A uniform distribution of power density (energy flux) in a stationary laser beam leads to a decrease in the overheating of the material in the center of the laser beam spot during laser powder bed fusion and a decrease in material losses due to its thermal ablation and chemical decomposition. The profile of the uniform cylindrical (flat-top) distribution of the laser beam power density was compared to the classical Gaussian mode (TEM00) and inverse Gaussian (donut) distribution (airy distribution of the first harmonic, TEM01* = TEM01 + TEM10). Calculation of the Péclet number, which is a similarity criterion characterizing the relationship between convective and molecular processes of heat transfer (convection to diffusion) in a material flow in the liquid phase, shows that the cylindrical (flat-top) distribution (TEM01* + TEM00 mode) is effective in a narrow temperature range. TEM00 shows the most effective result for a wide range of temperatures, and TEM01* is an intermediate in which evaporation losses decrease by more than 2.5 times, and it increases the absolute laser bandwidth when the relative bandwidth decreases by 24%. 

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Beam Shaping in Laser Powder Bed Fusion: Péclet Number and Dynamic Simulation

A method of determining the oscillation parameters of the elements of the rotating units of turbine-driven sets based on an analysis of variations in the characteristics of the output signals of a primary converter is described. Using as an example a newly designed approximate mathematical model, it is shown that it is theoretically possible to determine the oscillation parameters of the blades of turbomachines. A block diagram of a device for experimental testing of the proposed method is presented.

http://link.springer.com/content/pdf/10.1007/s11018-014-0361-z.pdf

Determination of the oscillation parameters of the blades of turbine-driven sets based on nonlinear approximation of the signals of primary converters mechanical measurements

Aluminum-based ceramics are used in industry to produce cutting tools that resist extreme mechanical and thermal load conditions during the machining of Ni-based and high-entropy alloys. There is wide field of application also in the aerospace industry. Microtexturing of cutting ceramics reduces contact loads and wear of cutting tools. However, most of the published works are related to the electrical discharge machining of alumina in hydrocarbons, which creates risks for the personnel and equipment due to the formation of chemically unstable dielectric carbides (methanide Al3C4 and acetylenide Al2(C2)3). An alternative approach for wire electrical discharge machining Al2O3 in the water-based dielectric medium using copper tape of 40 µm thickness and TiO2 powder suspension was proposed for the first time. The performance was evaluated by calculating the material removal rate for various combinations of pulse frequency and TiO2 powder concentration. The obtained kerf of 54.16 ± 0.05 µm in depth demonstrated an increasing efficiency of more than 1.5 times with the closest analogs for the workpiece thickness up to 5 mm in height. The comparison of the performance (0.0083–0.0084 mm3/s) with the closest analogs shows that the results may correlate with the electrical properties of the assisting materials.

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Electrical Discharge Machining of Al2O3 Using Copper Tape and TiO2 Powder-Mixed Water Medium

Aluminum-based ceramics exhibit excellent wear resistance and hot hardness that are suitable for various responsible applications allowing products to work under extreme mechanical and thermal loads (up to 1000 °C). The problem of high-precision forming complex-shaped parts is a known engineering challenge due to the insulating properties of aluminum-containing ceramics and the formation of chemically active carbides in a hydrocarbon medium. The alternative approach for electrical discharge machining non-conductive sintered Al2O3 in the water-based medium using nickel-chrome plasma-vapor-deposed coating of 12 mm, SnO powder suspension (particle diameter of ⌀10 µm, concentration of 150 g/L), and brass wire-tool is proposed. The productivity was evaluated by calculating the material removal rate and discharge gap for various combinations of pulse frequency and duration. The maximal material removal rate of 0.0014 mm3/s was achieved for a pulse frequency of 30 kHz and pulse duration of 1.7–2.5 μs. The recommended value of the interelectrode gap is 48.0 ± 4.9 µm. The possibility of electrical discharge machining aluminum-containing insulating ceramics without using hydrocarbons, carbon and copper-group assisting measures was proposed and shown for the first time. The chemical content of the debris in the interelectrode gap between components of the materials was thermochemically analyzed.

/pdf/electrical-discharge-machining-of-alumina-using-ni-cr-hthgfyzg.pdf

Electrical Discharge Machining of Alumina Using Ni-Cr Coating and SnO Powder-Mixed Dielectric Medium

As a grinding wheel rotates, every grain acquires a certain trajectory of movement, sequence, and duration of contact with a machined part. The grains can be divided into four groups: working, contacting, screened, and non-operational ones. The main characteristics of formation of the microrelief of the wheel work surface depend on the law of difference in altitude of cutting edges and corner radiuses of their tops. The studies on the kinematics of interaction between a grinding wheel and a machined surface during face grinding showed that overlapping of scratches across the width occurs at a smaller depth. The cutting depth of a grinding wheel does not depend on the value of longitudinal and cross feed, but it is determined by the law of grain distribution in the volume of abrasive layer as well as the shape of the tops of abrasive grains. It is established that abrasive grains, located in the work surface layer to the cutting depth, are in the most unfavorable conditions due to their small amount and highest difference in altitude. It leads to an increase in the size of the chip, occurrence of the highest cutting forces, and wear of grains.

Research on Formation of Microgeometry of Work Surface of Grinding Wheel

Increased productivity of Coordinate Measuring Machines, while providing given level of accuracy, is complex and actual problem of robotics and metrology. Therefore, this article provides a set of mathematical models that allow for prediction of values for performance and accuracy of advanced Coordinate Measuring Machines based on system dynamics method. The analysis of scientific literature and statistical data of exploitation CMMs Global Performance (DEA, Italy), CMM-750 (Lapik, Russia), FARO Arm 9 (FARO Technologies, USA) has identified 25 major factors of the process control and their mutual impact. Of the 16 basic factors are internal system parameters, 6 input actions and 3 external factors. As a result of the system analysis of the research object identifies the main characteristics of coordinate measuring machines that affect performance and measurement accuracy. We have done a general graph of causal relationships between modeled characteristics, on the basis of which is made up and numerically solved a system of nonlinear differential equations. In developing this system of equations is used in statistical data describing the cause-effect relationship between the internal model parameters and environmental factors. These solutions make it possible to practically interpret developed models and methods of system dynamics used in solving the problem.

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Oleg V. Zakharov

Papers

Mathematical models for estimating the degree of influence of major factors on performance and accuracy of coordinate measuring machines