Calculating the casting weight is important for the proper operation of every foundry, even a small and completely hobby one. After all, when choosing a material for your foundry project, you need one that will fit your budget while also fulfilling the functions appropriate for its intended purposes.
Thus, when selecting material, several factors must be taken into account, such as its strength, corrosion resistance or ductility, and then, based on these, the estimated load of the casting should be calculated, as it affects many issues - from manufacturing costs to the later usability of the elements, which may also be affected by their mass.
Do you want to learn how to precisely select the best material for your casting? Read the following article: How to choose the casting material?.
Foundries must calculate the estimated weight of the casting already during the quotation process, because weight is a factor that has a significant impact on the final cost of the project. The price of castings varies depending on the weight of the materials used to create specific elements.
This means that the valuation is based on the estimated weight, not the actual weight of the finished casting product.
To do a calculation to determine the estimated weight of the casting, you need to know a few details.
Before we get to them, it is worth mentioning that already at the calculation stage, you can also take into account the appropriate allowance needed for machining all elements.
To calculate the weight of individual elements of the casting, you need its detailed dimensions. These are primarily:
Depending on the shape of the casting, you may also need other dimensions, such as diameter (e.g. in the case of shafts and round bars), or cross-sectional area (when it has an irregular shape).
These data allow you to calculate the volume of the casting necessary to calculate its weight. However, the volume is best calculated using a computer-aided design program such as AutoCAD.
Another unit of measurement needed to calculate the weight of the casting is the density of the metal or alloy, i.e. the mass divided by the volume unit. For example, if the material has a density of 7.5 g/cm3, this means that there are 7.5 grams of mass in each cubic centimeter of the material.
To determine the density of the metal or alloy under consideration, use the density table. It is worth bearing in mind that some metals and alloys come in different grades, each of them having different density. For example, the density of stainless steel varies from 7.7 to 8 g/cm3, depending on the grade.
For example:
The density of cast iron marked EN-GJL-200 is: approx. 6.8 g/cm3
The density of hadfield cast steel marked L120G13 is: approx. 7.9 g/cm3
Density of nodular cast iron with designation EN-GJS-500-7 is: 7.15 g/cm3
It should be noted that each calculation - both from the on-line calculator and made independently with the help of these numbers - is only an estimate. Those are calculated based on nominal dimensions and standardized densities. In practice, the actual load of the metal or alloy from which the object will be made, may differ from the estimated weight due to differences in tolerances and composition observed during production.
Once you know the necessary dimensions, you can calculate the weight of the raw casting using the following formula.
Qrc = V x γ [kg]
where:
To get the weight of the metal or alloy, multiply the volume of the object by the density of the alloy. Then, to convert weight to kilograms, you need to divide the result of the product by 1000.
To calculate the weight of the casting with the allowance, use the following formula:
Qc = Qrc x k [kg]
where:
- 1.2 - for gray cast iron,
- 1.3 ÷ 1.5 - for malleable and nodular cast iron,
- 1.6 ÷ 1.8 - for cast steel,
- 1.3 ÷ 1.6 - for brasses and bronzes.
The estimated weight of the casting can also be calculated with the help of the aforementioned on-line calculators, in which one can select the type of material for the casting and enter the dimensions and desired shape.
Do you want to count it online? Check out this calculator:
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