This case study demonstrates how Altair Inspire’s topological optimization and Polynurbs are enabling a new way of product design that matches perfectly with additive manufacturing. This technology allows pushing way further and obtaining especial lightweight designs in a short period of time.
Sport assembly structure redesigned, lightened and optimized for Selective Laser Melting Technology and Filament Fused Fabrication Reinforced by Continuous Fiber with Altair Inspire by Julen Echaniz and Joaquin Romero
Urban mobility is going through a deep change over the last decade. Cars and traditional means of transport have alternatives growing in popularity thanks to the electrification. Despite not been new at all, bikes, skates and scooters are becoming very trendy as they are fast, cheap and require low maintenance. However, there is a downside: weight.
In this context Mondragon university decides to carry out a skate truck project in the Industrial Additive Manufacturing Master Degree where topological optimization, FEA and Design for Additive Manufacturing are taken as a baseline. It is a project developed by Julen Echaniz and Joaquin Romero using metal and polymer composite in which 3D printing capabilities are studied in this particular application.
Who is the skate oriented to?
This design is orientated to citizens who daily travel between 5-20km and may combine it with public transport. This includes urban transportation or even inter-urban transportation.
Same type of customer that is already adopting new means of transportation but give extra value to lightweight and maneuverability of a vehicle they will use every single day.
Taking into account the manufacturing process is already fixed means that personalization/differentiation may also be a key factor for the target customer.
The challenge was to produce a lightweight solution to improve usability. Especially in places like home, work or public transport where you must manipulate the skate by hand. In addition, this extra lightness supposes an improve in handling.
In a hypothetical electric version, this weight reduction will also help to obtain some extra km each charge maintaining the same battery capacity, or vice versa, extending the range with the same weight.
On the one hand, there were some design constrains. It had to be absolutely functional. The user was supposed to weight 100kg (skate mass was neglected for the calculations) and mechanical properties had to be same or better than the reference ones. Original sizes had to be respected, new parts should be compatible with the commercial elements already existing and should fit perfectly. On the other hand, material was free to choose with the proper justification.
The truck is composed by an axle and an articulation so four pieces had to be developed, two in metal and two in polymer composite.
The above images show the original design of the Axle and the Articulation components
This project supposed a new challenge that required us to think outside the box. There is a similar project but it kept a steel axle between the tires sacrificing lightness and making mechanical properties no longer a challenge. This is not an electric skate but the methodology would have been the same.
First, reference design was structurally analyzed with calculated loads to figure it out which were minimum mechanical properties. Then, after selecting the material, those designs were simplified and partitioned to prepare them for the topological optimization.
The above images show the Axle and the Articulation component with the design space ready for topology optimization
The above images show the Axle and the Articulation component after topology optimization
Once the simulation was over, Polynurbs were used for the design and some iterations were done until the required properties were achieved as shown below.
Polymer parts were a little more complicated to design. It is not possible to determine the strength of a part that has non-conventional fiber deposition so topological optimization was used to find out force lines and afterwards design for additive manufacturing setting in those positions the fibers.
In both cases shape factors were used for the topological optimization. Different symmetries were used but, in the end, only the vertical one was applied. It was also considered using an overhang control which is interesting in 3D printing. Nevertheless, manufacturability was set aside in exchange of better strength.
Whole project took about a couple of moths being Inspire a key factor shortening design period and permitting many iterations in a row until the target was hit.
It was an absolute success. All parts were printed with no issues, fitted perfectly with the rest of the elements, no problem at all on the assembly and, more importantly, it worked. All students and teachers could test it proving its resistance and functionality.
On the one hand, 40% weight reduction was achieved maintaining same security factor for the metal assembly. Parts have an appealing organic shape that helps differentiating to any other design.
Comparison of original and final designs
On the other hand, the polymer composite axel was 32% lighter and the articulation assembly´s weight only decreased in a 9%. Unfortunately, there was no reliable way of calculating the security factor of this particular pieces so designs were conservative. There is no doubt this numbers could improve in future with the experience acquired in the first iteration. They look square and robust for helping overcome prejudices about plastic being weak. All in all, it is still an interesting exercise of design for manufacturing.
The above images show the metal assembly on the left and the composite assembly on the right
All the data mentioned on the previous section is summarized on the next tables divided by materials.