21
Contemporary Machining Processes
does not generate substantial expenses, it may be supplied during the entire operation through the valve (11).
As with all manufactured engineering products, castings suffer from errors of
shape and size. In general, the so-called precision investment castings were found to
be precise at small sizes, but rather poor at large sizes, while the pressure die casting
and modern sand castings appeared to be highly accurate (Campbell, 2015). Castings
are an integral part of many industries and involve more than 25% of the metal processes. In the 21st century, sand casting and gravity die casting are the two major
industrial processes. However, an observation made from several foundries indicates
that the V-process is implemented more frequently than investment casting. Several
industries started adopting this process and found that it gives excellent yield and
aesthetics with a near-net-shape finish. As a result of the process implementation,
the machining cost is cut down drastically and the process proves to be environment
friendly as well (Senthil et al., 2020). Thus, the vacuum-sealed molding seems to be
one of the most promising processes with potential for further development.
1.4 DIAMOND AND ELECTRICAL DISCHARGE
DIAMOND GRINDING
Nowadays, new constructional alloy steel with chemical additions enhancing its
properties is widely applied, as well as tungsten, nickel, and aluminum alloys. These
materials are attractive, but due to their increased tensile strength, low thermal conductivity, low plasticity, and other special properties, they pose difficulties during
machining. Their carbon content increased from 0.1% to 0.7% abruptly reduces the
machinability of steels with titanium, molybdenum, tungsten, vanadium, and chromium additions, so that the specific output of grinding falls by 30%. All types of carbides cause fast tear and wear of grinding wheel’s abrasive grains. When steels with
austenite structure are ground, their special output falls by 25% in comparison with
martensite–troostite structures. Addition of silicon to alloys dramatically reduces
grinding machinability, while alloying of metals with more than 2–3% of Мо and W
also impairs it (Ivanova et al., 2018).
At the final stages of mechanical treatment of hard alloys and steels, organic-,
metal-, and ceramic-bonded abrasive diamond machining is widely used (Smirnov
et al., 2020). A typical bonded abrasive tool includes super hard grains (usually
diamond or cubic boron nitride with monocrystalline grains or microcrystals of
sizes ranging from one to several microns, characterized by a higher ductility and
mechanical strength), fillers (usually corundum, silicon carbide, boron nitride, etc.),
binders (sintered metal, electroplated, resin, ceramic, hybrid), modifiers (homogenizers, greases), and body (metal, ceramic, polymer) (Staniewicz-Brudnik et al.,
2015). Porous metal-bonded diamond grinding wheels had an excellent grinding
performance for hard-brittle materials (Su et al. 2006). Recently, the brazing superabrasive technique for diamond and cubic boron nitride has been considered as one
of the most promising approaches to the fabrication of grinding wheels. Compared
with conventional bonding methods, e.g., electroplating or sintering, a brazed tool
Contemporary Machining Processes
does not generate substantial expenses, it may be supplied during the entire operation through the valve (11).
As with all manufactured engineering products, castings suffer from errors of
shape and size. In general, the so-called precision investment castings were found to
be precise at small sizes, but rather poor at large sizes, while the pressure die casting
and modern sand castings appeared to be highly accurate (Campbell, 2015). Castings
are an integral part of many industries and involve more than 25% of the metal processes. In the 21st century, sand casting and gravity die casting are the two major
industrial processes. However, an observation made from several foundries indicates
that the V-process is implemented more frequently than investment casting. Several
industries started adopting this process and found that it gives excellent yield and
aesthetics with a near-net-shape finish. As a result of the process implementation,
the machining cost is cut down drastically and the process proves to be environment
friendly as well (Senthil et al., 2020). Thus, the vacuum-sealed molding seems to be
one of the most promising processes with potential for further development.
1.4 DIAMOND AND ELECTRICAL DISCHARGE
DIAMOND GRINDING
Nowadays, new constructional alloy steel with chemical additions enhancing its
properties is widely applied, as well as tungsten, nickel, and aluminum alloys. These
materials are attractive, but due to their increased tensile strength, low thermal conductivity, low plasticity, and other special properties, they pose difficulties during
machining. Their carbon content increased from 0.1% to 0.7% abruptly reduces the
machinability of steels with titanium, molybdenum, tungsten, vanadium, and chromium additions, so that the specific output of grinding falls by 30%. All types of carbides cause fast tear and wear of grinding wheel’s abrasive grains. When steels with
austenite structure are ground, their special output falls by 25% in comparison with
martensite–troostite structures. Addition of silicon to alloys dramatically reduces
grinding machinability, while alloying of metals with more than 2–3% of Мо and W
also impairs it (Ivanova et al., 2018).
At the final stages of mechanical treatment of hard alloys and steels, organic-,
metal-, and ceramic-bonded abrasive diamond machining is widely used (Smirnov
et al., 2020). A typical bonded abrasive tool includes super hard grains (usually
diamond or cubic boron nitride with monocrystalline grains or microcrystals of
sizes ranging from one to several microns, characterized by a higher ductility and
mechanical strength), fillers (usually corundum, silicon carbide, boron nitride, etc.),
binders (sintered metal, electroplated, resin, ceramic, hybrid), modifiers (homogenizers, greases), and body (metal, ceramic, polymer) (Staniewicz-Brudnik et al.,
2015). Porous metal-bonded diamond grinding wheels had an excellent grinding
performance for hard-brittle materials (Su et al. 2006). Recently, the brazing superabrasive technique for diamond and cubic boron nitride has been considered as one
of the most promising approaches to the fabrication of grinding wheels. Compared
with conventional bonding methods, e.g., electroplating or sintering, a brazed tool