Introduction:
CAM2, along with its consortium of
partner companies has been supporting Chalmers Formula Student (CFS) for four
years now. Chalmers formula student is a perfect platform where motivated
students build an AWD electric race car for competitions across Europe every
year. This makes it lucrative for students to utilize additive manufacturing
technologies to design and manufacture optimized components for their car. This
year, a lot of focus was kept on the suspension components of the car. This led
to two successful components, both built in AlSi10Mg, a commercially successful
Aluminium alloy.
The first part, the upright, was printed in close
collaboration with EOS, Finland and is designed by Robin Kristiansson. The
second part, the triangles have been printed & processed in close
collaboration with RISE, Mölndal & Quintus, Västerås and designed by Adil
Lokat. Both these components have shown good promise and have been used in this
year’s car to demonstrate their good performance.
Interview with students
The interview has been conducted with
both Robin and Adil who were project engineers in CFS’2021 and are students at
Chalmers. They have answered some questions for us.
What is the competition about and why is
it fun to do?
Formula Student is the largest
engineering competition between universities around the world. The competition
is about designing, manufacturing, and competing with a formula racing
automobile. The real-life project is a great experience since all the
activities from design to finalized race car are covered. It is also extremely
fun to be part of a team that is striving towards the same goal by designing a race
car with a high level of complexity.
What components were additively
manufactured in the 2021 car and what is the purpose of these components?
This year the main target for the Suspension
& Unsprang mass subgroup was to reduce the weight of the wheel package.
The CNC manufactured upright from 2020 shown promising possibilities for a weight
reduction. The upright should be able to transfer loads from the wheels to the
chassis and should also be connected to the hub motor and planetary gearbox. A
design volume was created, and a topology optimization was performed to find the
optimum load paths. To keep the structure as close as possible to the
optimization, Additive Manufacturing was used to build the complex geometry. With
the new uprights the total weight of the wheel package was reduced by 21 %. Another
example is the “triangles”, the structure that is connecting the linkages for
the wishbones. The additively manufactured method was used to enable an optimize
weight to stiffness ratio. This was done to reduce the compliance of the
suspension system.
If these components are structural, how
do you design for such heavy loads and be sure that they are safe?
To make sure that the components can
withstand the extreme loads both finite element analysis and material tensile
testing was performed. Apart from simulations and testing, post-processing of
the printed part was done to reduce the risk of failure. T6 heat treatment and
HIP treatment was done to normalize the induced stresses from the print and to
reduce the anisotropy of the material. Water quench and shot peening was done
to induce compressive stresses at the surface to reduce the risk of fatigue failures.
The benefit of shot peeing is also that defects of the surface can be reduced,
hence the risk of crack propagation can be minimized.
Would there have been disadvantages of
not having such components on the car?
There would be disadvantage in two ways.
First, the weight to stiffness and strength ratio would be less and by that result
in a heavier car. Since the mass will affect the performance of the car, the
mass should always be prioritized. Secondly, the manufacturing. CNC machining
is time consuming for the team and the materials waste is not preferable. The
possibility to outsource the AM will give more time for verification and
testing but also reduce the amount of material waste.
Does this cooperation help the team? How
do you see it moving ahead for the next competitions?
The cooperation is valuable and without AM
support the performance of the mentioned components would not be reachable. For
the next competition the goal it finalizes the rotating bar concept. The component
is the link between the heave and rolls damper. By utilizing the AM technology,
the stiffness to weight ratio could be increased significantly compared to the
current rotating bars.
Picture1: CAD model of Madeline (the CFS
2021 car)
Picture 2: The actual car at FS Alpe
Adria, Croatia in August 2021
Picture 3: Suspension assembly of the
car with the AM processed uprights.
Picture 4: Uprights after printing and
post processing. Printed in AlSi10Mg
Picture 5: Triangles after printing and sandblasting.
Pending machining and then assembled on car.