Laser Cutting

William Schrade

William Schrade

Knifemaker / Craftsman / Service Provider
Joined
Jul 30, 2012
Messages
609
Recently a friend of mine offered to laser cut some knives for me. 440c. I finished the knives and since have read that laser cutting is not good for the steel because it compromises the HT process. Any thoughts?
 
i think the rule of thumb for that is to add like 1/4 inch to all sides just to make sure all the good bits are ok. Another option is to laser cut out templates to use in either a mild steel or some sort of wood...really anything would work. I am just finishing off a batch of knives done with lasercut templates and it is beyond easy to do and you dont have to work around any overheated areas.

I do not know for sure on this one but i would guess there may be a way to heat treat it back to a normal state, but i do not know enough about how that would work to give any further advice for it.

Just try templates out, oh and another thing is that you can actually prototype slipjoints with laser cut acrylic with an impressive amount of accuracy.
 
There is an area, the Heat Affect Zone (HAZ) where the steel has been significantly heated. In a laser cut part it is frequently around 1/8". However, the area where the steel was heated enough to actually damage it is less than that. Assuming you removed a millimeter of compromised metal around the perimeter it is unlikely there is anything really wrong with your knives.

Waterjet is a popular alternative because it prevents HAZ and you don't have that nasty hard crust to grind through.
 
Years back I had Admiral laser cut a couple hundred blades for me. I found there was barely any HAZ, and the blades were easy to grind and finish. I now use waterjet on large batches, but if there was a laser cutter nearby, I would not hesitate to use him.
 
I am fortunate to have both our waterjet guy and laserguy within 5 minutes of where I work. The waterjet is more expensive, by quite a bit. The laser guy doesn't like cutting high carbon steels, because the carbon content causes excessive burning of metal while its being cut. This causes a larger heat affected zone then lower carbon steels. Also, the thicker the material, the larger the heat affected zone. Now high carbon stainless he says cuts much better, due to the chromium content... for reasons I'm sure he could explain better then I could. All this being said, when laser cutting the HAZ is much less then most would think. The laser gets through the metal fast enough to cause minimum heating of the surrounding area. It may be too hot to touch, but not hot enough to cause a change in the metallurgy much more then .010"-.020" on 1/8" material, and maybe a slight bit more on 1/4" material.
 
Is there not a way to return the "HAZ" back into usable steel? Or have I missed some thing? Jess
 
I should have mentioned that the blades were 1/8" stainless steel.

The HAZ is in two layers. The area on the edge is decarbed, as it was heated to a very high temperature as the steel was melted by the laser. This decarbed "skin" has to be ground away. It is usually only a few thousandths of an inch thick. The HAZ just inside this "skin" is steel that was heated to a high temp, but not melted. It will be air hardened, and will be much harder than the steel a few more hundredths of an inch farther from the edge.

A quick pass on the grinder along the edges takes care of the HAZ.
 
Thanks for your answers. I did grind away the HAZ but was afraid I did a lot of work for nothing. Going to try water jet next time.
 
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