<p>In sheet metal forming processes, friction has decisive effects on the strain distribution in the deformed sheets and the quality of the final product due to the large surface/thickness ratio of the blank sheets. It is well known that friction in sheet forming operations is dependent on local contact conditions such as surface roughness, contact pressure and sliding velocity. Adding complexity to this frictional behavior, some rolled sheets have oriented surface roughness and show considerable frictional anisotropy. A constant friction model without consideration of these relevant phenomena is regarded as the reason why sheet metal forming simulations often fail to produce satisfying results despite the well developed material models. </p>
<p>To develop a friction model which considers both of the varying conditions of local contact and the frictional anisotropy was the aim of this thesis. For this purpose, the analysis method of the friction test (draw-bend test) had to be examined for the capability to evaluate these parameters independently. Through careful study using finite element simulations, it was found that the conventional method has shortcomings in addressing pressure dependent friction due to the pressure non-uniformity existing in the test. Therefore, a new analysis method, which can evaluate pressure dependency of a friction coefficient, was developed. In the new method, contact pressure maps obtained from simulations were included in the analysis of test data.</p>
<p>The new analysis method was applied to friction measurement of aluminum sheets
with known anisotropic mill finish, and friction coefficients were obtained as functions of
contact pressure, sliding velocity and sliding direction. In the obtained friction model, a
friction coefficient is a continuous surface over the domain of contact pressure and sliding
velocity. Lastly, the new friction model was implemented into a finite element code and
the model was validated through circular cup drawing experiments and simulations. The
comparisons showed good agreements in the aspects of punch force, cup size and failure
location. Thus, the newly developed model can accurately predict the effects of anisotropic friction in sheet metal forming processes. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/16829 |
| Date | 18 March 2015 |
| Creators | KIM, YOUNG SUK |
| Contributors | JAIN, MUKESH K., METZGER, DON R., Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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