Average wall thickness of heat sink on radiator in automotive steering system is relatively thick, and there are many thin-walled structures and slender structures, with high dimensional accuracy requirements and high overall quality requirements. Heat dissipation effect of sand casting heat sinks is poor, production method is backward, cycle is long, cost is high, efficiency is low, which makes it difficult to meet growing market demand and technical update of heat sinks. Aluminum alloys have excellent thermal conductivity, and die-casting parts have characteristics of dense organization, high surface quality, and high dimensional accuracy. Die-casting aluminum alloy heat sinks have broad application prospects. Computer simulation software can simulate air inclusions and temperature fields in die-casting process, and predict parts that may cause defects in the entire cavity, so as to improve process more accurately and efficiently, reduce production costs, and improve efficiency. This project designs die-casting process of aluminum alloy heat sinks, uses Flow-3D software for simulation analysis, optimizes process by adding overflow grooves and improving size of inner gate, so as to obtain a reasonable die-casting process plan. Rationality of die-casting process was further verified through trial production.
According to structure of heat sink, die-casting process scheme of aluminum alloy heat sink was designed, then die-casting process scheme was numerically simulated using Flow-3D software. Simulation results showed that air entrainment defects appeared at four corners of lower part of heat sink. Process scheme was trial-produced, produced samples were inspected and sectioned, it was found that a large number of pores and pinholes appeared at corners, which was consistent with simulation results.
Graphic results
Heat sink has an overall size of 99mm×89mm×41.7mm, a weight of about 375g, a maximum wall thickness of 33mm, and a minimum wall thickness of 2.5mm, which is a small and medium-sized casting. Main body of heat sink is a cuboid with a thickness of 13mm. There is a 20mm high protrusion in the middle of heat sink, which is the thickest part of casting; there is an extension leg with a length of 28mm at each of four corners of casting, there are oblique ribs with a thickness of 2.5mm and a height of 26mm on the side of extension leg, which is thin-walled area of casting. Aluminum alloy material is ADC12 aluminum alloy, and DM180 horizontal cold chamber die-casting machine is selected. One-mold-two-piece method is used for production. Three-dimensional structure of aluminum alloy heat sink is shown in Figure 1.

 

Figure 1 Three-dimensional diagram of aluminum alloy heat sink

 

Figure 2 Schematic diagram of parting surface of aluminum alloy heat sink

 

Figure 3 Schematic diagram of heat sink with pouring system
First, die-casting process parameters are set in Flow-3D software, with pouring temperature of 680℃, mold preheating temperature of 200℃, and filling speed of 20m/s. Solid 3D model of initial process design was converted into STL format and imported into Flow-3D software for meshing.

 

Figure 4 Initial process temperature field simulation results

 

Figure 5 Initial process air entrainment simulation results

 

Figure 6 Actual production part sectioning results

 

Figure 7 Temperature field simulation results after process optimization

 

Figure 8 Air entrainment simulation results after process optimization

 

Figure 9 Die casting section after process optimization
By analyzing heat sink structure, a reasonable die-casting process was designed. Designed initial process was numerically simulated to predict location and severity of defects, analyze causes of defects. Process was optimized by adjusting size of inner gate. Simulation results after optimization showed that defects were effectively eliminated. Optimized scheme was trial-produced, produced samples were inspected and sectioned. Results showed that pores and pinholes were effectively eliminated, meeting use requirements while reducing scrap rate. Process was optimized by improving size of inner gate and other measures, and improved process was verified, which basically solved defects in initial process.