汽车刷洗器上壳体注塑模具设计
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毕 业 设 计(论 文)外 文 参 考 资 料 及 译 文设计(论文)题目: The Injection and Compression Molding 注塑模和压缩模 学生姓名: 学 号: 专 业: 所在学院: 指导教师: 职 称: 20xx年 2月 27日说明:要求学生结合毕业设计(论文)课题参阅一篇以上的外文资料,并翻译至少一万印刷符(或译出3千汉字)以上的译文。译文原则上要求打印(如手写,一律用400字方格稿纸书写),连同学校提供的统一封面及英文原文装订,于毕业设计(论文)工作开始后2周内完成,作为成绩考核的一部分。外文参考资料The injection and Compression MoldingInjection molding si principally used for the production of the thermoplastic parts, although some progress has been made in developing a method for injection molding some thermosetting materials. The problem of injecting a melted plastic into a mold cavity form a reservoir of melted material has been extremely difficult to solve for thermosetting plastics which cure and harden under such conditions within a few minutes. The principle of injection molding is quite similar to that of die-casting. The process consists of feeding a plastic compound in powdered or granular form from a hopper through metering and melting stages and then injecting it into a mold. After a brief coolling period, the mold is opened and the solidified part ejected. Injection-molding machines can be arranged for manual operation, automatic single-cucle operation, and full automatic operation. The advantage of injection molding are:(i) a high molding speed adapted for mass production is possible;(ii) there is a wide choice of thermoplastic materials providing a variety of usefull properties;(iii) it is possible to mold threads, undercuts, side holes, and large thin sections. Several methods are used to force or inject the melted plastic into the mold. The most commonly used system in the larger machines is the in-line reciprocating screw.The screw acts as a combination and plasticizing unit.As the plastic is fed to the rotating screw,it passes through three zones as shown: feed,compression, and metering. After the feed zone, the screw-flight depth is gradually reduced,forcing the plastic to compress. The work is converted to heat by shearing the plastic, making it a semifluid mass. In the metering zone, additional heat is applied by conduction from the barrel surface. As the chamber in front of the screw becomes filled, it forces the screw back, tripping a limit switch that activates a hydraulic cylinder that forces the screw forward and injects the fluid plastic into the closed mold.An antiflowback valve prevents plastic under pressure from escaping back into the screw flights.The clamping force that a machine is capable of exerting is part of the size designation and is measured in tons. A rule-of-thumb can be used to determine the tonnage required for a particular job. It is based on two tons of clamp force per square inch of projected area. If the flow pattern is difficult and the parts are thin,this may have to go to three or four tons.Many reciprocating - screw machines are capable of handing thermosetting plastic materials.Previously these materials were handled by compression or transfer molding.Thermosetting materials cure or polymerize in the mold and are ejected hot in the range of 375410.Thermoplastic parts must be allowed to cool in the mold in order to remove them without distortion.Thus thermosetting cycles can be faster.Of course the mold must be heated rather than chilled,as with thermoplastics.The design plastic injection mold first must have the certain,understanding to the plastic, the plastic principal constituent is a polymer. Like we often said the ABS plastic then is the propylene nitrile, the pyprolylene, the styrene three kind of monomers uses the emulsion, the main body or aerosol gathers the legitimate production,enable it to have three kind of monomers the high performance and may the compression molding, injects under the certain temperature and the pressure to the mold cavity, has the flow distortion, the obtaining cavity shape, after guarantees presses cooling to go against becomes the plastic product. The polymer member assumes the chain shape structure generally, the linear molecule chain and a chain molecule thought is the thermoplastic, may heat up the cooling processing repeatedly, but passes through heats up many members to occur hands over the association response, including forms netted the build molecular structure plastic usually is this, cannot duplicate injects the processing, also is the thermosetting plastics which said.Since is the chain shape structure, that plastic when processing contracts the direction also is with the polymer molecular chain under the stress function the orientation and the cooling contraction related, must be more than in the flow direction contraction its vertical direction in contraction. The product contraction also with the product shape, the runner, the temperature,guarantees presses factor and so on time and internal stress concerns.In the usual book provides the shrinkage scope is broad, considers is product wall thickness, the structure and the determination casts the temperature pressure size when the practical application and the orientation. The common product if does not have the core strut, the contraction correspondingly wants big. The plastic casts the mold basically to divide into the static mold and to move the mold.Injection molding is principally used for the production of thermolplastic part ,although some progress has been made in developing a method for injection molding some thermosetting materials .The problem of injecting a melted plastic into a mold cavity from a reservoir of melted material has been extremely difficult to solve for thermosetting plastics which cure and harden under such conditions within a few minutes 。The principle of injection molding is quite similar to that of die-casting . Plastic powder is loaded into the feed hopper and a certain amount feeds into the heating chamber when the plunger draws back . This plastic powder under heat and pressure in the heating chamber becomes a fluid. Heating temperatures range from 265 to 500F . After the mold is closed , the plunger moves forward some of the fluid plastic into the mold cavity under pressures ranging from 12000 to 30000 psi . Since the mold is cooled by circulating cold water , the plastic hardens and the part may be ejected when the plunger draws back and the mold opens .Injection-molding machines can be arranged for manual operation, automatic single-cycle operation , and full automatic operation . Typical machines produce molded parts weighing up to 22 ounces at the rate of four shots per minute , and it is possible on some machines to obtain a rate of six shots per minute . The molds used are similar to the dies of a die-casting machine with the exception that the surfaces are chromium-plated . The advantages of injection molding are :1. A high molding speed adapted for mass production is possible.2. There is a wide choice of thermoplastic materials providing a variety of useful properties.3. It is possible to mold threads , undercuts , side holes ,and large thin sections.The importance of Injecting the mold are :、Plastics have the density small, the quality light, the specific tenacity big, the insulating property good, the dielectric loss low, the chemical stability strong, the formation productivity high and the price inexpensive and so on the merits, obtained day by day the widespread application in the national economy and peoples daily life each domain, as early as in the beginning of 1990s, the plastic annual output already surpassed the steel and iron and the non-ferrous metal annual output sum total according to the volume computation.In mechanical and electrical (for example so-called black electrical appliances), domains and so on measuring appliance, chemical, the automobile and astronautics aviation, the plastic has become the metal the good substitution material, had the metal material plastic tendency.、Take the automobile industry as the example , as a result of the automobile lightweight, the low energy consumption development request, the automobile spare part material constitution occurred obviously has modelled the band steel the change, at present our country automobile plastic accounts for 5% which the automobile was self-possessed to 6%, but overseas has reached 13%, forecast according to the expert, the automobile plastic bicycle amount used will also be able further to increase.On modern vehicles, regardless of is outside installs the assorted items, the internal installation assorted items, the function and the structural element, all may use the plastic material, outside installs the assorted items to have the bumper, the fender, the wheel hub cap, the air deflector and so on; After the internal installation assorted items have in the display board, the vehicle door the board, the vice-display board, the sundry goods box lid, the chair, the guard shield and so on; The function and the structural element have the fuel tank, the radiator header, the spatial filter hood, the fan blade and so on.Statistics have indicated, our country in 2000 automobile output more than 200 ten thousand, the vehicle amounted to 1,380,000 tons with the plastic.Looked from the domestic and foreign automobile plastic application situation that, the automobile plastic amount used already became one of weight automobile production technical level symbols.、Injection of a molding formation as plastic workpiece most effective formation methods because may by one time take shape each kind of structure complex, the size precise and has the metal to inlay a product, and the formation cycle is short, may by mold multi-cavities, the productivity be high, when mass productions the cost isvery inexpensive, easy to realize the automated production, therefore holds the extremely important status in the plastic processing profession.Statistics have indicated, plastic mold composition all molds (including metal pattern) 38.2%, the plastic product gross weight about 32% is uses in injecting the formation, 80% above engineering plastics product all must use the injection formation way production. 4. counts according to the customs, our country in 2000 altogether imported mold 977,000,000 US dollars, in which plastic molding forms altogether 550,000,000 US dollars, occupied for 56.3%,2001 years altogether to import mold 1,112,000,000 US dollars, in which plastic molding forms altogether 616,000,000 US dollars, accounted for 55.4%.From the variety, the import volume biggest is the plastic molding forms.、Counts according to the customs, our country in 2000 altogether imported mold 977,000,000 US dollars, in which plastic molding forms altogether 550,000,000 US dollars, occupied for 56.3%, 2001 years altogether to import mold 1,112,000,000 US dollars, in which plastic molding forms altogether 616,000,000 US dollars, accounted for 55.4%.From the variety, the import volume biggest is the plastic molding forms. In compression molding the palstic material as powder or preforms is placed into a heated steel mold cavity,Since the parting surface is in a horizontal plane ,the upper half of the mold descends vertically.It closes the mold cavity and pressures for a predetermined period.A pressure of from 2 to 3 tons square inch and a temperaure at approximately 350F converts the plastic to a semiliquid which flows to all parts of the mold cavity.Usually from 1 to 15 minutes is required for curing,altough a recently developed alkyd plastic will cure in less than 25 secends. The mold is then opended and the molded part removed.If metal insers are desired in the parts,they should be placed in the mold cavity on pins or in the holes before the plastic is loaded.Also, the preforms should be preheated before loading into the mold cavity to eliminate gases,inprove flow,and decrease curing time.Dieletric heating is a convenient method of heating the preforms.Since the plastic material is placed directly into the mold cavity,the mold itself can be simpler than those used for other molding precesses.Gates and sprues are unnecessary.This also results in a saving in material,because trimmed-off gates and sprues would be a complete loss of the thermosetting plastic.The press require the full attention of one operator.However,several smaller presses can be operated by one operator. The presses are conveniently located so the operator can easilymove from one to the next.By the time he gets around to a particular press again,that mold will be ready to open.the thermosetting plastics which harden under heat and pressure are suitable for compression molding and transfer molding.It is not practical to moid shermoplastic materials by these methods,since the molds would have to be alternately heated and cooled.In order to harden and eject thermoplastic parts form the mold,cooling would be necessary.Types of molds for compression molding.The molds used for compression molding are classified into four basic types, namely ,positive molds,landed positive mold,flash-type molds,and semipositive molds.In a positive mold the plunger on the upper mold enters the lower mold cavity.since there are no lands or stops on the lower die ,the plunger completely trap the plastic material and descends with full pressure on the charge.A dense part with good electrical and physical properties is produced.The amount of plastic placed in the die cavity must be accurately measured,since it determines the thickness of the part .A landed positive mold is similar to a positive mold except that lands are added to stop the travel of the plunger at predetermined point.In this case,the lands absorb some of the pressure that should be exerted on the parts.The thickness of the parts will be accurately controlled,but the density may vary cansideraby.In a flash-type mold,flash redges are added ti the top and bottom molds.As the upper mold exerts pressure on the plastic,excess material is forced out between the flash ridges where it forms flash.This flash is further compressed.becomes hardened,and finally stops the downard thavel of the upper mold.A slight excess of the plastic material is always chared to ensure sufficient pressurs to produce a dense molded part.This type of mold is widely used because it is comparatively easy to construct and it controls thickness and density within colse limits.The semipositive mold is a combination od the flash type and landed posive molds.In addition to the flash ridges,a land is employed to restrict the travel of the upper mold.12译 文注塑模和压缩模尽管成型某些热固性材料的方法取得了一定进步,但注塑模主要(还是)用来生产热塑性塑件(这主要是因为)热固性塑料熔体的过程中,也会出现这种情况,这个问题一直非常难解决。住宿成型要换里和铸造十分相似。住宿成型的工艺过程包括:首先把料斗中的粉状或粒状的塑料混合物依次输送到定量去和熔化区,然后再注射到模具型腔中,经过短时冷却后,开模,推出成型塑件。注塑机分为手动,半自动及全自动操作。住宿模具有以下优点:(i) 较高的成型速度使大批量生产成为可能;(ii) 为成形具有不同使用性能的热塑性材料提供了较宽的选择;(iii) 可成型带有螺纹的塑件、侧向凹陷的塑件、带有侧孔的塑件和较大的薄壁件。熔融塑料注入模具中通常有几种方式。在大型注塑机上采用往复螺杆式的注入方式。螺杆同时具有注射和塑化的功能。树脂原料进入旋转的螺杆时,要经过三个区域:喂入区、压实区和塑化区经过喂入区后,为压实树脂原料,螺杆螺旋部分的深度逐渐降低,同时传递树脂原料间因剪切作用而产生的热量,使原料呈现半流动状态。在计量区,螺缸表面的加热装置对熔体进一步加热。当熔体充满螺杆前部区域时,螺杆在熔体压力的作用下后退,触动限位开关使液压缸工作,在液压力的作用下推动螺杆向前运动,将熔融塑料注射到闭合的模具型腔中。防倒流阀能够阻止受压熔体倒流进螺杆的螺旋区。注塑机的锁模系统所提供的锁模力由(塑件在分型面的投影)尺寸决定,锁模力以吨为单位。通常靠经验来决定塑件所需要的锁模力总吨数,一般在塑件投影面积上每平方英寸需要作用两吨锁模力。如果熔体流动困难或塑件较薄,锁模力应提高到三到四吨。许多螺杆式注塑机能生产热固性塑料。以前,热固性塑料由挤出模具或传递模具生产。热固性塑料熔体在模具内固化或发生聚合反应,并在温度为375410范围内推出热塑性塑料熔体必须在模具冷却成型,以保证推出时不发生变形。这种热硬化性循环速度很快。当然,生产热塑性塑件时,模具必须被加热,而不是冷却。设计塑料注射模具首先要对塑料有一定的了解,塑料的主要成分是聚合物。如我们常说的ABS 塑料便是丙烯腈、丁二烯、苯乙烯三种单体采用乳液、本体或悬浮聚合法生产,使其具有三种单体的优越性能和可模塑性,在一定的温度和压力下注射到模具型腔,产生流动变形,获得型腔形状,保压冷却后顶出成塑料产品。聚合物的分子一般呈链状结构,线型分子链和支链型分子认为是热塑性塑料,可反复加热冷却加工,而经过加热多个分子发生交联反应,连结成网状的体型分子结构的塑料通常是一此次性的,不能重复注射加工,也就是所说的热固性塑料。既然是链状结构,那塑料的在加工时收缩的方向也是跟聚合物的分子链在应力作用下取向性及冷却收缩有关,在流动方向上的收缩要比其垂直方向上的收缩多。产品收缩也同制品的形状、浇口、热胀冷缩、温度、保压时间及内应力等因素有关。通常书上提供的收缩率范围较广,在实际应用中所考虑的是产品的壁厚、结构及确定注塑时温度压力的大小和取向性。 一般产品如果没有芯子支撑,收缩相应要大些。 塑料注塑模具基本分为静模和动模。注射模主要是用来生产热塑性的零件,尽管有些工艺已经发展为可以用注射模来生产热固性材料的零件。在从一个熔化的熔料箱中把熔料注入型腔中,是相当难解决在这种情况下热固性塑料在几分钟内凝固的问题。注射模的工作原理跟锻造模十分相似。当柱塞向后拉时,塑料粉末被载入加料斗,还有一定数量的塑料进入了加热腔。塑料粉末在加热腔中受到热力和压力的作用下熔化。加热的温度范围在265500华氏度之间。压力在1200030000PMa之间作用下,柱塞向前移动,把熔化的塑料注入模具的型腔中。由于模具被流通的冷水冷却,塑料凝固成型,当柱塞向后拉出和开模,塑件脱模。注射机可以设计为人工、斗自动、全自动操作。以每分钟注射四次的速率,典型注射机生产的塑件可重达22盎司,某些注射机可达到每分钟注射六次。除了表面电镀外, 这类模具的用途与铸造模相似。注射模的优点是:1、 高速注射模适用于大批量生产是可能的;2、 热塑性材料的广泛选择产生了各种有用的特性。3、 螺纹模具,飞边,侧孔大的薄壁结构的应用成为可能。注塑模重要性有:、塑料具有密度小、质量轻、比强度大、绝缘性好、介电损耗低、化学稳定性强、成型生产率高和价格低廉等优点,在国民经济和人民日常生活的各个领域得到了日益广泛的应用,早在二十世纪九十年代初,塑料的年产量按体积计算已经超过钢铁和有色金属年产量的总和。在机电(如所谓的黑色家电)、仪表、化工、汽车和航天航空等领域,塑料已成为金属的良好代用材料,出现了金属材料塑料、以汽车工业为例,由于汽车轻量化、低能耗的发展要求,汽车零部件的材料构成发生了明显的以塑代钢的变化,目前我国汽车塑料占汽车自重的5%至6%,而国外已达13%,根据专家预测,汽车塑料的单车用量还将会进一步增加。在现代车辆上,无论是外装饰件、内装饰件,还是功能与结构件,都可以采用塑料材料,外装饰件有保险杠、挡泥板、车轮罩、导流板等;内装饰件有仪表板、车门内板、副仪表板、杂物箱盖、座椅、后护板等;功能与结构件有油箱、散热器水室、空滤器罩、风扇叶片等。据统计,我国2000年汽车产量200多万辆,车用塑料达138万吨。从国内外汽车塑料应用的情况看,汽车塑料的用量现已成为衡量汽车生产技术水平的标志之一。、作为塑料制件最有效的成型方法之一的注塑成型由于可以一次成型各种结构复杂、尺寸精密和带有金属嵌件的制品,并且成型周期短,可以一模多腔,生产率高,大批生产时成本低廉,易于实现自动化生产,因此在塑料加工行业中占有非常重要的地位。据统计,塑料模具约占所有模具(包括金属模)的38.2%,塑料制品总重量的大约32%是用于注射成型的,80%以上的工程塑料制品都要采用注射成型方式生产。、根据海关统计,我国2000年共进口模具9.77亿美元,其中塑胶模具共5.5亿美元,占56.3%,2001年共进口模具11.12亿美元,其中塑胶模具共6.16亿美元,占55.4%。从品种上来说,进口量最大的是塑胶模具。在压缩成型过程中,塑料原料是以粉状或锭料形式放置在加热的金属模具型腔中。因为分型面是水平面,上模就垂直下行。闭合模具后,预成型加压加热作用一段时间。在压力为23t/in和温度为华氏温度350的作用下,是塑料呈半液态,充满模具型腔。虽然近年来开发的酚醛树脂可在25S内塑化,但塑料通常的塑化需要115min。最后开模取出塑件。如果零件中含有金属嵌件,应在注入塑料前,讲嵌件放入型腔定位孔中。锭料在装入模腔前预热出去气体,增强流动性,以便于充满模具和缩短塑化时间。电介质加热时加热锭料的便利方法。因为塑料是直接加入模具型腔中的,所以压缩模比其他模塑料工艺的模具简单,不需要浇道和浇口,可以节省原料,因为清理浇道和浇口,对热固性塑料来说是极大的浪费。用于压缩模塑的压力机通常是垂直液压机。较大的压力机要求操作者全神贯注地操作;然而,一个操作者可以同时操作几台小型压力机,因此压力机要合理放置以便操作者能够方便你从一台到另一台进行操作,操作者要保证当他再次绕道特定压力机前时,模具恰好准备开模。热固性塑料在加热和加压作用下固化,这个特性决定其适合压缩模和传递模。因为压缩模要交替的加热和冷却,所以热塑性塑料实际上不是用于压缩成型。为了使热塑性塑料之间硬化并从型腔中顶出,就需要将塑件冷却。压缩模的类型。 用于压缩的模具可分为四种基本类型,分别是:不溢式压缩模、挡环不溢式压缩模、溢式压缩模和半溢式压缩模。在不溢式压缩模中,柱塞式凸模随上模进入下模模腔成型,因为下模没有挡环或限位装置,柱塞式凸模继续下行以全部压力施加在塑料上,这样就成产出具有良好电性能和物理性能的致密塑件。加入模腔的塑料剂量须精确计量,以为其影响零件的壁厚。挡环不溢式压缩模与不溢式压缩模类似,只是在预定点处增加了挡环,使柱塞式凸模在预定点停止运动,在这种模具中挡环吸收了原应作用在零件上的部分压力。这种压缩模可精确控制零件的壁厚,但是塑件密度的变化是相当大的。在溢式压缩模中,溢料会增加上下模的尺寸。当上模对塑料施压时,多余的塑料会从分型面处溢出。对溢料进一步施压,他就硬化最后在上模形成飞边。生产致密塑件通常需要使用的计算量稍多的原料来增加压力。这种类型的模具之所以在生产中广泛采用,是因为它想对比较容易制造,并能够控制塑件的厚度和致密度,使其更接近要求。半溢式压缩模是溢式压缩模和不溢式压缩模的组合类型,除了飞边外,采用的挡环可限制上模的移动。
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