Multi-Objective Optimization of A356 Engine Block Casting Process Parameters Based on Response Surface Method and NSGA-II Genetic Algorithm

Deng W., Luo K., Lei J., Song Z., Xu Y., Zhang Y.

This study conducted molding process research on castings of complex engine blocks with a new Al–Si–Cu aluminum alloy material. Numerical simulation and experimental validation were used to investigate the effects of different pouring system design schemes on the casting performance, defect formation and mechanical properties of aluminum alloy castings. Based on the casting structure and alloy casting properties, three types of casting systems (i.e., A, B, and C) were designed and analyzed by numerical simulation and testing. The study shows that the molding process of casting system scheme C is more optimal, the numerically simulated porosity is reduced by 4.13 and 1.9% compared with those of schemes A and B, respectively, the defect volume is reduced by 205.87 and 94.7 cm3 compared with those of schemes A and B, respectively, and the average cooling rate is improved by 47.6 and 26.5% compared with those of schemes A and B, respectively. After experimental verification, casting system C exhibited optimal mechanical properties, good CT scan and the microstructure of aluminum alloy analysis results, and numerical simulation results consistent with the actual trial production results, providing guidance for relevant theoretical research.

Du Z., Xu W., Wang Z., Zhu X., Wang J., Wang H.

To enhance the forming quality of the forging and minimize the forging cost in the concave radial forging process, this article examines the influence of process parameters (radial reduction ∆h, rotation angle β, friction coefficient μ) on the forging process through numerical simulation. A multi-objective optimization method is employed to balance the objective functions (strain homogeneity E, forging load F). First, sample points for different combinations of process parameters were obtained using a central composite experimental design. Then, a mathematical model between the process parameters and the objective function was established using the response surface method, which underwent variance analysis and sensitivity analysis. Finally, the optimal process parameter combination was determined based on the NSGA-II algorithm and satisfaction function. The optimization results were verified by finite element simulations. The optimized process combination: ∆h = 0.25 mm, β = 21.68°, μ = 0.05. The corresponding E and F are 0.241367 and 577.029, respectively. Compared with the initial process, the standard deviation of the overall strain was reduced by 14.25%, and the forging load was reduced by 1.76%. The results indicate that the quality of the forgings was significantly improved while the forging cost was reduced to some extent.

Paturi U.M., Vanga D.G., Duggem R.B., Kotkunde N., Reddy N.S., Dutta S.

Chen H., Gao Q., Wang Z., Fan Y., Li W., Wang H.

To improve the casting quality as well as the casting efficiency during the casting process, the effect of the interaction of process parameters and system structural parameters on the shrinkage volume and efficiency of the casting was investigated in this paper by using the response surface method for the simulation prediction of A356 alloy sand casting. The relationship between variables and response (shrinkage volume, solidification time) was established by Box-Behnken Design with pouring temperature (650–710 °C), mold preheating temperature (200–300 °C), width/thickness ratio of cross-section of sprue (1.2–1.5), width/thickness ratio of inner sprue section (2–4) and length/diameter ratio of straight sprue (1.5–2.5) as variables by the response surface method. The results are then optimized, and the optimal solution is selected by the NSGA-II algorithm and TOPSIS method. The results show that the changes in the cavities of the optimized and improved pouring system enhance the flow of the metal fluid and make the filling more complete. The gentle cooling of temperature is conducive to heat dissipation and layer-by-layer sequential solidification, which can effectively eliminate the casting's internal shrinkage loosening and shrinkage holes defects, thus forming a dense casting with good performance. After solving the optimized parameters and improving the pouring system, the solidification time (integrated solidification time) was reduced from 129.24 to 88.10s, and the shrinkage volume was reduced from 9.68 to 4.06 cm3.

Panwar V., Kumar Sharma D., Pradeep Kumar K.V., Jain A., Thakar C.

In the present analysis 15 experiments were performed in conjunction with the Box-Behnken architecture matrix based on the machining parameter's effect, like spindle speed, feed rate, and cutting width., A surface roughness mathematically framework was designed using the surface reaction methods of this model to aid a genetic algorithm. Which is used to decide the optimum machining parameters. Response surface methodology has been used in this paper due to certain advantages as compare to other methodology such as it needs fewer experiments to study the effects of all the factors and the optimum combination of all the variables can be revealed. Finally, a genetic algorithm was used to determine the optimum setting of process parameters that maximize the rate of content removal. The best surface roughness response value obtained from single-objective genetic algorithm optimization was 1.19 μm.

Žbontar M., Petrič M., Mrvar P.

The aim of this study was to determine the correlation between the size and the distribution of microstructural constituents and their cooling rate, as well as the correlation between the mechanical properties and the cooling rate of AlSi9Cu3 aluminum alloy when cast in high-pressure die casting (HPDC) conditions. In other words, the ultimate goal of the research was to determine the mechanical properties for a casting at different cooling rates. Castings with different wall thicknesses were chosen, and different cooling rates were assumed for each one. Castings from industrial technological practice were systematically chosen, and probes were extracted from those castings for the characterization of their mechanical properties. Special non-standard cylinders were created on which compressive tests were carried out. The uniqueness of this research lies in the fact that the diameters of the designed cylinders were in direct correlation to the actual wall thickness of the castings. This is important because the solidification of metal in the die cavity is complex, in that the cooling rates are higher on the surface of the casting than in the center. Local in-casting cooling rates were determined using numerical simulations. It was discovered that with increasing cooling rates from 60 K/s to 125 K/s the values for strength at 5% deformation increased on average from 261 MPa to 335 MPa.

Arulraj M., Palani P., Sowrirajan M.

Squeeze casting is one of the simplest processes of manufacturing of composite materials and it attains higher advantages of low material processing cost, easy handling of material, size, design and good stability of matrix structure. LM24 aluminium alloy reinforced with silicon carbide (SiC) and coconut shell ash (CSA) were used to prepare the composite. LM24 alloy had wide engineering applications, wherein the addition of SiC enhances the wear resistance and CSA particles offer significant technical and economic benefits. In the present study, the composite samples were prepared based on Taguchi experimental conditions L16 (4-levels and 5- parameters) through squeeze casting method. From the experimental results, percentage of reinforcement and squeeze pressure were most influential parameters on impact strength. The optimum casting condition was obtained by using Taguchi optimization. From microstructural study, applying high level of squeeze pressure improved the uniform dispersion, good bonding between the matrix and reinforcement. Also, 25% of impact strength was improved the composite using Taguchi optimum conditions compared than conventional alloys. Higher squeeze pressure seen to have refined dendritic structure with uniform distribution of reinforcement materials in the aluminium matrix.

Chen Z., Li C., Han X., Gao X., Gao H.

Xu Z., Wang S., Wang H., Song H., Li S., Chen X.

In this study, a twin-roll casting sheet of 6061 aluminum alloy was cooled using furnace, asbestos, air, wind and water. The effect of cooling rate on the microstructure and properties of twin-roll casting 6061 aluminum alloy sheet were studied. Optical microscope, scanning electron microscope, X-ray diffraction, microhardness tester and universal tensile machine were used to observe the microstructure and properties of twin-roll casting sheet of 6061 aluminum alloy. The results show that the higher the cooling rate, the smaller the grain size of the alloy and the smaller the number of precipitated phases in the matrix. Uniform grain size of the alloy could be obtained at a stable cooling rate. The hardness, tensile strength and elongation of the twin-roll casting sheet increased with cooling rate. Under wind cooling condition, the twin-roll casting sheet demonstrated excellent comprehensive performance, i.e., 88 MPa of yield strength, 178 MPa of tensile strength and 15% of elongation, respectively. A quantitative Hall–Petch relation was established to predict the yield strength of 6061 twin-roll casting sheets with different grain sizes and cooling rate.

Tian Y., Yang D., Jiang M., He B.

Automobile steering knuckle is an important part of the steering system, which is subjected to significant impacts and loads during its operation. Generally, cast aluminum steering knuckles are usually produced using some type of enhanced low-pressure casting process, like counter-pressure casting. Compared with aluminum forging and sand cast ductile iron, it can improve the production speed and achieve the adequate casting quality. In this study, various methodologies such as dynamic thermomechanical analysis, differential scanning calorimetry, and the laser flash method were employed to study the thermophysical properties of AlSi7Mg0.3. Further, the physical model of a counter-pressure casting system with an aluminum interior was established based on the combination of the tested and the theoretical properties of aluminum; this was achieved with the consideration of the presence of other factors including rapid solidification. The temperature field of the system was computed and verified by thermocouples at six different points during the tooling and the shrinkage simulation. It was observed that the plot shape of the computed temperatures and that of the simulated ones correlated; further, the difference between the peaks and the valleys was controlled to be 3% on an average, with the maximum variation of 7% at only one point. Moreover, all the predicted shrinkages were verified by the casting. This study provides a solid foundation for facilitating the simulation of the morphologies of the microstructure.

Bora T.C., Mariani V.C., Coelho L.D.

This paper presents an improved non-dominated sorting genetic algorithm II (NSGA-II) approach incorporating a parameter-free self-tuning by reinforcement learning technique called learner non-dominated sorting genetic algorithm (NSGA-RL) for the multi-objective optimization of the environmental/economic dispatch (EED) problem. To evaluate the performance features, the proposed NSGA-RL approach is investigated on ten multi-objective benchmark functions. Besides, to evaluate the effectiveness of the proposed approach, the standard IEEE (Institute of Electrical and Electronics Engineers) of 30-bus network with six generating units (with/without considering losses) is adopted, with operating cost (fuel cost) and pollutant emission as two conflicting objectives to be optimized at the same time. In comparison to literature, it was observed that the proposed approach provides a better satisfaction level in conflicting objectives with well distributed Pareto front, in comparison with the classical NSGA-II method, and to other existing methods reported in the literature. The NSGA-RL was found to be comparable to them considering the quality of the solutions obtained, with the advantage of non-time spent for parameters tuning.

Park J., Kim M.G., Kim J.H., Shin J., wLee K.L.

The use of aluminum silicon alloy is widely accepted in many fields of applications, including automotive, aerospace and military. Hypereutectic aluminum silicon alloys has silicon contents commonly between 14% and 20%. The use of hypereutectic aluminum silicon alloys give a number of benefits such as low specific gravity, high resistance to wear and reduced thermal expansion. In the continuous casting of hypereutectic Al-Si alloy billets, the size and distribution of primary silicon become important to obtain uniform and excellent physical properties. In this study, electromagnetic stirring technique was applied to control the size and distribution of primary silicon. Rotational move of melts induces the segregation of primary silicon around casting surface. Turbulent flow of melts by electromagnetic stirring enhances the distribution of primary silicon. In results, the distribution of primary silicon is greatly enhanced by applying two way electromagnetic stirring technique. Finally the mechanical and wear properties were examined and compared with different samples and discussed about the usefulness of electromagnetic stirring to control the size and distribution of primary silicon in billet casting.

Asanjarani A., Dibajian S.H., Mahdian A.

This paper presents one and multi-objective crashworthiness optimization of the tapered thin-walled square tube with indentations. In this study, effects of cross section, thickness, taper angle, number and radius of indentations (as design variables) on the beam's energy absorption capability during crashes are investigated. The crashworthiness of models is evaluated using two metrics: The specific energy absorption per unit mass (SEA) and the ratio between the average and maximum crushing forces ( CFE = F avg / F max ). The optimum values of the number and radius of the indentations, the taper angle, the tube thickness and the cross section using a combination of response surface (RS) model, genetic algorithm and desirability function optimization are obtained. Multi-objective optimization of the tubes is performed by maximizing a composite objective including CFE and SEA. Analyses involved in this paper are undertaken using finite element models and solver (Abaqus). Also the computer program MATLAB is used to perform all the analyses and the optimization. Multi-objective optimization of the tubes showed that the tapered thin-walled square tubes with indentations have significantly, better crush performance in comparison to those without indentations. It is found that maximum CFE requires large number and radius of indentations, thickness, and cross section with small taper angle, while maximum SEA requires medium number of indentations and radius, large thickness and small taper angle and cross section. Also, the sensitivity of the design variables on the tapered square beam's crash behavior performance is analyzed. The objective functions, including SEA and CFE, were formulated using the Response Surface Method.

Ibrahim M.F., Samuel A.M., Doty H.W., Samuel F.H.

The present study was carried out on a series of heat-treatable aluminum-based alloys, the objective being to determine the effect of aging time and temperature on the precipitation of Mg2Si and Al2Cu in these alloys. Tensile test bars (dendrite arm spacing ~24 µm) were solutionized for either 5 or 12 h at 540 °C (Al–Si–Mg alloys) or 495 °C (Al–Si–Mg–Cu alloys), followed by quenching in warm water (60 °C). Subsequently, the quenched samples were aged at 160 and 220 °C for times up to 200 h. Microstructural assessment was performed using thermal analysis technique, image analysis and field emission scanning electron microscopy. All heat-treated samples were pulled to fracture at room temperature. The results show that the presence of Sr delays the precipitation of Mg2Si or Al2Cu during the aging process. The precipitation of Mg2Si occurs in the form of spherical particles—rather than cuboid particles, thin platelets or short rods—regardless of the aging time or aging temperature. Particle coarsening takes place by the dissolution of some small particles and re-deposition onto larger ones. The shape and size of the precipitated Al2Cu particles are found to be strongly dependent on the aging conditions. The tensile behavior of Sr-modified 356 alloy revealed a wavy-type nature with respect to aging time instead of a single peak, due to variation in the size and distribution of the precipitates over several stages. The ultimate tensile strength–ductility relationships have been presented in the form of Q-charts reflecting the effect of aging conditions and melt treatment, i.e., modification with Sr on the alloy performance.

Zhou G., Ma Z., Li G., Cheng A., Duan L., Zhao W.

Possessing the unique properties of lower mass and higher performances, the structure with Negative Poisson’s Ratio (NPR) can be widely used in aerospace and vehicle industry. By combing the NPR structure filled core and the traditional crash box, a novel NPR crash box is first proposed in this work to improve the performances of the crash box. The performances of the novel NPR crash box are fully studied by comparing to the traditional crash box and the aluminum foam filled crash box. A parameterized model of the NPR crash box, which integrates the design parameters of the basic NPR cell structure, is built to improve the analysis and optimization efficiency, the accuracy of the parameterized model is also verified by comparing to traditional FEM model. Multi-objective optimization model of the NPR crash box is established by combining the parameterized model, optimal Latin square design method and response surface model approach. Non-dominated sorting genetic algorithm-II (NSGA-II) is then applied to optimize the design parameters of the basic NPR cell structure to improve the performances of the NPR crash box. The results indicate that the novel NPR crash box can improve the performances of the crash box remarkably and the combination of parameterized model and multi-objective genetic algorithms optimize the NPR crash box efficiently. The presented new method also serves as a good example for other application and optimization of NPR structure.