New generative design practices

3D printing and generally additive manufacturing practices, have opened new opportunities for design engineers.

Traditionally, designing a part was done by adopting a conventional way of thinking. Function of the part would dictate its attachment points and degrees of freedom. Then from this stage on, the part would be drawn with relatively straight faces cut from blocks of material on a CNC machine, or with draft angles required for injection molding, RTM or casting.

The conventional way of thinking restrains the design in a relatively known concept and expected shapes result from this.

However, straight face, machinable/ moldable shapes are not required any more with 3D printing. Much more biological shapes can be created like bone lattices.

Using the technology found in Nature is possible by either copying what can be seen on plants in animal bodies. But more dramatically, ground up designs can be achieved by reproducing the evolution process described by Darwin at an accelerated pace. This is called generative design. The idea is to start from functional constraints and grow parts according to specific senarios, then test/ compare the converging designs. The most appropriate design/ the one fulfilling the design criteria the best will be chosen.

The parts created with this process end up being remarkably "biological' in their shape. The benefits are mostly on weight saving for a given load baring.

Here is an example below created with the Siemens generative design module.

The original part is a stabilizer rotation bracket. The part is very standard in the fact that it is created from a block of alloy and CNC machined on 5 axis.

 

After applying the principles of generative design and selecting from a number of iterated senarios, the retained product is as followed:

 

 

Furthermore, once the strain directions and optimized generative design has been achieved, a second process can be engaged, by choosing the type of inner material filling pattern.

The inside of the part should not be plain in optimal generative designs, but hollow and made from organic type lattice patterns. The proper way to do this is by copying nature patterns were functions are created by the way material grow in different types of patterns. This is called biomimmicry.

We have previously seen the bone lattice pattern where non linear pattern changes are necessary to ensured the propagation of the efforts without strain accumulation.

Functions can be of certain types:

Flexibility

Cushioning

Rigidity

Fusing area

Adaptive strength section

Spring effect

Energy collecting ( heat, mechanical, solar )

 

These functions can be achieved by growing the patterns with a certain material in certain geometrical way, in certain direction. But also, interface functions can be explored like the PNP junction of a transistor. In this case, 3D printing with multiple materials is necessary.

Here is an example of lubricating/ elastic human cartilage cells:

And the scaffold structure of spring type tendon cells:

Or the stiff structure of pine wood cells:

At this stage of the concept, as of beginning of 2018, I can say that the production technology exists, but not the software modeling, analysis and results prediction.

One interesting point here is that traditional mechanical design still require the definition of rotation axis. We still have cylindrical shapes in these areas. The next step in mechanical engineering design will certainly be in re-thinking the degrees of freedom and parts joints. Look at how mammals bone joints are made. Also lots of very interesting functions and evolutionary solutions can be found in molluscs, invertebrates.

We are building up a library of functions with different types of solutions found in Nature. This might be the future of CAD design where the engineer will select a function for a certain type of part and the software will apply evolutionary solution found in Nature for the part, then optimize it through a certain number of iterative sequences through the generative design module.

 

In practical case, we have started adopting generative design and natural patterns infill out of single materials on our Siemens NX stations on most of our products. This is already visible with our new GenTech 3D printed hatch latches and Cloudtech retracts.