Sand Casting General Process
In general, casting costs are determined by aggregating material, labor, machine, and tooling costs.
aPriori represents sand casting as a process sequence that includes moldmaking and optional coremaking processes.
There are a number of alternative moldmaking processes:
• Vertical Automatic: Uses high volume machines such as DisaMatic and Loramendi.
• Horizontal Automatic: Uses high volume machines such as Hunter HMP and Roberts Sinto FBx.
• Manual Std Moldmaking: Appropriate for manual mold-making at low and medium production volumes. With this process, standard flasks are filled with sand, compacted, and transported (typically by conveyor) to a pouring station, and then on to a central cooling and breakout area.
• Manual Floor Moldmaking: Appropriate for casting large parts that require the flask to stay in place on the foundry floor. This process is used when it is not practical to move the flask. Used for large castings, the flask is built around the pattern and core boxes, and the crucible is brought to the flask for pouring. The flask then stays in place on the floor for cooling and breakout.
• Manual Pit Moldmaking: Appropriate for casting of very large parts in a pit. With this process, the pit serves as the drag and a wooden frame on top of the pit provides the cope and incorporates the feeder system.
There are also provides a number of alternative coremaking processes:
• No heat required: with these processes, the binder in the sand becomes rigid without heat. Modern core making tends to prefer no-heat processes with minimum environmental disposal problems.
o Isocure Gas: popular cold box core making process introduced in 1968 by Ashland (phenolic urethane cold-box binder). The starting point cost model prefers this method. Cores can be as small as 3/8” (9.5 mm).
o CO2 Cured: similar to Isocure, this process uses CO2 gas to set the binder. The process is sometimes known as Ecolotec. The starting point cost model considers this the second choice behind Isocure. Cores can be as small as 3/8” (9.5 mm).
o No Bake: developed in the 1960s, this method uses sand mixed with a chemical binder. The mixture cures at room temperature, but curing is relatively slow. Core sizes can go down to about 3” (76.2 mm). The method is often used for large cores, especially for floor molding.
o Manual Coremaking: for very large cores. Similar to No Bake, but cores are made by hand; a vibratory table is used to compact the sand into the corebox.
• Heat required: These processes require heat for the binder in the sand to become rigid.
o Hot Box: developed about 1953. Hot box cores use a thermoset resin and apply heat. Core sizes go down to about 2” (50.8 mm). This method is often used for large cores.
o Oil Core: uses an oil-based binder. The core must be baked to set. Core sizes can be as small as 3/8” (9.5 mm).
o Shell: invented in 1947 by J. Croning. With this method, sand is blown into a heated box and the sand pressing against the box sets to form a shell. The remaining sand in the center is poured out and can be reused. The result is hollow core.
For the current cost model, this method is used for cores only. The core is baked and is considered hollow. Shell cores allow excellent surface finish, but the baking is slow. Foundries sometime buy shell cores. Core sizes can be as small as 3/8” (9.5 mm).
o Stock Core: limited to Simple Hole GCDs. Stock cores are made by a relatively inexpensive extruder that extrudes a sand mixture through an extruding head. Usually, stock cores are limited to simple hole shapes with standard (stock) diameters. A stock core can be used if the hole doesn’t have a draft and if the hole axis is perpendicular to the parting direction of the mold.
If you have licensed the appropriate modules, your routing can include optional machining, heat treatment, and surface treatment processes, as well as testing, inspection, and packaging processes (which are part of the process group Other Secondary Processes).