Micro-Milling Process of Metals: A Comparison between Femtosecond Laser and EDM Techniques

Nowadays, micro-machining techniques are commonly used in several industrial fields, such as automotive, aerospace and medical. Different technologies are available, and the choice must be made considering many factors, such as the type of machining, the number of lots and the required accuracy specifications in terms of geometrical tolerances and surface finish. Lasers and electric discharge machining (EDM) are widely used to produce micro-components and are similarly unconventional thermal technologies. In general, a laser is particularly appreciated by the industry for the excellent machining speeds and for the possibility to machine essentially any type of materials. EDM, on the other hand, has a poor material removal rate (MRR) but can produce microparts on only electrically conductive workpieces, reaching high geometrical accuracy and realizing steep walls. The most common micro-application for both the technologies is drilling but they can make also milling operations. In this work, a comparison of femto-laser and EDM technologies was made focusing on micro-milling. Two features were selected to make the comparison: micro-channels and micro-pillars. The depth was varied on two levels for both features. As workpiece material, aluminum, stainless steel and titanium alloy were tested. Data regarding the process performance and the geometrical characteristics of the features were analyzed. The results obtained with the two technologies were compared. This work improves the knowledge of the micro-manufacturing processes and can help in the characterization of their capabilities.

Size-induced twinning in InSb semiconductor during room temperature deformation

Room-temperature deformation mechanism of InSb micro-pillars has been investigated via a multi-scale experimental approach, where micro-pillars of 2 µm and 5 µm in diameter were first fabricated by focused ion beam (FIB) milling and in situ deformed in the FIB-SEM by micro-compression using a nano-indenter equipped with a flat tip. Strain rate jumps have been performed to determine the strain rate sensitivity coefficient and the related activation volume. The activation volume is found to be of the order of 3–5 b3, considering that plasticity is mediated by Shockley partial dislocations. Transmission electron microscopy (TEM) thin foils were extracted from deformed micro-pillars via the FIB lift-out technique: TEM analysis reveals the presence of nano-twins as major mechanism of plastic deformation, involving Shockley partial dislocations. The presence of twins was never reported in previous studies on the plasticity of bulk InSb: this deformation mechanism is discussed in the context of the plasticity of small-scale samples.

Differences in Deformation Behaviors Caused by Microband-Induced Plasticity of [0 0 1]- and [1 1 1]-Oriented Austenite Micro-Pillars

A uniaxial compression test and scanning/transmission electron microscopy observations were performed to investigate the differences in mechanical behavior and deformed microstructure between focused ion beam-manufactured [1 1 1]- and [0 0 1]-oriented austenite micro-pillars with 5 μm diameter from duplex stainless steel. After yielding, the strain hardening of two orientation micro-pillars increased sharply as a result of the formation of a microband, namely microband-induced plasticity, MBIP. The same phenomenon could be observed in a [0 0 1]-oriented pillar due to the activation of the secondary slip system, while slight strain hardening behavior was observed in the [1 1 1] orientation because of the refinement of the microband. Furthermore, the trend of the calculated strain hardening rates of both [1 1 1]- and [0 0 1]-oriented micro-pillars were in good agreement with the experimental data. This study proved that MBIP can be helpful for the mechanical property enhancement of steels.

Measurements of periodically perturbed dewetting force fields and their consequences on the symmetry of the resulting patterns

We studied the origin of breaking the symmetry for moving circular contact lines of dewetting polymer films suspended on a periodic array of pillars. There, dewetting force fields driving polymer flow were perturbed by elastic micro-pillars arranged in a regular square pattern. Elastic restoring forces of deformed pillars locally balance driving capillary forces and broke the circular symmetry of expanding dewetting holes. The observed envelope of the dewetting holes reflected the symmetry of the underlying pattern, even at sizes much larger than the characteristic period of the pillar array, demonstrating that periodic perturbations in a driving force field can establish a well-defined pattern of lower symmetry. For the presented system, we succeeded in squaring the circle.