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A 3D-printed car

News International-French

9 Sep 2014

Local Motors partners with Cincinnati Incorporated, Oak Ridge National Laboratory and Sabic to develop a 3D-printed car.

Currently, producing a new car from a new design represents either a significant investment in tooling, or a large commitment in time for someone to produce a design free form if the tooling does not exist. In addition the need for all that production tooling is the result of just how many parts are required to produce the structure of a car. Just to create the cabin of a car, there are exterior body panels, trim, internal structure for rigidity, interior panels, dash covers... even the seats themselves contribute to a seriously overblown bill of materials. So the fundamental issue is, what can be done to reduce the initial investment in producing a design, reduce the part count, and reduce the follow-up investment that will be required if the design changes?

In that aim, the company uses a hybrid additive/subtractive machine developed at Oak Ridge National Labs. This machine uses a large diameter extrusion head to 3D print objects at high speed, then on the same head it also uses a router to come back and machine surfaces to a more precise specification where required. This means that the company can create car-scale forms very quickly and freely to machined precision, but without the necessity of forming tools, etc. The challenges are to figure out what the best structure looks like, what materials should be used and when. What is the best way to fasten to that structure, and so on.

One of the most important aspects of printing is getting just the right mixture of materials. Materials require different temperatures due to melting points and speed settings due to the elasticity of the material. The large scale printer, that the test pieces of the car were printed on, typically prints between 13 to 20% carbon fiber and 87 to 80% acrylonitrile butadiene styrene (ABS). Depending on the purpose of the print the mixtures of carbon fiber infused ABS will serve different needs. Rigidity, tensile strength, and elasticity are all factors that must be considered in the process of printing. Rigidity, the limit to which an object can bend, is wanted to be just the right flexibility so that in the end product if the structure were to encounter a great force the piece would not just break. For an end product to be structurally sound a good base is a necessity. The first several layers of a print run at a slower speed so that the base lays down more smoothly and really sticks to the print bed.

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