McAnulty, Tegan Maree
Description
With recent developments in rapid prototyping technologies, the
automotive industry has been able to move away from costly and
inefficient methods of prototyping. In fact, rapid prototyping
techniques now exist for nearly all the components in a car,
meaning time and money is saved in product development. One
exception to this trend, despite their ubiquity in automotive
applications, is formed sheet metal components.
Single point incremental forming...[Show more] (SPIF) is a sheet metal forming
technique with a fast turnaround that uses little to no custom
tooling.
It is a promising method for filling the gap in rapid prototyping
capability for sheet metal components.
However, despite significant research over the last two decades,
barriers to industrial viability still include the key issues of
fracture occurring in the sheet metal, or a final part being
rejected due to unacceptable dimensional error. These two issues
are affected by SPIF process parameters, but the extent of their
influences are not well understood.
By investigating the effect of process parameters on material
formability and geometric accuracy, this thesis seeks to address
these issues.
Case studies emphasise the impact of formability and geometric
accuracy on prototyping automotive components with SPIF.
Also emphasised is the importance of effective support walls and
optimal design of the forming surface that is used to generate
toolpaths for forming components.
A systematic review of the literature regarding the first key
issue, formability in SPIF, highlights significant
inconsistencies in published research about the effects of
process parameters. A hypothesis to explain this result presents
the idea of non-linear effects and parameter interactions, which
is supported by original experimental work. This shows the
difficulty of empirical prediction of formability when, for
example, a small change in one parameter may interact with
another to significantly influence the outcome of the final
part.
Identifying and following safe formability limits will minimise
the likelihood of fracture for the forming surface of a
component. Research in this thesis looks at the thickness
distribution of variable wall angle conical frustum (VWACF) parts
as a basis for defining a safe formability limit. However,
experimental results show this is not viable due to irregular
trends in the thickness distribution close to the fracture point
of the VWACF.
The second key issue of geometric error in SPIF is approached by
focusing on a single mode of error, namely `wall bulge', or
springback in flat walls of components. Experiments studied how
a variety of tool shapes and sizes affected its severity, and
found a trade-off with `pillowing', another mode of geometric
error. At the same time as flat-ended tools reduce pillowing in
the base, the experimental results show an increase in the amount
of bulging in the walls.
The findings of this thesis demonstrate the impact that a single
parameter change can have on multiple aspects of a component.
Also highlighted are the complexities of the SPIF process that
remain as barriers to industrial viability. This work contributes
to overcoming these barriers and achieving efficient rapid
prototyping of sheet metal components.
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