American Beryllia Corporation offers a wide range of manufacturing capabilities and services designed to meet virtually any application need. These capabilities encompass a variety of material preparation (forming), firing and finishing methods to suit exact customer requirements.

Material Preparation (Forming) Methods

Dry Pressing

Dry pressing involves compacting of ceramic powder to a particular shape or form in a tungsten-lined steel die. Pressure is applied by a simple, shaped punch or a compound, multi-stage die.

Dry processing allows high production rates with routine tolerances within +1% after firing. It is generally suitable for volume production of small parts and simple shapes such as bushings, spacers, washers and other substrates where the ratio of the part’s dimension in the processing direction (length) to its dimension normal to the pressing direction (width) is less than 3 to 1. Proper design and tight process control routinely produce parts that are free of distortions, cracks and other imperfections.

Isopressing

Isostatic pressing involves placing ceramic powder in a liquid-tight rubber mold which is subsequently immersed in a non-compressible fluid such as oil or water contained in a pressure vessel. When the fluid is pressurized, all surfaces of the mold receive equal pressure resulting in a uniform density. It is ideal for larger parts and shapes with a high ratio of length to cross section

While use of an internal mandrel facilitates formation of cylindrical or other simple internal shapes or cavities, external dimensions cannot be accurately controlled during isopressing and must be machined before or after firing. Tooling cost is usually lower but the process itself is slower and more expensive than dry pressing.

Hot Pressing

Hot pressing involves simultaneously subjecting ceramic powder to high temperature and pressure in heated graphite dies to achieve its final ceramic properties. Parts produced by this method show improved density and uniformity over-the-two-step forming and firing process.

Hot pressing is used to make parts with very large diameters ie: 24 inches (610 mm) and limited complexity. Compared to green forming and firing, it is the most expensive forming process and is only used for special ceramic combination requirements.

Extrusion

Extrusion involves continuously forcing a plasticized ceramic material through a shaped die. Typical products produced using this method include thermocouple tubes, rods and other parts with small cross-sections.

Tooling is relatively inexpensive and tubes can be produced with outside diameters as large as 0.250 inches (6.35 mm) to diameters as small as 0.030 inches (0.76 mm) with one or more holes as small as 0.005 mm for thermocouple wires running the length of the tubing.

Firing Method

Sintering

After forming, the ceramic is fired to high temperature (about 1600ºC for beryllia) to achieve its final density. During firing, pores are virtually eliminated and crystalline grains are bound together with virtually no glassy phase.

Grain size composition is controlled through a combination of special additives and careful attention to time and temperature variables. Each dimension of a ceramic part typically shrinks 17% as a result of sintering with a total volume reduction of 43%. Despite this reduction, the "as-fired" dimensions conform to all other physical specifications. Most production firing at American Beryllai Corporation is performed in periodic kilns with programmable instrumentation for precise time and temperature control.

Finishing Methods

Green Machining

Occasionally, it is more practical to machine a formed part before firing when the ceramic is soft and easier to machine. This "green machining" process entails a variety of conventional machining operations to meet dimensional specifications, provide particular features, or preparation for subsequent assembly.

Equipment required for finishing includes complex, highly accurate lapping machines; cylindrical, centerless and surface grinders; dicers and drills. Most of this equipment is automatically controlled to provide consistent dimensions and finishes, and reduce overall processing cost.

Precision Grinding

Both manual and automatic grinding techniques are used to achieve precise physical dimensions not possible in an "as-fired" part. Available methods include centerless, cylindrical, surface and inside diameter grinding using diamond wheels. Dimensional tolerances of +0.0001 inches (0.0025mm) can be met with simple and complex geometries.

Lapping and Polishing

Lapping and polishing is used to achieve specific surface finish, flatness and parallelism. In the lapping process, revolving flat surfaces abrade the ceramic part with a diamond or other abrasive lapping compound. The surface finish is controlled through selection of the proper abrasive, pressure and lapping cycle.

Dicing

Advanced, computer-controlled dicing equipment with diamond saw blades, similar to machines used for dicing integrated circuit wafers, is used to cut ceramic wafers into predetermined shapes and sizes. Linear cuts at any desired angle are also possible with this equipment.

Metalizing

Thick-film metallizing can be applied to fired ceramics to provide a bonding surface for subsequent attachment of chips or metal parts such as circuit leads, flanges, heat spreaders, seal rings, etc. The most commonly used technique for thick-film metallizing is screen printing, and spraying, roller coating and hand application are also used.

A molybdenum-manganese refractory metal composition is primarily used by American Beryllia Corporation and after application, it must be sintered at high temperature (1400ºC) before subsequent processing. Typical thicknesses for the fired metallizations are 100 to 1000 micro inches (2.5 to 25 microns). Sputtered thin film metallized patterns, which permit very tightly spaced fine lines to be applied to a ceramic substrate, are also available to meet special needs such as microwave circuits.