Plasma cleaning and laser cleaning are surface cleaning methods used to prepare surfaces for subsequent manufacturing processes such as welding, coating, and adhesive bonding. While laser cleaning relies on the power of light to remove contaminants, plasma cleaning uses an ionized gas called plasma.
Many manufacturers have trouble grasping the difference between laser cleaning and plasma cleaning. After all, both are non-contact processes that do not require solvents or chemicals like chemical cleaning, and they are sought after to replace abrasive techniques like sandblasting and dry ice blasting.
In this article, we’ll explain which technique achieves better results, and why. But before we discuss the difference, let’s do a quick overview of each method.
What is Plasma Cleaning
Plasma cleaning is a type of plasma treatment that removes surface contaminants by carbonizing them with plasma, an ionized gas that is so hot that the electrons are separated from the atoms. Plasma is obtained by heating up gas molecules, such as argon or oxygen, up to a point where they reach a higher energy state and become ionized (i.e., the atoms and molecules are electrically charged).
Plasma cleaning is a versatile process used to clean all types of surfaces, including plastics, metals, and ceramics. It is mostly used to remove organic contaminants like oil, dust, electrolyte, and paint. It is less efficient at removing other types of contaminants like rust and oxides.
What is Laser Cleaning
Laser cleaning is a process that uses laser ablation to remove surface contaminants. The laser beam—a concentrated ray of light of a specific wavelength—is directed at the surface. As contaminants absorb the laser beam’s energy, they are heated up to a point where their chemical bond with the substrate is broken, and they are vaporized into dust and fumes.
Laser cleaning is mostly used to remove contaminants from metals, but it can also be used to clean ceramics and stone. It is rarely suitable for plastics and rubber. This process can remove all types of pollutants, including oxide, corrosion, paint, oil, dust, and electrolytes. It is less efficient at removing thick mill scale, however.
The Main Differences Between Laser Cleaning and Plasma Cleaning
Speed of the Cleaning Process
Laser cleaning is much faster than plasma cleaning, whose duty cycle is relatively slow because it spends a large portion of its time moving mechanical parts and a small portion actually cleaning.
Laser cleaning uses ultra-fast rotating mirrors (galvo mirrors) to direct laser light. For example, in battery manufacturing, it only takes about 100 microseconds to move the laser beam from one cell to the next cell when preparing surfaces for welding.
Plasma cleaning needs to moves a nozzle above the surface to be cleaned using a gantry system. These mechanical movements, which are not as fast as galvo mirrors, slow down the cleaning process. In battery manufacturing, the nozzle needs to be moved above every single cell, making it a longer process than it needs to.
Mechanical Strength of Welds
When cleaning surfaces prior to welding, laser cleaning provides stronger, more consistent welds than plasma cleaning. This is especially important in industries with tight specification limits such as the battery industry, where quality insurance requires 6 sigma (3.4 defects per million) or even 7 sigma (0.02 defects per million)
Welds that are plasma cleaned will typically break under 1000 gf (grams-force). These welds are also highly inconsistent and have a hard time consistently meeting specification limits, with a Process Capability Index (Cpk) below 1.
With laser cleaning, welds will only break between 3000-5000 gf. Laser cleaning has no problem meeting specification limits, with a Cpk close to 2.
In some cases, plasma processing leaves carbonized residues stuck to the surface, and these contaminants can be quite hard to remove—even with a secondary cleaning step. Many manufacturers have encountered this problem when trying to remove oxides.
Like plasma cleaning, the performance of laser cleaning varies according to the contaminants that need to be removed. With laser cleaning, contaminants must absorb the laser’s wavelength at a good ratio. When this is the case, contaminants are vaporized into the air, and nothing remains on the surface.
At Laserax for example, our laser cleaning systems generate a 1,064 nm wavelength which is absorbed well by a range of contaminants that include oxides, dusts, oils, coatings, and electrolytes. Some contaminants such as clear coats cannot be removed properly using this wavelength.
Laser cleaning systems can be used to both clean and roughen surfaces, providing the complete surface preparation needed for applications like adhesive bonding. In contrast, plasma cleaning can only be used to remove contaminants.
Plasma technology was once the best method for cleaning applications that needed to avoid solvents, abrasives, and chemicals. Laser technology has since then progressed quickly and now achieves better results.
Many manufacturers have begun replacing plasma cleaning with laser technology to meet their production requirements for speed and consistency.