Robust Design enables use of green materials

VIRGIN MATERIAL

In most cases regarding standard designs, part variation leads to internal stresses in the design. You can see an example of this in the first column in the graph above.

The given parts in an assembly often have a function. It should be able to withstand a given force or pressure. Components are designed to, in the worst-case scenario (when tolerances are expected to be close to their boundaries), be able to withstand these loads.

The parts are left with a safety margin before the material and design limit: fatigue strength, yield strength, ultimate tensile strength, etc. – depending on the given situation.

GREEN MATERIAL

To RD8 experience – when you swap a virgin material with a greener alternative, two things happen:

• Mechanical properties drop: the mechanical properties are less good than the virgin material – at least in worst-case scenarios – the green alternative has more batch-to-batch variation.
• Increased form variation: the tolerance and form variation of the green produced material parts increase and lead to a further increase in internal stresses in the design.

With the same force/performance requirements, this often leads to a situation where the safety margin to the material limit is hard to maintain.

GREEN SOLUTION

The trick to enabling green materials is to eliminate the internal stresses in the designs enabling an increased safety margin. You do this by complexity reduction of part geometry – to know exactly what function each feature is – and make sure that each feature has a pre-defined function and does not overlap with other functions and hence create a conflict of interests between features.

The example below illustrates how internal stresses can be reduced by Robust Design.