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I'm trying to design a metal surface with micro-perforation for a product and light it from other side with LED, such that the perforated pattern appears only when lit.

In my previous prototype, which used laser drilling (20 micron holes) for perforation, there was considerable warping of the metal film (around 0.3 mm thick) which rendered the prototype unusable (aesthetically)

Another problem I had with the prototype was that the light was not getting through perforation evenly i.e., I was not able to see the light from different angles.

On initial research about laser micro-drilling I found that the thermal conductivity of material plays important role in heat affected zone, which could result in warping. The material used for prototype was stainless steel, which has comparably lower thermal conductivity than aluminium.

  • What care needs to be taken to avoid or reduce the HAZ and hence the warping?
  • For the visibility of light through perforation, will the hole size and spacing directly affect this?

I am trying to achieve the appearance like shown below Misfit Shine fitness band; the micro-perforation on dial is invisible when unlit.

Misfit Shine fitness band; the micro-perforation on dial is invisible when unlit.

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  • $\begingroup$ Do you have to use laser drilling? HIgh-pressure water jets do a cleaner job. If you must use lasers, what wavelengths & pulse durations are available? $\endgroup$ Mar 22 '16 at 15:12
  • $\begingroup$ What number and configuration of LEDs were used in your prototype? Are they directly underneath/behind the perforations, are there more perforations than light sources, etc.? $\endgroup$
    – Air
    Mar 22 '16 at 16:32
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    $\begingroup$ @CarlWitthoft Yes, i agree water jet does a cleaner job without HAZ. And from what I have known, water jet won't be able to produce holes under 100 micron. At this size (>100 micron), the perforation could rather be easily identified on the surface even when unlit. $\endgroup$
    – Aditya
    Mar 22 '16 at 16:58
  • $\begingroup$ @Air LEDs were placed directly under the perforated region. 1 LED for each perforated region.A region on my prototype had a couple of hundred holes. I am also looking at reducing the visibility of the perforated region when unlit. Could the size and spacing of holes play key role here? $\endgroup$
    – Aditya
    Mar 22 '16 at 17:05
  • $\begingroup$ How do Apple do it on their Bluetooth keyboard and trackpad? The powering-on LED is completely invisible when not on. $\endgroup$
    – jhabbott
    Mar 22 '16 at 17:51
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If you can use metalization to create your film, you could create a mask in the required pattern and just coat on top of it.

However I assume you only have a laser at your disposal. Your heat affected zone will depend on the speed at which you remove material. Higher power will tend to drill through faster and affect a smaller area but it may create more warping as you create a steeper heat gradient. There are two things I can think of trying that worked in other applications:

  1. use a backing that will spread the heat (aluminum/copper), it may reduce the amount of stress in the material
  2. try using different settings (power, travel speed) to reduce the stress in the material. Document your trials and see what works best. (Sorry I can't help further on what settings to use, my application/material was a bit different)
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  • $\begingroup$ I second this approach. Can you slow things down? Remove a small amount of material at a time and come back to the same hole after giving it enough time to cool down. $\endgroup$
    – geekly
    Jul 31 '17 at 14:32
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What about using a sintered metal? Powdered metals can be mixed and an acid might be able to remove one metal in specific spots allowing the light to shine through.

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  • $\begingroup$ You certainly don't need to use sintering to apply acid etching. $\endgroup$
    – Eric S
    Jul 31 '17 at 13:40
  • $\begingroup$ No, but the nature of sintered metals would make interesting effects with etching. Metals could be mixed and one etched away leaving ther other and a porous area left behind. $\endgroup$ Jul 31 '17 at 20:11

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