How to Calculate Shot Size in Injection Moulding Machine?

Shot Capacity is the maximum volume/weight of material that the screw can inject into one operation cycle. The shot capacity is also known as "Injection Capacity".

The shot weight of a product is the amount of material required to be injected into the mold to manufacture the product, including the feed system. While calculating the shot weight, the actual product, spruce, runner, gates, etc., are considered.

Shot weight is always lesser than the shot capacity. It is dependent on factors like material density, machine screw diameter. Maximum dosing also plays a part in determining the maximum shot weight of the machine.

The backward/refilling position in the barrel to fill the given shot weight is called "injection stroke" or shot size.

To calculate the shot size in injection molding, we should know the density of the raw material if we are using a high heat and high flow raw material with its density of 1.52g per cube centimeter. Then, we need the diameter of the screw. Let's take it as 28 mm, or 2.8 cm. Let's assume we have a shot weight of 40.6 gms. Thus, we can calculate volume as mass/density, which will be (40.6/1.52)= 26.71 cube centimeters. To calculate the injection stroke or shot size, we can put all values in the formula of shot volume, i.e., Shot Volume = π x r2 x Shot Size.

Shot Size = Shot Volume / π x r2    (where, r = radius of the screw)

Here, r=1.4 and shot volume is 26.71 cm^3. By putting all values in the formula, the shot size will come out to be 43.41 mm.

In the case of family molds, shot size can be calculated by considering the total number of cavities and each part's weight and applying the above principles.

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