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注塑模具设计与指导外文文献翻译、中英文翻译,注塑,模具设计,指导,外文,文献,翻译,中英文
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原文三INJECTION MOLD DESIGN AND GUIDEMold constructionA standard injection mold is made of a stationary or injection side containing one or more cavities and a moving or ejection side. Relevant details are shown in the figure below.Impression of a standard injection mold.High quality molds are expensive because labor and numerous high- precision machining operations are time-consuming. Product development and manufacturing costs often can be significantly reduced if sufficient attention is paid to product and mold design.The way in which the mold is constructed is determined by: shape of the part number of cavities position and system of gating material viscosity mold venting A simple mold with a single parting line is shown in the figure above. More complex molds for parts with undercuts or side cores may use several parting lines or sliding cores. These cores may be operated manually, mechanically, hydraulically, pneumatically or electro-mechanically.The figure below shows an example of a sliding cam. The cam pins that operate the cams are mounted under a maximum angle of 20 - 25 in the injection side. The angle is limited because of the enormous force that is exerted on these pins during mould opening and closing. Cammed mold for part with undercut cams move in vertical direction when mold is opened.Multi-cavity moldsThe number of cavities and mold construction depend both on economical and technical factors. Important is the number of parts to be molded, the required time, and price in relation to mould manufacturing costs. The figure below shows the relation between the total part costs and the number of cavities. Total part costs in relation to number of cavities.The gating system and gate location can limit the design freedom for multi-cavity molds. Dimensional accuracy and quality requirements should be accounted for. The runner layout of multiple-cavity molds should be designed for simultaneous and even cavity filling. The maximum number of cavities in a mold depends on the total cavity volume including runners in relation to the maximum barrel capacity and clamping force of the injection molding machine.Number of cavitiesA given molding machine has a maximum barrel capacity of 254 cm3, a plasticizing capacity of 25 g/s, 45 mm screw and a clamping force of 1300 kN. A PC part of 30 cm3, (shot weight 36 g) and a projected area of 20 cm2 including runners requires about 0.5/tons/ cm2 (5 kN/cm2 ) clamping force. The maximum number of cavities based on the clamping force would be 12. It is advisable to use only 80% of the barrel capacity, thus the number of cavities in this example is limited to 6. When very short cycle times are expected the total number of cavities may be further reduced. A 6-cavity mold in this example requires a shot weight of 216 g. The cooling time must be at least 8.7 seconds.Gate locationAppearance Whenever possible locate gates on non-visual surfaces thus eliminating problems with residual gate vestiges after the gate has been removed.Stress Avoid areas exposed to high external stress (mechanical or impact). The gate area has high residual stresses and also rough surfaces left by the gate act as stress concentrators.Pressure Locate the gate in the thickest section to ensure adequate pressure for packing out the part. This will also help prevent sink marks and voids forming.Weld lines Place gates to minimize the number and length of weld lines or to direct weld lines to positions that are not objectionable to the function or appearance of the part. When weld lines are unavoidable try to locate the gates close to the weld line location this should help maintain a high melt temperature that is beneficial to a strong weld line.WarpageAn incorrectly dimensioned or located gate may also result in undesirable flow patterns in the cavity. This can lead to moldings with visible weld line (see figure below). Influence of gate location on flow behavior of the melt.Undesirable flow patterns in the cavity can also lead to deformation by warping or bending (see figure below).Warpage due to unfavorable gate location.Gate typeAs important as selecting the optimal gate size and location is the choice of the type of gate. Gate types can be divided between manually and automatically trimmed gates. Manually trimmed gates Manually trimmed gates are those that require an operator to separate parts from runners during a secondary operation. The reasons for using manually trimmed gates are: The gate is too bulky to be sheared from the part as the tool is opened. Some shear-sensitive materials (e.g., PVC) should not be exposed to the high shear rates inherent to the design of automatically trimmed gates. Simultaneous flow distribution across a wide front to achieve specific orientation of fibers of molecules often precludes automatic gate trimming.Gate types trimmed from the cavity manually include: Sprue gate Edge gate Tab gate Overlap gate Fan gate Film gate Diaphragm gate External ring Spoke or multipoint gate Automatically trimmed gates Automatically trimmed gates incorporate features in the tool to break or shear the gate as the molding tool is opened to eject the part. Automatically trimmed gates should be used to: Avoid gate removal as a secondary operation. Maintain consistent cycle times for all shots. Minimize gate scars.Gate types trimmed from the cavity automatically include: Pin gate Submarine (tunnel) gates Hot runner gates Sprue gateRecommended for single cavity molds or for parts requiring symmetrical filling. This type of gate is suitable for thick sections because holding pressure is more effective. A short sprue is favored, enabling rapid mold filling and low-pressure losses. A cold slug well should be included opposite the gate. The disadvantage of using this type of gate is the gate mark left on the part surface after the runner (or sprue) is trimmed off. Freeze-off is controlled by the part thickness rather than determined the gate thickness. Typically, the part shrinkage near the sprue gate will be low; shrinkage in the sprue gate will be high. This results in high tensile stresses near the gate.Di mensions The starting sprue diameter is controlled by the machine nozzle. The sprue diameter here must be about 0.5 mm larger than the nozzle exit diameter. Standard sprue bushings have a taper of 2.4 degrees, opening toward the part. Therefore, the sprue length will control the diameter of the gate where it meets the part; the diameter should be at least 1.5 mm larger than or approximately twice the thickness of the part at that point. The junction of sprue and part should be radiused to prevent stress cracking A smaller taper angle (a minimum of one degree) risks not releasing the sprue from the sprue bushing on ejection. A larger taper wastes material and extends cooling time. Non-standard sprue tapers will be more expensive, with little gain. Edge gateThe edge or side gate is suitable for medium and thick sections and can be used on multicavity two plate tools. The gate is located on the parting line and the part fills from the side, top or bottom.Dimensions The typical gate size is 80% to 100% of the part thickness up to 3.5 mm and 1.0 to 12 mm wide. The gate land should be no more than 1.0 mm in length, with 0.5 mm being the optimum.Tab gateA tab gate is typically employed for flat and thin parts, to reduce the shear stress in the cavity. The high shear stress generated around the gate is confined to the auxiliary tab, which is trimmed off after molding. A tab gate is often used for molding P.Dimensions The minimum tab width is 6 mm. The minimum tab thickness is 75% of the depth of the cavity.Runner layoutThere are 3 basic layout systems used for multi-cavity systems. These can be catorigized as follows: Standard (herringbone) runner system H bridge (branching) runner system Radial (star) runner system Unbalanced runner systems lead to unequal filling, post-filling and cooling of individual cavities that may cause failures like: Incomplete filling Differences in product properties Shrinkage differences/warpage Sink marks Flash Poor mold release InconsistencyExample of unbalanced feed systems.Although the herringbone is naturally unbalanced, it can accommodate more cavities than its naturally balanced counterparts, with minimum runner volume and less tooling cost. With computer aided flow simulation it is possible to adjust primary and secondary runner dimensions to obtain equal filling patterns. Keep in mind that non-standard runner diameters will increase manufacturing and maintenance costs.Adjusting runner dimensions to achieve equal filling may not be sufficient in critical parts to prevent potential failures. Special attention is required for: Very small components Parts with thin sections Parts that permit no sink marks Parts with a primary runner length much larger than secondary runner length. It is preferred to design naturally balanced runners as shown in the figure below.Naturally balanced feed systems. The H (branching) and radial (star) systems are considered to be naturally balanced. The naturally balanced runner provides equal distance and runner size from the sprue to all the cavities, so that each cavity fills under the same conditions. When high quality and tight tolerances are required the cavities must be uniform. Family moulds are not considered suitable. Nevertheless, it might be necessary for economical reasons to mold different parts in one mold. The cavity with the largest component should be placed nearest to the sprue.Runners for multi-cavity molds require special attention. Runners for family molds, molds producing different parts of an assembly in the same shot, should be designed so that all parts finish filling at the same time. This reduces over- packing and/or flash formation in the cavities that fill first, leading to less shrinkage variation and fewer part-quality problems. Consider computerized mold- filling analysis to adjust gate locations and/or runner section lengths and diameters to achieve balanced flow to each cavity. The same computer techniques balance flow within multi-gated parts. Molds producing multiples of the same part should also provide balanced flow to the ends of each cavity. Naturally balanced runners provide an equal flow distance from the press nozzle to the gate on each cavity. Spoked runner designs work well for tight clusters of small cavities. However they become less efficient as cavity spacing increases because of cavity number or size.Ejection systemsThe method of ejection has to be adapted to the shape of the molding to prevent damage. In general, mould release is hindered by shrinkage of the part on the mould cores. Large ejection areas uniformly distributed over the molding are advised to avoid deformations. Several ejector systems can be used: Ejector pin or sleeve Blades Air valve Stripper plate When no special ejection problems are expected, the standard ejector pin will perform well. In case of cylindrical parts like bosses a sleeve ejector is used to provide uniform ejection around the core pin.Blades are poor ejectors for a number of reasons: they often damage parts; they are prone to damage and require a lot of maintenance. Blade ejectors are most commonly used with ribbed parts.Blade ejectors.A central valve ejector is frequently used in combination with air ejection on cup or bucket shaped parts where vacuum might exist. The air valve is thus only a secondary ejection device.A high-gloss surface can have an adverse effect on mould release because a vacuum may arise between cavity wall and the molding. Release can be improved by breaking the vacuum with an ejection mechanism.A stripper plate or ring is used when ejector pins or valves would not operate effectively. The stripper plate is often operated by means of a draw bar or chain.Three-plate molds, as shown in the figure below, have two parting lines that are used in multi-cavity molds or multiple gated parts. During the first opening stage automatic degating takes place when the parts are pulled away from the runners.Three plate mold with two stripper plates for ejection. RunnersUnlike sprees, which deliver material depth wise through the center of the mold plates, runners typically transport material through channels machined into the parting line. Runner design influences part quality and molding efficiency. Overly thick runners can lengthen cycle time needlessly and increase costs associated with regrind. Conversely, thin runners can cause excessive filling pressures and related processing problems. The optimum runner design requires a balance between ease of filling, mold design feasibility, and runner volume. Material passing through the runner during mold filling forms a frozen wall layer as the mold steel draws heat from the melt. This layer restricts the flow channel and increases the pressure drop through the runner. Round cross-section runners minimize contact with the mold surface and generate the smallest percentage of frozen layer cross-sectional area. As runner designs deviate from round, they become less efficient (see figure 7-20). Round runners require machining in both halves of the mold, increasing the potential for mismatch and flow restriction. A good alternative, the “round-bottomed” trapezoid, requires machining in just one mold half. Essentially a round cross section with sides tapered by five degrees for ejection, this design is nearly as efficient as the full-round design. The runner system often accounts for more than 40% of the pressure required to fill the mold. Because much of this pressure drop can be attributed to runner length, optimize the route to each gate to minimize runner length. For example, replace cornered paths with diagonals or reorient the cavity to shorten the runner.Runners for Multi-cavity MoldsFigure 7-23 Family MoldsThe runner diameter feeding the smaller part was reduced to balance filling.Runners for multi-cavity molds require special attention. Runners for family molds, molds producing different parts of an assembly in the same shot, should be designed so that all parts finish filling at the same time. This reduces over- packing and/or flash formation in the cavities that fill first, leading to less shrinkage variation and fewer part-quality problems. Consider computerized mold- filling analysis to adjust gate locations and/or runner section lengths and diameters to achieve balanced flow to each cavity (see figure 7-23). The same computer techniques balance flow within multi-gated parts. Molds producing multiples of the same part should also provide balanced flow to the ends of each cavity. Naturally balanced runners provide an equal flow distance from the press nozzle to the gate on each cavity. Spoked runner designs (see figure 7-24) work well for tight clusters of small cavities. However they become less efficient as cavity spacing increases because of cavity number or size.Other Gate DesignsPinpoint gates feed directly into part surfaces lying parallel to the mold parting plane. On the ends of three-plate runner drops, multiple pinpoint gates can help reduce flow length on large parts and allow gating into areas that are inaccessible from the part perimeter. For clean degating, the gate design must provide a positive break-off point (see figure 7-40) to minimize gate vestige Set in recesses or hidden under labels, properly designed and maintained pinpoint gates seldom require trimming. Because gate size must also be kept small, typically less than a 0.080-inch diameter, pinpoint gates may not provide sufficient packing for parts with thick wall sections. Parts with holes in the center such as filter bowls, gears, and fans often use the “filter-bowl” gate design to provide symmetrical filling without knit lines. Typically, the gate extends directly from a sprue and feeds the cavity through a continuous gate into the edge of the hole (see figure 7-41). Degating involves trimming away the sprue and conical gate section flush with the outer surface. Another design variation, the diaphragm gate, feeds the inside edge of the hole from a circumferential edge gate extending from a center disk (see figure 7-42). Degating usually involves punching or drilling through the hole.译文三注塑模具设计与指导模具结构一个标准的注塑模具是由定模和动模部分组成，由一个或多个型腔，以及一个可以移动的脱模部分组成。 有关的细节在下面的图片中被显示出。标准注塑模具的图片：图1 高质量高精度模具的价格是非常贵的。因为大量的劳动力和很多的高精密机器操作都被运用到生产制造中，经济消耗巨大。 产品发展和制造费用如果想要被极大地减少，我们就需要充分地重视和关注产品模具的设计。如下方面是我们在制造中应该解决的：制件的形状型腔的数量浇口的位置与浇口形式的选择材料的流动性模具的排气系统带有1个分型面的简单注塑模具如下图所示。 一个比较复杂的，用来成型结构复杂和带有侧抽芯结构的模具通常需要使用多次分型和侧抽芯结构。这种侧抽芯结构通常是通过人工，机械，液压以及电子机械装置来完成的。下面的图片是一个简单的滑动凸轮结构。控制凸轮的销被放置在定模一侧，其角度在20 - 25之间。 这个角度也是有限制的，这是由于它要在开模和合模中受到一个很大的力。当开模时这种模具是竖直方面移动的。图2 多型腔模具型腔的数目与它的结构主要取决于经济和技术这两个方面。 最重要的是，按照制件的数量来决定型腔的数量， 花费的时间，金钱以及与其相关的模具制造费用也要被考虑进去。下面的这个图，显示出模具型腔数量与制造全部费用的关系。图3 浇注系统与浇口位置限制了多型腔模具设计的随意性。同时，模具的尺寸精度和质量要求也需要被考虑。流道结构在设计时，应该将其设计为可以同时充满型腔的形式。 一个模具中型腔的最大数量应该取决于型腔的全部容量，包括流道和相关的最大注塑量，还需要考虑到注塑压力的大小。型腔数量一个给定的注塑机，他的最大注塑量是254立方厘米, 塑化能力是25 g/s, 45mm螺杆和1300 kN的锁模力。 一个体积是30立方厘米的PC制件(注射重 36 g), 他的投影面积是20平方厘米，包括流道，大约在0.5吨/CM2（0.5KN/CM2）的注塑压力。 以注塑压力为设计基准的模具，他的型腔数量最大是12个。建议型腔数量的容积是注塑机注塑量的80%。因此，通常情况下型腔数目被限制在6个以内。当循环周期很短时，型腔的数量建议被大打的减少。以这个为例，一个有6个型腔的模具，他的冷却时间必须不能低于8.7秒。 浇口位置外形 浇口无论被设计在什么位置，我们都不可能从外表面看到他的位置所在。因此在浇注系统被除去后，清除残余的废料是一个要被解决的问题。 应力 避免表面直接受到高压，避免浇口上存有残余应力和粗糙的表面，可以通过设置一个压力集合器来解决该问题。压力 把浇口设计在制件壁最厚的地方来确保有适当的压力来成型制件。这样也可以用来减少尺寸收缩。熔接痕 塑件表面的一种线状痕迹，是由注射或挤出中若干股流料在模具中分流汇合，熔料在界面处未完全熔合，彼此不能熔接为一体，造成的熔合印迹，影响塑件的外观质量以及力学性能。翘曲 不正确地形状尺寸或一个已经确定的浇口可能会造成一个难以预料的结果。这可能导致成型时的熔接痕会出现在明显的位置.(见下面的图片) 融料流动对浇口位置的影响图4 不理想的流动形式可能会产生翘渠与弯曲。（见下图）翘曲对产生浇口位置的不利影响。图5 浇口类型一个最为理想的浇口尺寸和浇口位置是非常重要的。 浇口类型通常被被分为人工和自动脱出两种。手动脱浇口系统是需要一个操作者在第2次分型时将制件与流道用手将他们分开。使用手动脱浇注系统的使用地方:浇口面积过大不能够在开模时被自动剪开。 一些修剪敏感的材料 (举例来说, pvc) 接触在一起，这样使其黏附在模具上面，不能自动脱浇。 同时的流动分别穿过一个宽的浇口，前面的部分无法通过自动脱浇注结构取出。浇口包括:直浇口边缘浇口扇行浇口爪形浇口平缝浇口点浇口轮辐浇口圆环浇口多点浇口自动脱浇口自动脱浇口是用工具将浇口自动的打破并剪掉，在模具打开取件时，其经常被使用的地方有如下：两次分型时避开浇口清除。 成型时间很短。 将浇口痕迹减小至最小。浇口类型包括:针点浇口潜伏式浇口热流道直流道推荐单型腔注塑模具与那些需要对称布置来成型的塑件来使用这种结构。 这种类型的浇道适合那些有较大壁厚的塑件，因为这样可以使保压变得更为有效。 一个短小的主流道是有利的, 这样可以促使熔料迅速填充满模具而且还可以减少压力损失，需要在浇口的对面设置一个冷料井。 使用这种类型的浇口的缺点就是留在制件和侧流道上的废料很难被清除掉。凝固是受塑件壁厚影响的，但是他并不能决定塑件的壁厚。很明显，主流道口附近的塑件收缩较低;而主流道口的收缩较明显。这样就造成了在主流道口处出现高的应力拉深。尺寸 在卧式注塑机用模具中，主流道一般垂直于分型面，而角式注塑机用模具的主流道则开设在分型面上，前者便于流道凝料的拔出，通常设计成2-4度的锥角，内壁的粗糙度在Ra=0.4um左右。主流道小端直径应该比注塑机的喷嘴孔径大0.5-1mm,通常取4-8mm，具体视制件大小及补料要求决定。大端直径应该比分流道深大约1.5mm左右。 一个小角度的流道废料很难从主流道中取出。 大的角度则会造成材料的浪费而且还会增加冷却时间。图6 边缘浇口：这种浇口相对于分流道来说断面尺寸较小，属于小浇口的一种。边缘浇口一般开设在分型面上，从制件的边缘进料。边缘浇口断面形状一般是矩形或者接近矩形。尺寸：典型的浇口尺寸是流道尺寸得80%-100%其数值一般为3.5 毫米，1.0-12 毫米宽。这种浇口的定位长度方向不应该多出1.0mm，0.5mm左右最为适宜。图7 定位浇口：定位浇口一般用于平、薄的制件，以便减小在型腔中剪切力。出现在浇口附近的高剪切力被限制在辅助片中，注塑完成后这个片就会被除掉。尺寸：最小量定位片宽度是 6 毫米， 最小量定位片厚度是洞的深度的 75%左右。图8 流道布局对于多型腔的模具有3种使用情况。 如下:标准的流道结构 H 形 (分枝式) 流道结构 星形流道结构非平衡流道也常使用，但是会产生一些不利影响:不能完全被充满产品的特性不同产品的收缩不同洗涤槽痕迹明显光泽度不好降低了模具的使用寿命各个制件的形状不一致非平衡流道的例子。图9 尽管人字型的流道是非平衡的，但是与平衡式相比它可以容纳更多的型腔，有更小的流道容量和更低得加工费用，可以使用电脑辅助软件来模仿塑料的流动以及对主流道和分流道的尺寸来保证设计的合理。记住非标准流道会增加使用制造费用。调整流道的直径来完成浇注，可能不能满足某些要求高的制件，会产生一些缺点，特别需要注意的是: 小的制件 带有薄壁的制件 制件表面不允许有沉积痕迹 制件的主流道长度要比分流道的长度要长的多。 平衡式流道：图10 H(分岐型) 和光线式的 (星型) 系统通常被被当做平衡式流道。 平衡式流道有着相同的流道长度和直径尺寸，所以每个型腔的情况大概相同。当要求质量和公差较好时，型腔就要统一。不过，对于在一个模具中成型不同制件来说，经济因素非常重要的，带有很大组件的型腔要放在主流道最近处。在设计多型腔模具的分流道时应特别注意。在一次填充成型一个组合件的不同制件时，分流道的设计必须满足使所有制件在同一时间完成充填，以避免先填充的型腔过度充填或飞溅，减少制件的收缩变形以及其他质量的问题。同时可以考虑利用计算机填充模拟分析来优化分流道的形状、尺寸，保证各型腔同时充填，并均衡的补料。同样计算机分析模拟还可以应用于多浇口制件的成型中。在同一制件的多型腔模具加工中，分流道对应的部位必须做成同一尺寸使得各个型腔充填在同一时间内完成。推出系统 模具推出系统需要适应注塑成型时塑件的形状，这样可以减少对塑件的破坏。一般的来讲，在成型时会受到来自型芯部分的收缩阻止。大的推出面积要同一的分布在整个成型中，这样可以用来避免发生变形。一些推出结构会被使用：推杆推出刀片式推出通气管之活瓣推件板推
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