laser welding woes...

[adamb4321]

I'm doing a cast implant beam for a client that decided he wanted it NP. I ordered some Cr/Co alloy from Bredent. All cast well, albeit apart from a slight rock.

I sectioned and laser welded back together which is were the fun started.

I always tack together on opposing quadrants, then seam weld on opposing quadrants and finally fill in with wire on opposing quadrants. This normally works very well and produces a strong weld and minimises distortion.

Yesterday I spent most of the morning and some of the afternoon welding and then re-sectioning and then re-welding again. Every time the beam has distorted really badly. It keeps warping upwards, welding on the opposite side to the warp should reverse the warp but on this beam once it starts moving in a direction nothing seems to stop it. After 5 hrs or so I've got it to a reasonable fit but it's still not as I'd like. Any suggestions as to whats happening?

 

[rlhhds]

I try to stay away from cast cr/oc like the plague for this reason. You are now losing your ass in the labor to try to help the dr save few bucks in alloy. I just tell my clients I do not cast NP because of the technical challenges associated with using it.

 

[adamb4321]

I don't usually have a problem welding Ni/Cr or Au Alloys or precious bonding. Is Cr/Co more awkward for some reason?

 

[droberts]

I always lute it together using GC resin and invest in stone. 100% accurate every time.
NP / Cr/Co, no problem. Takes longer for the stone to set, than it does to weld it...

 

[Toto]

I agree with investing in stone then welding - which ever side you hit with the welder it pulls towards that side ,sure you have noticed this -

 

[adamb4321]

Hi toto, I agree it pulls towards the side of the weld, normally. This beam didn't do that, counter welding to pull it back into position made no difference, it just pulled away which ever side I hit it on. What I did notice that after welding and resectioning the gaps were quite big even though the disc was only 0.25mm, it's like the metal contracted by a large amount when welding. If the gaps large I weld over the face of the cut to reduce it before welding together. It's damn annoying. Ultimately I'll have to remake it I think.

 

[Hary]

I rarely cut my bridges, this is what I do with my Co Cr bridges.

 

[adamb4321]

That does work but not in every case. depends how much you have to de-warp. Like I said in the other posts, my beam didn't respond to welding on the opposite side of the warp, it just warped more ie welding underneath like in the video didn't bend the bridge downwards, it just kept moving up.

 

[Hary]

That does work but not in every case. depends how much you have to de-warp. Like I said in the other posts, my beam didn't respond to welding on the opposite side of the warp, it just warped more ie welding underneath like in the video didn't bend the bridge downwards, it just kept moving up.

I have been using this Technic for more than 6 years I always have a good result. Try to squeeze a new metal and lower the settings, and try to balance your weld by going the opposite side. Good luck.