Laser cutting uses a focused laser beam to heat and remove material from sheet metal or other materials. There are three main forms of laser cutting: fusion cutting, which melts and ejects material; sublimation cutting, which vaporizes material along the cutting seam; and photochemical ablation for organic materials. The key components of a laser cutting system are the laser generator, beam delivery system, nozzle for assist gas, motion unit, and exhaust. The laser beam is focused onto the workpiece with a coaxial gas jet assisting the removal of melted or vaporized material.

1. Laser Cutting
Archish Bharadwaj V S
20082202
B.E, Materials Science Engineering
CEG, AU

2. Introduction
• In laser cutting and drilling, the focused laser beam is directed
onto the surface of the work piece to rapidly heat it up,
resulting in melting and/or vaporization, depending on the
beam intensity and work piece material
• Lasers can be used to effectively cut metal plates of
thicknesses up to about 10 cm. The cut surfaces are roughly
parallel and straight edged.
• The total heat input required for laser cutting is relatively
small. This results in a small heat-affected zone size, of the
order of 0.1 mm.
• Laser cutting is used for both straight and contour cutting of
sheet and plate stock in a wide variety of materials.

3. Schematic of the laser cutting process

4. Forms of Laser Cutting
• The process of laser cutting can occur in one of
the three forms:
1. Fusion cutting.
2. Sublimation cutting.
3. Photochemical ablation.

5. Fusion cutting
• This involves melting of the base material, which is then
ejected using a high-pressure assist gas.
• The assist gas may be an inert gas, in which case the energy
for melting is provided entirely by the laser beam. It may also
be oxygen (or air), which reacts with the base metal, and the
resulting exothermic reaction provides additional energy to
enhance the process.
• A major problem of fusion cutting is the formation of striations
on the cut surface and dross (molten material that clings to and
solidifies on the underside of the cut edge) at the lower cut
edge.
• However, the fusion cutting process is more efficient,
requiring less energy per unit volume of material removed as
compared to the other methods.

6. Sublimation Cutting
• In sublimation cutting, the work piece material is vaporized
along the cutting seam.
• This is often achieved using a pulsed beam, and a jet of inert
assist gas that is coaxial with the beam is used to blow away
the vapor produced.
• It is limited to thin sections since more energy is required to
remove a unit volume of material as compared to the latter.
• However, it has the advantage of a narrower kerf width and
higher quality surface.
• Pulsed beams with high peak power may be necessary when
surface quality is critical.

7. Photochemical Ablation
• Organic materials, ceramics or difficult-to-cut materials in
general are normally cut by this method.
• Organic compounds tend to absorb ultraviolet radiation in an
efficient manner.
• The photon energy levels of lasers based on ultraviolet
radiation range between 3.5 and 6.5 eV which corresponds
with the energy levels required for molecular bonding.
• So, an organic material is irradiated with an ultraviolet beam,
absorbs the beam’s energy in a very thin layer near the surface,
of the order of submicrons thereby breaking the molecular
bonds, causing ablative decomposition of the irradiated area.

8. Contd…
• The process occurs almost instantaneously (about 20 ns
duration), and since the thermal conductivity of organic
materials is relatively low, the resulting edges are well defined,
with minimal thermal damage to the surrounding area.
• Thus the cut region is cleaner and smoother compared to that
obtained using CO2 and Nd:YAG lasers.
• The process is sometimes referred to as cold cutting since little
heat is generated

9. Components of a Laser Cutting
System
• The basic components of a cutting system are illustrated in
figure (next slide), include
1. The laser generator that produces the beam.
2. A beam delivery system for directing the beam to the
workpiece.
3. A nozzle assembly, usually integral with the focusing
assembly and coaxial with the beam, for directing the assist
gas to the workpiece.
4. A motion unit for providing relative motion between the laser
beam and theworkpiece
5. An exhaust for the waste material.

10. Components of a laser cutting system

11. Working
• The beam normally emerges from the generator horizontally
and is deflected vertically downward by a bending mirror.
• The beam is then focused by the lens onto the work piece. At
the same time, a gas jet is directed through a nozzle attached to
the tip of the focusing assembly, onto the work piece.
• A typical nozzle diameter is 1–2 mm and the delivery
pressures are normally maintained at about 3–4 bar (45–60 psi
or 0.3–0.4 MPa) in the gas jet nozzle for cutting thin materials
at high speeds.
• At high gas pressures, it is often necessary to use relatively
thick lenses that can withstand the pressure.

12. Contd…
• It is preferable to use reflective optics (mirrors) rather than
transmissive optics at high pressures (>10kW)
• The distance from the nozzle tip to the work piece surface is
typically maintained constant at about 0.3 mm to minimize
expansion of the gas flow.
• Directly opposite the nozzle, on the other side of the work
piece, an exhaust system is provided to absorb the transmitted
beam, molten debris from the cut, and exhaust vapors.
• This normally consists of a vacuum pump that draws the
exhaust to a disposal unit.

13. THANK YOU