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CNC Laser Cutting
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The St. Ann's Sheet Metal Company, based in
Nottingham, has been trading since 1960. In this time we have built up a
reputation as a quality orientated sheet metal company in materials, workmanship
and customer support recognised by ISO 9002 accreditation, to achieve this we
use state of the art technology combined with a
determination to succeed, thus enabling us to give our customers a highly
competitive advantage.
Apart from our precision laser cutting service, St Ann’s Sheet Metal specialise
in light to medium fabrication work, CNC punching and bending facilities. We can
also offer competitively priced precision machining, quality powder coating and
plating processes. St. Ann's Sheet Metal are able to satisfy customer needs
efficiently and competitively. |
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Why Choose Laser
Cutting / Laser Profiling? |
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No
tooling cost-
Rapid prototyping-
Greater accuracy-
Quick turn around
The virtues of these services have been promoted fairly rigorously since the process started
to take off as a sub contract service around twenty five years ago.
One of the more important advantages is that of time (and
therefore cost) saving. The need for hard tooling is eliminated and this can
save many thousands of pounds and several weeks delay. Modifications can be made
instantly.
A large amount of work would, at one time, have been carried out
by gas cutting. It does not cause distortion through heat, it leaves
a clean edge and is able to include holes and cut outs of (almost) any shape and
size. It also provides customers with a consistent product that can, in
most cases, be integrated immediately into their product. The fact that standard
tolerances are around 20 percent of those for gas cutting is
an added bonus to many customers and not a strict requirement.
Our sheet metal cutting machinery provides a range of benefits to our
customers:
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In comparison with punching it gives a
superior edge finish that requires no de-burring or finishing.-
Intricate detail & marking are all possible.-
Lasers can cut complex shapes without the
need for tooling.-
Speed is comparable or faster than other
profile cutting methods.-
Localised heat distortion is reduced.-
A polished edge finish can be achieved on
stainless steel using a nitrogen assist gas.
This is a technology that has been used
in industry since the 1970's. The first common application was for sign-making,
mainly cutting acrylic. Since then the process has been adopted and adapted by
virtually every industry group, and is now a significant process in every
manufacturing economy.
The reasons for popularity of this service include:
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The accuracy of the cut part achievable-
The repeatability and consistency of the
process-
The level of detail achievable-
The range of materials which can be
processed-
The speed of the process-
The cost of parts-
The ease of changing parts (particularly
when compared to hard tooling etc)-
The lack of physical contact during the
process-
The small heat affected zone
Laser cutting machines can accurately produce
complex exterior contours. The laser beam is typically 0.15 mm (0.006 in)
diameter at the cutting surface with a power of 1000 to 2000 watts.
It can be complementary to the CNC/Turret process. The CNC/Turret process
can produce internal features such as holes readily whereas the laser process can produce external complex features easily.
It takes direct input in the form of electronic data from a CAD
drawing to produce flat form parts of great complexity.
Lasers work best on materials such as carbon steel or stainless steels. Metals
such as aluminium and copper alloys are more difficult to cut due to their
ability to reflect the light as well as absorb and conduct heat. This requires
lasers that are more powerful.
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The minimum radius for slot corners is 0.75
mm (0.030 in). Unlike blanking, piercing, and forming, the normal design
rules regarding minimum wall thicknesses, minimum hole size (as a percent of
stock thickness) do not apply. The minimum hole sizes are related to stock
thickness and can be as low as 20% of the stock thickness, with a minimum of
0.25 mm (0.010 in) for up to 1.9 mm (0.075 in). Contrast this with normal
piercing operations with the recommended hole size 1.2 times the stock
thickness.-
Burrs are quite small compared to blanking
and shearing. They can be virtually eliminated when lasers are used and
further, eliminate the need for secondary deburring operations.-
As in blanking and piercing, considerable
economies can be obtained by nesting parts, and cutting along common lines
using state of the art CAD software.
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How does Laser Cutting work?
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It works by melting, burning or vaporising the material, while an
assist gas is employed to "clear" the cut zone of the molten / burnt material or
the gas vapour. In the early days the setting of the laser to
produce the desired effect was very much a manual process and very complex.
The cutting process is very complex, but basically involves pre-piercing the
material outside the area of desired cut, moving the laser beam into the cutting
area to apply heat, and finally use an assist gas to remove the heated material
and produce the cut. The type of assist gas employed is critical, and is
dependent on the material to be laser cut; most commonly used are Oxygen (used
predominantly for carbon steels), Nitrogen (used for non-ferrous steels &
non-metals) and Argon (used for more exotic materials such as titanium), but we
also have the capability to cut in Compressed Air on most materials 2mm thick or
under.
The latest machines now come with many of the common parameters pre-programmed,
allowing much easier setting. However, the variations in batches of material
lead to serious issues in cut quality, and operators still require many hours of
training to run a laser efficiently and economically
Industrial machines are predominantly used to cut parts from
flat-sheet material. However, there are machines specially adapted to cut
tubular components, and multi-axis lasers used to cut pre-formed components. |
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Limitations When Using on Sheet Metal |
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The
cut-edge quality achievable depends on the type of material
and the thickness. As the thickness increases the striations on the cut-edge
become more prominent. Striations are lines on the cut-edge where the molten
zone meets the cool zone.
These striations affect the tolerance achievable. For example, in 2mm mild steel
we would offer +/-0.1mm accuracy. In 10mm steel the repeatable tolerance would
increase to +/-0.2mm, and at 20mm we would be maintaining +/-0.4mm.
Because a laser is made up of photons, parts of its energy can be reflected away
by materials such as aluminium and copper alloys. These materials are also
thermal conductors, meaning they distribute incoming heat more evenly throughout
their volume. For this reason, carbon alloy and stainless steel are popular work
piece materials. They are poor at absorbing heat, so heat is
concentrated into the laser's path more readily. Because the beams used in
cutting are "class 4" lasers, the machines are designed to ensure that human
operators are never exposed to them directly. All the cutting is done inside the
machine.
Other limitations include the maximum thickness we're able to
cut (see the chart above), the amount of detail achievable (it depends on the
thickness and material type - please ask us), and the types of materials
(particularly some plastics) we are unable to cut due to health & safety issues.
Despite the numerous advantages of laser profiling, it is not always the
most appropriate or most cost-effective method of producing a sheet metal blank.
CNC Punching is a cost effective way of making components out of sheet metal.
CNC Punching machines have lower capital cost than lasers and they do not use
electric power to nearly the same extent (nor do they have the need for various
cutting gases). It is also true that no laser machine can compete with punching
in the speed of producing a large number of similar holes or slots.
CNC Punching machines have lower capital cost than lasers and they do not use
electric power to nearly the same extent (nor do they have the need for various
cutting gases). It is also true that no laser machine can compete with punching
in the speed of producing a large number of similar holes or slots. Equally,
some jobs do not require the fine edge finish provided by laser. CNC punching
can therefore sometimes offer a viable and economical alternative.
The abbreviation CNC stands for computer numerical control, and refers
specifically to a computer "controller" that reads G-code instructions and
drives a machine tool, a powered mechanical device typically used to fabricate
components by the selective removal of material. CNC does numerically directed
interpolation of a cutting tool in the work envelope of a machine. The operating
parameters of the CNC can be altered via software load program.
In a production environment, a series of CNC machines may be combined into one
station, commonly called a "cell", to progressively machine a part requiring
several operations. CNC machines today are controlled directly from files
created by CAM software packages, so that a part or assembly can go directly
from design to manufacturing without the need of producing a drafted paper
drawing of the manufactured component. In a sense, the CNC machines represent a
special segment of industrial robot systems, as they are programmable to perform
many kinds of machining operations. |
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www.saintanns.co.uk |
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