Help Needed: Deep Black Stainless Steel Annealing on Monport GA 100 MOPA – Smooth Finish, No Surface Texture

Community Laser Talk
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Hi everyone,

I’m using a Monport GA 100 MOPA fiber laser and I’m struggling to achieve good black annealing results on stainless steel.

I’ve already searched the forum and found several similar threads, but unfortunately, none of them seemed to reach a clear conclusion or provide a working solution in the end. So I’m hoping someone here might be able to help.

The material I’m working with is 1.5 mm stainless steel with a K240 brushed finish. My lens is the 175×175 mm one.

My goal is to achieve a deep, rich black marking that is smooth to the touch, with absolutely no noticeable surface texture or material removal. Ideally, the black should be clearly visible from all viewing angles, not just from certain directions.

So far, I’m getting two different results, neither of which is what I’m looking for:

  1. Brownish and rough markings: The engraving is visible, but the surface feels rough and the result is more brown than black.
  2. Smooth but angle-dependent black: I can sometimes achieve a smooth, dark marking, but it only appears black when viewed from certain angles. When looking straight at it, the marking is almost invisible.
    I’m aiming for a fast black annealing process with a deep black finish, rather than actual engraving or surface etching.

My laser specifications:

Laser: Monport GA 100 MOPA
Frequency: 1–3000 kHz
Pulse duration: 2–500 ns
Lens: 175 × 175 mm
Material: 1.5 mm stainless steel, K240 brushed finish
Software: LightBurn

My questions:

  • Does anyone have proven starting parameters for achieving a deep, consistent black annealing result on this type of stainless steel?
  • Which frequency and pulse duration would you recommend?
  • What combination of power, speed, frequency and pulse width works best for a smooth black finish without noticeable surface texture?
  • Are multiple passes recommended, or is it better to achieve the desired result in a single pass?
  • Are there any specific hatch settings, line intervals or crosshatching techniques that make a significant difference?
  • I’m particularly interested in settings that produce a true, deep black from all viewing angles, with a smooth surface and no perceptible material modification.

I’ve spent quite some time experimenting, but I just can’t seem to get the results I’m after.

Any help, experience, or tested parameter combinations would be greatly appreciated!

Thanks in advance!

2

Hi Vincent,

I’d recommend doing a Material Test

The parameters all influence one another, so any parameter you can lock in is one less to worry about. I’d start with:

  • Single Pass
  • Fixed speed of maybe 1000mm/s
  • Power: 30% (or less with your 100W source)
  • Fixed Frequency of, idk, 200 kHz

Then, iterate over different Q-Pulses and Line Intervals.
Some would probably suggest iterating over Q-Pulse vs Frequency, but I found that the Line Interval tends to play a more important role. (Tighter = more energy density.)

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Import this file in “Laser Tools > Material Test Generator”

100W MOPA Stainless black.lbmt (1.9 KB)

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A consistent focus distance is crucial.

As a general rule: If you see sparks flying, it’s too much energy and, the stainless is melting instead of annealing, which leaves a rough surface. → Reduce power, lenghten the Q-Pulse, or..

…Defocus:
Focus on the surface and then move the Z axis down a millimeter or two. This widens the beam, leading to less energy density.

I’d recommend running the above material test preset once at the correct focal height, and another run with a 1-4mm defocus.

I hope, any of this helps! :slight_smile:
Feel free to post pictures of the results and the settings you used. Looking forward to see what you discover.

4

Aluminum is not simple to mark black…

Commarker has some suggested values on their site. This is for their 60W MOPA. They might have a 100W one somewhere.

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Even with this data, it’s wise to do a materials test as @Aaron.F advised. One of the issues with fiber machines is that if the size grows it can effect the oxide layer thickness and what color/darkness results.

One of the issues, is the spot size. Even with a large F254mm lens (~175x175mm) it has a spot size of about 30 microns. Sounds like you have the same lens I have. Since, with a fiber, interval is very, very important and you didn’t mention it I’ll try to elaborate.

If you examine the settings in the suggested post, they use an interval of 10 microns, with your spot size at 30 microns, you are covering the same area ~3 times. This is what produces the heat, change sizes that the metals an thermally conduct heat away from previous passes. Just keep it in mind.

This is from my M60 JPT M7 MOPA manual. Indicates if you’re using say a 200ns q-pulse width then the threashold frequency is 40khz. Anything under that will cause the source to reduce power.

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Your 100W likely has these thresholds also, but the frequency will be lower as the 100W pumps the fiber up twice as fast. You need to have access to your machines source manual to find this out.

Frequency is how many pulses/s your machine is producing. The lower the frequency, the more like coarse sandpaper are the results. Higher frequency is a much finer sandpaper. The frequency partially determines how aggressive the machine will be towards the material.

In the following photo, the coin on the left was done at a lower frequency and you can see how rough the bottom of the coin is. Both of these are in the same batch from Amazon.

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It’s always nice to see what people have done, either here or in finished projects. A photo would help here, along with the settings you used for that item.

Hope this helps… Good luck.

:grinning_cat: