Optimum selection of variable pitch for chatter suppression in face milling operations

Cutting capacity can be seriously limited in heavy duty face milling processes due to self-excited structural vibrations. Special geometry tools and, specifically, variable pitch milling tools have been extensively used in aeronautic applications with the purpose of removing these detrimental chatter vibrations, where high frequency chatter related to slender tools or thin walls limits productivity. However, the application of this technique in heavy duty face milling operations has not been thoroughly explored. In this paper, a method for the definition of the optimum angles between inserts is presented, based on the optimum pitch angle and the stabilizability diagrams. These diagrams are obtained through the brute force (BF) iterative method, which basically consists of an iterative maximization of the stability by using the semidiscretization method. From the observed results, hints for the selection of the optimum pitch pattern and the optimum values of the angles between inserts are presented. A practical application is implemented and the cutting performance when using an optimized variable pitch tool is assessed. It is concluded that with an optimum selection of the pitch, the material removal rate can be improved up to three times. Finally, the existence of two more different stability lobe families related to the saddle-node and flip type stability losses is demonstrated

A Critical Review of Biomarkers Used for Monitoring Human Exposure to Lead: Advantages, Limitations, and Future Needs

Lead concentration in whole blood (BPb) is the primary biomarker used to monitor exposure to this metallic element. The U.S. Centers for Disease Control and Prevention and the World Health Organization define a BPb of 10 μg/dL (0.48 μmol/L) as the threshold of concern in young children. However, recent studies have reported the possibility of adverse health effects, including intellectual impairment in young children, at BPb levels < 10 μg/dL, suggesting that there is no safe level of exposure. It appears impossible to differentiate between low-level chronic Pb exposure and a high-level short Pb exposure based on a single BPb measurement; therefore, serial BPb measurements offer a better estimation of possible health outcomes. The difficulty in assessing the exact nature of Pb exposure is dependent not so much on problems with current analytical methodologies, but rather on the complex toxicokinetics of Pb within various body compartments (i.e., cycling of Pb between bone, blood, and soft tissues). If we are to differentiate more effectively between Pb stored in the body for years and Pb from recent exposure, information on other biomarkers of exposure may be needed. None of the current biomarkers of internal Pb dose have yet been accepted by the scientific community as a reliable substitute for a BPb measurement. This review focuses on the limitations of biomarkers of Pb exposure and the need to improve the accuracy of their measurement. We present here only the traditional analytical protocols in current use, and we attempt to assess the influence of confounding variables on BPb levels. Finally, we discuss the interpretation of BPb data with respect to both external and endogenous Pb exposure, past or recent exposure, as well as the significance of Pb determinations in human specimens including hair, nails, saliva, bone, blood (plasma, whole blood), urine, feces, and exfoliated teeth

ICP-MS determination of trace elements in the serum samples of healthy subjects using different sample preparation methods

The concentration of some trace elements of clinical importance was studied in blood serum samples of healthy subjects (n=19, mean age 22 +/- 4.5 years) to determine reference ranges for the healthy urban population in Eastern Hungary. A sample preparation method has been developed using closed-vessel microwave digestion with an oxidizing acid mixture (nitric acid and hydrogen peroxide) for multielemental analysis and atmospheric wet digestion with the aqueous solution of trimethyl amine (TMAH) for the measurement of aluminum. Contamination of the samples with Al was observed during acidic microwave digestion because of the chemicals used. Trace element concentrations in the samples were measured with ICP-TIS. The reference ranges obtained were (in mug/L): Al 0.98-1.74, Cr 42.8-59.3, Mn 2.27-5.05, Fe 1282-2050, Co 0.22-0.88, Ni 0.03-16.33, Cu 691-1003, Zn 591-1217, Sr 30.37-47.37, Mo 0.73-1.19, Cd 0.02-0.62, and Pb 0.02-2.70. The results were compared to the reference ranges actually used in the clinical practice, some of which are available in the literature. The effect of the applied digestion methods on the obtained individual results and average concentration ranges was also studied