Technical Articles

Influence of Gate Size on Quality of Thin-walled Castings

Posted: 2014-12-05 01:10:35  Hits: 1375
Keywords: Investment Casting, Thin-walled Parts, A356 Thin-walled Casting, Al-alloy Fixed Parts. Aluminum Alloy Thin Wall Complex Parts
In recent years, precision investment casting is widely applied in the forming of aluminum alloy parts, especially for forming of aluminum alloy thin wall complex parts.
1.The Characteristics of Casting Structure
Al-alloy fixed parts is shown in Fig.1, the casting is mainly used in fixing for light-duty machinery. The casting is thin-walled, and with cross blades. There is necking in part A, which is a complex thin-walled part. It has certain representativeness in the aluminum alloy thin-walled part. Design the investment casting according to the structural characteristics, shown as Fig.2 – drawing of aluminum alloy fixed part.
2. Main Technical Parameters
2.1 The casting material is ZAlSi7Mg03 (A356), the liquidus temperature is 610℃. And the solidus temperature is 577℃.
2.2 Shell material: Ludox + silica sand fireproofing, with totally 6 layer shell mold, and 6mm thickness.
2.3 technological parameter: 710℃pouring temperature, 80mm/s pouring speed, 350℃ shell preheat temperature. Pouring in the air, and cool naturally.
2.4 Pouring way: Pouring from top.
3. The Runner Size Design and Simulation Results Analysis
The runner size formula of investment casting is:
Dg = 0.6~1 1     (1)
Ag = 0.4~0.9 2   (2)
In the formula, Dg and Ag are the runner diameter and sectional area. Dc and Ac are casting’s hot pitch diameter in the last solidification and sectional area.
According to Formula 1, for aluminum alloy fixed parts shown in figure 2, do casting simulation analysis under the help of ProCAST casting simulation software. Casting runner diameters are the 5 values between 0.6 to 1, namely 0.6 (16mm), 0.7 (19mm), 0.8 (21mm), 0.9 (24mm) and 1 (27mm). Respectively research and analyze thin-walled aluminum alloy fixed parts with 3mm, 2mm, 1mm wall thickness. The experimental scheme and simulated result is displayed in Table 1.
According to the values in Table 1, design linear diagram shown in Fig.3. It intuitively reflects the runner diameter size effects on shrinkages rate. It can be seen that for the same wall thickness, with the runner size increasing, the shrinkage rate increases as well, and the casting quality becomes poorer. But for the casting that uses the same runner size, with the decrease of the casting wall thickness, the shrinkage rate decreases too. From this we can see that during the investment casting of aluminum alloy thin-walled parts, use the lower limit of parameters in formula 1 and 2 for the runner sizes will help to improve the quality of the casting. And when the casting’s wall thickness is thinner, the parameter selection should be smaller.

4. Summary
4.1 Design the gate location according to the structural characteristics of aluminum alloy fixed parts, and determine the experimental scheme according the design methods of general investment casting runner.
4.2 According to the experimental scheme, use simulation software ProCAST to simulate investment casting values. The results show that during the investment casting of aluminum alloy thin-walled parts, use the lower limit of parameters for the runner sizes will help to improve the casting quality. When the wall thickness is thinner, the parameter selection will be smaller.

Miss Lavendie Lee 
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