Efficient Quantification of Free and Forced Convection via the Decoupling of Thermo-Mechanical and Thermo-Fluidic Simulations of Machine Tools

Abstract

Thermo-elastic deformations represent one of the main reasons for positioning errors in machine tools. Investigations of the thermo-mechanical behaviour of machine tools, especially during the design phase, rely mainly on thermo-elastic simulations. These require the knowledge of heat sources and sinks and assumptions on the heat dissipation via convection, conduction and radiation. Forced convection such as that caused by moving assemblies has both a large influence on the heat dissipation to the surrounding air. The most accurate way of taking convection into account is via computational fluid dynamics (CFD) simulations. These simulations compute heat transfer coefficients for every finite element on the machine tool surface, which can then be used as boundary conditions for accurate thermo-mechanical simulations. Transient thermo-mechanical simulations with moving assemblies thus require a CFD simulation during each time step, which is very time-consuming. This paper presents an alternative by using characteristic diagrams to interpolate the CFD simulations. The new method uses precomputed thermal coefficients of a small number of load cases as support points to estimate the convection of all relevant load cases (i.e. ambient conditions). It will be explained and demonstrated on a machine tool column.

Parallel computing in automation of decoupled fluid-thermostructural simulation approach

“…This can be achieved by introducing a clustering algorithm (CA) and characteristic diagrams (CDs) in the workflow. _____________ 1 Fraunhofer Institute for Machine Tools and Forming Technology IWU, Chemnitz, Germany 2 Dresden University of Technology, Institute of Scientific Computing, Dresden, Germany CDs are continuous maps of a set of input variables onto a single output variable and consists of multidimensional grids, refer to the work by Priber [2] and Naumann et al [3]. Using a limited number of CFD simulations, the environmental influences (parameters) on a machine surface can be mapped on to its corresponding heat transfer coefficient (HTC) values at certain optimal node points.…”

“…A single CFD simulation could take around one hour to complete. The realistic discretization or proper training of CDs would involve 158 CFD Simulations, (Glänzel et al [1]). Thus, approximately six days would be required to perform CFD simulations on a normal computational system.…”

“…When a machine tool is subjected to changes in environmental influences such as ambient air temperature, velocity or direction, then flow (CFD) simulations are necessary to effectively quantify the thermal behaviour between the machine tool surface and the surrounding air (fluid), ref Glänzel et al [1]. This two-step simulation procedure involving fluid and thermo-structural simulations is highly complex and time-consuming especially when complex geometries or dynamic components are considered.…”

Handling Ambient Temperature Changes in Correlative Thermal Error Compensation

“…This requires the adaptation of the heat transfer coefficients (HTCs), which are boundary conditions of the FE models. Naumann et al have shown how these HTCs can be obtained through fluid (CFD) simulations for natural and varying forced convection scenarios [12].…”

A review on enabling technologies for resilient and traceable on-machine measurements

“…machine learning and regression methods -Data driven methods generally require vast amounts of training data for modelling and are hardly transferable[21][22][23][24][25][26][27][28] thermomechanical behavior (incl. airflows → CFD & ambient temperatures), thus requires high computationnal power & detailed modelling[29][30][31][32][33]…”