Laser Cutting

[daxman1]

I have been doing some research on laser cutting and although it is a great option in many cases it may not work for aluminum. We are looking at sending out some aluminum parts to be formed. The parts are approximately 2' by 2' made from 2024-T0 material .032 thick. The material is currently hammer formed (this may be hydro formed at the new vendor) then heat treated to T3.

The vendor has asked if they could laser cut the parts. Everything I have read states that lasers do not cut copper and aluminum well because of their reflective and heat conductive properties. I have also been told that it can cause brittle edges that can cause stress risers if not reworked. I believe the vendor knows what he is doing but I'm hoping some here can enlighten me as to laser cutting aluminum.

Thanks

 

[WKTaylor]

Daxman1...

Are familiar with AWS C7.2M Recommended Practices for Laser Beam Welding, Cutting, and Allied Processes?

My company allows laser cutting... but mandates all aluminum parts made by laser-cutting/trimming shall have every LC edge trimmed/smoothed to remove the ragged heat/melt affected zone... in-order to attain a high quality edge as required for high fatigue/sonic applications.

For this reason I vastly prefer abrasive water-jet trimming for aluminum parts... treat the cut edges like machined/routed/sheared edges.

NOTE.
We are fighting Inconel 718 fire-finger-seal manufacturing processes that use only laser cutting. Under magnification the ragged/melted edge is evident.. regardless of surface finish quality specified on the drawing [high sonic area quality]. Cracking is occurring in the finger transition radii. The vendor is reticent about improving these edges... which meet's their quality standard... but does not meet intent of our process spec. I suspect that our fire-seal design is not optimum for this fabrication method.



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

BTW... lots of laser and water-jet cutting videos on YouTube.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[berkshire]

As Will says,
If you Lazer cut you are going to have a heat affected zone at the edges of the cut, every process I have been involved with, requires you to File,grind, buff this away. Lazer cutting is quicker than water jetting. But by the time you factor in the additional labor to clean up the edges you are back where you started. The argument that you are going to heat treat it anyway and the heat treat will take care of it, does not seem to quite work out in practice.
B.E.

You are judged not by what you know, but by what you can do.

 

[daxman1]

Thanks guys, that was the information I was looking for.

Dennis

 

[rb1957]

wot Dennis, no LPS ? (for Will at least)

another day in paradise, or is paradise one day closer ?

 

[berkshire]

rb1957,
I don't count ? Now ahhh is upset
B.E.

You are judged not by what you know, but by what you can do.

 

[rb1957]

nah, you "only" supported Will's information ... too late to the dance !

besides i did say "at least" ...

but I bore of this banter !

another day in paradise, or is paradise one day closer ?

 

[berkshire]

rb1957,
Ok , I am only yanking your chain.
B.E,

You are judged not by what you know, but by what you can do.

 

[rb1957]

i know, and figgering you to be a limie, I won't call you a "berk" !?

another day in paradise, or is paradise one day closer ?

 

[tbuelna]

The OP mentions hammer or hydro forming is involved, so it seems the part will be laser cut (trimmed) after forming. When trimming thin sheet metal parts after forming, there is one primary difference between laser and water jet to consider. Laser cutting does not impose force on the part, while water jetting does. So the fixturing required will typically be more complex for the water jet process. However, as noted above, for aerospace applications it is usually a requirement to remove any recast produced by laser cutting, and this process adds some cost.

 

[Sparweb]

Wil,

Does the AWS spec offer a way to estimate the depth of the HAZ?

I ask because I'm under the same pressure as the OP. Unfortunately a lot of laser cutting has been going under the radar here and my predecessors didn't put the brakes on soon enough. It's already become "accepted practice" and proving difficult to reel back, now. I am planning a strategy to mitigate the HAZ with extensive trimming requirements in a new process control document. Not much to go by, though, to judge how much is enough.


No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[berkshire]

I do not know the process at the OP's facility , but having been involved in fabricating aircraft parts for years . As I see it , if the original blank is lazer cut and there is a retrim operation later I think they can get away with that part of it. It would then follow that the part is drop hammered , hydroformed or stretch formed. Usually but not always then the part is heat treated , hand straightened then put into a trim fixture for perimeter trimming. Usually with a hand router. This may be where the vendor wants to get creative If he water jets I see nothing wrong with that, if he wants to use a lazer to me that would set off all kinds of alarm bells. This is where Daxman1 needs to see exactly what they are doing....
B.E.

You are judged not by what you know, but by what you can do.

 

[Sparweb]

Thank you berkshire,
The amount of trimming is the slippery issue. How much is enough? Is it so much that a special allowance must be made on the laser-cut size? Does anyone have numbers and measurements that have been shown to be reliable?
I've finally convinced everyone in the shop to pilot-size absolutely every single hole if they're going to laser-cut any parts (and water-jet too for that matter) which usually takes off 1/64" (0.4mm) or more from all hole edges. The surrounding edges are another matter entirely. I have read a lot of research and even found some encouraging fatigue test results on laser-cut holes with no re-trimming at all. I think I know the answer but a hunch is NOT proof. I don't want this to turn into a pet science project to get that proof, either.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[rb1957]

How big is the HAZ ? could you consider this as ineffective material, and increase eD accordingly ? ie deal with it analytically rather than physically.

another day in paradise, or is paradise one day closer ?

 

[Sparweb]

Just by looking at the external surface, I don't think you can know how deep the HAZ really is.
When you've handled and worked with the laser-cut materials, you can appreciate the annoying effects it has on just about every subsequent process, and how inconsistent the thickness of it can be. I have tried it myself, on plenty of examples which are strewn about my desk today, and every one of them is different.

So I'm still asking the question "How deep is the HAZ?" when I have the parts in front of me, because I'm not asking about aesthetics. I'm asking from a metallurgical point of view. Is the HAZ actually deeper than the visible discoloration? Does removing the rough also remove the HAZ? Doesn't seem like it from here.
And FAR 25.613 is at stake, for those who know what that means.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[berkshire]

I got into this about 22 years ago when a vendor wanted to plasma torch aluminum parts . As you can imagine the HAZ was even bigger, and the final answer there was, " We don't want you to do it." My personal opinion on cutting is, if you rout or water jet it is OK . If it involves heating the metal you had better have some serious proof that it is not going to affect the metallurgical properties.
B.E.

You are judged not by what you know, but by what you can do.