Laser cutting?! 2

[var10]

Hi,

When you cut 0.063" AL or just any aluminium sheet using a laser cutter, what are the adverse effects? - I noticed very rough outline finishes, but I've also seen very smooth ones from a different supplier on the same product. Just curious to know why?

Does the laser produce sheets which have smaller dimension than what it was programmed or a larger dim?

Example: If I have to program a 3mm hole with a laser cutter what could potentially be the end result? - 2.9mm or 3.1mm (Do not worry about what my drawing tolerances say, I want to know what a laser can do?)

If possible please give me an reasonable explanation.

Thanks,

V.

 

[cloa]

Laser Engineering would be a better forum.

http://www.eng-tips.com/threadminder.cfm?pid=1529

Use translation assistance for Engineers forum

Note the rules include No Student posting

 

[MikeHalloran]

Laser cutting machines have a tool offset setting just like any other CNC machine, so you specify the dimensions and tolerances you want, and let the operator worry about how to get there.

As a point of reference, the kerf for a laser cutter than can handle stainless steel sheet is somewhere between .007" and .025", depending on the thickness of the sheet and hence the beam power. If you call the cutting outfit and tell them the material and thickness you want to cut, they can decide which photon cannon to use and tell you how wide the kerf will be. This is only of interest if you are making some kinds of self-conjugate parts, but they can be helpful if you are nice and ask intelligent questions.

The typical cut finish, under magnification, looks like the cut was made by plunging a row of holes with a tiny drill, which is sort of how the process actually works. In stainless, it leaves a HAZ that 'welds funny', about .005" thick and slightly blue under magnification. I'm not sure what the HAZ looks like in aluminum; I'd guess an edge burr sort of like you get by cutting aluminum with a MIG welder, but on a smaller scale.

The edge finish of waterjet cut metal is generally a little better than lasercut, but the waterjet parts arrive covered with fine abrasive sand, unless you pay someone to wash them. Lasercut parts have always arrived clean for me, but I don't know if they come out of the machine clean or not.






Mike Halloran
Pembroke Pines, FL, USA

 

[Walterke]

Rough outline finish can be caused by bad settings on the laser machine. (especially in thin plates)
Tell the subcontractor you need a better finish, if they can't do it, find another subcontractor.

NX 7.5.5.4 with Teamcenter 8 on win7 64
Intel Xeon @3.2GHz
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Nvidia Quadro 2000

 

[tomwalz]

The laser melts ther metal and a gas or air blows the molten metal out ofthe hole.

A small diameter laser beam leaves a smoother finish probably.

The molten metal may react with the air or gas.

There is a heat effected zone. We use the "rule of thumb" figure of 0.010".

This is pretty mcuh the same as the o.oo5" given above with extra room.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[var10]

I am sure the sub-contractor who has been dealing with laser cutting for years know about the tool offset. But then why are all the parts I get from him have smaller internal dimensions? and larger external dimensions? Could it be the aluminium expanding? I have already changed two sub-contractors.

Is this possible what I said happens with 0.063" and 0.090" Alu?

 

[MikeHalloran]

It sounds like someone is cutting with too big an offset, or maybe the proper offset is being added twice.
Is it specified in your contract? The contract probably should specify that the drawing dimensions are to the cut edges. If the drawing is actually the intended toolpath, i.e. no offset is to be applied, the contract should say so.
Did someone add an offset in your drawing already?
You need to talk to the technical people at the cutter.
Do not delegate it.
You may have to go in person to straighten it out.





Mike Halloran
Pembroke Pines, FL, USA

 

[Walterke]

I am sure the sub-contractor who has been dealing with laser cutting for years know about the tool offset.

Never underestimate the stupidity of people. You may be surprised

NX 7.5.5.4 with Teamcenter 8 on win7 64
Intel Xeon @3.2GHz
8GB RAM
Nvidia Quadro 2000

 

[tomwalz]

Not sure I understand the external / internal dimension issue. Could this be caused by the shape of the laser cut being a cone instead of a straight line / cylinder. I have a laser cut piece on my desk now. The steel is 0.179" thick. The top of the cut is 0.748" and the bottom of the cut is 0.753". I measured across the post or attachment end.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[tomwalz]

Video explaining one reason for dimensional variation

http://www.youtube.com/watch?v=35nVJrJsUFc

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[JayMaechtlen]

AFIK most commercial laser cutting is with CO2 lasers, very often in CW or near CW mode. Some folks have no clue on how to run their machines, and sometimes the machine doesn't cooperate, and sometimes they start with crappy material - any of those factors can result in a poor quality cut.
Aluminum has always been unfriendly to lasers - reflective to the beam, and it sucks up power.
It also expands a lot as it changes temperature - so depending on the precision needed, the amount of cutting on a piece, etc - the material could be growing during the process - resulting in features that aren't within tolerance.
Make sure you specify edge finish and dimensional tolerance - if they don't meet the drawing, send them back!

jay


Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[var10]

My sub-contractor cuts steel ~10mm sheets and reckons it is likely to happen if they cut al with the same laser. So ive decided to machine it instead this time (it wont be cheap as laser) till I find a proper supplier.

Thanks all.

 

[JayMaechtlen]

A machine that cuts 10mm steel will have the power to cut Al up to maybe 6mm.
But getting good results requires some experience and knowhow.
If they can't show decent samples in the material you need done, then a different vendor or different process may be advisable.

fwiw, CNC turrets can do amazing work!



Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[WhynotZoidberg]

This might be drudging up an old post...

But anyhow, when I have a hole that I need to hold to a tight tolerance, I have them laser cut a smaller diameter and drill it out using that location, then perhaps reaming it.