Additive manufacturing is expected to transform and upgrade the traditional foundry industry to realize the integrated manufacturing and rapid and low-cost development of high-performance components with complex shapes. The additive manufacturing technology commonly applied in casting mold preparation (fusible molds, sand molds/cores and ceramic cores) mainly includes selective laser sintering (SLS) and binder injection threedimensional printing (3DP). In this work, the research status of SLS/3DPcasting processes on material preparation, equipment development, process optimization, simulation and application cases in aerospace, automotive and other fields were elaborated. Finally, the developing trends of the additive manufacturing technology in the future of foundry field are introduced, including multi-material sand molds (metal core included), ceramic core-shell integration and die-casting dies with conformal cooling runners.
In order to improve the surface machining quality of slow tool servo (STS) turning in complex surfaces, the optimal method of tool path generation (TPG) was studied. Taking into consideration the problem of large discrete errors and interpolation errors in TPG, equal height discretization method and interpolation algorithm for non-uniform nodes were proposd and the acceleration continuous condition was introduced. Simulation results showed that equal height discretization method could reduce the discrete error by more than 70%. The interpolation errors could be reduced to two orders of magnitude by transforming segment cubic Hermite interpolation into segment cubic spline interpolation. Finally, the processing experiments were performed. The results showed that the form error PV value for the workpiece of the toric surface obtained by equal height discretization method and non-uniformity processing and segment cubic spline interpolation reached 0.002mm. The PV value of the sinusoidal array surface was about 0.009mm, and its surface roughness value was 0.064μm. The results proved this method can effectively reduce the discrete errors and interpolation errors, as well as improve the surface machining quality.
Tunnel passing in high speed produces aerodynamic load on railway train, which brings about fatigue failure on the car-body, and damages passenger comfort due to interior penetration of the alternating wave. Experimental simulation of the alternating load remains a challenge concerning its accuracy and reliability. In this work, experiment approaches in terms of air compression and air suction were developed, in an attempt to simulate the air pressure variation when the train runs through tunnels. Pros and cons of the introduced methods were analyzed by theoretical calculation and numerical simulation, and further validated in experimental tests. It is revealed that in air compression means of eccentric wheel and stepping motor propulsion, pressure
Surface roughness is an important index to evaluate the quality of a machined surface. In order to accurately predict the surface roughness for slow tool servo (STS) turning, taking toric surface as an example, response surface methodology (RSM) was used to perform the process test. The second-order response surface prediction model was established and the variance analysis and reliability test were carried out. The results showed that the average prediction error was 7.6%. In order to obtain the best process parameters, standard particle swarm optimization (PSO) was used. The results showed that the global optimization ability of standard PSO was poor. In order to solve the problem, compression factor was introduced and particle swarm optimization with compression factor (WCF-PSO) was constructed, which enhanced the convergence of PSO effectively. WCF-PSO was used to optimize the process parameters and the results obtained were R t =0.87mm, a f =0.01mm/r, a p =0.05mm, Δθ=8.70°, with a corresponding surface roughness of Ra=0.0486μm. The results of the verification test showed that the actual value was Ra=0.0520μm, and the error was only 7.0%, indicating that WCF-PSO had a better optimization effect.
A pseudo-linear optical transmission system analytical model is built for the numerical analysis of dispersion compensation schemes. The system performance under the influence of intra-channel nonlinear effects and the initial pulse power is discussed for the data rates of 10, 40, 100 and 160 Gbit/s, respectively. We get the conclusion for the first time as we know the optimal dispersion compensation scheme for the optimal system performance is closely related to the system data rate and the proportion of the pre-dispersion compensation should be decreased while that of the post-dispersion compensation be increased with the increasing of system data rate. When the system data rate is higher than 160 Gbit/s, we can use the post-dispersion compensation scheme directly.
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