Precise Laser Peening parameters protect your metal parts
Once our material scientists have analyzed your metal component, we optimize the laser peening process to meet your requirements for reliability, endurance, and safety. We use finite element analysis modeling and our deep library of experience with metal parts to save time in prescribing laser peening parameters accurately and efficiently.
For each application development project, the Procudo® Laser Peening System uses a diode-pumped YLF laser. The diode mechanism provides precision, long-term consistency and durability. The laser emits a flat-top beam, which produces a smooth distribution of energy for consistent processing results. The Procudo® Laser Peening System’s light beam is set to 1053 nm in the red area of the light spectrum.
Residual Compressive Stress
The goal of laser peening is to produce high magnitude and deep residual compressive stresses from the surface of metals. We measure the depth of compressive residual stress in megapascals (MPa).
The key related laser parameters involved in producing these compressive residual stresses are the laser beam’s:
- Energy level
- Spot size
- And pulse width
These three key parameters of the laser beam can be expressed as a Power Density formula:
The power density (in gigawatts per square centimeters, or GW/cm2) is a function of the energy level (in Joules, or J) of the laser, the spot size (in square centimeters, or cm2) the laser delivers to the part, and the pulse width (in nanoseconds, or ns), which measures how long the laser beam hits the target part.
Laser peening parameters are all combined in the expression of the power density which is directly related to the magnitude and depth of compressive residual stresses produced in a metal.
Let’s explore the power density formula works to protect parts:
Deeper compressive residual stresses — far deeper than shot peening — preserve metals against corrosion and cracking more effectively.
The impact of the laser at the surface of the part is power density, or Gigawatts divided by the area receiving the laser force.
The Procudo® Laser Peening System produces a maximum energy level of 10 Joules, and the energy level is adjustable. While keeping the spot size and pulse width the same, energy level controls power density.
The pulse width is the length of time the laser beam pulse is emitted, measured in nanoseconds. The Procudo® Laser Peening System operates pulse width is between 8-16 nanoseconds, measuring full width at half-max.
Frequency or Pulse Rate
The pulse rate is the frequency at which the laser emits small plasma explosions. The Procudo® Laser Peening System can achieve up to 20 Hz, or 20 shocks per second.
The pattern of laser peening spots on the part, including overlapping spots, controls coverage and overlap of spots, making the process very controllable and repeatable.
The laser beam impact area at the surface of the part is the spot size. At constant energy and pulse width, smaller spot sizes create higher levels of power density. Larger spot sizes diminish the intensity, or power density of the beam.
The pattern of laser peening spots on the part, including overlapping spots. Controlling the overlap of new areas of com part geometries making the process very controllable and repeatable.
Here’s a more in-depth look at laser peening parameters.
Depth of Compressive Residual Stress
We start with the end goal in mind. That is, we focus first on the goal of creating deep compressive residual stresses that counteract cracking, corrosion, and other types of metal failure. The deeper these stresses penetrate through laser peening, the better we can improve fatigue life and fatigue strength for metal parts.
Laser peening can typically create these beneficial stress patterns 1-2 mm deep from the surface, 10 times deeper than conventional treatments, and we have achieved depths of 12 mm, when needed. For example, shot peening typically provides only 0.2 mm of residual stress.
How do we achieve deep compressive residual stress? The energy level, spot size, and pulse width constitute the power density (GW/cm2) which determines the magnitude and depth of compressive residual stress produced by a single laser peening shot for a specific metal. This is the measure of the power per unit area of radiation received by a surface.
We measure the impact of the laser at the surface of the part as power density, or Gigawatts divided by the area receiving the laser force in square centimeters. The higher the power density, the higher the magnitude and depth of compressive residual stress is achieved. There is a limit, however, a saturation point which becomes the design power density for the specific metal.
The pulse rate is the frequency at which we are emitting laser shocks – or small plasma explosions. The Procudo® Laser Peening System can achieve up to 20 Hz, or 20 shocks per second.
The Procudo® Laser Peening System produces a maximum energy level of 10 Joules, and the energy level is adjustable. While keeping the spot size and pulse width the same, you can directly control the power density by controlling the energy level.
The pulse width is the length of time the laser beam pulse is emits. Light moves quickly and lasers move powerfully, so we measure pulse width in nanoseconds. The Procudo® Laser Peening System operates between 8-16 nanoseconds to produce the plasma shock wave that imparts compressive residual stress. Although the pulse width is part of the power density calculation, for the same densities, longer pulse widths lead to increased treatment depth as seen for higher power density cases. Shorter pulse widths can increase surface magnitude as seen for the lower power density.
Aiming the laser beam from a wider angle increases the spot size, which lowers the power density. Regardless of the beam angle, however, laser peening creates a shock wave that is perpendicular to the surface of the part, even if the part has a convex or concave shape. Complex shapes, curves, and hard to reach areas of parts can benefit from this predictable effect.
The laser beam impact area at the surface of the part is the spot size. With a constant level of energy and pulse width, a smaller spot size creates higher power density (GW/cm2). A larger spot size diffuses the same amount of energy over a larger surface, diluting surface power density but increasing the processing rate. For the same power density, the spot size (> 1mm) does not affect the compressive residual stresses created in the metal.
We program the robotic controls of the Procudo® Laser Peening System to create a pattern of spots on the part for optimum fatigue life extension, controlling the overlap of new areas of compressive residual stress. We can set up the number of spots, as well as patterns of spot coverage to increase the magnitude and depth of compressive residual stresses produced by laser peening. Repeated laser peening in the same regions of the part has the effect of deepening beneficial compressive residual stress. The robotic controls give us the ability to control these patterns even when processing very complicated part geometries, making the process very controllable and repeatable.
Delivering Laser Parameters with Precision
These parameters help us deliver precisely engineered protection to fight all the potential threats to metals, including fatigue, corrosion, foreign object damage (FOD), fretting, and flaking. For each application development project, the Procudo® Laser Peening System uses a diode-pumped YLF laser (See the Product Data Summary, below). The diode mechanism provides precision, as well as long-term consistency and durability.
|Laser Type||YLF (yttrium lithium fluoride)|
Ultra-long life Quasi-Continuous-Wave (QCW) pump diodes
|Beam Characteristics||Flat-Top Beam, only 9.1% variation in energy distribution|
|Laser Amplification||Seeded Master Oscillator-Power Amplifier (MOPA)|
|Pulse Rate||Up to 20 Hz|
|Energy||Up to 10 Joules|
|Pulse Width||Natural laser pulse width of 22.6 ns, but selectable at 8-16 ns, maintained with variability of 0.07-0.14 ns|
|Processing capacity||29 in2/min, 187 cm2/min|
|Average Power||200 Watts|
|Power Cabinet||Power supplies and power distribution hardware|
|Optical Enclosure||Laser and beam diagnostic components|
|Control Cabinet||System controller, data acquisition/storage, environmental controls|
|Production Enclosures||Cell configurations vary per customer requirements|