Time estimation in mechanical engineering design
This thesis describes investigations into the phenomenon of time estimation in mechanical
engineering design. Time estimating in this context refers to estimating in advance the
approximate duration of a new design project, for the purpose of preparing schedules.
The thesis describes background to the estimation problem, including practical and
theoretical aspects of design, design management and market conditions. The research
presented is based on data gathered from industrial collaborators, therefore detailed
descriptions of the collaborating firms are included. A quantitative study is described
which demonstrates that current estimation techniques are not infallible; and that there
can be a statistically significant link between the estimated and actual completion times.
A process of grounded theorising, based on expert interviews, is presented. Models of
the design estimation task were generated by this process, and are included. Differences
were found in the models for the estimation of times in an Engineer to Order (ETO)
environment, and estimation in a Volume Manufacturing environment. The models were
corroborated firstly by checking if they could be recognised and endorsed by the experts
from which they were generated, and. secondly by checking if they could be recognised
and endorsed by an expert not involved in the original model generation.
Correspondence was found to be good. A modified model of time estimation is
presented, taking into account the findings of the corroboration exercise. Finally, an
example of a simple tool for assisting the estimation process is included.