Three Considerations to Determine Injection Molding Machine Size

Newsletter, Random Clues

1)  Do the mold dimensions fit between the machine tie bar spacing and within the platen?

2)  Is the machine clamp tonnage sufficient?  Calculate estimated machine clamp tonnage by multiplying the part’s projected surface area by the clamping force factor for the specified plastic material.  This simple calculation is a good rule of thumb, but other factors may need to be considered including material viscosity, wall thickness, length of flow, and quantity/location/size of gates.

3)  Does the shot size fall within 40-80% of the barrel capacity?  Make sure to convert the injection unit barrel capacity based on the specific gravity of polystyrene (PS=1.04) to the specific gravity of the plastic material being used in the part.  Heat sensitive crystalline materials (eg. acetal) should target the higher end of the barrel capacity while more robust, amorphous materials (eg. polycarbonate) can run toward the lower end of the barrel capacity.