Quality assurance measures for laser-welded assemblies

Definition of quality requirements even before process development

Quality assurance begins with the individual parts, as a prerequisite for reliable laser welding is the so-called "technical zero gap". This means that the individual parts must fit together exactly to within a few hundredths of a millimeter in order to achieve the desired result. The surface condition (burr formation, roughness, coating, degree of reflection) of the components to be welded can also have a significant influence on laser welding. In general, it makes sense to define the requirements for the individual parts as precisely as possible before the process is developed and to safeguard them during series production using suitable test procedures and scopes.

Laser-cut sheet metal or bent sheet metal parts are often used for welded assemblies. These often offer a considerable cost advantage compared to machined components. The greater manufacturing tolerances must be countered with intelligent fixture concepts: In most cases, it is possible to create the required zero gap for butt welds only by clamping the fixture. Alternatively, lap joints can also be used. In this way, welding processes can be made extremely robust even with relatively large individual part tolerances.

Cleanliness as a key quality factor

The cleanliness of the individual parts is of great importance for successful laser welding - especially with critical materials such as aluminum or copper. Contamination with oil or cooling lubricants from upstream production steps can have a negative effect on process stability during laser welding. Care must also be taken during handling, transportation and storage to prevent unintentional contamination of the components. For particularly sensitive welding processes, the use of suitable cleaning and testing processes (e.g. surface tension measurement) is recommended. The choice of cleaning process is based on the component geometry and the required cleanliness class. Very reproducible results can be achieved economically using laser cleaning.

Another factor is a clean production environment. Where cleanliness requirements are critical, laser welding in a clean room is also an option. However, it should be noted that contamination of the environment and, above all, of the product cannot be completely ruled out, especially during deep penetration welding. Comprehensive ventilation and extraction with an appropriate filter system is essential to prevent particles from settling in the production environment. The required technical cleanliness must be taken into account as early as the welding process development stage and the welding process must be designed accordingly. In the finished state, compliance with the cleanliness requirements can then be checked using a residual dirt analysis (extraction process), for example.

Integration of sensitive components

In the case of laser-welded assemblies whose function goes beyond the mechanical loads, sensitive components such as electronic modules, battery cells, sensors or electric motors must also be integrated in some cases. On the one hand, care must be taken during handling, but also during processing, to ensure that no damage occurs. On the other hand, potential safety aspects must be taken into account. The high monetary value of the components to be welded should also not be underestimated. For these reasons, it makes sense to evaluate possible faults and their effects as part of an FMEA (Failure Mode and Effects Analysis) and to implement appropriate measures before the start of production in order to avoid major damage.

At BBW Lasertechnik, we are familiar with the challenges involved in manufacturing complex laser-welded assemblies and apply customized quality concepts.

 

A contribution by Andreas Bürger and Stephan Wagner