This paper presents a brief introduction to competition-driven digital transformation in the machining sector. On this basis, the creation of a digital twin for machining processes is approached firstly using a basic digital twin structure. The latter is sub-grouped into information and data models, specific calculation and process models, all seen from an application-oriented perspective. Moreover, digital shadow and digital twin are embedded in this framework, being discussed in the context of a state-of-the-art literature review. The main part of this paper addresses models for machine and path inaccuracies, material removal and tool engagement, cutting force, process stability, thermal behavior, workpiece and surface properties. Furthermore, these models are superimposed towards an integral digital twin. In addition, the overall context is expanded towards an integral software architecture of a digital twin providing information system. The information system, in turn, ties in with existing forward-oriented planning from operational practice, leading to a significant expansion of the initially presented basic structure for a digital twin. Consequently, a time-stratified data layer platform is introduced to prepare for the resulting shadow-twin transformation loop. Finally, subtasks are defined to assure functional interfaces, model integrability and feedback measures.

The multifractal analysis (MFA) of the spatial microform area formed on the surface of steel C35 and aluminum alloy AA2024 at the face milling was implemented. The input information for the MFA was micro-images of the machined workpiece surface. Multifractal (MF) spectra and their main parameters are calculated for the surface of samples machined at various cutting conditions. Renyi’s numbers and fractal ordering parameters were chosen as the most informative MF parameters describing the surface structure. It is shown that the MF functions of the system correspond to their canonical forms. Quantitative relationships between the parameters of MF spectra for the surface area of microforms formed during machining surfaces of steel and aluminum alloy workpieces and the cutting conditions were obtained. The physical processes that are responsible for the formation of the observed MF spectra on the surface of the workpieces depending on feed and depth of cut at the face milling were discussed. The developed computational technique can be used to describe and analyze the state of spatial fractal structures formed on the surface of other materials.