课程设计外文文献.doc

毕业设计（论文）外文参考文献译文及原文 系 部 机械电气学部 专 业 机械设计制造及其自动化 年 级 200x级 班级名称 机械设计1班 学 号 x x 学生姓名 xxx 指导教师 xxx xx年x 月 目 录1 Representative Strcture of Injection Mol译文3外文42 Number of Mold Cavities译文5外文7注射模的典型结构 用于热塑性塑料注射成型的模具通常是溢料式模具，因为与传递模塑成型一样，在注射成型中，不需要额外的载料空间。但是，模具设计的基本类型有多种变化。所有材料最常使用的设计是两板模设计。型腔装在第一个模板上，凸模装载第二个模板上。主流道衬套并入定模的模板中。按照这种安排，就有可能使用直接中心浇口，使塑料进入单腔模或者是多腔模的分流道系统中。在大多数情况下，凸模、顶出装置以及分流道系统在动模中。虽然为了符合特定要求会有许多变化，但是这是注射模的基本设计。三板模设计的特点是具有包含型腔的第三个可移动的模板，因此对于多型腔操作，允许中心或偏置浇口进入每一个型腔。模具打开时有两次分模，一个塑件的脱模，另一个是去除分流道和主流道凝料。通过压力机常规功能不能成型的的带镶嵌件、螺纹和取芯的模塑件，要求在模具中安装分离的或零散的部件或者型芯。这些零撒的部件随着塑件被顶出。每一个生产周期后，这些部件必须与塑件分离，并重新安装在模具中。因此使用复制的部件以高效生产。液压缸或气缸被安装在模具中以抽出侧型芯部件。在模具设置料导柱，就能完成有角度侧抽芯，而不需要高成本的零散部件。有几种方法可用于旋松塑件上的内螺纹或外螺纹：为了提高生产率，常常使用价格相对较低的长行程的液压油缸驱动齿轮齿条机构进行自动脱螺纹。其他脱螺纹的方法包括使用通过双动油缸驱动的齿轮齿条或摩擦型弧刷。塑件的内部凸凹可以通过带料度的型芯（成型杆）成型，型芯的移动由将金属型芯与塑件分离的顶出杆驱动。1 Representative Strcture of Injection MolMolds used for injection molding of thermoplastic resins are usually flash mold,because in injection molding,as in transfer molding,no extra loading space is needed,However,there are many variations of this basic type of mold design.The design most commonly used for all types of materials is two-plate design.The cavities are in one plate,the plungers in the second plate.The sprue bushing is incorporated in that plate mounted to the stationary half of the mold.With this arrangement it is possible to use a direct center gate that leads either into a single-cavity mold or into a runner system for a multi-cavity mold.The plungers and ejector assembly and,in most cases,the runner system belong to the moving half of the mold.This the basic design of an injection mold,though many variations have been developed to meet specific requirements.A three-plate mold design features a third,movable plate which contains,the cavity,thereby permitting center or offset gating into each cavity for multicavity operation.When the mold is opened,it provides two openings,one for ejection of the molded part and the other for removal of the runner and sprue.Moldings with inserts or threads or coring that cannot be formed by the normal functioning of the press require installation of separate or loose details or cores in the mold.These loose members are ejected with the molding.They must be separated from the molding and reinstalled in the mold after every cycleHydraulic or pneumatic cylinders may be mounted on the mold to actuate horizontal coring members.It is possible to mold angular coring,without the need for costly loose details,by adding angular core pins engaged in sliding mold members.Several methods may be used for unscrewing internal or external threads on molded parts:For high production rates automatic unscrewing may be done at relatively low cost by the use of rack-and-gear mechanism actuated by a double-acting hydraulic long-stroke cylinder.Other methods of unscrewing involve the use of an electric gear-motor drive or friction-mold wipers actuated by double-acting cylinders.Parts with interior undercuts can be made in a mold which has provision for angular movement of the core,the movement being actuated by the ejector bar that frees the metal core from the molding.模具型腔的数目使用多个模具型腔可以获得更高的生产效率。但是更大的模具复杂性也显著增加了制造成本。值得注意的是，单型腔模具中的限制性因素是塑件的冷却时间，但是对于多星期模具，注射机的塑化能力逐渐成为限制因素。因此，工作周期的次数不会随着型腔数目成比例增加。对于模具最适宜的型腔数这个问题，没有一个确定的答案，因此这依赖于诸如塑件的复杂性、机器的类型和大小、模具的工作周期以及需要的塑件数量等方面的因素。如果能够对具有可能型腔数目的模具的成本和工作周期次数进行相对精确的估算，并且假设机器（和材料）的运行成本，就可以计算每小时塑件数量的保本值，并与要求的总产量进行比较。1、分流道塑料熔体用以进入模具型腔的流动通道称为分流道。分流道的横截面通常是圆形或梯形的。圆形横截面对原料流动的阻力最小，但在模具上需要两次机械加工，以为在分型面上两个板都要被切削。但是，在三板模设计中。优先选用梯形分流道，因为穿过分流道面时要求有滑动。三板模的操作必须去除分流道和主流道冷凝料。这些凝料必须重新塑化才能重复使用但是有可能通过保持材料为液态来完全出去分流道系统。这种模具称为热流道。材料通过热流道板保持液态，热流道板又是通过电子释热元件加热的。热流道模的优点是，在长期运行工作中，而且模具自动工作，消除了人为引起的各种变化。热流道模也具有某些不足：它需要花相当长的时间才能开始运行，并且在多腔模中平衡浇口与流体，以及防止流涎是很难的。在绝热流道模中可以部分解决这些问题，它是热流道模和三板模的结合，没有分流道系统凝料再塑化。绝热流道模比三板模要难于启动和操作，但是比热流道模要容易得多。2、浇口浇口连接着分流道与型腔。它必须允许足够的熔体流入模具来充满型腔。浇口的类型和尺寸，以及在模具中的位置都强烈地影响成型工艺和塑件的质量。浇口类型有两种：大型浇口和限制性浇口。限制性（针尖的）浇口的横截面通常是圆的，对于大多数热塑性塑料，其直径不超过0.060英寸。热塑性塑料的表现粘度是剪切速率的函数粘度随着剪切速率个速度的增大而减小。限制性浇口的使用是有利的，因为当塑料被迫通过小浇口时，塑料熔体的速率提高，加之一些动能量转化成热量，提高了塑料的局部温度，从而进一步降低了其黏性。塑料通过限制性浇口时也会使混合度更高。最常用的浇口类型是侧浇口，通过塑件侧边上某些点处的限制性浇口或者较大浇口而进行浇注。侧浇口在结构上容易实现，经常是唯一可行的浇口形式。对于大型塑件或者有特殊原因时侧浇口可以散开，被称之为扇形浇口。当要求朝一个方向流动时，可以使用薄膜浇口，它将扇形浇口延长至塑件的全长，但保持浇口非常薄。单型腔模最常用的浇口是主流道浇口。它从注射机喷嘴直接进料到塑件。因此压力损失最小。但是主流道浇口也存在一些不足：没有注塑冷料，浇口区域存在高的应力集中，以及需要去除浇口。隔板浇口除了有主流道以外，还有从主流道导向塑件的圆形区域。这种浇口形式适于成型空心管。因为整个区域被移动，所以隔板消除了浇口周围的应力集中，但这种浇口比主流道浇口要难于清理。外形浇口的目的与从内部成型空心管一样，只是它从外部进行浇铸。当浇口将流体直接导入塑件时，由于喷射可能会产生边面缺陷。将护耳从塑件延长至浇口被切除处即可解决这一问题，这种工艺称为护耳浇口。护耳必须在第二到操作中去除。潜伏式浇口是一种穿过型腔的浇口，经常应用于自动模具中。3、排气当熔融的塑料充入模具时，熔体取代了空气。型腔中原有的空气必须被迅速地排除，否则会点燃塑件并导致烧焦，或者会限定熔体进入型腔的流量而导致不完全填充。为了从型腔中排除出空气，通常在浇口对面开槽。沟槽通常深0.0010.002英寸，宽3/81英寸。顶杆与顶杆洞之间的间隙可以进行辅助排气。值得注意的是，浇口的位置与适宜的排气直接相关。4、分型面如果从闭合模具的内部向外看，那么模具型腔的匹配看上去像一条直线。在塑件上它看上去也像一条直线，称为分型面。一个塑件可以有几个分型面。影响模具设计中分型面的选择的因素有：模具类型、型腔数目。产品的形状。拔模角度、顶出方式、模具制造工艺、排气方式、塑件的壁厚、浇口的位置和类型。后处理和外观要求。5、冷却热塑性塑料的模具在型腔中容纳熔融塑料，并将其冷却凝固到顶出温度。模具具备冷却通道。通过调节冷却液的温度和流经通道的流速来控制模具温度。适当的冷却或冷却液循环对于相同的反复性的模具循环是必不可少的。2 Number of Mold CavitiesUse of multiple mold cavities permits greater increase in output speeds.However,the greater complexity of the mold also increase significantly the manufacturing cost.Note that in a single-cavity mold the limiting factor is the cooling time of the molding,but with more cavities in the mold the plasticizing capacity of the machine tends to be the limiting factor.Cycle times therefore do not increase prorate with the number of cavities.There can be no clear-cut answer to the question of optimum number of mold cavities,since it depends on factors such as the complexity of the molding,the size and type of the machine,cycle time,and the number of moldings required.If a fairly accurate estimate can be made of the costs and cycle times for molds with each possible number of cavities and a cost of running the machine(with material)is assumed,a break-even quantity of the number of moldings per hour can be calculated and compared with the total production required.1、RunnersThe channels through which the plasticized material enters the gate areas of the mold cavities are called runner.Normally runner are either full rough or trapezoidal in cross section.Round cross section offers the least resistance to the flow of material but requires a duplicate machining operation in the mold,since both plates must be cut at the parting line.In three-plate mold designs,however,trapezoidal runner are preferred,since sliding movements are required across the parting-line runner face.One can see from Fig.18-2 that a three-plate mold operation necessitates removal of the runner and sprue system,which must be reground,and the material reused.It is possible,however,to eliminate the runner system completely by keeping the material in a fluid state.This mold is called a hot-runner mold.The material is kept fluid by the hot-runner manifold,which is heated with electric cartridges.The advantage of a hot-runner mold is that in a long-running job it is the most economical way of molding-three is no regrinding,with its attendant cost of handling and loss of material,and the mold runs automatically,eliminating variations caused by operators.A hot-runner mold also presents certain difficulties:It takes considerably longer to become operational.and in multicavuty molds balancing the gate and the flow and preventing drooling are difficult.These difficulties are partially overcome in an insulated-runner mold,which is a cross between a hot-runner mold and a three-plate mold and has no runner system to design.An insulated-runner mold is more difficult to start and operate than a three-plate mold,but it is considerably easier than a hot-runner mold.2、GatingThe gate provides the connection between the runner and the mold cavity.It must permit enough material to flow into the mold to fill out the cavity.The type of the gate and its size and location in the mold strongly affect the molding process and the quality of the molded part.There are two types of gates:large and restricted.Restricted(pinpointed) gates are usually circular in cross section and for most thermoplastics do not exceed 0.60 in.in diameter.The apparent viscosity of a thermoplastic is a function of shear rate-the viscosity decreases as the shear rate and,hence,the velocity increase.The use of the restricted gate is therefore advantageous,because the velocity of the plastic melt increase as it is forced through the small opening;in addition,some of the kinetic energy is transformed into heat,raising the local temperature of the plastic and thus further reducing its viscosity.The passage through a restricted area also results in higher mixing.The mold common type of gate is the edge gate,where the part is gated either as a restricted or larger gate at some point on the edge.The edge gate is easy to construct and often is the only practical way of gating.It can be fanned out for large parts or when there is a special reason.Then it is called a fan gate.When it is required to orient the flow pattern in one directiona flash gate may be used,It involves extending the fan gate over the full length of the part but keep it very thin.The most common gate for single-cavity mold is the sprue gate.It feeds directly from the nozzle of the machine into the molded part.The pressure loss is therefore a minimum.But the sprue gate has the disadvantages of the lack of cold slug,the high stress concentration around the gate area,and need for gate removal.A diaphragm gate has,in addition to the sprue,a circular area leading from the sprue to the piece.This type of gate is suitable for gating hollow tubes.The diaphragm eliminates stress concentration around the gate because the whole area is removed,but the cleaning of this gate is more difficult than for a sprue gate.Ring gate accomplish the same purpose as gating internally in a hollow tube,but from the outside.When the gate leads directly into the part,there may be surface imperfection due to jetting.This may be overcome by extending a tab from the part into which the gate is cut.This procedure is called tab gating.The tab has to be removed as a secondary operation.A submarine gate is one that goes through the steel of the cavity.It is very often used in automatic molds.3、VentingWhen the melted plastic fills the mold,it displaces the air.The displaced air must be removed quickly,or it may ignite the plastic and cause a characteristic burn,or it may restrict the flow of the melt into the mold cavity,resulting in incomplete filling.For venting the air from the cavity,slots can be milled,usually opposite the gate.The slots usually range from 0.001 to 0.002 in.deep and from 3/8 to 1 in.wide.Additional venting is provided by the clearance between knockout pins and their holes.Note that the gate location is directly related to the consideration of proper venting.4、Parting LineIf one were inside a closed mold and looking outside,the mating junction of the mold cavities would appear as a line.It also appears as a line on the molded piece and is called the parting line.A piece may have several parting lines.The selection of the parting line in mold design is influenced by the type of mold,number of cavities,shape of the piece,tapers,method of ejection,method of fabrication ,venting,wall thickness,location and type of gating,inserts,postmolding operations,and aesthetic considerations.5、CoolingThe mold for thermoplastics receives the molten plastic in its cavity and cools it to solidify to the point of ejection.The mold is provided with cooling channels.The mold temperature is controlled by regulating the temperature of the cooling fluid and its rate of flow through the channels.Proper cooling or coolant circulation is essential for uniform repetitive mold cycling.