Laser cutting of metal has been around for a couple of decades now, but there still appears to be some confusion of which laser is suitable for which application. Alan Johnson investigates.
While metal can be successfully cut using plasma or oxy cutting machines, when it comes to accuracy and consistency it has to be a laser cutting machine, but which one – fibre or CO2?
However, David McHugh, MD of LMC Lasers, says companies shouldn’t compare laser, oxy or plasma as they all have a place in the metalworking world.
"If you want to measure it with a tape measure you cut it with a plasma or oxy machine, if you want to measure it with a vernier you cut it with a laser.
"For example, if you were cutting 16-20mm steel plate for a lamp post, which is going to be buried in concrete, a standard oxy profile machine, with plus or minus 0.5mm accuracy, will be ideal," McHugh told Manufacturers’ Monthly.
While he admits the latest plasmas have improved, he says some of the manufacturers’ claims are a little ambitious when they compare them to lasers and certain profiles.
"These high-definition plasma machines are excellent, but try and cut a finely detailed saw blade with a plasma; you just can’t do it.
"Also as the plasma nozzles and tips wear, the angle of the cut changes, dross increases and over the arc hours quality falls off.
"While with a laser, I can cut a part today then cut the same part one year later, and it will be exactly the same," McHugh said.
Plus he says the latest technology advances have made laser cutters even more suitable for lights-out-manufacturing.
"To date, the problem has been the limited range and types of materials that can be cut because the machines could only change focal length lenses and nozzles manually.
"They might be able to cut 2mm, 3mm and 4mm mild or similar, but nothing else. You can change so many parameters of the machine automatically, but not enough to go from 1mm mild to 10mm stainless.
"But you can now, for example we have just sold a machine to a company here in Melbourne with the full lights out automatic load/unload, automatic nozzle alignment, nozzle changer, and head changer.
"That means he will be able to go from 1mm mild to 10mm stainless with no human intervention.
McHugh describes it has a significant step. "We call the lights out automation Bytrans (a material storage load/unload system) and Bysort (removes the cut parts from the skeleton). Both are available on a number of our machines."
He predicts these types of machines will get more popular as manufacturers recognise the financial benefits of lights-out-manufacturing and full scale automation.
"Now you have the ability to go from 1mm mild steel to 10mm stainless steel, for example, without human intervention. These types of machines are designed to run 24 hours a day.
"We also now have 6kw laser machines which can cut 25mm thick steel plate as a daily function," McHugh said.
But for thinner materials, 3mm and under, he says a fibre, high-pressure nitrogen cutting machine might be appropriate.
"They are good on stainless steel, aluminium, copper and brass and all those materials that are highly reflective to the 10.6 micron CO2 wave length. In fact they will cut some of those materials faster than a 6kW machine will.
"The fibre machines we sell will cut up to 12mm mild steel however the problem with them is it’s such a small spot size, with very high energy concentration and very narrow kerf, making it more difficult to cut with oxygen as the assist cutting gas. But it is wonderful for high pressure nitrogen cutting of stainless and aluminium,
"We recently sold a fibre laser cutting machine, a wonderful piece of machinery, with very efficient with low power consumption.
"Only 2kW, but the fineness of the focal point, something like 10x smaller than a CO2 spot size, makes the energy concentration excellent," McHugh said.
Dr Fraser Dear, Product Line Manager with UK-based SPI Lasers, agrees that single mode fibre lasers have very small spot sizes, but says in many applications this is a positive feature that enables the application through the very high power density achievable or the resolution of the process.
"There are however many ways to achieve a larger spot size with a fibre laser if needed," Dr Dear told Manufacturers’ Monthly.
"Many fibre laser manufacturers will either supply or recommend optics components such as beam expanding and reducing telescopes which when combined with delivery optics can achieve a range of spot size configurations.
"In addition to this, multi-moded fibre delivery systems are available which increase the spot size significantly and allow many of the processing parameters of existing systems to be replicated.
"In some cases such as precision welding and marking, beam scanning solutions can be implemented where the beam is scanned across the surface of a part which can replicate a larger spot than achievable with an unmodified beam," Dr Dear said.
When it comes to operating costs; Dr Dear says the cost of fibre lasers has reduced to the point where the differences with CO2 technology are now increasingly marginal.
"And when the running costs of such systems are taken into account the differences can be significant.
"In order to generate laser output a CO2 source requires a number of high purity gas supplies, in addition to regular recharging of the laser cavity. In addition to this a high level of cooling is required to keep the internal chamber and optics cool.
"The optics themselves require maintenance and alignment and are not insignificant consumables from a financial perspective.
"Finally the energy efficiency of conversion from electrical input to optical output is in the region of 5-10%. When considering the higher power CO2 systems, this low conversion efficiency and subsequent high cooling requirements can lead to high energy costs per laser source.
"This may seem very low but laser systems are available with efficiencies in single digits simply due to complexity in generation of laser light and losses with the optical system," Dr Dear said.
As well, he says fibre laser sources essentially have no periodic maintenance consumable costs.
"The optical source is a monolithic structure in that there is no free space propagation of the light. This means that there is no alignment or maintenance of any optics as these are written into the optical fibre using fibre bragg gratings
"However, clearly in respect to the particular process being conducted, consumables may be required such as shield/processing gas."
While Dr Dear is a strong advocate for fibre lasers, he recognises they are not ‘the’ laser for all applications.
"There will always be applications for lasers operating within specific areas of the industry where a process is wavelength dependent or requires pulse parameters currently unavailable with fibre laser systems
"The advent of the fibre laser was revolutionary for the laser market as from a user perspective it offers significant benefits over a great number of the existing laser technologies.
"There is no question that the introduction of the fibre laser was disruptive to a number of the laser industries such as Nd:YAG and CO2, however it has taken time for the legacy systems to either reach their natural life and/or the users demand higher performances from their laser solutions."
Looking into his crystal ball, Dr Dear says short pulse and ultra short (fs) pulse lasers are increasingly being used in early stage process development but they still suffer from high capital cost and technology complexity.
"Longer wavelength fibre lasers, if they could be manufactured cost effectively, would address the eye safety concerns that remain one of the key differences between high power IR and NIR lasers," Dr Dear said.