The iron foundry needs to calculate the estimated rough casting weight during the quotation process. The estimated blank weight is very important to the price. Weight directly affects the price of steel castings. And too low and too high weight estimates will lead to deviations in price estimates.
As we said before, the iron and steel foundry directly calculates the production cost based on the rough weight of the casting instead of the mechanical weight. However, for new products, usually, buyers of castings do not know the weight of their blanks, and sometimes they do not even know the actual weight of the finished blanks. Therefore, casting suppliers must calculate or estimate the rough weight themselves.
Calculating rough weight is a complicated and difficult task. Only experienced engineers can get accurate results.
First, they need to consider the appropriate machining allowances for all machining positions. Secondly, calculate the volume of the rough casting. Finally, multiply the volume by the density of cast iron or cast steel.
The following are the common densities of cast iron, cast steel and cast aluminum.
Gray cast iron: 7.2-7.4 g/cm3
Nodular cast iron: 7.3 g/cm3
Cast steel: 7.8 g / cm3
Stainless steel: 7.7-7.9 g/cm3
Cast aluminum: 2.6 g / cm3
As for the machining allowance, for iron castings produced by automatic moulding lines, moulding machines, lost wax investment casting or die casting processes, it is usually calculated as 2-3mm. If the machining allowance is too small, it will affect the machining, and if it is too large, it will increase the cost of the rough casting.
As for hand-made green sand castings and resin sand castings, the machining allowance is 3 to 6 mm. Because these two casting processes will cause more surface defects and larger dimensional tolerances.
For large castings, such as those larger than 500mm or larger than 200kg, sufficient machining allowance (for example, 6 to 10mm) should be considered to eliminate surface defects and dimensional deformation factors.