塑胶射出讲义4

塑膠射出成形塑膠加工成形製程國立高雄應用科技大學 機械系 王珉玟Unit Operations in Polymer ProcessingThermoplastic and thermoset melt processes may be broken down into: pellets• Preshaping • Shaping • Shape Stabilization1 PDF created with pdfFactory trial version Unit Operations in Polymer ProcessingnnnPreshaping steps: n Solids handling and conveying: most processes usually involve feed in particulate form n Plastication: The creation of a polymer melt from a solid feed. n Mixing: often required to achieve uniform melt temperature or uniform composition in compounds n Pumping : The plasticated melt must be pressurized and pumped to a shaping device Shaping: The polymer melt is forced through the shaping devices to create the desired shape. Ø 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. Shape stabilization: n Involves the solidification of the polymer melt in the desired shape, through heat transfer成形加工原理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.流動 flow liquid 凝固 pellets 融化 melting solidify kazoo原理: 基本三步 驟：熔化、流動 及凝固。

首先將固體塑膠 材料加熱熔解成 液態，而後將其 射入模具中，再 行冷卻、凝固即 成零件。

2 PDF created with pdfFactory trial version 塑化(plasticization)•塑膠加工是由於塑膠在溫度及壓力作用下產生形變 •依溫度不同可以分為四種狀態:TgTf或TmTd充填•熔融狀態受高壓作動充滿模穴 •流動性差則會造成短射 •流動性佳及成形壓力過大易產生毛邊(分模面上) •加工前對物料特性需要能夠了解掌握 射出單元 夾模單元 模具3 PDF created with pdfFactory trial version 冷卻•熱塑性材料在低需玻璃轉換溫度脫模頂出成品 •熱固性材料在模具內經交聯(化學反應)硬化(hardening, curing)脫模頂出成品 •Cooling time依材料與成品形狀,大小,尺寸精度,外觀而定 射出單元 夾模單元 模具成形加工法Extrusion押出 n Post extrusion processes – Fiber spinning, film blowing … n Molding processes – Injection molding射出, compression molding壓縮(熱壓成 形), extrusion blow molding壓吹 … n Forming processes – Thermoforming, stretch blow molding, solid-phase processing … n Casting and rapid prototyping n Composites manufacturing n Rubber processingn4 PDF created with pdfFactory trial version 壓縮成形Compression Molding• Process for forming thermosets by applying heat and pressure. • A measured amount of thermoset powder, granules or pellets, is fed into the mold cavity. • Heat softens the material and pressure fills the cavity, then the material is cured. • Heat actually causes the polymer to transform into a highly cross-linked and networked structure. • Process is of limited use for thermosets because of the cooling time required of the mold. • Typical products include electrical insulators, pot handles, and some automotive parts.5 PDF created with pdfFactory trial version Compression MachinesCompression Moldingn nStandard thermosets of various types Molding compounds (mixtures of materials)n n nThermoset resin (30%) Reinforcement fibers (10%) Fillers (60%)n nBulk Molding Compound (BMC) Sheet Molding Compound (SMC)6 PDF created with pdfFactory trial version Bakelite 貝克來特三氯氰氨 美臘皿 聚鄰苯二酸二烯丙酯轉移成形(Transfer Molding)•將一定量的塑料置於加熱室加熱後 以柱塞將熔膠經流道系統填入模穴 •常用於鑲(坎)入成形 •IC封裝7 PDF created with pdfFactory trial version Transfer Molding• Process is a combination of 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 accommodate molding of more intricate thermoset parts.射出成形8 PDF created with pdfFactory trial version 押出成形Extrusion Moldingpellets•The extruder is the main device used to melt and pump thermoplastics through the shaping device called 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.多孔板 濾網組9 PDF created with pdfFactory trial version Extruder and die押出機Extruder押出模頭die10 PDF created with pdfFactory trial version Film BlowingExtruder and BlowerCoextrusionIn coextrusion two or more extruders feed a single die, in which the polymer streams are layered together to form a composite extrudate.21 PDF created with pdfFactory trial version Molding ProcessesMolding techniques for polymers involve the formation of three-dimensional components within hollow molds (or cavities)Ø Ø Ø Ø ØInjection Molding Thermoforming Compression Molding Blow Molding Rotational MoldingInjection Moldingn nnInjection 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. It is used for numerous products, ranging from boat hulls and lawn chairs, to bottle cups. Car parts, TV and computer housings are injection molded. The components of the injection molding machine are the plasticating unit, clamping unit and the mold.22 PDF created with pdfFactory trial version Injection moldingGenerally reciprocating screw – Screw rotates and forms metered volume of melt – Screw ceases to rotate and acts as a ram, being thrust forward to inject the melt into the mold.n n n n nThe mold consists of the following elements: Sprue and runner system Gate Mold cavity Cooling system (for thermoplastics) Ejector system23 PDF created with pdfFactory trial version Injection Molding CycleInjection molding involves two basic steps: n Melt generation by a rotating screw n Forward 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:n nInjection: The polymer is injected into the mold cavity. Hold on time: Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage. Cooling: The molding cools and solidifies. Screw-back: At the same time, the screw retracts and turns, feeding the next shot in towards the front Mold opening: Once the part is sufficiently cool, the mold opens and the part is ejected The mold closes and clamps in preparation for another cycle.n nnnMulticomponent injection moldingAlso 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.24 PDF created with pdfFactory trial version Battenfeld Multi-Material-TechnologyAdaptive rotary tableBattenfeld Multi-Material-TechnologyCover for rear lightcavity :2+2material : PMMA machine : BA 2700R2/400+400 BK25 PDF created with pdfFactory trial version Gas Injection Molding富 強鑫AUTO MODELL.V.T 訊號 (光學尺) 訊號射出訊號 24V 7.5HP 6~8 bar空壓機7~100 bar氮 氣 鋼 瓶氮 氣 鋼 瓶氮 氣 鋼 瓶GU-25AC110VFoaming• Plastics can also be produced as foams • Polyurethane, polyethyelene, and polystyrene are some of the foaming type materials. • Use of these materials is varied...from expanded polyethylenes and polystyrene (styrofoaming materials...such as drinking cups) to insulating foams or packing materials to structural foam used 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 kevlar have allowed for innovative structural composite materials.26 PDF created with pdfFactory trial version Molded foams27 PDF created with pdfFactory trial version MuCell- Process:Injection of a physical blowing agent into the barrel: The blowing agent is maintained under pressure and is kept in solution. Nitrogen or CO2 are used as blowing agents.Processing TechnologyGeneration of a single phase system MuCell™ injection of SCF (Co2 or N2)28 PDF created with pdfFactory trial version MuCell ProcessMuCell: Microcellular foam structureIrregular foam structure with voidsBlow Molding• Begins by forming a "blob" of polymer to form through heat and gravity. • Blob is called a parison or preform. • Preform is then clamped in a forming die, and compressed air forces 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 method of producing plastic bottles, hollow toys, balls, or even large plastic drums.29 PDF created with pdfFactory trial version Extrusion Blow MoldingInjection blow moldingThe parison is injection molded onto a steel rod (station 1). The rod and the parison are then rotated to the 2nd station (blow mold) to blow the parison to take up the mold shape. The road and the bottle are next rotated to the 3rd station at which the mold opens and the bottle is ejected.30 PDF created with pdfFactory trial version Stretch-blow molding• Highly sophisticated equipment involved to cause the blown bottle to have biaxial orientation in the wall. – Relatively low parison temperature – A stretch rod is used – High blow pressure – Rapid cooling to lock the orientation • Advantages: – Higher transparency (less light scattering) – Improved permeation resistance – Higher rigidity and impact resistance • Materials: PET, PVC, PP, (PS, ABS, PC)PET Stretch Blow MoldingThe 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)31 PDF created with pdfFactory trial version Reaction Injection MoldingThermoforming Variationsn n n n n n n n nVacuum Pressure Plug assist Reverse draw Free Drape Snap-back Matched die Mechanical32 PDF created with pdfFactory trial version Vacuum FormingnVacuum draws the part against the mold “cavity”Pressure FormingnAir pressure presses the sheet against the mold “cavity”33 PDF created with pdfFactory trial version Thermoforming• Advantages over injection molding: – Large formings – Thin-wall packaging – Short-run or prototype products • Disadvantages: – Polymer has to be preheated before forming – Range of available shapes limited – Good detail is difficult due to low pressure difference – Poor material distributionHard to form precision parts!!ThermoformingVarious thermoforming processes for thermoplastic sheet. These processes are commonly used in making advertising signs, cookie and candy trays, panels for shower stalls, and packaging.34 PDF created with pdfFactory trial version Liquid Transfer MoldingRotational Molding迥轉加工成形• Polymer is placed inside a heated drum that can rotate around at least 2 axis inside an oven. • Centrifugal force distributes the plastic evenly throughout the mold while heat fuses the resin to the shape of the mold. • Rotating mold is removed from 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 product removed. • 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.35 PDF created with pdfFactory trial version Rotational moldingLarge 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 premeasured quantity 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).Calendaring滾壓成形• Used for producing thermoplastic sheets and films. • A plastic compound is made into a pliable dough then fed through a series of graduated, heated rollers. • The thickness of the sheet or film is determined by the spacing between rollers.36 PDF created with pdfFactory trial version CalenderingLaminating貼合成形• Used to convert thermosetting materials into laminated sheets. • Incorporates high heat and pressure to "set" the polymer and bond it to reinforcing materials such 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 material with plastic resins which are stacked between two highly polished steel plates. • Heat and pressure (usually by a hydraulic press) applied causing plastic to cure and presses the plies of materials into a single sheet. • Products produced include kitchen counter tops and reinforced insulating tubes.37 PDF created with pdfFactory trial version Summary• Processing plastics involves several varied shaping or forming processes depending on the material and desired product. • The more common processes include:Injection Molding Compression Molding Transfer Molding Rotational Molding Extrusion Blow MoldingBlown film extrusion Thermoforming Calendaring Fibering Foaming Laminating38 PDF created with pdfFactory trial version 。