Injection Molding

Injection MoldingProcess Description ver. 1

ME 4210: Manufacturing Processes and Engineering Prof. J.S. Colton

1

Overview • Equipment • Process


2

Equipment Clamp

Mold

Barrel Hopper


3

Equipment


4

Machine schematic


5

Mold


6

Mold


7

Modular molds


8

Mold schematic


9

Mold runner

sprue

cavity

gate

sprue

nozzle

front

ejection pin

side


10

Process


11

Process • Pellets placed in hopper • Pellets fall into barrel through throat • Pellets packed to form solid bed – air forced out through hopper

• Pellets melted by mechanical shear between barrel and screw


12

Process • Melted plastic forms shot in front of screw – screw moves back as plastic moves forward (reciprocating screw)


13

Process • Screw moves forward to inject plastic into mold cavity

• Part cools and solidifies – next shot is made


14

Process • Mold opens • Ejection pins move forward to eject part

• Mold closes • Process starts again


15

Solid bed • Pellets crushed together • Air ejected


16

Melting zone • Solid bed melted by mechanical shear barrel

secondary mixing flow

screw flight solid bed


17

Homogenization zone • Melted polymer is homogenized thermally and color-wise.


18

Injection pressure • Typically 15,000 psi • Ranges from 3,000 to 40,000 psi • Hydraulic pressure is about 10x less


19

Process time Open and eject part

Close mold Injection

1

33 35

5

Pack and hold Part cooling

15


20

Pressure history Cycle time

Part ejection

Cooling

Pack

Gate freeze off

25

Injection

50 Fast closing

Cavity pressure (MPa)

Mold closed time

0 0

5

15

33 35

Time (s) ME 4210: Manufacturing Processes and Engineering Prof. J.S. Colton

21

Temperature history Cooling Part ejection

gate Pack

Gate freeze off

100

Injection

part Fast closing

Temperature (oC)

200

0 0

5

15

33 35

Time (s) ME 4210: Manufacturing Processes and Engineering Prof. J.S. Colton

22

Gates and freeze-off

Filling & Packing

Cooling


23


24

Injection Molding

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