Injection Molding Pennsylvania State University（注塑宾夕法尼亚州立大学）.pdf

Injection Molding Figure 1: Principles of injection molding. Injection molding cycle: Extruder Mold Pressure Inject Pack gate solidifies Extrude Solidify part solidifies Open Mold Eject Part Close Mold Injection Molding Injection Molding ECONOMICS Injection molding machine is expensive. Mold itself is expensive - Need mass production to justify these costs. N = total number of parts n = number of parts molded in one shot t = cycle time Production Cost ($/part) = Material Cost +Mold Cost/N +Molding Machine Cost ($/hr) ∗ t/n Injection Molding THE INJECTION MOLDING WINDOW Injection Molding PACKING STAGE When the mold is full, flow stops, so there is no longer a pressure drop. Pressure P ∗ is used to pack the mold. Packing pressure must be maintained until the gate solidifies. Clamping force to hold mold closed: ∗ ∗ R 2 ∗ F = P dA = 2πP rdr = πR P A 0 General Result F = P ∗A Example: Typical packing pressure P ∗ = 108 Pa for a total area of 2 ∗ 7 A = 0.1 m . Clamp force F = P A = 10 Nt= 1000 tons. This is why injection molding machines are so large. They have to keep the mold closed! Injection Molding SIZING AN INJECTION MOLDING MACHINE ∼ 8 Packing pressure = 10 Pa Clam