Clean Cut SS, What's the deal..

[ausman]

Gday all,

I have problem that has plagued me for a long time & i would like know your past experiense with this.

Why can i never never consistantly clean cut SS without dross.

I mean, when cutting SS i will 75% of the time get parts that have small burrs on the bottom edge.

I very rarely get burr less perfect SS cuts, & this is with any thickness from 0.5mm to 10mm SS (but more commonly the thinner mat).

I have 2 machines that both have the same problem. Amada FO & Panasonic.

I have also seen & had the same problems with both PRC & Rofin slab lasers.

I have tried many things inclding lens brands, shapes (Plano/ Meniscus etc, FL, focal height, power, feed, pressure,Nozzle types (Double/ single), Nozzle gap, nozzle dia, mode checks the list goes on.

I am sure i am not the only one who has this issue, i am starting to think it's related to the larger beam diameter as i have heard that the smaller beam in the Trumpf just loves stainless cutting.

Please give me your advise or past experience.

Much appreciated.

 

[krugtech]

Going too slow will cause dross. Where do you have the focal point? As far as i know beam quality on those resonators isn't the greatest but it's usable. Do you see any discoloration on the cut edge of the material? discoloration on the dross isn't important.

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[ausman]

Thanks for the reply,

Yes have had some success with feedrate, no discolouration on the edge.

I guess what i really want to know from anyone cutting stainless

What sucesss rate dou you have cutting stainless with a perfect bottom edge, can you pick up any random part through out any sheet at any time and have a perfectly clean & smooth bottom edge.

What machine are you using?

I would really appreciate your input.
Thanks

 

[cuttingedgelaser]

We are using Trumpf lasers and by changing beam diameter and lowering the gas we can produce a dross free part up to 3/4 inch stainless

 

[Foostrap]

Hi Ausman,

I've cut a lot of stainless 22Ga (0.8mm) to 1/2" (12.7mm) with no burr using Fanuc resonators, anywhere on the cut table. On thin material, the resonator power doesn't matter, you should be able to get a clean cut with a 2kW resonator for example. Of course, the more power you have, the faster it will cut. To get clean cut on thicker stainless, you will need more power (4kW for 1/2" for example).

First point, I assume you are using nitrogen for assist gas? If using air, you'll sometimes get a little bit of a small burr (you can't really see it, but you can feel it).
Second, what type of stainless is it? 316, 304? The type of stainless can make a difference when cutting with higher power resonator (5 or 6kW). To see if that is the case, try to cut it at lower power (like 4000W).
Third, are you getting the burr on a straight line, or only on corners? On thin material, if the power is not lowered when the machine slows down (on corners or arcs), it could result in a burr. That's why most current machines have some type of power fluctuation feature, where the power is automatically adjusted when feedrate lowers.
If you're getting a burr even on a straight line, I would check the focus. Focal point is very important to get a clean cut. If it is not stable, you'll get unstable cut results. Not sure what system your machine has. Unstable focus could also be caused by unstable sensing system (stand off distance between nozzle and material). If you can try to cut a small square with the sensing system disabled, to see if that could be part of it.
The gas pressure is also important. Too much gas pressure is not always good. For 16Ga (1.5mm) for example, gas pressure should be around 85psi (5bar), and nozzle of 1.5 or even 2.0mm.
Is the material stable on the cut table? Aren't the parts too close to each other?

Maybe lets start with a concrete example of a thickness you have problems with. What thickness? How much power are you using? What lens are you using? What's your gas pressure? What's the speed? What's the nozzle size, what's the stand-off?

You mentioned you've tried lots of things. Can we assume the cold and hot modes are good? External optics are good? Lens is good? Cooling of the optics is good? Laser power is good?
Does the burr seem to appear time related or randomly? If you let the machine sit without cutting for 5 min, then cut a small 2" square, will you have a clean cut all around? If you only get a burr when cutting for a while, then something may not be cooled properly.
Can you cut thicker mild steel with oxygen OK?

 

[HenryRollins]

What are you using for a gas source? Bottles, Doers or Bulk tank?
-HR

 

[krugtech]

I have a customer with a 4000 watt Bystar. We removed the adaptive optic and purged the beam path with N2. Clean cuts 1/2 stainless all day all over the table. The adaptive optics are convenient but my experience shows they degrade beam quality. If you're purging your beam path with oily shop air you'll never get anywhere.

did you buy the machines new or used? have they ever performed properly?

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[HenryRollins]

Usually Bypos issues are due to bad characteristic curves, air in the lines, or general parameters issues like piercing focus is deeper than cutting focus. The mirror can't react fast enough to correct itself when transitioning from pierce to lead in. When this happens I tell the customer to match piercing focus to cutting focus and the problem is solved, but we are still talking about another manufacturers machine and not Bystronic. If these machines use an auto-focus/focus correction device how is it operated? Air, electrically or with water pressure? Are the parts in the nest tipping up slightly and capacitive sensing/material sensing adjusting the nozzle height lifting it higher from the surface? Based on what was posted, it looks like it is a gas related issue like you could be losing pressure or unable to keep up with the pressure. If a few cases I have witnessed 3rd party nozzles being the cause of random cut issues. Most because of the threads on the nozzle are not perfect and come loose.

 

[krugtech]

I'm thinking this guy tried more N2 assist pressure and a big nozzle and the machine was in a small room. He passed out shortly after the assist gas purged the room of O2 and is now dead. It's our fault......

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[Foostrap]

I think he tanked his machine in the ocean. Unfortunately the network cable was still attached; it ripped of his router and he lost internet access.

 

[ausman]

Hello every one,

Just woke up from my nitro induced coma..
Kidding, i am a 1 man show so it's very difficult getting spare time when working 16 + hours every day.


Thanks for the valuable input, i am think Foostrap may be on the money but i have no problems at all cutting mild steel.

I can cut 1mm to 16mm Mild steel all day every day and have no problems at all, i get a very nice clean cut.

I am using Air liquide Laser grade Maxi16 nitrogen packs.

Machine is second hand but only has 6,000 beam on hours.

I mosty get the burrs below 1/4" thick SS.

The Amada does have a flexible AO mirror, but only used for beam length compensation.

The bellows is purged only with an amada delivered dessicant dryer/ filter setup (top quality dry & filtered air)

To give you an idea i have cut a job today,
6 sheets of 1.5mm 316 N4 SS
cutting several large plates from each sheet

I cut a 50x50mm test square & it it perfect without burrs

I cut the 1st sheet and 1 plate has burrs on every edge
the next an identical part has burrs on one edge only.

These are only small burrs that can be removed by rubbing a plate over the edge.


One issue i have that i belive is related

The sides of any cut (only on SS) are never 90 degrees to the top of the plate.

I mean the edges are really shaped like a trapezoid, some times really badly tappered . has any one seen this problem???

I never have this issue when cutting mild steel.

Cheers and thanks again for you help.

 

[Foostrap]

Hi Ausman,

When the edges are not straight, it can be the polarizing mirror that is bad (or you have no polarizing mirror, or you have 2). You'll also see this when cutting a circle; it will look round from the top, but oval from the bottom. But in your case, you can cut 16mm mild steel, so that is not the problem.
It is possible the beam is not perpendicular to your plate. I've seen this happening once on a 2.5kW. The beam was centered at the head, but it wasn't at the z-axis mirror (right before the lens).
If possible, check the alignment at the last mirror block. If it is not centered, center it by playing with the very first mirror coming out of resonator (that shouldn't throw off your parallelism that much). Then center again to the cutting lens.

Also try to lower the gas pressure; go lower until you get a hard burr. Then go back up a little bit. If it cuts more consistent at lower gas pressure, you may have a gas turbulence. That'll create some really unstable cutting.

 

[ausman]

Jackpot!

Replaced output coupler & back to single point mushroom nozzles & it's cutting better that i have ever seen.

There are absoluetly no burrs, you could rub the bottom laser cut edge across your lips without fear!

Now what do to with all my spare time that i will save from not having to use the flap wheel/angler grinder.

Many thanks for all your help.