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I recently did some research on the effect of cooling on CFRP/Al7075 drilling.But I read somewhere that liquids are forbidden for cooling operations on these multi layer plates !!! , And I wanted to know is this true? Do I have to change the subject of my research?

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    $\begingroup$ So where did you read that? $\endgroup$
    – Solar Mike
    Sep 28 at 20:32
  • $\begingroup$ Please add more information. At the least, add references to where you have read these restrictions. Also, you mention research. Unless liquid cooling is forbidden because things will explode, this sounds like it might be a good place to test the limits of what is "forbidden" $\endgroup$
    – hazzey
    Sep 28 at 20:46
  • $\begingroup$ I think it might be the CFRP. I've heard of concerns about water penetrating the material at the edges where the fiber ends are exposed in other applications. In this case the concern might be the coolant getting in. Check for coolant recommendations on CFRP on its own. $\endgroup$
    – DKNguyen
    Sep 28 at 20:49
  • $\begingroup$ @SolarMike hi. in this article (Influence of different cooling strategies on the process temperatures and chip transport quality in one-shot drilling CFRP/Al-stacks) $\endgroup$ Sep 28 at 21:10
  • $\begingroup$ @hazzey hi. in this article (Influence of different cooling strategies on the process temperatures and chip transport quality in one-shot drilling CFRP/Al-stacks) and this Section ( In order to support chip transport and heat dissipation during drilling, the use of cutting fluids is generally recommended. However, for most stack machining operations settled in aerospace applications, liquid cutting fluids are prohibited due to quality and automation requirements. Although alternative, non-liquid cooling strategies exist, these CFRP/Al-stacks are usually drilled under dry conditions) $\endgroup$ Sep 28 at 21:15
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According to this article:

A Phased Approach to Optimized Robotic Assembly for the 777X

drilling multi-material composites does require some special trickery, especially when automated assembly is part of the process:

There were lessons learned relating to process capabilities whereby technologies were added or modified to prevent the need to return to hole locations for further processing. Additional cutting lubricants and methods were specified to allow layer by layer drilling optimization specifically targeted for one-up assembly.

The cooling/chip evacuation methods were varied during single hole drilling per current material layer of stack. The reason for this is explained on the document to be:

Critical for one-up assembly as the fastening immediately follows the drilling process, composite stacks are drilled dry and metallic substructure layers drilled with minimal air/oil mist. This keeps the prepared hole dry and clean. To keep the evacuation system clean from carbon build-up when drilling dry or with air/oil mist, a coolant jet was added downstream of the nose piece to enable the line to be washed.

So each material in the stack requires its own specific method for cooling and "chip" evacuation (drilling CFRP does not produce chips as they are traditionally considered in machining, but anyway).

Other articles suggest that using liquid coolants when drilling CFRP results in less tool wear and better finish, but the reason not to use liquids when drilling CFRP (or layers of it in a stack) in this specific case seems to deal with the requirement that the hole must be both clean and dry before fasteners can be installed. Plastic composites are always a little porous to some extent and drilling will slightly break up the surface, further making it more permeable. Coolant residue in a joint sealed by a fastener would elevate the risk of corrosion in the joint.

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The paper quoted is Open Access, and gives the reason in the opening paragraphs:

for most stack machining operations settled in aerospace applications, liquid cutting fluids are prohibited due to quality and automation requirements

They in turn cite

Rivero A, Aramendi G, Herranz S, de Lacalle LL (2006): An experimental investigation of the effect of coatings and cutting parameters on the dry drilling performance of aluminium alloys. The International Journal of Advanced Manufacturing Technology, 28(1-2): p. 1-11.

The abstract of this paper states that:

As a result of the need to automate assembly in the aircraft industry, along with economic and ecological reasons, industry and research institutions have been pushed to develop dry drilling for aluminium alloys to eliminate the need for cooling fluids.

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    $\begingroup$ I feel like since we've managed to have wet milling machines for a century, having a waterproof robot doesn't seem like it would be too hard. $\endgroup$
    – Tiger Guy
    Sep 28 at 23:53
  • $\begingroup$ @TigerGuy I too wonder what is meant by "automation requirements"? Maybe the gooey dust gets in the way of self indication? $\endgroup$
    – DKNguyen
    Sep 29 at 0:32
  • $\begingroup$ I added quote from abstract of Rivero et al paper, but this still does not give a satisfactory answer to the question IMO. We must go deeper... $\endgroup$
    – Jpe61
    Sep 29 at 16:00

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