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DRAGON INNOVATION, INC.
!
DESIGN	
  FOR	
  MANUFACTURING	
  
!
COURSE 5: INJECTION MOLDING
!
!
!
!
!
!
!
SCOTT N. MILLER |...
•Overview
•Molding Process
•Part Design
•Materials
•Techniques
•Shot Nomenclature
•Tooling Fabrication
AGENDA
Overview
Recommended References
www.matweb.c
om
Typical Engineering Molded Parts (Examples)
• Housings / Brackets
• Transmissions
• Joints
Injection Molding Advantages
• Supports highly integrated design - Complex geometry
and fine details possible
• Low part co...
Injection Molding Disadvantages
• High tooling costs and long lead-times
• Difficult to make changes
• Large undercuts are...
Molding Process
Molding Cycle
1. Melt Shot
2. Clamp and Fill
3. Pack (Gate Freeze)
4. Cool
5. Eject
Molding Process
Three Plate Mold
Part Design
Temp and Pressure
12k psi @
440F
Shrinkage
Design Guidelines
• Design for 2mm uniform wall thickness (0.5mm –
6mm).
• Ribs 80% wall thickness.
• Draft depends on tex...
Part Features
Use 2mm Uniform Wall Thickness
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Uniform Wall Thickness, con’t
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Gusset Bosses & Avoid Shrink Marks
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Draft Overview
Reference: http://www.diecastingdesign.org/design/basic/draft/
Use at 0.5 - 1.0 Degree Draft Angle (depends on texture)
Avoid Penetrations and Weld Lines
???
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Avoid Undercuts if Possible
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Avoid Undercuts if Possible
Lifter (Undercut)
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Screw Bosses
No Flatheads!
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Use Shut-Offs Instead of Slides
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Use Shut-Offs con’t
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Integrate Joint into Parts
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Living Hinge
Hide Rib Shrink Marks
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Materials
Materials
•Thermoplastic polymers (95%). Can go through molding
cycle many times (i.e. similar to ice). No chemical bonds
...
Materials, con’t
•Additives
- Enhance a specific property (UV, stiffness, color,
flame retardants, etc). All have side effec...
Example: Chi Mei Polylac PA-747
http://www.matweb.com/
Resin Comparison
Resin Use
Yield
(MN/m2)
Modulus
(MN/m2)
Heat Deflect
(1.8 MPa : C)
Cost
($/kg)
Shrink
(cm/cm)
ABS Housings...
Techniques
Use Moldflow Simulation
Use a clear shot to see mechanism (ABS -> PC)
Other Techniques
• Steel Safe Design
• Add additional ribs after first shots
• Use Inserts around change areas
• Review mol...
Other Types of Molding
• Co-Injection / Overmolding (toothbrush)
• Gas Assist
• Low pressure (EE)
Calc Molding Size
• Assume holding 2 - 5 tons / sq. in
• Assume 50% cavity pressure lost due to friction
• Calc surface ar...
Shot Nomenclature
Shot
Shot Nomenclature
Shot Nomenclature
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Shot Nomenclature, con’t
Tooling Fabrication
Tool Shop
EDM
Open Tools
Polishing
Finished Tools
Questions?
dragon@dragoninnovation.com
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Design for Manufacturing - Class 5 - Injection Molding

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Lecture five in the Design for Manufacturing Course focuses on one of Scott’s favorite topics: Injection Molding. It’s really the core of the mechanical system for the hardware products built today. This lecture will cover a brief overview of injection molding, how the actual process works, and then spend time on part design. There’s really a unique series of design constraints that you want to follow in terms of best practice to make the best use of this process.

Read more on this course: http://blog.dragoninnovation.com/2014/07/25/dfm-course-5-injection-molding/

Learn more about Design for Manufacturing: http://blog.dragoninnovation.com/category/design-for-manufacturing-course/

About Dragon Innovation

Dragon Innovation works with entrepreneurs to launch hardware products and scale companies. Founded by a team of hardware experts, Dragon provides a clear path from prototype through production with unmatched manufacturing expertise and trusted connections. Dragon's client roster includes Coin, MakerBot, LIFX, Scout, Romotive, Sifteo, Orbotix, FormLabs and over 100 more companies paving the road for how new technology gets made.

Connect with Dragon Innovation

Website: http://www.dragoninnovation.com
Blog: http://blog.dragoninnovation.com
Twitter: http://twitter.com/dragoninnovate
Slideshare: http://www.slideshare.net/dragoninnovation

Published in: Technology
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Design for Manufacturing - Class 5 - Injection Molding

  1. 1. DRAGON INNOVATION, INC. ! DESIGN  FOR  MANUFACTURING   ! COURSE 5: INJECTION MOLDING ! ! ! ! ! ! ! SCOTT N. MILLER | CEO | @DRAGONINNOVATE | WWW.DRAGONINNOVATION.COM
  2. 2. •Overview •Molding Process •Part Design •Materials •Techniques •Shot Nomenclature •Tooling Fabrication AGENDA
  3. 3. Overview
  4. 4. Recommended References www.matweb.c om
  5. 5. Typical Engineering Molded Parts (Examples) • Housings / Brackets • Transmissions • Joints
  6. 6. Injection Molding Advantages • Supports highly integrated design - Complex geometry and fine details possible • Low part cost • High volume production • Wide range of thermoplastic materials and fillers • Wide range of sizes • Low scrap rate • High reproducibility & Reasonable tolerances • Little post production required • Good surface finish • Can be fully automated • Reduces piece count • Simplifies assembly
  7. 7. Injection Molding Disadvantages • High tooling costs and long lead-times • Difficult to make changes • Large undercuts are difficult • Requires nearly uniform wall thickness • Limited to Thermoplastic materials • Cannot produce very large parts as a single piece.
  8. 8. Molding Process
  9. 9. Molding Cycle 1. Melt Shot 2. Clamp and Fill 3. Pack (Gate Freeze) 4. Cool 5. Eject
  10. 10. Molding Process
  11. 11. Three Plate Mold
  12. 12. Part Design
  13. 13. Temp and Pressure 12k psi @ 440F
  14. 14. Shrinkage
  15. 15. Design Guidelines • Design for 2mm uniform wall thickness (0.5mm – 6mm). • Ribs 80% wall thickness. • Draft depends on texture and resin. Assume 0.5 deg. • Use rounds and fillets. No sharp edges except parting line. • Shoot for planar parting line if possible. • Tolerance is a function of the resin, part geometry and mold construction. • ABS: +/- 0.1mm • ABS Hole: +/- 0.05mm up to 6mm diameter. • Surface Finish: SPI A-1 Grade 3: 6000 Grit Diamond Reference: Product Design for Manufacture and Assembly. Geoffrey Boothroyd,, Peter Dewhurst and Winston Knight.
  16. 16. Part Features
  17. 17. Use 2mm Uniform Wall Thickness Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  18. 18. Uniform Wall Thickness, con’t Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  19. 19. Gusset Bosses & Avoid Shrink Marks Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  20. 20. Draft Overview Reference: http://www.diecastingdesign.org/design/basic/draft/
  21. 21. Use at 0.5 - 1.0 Degree Draft Angle (depends on texture)
  22. 22. Avoid Penetrations and Weld Lines ??? Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  23. 23. Avoid Undercuts if Possible Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  24. 24. Avoid Undercuts if Possible
  25. 25. Lifter (Undercut) Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  26. 26. Screw Bosses No Flatheads! Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  27. 27. Use Shut-Offs Instead of Slides Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  28. 28. Use Shut-Offs con’t Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  29. 29. Integrate Joint into Parts Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  30. 30. Living Hinge
  31. 31. Hide Rib Shrink Marks Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  32. 32. Materials
  33. 33. Materials •Thermoplastic polymers (95%). Can go through molding cycle many times (i.e. similar to ice). No chemical bonds between strands. •Thermosets (5%). Chemical react during process to form cross linked polymer chains. Irreversible. Excellent creep, dimensional stability, temperate and chemical resistance. Ex: phenolics and epoxies.
  34. 34. Materials, con’t •Additives - Enhance a specific property (UV, stiffness, color, flame retardants, etc). All have side effects. - Add chopped fiber (up to 30% volume). Strength and stiffness, lose on impact, abrasion and tool live (cut down to 1/3). Properties approaching metal. •Need to operate below 250C (400C max) •Low specific gravity (0.8 - 1.8) Steel = 7. Strength to weight ratio good. Automotive. •Some materials are transparent. •Very sensitive to changes in temperature (vs steel) •Good electrical insulation
  35. 35. Example: Chi Mei Polylac PA-747 http://www.matweb.com/
  36. 36. Resin Comparison Resin Use Yield (MN/m2) Modulus (MN/m2) Heat Deflect (1.8 MPa : C) Cost ($/kg) Shrink (cm/cm) ABS Housings 39 1,800 86 $2.09 0.004 PC Lenses 65 2,400 128 $2.81 0.007 POM Gears 65 2,800 105 $1.48 0.02 Polyamid e Strength 123 2,750 65 $3.63 0.013 PP Food 36 1,380 93* $1.76 0.015 Aluminu m 276 68,900 $1.75 Steel 435 205,000 $0.39 http://www.matweb.com/ http://www.nhh.com.hk/eng/trading/price_trend.asp
  37. 37. Techniques
  38. 38. Use Moldflow Simulation
  39. 39. Use a clear shot to see mechanism (ABS -> PC)
  40. 40. Other Techniques • Steel Safe Design • Add additional ribs after first shots • Use Inserts around change areas • Review mold drawings carefully. Watch out for cooling lines.
  41. 41. Other Types of Molding • Co-Injection / Overmolding (toothbrush) • Gas Assist • Low pressure (EE)
  42. 42. Calc Molding Size • Assume holding 2 - 5 tons / sq. in • Assume 50% cavity pressure lost due to friction • Calc surface area of combined parts and runners • Look up injection molding pressure (ABS = 1k bar) • Calculate cavity pressure (Molding Pressure * 0.5) • Calculate Tonnage: F = P * A
  43. 43. Shot Nomenclature
  44. 44. Shot
  45. 45. Shot Nomenclature
  46. 46. Shot Nomenclature Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
  47. 47. Shot Nomenclature, con’t
  48. 48. Tooling Fabrication
  49. 49. Tool Shop
  50. 50. EDM
  51. 51. Open Tools
  52. 52. Polishing
  53. 53. Finished Tools
  54. 54. Questions?
  55. 55. dragon@dragoninnovation.com

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