Silicon Carbide remains strong even at high temperatures and exhibits excellent resistance to thermal shock, acids and alkalis as well as having excellent wear resistance properties.
Machinability of MMCs is limited by brittle fracture of SiC particles and ploughing of the matrix material [1].
Workpiece defects have been observed on machined surfaces due to crushed or pulled-out SiC particulates [2]. These workpiece defects include pits, matrix tearing and swelling that occur as result of crushed SiC particulates being compressed or removed during manufacturing [3.
Cutting Tools
Cutting tools used for SiC machining must withstand severe conditions of high strain rate, temperature and corrosion. As such, their materials must withstand high levels of dynamic loads while still remaining structurally sound, and be long-lived enough to withstand repeated use over time.
Tungsten carbide (WC) is an attractive choice for cutting tools as it offers excellent toughness, wear resistance and thermal conductivity. Unfortunately, its main constituents – W and Co – may become scarce over time as natural resources diminish – making the long-term supply an issue. Other alternatives could include titanium or vanadium carbides.
Chemical resistance should also be an essential consideration when choosing a cutting tool material, since your tool will come into contact with chemicals during machining that could contaminate and degrade it over time.
There is an assortment of cutting tools available, ranging from linear and rotary tools. Linear tools include tool bits (single-point cutting tools) and broaches; while rotary tools include drills, countersinks and counterbores, taps and dies, taps & dies and reamers. Ceramic-specific cutting tools often consist of cemented carbide blades which make for effective ceramic machining while other cutting tools may include silicon carbide (SiC) or diamond components.
Cooling
Machining processes often produce excessive heat during their cutting processes, which negatively impacts material machinability and ultimately causes residual stresses and poor mechanical properties of machined surfaces [74]. Effective cooling applications are essential in order to reduce cutting force and improve machinability of workpieces; such applications remove excess heat from working area by expediting chip evacuation, creating film layer between cutting tool and chips, as well as lubricate friction reduction – but chemical-based coolants could pollute the environment, affect human health negatively, or raise operating costs significantly [75].
Machining of SiCp/Al composites requires a special approach in order to prevent early tool wear and preserve the integrity of the machined surface. One popular approach involves the use of uncoated cemented carbide inserts or TiAlN coated tools with hardness between 60 and 65 HRc, along with cryogenic coolants to increase their cooling and lubricating effects.
Cryogenic cooling can help decrease cutting forces and heat impacts during milling, and lower tool changes and cycle times as a result of its use. Furthermore, using cryogenic cooling eliminates toxic chemicals from work areas – an advantage reported by Gu et al. in their study on improving machinability of SiCp/Al composite with high SiC fraction using cryogenic cooling system resulting in high integrity machined surface as well as reduced brittle fracture.
Lubrication
Traditional machining processes use different kinds of cooling and lubrication techniques that all have high coolant costs, negatively affect human health and the environment, and may not be sustainable in the long term. To address this challenge, researchers are exploring various cooling/lubrication methods which might provide sustainable alternatives to conventional ones.
Machinability of MMCs reinforced with SiC varies depending on how particles interact with a cutting tool during machining, temperature development and forces encountered [142]. As a result, machined surfaces may exhibit ploughed furrows, shallow pits, matrix tearout and pulled SiC fragments from within the material itself [149].
Researchers have employed various lubrication strategies to address surface defects. These include the atomized spraying of solid lubricants (e.g. graphite), nanofluids (e.g. NH3, SiO2), ionic liquids and electrolytic in-process dressing (ELID). Of these approaches, MQL offers multiple advantages that include lower production expenses, protection of worker health and environmental sustainability while increasing shear strength of tools.
CO2 assisted cryo cutting with MQL displays excellent machining performance for an Al6063/SiCp/65p composite plate, due to reduced adhesion between workpiece and tool due to CO2 assisted cutting’s low temperature environment, which allows SiC particles to interact more efficiently with cutting tools than flood cutting does.
Tool Wear
Silicon Carbide (SiC) is a hard material with exceptional mechanical properties and high resistance to corrosion, heat shock, and other extreme conditions. Due to these superior properties, SiC is often used as reinforcement in metal matrix composites (MMCs) for applications requiring wear resistance and thermal shock resistance.
However, MMCs with SiC reinforcement can be challenging to machine due to their brittleness and difficult fracture characteristics [1, 2]. This leads to substandard machined surfaces, increased tool wear, decreased cutting force and ultimately lower productivity and efficiency resulting in decreased productivity and efficiency.
Numerous techniques have been devised to enhance the machinability of MMCs with SiC reinforcement, such as employing multicoated carbide tools, adjusting cutting speed and feed rate, and employing ultrasonic vibration. Studies have been performed on how each factor affects MMCs with sic reinforcements.
MRR and surface roughness (SR) of machined surfaces depend on various electric parameters during EDM, such as gap voltage, peak current, pulse on time, pulse off time as well as non-electrical parameters like flushing which impact workpiece machinability as well as wear on ceramic tools.
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