Jarosław Nowak

The Material Flow Analysis in the Modified Orbital Forging Technology

The main aim of this work is the computer aided design of the new orbital forging process. The finite element model was developed and used in research on possibility of modification of the classical orbital forging technology based on the Marciniak press to obtain more effective process. Obtained numerical results from simulations of the new orbital process are compared with the experimental analysis, performed on the orbital press with the developed device. However, due to the novelty of the developed approach the investigation on direction of material flow during deformation is of particular interest in this work. Direction of material flow and strain path change effect due to incremental character of deformation is analyzed. Obtained results confirm good predictive capability of the FE model and are the basis for the comparison of the two processes and discussion on the effectiveness of the modified incremental forming process.

Modification of Flow Stress Model Based on Internal Variables

In the paper a flow stress model based on the dislocation theory in consideration of the recrystallization is shortly presented. The model contains two parts: a classic model of dislocation evolution and recrystallization model. The latter considers different kinds of recrystallization as the same process rooted in nucleation and grain growth. The results of the model parameters identification and the simulation are presented in this paper. Then disadvantages of the model are considered and new proposal for improvement the model are presented. Results of preliminary simulation are presented as well

Modeling of Recrystallization with Recovery by Frontal Cellular Automata

The objective of the paper is modeling of material softening after the deformation. The main problem of almost every model with digital material representation is consideration of recrystallization as the only mechanism of material softening. Static recovery is introduced into the model based on frontal cellular automata. An influence of static recovery on softening process is twofold. Static recovery effects on a decrease of dislocation density directly and on growing rate of recrystallized grain indirectly. Because of static recovery the recrystallization slows down and the time of recrystallization is extended. Simulation consists of two stages. During the deformation, distortion of the cells, evolution of dislocation density, nucleation and grain growth are considered, while after the deformation, the processes of softening are considered only. Comparison of simulation results with experimental data are presented as well.

Development of Flow Stress Model Based on Internal Variables

In the paper a flow stress model based on the dislocation theory in consideration of the recrystallization is briefly presented. The model consists of two parts: the classic model of the dislocation evolution and recrystallization model. The latter deal with various types of recrystallization as the same process rooted in nucleation and grain growth. The results of the model parameters identification and the simulation are presented in this paper. Then disadvantages of the model are considered and new proposal for improvement the model are presented. The results of preliminary simulation are presented as well.

Computer-Aided Design of Manufacturing Chain Based on Closed Die Forging for Hardly Deformable Cu-Based Alloys

Two copper-based alloys were considered, Cu-1 pct Cr and Cu-0.7 pct Cr-1 pct Si-2 pct Ni. The thermal, electrical, and mechanical properties of these alloys are given in the paper and compared to pure copper and steel. The role of aging and precipitation kinetics in hardening of the alloys is discussed based upon the developed model. Results of plastometric tests performed at various temperatures and various strain rates are presented. The effect of the initial microstructure on the flow stress was investigated. Rheologic models for the alloys were developed. A finite element (FE) model based on the Norton–Hoff visco-plastic flow rule was applied to the simulation of forging of the alloys. Analysis of the die wear for various processes of hot and cold forging is presented as well. A microstructure evolution model was implemented into the FE code, and the microstructure and mechanical properties of final products were predicted. Various variants of the manufacturing cycles were considered. These include different preheating schedules, hot forging, cold forging, and aging. All variants were simulated using the FE method and loads, die filling, tool wear, and mechanical properties of products were predicted. Three variants giving the best combination of forging parameters were selected and industrial trials were performed. The best manufacturing technology for the copper-based alloys is proposed.

Flow Stress Model Based on Internal Variables

In the paper a flow stress model based on internal variables is shortly presented. The multiplicative model contains three parts. In the model, the normalized dislocation density ρm was considered, as a strain function only, independently to the strain rate and the temperature. Influence of varying processing conditions (the strain rate and the temperature) is introduced as a factor. The first one is a model of so called master curve. It is an internal variable model based on dislocation density and its output value strongly depends on strain and very weakly on temperature and strain rate. The second factor introduces varying deformation conditions. Changes of flow stress do not occur instantly with the change of deformation conditions, but it requires some strain for transition. The third part considers influence of recrystallization. The results of the model parameters identification and verification in varying deformation conditions are presented in this paper.