View Full Version : Injection Machine Tonnage Calculation

11-02-2008, 10:39 AM
How do you calculate what tonnage machine to use and the volume of ABS materials. Let make the calculate easy, let start with the mold with 36 cavities and each cavity is 2" x 2" x 0.3"

So from the above calculation I get 43.2 cubic inches of ABS. Am I right, so what is the tonnage and weight of ABS. The injection machines usually listed tonnage and weight of material. What size of machine should be able inject this sample products.


11-02-2008, 01:13 PM
The tonnage is going to be based on two factors, the injection pressure and the cross sectional area at the parting plane. you will have to include your runners and sprue in the cross section calculations. This will give the bare minimum tonnage needed to hold the dies together, depending on how controlled the injection pressure is you'll most likely want to allow for a little variation and go with a bigger capacity. As for weight of the material just lookup the density and go from there, again be sure to include the volume of the runners and the sprue.

11-02-2008, 05:40 PM
Thanks for the information Rkremser, every cavities are very close together. So the total mold area is 12.5" x 12.5"

Where do you lookup the density of particular plastics like ABS, PVC?


Jim G
11-24-2008, 01:19 PM
As was said before,
you need to know the total surface area of part/runners on the parting line of the mold.

Multiply that by 15,000psi and divide by 2000lbs/ton.
This will give you an approximate clamp tonnage.
(note) Some machines can inject at up to 30,000psi which would
require a higher clamp tonnage.

This should give you a good reference though.

The specific gravity of ABS is ~ 1.04-1.25 depending on grade and fillers.

12-24-2008, 11:48 AM
As a general rule of thumb you use 2-5 tons per square inch of projected area. The projected area is the area of the shadow that would be created if you shine a light on the molded part. High flow materials generally take more clamping pressure.