108 Figure 6.5 Final bending angle remained after straightening (at 1 kW laser . power of and 0.8 m/min scanning speed) by three schemes for strips of different thicknesses and types: (a) as formed, (b) stress relieved and (c) annealed .
Introduction
Laser beam machining is used in the electronics industry for wire stripping and circuit cutting. In solid-state lasers, light energy is used as the pump source, while in semiconductor lasers, electrical energy is used as the pump source.
Laser Forming Process
Laser Bending
In aerospace industries, laser-based forming can be used to produce structures from aluminum and titanium. Although there is no comprehensive report in open literature on the existing share of laser forming in the manufacturing sector, information obtained in several research articles and a number of funded projects shows its increasing importance.
Laser assisted bending
Laser-assisted bending can also be used to bend brittle materials (Bammer et al. 2011, Xu et al. 2013). 2015) performed laser-assisted bending of sharp angles with small fillet radius on stainless steel sheets.
Laser Straightening
For the deformation of thin metal sheets, BM is used. The bending angle produced in BM lies in the range of 1°–. These values play an important role in the result of the simulation process. The temperature-dependent material properties of mild steel were taken from Zhang et al.
Application of Laser Bending and Straightening
Advantages and Disadvantages
High processing speed can be achieved by eliminating the flow time associated with the design, manufacture and placement of tools and dies. Fine control mechanisms make it highly energy efficient compared to other heat-based bending processes such as flame bending.
Scope of the Present Thesis
It is suitable for low and medium thickness, but high thickness sheet metal is not easy to bend. The workpiece materials used in this thesis have significant utility in various aspects of industrial applications.
Organization of the Thesis
The effect of laser power, scanning speed, number of laser passes and workpiece thickness are discussed. The process of laser-assisted bending with an electromagnet has been numerically modeled and good agreement with experimental results has been achieved.
Introduction
Laser Bending Mechanism
Temperature Gradient Mechanism
TGM is the most frequently occurring mechanism in most sheet metal bending cases. 2001), and Vollertsen and Rodle (1994) reported that the direction of bending is affected by laser beam diameter, scanning speed and workpiece thickness. The direction of bending is against the laser beam during cooling, which is the result of shrinkage and shortening of the material in the upper layers.
Buckling Mechanism
It was reported that with constant laser beam diameter and laser power, more bending occurred with longer irradiation time.
Upsetting Mechanism
Experimental study on Laser Based Bending and Straightening
- Effect of Process Parameters in Laser Bending and
- Material Processed by Laser Forming Process
- Effect of Laser Forming on Mechanical and Microstructural
- Edge Effect in Laser Bending Process
- Curvilinear Laser Bending Process
- Laser Straightening
The bending angle increases with increasing scan speed at higher power due to the resulting high temperature gradient (Barletta et al. 2006). Zahrani and Marasi (2013a) studied the relative variation of bending angle (RBAV) and concave depth of longitudinal distortion (CDLD) during laser bending.
Modelling of Laser Forming Process
- Analytical models on laser bending
- Numerical models on laser bending
- Soft Computing models
- Inverse Modeling
In general, the accuracy of prediction for analytical expressions ranges from about 10% to 50% to estimate the bending angle (Dixit et al., 2015). 2007b) established an analytical model for estimating the temperature field during laser forming using convection and radiation boundary conditions.
Optimization of Laser Forming Process
The Charpy impact value of raw strip was 166 J. The impact value was reduced to 148 J and 143 J for formed and stress-relieved straightened strip, respectively. The variation of the bending angle along the laser scanning direction (width direction) is called edge effect.
Major Gaps from the Literature
Scope and Objectives of the Present Thesis
Introduction
Details of the experimental setup, working procedure and methods, workpiece types and dimensions, laser parameters, type of work material were discussed. This chapter focuses mainly on methodology of the work; the research outcomes were reported in detail in subsequent chapters.
Experimental Study on Laser Machine and other Instruments
- CO 2 Laser Machine
- Optical profile projector
- Dial Indicator with magnetic base (Plunger type)
- Sample preparation
This chapter discusses all experimental setups and equipment used for experimental work (laser bending and pointing) as well as its finite element method (FEM) modeling. For laser bending, permanent magnet laser-assisted guidance, electromagnet for bending and laser guidance, special experimental installations were used.
Studies on Mechanical Properties of workpiece
Universal Testing Machine
Impact Testing Machine
Study on Metallographic Sample Preparation and Examination
- Precision Saw
- Sample Molding Press Machine
- Polishing Machine
- Optical Microscope…
- Scanning Electron Microscopy (SEM)
- Microhardness Testing
- Electric high temperature furnaces
In most cases, Vollertsen's formula overpredicts the bending angle due to a reduction in absorbency. The bending angle remaining after four laser passes is shown for different cases in Figure 6.6.
FEM Model of Laser Bending and Straightening
Thermal and Mechanical Properties of the Materials
Thermal and Mechanical Analysis
To avoid the rigid body motion, the clamped side of the subject was fully constrained in mechanical analysis (zero displacement and rotation). Convective heat transfer occurred between the subject and the surroundings after the laser beam irradiation.
Mesh sensitivity and time increment analysis
A relatively finer mesh was used in the zone between the laser scanning line and the free edge. As shown in Figure 3.15, the mesh sensitivity in the zone between the clamped side and the laser-irradiated zone was low and it was considered sufficient to have four distributions along the length.
Conclusion
Improving the efficiency of laser bending of mild steel by coating it with black enamel paint. The black spray paint gave the advantages of a rapid increase in bending angle due to its high absorption.
Experimental Plan
A commercially available black spray paint (EZMatch, Aerosol paint black.) was used on the workpiece surface before subjecting it to laser irradiation. The black spray paint is three times cheaper than the commonly used graphite spray.
Results and Discussion
High laser power and low scan speed (Case 1)
Effect of coating: Figure 4.1 shows a rapid increase in bending angle with application of black spray paint due to the fact that it increases surface absorption, keeps the surface safe from high force and makes the process more efficient. Thus by applying proper coating strategies, the desired bending angle can be obtained even with low power to make the process efficient and cost effective.
High laser power and high scan speed (Case 2)
Low laser power and high scan speed (Case 3)
Low laser power and low scan speed (case 4)
In the case of stress-relieved strips, no significant change in bending angle was observed. The bending angle increases with increasing laser power and decreases with increasing scan speed for a given applied current.
Comparative study on effect of coating for all cases
Comparison with Simulation Result
Conclusion
It should also be noted that the coating can only be applied once at the beginning of the bending processes, as there is no significant difference in the bending angle for CAAP up to the 4th pass. It was found that only in the low power and high speed case, the application of the coating after each pass results in a significantly larger bending angle compared to the other cases.
Introduction
If the desired accuracy in the bend angle is high and the model error is large, then the accuracy in the bend angle is achieved by increasing the number of passes. In each pass, the target bending angle is chosen taking into account the uncertainty in the prediction.
Problem definition
Strategy for Choosing the Process Parameters of Line Heating
On the next pass, the target bend angle becomes (B–a) ormax, whichever is lower. This procedure is repeated until the total desired bend angle is achieved with the prescribed accuracy.
Experimental Verification of the Strategy
For Mild Steel (AH36)
For Aluminum Alloy (5052-H32)
For Stainless Steel (SS304)
Improving the Strategy with Experiential Learning
For simplicity, the error for both sides of the most likely estimate can be taken as the maximum. The following expression can be used for the probability of obtaining a prediction within the error range of the model:.
Estimation of Coefficient of Proportionality (k p )
The change in kp value with the number of passes to achieve a smaller bending angle of 2° is also shown in Figure 5.4 for aluminum alloy (5052-H32), mild steel (AH36) and stainless steel (SS304) plates. Thus, in the case of a smaller bending angle, the value of kp fluctuates with increasing number of passes.
Conclusion
Later, the model prediction error was taken as ±20% for estimating the reduction in the number of passes for a required bend angle. The bending angle in a laser pass was between 2.5° and 3° for steels, but less than 1.6° for aluminum alloy due to its high reflectivity and thermal conductivity.
Introduction
A study of the effect of laser beam geometries on laser bending of sheet metal by the bending mechanism. Numerical and experimental investigation of laser forming process, Journal of Materials Processing Technology, Vol.
Laser Assisted Straitening Setup
Results and Discussion
Validation of FEM simulation …
A few simulations were performed for some selected cases (9 simulations) considering Scheme 1 (4 continuous laser passes) to compare the bending angle and workpiece profile with the experimental result.
Selection of laser scan scheme
Angle reduction during annealing
A set of experiments was performed to determine the effects of laser power, scan speed, and scan sequence. The full factorial experimentation was chosen to predict the effect of parameters on laser alignment.
Effect of laser power and scan speed for as-formed
It is worth noting that at a laser power of 1000 W and a scanning speed of 800 mm/min, it was possible to completely align a 1.5 mm thick strip.
Effect of laser power and scan speed for stress-relieved
The perfect straightening, with no remaining bend angle, took place at a laser power of 900 W and a scanning speed of 800 mm/min for 1 mm strips. For a 1.5 mm strip, perfect straightening occurred at a laser power of 1000 W and a scanning speed of 800 mm/min.
Effect of laser power and scan speed for sub critically
The stress-relieved specimens showed significant improvement over previous experiments on formed steel in both result and process. The final shape of the profile in the case of stress-relieved and annealed specimens was either straight or straight with a very small increasing step (Type 3 and Type 2 in Figure 6.4).
Microhardness Tests
At a fixed laser power of 900 W, the hardness value decreases with increasing scanning speed from 800 mm/min to 1000 mm/min (Figure 13a). Due to the stress relief action, the hardness value increased compared to the steel that was formed.
Microstructure evolution
The transition from base material to laser irradiated area with transition in grain size can be clearly seen in Figure 6.17 b. The laser irradiated area (Figure 6.18 c) consisted of smaller grains compared to base material area with an average grain size of 27 µm.
Tensile and Charpy Impact Tests
Intelligent System Design and Engineering Application (ISDEA), 2010 International Conference on, Vol. 3D laser forming of saddle shapes. A numerical study of the temperature gradient mechanism in laser forming using different laser beam geometries.
Conclusion
Introduction
Various process parameters such as laser power, scan speed, laser beam spot diameter and number of scans have a great influence on the process. In addition, due to the effect of magnetic force, the final bend may vary during reading, which may affect the accuracy of the process.
Magnetic Force Measurement Based on Current and Air Gap
Development of the electromagnet
In this work, an electromagnetic force is used to assist the laser bending and guiding process. The objective of this work is to achieve the desired bending and direction by suitable laser assisted bending process.
Electromagnetic force measuring setup
The material of the core is similar to the non-grain oriented electrical steel used in electrical machines. The free end is connected to a scale, while the other end of the scale is attached to the arm of the tripod as shown.
Experimental Plan
Due to the electromagnetic force, the free end was pulled and the force displayed on the digital scale was recorded. The laser beam was irradiated at a distance of 100 mm away from the free edge (the middle of the strip).
Results and Discussion
- Magnetic Force Result Based on Current and Air Gap
- Validation of FEM with Experimental for Bending
- Edge Effect
- Microhardness Evaluation
- Result of Laser Assisted Straightening
The laser scanning speed has a significant effect on the bending angle when the laser power and applied current are constant. The variation of the bending angle with laser power, scan speed and applied current for 1.5 mm and 2 mm thick tape is shown in Table 7.3.
Conclusion
Electromagnetic power assisted laser straightening was much more efficient than conventional laser straightening due to the reduction in the number of laser passes. Another encouraging observation about the proposed electromagnetic force-assisted laser bending is that it can be simulated with reasonable accuracy.
Introduction
Overall Conclusion
It was difficult to achieve a bending angle of less than 0.1° with the laser on steel. At high power, low scan speed, and higher magnetic strength, the bending angle reached saturation after the plate was clamped by the magnet.
Scope for Future Work
Effects of clamping in the laser forming process, Journal of Manufacturing Science and Engineering, Vol. Analysis and synthesis of laser forming process using neural networks and neuro-fuzzy inference system.
