Ceramic forming techniques

Last updated March 23, 2024

Ceramic forming techniques are ways of forming ceramics, which are used to make everything from tableware such as teapots to engineering ceramics such as computer parts. Pottery techniques include the potter's wheel, slip casting and many others.

Methods for forming powders of ceramic raw materials into complex shapes are desirable in many areas of technology. For example, such methods are required for producing advanced, high-temperature structural parts such as heat engine components, recuperators and the like from powders of ceramic raw materials. Typical parts produced with this production operation include impellers made from stainless steel, bronze, complex cutting tools, plastic mould tooling, and others. Typical materials used are: wood, metal, water, plaster, epoxy and STLs, silica, and zirconia.

This production operation is well known for providing tools with dimensional stability, surface quality, density and uniformity. For instance, on the slip casting process the cast part is of high concentration of raw materials with little additive, this improves uniformity. But also, the plaster mould draws water from the poured slip to compact and form the casting at the mould surface. This forms a dense cast.

Slip casting

There are many forming techniques to make ceramics, but one example is slip casting. This is where slip or, liquid clay, is poured into a plaster mould. The water in the slip is drawn out into the walls of the plaster mould, leaving an inside layer of solid clay, which hardens quickly. When dry, the solid clay can then also be removed. The slip used in slip casting is often liquified with a substance that reduces the need for additional water to soften the slip (unless crazing is wanted); this prevents excessive shrinkage which occurs when a piece containing a lot of water dries; another approach is to dry items slowly.^[1]

Slip-casting methods provide superior surface quality, density and uniformity in casting high-purity ceramic raw materials over other ceramic casting techniques, such as hydraulic casting, since the cast part is a higher concentration of ceramic raw materials with little additives. A slip is a suspension of fine raw materials powder in a liquid such as water or alcohol with small amounts of secondary materials such as dispersants, surfactants and binders. Pottery slip casting techniques employ a plaster block or flask mould. The plaster mould draws water from the poured slip to compact and form the casting at the mould surface. This forms a dense cast removing deleterious air gaps and minimizing shrinkage in the final sintering process.

Additive manufacturing

Ceramic shell casting

Ceramic shell casting techniques using silica, zirconia and other refractory materials are currently used by the metal parts industry for 'net casting', forming precision shell moulds for molten metal casting. The technique involves a successive wet dipping and dry powder coating or stucco to build up the mould shell layer. The shell casting method in general is known for dimensional stability and is used in many net-casting processes for aerospace and other industries in molten metal casting. Automated facilities use multiple wax patterns on trees, large slurry mixers and fluidic powder beds for automated dipping.

Technical ceramics

When forming technical ceramic materials from dry powders prepared for processing, the method of forming into the shape required depends upon the method of material preparation and size and shape of the part to be formed. Materials prepared for dry powder forming are most commonly formed by "dry" pressing in mechanical or hydraulic powder compacting presses selected for the necessary force and powder fill depth. Dry powder is automatically discharged into the non-flexible steel or tungsten carbide insert in the die and punches then compact the powder to the shape of the die. If the part is to be large and unable to have pressure transmit suitably for a uniform pressed density then isostatic pressing may be used. When isostatically pressed the powder takes the shape of a flexible membrane acting as the mould, forming the shape and size of the pressed powder. Isostatic presses can be either high speed, high output type of automatic presses for such parts as ceramic insulators for spark plugs or sand blast nozzles, or slower operating "wet bag" presses that are much more manual in operation but suitable particularly for large machinable blanks or blanks that will be cut or otherwise formed in secondary operations to the final shape.

If technical ceramic parts are needed where the length to diameter ratio is very large, extrusion may be used. There are two types of ceramic extruders one being piston type with hydraulic force pushing a ram that in turn is pushing the ceramic through the loaded material cylinder to and through the die which forms the extrudate. The second type of extruder is a screw, or auger, type where a screw turns forcing the material to and through the die which again shapes the part. In both types of extrusion the raw material must be plasticized to allow and induce the flow of the material in the process.

Complex technical ceramic parts are commonly formed using either the injection moulding process or "hot wax moulding." Both rely on heat sensitive plasticizers to allow material flow into a die. The part is then quickly cooled for removal from the die. Ceramic injection moulding is much like plastic injection moulding using various polymers for plasticizing. Hot wax moulding largely uses paraffin wax.

Other techniques

There are also several traditional techniques of handbuilding, such as pinching, soft slab, hard slab, and coil construction.

Other techniques involve threading animal or artificial wool fiber through paperclay slip, to build up layers of material. The result can be wrapped over forms or cut, dried and later joined with liquid and soft paperclay.

When forming very thin sheets of ceramic material, "tape casting" is commonly used. This involves pouring the slip (which contains a polymer "binder" to give it strength) onto a moving carrier belt, and then passing it under a stationary "doctor blade" to adjust the thickness. The moving slip is then air dried, and the "tape" thus formed is peeled off the carrier belt, cut into rectangular shapes, and processed further. As many as 100 tape layers, alternating with conductive metal powder layers, can be stacked up. These are then sintered ("fired") to remove the polymer and thus make "multilayer" capacitors, sensors, etc. According to D. W. Richerson of the American Ceramic Society, more than a billion of such capacitors are manufactured every day. (About 100 are in a typical cellular telephone, and about a thousand in a typical automobile.)

Gel casting is another technique used to create engineering ceramics.

Related Research Articles

Pottery is the process and the products of forming vessels and other objects with clay and other raw materials, which are fired at high temperatures to give them a hard and durable form. The place where such wares are made by a potter is also called a pottery. The definition of pottery, used by the ASTM International, is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products". End applications include tableware, decorative ware, sanitaryware, and in technology and industry such as electrical insulators and laboratory ware. In art history and archaeology, especially of ancient and prehistoric periods, pottery often means vessels only, and sculpted figurines of the same material are called terracottas.

<span class="mw-page-title-main">Sintering</span> Process of forming and bonding material by heat or pressure

Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plastics, and other materials. The nanoparticles in the sintered material diffuse across the boundaries of the particles, fusing the particles together and creating a solid piece.

Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed, and injected into a mould cavity, where it cools and hardens to the configuration of the cavity. After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mould-maker from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers that do not melt during the injection moulding of some lower-temperature thermoplastics, can be used for some simple injection moulds.

Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and reducing the cost of the final product.

Moulding or Molding see spelling differences) is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix. This itself may have been made using a pattern or model of the final object.

<span class="mw-page-title-main">Selective laser sintering</span> 3D printing technique

Selective laser sintering (SLS) is an additive manufacturing (AM) technique that uses a laser as the power and heat source to sinter powdered material, aiming the laser automatically at points in space defined by a 3D model, binding the material together to create a solid structure. It is similar to selective laser melting; the two are instantiations of the same concept but differ in technical details. SLS is a relatively new technology that so far has mainly been used for rapid prototyping and for low-volume production of component parts. Production roles are expanding as the commercialization of AM technology improves.

Hot isostatic pressing (HIP) is a manufacturing process, used to reduce the porosity of metals and increase the density of many ceramic materials. This improves the material's mechanical properties and workability.

Slip casting, or slipcasting, is a ceramic forming technique, and is widely used by commercial industry as well as contemporary fine artists as a way of making various ceramic forms. This technique is suitable for simple functional objects such as cups and plates, as well as more complicated shapes like figurative ceramics that would be difficult to be reproduced by hand or other forming techniques. The technique involves a clay body slip which is essentially a liquid version of clay, usually prepared in a blunger, being poured into plaster moulds and allowed to form a layer, the cast, on the internal walls of the mould.

Metal injection molding (MIM) is a metalworking process in which finely-powdered metal is mixed with binder material to create a "feedstock" that is then shaped and solidified using injection molding. Metal injection molding combines the most useful characteristics of powder metallurgy and plastic injection molding to facilitate the production of small, complex-shaped metal components with outstanding mechanical properties. The molding process allows high volume, complex parts to be shaped in a single step. After molding, the part undergoes conditioning operations to remove the binder (debinding) and densify the powders. Finished products are small components used in many industries and applications.

<span class="mw-page-title-main">Ceramic engineering</span> Science and technology of creating objects from inorganic, non-metallic materials

Ceramic engineering is the science and technology of creating objects from inorganic, non-metallic materials. This is done either by the action of heat, or at lower temperatures using precipitation reactions from high-purity chemical solutions. The term includes the purification of raw materials, the study and production of the chemical compounds concerned, their formation into components and the study of their structure, composition and properties.

Titanium powder metallurgy (P/M) offers the possibility of creating net shape or near net shape parts without the material loss and cost associated with having to machine intricate components from wrought billet. Powders can be produced by the blended elemental technique or by pre-alloying and then consolidated by metal injection moulding, hot isostatic pressing, direct powder rolling or laser engineered net shaping.

This is a list of pottery and ceramic terms.

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various time setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. Heavy equipment like machine tool beds, ships' propellers, etc. can be cast easily in the required size, rather than fabricating by joining several small pieces. Casting is a 7,000-year-old process. The oldest surviving casting is a copper frog from 3200 BC.

A green body is an object whose main constituent is weakly bound clay material, usually in the form of bonded powder or plates before it has been sintered or fired.

Tape casting is a casting process used in the manufacture of thin ceramic tapes and sheets from ceramic slurry. The ceramic slurry is cast in a thin layer onto a flat surface and then dried and sintered. It's a part of powder metallurgy.

Compaction of ceramic powders is a forming technique for ceramics in which granular ceramic materials are made cohesive through mechanical densification, either by hot or cold pressing. The resulting green part must later be sintered in a kiln. The compaction process permits an efficient production of parts to close tolerances with low drying shrinkage. It can be used for parts ranging widely in size and shape, and for both technical and nontechnical ceramics.

3D metal moulding, also referred to as metal injection moulding or (MIM), is used to manufacture components with complex geometries. The process uses a mixture of metal powders and polymer binders – also known as "feedstock" – which are then injection-moulded.

A variety of processes, equipment, and materials are used in the production of a three-dimensional object via additive manufacturing. 3D printing is also known as additive manufacturing, because the numerous available 3D printing process tend to be additive in nature, with a few key differences in the technologies and the materials used in this process.

Material extrusion-based additive manufacturing (EAM) represents one of the seven categories of 3d printing processes, defined by the ISO international standard 17296-2. While it is mostly used for plastics, under the name of FDM or FFF, it can also be used for metals and ceramics. In this AM process category, the feedstock materials are mixtures of a polymeric binder and a fine grain solid powder of metal or ceramic materials. Similar type of feedstock is also used in the Metal Injection Molding (MIM) and in the Ceramic Injection Molding (CIM) processes. The extruder pushes the material towards a heated nozzle thanks to

Polymer derived ceramics (PDCs) are ceramic materials formed by the pyrolysis of preceramic polymers, usually under inert atmosphere.

References

↑ "Cracking and Warping". marjonceramics.com. Retrieved 2021-06-03.
↑ Wang et al. Additive Manufacturing of Ceramics from Preceramic Polymers: A Versatile Stereolithographic Approach Assisted by Thiol-Ene Click Chemistry, Additive Manufacturing 2019 volume 27 pages 80 -90

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[1] "Cracking and Warping". marjonceramics.com. Retrieved 2021-06-03.

[2] Wang et al. Additive Manufacturing of Ceramics from Preceramic Polymers: A Versatile Stereolithographic Approach Assisted by Thiol-Ene Click Chemistry, Additive Manufacturing 2019 volume 27 pages 80 -90

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