A GENERAL METHODOLOGY FOR MACHINE TOOL ACCURACY ENHANCEMENT: THEORY, APPLICATION AND IMPLEMENTATION (COMPENSATION, CNC, SOFTWARE)

The accuracy of a machine tool is the limiting factor in the accuracy of finished parts. Errors in the machine tool motion produce a one-to-one error correspondence in the final workpiece. These errors in motion are caused by geometric errors of the structural elements and by thermally-induced errors caused by the machining process itself. It is impossible to completely eliminate errors by design and/or manufacturing modifications. Even a small geometric error of one machine element will be amplified at the cutting tool by the long travel ranges of the slides and the tool offsets. Mechanical design cannot eliminate thermally-induced errors because of continuous heat generation by drive motors, friction in slideways, spindle and leadscrew bearings and the cutting tool-workpiece interface. Rather than attempting to eliminate errors, this study provides a methodology for predicting errors and compensating for them in real-time, thus improving the accuracy of machined workpieces. A general mathematical model is developed, determining the total error at the cutting tool tip contributed by the errors of each machine elements and their thermally-induced variations. Homogeneous coordinate transformations for each element of the machine tool are employed. In order to predict each error component, a methodology for the machine tool error calibration is determined. A flexible and modular software compensation system is developed based on the models created in the methodology. The compensation system predicts the errors of the machine tool using a combination of data taken from various sensors on the machine tool and established error relationships. Finally, the methodology is implemented on a two-axis turning center. The predictions for geometric and thermally-induced errors for this machine are generated using least squares curve fitting techniques on the error data. A single-board microprocessor-based system translates errors into servo counts, which are injected into the machine tool controller in real-time. To demonstrate the validity of the model and methodology, cutting tests were performed under transient thermal conditions on a computerized numerical control (CNC) turning center. Accuracy enhancements of up to 20 times were obtained

Proposal for a Standardized Test Artifact for Additive Manufacturing Machines and Processes

Historically, standardized test parts are used to quantitatively evaluate the performance of a machine or process. While several different additive manufacturing (AM) test parts have been developed in the past, there are no current standard test parts. This paper reviews existing AM test parts, discusses the purposes of the studies, and describes important features and characteristics found in these test parts. A new test part intended for standardization is proposed. This part incorporates the most useful features seen in previous test parts. These features are designed to highlight process capabilities and test machine accuracy. The design has been validated through builds by several AM processes.Mechanical Engineerin

Effect of iloprost on erythrocyte deformability in rat's lower extremity undergoing an ischemia reperfusion injury

Arslan, Mustafa/0000-0003-4882-5063WOS: 000318058700002PubMed: 23514550Aim: Ischemia reperfusion injury (I/R) in lower extremity is a frequent and important clinical phenomenon. The protective effect of iloprost on local and distant organ injury due to I/R has been well documented but its effect on erythrocyte deformability needs further investigation. Our aim was to investigate the effect of iloprost on erythrocyte deformability in the infrarenal aorta of rats undergoing I/R. Materials and methods: Our study was conducted with 18 Wistar albino rats. Rats were divided into the 3 groups; the randomized control group (group C; n=6), I/R group without iloprost (group I/R; n=6) and I/R group with iloprost 10 mcg.kg(-1), 30 min infusion (group I/R-I; n=6). Packs of erythrocytes were prepared from heparinized blood samples and deformability measurements were done. Results: The comparisons of the control and I/R-I groups revealed similar results (p=0.951). The values of the IR group were significantly higher than those of the control and IR-I groups (p=0.006, p=0.011, respectively). Conclusion: In our study, we detected the unfavourable effects of I/R on erythrocyte deformability, which may lead to disturbance in blood flow and hence tissue perfusion in the infrarenal rat aorta. We also found that Iloprost had beneficial effects by reversing the undesirable effects of I/R (Fig. 1, Ref. 15). Full Text in PDF www.elis.sk

Machine tool calibration: Measurement, modeling, and compensation of machine tool errors

International audienceAdvanced technologies for the calibration of machine tool are presented. Geometric, kinematic, thermally-induced and load-induced errors are classified into errors within one-axis as intra-axis errors, errors between axes as inter-axis errors, and as volumetric errors. As the major technological elements of machine tool calibration, the measurement methods, mathematical models and compensation approaches of the machine tool errors are addressed. The criteria for selecting a combination of the technological elements for machine tool calibration from the point of view of accuracy, complexity, and cost are provided. Recent applications of artificial intelligence and machine learning in machine tool calibration are introduced. Remarks are also made on future trends in machine tool calibration

Thermal issues in machine tools

ISSN:0007-8506ISSN:1660-277