Simulation of microstructural evolution in directional solidification of Ti-45at.%Al alloy using cellular automaton method

The microstructural evolution of Ti-45 at.%Al alloy during directional solidification was simulated by applying a solute diffusion controlled solidification model. The obtained results have shown that under high thermal gradients the stable primary spacing can be adjusted via branching or competitive growth. For dendritic structures formed under a high thermal gradient, the secondary dendrite arms are developed not very well in many cases due to the branching mechanism under a constrained dendritic growth condition. Furthermore, it has been observed that, with increasing pulling velocity, there exists a cell/dendrite transition region consisting of cells and dendrites, which varies with the thermal gradient in a contradicting way, i.e. increase of the thermal gradient leading to the decrease of the range of the transition region. The simulations agree reasonably well with experiment results

Numerical simulation and optimization of Al alloy cylinder body by low pressure die casting

Shrinkage defects can be formed easily at Critical location during low pressure die casting (LPDC) of aluminum alloy cylinder body. It has harmful effect on the products. Mold fi lling and solidifi cation process of a cylinder body was simulated by using of Z-CAST software. The casting method was improved based on the simulation results. In order to create effective feeding passage, the structure of casting was modifi ed by changing the location of strengthening ribs at the bottom, without causing any adverse effect on the part’s performance. Inserting copper billet at suitable location of the die is a valid way to create suitable solidifi cation sequence that is benefi cial to the feeding. Using these methods, the shrinkage defect was completely eliminated at the critical location

Numerical simulation of low pressure die-casting aluminum wheel

The FDM numerical simulation software, ViewCast system, was employed to simulate the low pressure die casting (LPDC) of an aluminum wheel. By analyzing the mold-fi lling and solidifi cation stage of the LPDC process, the distribution of liquid fraction, temperature field and solidification pattern of castings were studied. The potential shrinkage defects were predicted to be formed at the rim/spoke junctions, which is in consistence with the X-ray detection result. The distribution pattern of the defects has also been studied. A solution towards reducing such defects has been presented. The cooling capacity of the mold was improved by installing water pipes both in the side mold and the top mold. Analysis on the shrinkage defects under forced cooling mode proved that adding the cooling system in the mold is an effective method for reduction of shrinkage defects

Application of numerical simulation on cast-steel toothed plate

A three-dimensional Computer Aided Design (CAD) model is established by using Pro/E software. The finite volume method (FVM) numerical model and ViewCast simulation software are used to study both the casting solidification process and filling process of toothed-plate. Based on the simulation, the casting shrinkage and solidification process are forecast visually in the form of images. The mould-filling simulation verify whether the liquid metal pour the mould smoothly and /quietly/evenly. Two optimization schemes are completed based upon the simulation. The production of the casting shows that these optimization methods are very helpful to reduce the casting defect and improve the quality of product

Casting process design and wear properties of a high chromium cast iron hammer

In this article, both chemical composition and structure of a high chromium iron hammer head were designed and analyzed respectively. Also, the casting process was investigated and optimized through numerical simulation using commercial software View Cast. On the basis of numerical simulation and optimization, several hammer heads with fine surface quality and no internal defects were cast into one mold through shell molding and string casting process. In addition, heat treatment of the as-cast hammer head was carried out. Consequently, the microstructure was observed, and wear resistance was tested. After being quenched at the temperature of 950℃ and tempered at the temperature in the range of 230-260℃, the microstructure of the hammer is made up from tempered martensite, retained austenite and network eutectic carbides. The hardness is 60 HRC. Experimental result shows that the wear loss is slowly increased with an increase in load and rotating speed

Surface stress evolution and cracks prevention of ingots during the upsetting process

In this research, surface axial stress and propagation of surface transverse cracks on large ingots during hot forging process was studied using finite element modeling. The simulation results show that surface axial stress changes from compressive to tensile during the upsetting process. Large ingots which need to be upset and stretched several times are easy to form cracks at anvil overlapping part during stretching process. These surface transverse cracks are crack source and may rapidly propagate under surface axial tensile stress during the upsetting process. The effect of material, temperature, height-diameter ratio of billet, deformation speed, and friction coefficient between anvil and billet on the changing of surface axial stress was investigated. The results show that critical transformation point of surface axial stress from compressive to tensile has an obvious relationship with drum shape of the billet. In order to eliminate the surface axial tensile stress and prevent propagation of surface transverse cracks, a slim waist forging process was proposed based on the surface stress analysis. A quantitative designing method of slim waist billet was established for guiding industrial production

Finite element analysis of welding residual stress of aluminum plates under different butt joint parameters

A thermal-elastoplastici finite element method was built to simulate the process of variable polarity plasma arc welding (VPPAW) for aluminum alloy plates. The welding temperature and stress fields of the aluminum plates with different butt joint parameters(intervals of the joints: D=0.3 mm, 2 mm; and unfitness of the joints: L= 0.3 mm, 2 mm) were calculated using a 3D double-ellipsoidal heat source model. The residual stresses of the welded plates were predicted; the results showed that the unfitness of the joint has a greater impact on the welding residual stresses than that of the interval. The simulated and experimental results were compared and they are consistent well with each other

Research on the grinding performance of high pressure sintering SiCp/Al matrix composites

The two-dimensional vertical grinding test equipment was used to grind SiCp/Al composites which were prepared by high pressure sintering method. The SEM observation of grinding morphology showed that grinding damage can be prevented by SiC particles reinforcement, 60% volume fraction of SiC particles of SiCp/Al composite can hinder grinding depth and grinding performance was improved with the sintering pressure and temperature increasing. In addition, some scratches and exfoliated pits of SiC particles were observed on the surface of 60% volume SiCp/Al composite as the increase of grinding grain, while the depth of these scratches was shallower, there was no large area exfoliated pits of SiC reinforcements