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Introduction
This article will take an in-depth look at ceramic machining.
The article will bring more detail on topics such as:
Principles of Ceramic Machining
Types and Methods of Ceramic Machining
Categories and Types of Ceramics
Advantages, Disadvantages and Applications of Ceramics in Ceramic Machining
And Much More…
Chapter 1: Principles of Ceramic Machining
This chapter will discuss what ceramic machining is, how it is performed, and other considerations regarding ceramic machining.
What is Ceramic Machining?
Ceramic machining is a set of processes designed to cut and remove ceramic materials to achieve the necessary tolerance for a part. It involves the use of milling, drilling, grinding, and turning of the ceramic workpiece. The machining of ceramics can take place at two points in the manufacturing process, which are green body machining and full density machining.
Green body ceramic machining is completed after a ceramic part has been bisque fired but has not been fired to full density. The process can be performed using steel and conventional tools. Full density machining is more difficult and requires the use of special tools that are sufficiently durable to remove material from the workpiece and requires the use of diamond cutters.
Ceramic machining, as with metal machining, is a material removal process that requires exceptional control and monitoring. It is used to reach tighter tolerances and create fine features for surface finishes and diameter dimensions. With green ceramics, the machining process is completed using common methods since the material has not been hardened.
Ceramic products, parts, and components are hard, brittle, heat and corrosion resistant, have high strength, low density, high stiffness, and are wear resistant with thermal stability. Ceramics are made by shaping and firing a nonmetallic mineral, such as clay, at a high temperature.
Why Ceramics Have to be Machined
For fired ceramics, machining is necessary when parts do not meet the necessary tolerances. Although green ceramic machining can achieve certain tolerances, there are aspects of ceramic parts, such as the diameters of holes and tolerances of surfaces, that have to be machined after the material has been fired. Ceramic tubes and rods require the addition of special features, which cannot be achieved by green ceramic machining.
A key part of the production of ceramic pieces is sintering that hardens the ceramic material. The sintering process can cause shrinkage and warpage that has to be corrected by machining the ceramic piece to the prescribed tolerance. Additionally, ceramic parts and components, especially those for technical applications, can have complex and intricate design features that can only be added by machining.
How is Ceramic Machining Performed?
Ceramic machining includes milling, drilling, grinding, and turning, which are shaping processes that are performed on ceramics that have been fired to their full density. The removal methods used to form ceramic components are the same as those used to machine metals. The basic difference between machining metal and machining ceramics is the hardness and density of ceramics, which requires the use of cutting tools with exceptional strength and durability.
The machining of green ceramic components is completed using traditional machining tools due to the properties of green ceramic material. Tools for the process are made of steel, carbon steel, or stainless steel. Parts that require exceptionally precise shaping may be unable to be machined as green ceramics and are machined at the end of the manufacturing process.
Making Ceramics
The machining of ceramics begins with the manufacturing of ceramic parts, components, and products. Ceramics manufacturing is one of the oldest industries on earth. It began with the discovery of methods to shape and form clay for utensils, bowls, and household items. Over the centuries, ceramic products have become an essential part of a variety of industrial processes. The manufacture of ceramic components involves several steps, which begins with the raw clay material.
Mixing
Mixing is a step where the ceramic ingredients are made into slurries through the addition of water or other chemicals. After mixing, the forming process begins where the base material is produced through a number of processes, like slip casting, extrusion, injection molding, and pressing, for dry powders. During forming, the basic shape of the ceramic is created.
Sintering
Sintering or firing is used to dry and solidify the ceramic piece. The formed clay is hardened at temperatures up to 1832 °F (1000 °C). During sintering, the molecules of the clay melt, but the shape of the clay does not decompose. Sintering is completed in two steps, which are bisque firing and glaze firing.
Bisque Firing - With bisque firing, items are heated in a kiln until they turn glass-like. The temperature rises slowly to remove any water remaining in the material. At 662°F (350°C), the water molecules vaporize. At 932°F (500°C), all the water is gone, leaving the clay dehydrated and changed into hard ceramic material.
Bisque firing continues up to 1742°F (950°C) until the clay becomes less fragile but is still porous enough to accept glazes. Once sintering is completed, the ceramic is allowed to slowly cool to avoid breakage due to rapid temperature changes, and it becomes bisqueware.
Glaze Firing - In glaze firing, a coating is applied to the bisqueware to color it, decorate it, or improve its properties. The kiln is slowly heated to the required temperatures to apply the glaze and slowly cooled.
Considerations in Ceramic Machining
Some difficulties could arise in the ceramic manufacturing and machining processes. This section introduces some of the difficulties that one may face and some solutions to assist the ceramic machining processes.
Deformation in Ceramic Products
Unintended alteration of the product is the most common and detrimental defect in the ceramic industry. The main cause of deformation is improper kiln-drying tactics. Temperature changes can also cause deformation if they are done by rapidly heating or cooling the kiln during the firing process. Therefore, the temperature control should be watched carefully.
Cracking in Ceramic Products
Rapid temperature changes can also cause cracks on the product surface. This causes uneven shrinking inside and outside the ceramic product.
Foaming in Ceramic Products
Foaming occurs when insufficient oxidation during the decomposition of the porcelain tile causes the glaze to form bubbles on the ceramics. In billet glaze, sulfate and organic impurities are what cause the foaming of the product.
Chapter 2: Ceramic Machining Methods
The manufacture of ceramics produces an assortment of parts, products and components of different sizes, shapes, and strengths. The greatest expense in the manufacture of ceramic is its machining, which can be 50% up to 90% of a part’s cost. The efficiency of machining ceramics is measured by the material removal rate (MRR), which is the amount of material removed from a surface for one minute.
There are two forms of machining each of which is designed to fit the needs of the types of ceramic being processed. The tools for machining dense ceramic material are more robust and stronger than those used to process green ceramic material. The timing of the machining of the types of ceramics differs in that green ceramics are machined prior to being hardened while dense ceramics are machined as a last time in the manufacturing process.
Abrasive Machining
Large chip machining techniques, including milling, planing, broaching, and turning, can be replaced by abrasive machining. The surface quality and accuracy of abrasive machining are superior to large chip procedures with the added benefit of little to no burrs. Abrasive machining makes difficult-to-machine materials, such as dense ceramics, machinable.
Grinding Process
The types of grinding include reciprocating, internal, external, centerless, and creep feed. It includes an abrasive rotating wheel that removes material from the surface of the workpiece with the grinding zone flushed with a coolant that cools the grinding zone and lubricates the point of contact. As the coolant flows over the grinding zone, it removes microchips and debris from the grinding process.
Abrasive materials for ceramics include diamonds and cubic boron nitride (CBN) of different grit sizes that are pressed into a resin with diamond being the material of choice. Despite being harder, diamond wears out quicker than cubic boron nitride.
Honing Process
Honing uses fixed abrasives with diamond being the abrasive of choice for ceramics. The slower speeds used in honing are the distinction between it and grinding. Honing is used to repair dimensional tolerance flaws with polishing internal cylindrical surfaces being its most common use, such as the cylinder walls of car engines.
Applications like the latter can be fully automated with total control over every step of the process, including automatic part dimension gauging. Honing is also used to finish external surfaces, such as the outer surfaces of ball and roller-bearing races, valves, and gear teeth. Since honing is a lower-speed process, it produces less heat than grinding. As a result, the harm and workpiece distortion brought on by heating is reduced. The quantity of cutting fluid used is also influenced by how little heating occurs during honing. The necessity for cooling is less of an issue, but lubricity must be achieved using chemicals. Unlike in grinding, it doesn't seem like any significant attempts have been made to create honing fluids expressly for use with sophisticated ceramics.
Ultrasonic Machining Process
Rotary ultrasonic machining and ultrasonic impact machining fall within the category of ultrasonic machining. Both techniques involve vibrating the tool at a frequency of typically 20 kHz along its axis, which is set parallel to the surface of the workpiece. Otherwise, the two approaches diverge greatly. Diamond-coated grinding tools, most frequently core drills, are used in drilling or vertical milling configurations during rotary ultrasonic machining. Only the fact that the rotating tool vibrates with an amplitude of 0.025 to 0.05 mm while pressed on the workpiece separates it from regular milling and drilling operations.
The vibration reduces friction, aids in reducing fluid access, and makes it easier to remove swarf. The end result is an increase in the machining rate. The tools typically have a diameter of no more than 50 mm. Rotating ultrasonic machining has also used small grinding and thread-cutting wheels in addition to core and solid drills. Cutting fluids, bond and abrasive qualities, and the impact of grinding parameters should all be given equal weight when considering this process. Therefore, advancements in the ceramic grinding technique ought to be transferable to rotary ultrasonic machining.
The tool does not contain abrasive materials and does not make contact with the workpiece when using ultrasonic impact machining. This technique involves circulating an abrasive-containing slurry between the vibrating tool and the workpiece. The fluid and abrasive particles are vibrated by the tool. Particles striking the workpiece cause indentation and fracture, which lead to material removal. The distance between the workpiece and the vibrating tool significantly impacts the pace of removal. Ultrasonic impact grinding is likely the most popular machining technique for advanced ceramics, second only to grinding. Higher vibration frequencies and specialized fluids may enable faster machining through ultrasonic impact grinding.
Lapping and Polishing Process
Similar to honing, lapping is mostly a finishing procedure used on objects that have already been machined to near their final dimensions. However, in contrast to honing, lapping uses a loose or free abrasive technique. With lapping, the workpiece is pressed against a stiff surface, frequently cast iron coated in a slurry of abrasive particles. Some of these particles cause a cutting action on the workpiece when they become embedded in the surface of the lapping tool. The elimination procedure also involves other particles that roll between the two surfaces.
Lapping and polishing are occasionally distinguished from one another as separate processes. However, this is not always the case. Lapping simply uses a firmer, more rigid surface, whereas polishing uses a softer, more flexible one. Lapping is used to acquire accurate tolerances, eliminate damage, and enhance surface smoothness. In contrast, polishing is mostly used to repair damage and create extremely smooth surfaces.
Liquid Abrasive Jet-Cutting Process
Instead of shaping or surface finishing, liquid jet systems are typically used for cutting. Porous materials with very high cutting rates are regularly subjected to this technique. However, liquid jet cutting is ineffective on advanced ceramics, which are hard and dense with substantially lower cutting rates.
The use of liquid jet cutting on modern ceramics has been made possible by the addition of abrasive grit to the fluid stream. This method combines localized fracture, brought on by liquid cavitation, with slurry erosion removal procedures. However, the inclusion of these abrasive particles will create another type of machine damage. Components needing a close tolerance and fine surface quality are not something for which the liquid abrasive jet process is particularly well-suited.
Non-Abrasive Machining
Some of the non-abrasive machining methods include:
Electrical Discharge Machining (EDM)
Electrical energy can also be used for ceramic machining. This is known as electrical discharge machining (EDM) and has found many applications for advanced ceramic machining in the past years. EDM requires the ceramic workpieces to have an electrical resistivity of less than 100Ω-cm. This implies that Electrical Discharge Machining cannot be used for machining glasses and some ceramics.
EDM has been successfully applied on silicon-infiltrated silicon carbide, siliconized silicon carbide, and hot-pressed silicon carbide materials. In order to extend the application of EDM to other ceramics, the resistivity of the materials needs to be reduced to meet the required range. It is not clear, however, whether EDM is a low-damage machining method since it typically leaves a surface layer of melted or heat-affected material containing a high level of residual stress and numerous microcracks.
Laser Beam Cutting
Focused laser beams have been widely used for the precise cutting of a variety of materials such as metal, wood, and even ceramics. Innovative approaches have been applied, such as using two laser beams intersecting within the workpiece to cut blind kerfs. This technique uses certain cutting geometries, especially when some parts of the workpiece need to be removed.
Friction Cutting and Microwave Cutting Processes
Friction cutting uses a circular blade rotating at a speed where it produces more heat than the material needing to be cut. For friction cutting, alumina and silicon nitride are sliced into small slots using a spinning, mild steel disk that is then water cooled. For the microwave cutting process, sintered alumina is penetrated by localized 17 microwave heating. In this procedure, local melting and an explosive discharge of the molten material occurs from below the surface when penetrated by a wafer of sintered alumina. These techniques work well for cutting and slicing tasks, but they are typically ineffective for producing a contoured surface with a tight tolerance.
Combined Methods
Some of the combined methods include:
Thermally-Assisted Turning Process
Some engineered ceramics claim to operate well when heated with a plasma torch while being turned. The workpiece material is heated up to a maximum temperature of 1000°C using this technique before being cut using a polycrystalline diamond compact (PDC) or CBN cutting tool. Where machinability is enhanced, it is due to a change in the deformation and removal processes from more rigid to more plastic ones at the higher temperature.
In spite of an 8-fold reduction in tool wear when turning silicon nitride, the level of tool wear is still too high. By heating with a plasma torch, materials susceptible to thermal shock, such as alumina and zirconia, still do not exhibit increased machinability. Engineers are able to make ceramic material more pliable in reaction to mechanical forces by heating it with a laser source first, then cutting it with a diamond tool. Due to the limited tool life and subpar surface smoothness, thermally assisted turning does not lend itself to high volume production.
Mechanical-Electrical Discharge
As documented, it is now possible to combine electrical discharge with ultrasonic machining techniques. After much experimentation, engineers now know how to use a metal-bonded diamond tool to manufacture titanium diboride. Under selected conditions, they achieve higher material removal rates and a higher removal ratio of 110 (workpiece loss/wheel loss). It is still necessary, however, to investigate whether this technology can be used with additional materials that have adequate conductivity for EDM.
Chemical-Electrical Discharge
Some engineers described chemical-electrical discharge as combining electrochemical reactions in an electrolyte with wire electrical discharge machining. This technique is used on silicon carbide, non-conducting glass, alumina, and silicon nitride specimens that are submerged in an appropriate electrolyte solution to allow for conduction.
This technique enables efficient cutting of surface contours without having to make direct contact between the tool and the workpiece. According to reports, the ceramics can be cut at a rate between 0.12 and 0.14 mm/min. However, the viability of this technology for mass manufacturing sophisticated ceramics requires more investigation.
Green Ceramic Machining (GCM)
Green ceramic machining is a cost effective and tool saving method for machining ceramic parts. It is performed prior to the sintering process when the ceramic shape is held together by the binder, which influences the strength and plasticity of the ceramic material. Green ceramics are pressed together and shaped with high density packing to precision shapes with accurate dimensions.
Unlike dense ceramic material, green ceramics can be machined using the same tools that are used for shaping metals. The particles of the material can cause wear on tools but not as great as dense fired ceramics. Although diamond tools can be used, they are not necessary due to the plasticity of the ceramic material. Green ceramics can be machined using all of the normal machining processes including turning, milling, grinding, and drilling. The limitations to the process are in regard to the depth of the cuts, which need to be controlled using wear plates, and their feed rate. Additionally, the location of the machining on the workpiece can influence the speed of the process.
Green ceramic machining is used to create complex and multidimensional features on a workpiece that cannot be completed after the sintering and firing process. In some instances, machining processes performed after sintering can be time consuming and expensive leading to long production runs, which makes green ceramic machining more attractive. .
Guidelines for Machining Ceramics
There are certain considerations that have to be examined when making the decision to machine ceramics. Ceramics are a strong, durable, and malleable material that have properties that make them appropriate for a wide variety of applications. Their properties are the reason they are so widely used, but there are factors that users need to be aware of before machining ceramics.
The choice of method for machining ceramics has to fit the type of ceramic since the various types react differently to certain machining procedures. Mullite is suited for laser cutting while zirconia, a delicate ceramic, is cut and molded using abrasive methods. Knowledge of the ceramic material can assist in matching the material to the proper tool.
As is typical with all forms of manufacturing, prototyping is a necessity with ceramic parts. This is especially true for complex parts with intricate designs. Once a prototype is created, it should be tested and studied before moving forward with larger numbers of the part. A prototype makes it possible to go back to the design and make adjustments.
Although machining of ceramic parts is similar to machining other forms of materials, there are rules that apply specifically to ceramics during the design phase, which are:
No pointy edges
Make oval designs round
Sharp corners and edges increase the risk of breakage
Corner pockets are an alternative to sharp corners
Holes and slots should be spaced and not in close proximity
Results of Incorrect or Improper Machining of Ceramics
Regardless of the strength, hardness, and other positive properties of ceramic materials, when they are improperly machined, they can lose their strength and be defective. Ragged cutting, uneven deformed edges cause ceramics to lose their rigidity. The process of machining is designed to bring ceramic parts up to the proper tolerances. This is completed in accordance with design parameters. Any slight neglect in this process can cause ceramic material failure.
Ceramic tubes may seem to be an inconsequential aspect of a mechanism. When a ceramic tube has not been machined to its proper dimensions, it can cause catastrophic damage to a process and become dangerous. This is also true in the case of geometric shapes that have to be machined to exacting tolerances to be able to fit into a completed design.
A vital aspect of machining is correcting the errors or defects that occur during the firing process, which can result in shrinkage and warping. The machining process corrects and grinds away such errors to put a ceramic part in the right tolerance. The machining process has to be completed with the greatest amount of precision to achieve the best results and ensure the quality of the final product.
The biggest failure in the machining of ceramics is the creation of micro cracks and fractures that are created by improper use of machining tools or using the wrong machining tools. Ceramic material is very brittle and susceptible to damage from cracks. Since this is a common part of ceramic manufacturing, manufacturers are very careful to inspect their finished products using bright light or piezoelectric inspection methods.
Chapter 3: Leading Ceramic Machine Manufacturers
Obviously, ceramic machining is a complex process. Luckily, there are many manufacturers of ceramic machining equipment that have essentially perfected this process. This chapter will simply discuss leading manufacturers of ceramic molding machines, along with the unique features of their leading machines, available in the United States and Canada.
Haas Automation:
Model: DT-1
Unique Features:
High-speed drilling and tapping capabilities.
Compact footprint suitable for small workshop spaces.
20-station automatic tool changer for efficient tool changes.
High-performance spindle for precision machining.
DMG Mori:
Model: DMU 50
Unique Features:
5-axis simultaneous machining for complex ceramic parts.
Integrated rotary table for multi-sided machining.
High rigidity and precision for optimal surface finishes.
Intelligent control system for efficient operation.
Makino:
Model: T1
Unique Features:
Thermal stability and rigidity for high-accuracy machining.
Advanced technologies for reducing cycle times.
High-speed spindle for efficient ceramic cutting.
User-friendly interface and programming capabilities.
Okuma:
Model: GENOS M460V-5AX
Unique Features:
5-axis simultaneous machining for complex ceramic geometries.
Powerful spindle for high material removal rates.
Thermo-friendly structure to minimize thermal distortion.
Intelligent machine control for enhanced productivity.
FANUC:
Model: Robodrill D21MiB5
Unique Features:
Compact and versatile machine for ceramic machining.
High-speed spindle for efficient cutting and drilling.
Easy integration with automation systems.
FANUC CNC control for precision and reliability.
Please note that the availability of specific models may vary over time, so it's always recommended to check with the manufacturers for the most up-to-date information and to determine the best machine for your specific ceramic machining needs.
Leading Manufacturers and Suppliers
Chapter 4: Categories and Types of Ceramics
This chapter will discuss the types of ceramics based on their categories.
Pottery Ceramics
Both the phrases pottery and ceramic refer to items made out of clay, fired to hardness, and then decorated or glazed. Rock that has weathered naturally produces clay. It is a useful material for producing dinnerware since it is pliable, flexible, and will permanently solidify if baked at high temperatures. There are three major types of ceramic and pottery materials: porcelain, stoneware, and earthenware.
Earthenware
Potters have fired earthenware in ovens for countless years. When the Roman Empire was at its height, ceramics were employed as amphorae to ship wine and olive oil to the furthest reaches of the realm. However, liquids may leak through these containers, allowing goods like oil to go rancid after repeated use for an extended period. Earthenware, however, can be fired at lower temperatures than other conventional ceramics like stoneware and porcelain, reaching as low as 1200 °F (648 °C).
Some earthenware potters coat their works with varnish to seal in the moisture. However, due to the reduced firing temperature, one may still scratch and harm it with a knife. These days, terracotta planters, other kitchenware, and most of the bricks used in construction are made of earthenware. Earthenware is a common choice for new potters. The ease of working with earthenware clay contributes to its appeal. It is less flexible and fragile than other types of pottery.
Porcelain
The popularity of porcelain increased in Europe and North America in the 1700s, making it the last type of pottery to reach the West. It has been prized for its toughness and durability in China for long before that point. In the past, porcelain was fired at temperatures considerably higher than stoneware. Typically, the final firing temperature was in the range of 2600 °F (1426 °C).
The main difference between stoneware and porcelain today is that porcelain is typically manufactured with white clay. Almost any white clay or bone ash will do, although the white mineral kaolin is usually used for porcelain. However, kaolin is less forgiving and more difficult to deal with than other clays. It is also more vulnerable in modern society.
Sculptors can also carve porcelain into more delicate shapes than they can with stone or earthenware. Since the 18th century, porcelain has been prized by collectors, and it has been used to recreate anything from the flowing mane of a horse to the folds of a robe. For contemporary potters, the lines between porcelain and stoneware are becoming less apparent as new technologies and ideas are developed.
Stoneware
Stoneware came into production after the invention of earthenware. Compared to earthenware, it takes a long time to fire. Most stoneware is fired at temperatures between 2000°F and 2400° F (1093 and 1315 °C), which is hotter than volcanic lava. Stoneware is vitrified at these extremely high temperatures, turning the exterior glazes into glass. Stoneware can currently be produced using a variety of clay shades, unlike porcelain, which is now almost exclusively white. Additionally, some stoneware has different clay colors blended in for a distinctive twist.
Stoneware exhibits many favorable qualities over traditional ceramics; it is sturdy, hardy, and nonporous. As a result of its durable, fashionable, and versatile nature, it can be used for everything from a personalized trophy to a baking dish. It can also survive the heat from a microwave, dishwasher, or even oven under the right conditions. Stoneware also holds and distributes heat more evenly than other materials, making it perfect for drinking coffee and tea.
Sanitary equipment like sinks and baths are made of stoneware. Stonewares are also used in the chemical sector to create pumps, valves, absorption towers, drainage pipes, underground cable sheathings, sewerage pipes, and residential pipes. Despite being more affordable than many other building supplies, however, they are fragile and have little market value once damaged.
Advanced Ceramics
Some advanced ceramics include:
Fire Bricks
Bricks are typical ceramics because they are usually made by heating materials that resemble clay, like sand. Many homes include this kind of ceramic. It has a wide range of properties based on how it was manufactured. This ceramic is tough, heavy, and generally able to tolerate high temperatures. Fire bricks can be used in chimneys, fireplaces, and on walls. Additionally, they are commonly used in landscaping because of these qualities.
Tungsten Carbides
Tungsten carbide is a thick and durable material composed of the same amounts of carbon and tungsten. These ceramics are strong, thick, hard, long-lasting, and exhibit little electrical resistance. Because of these qualities, many items are made from this material ranging from various cutting tools to golf clubs.
Bone China
By introducing powdered bone ash to the standard ceramics recipe, ceramicists created a less-brittle variety of porcelain known as bone china. As a bonus, it looked ivory-white, similar to traditional porcelain. Today's world has largely replaced pure porcelain with this material. Bone china is considered by many to be a stronger type of porcelain.
Bone china is naturally colorless or white, whereas unfired porcelain clay can be cream or white. Bone china is fired twice. The first time (bisque firing) allows the material to form into a translucent, glass-like form, and the second firing (glaze firing) is performed at a lower temperature to melt this material into more specific forms with a protective shell.
The shell is physically strong and affords bone china a strong resistance to chipping wear. The presence of feldspar, kaolin, phosphates, quartz, and other materials helps provide this strength.
Glass Ceramics
Glass ceramics are one of the many different types of ceramics made by controlling crystallization, resulting in properties akin to glass but with ceramics' strength and hardness. Modern manufacturing techniques are used to create glass ceramics, producing materials with desirable qualities that include zero porosity, mechanical strength, durability, high temperature resistance, transparency, and biocompatibility.
Glass ceramics have excellent superconductivity and chemical resistance. They are used to make cookware, bakeware, and stovetop accessories. Additionally, this ceramic is frequently used in industrial, scientific, and medical equipment.
Silicon
Another common ceramic substance viewed as superior because of its chemical characteristics is silicon. This ceramic is widely distributed and makes up around 90% of the earth's crust. Additionally, silicon is typically present in the clays used to make conventional pottery. For instance, silicate minerals like kaolinite and silica ceramic are used to manufacture porcelain and burnt bricks, respectively.
Silicon is the preferred choice for manufacturing semiconductors due to its ability to bond atoms, strength, and abundance. Crystalline silicon, which is related to polycrystalline silicon, is used to make exceptionally high purity semiconductors, such as integrated circuits and solar panels. High-quality silicon minerals are also used to make cement aggregate, glass, and ceramics. Silicon, therefore, is the most widely utilized raw material in the construction sector.
Silicon Carbide
Another type of ceramic material is silicon carbide, a superior semiconductor made of silicon and carbon. It naturally occurs as a rare stone called moissanite. Ceramics made of silicon carbide are strong and incredibly hard. There are around 250 distinct crystalline materials that contain this semiconductor.
Although this porcelain is naturally white, additional substances, like iron, sometimes color it. It also exhibits a low thermal conductivity. Examples of applications for this ceramic include cutting tools, furnaces, braking discs, abrasives, heating elements, lights, and electrical power systems. The natural form of silicon carbide is prized as a jewel because it resembles diamonds in appearance and toughness. It is a more durable substitute for synthetic zirconia.
Silicon Nitride
Silicon nitride is a high-performing ceramic that consists of silicon and nitrogen (Si3N4). It is characterized by having exceptional strength, toughness, hardness, and outstanding chemical and thermal stability. The five types of silicon nitride ceramic result from their fabrication, which determines their properties and applications.
The five types of silicon nitride are:
Reaction Bonded (RBSN) – RBSN is made by nitriding a silicon compact at 2642 °F (1450 °C), during which the silicon nitride grows in the porosity of the compact. The result is an increase in the ceramic’s density, making it ideal for producing net-shaped parts.
Hot Pressed (HPSN) – HPSN is used to produce cutting tools. It must be diamond-cut due to its density and hardness, which makes its parts more expensive.
Sintered Reaction Bonded (SRBSN) – SRBSN is a new form of RBSN. It has been designed to remove the porosity of RBSN and improve its mechanical properties. SRBSN has exceptional toughness and impact resistance.
Gas Pressure Sintered (GPSN) – GPSN uses gas pressure and heat of around 3632 °F (2000 °C) to inhibit pyrolysis of silicon nitride and promote silicon nitride grain growth. The result is a ceramic with high toughness and a density of >99%. GPSN is strong and wear-resistant, with good process performance.
Sintered (SSN) – The SSN process takes silicon nitride ceramic material and densifies it with pressureless sintering in a nitrogen atmosphere. Different combinations of additives are used to help in the densification to make a ceramic with excellent mechanical properties.
Titanium Carbide
Titanium carbide is a ceramic material that is very strong, heat-resistant, and dark in color. This material is extremely durable, wear-resistant, heat-resistant, and corrosion-resistant. It is frequently found in watch movements, heat shields, machine parts, and tool bits.
Boron Carbide
Boron carbide ceramics consist of boron and carbon, which makes it one of the hardest known substances. The extreme hardness of boron carbide is between 9.5 and 9.75 on the Mohs hardness scale. It is resistant to chemical reactions and provides shielding against neutrons.
Known as the black diamond, boron carbide has been shown to be a p-type semiconductor. Its extreme hardness makes it wear-resistant. Boron carbide’s good mechanical properties and low specific gravity make it ideal for producing lightweight armor.
Boron carbide is produced using fusion with carbon or by a magnesiothermic reaction. It can also be manufactured using pressureless sintering at temperatures of 4172 to 4352 °F (2300 to 2400 °C) using various sintering aids.
Structural Ceramics
Structure ceramics are often made of clay and are pressed into the desired shape. Their effective insulating qualities can be changed by adjusting their density. The ceramic's insulating characteristics decrease with increasing density. Bricks, dinner bricks, dinner plates, and statues are all examples of structural ceramics.
Refractory Ceramics
Refractory ceramics maintain their strength and shape under extreme heat. They are employed in furnaces and kilns for this reason. They are produced utilizing a variety of oxides, including zinc oxide, titanium dioxide, and silicon dioxide.
Electrical Ceramics
Excellent electrical qualities are a hallmark of electrical ceramics, often known as electroceramics. They are useful for various applications because they have good mechanical, thermal, and electrical qualities. Electrical ceramics become more conductive as the temperature rises. Examples of electrical ceramics include ceramic rapid ion conductors and dielectric ceramics.
Magnetic Ceramics
Oxide materials with a certain form of permanent magnification (ferrimagnetism) are called magnetic ceramics. Ferrites, crystalline minerals formed of iron oxide combined with another metal, are the basis of magnetic ceramics. Transformers, telephony, and data storage are just a few applications of magnetic ceramics.
Abrasive Ceramics
Ceramic abrasives, which are used to cut or grind away other softer materials, can be either natural or synthetic. They are extremely durable, wear-resistant, and hard; a diamond would be the most notable abrasive ceramic.
Comparison of Metal to Ceramics
The basic definition of a metal is a material that occurs naturally or is a combination of materials formed in manufacturing. They are shiny, ductile, and malleable and are found on the earth’s crust. Metals can be found in pure form or inside rocks or ore from which the pure metal is processed. The attraction of metals is their ability to be shaped and configured to produce various products.
Ceramics are non-metallic inorganic materials made up of non-metallic compounds that can be shaped and hardened. They are brittle, corrosion resistant, and exceptionally hard. Ceramics are made of a mixture of clay, various elements, powders, and water that is bound together with a binder and shaped into products, parts, and components.
Comparison of the Properties of Ceramics and Metals
Ceramics
Metals
Electrical and thermal insulators
Conductors of heat and electricity
Harder than metals
Ductile and malleable
Used to cut metals
Have a variety of melting points
Dull or matte
Shining with a luster
Covalent bonds
Metallic bonds
Will not bend
Easily bent and shaped
Made up of nonmetallic materials
Composed of multiple elements
Brittle and fracture easily
Denser
Chapter 5: Advantages, Disadvantages and Applications of Ceramics in Ceramic Machining
This chapter will discuss the applications, benefits, and disadvantages of ceramics as used in ceramic machining.
Advantages of Ceramics in Ceramic Machining
They are frequently used as cutting tools and abrasive powder due to their extreme hardness.
Due to their high melting point, they are perfect for use as refractory materials.
They are also effective thermal insulators, which is another reason to use them as refractory materials.
Due to their high electrical resistance, they are perfect for use as insulators.
Their low mass density allows them to make lightweight ceramic components.
They typically resist corrosion because they are already oxidized due to the special formation of their chemical bonds.
They are cost-effective since they are readily available.
Glazed ceramic material is durable and resists stains.
Disadvantages of Ceramics in Ceramic Machining
They are not particularly stretchy.
They lack significant tensile strength.
There is a wide range of strength variance, even with similar specimens.
They are challenging to create and form.
Their dimensional tolerances are challenging to maintain throughout processing.
Ceramic products exhibit poor shock resistance causing them to break when impacted.
They have a low friction coefficient, allowing other materials to slide easily off them.
Applications of Ceramics in Ceramic Machining
Due to their great abrasion resistance, technical ceramics like silicon carbide and tungsten carbide are utilized in body armor, mining wear plates, and machine components.
A ceramic called uranium oxide (UO2) is utilized as fuel for nuclear reactors.
Zirconia is a type of ceramic used to create oxygen sensors, fuel cells, jewels, and ceramic knife blades.
A ceramic called barium titanate is used to create transducers, capacitors, heating elements, and data storage components.
Another ceramic called steatite is employed as an electrical insulator.
The Difficulties of Machining Ceramics
Several difficulties can arise when machining ceramics due to their properties and characteristics. The machining process is challenging due to ceramics' high hardness, brittle nature, and their resistance to machining. Conventional machining has proven to be unsuccessful because the cutting action of conventional tools works on the principle of chip formation by shearing, which leads to breakage in ceramics due to their brittleness.
Machining of ceramics is a delicate process that requires control, attention to detail, and craftsmanship. It is for this reason that many manufacturers have opted for CNC machining of ceramics to avoid the problems of manual machining. During the machining process, due to ceramic material being brittle, products can develop micro cracks and fissures that make a product useless.
Machining ceramics can cause surface damage, edge chipping, and pitting. Achieving dimensional accuracy and minimizing collateral damage, such as surface cracks, requires close monitoring of the machining process.
Conclusion
The mixed, shaped, and formed ceramic materials are used to produce industrial and commercial parts and components. An essential part of their production is machining, which is used to enhance the features and tolerances of ceramic items. Machining of ceramics is like machining of metal parts where portions of the surface of an object is removed, a process that alters the size and shape of the ceramic piece.
Unlike machining metal, the machining of ceramics requires special tools that can match the hardness, strength, and toughness of the material. Ceramics are very dense and hard, which necessitates that they receive extensive, specialized, and precision machining that includes drilling, turning, grinding, and milling.
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