Jürgen Leopold

Microstructural evolution of Ti6Al4V in ultrasonically assisted cutting: Numerical modelling and experimental analysis

HIGHLIGHTSThe effect of ultrasonically assisted cutting on microstructure is elucidated.Microstructural evolution is compared for new and conventional cutting.Experimental results for ultrasonically assisted cutting of Ti64 are presented. ABSTRACT This paper aims to elucidate the effect of ultrasonically assisted cutting (UAC) on microstructure in a machined surface and a chip of Ti6Al4V alloy. To investigate microstructural evolution, a FE‐based cutting model with an enhanced material formulation and temperature dependent material properties was developed. A Johnson‐Mehl‐Avrami‐Kolmogorov (JMAK) model for the Ti6Al4V alloy was employed to simulate dynamic recrystallization and predict a resultant grain size. Due to a specific thermomechanical load in UAC, the distributions of strains, strain rates and temperatures in a workpiece in the machining process were investigated. In this study, five points under the machined surface and ten points under the unmachined one were tracked to compare the evolution of a grain size and its average magnitude in the alloy subjected to conventional cutting (CC) and UAC. Besides of numerical modelling and experimental studies for the resultant grain size were compared and additional validation using microhardness measurements were conducted. The results showed that the average grain size of the machined surface and the chip in case of UAC was larger and more uniform than that in case of CC. The study also presents discussions about the effect of a vibration amplitude, a feed rate and a cutting speed on the average grain size in machining of Ti6Al4V. The comparison between CC and UAC indicates that the change in average grain size in UAC was smaller than that in CC, thus demonstrating a lower level of damage in UAC.

Analysis of Clamping within a Fixing System

The complex workpiece-fixing behaviour during machining is essential for the fixture development process, especially when using innovative intelligent Piezo-electric clamping systems being very susceptible to transverse forces. Therefore, the loads acting on fixture components have been analysed and a model for predicting the reaction forces due to clamping and process loads is presented. First, a complex finite element model is used to obtain detailed information about the behaviour during the process. Second, a faster model with fewer elements is developed, validated and used for the variation of process parameters. Finally, both results are combined to an analytical model. This empiric equation allows to predict the reaction forces depending on several process parameters. The usability of this method has been exposed by modelling shape grinding of a nozzle guide vane.

Clamping Modeling - State-of-the-Art and Future Trends

Automated assembly is generally confined to mass production environments such as the manufacture of cars and white goods. Even in this environment high-level automated assembly is restricted to the OEMs where production volumes are high and flexibility and the ability to quickly reconfigure systems are not major drivers. In the aerospace industry the problem is further complicated by the move to thin walled monolithic parts and the increasing use of composite structures. Monolithic structures have been introduced to reduce the costs of assembling large numbers of components. Although the benefit of using monolithic parts is a large reduction in overall manufacturing costs the downside is a more difficult component to handle and assemble. In addition, there are thin walled components with sometimes-internal stresses and in our case made of nickel based alloys, which only can be cut with difficulties. Machining the flexible structure and maintaining close tolerance is difficult, transferring to assemble is difficult as well. Machining fixtures are used to locate and constrain a workpiece during a machining operation. To ensure that the workpiece is manufactured according to specified dimensions and tolerances, it must be appropriately located and clamped. Minimizing workpiece and fixture tooling deflections due to clamping and cutting forces in machining is critical to machining accuracy. An ideal fixture design maximizes locating accuracy and workpiece stability, while minimizing displacements. In this paper, a review of the state of the art approaches of Clamping modeling is provided. The current drawbacks of the existing approaches and the research areas to focus on in the near future are also identified.