Runner Volume and Runner Area for Assembly Molding
As with Plastic Molding, Assembly Molding's runner system model is used to calculate to important quantities:
• Runner area: area of the projection of the runners onto the parting plane. This quantity plays a role in the calculation of required clamp force and required shot size, which are used in
Machine Selection for Insert Injection Molding.
• Runner volume: total volume of all runners. This quantity plays a role in the calculation of material utilization and injection time. See
IM Material Utilization in the Plastic Molding chapter and
Insert Injection Molding Formulas.
The section
Runner System Model describes in detail the model of the runner system used by the Plastic Molding process group. The Assembly Molding process group uses the same model, modified to accommodate intra-part, inter-component runners, that is, runners between the plastic Subcomponents of a part.
Compared to runner area as computed for the Plastic Molding process group, runner area for Assembly Molding is greater by the following quantity:
Runner Area Supplement = Number of Cavities *
Inter-component Runner Length Per Part * Inter-component Runner Diameter
And compared to runner volume as computed for the Plastic Molding process group, runner volume for Assembly Molding is greater by the following quantity:
Runner Volume Supplement = Number of Cavities *
Inter-component Runner Length per Part *
* (Inter-component Runner Diameter/2)2
These quantities are a function of the following:
• Inter-component runner length per part: this is the total length of the runners between the subcomponents of given part. It is assumed to be half the length of the diagonal of the part's bounding rectangle (in a plane normal to the draw direction):
Inter-component Runner Length Per Part = sqrt(Part Length2 + Part Width2) / 2
• Inter-component Runner Diameter: the diameter of each inter-component runner is assumed to be the same as the diameter of the runner branch that feeds a single cavity. This value is 25% greater than the part’s Max Thickness (bounded below by the value of the cost model variable minRunnerDia—2.032mm in starting point VPEs).
• Number of cavities: see
Number and Layout of Mold Cavities in the Plastic Molding chapter.
See the formulas for
Runner Area and
Runner Volume in the
Runner System Model section of the Plastic Molding chapter.