Numerical investigation of hot bulk forming processes with respect to the resulting residual stress distribution

Abstract

The cost‐ and time‐efficient design of today's manufacturing processes is closely linked to numerical simulations. By developing and applying suitable simulation models, component properties can be specifically predicted and, if necessary, modified according to the customer's specifications. One important aspect of this is the adjustment towards advantageous residual stress profiles, for example to increase service life or wear resistance. Hot forming processes offer the advantage of the interaction of thermal, mechanical and metallurgical effects. In particular, cooling after prior heating and forming, in this case upsetting, results in a phase transformation on the microscale in the material. The residual stress state, which arises from dislocations in the atomic lattice, will be considered in more detail in this contribution.Here, the focus lies on the analysis of microscopic characteristics utilizing a multi‐scale Finite Element model in terms of a FE2 approach.

On the three‐dimensional numerical analysis of residual stresses on two scales in hot bulk forming parts

“…Due to the position, stress component 𝜎 22 resembles the tangential stress in the examined point. Qualitatively, there is good accordance achieved compared to a previously investigated two-dimensional boundary value problem regarding both cooling strategies [18,27]. A detailed discussion of the stress evolution regarding cooling in water that leads to tensile stresses in P1 in the final state (cf.…”

“…The stresses are weakened when the phase transformation front, which progresses from left to right through the geometry [18, 19], reaches the bulk material. In contrast to the two‐dimensional analysis carried out in [27], the stress does not change its sign, that is, the stress value is reduced but remains compressive. Thus, in the final state, compressive stresses are present in particularly in the spray exposed region around P1 (cf.…”

“…Single‐scale finite element simulations showed that utilizing a spray cooling device allows to induced targeted compressive residual stresses inside the component during its manufacturing process. Comparing the 3D analysis to previous results of 2D simulations [18, 27], the impact of the third dimension becomes apparent. In order to investigate not only the macroscopic but also the microscopic residual stress distribution in the specimen, a one‐way coupled microscopic analysis has been carried out.…”

“…This shows the importance of considering the third dimension, including the heat flux over the height of the component. Thereby, the simulative results are closer to the experimental findings than in a 2D analysis [18, 27]. In future investigations, it is inevitable to model the complete formed cylinder during its cooling process to improve the results and to come even closer to experimental measurements.…”

“…As already proposed in [18, 19, 27–29], microstructural investigations are important to distinguish between macroscopic and microscopic residual stresses. The latter can cause microcracks or prolong microscopic crack growth although there are macroscopically no characteristics of failure.…”