Ultrashort Pulse Laser Surface Texturing for Injection Mold Functionalization

Micro texturing of injection molds for plastic part functionalization has been of growing interest in recent years. Especially for laser texturing it has been successfully demonstrated at lab scale that microscopic surface features can be replicated in plastics at highest structural precision. This paper focusses on high-rate laser surface texturing of injection mold steel 40CrMnMo7 for injection molding of plastic parts with hydrophobic surface behavior. In this study, an ultrashort pulse laser system was used providing an average maximum laser power of 70 W. At first, the most important process parameters like fluence (0.37 – 2.87 J/cm²) and pulse repetition frequency (PRF, 2 – 16 MHz) were varied in order to determine optimal parameter settings for high quality and high throughput laser machining using a polygon scan system with a scanning speed of 100 m/s. In addition, the influencing effect of the microstructure topography on hydrophobicity was examined. Particularly, the laser texturing of the mold sidewalls was challenging as the processing angle was tilted to 45° that was helpful for defect-free demolding of the injection molded 3D-part. Finally, a whole 3D-injection mold was laser textured for injection molding of a small plastic box with a processed surface area > 40 cm² to prove the feasibility of the process.

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