Hi Kix!
Are you using a Special Metals "Monel 67" filler rod for the ER Cu-Ni to weld Cu-Ni to an Austenitic Stainless such as 304L and getting good results as far as not experiencing undercut on the Monel side?
Here's the product sheet for the above mentioned rod:
http://www.specialmetalswelding.com/products/datash/fm67.pdfHere's a .pdf on the (Nickel FM 61) Er Ni-1 rod that you mentioned, and are having problems with on the Cu-Ni toe of the fillet weld (Please correct me if I misinterpreted you)?
http://www.specialmetalswelding.com/products/datash/fm61.pdfThe first thing I notice in the different chemical compositions is the huge variation in the amount of Cu between the ER Cu-Ni filler, and the Er Ni-1 filler which would obviously explain why there's no undercut with the ER Cu-Ni filler as opposed to the ER NI-1 filler... Are you depositing a "barrier" (Buttering) layer on the 304L with ER Ni-1 or on the Cu-Ni member? Almost as important, are you making darn sure that both members are very clean prior to welding?
By any chance, do you visit this site?
http://www.specialmetalswelding.com/Here's a good .pdf for reference:
http://www.specialmetalswelding.com/publica/joining.pdfHere's another good one if you also work with Inconel 600 or 690:
http://www.specialmetalswelding.com/publica/Special%20Metals.pdfHere's a good one on fabricating:
http://www.specialmetalswelding.com/publica/fab.pdfI would suggest you check out the info in at least the first three .pdf's in order to arrive at an appropriate explanation as to why you're experiencing the difficulties you mentioned... I would then go to the following link to the selector guide, (One must register first) and when they approve your registration, you can log in and the link will match you with the appropriate filler metal specifically for your application for which I only have some info regarding the application itself so, your own query will most likely be more complete than my own since certain variable may need to be included in the selector guide that I may not have at my disposal currently. Here's the link to the selector:
http://www.specialmetalswelding.com/wpcselector/login.aspx?ReturnUrl=%2fwpcselector%2fdefault.aspxAnywho, good luck with your hunt!
Respectfully,
Henry