The dynamic properties of machine tools are frequently calculated by means of finite-element (FE) models. Usually, in a first step, the structural components, such as machine bed, slides, columns, spindle housing, spindle, and work piece, are meshed. In a second step, these components are positioned relatively to each other and are connected by joints. Usually, the joints comprise a three-dimensional spring–damper element (SDE) and constraints that connect the SDE to adjacent structural components. Commercial FE programs do rarely offer insight into the underlying constraint equations. Rather, the constraints are realized by selecting the faces or nodes to connect and the type of constraint over a graphical user interface. Moreover, when insight into the underlying equations is offered, it is normally difficult to implement user-defined constraint equations. So far, literature lacks a coherent and in-depth description of constraints that are used for assembly of machine tool FE components. This drawback is addressed here. Different common constraints are revisited while particular focus is put on simulating moving machine axes. Common multipoint constraints (MPC) are supplemented by a shape function based node weighting. Thus, two new MPC are introduced, which improve model quality for ball screw joints (named node-to-beam (NB)-constraint) and linear guides (named RBE4-constraint). A three-axis milling machine serves as an application example for the different constraints. Simulation results are compared to experimentally derived results. Both, frequency response functions (FRF) and time-domain forced responses are considered. Showing reasonable correlation, the comparison of simulation and experiment indicates the validity of the constraints that have been introduced.
In this paper, the approach and main advances made in multi-process hybrid production cells (HyProCell) for rapid individualised laser-based production are compiled and discussed, including highlights and achievements. HyProCell constructs automated manufacturing platforms that integrate highly flexible laser-based additive build processes with more conventional yet precise subtractive machining processes and include novel solutions like automatic powder removal system/machines and robot arms in integrated multi-process production cells. The HyProCell approach can either build parts additively from scratch and finish them in a coherent production single line/cell or prepare parts by machining and add laser-based additive features, achieving otherwise impossible shapes. In addition to producing new parts, existing parts can be repaired or improved by adding new details with the HyProCell hybrid concept. The research work includes the design of pilot cell facilities, the development of the, and a new modular architecture including a middleware and integration layer to ensure automation with improved pallet handling systems. Finally, the MES and data management methodologies for future improvements and pilot facility implementation were made.
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