Laser ablation occurs when a laser beam removes material from a localized area. Used in various industrial applications, this process can create permanent marks (laser marking), remove contaminants and coatings from surfaces (laser cleaning), modify a part’s roughness (laser texturing), cut through a surface (laser cutting) and much more.
It was invented in 1958 when Gordon Gould proposed the Q-switching method to produce pulsed laser beams. As you will discover, pulsed lasers can reach the high peak power typically required to remove material.
- How Does the Laser Ablation Process Work?
- What Are the Laser Ablation Parameters?
- What Are the Industrial Applications of Laser Ablation?
- What Are the Benefits of Laser Ablation?
How Does the Laser Ablation Process Work?
In today’s manufacturing industry, CO2 and fiber laser systems are widely used to generate laser ablation. Although these lasers are used with different materials, they generate laser ablation in the same way. Here’s how:
All materials have an ablation threshold. It is a property that is unique to each material. When the intensity generated by a laser is above the material’s ablation threshold, the material is ablated. But if the intensity is below the ablation threshold, nothing happens, except a slight increase in temperature.
Materials that are expelled from the surface are vaporized into fumes. Although these fumes are minimal, a fume extraction system is usually required near the laser to avoid accumulation and obstruction of the light beam.
What Are the Laser Ablation Parameters?
Laser parameters are the key to mastering laser ablation. By adjusting them, laser experts can optimize the laser process for different applications. You will find the most important laser parameters to consider explained below. Take note that for laser cutting, different parameters need to be adjusted.
Wavelength
When the laser light hits a surface, it is partly reflected, partly absorbed. The absorbed laser energy is converted into heat which ablates the material.
Because they have a different laser source, each type of laser emits a different wavelength. The laser that emits the wavelength that is the least reflected by the material should be favored. Fiber lasers, for example, work more efficiently with metals whereas CO2 laser with plastics and other organic materials.
Beam Diameter
The larger the diameter of the focused beam, the more dispersed the laser energy—up to a point where laser ablation is impossible and laser welding starts to occur. By reducing the beam diameter (also known as the spot size), more energy can be transferred to a smaller area, hence creating more energy-efficient ablation.
Beam Quality
The beam quality (also known as M2) measures how well a laser beam can be focused. The closer the laser beam tends towards a M2= 1, the more efficient the laser will be for ablation.
Beams with a high M2 factor are unfocused and fail to generate the high energy required for ablation. However, they are often ideal for laser welding.
Focal Distance
The focal distance is where the laser beam is focused on the targeted area, allowing it to generate high-quality results.
It can be changed by using various focusing optics or, in some cases, with the use of 3D heads. These heads can be equipped with sensors that automatically adjust the focal distance on the part to always generate optimal results.
Laser Power
Provided in watts, the laser power is the average power of the laser beam.
A 100W pulsed laser can reach high energy peaks of 10,000W, but its average power over time is still 100W. Conversely, a 1,000W continuous-wave lasers consistently generates 1,000W of power but can never reach more than that.
Pulsed lasers are the preferred tools to ablate materials because of their higher peak powers. Surfaces can be treated faster by increasing their average power.
Pulse Length
The pulse length, also known as pulse duration or pulse width, is the time between the beginning and the end of a pulse. It may be expressed in microseconds (one-millionth of a second), nanoseconds (one billionth), picoseconds (one trillionth) or femtoseconds (one quadrillionth).
Short pulses can reach the high energy peaks required for most laser applications. By limiting thermal effects, they also prevent undesirable melting. The Laserax fiber lasers typically generate short pulses of 100 ns or 125 ns.
Pulse Repetition Rate
The pulse repetition rate (also known as pulse frequency) is the number of pulses per second. For example, the default setting for our 100W pulsed lasers is 100,000 pulses per second, each containing 1 mJ of energy. Similarly, our 50W lasers have a nominal repetition rate of 50,000 pulses per second.
Increasing the number of pulses per second reduces the amount of energy per pulse. Our 50W laser could generate 100,000 pulses per second instead of 50,000, but each pulse would contain 0.5 mJ instead of 1.
If the energy per pulse is too low, ablating materials will be impossible.
Scanning Speed
The scanning speed is the speed at which the mirrors rotate in the laser to move the laser beam. The faster they rotate, the faster the scanning speed. This parameter is used to change the spacing between pulses and hence control how energy is distributed.
Pulse Spacing
The pulse spacing is a direct result of the scanning speed. If laser pulses are closer to one another, more energy is sent to the same area. Pulse spacing is used to ablate materials in different ways. For instance, laser engraving requires a very tight pulse spacing to dig deep into materials.
Number of Passes
A single laser pass is usually enough for a material to be ablated. This is the case when etching permanent marks or removing paint from a surface.
In certain cases, several laser passes deliver better results as it avoids overheating an area. This is the case when engraving deep marks into a material or when removing thick mill scale layers from a surface.
What Are the Industrial Applications of Laser Ablation?
Now that you know how laser ablation works, let’s look at its industrial applications. As you’ll see, ablation is used in many laser processing applications.
Laser Marking
Laser marking creates permanent markings directly onto part surfaces. It is often used to implement part traceability by creating identifiers such as data matrix codes, QR codes, alphanumerical characters and serial numbers. It is also used to identify products with logos. Laser marking can be performed on most metals, several plastics as well as other organic materials.
Laser etching and laser engraving, the most common laser marking processes, use laser ablation at different intensities. For typical barcodes, ablation is performed within 100 microns into the surface, but a deep engraving can also be used to dig even deeper.
Not all laser marking processes use laser ablation. Laser annealing, for instance, does not ablate materials; it marks metals like stainless steel by inducing a color change under the surface, which preserves the material’s corrosion resistance.
Laser Cleaning
Laser cleaning can remove thin films of materials like rust, oxide and paint from surfaces by breaking the chemical bond that holds them together.
As explained earlier, every material has an ablation threshold. Since the ablation threshold of rust, paint and oxide is lower than that of metals, the laser parameter can be set so that the beam’s intensity ablates them without impacting the base material.
The vaporization of contaminants and coatings from metals usually requires a high-power laser (100W and more). You can watch these videos for examples of laser cleaning applications:
LASER RUST REMOVAL
LASER OXIDE REMOVAL
LASER PAINT REMOVAL
Laser Texturing
Laser texturing uses laser ablation to prepare surfaces for subsequent manufacturing steps. By modifying the surface roughness, surfaces can be prepared for processes like adhesive bonding, painting, thermal spray coating and laser cladding.
In the following picture, you can see a textured and non-textured surface up close.
What Are the Benefits of Laser Ablation?
Like all technologies, laser ablation has advantages and disadvantages. We’ve summed them up here to help you understand if laser ablation is right for you, whether you need it for laser marking, laser cleaning or laser texturing.
Advantages of Laser Ablation
Laser ablation is a non-contact process that functions without consumables, except for laser cutting. As such, it requires low maintenance and helps reduce operative costs.
Since it replaces technologies that use chemicals, abrasive media, and other types of consumables, it also helps manufacturers reduce their environmental footprint and meet environmental protection regulations.
Laser ablation is also easy to automate, making it a sound choice for production lines and allowing many manufacturers to reduce manual labor.
Disadvantages of Laser Ablation
When enclosed properly, laser technology is completely safe. But to achieve this, you must follow laser safety standards. Ideally, laser ablation is performed in a Class-1 laser safety enclosure
Material processing could also release fumes and particles into the air. For this reason, a fume extraction system is almost always needed near the laser system.
Finally, although laser technology offers a huge return on investment due to its low operative costs, it typically requires a higher initial investment than its alternatives.