Volumes of production

Pressure-assisted slip casting molds typically require volumes of approximately 10,000 pieces to justify the use of the plastic tooling.

Unit price vs. capital investment

Cost-effective unit parts, which are the result of several factors, outlined above. In the Flexiform pressure-assisted drain-casting project, mold costs are significantly reduced.

Speed

Conventional slip casting (p.140) can require anything up to an hour for casting, de-molding, and drying. Pressure-assisted slip castings can typically result in a reduction in time of 30 percent.

Surface

Superior quality finish compared with conventional slip casting, with reduced casting seams resulting in less felting than with the conventional method.

Types/complexity of shape

From small and simple to large and complex parts with undercuts. Anything, from bathroom products to art objects and dinnerware, can be made using this process. Just think of the U-bends on the underside of a toilet to glean an understanding of the types of complexity possible.

Scale

From small teacups to toilets and baths.

Tolerances

As is the case with any fired piece, molds need to be made that take account of a reduction in size once the product has been fired.

Relevant materials

Suited to most types of ceramic material.

Typical products

Complex tableware, which can require four-part molds for teapots and coffee pots with integral handles. Apart from its large-scale use in sanitary ware, it is in the area of advanced ceramic technology that pressure-assisted slip casting is attracting the strongest interest.

Similar methods

Ceramic slip casting (p.140) and compression molding (p.174).

Sustainability issues

Water is used to aid the ceramic flow instead of the organic solvents or binders that were previously used. This water can be cleaned and recycled back into the process to reduce waste and consumption of raw materials. Further material reductions are made through the increased durability of the plastic molds, which can withstand extensive use.

Further information

www.ceramfed.co.uk

www.cerameunie.net

www.ceram.com

www.ideal-standard.co.uk

Viscous Plastic Processing (vpp)

Product	teacup from the Old Roses range
Designer	Harold Holdcroft
Materials	bone china ceramic
Manufacturer	Royal Doulton
Country	UK
Date	1962

VPP technology was used to enhance the properties of bone china, so that these uniquely British teacups could be injection molded. A combination of design and the cost-effectiveness of this process means that 100 million cups have been sold since 1962.

As the technology behind materials and manufacturing techniques progresses, the previously barren spaces between different families of materials are bridged. Of all the material families, plastics make up the group that is the most versatile in terms of production techniques available. However, other materials, such as metals and ceramics, are all being explored to find new ways of mass-producing components using plastic-state forming techniques. This allows materials that have traditionally limited means of forming, including ceramics, to be formed using methods such as injection molding (see p.196).

The material and the method of production go hand in hand in the sense that the properties of the materials dictate the complexity of production that is available. One of the problems in forming ceramics involves the need to eliminate the inherent microstructural defects in ceramic materials. These defects reduce the strength of the material, making it brittle. Viscous plastic processing, or VPP, is a method of enhancing the properties of ceramic materials that eliminates these flaws, resulting in a way of processing ceramics that is much more flexible and, to use the technical term, “plastic” in its nature. The process involves ceramic powders being mixed with a viscous polymer under high pressure. This mixture can then be used to form components through a range of fabrication techniques, including extrusion (see p.96) and injection molding.

–  The process can be applied to a wide range of ceramic materials and offers materials with good “green” strength.

–  Limited number of manufacturers.