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Advanced Welding Processes Episode 1 Part 10

Tham khảo tài liệu 'advanced welding processes episode 1 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 8 High Energy Density Processes 8.1 Introduction Advances in the high-energy processes high-current plasma electron beam and laser welding have been concerned with the application of the technology to the fabrication of engineering materials. The power density of these processes is significantly higher than that of the common arc welding processes 124 and normally above 109 Wm-2 typical values are compared in figure 8.1. As a consequence of the high energy concentration the mechanism of weld pool formation is somewhat different from that normally found in other fusion welding processes. The material in the joint area is heated to very high temperatures and may vaporize a deep crater or hole is formed immediately under the heat source and a reservoir of molten metal is produced behind the keyhole. As the heat source moves forward the hole is filled with molten metal from the reservoir and this solidifies to form the weld bead. The technique has been called keyhole welding. The high energy density processes which operate in the keyhole mode have several features in common i they are normally only applied to butt welding situations ii they require a closed square butt preparation with good fit up iii the weld bead cross sections have high depth to width ratios i.e. as narrow gap welds iv they allow full penetration of a joint to be achieved from one side v they can be used to limit distortion and thermal damage. 176 Advanced Welding Processes Power Density W m2 1.000E 15 1.000E 14 1.000E 13 1.000E 12 1.000E 11 1.000E 10 1.000E 09 1.000E 08 1.000E 07 1.000E 06 1.000E 05 GTAW GMAW PLASMA YAG LASER co2 LASER ELECTRON BEAM Process Figure 8.1 Comparative power density of various welding processes. After Quigley 124 and Ireland 152 . Figure 8.2 Mechanism of keyhole .