Laser Welding of broken blades

I have got to believe that your heat treat would be out the window at that point. Welding is the fusion of two or more surfaces and that is done using heat. That level of heat cannot really be kept isolated and will destroy the HT of a good section of the blade around it. If it were purly to hang on a wall as a keepsake then it would work, but as a worker, IMHO, it would be bad. Steven
 
If this is with regards to that old slipjoint. I doubt that collectors value will improve with a welded blade....I would think rather the opposite.

If you want to use it. I think it would be much better to have the knife refitted with a new blade by an expert (slipjoint knife maker)....that *might* actually improve value and is functionally the only sensible alternative.
 
The old Jonathan Crookes folder just got me thinking about it. I'm new to knife collecting. I can't see that it would be economic to try to fix it up - it only cost me $2. I'm more interested in the history. But I was wondering if there was a way to weld with minimal heat transfer - so I googled it and came up with references to laser welding. Here's a lab welder that is advertised as being able to weld delicate equipment.

http://www.harrisdiscount.com/products.php?section=1&catid=21&id=39
 
Welding is welding, meaning melting metal and way beyond the temperature at which the temper is drawn (actually even beyond the austinization temperature). Minimal heat transfer means only that you are going to heat the material so focussed and applied so quickly that the total applied energy is actually fairly small, so once the heat is disscipated, the temperature increase of the workpiece is minimal. HOWEVER, right where you are welding, the temperature is normal welding temperature. So if you had a blade that is broken in half and you have a really good laser system, you might be able to weld the pieces without drawing the temper from most of the blade but along the entire weld the temper will be drawn, rendering essentially the blade useless, not to mention that you might introduce some significant local stresses and fault lines. Even if everything works out alright, which I have my doubts it will with out some mechanical actions, you will still need to normalize and re-heattreat and probably do some grinding and blending as well. I would think it will entail the same steps as reforging a broken blade would.

Finally, I am not even sure whether you can weld all stainless steels :confused:.
 
Ummmmh, ya? I look at the cross-section of that weld and while I admit it is a very nice weld, there is no way in hell I would want one of those in the middle of any of my blades....I would love to see what the crystal structure is within the weld.
 
I would think the welded blade could be reground, normalized, hardened, and tempered.
Bill
 
Normalizing, hardening, and tempering is "re-heat treating."
Bill
 
Looks like Bill is right on this. Knife blades seem to be more "organic" than I thought. Once they're "born" you don't want to mess with them. Here's an answer I got back from a rep of the company above. Thanks for everyone's input.

Mike,

The ability to successfully weld a broken knife blade depends on the knife material. Most knife materials are fairly unweldable so I would have to use filler material to join the blade back together. I have a variety of filler material that I can use. The pulsed Nd:YAG laser welding process is the lowest heat input fusion welding process in the industry. Thus, it will have the least effect on the blade temper. How much of an effect is hard to say. It depends on laser power used and other welding parameters. In general the heat affected zone is very small and almost non-existent.

Joe Kwiatkowski
Precision Joining Technologies, Inc.
 
Well, again, would you like some filler material in your blade? There are people the break a blade made from a continuous piece of evenly heattreated steel. I would think a welded blade, jointed with some filler material would last very long.
 
I'm with you 100%. That's what I was trying to say - just didn't get it across very well. Once a blade is broken, I guess it's broken. Impossible to make it new again. Replace it or leave it alone. Filler in the middle of a blade isn't going to act the same.
 
as far as I know with typical equiptment welding heat treatable steels is impossible, looks like these guys do it with specialized equiptment. allot happens to steel when its melted and cooled, alloying elements get burned off or move around unevenly, stress is introduced, etc. so I think even if tool steels can be welded with this process, are they really the same afterwords? also how thick is your blade? they stated that the penetration is AS MUCH AS .06" (a little less than 1/16") so if the blade is more than 1/8" thick then welding on bolth sides would not penetrate completely. typically if complete penetration is desired the parts are beveled and the subsequent "v groove" or other groove is filled with weld, often with a gap at the root. this would of course be much more visible. I dont have any experience with laser welders, but I could see burn through being a problume at the verry edge where its really thin.
 
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