2 used as components for micro-systems. Two process methods commonly used for the
fabrication of high aspect-ratio micro-structures are based on direct micro-machining with a frequency CO
2
carbon dioxide laser and Nd: YAG neodymium-doped yttrium aluminium garnet laser using nanosecond pulse widths. CO
2
lasers are an excellent alternative to the traditional methods of engraving or marking metal process. CO
2
laser marking has substantial advantages against Nd: YAG laser marking in terms of speed,
and the cost of maintenance. Etching or marking metal with CO
2
lasers provides many advantages over etching, engraving, and marking with contact implements like scribers or
manual laser laden process like electro chemical etching [1].
1.2 Problem Statements
This research will focus on a study about micromachining using CO
2
laser machine in order to analyze the width of etching using different setup of parameters. In particular,
the study will evaluate the influencing machining parameters such as cutting speed, power and gas pressure to the surface finish.
1.3 Objectives of the Research
There are several objectives that will be achieved in this study. Those include: a
To conduct a literature study on CO
2
micro machining process. b
To assess the parameters affecting the CO
2
micro machining process. c
To analyze the mechanism, behavior and characteristic of CO
2
laser machine. d
To design an experiment in order to determine the significant of the parameters. e
To analyze the outcome of laser applications on the surface material Grade 43A of mild steel.
3
1.4 Scope
The focus of the study is on the CO
2
laser characteristic and properties. The study will be conducted by performing an experiment with diverse parameters in order to explore
different of result on mild steel’s surface. The characteristic of the etched surface will be
analyzed in order to determine the relationship between the cutting parameter with the resulting etched surface.
4
CHAPTER 2
LITERATURE REVIEW
2.1 Fundamental Principle of Laser
Figure 2.1: Energy states of Laser Active Medium
The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation which is a device that emits light through a specific mechanism [2]. A typical
laser emits light in a narrow, low-divergence beam and with a well-defined wavelength corresponding to a particular color if the laser is operating in the visible spectrum [3].
A laser consists of a gain medium a material containing gas, liquid, solid or free electrons with appropriate optical properties inside an optical cavity that supplies energy
to the gain medium. In its simplest structure, a cavity consists of two mirrors arranged
5 such that light bounces back and forth, each time passing through the gain medium. One
of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror. The gain medium transfers external energy into the laser
beam. The gain medium is energized, or pumped, by an external energy source.
The pump energy is absorbed by the laser medium, placing some of its particles into high-energy quantum states. When energy is applied to a laser active medium Fig. 2.1
electrons are raised to an unstable energy level then spontaneously decay to a lower relatively long-lived metastable state. Electrons in this state will not spontaneously return
to their ground energy level; therefore it is possible to pump large amounts of energy into the material thus obtaining a population inversion in which most of the atoms are in a
metastable state. If the phenomenon can be multiplied, we arrive to the fact that the percentage of atoms with high energy levels will be superior to the percentage of atoms
in normal state [4]. This phenomenon is known as population inversion. Devices where
light from an external source is amplified are normally called optical amplifiers [5].
After this population inversion has been achieved, lasing action is initiated by an electron which spontaneously returns to its ground state producing a photon. If the photon
released is of exactly the right wavelength it will stimulate an atom in a metastable state to emit a photon of the same wavelength Stimulated Emission.
The optical cavity contains a coherent beam of light between reflective surfaces so that the light passes through the gain medium more than once before it is emitted from the
output aperture or lost to absorption. As light circulates through the cavity, passing through the gain medium, if the gain in the medium is stronger than the resonator losses,
the power of the circulating light can rise exponentially [4]. Many of these stimulated
photons will be lost when they hit the side of the lasing medium. However if the photons travel parallel to the long axis of the optical cavity they will continue to stimulate
emissions of photons having the same wavelengths which combine coherently until they reach the mirrored ends of the optical cavity.
6 When the beam strikes the totally reflecting mirror in the optical cavity the beam is
reversed and continues to stimulate emissions of photons which increase in intensity until the beam reaches the partially reflecting surface of the optical cavity. A small portion of
the coherent light is released while the rest is reflected back through the lasing medium to continue the process of stimulating photons. Laser radiation will continue to be produced
as long as energy is applied to the lasing medium.
2.2 CO
