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PLASTICS INJECTIONCost Estimation
Procurement GroupManufacturing Enhancement Center
Global Manufacturing DivisionPanasonic Corporation
1. Plastics resin (1) Category High Molecular Substance
Protein
Starch
Fiber Natural Natural Rubber
Oil resin Pine resin
Resin Thermosetting
resin
Synthetic (Phenol, Bakelite)
resin
Thermoplastic
PLASTICS resin
(Polystyrene Polyethylene
Polypropylene, etc)
High Molecular Substance has a molecular weight exceeding 10,000.
(2) What is plastic? The name Plastics is given to a huge range of man-made materials
which can be shaped when heated and made to keep their shape.
Plastics belong to ORGANIC MATERIALS.
ORGANIC MATERIALS
OIL, COAL,
ORGANISMS OF ANIMALS & PLANTS
PROTEIN, WOOD, COTTON, WOOL, HAIR, SKIN,NAIL, PAPER, ETC
INORGANIC MATERIALS
STONE, GLASS, CERAMICS, SOIL, ETC
(3) Comparison of materials & work process 1) Comparison of material
MATERIAL ADVANTAGE DISADVANTAGE
CERAMIC
• Heat-resistant • Easily formed into
complicated shapes
• Non-flammable Excellent insulator
• Fragile
PLASTICS • Rust- proof
• Light
Easily formed into complicated shapes
• Poor heat- resistant • Poor mechanical strength • Flammable • Difficult to be disposed
METAL • Highly conductive • Hard • Heat-resistant
Non-flammable
• Rust easily
2) Comparison of work process
MATERIAL MAIN WORK PROCESS
CERAMICS Sintering
PLASTICS
• Injection molding • Extrusion molding • Compression molding • Transfer molding • Blow molding • Vacuum molding • Expandable molding
METAL
• Die casting • Machining (cutting, milling drilling, grinding, buffing, etc) • Stamping • Forging • Etching
(4) Nature of plastics
1) Plastics are entirely man-made.
2) Plastics are made from chemicals which come from
natural products like oil, gas, and coal.
3) Chemicals are not mysterious things found only in a
scientist's laboratory.
4) Organic materials are made up of chemical elements like
carbon, oxygen, hydrogen, nitrogen sulfur, etc.
5) Plastics are made by mixing together the atoms of these
various elements.
6) Every plastic you see is made by forming compounds
(mixtures) of atoms. It never happens naturally. Engineers
have to make it happen.
(5) General characteristics of plastics
ADVANTAGES DISADVANTAGES
1. Excellent electrical properties
2. Light and strong
3. Excellent chemical resistance
4. Easy coloring
5. Easily formed into various shapes
6. Suitable for mass production
7. Non-toxic in general
1. Subject to heat deformation
2. Soft surface results in scratches
3. Poor mechanical strength
4. Some are attacked by solvents.
5. Difficult disposal after use.
2. Plastics material
(1) Synthetic resins widely interpreted
PF (Phenol)
Thermo setting resins UF (Urea)
UP (Unsaturated polyester)
EP (Epoxy) , etc.
PS (Polystyrene)
AS
ABS
PE (Polyethylene)
Thermo plastic resins PP (Polypropylene)
PVC (Polyvinyl chloride)
POM (Polyacetal)
Synthetic resins PA (Poyamide(Nylon))
PC (Polycarbonate),etc
Neoprene
Synthetic rubbers Chloroprene
Butadien
Nitrile rubber
Nylon
Synthetic fibers Vinylon
Acrylic
Polyester, etc
Synthetic leathers Nylon
Vinyl chloride, etc
(2) Type of plastic molding materials
1) Thermosetting resin
Type Density Characteristics Use
PF
Phenol
resin
1.4
(For general
use)
<Advantages>
Physical properties can be changed by filler.
Excellent moldability.
Resin itself has good mechanical strength, electric
properties, heat resistance and chemical resistance.
<Disadvantage>
Water and acid-resistant but not alkali-resistant.
Electric properties are good but arc resistance is
especially low.
Since natural color is light orange, coloring is limited.
*Plugs
*Handles and
knobs of heating
appliances
*Switches
*Sockets
Laminate examples
*PC board
*Various terminal
boards
UF
Urea
resin
1.5
(For general
use)
<Advantages>
Unlimited coloring.
Moldability excellent, but inferior to that of phenol.
<Disadvantage>
Water resistance, heat resistance, mechanical
strength and impact strength inferior to those of
phenol.
*Tableware
*Toy parts
*Buttons
*Poly wood
adhesives
UP
Polyester
resin
1.8～2.3
Glass fiber
base
<Advantages>
Excellent electric insulation, arc resistance, high-
frequency resistant properties, heat resistance and
acid resistance.
Colorless and transparent, and can be freely
colored.
<Disadvantages>
Inferior in weather and alkali resistance.
*TV tuner segments
*Gears
*Switches
Laminate examples
*Furniture, cabinets,
building materials
EP
Epoxy
Resin
1.6～2.0
Mineral
filling
<Advantages>
Excellent in electric properties, mechanical strength,
water resistance, chemical resistance, machinability
and especially arc resistance.
Low shrinkage rate.
<Disadvantages>
Limited coloring.
*Switches
*Plugs, sockets
*Materials of simple
low-cost molds
*Coatings
*PC boards
*Semiconductor
sealing material
1) Thermosetting resin
2) Thermoplastic resin
Type Density Characteristics Use
PS
(styrene resin)
Polystyrene
1.05 <Advantages>
High moldability; colorless and transparent, and can
be freely colored.
Excellent electrical properties.
Inexpensive.
<Disadvantage>
Low impact strength.
*Cabinets of radios,
tape recorders etc.
*Knobs
*Scale plates
*TV cabinets
PSAN
As resin
1.08 <Advantages>
High tensile strength, practical impact strength,
practical heat-resistant temperature and high
reverse hardness.
Less crazing due to strain after molding.
Virtually transparent and can be freely colored.
Well-balanced physical properties.
<Disadvantage>
Complete colorless and transparent products
cannot be obtained in the polymerization process.
*Battery housings
*Electric fan vanes
*Refrigerator
vegetable cases
*Scale plates
2) Thermoplastic resin ABS
ABS resin
1.05
<Advantages>
Improved impact and heat resistance, with the
mechanical and electrical properties of styrene
maintained.
Good surface hardness and oil resistance.
<Disadvantages>
Low weather resistance. Especially subject to
damage by ultraviolet rays.
Difficult to obtain transparent products.
*Cabinets of radios,
tape recorders etc.
*Knobs (plated)
*Cleaner body
*Computer housing
PE
Polyethylene
High
pressure
0.92
Medium
pressure
0.935
Low
pressure
0.955
<Advantages>
・Good electrical properties, especially high frequency
insulation. Mechanical properties resistant to low
temperatures.
Excellent water and chemical resistance.
Light.
Inexpensive.
<Disadvantages>
No suitable adhesives. Difficult to print or coat.
Unless residual strain is removed, stress cracks
may develop into fractures.
*Dry cell sealing
plates
*Small parts of
washing machines
*Polyethylene bags,
agricultural films
*Electric wires,
feeders
*Bottles, containers,
buckets
*Molded foams
2) Thermoplastic resin
Type Density Characteristics Use
PP
Polypropylen
e
0.91 <Advantages>
Especially good high-frequency properties and
voltage withstanding.
Resistant to high temperatures.
Battery lids, taking advantage of hinge properties
Good rigidity, elasticity and tensile strength.
Especially resistant to bending fatigue and used as
hinges.
<Disadvantage>
No suitable adhesives due to high chemical
resistance.
*Washing machine
tanks and pulsator
PVC
Polyvinyl
chloride
1.4 <Advantages>
Self-extinguishable.
Excellent in water resistance, acid resistance and
alkali electrical property.
<Disadvantages>
Decomposes at a high temperature and produces
putrefactive gas.
Use in contact with other plastics may cause
unexpected troubles.
*Electric wires
*Nameplates
*Electric wiring pipes
*Carrying cases
*Water pipes
*Eaves troughs
2) Thermoplastic resin PMMA
Acrylic resin
1.2 <Advantages>
Excellent in transparency and ultraviolet ray
permeability.
Excellent in light fastness, weather resistance,
chemical resistance, electrical properties, high-
frequency properties and mechanical strength.
<Disadvantage>
Slightly inferior in moldability.
*Scale plates,
nameplates
*Record player
covers
*Contact lenses
*Optical lenses
*Buttons
*High-grade
coatings
*Advertizing lamps,
signboards
POM
Polyacetal
1.4
<Advantages>
Good mechanical properties, such as fatigue
durability, abrasion resistance, creep property,
organic-solvent resistance, tensile strength and
bending strength.
Excellent heat resistance.
<Disadvantages>
Low dimensional stability. Not resistant to acids,
alkalis and ultraviolet rays.
No suitable adhesives.
*Gears
*Shafts, bearings
*Pulleys
*Snaps, taking
advantage of spring
property
PA
Polyamide 1.15
<Advantage>
Good mechanical properties, especially abrasion
resistance and mechanical strength.
Heat resistance also good
<Disadvantages>
Has high water absorbency and lacks dimensional
stability.
Weather resistance is low enough to cause
discoloration.
*Gears
*Bearings
*Coil bobbins
*Scoops for hot
plates
*Wires for electric
blankets
PC
Polycarbonate
1.2 <Advantages>
Very good rigidity.
Excellent in impact strength, tensile strength, creep
property and heat resistance.
Good transparency and dimensional stability.
<Disadvantage>
Subject to damage by alkali or various solvents
such as ketone.
*Compact discs
*Camera bodies
*Steam iron tanks
*Nails, screws
*Nursing bottles
*Automobile
bumpers
2) Thermoplastic resin
2) Thermoplastic resin PPO 1.1～1.4 <Advantages>
Heat resistant and, as mechanical properties, hard
and very tough.
Good in dimensional stability and electrical
properties.
This resin's properties do not change even at
180℃, and are not influenced by wide frequency
changes.
Self-extinguishing
Solder resistant
<Disadvantage >
Inferior for formability and expensive.
*Coil bobbins
*Housing of pump
parts
*Medical instruments
PEI
Polyester
imide
1.27 <Advantages>
Transparent
Excellent in weather resistance and heat(200℃)
resistance.
Excellent also in electrical properties for a wide
range of temperature conditions.
Resistant to chemicals(fatty hydrocarbons, acids,
alkalis)
Excellent in fluidity and formability
Good in dimensional stability
The resin generates little smoke when burning
*Connectors,
bobbins
*IC sockets
*Filters, pump parts
(3) Relation between endurable temperature and prices
(℃) 300 250
200 150
100
50
0
0 1 3 5 10 30 50 100 300 500 PRICE(US$/kg)
PS HDPE
PVC PP
ABS
POM
PPO
PBT PC
PA
PTFE
PPS
PEEK
PA
PES
PEI
PI
PAI
General plastic
Engineering plastic
Super engineering plastic
(4) Relation between tensile strength and heat distortion temperature
TENSILESTRENGTH
GENERAL-PURPOSE ENGINEERING PLASTIC
(kg/cm2) 1000
500 100 50 100 500
HEAT DEFORMATION TEMPERATURE(℃ )
SUPER HEAT – RESISTANTENGINEERING PLASTIC
PA6PET PPO
POM PC
PBT
PVCPS
PP
HDPE
LDPE
GENERAL – PURPOSEPLASTIC
3. Coloring methods
Synthetic resins are sometimes used after they are colored according to their use.
Many coloring methods are available.
The following are major coloring methods.
COLORED PELLET
MASTER BATCH
DRY COLOR House wares
LIQUID COLOR House wares
Coloring Application
Industrial Products
Industrial Products
(1) Colored pellet Colored pellets are made by pelleting the extrusion plastic combined with coloring agent and pigment in a machine. • Coloring charges are the highest among alI the coloring methods. • Compounds are uniformly colored.
Striking color is available. • Colored pellets are widely used for thermoplastic resins. • No coloring facilities are necessary.
(2) Master batch A master batch is a mixture of concentrated pigment and natural pellets.A plastic injection manufacturer can get any mixture ratio
according tocustomers’ requirements in a mixer by itself.
-• A master batch occasionally produces non uniform parts on the - surface of a product due to insufficient coloring and ill suited machine
conditions. • Coloring charges are lower than those of colored pellets. • A new type of master batch mixed with
Anti-static additives Ultraviolet ray absorbents Flame retards has become into wide use.
(3) Dry color
(4) Liquid color
Dry color is in micro-powder form and made of pigment and dispersion agent. • Coloring charges are the lowest among all the coloring methods. • Dry color sometimes causes contamination of workplaces. • Dry color is seldom used in Matsushita.
Liquid color is in liquid form and made of pigment and liquid dispersion agent. • No preparatory mixing facilities are necessary. • Liquid color has great effect on characteristics of plastic resins. • Storage life of liquid Color is short. • Liquid color is seldom used in Matsushita.
Clas- sifi- cation
Molding Method
Plastic Com
pres
si-
on
Tran
sfer
Inje
ctio
n
Ext
rusi
on
Blo
w
Vac
uum
Exp
ansi
on
Phenol 〇 〇 〇 △
Urea 〇 〇 〇
Melamine 〇 〇 △
Epoxy 〇 △ △
The
rmos
ettin
g r
esin
s
Polyester 〇 〇 △
Vinyl chloride 〇 〇 〇 〇 〇
Polystyrene 〇 〇 〇 〇 〇
Polyethylene 〇 〇 〇 〇
Polypropylene 〇 〇 〇 〇
Polyamide 〇 〇
Polyacetal 〇 〇
Polycarbonate 〇 〇 〇
The
rmop
last
ic
resi
ns
Polymetacrylate 〇 〇
A Wide Variety of plastic molding ways is available.
4. Plastics molding
(1) Major plastics molding
(2) Plastics molding methods Molding Method Outline Structure
Application Areas
Injection
molding
Plastic molding material is heated and melted in injection molding machine cylinder, filled by pressure into a tightly shut mold cavity with injection plunger or screw and taken out as molded product after solidified or hardened.
Exterior acces- sories and small parts of electric home appliances
Extrusion
molding
Thermoplastic resin material is heated and pressurized inside extrusion molding machine. Thus fluidized material is continuously extruded From mold to obtain desired shape. Plastic products produced by this method include pipes, bars, extruded profiles, coated electric wires, sheets, films, monofilaments and fibers.
Shelves for wooden
cabinet, vinyl-coated
electric wire, pipes,
boards
Compression
molding
Plastic molding material is put into mold cavity,
molded by heating and compressing, then taken
out after cooled and solidified.
In general this method is used for thermosetting
plastic molding, although it is also used for special
thermoplastic resin molding (e.q. records).
Wiring sockets/ switch cases, knobs of heating equipment, insu-
lating terminals
(2) Plastics molding methods
Transfer
molding
A thermosetting resin molding method; molding
material, plasticized in heating chamber, is pressure
-injected into heated mold cavity. There are two
types of transfer molding machines: pot type
and plunger type, which is equipped with an
auxiliary ram.
Sockets, switch cases etc.
Blow
molding
Resin, heated and melted in molding machine
cylinder, is extruded in tube shape (parison) and
put between molds.
Compressed air is blown in for material to tightly
adhere to mold. At the same time the material
is cooled and molded with its interior vacant.
Tubular battery cases, dehumidi- fier tanks of air conditioners, bottles, dolls
Vacuum
molding
Material, molded into sheet beforehand, is heated
and softened, then placed over mold (metal,
wooden, thermosetting resin etc.). Peripheral area
of the sheet being fixed, mold interior is evacuated
for the sheet to tightly adhere to mold.
Either male or female mold is used.
Refrigerator inner body, globe of lighting appli-
ances
Expansion
molding
Resin material containing foaming agent is pre-foamed with water vapor used as heat source. It is then either put into mold and foamed with high expansion rate (25 to 50times), or heated and melted in injection molding machine cylinder, pressure-injected into pressurized mold and foamed with low expansion rate (1.1 to 2 times).
Packing materials, heat insulating materials
(1) Machine (Injection molding)
Small size machine : 10 - 70 t
Large size machine : 550 t over
Medium size machine : 80 – 450 t
(4) Name of injection parts
1) Molded products with a sprue and runners
2 ) M o l d e d p r o d u c t s w i t h a s p r u e a n d r u n n e r s g a i n e d i n a s h o t
Sprue and runners are the passage of melted compounds to a mold and will be disposed of or recycled for reproduction.
(5) Injection molding methods
1) Outline of injection molding
Most of plastic parts used by Panasonic Group of companies are made
through injection molding.
Only thermoplastic resins can be used for injection molding machines.
Injection molding is a way of injecting melted compounds (mixtures) into
a mold, which is a hollow shape, inside which parts are made so that they
take on the same shape.
INJECTION MOLDING MACHINE
2) Operation of injection molding
A CYCLE OF INJECTION MOLDING
(1) CLAMPING
The clamping block closes and holds the mold by hydraulic
power tightly.
Melted compounds are fed into a heated cylinder with a
revolving screw inside.
(2) INJECTION
The revolving screw advances and then melted compounds
are injected into a mold through a nozzle at a very high
pressure ranging from 250 to 450kg/cm.2
The mold is fully filled with melted compounds
(3) HOLDING PRESSURE
Injected compounds are left under pressure for a while.
(4) COOLING
The screw retreats and the pressure is released. Injected compounds are cooled by circulating cooling water in a built-in pipe. In the meantime, the cylinder is filled with compounds for the next injection.
(5) OPERATING MOLD OPENING --- REMOVAL OF PARTS--MOLD CLOSING
The mold is opened and the parts with sprues and runners are removed.
Then the mold is closed for the next cycle.
(6) Molds for injection molding Two types of injection molds are available. They are a two-plate and three-plate molds. A mold is a hollow shape, inside which products are made so that they take on the same shape. Or the shape might be solid and the shape is constructed around it. When the two or three plates of a mold are fitted together, the space inside is the shape and size of the product being made. 1) Two-plate mold * A two-plate mold is commonly used for most types of parts. * A two-plate mold is not suitable for pinpoint gates. * Products are removed from the mold together with sprues and runners when the
mold opens.
2) Three-plate mold * Molds with pinpoint gates must be three-plate ones. * Sprues and runners are automatically removed from the gates when the mold
opens.
3) Points on injection mold
It is not too much to say that
“The quality of a plastic injection part is largely dependent
upon the quality of its mold.”
A good mold is the very gist to get good injection parts.
WHAT IS A GOOD MOLD?
A good mold is one
・ which enables parts to be released smoothly.
・ which is well designed, trouble free and long lasting.
・ which has a reasonable price and a short manufacturing
period for completion.
<BREAKDOWN OF MOLD COST IN JAPAN>
MOLDS FOR APPEARANCE PARTSMOLDS FOR APPEARANCE PARTS
0 50 100
Machining
50%
Finishing Assembling
16%
Design
15%
Material
Cost 10%
Others
MOLDS FOR INTERNAL PRECISION PARTSMOLDS FOR INTERNAL PRECISION PARTS
Machining
60%
Design
13%
Finishing
Assembling
12%
Adjust-
ment
8%
Material Cost 4% Others 3%
It is quite difficult to grasp the mold cost.
The following breakdown of the mold cost was given by
Corporate Manufacturing Innovation Division and shows how small the share
of the material cost is. It ranges from 4 to 10%.
(7) Types of gates A wide range of types of gates is available. But the selection of types of gates is quite important because it has a great influence upon the precision and quality of the parts we purchase.
There are many factors and requirements for the selection, such as the precision, appearance, shape and flatness of the parts and others. The major types of gates are shown below.
Pin point GateSide Gate
Direct Gate (Standard Gate)
Tunnel Gate(Submarine Gate)
Fan Gate
Gate
Runner
(Film Gate)
(8) Undercut
An undercut is an projection on a molded part which makes
ejection from the simple two plate mold almost impossible.
1) Types of undercuts
Undercuts can be classified as internal undercut, external undercut,
circular undercut and an undercut on the side wall of a part formed
by a core pin.
• Undercuts are frequently necessary in a molded plastic part.
However, these should be avoided whenever possible, as they
increase mold costs and part prices and lengthen the molding cycle.
• Undercuts may be molded by means of
(a) Split mold
(b) Movable side cores (slide cores) that must be drawn away from
the part before the part can be extracted from the mold.
Split mold
Slide core
2) Samples for parts with undercuts
(9) Defects of injection molded products and causes
De- facts
Example Molding-machine- and Condition-related Causes
MOLD-and Material-related Causes
Sho
rt sh
ot
• Insufficient injection capac-ity of machine
• Insufficient material supply • Insufficient injection
pressure • Low resin temperature
and flowability • Low injection speed • Excessive pressure loss
due to high resistance of nozzle part
• Poor gate balance • Insufficient ventilation • Excessively small gate, runner,
and, sprue • Low mold temperature • Cold slag clogging • Excessive thinness of product • Poor flow of resin
Fla
sh
• Excessive injection pres-sure
• Insufficient mold-clamping pressure
• Excessive material supply • High resin temperature • Long maintenance of
injection pressure
• Mold cores not aligned, or con - tact surfaces insufficient
• Excessively large cavity proje -ction surface area
• Low resin viscosity at molding
Sin
k m
ark
• Low injection pressure • Short maintenance of
injection pressure • Low injection speed • Insufficient material supply • High resin temperature
• High mold temperature, or un -even distribution of temperature
• Small gate • High resistance due to thin
runner and sprue • Thick area existing in cavity • High contraction rate of resin •
Silv
er
streak
• Poor plasticity • Overheated and
decomposed resin • High injection speed • High injection speed due
to high injection pressure • Screw draws air in.
(Insufficient back pressure and compression rate)
• Low mold temperature • Insufficient ventilation • Improper location of gate • Defect in cavity design • Insufficient drying of resin
Flo
w m
ark
• Low resin temperature and poor fulowability
• Low injection speed • Excessively small nozzle • Insufficient injection
maintenance pressure
• Low mold temperature • Improper cooling of mold • Poor flow of resin
De- facts
Example Molding-machine- and Condition-related Causes
MOLD-and Material-related Causes
De- facts
Example Molding-machine- and Condition-related Causes
MOLD-and Material-related Causes
Clo
udy appeara
nce
• Unevenly melted and partially overheated resin
• Cold nozzle • Excessively high or low
injection speed • Overheated and
decomposed resin
• Excessively high or low mold temperature
• Excessively small gate, runner, and sprue
• Water or oil contamination on mold surface
• Insufficient drying of resin • Volatility of resin lubrication
agent
Poor w
eld
lin
es
• Low resin temperature and poor flowability
• Low injection pressure • Low injection speed • Cold nozzle
• Excessively long flow from gate to weld
• Low mold temperature • Inappropriate location and
number of gates • Insufficient drying of resin • Poor flow of resin
Void
• Low injection pressure
• Insufficient injection
maintenance pressure • Excessively high or low
injection speed • Short pressure
maintenance duration
• Insufficient ventilation • Defects in cavity design
(Existence of thick areas or substantial fluctuation in thickness)
• Inappropriate gate location • Excessively small gate, runner,
and sprue • Large contraction rate of
material
De- facts
Example Molding-machine- and Condition-related Causes
MOLD-and Material-related Causes
Bla
ck
stre
ak
• Partially overheated resin while accumulated in cylinder
• Defect in nozzle installment
• High injection speed • Long material
accumulation time • High cylinder temperature
and injection pressure
• Grease or oil contamination on inner mold surface
• Overheating and decomposition due to friction at gate
• Insufficient ventilation • Excessive amount of lubrication
agent
Cra
ckin
g/cr
azin
g
• High injection pressure • Low resin temperature
and poor flowability • Excessive injection
maintenance pressure • Long pressure
maintenance time
• Wide gate • Low mold temperature • Faulty release from mold • Defect in cavity design • Inappropriate annealing
END
