a b s t r a c tThis paper describes the history of Incremental Sheet Forming (ISF) focusing on technological developments. These developments are in general protected by patents, so the paper can also be regarded as an overview of ISF patents in addition to a description of the early history. That history starts with the early work by Mason in 1978 and continues up to the present day. An extensive list of patents including Japanese patents is provided.The overall conclusion is that ISF has received the attention of the world, in particular of the automotive industry, and that most proposed or suspected applications focus on the flexibility offered by the process. Only one patent has been found that is explicitly related to the enhancement of formability. Furthermore, most patents refer to TPIF (Two-Point Incremental Forming) as a process.Besides simply presenting a historical overview the paper can act as an inspiration for the researcher, and present a rough idea of the patentability of new developments.

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In Incremental Sheet Forming (ISF) strains can be obtained well above the Forming Limit Curve (FLC) that is applicable to common sheet forming operations like deep drawing and stretching. This paper presents an overview of mechanisms that have been suggested to explain the enhanced formability. The difference between fracture limit and necking limit in sheet metal forming is discussed. The necking limit represents a localized geometrical instability. Localized deformation is an essential characteristic of ISF and proposed mechanisms should stabilize the localization before it leads to fracture. In literature six mechanisms are mentioned in relation to ISF: contact stress; bending-under tension; shear; cyclic straining; geometrical inability to grow and hydrostatic stress. The first three are able to localize deformation and all but the last, are found to be able to postpone unstable growth of a neck. Hydrostatic pressure may influence the final failure, but cannot explain stability above the FLC.

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