Transcription of Injection Molding - Pennsylvania State University
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Injection Molding - Pennsylvania State University
Injection MoldingFigure 1: Principles of Injection Molding cycle:ExtruderMoldPressureInjectPackgate solidifiesExtrudeSolidifypart solidifiesOpen MoldEject PartClose Mold1 Injection Molding2 Injection MoldingECONOMICSI njection Molding machine is itself is expensive - Needmass productionto justify these total number of partsn= number of parts molded in one shott= cycle timeProduction Cost ($/part) = Material Cost+Mold Cost/N+ Molding Machine Cost ($/hr) t/n3 Injection MoldingEJECTIONF igure 2: The molded partcannothave any enclosed curves or the part willnot eject from the mold!4 Injection MoldingTYPES OF GATES5 Injection MoldingTHE Injection Molding WINDOW6 Injection MoldingCENTER-GATED DISKF igure 3: Mold used in conjunction with a constant volumetric flow 4: Position of an advancing flow 1 - Flow in the RunnerQ= R20dz(t)dtz(t) =Q R20tPressure builds during filling of the runner, given by the Hagen-PoiseuilleLaw:Pi(t) =8 Q R40z(t) =8 Q2 2R60t7 Injection MoldingCENTER-GATED DISKAtt=t0, the runner is filled (z=Lr)t0= R20 LrQPi(t0) =8 QLr R40 Fort>t0, the runner is full and the pressure drop along the runner isalways constant: Pr=Pi P0=8 QLr R40 Part 2 - Flow in the disk cavityFigure 5: Position of the advancing front in the disk indicated byR (t).
Injection Molding CENTER-GATED DISK At t = t 0, the runner is filled (z = L r) t 0 = πR2 0 L r Q P i(t 0) = 8µQL r πR4 0 For t > t 0, the runner is full and the pressure drop along the runner is always constant: ∆P r = P i −P 0 = 8µQL r πR4 0 Part 2 - Flow in the disk cavity
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