LASER BEAM MACHINING

Laser beam machining (LBM) is a non-traditional

subtractive manufacturing process, a form of

machining, in which a laser is directed towards the

work piece for machining.

This process uses thermal energy to remove

material from metallic or nonmetallic surfaces.

The laser is focused onto the surface to be worked

and the thermal energy of the laser is transferred

to the surface, heating and melting or vaporizing

the material.

Laser beam machining is best suited for brittle

materials with low conductivity, but can be used

on most materials.

APPLICATIONS

WORKING

Laser beam is focused on the work piecematerial, to remove the unwanted material fromthe work piece by heating often. In the laserbeam machining the metal removal rate mustdepend on the wave length used in the lasermachine.

The punch is a light

beam

WORK MATERIALS

METALS WITH HIGH HARDNESS AND STRENGTH

SOFT METALS

CERAMICS

GLASS AND GLASS EPOXY

PLASTICS

RUBBER

CLOTH

WOOD

LASERS

GAS LASERS : An electric current is liberated from a gas to generate a consistent light. Some of the

most commonly used gases consist of; He-Ne, Ar, and CO2. Fundamentally, these gases act as a

pumping medium to ensure that the necessary population inversion is attained.

SOLID STATE LASERS : They are designed by doping a rare element into various host materials.

Unlike in gas lasers, solid state lasers are pumped optically by flash lamps or arch lamps. Ruby is

one of the frequently used host materials in this type of laser. A Ruby Laser is a type of the solid

state laser whose laser medium is a synthetic ruby crystal. These ruby lasers generate deep red light

pulses of a millisecond pulse length and a wavelength of about 694.3 nm. The synthetic ruby rod is

optically pumped using a xenon flashtube before it is used as an active laser medium.

EXCIMER LASERS : The state is different than in solid state or gas lasers. The device utilizes a

combination of reactive and inert gases to produce a beam. This machine is sometimes known as

an ultraviolet chemical laser.

LASER CHARACTERISTICS

APPLICATION TYPE OF LASER

Large holes upto 1.5 mm dia.

Large holes (trepanned)

Small holes > 0.25 mm dia.

Drilling (punching or percussion)

• Ruby, Nd-glass, Nd-YAG

• Nd-YAG, CO2

• Ruby, Nd-glass, Nd-YAG

• Nd-YAG, Ruby

Thick cutting

Thin slitting of metals

Thin slitting of plastics

• CO2 with gas assist

• Nd-YAG CO2

Plastics Metals Organics

Non-metal Ceramics

• CO2

• Nd-YAG, ruby, Nd-glass

• Pulsed CO2

• Pulsed CO2, Nd-YAG

LASER CONSTRUCTION

Gas lasers can be axial flow, as shown in fig.

9.6.12, transverse flow and folded axial flow.

The power of a CO2 laser is typically around

100 watt per meter of tube length.

Thus to make a high power laser, a rather

long tube is required which is quite

inconvenient.

For optimal use of floor space, high-powered

CO2 lasers are made of folded design.

CO2 LASER.

LASER CONSTRUCTION

The flash tube is operated in pulsed mode by charging

and discharging of the capacitor.

Thus the pulse on time is decided by the resistance on

the flash tube side and pulse off time is decided by the

charging resistance. There is also a high voltage switching

supply for initiation of pulses.

SOLID-STATE LASER.

LASER CONSTRUCTION

ND-yag laser is pumped using flash

tube. Flash tubes can be helical, as

shown in fig. 9.6.10, or they can be flat.

Typically the lasing material is at the

focal plane of the flash tube. Though

helical flash tubes provide better

pumping, they are difficult to maintain.

ND-YAG LASER.

CUTTTING DEPTH

The cutting depth of a laser is directly proportional to the quotient obtained by dividing the power of

the laser beam by the product of the cutting velocity and the diameter of the laser beam spot.

t ∝ P/vd

t ≡ Depth of cut

P ≡ laser beam power

v ≡ cutting velocity

d ≡ laser beam spot diameter.

The depth of the cut is also influenced by the workpiece material. The material’s reflectivity, density,

specific heat, and melting point temperature all contribute to the lasers ability to cut the workpiece.

PROCESS

In the process the negatively charged electrons are rotates around the positively charged nucleus in

the specified orbital path. Based on the variety parameters like atoms, electrons, electron structure,

plus the presence of electromagnetic field the radii and the geometry of orbital paths are changes. The

energy of the orbital must be related to the single energy levels.

At the zero level condition the atom is considered at the ground level, this is because all the electrons

occupy the lower potential energy. From the external sources, the ground level electrons absorb some

energy to stimulate high stage. At the elevated temperatures the electronic vibrations are increased,

and in chemical reactions they absorb energy from the photons which are external sources. The

electrons are moving from the lower to higher energy level.

PROCESS

When the electron reaches the higher energy level, at that instance we observe the unstable band of

energy. By releasing the photons within a short time, it reaches the ground level. So the process is

known as the spontaneous emission. The existing photon and the emitted photon have the same

frequency.

In some conditions the energy state changes the positions of the electrons into the metastable energy

band. In a material if the electrons are pumped to the higher metastable state, and are compared to

the atoms present in the ground state where the phenomenon is known as population inversion.

They are returned to the ground level in the form of rush, moved

by a photon of appropriate energy or frequency which is called as

stimulated emission.

If the photon is stimulated with a suitable energy at such instance the electron moves down to the lower energy

state, and comes to the original position. This emits photon by recreation having some longitudinal phase and

progressive phase which is available. Coherent laser beam is created in this way.

ADVANTAGES

Since the rays of a laser beam are monochromatic and parallel it can be focused to a very small

diameter and can produce energy as high as 100 MW of energy for a square millimeter of area.

It is especially suited to making accurately placed holes.

Laser beam machining has the ability to engrave or cut nearly all materials, where traditional cutting

methods may fall short.

The cost of maintaining lasers is moderately low due to the low rate of wear and tear, as there is no

physical contact between the tool and the workpiece.

The machining provided by laser beams is high precision, and most of these processes do not

require additional finishing.

Laser beams can be paired with gases to help the cutting process be more efficient, help minimize

oxidization of surfaces, and/or keep the workpiece surface free from melted or vaporized material.

DISADVANTAGES

The initial cost of acquiring a laser beam is moderately high.

There are many accessories that aid in the machining process, and as most of these accessories are

as important as the laser beam itself the startup cost of machining is raised further.

Handling and maintaining the machining requires highly trained individuals.

Operating the laser beam is comparatively technical, and services from an expert may be required.

Laser beams are not designed to produce mass metal processes. For this reason production is

always slow, especially when the metal processes involve a lot of cutting.

Laser beam machining consumes a lot of energy.

Deep cuts are difficult with workpieces with high melting points and usually cause a taper.

APPLICATION

Lasers can be used for welding, cladding, marking, surface treatment, drilling, and cutting among

other manufacturing processes.

It is used in the automobile, shipbuilding, aerospace, steel, electronics, and medical industries for

precision machining of complex parts. Laser welding is advantageous in that it can weld at speeds

of up to 100 mm/s as well as the ability to weld dissimilar metals.

Laser cladding is used to coat cheep or weak parts with a harder material in order to improve the

surface quality.

Drilling and cutting with lasers is advantageous in that there is little to no wear on the cutting tool

as there is no contact to cause damage.

Milling with a laser is a three dimensional process that requires two lasers, but drastically cuts costs

of machining parts.

Lasers can be used to change the surface properties of a workpiece. Laser beam machining can also

be used in conjunction with traditional machining methods. By focusing the laser ahead of a cutting

tool the material to be cut will be softened and made easier to remove, reducing cost of production

and wear on the tool while increasing tool life.