Test Methods in Process Evaluation

In markets such as automobile industry or medical technology a constant process monitoring is often required. What functionalities and which process parameters should be monitored and qualified in production is verified in the evaluation process.

During the evaluation process of a welding technique, components are tested of weldability by our application engineers. At first the overall impression of the welding partners is checked due to color, evenness of the welding zone, a correct fit, general dimensions, fiber distribution, etc.

In some cases additional, detailed investigations of materials or components are necessary.

Pre- and In-Process
  • In-Process
    • Spectroscopy

      Testing the transparency of plastics during the evaluation process with the working laser has been proofed as good in most cases. But since each additive that is mixed into the plastics changes optical behaviors of the base material, material transparency may change also with wavelength. So, critical components should be examined over a bigger wavelength range. A spectroscopy measurement determines the transparency of the material in dependent of the wavelength. Thus, the most suitable laser source can be selected. The measurement curve represents a polycarbonate filled with additives. The transparency degrades constantly from 800 nm to 1100 nm. Thus, a laser source that radiates at 808 nm is recommended.

      But if this material is used as the absorbent welding partner, transparency should be low and lasers with wavelength of 980 nm or 1070 nm are a better choice.

    • Optical penetration depth

      The determined absorption of the spectroscopic measurement is a value representing the entire thickness of the sample and is therefore not necessarily an adequate measure of the weldability. For this, the optical penetration depth is used which is a measure of the energy distribution in the material that is generated by conversion laser energy into heat. It is determined experimentally with spectroscopy investigations on thin sections.

    • Contact in the joining plane

      The principal of laser penetration welding is based on contact between the joining partners in the welding zone. Otherwise, effective heat conduction cannot be ensured. The grade of contact can be visualized using pressure paper that changes color intensity depending on pressure.

  • Post-Process

    During evaluation the product monitoring methods are qualified that will be used in production.

Post-Process

Precise and reliable process control can ensure reliable functionality in your products.

In order to ascertain a seamless supversvision of all processes, an evaluation of which parameters need to be continually supervised is necessary. During this evaluation, it is investigated which factors are relevant for a concrete application, while the concrete test process is chosen in the production stage.

Quality assurance of the welding process is performed through measurements during and after welding. Among them are tests of the optical attributes prior to welding as well as measurements of laser output, welding time, elasticity and other dimensions during welding. Downstream the welding, tests using ultrasonic and x-rays as well as computer tomography allow conclusions on the quality of the weld.