Cooling of motor spindles - a review

Thermally induced loads in motor spindles can cause a number of undesired effects. As a result, the process capability of spindles, and thus, the productivity of a process can decrease. Future motor spindles will be exposed to higher mechanical and especially thermal loads due to trends aiming to increase power densities and maximum speeds. These trends are amplified by increasingly powerful drive concepts and developments in bearing technology. Therefore, researchers assume that it will not be possible to raise the performance potential of spindles due to insufficient cooling of its heat sources. A series of different cooling concepts have been researched and developed in recent decades. These developments have been made for different purposes. They also differ considerably in terms of their cooling principles and cooling performance. In this article, these cooling approaches and the motivations for their development are described. Firstly, the causes of heat development in motor spindles are described in a historical context. Subsequently, the effects of heat development on the manufacturing-relevant properties of motor spindles are revealed. Finally, current deficits in the area of spindle cooling and the need for the development and transfer into industrial practice of more efficient and cost-effective cooling concepts to overcome future challenges are discussed. © 2020, The Author(s)

Multivariate time series data of milling processes with varying tool wear and machine tools

Machining is an essential part of modern manufacturing. During machining, the wear of cutting tools increases, eventually impairing product quality and process stability. Determining when to change a tool to avoid these consequences, while still utilizing most of a tool's lifetime is challenging, as the tool lifetime can vary by more than 100% despite constant process parameters [1]. To account for these variations, all tools are usually changed after a predefined period of time. However, this strategy wastes a significant proportion of the remaining lifetime of most tools. By monitoring the wear of tools, all tools can potentially be used until their individual end of life. Research, development, and assessment of such monitoring methods require large amounts of data. Nevertheless, only very few datasets are publicly available. The presented dataset provides labeled, multivariate time series data of milling processes with varying tool wear and for varying machine tools. The width of the flank wear land VB is used as a degradation metric. A total of nine end milling cutters were worn from an unused state to end of life (VB ≈ 150 µm) in 3-axis shoulder milling of cast iron 600–3/S. The tools were of the same model (solid carbide end milling cutter, 4 edges, coated with TiN-TiAlN) but from different batches. Experiments were conducted on three different 5-axis milling centers of a similar size. Workpieces, experimental setups, and process parameters were identical on all of the machine tools. The process forces were recorded with a dynamometer with a sample rate of 25 kHz. The force or torque of the spindle and feed drives, as well as the position control deviation of feed drives, were recorded from the machine tool controls with a sample rate of 500 Hz. The dataset holds a total of 6,418 files labeled with the wear (VB), machine tool (M), tool (T), run (R), and cumulated tool contact time (C). This data could be used to identify signal features that are sensitive to wear, to investigate methods for tool wear estimation and tool life prediction, or to examine transfer learning strategies. The data thereby facilitates research in tool condition monitoring and predictive maintenance in the domain of production technology

Thermally Induced Clamping Force Deviations in a Sensory Chuck for Thin-Walled Workpieces

Deviations between nominal and actual tolerances are a challenging problem during turning processes of thin-walled workpieces. One main cause of these deviations is the clamping force applied by the turning chuck to hold the workpiece. Due to the low stiffness of thin-walled workpieces, large workpiece deformations can occur even when clamping forces are low. For this reason, the clamping force needs to be precisely adjusted. A possible approach are chucks with integrated actuators. As a result of the more direct power transmission, these chucks have a potentially higher clamping force accuracy compared to conventional external actuation. However, integrated actuators are additional heart sources resulting in thermal loads and thermally induced deformations of the chuck components. Due to the resulting mechanical distortion of the chuck system, the precise adjustment of clamping forces is not possible. Thus, this paper evaluates the thermally induced clamping force deviations on a novel turning chuck with four integrated electric drives. A test bench is used to analyse both a single drive and the combination of all four drives regarding the temperature effect on the clamping force adjustability. A clamping force deviation of up to 26% is observed. Based on the measured chuck temperature, a compensation method is introduced leading to a clamping force accuracy of 96.9%

Interactive effects of Pgi genotype and temperature on larval growth and survival in the Glanville fritillary butterfly

1.Genetic polymorphism in the gene phosphoglucose isomerase (Pgi) encoding for a glycolytic enzyme has been shown to affect many traits in adult insects, including flight metabolism, running speed, fecundity and longevity, but it is not known to what extent Pgi genotypic effects are consistent across different life stages. 2.In the Glanville fritillary butterfly, heterozygous AC adult individuals for a single nucleotide polymorphism (SNP) (AA111) in the coding region of Pgi have superior fitness to the common homozygotes (AA) in practically all life-history traits. 3.Here, we studied associations between Pgi SNP AA111 and larval and pupal weights, larval development time in three different temperatures and adult longevity. Small body size and limited mobility of larvae offer little buffer against changes in ambient temperature; hence, temperature is expected to affect greatly larval growth and development. 4.In contrast to adults, larval performance was superior in AA homozygotes in two respects. First, survival was higher in AA homozygotes under stressful conditions, represented by the low-temperature treatment in which survival was generally low. Second, the AA homozygotes had heavier pupae. In spite of the latter result, adult life span was longer in the AC heterozygotes, in support of previous studies. 5.The results on larval growth are consistent with the hypothesis of a trade-off between thermal stability and kinetic efficiency between the different isoforms of the PGI enzyme, but the results also indicate unexpected differences in the genotypic effects at different life stages