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Why do we use composite aluminium or titanium stacks in airplanes? What are their machining conditions?

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  • $\begingroup$ I rephrased your question a bit and expanded the acronyms (like "/al" and "/ti") you used. I hope this is what you meant to ask. If not, please edit again to clarify. $\endgroup$ – Bianfable Dec 2 '19 at 8:09
  • $\begingroup$ This is more accurate , thanks $\endgroup$ – Mohamad ghasemian Dec 2 '19 at 8:59
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    $\begingroup$ What do you mean by 'stacks'? Does 'machining conditions' mean that you want the feed rate and tool speed? $\endgroup$ – Robin Bennett Dec 2 '19 at 10:24
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I've boldfaced the parts of this abstract that answer the question.

Abstract: Ever since the advent of fiber reinforced polymer materials in the field of Aerospace, Metal-FRP stacks started to gain importance due to their superior fatigue performance, phenomenal low weight and good specific strength. However the machining, specially drilling these multi stack materials has always proved to be a challenge ... The very properties that make the FRP composite superior make it a challenge for machining. The mechanism of machining viewed here is more or less fracturing and breakage of the fibers present in the system. This breakage of fiber also induces fractures in the tool resulting in accelerated tool wear. These characteristics render the process unreliable. Also the temperature during the machining of composites is higher than while machining a metal due to the lower thermal conductive properties of the composite. When two such extremely different elements are brought together in the form of a FRP-Metal stack, various challenges are faced to achieve required hole size, quality, tool life, ...

-- Peter Mueller-Hummel, Prithvi Sripathy, and Abdelatif Atarsia, "Fail Safe Drilling of CFRP/Titanium and /Aluminium Stack with H8 Quality for Aerospace Applications," SAE International, 2013.

Cutting speed, cut depth, and feed rate depend strongly on the particular stack's composition: which metals, which composites (carbon, aramid, fiberglass), their ratio, each layer's thickness.


Metal/composite stacks are used all over an airframe. The 2011 article "A review: Fibre metal laminates, background, bonding types and applied test methods" by Sinmazçelik et al calls them FML's, fiber metal laminates, and figure 3 from there shows where they're found on the Airbus A380: enter image description here

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  • $\begingroup$ Oh, it's allmost as if the answer begged the question :) $\endgroup$ – Jpe61 Dec 2 '19 at 18:53
  • $\begingroup$ Would you please explain where the stack is on an airplane? $\endgroup$ – Michael Hall Dec 2 '19 at 20:07
  • $\begingroup$ thanks for your answer . I mean, why aren't these substances used separately? What is the reason for composite and aluminum sheets to stick together? $\endgroup$ – Mohamad ghasemian Dec 4 '19 at 14:58
  • $\begingroup$ To combine the properties of both materials, however is needed for that part: stiffness, tensile strength, load transmission, corrosion resistance, heat conductivity. $\endgroup$ – Camille Goudeseune Dec 4 '19 at 18:08
  • $\begingroup$ What causes defects in composite and aluminum plates during drilling operations? $\endgroup$ – Mohamad ghasemian Dec 18 '19 at 22:29
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Aluminum and titanium are used in aircraft because they are light weight materials that are strong and durable like steel, however they are non-ferrous unlike steel meaning no rust. The two metals are usually composited with another material such as carbon, composites are known for being stronger than using one base material because it will alter the chemical or physical properties. This makes them ideal for stacks in the aircraft because of their properties. And I don't understand what you mean by machining.

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