Chances and Limitations in the Application of Laser Chemical Machining for the Manufacture of Micro Forming Dies

Abstract

Laser chemical machining, a non-conventional processing method based on thermally activated electrochemical material dissolution, represents a promising technology for manufacturing metallic dies for micro forming applications. Prior to widespread industrial acceptance the machining quality of laser chemical machining should be characterized. For this purpose, laser chemical machining is compared with micro milling regarding both the dimensional accuracy and the surface quality. Therefore, square micro cavities exhibiting side walls between 100 μm and 400 μm in length and 60 μm in depth are machined with both manufacturing processes into the cobalt-chrome alloy Stellite 21. The geometrical features are investigated using laser-scanning confocal microscopy and scanning electron microscopy. On the one hand, laser chemical machining is more suitable for manufacturing cavities with dimensions < 200 μm due to higher shape accuracy with stable mean edge radii of (11.2 ± 1.3) μm as a result of roughing and finishing steps. On the other hand, the finish quality of micro milling with mean surface roughness Sa of 0.2 μm could not be achieved with laser chemical machining due to in-process induced waviness. Finally, the metallographic analysis of the surface-near layers reveals that both manufacturing processes ensure gentle machining without any noticeable micro structural impact.

Dynamic Process Behavior in Laser Chemical Micro Machining of Metals

“…In addition, LCM can be used for the fabrication of micro tools for forming applications. In [10], micro die cavities with dimensions < (300 × 300 × 60) µm 3 were machined from a cobalt-chromium alloy by LCM and compared to micro milling. Despite lower removal rates, LCM results in smoother removal, higher shape accuracy (deviations <3%) and smaller edge radii (<12 µm).…”

Tooling

“…This makes a subsequent finishing step necessary. Therefore, a two-step strategy with a roughing step based on single scans with velocities <40 μm/s and a finishing step based on multi-scans with feed velocities >50 μm/s is assumed to be the expedient approach [Mes18]. The results hereof are discussed in Sect.…”

“…Next, the tool material Stellite 21 (a cast cobalt-chrome alloy) is used to show the dimensional accuracy and the surface quality of laser chemically machined forming cavities, which are of interest for micro cold forging. Here, square micro cavities with side lengths of 150 and 300 μm and depths of 60 lm were targeted [Mes18].…”

Influence of Laser-Induced Bubble Formation on Laser Chemical Machining

“…Non-conventional machining processes are alternative machining processes, especially for metal workpieces and among them, laser chemical machining (LCM) is very important [2]. Laser chemical machining combines the advantages of laser processing, such as precise and localized energy input, and the advantages of electrochemical processing with a gentle energy impact without significant heat impact [3], which is why the unprocessed microstructure of the materials is not affected [4].…”

“…Within a suitable process window, a gentle ablation is generated without a detectable heat-affected zone and without remelting processes in the material, which is the main advantage of laser chemical machining compared to other laser based non-conventional ablation processes [4].…”