1. SHAPING PROCESSES FOR PLASTICS
SME Video - Plastic Processes
Plastic Blow Molding (vts_12)
Properties of Polymer Melts
Extrusion
Sheet, Film and Spinning
Coating Processes
Injection Molding
In-class Assignment
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

2. Two Types of Plastics Thermoplastics
Chemical structure unchanged during heating
Polymer melt - high viscosity & viscoelasticity
Thermosets
Curing process during heating
Cross‑linking of molecular structure
Once cured, they cannot be remelted
Plastic molding is a net shape process
Less energy is required than for metals
Strength‑to‑weight ratios are competitive
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

3. Viscosity Relationships
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

4. Viscoelasticity - Die Swell Example
Extruded polymer "remembers" its previous shape
Die swell, a manifestation of viscoelasticity in polymer melts
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

5. Extruder for Thermoplastics & Elastomers
Extruder Barrel:
Electric heaters melt feedstock
Application:
Door and window moldings
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

6. Extrusion Die for Solid Cross Section
(a) Die cross section to obtain
(b) Square extruded profile
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

7. Extrusion Die for Hollow Shapes
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

8. Extrusion Die for Coating Wire
cross‑section of die for coating of electrical wire
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

9. Injection Molding Machine
A large (3000 ton capacity) injection molding machine (Photo courtesy of Cincinnati Milacron).
Polymer is heated and forced into a mold cavity
Net shape
Typical cycle time 10 to 30 sec
Mold may contain multiple cavities
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

10. Injection Molding Machine
Diagram of an injection molding machine, reciprocating screw type (some mechanical details are simplified)
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

11. Injection Molding Cycle
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

12. Two-Plate Mold (b) open (a) closed Mold has two cavities
Comment on shrinkage
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

13. Another option: Hot‑Runner Molds
Three-Plate Mold
(b) open
(a) closed
Mold has two cavities
Another option: Hot‑Runner Molds
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

14. Toggle Clamps and Hydraulic Clamps
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

15. SME Video
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

16. In-class Assignment 1 of 2
In casting experiments performed using a certain alloy and type of sand mold, it took 155 sec for a cube‑shaped casting to solidify. The cube was 50 mm on a side.
(a) Determine the value of the mold constant in Chvorinov’s Rule
(b) If the same alloy and mold type were used, find the total solidification time for a cylindrical casting in which the diameter = 30 mm and length = 50 mm.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

17. In-class Assignment 2 of 2
A sand core located inside a mold cavity has a volume of in3. It is used in the casting of a cast iron pump housing. Determine the buoyancy force that will tend to lift the core during pouring.
Sand core density = lb/in3
Cast iron density = lb/in3
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

18. Test 1 Review Discussion
100 multiple choice
2 problems with calculations similar to in-class examples
2 challenge problems with calculations similar to in-class assignments
Manufacturing economics problems will not be on the test
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

19. Manufacturing Economics
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

20. Time Permitting Content
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21. Defects in Extrusion Melt fracture caused by turbulent flow
Velocity profile of melt through die opening can lead to defects
Bambooing
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

22. Sheet and Film: Slit Die Extrusion
Application: product wrapping material, grocery bags and garbage bags
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

23. Blown-film, Calendering & Spinning
Blown‑film process for high production of thin tubular film
Sheet out of rubber or rubbery thermoplastics (plasticized PVC)
Melt spinning of continuous filaments
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

24. Planar Coating Process
Roll method
Doctor-blade method
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

25. Alternative Injection Molding Machine Designs
Screw preplasticizer
Plunger type
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

26. Reaction Injection Molding (RIM)
Application: bumpers and fenders
RIM polyurethane parts possess a foam internal structure surrounded by a dense outer skin
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

27. Compression Molding
Molding compound available in several forms: powders or pellets, liquid, or preform
compressed and cured
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

28. Transfer Molding Pot transfer molding Plunger transfer molding
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

29. Extrusion Blow Molding
(1) extrusion of parison
(2) parison is pinched
(3) the tube is inflated
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

30. Other Blow Molding Processes
Injection blow molding:
Stretch blow molding:
Polyethylene terephthalate (PET)
Very low permeability
Strengthened by stretch blow molding
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

31. Rotational Molding
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32. Vacuum Thermoforming
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

33. Thermoforming Pressure thermoforming: Vacuum thermoforming:
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

34. Mechanical thermoforming
Vacuum thermoforming
Application:
boat hulls and shower stalls
Mechanical thermoforming
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

35. Polymer Foam Polymer‑and‑gas mixture Porous or cellular structure
Polystyrene (Styrofoam, a trademark)
Polyurethane
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

36. Extruder Relationships
Typical Pressure Gradient in an Extruder
Extruder and Die Characteristic
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e