LIST OF TABLES
CHAPTER 2: LITERATURE REVIEW ON LASER BENDING PROCESS
2.6 Materials Processed by Laser Bending Process
The laser bending process can be applied to a wide range of materials including metals, non- metals, composites, plastics and ceramics. Researchers studied laser bending of various materials useful to the manufacturing industry, such as low or high carbon steel, high strength steel, stainless steel, aluminum alloys, titanium alloys nickel alloy, plastics. Table 2.2 summarizes the studies carried out in the laser bending.
With the recent developments in computer hardware and advanced simulation software, a number of researchers used numerical methods as a tool to simulate the laser bending of various materials such as metals, metal–matrix composite and non-metals (Cheng and Lin 2001, Chan and Liang 2001, Hu et al. 2001, Hu et al. 2002, Shichun and Zhong 2002, Zhang et al. 2002, Zhang et al. 2004, Zhang and Michaleris 2004, Hsieh and Lin 2004a, Liu et al.
2007). Chan and Liang (2000a) studied the deformation behavior of Al6013/SiCp aluminium matrix composite sheets during the laser bending process. A smaller bend angle was obtained when the laser scanning direction was parallel to the rolling direction of the sheet in comparison with that obtained during transverse scanning to the rolling direction. Similar results were obtained by Chan and Liang (2000b) for two aluminium based metal matrix composites, viz.
Al2009/20 vol% SiCw and Al2009/20 vol% SiCp. Chan and Liang (2001) studied the influence of reinforcement with 15% and 20% volume fraction of SiC particles on the coefficient of thermal expansion and bend angle on two metal-matrix composites (Al2024/15SiCp and Al2024/20SiCp).
Brittle materials such as ceramics and the materials with low formability, viz. aluminum oxide, glass, cast iron are difficult to form with conventional tools and dies since cracks may generate on the worksheet during the mechanical bending operation. The brittle materials like single crystal silicon, mono-crystalline silicon, borosilicate glass, aluminum oxide Al2O3, silicon, etc. have been deformed by researchers using laser bending process (Wu et al. 2010a,b).
Okamoto et al. (2004) investigated the bending of plastic specimen with the Nd:YAG laser beam. Zhang et al. (2004) used low power lasers, including the continuous wave (CW) CO2
laser, the Nd:YAG laser with a nanosecond pulse width and the fiber laser, to study the bending behaviors of ceramic, silicon and glass. They found that the bend angle over 1° can be obtained with higher laser power and multiple scans. Wang et al. (2011) studied laser bending of a single
Table 2.2. Summary of selected studies on the laser bending of various materials.
Reference Material Specimen
size (mm) Remarks
Akinlabi et
al. 2014 Mild steel 200×50×3
It was observed that the number of scans, scan speed, laser power, beam diameter and cooling effect has a contribution of 32%, 27%, 21%, 18% and 2% respectively on the bend angle.
Kgomari and Mbaya
2010
High strength
steel (A715) 3.5 mm thickness
A correlation was developed between microstructure and mechanical properties for both laser and mechanical forming.
Chen et al.
1999 Stainless steel
AISI 301 10×0.8×0.1 Using a beam expander, a line shape laser beam was used to bend the worksheet.
Gisario et
al. 2011 Aluminum alloy,
AA 6082 T6 19×69×2 Spring-back control was investigated for the laser assisted bending process.
Chen et al.
2002
Titanium alloys, Ti ‒ 6Al ‒ 4V
50×40×1 Effect of scanning path curvature on the laser bending process was investigated.
Akinlabi
2013 90×30×1 Titanium alloy was successfully bent.
Okamoto et al. 2004
Plastics, high density polyethylene
20×5×1 Deformation mechanism of the plastic material was studied under the laser bending process.
Wu et al.
2010a Silicon Sheet 20×5×0.1‒0.3 A large bend up to 40° was produced.
Wu et al.
2010b
borosilicate glass and Al2O3
10‒20×3‒
20×0.15
It was observed that an elevated substrate temperature needs to be applied to prevent the brittle fracture. The glass cannot be bent with Nd:YAG laser.
Chan and Liang 2000b
Al6013/SiCp
aluminium matrix
10 mm width, 0.32 mm thickness
Studied the effect of reinforcement on bend angle.
Shen et al.
2009 metal/ceramic
bilayer 50×37.5×0.6 Numerically studied laser bending of the metal/ceramic bilayer material.
Carey et al.
2007 Fibre metal
laminates 100×100×0.15
Studied the effect of various parameters on the laser bending of glass fibre based fibre metal laminates.
Size is given in the order as length×width×thickness (mm)
crystal silicon sheet of 0.2 mm thickness with the Nd:YAG laser. The mechanism of pulsed laser bending of thin silicon sheet was a hybrid mechanism of TGM and BM. A bend angle of up to 6.5º was achieved in silicon sheets with six laser scans. Xu et al. (2013) investigated the laser bending of the silicon sheet. They studied the bending mechanism of the brittle materials.
It was observed that when the temperature is higher than the brittle–ductile transition threshold, the plastic deformation takes place and the sheet bends permanently.
Chen et al. (1998) produced deformation in the stainless steel and ceramic specimens with a precision of the order of tens of nanometers using a pulsed laser beam. The authors suggested that the process is suitable for removing distortions on magnetic head components to achieve a better contact between the magnetic disk head and the hard disk surface. Tam et al. (2001) used laser micro-bending process for fine adjustment of the bearing surface curvature of ceramic magnetic sliders. Zhang et al. (2001) studied the micro-scale bending of ceramic, silicon, and stainless steel samples using pulsed and continuous wave (CW) lasers. They observed that for similar stress affected zone, the CW laser produced more bending than the pulsed laser. However, the pulsed laser caused less surface composition change and thermo- mechanical damage to the specimens in comparison with that obtained for CW laser. In addition, the bend angle becomes larger with the increase in number of laser scans, once the temperature gradient in the scanning area is large enough. Matsushita (2003) used laser micro- bending technology for roll and pitch angle adjustment of the magnetic head suspension and air bearing surface adjustment of the magnetic head slider. Zhang and Xu (2005b) described a laser forming based technique to adjust curvatures of silicon micro-cantilevers used for chemical and biological detection. They were successful to adjust the curvatures by an amount of 3.5 μrad in cantilevers of dimension of length 110 μm, width 13 μm and thickness 0.6 μm.
Ming et al. (2010) described the manufacturing of metallic micro-structures using lasers. Micro grid array structures were replicated on a metallic foil surface with high spatial resolution at micron levels.
Observations
A number of materials including metal, non-metals, ceramics and composites are successfully bent by laser irradiations. However, some important materials including magnesium alloys, beryllium alloys, composites, corrugated structures, functionally graded materials, smart materials and plastics are not investigated for the laser bending process. These are to be explored in detail by carrying out numerical as well as experimental investigations.