No abstract

Machining dynamic stability has been enhanced through a damping coating based on a novel carbon-based nanocomposite material. The coating was synthesized using a plasma enhanced chemical vapor deposition method, and deposited on to the round-shank boring bar used for internal turning and tested during machining. Comparisons between an uncoated and a coated boring bar were carried out at 0.25 mm and 0.5 mm depth of cut using a five times length to diameter ratio overhang, which are typical conditions known to generate detrimental mechanical vibrations. From sound pressure measurement it was found that the measured absolute sound level during process could be reduced by about 90% when using the tool coated with damping layer. Surface roughness measurements of the processed workpiece showed decreased Ra values from approximately 3-6 lm to less than 2 lm (and in 50% of the cases <1 lm) when comparing an uncoated standard tool with its coated counterpart. Moreover, it was found that the addition of an antivibration coating did not adversely affect other tool properties, such as rigidity and modularity.

Nanostructured Cu:CuCNx composite coatings with high static and dynamic stiffness were synthesized by means of plasma-enhanced chemical vapor deposition (PECVD) combined with high power impulse magnetron sputtering (HiPIMS). Scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDS) mapping from cross-sectioned samples reveals a multi-layered nanostructure enriched in Cu, C, N, and O in different ratios. Mechanical properties of the coatings were investigated by Vickers micro-indention and model tests. It was observed that copper inclusions as well as copper interlayers in the CNx matrix can increase mechanical damping by up to 160%. Mechanical properties such as hardness, elastic modulus and loss factor were significantly improved by increasing the discharge power of the sputtering process. Moreover the coatings loss modulus was evaluated on the basis of indentation creep measurements under room temperature. The coating with optimum properties exhibited loss modulus of 2.6 GPa. The composite with the highest damping loss modulus were applied on the clamping region of a milling machining tool to verify their effect in suppressing regenerative tool chatter. The high dynamic stiffness coatings were found to effectively improve the critical stability limit of a milling tool by at least 300%, suggesting a significant increase of the dynamic stiffness.

QC 20160209

R apid energy deposition into targets and beam absorbers in a high-energy accelerator leads to a temperature rise at an enormous rate, giving rise to thermally induced stress waves. U nderstanding and predicting the resulting stresses are crucial for robust design and safe operation of such devices. In this paper, closed-form expressions for the induced stresses in cylindrical rods subjected to rapid partial energy deposition have been directly derived; they are then used to estimate the highest stress of long cylindrical absorbers and to test the accuracy of thermal shock simulation using nite element analysis (F EA) codes. Characteristics of such stresses were discussed in detail. It was found that AN SYS may produce accurate details in thermal shock simulation if element size and time step used in the simulation model meet the criteria proposed by Zheng and co-workers in another paper. NOTATION c sonic velocity (m/s) E Young's modulus (Pa) g integersˆ1, 2, 3, . . . J n …x † Bessel function of the rst kind of order of n, nˆ0, 1 k integersˆ1, 2, 3, . . . k n one of the zeros of J 1 …kR †ˆ0 n integersˆ1, 2, 3, . . . r radius (m) r 0 mean radius of the spatial temperature transition zone (m) R radius of cylinder (m) t time (s) t rm time when the second stress wave reaches the centre-line of the cylinder (s) t 0 nite rise-time of the temperature (s) T (r, t) temperature rise with respect to the reference temperature (8C) T 0 temperature (8C) u radial displacement (m) Y 1 …x † Bessel function of the second kind of rst order a coef cient of thermal expansion (m/m 8C) d width of the temperature transition zone (m) e strain · Poisson' s ratio r density (kg/m 3 ) s stress (Pa) t time duration of a pulse (s)