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Title: The mechanics of incremental sheet forming
Author: Jackson, Kathryn Pamela
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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Incremental sheet forming (ISF) is a flexible process where an indenter moves over the surface of a sheet of metal to form a 3D shell incrementally by a progression of localised deformation. Despite extensive research into the process, the deformation mechanics is not fully understood. This thesis presents new insights into the mechanics of ISF applied to two groups of materials: sheet metals and sandwich panels. A new system for measuring tool forces in ISF is commissioned. The system uses six loadcells to measure reaction forces on the workpiece frame. Each force signal has an uncertainty of ±15 N. This is likely to be small in comparison to tool forces measured in ISF. The mechanics of ISF of sheet metals is researched. Through-thickness deformation and strains of copper plates are measured for single-point incremental forming (SPIF) and two-point incremental forming (TPIF). It is shown that the deformation mechanisms of SPIF and TPIF are shear parallel to the tool direction, with both shear and stretching perpendicular to the tool direction. Tool forces are measured and compared throughout the two processes. Tool forces follow similar trends to strains, suggesting that shear parallel to the tool direction is a result of friction between the tool and workpiece. The mechanics of ISF of sandwich panels is investigated. The mechanical viability of applying ISF to various sandwich panel designs is evaluated by observing failure modes and damage under two simple tool paths. ISF is applicable to metal/polymer/metal sandwich panels. This is because the cores and faceplates are ductile and largely incompressible, and therefore survive local indentation during ISF without collapse. Through-thickness deformation, tool forces and applicability of the sine law for prediction of wall thickness are measured and compared for a metal/polymer/metal sandwich panel and a monolithic sheet metal. The mechanical results for ISF of sheet metals transfer closely to sandwich panels. Hence, established knowledge and process implementation procedures derived for ISF of monolithic sheet metals may be used in the future for ISF of sandwich panels.
Supervisor: Allwood, Julian Mark Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Incremental sheet forming ; Sheet metal ; Sandwich panel ; Deformation mechanics ; Tool forces ; sine law