Implementation of an open-die forging process for large hollow shafts for wind power plants with respect to an optimized microstructure
To realize large wind power plants in an economically feasible way, it is necessary to identify potential for lightweight design of the generator hollow-shafts, which are commonly produced by casting. The weight of these shafts can significantly be reduced by producing them by open-die forging, since the forming of the material leads to a higher strength, which allows to reduce the wall thickness noticeable. This paper describes the development and implementation of a forging process for hollow shafts with respect to an optimized microstructure. To numerically investigate this process, a realistic finite element simulation model was developed in a first step. The kinematic of the tools has been implemented authentically to provide a realistic material flow and process conditions. Additionally, a material model for the steel 42CrMo4 was integrated into the simulation model to predict the resulting microstructure. Using the implemented FE model, the forging process was optimized manually to achieve a homogeneous and fine-grained microstructure. The optimization was based upon a variation of different forging parameters and the sequence of forging steps. In the next step, a forging on laboratorial scale was performed to validate the simulation model. For this purpose, after forging, specimens from the hollow shaft were evaluated by metallography to determine the final grain size. A comparison of the results with the numerical simulation showed a general agreement of the measured grain size with the numerically calculated grain size. Based upon these results, the process model was transferred to an FE model with an industrial scale. By this it was possible to analyze the transferability of the used FE model regarding the assumptions about the kinematics and the sequence of the forging steps. A numerical investigation of the industrial process proved the scalability of the process to an industrial relevant geometry.
Influence of anvil shape and process parameters on mandrel forging of large cylindrical forgings
In mandrel forging, anvil shape and process parameters affect the quality of large cylindrical forgings. In this paper, five different anvil shapes are introduced involving a long flat anvil, a short flat anvil, a double-sided bevel anvil, a single-sided bevel anvil, and a short-shaped anvil. The effects of process parameters are studied including tool speed, reduction, mandrel rotation angle, feed rate, and forging sequence. The research is carried out by a combination of numerical simulations and experiments to find out reasonable process parameters that can obtain high-quality large cylindrical forgings. The results show that the use of a long flat anvil is the most efficient, but the core of the ingot may be insufficiently forged, the forming force is uneven and the required forming force is the largest; the efficiency of using a short flat anvil is the lowest, but it can improve the quality of the forgings compared to using a long flat anvil; using a short-shaped anvil is relatively efficient, and the forged ingot is best and the forging force is relatively lower. Especially, when the short-shaped anvil works under unequal feed rates with a forging sequence from both ends to middle, it can obtain high-quality forgings and the forming force is uniform and lowest. The research has certain guidance and contribution to the mandrel forging of large cylindrical forgings.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.