This work presents a preliminary investigation into the quality assessment of Probeless Friction Stir Spot Welding (PFSSW) joints in dissimilar aluminum alloys using laser thermography. This innovative process based on friction stir spot welding, demonstred good capabilities for aluminum joints. To evaluate the quality of these innovative joints in a nondestructive way a long-pulsed laser thermography preliminary procedure has been proposed. The study compares thermographic assessments with conventional testing on two specimens: deemed acceptable and not. Results indicate that preliminary procedure based on laser thermography can effectively assess weld quality, estimating the size of welded zones with an error margin of 3% relative to ultrasonic test UT.
The present work constitutes a preliminary step toward the ultimate goal of developing a thermographic procedure for the non-destructive evaluation of the mechanical strength of these joints using laser thermography, with a simplification of the equipment.
Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. The laser Assisted Friction Stir Welding (LAFSW) combines a Friction Stir Welding machine and a laser system. Laser power is used to preheat and to plasticize the volume of the workpiece ahead of the rotating tool; the workpiece is then joined in the same way as in the conventional FSW process. In this work an Ytterbium fiber laser with maximum power of 4 kW and a commercial FSW machine were coupled. Both FSW and LAFSW tests were conducted on 3 mm thick 5754H111 aluminum alloy plates in lap joint configuration with a constant tool rotation rate and with different feed rates. The two processes were compared and evaluated in terms of differences in the microstructure and in the micro-hardness profile.
The process of Selective Laser Melting (SLM) is an innovative technology for rapid prototyping that can be included among the SFF (Solid Freeform Fabrication) techniques, which are characterized by "free-form" manufacturing of solid parts. SLM is an additive technology that operates starting from the data encoded in the three-dimensional computer aided design (CAD) file of the component to be built. After the slicing operation made on the 3D model of the component, the consequent data file is sent to a computer-controlled laser device that fuses successive layers of metal powder to create the three-dimensional product. The SLM is a technological process which involves optical, thermal and solidification phenomena; thus the analysis of the process is rather complex. This work aims to study the molten/solidified zone in SLM samples through the experimental analysis of the shape and the size of laser tracks. The functional relationships between dimensional parameter of the molten/solidified track and the main parameters used to control the process was identified.
Friction stir welding is a relatively new joining technique. This technique, which is considered a derivative of the more
common friction welding method, was developed mainly for aluminum and its alloys. In recent years, this method has
been used to join various other alloys.
FSW has many advantages, including the following: the welding procedure is relatively simple with no consumables or
filler metal; joint edge preparation is not needed; oxide removal prior to welding is unnecessary; high joint strength has
been achieved in aluminum and magnesium alloys; FSW can be used with alloys that cannot be fusion welded due to
crack sensitivity.
The drawbacks of FSW include the need for powerful fixtures to clamp the workpiece to the welding table, the high
force needed to move the welding tool forward, the relatively high wear rate of the welding tool, and weld speeds in
FSW are slower, which can lead to longer process times.
To overcome these drawbacks, a fiber laser-assisted friction stir welding system was designed (FLAFSW). The system
combined a conventional commercial friction machine and a fiber pumped laser system. The scope is to investigate the
influence of the laser assistance on the weld quality.
A number of different aluminum plates, which are still mentioned to be difficult to be joint as intermetallic phases appear
during melting welding techniques, were used. The evaluation of quality was performed through analysis of appearance,
mechanical and microstructure characterization of the weld.
Worldwide manufacturers have already recognized the advantages of using laser welding for a number of applications.
Although laser welding is usually performed autogenously, the use of wire filler allows a broader range of welding applications.
In this paper a finite element model for key-hole laser welding sources based on experimental observations is presented.
The shape for the heat source can be easily changed so to simulate both autogeneous and wire filler laser welding.
In the thermal and mechanical calculations the material properties were considered with full temperature dependence.
Austenitic stainless and aluminum alloy welds were chosen to validate the model. Simulations of out-of-plane welds were computed using a local coordinates system. A personal computer was used for the calculations.
For different plate thicknesses and weld geometries, the calculated fused zones were found in very good agreement with the experimental ones, which proved that the thermal history was computed correctly.
When materials with thermal induced microstructure changes are welded, the microstructure in every point of the heat affected zones can be determined as a function of the local temperature cycle.
The laser forming process of metal sheet has been investigated and has proved to be adequate to rapid prototyping. In order to successfully apply this technique, a deep understanding of laser-material interaction is required. Since the AISI 304 stainless steel is widely used for deformation processes, the authors decided to investigate its laser forming behavior. The forming effect has been evaluated in terms of the bending of sheet-shaped specimens. The influence of the main technological and geometrical parameters of the process were investigated by a factorial design, i.e. ANOVA and Surface Response. The experimental results were used to built a neural network that is able to predict some process parameters once the designer has fixed the initial and final geometry of the specimen. The obtained results show that the laser bending of AISI 304 can be a valid alternative to conventional forming and prototyping techniques.
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