tailieunhanh - Advanced Welding Processes Episode 2 Part 4

Tham khảo tài liệu 'advanced welding processes episode 2 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 184 Advanced Welding Processes welds may be made. The shielding requirement may be met by carrying out the welding operation in a glove-box which is vacuum purged and backfilled with argon or using a trailing shield of the type shown in figure . The major problem experienced with this material is undercut this may be alleviated by i careful selection of welding parameters on thicknesses up to 3 mm ii pulsed operation with controlled current decay on each pulse iii cosmetic runs with plasma or GTAW and filler iv magnetic arc oscillation along the axis of the weld. Welding parameters for plasma keyhole welding of titanium are given in Appendix 7. Plasma Torch Figure A trailing shield. Aluminium. Plasma keyhole welding of aluminium is possible if electrode positive polarity is used as discussed above. It is also possible to use advanced power sources with the capability of variable-polarity operation and significant improvements in quality and cost have been reported using these techniques 138 . It has been found that acceptable results are achieved with 15-20 ms of DC electrode negative operation and electrode positive pulses of 2-5 ms duration. Summary plasma keyhole welding The plasma keyhole welding process may be used for making square butt welds in a wide range of materials in the thickness High Energy Density Processes 185 range from 2 to 10 mm. It gives high welding speeds and guaranteed penetration from one side of the joint. Although the number of parameters which influence the process performance is large and their interaction is complex the arc power gives a useful indication of the overall performance capabilities. The major limitation of the process is undercut but this may be controlled by careful selection of the operating parameters or pulsed operation. Laser Welding The laser is a non-arc heat source and consists of a high-energy coherent beam of light of a fixed wavelength. The high-intensity beam is produced by stimulating emission