Injection Molding

Injection MoldingProcess Description ver. 1

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

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Overview • Equipment • Process

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

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Equipment Clamp

Mold

Barrel Hopper

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

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Equipment

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

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Machine schematic

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

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Mold

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

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Mold

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Modular molds

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

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Mold schematic

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

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Mold runner

sprue

cavity

gate

sprue

nozzle

front

ejection pin

side

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

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Process

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

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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

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

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

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

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Process • Screw moves forward to inject plastic into mold cavity

• Part cools and solidifies – next shot is made

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

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

• Mold closes • Process starts again

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

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Solid bed • Pellets crushed together • Air ejected

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

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Melting zone • Solid bed melted by mechanical shear barrel

secondary mixing flow

screw flight solid bed

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

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

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

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

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

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Process time Open and eject part

Close mold Injection

1

33 35

5

Pack and hold Part cooling

15

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

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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

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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

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Gates and freeze-off

Filling & Packing

Cooling

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