Must Know

This course provides a focused overview of the material, part-design, tooling, and molding considerations that have the greatest influence on plastic component quality and reliability. It emphasizes the interactions engineers need to recognize when designing a component and working with mold builders, processors, and manufacturing personnel.

Core Topics

• Material behavior and selection
• Plastic-specific part-design considerations
• Designing the part for molding and tooling
• Mold design features that influence part quality
• Tooling options for difficult part geometry and insert molding
• Critical molding-process variables

Detailed Course Outline

1. Material Behavior and Selection
   • Application loads, temperature, time, and environmental conditions
   • Material properties at use temperatures and extremes
   • Creep and time-dependent material behavior
   • Moisture effects on properties and dimensions
   • Chemical resistance and environmental stress cracking
   • UV exposure and stabilizer limitations
   • Mold shrinkage and material-related dimensional variation
2. Plastic Part Design
   • Equivalent stiffness when converting metal designs to plastic
   • Increasing section modulus through geometry
   • Uniform wall thickness
   • Coring thick sections
   • Rib design
   • Fillets and corner design
   • Sink marks and cosmetic considerations
   • Weld lines and their effect on strength and appearance
3. Designing the Part for Molding
   • Realistic molded-part tolerances
   • Environmental effects on finished dimensions
   • Wall thickness and its effect on filling pressure
   • Draft requirements
   • Undercuts
   • Thin and fragile mold-steel conditions
   • Parting-line location
   • Gate location and gate vestige
   • Functional and cosmetic surfaces requiring special consideration
4. Mold Flow and Fill Considerations
   • Relationship between wall thickness and material flow
   • Using geometry to improve filling
   • Runner and gate effects on fill pattern
   • Balancing fill patterns
   • Predicting weld-line locations
   • Using mold-flow analysis as an engineering tool
   • Recognizing the assumptions and limitations of mold-flow analysis
5. Part and Tool Design Interaction
   • Reviewing the part design from the mold builder's perspective
   • Identifying geometry that creates difficult or fragile tooling
   • Evaluating parting-line options
   • Evaluating gate locations
   • Protecting sealing and other critical functional surfaces
   • Designing areas likely to require future modification or repair
   • Considering tool size, complexity, weight, cost, and maintainability during part design
6. Basic Mold Tool Design
   • Mounting and machine-interface requirements
   • Getting material to the cavities
   • Runner and gate design
   • Allowing trapped gases to escape
   • Producing the required component geometry
   • Compensating for material shrinkage
   • Cooling the molded component
   • Ejecting the finished part
   • Selecting appropriate mold steels
7. Venting and Part Quality
   • Venting runners and last-to-fill locations
   • Perimeter venting
   • Material-specific vent requirements
   • Trapped gas and incomplete filling
   • Dieseling and material burning
   • Venting below the parting line
   • Using inserts and moving features to maintain difficult vents
8. Tooling Difficult Geometry
   • Straight-pull tooling where possible
   • Telescoping shutoffs
   • Slides
   • Lifters
   • Core pulls
   • Rotating cores
   • Retractable pins
   • Holding inserted components during mold filling
   • Managing witness lines and sealing requirements
9. Cooling and Process Monitoring
   • Uniform cavity and core cooling
   • Cooling-line placement and flow
   • Turbulent coolant flow
   • Scale buildup and heat-transfer loss
   • Effect of cooling rate on dimensions and material properties
   • Cavity-pressure monitoring
   • Process fingerprinting
10. Critical Molding-Process Variables
    • Repeatable cavity conditions
    • Material moisture content
    • Melt temperature
    • Barrel residence time
    • Volumetric fill rate
    • Shear and nonlinear viscosity effects
    • Mold temperature and cooling rate
    • Pack pressure and pack time
    • Overall cycle time
11. Putting the System Together
    • Understanding how material, part design, mold tooling, and process interact
    • Recognizing design decisions that create downstream tooling or processing problems
    • Working effectively with mold builders and molding personnel
    • Addressing problems at their source rather than compensating for them downstream
    • Using the complete system to produce a reliable plastic component

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