Dissertation > Excellent graduate degree dissertation topics show

Study on the Stability of Dual Laser-beam Bilateral Synchronous Welding for T-structure of Aluminium alloys

Author: OuYangZiPeng
Tutor: LiuRenPei
School: Nanjing University of Aeronautics and Astronautics
Course: Materials Processing Engineering
Keywords: T-joint Dual Laser-Beam Bilateral Synchronous Welding stability of the keyhole behavior of the molten pool metallurgy mechanism
CLC: TG457.14
Type: Master's thesis
Year: 2012
Downloads: 76
Quote: 0
Read: Download Dissertation


The T-type joint welding technology of Dual Laser-Beam Bilateral Synchronous Welding(DLBSW) is a new process for joining fuselage skin-stringer in airplane industry. Compared withconventional riveting process, the manufacturing of the fuselage can be greatly simplified usingDLBSW technology. Meanwhile, the DLBSW process is successful to avoid breaking the integrity ofthe bottom skin which has proved to be one of the most effective methods for joining airplanestructures of aluminum alloys. However, due to the characteristics of aluminum alloys and theparticularity of DLBSW technology for T-structure, research on the stability of the keyhole, thebehavior of the molten pool and the metallurgy mechanism specific to the new technological is still inthe preliminary stage in civil aircraft industry. Aiming at the DLBSW technology for T-structure ofAluminium alloys to be adopted in large passenger aircraft, this thesis will do the research on thesethree aspects mentioned above.First of all, force conditions of the particular keyhole developed during the DLBSW process forT-Structure were studied. The magnitude and orientation of the steam pressure, surface tension andgravity and so on were investigated, mechanics models for different sections of the keyhole wereestablished. On the basis of welding process parameters, pressure gradient acting on the keyhole wallwas calculated and the travelling speeds of the keyhole wall relative to the workpiece were figured upby means of Navier-Stokes Equations. The travelling speeds were then analyzed comparatively withthe moving speed of the laser-beam, and the stability of the keyhole was discussed.Secondly, a3D model which is suitable for the DLBSW process for T-structure of Aluminiumalloys on the problems of solid/liquid phase transformation for welding pool was established bycombining fluid flow dynamical equations and porous medial flow equations. The latent heat of phasechange was considered as common source term, and the welding heat sources were dealed asadditional source terms. The fluid flow, temperature field and liquid fraction field were calculated, theeffects of buoyancy and surface tension on the behavior of the molten pool were studied. The resultproved that the calculated weld shape was agreed well with the transverse macrosection of aDLBSW joint, Marangoni effect plays a leading role in driving the flow of the molten pool and theheat transfer in the molten pool. Due to the negative surface tension gradient of aluminum alloy, thehigher the temperature is, the faster the molten metal flows within the pool.At last, on the basis of the technology and relation theory of DLBSW technology for T-structure of Aluminium alloys, macroscopical shape, microstructures, composition distribution, microelementcontent of the welded joint were analyzed by metallographic and Scanning Electron Microscope(SEM). The results indicated that a satisfied weld appearance was obtained under the optimizedprocess parameters, the surface of observed joint is smooth free from appearance defects. Thesolidification structure of the joint was characterized and it was found that the crystallizingmorphology from the fusion line to the weld center was: coarse columnar crystals, cellular crystal,crystiform dentrite, dentrite and equiaxed grains. The fusion area was divided into top-fusion area andbottom-fusion area and their structure and properties were different. There were no obvious meltinglosses of alloying element Cu, Mg, Si in the weld observed by line scanning, but there was a seriousgravitational segregation of Si. Meanwhile, two different porosities existed in typical T-joint:metallurgical porosity and process porosity, and their induced mechanisms and avoided measureswere discussed.To sum up, researches on the stability of the keyhole, the behavior of the molten pool and themetallurgy mechanism during DLBSW process could establish a theoretical foundation for thestability and continuity of welding process for T-structure of airplane panel.

Related Dissertations

  1. Simulation Analysis on Temperature Stress of RCC Arch Dam and Its Construction Joints Design Research,TV642.2
  2. The Matlab Implementation of Joint Source and Channel Decoding of Turbo Code Based on Meanmatch,TN911.22
  3. Study on the Design and Biomechanical Behaviors of Individualized Artificial Knee Joint,R318.1
  4. Marine Boiler Superheater Tubes Expansion Port Stress and Strain Analysis,TQ051.5
  5. Based on statistics of the lognormal distribution heteroscedasticity model inferred,O212.1
  6. Mapping Quantitative Trait Loci and Domestication Analysis for Seed Size and Shape Traits in Soybean (Glycine Maxl.Merr.),S565.1
  7. QTL Analysis for Yield in a Japonica Rice (Oryza Sativa L) RIL Population,S511.22
  8. The Establishment and Preliminary Application of the Three-dimensional Finite Element Model of Ankle Joint,R687.3
  9. The exoskeleton elderly assisted walking device designed,TH789
  10. The Application Study of Delay-enhanced MRI in Normal Cartilage and Phase Ⅰ and Ⅱ of Cartilage Lesions of the Knee,R445.2
  11. Preliminary Effects of Clavicular Hook Plate Technique on Treating Acromioclavicular Joint Dislocation,R687.3
  12. Applied Anatomic Study of the Parameters of Screw Fixation for the Sacroiliac Joint,R687.3
  13. Tianjin foreign education systems management problems of foreign students study,G648.9
  14. Ankle-brachial index combined ultra- sensitivity C-reactive protein determination of the value of coronary artery disease,R541.4
  15. No mean contact number tort liability,D923
  16. Study on the Criminal Subject of Bribery,D924.392
  17. Research on Whispered Speaker Identification in Channel Mismatch Conditions,TN912.34
  18. Research and Design on Experimental Platform of Rubber Belt Joint Dynamic Durable,TH222
  19. The Combination of Hysteroscopy and Laparoscopy in Diagnosis and Treatment of Female Infertility,R713
  20. Open border with the province , \,F127
  21. The Essential Attribute of Joint Tort,D923

CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding process > Welding of a variety of metal materials and components > Welding of metallic materials > Aluminum
© 2012 www.DissertationTopic.Net  Mobile