31
Contemporary Machining Processes
5. With a complex movement of the electrode
(a) Cutting with wire (rod)
(b) Cutting by means of the tubular-contour method
The ECM is perhaps most widely applied to copying of shaped surfaces and piercing
of profiled holes, calibration of spline holes after heat treatment, and deburring with
an accuracy of 0.2–0.3 mm (Koryagin et al., 2000).
The following are usually listed among the advantages of ECM (Saxena
et al., 2018):
1. Independence of workpiece hardness.
2. Possibility to machine complex shapes.
3. Lack of tool wear and high surface finish as dissolution occurs at the atomic
level.
4. Material removal rates can be controlled with electrical parameters (voltage, current, energy) and pulse characteristics (pulse frequency, time, duration, duty cycle).
5. Process forces and size effects don’t affect results of machining.
At present, many variations of the ECM are implemented, but the oldest electrochemical polishing process (ECP) is still in use. The mechanism of the electrochemical polishing process is explained as follows (Łyczkowska-Widłak et al., 2020).
According to one hypothesis, the factor that has the greatest influence on surface
smoothening during electropolishing is the emergence of a highly viscous layer on the
anode as a result of the polarization of the processed material. The anodic diffusion
layer is flat on the side facing the solution and the cathode, while on the side adjacent
to the anode it takes the form of an anodic surface. This layer is characterized by a
high electric resistance and is thinner on its micro-peaks than on micro-valleys. As
a result, the peaks of roughness are dissolved first, because a higher density current
passes through them. According to another hypothesis, acceptors of the metal dissolution process, such as particles of water and anions, play an important role. Water
causes hydration of metal ions, detaching them from the surface, promoting the diffusion of the acceptors toward the surface of electrochemically polished elements.
During electropolishing, the gradient of concentration of the acceptors increases at
micro-peaks, so that they are the first to be subjected to anodic dissolution, while in
micro-indentations, the dissolution process is slightly delayed until the metal ions
close to micro-peaks are released from the metal surface (Łyczkowska-Widłak et al.,
2020). Electrochemical polishing has been widely used for fine polishing of metals,
with an initial average surface roughness Ra to the order of 1 µm down to a mirror finish (Chang et al., 2019). Some studies report that electropolishing results in nanometer
size roughness (Allain and Echeverry-Rendón, 2018), while in the case of 2D-layered
materials, the ECP provided results down to a monolayer (Sebastian et al., 2019).
In order to overcome some shortcomings and further improve the polishing process, electrochemical mechanical polishing (ECMP) technology is employed that
Contemporary Machining Processes
5. With a complex movement of the electrode
(a) Cutting with wire (rod)
(b) Cutting by means of the tubular-contour method
The ECM is perhaps most widely applied to copying of shaped surfaces and piercing
of profiled holes, calibration of spline holes after heat treatment, and deburring with
an accuracy of 0.2–0.3 mm (Koryagin et al., 2000).
The following are usually listed among the advantages of ECM (Saxena
et al., 2018):
1. Independence of workpiece hardness.
2. Possibility to machine complex shapes.
3. Lack of tool wear and high surface finish as dissolution occurs at the atomic
level.
4. Material removal rates can be controlled with electrical parameters (voltage, current, energy) and pulse characteristics (pulse frequency, time, duration, duty cycle).
5. Process forces and size effects don’t affect results of machining.
At present, many variations of the ECM are implemented, but the oldest electrochemical polishing process (ECP) is still in use. The mechanism of the electrochemical polishing process is explained as follows (Łyczkowska-Widłak et al., 2020).
According to one hypothesis, the factor that has the greatest influence on surface
smoothening during electropolishing is the emergence of a highly viscous layer on the
anode as a result of the polarization of the processed material. The anodic diffusion
layer is flat on the side facing the solution and the cathode, while on the side adjacent
to the anode it takes the form of an anodic surface. This layer is characterized by a
high electric resistance and is thinner on its micro-peaks than on micro-valleys. As
a result, the peaks of roughness are dissolved first, because a higher density current
passes through them. According to another hypothesis, acceptors of the metal dissolution process, such as particles of water and anions, play an important role. Water
causes hydration of metal ions, detaching them from the surface, promoting the diffusion of the acceptors toward the surface of electrochemically polished elements.
During electropolishing, the gradient of concentration of the acceptors increases at
micro-peaks, so that they are the first to be subjected to anodic dissolution, while in
micro-indentations, the dissolution process is slightly delayed until the metal ions
close to micro-peaks are released from the metal surface (Łyczkowska-Widłak et al.,
2020). Electrochemical polishing has been widely used for fine polishing of metals,
with an initial average surface roughness Ra to the order of 1 µm down to a mirror finish (Chang et al., 2019). Some studies report that electropolishing results in nanometer
size roughness (Allain and Echeverry-Rendón, 2018), while in the case of 2D-layered
materials, the ECP provided results down to a monolayer (Sebastian et al., 2019).
In order to overcome some shortcomings and further improve the polishing process, electrochemical mechanical polishing (ECMP) technology is employed that