A novel, patent pending nozzle assembly enables faster changeover between assist gases in laser processes that use different gases for piercing and for cutting or trepan drilling.
In QCW fiber laser cutting of high strength low alloy (HSLA) steel, for example, the best and most consistent quality is achieved using compressed air for piercing and oxygen for cutting the profile of a hole, slot, or other feature.
High-pressure compressed air allows for fast consistent piercing using LASERDYNE SmartPierce™. With this pierce point, low-pressure oxygen is the ideal assist gas to produce dross free cuts with minimum taper and at the highest speeds while minimizing operating costs.
It Starts With Piercing
|Figure 1: Prima Power Laserdyne standard
coaxial cutting nozzle for high power
QCW fiber laser cutting
No matter the material type and thickness, the laser cutting operation starts with a piercing process. The quality of the pierce point governs the overall quality of the cut.
High power QCW fiber laser cutting using a standard Prima Power Laserdyne cutting nozzle (Figure 1) and oxygen assist gas gives cut quality that is acceptable in terms of dross and taper. It also gives competitive cutting speed.
Piercing with oxygen, on the other hand, has proven to be difficult and unsuitable for cutting thick HSLA steel, particularly when striving for fast pierce times and spatter free pierces.
While repeatable pierces with oxygen are achieved using low laser peak power, this comes at a high cost in terms of cycle time (0.54 seconds for 8 mm thick material). Furthermore, spatter quickly accumulates on the cover slide that protects the lens making this process impractical.
A faster, more reliable process uses high-pressure compressed air. Compressed air is relatively low cost and produces minimal spatter.
Next Is Cutting
Once the pierce is complete, the laser and process parameters are changed to cutting with oxygen. Low-pressure oxygen helps to produce dross free cuts at the highest rates for a given average laser power.
The downside of this process – high pressure, compressed air piercing and low-pressure oxygen cutting – is the time to purge the gas lines required for consistent cutting after the pierce. With a traditional assist gas configuration, the time for changeover of gases between piercing and cutting is a minimum of two seconds. Even with a change to the assist gas hardware, the time for changeover is still 0.7 seconds.
While this may not seem like much time, multiply it by hundreds of features and the total time is quite significant – hours per day of unproductive time.
|Figure 2: Dual assist gas laser cutting
nozzle (Patent Pending). Compressed air
is delivered non-coaxially while
low-pressure oxygen is delivered coaxially.
This wasted time is nearly eliminated by providing a nozzle assembly containing both coaxial and directional non-coaxial assist gases (Figure 2). Directional non-coaxial gas – in this example, compressed air – gives protection to the optics while delivering gas needed for piercing. Meanwhile, coaxial gas – in this case, oxygen – provides assistance during cutting.
The process based on this dual gas nozzle is robust as demonstrated through cutting of thousands of holes. It has already lead to reductions in cycle time of about 30%.