Lasering coated brass plates

[Abdul Baseer Hai]

Hi All

i need to laser about 100 precut coated brass plates from DTC. These are the ones with an ornamental border aroud them.

I get a hazy unclean finish when i laser. Not the bright clean gold i require.

I have a 50 watt explorer and am using the following settings:

Speed 100
Power 40
DPI 600
PPI 400

I need urgent help regarding the proper settings.
Any input will be helpful

[Joe Pelonio]

Sounds like not enough power to get all the way through the coating. On my 45 watt I'd use speed 100 power 55. If it's just lettering I'd set it to 300 or 400 dpi.

[Bruce Volden]

Maybe this is old hat, but why do most of you guys run everything at 100 power or 100 speed (a generality)?? In this case SLOW DOWN and give the beam more dwell time. Imagine waving your hand over a lit match, move fast=not much heat, move slow=BURNS don't it! We have at our command many various settings to toy with but it seems everyone is stuck @ 100/100??Some of the coatings (powder coated to name one) have required a couple passes to get through, and even had I ran @ 100/100 (or there abouts) it STILL would have required 2 passes. Maybe I'm just getting old and "frumpy" but I do know sometimes we just have to sloooowwwww down 8>) Not meaning to offend anyone.


Bruce

[Joe Pelonio]

Maybe this is old hat, but why do most of you guys run everything at 100 power or 100 speed (a generality)?? In this case SLOW DOWN and give the beam more dwell time. Imagine waving your hand over a lit match, move fast=not much heat, move slow=BURNS don't it! We have at our command many various settings to toy with but it seems everyone is stuck @ 100/100??Some of the coatings (powder coated to name one) have required a couple passes to get through, and even had I ran @ 100/100 (or there abouts) it STILL would have required 2 passes. Maybe I'm just getting old and "frumpy" but I do know sometimes we just have to sloooowwwww down 8>) Not meaning to offend anyone.


Bruce
Bruce,

Now I can only speak for myself but when the manual that came with the laser calls for speed 100 for a particular item one would expect that to be correct. I gave the speed as 100 since that's what my book says. In fact it suggests 100 speed for most materials, other than say wood which calls for speed 30.

Your suggestion makes sense if you figure less speed means you can use less power, if using more power shortens the tube life. On the other hand when running 10 hours a day to complete a big job you need to minimize the run time. Changing from speed 100 to speed 80 can make a pretty singificant difference on a run of several thousand items when trying to meet a deadline.

I often do use 95 where 100 is called for, on small jobs but was thinking that when it changes direction it moves a lot farther beyond the last engraving point and that it might cause additional wear than, say at speed 95 because of that extra movement.

[Mike Null]

I think we're talking apples and oranges here. The thing is speed is not remotely the same on all machines. My old machine ran 100% at 40" per second my new one runs at 140" per second at 100% speed.

The point about dwell time is accurate. Another way to increase dwell time is to increase the resolution. This is especially helpful on coated brass as some have thicker finishes.

I make it a point to polish coated brass with car polish as a finishing touch.

[Barbara Buhse]

ok, everyone go ahead and give me a hard time for asking this, but I have to ask it anyway...
did you make sure there is no plastic coating on the plates?
Depending on where I order from, sometimes they have a protective plastic, sometime they don't. Sometimes its stuck on so well, you wouldn't know its there until you try to engrave it.

[Abdul Baseer Hai]

Barbara, almost all of them have a protective coating. If you had a hard time figuring where your plates have the plastic then maybe the stock is old and the elements have done their stuff.

Mike:
What car polish do you use. Is it just ordinary car wax?

Abdul

[Bruce Volden]

Not meaning to offend anyone...my car's speedometer goes to 140mph, it's never been close! A manual might suggest points to try for power / speed, the final result is a matter of subjectivity. If one can achieve the same results and save wear and tear on equipment that obviously would be the way to go. In my experiences, software is the only thing I know of that is capable of 100/100 24hours / 7 days. I have been working with some sophisticated high tech machinery for 25+ years now and have NEVER seen them perform as suggested by manufacturer for very long when run "flat out". Yes they will run fine for a while, but sooner or later it's time to fix sumpin'. I too have run my lasers wide open to save a few minutes, I will have future projects that will warrant this. But as a rule I ease back. Basically folks', I'm LAZY. I've replaced too many kevlar belts, coated mirrors, laser tubes, ball screw couplings, etc...by easing back I have learned I get a much greater MTBF (mean time between failure), thus offsetting time saved by running 100/100. I am not trying to preach here, rather I liken it to trying to teach.


Bruce

[Larry Alles]

Are you sure that the coated brass is laserable. Some older coated brass
is not. Does it give you a dull finish. Try doing 2 passes.

[Mike Null]

The polish I was referring to is Turtle Wax Polishing Compound. It is a mild abrasive but just enough to remove the traces of lacquer that might remain and polishes at the same time. It is not wax.

[Rodne Gold]

If your lasers motion system can handle the high speed and you are not at 100% power , then use the highest speed you can.
Time is money in lasering and reducing cycle times with acceptable results is the ultimate holy grail.
At 100% speed and 40% power , you would have almost no benefit to reducing speed to lets say 50% and power to 20% and can indeed have problems doing so. You might gain a small advantage in terms of the quality of the engraving due to the motion system going slower , but you would most likely also increase the heat affected zones of the material.
A laser fires a pulse of a set power , ideally this pulse thermally shocks the material and promotes vaporisation. Setting speed slower and Reducing power in this case might not enable the single lower powered pulse to allow the material to reach a thermal level where it vaporises and the closer spacing of the pulses (dot on top of dot) will generally heat the surrounding area so that the next dot is not working on vaporising a "cold" surface or substrate. The problem here is that one is actually putting heat into the material and this affects the material and the cut edge or material adjacent to the dot.
PPI is NOT adjustable in terms of raster engraving on the explorer , it is only relevant in vector cutting , thus one has no real control of how many times the laser fires in an inch of scan when engraving , only when cutting (this probably applies to most lasers)
DPI is the relevant control for how dots overlap when engraving.
What will determine the quality of engraving at top speed is the motion system , how much slop it has and what type of position feedback is used and the ramp characteristics of the acceleration system as well as the type of pulse and how long the pulse takes to reach its max power. One cannot really extrapolate from one laser system to another in terms of how speed works due to these and many other variables.
One of the biggest problems running at high speeds is the inertia of the whole system , often the kinetic energy of the system translates to increased vibration thru the whole system and this translates to very small micro movements of the piece being lasered , especially cos most lasered stuff is not stuck down , and its this vibration of the pieces that can worsen crispness and engraving results.
A lot depends on the way one uses their lasers , we use 6 lasers in a production type environment and the extra capacity for work running at high speed more than compensates for increased maintenance in terms of the motion system.
For example we had 10 000 labels to do at $1 each and reduced cycle time from 1 min each to 14 secs , ie we boosted production from $60 an hour to $240 an hour , you dont need to do many hours at that rate to more than cover the costs of a few bearings or belts.
If one were doing the occasional gift etc , the scenario might be different.
You need a 10x or higher mag loupe to inspect engraved pieces , often looking at the surface finish will tell you whats going wrong. In the case of the brass , it would tell you if you are under or over "burning" the piece and you can adjust your engraving strategy accordingly.
Doing any job in 2 passes is generally a recipe for problems for various reasons , in the first place it probably means that your setting are not right or the laser is underpowered for the job , it puts heat into the job piece , it leads to misregistration problems on the 2nd pass and the laser is now not working on "virgin" material , it is working on pre vaporised areas which might have different characteristics to the virgin surface, focus will also be off optimal.
We never rely on mnfgrs settings for engraving or cutting , lasers differ in power , materials differ in composition etc , so we always test the materials by using small filled blocks and varying power and speed and dpi to see what gives best results in the shortest time.