Laser rust removal or sandblasting: which process costs really count?

Sandblasting and laser-based material removal can both be sensible on corroded metal surfaces. They differ considerably, however, in blasting media, set-up effort, local processing, rework and disposal. The same process can therefore be cost-effectively convincing on a large steel surface and unsuitable on a small, precise component.

The technical principles of laser-based material removal are already explained in the article How does laser ablation work when cleaning metal?. This article deals solely with the economic view of the process compared with an abrasive blasting process.

Why the machine price is not enough for the comparison

A common mistake in investment decisions is to place two machine prices side by side.

That does not answer the question of what a finished component costs, however.

After all, a company does not buy a laser or a blasting system in order to own machines. It wants to produce a defined surface within an acceptable time and at calculable costs.

All process steps have to be considered for that.

With blasting, blasting media, compressed air, protective equipment, reprocessing or disposal can play a role, for example. With a laser process, power supply, extraction technology, filters, protective components and, where applicable, maintenance are added.

Fraunhofer IFAM describes abrasive blasting processes as processes in which blasting particles are applied to a surface in a targeted manner. In the vacuum suction blasting technique developed there, these particles are extracted again immediately. The fact that a dedicated return and extraction system is developed for this already shows that the blasting medium and its handling are part of the process chain.

The comparison figure should therefore always be:

Cost per approved component or per area actually processed.

What costs arise with sandblasting

Sandblasting is an established term, although different blasting media are used in professional processes depending on the application.

The costs are not made up of blasting time alone.

Depending on the system and the task, the following can be relevant:

• Blasting media
• Compressed air generation
• Blasting cabinet or enclosure
• personal protective equipment
• Extraction and filter technology
• Collection of the blasting material
• Reprocessing or replacement of the medium
• Cleaning of the component
• Cleaning of the workplace
• Disposal of contaminated residues

How high these items turn out to be depends heavily on the blasting system, the material and the contamination.

A closed, automated blasting process has to be assessed cost-effectively in a completely different way from mobile use on a large structure.

The DGUV, too, treats blasting work as a separate area of work with specific requirements. For a cost analysis, that means: workplace design and protective measures are not a theoretical addition but part of real operations.

Which items count in the laser process

A laser-based process is not free of charge either, simply because no conventional blasting media are used.

The following should be considered, among other things:

• Investment or hire costs
• Electricity
• Process extraction
• Filters
• Protective windows and other wear parts
• Maintenance
• Safeguarding the workplace
• Training and instruction
• Operating time

Material removal also produces particles and other process emissions. The removed material does not disappear.

The DGUV guidance document FBHM-139 therefore expressly deals with both laser radiation and the hazardous substances produced during cleaning and coating removal.

The economic difference is therefore not that one method has secondary processes and the other does not.

What matters is which secondary processes arise for the specific application and how much effort they involve.

Blasting media and consumables

In an abrasive blasting process, the blasting media perform an active function in the process.

They strike the surface and produce a mechanical effect there.

Depending on the process, they can be used several times, reprocessed or disposed of after the process. As contamination increases, the question can also arise of how to deal with the mixture of blasting media and removed material.

With the laser, this conventional blasting medium is not required.

Fraunhofer IFAM expressly names the absence of any need for abrasive media as a difference between laser-based coating removal and mechanical processes.

That does not eliminate every consumable item, however.

Filters in the extraction technology and protective components can still cause operating costs.

For a clean comparison, the catchphrases “with consumables” and “without consumables” should therefore not simply be set against each other.

An annual calculation is better:

How many kilograms or tonnes of medium are needed?

How often are filters changed?

What disposal costs arise?

What storage and logistics space is needed?

Only that produces a relevant figure.

Set-up time and working environment

On small jobs, set-up time can have a greater influence than the actual processing.

If a component is treated for only ten minutes but has to be set up, masked or transported for an hour beforehand, the ancillary times dominates.

Depending on the set-up, blasting work can require a cabinet, an enclosure or protective measures against escaping blasting media.

A hand-held laser likewise requires a safely controlled working area.

Which system is set up more quickly therefore depends heavily on the site of use.

In a permanently installed blasting cabinet, the set-up effort per series component is low.

With mobile work on a machine or structure, the situation can look different.

The laser can be brought locally to the workpiece, but it requires a safety concept that matches the class and the application.

So the question is not:

Which process requires set-up?

But rather:

What set-up is necessary at this particular workplace?

Large surface or local area?

This is where cost-effectiveness can shift considerably.

On a large, robust steel surface, an abrasive blasting process can achieve high area coverage rates.

If an entire structure is to be blasted completely anyway, the local precision of a laser may not be an economic advantage.

Things look different if only a small area has to be treated.

Examples are:

• a weld zone
• a repair point
• a contact area
• a locally corroded section
• a defined coating area

For laser-based coating removal, Fraunhofer IFAM highlights precisely this selective local processing. Coatings can be removed in defined areas without necessarily including adjacent surfaces.

That changes the relevant surface area.

On a component measuring ten square metres, the processing actually necessary may amount to only 0.5 square metres.

For an economic calculation, the complete component surface should therefore never be applied automatically.

Rework and surface condition

The cheapest process is not necessarily the one with the shortest actual processing time.

What is relevant is the condition required afterwards.

An abrasive process changes the surface topography in a targeted way. That can be expressly desirable, for example when a defined roughness is needed for a subsequent coating process.

Fraunhofer IFAM uses abrasive vacuum suction blasting precisely for cleaning and roughening surfaces before bonding processes, among other things.

The mechanical effect is therefore part of the desired result there.

A laser process, by contrast, can be aimed selectively at an existing layer.

Where a surface is to be processed as locally as possible or an existing geometry preserved, this can represent an advantage.

For the cost comparison, the first thing that has to be defined is therefore:

What surface result is required?

Only then can it be judged whether additional rework is necessary.

Disposal and process residues

Both processes remove material.

With blasting, the blasting medium used is added on top.

Depending on the system, this medium is collected and possibly reprocessed. If it is contaminated by the removed coating, its further treatment has to be taken into account accordingly.

With the laser, no additional abrasive blasting particles are produced. The removed layer is released as process debris, however, and should be captured with suitable process extraction.

What disposal requirements apply depends on the coating that has been removed.

Old paint, for example, can contain different substances from a pure rust layer.

A cost calculation should therefore always start from the material actually processed.

The statement “lasers produce no waste” would be wrong.

The correct difference is:

No additional conventional blasting medium is introduced into the removed material.

Staff and operating time

Staff costs, too, can have different effects.

A hand-held process ties up an operator directly during processing.

Automated blasting systems, by contrast, can process large quantities with a smaller manual share.

Laser processes can likewise be automated.

That changes the calculation again.

For one-off pieces or mobile work, the working time needed per job is often the relevant factor.

For series components, by contrast, the following should be examined:

• How many parts can a system manage per shift?
• How long do loading and unloading take?
• How high is system availability?
• Which inspection steps are needed?
• How many operating staff are actually tied up?

The choice between processes should therefore not be made in isolation from the production model.

Downtime and component transport

Logistics is a frequently underestimated cost factor.

If a large machine component has to be transported to a blasting operation, dismantling, transport and possible downtime arise.

If the processing can take place directly at the machine, that changes the calculation.

Conversely, a mobile process is not automatically cheaper.

If extensive shielding or shutdown areas have to be set up for safe mobile use, costs arise as well.

For maintenance tasks, the entire time should therefore be considered:

From machine shutdown to machine released again.

Not merely:

From start to end of the actual surface removal.

With production systems in particular, an hour of downtime can have a higher economic value than the processing itself.

What a robust comparative calculation looks like

A sensible calculation starts with a specific reference component.

The same boundaries are then defined for both processes:

initial condition, area, desired final condition and quantity.

All process times are then recorded.

These include:

• Setting up
• actual material removal
• necessary interim inspection
• Rework
• Cleaning
• Disposal
• Changeover
• Approval

Consumption and system costs are taken into account in addition.

Only after that does a figure per component or square metre emerge.

This calculation is considerably more meaningful than the question of which process is fundamentally cheaper.

When sandblasting can be cost-effectively stronger

Sandblasting and other abrasive blasting processes can be very cost-effective, particularly on large, robust surfaces.

That applies especially when:

• a high area coverage rate is needed,
• a defined roughening is desired,
• a suitable blasting system is already available,
• large areas are processed completely,
• the workpieces fit into the existing process without difficulty.

In such a scenario, a laser-based process first has to offer a specific additional benefit in order to make economic sense.

A modern blasting system should therefore not be regarded as a technically outdated method.

It simply solves a different task.

When the laser can play to its strengths

Laser-based material removal becomes cost-effectively interesting above all where the precision of the process avoids a real secondary process.

Examples can be:

• only small partial areas are treated,
• adjacent areas are to be preserved,
• Blasting media would be problematic in the surroundings,
• a mobile component is to be treated on site,
• automated local processing is needed,
• Coating removal is to be sharply delimited.

Fraunhofer IFAM describes precisely this local and selective coating removal as a strength of the laser-based process.

The technical differences between pulsed and CW systems are examined in more depth in the existing article Pulsed laser or CW: which energy input suits the component?.

Conclusion: compare process costs, not machine prices

Laser rust removal or sandblasting: which process costs really count?

Not the purchase price alone.

A robust decision takes into account:

• actual processing area
• Area coverage rate
• Set-up time
• Blasting media or filters
• Energy demand
• Staff
• Rework
• Workplace cleaning
• Disposal
• Component transport
• Downtime

Sandblasting can be cost-effectively very strong on large, robust surfaces.

The laser can play to its strengths above all where work is to be carried out locally, selectively and without additional blasting media.

There is therefore no blanket winner.

The cost-effectively correct method follows from the specific component and the complete process chain.

Sources

• Fraunhofer IFAM – Abrasive pre-treatment with vacuum suction blasting — information on abrasive surface processing, blasting medium, extraction and automated pre-treatment.
• Fraunhofer IFAM – Surface decoating by laser — information on local and selective laser-based coating removal.
• DGUV – Strahlarbeiten — regulations and guidance on working with blasting equipment.
• DGUV – FBHM-139 “Strahlarbeiten – Reinigen und Entschichten mit Laserstrahlung” — edition 06/2024.

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