In order to explore the extrusion law of large-scale and small-scale hollow thin-wall aluminum profiles for rails, simulation software HyperXtrude is used to numerically simulate the extrusion process of the profiles, the influences of mold structure and process parameters on the extrusion are analyzed, and the forming rules of two large-scale and small-scale profiles with similar shapes are compared. The results show that, in terms of mold structure, the modification of welding chamber and drainage groove has the most obvious influence on large-scale and small-scale profiles, for instance, the change in welding chamber significantly reduce the maximum deformation of the small-scale profile, with a reduction of 42.82%, while that for the large-scale profile is 25.34%. The change in drainage groove structure shows different impact trends-after altering the drainage groove, the maximum deformation reduction of the large-scale profile is 40.88%, while that of the small-scale profile is 24.72%. The drainage groove of small-scale profile is relatively shorter, and the modification of the drainage groove of large-scale profile is more complicated, so that the change of drainage groove has a more significant impact on large-scale profile. Moreover, in terms of process parameters, according to the changes of metal deformation, metal flow rate and the SDV values of the profile exit section under different conditions, it is found that the extrusion speed and the die temperature have more significant impact on the large-scale profile, while the billet diameter has a more pronounced effect on the small-scale profile. This research provides theoretical support for optimizing the extrusion process of aluminum profiles.

To explore the influence of the non-uniformity of quenching temperature on large-scale thin-wall multi-chamber aluminum alloys, uncover the influence patterns of process parameters and develop an optimization strategy, a numerical model describing the quenching process of large-scale thin-wall aluminum alloys was established based on the Workbench software platform, which was used to systematically analyze the effects of quenching method, cooling strength, nozzle spacing and operating speed on the temperature field. Then, a response surface method was employed to perform multi-objective optimization of key process parameters, and a three-dimension heat transfer model was established to address the structural characteristics and quenching process requirements of large-scale thin-wall aluminum alloys. By incorporating the convective heat transfer boundary conditions between the profile and the cooling medium, and by integrating the actual nozzle arrangement in actual production, numerical simulations were conducted to analyze the evolution of temperature field in the quenching process. The results show that the use of stepped quenching can improve the uniformity of the temperature field during the quenching of profiles and ensure the critical cooling rate in the sensitive area. With the increase of cooling intensity of the strong cooling zone, the cooling rate of the profile increases, while the uniformity of the temperature field decreases. With the increase of longitudinal nozzle spacing in the strong cooling zone, the temperature difference of the profile in the strong cooling zone decreases, and at the same time, the cooling rate of the profile slows down. With the increase of running speed of the profile, the cooling rate of the profile first increases and then decreases. Response surface analysis results indicate that the optimal quenching process parameters for large-scale thin-wall aluminum alloys are: a cooling intensity of 0.92 in the strong cooling zone, a profile running speed of 27.6 mm/s, and a longitudinal nozzle spacing of 280 mm in the strong cooling zone. By employing an alternating cooling mode of mist and high-intensity jet cooling in the strong cooling zone, the optimized scheme successfully reduces the quenching temperature difference to 19.8 ℃ and eliminates temperature recovery.

To study the distribution of soot particles and the efficiency of fume extraction inside the SLM (selective laser melting) forming bin, this research analyzed the flow law of shielding gas and soot particles in the forming bin with Fluent discrete phase model (DPM) based on the established model of the large-format porous wind wall forming bin. Then multi-objective genetic algorithm (MOGA) was used to optimize the structure of the porous wind wall forming bin. The length of air inlet P₁, the radius of wind wall hole P₂, the length of conical protection plate P₃ and the shaft length of wind wall hole P₄ were taken as optimization variables, and the average flow velocity of shielding gas in the middle section of the forming bin, the concentration difference of smoke particles at the inlet and outlet of the forming bin and the maximum concentration of smoke particles in the entire forming bin were taken as optimization objectives. The response surfaces and sensitivity analysis results of each optimization variable and optimization target were obtained, and the optimization target before and after optimization was compared. The results show that for the four optimized variables, the order of influence on the flow velocity of the shielding gas in the middle section of the forming bin is P₂>P₄>P₃>P₁; the order of influence on the concentration difference of inlet and outlet particles is P₂>P₄>P₁>P₃; the order of influence on the maximum particle concentration in the porous air wall forming bin is P₂>P₁>P₃>P₄; the pore size of the porous wind wall plays a key role in the flow of dust particles in the forming bin. Through multi-objective genetic algorithm, the optimized length of gas inlet is 358 mm, the radius of wind wall hole is 20 mm, the length of conical protection plate is 589 mm, and the shaft length of wind wall hole is 6 mm. Compared with that before the optimization of the structure of the forming bin, the flow velocity of the shielding gas in the middle section of the forming bin after the optimization increases by 11.3%; the concentration difference between the inlet and outlet particles decreases by 16.8%; the maximum particle concentration in space decreases by 23.9%; the trend of outward diffusion of soot particles decreases, and the flow velocity of the shielding gas passing 30 mm above the forming table increases by 21%, indicating that the shielding gas can carry the soot particles out of the forming bin more efficiently.