Introduction
The geometry of the beam on temperature gradient mechanism dominates process significantly controls the bending angle, radius of bending edge (radius of curvature) and edge effect (Jamil et al. 2011b). The laser beam diameter is one of the key energy control parameters. There are two classes of FSP— the Volume FSP (VFSP) that affects the full thickness and the Surface FSP (SFSP) that affects the material to about 2 mm depth from the surface (Nascimento et al. 2009).
Laser Bending
Application of Laser Bending
Advantages and Disadvantages
The process can be used to achieve precise, accurate and small bend angles, especially microbending, which may not be possible with mechanical bending. It can be used for bending small parts required for miniaturization as well as large parts for the aerospace and shipbuilding industries.
Scope of the Present Thesis
Organization of the Thesis
For mass production, the laser bending process is not recommended due to its slow operation compared to the traditional punch and die technique. The effect of various process parameters such as laser power, scanning speed, laser beam diameter, number of laser passes, thickness and width of the workpiece is discussed.
Introduction
Laser Bending Mechanism
Temperature gradient mechanism
It is generated when the diameter of the laser beam is much smaller compared to the thickness of the workpiece. 2002) and Kant and Joshi (2012a) observed that the diameter of the laser beam, the scanning speed and the thickness of the workpiece affect the bending direction. TGM works in the following two steps, namely heating and natural cooling of the workpiece:.
Buckling mechanism
At constant laser beam diameter and laser power, sheet blanks bent more for longer irradiation time. Higher laser beam diameters (about 10 times the plate thickness) enabled buckling mechanism for laser forming.
Upsetting mechanism
The bending angle decreased with increasing relative density, average cell size and sheet thickness. The bending angle decreased by and 12.3%, when the relative density increased by 40%, the sheet thickness by 100% and the average cell size by 66.6%, respectively. The bending angle was highest in the middle of the workpiece along the scanning direction.
Material Processed by Laser Forming Process
Carbon steel
Dearden and Edwardson (2003) generated 3-D complex shaped in the mild steel plate by using Nd:YAG, Q-switched laser. 2008) investigated the bending angle in laser forming of cold-rolled grade 1008-1012 steel using continuous wave fiber laser. Safari and Farzin (2013) studied laser bending of custom mild steel blanks using continuous wave CO2 laser at the maximum power of 2 kW.
Stainless steel
Laser bending of TGM and BM was studied for multipath and multiscan irradiation. Shen and Yao (2009) conducted a detailed investigation on the mechanical properties of low carbon steel sheets after laser bending.
Aluminum and aluminum alloys
The length of the subject had little influence on the bending angle (Chen et al. 2004b). It was also observed that the bending angle was reduced with the increase of the thickness.
Aluminum foam
Nickel alloy
1998) observed that the bending angle of thin A42 nickel alloy steel sheet increases linearly with increasing number of irradiations. 2015) studied the laser bending of prestressed thin-walled nickel microtubes. There is minimal thinning on the extrudates, which is useful for bending thin-walled microtubes.
Brittle materials
Laser bending of Al2O3. ceramics were very sensitive to processing parameters; however, bending angles greater than 2 can be obtained. Titanium alloys are extremely difficult to bend due to their brittleness. 2017) studied the laser-assisted bending of Grade-2 titanium sheets.
Magnesium and magnesium alloys
2010b) studied the laser bending of three different brittle materials, borosilicate glass and Al2O3 ceramics, using continuous wave CO2 laser irradiation and monocrystalline silicon with Nd:YAG pulsed laser irradiation. Sharp bending angles (>140°) with small rounding radii could be obtained. 2016) improved spring effect by external force laser-assisted sheet bending of titanium alloys.
Plastics
Curvilinear Laser Bending Process
It was obtained by different process parameters, namely the pitch of the spiral path, the number of spiral paths, the in-to-out spiral path and the reverse out-to-in spiral path.
Process Parameters in Laser Bending
- Effects of laser power
- Effects of scan speed
- Effects of laser beam diameter and geometry
- Effects of number of laser passes
- Effects of workpiece geometries
- Effects of absorptivity on laser bending
- Effects of thermal properties
- Effects of mechanical properties
- Effects of force cooling
- Effects of external load
- Effects of clamp
The temperature variation between the top and bottom surfaces of the workpiece increases with the decrease of the laser beam diameter. Barletta et al, 2006 The bending angle improved by applying a suitable coating in the scan line of the workpiece.
Edge Effect in Laser Bending Process
They investigated the effect of process parameters, namely laser power, scanning speed, laser beam diameter, workpiece thickness, and scan path position from the free edge of the workpiece on RBAV and CDLD. As the heating position decreased from the free edge of the workpiece, the CDLD decreased, but there was no effect on RBAV.
Process Modelling of Laser Forming Process
- Analytical models on laser bending
- Numerical models on laser bending
- Soft computing models
- Inverse modelling
In this section, a brief overview of the analytical model of the linear laser bending process is presented. Romer and Maijer (2000) calculated the power density profile of the laser beam using inverse analysis.
Process Optimization of Laser Forming Process
Eideh and Dixit (2013) used inverse estimation by measuring temperature at two locations based on heuristic methods. The goal was to minimize the total error between predicted and measured temperatures at two locations. 2013) estimated workpiece absorbency based on a combined approach of experimental and simulation results.
Effect of Laser Forming on Mechanical and Microstructural
The effects of laser forming on microstructural properties
The effects of laser forming on mechanical properties
Major Gaps from the Literature
Scope and Objectives of the Present Thesis
Experimental and numerical investigation of single and multi-pass laser bending of strips is carried out to evaluate the bending angle. Experimental study and FEM simulation study are planned for laser bending of friction tube welded plate.
Introduction
Chemical Compositions of the Materials
Field Emission Scanning Electron Microscopy
For high-resolution, high-magnification imaging, a cold field emission (FE) gun gives the best results. Field emission scanning electron microscopy (FESEM) gun emits the electron from a much smaller area than SEM, which helps to get better magnification, resolution and image quality.
Experimental Study on Laser Machine and other Instruments
- CO 2 laser machine
- Sample preparation
- Temperature measuring instrument
- Coordinate measuring machine (CMM)
Thermocouple and pyrometers were used to measure experimental temperature from the underside of the workpiece at different laser process parameters. Similarly, pyrometers were used to measure the temperature of aluminum alloy (5052-H32) on the underside of the workpiece.
Study on Mechanical Properties of Workpiece
Universal testing machine
Bending test applies tensile stress in the convex side of the specimen and compressive stress in the concave side. After the specimen was placed in the fixture, the upper surface was convex and the lower surface was concave.
Study on Metallographic Sample Preparation and Examination
- Precision hack saw
- Sample molding press machine
- Polishing Machine
- Optical microscope…
- Microhardness testing
- Non-contact profilometer
All samples were polished with 400‒2000 grit silicon carbide abrasive paper and finally polished on velvet cloth using 1 m aluminum MicroPolish particles (Fig. 3.15). The surface roughness of the base material and friction stir-processed samples before laser irradiation was measured using a non-contact 3D optical surface profilometer (Make: Taylor Hobson®; Model: CCI-Lite).
Experimental Setup of Friction Stir Welding (FSW) and Friction
Fabrication of friction stir welding and processing tools
For the preparation of friction tube welded plates, the shoulder diameter of the tool was taken as 15 mm and the pin diameter as 5 mm to prepare friction tube welded plates. On the other hand, cylindrical tool without pin was used for friction stir processing (FSP).
Preparation of sheets by friction stir welding and friction stir
In case of FSW, it was found that the surface defect free joints could be produced by selecting four levels of traverse speeds namely and 132 mm/min for 1500 rpm tool rotation speed. Therefore, the throughput speed was reduced to 22 mm/min, which could achieve flawless welding.
FEM Model of Laser Bending
Thermal and mechanical properties of the materials
Although temperature-dependent material properties are available, some batch-to-batch variation may occur. The temperature-dependent material properties of mild steel and stainless steel were taken from Zhang et al.
Thermal and mechanical analysis
In this work, an inverse procedure was used to determine temperature-dependent properties of aluminum alloy (5052-H32). To avoid the rigid body motion, the clamped side of the subject was fully constrained in mechanical analysis (zero displacement and rotation).
Mesh sensitivity and time increment analysis
As illustrated in Table 3.2, mesh sensitivity study was performed by varying the mesh size and comparing the simulation time with the bend angle. The results of laser-assisted bending using magnetic force for fine meshes are shown in Table 3.10.
Measurement of Edge Effect and Springback Effect
The edge effect
For all workpiece thicknesses (1 mm, 1.5 mm and 2 mm), 3 elements were taken in the thickness direction. According to this meshing scheme, the total number of elements generated in the model was 32,400.
Springback effect…
Conclusion
Name of Specimens Name of Machine Used to Cut Specimen Name of Test Name of Instrument Used to Test Specimen Result/Output Yield Result.
Introduction
For the Fourier number in the range 6.6-6.8, the bending direction was uncertain, i.e. sometimes positive and sometimes negative due to dominance of buckling mechanism. The aim of this work is to evaluate the effect of laser power, workpiece geometry (length and width), laser spot diameter and type of heat source (stationary and moving heat sources) on the bending angle of the small workpieces.
Experiment and FEM Simulation
For each specimen, 5 mm length was used for clamping on one side of the specimen parallel to the scanning direction. The total warm-up time depends on the scanning speed and the width of the workpiece.
Results of Experimental and Numerical Studies
Effect of laser power
In the case of the moving heat source, the bending angle was negative for the range 100200 W. In the case of the moving heat source, the bending direction was negative for the laser power 100 W250 W.
Effect of laser beam diameter
Here, for a laser beam diameter of 8 mm, the bending angle was very small and the bending was away from the heat source (negative) for both the stationary and moving heat sources, as shown in figure. The bending direction was negative in the range of 100 W 150 W laser power, but the plate started to bend in the positive direction after 150 W for a stationary heat source.
Edge effect
For 250 W laser power, the bending angle deviation between stationary and moving heat source was approx. 2° and the bending angle was the maximum at the center of the bent workpiece in both experimental and simulation results (Fig. 4.5 a). For 100 W laser power, the bending angle was larger in the center of the subject in both experimental and simulation results.
Temperature Distribution by Simulation
The Fourier number was calculated at different laser powers, for the workpiece with a size of 25 mm 20 mm 2 mm, a laser beam diameter of 4 mm and a scanning speed of 20 mm/s. For laser power in the range of 100–250 W, the bending angle direction of the workpiece was away from the laser source (negative bending).
Conclusion
A bending angle of about 2.5 could be achieved with a moving heat source and 4.5 with a stationary heat source. With a stationary heat source, the bending angle is more uneven across width (along the scan direction) compared to a moving heat source.
Introduction
Experimental and numerical studies are conducted to explore the insight of the process parameters in terms of bending angle, edge effect, temperature distribution, stress, plastic deformation, flexural strength, microhardness and microstructure during single and multi-pass mode of operation.
Experiment and FEM Simulation
Experimental setup and procedure
Microhardness tests were performed on a microhardness tester (Make: Buehler; Model: Micromet-2101) in the transverse direction (perpendicular to the thickness and scanning direction) and in the mid-thickness of the bent workpiece. The hardness was measured using the microhardness tester of (Fig. 3.17) with an input force of 500 gf and a dwell period of 20 seconds.
Design of experiment
FEM simulations
Results and Discussion
- Experimental and FEM results
- Microhardness
- Flexural test
- Main effects of factors on bend angle and flexural strength
- Microstructure
The bending angle increased with the increase in the number of passes due to preheating of the workpiece in the previous pass. 5.7 (a), (c) and (f), the bending angle is found to increase with increase in the number of passes, laser power and width.
Conclusion
As the number of laser passes increased, the average grain size of the laser-irradiated strip decreased. The average grain size increased with laser irradiated strip thickness for a given set of laser parameters.
Introduction
In this work, instead of one pyrometer, two pyrometers were used to measure the temperature of the sheet at two locations in the experiment, as was done by Eideh and Dixit (2013) to estimate thermal parameters. The procedure of how to measure the temperature using two pyrometers has been described in detail in Chapter 3, Section 3.3.3.
Methodology for Inverse Estimation of Material Properties
Heuristic algorithm for optimization
If the new root mean square error (RMS) new is greater than the old root mean square (RMS) old, then keep the old point as the current point. If the new root mean square error (RMS)new is less than the old root mean square (RMS)old, then the current point is accepted as the center of current cell.
Determination of mechanical properties
Results for Inverse Determination of Material Properties
Laser bending was performed on raw, cement-coated and friction-stirred aluminum alloys (5052-H32) and mild steel sheets (AH36) shown in Fig. The surface roughness of the friction stir treated plates was measured with a non-contact optical profilometer.
Result and Discussion of Laser Bending in Friction Stir Weld
Tensile test results
The data used in simulation for weld zone provided in Table 6.4 is for room temperature. All tensile tests show that the failure occurs in the weld zone due to reduced strength and thinner diameter of the welded zones. 2008) also found that after surface friction stirring of aluminum alloy 5052-H32 sheets, its ductility improved in the stirring zone, but the strength decreased.
Fracture test
Validation of FEM Result
This was due to the greater distance at the welding zone in the former case. When the scan was performed across the welding direction, the bending angle in some cases increased with increasing weld thickness.
Conclusion
It was observed that the welding conditions (tool rotation and welding speed) in friction stir welding have a profound influence on the bending behavior. The smaller variability in results as well as closeness to simulation provided confidence in the robustness of the laser bending process for bending friction stir welded sheets.
Introduction
In particular, the effect of the process parameters on microstructure development (Morisada et al. 2007), deformation behavior and improvement of mechanical properties (Tewari et al. The previous research showed that the cement coating provides much better absorption capacity compared to graphite grease and lime coating (Singh et al.
Experimental Procedure
Therefore, the laser bending of friction stirred plates is compared with that of cement-coated plates for aluminum alloy (5052-H32) and mild steel (AH36). Model: 8801J4051) as shown in Fig. For the hardness test, all laser-irradiated base plates (raw) and friction stir-worked plates were polished with silicon carbide sandpaper with a grit size of 400-2000.
Results and Discussion
- Tensile strength
- Surface roughness
- Bend angle
- Microhardness
- Microstructure
Twelve measurements were made per sample on friction stir processed area along the width (tool traverse) direction. The 3D non-contact optical profilometer image of friction stir processed skin is shown in Fig.
Conclusion
Introduction
Details of Experiment
Neural Network Modelling
Selection of training and testing data set for MLP neural
Implementation of MLP neural network
Selection of training and testing data set for RBF neural
Implementation of RBF neural network
Upper and lower bound estimation
Results and Discussion
Validation of FEM model
Results of neural network model
Parametric study
Inverse analysis
Conclusions
Introduction
Procedure of Experiments
Preparation of magnetic and nonmagnetic workpiece
Measurement of magnetic force
Experiments on laser assisted bending
Result and Discussion
Measurement of magnetic force
Validation of FEM model
Simulation results
Edge effect
Simulation of evolution of the bend angle with time
Microhardness
Temperature distribution
Conclusion
Introduction
Effect of Laser Parameters on Bending of Small Sized Sheet
Effect of Single and Multi-pass on Laser Bending of Mild Steel
Effect of Laser Parameters as well as Welding Parameter on Laser
Effect of Laser Absorptivity on Bending of Friction Stir Processed
Laser Assisted Bending by Mechanical Load
Laser Assisted Bending by Magnetic Force
Overall Conclusion
Scope for Future Work
