Lost foam casting starts out by forming the desired cast shape into a block of foam. When internal features are desired in the part a core is used. The desired part is then attached, via an adhesive, to a gating and runner system to help in metal flow and material cooling. Sand is then moistened slightly to allow the sand to adhere to the part. If too much water is added the mold could explode when pouring the molten metal. The sand is then packed around the part, with the pour cup of the runner on the surface of the sand. When running high volumes of the same part, green sand will be used. Green sand can be used over many times, which reduces the material costs. The molten metal is then poured into the mold. Following the cooling of the mold the cast parts are removed. The runner system is then removed and the part is polished. Secondary machining operation can follow the casting operations to yield better surface finish.
Object.....................................Styrofoam Dimensions........................After Metal has Cooled
Large Balls..............................Diameter of 1.42"...............................1.39"
Small Balls...............................Diameter of 1.00".............................. 0.95"
Heart.......................................w=5.9",h=5.82"..................................w=5.7", h=5.3"
Square Thing............................Bottom=1.9" x 1.9" x 1.9"..................Bottom=1.89" x1.88"
"h" with Thin Section ................h=2.28" wt=1.08................................h=2.26" wt=1.10"
.................................................ht=.59" hb=.59".................................ht=.59" hb=.657"
................................................web=.14" wb=.95"............................web=.14" wb=.1.06"
The resulting parts turned out much better then expected. Shrinkage accrued on most parts as expected. When in a production environment the shrinkage is calculated and the mold is modified to accommodated the changes. The shrinkage is definitely proportional to the initial thickness (similar to a percent). Some of the parts expanded in size which can be accounted for by the pour mold preparation.
| Design Feature | Expected Outcome |
| Web | usually will have a wavy look due to the difference in temperature cooling rates between the part and the web |
| Surface Finish | directly related to mold preparation (good mold finish good part finish) |
| Internal Core | can lead to a exploding pour if the core is not dried properly
with proper design there is usually no problems |
| Long Narrow Sections | can lead to a short fill if only one runner is used |
| Large Sections | no problems if shrinkage rates are designed into the mold system |