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ISF can be classified into Single-Point Incremental Forming (SPIF), Two-Point Incremental Forming (TPIF) or Double-Sided Incremental Forming (DSIF) depending on the type and number of tools deployed.
Single-Point Incremental Forming
SPIF involves only one point of contact between a tool and the sheet metal being formed, so the process requires the least manufacturing equipment.
However, the simple configuration results in a relatively low forming accuracy due to springback of the sheet metal after being released from the clamps, which limits applications in industry and manufacturing potential for complex geometries.
To address the limitations of SPIF, two process variants have been developed to reduce thinning and control springback. These variants can further enhance material formability and improve geometrical accuracy.
Two-Point Incremental Forming
Two-point incremental forming (TPIF) introduces a partial male die or female die to create a second point of contact with the sheet. The partial die provides the sheet with a supporting force, so less tensile force is needed to achieve the required plastic deformation.
Springback is reduced because of the lowered stress gradient across the sheet's thickness. However, the flexibility of the ISF process is compromised by the need to design and manufacture a partial die.
Double-sided Incremental Forming
Double-sided incremental forming (DSIF) adapts SPIF by introducing a second forming tool on the opposite side of the sheet metal. One tool (the master tool) takes the role of forming, while the other (the slave tool) provides local support to the sheet. The two tools can be independently controlled and their relative positions can be adjusted.
In addition to maintaining all the advantages of SPIF, DSIF improves forming accuracy as well as process flexibility when manufacturing more complicated geometries of sheet metal parts.
In some publications (see the cranial implant case study), researchers have used DSIF as a dieless method of forming geometries that may otherwise benefit from a die or backing plate.
A part with a complex geometry, or which requires very large deformations, is prone to fracture damage and geometric deviation from its target geometry. One approach to mitigating these issues is to introduce more forming passes.
Multi-Pass ISF
In multi-pass ISF, the final geometry is created through a series of intermediate geometries comprising smaller and simpler deformations which can be achieved without severe sheet thinning or fracture damage. The design of intermediate geometries is dependent on experience and trial-and-error testing, and using multiple passes requires a long forming time.
The process can optimise thickness distribution, improve material formability, and improve geometric accuracy.
As proposed by Duflou et al. in 2008: Process window enhancement for single point incremental forming through multi-step toolpaths
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