Filtern
Erscheinungsjahr
- 2015 (36) (entfernen)
Dokumenttyp
Sprache
- Englisch (28)
- Deutsch (7)
- Mehrsprachig (1)
Schlagworte
- Laser beam welding (7)
- Solidification cracking (5)
- Hot cracking test (4)
- High power laser beam welding (3)
- Hot cracking (3)
- Keyhole (3)
- Local reduced pressure (3)
- Mobile vacuum (3)
- Duplex stainless steel (2)
- Electromagnetic weld pool support (2)
Eingeladener Vortrag
- nein (4)
Experimental study and numerical simulation of hot crack formation for novel laser weldability test
(2015)
Partial penetration welding with a fiber laser at a 9-kW laser power was carried out on 20-mm-thick plates at different positions and analyzed by both experimental and numerical methods. Experiments were carried out for four different angular positions at 1.5 m/min welding speed. All four cases showed a tail-like structure of molten pool on the top surface. The in-depth mechanisms of the energy input characteristics in fiber laser position welding for eight different positions were studied by numerical simulation using the volume-of-fluid (VOF) method. Experimental and numerical results were compared for four cases and showed fair agreement. Observation of flow pattern and bead shape revealed that gravity had little influence on bead shape and flow structure, but changed the pore structure considerably. Flow structure showed a periodic behavior which probably nullified the effect of gravity in position welding. Most of the laser rays reached the bottom of the keyhole without interruption and then multiple reflections started within the keyhole. The first five reflections inside the keyhole delivered around 70 % of the total energy.
Selective Laser Melting (SLM) and Laser Metal Deposition (LMD) are prominent methods in the field of additive manufacturing technology. While the powder-bed based SLM allows the manufacturing of complex structures, buildrate and part volumes are limited. In contrast, LMD is able to operate with high deposition rates on existing parts, however shape complexity is limited. Utilizing their respective strengths, a combination of these two additive technologies has the potential to produce complex parts with high deposition rates.
In this paper, a process chain consisting of additive technologies SLM and LMD is described. The experiments are conducted using the alloys Ti-6Al-4V and Inconel 718. A cylindrical test specimen is produced and the microstructure along the SLM-LMD zone is described. In addition, this process chain was tested in the manufacturing of a turbine blade. The feasibility of implementing this process chain for small batch production is discussed. The results are evaluated to show advantages and limitations of the SLM-LMD process chain. This paper is relevant for industrial or scientific users of additive manufacturing technologies, who are interested in the feasibility of a SLM-LMD process chain and its potential for increased deposition rates.
Life Cycle Assessment (LCA) is applied in evaluating environmental impacts of state-of-the-art welding technologies. Manual Metal Arc Welding (MMAW), Laser Arc-Hybrid Welding (LAHW) and two Gas Metal Arc Welding (GMAW) variants are used to join a plate of 20 mm thick structural steel. The LCA results indicate that for 1 m weld seam, MMAW causes the highest environmental impacts in global warming potential (GWP), eutrophication potential (EP), acidification potential (AP), and photochemical ozone creation potential (POCP) among the selected processes, and the LAHW variant performances the least. Filler material and electricity consumptions generally dominate the impacts and reach shares of up to 80% and 61% in the respective impact categories. However, electrode coating consumption in MMAW remarkably contributes impacts on AP and EP, for instance 52% of AP and 76% of EP. Strategies for improvement of the applied welding technologies are discussed.
The development of the vapour plume during the laser beam welding of metals with propagation directions along the laser beam axis leads to a reduction of the absorbed laser power in the keyhole. The main reasons are the scattering of the laser radiation on the condensed phase of metallic vapour as well as the defocusing of the laser beam due to the density gradient in the vapour plume. These unfavourable effects can be significantly mitigated by the application of a reduced ambient pressure thus decreasing the interaction between the laser beam and evaporation products, which leads to more stable welding process and results in increased penetration depth, as known from previous studies. A conventional technique use a vacuum chamber principle, similar to that, used for electron beam welding. Application of this technique is restricted by the chamber size and reduces thus the advantages of this approach especially for large components. We demonstrate a possibility of mobile local vacuum application, which allows to generate a reduced pressure only in small region around the keyhole. By using of specially designed mobile pressure lock which can be moved along the welding direction absolute pressure of around 200 mbar could be obtained. This is sufficient to increase the welding depth by around 50%. Coupons from S355 were welded with an incremental laser power from 5 kW to 12 kW at atmospheric pressure and compared to those welded at ambient pressure of 200 mbar. The evaluation of the longitudinal section revealed an increase of the welding depth by about 35%. Furthermore, the welding trials in butt joint configuration on 15 mm thick plates at various laser beam power performed for atmospheric and reduced ambient pressure of around 200 mbar. The increase in welding depth up to 40% was established for reduced pressure. Particularly, low welding speeds under reduced pressure were especially advantageous in terms of increasing the welding depth.