1. SHAPING PROCESSES FOR PLASTICS
Die Design
Production of Sheet, Film, and Filaments
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

2. Die Configurations and Extruded Products
The shape of the die orifice determines the cross‑sectional shape of the extrudate
Common die profiles and corresponding extruded shapes:
Solid profiles
Hollow profiles, such as tubes
Wire and cable coating
Sheet and film
Filaments
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

3. Extrusion of Solid Profiles
Regular shapes such as
Rounds
Squares
Irregular cross sections such as
Structural shapes
Door and window moldings
Automobile trim
House siding
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

4. Extrusion Die for Solid Cross Section
Figure (a) Side view cross‑section of an extrusion die for solid regular shapes, such as round stock; (b) front view of die, with profile of extrudate. Die swell is evident in both views.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

5. Hollow Profiles
Examples: tubes, pipes, hoses, and other cross‑sections containing holes
Hollow profiles require mandrel to form the shape
Mandrel held in place using a spider
Polymer melt flows around legs supporting the mandrel to reunite into a monolithic tube wall
Mandrel often includes an air channel through which air is blown to maintain hollow form of extrudate during hardening
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

6. Extrusion Die for Hollow Shapes
Figure Side view cross‑section of extrusion die for shaping hollow cross‑sections such as tubes and pipes; Section A‑A is a front view cross‑section showing how the mandrel is held in place; Section B‑B shows the tubular cross‑section just prior to exiting the die; die swell causes an enlargement of the diameter.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

7. Wire and Cable Coating
Polymer melt is applied to bare wire as it is pulled at high speed through a die
A slight vacuum is drawn between wire and polymer to promote adhesion of coating
Wire provides rigidity during cooling - usually aided by passing coated wire through a water trough
Product is wound onto large spools at speeds up to 50 m/s (10,000 ft/min)
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

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

9. Polymer Sheet and Film
Film - thickness below 0.5 mm (0.020 in.)
Packaging - product wrapping material, grocery bags, and garbage bags
Stock for photographic film
Pool covers and liners for irrigation ditches
Sheet - thickness from 0.5 mm (0.020 in.) to about 12.5 mm (0.5 in.)
Flat window glazing
Thermoforming stock
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

10. Materials for Polymer Sheet and Film
All thermoplastic polymers
Polyethylene, mostly low density PE
Polypropylene
Polyvinylchloride
Cellophane
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

11. Sheet and Film Production Processes
Most widely used processes are continuous, high production operations
Processes include:
Slit‑Die Extrusion of Sheet and Film
Blown‑Film Extrusion Process
Calendering
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

12. Slit‑Die Extrusion of Sheet and Film
Production of sheet and film by conventional extrusion, using a narrow slit as the die opening
Slit may be up to 3 m (10 ft) wide and as narrow as around 0.4 mm (0.015 in)
A problem is uniformity of thickness throughout width of stock, due to drastic shape change of polymer melt as it flows through die
Edges of film usually must be trimmed because of thickening at edges
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

13. Slit Die Extrusion
Figure One of several die configurations for extruding sheet and film.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

14. Blown‑Film Extrusion Process
Combines extrusion and blowing to produce a tube of thin film
Process sequence:
Extrusion of tube
Tube is drawn upward while still molten and simultaneously expanded by air inflated into it through die
Air is blown into tube to maintain uniform film thickness and tube diameter
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

15. Blown-film Process
Figure Blown‑film process for high production of thin tubular film.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

16. Calendering
Feedstock is passed through a series of rolls to reduce thickness to desired gage
Expensive equipment, high production rates
Process is noted for good surface finish and high gage accuracy
Typical materials: rubber or rubbery thermoplastics such as plasticized PVC
Products: PVC floor covering, shower curtains, vinyl table cloths, pool liners, and inflatable boats and toys
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

17. Figure 13.17 A typical roll configuration in calendering
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

18. Fiber and Filament Products
Definitions:
Fiber - a long, thin strand whose length is at least 100 times its cross‑section
Filament - a fiber of continuous length
Applications:
Fibers and filaments for textiles
Most important application
Reinforcing materials in polymer composites
Growing application, but still small compared to textiles
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

19. Materials for Fibers and Filaments
Fibers can be natural or synthetic
Natural fibers constitute ~ 25% of total market
Cotton is by far the most important staple
Wool production is significantly less than cotton
Synthetic fibers constitute ~ 75% of total fiber market
Polyester is the most important
Others: nylon, acrylics, and rayon
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

20. Fiber and Filament Production - Spinning
For synthetic fibers, spinning = extrusion of polymer melt or solution through a spinneret, then drawing and winding onto a bobbin
Spinneret = die with multiple small holes
The term is a holdover from methods used to draw and twist natural fibers into yarn or thread
Three variations, depending on polymer :
Melt spinning
Dry spinning
Wet spinning
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

21. Melt Spinning
Starting polymer is heated to molten state and pumped through spinneret
Typical spinneret is 6 mm (0.25 in) thick and contains approximately 50 holes of diameter 0.25 mm ( in)
Filaments are drawn and air cooled before being spooled onto bobbin
Significant extension and thinning of filaments occur while polymer is still molten, so final diameter wound onto bobbin may be only 1/10 of extruded size
Used for polyester and nylon filaments
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

22. Melt Spinning Figure 13.18 Melt spinning of continuous filaments
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

23. Dry Spinning
Similar to melt spinning, but starting polymer is in solution and solvent can be separated by evaporation
First step is extrusion through spinneret
Extrudate is pulled through a heated chamber which removes the solvent, leaving the polymer
Used for filaments of cellulose acetate and acrylics
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

24. Wet Spinning
Similar to melt spinning, but polymer is again in solution, only solvent is non‑volatile
To separate polymer, extrudate is passed through a liquid chemical that coagulates or precipitates the polymer into coherent strands which are then collected onto bobbins
Used to produce filaments of rayon (regenerated cellulose)
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

25. Subsequent Processing of Filaments
Filaments produced by any of the three processes are usually subjected to further cold drawing to align crystal structure along direction of filament axis
Extensions of 2 to 8 are typical
Effect is to significantly increase tensile strength
Drawing is done by pulling filament between two spools, where winding spool is driven at a faster speed than unwinding spool
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

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