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Dr. Lou Reifschneider

TEC 315 Injection Mold Design Details Product design influenced by what type of mold can be made economically. Dr. Lou Reifschneider. Mold Design Topics. Basic Function of Molds Mold Nomenclature & Operation Classification Two-plate vs. Three-plate Cold runner vs. Hot runner

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Dr. Lou Reifschneider

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  1. TEC 315Injection Mold Design DetailsProduct design influenced by what type of mold can be made economically. Dr. Lou Reifschneider

  2. Mold Design Topics • Basic Function of Molds • Mold Nomenclature & Operation • Classification • Two-plate vs. Three-plate • Cold runner vs. Hot runner • Cavitation: single, multiple, family • Ejection Mechanisms • Gate Designs • Venting the mold - avoid gas traps

  3. Tasks of the Injection Mold • Distribute the melt from nozzle to cavity - sprue, runner, gate, (cavity number) • Shape part - cavity design (cores, side actions,…) • Cool molten resin - uniformly, quickly • Eject the part - reliably, without part damage 1 of 2

  4. Additional Tasks for Mold • Withstand molding forces - no deflection - maintain cavity shape • Maintain mold half alignment - no mismatch - insures cavity shape • Guide moving parts of mold - no binding - side actions, stripper plates, twist-off 2 of 2

  5. Cooling Lines Basic Mold Components Sprue Bushing Top Clamp Plate Locator Ring Cavity, A Leader Pin & Bushing Core, B Core Support Plate Return Pin & Spring Parallel KO Pin Ejector Retainer Plate Pillar Sprue Puller Ejector Plate 2 Plate Mold Bottom Clamp Plate Knockout Bar

  6. Mold Nomenclature (1/4) • Top Clamping Plate, “A support plate” holds “A” side to stationary platen • Locating Ring, ‘Sprue Bushing Retainer Ring’ locates mold to wrt stationary platen • Cavity Retainer plate, “A plate” defines cavity features, holds leader pins • Core Retainer plate, “ B plate” forms parting line, defines core features • Support Plate, “B support plate” keeps B plate from bending, aligns ejectors

  7. Mold Nomenclature (2/4) • Bottom Clamping Plate, “ Ejector Box Base” holds ejection system to movable platen • Parallels, “Ejector Box Rails” bridge betw B support and Ejector Box Base • Ejector Retainer Plate keeps ejector pins traveling with ejector plate, counter sunk for ejector pins • Ejector Plate linkage betw ejector rod and ejector pins

  8. Mold Nomenclature (3/4) • Pillars support betw Ejector Base and B support • Sprue Bushing mating passage from nozzle to mold sprue • Sprue Puller Pin beneath cold well, grabs sprue @ demolding • KO Pin (Knock Out Pin) pushes part out of mold, retracts due to ejector retainer plate

  9. Mold Nomenclature (4/4) • Return Pins, safety pins, ejector return pins forces ejector plate back @ mold closing • Leader Pins, “guide pins” hardened, ground, press fit into A plate -- aligns mold halves • Bushings hardened, ground, press fit into B plate -- bearing surface for leader pin • Cooling Lines passages for water cooling of molten plastic -- location & number affects part warpage

  10. MOLD OPERATION: READY TO OPEN Next Shot Ready Part Beginning to Freeze 2 Plate Mold

  11. MOLD OPERATION: OPEN 2 Plate Mold

  12. MOLD OPERATION: Knock-out Bar Pushes Ejector Plate 2 Plate Mold

  13. MOLD OPERATION: KO Pins retract (due to spring return) 2 Plate Mold

  14. MOLD OPERATION: Mold Closing 2 Plate Mold

  15. MOLD OPERATION: ready for next cycle 2 Plate Mold

  16. MUD: 3-D Section View 2-Plate Mold Sprue Bushing Cavity Plate Leader Pin Blind Pocket Blind Pocket Cooling Line Holes Core Plate Ejector Retainer Plate Return Pin K.O. Pin Holes Ejector Plate Sprue Puller

  17. Classification of Molds • Processed Material - thermoplastic vs. thermoset - cooled mold vs. heated mold • Basic Design - two-plate vs. three-plate, … • Number of Cavities - single, multiple, family 1 of 2

  18. Classification of Molds • Ejector System - pins, stripper plates, lifters, side-actions • Runner System • symmetry (family, H pattern, manifold) • cross-section (round, trapezoid) • cold vs. hot 2 of 2

  19. DME Two Plate Mold 1) top clamping plate2) A plate (cavity)3) B plate (core)4) core support plate5) ejector housing6) ejector retainer plate7) ejector plate8) locating ring9) sprue bushing10) return pins11) sprue puller pin Plastics Engineers Handbook, Fig. 7-3

  20. DME Two Plate Mold with Molded Parts Plastic melt flows throughsprue bushing, then intorunners,then intogatesbefore entering part cavities. Plastics Engineers Handbook, Fig. 7-14

  21. DME Three Plate Mold (alternative) This cup shaped product is best filled from the center.A three plate mold permits gating away from parting plane of mold while still using a cold runner delivery system. Plastics Engineers Handbook, Fig. 7-15

  22. DME Two Plate Mold Insulated Runner This cup shaped product is best filled from the center.To minimize waste, an insulated runner achieves the gating advantage of a three plate mold without the higher cost of a hot runner manifold (next slide). Plastics Engineers Handbook, Fig. 7-16

  23. DME Two Plate Mold Hot Runner Like a three plate mold, a hot runner manifold minimizes waste. Hot tip valves or needle valves achieve better packing control than insulated runners.Hot runner manifold molds are the most expensive of those depicted. Recommended for high volume, special gating applications. Plastics Engineers Handbook, Fig. 7-17

  24. Hot Runner Manifold by DME

  25. Valve GatedHot Runner Manifold by DME

  26. Part Ejection Basics • Draft facilitates ejection of part. • Ejectors placed on moveable half of mold • core features should be on moveable half to promote part sticking to this half, not the stationary half. • Knock Out (KO) pins most common. • Lifters used for undercuts. • Side actions for more severe undercuts. • Cam action or hydraulic

  27. Part Ejection Issues: Draft What is wrong with this part design?

  28. Ejector Pin Design Detail K.O. Land clearance .001”

  29. Part Ejection Issues: Ejector Pin Pads

  30. Part Ejection Issues: Cavity Orientation to Pull

  31. Part Ejection Issues: Undercut and Holes

  32. Part Ejection Issues: Holes Hole size depends upon wall thickness and draft

  33. Part Ejection Issues: External Threads

  34. Cam Actuated Side-Action When mold opens, cam clears undercut, then part ejected. Progressive Components, www.procomps.com

  35. Gating Systems Gating trim method • manual - sprue, tab, disk, spoke, edge • automatic - submarine, banana, pinpoint • automatic - hot drop via hot runner system Cosmetic Concerns? - consider: banana gate or hot drop

  36. Gate Design Rules • Gate location for acceptable weld lines. • Location and size to prevent jetting. • Gate at thickest area of part for maximum effective packing time. • Gate thickness from 50% to 80% wall thickness. Submarine and pin gates ~ 0.03” to 0.08” or 60% of wall thickness. • Fiber filled resins - larger gates. • Start undersized - can always enlarge later.

  37. Gating: Nomenclature

  38. Sprue Gate Sprue Sprue Gate CORE CAVITY

  39. Gating: Disk Gate

  40. Tab Gate Cavity Runner Tab gate Parting Plane

  41. Sub-gate Cavity Runner Sub gate Gate Diameter Knife Edge: Automatic Degating Parting Plane 20° ~45°

  42. “Knife-edge” cuts gate from part during opening Mold opens Part KO Part already detached KO Pins retract & Mold closes Sub-gate Degating Part Subgate KO Pins

  43. Mold Venting Shut off: seals plastic in with clamp pressure Air in cavity must be allowed to escape during injection to avoid defects. Vents are placed at the last points to fill. CORE Sprue Vent gaps vary with resin: PA 0.00075 in PC, ABS 0.0025 in CAVITY Vent: lets air out, not plastic vent gap

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