tailieunhanh - Advanced Welding Processes Episode 1 Part 7

Tham khảo tài liệu 'advanced welding processes episode 1 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Advanced GTAVV 105 above it is normal for this type of unit to have mains voltage stabilization plus low-voltage remote control. A further development of this technology is the use of high-frequency transistor reversing switch circuits which when added to the output of a conventional or inverter-based DC power source enable a square wave AC output to be obtained. It is reported 87 that a unit of this type is capable of reversing the polarity of the output within 100 pcs and gives effective cathodic cleaning on aluminium alloys with 20 ms electrode negative polarity and 4 ms positive . a pulse frequency of Hz. Cold- and hot-wire additions in GTAW A useful feature of the GTAW process is the ability to control weld pool temperature and size by means of independent cold-wire addition. This is used in manual welding operations to control the weld profile and penetration particularly in positional work. Mechanized wire addition by means of a separate hand-held wire dispenser or a torch-mounted feed system are available for manual operation but although these can increase the operating efficiency of the process they tend to be restricted to simple weld geometry and joints with good access. Figure Dabber TIG welding system for rebuilding the cutting edge of an end mill left workpiece centre torch right filler wire delivery system. 106 Advanced Welding Processes In automated GTAW the wire is normally fed at a set constant rate and the element of control exerted by the welder is lost. A mechanized wire-feed addition system called Dabber GTAW t which feeds the wire with a reciprocating motion similar to that used by manual welders has been introduced 88 . The frequency of wire addition may be set between 2 and 10 Hz. A controlled low heat input deposit may be achieved and the technique is particularly useful for building up fine edges of cutting tools figure or components such as turbine blades. Hot-wire GTAW Normally GTAW is regarded as a .