Laser Cutting Machines by nikeborome


									Laser Cutting Machines
Courtesy: GSI Lasers

Laser Cutting Basics
Laser cutting is the process of using a laser to cut materials, usually in industrial manufacturing. Laser
cutting works by directing the output of a high power laser, and focussing it to a small spot on the
material to be cut. The material then either melts or vapourises. Removal of molten material is
achieved by using a relatively high pressure assist gas. As the beam moves relative to the material a
cut channel (the kerf) is formed, having an edge with a high quality surface finish.

Laser Cutting Market
In 2008, 29% by revenue of all lasers were sold for use in Materials Processing applications,
amounting to over $2 billion in systems revenue. This is by far the largest application area for non-
diode lasers (which are mainly used for communications and storage applications). Of all the units
sold into industrial laser applications, 22% are used for laser cutting applications, and the vast
majority of these are used for the cutting of metal sheets. This is a global market, with 45% of the flat
sheet cutting systems being sold into Asia, 37% to Europe and 17% to North America.

Cutting Machine Basics
A laser cutting system has three major sections:

The Laser:
The type of laser is chosen dependant on the material, its thickness and the size of the parts to be cut.
For fine cutting in thin metal sheets a Fiber Laser will offer the finesse needed. In thicker metal sheets
a high power fast axial flow CO2 laser will provide the speed needed for economic processing. For
non-planar metal components where a robot might be employed for 3D cutting an Nd:YAG solid state
laser utilising Fibre Optic Beam Delivery will be the laser of choice. For plastic, textile and wooden
components a sealed CO2 laser (either DC or RF excited) will provide a very economic cutting

The Beam Delivery:
The laser beam is transmitted to the focusing head via a series of mirrors or through an optical fibre.

The focusing, or cutting head uses a lens to focus the beam down to a spot down to 10µm in case of
fine Fiber Laser cutting up to a few hundred microns in the case of thicker section high power CO2
laser cutting. The focused laser beam will vaporize and or melt a small area of the work piece.

A pressurized gas, or "assist gas", will be introduced beneath the lens, coaxially with the laser beam,
to push the molten material out of the cut zone.

The Motion system:
Various configurations are used to provide the relative motio between the focussed laser spot and the
workpiece to allow the desired cut path to be followed.
Overview of Industrial Laser Cutting System Types
There are generally three different configurations of industrial 2D laser cutting machines based on the
way that the laser beam is moved over the material to be cut or processed: Moving material, Hybrid,
and Flying Optics systems. For all of these, the axes of motion are typically designated as the X and Y
axes, for the long and short direction of travel respectively. If the height of the cutting head over the
workpiece may be controlled, it is designated as the Z-axis.

Moving material lasers have a stationary cutting head and move the material under it. This method
provides a constant distance from the laser generator to the work piece and a single point from which
to remove cutting effluent. It requires fewer optics, but requires moving the work piece, which can be
an issue for large or heavy items.

Hybrid lasers provide a table which moves in one axis (usually the X-axis) and move the head along
the shorter (Y) axis. This results in a more constant beam delivery path length than a flying optic
machine and may permit a simpler beam delivery system. This can result in reduced power loss in the
delivery system and more capacity per watt than flying optics machines.

Flying optics systems feature a stationary table and a cutting head (with laser beam) that moves over
the work piece in both of the horizontal dimensions. Flying-optics cutters keep the work piece
stationary during processing, and often don't require material clamping. The moving mass is constant,
so dynamics aren't affected by varying size and thickness of work piece. Flying optics machines are
the fastest class of machines, with higher accelerations and peak velocities than hybrid or moving
material systems.

Flying optic machines must use some method to take into account the changing beam length from
near field (close to lase output) cutting to far field (far away from laser) cutting. Common methods for
controlling this include collimation, adaptive optics or the use of a constant beam length axis.

The above is written about X-Y systems for cutting flat materials. The same discussion applies to five
and six-axis machines, which permit cutting formed work pieces. In addition, there are various
methods of orienting the laser beam to a shaped work piece, maintaining a proper focus distance and
nozzle standoff, etc.

For 3D cutting applications the Process Head from a solid state Nd:YAG laser can be mounted on an
industrial robot. Full flexibility in the movement of the robot is provided by using a Fibre Optic Beam
Delivery system.

Specific Types of Cutting Systems
Flat bed plastics/textiles/wood
These systems are generally of the moving optic type. They range
from table-top sized systems using low power CO2 lasers, to
systems with cutting area of 2 x 3m using higher powered sealed
off DC CO2 lasers. The photograph shows a typical system of this

2D Flat Bed Metal Cutting
This is the biggest sector for cutting systems with around 3000
systems being sold per year , with most of these being of the
moving optic type, though some of the systems for larger sheets are
of the hybrid type.
The CO2 laser flat bed cutters typically use a 5” (127mm) or 7.5” (190mm) focal length lens. These
produce a 0.2mm to 0.4mm spot size on the work piece. For cutting of materials more than a mm or
so in thickness, focussing to a very small spot size does not help as the kerf is too small for ejection of
molten material and to allow separation of the parts.

Metal cutting speeds for a given laser depend on the edge quality required, and on the thickness and
type of material. Typically cuts will be at a few m/min for material around 6mm thick, increasing to
around 10m/min for 2mm thick steel.
Most of the sheet metal applications can be addressed with a system using a 2kW to 4kW CO2 laser.
Due to their better beam quality a slab laser will have a faster processing performance to a similarly
powered fast axial flow laser.

Interestingly the Fiber Laser is beginning to penetrate the flat sheet m cutting sector for millimetre
type thicknesses which has long been the total preserve of CO2 lasers. Only a few systems have been
installed so far this application, but it does indicate how the Fiber Laser is penetrating mature laser
metal processing applications.

For thinner sheets (sub-mm thickness) Fiber Lasers are well established as the laser of choice. A
particular application they have adressed is cutting solder paste screens used in manufacture of
printed circuit boards. Typically these screens are made from 0.2mm thick Stainless Steel.

The advantages of the Fiber Laser in cutting applications are generally better efficiency, lower
consumable costs and mch lower process gas cost than using a CO2 laser.

The Fiber Laser is maturing rapidly as a technology for use in all aspects of metal fabrication from
high finesse to thick section, and easily covers the typical job shop application areas. This shows that
its transition from its scientific and low power telecoms heritage into the metal fabrication arena is
real and will only strengthen in the coming years.
Tube cutting systems
Specialised tube cutting systems are now available for use with round, oval and rectangular section
tubes. Generally they are of the Hybrid type, where the tube is rotated under the laserbeam, which
will move along the tube in the cut ing area.

A special type of tube cutting machines are directed at the
manufacture of medical stents used in the treatment of blocked
arteries. These are made from small diameter (~1mm) tubes, either
of stainless steel or Nitinol (a ‘memory metal’). They demand very
high precision cutting with fine features and low levels of dross
from the cut. Dedicated systems for this application provide high
accuracy cutting using a fixed beam delivery point and rotating and
fedding the tube longitudinally through the laser focus.

Robot Cutting
In the applications above the parts have an essentially flat cutting area. This does not cover all parts to
be cut, and there are growing number of 3D components to be cut. In these areas the use of a robot
arm to direct the output from a solid state laser fed through a fibre optic beam delivery system offers
unparalled flexibility. The ability to easily integrate with existing robots is particularly attractive to
the automotive industry as it allows capital investment to remain relatively low while providing
versatility and redeployment for future needs.

Hydroformed Cutting
Hydroformed and rectangular cross-sectio tubes have become popular for new truck and sport utility
vehicle (SUV) frames, engine cradles, roof pillars, and suspension members. The ability to achieve
high stiffness, exotic shapes, and minimal weight from these structures could drive their appl cations
to even more platforms.

For the manufacturer, the challenge is in cutting these closed tubes with only single-sided access. In
the past, the members were produced from folded and spot-welded assemblies that could be punched
easily with conventional tooling as flat sheet before forming. Laser robotic cutting cells with fiber-
delivered laser beams have been helpful in this area, and end users also are looking to laser robot
systems for option holes, short-run production, and prototype systems in sheet metal parts.
Remote Cutting
A new cutting format that has become available with the advent of excellent beam quality fiber lasers
with reasonable power levels, is the use of a galvanometer scan head to enable the very high speed
cutting of thin metal sheets and foils over a scan area of order 100mm square.

This type of application is limited to thin sheets because there is no possibility to introduce the high
pressure assist gas usuallly employed in cutting operations, which is vital for clearing the dross from
thicker section kerfs.

Typically a Scan Head Systems has been used with lasers for marking applications, and so the scan
head driver software and interfaces have been optimised for these applications. Using these
applications directly in remote cutting applications does not produce the optimum cycle times, but
system driver software that has knowledge of the laser performace parameters, as well as the scan
head characteristics will produce the fastest processing times.

Laser Glass Separation
Laser Glass separation (also sometimes called Zero Width Cutting) is a special cutting technique for
thin sheet glass, often used in the manufacture of LCD, TFT and PDP screens. Generally these cutting
systems are of the flying optic design of 2D cutting, but have the added complication of the need for a
water mist spray to be following the cutting head. Thus the cutting head arrangement must be rotated
round as the direction of cutting changes.

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