Laser ablation is a lesser-known technique among the many laser techniques used industrially for several processes. Gordon Gould invented the technique when he switched to the Q-switching method as which produces pulsed laser beams with high peak power that can ablate different materials.
Laser ablation is applicable for marking, cutting, texturing, and cleaning different materials. This article will introduce the process, its parameters, associated processes, and advantages/disadvantages to help you learn more about the technique. Read on.
What is Laser Ablation?
Laser ablation is a technique that involves using a laser marking machine to remove materials from a part. The laser machines used are mainly CO2 or fiber laser technology, as they can generate pulsed laser beams with high peak power required to remove the materials.
All laser machines used for ablation work the same way, depending on the materials. Every material has its ablation threshold above it, and the material is ablated and vaporized into fumes. Below it, the material’s temperature will only increase, and laser welding occurs. Due to the formation of fumes, you need a fume extraction system.
What Are the Laser Ablation Parameters?
Laser ablation uses the same marking machines as other laser techniques. However, you need to optimize different parameters of the laser marking machine to tailor it for different applications. Below are the most important parameters you should consider and how to optimize them.
· Wavelength
Laser beams are reflected and absorbed when they hit a workpiece’s surface. The laser energy must be absorbed and converted to heat for ablation to occur. The extent of reflection and absorption of the laser beam depends on the marking machine’s wavelength and the material to be marked. Every laser machine has a different wavelength, and you should choose one that has is least reflected. For example, you can use a fiber laser for metals and CO2 for plastics and other organic materials.
· Beam Diameter
The larger the beam diameter, the more the dispersion of laser energy. Therefore, ablation might not be possible with laser machines with high beam diameters. If you want efficient energy use, you should reduce the beam diameter. For example, the 100W laser cleaning machine has an adjustable beam diameter of 4.0mm±0.5mm.
· Beam Quality
Beam quality measures the focus-ability of a laser beam. It is measured in M2, and highly efficient laser ablation machines have a value close to 1. Machines having a high M2 value are hard to focus and can’t generate high energy for ablation.
· Focal Distance
The focal distance is where the laser beam is focused on the targeted area. You can change it by using various focusing optics to generate optimal results.
· Laser Power
This is the energy that the laser marking machine measured in watts. Pulsed lasers are preferred for ablation because they generate high laser power.
· Pulse Length
This is the time between the pulse’s beginning and end expressed in microseconds, nanoseconds, picoseconds, or femtoseconds. Laser marking machines with short pulses can generate high energy peaks required for most laser applications. However, they need much control to prevent melting.
· Pulse Frequency
This is the number of pulses per second. For example, in the 100W laser cleaning machine with 100,000 pulses per second, each pulse will deliver 1mJ or energy. If you increase the number of pulses per second, you will reduce the energy per pulse and make ablation impossible.
· Scanning Speed and Pulse Spacing
Scanning speed depends on the rotating speed of the mirrors that moves the laser beam. The higher the rotation speed, the higher the scanning speed. The scanning speed determines the spaces between pulses and the energy administered to the surface. The closer the pulse spacing, the higher the energy focused on a particular part. You can use laser ablation for different purposes by controlling the pulse spacing. For example, laser engraving should have a tight pulse spacing.
· Number of Passes
This is the time the laser beam passes over the material for ablation. Depending on several factors, a material can require a single or multiple laser pass. For example, multiple laser passes will allow you to avoid overheating parts during ablation, while single laser passes can be enough for some materials.
What Are the Industrial Applications of Laser Ablation?
The technique is integral and applicable in many laser processing applications. Below are several industrial applications of laser ablation.
· Laser Marking
Laser marking involves using a laser beam to create permanent markings on a part’s surfaces. It is an essential process in achieving part traceability. Different laser marking processes use laser ablation, with laser etching and engraving being the most common. However, not all laser marking processes ablate their workpiece. For example, laser annealing induces a color change instead of ablating the material.
· Laser Cleaning
Laser ablation is applicable in cleaning some materials of rust (where it is termed laser rust removal), oxide, and paint. Machines used for rust removal must have high laser power, e.g., the 100W laser cleaning machine can break chemical bonds that hold the materials together to the workpiece. It works by targeting the different ablation thresholds of the materials, and in this scenario, rust, oxide, and paint have a lesser threshold than the workpiece. Therefore, you can target them without impacting the base material.
· Laser Texturing
You can use laser ablation to modify the surface of a workpiece for processes such as painting, thermal spray coating, and adhesive bonding.
What Are the Benefits of Laser Ablation?
Laser ablation also has its merits and demerits. Below are a few to note whether you use it for marking, cleaning, or texturing.
Advantages of Laser Ablation
- It is a non-contact process
- It requires low maintenance and operative costs.
- There is a lesser environmental footprint due to the lack of dangerous consumables such as chemicals and abrasive media
- It is automated and can help reduce the need for reducing manual labor.
Disadvantages of Laser Ablation
- Laser ablation requires a strict follow of laser safety standards (ideally a Class-1 laser safety enclosure)
- It sometimes generates fumes and can need a fume extraction system
- It requires a high initial investment than other techniques
What HeatSign Can Do for You
Laser ablation has several applications in industrial part marking, cutting, rust removal, and texturing. This article discusses everything you need to know about the technique and how to work on the different parameters after getting a laser machine. Contact our team to know more about laser ablation and the machines you can use.
FAQs
The guide mentions the 'ablation threshold.' What is this and why is it important?
The ablation threshold is the minimum amount of laser energy required to vaporize a material. It is important because the laser must operate above this threshold for ablation to occur. If the energy is below the threshold, the material will only heat up, which could result in a different process like laser welding instead of material removal.
How does the laser's wavelength affect the ablation process?
The wavelength is a critical parameter because it determines how well the laser’s energy is absorbed by the material. For ablation to be efficient, you must choose a laser with a wavelength that the material absorbs well. For example, the guide recommends a fiber laser for metals and a CO2 laser for plastics, as their respective wavelengths are a good match.
What is the difference between pulse length and pulse frequency in a laser system?
Pulse length is the duration of a single laser pulse, measured in units like nanoseconds. Pulse frequency is the number of pulses that are fired per second. Both are important for controlling the energy delivered; a short pulse length can create a high energy peak, while a lower frequency delivers more energy per individual pulse.
The guide says laser ablation is used for laser cleaning. How does it clean without damaging the base material?
It works by targeting the different ablation thresholds of the materials. Contaminants like rust, oxide, and paint have a lower ablation threshold than the underlying workpiece. This allows the operator to set the laser to a power level that is high enough to vaporize the contaminant but is still below the threshold of the base material, leaving it unharmed.
Are all laser marking processes considered a form of laser ablation?
No, not all laser marking processes involve ablation. The guide clarifies that while processes like laser etching and engraving do use ablation to remove material, other methods do not. For example, laser annealing is a marking process that works by inducing a color change on the material’s surface through heat, rather than ablating it.
How can I control the depth of the mark when using laser ablation for engraving?
The depth can be controlled by several parameters. The guide mentions that you can use a tighter pulse spacing, which focuses more energy on one area, or you can increase the number of passes, which involves passing the laser beam over the material multiple times to avoid overheating while achieving the desired depth.
Why is beam quality, measured in M2, so important for an efficient ablation process?
Beam quality is important because it measures how well the laser beam can be focused. A laser with a high-quality beam (an M2 value close to 1) can be focused into a very small, intense spot. This is necessary to generate the high energy density required for efficient ablation.
What are the main disadvantages or challenges associated with using laser ablation?
The main disadvantages are the high initial investment cost for the equipment and the strict safety requirements. The process often generates fumes, which requires a fume extraction system, and operators must adhere to safety standards, ideally using a Class-1 laser safety enclosure.
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