This study was aimed at improving the thermal modeling of the orthogonal machining
process. The first goal was to improve the prediction of the heat partition coefficient (β) and the
second was to improve the prediction of the temperature distribution in the tool.
The fraction of heat generated in the primary shear zone that is conducted into the
workpiece is termed as the heat partition coefficient (β). β is a key factor in the calculation of
the shear plane temperature and in calculating the cutting forces based on material flow stress.
The aim of this study was to identify models for accurate estimation of the heat partition
coefficient.
This study utilized a new approach to obtain the heat partition coefficient for the primary
shear zone using the steady state heat transfer analysis capability in ABAQUS/Standard. 2D heat
transfer elements that include mass convection were used to model the flow of material through
the workpiece and chip. Heat was applied along the shear plane and the resulting steady state
temperature fields were obtained. The heat partition coefficients obtained from these analyses
were compared with those predicted by the available analytical models as well as with the
coefficients obtained from the thermomechanical analyses carried out using ABAQUS/Explicit.
It was found that β is a unique function of the thermal number Nt, above the value Nt= 2.0. It was
also found that the βs obtained from FEA were closest to the predictions of Wiener’s model.
Transient FEA results show that the time constant of the thermomechanical coupling
determining the tool temperature is of the order of 940 μs, carrying the temperature to not reach
steady state over the 3600 μs typically used in our analysis. To obtain the steady state
temperature distribution in the tool, two different approaches were utilized. The first was a multi
step analysis approach in which the thermomechanical and the steady state thermal analysis capabilities of ABAQUS were employed sequentially. The power dissipation and the stable chip
geometry obtained from the first thermomechanical step were used as inputs for the second step
of the analysis, which was a steady state heat transfer analysis. A third analysis step, a
thermomechanical analysis, was carried out, with the steady state temperatures from the second
step and the stable chip geometry from the first step as initial conditions. It was observed that the
temperature decreased in the third step, implying that the steady state analysis overpredicted the
steady state temperatures. This may be attributed to the fact that the decrease in plastic and
frictional power with increase in temperature is not accounted for in the steady state analysis.
The second approach involved scaling the specific heat of the tool by a factor of 1/50 and
carrying out a one step thermomechanical analysis. For a linear thermal analysis, this is expected
to reduce the thermal time constant by a factor of 50. The actual thermal time constant decreases
to 185 μs. It is found that the temperature distribution in the tool converges to within 10° C (1%)
of the steady state temperatures. The rake face temperature distribution is used to evaluate the tool wear based on Usui’s tool wear model. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering.
| Identifer | oai:union.ndltd.org:WICHITA/oai:soar.wichita.edu:10057/1608 |
| Date | 12 1900 |
| Creators | Deshpande, Amit Anand |
| Contributors | Madhavan, Viswanathan |
| Publisher | Wichita State University |
| Source Sets | Wichita State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | xiv, 95 leaves, ill., 1471803 bytes, application/pdf |
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