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Remanufacturing and Advanced Machining
Various mixtures and greases spread directly on a workpiece surface before further processing constitute a distinct group of the protective temporary technological
coatings. These are simplified coatings that provide significant protection, though
more limited than normal coatings do (Alexenko et al., 2016).
Various metal coatings are used to protect components and workpieces during hot
working. As a rule, metal coatings based on iron, aluminum, chromium, and copper
are used. Coating of a workpiece surface is realized, e.g., by cladding with mild steel
or copper, or by plasma deposition of thin layers of heat-resistant alloys. Electroplating
with copper coatings affords protection of individual sections of steel shafts and gears
from carburization during chemical thermal treatment. Aluminum-based coatings
are formed by diffusion saturation and provide high thermal resistance.
Coating systems can be distinguished from any known type of coating because
they employ two protective layers. One of them may be used during hot forming or
heat treatment, while the other may remain as a protective coating during further
exploitation of a component. Direct comparisons of performance of a homogeneous
single-layer coating system with that of a double-layer coating system demonstrate
that the latter can significantly reduce surface temperature and interfacial normal
stress (Yang et al., 2009). Even though the double-layer system is more resource-consuming, it is still economically effective due to enhanced protection and subsequent
improvement of final product quality.
2.2.4 TemPorary ProTecTive coaTings in micromachining
Temporary technological coatings can also be used in microscale machining processes. Application of sacrificial protective paraffin coating is reported to substantially improve surface quality during drilling. The amount of overcutting was
reportedly reduced from 4.75 to 0.56%, basically suppressing overcutting and
restricting the crack initiation process (Baek et al., 2013).
Similarly, Zhao, Huang et al. (2021) publish their results on micro-ultrasonic
machining (μUSM), where a slight lateral vibration at the end of a tool inevitably
occurs due to tool manufacturing installation errors and mechanical system vibrations. These vibrations cause overcutting and edge breakage, creating undesirable
effects on heat transfer and flow deflection. Hence, the authors present a new fabrication method that ensures high surface integrity by applying a protective coating on
the substrate. PE-Wax coating of 400 μm thickness, feed rate of 4 μm/s, 60% ultrasonic power, and 25% slurry concentration proves optimum. These conditions ensure
decrease of overcutting from 74.3 to 28 μm (62.3% improvement) and of weighted
edge damage from 52.3 to 16 μm (69.4% improvement). Finally, a 65.85% improvement in the surface integrity index arises on application of a temporary protective
coating during μUSM (Zhao, Huang et al., 2021).
2.3 HIGH TEMPERATURE COATINGS
Due to harsh work conditions, turbine blades are usually covered with coatings
that display various properties like oxidation and hot corrosion resistance, strength
Remanufacturing and Advanced Machining
Various mixtures and greases spread directly on a workpiece surface before further processing constitute a distinct group of the protective temporary technological
coatings. These are simplified coatings that provide significant protection, though
more limited than normal coatings do (Alexenko et al., 2016).
Various metal coatings are used to protect components and workpieces during hot
working. As a rule, metal coatings based on iron, aluminum, chromium, and copper
are used. Coating of a workpiece surface is realized, e.g., by cladding with mild steel
or copper, or by plasma deposition of thin layers of heat-resistant alloys. Electroplating
with copper coatings affords protection of individual sections of steel shafts and gears
from carburization during chemical thermal treatment. Aluminum-based coatings
are formed by diffusion saturation and provide high thermal resistance.
Coating systems can be distinguished from any known type of coating because
they employ two protective layers. One of them may be used during hot forming or
heat treatment, while the other may remain as a protective coating during further
exploitation of a component. Direct comparisons of performance of a homogeneous
single-layer coating system with that of a double-layer coating system demonstrate
that the latter can significantly reduce surface temperature and interfacial normal
stress (Yang et al., 2009). Even though the double-layer system is more resource-consuming, it is still economically effective due to enhanced protection and subsequent
improvement of final product quality.
2.2.4 TemPorary ProTecTive coaTings in micromachining
Temporary technological coatings can also be used in microscale machining processes. Application of sacrificial protective paraffin coating is reported to substantially improve surface quality during drilling. The amount of overcutting was
reportedly reduced from 4.75 to 0.56%, basically suppressing overcutting and
restricting the crack initiation process (Baek et al., 2013).
Similarly, Zhao, Huang et al. (2021) publish their results on micro-ultrasonic
machining (μUSM), where a slight lateral vibration at the end of a tool inevitably
occurs due to tool manufacturing installation errors and mechanical system vibrations. These vibrations cause overcutting and edge breakage, creating undesirable
effects on heat transfer and flow deflection. Hence, the authors present a new fabrication method that ensures high surface integrity by applying a protective coating on
the substrate. PE-Wax coating of 400 μm thickness, feed rate of 4 μm/s, 60% ultrasonic power, and 25% slurry concentration proves optimum. These conditions ensure
decrease of overcutting from 74.3 to 28 μm (62.3% improvement) and of weighted
edge damage from 52.3 to 16 μm (69.4% improvement). Finally, a 65.85% improvement in the surface integrity index arises on application of a temporary protective
coating during μUSM (Zhao, Huang et al., 2021).
2.3 HIGH TEMPERATURE COATINGS
Due to harsh work conditions, turbine blades are usually covered with coatings
that display various properties like oxidation and hot corrosion resistance, strength