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The word plastics is from the Greek word Plastikos,
    meaning “able to be shaped and molded”


Ken Youssefi       Mechanical Engineering   1
Why Design with Plastics?
•    Light weight, high weight to         •   Relatively low cost compared
     strength ratio, particularly when        to metals and composites
     reinforced




                Density                                   Cost

    Ken Youssefi            Mechanical Engineering        2
Why Design with Plastics?
• Corrosion resistance
• Low electrical and thermal conductivity, insulator
• Easily formed into complex shapes, can be
  formed, casted and joined.
• Wide choice of appearance, colors and
  transparencies




Ken Youssefi        Mechanical Engineering   3
Disadvantages of using Plastics

• Low strength
• Low useful temperature range (up to 600 oF)
• Less dimensional stability over period of time
  (creep effect)
• Aging effect, hardens and become brittle over time
• Sensitive to environment, moisture and chemicals
• Poor machinability



Ken Youssefi     Mechanical Engineering   4
Ken Youssefi   Mechanical Engineering   5
Mechanical Properties of Various Plastics




     Steel: 350 to 1900 MPa             Brass: 200 to 850 MPa
                     Aluminum: 100 to 550 MPa
Ken Youssefi            Mechanical Engineering         6
Polymers
 •   The earliest synthetic polymer was developed in 1906, called Bakelite.

 •   The development of modern plastics started in 1920s using raw
     material extracted from coal and petroleum products (Ethylene).
     Ethylene is called a building block.

 •   Polymers are long-chain molecules and are formed by polymerization
     process, linking and cross linking a particular building block (monomer, a
     unit cell).

 •   The term polymer means many units repeated many times in a
     chainlike structure.

 •   Most monomers are organic materials, atoms are joined in covalent
     bonds (electron-sharing) with other atoms such as oxygen, nitrogen,
     hydrogen, sulfur, chlorine,….



Ken Youssefi              Mechanical Engineering            7
The structure of polymers




Ken Youssefi       Mechanical Engineering   8
Classification of polymers
There are two major classifications of polymers

Thermoplastics
As the temperature is raised above the melting point, the secondary bonds
weaken, making it easier to form the plastic into any desired shape. When
polymer is cooled, it returns to its original strength and hardness. The process
is reversible. Polymers that show this behavior are known as thermoplastics.



Thermosetting Plastics (thermosets)
Thermosetting plastics are cured into permanent shape. Cannot be re-melted to
the flowable state that existed before curing, continued heating for a long time
leads to degradation or decomposition. This curing (cross-linked) reaction is
irreversible. Thermosets generally have better mechanical, thermal and
chemical properties. They also have better electrical resistance and dimensional
stability than do thermoplastics.



Ken Youssefi               Mechanical Engineering            9
Polymer’s Structures
  Bonding – monomers are linked together by covalent bonds, forming a
  polymer chain (primary bonds). The polymer chains are held together by
  secondary bonds. The strength of polymers comes in part from the
  length of polymer chains. The longer the chain, the stronger the polymer.
  More energy is needed to overcome the secondary bonds.


      Linear polymers                        Branched polymers




A sequential structure resulting in    Side branch chains are attached to the
thermoplastics like nylon, acrylic,    main chain which interferes with the
polyethylene. A linear polymer         relative movement of the molecular chains.
may contain some branched and          This results in an increase in strength,
cross-linked chains resulting in       deformation resistance and stress cracking
change in properties.                  resistance. Lower density than linear chain
                                       polymers.
Ken Youssefi               Mechanical Engineering            10
Polymer’s Structures
Cross-linked polymers
Three dimensional structure, adjacent chains are linked
by covalent bonds. Polymers with cross-linked chains
are called thermosetting plastics (thermosets), epoxy
and Silicones.
                  Cross-linking is responsible for providing hardness,
                  strength, brittleness and better dimensional stability.


Network polymers
A three dimensional network of three or more
covalent bonds. Thermoplastic polymers that have
been already formed could be cross-linked to
obtain higher strength. Polymers are exposed to
high-energy radiation.


 Ken Youssefi              Mechanical Engineering              11
Additives in Plastics
     Additives are added to polymers in order to obtain or improve certain
     properties such as strength, stiffness, color, resistance to weather
     and flammability.

     Plasticizers are added to obtain flexibility and softness, most
     common use of plasticizers are in PVC.

     Ultraviolet radiation (sunlight) and oxygen cause polymers to become
     stiff and brittle, they weaken and break the primary bonds. A typical
     treatment is to add carbon black (soot) to the polymer, it absorbs
     radiation. Antioxidants are also added to protect against
     degradation.

     Fillers such as fine saw dust, silica flour, calcium carbide are
     added to reduce the cost and to increase harness, strength,
     toughness, dimensional stability,…..




Ken Youssefi              Mechanical Engineering              12
Additives in Plastics
   •   Colorants are added to obtain a variety of colors. Colorants are
       either organic (dye) or inorganic (pigments). Pigments provide
       greater resistance to temperature and sunlight.


   •   Flame retardants such as chlorine, phosphorus and bromine, are
       added to reduce polymer flammability. Teflon does not burn and
       nylon and vinyl chloride are self-extinguishing.


   •   Lubricants such as mineral oil and waxes are added to
       reduce friction.




Ken Youssefi              Mechanical Engineering             13
Applications of Thermoplastics
 Design requirement: strength

 Applications: Valves, gears, cams, pistons, fan blades, …

 Plastics: nylon, acetal (delrin), polycarbonate, phenolic



 Design requirement: wear resistance

 Applications: bearings, gears, bushings, wheels, ….

 Plastics: nylon, acetal (delrin), polyurethane, phenolic, polymide




Ken Youssefi              Mechanical Engineering             14
Applications of Thermoplastics
Design requirement: functional and decorative

Applications: knobs, handles, cases, moldings, pipe fittings, …

Plastics: ABS, acrylic, polyethylene, phenolic, polypropylene, polystyrene


Design requirement: functional and transparent

Applications: lens, goggles, signs, food processing equipment, …

Plastics: acrylic, polycarbonate, polystyrene, polysulfone


Design requirement: hollow shapes and housings

Applications: pumps, helmets, power tools, cases, …

Plastics: ABS, polyethylene, phenolic, polypropylene, polystyrene, polycarbonate

Ken Youssefi               Mechanical Engineering            15
Popular Plastics
   Polyethylene (LDPE (low density) and HDPE (high density)
   Properties: good chemical and electrical properties, strength
   depends on composition

   Applications: bottles, garbage cans, housewares, bumpers, toys, luggage


   Acetal (Delrin)
   Properties: good strength, good stiffness, good resistance to heat,
   moisture, abrasion and chemicals

   Applications: mechanical components; gears, bearings, valves, rollers,
   bushings, housings

   ABS
   Properties: dimensionally stable, good strength, impact and toughness
   properties, good resistance to abrasion and chemicals
   Applications: automotive components, helmets, tool handles, appliances,
   boat hulls, luggage, decorative panels
Ken Youssefi              Mechanical Engineering          16
Popular Plastics
  Polycarbonates
  Properties: very versatile and has dimensional stability, good
  mechanical and electrical properties, high resistance to impact and
  chemicals
  Applications: optical lenses, food processing equipments, electrical
  components and insulators, medical equipments, windshields, signs,
  machine components


  Nylons
  Properties: good mechanical and abrasion resistance property, self-
  lubricating, resistant to most chemicals but it absorbs water, increase in
  dimension is undesirable

  Applications: mechanical components; gears, bearings, rollers, bushings,
  fasteners, guides, zippers, surgical equipments,


Ken Youssefi              Mechanical Engineering             17
Applications of Thermosetting Plastics

 Epoxies
 Properties: good dimensional stability, excellent mechanical and
 electrical properties, good resistance to heat and chemicals

 Applications: electrical components requiring strength, tools and dies, fiber
 reinforced epoxies are used in structural components, tanks, pressure
 vessels, rocket motor casing


 Phenolics
 Properties: good dimensional stability, rigid, high resistance to
 heat, water, electricity, and chemicals

 Applications: laminated panels, handles, knobs, electrical components;
 connectors, insulators



Ken Youssefi              Mechanical Engineering              18
Applications of Thermosetting Plastics

 Polyesters (thermosetting, reinforced with glass fibers)
 Properties: good mechanical, electrical, and chemical properties,
 good resistance to heat and chemicals

 Applications: boats, luggage, swimming pools, automotive bodies, chairs



 Silicones
 Properties: excellent electrical properties over a wide rang of
 temperature and humidity, good heat and chemical properties

 Applications: electrical components requiring strength at high temp.,
 waterproof materials, heat seals




Ken Youssefi              Mechanical Engineering             19
Website: www.ge.com/plastics
                                                       Plastics




                                                Stress vs. Strain
                                                curve




Ken Youssefi           Mechanical Engineering   20
Structural and mechanical Appl. Light duty mechanical & decorative
                            Gears, cams, pistons, rollers, fan Handles, knobs, steering wheel,
                            blades, rotors, pump impellers, tool handles, pipe fittings, camera
                            washing machine agitators          cases, eyeglass frames
                        ABS                                                  X
                        Acetal (Delrin)       X
                        Acrylic                                              X
                        Cellulosics                                          X
                        Fluoroplastics
                        Nylon                    X
 Thermoplastics




                        Phenylene Oxide
                        Polycarbonate
                        Polyester
                        Polyethylene                                         X
                        Polyimide
                        Polyenylene sulfide
                        Polypropylene            X
                        Polystyrene                                          X
                        Polysulfone                                          X
                        Polyurethane
                        Polyvinyl chloride                                   X
Thermosets




                        Phenolic                 X                           X
                        Polyester
                        Polyurethane
                  Ken Youssefi                Mechanical Engineering    21
Parts for wear applications       Optical and transparent parts
                                 Gears, bearings, bushings,        Lenses, safety glasses,
                                 tracks, wheels, ware strips       signs, refrigerator shelves,
                                                                   windshields
                        ABS
                        Acetal (Delrin)          X
                        Acrylic                                                  X
                        Cellulosics                                              X
                        Fluoroplastics           X
                        Nylon                    X
 Thermoplastics




                        Phenylene Oxide
                        Polycarbonate                                            X
                        Polyester
                        Polyethylene             X
                        Polyimide                X
                        Polyenylene sulfide      X
                        Polypropylene
                        Polystyrene
                        Polysulfone                                              X
                        Polyurethane             X                               X
                        Polyvinyl chloride
Thermosets




                        Phenolic
                        Polyester                X
                        Polyurethane             X
                  Ken Youssefi                Mechanical Engineering        22
Small housing & hollow shapes     Large housing & hollow shapes
                                 Phone and flashlight cases,       Boat hulls, large appliance
                                 helmets, housings for power       housings, tanks, tubs,
                                 tools, pumps, small appliances    ducts, refrigerator liners
                        ABS                    X                                X
                        Acetal (Delrin)
                        Acrylic
                        Cellulosics              X
                        Fluoroplastics
                        Nylon
 Thermoplastics




                        Phenylene Oxide          X                              X
                        Polycarbonate            X
                        Polyester                X                              X
                        Polyethylene             X                              X
                        Polyimide
                        Polyenylene sulfide
                        Polypropylene
                        Polystyrene              X                              X
                        Polysulfone              X                              X
                        Polyurethane
                        Polyvinyl chloride                                      X
Thermosets




                        Phenolic                 X
                        Polyester                X                              X
                        Polyurethane                                            X
                  Ken Youssefi                Mechanical Engineering       23
Structural & Light    Small       Large    Parts for    Optical and
                        Plastic    Mechanical duty       housing &   housing wear          transparent
                                                mech &   hollow      & hollow applications parts
                                                deco     shapes      shapes
                        ABS                       X        X           X
                        Acetal (Delrin)     X                                      X
                        Acrylic                   X                                            X
                        Cellulosics               X        X                                   X
                        Fluoroplastics                                             X
                        Nylon               X                                      X
 Thermoplastics




                        Phenylene Oxide                    X           X
                        Polycarbonate                      X                                   X
                        Polyester                          X           X
                        Polyethylene              X        X           X           X
                        Polyimide                                                  X
                        Polyenylene sulfide                                        X
                        Polypropylene       X
                        Polystyrene               X        X           X
                        Polysulfone               X        X           X                       X
                        Polyurethane                                               X           X
                        Polyvinyl chloride        X                    X
Thermosets




                        Phenolic           X      X        X
                        Polyester                          X           X           X
                        Polyurethane                                   X           X

                  Ken Youssefi              Mechanical Engineering            24
Manufacturing Processes for Plastics

Fabrication of Plastics
   Injection Molding


Ejector pin            Molded part
                             Heaters                          Granular
                                                              plastic




                                                            Plunger
                                                 Torpedo




 Ken Youssefi           Mechanical Engineering         25
Ken Youssefi   Mechanical Engineering   26
DFM Design Guidelines
                 Injection Molding
Provide adequate draft
angle for easier mold
removal.




                                           Minimize section thickness,
                                           cooling time is proportional to
                                           the square of the thickness,
                                           reduce cost by reducing the
                                           cooling time.

Ken Youssefi             Mechanical Engineering        27
DFM Design Guidelines
                  Injection Molding


Keep rib thickness less than
60% of the part thickness in
order to prevent voids and
sinks.
                                             Avoid sharp corners, they
                                             produce high stress and
                                             obstruct material flow.




Ken Youssefi            Mechanical Engineering        28
DFM Design Guidelines
                 Injection Molding




Provide smooth transition,           Keep section thickness uniform
avoid changes in thickness           around bosses.
when possible.


Ken Youssefi          Mechanical Engineering       29
DFM Design Guidelines
                    Injection Molding
• Use standard general tolerances, do not tolerance;
     Dimension       Tolerance    Dimension       Tolerance
     0 ≤ d ≤ 25      ± 0.5 mm     0 ≤ d ≤ 1.0    ± 0.02 inch
     25 ≤ d ≤ 125    ± 0.8 mm     1 ≤ d ≤ 5.0    ± 0.03 inch
     125 ≤ d ≤ 300   ± 1.0 mm     5 ≤ d ≤ 12.0   ± 0.04 inch
     300             ± 1.5 mm     12.0           ± 0.05 inch
•    Minimum thickness recommended;
    .025 inch or .65 mm, up to .125 for large
     parts.
•   Round interior and exterior corners to .       Standard thickness
    01-.015 in radius (min.), prevents an          variation.
    edge from chipping.
Ken Youssefi            Mechanical Engineering         30
Rotational Molding

  Rotational molding process consists of six steps
 • A predetermined amount of plastic, powder or liquid
   form, is deposited in one half of a mold.
 • The mold is closed.
 • The mold is rotated biaxially inside an oven.
 • The plastics melts and forms a coating over the
   inside surface of the mold.
 • The mold is removed from the oven and cooled.
 • The part is removed from the mold.




Ken Youssefi          Mechanical Engineering         31
Rotational Molding Machines




  Vertical wheel machine

                                                     Turret machine




      Shuttle machine
                                                    Rock and roll machine
Ken Youssefi               Mechanical Engineering             32
Rotational Molding
 Advantages
       •   Molds are relatively inexpensive.
       •   Rotational molding machines are much less
           expensive than other type of plastic processing
           equipment.
       •   Different parts can be molded at the same time.
       •   Very large hollow parts can be made.
       •   Parts are stress free.
       •   Very little scrap is produced




Ken Youssefi           Mechanical Engineering     33
Rotational Molding
 Limitations

         •     Can not make parts with tight tolerance.
         •     Large flat surfaces are difficult to achieve.
         •     Molding cycles are long (10-20 min.)


   Materials
     Polyethylene (most common), Polycarbonate (high heat
     resistance and good impact strength), Nylon (good wear
     and abrasion resistance, good chemical resistance, good
     toughness and stiffness).

Ken Youssefi            Mechanical Engineering        34
Rotational Molding
   Nominal wall thickness
• Polycarbonate wall thickness is typically between .06 to .
  375 inches, .125 inch being an ideal thickness.
• Polyethylene wall thickness is in the range of .125 to .25
  inch, up to 1 inch thick wall is possible.
• Nylon wall thickness is in the range of .06 to .75 inch.




Ken Youssefi        Mechanical Engineering     35
Rotational Molding Examples




Ken Youssefi     Mechanical Engineering   36
Rotational Molding Examples




Ken Youssefi     Mechanical Engineering   37
Blow Molding
    Blow molding is generally the same process as glass blowing
    adapted to polymers.
    In extrusion blow molding a tube is extruded and clamped in a
    split mold. Air under pressure (50-100 psi) is injected into the
    tube blowing the plastic outward to fill the mold cavity.




Ken Youssefi            Mechanical Engineering         38
Blow Molding
  • Blow molding is used for medium size, hollow thin-walled
    shapes; containers, tool cases, hollow structures, ….
  • Blow molding is limited to thermoplastics such as
    polyethylene, polycarbonate, ABS.
  • Wall thickness between .015 - .125
  • Maximum tolerance .01 - .04




Ken Youssefi        Mechanical Engineering      39

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Plastics

  • 1. The word plastics is from the Greek word Plastikos, meaning “able to be shaped and molded” Ken Youssefi Mechanical Engineering 1
  • 2. Why Design with Plastics? • Light weight, high weight to • Relatively low cost compared strength ratio, particularly when to metals and composites reinforced Density Cost Ken Youssefi Mechanical Engineering 2
  • 3. Why Design with Plastics? • Corrosion resistance • Low electrical and thermal conductivity, insulator • Easily formed into complex shapes, can be formed, casted and joined. • Wide choice of appearance, colors and transparencies Ken Youssefi Mechanical Engineering 3
  • 4. Disadvantages of using Plastics • Low strength • Low useful temperature range (up to 600 oF) • Less dimensional stability over period of time (creep effect) • Aging effect, hardens and become brittle over time • Sensitive to environment, moisture and chemicals • Poor machinability Ken Youssefi Mechanical Engineering 4
  • 5. Ken Youssefi Mechanical Engineering 5
  • 6. Mechanical Properties of Various Plastics Steel: 350 to 1900 MPa Brass: 200 to 850 MPa Aluminum: 100 to 550 MPa Ken Youssefi Mechanical Engineering 6
  • 7. Polymers • The earliest synthetic polymer was developed in 1906, called Bakelite. • The development of modern plastics started in 1920s using raw material extracted from coal and petroleum products (Ethylene). Ethylene is called a building block. • Polymers are long-chain molecules and are formed by polymerization process, linking and cross linking a particular building block (monomer, a unit cell). • The term polymer means many units repeated many times in a chainlike structure. • Most monomers are organic materials, atoms are joined in covalent bonds (electron-sharing) with other atoms such as oxygen, nitrogen, hydrogen, sulfur, chlorine,…. Ken Youssefi Mechanical Engineering 7
  • 8. The structure of polymers Ken Youssefi Mechanical Engineering 8
  • 9. Classification of polymers There are two major classifications of polymers Thermoplastics As the temperature is raised above the melting point, the secondary bonds weaken, making it easier to form the plastic into any desired shape. When polymer is cooled, it returns to its original strength and hardness. The process is reversible. Polymers that show this behavior are known as thermoplastics. Thermosetting Plastics (thermosets) Thermosetting plastics are cured into permanent shape. Cannot be re-melted to the flowable state that existed before curing, continued heating for a long time leads to degradation or decomposition. This curing (cross-linked) reaction is irreversible. Thermosets generally have better mechanical, thermal and chemical properties. They also have better electrical resistance and dimensional stability than do thermoplastics. Ken Youssefi Mechanical Engineering 9
  • 10. Polymer’s Structures Bonding – monomers are linked together by covalent bonds, forming a polymer chain (primary bonds). The polymer chains are held together by secondary bonds. The strength of polymers comes in part from the length of polymer chains. The longer the chain, the stronger the polymer. More energy is needed to overcome the secondary bonds. Linear polymers Branched polymers A sequential structure resulting in Side branch chains are attached to the thermoplastics like nylon, acrylic, main chain which interferes with the polyethylene. A linear polymer relative movement of the molecular chains. may contain some branched and This results in an increase in strength, cross-linked chains resulting in deformation resistance and stress cracking change in properties. resistance. Lower density than linear chain polymers. Ken Youssefi Mechanical Engineering 10
  • 11. Polymer’s Structures Cross-linked polymers Three dimensional structure, adjacent chains are linked by covalent bonds. Polymers with cross-linked chains are called thermosetting plastics (thermosets), epoxy and Silicones. Cross-linking is responsible for providing hardness, strength, brittleness and better dimensional stability. Network polymers A three dimensional network of three or more covalent bonds. Thermoplastic polymers that have been already formed could be cross-linked to obtain higher strength. Polymers are exposed to high-energy radiation. Ken Youssefi Mechanical Engineering 11
  • 12. Additives in Plastics Additives are added to polymers in order to obtain or improve certain properties such as strength, stiffness, color, resistance to weather and flammability. Plasticizers are added to obtain flexibility and softness, most common use of plasticizers are in PVC. Ultraviolet radiation (sunlight) and oxygen cause polymers to become stiff and brittle, they weaken and break the primary bonds. A typical treatment is to add carbon black (soot) to the polymer, it absorbs radiation. Antioxidants are also added to protect against degradation. Fillers such as fine saw dust, silica flour, calcium carbide are added to reduce the cost and to increase harness, strength, toughness, dimensional stability,….. Ken Youssefi Mechanical Engineering 12
  • 13. Additives in Plastics • Colorants are added to obtain a variety of colors. Colorants are either organic (dye) or inorganic (pigments). Pigments provide greater resistance to temperature and sunlight. • Flame retardants such as chlorine, phosphorus and bromine, are added to reduce polymer flammability. Teflon does not burn and nylon and vinyl chloride are self-extinguishing. • Lubricants such as mineral oil and waxes are added to reduce friction. Ken Youssefi Mechanical Engineering 13
  • 14. Applications of Thermoplastics Design requirement: strength Applications: Valves, gears, cams, pistons, fan blades, … Plastics: nylon, acetal (delrin), polycarbonate, phenolic Design requirement: wear resistance Applications: bearings, gears, bushings, wheels, …. Plastics: nylon, acetal (delrin), polyurethane, phenolic, polymide Ken Youssefi Mechanical Engineering 14
  • 15. Applications of Thermoplastics Design requirement: functional and decorative Applications: knobs, handles, cases, moldings, pipe fittings, … Plastics: ABS, acrylic, polyethylene, phenolic, polypropylene, polystyrene Design requirement: functional and transparent Applications: lens, goggles, signs, food processing equipment, … Plastics: acrylic, polycarbonate, polystyrene, polysulfone Design requirement: hollow shapes and housings Applications: pumps, helmets, power tools, cases, … Plastics: ABS, polyethylene, phenolic, polypropylene, polystyrene, polycarbonate Ken Youssefi Mechanical Engineering 15
  • 16. Popular Plastics Polyethylene (LDPE (low density) and HDPE (high density) Properties: good chemical and electrical properties, strength depends on composition Applications: bottles, garbage cans, housewares, bumpers, toys, luggage Acetal (Delrin) Properties: good strength, good stiffness, good resistance to heat, moisture, abrasion and chemicals Applications: mechanical components; gears, bearings, valves, rollers, bushings, housings ABS Properties: dimensionally stable, good strength, impact and toughness properties, good resistance to abrasion and chemicals Applications: automotive components, helmets, tool handles, appliances, boat hulls, luggage, decorative panels Ken Youssefi Mechanical Engineering 16
  • 17. Popular Plastics Polycarbonates Properties: very versatile and has dimensional stability, good mechanical and electrical properties, high resistance to impact and chemicals Applications: optical lenses, food processing equipments, electrical components and insulators, medical equipments, windshields, signs, machine components Nylons Properties: good mechanical and abrasion resistance property, self- lubricating, resistant to most chemicals but it absorbs water, increase in dimension is undesirable Applications: mechanical components; gears, bearings, rollers, bushings, fasteners, guides, zippers, surgical equipments, Ken Youssefi Mechanical Engineering 17
  • 18. Applications of Thermosetting Plastics Epoxies Properties: good dimensional stability, excellent mechanical and electrical properties, good resistance to heat and chemicals Applications: electrical components requiring strength, tools and dies, fiber reinforced epoxies are used in structural components, tanks, pressure vessels, rocket motor casing Phenolics Properties: good dimensional stability, rigid, high resistance to heat, water, electricity, and chemicals Applications: laminated panels, handles, knobs, electrical components; connectors, insulators Ken Youssefi Mechanical Engineering 18
  • 19. Applications of Thermosetting Plastics Polyesters (thermosetting, reinforced with glass fibers) Properties: good mechanical, electrical, and chemical properties, good resistance to heat and chemicals Applications: boats, luggage, swimming pools, automotive bodies, chairs Silicones Properties: excellent electrical properties over a wide rang of temperature and humidity, good heat and chemical properties Applications: electrical components requiring strength at high temp., waterproof materials, heat seals Ken Youssefi Mechanical Engineering 19
  • 20. Website: www.ge.com/plastics Plastics Stress vs. Strain curve Ken Youssefi Mechanical Engineering 20
  • 21. Structural and mechanical Appl. Light duty mechanical & decorative Gears, cams, pistons, rollers, fan Handles, knobs, steering wheel, blades, rotors, pump impellers, tool handles, pipe fittings, camera washing machine agitators cases, eyeglass frames ABS X Acetal (Delrin) X Acrylic X Cellulosics X Fluoroplastics Nylon X Thermoplastics Phenylene Oxide Polycarbonate Polyester Polyethylene X Polyimide Polyenylene sulfide Polypropylene X Polystyrene X Polysulfone X Polyurethane Polyvinyl chloride X Thermosets Phenolic X X Polyester Polyurethane Ken Youssefi Mechanical Engineering 21
  • 22. Parts for wear applications Optical and transparent parts Gears, bearings, bushings, Lenses, safety glasses, tracks, wheels, ware strips signs, refrigerator shelves, windshields ABS Acetal (Delrin) X Acrylic X Cellulosics X Fluoroplastics X Nylon X Thermoplastics Phenylene Oxide Polycarbonate X Polyester Polyethylene X Polyimide X Polyenylene sulfide X Polypropylene Polystyrene Polysulfone X Polyurethane X X Polyvinyl chloride Thermosets Phenolic Polyester X Polyurethane X Ken Youssefi Mechanical Engineering 22
  • 23. Small housing & hollow shapes Large housing & hollow shapes Phone and flashlight cases, Boat hulls, large appliance helmets, housings for power housings, tanks, tubs, tools, pumps, small appliances ducts, refrigerator liners ABS X X Acetal (Delrin) Acrylic Cellulosics X Fluoroplastics Nylon Thermoplastics Phenylene Oxide X X Polycarbonate X Polyester X X Polyethylene X X Polyimide Polyenylene sulfide Polypropylene Polystyrene X X Polysulfone X X Polyurethane Polyvinyl chloride X Thermosets Phenolic X Polyester X X Polyurethane X Ken Youssefi Mechanical Engineering 23
  • 24. Structural & Light Small Large Parts for Optical and Plastic Mechanical duty housing & housing wear transparent mech & hollow & hollow applications parts deco shapes shapes ABS X X X Acetal (Delrin) X X Acrylic X X Cellulosics X X X Fluoroplastics X Nylon X X Thermoplastics Phenylene Oxide X X Polycarbonate X X Polyester X X Polyethylene X X X X Polyimide X Polyenylene sulfide X Polypropylene X Polystyrene X X X Polysulfone X X X X Polyurethane X X Polyvinyl chloride X X Thermosets Phenolic X X X Polyester X X X Polyurethane X X Ken Youssefi Mechanical Engineering 24
  • 25. Manufacturing Processes for Plastics Fabrication of Plastics Injection Molding Ejector pin Molded part Heaters Granular plastic Plunger Torpedo Ken Youssefi Mechanical Engineering 25
  • 26. Ken Youssefi Mechanical Engineering 26
  • 27. DFM Design Guidelines Injection Molding Provide adequate draft angle for easier mold removal. Minimize section thickness, cooling time is proportional to the square of the thickness, reduce cost by reducing the cooling time. Ken Youssefi Mechanical Engineering 27
  • 28. DFM Design Guidelines Injection Molding Keep rib thickness less than 60% of the part thickness in order to prevent voids and sinks. Avoid sharp corners, they produce high stress and obstruct material flow. Ken Youssefi Mechanical Engineering 28
  • 29. DFM Design Guidelines Injection Molding Provide smooth transition, Keep section thickness uniform avoid changes in thickness around bosses. when possible. Ken Youssefi Mechanical Engineering 29
  • 30. DFM Design Guidelines Injection Molding • Use standard general tolerances, do not tolerance; Dimension Tolerance Dimension Tolerance 0 ≤ d ≤ 25 ± 0.5 mm 0 ≤ d ≤ 1.0 ± 0.02 inch 25 ≤ d ≤ 125 ± 0.8 mm 1 ≤ d ≤ 5.0 ± 0.03 inch 125 ≤ d ≤ 300 ± 1.0 mm 5 ≤ d ≤ 12.0 ± 0.04 inch 300 ± 1.5 mm 12.0 ± 0.05 inch • Minimum thickness recommended; .025 inch or .65 mm, up to .125 for large parts. • Round interior and exterior corners to . Standard thickness 01-.015 in radius (min.), prevents an variation. edge from chipping. Ken Youssefi Mechanical Engineering 30
  • 31. Rotational Molding Rotational molding process consists of six steps • A predetermined amount of plastic, powder or liquid form, is deposited in one half of a mold. • The mold is closed. • The mold is rotated biaxially inside an oven. • The plastics melts and forms a coating over the inside surface of the mold. • The mold is removed from the oven and cooled. • The part is removed from the mold. Ken Youssefi Mechanical Engineering 31
  • 32. Rotational Molding Machines Vertical wheel machine Turret machine Shuttle machine Rock and roll machine Ken Youssefi Mechanical Engineering 32
  • 33. Rotational Molding Advantages • Molds are relatively inexpensive. • Rotational molding machines are much less expensive than other type of plastic processing equipment. • Different parts can be molded at the same time. • Very large hollow parts can be made. • Parts are stress free. • Very little scrap is produced Ken Youssefi Mechanical Engineering 33
  • 34. Rotational Molding Limitations • Can not make parts with tight tolerance. • Large flat surfaces are difficult to achieve. • Molding cycles are long (10-20 min.) Materials Polyethylene (most common), Polycarbonate (high heat resistance and good impact strength), Nylon (good wear and abrasion resistance, good chemical resistance, good toughness and stiffness). Ken Youssefi Mechanical Engineering 34
  • 35. Rotational Molding Nominal wall thickness • Polycarbonate wall thickness is typically between .06 to . 375 inches, .125 inch being an ideal thickness. • Polyethylene wall thickness is in the range of .125 to .25 inch, up to 1 inch thick wall is possible. • Nylon wall thickness is in the range of .06 to .75 inch. Ken Youssefi Mechanical Engineering 35
  • 36. Rotational Molding Examples Ken Youssefi Mechanical Engineering 36
  • 37. Rotational Molding Examples Ken Youssefi Mechanical Engineering 37
  • 38. Blow Molding Blow molding is generally the same process as glass blowing adapted to polymers. In extrusion blow molding a tube is extruded and clamped in a split mold. Air under pressure (50-100 psi) is injected into the tube blowing the plastic outward to fill the mold cavity. Ken Youssefi Mechanical Engineering 38
  • 39. Blow Molding • Blow molding is used for medium size, hollow thin-walled shapes; containers, tool cases, hollow structures, …. • Blow molding is limited to thermoplastics such as polyethylene, polycarbonate, ABS. • Wall thickness between .015 - .125 • Maximum tolerance .01 - .04 Ken Youssefi Mechanical Engineering 39