Application of a Supersonic Fluidic Oscillator to
Improve Performance of the Superplastic Forming Process
The Superplastic Forming (SPF)
process involves gas injection from a variable pressure supply into a die, to
form a heated metallic sheet over the surface of the die into a complex
automotive body panel shape. The existing process involves excessive forming
times to allow relaxation of residual stresses and avoid part cracking and
tearing. Previous research shows that multi-pulse pressure forming has a
favorable effect on overall material formability and properties hence, reducing
the required manufacturing time.
A Supersonic Fluidic Oscillator (SFO), due to an
absence of moving parts, is capable of reliably generating the required
pressure fluctuations under the extremely high temperatures present in the SPF
process.
Our research collaboration with AEM began over five
years ago with a Natural Sciences and Engineering (NSERC) Engage grant. In this
work a supersonic fluidic "load" oscillator, previously investigated for
a different application, was studied using a commercially available
finite-volume computational package (ANSYS Fluent). The predicted oscillation
frequency compared reasonably well with certain, but not all, of the previously
published results. Determination of the reasons for discrepancies lead to our
additional studies. Another concern is the excessive computational time
required to achieve the numerical results for just one set of design
parameters.
Two subsequent studies which were supported by Ontario
Centres of Excellence (OCE) VIP I grants. The first involved the design, construction and instrumentation of an experimental test
facility to obtain reliable data to evaluate the accuracy of the computational
fluid dynamic model of the SFO and make recommendations for improvements to the
model. The second involved investigating
methods of overcoming the extremely large computational times. This research
led to certain refinements of the computational model which improved the
accuracy however, the parallel implementation did not reduce the computational
time to an acceptable level.
The observed ability of the SFO to provide suitable
oscillations led to an investigation of the performance of the device while
pressurizing a chamber under conditions closer to those found in the actual SPF
process. A two-year OCE VIP II research grant supported this research which
included three separate but related projects. The first resulted in a MASc
thesis in which a high-pressure (approximately 4 MPa) cold model was designed, constructed and tested. The second also resulted in a second
MASc thesis which a refined CFD simulation of the overall process which was
compared with the experiments. The third project involved the development of a
low-order mathematical model of the SFO application for use in the practical
industrial design of the device for a specific implementation. This project was
initiated by a PhD student who is currently being supported with a MITACS Accelerate
Internship.