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Technical Ceramic Machining Glossary
55 terms that turn up on a ceramic quote, drawing or datasheet, defined for the person buying the part rather than for a materials scientist.
Materials
- Advanced ceramic
- An engineered ceramic made from refined synthetic powders for a technical function, rather than a clay based traditional ceramic. Also called technical ceramic or fine ceramic.
- Alumina
- Aluminium oxide. The most widely used technical ceramic, sold by purity, commonly 96%, 99.5% and 99.8%. Full guide
- Aluminium nitride
- An electrically insulating ceramic with high thermal conductivity, around 180 W/mK, used where heat must leave a device that must stay isolated. Full guide
- ATZ
- Alumina toughened zirconia. A zirconia matrix with alumina added for hardness and ageing resistance. Full guide
- Boron nitride
- A soft, machinable, self lubricating ceramic that tolerates very high temperature in inert atmosphere. Sometimes called white graphite.
- Cordierite
- A low expansion oxide ceramic used where thermal shock resistance matters more than strength, for example kiln furniture and setters.
- Glassy phase
- The non alumina fraction at the grain boundaries of lower purity alumina, usually silica based. It aids sintering and metallising but is attacked first by plasma and chemicals. Full guide
- Macor
- A machinable glass ceramic containing mica crystals in a glass matrix. It cuts with conventional tooling and needs no firing afterwards. Full guide
- Silicon carbide
- A very hard, stiff, thermally conductive non oxide ceramic. Sintered grades resist chemistry better than reaction bonded grades, which contain free silicon. Full guide
- Silicon nitride
- A tough non oxide ceramic with excellent thermal shock resistance, used for bearing elements, hot section parts and semiconductor handling. Full guide
- Technical ceramic
- See advanced ceramic. The term used in this glossary for engineered ceramics such as alumina, zirconia, silicon carbide and silicon nitride.
- Y-TZP
- Yttria stabilised tetragonal zirconia polycrystal. 3Y-TZP, with 3 mol% yttria, is the standard tough industrial grade. Full guide
- Zirconia
- Zirconium dioxide. The toughest common technical ceramic, stabilised with yttria or magnesia to hold a useful crystal phase at room temperature. Full guide
- ZTA
- Zirconia toughened alumina. An alumina matrix with zirconia added, sitting between alumina and zirconia on toughness and price. Full guide
Properties
- Dielectric strength
- The voltage a material withstands per unit thickness before it breaks down, quoted in kV/mm. Purity and density raise it, porosity lowers it.
- Flexural strength
- The stress a bar of material carries in bending before it breaks, quoted in MPa. The usual strength figure for ceramics, because they are not tested in tension.
- Fracture toughness
- Resistance to a crack spreading, quoted in MPa m^0.5. The property that predicts whether a ceramic part survives handling and impact. Full guide
- Grain size
- The average size of the crystals in a sintered ceramic. Finer grain generally means higher strength, cleaner ground edges and better plasma behaviour.
- Hardness
- Resistance to indentation, usually quoted in Vickers (HV). It predicts abrasive wear resistance and it also predicts how long the part takes to grind.
- Theoretical density
- The density a material would have with zero porosity. Real parts are quoted as a percentage of it, and the remainder is pores.
- Thermal expansion
- How much a material grows when heated, quoted in ppm/K. The number that decides whether a ceramic to metal joint survives thermal cycling. Full guide
- Thermal shock resistance
- The ability to survive a fast temperature change. It rises with strength and conductivity and falls with expansion and stiffness.
- Transformation toughening
- The mechanism that makes zirconia tough. Grains ahead of a crack change phase and expand slightly, clamping the crack shut. Full guide
- Weibull modulus
- A number describing how consistent a brittle material strength is. A higher modulus means less scatter between parts, which matters more than the average for design.
Process
- Bisque machining
- Machining a part after a partial firing, when it is stronger than green but still soft enough to cut. A middle route between green and hard machining. Full guide
- Binder burnout
- The slow low temperature stage of a firing cycle that removes the organic binder holding the green part together. Full guide
- Blank
- The piece of sintered or green ceramic a part is machined from. Stock plate, rod and tube are the cheap options; a pressed blank made for one part adds tooling and lead time.
- Creep feed grinding
- Grinding with one slow deep pass instead of many shallow ones. Faster on deep forms and gentler on the part, but it needs a rigid machine and heavy coolant. Full guide
- Dressing
- Restoring the form and exposing fresh diamond on a loaded grinding wheel. Dressing time and wheel wear are real line items on a ceramic quote. Full guide
- Green machining
- Machining the part before sintering, while the body is soft. Cheap and fast, but every dimension then shrinks 15 to 25% in the kiln. Full guide
- Hard machining
- Grinding a part after sintering, with diamond. Slower and dearer, and the only way to hold a tight tolerance or a fine finish. Full guide
- Isostatic pressing
- Pressing powder with equal pressure from all directions, which gives a more uniform green density and therefore more predictable shrinkage than uniaxial pressing.
- Lapping
- Running a part against a flat plate with loose abrasive between them. The operation that produces real flatness and removes grinding damage. Full guide
- Metallising
- Firing a metal layer, classically molybdenum and manganese, onto a ceramic surface so it can be plated and brazed to metal. Full guide
- Polishing
- Improving surface finish with fine abrasive on a soft carrier. It removes almost no material and does not correct form. Full guide
- Rotary ultrasonic machining
- Machining with a rotating diamond tool that also vibrates at ultrasonic frequency. Very low cutting force, so it suits small holes and fragile features. Full guide
- Sintering
- Firing a pressed powder body so the particles bond and the pores close. The part becomes dense and strong, and shrinks 15 to 25% on every dimension. Full guide
- Setter
- The plate or fixture a part sits on in the kiln. Friction against the setter restrains shrinkage locally, which is one source of as-fired distortion.
- Shrinkage factor
- The multiplier a shop applies to green dimensions so the fired part lands on size. It is measured from that shop own batches of that powder. Full guide
- Subsurface damage
- Microcracks left below a ground surface. They are deeper than the roughness suggests and they lower the effective strength of the part until finishing removes them. Full guide
Design
- As fired
- A surface left as it came out of the kiln, with no grinding. Tolerance is roughly 1% of the dimension and the finish is rough. Full guide
- Chamfer
- A defined angled cut on an edge. On ceramic it is functional, not cosmetic, because an unchamfered edge chips and every chip is a crack origin. Full guide
- Chipping
- Small pieces breaking away at an edge, hole exit or thin section. The most common ceramic scrap cause and the reason edges need a defined treatment. Full guide
- Datum
- The reference surface everything else is measured from. On a ceramic part it should be a ground surface, not an as-fired one. Full guide
- First article inspection
- A full dimensional report on the first part of a new order, used to agree that the process is right before the rest is made. Full guide
- Flatness
- How close a face is to a perfect plane. Checked against an optical flat on small parts and on an interferometer or CMM for demanding work. Full guide
- Hermetic seal
- A joint that does not leak gas above a stated rate. Specified as a leak rate, which decides both the process and the inspection. Full guide
- Optical flat
- A very flat reference disc placed on a part under monochromatic light. The interference bands that appear are counted to read flatness quickly. Full guide
- Ra
- Average surface roughness in micrometres. As ground is typically 0.2 to 0.4 µm, lapped 0.05 to 0.1 µm, and polishing goes below that. Full guide
- Tolerance stack
- The accumulated effect of individual tolerances on an assembly. On ceramic parts it matters twice, because as-fired and ground surfaces behave very differently.
Commercial
- EXW
- Ex works. The buyer collects from the supplier premises and carries the freight risk from there. Worth agreeing early on fragile parts.
- Lead time
- Calendar time to delivery. On ceramic it is usually set by blank availability and kiln scheduling, not by machine hours. Full guide
- MOQ
- Minimum order quantity. In ceramic machining there is often no real minimum for ground parts, but pressed blanks carry a tooling cost that sets an economic minimum.
- NDA
- A non disclosure agreement covering drawings and specifications shared during quoting. Ask for one before sending sensitive files, not after.
- RFQ
- Request for quotation. On a ceramic part it should state grade, quantity, which features are ground, finish requirements and the date you need it. Full guide
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