Process monitoring is a major issue in production with the target to ensure functionality and quality of the product. In order to achieve this target, quality control methods are defined before, during or after each process step. Such methods are evaluated during process development before implementation into production.

Monitoring methods are versatile and should be adapted to the overall production process. Here both can be relevant, the controlling of active parameter or the passive monitoring of single process steps. For an early detection of bad parts a cross-production monitoring is recommended. Indicators of weldability may be identified with simple monitoring methods. Components can be verified prior welding on dimensions, evenness and fit.

Depending on the welding technique either monitoring or controlling methods are applicable during welding. Downstream quality control may also be appropriate, as long as the components are not damaged. The condition of the components as well as production environment determines which monitoring methods are most suitable.

Quality control for Laser plastic welding can be divided in three phases:

1. Pre-pprocess, monitoring prior welding
2. In-process, an in-process monitoring or controlling
3. Post-process, a downstream monitoring

In all three phases welding technology related quality control methods are available. As an example the pictures below shows a choice of methods for laser welding plastics.

Welding relevant data like optical properties, dimensions or shape of the welding zone are in general identified in pre-process and based on materials and design. Path measurement and pyrometer are the most commonly used methods during welding. But a statement on the welding quality is only possible in post-process. Since most of the methods used in this phase damage the components, they are only tested on randomly selected samples.

In the following a few common test methods are described in more detail.