Abstract:
Single Point Incremental Sheet Forming (SPISF) is a well-known flexible alternative to conventional generative
manufacturing processes. In SPISF, the geometry to be formed is fragmented into series of 2D slices and the
plastic deformation is achieved through layer by layer movement of a Numerically Controlled (NC), hemispherical or ball end forming tool. The whole plastic deformation is the sum of all localized strains developed
during each increment. Spiral, constant z incremental toolpaths, and their variants are common conventional
toolpaths for SPISF. Several researchers have investigated these toolpaths extensively. Fractal Geometry Based
Incremental Toolpath (FGBIT) is a recently developed toolpath for SPISF that improves the process formability
and stress distribution. Unlike conventional toolpaths, FGBIT deforms the base region of the formed geometry
which induces work hardening and residual stresses into the work piece. This may lead to the forming of high
strength components. The residual stress distribution over the base region of the formed component (square cup)
has been investigated in this study.
Further, a comparison based on residual stress distribution between FGBIT and conventional incremental
toolpaths is presented. Residual stresses have been measured by using nanoindentation technique. Pile up
generation near the periphery of the indent is investigated for conventional and FGBIT based toolpaths. It has
been observed from the experimental results that, the strength of the formed component increases due to induced compressive surface residual stresses while using FGBIT hence, metal components with high fatigue life
and better strength-to-weight ratio can be formed.
