Because ceramics employ many different types of manufacturing processes, the following is a basic outline. It will give you a good idea of what it takes to manufacture a ceramic component. It is important to note that all ceramics start as granular powder made up of a base material such as Alumina or Zirconia, mixed with other stabilizers and binders that give each "ceramic body" its own unique characteristics.
There are several basic forming methods.
STEP 1: The Forming Process
Here are are a few:
Isostatic Pressing is the use of force pressures of equal proportion from all directions. This can be achieved with fluid or by dry pressing. Isopressing is commonly used to form complex ID configurations by compressing powder around a pin.
Extrusion is done in the same manner that most materials are extruded, by forcing material through a die. This is a standard process for tubes, rods and bar stock material.
Injection Molding of ceramics is also similar to the processes used for other materials. Injection molding is used mainly for very intricate or high volume components. The cost for injection mold tooling is expensive but when amortized across high volumes it can mean a lower per part cost.
Mechanical Pressing utilizes steel or carbide tooling that creates a "net or near net" shape. By filling the tool with powder and applying uniaxial pressures to compress the powder.
The above forming methods can also be used to make "blanks" for further processing.
STEP 2: Green Machining
The machining of a ceramic in the unfired state is called green machining. Green machining of ceramics is done whenever possible since the machining of ceramics after firing is very costly. The machining centers found in our plant are very similar to those found in standard machine shops: CNC mills, and CNC lathes drilling equipment, cut-off saws, surface grinders, rotary grinders, as well as many machines that have been custom made in-house. However, the extremely abrasive nature of ceramics requires the use of carbide and PCD tools and abrasive wheels.
STEP 3: Firing
In order for ceramics to be hard and dense, they must be "sintered", or fired to high temperatures for prolonged periods of time in gas or electric kilns. Typical firing temperatures for alumina, mullite, and zirconia reach 2850°F - 3100°F. Typical firing cycles can range from 12 - 120 hours depending upon the kiln type and product. Ceramics shrink approximately 20% during the sintering process. Non-uniform shrinkage as a result of standard forming and machining processes can cause deformation of the ceramic. Experience and knowledge of ceramic processing allows you to utilize specific machining and firing methods to help limit these effects.
STEP 4: After Firing Operations
Diamond Grinding - Post firing machining may be required to achieve tight tolerances and surface finishes. At this stage ceramics can only be machined with diamonds, so tooling can be costly. Standard machine shop equipment can be modified with diamond plated or impregnated wheels, drills and assorted tools, as well as necessary recirculating and filtered coolant systems.
Glazing - One of the reasons that parts are glazed is to make it easy to remove unwanted residue. For instance, spark plugs are glazed to reduce areas of potential arcing in high voltage environments. This process involves dipping, brushing or spraying a glass coating onto the surface of the fired ceramic. The glazed ceramic must then be fired to 1500°F - 2700°F to sinter the glazed coating.
Cleaning - Most fired alumina ceramics can become dirty through handling, machining or inspecting. These oils, dirts and metal marks can be removed using a variety of techniques. Ultrasonic cleaning in mildly acidic or basic solutions at elevated temperatures is commonly done. There are also special cleaning and packaging options which may be desirable for applications sensitive to contamination.
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