Injection Molding Machine
Projected area is the area that the part and runner system cover when viewed perpendicular to the mold parting plane. It is not the real surface area of the part but its shadow in the mold opening direction. It is the basic input of the clamping force calculation: if the same part is laid on its side and placed in the mold, the projected area — and so the required tonnage — changes.
Part designers often confuse "surface area" and "projected area". Think of a deep bucket: its surface area is large, but viewed from the mold opening direction only the area of its circular opening is seen. The force trying to open the mold acts only on this projection.
In multi-cavity molds, the projections of all the cavities and of the runner channels are added together. In a hot runner mold the runner share is very small; with a cold runner it can reach 10–20% of the part.
A worked example: a 200 × 150 mm rectangular lid gives a projection of 20 × 15 = 300 cm² per cavity. In a four-cavity mold that is 1,200 cm², and with a 15% allowance for the cold runner the total becomes 1,380 cm². For polypropylene the cavity pressure factor is 0.40 ton/cm², and the multiplier for a part of standard wall thickness is 1.00: 1,380 × 0.40 = 552 tons as the raw value. When a 15% safety margin is added on top, a 635 ton machine is needed.
The factor changes with the material and the wall thickness of the part. If the same mold ran with ABS, the factor would be 0.50 instead of 0.40 and the required tonnage 793.5 instead of 635; for a thin-walled packaging part the multiplier rises to 1.35 because of flow resistance. Glass fiber reinforcement also raises the tonnage. That is why, even if the projected area is measured correctly, the tonnage decision cannot be made without knowing the material and wall thickness.
Yes. The 3D file analysis tool on the site processes the STL file in the browser, calculates the silhouette projection on three axes and gives the tonnage for the chosen mold opening direction; the file is not uploaded to the server.