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1、模具毕业设计论文外文翻译-推荐下载 Injection Molding The basic concept of injection molding revolves around the ability of a thermoplastic material to be softened by heat and to harden when cooled .In most operations ,granular material (the plastic resin) is fed into one end of the cylinder (usually through a feedin
2、g device known as a hopper ),heated, and softened(plasticized or plasticated),forced out the other end of the cylinder,while it is still in the form of a melt,through a nozzle into a relatively cool mold held closed under pressure.Here,the melt cools and hardens until fully set-up.The mold is then o
3、pened,the piece ejected,and the sequence repeated. Thus,the significant elements of an injection molding machine become :1)the way in which the melt is plasticized (softened) and forced into the mold (called the injection unit); 2)the system for opening the mold and closing it under pressure (called
4、 the clamping unit);3)the type of mold used;4)the machine controls. The part of an injection-molding machine,which converts a plastic material from a sold phase to homogeneous seni-liguid phase by raising its temperature .This unit maintains the material at a present temperature and force it through
5、 the injection unit nozzle into a mold .The plunger is a combination of the injection and plasticizing device in which a heating chamber is mounted between the plunger and mold. This chamber heats the plastic material by conduction .The plunger,on each storke; pushes unmelted plastic material into t
6、he chamber ,which in turn forces plastic melt at the front of the chamber out through the nozzle The part of an injection molding machine in which the mold is mounted,and which provides the motion and force to open and close the mold and to hold the mold close with force during injection .This unit
7、can also provide other features necessary for the effective functioning of the molding operation .Moving plate is the member of the clamping unit,which is moved toward a stationary member.the moving section of the mold is bolted to this moving plate .This member usually includes the ejector holes an
8、d moldmounting pattern of blot holes or “T” slots .Stationary plate is the fixed member of the clamping unit on which the stationary section of the mold is bolted .This member usually includes a mold-mounting pattern of boles or “T” slots.Tie rods are member of the clamping force actuating mechanism
9、 that serve as the tension member of the clamp when it is holding the mold closed.They also serve as a gutde member for the movable plate .Ejector is a provision in the clamping unit that actuates a mechanism within the mold to eject the molded part(s) from the mold .The ejection actuating force may
10、 be applied hydraulically or pneumatically by a cylinder(s) attached to the moving plate ,or mechanically by the opening storke of the moving plate. Methods of melting and injecting the plastic differ from one machine to another and are constantly being improred .couventional machines use a cylinder
11、 and piston to do both jobs .This method simplifies machine construction but makes control of injection temperatures and pressures an inherently difficult problem .Other machines use a plastcating extruder to melt the plastic and piston to inject it while some hare been designed to use a screw for b
12、oth jobs :Nowadays,sixty percent of the machines use a reciprocating screw,35% a plunger (concentrated in the smaller machine size),and 5%a screw pot. Many of the problems connected with in jection molding arises because the densities of polymers change so markedly with temperature and pressure.Athi
13、gh temperatures,the density of a polymer is considerably cower than at room temperature,provided the pressure is the same.Therefore,if modls were filled at atmospheric pressure, “shrinkage”would make the molding deviate form the shape of the mold. To compensate for this poor effect, molds are filled
14、 at high pressure.The pressure compresses the polymer and allows more materials to flow into the mold,shrinkage is reduced and better quality moldings are produced.Cludes a mold-mounting pattern of bolt holes or “T” slots.Tie rods are members of the clamping force actuating machanism that serve as t
15、he tension members of clamp when it is holding the mold closed.Ejector is a provision in the claming unit that actuates a mechanism within the mold to eject themolded part(s) form the mold.The ejection actuating force may be applied hydraulically or pneumatically by a cylinder(s) attached to the mov
16、ing plate,or mechanically by the opening stroke of the moving plate. The function of a mold is twofold :imparting the desired shape to the plasticized polymer and cooling the injection molded part.It is basically made up of two sets of components :the cavities and cores and the base in which the cav
17、ities and cores are mounted. The mold ,which contains one or more cavities,consists of two basic parts :(1) a stationary molds half one the side where the plastic is injected,(2)Amoving half on the closing or ejector side of the machine. The separation between the two mold halves is called the parti
18、ng line.In some cases the cavity is partly in the stationary and partly in the moving section.The size and weight of the molded parts limit the number of cavities in the mold and also determine the machinery capacity required.The mold components and their functions are as following : (1)Mold Base-Ho
19、ld cavity(cavities) in fixed ,correct position relative to machine nozzle . (2)Guide Pins-Maintain Proper alignment of entry into mold intrior . (3)Sprue Bushing(sprue)-Provide means of entry into mold interior . (4)Runners-Conrey molten plastic from sprue to cavities . (5)Gates-Control flow into ca
20、vities. (6)Cavity(female) and Force(male)-Contorl the size,shape and surface of mold article. (7)Water Channels-Control the temperature of mold surfaces to chill plastic to rigid state. (8)Side (actuated by came,gears or hydraulic cylinders)-Form side holes,slots,undercuts and threaded sections. 注射成
21、型 注射成型的基本概念是使热塑性材料在受热时熔融，冷却时硬化，在大部分加工中，粒状材料（即塑料树脂）从料筒的一端（通 常通过一个叫做“料斗”的进料装置）送进，受热并熔融（即塑化 或增塑），然后当材料还是溶体时，通过一个喷嘴从料筒的另一端挤到一个相对较冷的压和封闭的模子里。溶里在模腔里冷却，硬化， 直至完全固化。然后将模子打开，推出工件，并重复以上工序。 因此，注塑成型机的重要组成部分是：1）将溶体塑化并挤进进模腔（称做“注塑单元”）；2）开模和加压合模统称为“合模系统”）；3）使用上下模具；4）机器控制。 注射装置通过家热将固态塑料转化成均匀的半液态塑体。它保 持塑料当前温度并加压使之通过喷嘴
22、进入模具。柱塞集塑化和注射 为一体。在柱塞与模具之间没有加热室，几热室通过热传导加热塑料。每次行程，柱塞将待熔化塑料推入加热室，依次将熔化的塑料 挤到加热室前端并通过喷嘴注射出去（注射到模具中去）合模装置是注射成型机的一个部分，该装置上安装有模具。合 模装置提供运动和动力以开模几合模，并且在注射过程中提供压力 保持模具紧闭同时，该装置还提供成型工艺有效运动所必需的其它 特性。动模板是合模装置的一部分，在合模时向定模板移动。型腔 的运动部分用螺栓固定在动模板上，动模板通常动模板通常含顶出杆，螺栓空或T型槽的安装模具的型板。拉杆是合模力驱动机构中 的一个构件，当夹具保持动模闭合时，拉杆起夹具的拉力
23、构件的作用。顶出器是合模装置的一个部件，它驱动模具中的执行机构从模 具中顶出成型制品。顶出力可由液压或气动装置通过装在动模板上 的油（气）缸来施加，或者通过动模板开模行程来施加。 塑料熔融与塑料注射的方式随机器的不同而不同,并不断得以改 善。常规的机器采用一个料筒和一个活塞来进行熔融和注射。虽然这种方式简化了机器的结构，但却使注射的温度和压力控制成了一个固有的难题。有的机器用一个塑化挤压器来熔化塑料，用一个活塞进行注射。另外，还有一些已设计出来的机器采用一个螺杆来完成熔融和注射。目前，百分之六十的机器采用往复式螺杆，百分之三十五的机器采用柱塞；百分之六十的机器采用螺罐。 聚合物的密度在不同的温
24、度和压力下变化很大，并由此产生了注射成型的许多问题。在压力不变的情况下，在高温下的聚合物的密度比在低温下的要低得多，因此，如果在大气压下向模子充模，成型件回因“收缩”而与模子的形状形成偏差。 为了补偿这一偏差，模子充料在高压下进行。高压压缩了聚合物并能使更多的材料流入模腔。这样，“收缩”就减少了，生产的成型件的质量就得以提高。 模具的功能有两方面：一是使可塑聚合物按希望的形状成型，而是使其冷却定型。注射模具基本由两套部件组成：型腔和型芯，安装型腔和型芯的模板。具有一个型腔或多个型腔的模具由两个基本部分组成：（1）注射塑料一侧的定模（2）闭合及顶出机器一侧的动模。两哈夫对开的定模、动模分界线叫做
25、分型面。有时，型腔一部分在定模中，一部分在动模中。塑料成型制品的尺寸和重量限制了一副模具中型腔的数目，并且取得了所需的注射机床生产能力。模具的零部件及其功能如下： （1）模板保持型腔相对注射机床的喷嘴具有固定、正 确的位置。 （2）导柱保持定模、动模哈夫在合模时具有正确的相 对位置。 （3）主流道衬套提供熔融塑料流入模具内部的通道。 （4）流道将容忍塑料从浇注口传送到各型腔。 （5）浇口控制熔融塑料流入型腔。 （6）凹模（阴模）和凸模（阳模）控制成型塑料制品的尺寸、形状及表面纹理。 （7）冷却水道控制模具表面温度，使塑料制品冷固成型。 （8）侧板（由凸轮、齿轮或液压油缸驱动）形成制品的侧孔、侧槽、侧凹螺纹部分。