High pressure coolant effect on PVD coated inserts during end milling of Ti-6AL-4V

Titanium alloys are being employed extensively in engineering and aerospace applications for their high strength to weight ratio, mechanical strength and ability to withstand high temperatures. Out of the different alloys of titanium available, the most commonly used alloy is Ti-6Al-4V. It is also called `Grade-5 titanium alloy\u27 or `á+â titanium alloy\u27. High speed machining of titanium alloys generates high temperatures in the cutting zone, promoting accelerated tool wear and reducing the efficiency in metal cutting. Consequently, the ability of the coolant to remove heat from the cutting zone plays an increasingly important role in the economics of the process as well as on the life of tool inserts. With the introduction of thru-tool coolant delivery, the coolant can now be delivered directly at the point of machining without having to flood the area of machining. This research tries to address the effects that high pressure and thru-tool coolant has on insert wear while end milling Ti-6Al-4V. The parameters used in this study are speed, feed, axial depth of cut, radial depth of cut and coolant pressure. A structured design of experiments along with a central composite design approach is used to determine the main effects of coolant pressure and its interactions with the remaining parameters. The results show that, within the parameters of this experiment, coolant pressure was not a significant main effect. However, pressure seems to react positively with feed rate. Contributions from this research can be used to recommend settings of the cutting factors in order to obtain the minimal tool wear

Terminated LDPC Convolutional Codes with Thresholds Close to Capacity

An ensemble of LDPC convolutional codes with parity-check matrices composed of permutation matrices is considered. The convergence of the iterative belief propagation based decoder for terminated convolutional codes in the ensemble is analyzed for binary-input output-symmetric memoryless channels using density evolution techniques. We observe that the structured irregularity in the Tanner graph of the codes leads to significantly better thresholds when compared to corresponding LDPC block codes.Comment: To appear in the proceedings of the 2005 IEEE International Symposium on Information Theory, Adelaide, Australia, September 4-9, 200

High Pressure Coolant Effect on PVD Coated Inserts During End Milling of Ti-6Al-4V

Titanium alloys are extensively used in engineering and medical applications. The most common alloy of Titanium, \u27Grade-5 or \u27α + β\u27, accounts for 50% of all aerospace applications. High speed machining of titanium alloys generates high temperatures in the cutting zone, thereby increasing the cycle time and decreasing tool life. Consequently, the ability of the coolant to remove heat from the cutting zone plays an increasingly important role in the economics of the process as well as on the life of tool inserts. This work addresses the effect that high pressure, thru-tool coolant has on insert wear while machining Ti-6Al-4V. The parameters used for this study are speed, feed, axial and radial depths of cut and coolant pressure. The methodology used is design of experiments and response surface methodology. The anticipated contributions include a quantification of the effect of coolant pressure on tool insert wear and its interactions with other machining parameters

Distance Bounds for an Ensemble of LDPC Convolutional Codes

An ensemble of $(J,K)$ -regular low-density parity- check (LDPC) convolutional codes is introduced and existence-type lower bounds on the minimum distance $d _ {rm L}$ of code segments of finite length $L$ and on the free distance $d _{rm free}$ are derived. For sufficiently large constraint lengths $nu$ , the distances are shown to grow linearly with $nu$ and the ratio $d_ {rm L}/nu$ approaches the ratio $d _{ {rm free}}/nu$ for large $L$ . Moreover, the ratio of free distance to constraint length is several times larger than the ratio of minimum distance to block length for Gallager's ensemble of $(J,K)$-regular LDPC block codes

Iterative Decoding Threshold Analysis for LDPC Convolutional Codes

An iterative decoding threshold analysis for terminated regular LDPC convolutional (LDPCC) codes is presented. Using density evolution techniques, the convergence behavior of an iterative belief propagation decoder is analyzed for the binary erasure channel and the AWGN channel with binary inputs. It is shown that for a terminated LDPCC code ensemble, the thresholds are better than for corresponding regular and irregular LDPC block codes

Stability for Rayleigh–Benard Convective Solutions of the Boltzmann Equation

International audienceWe consider the Boltzmann equation for a gas in a horizontal slab, subject to a gravitational force. The boundary conditions are of diffusive type, specifying the wall temperatures, so that the top temperature is lower than the bottom one (Benard setup). We consider a 2-dimensional convective stationary solution, which is close for small Knudsen number to the convective stationary solution of the Oberbeck-Boussinesq equations, near above the bifurcation point, and prove its stability under 2-d small perturbations, for Rayleigh number above and close to the bifurcation point and for small Knudsen number