Process Calculator Provides For Even More Efficient Process Development
What began as a tool used by Prima Power Laserdyne Applications Engineers in their CW and QCW fiber laser process development projects is now being made available free of charge to users of LASERDYNE systems.
The calculator, which runs in Microsoft Excel, helps process engineers and laser system operators more efficiently develop new processes as well as better understand the likely impact of changes made to existing processes.
Parameters for 2-4 kW CW fiber lasers and 3-20 kW QCW fiber lasers are available options in the ‘Laser’ menu.
The calculator began as a tool used by Prima Power Laserdyne Applications Engineers in their process development projects. Soon, they found themselves using it to answer questions frequently asked by users of LASERDYNE systems such as:
- “What is the depth of focus for a 200 mm focal length lens?” or
- “What pulse rate should I use for cutting 3 mm thick stainless steel at 300 mm/ minute?”
Still wondering if you can make use of the calculator? Following are some examples to help you decide.
Developing laser drilling parameters
Prima Power Laserdyne Applications Engineers often use the calculator to define a set of laser and process parameters that gets them “into the ballpark” before they go onto the laser machine to finish developing a new process. For drilling applications, their goal is to minimize time on the machine to produce the correct size and quality of hole.
Experience will provide an idea about the energy and peak power density required to produce a quality hole of a given length. For example, a recent article about controlling cracking in laser drilling Hastelloy X documented a relationship between crack length and peak power.
With starting values for pulse energy and peak power, the process calculator provides a tool for determining the optics configuration that will give the correct hole diameter and peak power density. It is also used to identify other laser parameters.
Laser cutting process development
The process is similar for cutting applications, though the range of parameters can be quite different based on the application requirements. For example, in some applications, the main goal is speed (cycle time) with edge finish of secondary interest.
On the other hand, there are also many cutting applications (for example, cutting vane slots in stator rings) that require precise control of the cut edge finish and heat input given the intricacy of the pattern and precision required of the finished part.
Using the calculator, the first step in the process is to select a laser source from the menu. Next, the user enters a value of peak power within the limits of the laser and the particular type and thickness of material being cut.
Following this, the focal point position is specified. The focal point position for cutting is typically related to the type of assist gas used for the application. For oxygen-assisted cutting, the focal point will usually be located at the top surface of the material (Defocus = 0), whereas the focal point will be located into the material (Defocus = a negative fraction of the material thickness) for nitrogen-assisted cutting.
The focused beam diameter is automatically calculated from the optics configuration and any defocus. Next, a cutting speed dictated by the part design (intricacy) and precision and by the machine dynamics is specified.
From here, the pulse frequency can be adjusted within the calculator to achieve a % overlap (see bottom portion of the calculator) consistent with the requirements of the application. The general rule of thumb is that an overlap of 75% to more than 90% should be used for applications requiring a high quality, burr-free edge finish. On the other hand, an overlap as low as 50-60% can be used for applications in which speed or cycle time is the main goal.
In the typical application, the final step will be to adjust the pulse width to achieve a value of average power consistent with the part geometry and precision.
“The calculator will help users plan a process that will get them close before they get onto the laser machine.”
Pulse overlap in laser welding
A 70% overlap is generally considered a lower limit for hermetic (leak-tight) welds in pulsed laser welding. Using the initial inputs, the calculator determines the overlap percentage and color codes the ‘Pulse overlap’ cell based on the degree of overlap.
In the example pictured below, the combination of laser beam and process parameters gives an overlap of 83%, more than adequate for a leak tight weld as indicated by the green highlighted cell.
Ready to make use of the calculator?
Why not make use of this new calculator rather than guess at the answer or search the internet for the correct formulas?
You can request your FREE desktop version of the calculator by e-mailing firstname.lastname@example.org.
Also, please note that the upcoming Advanced Training class will include a session on use of the calculator for process development.