New Local Motors research demonstrates advantages, challenges of 3D-printing vehicles
Consulting firm Wohlers Associates originally forecasted the 3D-printing industry would reach $10.8 billion in revenues by 2021. One year after making those projections, the firm updated its figures and now project revenues to exceed $21 billion by 2020.
This two-fold increase is mostly due to more companies and individuals learning of the cost savings and environmental benefits that come with additive manufacturing. But improvements in both processes and materials properties are necessary for big area additive manufacturing (BAAM) to make a significant impact in commercial manufacturing, according to a report from Local Motors engineers in Knoxville.
The overview, entitled “Breaking the Mold: Additive Manufacturing and Reshaping the Automotive Industry,” tested the mechanical properties of parts produced by BAAM, including fatigue, fiber alignment and distribution. Our engineers measured tension and flexure failure, along with fatigue in 20% carbon-filled ABS (plastic) under different conditions. Indirect temperature differential between newly printed material and the previous layer was one of the primary variables observed during testing.
Dr. Kyle Rowe, advance materials engineer at Local Motors and one of the study’s authors, said the primary benefits of additive versus traditional manufacturing is the capacity to produce very complex and efficient part geometries, and the ability to rapidly change part design. This translates to decreased design-to-manufacturing times since only materials and CAD files are changed throughout the process. Delamination - or materials failure caused by thermal stress, impact and other factors - remains a challenge in BAAM endeavors since materials contract as layers are added. Mitigating these types of issues is key to furthering the use of BAAM in the automotive and other industries.
“There are multiple ways to avoid [delamination]. They include using new polymers and fillers in materials, part design using simulations to predict thermal stresses, and modifying the design based on that feedback,” Dr. Rowe said. “Printing process improvements, heated build chambers and annealing (slowly cooling) the part after printing will also mitigate delamination.”
Recyclability of materials is another factor that has contributed to the growing popularity of additive manufacturing in various industries. But the process of recycling isn’t as simple as grinding up used material and re-melting it for a new print. Material properties diminish with each new thermal cycle, with the level of decline varying based on the material and filler. In a highway-ready 3D-printed car, for instance, the amount of recycled material that could potentially be used would depend on where the new material properties fall in the performance specifications for the damaged part.
“A fender could probably use all recycled material, but a crash structure could only use about 20% recycled material,” Dr. Rowe said. “At the end of a polymer's life it may end up as a cup holder when it started as a part of the body structure. We are actively working on creating material maps which will give us a way to figure out how much recycled material to use to maintain the desired level of performance.”
Tooling costs in automotive manufacturing are expected to increase by 64% and reach $15.2 billion by 2018, according to the 2013 Automotive Vendor Study by MoldMaking Technology. Additive manufacturing greatly reduces tooling, making it an integral process in automotive manufacturing to keep costs under control.
The aerospace sector provides a good example of multi-material structures, also known as sandwich composites, that additive manufacturing can bring to automotive manufacturing. Dr. Rowe said aerospace combines traditional materials, such as aluminum, with advanced polymeric composite structures like closed cell foams and carbon fiber fabric composites, to provide an optimized, functionally graded part.
“Using additive manufacturing to, for example, print an A-pillar (windshield support) would allow automotive engineers to begin a print with a structural material to give the part form and function,” he said. “After printing, the part could then be filled with a high density, closed cell foam and then reinforced externally with a carbon fiber fabric, or have a reinforcing metallic structure bonded in.” This process results in an optimized, structural part that didn't require molds or forms to make, thus drastically reducing manufacturing time and costs.
There are few organizations producing structural parts on this scale or at this pace right now, so there’s still a long way to go with this research.
“The interesting thing about our current research is that it is enabling us to make stronger and lighter vehicle structures which ultimately condense down to safer structures that are also efficient,” he said. “Our next round of research is going to focus on energy absorption (crash testing) and the impact of environmental conditions on mechanical properties.”
Local Motors engineers will be working on mapping mechanical properties to the temperature differential between the newly extruded polymer and the previous layer as it pertains to additive manufacturing in the coming weeks. The entire “Breaking the Mold” report can be downloaded here.