Originally Posted by
unworthy1
TiG welding combined with the development of steel alloy tubes (like Reynolds 853) that are much less prone to damage caused by the higher and more concentrated heat of welding. Lugless construction was always an option in olden times (see fillet-brazed), but required more skillful brazers than lugged construction did. Now that there has been a generation of TiG welders in Taiwan becoming highly skilled at mass producing aluminum frames, and that skill has been passed on to ROC Chinese welders, the only people using lugs (still available, BTW) are artisan builders and the occasional mass-produced "experimentals". Lugs are not for Giant factories and robots, and the highest output/highest margins they demand.
I'm not a frame builder, but I'd guess that any brazed frame (lugged or fillet-brazed) would be more repairable than a welded frame: you can heat the bronze or silver alloy and "un-glue" it, but a weld is a weld.
+1
The development of air-hardening steels like 853, S3, and OX Platinum have made the tubing far less susceptable to weakening in the HAZ (heat affected zone) at the TIG welded tubing joints than older alloys. In fact, air-hardening steels actually
gain strength from the heat in the welding process. Brazing, whether fillet brazing or brazed lugs, is done at much lower temperatures than welding, so until the air-hardening alloys were developed, brazing was the preferred joining method; the strength of the steel wasn't compromised by the high welding temperatures in the HAZ around the tube joints where the stresses are highest.
Another advantage of TIG welding is that framebuilders aren't limited to the angles of lugs; joints can be welded at any angle.