Ceramic manufacturing is the process of making objects from inorganic, non-metallic materials. This can be done either by the action of heat or at lower temperatures by means of precipitation reactions from high-purity chemical solutions. This article covers a step-by-step process of manufacturing advanced ceramics.
Raw Material Processes
The raw materials for making advanced ceramics can be found in powder form. Before forming the suitable blend of raw materials is mixed to make the stock material that would be used in the forming processes. This is generally one of 3 types:
- A spray-dried powder
- An aqueous slip
- A dough feedstock
Spray Dried Powder
Spray drying is a very important technique for producing an absolutely free-flowing, granulated powder, which is the perfect feedstock for a number of pressing processes. The substance blend is first of all milled in a ball mill in a solvent, like water making use of ceramic balls. At this point inclusion of around 5% of organic binder to the slurry feedstock before spray drying is done. The binder which includes a lubricant and pressing aids, assists to give the material high-quality green strength in the upcoming pressing stage. One important stage in the process is the spray and dry which is done by atomizing the products in a hot air stream.
Aqueous slip is made by milling jointly the raw material blend in a ball mill in the water together with an organic dispersant to create a fluid, extremely concentrated slurry, that is employed for slip and pressure casting to make a high green density part.
Ceramic Dough Feedstock
Ceramic dough feedstock is made by blending the ceramic raw material mix with water or any solvent along with a blend of organic binder and plasticizer to make a clay-like plastic body which is usually deformable under pressure.
Consolidation seeks to manufacture a near-net shape part with adequate strength for future handling.
- Uniaxial Pressing
- Uniaxial or die pressing
The procedure includes the uniaxial compaction of a spray-dried powder in a rigid (typically tool steel) die.
Isostatic pressing is a consolidation procedure, there are actually two types. In each of the cases, a spray-dried powder is set in a flexible rubber or polyurethane bag that is exposed to an isostatic pressure.
Slip casting also referred to as drain casting, is a small to medium volume consolidation technique for typically simple shapes like tubes and crucibles along with more complex shapes like ladles.
A variation on slip casting is pressure casting. In this instance, pressure is put on the slip in the mold that enables thicker walled or solid parts to be cast.
Extrusion is a medium to high volume consolidation technique for manufacturing simple shapes like small diameter tubes. The dough feedstock gradually changes shape when under intense pressure along with the binders in the mix.
Green machining is the machining of an un-fired ‘green’. These must be performed once the consolidation method employed cannot create the needed shape. For instance, the most convenient way to make a part such as a weld location pin would be to green machine an isostatically pressed rod.
Sintering is the process through which the consolidated green ceramic part is fired to give a dense, advanced technical ceramic. Right before or in this particular stage any organic additives have to be taken out.
Diamond grinding is usually done on a sintered part; it is done for a better surface finish or to take out surface flaws and hence is an alternate process.
Final machining procedures consist of grinding, cutting, honing and lapping, and polishing. All these processes need diamond tooling because of the high hardness of dense advanced ceramics.
Inspection is the last stage of the ceramic manufacturing process and usually includes a visual inspection of the part and a dimensional inspection of a drawing. Visual inspection includes looking for cracks or flaws in the part and to ensure the part is clean.