HyperXtrude Process Model Validation
- The figure below shows the 3-D model of flat die and conical die experiments in HyperXtrude. The model consists of sleeve, die, billet, bearing and profile. For the purposes of saving simulation time and taking advantage of symmetry, a half model was simulated rather that a full 360-degree model. Nevertheless, for the sake of completeness, the results of both of these models were compared later; less than 1% difference in results was found with identical mesh size in both cases.
Process conditions are the initial conditions that are used in the computation and they were set corresponding to the experiments. The ram acceleration time in the simulation was set to the time that roughly corresponds to breakthrough load. Tooling and billet temperatures are specified along with butt length and ram velocity. In order to account for internal heat generation in the code, it is assumed that 90% of the work is converted into heat.
Coupled thermo-mechanical validation of load-temperature responses
The results of the simulation model were compared to experimental data. The correlation obtained is presented below. Note that TC1, TC2, TC3 and TC4 in the temperature plots refer to location of thermocouples in the experiments. One of the challenges was the determination of convection coefficients at the tool-work piece interfaces and determination of the right friction coefficient in bearing region. Friction is generally fine-tuned [Tekkaya et al] by “what-works-best” approach. Convection coefficient were zeroed on by following a ‘6-Step’ procedure developed during the course of the research. [A.E. Tekkaya, P.A.F. Martins,(2009), Accuracy, reliability and validity of finite element analysis in metal forming: a user's perspective, Engineering Computations, Vol. 26 Iss: 8, pp.1026 – 1055]
As seen above on the figure to the right, modification of the sine hyperbolic model enables the process model to capture the characteristic stress softening response owing to dynamic recrystallization in magnesium alloys.