Tooling
Cost EstimationTooling cost estimation includes pattern and core box for sand casting, and metal mould for die casting as well as investment casting (for wax patterns). Their cost is driven by the material and manufacturing (mainly machining) of the tooling. The material is decided depending on the tool life required, which is in turn influenced by the order quantity. The tool manufacturing cost is driven by its geometric complexity.
The shape complexity X can be estimated from the solid model of the casting based on its surface area, volume and number of cored features as follows:
The area complexity factor is derived by comparing the surface area of a part with the surface area of a cube of equal volume. This is based on the assumption that a cube is the simplest shape (considering manufacturing, otherwise it should be a sphere) and has the least surface area for a given volume. Thus the area complexity factor for a cube is 0, and increases for other shapes. Hammering a cube into a plate increases its surface area, but not necessarily increase its geometric complexity significantly, as (erroneously) indicated by the area complexity factor. Hence we also consider the complexity introduced by other features, particularly those requiring cores. A part with no cores has a core complexity factor of 0. With just one core added, the factor jumps to 0.293. With every additional core, the factor becomes 0.423, 0.500 and 0.553. If the number of cores is already large, adding one more will not significantly increase the core complexity factor.
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Material Cost Estimation |
Material cost includes direct and indirect materials. Cast metal or alloy that appears in the product constitutes direct material cost. This can be determined from the casting weight. However, the actual amount of metal consumed is more, owing to irrecoverable losses during melting, pouring and fettling. The direct material cost is given by:
The melting loss factor is highest for cupola (1.1 or more), followed by oil/gas fired furnace, electric arc furnace and the least for induction furnace (as low as 1.01).
Indirect materials are essential for production but are not included in the product. Moulding sand, dispensable cores and feeding aids constitute indirect materials, depending on the process. The cost of moulding sand depends on the type of sand (silica, olivine, zircon, sodium silicate, etc.), composition (amount of binder), mould size and layout. Core sand cost mainly depends on the type of sand (depending on the core-making process) and volume of cores. Cost modifiers for mould rejection, core rejection, casting rejection and sand reclamation need to be considered.
Sand recycling factor indicates how much new sand is required for each mould or core. A low factor (say 0.01) implies high recycling (say 99%), where as a factor of 1 indicates a process that requires completely fresh sand for each mould or core. The rejection factor is included to take into account breakages or damages. A value of 1 indicates zero damages. The mould sand cost is divided by the number of casting cavities to obtain the cost of mould sand cost per casting.
The cost of indirect materials (such as insulating sleeves, chills and chaplets) also needs to be added depending on their use.