1. PDT 151 Introduction to Materials Processing Technology
Lecturers
Assoc. Prof. Dr. Che Mohd Ruzaidi Ghazali (ABAH)

2. PDT 151: Introduction to Materials Processing Technology
Polymer Processing

3. Processing Technology? Always relate or refer to
Manufacturing
Manufacturing is the application of physical and chemical processes to alter the geometry, properties, and appearance of a starting material to make parts or products for a given application

4. What are plastics and polymers? Polymer Rheology
Major Plastics Molding Processes
Extrusion
Injection Molding
Thermoforming
Compression Molding
Molding Machine

5. Giant molecules with repeating units (monomer)
Chain of organic molecules
Properties:
Lightweight
Corrosion-resistant
Low strength
Low stiffness
Relatively inexpensive
Very formable
Temperature concerns
smaller M w
larger M
Giant molecules with repeating units (monomer)

6. polytetrafluoroethylene
What are polymers?
polypropylene
(PP)
polyethylene
(PE)
polyvinyl chloride
(PVC)
polytetrafluoroethylene
(PTFE)

7. Classification: Chemistry
polyethylene
(PE)
polyvinyl chloride
(PVC)
polytetrafluoroethylene
(PTFE)
polypropylene
(PP)
polymethyl methacrylate
(PMMA)
polystyrene
(PS)

8. Classification: Chemistry
polyhexamethylene adipamide
(Nylon)
polyethylene terephthalate
(Polyester, PET)
polycarbonate
(PC)

9. Two Types of Plastics Thermoplastics Thermosets
Chemical structure remains unchanged during heating and shaping
More important commercially, comprising more than 70% of total plastics tonnage
Thermosets
Undergo a curing process during heating and shaping, causing a permanent change (called cross‑linking) in molecular structure
Once cured, they cannot be remelted

10. Families of Plastics Thermoplastics Thermosets Acetals Acrylic
Cellulose (Acetates)
Fluorocarbons
Teflon
Nylon
Polycarbonate
Polyethelene
Polystyrene
Vinyl
Thermosets
Epoxies
Melamines
Phenolics
Bakelite
Polyesters
Silicones
Sealant
Urea-formaldehyde
Environmental concerns

11. Plastic Family Properties
Thermoplastics
Reversible softening & hardening
Softening range (not melting point)
Weak bonds between molecules
Properties inverse with temperature:
Stiffness
Hardness
Ductility
Solvent resistance
Thermosets
Irreversible hardening reaction
Strong bonds between molecules (cross-linking)
Compared with Thermoplastics:
Stronger
Rigid
Heat resistance
Brittle
Low impact toughness
Lower ductility

12. Classification: Structure
Linear
thermoplastic
Branched
thermoplastic
Network
thermosetting
Crosslinked
thermosetting

13. Classification: Structure
random coil
(amorphous)
partially extended
(semi-crystalline)

14. Elastomers Exceptional elastic deformation Near-complete* recovery
Viscous deformation is permanent
Twisted/coiled molecular chains
Can be cross-linked (vulcanization)
Degradable
Insulative
Chemical forms
Natural
Rubber
Synthetic
Polyisoprene (Santoprene)
Silicone rubber
Urethanes

15. polydimethylsiloxane
Elastomers
polychloroprene
(Neoprene rubber)
polyisoprene
(natural rubber)
polydimethylsiloxane
(silicone rubber)
polyisobutylene
(butyl rubber)

16. Plastic Utility Degradable UV Light Flammable, Oxidation
Modifiable Properties
Color
Conductivity
Adhesiveness
Mechanical
Additives Make Polymers into Plastics
Stabilizers, Flame retardants
Dyes (translucent), Coloring Agents (opaque)
Anti-statics, Anti-microbials
Plasticizers (improve flow), Lubricants (improve moldability)
Reinforcements, Fillers

17. Classification: Structure
a) random
COPOLYMERS
more than one “mer”
b) alternating
c) block
d) graft

18. Economics of Plastics Compared with Metals (+):
Lower fabrication tooling costs
Higher production rate
Greater DFA (Design For Assembly) potential
Snap fits/fastener-less assembly
Friction/ultrasonic/solvent welding
Self-tapping fasteners
Lower reuse cost (scrap)*
Lower finishing costs
Lower density
Compared with Metals (-):
Higher cost / weight
Lower impact resistance
Lower strength
Lower stiffness
Smaller operational temperature range
Lower resistance to:
Flame
Solvents
Light (UV)

19. Plastic Shaping Processes
Almost unlimited variety of part geometries
Plastic molding is a net shape process; further shaping is not needed
Less energy is required than for metals because processing temperatures are much lower
Handling of product is simplified during production because of lower temperatures
Painting or plating is usually not required

20. Viscosity of Polymer Melts
A fluid property that measures the resistance to flow – quotient of shear stress to shear rate within a fluid
Due to its high molecular weight, a polymer melt is a thick fluid with high viscosity
Important because most polymer shaping processes involve flow through small channels or die openings
High flow rates lead to high shear rates and shear stresses, so significant pressures are required to process polymers

21. Viscosity
Like liquid metals, polymer viscosity is dependent on temperature
Unlike liquid metals, polymer viscosity depends on shear rate
“Non-Newtonian fluid”
“Shear thinning”

22. Viscoelasticity Viscous and elastic (pseudoplastic) properties
Possessed by both polymer solids and polymer melts
Example: die swell in extrusion, in which the hot plastic expands when exiting the die opening
Swell ratio, rs = Dx/Dd

24. Extruder Sectional View
Components and features of a (single‑screw) extruder for plastics and elastomers

25. Extruder Screw Divided into sections to serve several functions:
Feed section - feedstock is moved from hopper and preheated
Compression section - polymer is transformed into fluid, air mixed with pellets is extracted from melt, and material is compressed
Metering section - melt is homogenized and sufficient pressure developed to pump it through die opening

26. Dies 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

27. Side view cross‑section of die for coating of wire by extrusion
Extruding a Coated Wire
Side view cross‑section of die for coating of wire by extrusion

28. Injection Molding
Polymer is heated to a highly plastic state and forced to flow under high pressure into a mold cavity where it solidifies; molded part is then removed from cavity
Produces discrete components almost always to net shape
Typical cycle time 10 to 30 sec, but cycles of one minute or more are not uncommon
Mold may contain multiple cavities, so multiple moldings are produced each cycle

29. Injection Molded Parts (Moldings)
Complex and intricate shapes are possible
Shape limitations:
Capability to fabricate a mold whose cavity is the same geometry as part
Shape must allow for part removal from mold
Part size from  50 g (2 oz) up to  25 kg (more than 50 lb), e.g., automobile bumpers
Injection molding is economical only for large production quantities due to high cost of mold

30. Polymers for Injection Molding
Injection molding is the most widely used molding process for thermoplastics
Some thermosets, elastomers, metals and ceramics are also injection molded
Modifications in equipment and operating parameters must be made

31. Injection Molding Machine
Two principal components:
Injection unit – melts and delivers polymer melt, operates much like an extruder
Clamping unit – opens and closes mold each injection cycle

32. Injection Molding Machine
A large (3000 ton capacity) injection molding machine
(courtesy Cincinnati Milacron)

33. Typical molding cycle:
Injection Molding Cycle: Stage 1
Typical molding cycle:
(1) mold is closed

34. Typical molding cycle: (2) melt is injected into cavity
Injection Molding Cycle: Stage 2
Typical molding cycle:
(2) melt is injected into cavity

35. Typical molding cycle:
Injection Molding Cycle: Stage 3
Typical molding cycle:
(3) screw is retracted

36. Typical molding cycle: (4) mold opens and part is ejected
Injection Molding Cycle: Stage 4
Typical molding cycle:
(4) mold opens and part is ejected

37. The Mold Custom‑designed and fabricated for the part to be produced
Various types of mold for injection molding:
Two-plate mold
Three-plate mold
Hot-runner mold
Cavity
Mold

38. Shrinkage
Reduction in linear size during cooling from molding to room temperature
Polymers have high thermal expansion coefficients, so significant shrinkage occurs during cooling in mold
Typical shrinkage values for selected polymers:
Plastic Shrinkage, mm/mm (in/in)
Nylon‑6,
Polyethylene
Polystyrene
PVC

39. Compensation for Shrinkage
Dimensions of mold cavity must be larger than specified part dimensions:
Dc = Dp + DpS + DpS2
where Dc = dimension of cavity;
Dp = molded part dimension, and
S = shrinkage value

40. Shrinkage Compensation Factors
Fillers in the plastic tend to reduce shrinkage
Injection pressure – as pressure is increased, it forces more material into the mold cavity, and shrinkage is reduced
Compaction time - similar effect - forces more material into cavity during shrinkage
Molding temperature - higher temperature lowers the polymer melt viscosity, allowing more material to be packed into mold and reducing shrinkage

41. Thermoforming
Flat thermoplastic sheet or film is heated and deformed into desired shape using a mold
Heating usually accomplished by radiant electric heaters located on one or both sides of starting plastic sheet or film
Widely used in packaging of products and to fabricate large items such as bathtubs, contoured skylights, and internal door liners for refrigerators

42. Vacuum thermoforming: (1) a flat plastic sheet is softened
Thermoforming Process - Step 1
Vacuum thermoforming: (1) a flat plastic sheet is softened

43. Vacuum thermoforming: (2) sheet is placed over mold cavity
Thermoforming Process - Step 2
Vacuum thermoforming: (2) sheet is placed over mold cavity

44. Vacuum thermoforming: (3) vacuum draws sheet into the cavity
Thermoforming Process - Step 3
Vacuum thermoforming: (3) vacuum draws sheet into the cavity

45. Compression Molding
Thermosets with axisymmetric shapes

46. Blow Molding
Hollow shapes

47. Additive Manufacturing
Stereolithography
Additive Manufacturing
“Rapid prototyping”

48. You should have learned
The difference between plastics and polymers
Viscoelastic properties of polymers
Key plastics molding processes
Extrusion
Injection Molding
Thermoforming
Compression Molding