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Injection Molding (MIT 2.008x Lecture Slides)
- 1. 2.008x Injection Molding MIT 2.008x Prof. John Hart
- 2. 2.008x
- 3. 2.008x Plastics: 1950-2014 Data from Statista http://www.statista.com/statistics/282732/global-production-of-plastics-since-1950/ 0 50 100 150 200 250 300 350 1950 1960 1970 1980 1990 2000 2010 2020 Volume[millionmetrictons] Year
- 4. 2.008x Adapted from: Figure 1, "Ideas in Motion Control from Moog Industrial" Newsletter Issue 34 © Moog, 2014 In North America and Europe, injection molding is used to process >10 million tons (10 billion kg) of polymers per year Packaging Automotive parts Technical parts Electronics and telecommunications Medical, pharmaceutical, and optical products White goods, construction
- 6. 2.008x An IM machine in the MIT manufacturing shop
- 7. 2.008x Agenda: Injection Molding § Fundamentals of polymers § Mold tooling § Process parameters and equipment § Cycle time, cooling, and shrinkage § Defects and design guidelines § Advanced topics
- 8. 2.008x Injection Molding: 2. Fundamentals of polymers
- 9. 2.008x IM feedstock: polymer pellets
- 11. 2.008x Kalpakjian and Schmid, Manufacturing Engineering and Technology Groover, Fundamentals of Modern Manufacturing Poly (many) + mer (structural unit) -[C2H4]n- = poly[ethylene]
- 12. 2.008x The ‘families’ of materials: modulus vs. density Ashby, Materials Selection in Mechanical Design.
- 13. 2.008x Manufacturing Engineering & Technology (7th Edition) by Kalpakjian, Schmid. © Upper Saddle River; Pearson Publishing (2014). “Giant Dishes.” Daryl Mitchell (CC BY-SA 2.0) via Flikr “Hydraulic seal kit cylinder seals o ring.” Devendra Dave (CC BY-SA 2.0) via Flikr
- 14. 2.008x Polymer network architectures ThermosetThermoplastic (semi-crystalline) (amorphous, linear) (amorphous, crosslinked) à In all cases, the polymer chain length, interactions, bonding influence the part mechanics
- 15. 2.008x What does the polymer ‘feel’ during injection molding? à heat and pressure
- 16. 2.008x What does the polymer ‘feel’ during injection molding? à heat and pressure
- 17. 2.008x J.L. Throne, Technology of Thermoforming
- 18. 2.008x J.L. Throne, Technology of Thermoforming
- 19. 2.008x Kalpakjian and Schmid, Manufacturing Engineering and Technology
- 20. 2.008x Viscosity: resistance to shear *at typical injection shear rate and melt temperature Material Dynamic viscosity Water (room temp) 1×10-3 kg/m-s [Pa-s] Honey 10 Liquid thermoplastic* 102-103 Molten aluminum (600 C) 3×10-3 y U ¶ ¶ = µt Ux(H) = Ux Ux(y) Ux(0) = 0 h Ux x y
- 21. 2.008x Viscosity of polypropylene versus shear rate and temperature From Solidworks Plastics µ = k !γ(n−1) 100 C 250 C Ux(H) = Ux Ux(y) Ux(0) = 0 h Ux x y
- 22. 2.008x Injection Molding: 3. Mold tooling and configurations
- 23. 2.008x Injection molding of LEGO bricks Excerpt from: https://www.youtube.com/watch?v=y1Zhpdx-XtA
- 24. 2.008x The injection molding machine Groover, Fundamentals of Modern Manufacturing
- 25. 2.008x Key features of mold tooling Protomold ‘demo mold’
- 26. 2.008x Video: MIT 2.008 injection molds and machine
- 27. 2.008x An injection molded cap § What features do you notice? § Compare quality to LEGO bricks; what is different? § What do the molds look like (draw the molds)?
- 28. 2.008x
- 30. 2.008x Multi-part / multi-cavity molds Kalpakjian and Schmid, Manufacturing Engineering and Technology
- 31. 2.008x Kalpakjian and Schmid, Manufacturing Engineering and Technology Three-plate mold Two-plate mold
- 32. 2.008x Kalpakjian and Schmid, Manufacturing Engineering and Technology Hot runner mold (three plates)
- 33. 2.008x Lego bricks: three-plate mold http://www.cnet.com/pictures/how-lego-makes-its-bricks-photos/
- 35. 2.008x Injection Molding: 4. Injection process parameters
- 36. 2.008x How would you choose an IM machine? (important specs?) § Clamping force: force available to hold plates together. § Injection pressure: maximum pressure that can be developed to force the plastic into the mold cavity. § Shot size: amount of material that can be transferred to the mold (i.e., the part volume plus runners, gates, etc).
- 37. 2.008x Specs of the IM machine at MIT
- 38. 2.008x Specs of the IM machine at MIT
- 39. 2.008x à Let’s relate the machine specifications to a basic model of the mold filling process
- 40. 2.008x
- 43. 2.008x Simple scaling of injection parameters for a 2D rectangular channel ÷ ÷ ø ö ç ç è æ µ ÷ ø ö ç è æ =D =D 2 3 2 3 12 12 h wL F h L P wh QL P fill clamp fill t µ t µ µ
- 44. 2.008x Simulating injection using Solidworks Plastics A simple plate: § L = W = 100 mm § h (thickness) = 2 mm § Polypropylene (PP) § Tmelt = 250C § Tmold = 70C à Above, we predicted injection pressure DP = 3 MPa
- 46. 2.008x Viscosity of polypropylene versus shear rate and temperature From Solidworks Plastics µ = k !γ(n−1) 100 C 250 C Ux(H) = Ux Ux(y) Ux(0) = 0 h Ux x y
- 48. 2.008x Injection Molding: 5. Cycle time, cooling, and shrinkage
- 51. 2.008x How do we model cooling of the part? 2 2 2 2 y T y T c k t T p ¶ ¶ = ¶ ¶ = ¶ ¶ a r Mold Mold Part x y L h h/2 h/2
- 52. 2.008x Exact solution for a plate Tm = melt temperature Tw = wall temperature Te = ejection temperature Drawing from Leinhard, A Heat Transfer Textbook Also see BASF ‘estimating cooling time’ http://www2.basf.us/PLASTICSWEB/displayanyfile?id=0901a5e1801499d3 a4 2 h tcool = MoldMold Part a = thermal diffusivity = k / rcp ~0.1 mm2/s for thermoplastics ÷ ÷ ø ö ç ç è æ - - = we wm cool TT TTh t pap 4 ln2 2 à We define the cooling time as the time until the temperature at the centerline of the part reaches the specified ejection temperature ‘Rule of thumb’ if (Tm-Tw) ≈ 10(Te-Tw)
- 53. 2.008x Cooling time scaling for plate geometry Tm = 200 ºC = 473 K Tw = 77 ºC = 350 K tcool = h2 4α tcool = h2 π2α ln 4 π Tm − Tw Te − Tw
- 54. 2.008x How do process parameters vary with part size? ΔP = 12µ τ fill L h " # $ % & ' 2 Fclamp ∝ µ τ fill wL3 h2 " # $ % & ' tcool ∝ h2 4α
- 55. 2.008x Pack Close Fill Eject Gatefreezes Time Pressure[MPa] 5 10 15 Cool Cycle time Pressure vs time
- 56. 2.008x
- 57. 2.008x Residual stress in LEGO® block (polarized imaging) 2.008x
- 58. 2.008x Polymers change volume with pressure and temperature à imagine a sponge that tries to shrink but is glued to the inside walls of a rigid container: residual stress!
- 59. 2.008x http://www.lati.com/pdf/technical_data/dimensional-molding-shrinkages.pdf Practically, how much shrinkage? Longitudinal shrinkage (parallel to flow) Lateralshrinkage(perpendiculartoflow)
- 60. 2.008x In other words… § Polymers shrink during cooling; that’s a fact. § If the shrinkage is constrained by the mold, residual stresses are ‘trapped’ because the part cannot relax as the polymer shrinks. § During injection molding, the variation in shrinkage both globally and through the cross section of a part creates internal stresses or residual stresses that act on a part with effects similar to externally applied stresses. § These residual stress can cause the part to will warp upon ejection from the mold or crack when loaded during use.
- 61. 2.008x Injection Molding: 6. Defects and the ‘process window’
- 62. 2.008x The injection molding ‘process window’
- 64. 2.008x Flash
- 66. 2.008x
- 67. 2.008x Protomold ‘design cube’ § What is the molding orientation? § Where are the ejector pins? § What defects do you notice? § …
- 68. 2.008x Ribs Undercuts ‘Living’ hinges Straight-pull transverse hole Side-pull transverse hole Surface finishes Thick and cored out sections
- 70. 2.008x Simulation: cooling time 309 s 1.4 s 63 s 124 s 186 s 248 s
- 71. 2.008x Simulation: shrinkage 0.45 mm 0.01 mm 0.10 mm
- 73. 2.008x Corners, fillets and hinges (‘living hinges’) R = 0.2 mm 2 mm R = 1 mm Fillets Corner radius 2 mm 0.25 mm Hinges Note blistered edges
- 74. 2.008x Draft angles 2 mm Fins on Protomold cube à Draft angles enable easier part ejection. à The required draft angle depends on thickness, and surface texture. LEGO brick 100 µm
- 76. 2.008x The process window always applies, but the conditions are different everywhere in your part! à Therefore it’s not good enough to be in the process window! à Beware of common defects, design for maximum uniformity, and reduce risk by following DFM guidelines (see supplements)
- 77. 2.008x Injection Molding: 7. Advanced topics
- 78. 2.008x Molding with ‘side action’ Animation from protomold Elbow fitting: http://www.plastic-injectionmoulds.com/sale-1133447-household-plastic-injection- molded-parts-pvc-pb-pp-for-water-tank-fitting.html
- 79. 2.008x
- 80. 2.008x Insert molding Plastic molded item Metal terminal
- 81. 2.008x Overmolding (two plastics) How? § Insert brush § Mold rigid base (white) § Mold elastomer (black) at lower temperature
- 82. 2.008x Metal injection molding (MIM) à Perform injection molding using a metal powder mixed with polymer binder; then anneal the part to achieve higher density (with significant shrinkage)
- 83. 2.008x 8. Conclusion: the big four Injection Molding Machining Rate High Low-Medium Quality Good As good or better! Cost Low (at high volume) Almost always greater Flexibility Low (tooling cost high) High (within machine constraints)
- 84. 2.008x References 1 Introduction Photo of Electrical Plug by User: Taken on PIxabay.com. This work is in the public domain. Image of Plastic Production Industry © John Hart. Adapted from http://www.statista.com/statistics/282732/global-production-of-plastics-since-1950/ Image of Plastic Production Industrial Branches by Burkhard Erne © MOOG Inc. 2013. All Rights Reserved. Video of Process Overview © A. Routsis Associates Inc. 2015 2 Fundamentals Photo of Pellet Costs © 1999-2016 Alibaba.com. All Rights Reserved. Polymer Representation: Figure 8.2(3) from Title: Fundamentals of Modern Manufacturing; Author: Mikell P. Groover; Publisher: Wiley; 4 edition (2010); ISBN: 978-0470-467002 Polymerization Reaction: Figure 7.3b from Title: Manufacturing Engineering & Technology (6th Edition); Authors: Serope Kalpakjian, Steven Schmid; Publisher: Prentice Hall; 6 edition (January, 2009); ISBN-13: 9780136081685
- 85. 2.008x References Modulus vs. Density Plot: Figure 4.2, page 60 from Title: Material Selection in Material Design; Author: Michael Ashby; Publisher: Butterworth-Heinemann; 4 edition (2011); ISBN: 9780080952239 Stress-Strain Comparison: Figure 7.10 from Title: Manufacturing Engineering & Technology (7th Edition); Authors: Serope Kalpakjian, Steven Schmid; © Prentice Hall; (2013); Photo of Giant Dishes by Daryl Mitchell on Flickr. (CC BY-SA) 2.0 Photo of Hydraulic Sealing by Devendra Dave on Flickr. (CC BY-SA) 2.0 Networked Polymer Structure: Figure 7.5d from Title: Manufacturing Engineering & Technology (6th Edition); Authors: Serope Kalpakjian, Steven Schmid; © Prentice Hall; (2009) Image of Semicrystalline Polymer by Dr. Michael Eastman, P.I.; © Copyright UTEP 2010 Stress-Strain Comparison of Amorphous Thermoplastics: Figure 2.12 from Title: Technology of thermoforming; Author: James L. Throne; © Hanser/Gardner Publications; (1996); Tensile Strength vs. Temperature: Figure 2.26 from "International Plastics Handbook" by Osswald et al. © Hanser Publishers (2006).
- 86. 2.008x References Glass Transition Temperature: Table 7.2 from Title: Manufacturing Engineering & Technology (7th Edition); Authors: Serope Kalpakjian, Steven Schmid; © Prentice Hall; (2013); Image of Viscosity Shear Thinning ©Dassault Systemes; SolidWorks Corporation 2016 3 Mold Tooling + Conf Video of LEGO © User: Mister Rolls on YouTube Injection Molding Machine: Figure 13.21 from Title: Fundamentals of Modern Manufacturing; Author: Mikell P. Groover; © Wiley; (2010); Multi Cavity Mold: Figure 19.10 from Title: Manufacturing Engineering & Technology (7th Edition); Authors: Serope Kalpakjian, Steven Schmid; © Prentice Hall; (2013); Injection Molding Molds: Figure 19.11 from Title: Manufacturing Engineering & Technology (7th Edition); Authors: Serope Kalpakjian, Steven Schmid; © Prentice Hall; (2013); Photo of LEGO Mold © Daniel Terdiman / CNET. Video of Ball Point Pen Clips © ARBURG.
- 87. 2.008x References 6 Cycle Time Shrinkage Cooling of Slab: Figure 5.6 from Title: A Heat Transfer Textbook (4th Edition); © 2000-2015, John H. Lienhard IV and John H. Lienhard V. All Rights Reserved. Specific Volume vs. Temperature and Pressure © John Hart. Image adapted from cnf- moldmaking.com, original image Copyright © 2011 CNF Molds & Plastic Co., Limited. Image of Shrinkage © LATI S.p.A. 2008 8 Advanced Image of Side-Action © Proto Labs 1999–2016 Image of Pipe Fitting © Westside Wholesale Inc. 2016. All Rights Reserved. Photo of Side Action Tooling © 1999-2016 Alibaba.com. All Rights Reserved.