Fig. 1. The thermal command center integrated a water pump, thermostat housing and bypass valves in a single complex cast assembly.
• Reduction in weight or heavy sections of the casting is possible because it is not necessary to be able to draw sand components from molds. This leads to improved casting quality by eliminating heavy sections vulnerable to porosity. However, 3-D printing holds some
disadvantages compared to conven- tional tooling: • The cost per sand mold is much higher, and the time to manufacture is generally much longer.
• The cost per printed sand com- ponent generally is linked to the size of the cuboid containing the printed part. As is the case for the core depicted in Figure 2, a small 3-D printed component occupying a large volume of unprinted sand would be expensive. This is because current 3-D printing machines use activated sand for which only a small percentage can be recycled. Similarly, large molds will be much more expensive than their tooled equivalents if the cost of the tooling is eliminated from the comparison. Future developments with pheno- lic binders may improve the cost effectiveness of low printed density cores since the sand can be recycled.
• Once soft tooling is made, it is possible to manufacture castings at a much quicker rate for most cores and mold components than by 3-D printing. Because only two parts were
required at fi rst, it was decided to manufacture these castings using 100% 3-D printed sand molds.
Computer Aided Engineering Crucial T e cost of 3-D printed sand is
high in comparison to sand molds and cores produced by soft tooling, making the use of simulation upfront critical. Simulations assist the engineer in gat- ing and chilling strategies for com- plex castings. T is strategy leverages preemptive casting development rather than trial and error development. For the thermal command center,
a variety of analysis techniques were conducted through the use of solidifi - cation modeling software. First, a 3-D mesh of the casting was built, and a natural solidifi cation simulation was run. Natural solidifi cation illustrates how the casting would solidify if it were fi lled with aluminum at a uni- form temperature of 1,292F (700C). T e natural solidifi cation provides crit- ical information such as which parts
of the casting will solidify fi rst and which will solidify last. Figure 3 shows what parts of the thermal command center will solidify last. T e engineer used this information to determine the orientation in which to cast the part, as well as locations to feed the casting with in-gates and risers. After an initial gating system was
designed, the mold fi lling was simu- lated. T is analysis provided invalu- able information regarding the metal temperature and velocity during the fi lling process. T e part was cast using a low pressure sand casting process in which the sand mold was fi lled from below. In this process, nitrogen gas is used to pressurize the aluminum in the furnace and force it up a ceramic tube
Fig. 3. A natural solidifi cation of the thermal command center was predicted.
August 2016 MODERN CASTING | 39
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