Laser cutting is a technology that uses a laser to cut materials, and is
typically used for industrial manufacturing applications, but is also starting
to be used by schools, small businesses, and hobbyists. Laser cutting works
by directing the output of a high-power laser most commonly through
optics. The laser optics and CNC (computer numerical control.) are used to
direct the material or the laser beam generated. A typical commercial laser
for cutting materials involved a motion control system to follow a CNC or G-
code of the pattern to be cut onto the material. The focused laser beam is
directed at the material, which then either melts, burns, vaporizes away, or
is blown away by a jet of gas,[1] leaving an edge with a high-quality surface
finish. Industrial laser cutters are used to cut flat-sheet material as well as
structural and piping materials.
History
In 1965, the first production laser cutting machine was used to drill holes
in diamond dies. This machine was made by the Western Electric
Engineering Research Centre. In 1967, the British pioneered laser assisted
oxygen jet cutting for metals. In the early 1970s, this technology was put
into production to cut titanium for aerospace applications. At the same
time CO2 lasers were adapted to cut non-metals, such as textiles, because,
at the time, CO2 lasers were not powerful enough to overcome the thermal
conductivity of metals.
Industrial Process
Laser cutting of steel with cutting instructions programmed through the
CNC interface Generation of the laser beam involves stimulating a lasing
material by electrical discharges or lamps within a closed container. As the
lasing material is stimulated, the beam is reflected internally by means of a
partial mirror, until it achieves sufficient energy to escape as a stream of
monochromatic coherent light. Mirrors or fiber optics are typically used to
direct the coherent light to a lens, which focuses the light at the work zone.
The narrowest part of the focused beam is generally less than 0.0125
inches (0.32 mm). In diameter. Depending upon material thickness, kerf
widths as small as 0.004 inches (0.10 mm) are possible. In order to be able
to start cutting from somewhere other than the edge, a pierce is done
before every cut. Piercing usually involves a high-power pulsed laser beam
which slowly makes a hole in the material, taking around 5–15 seconds for
0.5-inch-thick (13 mm) stainless steel, for example.
The parallel rays of coherent light from the laser source often fall in the
range between 0.06–0.08 inches (1.5–2.0 mm) in diameter. This beam is
normally focused and intensified by a lens or a mirror to a very Small spot
of about 0.001 inches (0.025 mm) to create a very intense laser beam. In
order to achieve the smoothest possible finish during contour cutting, the
direction of beam polarization must be rotated as it goes around the
periphery of a contoured workpiece. For sheet metal cutting, the focal
length is usually 1.5–3 inches (38–76 mm). Advantages of laser cutting over
mechanical cutting include easier work holding and reduced contamination
of workpiece (since there is no cutting edge which can become
contaminated by the material or contaminate the material). Precision may
be better, since the laser beam does not wear during the process. There is
also a reduced chance of warping the material that is being cut, as laser
systems have a small heat affected zone. Some materials are also very
difficult or impossible to cut by more traditional means.
Laser cutting for metals has the advantages over plasma cutting of being
more precise and using less energy when cutting sheet metal; however,
most industrial lasers cannot cut through the greater metal thickness that
plasma can. Newer laser machines operating at higher power (6000 watts,
as contrasted with early laser cutting machines' 1500 watt ratings) are
approaching plasma machines in their ability to cut through thick
materials, but the capital cost of such machines is much higher than that of
plasma cutting machines capable of cutting thick materials like steel plate.
TYPES
HACO fiber laser cutting machine with an integrated loading and
unloading system. Suited for cutting, boring, and engraving.
The neodymium (Nd) and neodymium yttrium-aluminium garnet (Nd:
YAG) lasers are identical in style and differ only in application. Nd is used
for boring and where high energy but low repetitions are required. The
Nd:YAG laser is used where very high power is needed and for boring and
engraving. Both CO2 and Nd/Nd: YAG lasers can be used for welding.
Common variants of CO2 lasers include fast axial flow, slow axial flow,
transverse flow, and slab.
CO2 lasers are commonly "pumped" by passing a current through the gas
mix (DC-excited) or using radio frequency energy (RF-excited). The RF
method is newer and has become more popular. Since DC designs require
electrodes inside the cavity, they can encounter electrode erosion and
plating of electrode material on glassware and optics. Since RF resonators
have external electrodes they are not prone to those problems. CO2 lasers
are used for industrial cutting of many materials including titanium,
stainless steel, mild steel, aluminium, plastic, wood, engineered wood, wax,
fabrics, and paper. YAG lasers are primarily used for cutting and scribing
metals and ceramics.
In addition to the power source, the type of gas flow can affect performance
as well. In a fast axial flow resonator, the mixture of carbon dioxide, helium
and nitrogen is circulated at high velocity by a turbine or blower.
Transverse flow lasers circulate the gas mix at a lower velocity, requiring a
simpler blower. Slab or diffusion cooled resonators have a static gas field
that requires no pressurization or glassware, leading to savings on
replacement turbines and glassware.
The laser generator and external optics (including the focus lens) require
cooling. Depending on system size and configuration, waste heat may be
transferred by a coolant or directly to air. Water is a commonly used
coolant, usually circulated through a chiller or heat transfer system. A laser
micro jet is a water-jet guided laser in which a pulsed laser beam is coupled
into a low-pressure water jet. This is used to perform laser cutting
functions while using the water jet to guide the laser beam, much like an
optical fiber, through total internal reflection. The advantages of this are
that
the water also removes debris and cools the material. Additional
advantages over traditional "dry" laser cutting are high dicing speeds,
parallel kerf, and omnidirectional cutting.
4000 watt CO2 laser cutter There are three main types of lasers used in
laser cutting. The CO2 laser is
Fiber lasers are a type of solid state laser that is rapidly growing within the
metal cutting industry. Unlike CO2, Fiber technology utilizes a solid gain
medium, as opposed to a gas or liquid. The “seed laser” produces the laser
beam and is then amplified within a glass fiber. With a wavelength of only
1.064 micrometres fiber lasers produce an extremely small spot size (up to
100 times smaller compared to the CO2) making it ideal for cutting
reflective metal material. This is one of the main advantages of Fiber
compared to CO2. Methods There are many different methods in cutting
using lasers, with different types used to cut different material. Some of the
methods are vaporization, melt and blow, melt blow and burn, thermal
stress cracking, scribing, cold cutting and burning stabilized laser cutting.
Vaporization cutting in vaporization cutting the focused beam heats the
surface of the material to boiling point and generates a keyhole. The
keyhole leads to a sudden increase in absorptivity quickly deepening the
hole. As the hole deepens and the material boils, vapour generated erodes
the molten walls blowing ejecta out and further enlarging the hole. Non
melting material such as wood, carbon and thermoset plastics are usually
cut by this method. Melt and blow Melt and blow or fusion cutting uses
high-pressure gas to blow molten material from the cutting area, greatly
decreasing the power requirement. First the material is heated to melting
point then a gas jet blows the molten material out of the kerf avoiding the
need to raise the temperature of the material any further. Materials cut
with this process are usually metals. Thermal stress cracking Brittle
materials are particularly sensitive to thermal fracture, a feature exploited
in thermal stress cracking. A beam is focused on the surface causing
localized heating and thermal expansion. This results in a crack that can
then be guided by moving the beam. The crack can be moved in order of
m/s. It is usually used in cutting of glass. Stealth dicing of silicon wafers
Further information: Wafer dicing The separation of microelectronic chips
as prepared in semiconductor device fabrication from silicon wafers may
be performed by the so-called stealth dicing process, which operates with a
pulsed Nd: YAG laser, the wavelength of which (1064 nm) is well adopted
to the electronic band gap of silicon (1.11 eV or 1117 nm).
Reactive cutting also called "burning stabilized laser gas cutting", "flame
cutting". Reactive cutting is like oxygen torch cutting but with a laser beam
as the ignition source. Mostly used for cutting carbon steel in thicknesses
over 1 mm. This process can be used to cut very thick steel plates with
relatively little laser power. Pulsing Pulsed lasers which provide a high-
power burst of energy for a short period are very effective in some laser
cutting processes, particularly for piercing, or when very small holes or
very low cutting speeds are required, since if a constant laser beam were
used, th
e heat could reach the point of melting the whole piece being cut.
Most industrial lasers have the ability to pulse or cut CW (continuous
wave) under NC (numerical control) program control.
Double pulse lasers use a series of pulse pairs to improve material removal
rate and whole quality. Essentially, the first pulse removes material from
the surface and the second prevents the ejecta from adhering to the side of
the hole or cut. Power consumption[edit] The main disadvantage of laser
cutting is the high power consumption. Industrial laser efficiency may
range from 5% to 45%. The power consumption and efficiency of any
particular laser will vary depending on output power and operating
parameters. This will depend on type of laser and how well the laser is
matched to the work at hand. The amount of laser cutting power required,
known as heat input, for a particular job depends on the material type,
thickness, process (reactive/inert) used, and desired cutting rate.
