Tham khảo tài liệu 'the welding of aluminum & its alloys part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TIG welding 115 autogenous and a wire feed is not required although this can be easily provided from a spool of wire fed from a cold wire feed unit. The wire should be fed into the leading edge of the weld pool at a similar angle to that used in manual welding. Both the start of the wire feeding and carriage travel should be delayed until the weld pool is well established. When ending the weld the current should be tapered down and the wire feed speed adjusted to provide crater filling. DCEN helium TIG is ideally suited to mechanisation since full advantage can be taken of the increase in travel speed which may be up to 10 times that of an argon shielded AC-TIG weld. It is also possible to weld thick plates up to 18 mm thick in a single pass square edge preparation with no filler metal making this a very cost-effective method. The high travel speeds possible with the technique may lead to undercutting particularly if the welding current is increased in the expectation that this will permit even higher travel speeds to be achieved. Short arc lengths are necessary when autogenous welding typically mm and in some circumstances the electrode tip may be below the surface of the plate with the arc force depressing the weld pool surface. Contraction during cooling will cause upsetting to occur resulting in a local thickening of the joint and providing sufficient excess weld metal that the joint is not underfilled. TIG spot and plug welding By overlapping two plates a spot weld can be achieved by using the DCEN TIG process to fuse through the top plate and melt into the lower plate. Initial use of the process was carried out without a filler wire but hot cracking problems with the alloys meant that it was confined to pure aluminium up to 2 mm thick. The development of automatic wire feeding systems capable of feeding wire into the weld pool as the weld is terminated has helped in extending the range of alloys that could be welded. Even with this improvement .
