1 Empty plaster molds.

2 Molds filled with slip.

–  Ideal for producing hollow ware.

–  Complex forms can easily be achieved.

–  Efficient use of material.

–  Lends itself well to low-production runs.

–  Labor-intensive.

–  Limited control over tolerances.

–  Slow production rate.

–  Large-scale production requires many molds, which themselves require storage.

Volumes of production

Versatile production volumes—anything from small-scale craft batch production to factory production.

Unit price vs. capital investment

Slip casting is economical for small quantities because inexpensive molds can be made in small workshops while maintaining fairly low unit prices. However, in industrial production the plaster molds have a limited life and need to be replaced after approximately 100 castings.

Speed

Slip casting can be summarized by saying that “time equals thickness.” Because of the number of operations and drying times involved, even as an industrial process slip casting still has one foot in the craft tradition, with a fair degree of labor involved.

Surface

Slip casting is a great process for achieving surface patterns on objects (such as raised flower patterns). As with all ceramic products, glazing is required.

Types/complexity of shape

Shapes can range from small and simple to large and complex, and can include parts with undercuts. Anything from bathroom products to art objects and dinnerware can be made with this process.

Scale

Large molds can become very heavy and, given the massive amount of slip that would be needed to fill the void, slip casting may not be suited to large shapes. There is also a need for a kiln that is large enough to fire the finished product. Products such as tableware represent the average size.

Tolerances

It is hard to achieve high tolerances because the parts shrink considerably during firing and, even before that, inside the mold as the water is being drawn out of the slip.

Relevant materials

All types of ceramic.

Typical products

Slip casting is used to make any type of hollow product, from one-off pieces of tableware such as teapots, vases, and figurines to high volumes of sanitary ware.

Similar methods

Pressure-assisted slip casting (p.234) and tape casting (a process used for making multilayered capacitors for the electronics industry, involving laying down thin sheets of ceramic-loaded polymers that are laminated with other materials).

Sustainability issues

The excess slip collected during molding and after trimming is recycled back into the process to reduce material consumption and minimize the use of raw resources. The process is largely labor-assisted, which reduces the use of power and helps to balance out high energy consumption during the firing stage.

Further information

www.ceramfed.co.uk

www.cerameunie.net

Hydroforming Metal

AKA Fluid Forming

Product	T-section of a concept for a handrail system
Designers	Amelie Bunte, Anette Ströh, André Saloga, and Robert Franzheld, students at the Bauhaus University in Weimar; engineering by Kristof Zientz and Karsten Naunheim, students at Darmstadt University of Technology
Materials	hydroformed powder-coated steel; stainless steel tubes
Manufacturer	college project
Country	Germany
Date	2005

This deceptively simple, white-powder-coated steel junction from a student project for handrail systems illustrates the ability of hydroforming to create a complex form that changes from one diameter to another through a complex curve. This could otherwise only be made using conventional forming techniques that would then need to be welded together.

Hydroforming is a fairly new process for forming steel and other metals. It works by forcing a water and oil solution into a cylinder, or other closed shape, that is confined by a die. In essence, the process makes it possible to “inflate” metal tubes and form metal sheets into elaborate shapes by forcing them against a die. The water pressure of up to 15,000 psi expands the material, forcing it to conform to the shape of the die to form the required component.

Tubes and cylinders are the most common starting points for hydroforming, although panel hydroforming at high pressures also exists for forming pillow shapes from two panels sealed together.

A number of benefits have resulted from this process, including parts with reduced weight and faster production times than with similar methods, such as superforming aluminum (see p.70) and inflating metal (see p.76). In order for the full potential of hydroforming to be exploited, designers need to think of it as a way of reducing costs by making something from a single material rather than having to produce a multitude of parts that need to be joined together.