Forming Methods
CoorsTek has a wide range of prototyping and processing capabilities using a variety of technical ceramic component forming methods. This variety creates an advantage over other manufacturers for unique and specific product development and manufacturing requirements. Our engineers can identify the best forming method for the components and production volumes needed by our customers, preventing the use of a less than optimal forming method due to lack of expertise or equipment. Throughout the world, CoorsTek has immense forming capabilities and expertise that can be specifically geared to handle almost any geometry and production requirement.
Working directly with a customer’s team, our engineers identify the most efficient method for their unique requirements. No matter what your component design may be, we likely have a forming process that will fit your needs.
Dry Powder Compaction Forming Methods
Dry Powder Compaction includes three different pressing sub-processes to best suit the target geometry: dry pressing, isostatic pressing, and roll compaction.
Dry Pressing
Excellent method for high volume, custom components with pressing compaction operations ranging from two to 1,500 tons and can produce anything from simple shapes to highly complex geometries.
Dry press tooling contains a die, ejector, punch, and fill shoe and has three steps:
- The fill shoe deposits ceramic powder into the die cavity and then retracts to level off the material with the top of the die.
- The punch moves into the die cavity while an ejector below the die cavity lowers. The punch and ejector compact the powder. After full compaction, the ejector pushes the pressed part out.
- The fill shoe moves over the die, pushing the part away from the tooling and deposits new ceramic powder into the die.
After pressing, oxide components typically do not require a separate de-binding operation. For non-oxides, the sintering kiln environment may not be appropriate for binder removal and a separate binder burnout step may be required.
Isostatic Pressing
Equal pressure is applied in all directions while compacting the ceramic powder. It is an excellent method for low and medium volume production, uniform densities, shrinkage control during sintering, and advantageous for some larger geometries.
The mold is an elastomeric sack filled with ceramic powder, sealed off, and placed inside a pressure chamber with liquid surrounding it. The liquid is pressurized to compact the powder in the mold. Steel arbors inside the rubber sack create the inside surface of the component.
Roll Compaction
This process is most often used for manufacturing ceramic substrates. Spray dried ceramic powder with an added binder to make the composition plasticized.
The plasticized ceramic material is squeezed between the rollers to press it into the desired thickness. Any excess material, usually from the tapes' edge, is cutoff and recycled. Compacted material is then rolled onto a take-up reel.
Pressed materials are unrolled later and sent through a kiln for binder removal and sintering.
Wet Processing
The wet processing method is used to manufacture components ranging from body armor to substrates for electronic devices. There are two categories in wet processing: slip casting and tape casting.
Slip Casting
Slip casting is used for forming technical ceramic components like body armor. The process begins by dispersing a ceramic powder inside a liquid carrier to make a slurry, or slip, which is cast into a porous mold. The capillary forces of the mold pull liquid into the porosity, and the ceramic particles, which are larger than the pores, cast against the mold wall and build up in thickness. When the target thickness is reached, the excess slip is drained, leaving a green component ready for firing in a kiln.
For higher volume production, the rate of casting can be accelerated through the application of external pressure. This is called pressure casting. A porous plastic mold is often used to provide the strength needed for higher casting pressures.
Tape Casting
For high-end, thin-film ceramic substrates, tape casting is the preferred method. Unlike roll compaction used for thick-film tape, this process is more suitable for lithography-based electronic circuits. This method is also used to manufacture components like those needed for igniters.
Tape casting is similar to slip casting. To make the tape, a ceramic slurry is cast onto a moving sheet of mylar. The mylar moves the slurry under a doctor blade to set the thickness of the tape. The tape is then added to a reel, similar to roll compaction, and sent for firing.
Plastic Forming
The third category of technical ceramic forming methods is plastic forming. In plastic forming, the feedstock material is ceramic powder dispersed within a plastic medium. This mixture is then forced into a die under pressure to shape the component.
There are three different processing methods for plastic forming: extrusion, injection molding, and wet processing.
EXTRUSION
Extrusion is a continuous process ideal for long, straight components with constant cross-sections and for components with high aspect ratios. We extrude hundreds of standard shapes and sizes but we also create many custom extrusions.
The process uses a plastic-ceramic material mixture that is forced through an extrusion die and solidifies for handling prior to firing. The extruded components are usually cut to a target length prior to firing.
INJECTION MOLDING
Similar to plastic injection molding, ceramic injection molding uses a plastic filled ceramic, removing the plastic after molding. This method is preferred for complex, three-dimensional shapes with high volume production needs but can be used for lower volume production scenarios.
This process uses a feed screw chamber that forces the ceramic mixture through a feed tube into the mold cavity. Once molded, the die separates to release the component and a de-binding operation is done before sintering. Read more >>
WET MOLDING
In this method the ceramic material is mixed with water, giving it characteristics similar to clay, and placed between to mold platens, typically plaster, then pressed to shape. The plaster absorbs excess water forced from the component during pressing.
Specialized Forming
Specialized Forming: Chemical Vapor Deposition & Pressure Assisted
Chemical vapor deposition( CVD) is the process of reacting a gas within a chamber to form a structural part. It can also be used to apply a coating on a component. These ultra-high purity ceramics are formed by layering another composition onto a ceramic surface or substrate and takes place in a gas-tight reactor. Pre-cursor gases flow into the reactor. At a controlled temperature the gases react to deposit silicon and carbon atoms, which form into silicon carbide (SiC) on the structure.
To create a freestanding CVD component, the SiC molecules are added layer-by-layer onto a graphite substrate until the thickness is structurally sound. The graphite tooling is then removed. When added as a coating, CVD SiC is applied onto a pre-sintered part. Because the CVD reaction takes place at temperatures nearing 1000°C, it is necessary for the substrate material to have the same thermal expansion rate as the coating, preventing cracking. This unique process creates an ultra-high purity ceramic generally used for semiconductor fabrication.
PRESSURE ASSISTED FORMING: HOT PRESSING AND HOT ISOSTATIC PRESSING
Certain materials need to be formed and fired using pressure assisted options, where both temperature and pressure are applied at the same time. These methods ensure refractory materials maintain the intended shape and material density during the firing process. CoorsTek offers two pressure assisted forming and firing methods:
- Hot pressing applies pressure uniaxially (in one direction) during the forming and firing process, similar to the dry pressing forming method.
- Hot isostatic pressing (HIP) is similar to the isostatic forming method—employing force in every direction through a pressurized gas medium at temperature.
Related Information
Looking to further explore the properties of technical ceramics or learn more about component design and manufacturing. Download our award-winning ebooks:
- A View to a Kiln explores our methods and processes used to manufacture technical ceramic components used in many industry applications. Our engineers take ideas from concept to firing and finishing.
- Ceramics: The Powerhouse of Advanced Materials explores the various properties of technical ceramics – mechanical, thermal, electrical, and chemical – and how they outperform metals and polymers in a myriad of industries.
