Hohlform

Hohlform, literally “hollow form” in German, is a term used in crafts and manufacturing to denote a mold or form designed to produce a hollow object. A Hohlform creates an interior cavity; in practice this is achieved either by rendering the form in two or more parts or by introducing an internal core during the shaping process. The hollow form can be used in metal casting, ceramics, glass, and plastics, among others, to minimize material use, control weight, or produce thin-walled shells with stable geometry.

Construction: In multi-part molds, the external shell defines the outer surface while a removable core defines the hollow interior. Common materials for Hohlformen include plaster and silicone for prototypes, metal or ceramic for industrial patterns, and ceramic slipcasting molds. In metal casting, sand cores, ceramic cores, or collapsible cores create cavities; in plastics and glass, techniques such as injection molding with internal cores or blow molding generate hollow parts.

Considerations: Wall thickness uniformity, draft angles, venting to avoid air traps, and ease of demolding influence design. Temperature, cooling, and shrinkage must be accounted for to prevent warping or collapse of the hollow interior. Core removal can be difficult for complex geometries, so mold design often uses segmented or collapsible cores.

Applications: Hohlformen are used for statues and decorative objects, vessels, containers, automotive and consumer-product parts, and architectural components. The term also appears in sculpture to refer to hollow, lightweight forms.