Adoption of Additive Manufacturing for Transportation Applications
Additive manufacturing is a new process for the production of components and parts made of metal, plastics or composites. The process can take a computer aided design, prototype, or existing part and have it reproduced in a much shorter time than using traditional manufacturing processes, such as welding, casting or machining, which involve acquisition time, molds and specialized subcontractors. The process basically adds layers of powders or strands of plastic and consolidates them by use of lasers, binders or thermal action. Plastic parts are generally used for prototypes, whereas metal parts consolidate the metal powders by either laser fusion or binding them and subsequently sintering the powders at elevated temperatures. This process is virtually unused by transportation fabricators that provide components for the transportation community. Moreover, the physical and mechanical properties of the additive-manufactured components are largely undefined or uncharacterized, including yield strengths, fatigue strength, and energy absorption properties sustained upon impact if they are to be used for gears, proximity switches, light pole bases, enclosures for electrical boxes and junctions and other smaller components. Present approximate volume is limited to 12”L x 10”H x 10”W, although this max volume will probably increase with greater adoption of this process by manufacturers. Equipment used for this process is relatively expensive, even for smaller “desk-top” units.
The objective of this research is to compare wrought, cast and machined parts with the same parts produced by additive manufacturing. This comparison must include actual differences in their tensile and yield strength and fatigue strength in tension and rotating bending for steel and aluminum parts. Impact toughness properties at different temperatures for steel parts would also be determined. Parts would include gears, flat sections and round bars for direct comparison. This research would provide designers and engineers where additive parts could be used as replacements, or when their use in certain locations or applications is not appropriate.
SCOBS global focus : Foster innovation; enhance maintenance; minimization of traffic disruption
SCOBS prioritized objectives:
Determine the properties of components derived from additive manufacturing.
Provide for rapid replacement of existing transportation components when traditional manufacturing processes would require longer acquisition time, thereby placing the transportation structure back in service to minimize traffic disruption.
Provide future lower costs for additive components as the process is sequentially adopted with greater frequency by fabricators.
Internet searches and discussions with suppliers of additive manufacturing equipment and users indicate that there are two prominent additive manufacturing methods used to build and process the components from metal powders. The first method uses deposition of metal powders which are melted and fused by use of lasers, layer by layer, derived from software that translates the geometry of the part. The part geometry can be obtained from either computer-aided drawings, or from laser scanning of an actual part, or from coordinate measuring machines. The laser fusion method results in substantial presence of residual stresses which must be relieved in order to achieve part stability and dimensionality. If precision of dimensions is required, the parts must be further machined. The second process also deposits metal powders, but the particles and layers are held together by a binder. The so-called as-deposited “green” part is held together by the binder and coherence may be further augmented with specially formulated metal rods. The part is then sintered at elevated temperatures, whereby metal particles are fused and the binder vaporizes. Parts will sustain shrinkage of up to 20% and may contain 1-4% porosity. However, this process can presently deposit volumes up to 24 in3 per day and its resolution is about 50 microns.
|Sponsoring Committee:||AKC70, Fabrication and Inspection of Metal Structures
|Research Period:||24 - 36 months|
|RNS Developer:||Christopher Hahin, MetE, CorrE, PE Illinois DOT Bureau of Materials, Chris.Hahin@Illinois.gov|
|Index Terms:||Three dimensional printing, Components, Physical properties, Mechanical properties, Structures, Structural members, |
Bridges and other structures