Pulsed laser or CW: which energy input suits the component?

For industrial users it is above all the base material, the layer thickness, the required surface condition and the necessary process time that are decisive. A system that is convincing at removing a thin coating precisely is not automatically the best choice for a large, robust metal surface.

The comparison therefore does not show which type of laser is fundamentally “better”. What matters is which technology offers the more sensible balance of quality, speed and process reliability for the specific processing task.

What distinguishes pulsed and continuous wave operation?

The two terms pulsed laser and CW laser describe two fundamentally different ways of providing laser energy. In a pulsed system the energy is emitted in individual pulses of limited duration. Between these pulses there is no energy present, or considerably less. A CW system works continuously; CW stands for “continuous wave”.

In practice this difference means that the energy enters the surface with a different timing. A pulsed system can reach a high peak power within a very short period. The average power can nevertheless be comparatively low. In a CW system the set power acts continuously throughout processing. This can produce different temperature profiles and removal mechanisms.

For cleaning and coating removal, the Fraunhofer Institute for Laser Technology ILT describes both pulsed and continuously operating laser sources. Which source is used depends on the specific processing task. It is precisely this application-related view that is decisive for B2B users.

Why 300 watts cannot be compared directly with 2,000 watts

On a data sheet the arithmetic looks simple at first: 2,000 watts is considerably more than 300 watts. For a technical comparison between pulsed and CW systems, however, this view falls short. The wattage figure describes a power. On its own it does not yet say in what temporal structure the energy reaches the surface.

In a pulsed laser the energy is concentrated into individual pulses. Variables such as pulse energy, pulse duration and frequency therefore have to be taken into account as well. In a CW system the power is transferred continuously. A 300 W pulsed system and a 2,000 W CW system are therefore not two variants of the same tool in which the second machine is simply “stronger”. They can have different task profiles.

A pulsed system can make sense, for example, where a thin layer is to be processed in a controlled way and the energy input needs to be as precise as possible. A CW system, by contrast, can have advantages on robust, larger surfaces where a high processing output is required. The right basis for comparison is therefore not watts alone. What matters is: how quickly does the system reach the required surface condition on the actual component?

Peak power, pulse energy and average power

In a pulsed system in particular, several technical variables are relevant. The pulse energy states how much energy a single pulse contains. The pulse duration describes how long that pulse lasts. A comparatively high pulse energy combined with a very short pulse duration can produce a high instantaneous, or peak, power. At the same time the frequency determines how many pulses are generated per second.

This makes clear why looking at the average wattage alone is not enough. Two pulsed systems with identical average power can behave differently on the same surface because of different pulse parameters. For a user, at least the following variables are therefore of interest:

• average power, pulse energy and pulse duration
• Frequency
• available scan width
• Focus and beam geometry
• possible travel speed

Only together do these parameters give a technical picture. That does not mean, however, that a buyer has to work out all the laser physics themselves. What matters for the selection is rather to describe the real application as precisely as possible. How these variables interact during removal is explored in more depth in the article on the influencing variables on metal surfaces.

How the thermal effect arises

Laser energy is absorbed by a surface and partly converted into heat. How strongly the base material is affected thermally depends, among other things, on the energy introduced, the interaction time, the material properties and the movement of the beam.

Because of their short interaction times, pulsed systems can allow a controlled energy input for certain tasks. That is of particular interest where a thin top layer on a more sensitive substrate is to be processed. In a CW system, energy is introduced continuously. On robust components this can allow a high throughput. If the work is too slow, however, or too much energy is concentrated on a small area, the heat input can increase.

Once again it follows that CW does not automatically mean “too hot”, and pulsed does not automatically mean “no heat”. Both systems have to be parameterised correctly. The material and the travel speed play just as much a part as the laser source. The thermal conductivity of the base material is relevant too: aluminium can distribute the heat introduced differently from stainless steel, for example. The technical selection should therefore always be based on the actual material.

What role the area coverage rate plays

In industrial use it is not only the visual result that counts. The processing time matters just as much. Companies need to know how much surface, or how many components, can be processed within an hour or a shift. The area coverage rate depends, among other things, on:

• The type and thickness of the layer
• The laser source and power
• Scan width and processing speed
• the passes required
• the required final condition

A very precise process can work excellently in technical terms but be too slow for a large production volume. Conversely, a business that processes only a few high-value components a day may not need a maximum area coverage rate.

This is where a fundamental difference between usage profiles becomes apparent. A restoration business can have a different optimum from a structural steel fabricator. A toolmaker can have different requirements from a company that works on large metal structures. The question of the design should therefore always be answered together with the productivity actually needed.

Rust, paint and oxide layers place different demands

Not every layer to be removed reacts in the same way.

Rust

Corrosion products can range from light flash rust to heavily developed layers. With thin corrosion, a controlled pulsed process can be of interest. On large, robust surfaces and with a corresponding degree of rust, a power-oriented system can offer advantages. The overarching field of application is covered on the page treating rust on metal with laser technology.

Paint

Paint systems can consist of several layers. Primer, intermediate coat and top coat can have different optical and thermal properties. During processing, the behaviour can therefore change as soon as a new layer is reached. If only a defined area is to be exposed, precision can be more important than maximum area coverage rate. For complete paint removal over a large area, by contrast, process time can be weighted more heavily.

Oxide layers

Oxides occur in very different thicknesses. Thin layers and heat tint on weld seams differ markedly from heavy scale. Here, too, there is therefore no general recommendation: the right choice depends on the layer and the target condition.

Sensitive and robust components

A key decision factor is the value, or rather the sensitivity, of the component. With high-value visible surfaces, thin metal parts, tool contours or restoration applications, controlled processing is often the priority. Here the ability to set parameters very precisely can be particularly important.

With solid steel components, robust system components or large areas, by contrast, productivity can be weighted more heavily. That does not mean that a CW system is only suitable for rough work in principle. It merely means that the advantages of higher continuous power become particularly relevant where the component and the desired result permit this energy input. The following questions can help with the selection:

• How valuable is the component and how sensitive is the surface?
• What is the maximum change that may occur?
• How large is the area to be processed?
• Does a visible surface have to be preserved?
• Will the part subsequently be painted, bonded or welded?
• How fast does the process have to be?

This information is considerably more meaningful than the question of a particular wattage.

Mobile use and larger areas

The working environment also influences the choice. A compact pulsed laser can be of interest where an operator frequently has to switch between different components or sites. In workshops, in restoration work, in mould and tool making or for localised maintenance work, mobility plays a major role.

A more powerful wheeled system, in turn, can be a better fit for applications in which larger contiguous areas are processed. Power supply, cooling, extraction and workplace organisation have to be taken into account here.

The size of the machine alone does not tell the whole story either. What is decisive is what the overall work process looks like. If a component is difficult to transport, the system may have to be brought to the workpiece. With series components, by contrast, a stationary processing cell can make more sense. The overview of Beamlux systems and power classes shows different versions for such application profiles.

Series production and automation

In series production the assessment changes. Here it is not only a question of whether an operator can process a surface — the process has to be repeatable. A scanner, an axis or a robot can guide the processing head along a defined geometry. This makes speed, distance and processing path reproducible. That can be relevant for both pulsed and continuous systems.

Fraunhofer ILT and Fraunhofer IWS work on laser-based surface pre-treatment and the integration of such processes into automated production sequences. Typical tasks can be:

• local preparation of a bonding surface
• Processing of a subsequent weld area
• Removal of a functional layer
• Cleaning of a defined tool contour
• Preparation of a surface for coating

For series processes, cycle time has to be considered alongside surface quality. A system can work technically and still fail to reach the required output quantity. Conversely, maximum processing performance can be unnecessary if the laser process is already working faster than the following production step. The machine therefore has to fit into the overall process.

What data is needed for a selection

A sound machine selection does not begin with the question of a model. It begins with the component. For an initial technical assessment, the following information should be available wherever possible:

• Base material: steel, stainless steel, aluminium, copper or another material
• Layer to be removed: rust, paint, oxide, scale or process residue
• Layer thickness: a light surface film or a heavy build-up
• Area: a few square centimetres, individual components or several square metres
• Frequency of use: occasional, daily or continuous within the production process
• Target condition: visually clean, technically defined, ready for welding, bonding or coating
• Mobility: workshop, changing sites or a permanently integrated system

This information produces a considerably better requirements profile. Only then is it worth comparing specific power classes.

Why the material test matters more than the data sheet

Data sheets are necessary, but they cannot fully replace a real processing trial. Within a short time, a material test shows which questions are actually relevant: is the layer removed cleanly? What does the base material look like afterwards? How fast can the work proceed? How wide can the scan be? How many passes are needed? And how far does a pulsed system differ from a CW system on this particular component?

The direct comparison in particular can be surprising. A system with lower nominal power can be more cost-effective in a precise application if less rework is required. Conversely, higher continuous power on a robust surface can reduce processing time so markedly that it is clearly advantageous cost-effectively. Beamlux therefore offers material tests and live demonstrations for specific applications.

Safety with pulsed and CW systems

Regardless of which technology is chosen, powerful open laser applications have to be planned safely. Hand-held cleaning systems can be class 4 lasers. The DGUV guidance document FBHM-139 “Strahlarbeiten – Reinigen und Entschichten mit Laserstrahlung”, edition 06/2024, covers such hand-held class 4 systems.

Among other things, the risk assessment must take into account direct and reflected laser radiation as well as hazardous substances produced during the process. Process extraction is therefore an important issue regardless of the design. In addition, the following can be required:

• Securing the laser area and suitable shielding
• Laser safety goggles and instruction
• Access control
• Assessment of reflective surfaces
• Fire precautions and suitable filter technology

For laser safety in the workplace, the TROS Laserstrahlung rules issued by the BAuA are also relevant. A more powerful system must therefore never be assessed solely on the basis of processing speed: the workplace and the safety concept have to suit the application as well. The page safety information on laser class 4 summarises the key points.

Conclusion: the answer depends on the component

Which energy input suits the component does not follow from a single wattage figure. The two technologies have different properties. Pulsed systems can offer advantages in particular for controlled, precise and locally confined tasks. CW systems can convert their higher continuous power into productivity on robust surfaces and large areas. What is decisive, however, is always the specific material and the layer to be removed.

For a B2B selection, at least the following factors should be considered together: base material, type of coating, layer thickness, desired surface condition, required area coverage rate, daily utilisation, mobility requirements, degree of automation and safety requirements. Only from these can it be derived which technology suits the task.

At the same time this means: a pulsed laser with 200 or 300 watts can be the technically and cost-effectively better solution for a particular application than a considerably more powerful CW system. On a different surface the result can be exactly the other way round. The decision should therefore be made on the original material wherever possible.

Sources

• Fraunhofer Institute for Laser Technology ILT — “Reinigen”: information on pulsed and continuous laser processing for cleaning, paint removal and surface preparation.
• Fraunhofer Institute for Material and Beam Technology IWS — information on laser-based surface pre-treatment and automated joining processes.
• DGUV — FBHM-139 “Strahlarbeiten – Reinigen und Entschichten mit Laserstrahlung”, edition 06/2024.
• BAuA — TROS Laserstrahlung, July 2018 version.

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