塑料制品的分析与机构设计

1、125/125HYPERLINK /第一章 绪论随着塑料工业的飞速进展和通用塑料与工程塑料在强度和精度等方面的不断提高，塑料制品的应用范围也在不断地扩大，如：家用电器、仪器仪表、建筑器材、汽车工业、日用五金等众多领域，塑料制品所占的比例正迅速增加，由于在工业产品中，一个设计合理的塑料件往往能代替多个传统金属结构件，加上利用工程塑料特有的性质，能够一次成型特不复杂的形状，同时还能设计成卡装结构，成倍地减少整个产品中的各种紧固件，大大地降低了金属材料消耗量和加工及装配件工时，因此，近年来工业产品塑料化的趋势不断上升。塑料模具是用于成型具有一定形状尺寸的塑料制品的成型工具。模具是塑件生产的重要工艺装

2、备之一。不同的塑料成型方法使用着不同模塑工艺和原理及结构特点各不相同的塑料模具。对塑件质量的优劣及生产效率的高低，除其他的因素外，模具的因素也是一个重要的因素。在现代塑件生产中，合理的模塑工艺、高效的模塑设备、先进的塑料模具和制造技术是必不可少的，尤其是塑料模具对实现塑料加工工艺要求，塑件的使用要求和造型设计起着重要的作用。作为产品生命周期的重要一环，模具的质量的好坏直接阻碍着产品的质量。塑料模具设计与制造是一项综合性的工作，围绕塑件成型生产涉及到成型物料，成型设备，成型工艺，成型模具及模具制造等各个方面，而这些便构成了塑件成型生产的系统。注塑成型是塑料加工中最普遍采纳的方法。该方法适用于全部

3、热塑性塑料和部分热固性塑料，制得的塑料制品数量之大是其他成型方法望尘莫及的。由于注塑成型加工实现了生产自动化、高速化，因此具有极高的经济效益。作为注塑成型加工的要紧工具之一注塑模具，在质量、精度、制造周期以及注塑成型过程中的生产效益等方面水平高低，直接阻碍产品的质量、产量、成本及产品的更新换代，同时也决定着企业在市场竞争中的反应能力和速度。本设计从塑料注射成型的成型物料、成型设备、成型模具几个方面讲述气压瓶盖注射成型设计。第二章 塑料制品的分析2.1 塑件的作用及结构 此塑件是一个气压瓶盖。其形状比较复杂，尺寸较大，外观质量要求比较高。制品外表面不同意出现划伤、气泡、缩孔等缺陷，且要求较低的表

4、面粗糙度值，因此精度要求取9级（GB/T1800.31998），材料用ABS热塑性材料。塑件图:图一 塑件图2.2 塑件材料的性能分析该塑料制品选用ABS塑料成型，ABS是丙烯晴、丁二烯和苯乙烯三种单体的三元共聚物。ABS具有较高的强度、硬度、耐热性及耐化学腐蚀性，流淌性好，吸湿性大；具有弹性和较高的冲击强度；它具有优良的介电性能及成型加工性能等综合性的优良性能，且价格廉价，原料易得。材料的各种性能用途如表一所示：结构特点线性结构非结晶型使用温度小于70性能特点机械强度较好，有一定耐磨性成型特点成型效果好，成型前原料要干燥适用注射机类型螺杆柱塞式均可密度(g/cm)1.031.07注射压力(M

5、Pa)60100 螺杆转速(r/min)30计算收缩率(%)0.30.8模具温度()5080预热温度()8085时刻/h23吸水率24h(%)0.3拉伸屈服强度(MPa)1800抗拉屈服强度(MPa) 50喷嘴温度()170180 表一 ABS的性质及成型条件第三章 注射机型号的确定3.1 注射机选用原则 模具是安装在注射机上使用的，在生产塑件时模具与机床是一个不可分割的整体。因此在设计模具时，除了应当了解注射成型的工艺过程外，还应对所选用注射机的有关技术规范和性能参数有全面的了解。注射机的选用包括两方面的内容：一是确定注射机的型号，使塑料、塑件、注射模及注塑工艺等所要求的注射机的规格参数在所

6、选的规格参数可调的范围内；二是调整注塑机的技术参数至所需的参数。3.2 注射模与注射机的关系3.2.1注射量的计算依照零件的三维模型，利用三维软件可直接查询出塑件的体积为 G1=86925.5 mm3，取密度=1.07g/cm3,M=V1=1.0786925.5=93.01g据经验公式,浇注系统凝料容量G为制件体积的0.15,即12.9 cm3。一次注射所需塑料总体积G=nG+G=99.9 cm3 13.2.2 塑件和流道凝料在分型面上的投影面积及所需锁模力的计算锁模力是在成型时锁紧模具的最大力。用于实现动、定模紧密闭合，保证塑料制品的尺寸精度，尽量减少分型面处的溢边（或毛边）厚度和确保操作者

7、的人身安全。流道凝料(包括浇口)在分型面上的投影面积A2,在模具设计前是个未知数,依照多型腔模的统计分析,A2是每个塑件在分型面上的投影面积A1的0.2-0.5倍,因此可用0.5A1来进行估算,因此A=A1+A2=A1+0.5A1=1.5A1=1.514361.24=21541.86mm2式中 A=()+392.64=14361.24FAP型 =21541.86mm230MPa=646.26kN式中型腔压力P型 取30MPa.A 塑料与浇注系统在分型面上的投影要积 P型型腔内内平均压强3.2.3 选择注射机依照每一生产周期的注射量和锁模力的计算值,可选用SZ-160/1000，(上海第一塑机厂

8、),见表二:型号SZ-160/1000注射压力（MPa）132公称注射量(cm3)179锁模力（KN）1000螺杆（柱塞）直径(mm)44模具最小厚度（mm）170模板最大行程（mm）280喷嘴球半径（mm）10模具最大厚度（mm）360定位圈尺寸（mm）120拉杆内间距（mm）360260移模行程（mm）280注射速率（g/s）110塑化能力（g/s）10.5表二 SZ-160/1000注射机的有关参数3.2.4 注射机有关参数的校核（1）注射量的校核据式 G0.8G 式中：G塑件与浇注系统的体积（cm3） G 注射机的注射量（cm3）0.8最大注射容量的利用系数 已知：V件=99.9cm3

9、1790.8=143.2cm3 因此满足要求 （2） 锁模力的校核 F EQ EQ F(kPA,1000) （KN） 式中： F注射机的额定锁模力（N） A塑料制品与浇注系统在分型面上的总投影面积（m2） P熔融塑料在型腔内的平均压力（Mpa）取35Mpa K安全系数取1.11.2那个地点取1.2 代入数据得 = EQ = 775.51KN1000KN因此满足要求（3） 型腔数的校核按最大注射量确定型腔数 n = EQ F(kM-m,m) 其中 k系数0.8 M公称注射量179 m浇道、流道的体积 m制品体积代入数据得n=1.451 因此，型腔数校核合格。3.2.5 最大注射压力Pmax最大注

10、射压力是指注射机料筒内柱塞或螺杆施于熔融塑料上的单位面积压力（注射时）。成型塑件所需要的注射压力是由塑料品种、注射喷嘴的结构式、塑件形状的复杂程度以及浇注系统的压力损失等因数决定，注射机的最大注射压力要大于成型塑件所要求的注射压力(60-110MPa)，即Pmax110MPa3.2.6 模具与注射机安装部分相关尺寸的校核A设计模具的长、宽方向尺寸时要与注射机模板尺寸和拉杆间距相适应，应注意模具能否穿过拉杆间的空间装卡到模板上。B模具安装在注射机上必须使模具主浇道中心线与料筒、喷嘴的中心线重合，因此在注射机定模板上有一定位孔，要求模具的定位圈与之相配合。C注射机喷嘴头的球面半径R1应与相接触的模

11、具主浇道始端凹下的球面半径R2相配合， R2= R1+（12）mm。D模具能恰当、稳固的装卡在注射机的动、定模板上。3.2.7其他尺寸的校核（1）开模行程的校核关于全液压式锁模机构的注射机，其最大开模行程等于动模与定模之间的最大开距（L）减去模具的厚度（H）。当模具厚度增大，则开模行程减小。对单分型面注射模，开模行程可按下式公式校核：S=L-HH+H+(510) mm式中 S： 注射机的最大开模行程； H： 塑料制品的推出距离；H： 制品高度（包括浇注系统）；已知S=300 mm H+H+10= 45+60+10 = 115mm 400500，导柱直径d取3035，先取d=32mm；d=42m

12、m；d=42mm；D=48mm。图七 导柱7.2导套的形式导套结构形式如图所示：图八 导套 第八章 推出机构设计把塑料制品从凹模或凸模上脱出来的机构即为推出机构或脱模机构，它是注塑模具的重要组成部分。推出机构的形式和推出方式与塑料制品的形状、结构和塑料性能有关。对推出机构设计的要求：塑料制品脱模后，不能使塑料制品变形。推力分布均匀，推力面积要大，推杆尽量靠近凸模，但也不要距离太近。1.塑料制品在推出时，不能造成碎裂。推力应作用在塑料制品承受力大的部位，如塑料制品的肋部、凸缘及壳体壁等。2.不要损坏塑料制品的外观美。3.推出机构应准确、动作可靠、制造方便、更换容易。4.推出机构的零件包括：推杆、

13、推板和推管等。8.1脱模力的计算通过注射机的高压注射塑料在模具内冷却定型，现在塑料收缩将型芯包紧，这一包紧力是开模后塑件脱出时所必须克服的，此外还有不通孔带来的大气压力，塑料及型芯的粘附力，摩擦力及机构本身运行时所产生的摩擦阻力。开始脱模时的瞬时阻力最大，脱模力的计算一般总是计算初始脱模力。由t/D=2.5/130=1/52270度).对精度较高的塑件,模温宜取50-60度,对高光泽.耐热塑件,模温宜取60-80度. 3、如需解决夹水纹，需提高材料的流淌性，采取高料温、高模温，或者改变入水位等方法。 4、如成形耐热级或阻燃级材料，生产3-7天后模具表面会残存塑料分解物，导致模具表面发亮，需对模

14、具及时进行清理，同时模具表面需增加排气位置。ABS树脂是目前产量最大，应用最广泛的聚合物，它将PS，SAN，BS的各种性能有机地统一起来，兼具韧，硬，刚相均衡的优良力学性能。ABS是丙烯腈、丁二烯和苯乙烯的三元共聚物，A代表丙烯腈，B代表丁二烯，S代表苯乙烯。 ABS工程塑料一般是不透明的，外观呈浅象牙色、无毒、无味，兼有韧、硬、刚的特性，燃烧缓慢，火焰呈黄色，有黑烟，燃烧后塑料软化、烧焦，发出专门的肉桂气味，但无熔融滴落现象。ABS工程塑料具有优良的综合性能，有极好的冲击强度、尺寸稳定性好、电性能、耐磨性、抗化学药品性、染色性，成型加工和机械加工较好。ABS树脂耐水、无机盐、碱和酸类，不溶于

15、大部分醇类和烃类溶剂，而容易溶于醛、酮、酯和某些氯代烃中。ABS工程塑料的缺点：热变形温度较低，可燃，耐候性较差。塑料注射模具 塑料注射模具是现在所有塑料模具中使用最广的模具，能够成型复杂的高精度的塑料制品。本文只是粗略介绍一下。 设计塑料注射模具首先要对塑料有一定的了解，塑料的要紧成分是聚合物。如我们常讲的ABS 塑料便是丙烯腈、丁二烯、苯乙烯三种单体采纳乳液、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，产生流淌变形，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

16、工，而通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，也确实是所讲的热固性塑料。 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，在流淌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、保压时刻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。 一般产品假如没有芯子支撑，收缩相应要大些。 塑料注塑模具差不多分为静模和动模。 在注塑机的注射头一边的带浇口套的为静模，静模一般有浇口套、靠板、模板组

17、成，简单模具（特不是静模没有芯子的模具）也能够不使用靠板，直接用厚一点的模板就能够了。浇口套一般为标准件，除非专门缘故，不建议取消。浇口套的使用有利于安装模具、更换方便，不用自己抛光。有些专门模具浇口套可用钻出来或用锥度线割割成。部分模具必须静模脱模时，还得加上静模脱模机构。动模的结构一般为动模板、动模靠板、脱模机构以及模脚和装机固定板。 脱模机构中除了脱料杆，还有回位杆，部分模具还要增加弹簧以实现例如自动脱模等功能。还有导柱、冷却水孔、流道等也是不可少的模具的差不多结构。因此，斜导模具还有斜导盒、斜导柱等。 当为一产品设计模具时，首先要设定模具的差不多结构尺寸以备料，来加快模具制造的速度。复

18、杂产品应先绘制好产品图，再定好模具的尺寸。现在的模具差不多上要进行热处理，加高模具的硬度，提高模具使用寿命。在热处理前，先对模板进行初步加工：钻好导柱孔、回位孔（动模）、型腔孔、螺丝孔、浇口套孔（静模）、拉料孔（动模）、冷却水孔等，铣好流道、型腔，有些模具还应铣好斜导盒等。现在的一般周密模具的模板一般用Cr12、Cr12Mov和一些专业模具钢,Cr12等硬度不能太高，在HRC60度时经常开裂，模板的常用硬度一般为HRC55度左右。芯子的硬度可在HRC58以上。假如材料为3Cr2W8v，制造后再氮化处理表面硬度，硬度应为HRC58以上，氮化层应越厚越好。 浇口直接关系到塑件的美观，浇口设计不行的

19、话，容易产生缺陷。在没有任何阻挡的情况下专门容易产生蛇型流。关于要求高的产品，还应设计溢流和排气。溢流处能够用顶杆，不要在模板上留有溢流飞边，才不至于阻碍模具寿命。1、A. Mold ComponetsMolds used in injection molding consist of two halves; one stationary and one movable. The stationary half is fastened directly to the stationary platen and is in direct contact with the nozzle of th

20、e injection unit during operation. The movable half of the mold is secured to the movable platen and usually contains the ejector mechanism. There are many possible mold designa, including multiple piece molds for complicated parts. On production molding equipment many articles may be shot at the sa

21、me time by the use of multiple cavity molds. The use of a balanced runner system carries the plastic from the sprue to each individual cavity. At this poin the material passes through a gate into the cavity. The gate is a restriction, smaller then the runner, to provide for even filling of the mold

22、cavity and to allow the products to be easily removed form the runner system. With most injection molding system, the articles can be snapped away from the runner or sprue without additional trimming. Prouducts that have been injection molded can usually be identified by finding where the gate was b

23、roken off. The gate will usually be located at the edge or parting line of an object or in the center of cylindrical product. Molds are expensive, as are the machines. Yet, once the product has been designed, molds made, and production stared, articles can be produced in quantity at low cost. Virtua

24、lly all thermoplastics can be injection molded through variations in mold and machine design. Mold (and die) parts that are mass-produced and standardized in shape and dimension are referred to as “standards” (or “standard parts”). Specialized operators of milling machines, lathes, lathes, electroni

25、c discharge machining (EDN) equipment and grinders produce mold components independently of each other, following detaied mold part drawings. Finally, all these items come together with the standard mold base and hardware and are assembled by the mold maker. Today, standard components for the moldma

26、king industry are marketed by a number of companies. Fig.3.1.1 illustrate the standard components for Molds.Table 3.1.1 Status of standardization (1998) components for Compression, Injection, and Die-Cast MoldPos. No.DenominationStandardDINISO1Plate, plain16760-16753-22Plat, drilledV 16760-2/3Suppor

27、t pillarDIN ISO 10073100734Centring sleeve1675994495Locating guide pillar1676180176Locating guide busch1671680187Ejector pin, cylindrical head1530-A67518Shouldered ejector pin, cylindrical head1530-C86949Ejector pin, conical head1530-D/10Flat ejector pin1530-F869311Ejector sleeve16756840512Sprue pul

28、ler insert16757/13Sprue bushing16752-11007214Angle pin/840415Locating unit, round and falt/840616Locating ring1676310907-110907-217Thermal insulating sheet167131560018Cooling connectors16766/B Mold Construction The construction of the mold for injection molding begins with the working drawing. From

29、it the tequirements for the mold can be specified. These would include the material from which the mold should be made, the availability of equipment for machining the mold, and the mold capacity of the die set on the machine. Cold rolled steel is an ideal material for laboratory molds, since it mac

30、hines well, is fairly inexpensive, and holds up well for nozzle pressure and wear. Its major disadvantage is that it will rust quickly unless protected by mold telease or wax during storage. Complicated mold cavities need specialized machining and polishing, therefore, circular cavities which can be

31、 turned and polished on the lathe require less equipment and machining skill. Similar molds may also be machined from aluminum, and they have the advantage of not rusting. Excessive wear develops on the sprue due to the high nozzle pressure on the soft aluminum, but this can be overcome by the use o

32、f a steel cover plate on the top of the mold. Another method of mold construction is by the casting process using an aluminum filled epoxy resin. This type of mold is particularly suited to products of intricate design and products that are difficult to machine. The cast epoxy is strong and gives go

33、od surface detail, however, it is brittle and should have a steel top plate attached to absorb the wear of the nozzle. A pattern of the product must be secured or made and placed on a mold plate. The drag of a small steel flask is placed around the pattern and the epoxy resin is poured to fill the m

34、old half. When this half of the mold has been cured, the cope is placed over it and the remainder of the mold poured. Upon curing, the flask is removed, all surfaces machined smooth, dowel pinholes drilled, and dowels inserted. A steel cap plate should be bolted to the top halves and the sprue, runn

35、ers, and gates machined. Instructions for mixing, pouring, and curing the aluminum filled epoxy should be followed according to the manufacturers specifications.2. Hot Runner Systems Hot runners are classified according as they are heated: insulated-runner systems (it is not described in this articl

36、e) and genuine hot-runner systems. The latter can be further sub-classified according to the type of heating: internal heating, and external heating. Heating is basically performed electrically by cartridge heaters, heating rods, band heaters, heating pipes and coils, etc. To ensure uniform flow and

37、 distribution of the melt, usually a relatively elaborate aontrol system comprising several heating circuits and an appropriate number of sensors is needed. The operating voltage is usually 220 V to 240 V, but small nozzles frequently have a low voltage of 5 V, and also 15 V and 24 V operating volta

38、ge. Runner systems in conventional molds have the same temperature level as the rest of the mold because they are in the same mold block. If, however, the runner system is located in a special manifold that is heated to the temperature of the melt, all the advantages listed below accrue. Runner mani

39、folds heated to melt temperature have the task of distributing the malt as far as the gates without damage. They are used for all injectionmolded thermoplastics as well as for crosslinking plastics, such as elastomers and thermosets. In the case of thermoplastics, these manifolds are usually referre

40、d to as the hot-runner system, the hot manifold, or simply as hot runners. For crosslinking plastics, they are known as cold runners.A. Hot-Runner Systems Hot-runner systems have more or less become established for highly-automated production of molded thermoplatic parts that are produced in large n

41、umbers. The decision to use them is almost always based on economics, i. e. production size. Quality considerations, which played a major role in the past, are very rare now because thermoplastics employed today are almost all so that they can be processed without difficulty with hot-tunner systems

42、that have been adapted accordingly. Hot-tunner systems are available as standard units and it is hardly worthwhile having them made. The relevant suppliers offer not only proven parts but also complete systems tailored to specific needs. The choice of individual parts is large.B. Economic Advantages

43、 and Disadvantages of Hot-Runner Systems 1. Economic Advantages Savings in materials and costs for regrind. Shorter cycles; cooling time no longer determined by the slowly solidifying runners; no nozzle retraction required. Machines can be smaller because the shot volume-around the runners-is reduce

44、d, and the clamping forces are smaller because the runners do not generate reactive forces since the blocks and the manifold block are closed. 2. Economic Disadvantages Much more complicated and considerably more expensive. More work involved in running the mold for the first time. More susceptible

45、to breakdowns, higher maintenance costs (leakage, failure of heating elements, and wear caused by filled materials). 3. Technological Advantages Process can be automated (demolding) because do not need to be demolded. Gates at the best position; thanks to uniform, precisely controlled cooling of the

46、 gate system, long tlow paths are possible. Pressure losses minimized, since the diameter of the runners is not restricted. Artificial balancing of the gate system; balancing can be performed during running production by means of temperature control or special mechanical system (e. g. adjustment of

47、the gap in a ring-shaped die or use of plates in flow channel. Natural balancing is better). Selective influencing of mold filling; needle valve nozzles and selective actuation of them pave the way for new technology (cascade gate system: avoidance of flow lines, in-mold decoration). Shorter opening

48、 stroke needed compared with competing, conventional three-platen molds. Longer holding pressure, which leads to less shrinkage. 4. Technological Disadvantages Risk of thermal damage to sensitive materials because of long flow paths and dwell times, especially on long cycles. Elaborate temperature c

49、ontrol required because non-uniform temperature control would cause different melt temperatures and thus non-uniform filling.C. Design of a Hot-Runner System and its Components Hot-runner molds are ambitious systems in a technological sense that involve high technical and financial outlay for meetin

50、g their main function of conveying melt to the gate without damage to the material. D. Externally/Internally Heated Systems The major advantages and disadvantages of the two types .E. Externally Heated System 1. Advantage Large flow channel cause low flow rare and uniform temperature distribution. 2

51、. Disadvantage The temperatures required for external heating have to be very much higher. For PA 66, for example, the mold temperature is approximately 100 and the manifold temperature is at a temperature difference of approximately 170 from the mold block, which means. Special measures required fo

52、r fixing the hot-runner nozzles to the gates because of the considerable themal expansion. Risk of disruption if this is not adepantely resolved. Higher heating power (over 500 W per 100 mm line for a typical cross-section measuring 407mm2). Insulation from the mold block. Large ,unsupported ateas a

53、nd therefore, with large-surface molds, risk of bowing of the mold platen on the feed side if this has not been designed thick enough and thus, as a direct consequence, the mold becomes very heavy. F. Internally Heated System A frozen layer of plastic forms on the inner surface of the channel and fu

54、nctions as an insulation layer. The heat requirement of the system is much lower (toughly 55 W per 100 mm length of inside tube). The temperature differences between mold and manifold blocks are negligible; therefore measures that would have been necessary for large heat expansion are not needed. Th

55、e hot manifold of an internally heated system if a compact block that is bolted tightly to mold. Consequently, the mold is very rigid and no measures are required for centering the nozzles and gates. This also allows the plate on the machine side to be manufactured as one block consisting of fixed m

56、old with inbuilt manifold and corresponding rigidity. The melt volume is small and so the dwell times of the flowing melt are short. On the other hand, the flow rates are very much greater and this can damage the material. It is not advisable to use internally heated systems for sensitive materials.

57、 When deciding on a certain system, advice can be obtained from suppliers.3.Forming Theory The confidence level in successfully forming a sheetmetal stamping increases as the simplicity of the parts topography increases. The goal of forming with stamping technologies is to produce stampings with com

58、plexgeometric surfaces that are dimensionally accurate and repeatable with a certain straindistribution, yet free from wrinkles and splits. Stampings have one or more forming modes that create the desired geometries. These modes are bending, stretch forming and drawing. Stretching the sheetmetal for

59、ms depressions or embossments. Drawing compresses material circumferentially to create stampings such as beer cans.As the surfaces of the stamping become more complex, more than one mode of formingwill be required. In fact, many stampings have bend, stretch and draw features produced in the form die

60、. The common types of dies that shape material are solid form, stretch form and draw.Solid Form The most basic type of die used to shape material is the solid form die. This tool simply displaces material via a solid punch crashing the material into a solid die steel on the press downstroke. The res