1 / 42

Injection Molding

Injection Molding. 2.810 Fall 2002 Professor Tim Gutowski. 1862 first synthetic plastic 1866 Celluloid 1891 Rayon 1907 Bakelite 1913 Cellophane 1926 PVC 1933 Polyethylene 1938 Teflon 1939 Nylon stockings 1957 velcro 1967 “The Graduate”. Short history of plastics. Outline.

mayes
Télécharger la présentation

Injection Molding

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Injection Molding 2.810 Fall 2002 Professor Tim Gutowski

  2. 1862 first synthetic plastic 1866 Celluloid 1891 Rayon 1907 Bakelite 1913 Cellophane 1926 PVC 1933 Polyethylene 1938 Teflon 1939 Nylon stockings 1957 velcro 1967 “The Graduate” Short history of plastics

  3. Outline • Basic operation • Cycle time and heat transfer • Flow and solidification • Part design • Tooling • New developments • Environment

  4. Readings • Tadmore and Gogos • Molding and Casting pp584 -610 • Boothroyd Dewhurst • Design for Injection Molding pp 319 - 359 • Kalpakjian see Ch 18 • Injection molding case study;Washing machine augers; see on web page

  5. 30 ton, 1.5 oz (45 cm3) Engel Injection Molding Machine for wheel fabrication

  6. * Schematic of thermoplastic Injection molding machine Process & machine schematics * * Source: http://www.idsa-mp.org/proc/plastic/injection/injection_process.htm

  7. Process Operation • Temperature: barrel zones, tool, die zone • Pressures: injection max, hold • Times: injection, hold, tool opening • Shot size: screw travel Processing window Temp. Thermal degradation Flash Short-shot Melt Pressure

  8. Time(sec) Time(sec) Typical pressure/temperature cycle * * Cooling time generally dominates cycle time * Source: http://islnotes.cps.msu.edu/trp/inj/inj_time.html

  9. Calculate clamp force, & shot size F=P X A = 420 tons 3.8 lbs = 2245 cm3 =75 oz Actual ; 2 cavity 800 ton

  10. Clamp force and machine cost

  11. Heat transfer Note; aTool>apolymer 1-dimensional heat conduction equation : qx qx + Dqx Fourier’s law Boundary Conditions: The boundary condition of 1st kind applies to injection molding since the tool is often maintained at a constant temperature

  12. Tii t TW x -L +L Heat transfer Let Lch = H/2 (half thickness) = L ; tch = L2/a ; DTch = Ti – TW (initial temp. – wall temp.) Non-dimensionalize: Dimensionless equation: Initial condition Boundary condition Separation of variables ; matching B.C.; matching I.C.

  13. Temperature in a slab Centerline, q = 0.1, Fo = at/L2 = 1 Bi-1 =k/hL

  14. Reynolds Number Reynolds Number: For typical injection molding For Die casting * Source: http://www.idsa-mp.org/proc/plastic/injection/injection_process.htm

  15. F v F/A h m 1 v/h Viscous Shearing of Fluids Newtonian Viscosity Generalization: Typical shear rate for Polymer processes (sec)-1 Extrusion 102~103 Calendering 10~102 Injection molding 103~104 Comp. Molding 1~10 Injection molding “Shear Thinning” ~ 1 sec-1 for PE

  16. Viscous Heating Rate of Heating = Rate of Viscous Work Rate of Temperature rise Rate of Conduction out Brinkman number For injection molding, order of magnitude ~ 0.1 to 10

  17. Non-Isothermal Flow Flow rate: 1/t ~V/Lx v Heat transfer rate: 1/t ~a/(Lz/2)2 Small value => Short shot For injection molding For Die casting of aluminum * Very small, therefore it requires thick runners

  18. Injection mold die cast mold

  19. Fountain Flow * ** * Source: http://islnotes.cps.msu.edu/trp/inj/flw_froz.html ; ** Z. Tadmore and C. Gogos, “Principles of Polymer Processing”

  20. Shrinkage distributions Transverse direction sample V=3.5cm/s V=8cm/s * Source: G. Menges and W. Wubken, “Influence of processing conditions on Molecular Orientation in Injection Molds”

  21. Gate Location and Warping Shrinkage Direction of flow – 0.020 in/in Perpendicular to flow – 0.012 2.0 60 1.96 Sprue 60.32 1.976 2.0 Before shrinkage After shrinkage Air entrapment Gate Center gate: radial flow – severe distortion Edge gate: warp free, air entrapment Diagonal gate: radial flow – twisting End gates: linear flow – minimum warping

  22. LDPE 0.030 Acetal 0.030 LDPE PP PP with flow 0.025 0.025 Acetal 0.020 PP across flow 0.020 Nylon 6/6 0.015 Nylon 6/6 Shrinkage Shrinkage 0.015 0.010 0.005 PMMA 0.010 0.000 6000 10000 14000 18000 0.005 8000 12000 16000 PMMA Pressure on injection plunger (psi) 0.000 100 120 140 160 180 200 220 240 Mold Temperature (F) Effects of mold temperature and pressure on shrinkage

  23. Where would you gate this part?

  24. Sink mark Weld line, Sink mark Gate Weld line Mold Filling Solidified part Basic rules in designing ribs to minimize sink marks * Source: http://www.idsa-mp.org/proc/plastic/injection/injection_design_7.htm

  25. * * Injection Molding * Source: http://www.idsa-mp.org/proc/plastic/injection/injection_design_2.htm

  26. Where is injection molding? DLtotal = DLmold + DLshrinkage

  27. LDPE 0.030 Acetal PP with flow 0.025 0.020 PP across flow 0.015 Nylon 6/6 Shrinkage 0.010 0.005 PMMA 0.000 6000 10000 14000 18000 8000 12000 16000 Pressure on injection plunger (psi) Effects of mold temperature and pressure on shrinkage

  28. Nozzle Sprue Tooling Basics Core Plate Cavity Plate Moulding Core Cavity Basic mould consisting of cavity and core plate Cavity Runner Gate Melt Delivery

  29. Nozzle Knob Runner Cavity Part Stripper plate Core Tooling for a plastic cup

  30. Knob Nozzle Nozzle Runner Cavity Runner Cavity Cavity Part Part Part Stripper plate Tooling for a plastic cup

  31. Tooling * * * * * ** * * Source: http://www.idsa-mp.org/proc/plastic/injection/; ** http://www.hzs.co.jp/english/products/e_trainer/mold/basic/basic.htm (E-trainer by HZS Co.,Ltd.)

  32. Part design rules • Simple shapes to reduce tooling cost • No undercuts, etc. • Draft angle to remove part • In some cases, small angles (1/4) will do • Problem for gears • Even wall thickness • Minimum wall thickness ~ 0.025 in • Avoid sharp corners • Hide weld lines • Holes may be molded 2/3 of the way through the wall only, with final drilling to eliminate weld lines

  33. New developments- Gas assisted injection molding

  34. New developments ; injection molding with cores Injection Molded Housing shown in class Cores used in Injection Molding Cores and Part Molded in Clear Plastic

  35. Environmental issues • Petroleum and refining • Primary processing • Out gassing & energy during processing • End of life

  36. Environmental loads by manufacturing sector EPA 2001, DOE 2001

  37. The estimated environmental performance of various mfg processes (not including auxiliary requirements) *Energy per wt. normalized by the melt energy ** total raw mat’l normalized by the part wt.

  38. The printer goes in the hopper…

  39. And comes out….

  40. The problem with plastics is…

  41. Or remanufacture….

  42. Summary • Basic operation • Cycle time and heat transfer • Flow and solidification • Part design • Tooling • New developments • Environment

More Related