LPKF has developed a range of process monitoring techniques for verification of the welding process. These techniques cover all types of laser welded applications from standard lap and T joints to radial welds. Laser plastic welding itself is a robust process, but LPKF's process monitoring modules offer an added layer of quality control.
Melt travel monitoring, also known as collapse control, is the most widely used monitoring technique for quasi-simultaneous welding. A weld rib built into the lower part is designed to melt and collapse as force is applied during the welding process. The distance of collapse can be precisely measured, ensuring that all geometric tolerances have been overcome and a consitent joint is created. The closed loop process will stop once a desired variant has been met, either a set time, distance of collapse or when a fixed stop is reached.
A pyrometer can be used to measure the temperature signal from the weld joint. This information can be passed to the laser control to automatically adjust the laser output and attempt to compensate for parts without proper energy input in the joint. The temperature must stay within a specific enery envelope, too much energy and the plastic will degrade, too little and no weld is created.
Radiation emitted from burns or scorches ranges from visible to infrared, if radiation is detected within these wavelengths the burn detedction module can distinguish them quite easily from the intended infrared radiation from the laser.
Refelction diagnosis is a patented quality control method designed to detect gaps at the weld interface. In this method a secondary, test beam is applied to the joint. The reflection diagnosis module records the reflected signal of this test beam. If a gap exists at the joint the test beam will have one more surface to reflect from causing an added peak in monitored reflection of the test beam.
This method is well suited for applications with a strong contrast in color between the two parts, i.e. natural polymers welded to black polymers. The camera can detect inconcistencies in color of the joint, areas in the weld with gaps will appear lighter in color than areas with good bonding. The camera can also measure the consistency of the weld bead tickness for aesthetic quality purposes.
The process parameters in the default laser plastic welding process provide a reliable process in and of themselves. Deviations from these set values are immediately detected and can issue warnings about part variations or bad welds, reducing the cost or need for post weld inspection.
LPKF's process capturing softwrae ProCat is a universal data interface, recording measurment data from a variety of tracking components and sensors. The software can compare the results with predefined process specifications and analyze the findings.