| 1. |
- Li, W-B, et al.
(författare)
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Modeling of the laser cladding process : preheating of the blown powder material
- 1995
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Ingår i: Lasers in engineering (Print). - 0898-1507 .- 1029-029X. ; 4:4, s. 329-341
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Tidskriftsartikel (refereegranskat)abstract
- Laser cladding is a high precision method of improving the wear and corrosion resistance of metal surfaces. The process gives high quality, porosity free surface layers, with low dilution of the substrate material and with excellent bonding to the substrate. Most frequently metal powder is used as cladding material and there are basically two different methods of application: i) a pre-placed bed of powder on the substrate surface; ii) powder blown into the beam-substrate interaction zone by an inert gas stream, The blown powder cladding process is much more flexible with respect to surface geometries and is therefore the most frequently used method in industry and the subject of this paper. As the blown particles travel through the laser beam on their way to the laser-substrate interaction zone they become heated. This paper gives the results of a theoretical model which investigates the level of pre heating experienced by the particles and the effects of various parameters on this pre heating. The results are important, as the powder particle temperature is expected to be an important parameter in the modelling and control of the cladding process.
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| 2. |
- Li, W.-B, et al.
(författare)
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Redistribution of the beam power in laser cladding by powder injection
- 1996
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Ingår i: Lasers in engineering (Print). - 0898-1507 .- 1029-029X. ; 5:3, s. 175-183
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Tidskriftsartikel (refereegranskat)abstract
- In the process of cladding by using blown powder, the laser light passes through the injected powder and is incident on the surface of the substrate. As a result of the presence of the powder cloud there will be a reduction in the laser beam irradiance experienced by the melt pool below it. This effect will be more pronounced where the cloud is at it's deepest. The original laser power density distribution will therefore be altered by passage through the powder stream. The present paper quantitatively describes this phenomenon and suggest some equations by which the redistribution of the power density of the laser beam through the powder cloud can be evaluated. The significance of the redistribution of the laser beam and its possible effect on the temperature in the substrate is also discussed.
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| 3. |
- Tan, Z., et al.
(författare)
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Empiric model for controlling springback in V-die bending of sheet metals
- 1992
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Ingår i: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 34:1-4, s. 449-455
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Tidskriftsartikel (refereegranskat)abstract
- A process model is presented for v-die bending of sheet metals. This model is especially valuable to control a press brake equipped with a computer integrated controlling and planning system. A bent part recovers elastically on release of load, and the springback varies with both material and process parameters. A desired bend angle is obtained by controlling the punch insertion depth so that the springback can be compensated by right amount of overbending. The model combines analytical method with trial and error work to establish the relationship of punch insertion depths and corresponding unloaded bend angles. To apply this model, three trial bendings are required for sheet metal and tool combination, so that three coefficients in the half-empiric model can be obtained in a regressive way. Experiments have shown that process parameters affect springback more obviously than material properties do, and the model predicts accurate punch insertion depths for desired angles in air bending. The model is simple, so it can easily be used for real time control
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| 4. |
- Tan, Z., et al.
(författare)
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On analysis and measurement of residual stresses in the bending of sheet metals
- 1994
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Ingår i: International Journal of Mechanical Sciences. - : Elsevier BV. - 0020-7403 .- 1879-2162. ; 36:5, s. 483-491
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Tidskriftsartikel (refereegranskat)abstract
- A new method for evaluating distribution of residual stresses in bent sheet metals is presented. Due to the non-uniform distribution of strain and stress across thickness, springback on unloading induces residual stress in a bent specimen. The authors have formulated the problem and shown that the springback and residual stresses can be expressed as a function of geometric parameters and material properties of sheet metals, e.g. bending curvature, thickness, Young's modulus, work-hardening index, etc. The layer-removing method was used to determine the residual stresses in the study. By simulating the layer-removing process, analytical measurement of the residual stress was made. The analytical results were compared with the experimental data measured, and a good agreement was found.
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| 5. |
- Zhang, Zhao, et al.
(författare)
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The Simulation of Precipitation Evolutions and Mechanical Properties in Friction Stir Welding with Post-Weld Heat Treatments
- 2017
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 26:12, s. 5731-5740
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Tidskriftsartikel (refereegranskat)abstract
- A finite element model of friction stir welding capable of re-meshing is used to simulate the temperature variations. Re-meshing of the finite element model is used to maintain a fine mesh resolving the gradients of the solution. The Kampmann–Wagner numerical model for precipitation is then used to study the relation between friction stir welds with post-weld heat treatment (PWHT) and the changes in mechanical properties. Results indicate that the PWHT holding time and PWHT holding temperature need to be optimally designed to obtain FSW with better mechanical properties. Higher precipitate number with lower precipitate sizes gives higher strength in the stirring zone after PWHT. The coarsening of precipitates in HAZ are the main reason to hinder the improvement of mechanical property when PWHT is used.
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