Because of the similar name, people sometimes misunderstood and thought that they are one method with different name. However, they are totally different casting method. The similar process in both cases is pattern prcocess. In lost wax casting, this is made from wax with low melting temperature (50⁰C~90⁰C). In lost foam casting, the pattern is made from expanded polystyrene (EPS). At the first step the mold for lost wax pattern is create, the molten wax is poured into mold and after that it becomes a solid pattern. In lost foam casting, a solid EPS block is cut exactly into the desired shape by using hand or machine. If the quantity is large enough, the pattern can be mass- produced by a process similar ejection. The complex foam pattern can be assembled by gluing single parts and the finish pattern is connect as a cluster.
There are literally different between two casting methods. In lost wax casting (as known investment casting), the wax pattern is covered by standard suspension (sand and additives), After the cover is dried, it will be formed around the wax mold inside, call “shell”, then the pattern is heated, the wax is molten and leaked out the shell. The space inside is mold cavity and next process is pouring the molten metal into shell and wait until the metal is gradually solid, and finally the shell cover is broken by vibration method.
(Wax pattern before the suspension has been added)
In other sides, lost foam casting is a little bit simpler. The cluster of patterns is dipped into special painting and put into metal container. The sand is covered the pattern and compacted around the EPS pattern to support it. Same as other methods when the molten metal is poured into the container, the EPS pattern instantly vaporizes and the alloy fills the void to create the finished casting.
(EPS pattern after dipping into special paint, is arranged into metal container, preparing for pouring)
The biggest advantage of both of these forms can deliver complex castings with excellent ‘as-cast’ surface finishes that are dimensionally accurate, no machining. However, it is appreciated that the lost foam casting can be less expensive option with simplier production line and fewer steps. Lost foam casting can create the casting object in the range from 0.5 to 300 kg. The only one disadvantage is EPS pattern is delicate, easily damaged.
Based on the requirement of casting part, the ultimate decision regarding to the most appropriate option should be made by expert and design team at the early stage.