Machining stability and machine tool dynamics

Machining is a common manufacturing process in industry due to its high flexibility and ability to produce parts which excellent quality. The productivity and quality in machining operations can be limited by several process constraints one of which is the self-excited chatter vibrations. Under certain conditions, the process may become unstable yielding oscillations with high amplitudes which result in poor surface finish and damage to the cutting tool, part and the machine tool itself. Stability analysis of the dynamic cutting process can be used to determine chatter-free machining conditions with high material removal rate. Since chatter is a result of the dynamic interactions between the process and the structures both cutting and machine tool dynamics are important elements of the stability analysis. In this paper, methods developed for stability analysis of cutting processes and machine tool dynamics will be presented. Implications of these methods in the selection of process parameters and machine tool design will be also discussed with example applications

The magnetic properties of plastically deformed steels.

This study concentrates on low carbon pearlitic steels. Two sets of experiments are carried out, the first on a section of semi-killed gas pipe and the second on specially prepared alloys of iron and carbon with pearlite fractions varying from 0.19% to 100%. Their magnetic properties are studied both in the as received state and after tensile plastic deformation. In addition, four different heat treatments are applied to the low carbon steel. Standard magnetisation and fluxmeter techniques are used to determine the bulk magnetic properties, with further use of a vibrating sample magnetometer for coercivity measurements. The Barkhausen noise of the samples is also recorded and High Voltage Lorentz Electron Microscopy used to directly observe the domain configurations and the interaction of the domain walls with dislocation tangles. The changes in the magnetic properties after tensile deformation are similar to those due to elastic compressive stress, with an additional increase in the coercivity. For the initial magnetisation curve initial permeability (J-Li) and maximum relative permeability both decrease, while the field at which the latter occurs (Hm) increases. The hysteresis curve shears over reducing the maximum differential permeability and the remanence and also increasing the coercivity. These results and the change in the shape of the hysteresis curve, most noticeable in the low carbon steels, are explained in terms of the reduction in easy domain wall movement due to the dislocation tangles, as observed under the electron microscope, and to the magnetostrictive effect of the compressive residual stress. Inter-relationships are found between coercivity and both J-Li and Hm. The coercivity io also found to vary linearly with both Vickers Hardness and Yield Stress. The Kneppo formula for the initial magnetisation curve is found to hold better for the higher carbon content steels with the fit deteriorating with increasing plastic deformation

NASA Space Engineering Research Center for Utilization of Local Planetary Resources

Progress toward the goal of exploiting extraterrestrial resources for space missions is documented. Some areas of research included are as follows: Propellant and propulsion optimization; Automation of propellant processing with quantitative simulation; Ore reduction through chlorination and free radical production; Characterization of lunar ilmenite and its simulants; Carbothermal reduction of ilmenite with special reference to microgravity chemical reactor design; Gaseous carbonyl extraction and purification of ferrous metals; Overall energy management; and Information management for space processing

Project LOCOST: Laser or Chemical Hybrid Orbital Space Transport

A potential mission in the late 1990s is the servicing of spacecraft assets located in GEO. The Geosynchronous Operations Support Center (GeoShack) will be supported by a space transfer vehicle based at the Space Station (SS). The vehicle will transport cargo between the SS and the GeoShack. A proposed unmanned, laser or chemical hybrid orbital space transfer vehicle (LOCOST) can be used to efficiently transfer cargo between the two orbits. A preliminary design shows that an unmanned, laser/chemical hybrid vehicle results in the fuel savings needed while still providing fast trip times. The LOCOST vehicle receives a 12 MW laser beam from one Earth orbiting, solar pumped, iodide Laser Power Station (LPS). Two Energy Relay Units (ERU) provide laser beam support during periods of line-of-sight blockage by the Earth. The baseline mission specifies a 13 day round trip transfer time. The ship's configuration consist of an optical train, one hydrogen laser engine, two chemical engines, a 18 m by 29 m box truss, a mission-flexible payload module, and propellant tanks. Overall vehicle dry mass is 8,000 kg. Outbound cargo mass is 20,000 kg, and inbound cargo mass is 6,000 kg. The baseline mission needs 93,000 kg of propellants to complete the scenario. Fully fueled, outbound mission mass is 121,000 kg. A regeneratively cooled, single plasma, laser engine design producing a maximum of 768 N of thrust is utilized along with two traditional chemical engines. The payload module is designed to hold 40,000 kg of cargo, though the baseline mission specifies less. A proposed design of a laser/chemical hybrid vehicle provides a trip time and propellant efficient means to transport cargo from the SS to a GeoShack. Its unique, hybrid propulsion system provides safety through redundancy, allows baseline missions to be efficiently executed, while still allowing for the possibility of larger cargo transfers

Avon Alkaline Igneous Province, Missouri: Characterization of subcontinental mantle source and evolution via chemical analysis of olivine

This article presents the crystallization age of, and composition of olivine phenocrysts within an alnoite of, the Avon Alkaline Igneous Province (AAIP) of Ste. Genevieve County, Missouri. The AAIP is an ultramafic igneous province consisting of approx. 80 known intrusives of diverse lithology and texture. 40Ar/39 Ar geochronology indicates an emplacement age of 386 +/- 1 Ma, which establishes the AAIP as the only known Devonian-age ultramafic igneous body in the Midwestern U.S. Study of the AAIP provides a unique opportunity to characterize the Devonian-age subcontinental mantle and the processes that generated the suite of ultramafic rocks present in the province. The compositions of 52 olivine crystals are characterized using electron microprobe analysis. Olivine major element compositions are homogeneous, Mg-rich (Fo86.9-Fo89.9), and exhibit variation in trace element (e.g., Ni, Cr, Co, Ti, P) abundances consistent with fractional crystallization. These results indicate that AAIP olivines are phenocrysts rather than mantle xenocrysts. Olivine geothermometry indicates derivation at temperatures of approx. 1500-1750⁰C at pressures of 1.6 to 5.4 GPa. Olivine trace element discrimination diagrams indicate AAIP magmas were derived from mantle sources with a compositional alkalic affinity, similar to other continental alkaline rocks and kimberlite. A mantle origin via partial melting of peridotite mantle is suggested due to the high Mg content, results of geothermometric modeling, and high Ca and Ti abundance within olivine phenocrysts. Disequilibrium textures observed in alnöite olivine are consistent with resorption of magmatic olivine as a result of decompression and fractional crystallization --Abstract, page iv

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Development of chatter threshold boundary for milling of metals

This study reports on a novel experimental method for the prediction of chatter based on the chaos theory. The variation of Poincaré sections of the reconstructed phase space attractor is able to identify the transition of the milling system from a stable to an unstable condition, continuously during the milling process. Two mathematical tools are used to measure the variation of Poincaré sections they being; image correlation and a designed regression model. Image correlation uses Poincaré sections as a pattern and the computation of Pearson’s coefficient assists to develop a chatter threshold boundary. Titanium is the main material in this research, as chatter is more applicable during cutting of titanium due to its specific mechanical properties. Moreover, the method is used in detection of chatter during milling of stainless steel and aluminum in order to demonstrate the method can detect chatter during cutting of other metals. The new method can be used to detect chatter on-line, as it is independent of the cutting parameters and dynamics of the milling process, and can be integrated in the cutting machines. The method does not need expensive equipment and complex process, so it can be easily used in normal production workshop environment. A regression model computes the trend of changes in the Poincaré sections and gives a numerical output value to define the boundary between the stable and unstable state of the milling process. These mathematical tools can be used in expert software to monitor the milling process on-line and detect the onset of chatter