Investment casting process planning generally consists of proper choice of suitable casting process and various investment casting materials. Now in order to have continuous cost reduction in casting process, it is essential to build up an easy-to-use casting cost estimation methodology. It is also important to note that any comprehensive investment casting cost estimation methodology must have ability to identify the most important parameters in casting cost. The most important attributes of investment casting are cost estimation of material and tooling process.
Material Cost Estimation
In investment casting material cost estimation the two vital factors that plays the major role are cost estimation of in-direct and direct materials.
Direct Material Cost:Now in case of direct material cost, the cost estimation is made on materials like cast metal or alloy that appears in any product constitutes.However, in case of direct material cost, the metals or alloys that are used can be determined from weight of investment casting.Direct material cost can be measured as:
C = c unit_metal x ; wcast × fm ×fp ×ff
Where, Cunit_metal = Unit metal cost
Wcast = Casting weight = pc × Vcast
pc= Casting metal density
Vcast = Casting volume
fm, fp, ff = Factors for metal loss in melting, pouring and fettling respectively
In-direct Material Cost : Depending upon the casting process in-direct materials consist of moulding sand, dispensable cores and feeding aids.
Moreover the most essential point that one need to consider in case of in-direct material cost is the price of moulding sand. The price of moulding sand actually relies upon on the type and composition of sand, and size of mould. The cost of core ore sand also depends on the kind of sand and quantity of cores. In addition to this the cost modifiers are need to understood very effectively for mould rejection or core rejection.
Indirect material cost can be calculated as:
x frm/n mould sand= Cms xWms frm /nc
Cost core sand = Cs Wcs fcc frc
nc= Number of casting (cavities) per mould
Cms= Cost per unit weight of mould sand (1NR/Kg)
Ccs = Cost per unit weight of core sand (1NR/Kg)
frm = Mould rejection factor
f cm = Mould sand recycling factor
f cc = Core sand recycling factor
f rc = Core rejection factor
Wms= Weight of mould sand
Wcs= Weight of core sand
Now the point to be noted is in case of indirect material cost sand recycling factor plays a very significant function. It helps in indicating the actual quantity of new sand required for each mould or core. The rejection factor is considered to measure the account breakages or damages. Moreover, the mould sand cost is finally divided by the number of casting cavities to find the price of mould sand cost per casting.