RCWI...
Aerospace welding is significantly different than industrial welding for a host of reasons that have taken me ~38-years to fully grasp.
NOTE.
My best mentor/teacher was a MASTER [my term] USAF Depot engine component welder who I worked with for +7 years. He could weld anything that was weldable... but applied a LOT of brain-power and 'set-up' before, and used amazing hands-on-skills during, weld operations. I did the easy part and presented suggestions on what needed repair, why repair was needed and what the part was used for. He studied each issue in amazing 'depth' and then announced 'I CAN DO this' or 'I CAN'T/WON'T DO this'. In either case, I trusted him and recorded the minutiae of his comments, concerns and the actual work. This is when I saw the blend of skill/art/experience/science in welding aerospace parts. I also learned another lesson: this is such a variable skill that You must know/trust Your welder to do the work to the highest level when chips are down and skin is on the table. This is when I learned that experience, skills and MUTUAL TRUST with Your welder is an absolute priority. There are times today, when I see a potential salvage repair for a part/Assy... but cannot trust that the 'right welder for the job' will actually be assigned to do the job... hence I WON'T allow the part to be weld repaired.
RANDOM THOUGHTS.
Engineers MUST know the materials [base/filler], joint design, welding specs, weld-processes and actual application [how critical is it?] before starting any job; as well as what has to happen before-hand [NDI for-extent of damage] and afterwards [post-weld NDI, re-machining/grinding to contour, finish restoration, etc].
Welding on new parts/assemblies is far different than repair-welding on parts/Assys that have been in-service a long time.
There is a substantial difference between each of the major alloy groups [Magnesium, Aluminum, Steel, Stainless steels, Heat-Resistant Alloys, Titanium, Ti, Cu, etc] for welding practices.
Welding wrought materials can be substantially different than welding on 'wraskley-castings' .
Base metal considerations**, weld filler selection, welding equipment parameters, careful cleaning and sculpting of bare-metal to-be-welded-surfaces, pre-weld heating, dry/inert gas saturation of the weld, actual welding sequence, post weld cool-down, post-weld re-heat treatment or stress relief, etc... are all massively important.. just to name a few of the 'big-ticket elements of concern'.
**some older aerospace drawings allow multiple base-material options: knowing EXACTLY what You are welding-on can be a challenge and may be a serious factor in up/down decision making.
Good aerospace welding practices dictate welding/testing of samples to verify materials, processes, techniques, etc. This is where a highly experienced master welder can make a difference for 1-off jobs of all-kinds: They already know how [by prior experience] to get desired results 'down to the gnat's-ass'.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]