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MEGR 3232
Plastics Design –
Exam 3 Review Notes
Additive Manufacturing • Mold Design
• Draft Angles • Ribs & Gussets • Bosses
• Wall Thickness • Hinges
( 2025–2026 Study Year )
,Table of Contents
MEGR 3232 Exam 3 Review Notes (2025–2026 Study Year)
__________________________________________________________
[ 1 ] Additive Manufacturing & DDM Overview
● Direct Digital Manufacturing (DDM)
● CAD → Machine → Finished part
● FDM, SLA, SLS, DMLS
● Why additive manufacturing matters
● New design freedom
[ 2 ] Benefits of Additive Manufacturing
● Faster time to market
● No tooling
● Low upfront cost
● Easy customization
● Free iterations
● Ideal for low‐volume production
[ 3 ] Limitations of Additive Manufacturing
● Anisotropy (weak between layers)
● Layer lines
● Cost per part vs volume
● When molding becomes cheaper
[ 4 ] Industrial Applications
● Automotive
● Aerospace
● Space
● Medical (hearing aids, dental, prosthetics)
● Custom consumer products
● Strong metal parts (DMLS)
,[ 5 ] Additive Manufacturing for Tools
● Jigs & fixtures
● Short‐run molds
● Conformal cooling
● Complex tooling geometries
● AM‐based molding processes
[ 6 ] Plastic Part Design Fundamentals
● Part features vs assembly features
● Strength & stability
● Nominal wall thickness
● Rounds & fillets
● Ribs & gussets
● Bosses
● Snap fits & alignment features
[ 7 ] Machined Parts: Material Removal
● Minimize removal
● Avoid unnecessary machining
● Exposed surfaces = cost drivers
[ 8 ] Thick Molded Parts & Cooling Problems
● Slow cooling
● Uneven shrinkage
● Sink marks
● Warpage
● Use ribs instead of thick mass
[ 9 ] Mold Opening Direction & Side Actions
● Material removal relative to pull direction
● When side actions are required
● Why side actions increase cost
[ 10 ] Hollow Parts & Moldability
● Why fully hollow parts cannot be injection molded
● Alternatives (rotational molding)
, [ 11 ] Multiple Pull Directions
● Features facing different directions
● Side pulls
● Simplifying geometry for mold release
[ 12 ] Draft Angles
● Why draft is required
● Minimum draft (0.5° per side)
● Multiple pull directions = multiple draft directions
[ 13 ] Nominal Wall Thickness
● Cardinal rule: uniform thickness
● Max variation: 20%
● Recommended thickness (amorphous vs crystalline)
● Structural foam & gas‐assist for thick parts
[ 14 ] Equivalent Stiffness & Geometry
● Steel vs aluminum vs nylon
● Geometry changes to match stiffness
● EI equivalence
[ 15 ] Wall Thickness Problems: Racetracking & Air Traps
● Thin areas = fast flow
● Thick areas = slow flow
● Weld lines
● Air traps
● Correct vs incorrect designs
[ 16 ] Flow Leaders & Thickness Variation
● When racetracking is useful
● Filling large thin parts
● Guiding flow intentionally
[ 17 ] Coring
● Removing material inside thick areas
● Reducing sink, warpage, cooling time
● Saving material
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MEGR 3232
Plastics Design –
Exam 3 Review Notes
Additive Manufacturing • Mold Design
• Draft Angles • Ribs & Gussets • Bosses
• Wall Thickness • Hinges
( 2025–2026 Study Year )
,Table of Contents
MEGR 3232 Exam 3 Review Notes (2025–2026 Study Year)
__________________________________________________________
[ 1 ] Additive Manufacturing & DDM Overview
● Direct Digital Manufacturing (DDM)
● CAD → Machine → Finished part
● FDM, SLA, SLS, DMLS
● Why additive manufacturing matters
● New design freedom
[ 2 ] Benefits of Additive Manufacturing
● Faster time to market
● No tooling
● Low upfront cost
● Easy customization
● Free iterations
● Ideal for low‐volume production
[ 3 ] Limitations of Additive Manufacturing
● Anisotropy (weak between layers)
● Layer lines
● Cost per part vs volume
● When molding becomes cheaper
[ 4 ] Industrial Applications
● Automotive
● Aerospace
● Space
● Medical (hearing aids, dental, prosthetics)
● Custom consumer products
● Strong metal parts (DMLS)
,[ 5 ] Additive Manufacturing for Tools
● Jigs & fixtures
● Short‐run molds
● Conformal cooling
● Complex tooling geometries
● AM‐based molding processes
[ 6 ] Plastic Part Design Fundamentals
● Part features vs assembly features
● Strength & stability
● Nominal wall thickness
● Rounds & fillets
● Ribs & gussets
● Bosses
● Snap fits & alignment features
[ 7 ] Machined Parts: Material Removal
● Minimize removal
● Avoid unnecessary machining
● Exposed surfaces = cost drivers
[ 8 ] Thick Molded Parts & Cooling Problems
● Slow cooling
● Uneven shrinkage
● Sink marks
● Warpage
● Use ribs instead of thick mass
[ 9 ] Mold Opening Direction & Side Actions
● Material removal relative to pull direction
● When side actions are required
● Why side actions increase cost
[ 10 ] Hollow Parts & Moldability
● Why fully hollow parts cannot be injection molded
● Alternatives (rotational molding)
, [ 11 ] Multiple Pull Directions
● Features facing different directions
● Side pulls
● Simplifying geometry for mold release
[ 12 ] Draft Angles
● Why draft is required
● Minimum draft (0.5° per side)
● Multiple pull directions = multiple draft directions
[ 13 ] Nominal Wall Thickness
● Cardinal rule: uniform thickness
● Max variation: 20%
● Recommended thickness (amorphous vs crystalline)
● Structural foam & gas‐assist for thick parts
[ 14 ] Equivalent Stiffness & Geometry
● Steel vs aluminum vs nylon
● Geometry changes to match stiffness
● EI equivalence
[ 15 ] Wall Thickness Problems: Racetracking & Air Traps
● Thin areas = fast flow
● Thick areas = slow flow
● Weld lines
● Air traps
● Correct vs incorrect designs
[ 16 ] Flow Leaders & Thickness Variation
● When racetracking is useful
● Filling large thin parts
● Guiding flow intentionally
[ 17 ] Coring
● Removing material inside thick areas
● Reducing sink, warpage, cooling time
● Saving material
