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I am currently having an issue where features of my machined parts are warping. I am using Alloy 7050 Type I and Type III in this particular case. Using a feeler gauge and a certified, calibrated granite slab, I am getting out-of-flatness measurements up to .009, which is significantly out of tolerance relative to my requirements.

I have decided to construct a statistically-designed experiment (design of experiments) to find which specific factors are playing a role, but I want to ensure that I am including all of the factors which may contribute. I don't want to lead the conversation too much by posting what I already listed, but I am looking for others' opinions on what might cause this kind of warping/deflection.

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  • $\begingroup$ Are the components within tolerances when they are first machined? $\endgroup$
    – Dave Coffman
    Jan 20, 2015 at 20:56
  • $\begingroup$ are you doing flatness or parallel? Wouldn't a feeler gauge on a table give you parallel? $\endgroup$
    – andy mcevoy
    Jan 20, 2015 at 22:29
  • $\begingroup$ We are doing the original fabrication. We are the original machining. Before us, it's a raw block of aluminum. $\endgroup$
    – Tim D
    Jan 21, 2015 at 21:45
  • $\begingroup$ Flatness and parallel are the same in this instance. We are measuring the flatness of the relevant feature using the table, or how parallel the feature is to the table. $\endgroup$
    – Tim D
    Jan 21, 2015 at 21:46

4 Answers 4

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The work history and temperature history of any metal can make a big difference in the final shape after machining. If the material was cold worked (e.g. rolled) there may be significant residual stresses within the material. When you start selectively removing material, those stresses may cause the part to warp into a new shape. Cast metals and ones that have been given surface treatments can have the same problem.

You might be able to address the problem by roughing the part to near-final shape and then running a finishing pass to remove that last little bit of material. Otherwise take a look at the specifications of the material. You may need to heat treat the part to relieve those stresses.

This is a problem that can exist with just about any metal, not just Al.

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  • $\begingroup$ Thanks! We have actually seen quite a bit of success when we "skin" or rough the parts, as you say. Unfortunately, this adds another operation, which increases our costs on a per part basis, which we are trying to avoid. We have also gotten away with not having to do this type of operation previously, which is why I'm trying to narrow down the list of possible causes. The heat lot of the material may have something to do with it, but it's also possible it's something more simple such as cutting tool life or spindle speed. $\endgroup$
    – Tim D
    Jan 21, 2015 at 21:52
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Compared to most other metals, aluminum is a relatively low performance material. It's useful mainly for low speed, low volume, low temperature variation, and "coarse" applications.

It tends to "warp," or otherwise break down in high speed, high volume applications requirement "fine" performance from metals such as injection molding.

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    $\begingroup$ Sorry, but high-grade aluminum is in no way a "low performance" material when you're dealing with structural components. We're using Alloy 7050 Type I and Type III in this particular case. $\endgroup$
    – Tim D
    Jan 21, 2015 at 21:47
  • $\begingroup$ The question has been updated with more information. Would you like to update your answer? $\endgroup$
    – hazzey ♦
    Jan 31, 2016 at 2:57
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Ive been cutting, plating ,sawing, drilling aluminium and castings for over 30 years Alumininium alloys cool rapidly after the material is poured and rolled to form a standard plate thickness and depending upon the cooling rate a "grain" structural size variation is formed within the material . larger grains form at the outer layer and reduce in size accordingly to the cooling of the material and the compression of the rollers , the material grain size delta has inherent boundary stresses and removing material from each of the faces unevenly can cause warp-age due to stress imbalances , now this would tend to be on smaller proportionately thinner plates under a inch thick say, back in the days of manual machining plate Aluminium we used to skim one face with a fly cutter turn over the plate, break the skin on the 2nd face and then do a "spring cut of thous(0.005)or 0.12 mm by fully opening vice and then applying a light clamping force this then sets an unstressed Flat surface ,also if the machine you are using is not rigid enough !! . or your feeds and speeds could be wrong and the swarf is not taking the heat away from the work surface , there is a multitude of possible causes without seeing a dimensioned atricle drawing and your production methods its impossible to point the finger in one direction

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Check the coolant temperature (It should be below 28 degree Centigrade) which used for cooling the heat where it is being generated during machining operation due to shearing force as well as reduce the tool diameter meter in order to reduce the the amount of cutting force

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  • $\begingroup$ A 3 year old problem... $\endgroup$
    – Solar Mike
    Jun 24, 2018 at 11:08

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