塑胶射出成形-
1
塑胶射出成形-
塑胶加工成形制程
国立高雄应用科技大学
机械系
王珉玟
Unit Operations in Polymer Processing
Thermoplastic and thermoset melt processes may be broken
down into:
Preshaping
Shaping
Shape
Stabilization
pellets
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nPreshaping steps:
nSolids handling and conveying: most processes usually involve feed
in particulate form
nPlastication: The creation of a polymer melt from a solid feed.
nMixing: often required to achieve uniform melt temperature or
uniform composition in compounds
nPumping: The plasticated melt must be pressurized and pumped to
a shaping device
nShaping:
The polymer melt is forced through the shaping devices to create
the desired shape.
The flow behavior (rheology) of polymer melts influences
the design of the various shaping devices, the processing
conditions and the rate at which the product can be shaped.
nShape stabilization:
nInvolves the solidification of the polymer melt in the desired shape,
through heat transfer
Unit Operations in Polymer Processing
Plastic pellets are placed into a bin to be fed into a channel by a screw
mechanism. As the pellets travel down the channel, they are heated and melt.
At the end of the pipe is a nozzle (called a 'sprue'), where the molten plastic is
injected into a mold. After the molten material has solidified, the mold is opened,
and the piece is pushed out ('ejected') and collected.
kazoopelletsliquid融化
melting
流动flow
凝固
solidify
原理:
基本三步
骤:熔化,流动
及凝固.
首先将固体塑胶
材料加热熔解成
液态,而后将其
射入模具中,再
行冷却,凝固即
成零件.
成形加工原理
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塑化(plasticization)
塑胶加工是由於塑胶在温度及压力作用下产生形变
依温度不同可以分为四种状态:
TgTf或TmTd
射出单元
夹模单元模具
充填
熔融状态受高压作动充满模穴
流动性差则会造成短射
流动性佳及成形压力过大易产生毛边(分模面上)
加工前对物料特性需要能够了解掌握
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射出单元
夹模单元模具
冷却
热塑性材料在低需玻璃转换温度脱模顶出成品
热固性材料在模具内经交联(化学反应)硬化(hardening,
curing)脱模顶出成品
Cooling time依材料与成品形状,大小,尺寸精度,外观而定
nExtrusion押出
nPost extrusion processes
0Fiber spinning, film blowing …
nMolding processes
0Injection molding射出, compression molding压缩(热压成
形), extrusion blow molding压吹…
nForming processes
0Thermoforming, stretch blow molding, solid-phase
processing …
nCasting and rapid prototyping
nComposites manufacturing
nRubber processing
成形加工法
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压缩成形
Process for forming thermosetsby applying heat and
pressure.
A measured amount of thermoset powder, granules or
pellets, is fed into the mold cavity.
Heat softens the materialand pressure fills the cavity,
then the material is cured.
Heat actually causes the polymer to transform into a
highly cross-linkedand networked structure.
Process is of limited usefor thermosets because of the
cooling timerequired of the mold.
Typical products include electrical insulators, pot
handles, and some automotive parts.
Compression Molding
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Compression Machines
Compression Molding
nStandard thermosets of various types
nMolding compounds (mixtures of materials)
nThermoset resin (30%)
nReinforcement fibers (10%)
nFillers (60%)
nBulk Molding Compound (BMC)
nSheet Molding Compound (SMC)
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三氯氰氨
美腊皿
Bakelite
贝克来特
聚邻苯二酸二烯丙酯
转移成形(Transfer Molding)
将一定量的塑料置於加热室加热后
以柱塞将熔胶经流道系统填入模穴
常用於镶(坎)入成形
IC封装
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Process is a combinationof injection and
compression molding.
Similar to compression molding, heat and
pressure are used to form the material, and then
forced (transferred) to the mold cavity...which is
similar to injection molding.
Process was derived from compression molding to
accommodatemolding of more intricatethermoset
parts.
Transfer Molding
射出成形
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押出成形Extrusion Molding
The extruderis the main device used to melt and pump thermoplastics
through the shaping devicecalled die.
There are basically two type of extruders: single-and twin-screw.
A single screw extruder consists of a screw that rotates within a metallic
barrel.
pellets
多孔板
滤网组
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Extruder and die
押出机Extruder
押出模头die
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Profile extrusion异形押出
Annular (Tubular) Dies
In a tubular die the polymer melt exits through
an annulus. These dies are used to extrude
plastic pipes. The melt flows throughthe
annular gapand solidifies at the exitin a cold
water bath.
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Flat film and sheet process
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Cast Film Extrusion
nIn a cast film extrusion process, a thin film is extruded through a slit
onto a chilled, highly polished turning roll, where it is quenched from
one side. The speed of the roller controls the draw ratio and final film
thickness. The film is then sent to a second roller for cooling on the
other side. Finally it passes through a system of rollers and iswound
onto a roll.
nThicker polymer sheets can be manufactured similarly. A sheet is
distinguished from a film by its thickness; by definition a sheet has a
thickness exceeding 250 μm. Otherwise, it is called a film.
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Sheeting Dies
One of the most widely used extrusion dies is the coat-hangeror
sheeting die. It is used to extrude plastic sheets. It is formedby the
following elements:
nManifold: evenly distributes the melt to the approach or land region
nApproach or land: carries the melt from the manifold to the die lips
nDie lips: perform the final shaping of the melt.
nThe sheet is subsequently pulled (and cooled simultaneously) by a
system of rollers
Chill-roll stack for film extrusion.
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Wire coating
The design problems concern providing uniform coating
at highest extrusion rate possible. Important process
variables include: pressure and feed rate.
Wire drawing
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Secondary Shaping
nSecondary shaping operationsoccur immediately afterthe extrusion
profile emerges from the die.
nIn general they consist of mechanical stretchingor forming of a
preformed cylinder, sheet, or membrane. Examples of common
secondary shaping processes include:
Fiber spinning
Film Production(cast and blown film)
nFiber spinning is used to
manufacture synthetic fibers.
nA filament is continuously extruded
through an orifice and stretched to
smaller diameters.
nThe molten polymer is first
extruded through a filter or "screen
pack", to eliminate small
contaminants. It is then extruded
through a "spinneret"纺口, a die
composed of multiple orifices (it can
have 1-10,000 holes). The fibers are
then drawn to their final diameter,
solidified (in a water bath or by
forced convection) and wound-up.
Fiber Spinning
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Used to produce thin film hollow tubes.
Somewhat of a combination of extrusion,
blown molding and calendaring.
As material is extruded, air is forced through
the center of a die, causing the material to
expandto the diameter of the mold.
Mold is openat the end, and the material is
continuously taken up on rollers.
During the take up process, the walls on the
"tube may be seamed welded and perforated
such as the case with garbage bags.
Blown Film Extrusion
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Film Blowing
nFilm Blowing Systems
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Film Blowing
Extruder and Blower
Coextrusion
In coextrusion two or more extruders feed a single die, in whichthe
polymer streams are layered together to form a composite extrudate.
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Molding Processes
Molding techniques for polymers involve the formation of
three-dimensional components within hollow molds (or
cavities)
Injection Molding
Thermoforming
Compression Molding
Blow Molding
Rotational Molding
Injection Molding
nInjection molding is the most important process used to manufacture
plastic products. It is ideally suited to manufacture mass produced
parts of complex shapes requiring precise dimensions.
nIt is used for numerous products, ranging from boat hulls and lawn
chairs, to bottle cups. Car parts, TV and computer housings are
injection molded.
nThe components of the injection molding machine are the plasticating
unit, clamping unit and the mold.
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Injection molding
Generally reciprocating screw
0Screw rotates and forms metered volume of melt
0Screw ceases to rotate and acts as a ram, being thrust
forward to inject the melt into the mold.
The mold consists of the following
elements:
nSprueand runner system
nGate
nMold cavity
nCooling system (for thermoplastics)
nEjector system
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Injection Molding Cycle
Injection molding involves two basic steps:
nMelt generation by a rotating screw
nForward movement of the screw to fill the mold with melt and to
maintain the injected melt under high pressure
Injection molding is a "cyclic"process:
nInjection: The polymer is injected into the mold cavity.
nHold on time: Once the cavity is filled, a holding pressure is
maintained to compensate for material shrinkage.
nCooling: The molding cools and solidifies.
nScrew-back: At the same time, the screw retracts and turns, feeding
the next shot in towards the front
nMold opening: Once the part is sufficiently cool, the mold opensand
the part is ejected
nThe mold closes and clamps in preparation for another cycle.
Multicomponentinjection molding
Also referred to by the industry as multi-color molding or
multi-material molding. Two or more materials are
involved and molded sequentially.
Insert molding may be considered a special case. In this
case, the insert is typically made of metal and could be
produced using any manufacturing process.
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Adaptive rotary table
Battenfeld Multi-Material-Technology
Cover for rear light
cavity: 2 + 2
material: PMMA
machine: BA 2700R2/400+400 BK
Battenfeld Multi-Material-Technology
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AC110V
氮
气
钢
瓶
氮
气
钢
瓶
氮
气
钢
瓶
L.V.T 讯号
(光学尺) 讯号
射出讯号
24V
空压机
7.5HP
6~8 bar
7~100 bar
富
强鑫
AUTO MODEL
GU-25
Gas Injection Molding
Plastics can also be produced as foams
Polyurethane, polyethyelene, and polystyreneare some of
the foaming type materials.
Use of these materials is varied...from expanded
polyethylenes and polystyrene (styrofoamingmaterials...such
as drinking cups)to insulating foamsor packing materials
tostructural foamused in construction.
Elastomer foams(foam rubber) are produced in a number
of ways including molding and compressed extrusion.
Products include cushions, flotation devices, and many
others.
Recent advances in foaming and reinforcing materials such
a kevlarhave allowed for innovative structural composite
materials.
Foaming
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Molded foams
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MuCell-Process:
Injectionofa physicalblowingagentintothebarrel:
Theblowingagentismaintained under pressureandis
keptin solution.
NitrogenorCO2 areusedasblowingagents.
ProcessingTechnology
MuCell injection of SCF (Co2or N2)
Generation ofa singlephasesystem
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MuCellProcess
MuCell:
Microcellular foam
structure
Irregularfoam
structurewith
voids
Begins by forming a"blob"of polymer to form through
heat and gravity.
Blob is called a parison or preform.
Preformis then clamped in a forming die, and
compressed airforces the parison to expand and conform
to the mold cavity.
Compare to blowing up a balloon inside a bottle.
After cooling, the split mold opens and the part is
ejected.
Economical methodof producing plastic bottles, hollow
toys, balls, or even large plastic drums.
Blow Molding
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Extrusion Blow Molding
Injection blow molding
The parisonis injection molded onto a steel rod (station 1). The rod and the
parisonare then rotated to the 2nd station (blow mold) to blow the parisonto
take up the mold shape. The road and the bottle are next rotatedto the 3rd
station at which the mold opens and the bottle is ejected.
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Stretch-blow molding
Highly sophisticated equipment involved to cause the blown bottle to
have biaxial orientationin the wall.
0Relatively low parisontemperature
0A stretch rod is used
0High blow pressure
0Rapid coolingto lock the orientation
Advantages:
0Higher transparency (less light scattering)
0Improved permeation resistance
0Higher rigidity and impact resistance
Materials: PET, PVC, PP, (PS, ABS, PC)
PET Stretch Blow Molding
The material was first stretched for a certain length, and
subsequently, air pressure was applied.Inflation was observed
initially at the top of the preform,and gradually extended to the
lower part.(Source: http://www.riken.go.jp)
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Reaction Injection Molding
Thermoforming Variations
nVacuum
nPressure
nPlug assist
nReverse draw
nFree
nDrape
nSnap-back
nMatched die
nMechanical
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Vacuum Forming
nVacuum draws the part against the
mold "cavity"
Pressure Forming
nAir pressure presses the sheet against
the mold "cavity"
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Thermoforming
Advantages over injection molding:
0Large formings
0Thin-wall packaging
0Short-run or prototype
products
Disadvantages:
0Polymer has to be
preheated before forming
0Range of available
shapes limited
0Good detail is difficultdue
to low pressure difference
0Poor material distribution
Hard to form precision parts!!
Various thermoforming processes for thermoplastic sheet.
These processes are commonly used in making
advertising signs, cookie and candy trays, panels for
shower stalls, and packaging.
Thermoforming
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Liquid Transfer Molding
Polymer is placed inside a heated drumthat can rotate
around at least 2 axis inside an oven.
Centrifugal forcedistributes the plastic evenly
throughout the mold while heat fuses the resinto the
shape of the mold.
Rotating mold is removedfrom the oven and allowed to
cool, usually by spraying water on the metal mold.
Upon cooling the 2 piece mold is opened, and the hollow
productremoved.
Generally used for large parts, however smaller items
can also be produced using this method.
Example of a product from using rotational molding is a
plastic water storage tank.
Rotational Molding迥转加工成形
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Rotational molding
Large hollow parts can
fabricated by rotational
molding. The thin-walled metal
mold is made of two pieces
and designed to rotated about
two perpendicular axes. A
premeasuredquantity of
thermoplastic powders is
placed inside the mold. The
mold is then heated in a large
oven while it is rotated about
the two axes. The heat fuses
the powder without melting it
(sintering).
Used for producing thermoplastic sheets and films.
A plastic compoundis made into a pliable dough
then fed througha series of graduated, heated
rollers.
The thickness of the sheet or film is determined by
the spacingbetween rollers.
Calendaring滚压成形
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Calendering
Used to convert thermosetting materialsinto laminated
sheets.
Incorporates high heat and pressureto "set" the polymer
and bond it to reinforcing materialssuch as cloth, paper,
wood, or fibers.
Can be used on a variety of shapes; particularly common
for laminated sheet production.
Steps involve impregnating the reinforcing materialwith
plastic resins which are stacked between two highly polished
steel plates.
Heat and pressure(usually by a hydraulic press) applied
causing plastic to cureand presses the plies of materialsinto
a single sheet.
Products produced include kitchen counter tops and
reinforced insulating tubes.
Laminating贴合成形
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Processing plastics involves several varied shaping or
forming processes depending on the material and desired
product.
The more common processes include:
Summary
Injection Molding
Compression Molding
Transfer Molding
Rotational Molding
Extrusion
Blow Molding
Blown film extrusion
Thermoforming
Calendaring
Fibering
Foaming
Laminating
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