended to be the final replacement part, it doesn't need to meet the same stringent operating requirements. The additive manufactured part can bridge the gap, much like a spare tire on a car miles from an auto shop.

The Expensive and the Complicated

Additive manufacturing is particularly well suited to certain needs. For instance,sensor components often require specialized manufacturing techniques, making new units costly and repairs impossible. But researchers have successfully produced such components using inexpensive additive manufacturing techniques.

It's also handy at building structures traditional manufacturing processes struggle with, such as those with complex internal geometries or fine mesh structures across curved surfaces.

Single parts with functional subassemblies also fit the capabilities of additive manufacturing well. A classic example is the adjustable wrench. In traditional manufacturing, the knurled worm screw,adjustable jaw, and handle are produced separately and then assembled. An additive manufacturing machine can make the same part in a single build by using a support material in the gaps between the operating parts, which can later be washed away.

Although part production using multiple materials is still a new development,several companies and academic institutions have demonstrated the capability. For example, an aerosol jetting technology can produce fully functional embedded passive circuitry overlaid onto other material surfaces. The same technology can also produce specific patterns of solar cells.

Applications such as these could eventually revolutionize the manufacturing industry. But currently it is the military benefits, not civilian, that could prove most profound. When one missing part in the field can put our warfighters at great risk, additive manufacturing is a technology we cannot afford not to build.

—by James Barkley

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