What power does a laser cleaner need for your own task?

Four factors determine the assessment: which layer is to be removed, how thick it is, how much area is involved and on which base material it sits. Added to this are the place of use, handling and occupational safety.

How pulsed and continuously operating systems deliver energy and which characteristic values describe a laser source are covered in separate magazine articles. This article is about one question: which wattage class can suit which task?

Why the wattage class is a planning question

The wattage is the figure that is quickest to find in quotations. Accordingly, it often becomes the starting point for the selection: people compare figures and take the class that is “bound to be enough”.

Whether a laser cleaner solves a task, however, is decided on the surface of the workpiece. The Fraunhofer Institute for Laser Technology ILT names wavelength, intensity, the interaction time of the radiation with the layer and the material properties as influencing factors in cleaning with laser radiation. The rated power is only one variable among several.

In addition, pulsed and continuously operating machines with a similar wattage rating are not readily comparable. Wattage classes can therefore be compared primarily within the same design — and only once the task has been described.

Three rough power ranges as guidance

There is no generally binding classification of cleaning lasers by wattage. Manufacturers use their own tiers. Clean-Lasersysteme GmbH, for example, divides its systems into three ranges:

• 12 to 100 watts for small-area applications, oxide layers and thinner layers
• 150 to 600 watts for medium-sized to large applications and moderate layer thicknesses
• from 1,000 watts for large-area applications and greater layer thicknesses, stated by the manufacturer as up to 1 mm

This is the guidance of a single manufacturer, not a standard. It does, however, show a basic pattern: as the area grows and the layer gets thicker, the appropriate power class shifts upwards. Such a classification does not replace the description of your own task and the trial on the workpiece.

Type of layer: what is to be removed

The layer sets the direction. Fraunhofer ILT names, among other tasks, the removal of oxide layers and of particulate and film-like contamination such as greases or oils. The DGUV publication FBHM-139 describes the removal of corrosion and passive layers, of paint and coating materials and of process residues.

For choosing the wattage class, these tasks can be roughly divided into two groups:

• thin deposits and films, such as oxide layers, oil and grease films or process residues — here controlled processing is often the priority
• built-up layers, such as paints, coating materials or pronounced corrosion — here the amount of material to be removed plays a greater role

A layer does not have to be uniform. FBHM-139 points out that coatings can consist of different components or be applied in several layers. Whether a setting that detaches the topcoat is also suitable for the layer beneath can only be established on the component.

Layer thickness and target condition

As the layer thickness increases, so does the material that has to be removed. Whether a lower-power machine removes a thick layer in several passes or whether no removal takes place depends on the layer and the settings. A higher-power machine can complete the same task in fewer passes — provided the layer and base material tolerate the higher energy input. Where possible, the layer thickness should therefore be measured or taken from documentation rather than estimated by eye.

The target condition also needs to be clarified. Does the layer have to be removed completely, or is it sufficient to take off a top layer? Is the metal subsequently to be welded, bonded or recoated? The higher the requirement for the final condition, the more weight controlled processing can carry compared with pure removal speed.

Area and frequency of use

The area changes the calculation most clearly. Individual contact points, weld zones or tool contours often cover a few square centimetres, whereas steel structures or containers cover square metres.

What counts here is not the size of the component but the area that actually has to be processed — and how often that happens. Three figures provide a useful basis:

1. the area processed per component or per job
2. the number of components or jobs per week or month
3. the time available for it

This shows the minimum area coverage rate that has to be achieved. If the requirement is low, a smaller class can be sufficient, even if a larger one would be faster. If it is high, the processing time with a smaller class can become a bottleneck. Area figures from brochures always apply to a particular layer on a particular substrate.

Base material and heat sensitivity

The base material limits how much power can actually be used on the component. FBHM-139 describes absorption as the uptake of radiation, in which the energy is partly transferred into the medium and converted into heat. Whether this heat becomes a problem depends on the material, the wall thickness and the process control.

A freely accessible study on paint removal from aluminium aircraft skin with a pulsed laser at 1064 nm illustrates the relationship: above a suitable range of power density, the aluminium surface reached melting temperature, and grooves and significant damage occurred. Too low a scanning speed also damaged the base material. The authors further describe how the temperature fields of successive pulses overlap and heat can accumulate.

The values from this study cannot be transferred to other machines. The direction, however, can: more energy on the same spot does not automatically mean more cleaning, but beyond a certain point can attack the base material.

Thin sheet metal, heat-sensitive materials and high-quality visible surfaces can therefore require lower power or very careful parameter setting. With solid components there can be more latitude — this too has to be checked on the workpiece. With bare surfaces, reflection comes into play: FBHM-139 names the reflection properties and geometry of the workpiece as points to be taken into account in planning.

Why more watts are not automatically better

The assumption that additional power at least does no harm is widespread. It falls short for several reasons:

• Base material: Power that the workpiece cannot tolerate has to be reduced on the machine. It is then listed in the data sheet but not used.
• Handling: At Beamlux, the continuous wave machines with 1,500 watts and more are wheeled and water-cooled. In confined spaces or at changing locations, a portable machine can be more practical.
• Hazardous substances: According to the BGHM, which mixtures of hazardous substances are produced depends on the substances removed and also on the laser used. A change of power class therefore also affects extraction and the risk assessment.
• Protective measures: According to FBHM-139, they depend both on the power or energy density of the laser and on the application.
• Price: The purchase price cannot be read from the wattage, because pulsed machines and continuous wave machines are technically constructed differently.

More power can save time where large areas with built-up layers occur on a base material that tolerates the energy input. Outside this framework, it is not automatically an advantage.

Design, cooling and place of use

The machine around it usually changes along with the wattage class:

• Carried or wheeled: A portable machine with a carrying strap reaches places that a wheeled machine has difficulty getting to. A wheeled machine is better suited to the workshop, the production hall and longer processing runs.
• Cooling: The portable pulsed machine from Beamlux is air-cooled; the BL CW 2000 and the laser welding machine are water-cooled.
• Power supply: The portable pulsed version can be operated on battery. For the other machines, the power supply at the place of use should be clarified in advance.

With hand-held machines, weight also matters: the DGUV publication names possible physical strain that should feed into the selection.

Beamlux machines by power class

Beamlux offers systems in two designs. Which version suits your own task follows from the previous sections.

Pulsed at 200 and 300 watts

• BL Portable Pulse: portable with carrying strap, 1064 nm, air-cooled, battery operation possible
• BL Compact Pulse: wheeled on four castors, 1064 nm, for the workshop and continuous operation; a 1,000 W version on request

Continuous wave from 1,500 to 6,000 watts

• BL CW 2000: wheeled, 2,000 W continuous wave, 1064 nm, water-cooled, hand-held head; the series comprises 1,500, 2,000, 3,000 and 6,000 W
• BL Welding Machine: wheeled, water-cooled, continuous wave fibre laser with 1,500, 2,000, 3,000 or 6,000 W; in addition to welding and cutting, also for weld seam cleaning and rust removal on steel, stainless steel, galvanised sheet and aluminium for 1,500 to 3,000 W, 6,000 W on request

The pulsed machines are intended for precise and localised work as well as for the workshop and continuous operation, the CW machine for larger areas, production and maintenance. This assignment is a starting point, not a fixed rule.

Protective measures in every power class

A lower wattage class does not mean that occupational safety no longer applies. The DGUV publication FBHM-139 refers to hand-held class 4 lasers for cleaning and coating removal. Which laser class a machine has is stated in its documentation. A few points for the selection can be taken from the publication:

• According to the guidance on process selection, knowledge of the laser characteristics is required to choose suitable protective measures.
• Laser safety goggles are to be derived from the maximum power or energy density in the respective wavelength range. A change of power class can therefore require different goggles.
• Operation requires effective extraction that is applied as directly as possible at the processing point.
• The energy of the laser radiation used is sufficient to ignite an explosive mixture or flammable substances.
• For handling lasers of classes 3R, 3B or 4, the publication, with reference to § 5 OStrV, names the appointment of laser safety officers.

This article does not replace a risk assessment or legal advice. The specific protective measures are defined in the risk assessment for the respective workplace and the respective machine.

Material test before the purchase decision

The DGUV publication advises defining use cases and process limits before the decision is made and testing the suitability of a system on the real component.

A meaningful test uses an original component or a sample with the same layer on the same base material. The following should be recorded:

1. Machine, power class and settings
2. Number of passes needed to reach the required condition
3. measured time for a defined area
4. Condition of the base material after processing
5. Observations on fume, residues and extraction

Where possible, comparing two power classes on the same component can be revealing. It shows whether the higher class actually shortens the time or whether the base material limits the usable power. With these values, the planned area can be converted into a reliable processing time — and the right wattage class chosen for the laser cleaner.

Sources

• DGUV – Fachbereich AKTUELL FBHM-139 “Strahlarbeiten – Reinigen und Entschichten mit Laserstrahlung” — as of 20 June 2024; hand-held class 4 lasers, absorption, extraction, ignition hazard, ergonomics, laser safety goggles and guidance on process selection.
• BGHM Magazin – “Reinigen und Entschichten mit Laserstrahlung” — issue 05/2024; composition of the mixtures of hazardous substances depending on the substances removed and on the laser used.
• Fraunhofer ILT – Cleaning — influencing factors wavelength, intensity, interaction time and material properties; cleaning with pulsed or continuous laser radiation.
• Clean-Lasersysteme GmbH – overview of laser systems — manufacturer classification into Low, Mid and High Power with assigned areas and layer thicknesses.
• “Research on Laser Cleaning Technology for Aircraft Skin Surface Paint Layer” – journal article in Materials, freely accessible via PubMed Central — damage to aluminium at excessive power density and insufficient scanning speed, and heat accumulation during pulsed paint removal.
• Beamlux – product overview of laser cleaning machines and laser welding machines — design, power classes, cooling, main areas of use and prices of the models mentioned.

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