Spot welding problems

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First, let me start by saying I am not a welder and have gained new respect for the field since I have been given the responsibility of resolving this problem.  I have a Miller shop master welder. It has a spot weld setting with adjustable spot time, wire feed rate, burn back, amperage, etc.I am welding a piece of stainless steel hinge to a 1/4" thick piece of aluminum.  it is a 6061 or 6063 grade alum. The hinge has a .125 hole in it.    I keep having problems with inconsistent welds.  a majority of time time I get a big build up on the front side with a lot of splatter and adhesion to the nozzle but no penetration through the back side.  I can pull it apart very easily  Then some times it will blow a hole right through without changing a setting.   I have suspended the feed cable from the machine to the gun from the ceiling to ensure a good consistent feed path.  Occasionally it will weld perfectly with a nice pretty puddle on the front and a tiny nipple on the back side and I can't pull it apart.  I have tried adjusting all the settings and had a repair tech out several times.  When he left the first day it was working ok and then it went back to incosistency without changing any settings.  I read on another thread that it could be because I am using 75/25 argon nitrogen mix and I should try using pure argon.  can  anyone offer any advice?
Reply:I would never consider welding stainless (or any steel) to alum."SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:First, let me start by saying I am not a welder and have gained new respect for the field since I have been given the responsibility of resolving this problem.I have a Miller shop master welder. It has a spot weld setting with adjustable spot time, wire feed rate, burn back, amperage, etc.I am welding a piece of stainless steel hinge to a 1/4" thick piece of aluminum. it is a 6061 or 6063 grade alum.
Reply:Need a little more then a Miller Shop Master....Fronius Cold Weldhttp://www.fronius.com/cps/rde/xchg/...8_ENG_HTML.htmLots of $$$$