A technical and commercial comparison of fbre laserand Co2 laser cutting Part 2:

This is the second part of the article releases in International Metalworking News for Asia’s December 2013 issue of Laser Technologies, titled: A technical and commercial comparison of fbre laser and CO2 laser cutting. To give you a recap, the previous article ended with a background information of CO2 laser cutting machine and how fbre and disk laser technologies are direct extension of Nd:YAG lasers.

The choice

First of all we need to establish a level playing feld – and the most obvious leveller is purchase price. A 5 kW CO2 laser cutting machine costs about the same as a 3kW fibre one, so we will investigate a comparison between these two types.

There are enough interlinked criteria involved in the direct choice of the two types of machine to drive anyone crazy. Fortunately the big laser cutting machine manufacturers have begun to generate genuine comparative information rather than useless ‘fastest speeds’ data and I am grateful for the information supplied to me by both TRUMPF and Bystronic in the preparation of this paper.

Although the detailed data can be confusing, there are only two basic considerations for the laser user; how expensive will it be to produce my parts? And is the cut quality good enough? If we are comparing two machines which involve similar capital investment, the expense of the parts is highly dependent on the time it takes to make them – and the costs per hour of running the machine.

Cutting speeds

At frst glance the production time must be related to the cutting speed – and, in the past, the sales people have concentrated on a comparison of the highest speed at which the laser can cut any given material. But this fgure isn’t that useful in a general engineering context – for the same reasons that the top speed of your car has very little impact on how fast you can drive from one side of town to the other.

A 3 kW fbre laser can cut 1 mm thick stainless steel at about 30 m/min (20 ips) and a 5 kW CO2 machine will only achieve about one third of this speed. However – if you are cutting typical job shop components the speed advantage of the fbre laser might only result in a 25% – 50% increase in productivity rather than the hoped for 300%. This is because the machines spend most of their time accelerating, decelerating and stopping to pierce the material. Videos are now available from TRUMPF and Bystronic which demonstrate this point very clearly and show that the speed differential gets progressively smaller as the complexity of the cut part increases. Other work by Bystronic also makes the point that machine acceleration rates are just as important as laser type if you need the fastest production times. This is particularly true when cutting thin section materials – where a high acceleration (but more expensive) cutting machine attached to a CO2 laser can beat a fbre laser attached to a lower acceleration machine.

So – fbre lasers are considerably faster than their CO2 counterparts when cutting thin section material in large simple shapes – like refrigerator doors for example. When assessing the purchase of a machine for this type of job it is important to remember that the overall job time includes the changeover time from sheet to sheet. If you are cutting a full sheet of steel into two refrigerator doors in 3 minutes, the speed of the sheet changeover mechanism might have a considerable effect on production costs.

As material thicknesses increase to 4 mm (0.16 in) the cutting speeds of both lasers start to convePrime Hype DF 2016 EP