Apiwat Muttamara
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Transcript of Apiwat Muttamara
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Apiwat Muttamara
Polymer and
Plastics Manufacturing
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Outline
• Polymer
• Equipment and process steps
• Design for manufacturing, tooling and defects
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Materials
Solid materials
metals ceramics
Plastics
thermoplastics
thermosetts
elastomers
Plastic: Greek, plastikos, means to form or mold
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Automotive Plastics and Composites Use
• Exterior– doors– hoods – fenders – bumper covers (most cars have soft fascia)
• Interior– instrument panels, door trim, seats, consoles
• Engine– valve covers, intake manifolds, fluid containers, etc.
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Plastics History
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Thermoplastics & Thermosets
amorphousor
semicrystallinecross-linked(3D network)
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THERMOPLASTIC, THERMOSET:
• Thermoplastics are resins that can be reground after molding, and molded again.
• Thermoplastic are often compared to Wax.
• Thermosets can be molded once only; they tend to be denser materials for special purposes , thermosets are often compared to an egg; once the egg is hard boiled it can't be returned to a liquid and recooked as sunny side up.
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Polymer poly = many
mer = part
A polymer is a long chain molecule
that is composed of a large number
of repeating units of identical structure.
• While the term polymer in popular usage suggests "plastic",
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Petroleum
These different hydrocarbons have different boiling points, which means they can be separated by distillation
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Polymerization of Polyethylene
n = degree of polymerization
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Thermoplastics
Amorphous
Transparent
Semicrystalline
TranslucentOpaque
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Fringed-micelle model of semicrystalline polymers
โมเลกลุมกีารจดัเรยีงโดย
สว่นหน่ึงเรยีงตัวอยา่งไมเ่ป็นระเบยีบ(amorphous region)
และบางสว่นจดัเรยีงอยา่งเป็นระเบยีบ(crystalline region)
SEMI-CRYSTALLINE POLYMERS(พอลิเมอรก่ึ์งผลึก)
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YIELD AND TENSILE STRENGTHS OF PLASTIC POLYMER
Specimen breaks
YIELD
Yield stress (sy) ความเค้นท่ีพบการเสยีรูปพลาสติก(plastic deformation)
Tensile strength (TS) (สำาหรบัพอลิเมอร์) ความเค้นท่ีชิน้งานแตกหัก ** (ทั่วไป) ความเค้นสงูสดุบนกราฟ engineering
stress-strain
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STAGES OF DEFORMATION OF A SEMI-CRYSTALLINE POLYMER
MACROSCOPIC DEFORMATION
Note: พบลักษณะคอดก่ิวภายใต้การดึง เรยีกวา่ Necking
necking
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STAGES IN DEFORMATION OF A SEMICRYSTALLINE POLYMER
Before deformation
Elongation of amorphous tie chains
Tilting of lamellar chain folds
Separation of crystalline block segment
Orientation of block segments
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Thermoplastic and Thermosetting Polymers
Polymers
Thermosets Thermoplastics (crosslinked and network polymers)vulcanized rubbers, Polyurethane Epoxy, Polyester
High Commodity Engineering Performance Amorphous Semicrystalline
PVC, PS PE, PP
Amorphous Semicrystalline
Polyetherimide PolysulfonePolyphenylene Sulfide (PPS)
Amorphous Blends Semicrystalline ABS, PC
PPE, AcrylicPPE/Nylon
PC/PBTABS/PC
AcetalPBT, PET
Polyamide (Nylon)
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Phenolics (named Bakelite by Leo Bakeland) - Resin could be shaped and hardened with heat - Phenol and formaldehyde reaction after heat - Replacement for shellac, natural plastic (1907)
Early Plastics
Nylon66 - W. H. Carothers of DuPont (1920’s)PVC - W. Semon of B.F. Goodrich (1929)
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Codes for plastics
Recycling of Plastics
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Polymer Additives A polymer contains several additives to aid during processing,
add color, or enhance the mechanical properties. Fillers reinforcing fillers improve mechanical properties non-reinforcing fillers (or extenders) reduce cost Plasticizers reduce Tg therefore the flexibility is improved Stabilizers prevent degradation of polymer from heat or UV Colorants add color to polymers Flame Retardants enhance the flammability resistance
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Amorphous Commodity ThermoplasticsKey Characteristics
• Low cost• Low temperature resistance• Low strength• Good dimensional stability• Bonds well• Typically transparent
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Amorphous Commodity ThermoplasticsMaterials
• Polymethyl methacrylate (PMMA) • Polystyrene (PS)• Acrylonitrile butadiene styrene (ABS)• Polyvinyl chloride (PVC)• Polycarbonate (PC)
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Acrylic (PMMA) Strengths
• Availability of all ranges of optical transparency, including opacity
• Rigidity• Surface hardness• Half the weight of glass• Heat resistance• Low impact strength
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Acrylic (PMMA)
• Protective glazing• Windows• Toys• Point of purchase (POP)
displays
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Polystyrene (PS)
• Low impact resistance• Brittle after UV exposure• Cannot be used at elevated
temperatures• Mechanical stress
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Acrylonitrile Butadiene Styrene (ABS)
• Good impact resistance• Easily formable• Many different formulations
EX. Computer housingsConsumer electronicsAutomotive
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Polyvinyl Chloride (PVC)Strengths
• Low cost• Good chemical
resistance• Versatile• Naturally UV resistant• Good strength
Packaging
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Polycarbonate (PC)
• Vandal resistant windows• Machine guards• Outdoor signs• Sky lights• Backboards• Bike, roller blading protective
wear
Excellent toughness Excellent strength
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Semi-Crystalline Commodity Plastics
• Polyethylene (PE)– High density polyethylene (HDPE)– Low density polyethylene (LDPE), (LLDPE)
• Polypropylene (PP)• Polyethylene Terephthalate (PET)
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Low Density Polyethylene (LDPE)High Density Polyethylene (HDPE)
• Films• Industrial trash bags• Liners• Shipping bags• Marine industry• Playgrounds• Bathrooms• Pipe• Automotive
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Polypropylenes (PP)Applications
• Packaging• Automotive• Consumer/durable goods• Vacuum formed parts• Fiber/carpet
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Polyethylene Terephthalate (PET)
• High dimensional stability under heat• High stiffness and hardness• Good bearing strength• Good electrical properties• Good resistance to chemicals• Good stress-cracking resistance• Excellent flow characteristics
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Plastic Processes
• Thermoplastic– Extrusion– Blow mold– Rotational Molding– Injection– Thermo forming– Injection molding
• Thermosetting– Compression– Transfer
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Plastics Processing: Compression and Transfer Molding
• used mostly for thermosetting polymers• mold is heated and closed using pressure• plastic flows to fills the cavity• flash must be trimmed by finishing
dishes, handles for cooking potsskis, housing for high-voltage switchessome rubber parts like shoe solesand even composites such as fiber-reinforced parts
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Plastics Processing: Compression and Transfer Molding
compression molding
transfer molding
(more complex shapes)
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Plastics Processing: Extrusion
pelletsopen cross-sections (channels) closed cross-sections (tubes, pipes) pelletsopen cross-sections (channels) closed cross-sections (tubes, pipes)
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Plastics Processing: Blow molding
heated glass
3-piece mold
(a) The hollow piece of heated glass (parison)is first created by a blow mold(see text-book Fig 17.25)
(b) The mold is put together
(c) Plunger and hot air push theglass up
(d) Hot air blows the glass out towardsthe mold surface
(e) Mold comes apart, bottle is removed
heated glass
3-piece mold
(a) The hollow piece of heated glass (parison)is first created by a blow mold(see text-book Fig 17.25)
(b) The mold is put together
(c) Plunger and hot air push theglass up
(d) Hot air blows the glass out towardsthe mold surface
(e) Mold comes apart, bottle is removed
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The process generally makes use of polyethylene powders, other powders, and liquids. However, nylon, elastomers, fluoropolymers, and polypropylene can also be used
Rotational Molding
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Sample
Rotational molding, otherwise known as rotomolding or rotational casting, is a thermoplastic processing method for producing simple to complex, leak-proof hollow parts that can be filled with foam.
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Plastics Processing: Thermoforming
Sheet of plastic Heated (soft) Molded using a shaped die
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Vacuum thermoforming
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ThermoformingHeater
Plastics sheetClamping
Vacuum
*
**
* Source: R. Ogorkiewicz, “Engineering Properties of Thermoplastics.”; ** http://www.arrem.com/designguide/dgprocesscap.htm
Thin corner
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Plastics Processing: Injection Molding
- Probably the most common, most important, most economical process
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Injection Molding Machine
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Steps of Injection Molding – Mold closing
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Mold filling
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Packing, holding, cooling
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Mold opening, part removal
Ejector pins
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Mold Structure
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Mold Structure - Cavity and core
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Mold Structure: Parting line
A dividing line between a cavity plate and a core plate of amold.- Make a parting line on a flat or simple-curved surface so that flash cannot be generated.- Venting gas or air.
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Two plate mold
One parting line
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Three plate mold
Two parting lines
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Melt Delivery
Sprue A sprue is a channel through which to transfer molten plastics injected from the injector nozzle into the mold.
Runner A runner is a channel that guides molten plastics into the cavity of a mold.
Gate A gate is an entrance through which molten plastics enters the cavity.
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Gate- Delivers the flow of molten plastics. - Quickly cools and solidifies to avoid backflow
after molten plastics has filled up in the cavity. - Easy cutting from a runner- Location is important to balance flow and
orientation and to avoid defects.
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Runner cross section
Runner cross section that minimizes liquid resistance and temperature reduction when molten plastics flows into the cavity.
- Too big- Longer cooling time, more material, cost
- Too small- short shot, sink mark, bad quality
- Too long- pressure drop, waste, cooling
Hot runner, runnerless mold
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Runner balancing
Balanced
Not balanced
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Defects
Molding defects are caused by related and complicated reasons as follows: * Malfunctions of molding machine * Inappropriate molding conditions * Flaws in product and mold design * Improper Selection of molding material
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Weldline
This is a phenomenon where a thin line is created when different flows of molten plastics in a mold cavity meet and remain undissolved. It is a boundary between flows caused by incomplete dissolution of molten plastics. It often develops around the far edge of the gate.
CauseLow temperature of the mold causes incomplete dissolution of the molten plastics. SolutionIncrease injection speed and raise the mold temperature. Lower the molten plastics temperature and increase the injection pressure. Change the gate position and the flow of molten plastics. Change the gate position to prevent development of weldline.
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Flashes
Flashes develop at the mold parting line or ejector pin installation point. It is a phenomenon where molten polymer smears out and sticks to the gap.
CausePoor quality of the mold. The molten polymer has too low viscosity. Injection pressure is too high, or clamping force is too weak. SolutionAvoiding excessive difference in thickness is most effective.Slow down the injection speed.Apply well-balanced pressure to the mold to get consistent clamping force, or increase the clamping force.Enhance the surface quality of the parting lines, ejector pins and holes.
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Short shotThis is the phenomenon where molten plastics does not fill the mold cavity completely. and the portion of parts becomes incomplete shape.
CauseThe shot volume or injection pressure is not sufficient.
Injection speed is so slow that the molten plastics becomes solid before it flows to the end of the mold. SolutionApply higher injection pressure. Install air vent or degassing device. Change the shape of the mold or gate position for better flow of the plastics.
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Warpage
This deformation appears when the part is removed from the mold and pressure is released.
CauseUneven shrinkage due to the mold temperature difference (surface temperature difference at cavity and core), and the thickness difference in the part. Injection pressure was too low and insufficient packing.
Solution Take a longer cooling time and lower the ejection speed. Adjust the ejector pin position or enlarge the draft angle. Examine the part thickness or dimension. Balance cooling lines. Increase packing pressure.
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Sink marks
-Equal cooling from the surface-Secondary flow-Collapsed surface
Sink Mark
ts
t
ts < t
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CAE (computer aided engineering)
Process simulationMaterial data baseCADMOLDFLOWC-Flow
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Considerations in design of injection molded parts
Guideline (3) gate location determines weld lines
weld lines
* Source: http://www.idsa-mp.org/proc/plastic/injection/injection_design_7.htm
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Injection Molding: molds with moving cores and side-action cams
- If the geometry of the part has undercuts [definition ?]
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Mold Structure: Undercut, Slide core
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Designing injection molds: typical features
[source: www.idsa-mp.org]
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(a) Shut-off hole:no side action required
(b) Latch:no side action required
(c) Angled Latch:Side action cam required
(a) Shut-off hole:no side action required
(b) Latch:no side action required
(c) Angled Latch:Side action cam required
Designing injection molds: typical features