Combining CO2 laser and electrochemical machining

[Joe Hillmann]

Over the weekend I have been working on a system that will allow someone with a low powered CO2 laser cut thin metals and etch into thicker metals accurately and without distortion. I will give a brief description of how I am doing it and as I figure out safer ways to do it I will post them as well.

First I am going to point out that this method does NOT work with aluminum at the moment due to aluminum oxide.

If I am cutting the metal it needs to be .010 or thinner otherwise the cutting will start to distort as the metal gets thicker, if you are just wanting to etch the metal then thickness doesn't matter.

I take the metal that I want to cut and spray it with an acrylic clear coat on both sides. Once the clear coat dries I laser vector whatever shape I want the metal to be into the clear coat which then allows electrical contact with the metal below.

Then I hook a positive 3.3 volts from a rewired computer power supply to the work piece and the negative to a piece of metal that I don't care if it gets eaten up. I submerge both pieces of metal into a bath of salt water and turn on the power and about 3 minutes later the workpiece can be taken and all of the vector lines you cut with the laser should now be cut all the way through the metal .

The same method can also be used for etching into the metal by pulling the part out of the bath before it cuts through.

Before anyone trys this I want to point out that using salt water for this is dangerous and I am looking for a different electrolyte to make it safer. The salt become hydrochloric acid and chlorine gas when the current is run through it as well as the water creating oxygen and hydrogen. Plus if somehow the computer power supply was rewired wrong you could be playing with dangerous amounts of electricity and water.

[Rangarajan Saravana kumar]

Hi,

Some photos added will be nice to see the outcome??

Vectoring using CO2 laser for the masking sticker for our Electrochemical Etcher.. but new to see the cutting thru..

Rgds,
Saravanakumar

[Joe Hillmann]

It will be a couple days before I get photos up. The only sheet metal I have to play with at the moment is aluminum and using salt water for an electrolite doesn't work with it.

[Rodne Gold]

You can do the same process for the aluminium , but instead of electro-etching it , just use some caustic soda.
(sodium hydroxide I think)- try with various dilutions (obviously you don't need electricity for this)

[Ernie Balch]

For etching steel, brass, copper and nickel silver you can use ferric chloride. Radio Shack sells it as circuit board etch.

[Patrick Richard]

Interesting idea that I may well try, lasers being too slow for what I'm working on. Actually you could use the same method, with ferric chloride, to make circuit boards. I know, it's probably been done before, but I know what I know and nothing else.

It is much more elegant and reproducible than the toner transfer method I previously used. Something you may or may not know; prepare to agitate the metal in the etching solution or you will have unsightly effects due to viscosity. I'll try to add a picture later.

EDIT

Here is what I meant

229193

A properly agitated solution yields:

229194

My photos were taken with a cell phone so excuse the quality

[Richard Rumancik]

. . . Vectoring using CO2 laser for the masking sticker for our Electrochemical Etcher.. but new to see the cutting thru..

Rangarajan - are you saying that you are currently using the same technique for etching metal? If so please clarify exactly what you are doing, what equipment you are using, and post a photo is possible.

[Richard Rumancik]

Joe, a few questions . . .

The difficult part of this method is finding a resist that will remove cleanly with the laser. You say that you used an acrylic clear coat. Can you tell us what brand/part number? I have tried numerous paints, lacquers, enamels, acrylics etc and can't find something that the laser will remove cleanly. There is always residue that results in uneven conductivity. Did you just scrub the lines after lasering to clean residue? I'd like to find something that does not require mechanical cleaning as abrasion can damage the resist as well.

What metal were you etching, and how thick was it? Three minutes sure seems fast. Any guess as to currrent?

I don't know if there are any electro-etch electrolytes suitable for aluminum. You may have to use a non-electrolytic process as Rodne suggests. For brass, steel, stainless, silver the electrolytic process is better in my opinion. But you need to adjust the electrolyte and cathode for the material being etched.

Regarding the power supply - if anyone rigs something up it is best to ensure it is properly isolated. One way is to use a linear supply with a simple bridge rectifer on the output. A GFI, fuse, and suitable grounding on the input would be a good idea. You might also want to put a breaker or fuse on the output so that when (not if) you short the anode and cathode you don't burn anything up. I'm not sure how well computer supplies tolerate direct shorts. A more sophisticated supply will allow control of voltage and current but that is a more difficult DIY project.

[Joe Hillmann]

At the moment the best resist I have found is black rust-oleum which is far from ideal because it isn't clear so it then has to be removed somehow adding an extra step. Before the black paint I tried disloving acrylic scraps in acetone then dipping the metal into that which only worked if the metal was perfectly clean otherwise it would peal off in sheets. I am thinking layout fluid may work but I don't have any so haven't tried it. I have found that I can do aluminum if after I laser it I trace the lines with a scribe to break the oxide layer on it but that adds another step and causes the accuracy, especially on straight lines to go down.

I have played with copper, stainless, shimstock, and aluminum. Once you get thicker than .010" the cut lines start to get wider and not as neat.

I don't know what the current was (I can't find my multimeter) but I was playing with 6 volts and 12 volts. With all the lines of the same voltage tied together so I don't know what the amps was.

I think that if I bake baking soda to 200 degrees I can then replace the salt with the cooked soda and it will no longer produce chlorine and if I run it a 6 volts very little hydrogen is produced whereas at 12 volts it bubbles like crazy..

As far as the powersupply if you hook the brown wire to any orange wire when you create a dead short anywhere in the system the protection will kick in so all you have to do is disconnect the green wire from ground for a second then reconnect it and it will reset itself.

Also the anode works best if it is stainless. And there should really be some type of water circulation and filtration but I won't worry about that until I get everything else working.

[Richard Rumancik]

I did try Sprayon Layout fluid a few years ago. Layout fluid is usually a colored lacquer. I don't have my test samples handy to say exactly what it did, but it was not an answer for my needs. From what I recall it tended to flake off adjacent to the laser line. I also tried transformer winding varnish. Not the answer. I can tell you about 20 things that won't work, at least not the way I would like.

You want to have something that makes a tenacious bond while electro-etching and then is easy to remove. Unfortunately this is unlikely as these requirements are contradictory. So I will be happy to get the tenacious bond, then figure out how to remove the material after etching. There is likely to be a solvent, paint remover, or chemical that will remove the remaining material after etching.

I am optimistic that there is a suitable resist that works with a co2 laser but as far as I know, no one has found it, as I have done a lot of searching. Most people find something that almost works.

For copper and brass I would suggest copper sulphate. For stainless I have a recipe for electrolytic etching as follows courtesy Oppi Untracht but I have not tried it:
37% hydrochloric acid: 1 volume; water: 3 volumes; use stainless cathode at 6V

You may not like this solution as you are more worried about gases generated than I am. I think that if you have adequate ventilation you should be safe. Obviously working with acid requires more precautions than copper sulfate or salt solutions, but stainless steel is harder to etch as it was designed to be that way.

[Patrick Richard]

I found this link http://www.nontoxicprint.com/acrylicresistetching.htm about Intaglio printing. The author suggest acrylic paint.

[Joe Hillmann]

I found out there is a paint that is actually made for this application it is called etch primmer or at least that is what I was told. As far as it taking 3 minutes to cut a piece of metal that was .004 or .005 shim stock. Thicker metals take longer and need the fluid to be moving over the metal.

[Rodne Gold]

Etch in etch primer is not "etch resist" , it etches using phosphoric acid and thus keys into the metal , we have tried it + an overcoat of automotive paint and they couldn't withstand the etch (warm ferric chloride)...in your case you need anything non conductive that can withstand some bubbling cavitation and a little bit of heat. Our biggest problem with lasered etching is that the laser (the Co2 ones) leave a slight residue on the places you engraved leading to a inconsistent etch. We solved it by using a mylar self adhesive vinyl as the resist and sandblasting after lasering to expose bare metal. It's terrible stuff to remove....

[Richard Rumancik]

There is a lot of good information and clear pictures on the nontoxicprint site that Patrick posted.

I have often thought that there should be some kind of acrylic-based material that would ablate well with the laser, given that acrylic sheet vaporizes so well. But what works for printmaking may not necessarily work well with a laser. They are using metal tools to scratch and remove the acrylic resist, which is a bit different than using a laser beam to remove the acrylic resist. The fundamental problem is that the laser tends to leave residue, whereas a graver used by an artist tends to gouge the resist right down to bare metal.

I have been tempted to try some of the acrylic resists used by the printmakers but the R&D can get a bit expensive when you need to buy and ship a litre of resist across the country - and I really only need a few millilitres to find out if it works or not. Each experiment can end up costing $50 in materials. At least with spray cans, it is usually below $10. (I would pay $50 a litre for something that actually worked with a laser though.)

An etch primer is a primer that is usually used on metals to prepare the surface for a topcoat. Some materials are quite hard to bond to (like brass) and an etch primer will chemically alter the surface (etch) it to make it more receptive to bonding. (The word "etch" here is because of the self-etching characteristics of the primer; it has nothing to do with the electro-etch process.) So even though a an etch primer might provide a tenacious bond to metal, the question remains - how cleanly will the laser remove it? And - will it flake adjacent to the laser scribe mark? These are the two main issues I have been trying to resolve.

If anyone tries an etch primer (or anything else for that matter) please let us know your results.

[Joe Hillmann]

Richard.

I am coming up with the same issue of cost to find a mask that works well. Each item I think of trying may only cost $10 but if I have to try 25 things before I find one that works it starts to add up. So far I have only been trying things that I have laying around at home so haven't spent much other than for the power supply.

[Joe Hillmann]

Etch in etch primer is not "etch resist" , it etches using phosphoric acid and thus keys into the metal , we have tried it + an overcoat of automotive paint and they couldn't withstand the etch (warm ferric chloride)...in your case you need anything non conductive that can withstand some bubbling cavitation and a little bit of heat. Our biggest problem with lasered etching is that the laser (the Co2 ones) leave a slight residue on the places you engraved leading to a inconsistent etch. We solved it by using a mylar self adhesive vinyl as the resist and sandblasting after lasering to expose bare metal. It's terrible stuff to remove....


Do you think that the poor etch is caused by residue left from the laser or maybe it is from oxides on the metal that was there all along? Either way sandblasting would remove it.

[Rodne Gold]

The solution to the residue problem on painted and other resists is actually easy to cure and low tech , put some cream based abraisive kitchen cleaner on your fingertips and gently massage it over the plate , wash off and hey presto. The object when chemically etching is to get as much bite in as short a time , so you avoid undercuts and losing insides of very small letters. Cheap sign vinyl is a great resist , comes off with a heat gun , not too laser friendly , but kiss cutting it isnt an issue if you got a good extraction system , limited in detail you can get tho.
I found the spray cans you get at automtive stores to work well as resists for not such deep etches.. But I'm speaking about chemical , not electro.
Seems there are 2 types of Electro etching , AC which leaves a cerdec type black mark in a short time and DC which "bites".

[Ernie Balch]

I use genesis AQ-3000 photo resist for etching projects. It is UV sensitive and has a short exposure time. It gives a high resolution image that sticks very well to metals. Of course the photo resist process is not as easy as laser patterning but it is designed to hold up against strong etchants. I don't know if it can be laser ablated cleanly, that is an experiment I have been wanting to run.

Slight residues that interfere with etching is a common problem in the electronics industry so they do an oxygen plasma clean to remove a thin layer of organics. Sometime an ozone/UV treatment is enough to improve the etching. About 35 years ago I developed a technique where a strong chemical oxidizer was used as pretreatment prior to gold etching. The dip and rinse cleaned up any resist residue and allowed us to get a very uniform gold pattern etch.

ernie

[AL Ursich]

The Etch-O-Matic I have uses a AC Power Supply and you use a big DIODE on the ground leg for Deeper Etching.... The Diode turns the AC into DC.... OR at least partially rectified...


http://en.wikipedia.org/wiki/Rectifier Half-wave Rectification.

[Rangarajan Saravana kumar]

Richard,

We do a masking stencil out of our epilog laser and apply the electro chemical etcher to etch on metal, instead using photo stencil. Because, photo stencil is applied for a good quantity with same matter. with
laser, we can change and cut out masking tape and apply. Minimize time also. Hope this clarifies

[Patrick Richard]

I like the abrasive kitchen cleaner idea. Keeps it simple

[Richard Rumancik]

I use genesis AQ-3000 photo resist for etching projects. . . . I don't know if it can be laser ablated cleanly, that is an experiment I have been wanting to run. . . .

Well, Ernie, I think you should get right on it . . . and let us know how it turns out!

I have seen that some manufacturers use laser ablation in addition to regular UV processing of photo resist - perhaps it is to get finer details than they could otherwise. But I have no idea of the type of resist used and the type of lasers used. And getting my hands on various types of photoresist is even harder than specialized paints. Photoresist might be overkill if one just wants to use laser patterning alone, as you don't need the photosensitive properties and I assume that adds a lot to the cost of the material. Plus you need to expose the whole panel, develop, etc. But it would still be interesting to know if it does work.

I have also been tempted to try dry film photoresist but would actually prefer a sprayable or brushable product as it is more versatile in its application.

Maybe I am expecting too much in hoping for a clean removal of the resist by the laser. A liquid abrasive cleaner might be gentle enough, if a good bond can be achieve in the first place. I am always worried about damaging small details. The vinyl mask can work for very coarse etching but the centers of letters fall off if it has small text. Any sandblasting or abrasion will likely blow them away.

[Rodne Gold]

Hiya Richard m The photosensitive resists will hold the best detail but are a bear to apply , you really need a turntable that spins the plate to distribute the fluid evenly.
The most common way of etching is to screenprint using an acid resist ink that simply washes off in an alkai solution , the ink is not that expensive. Never tried to laser the photoresists - kinda defeats the object as you would have to pre expose it and then laser. I havent tried lasering the inks tho.
The gold/silver shiny polyester vinyls we use have exceptional tack and the sandblasting actually further "presses" it on the metal so you dont get the middles of letters dissapearing. downside is that its a LOT of work to remove it!!!
However NO resist can combat undercutting , where the etch actually cuts under the resist , on a very deep etch (like for paint filling etc) and no matter what you do , detail will dissapear.

[Rodne Gold]

Ok , just arrived at work to find 2 stunning brass plates wonderfully etched - My workshop manager and I had talked about the process and unbenown to me , he had googled it tried it.
We used a 20% copper sulphate solution and a car battery and another brass plate as the cathode, 20 minutes gave enough etch to paint fill perfectly and 40 mins gave about a .5mm (0.02") etch which is VISIBLY deep with a paint fill.. We lost no detail at all , used quite complex graphics too. We used spray on automotive duco as a resist and the fingertip rubbing method to clear residue. going to try stainless steel today. Will take pics during the course of the day.

[Rodne Gold]

Here's some pics , not great quality , but good enough to illustrate.

[Patrick Richard]

Call me easy to please but I think that's pretty darn good

[Rodne Gold]

Pics dont do the real life output justice , the plates we used were about 6" x 6" , we using ferric sulphate as the solution for the Stainless. I want very fine detail and letters etc on the SS and we gonna do 2 trials , a normal etched and the same thing as bas relief (letters standing proud) , we also gonna do a trila full plate piercing , ie eat right thru. There are some "issues" with the brass in that we used a sacrificial plate ( which got copper plated by the etch) that was the same size as the etced plate and thus the outsides of the etched plate were deeper than the middle , easily solved by using a smaller plate. We will do tests on monday as to voltage and current , solution loading and dist

[Richard Rumancik]

I have been using the electro-etch procedure as well - I gave up on ferric chloride some time ago as it is too hit-and-miss for my taste. As the ferric chloride solution is used, its strength is reduced, and it is therefore not predictable at all. Electro-etch provides a lot more control in my opinion. You can control the etch rate by controlling voltage/current whereas with ferric chloride you have to keep checking a lot. The copper sulfate solution is not depleted like ferric chloride.

If you want to cut through metal more than about .005"/.1 mm thick you pretty much need to etch from both sides or there will be probably be too much undercutting. This means registering the two patterns very accurately (say .003" dia. tolerance zone or better) which is a challenge. Otherwise you will get a very rough cutout.

[Chuck Stone]

At the moment the best resist I have found is black rust-oleum which is far from ideal because it isn't clear so it then has to be removed somehow adding an extra step.

I do it (not electric, but chemical like Rodney mentioned) using bumper sticker material. Got 100 sheets for
around $20. I put one on either side of the metal and etch, flip, reverse the image and etch again.
Then you throw it in the sodium hydroxide solution or ferric chloride (depending on the material) and
agitate. Eats away whatever isn't masked and gives a good 'cut'.
A bit more costly masking, but it works well.




I think that if I bake baking soda to 200 degrees I can then replace the salt with the cooked soda

Yep.. sodium carbonate instead of sodium bi carbonate. Also called soda ash. Much cheaper than
buying it (Calgon, Arm & Hammer Washing Soda etc.)

[Rodne Gold]

If you use Ferric , you need to add Citric acid to it , it then does not deplete the bite or give an inconsistent bite/etch. ( http://www.lawrence.co.uk/acatalog/etch.pdf ) The fastest and most effective etch is the plate upside down being sprayed with about 40 degree C ferric . We actually made a ferric etching plant , using home irrigation stuff as spray nozzles , 300w aquarium heaters in a sump tank to get to the 40 degrees. Expensive part was the pump , a specialised acid pump. the issue with ferric is that anything metal near the tanks etc gets corroded and once , when the spray nozzles got clogged , the output of the acid pump came loose and sprayed ferric EVERYWHERE!!!... big mess.

[Richard Rumancik]

I was aware some people added citric acid but never tried it. Due to all the issues mentioned I went to electro-etch before I tried that option.

Rodne, I know you have been a long-time advocate of ferric chloride but I will guess that once you have done more testing with electro-etch you will give up the ferric chloride. Maybe it has its place. If you want to do further experimentation you will probably want to get a power supply that can be controlled rather than using a car battery.

Ferric used to be commonly used by PCB manufacturers but I think it is mainly used by electronic hobbyists now as there are better/cleaner/safer chemicals and techniques for etching circuit boards. I think a lot of artists have gone away from ferric chloride as well (using newer passive and electro-etch methods). Even the inventor of the "ferric chloride + citric acid" recipe (Kiekeben) seems to have evolved his research into using copper sulfate with the addition of sodium chloride (regular salt) for "passive" (non-electro-etch) etching.

I dislike using the upside-down option (which allows gravity to keep the plate cleaner) because you cannot see what is going on without removing the plate from the bath.

There is still some mess with electro-etching, as there is with any etching setup (electro or passive) but overall I think the electro-etch is more manageable. It does not need the heaters, although a continuous filter and pump might be a nice add-on for higher volume work to keep the solution cleaner. It does not need the jet spray. The solutions are generally not as difficult to handle or pump as ferric chloride.

[Rodne Gold]

The reason to use chemical etching is speed , 2-3 mins in heated sprayed ferric will give a deep enough to fill etch and really big plates are no problem.

[Ernie Balch]

In chemical etching the process variables are: Time ,Temperature, Agitation and Concentration in general etch rate increases with each.

Electro-chemical etching also adds voltage to the list. You have to control the field strength over the substrate to get even etching. Distance to the electrode directly affects the etch rate.

ernie

[Richard Rumancik]

In chemical etching the process variables are: Time ,Temperature, Agitation and Concentration in general etch rate increases with each.

Electro-chemical etching also adds voltage to the list. You have to control the field strength over the substrate to get even etching. Distance to the electrode directly affects the etch rate.

ernie


You are correct. But with electro-etch you can use room temperature so don't need heaters. Agitation is not mandatory. I believe the concentration will maintain itself over time - generally you do not need to test concentration or renew the solution. So if you keep all these things uniform (including distance to cathode) you are dealing mainly with voltage/current vs. time. Of course, if you WANT to adjust a bunch of variables (heat the solution, agitate, use different concentrations, you can.) But it is not necessary; you can make it as complicated as you wish or need for your circumstance.