Thermoplastic Injection Molding

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Thermoplastic InjectionMolding

• An Overview

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Injection Molding

• Topics to be Covered
• Part Design
• Tooling Design
• Machine

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Part Design

• Constant Wall Thickness
• Nonuniform cooling leads to problems of voids,
  warpage and sink
• Radius Corners
• Improves plastic flow
• Reduce stress concentration
• Draft Angles
• Slight angle on walls perpendicular to parting
  line

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Part Design

• Shrinkage
• Amount part will reduce in size as it cools to
  room temperature
• Plastic dependent

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Tooling Design

• Mold Plates
• Ear Plates
• Ejector Pin Plates
• Mold Pins
• Sprue
• Runner
• Gate
• Vent

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Machine

• Process Cycle
• Polymer pellets fed into cylinder
• Plasticate in cylinder
• Inject polymer into mold
• Cool part
• Eject part

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Machine

• What happens in barrel?
• Conveying
• Compaction
• Melt film formation
• Melt pool formation
• Melting complete

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Machine

• Process Parameters
• Screw speed
• Injection speed
• Injection pressure
• Back pressure
• Shot size
• Barrel temperature
• Mold temperature
• Cooling time

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Machine

• Projected Area Press Capacity
• Includes mold cavity and runner system
• 2 to 2.5 tons per square inch of projected area

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