5 Steps Towards Lightweight
Creating lightweight structures seems very straight forward….step by step remove as much material as possible. It’s that simple, right?
I always use 5 steps: understand the product, define the production process, select the material, integration of parts and functionality and finally geometry optimisation. These steps are very intertwined and actually always executed in parallel. I will briefly discuss each of these steps using the lightweight upright as an example.
1. Design Intent
No matter if you start with a clean sheet design or create a lightweight version of an existing product or system, question number one is always: what should it do? What is it’s desired functionality? It’s intent.
Let’s take the motorsport upright as an example. The functionality of the motorsport upright is: transferring the various tire forces from the wheels via the upright, through the suspension arms and into the chassis. On top of that it also has to house a wheel bearing, braking system and various sensors. Key performance parameters are a high camber stiffness combined to a low un-sprung mass.
Benchmarking the original design gives us the suspension joint coordinates, information about the suspension envelope and the available design domain. Lastly, understanding how the parts are used will define the loads acting on the upright in a variety of conditions and situations.
2. Production process
The selection for a manufacturing method is strongly linked with the material selection. In fact in most cases the process and material is selected in parallel, simply because not all materials are available with all manufacturing methods, and vice versa.
For the motorsport upright we have chosen additive manufacturing as the production method of choice. The vision is to offer customer specific products for motorsport and high performance sports cars. For an upright these customisations can be for example a specific brake caliper orientation, or an optimised wheel bearing position. This results in products with a low production volume, often a series of just 1. Limited volume combined with complex lightweight geometries makes additive manufacturing suited for the manufacturing of the uprights.
As mentioned before, the material selection is linked to the manufacturing process and vice versa. Additive manufacturing is still a relative young manufacturing technology, the list of available materials is therefor still limited. Weight reduction and high stiffness are two of the main design drivers for the upright, so specific stiffness is a good starting point in the material selection. Other relevant material selection properties are ease of post processing, fatigue, corrosion resistance and thermal behavior.
Part and function integration reduces the number of joining interfaces. This safes on assembly time and effort, minimises the tolerance stack-up and safes weight associated with fasteners or other joining methods. The original upright consisted of 9 parts, with additional part and functional integration being in the works.
5. Geometry Optimisation
With steps 1 to 4 we have created the framework for geometry optimisation. We have the material properties, know the design rules related to manufacturing, defined the design domain and finally we understand the load cases.
We can define the optimisation targets. For the upright we specified a desired stiffness for the various suspension pick-up points, since this defines the all so important camber stiffness criteria. A generative design or topology optimisation tool can support the engineer in creating the optimal geometry with only material in those places where it contributes in achieving the optimisation targets.
The described steps can be applied to all products, in all industries, using all manufacturing methods and materials.