During process trials, it is possible to find a set of parameters that produces a very good result.

The right power. The right speed. The correct focal position. A sound weld cross-section. This is an important result, but it is not sufficient in serial production.

The actual process must remain stable even when successive parts are not identical, the material batch changes, the surface has slightly different properties, or the operating conditions of the production station change slightly. Therefore, the objective of technology development should not be to find one “ideal” set of settings.

The objective is to establish a stable process window.

Laser power is only one of the parameters

One common simplification when selecting a technology is to focus primarily on the nominal power of the laser source.

However, the way the beam interacts with the material also depends on many other factors, including:

• spot size,
• power density,
• focal position,
• energy distribution within the beam,
• welding speed,
• the shape of the path,
• beam incidence angle,
• the method of power modulation.

Therefore, two systems with the same nominal power can behave differently. This is particularly important for materials such as copper, which at ambient temperature absorbs a relatively small proportion of the energy delivered by typical industrial lasers while at the same time dissipating heat very quickly.

In processes requiring deep penetration, the stability of the vapour channel, known as the keyhole, also becomes important. Its behaviour affects, among other things, weld penetration depth, the formation of voids, and spatter.

Advanced beam shaping can improve process stability in some applications. However, it cannot replace proper part preparation, gap control, or appropriate clamping.

What is a process window?

A process window is the range of parameters within which the joint continues to meet the requirements despite small changes in process conditions.

When defining the process window, it is necessary to check how changes in selected parameters affect, among other things:

• weld depth and width,
• mechanical strength,
• electrical resistance,
• the presence of voids,
• spatter formation,
• the thermal impact on adjacent components.

The objective is not to find the settings that produce the best single weld cross-section. It is much safer to select conditions that are sufficiently far from the boundary of lack of fusion, excessive penetration, or damage to other product components.

The narrower the process window, the greater the risk that natural differences between successive parts will begin to cause quality problems.

Monitoring does not yet mean quality control

Modern laser welding stations can be equipped with systems that collect and analyse process data.

Monitoring makes it possible to detect a situation in which the welding process differs from a previously recorded reference. However, this does not automatically mean that the system knows the actual quality of the resulting joint.

Therefore, effective process control should operate at several levels. Before welding, the presence, position, and clamping of the part can be checked.

During welding, it is possible to monitor the condition of the equipment and the signals generated in the beam interaction area. After the joint has been produced, the position and appearance of the weld, the path, and any visible spatter can be assessed.

During process validation, however, actual tests of the joint properties are still required: cross-section analysis, mechanical testing, resistance measurements, leak-tightness testing, or durability testing – depending on the function of the product.

Data only become valuable after correlation

A monitoring signal may show that something unusual happened while a particular weld was being made.

However, to determine whether this indicates a defect, a sound joint, or simply a result that requires additional inspection, the process data must be compared with the results of tests on actual welds.

Only this type of correlation makes it possible to establish reliable assessment criteria.

Monitoring is therefore a highly valuable tool supporting quality control.

However, it does not replace prior understanding of the process and validation of the joint properties.

Stability must be confirmed in production

Even a well-defined process window and extensive monitoring require further verification after serial production has started.

Over a longer period, phenomena appear that are difficult to encounter during a short trial run.

Material batches change. The production station heats up. Tooling wears. Clamping and optical elements become contaminated. Consumable parts are replaced.

Each of these factors can affect the behaviour of the technology.

Therefore, a scalable process requires not only appropriately selected parameters, but also inspection procedures, proper recipe management, calibration, and maintenance of the production station.

Repeatability is more important than a single ideal result

A mature laser welding process should not be assessed on the basis of one ideal weld.

It is far more important to determine whether the required result can be achieved consistently despite the natural variation present in serial production.

Therefore, it is worth considering the following together: process window + monitoring + validation + real production conditions.

Only together do they provide the foundation for building a process that can be scaled safely.

Does your process have a sufficiently wide process window for serial production?

A sound result from a single trial does not yet confirm the robustness of the technology against natural production variation. Before scaling, it is worth checking the range within which the process remains stable and which parameters have the greatest impact on joint quality.

During a free consultation, Nextomation experts will help assess the application, identify the key process variables, and determine the scope of trials required to establish a stable process window before implementation in serial production.

Consult us on scaling your laser welding process

Read also

Laser welding in serial production – how to move from process trials to a stable process? (part I)

Learn about the complete path from the first tests to a technology that is ready to operate on the target production station.

Not everything can be corrected with the laser. How do product design and clamping affect weld quality? (part II)

See how product geometry, gaps, and tooling affect the width of the available process window.

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