NANOCLEAN

Collaborative project

Curved surfaces

Key in this technology is the ability to apply surface structures to freeform curved surfaces. For this a dedicated 5-axis machine was developed by Lightmotif. A kinematic model of the 5 axis machine was developed and integrated into Lightmoitif’s laser structuring software.


The structuring approach is based on a step and scan procedure. The surface is meshed into tiles that are individually structured by using a laser glavo scanner. The 5 axis machine is used to accurately position the galvo scanner in respect to each tile. The meshes are created using CAD data and the needed surface structure is distributed into each individual tile.


A first test was performed on a ø 50 mm stainless steel ball. Half of the ball was structured, appearing black due to the increased light absorption of the structures. The other half was machined with the edges of the individual tiles, illustrating the tiling approach. This is well visible on the cover page picture.

Demonstrator

The project demonstrator is a plastic mirror cup. The mould was designed and fabricated by Maier. A 3D measurement of the cavity surface was performed to verify the surface accuracy needed for the laser micro-nano structuring.

The surface description from the CAD model was used by Lightmotif to generate the tile distribution and calculate the needed relative machine positions. The mould was calibrated and aligned to the laser structuring machine using the machine’s integrated optical sensor systems. The laser structuring, shown on two pictures below, was performed successfully. The injection moulding of structured plastic mirror cups using this mould is ongoing.

Flat moulds

A mould for flat cavity inserts was designed and fabricated by Maier. Several inserts have been laser structured by Lightmotif and used for injection moulding of test plaques. In the first experiments various  structures have been applied to the insert. The injection moulding of the micro-nano structures was optimized by Maier and Gaiker-IK4. Analysis by SEM and confocal microscopy was performed by the University of Twente to understand the replication behaviour.

The plastic test plaques have been tested for various properties by Gaiker-IK4 and CRF. Most importantly the super water repelling behaviour was studied by contact angle measurements and falling droplets experiments.

 

Besides applications as self-cleaning surfaces, the structures can also be adapted towards improved haptics: silky soft surfaces are generated by specific microstructures.

The structured surfaces are also highly anti-reflective. This is illustrated in the two pictures at the bottom right. A bright light reflects from the non-structured area, whereas the blinding reflection disappears on the micro-nano structured surface.

3D moulds

In order to apply these advanced functionalities onto real products the technology had to be developed towards 3D curved surfaces. Several aspects are affected by the transition from 2D to 3D surfaces, like what structures are capable of releasing from inclined surfaces in the mould and how to accurately laser machine the structures into a complex mould in the first place.

A specific mould was designed by Maier consisting of several inserts that could be individually structured. The inserts were equipped with surfaces showing various draft angles and a cylindrical surface. Lightmotif applied laser structures using different strategies and together with the Univeristy of Twente the results were analyzed and improved structures were chosen. Again Gaiker-IK4 performed analysis of the functional properties of the surfaces.


 

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