澆口設計的影響衝擊 澆口形式 流道系統的形式 流道形式的考慮 決定模穴的數目 流道平衡 Lesson 9. 澆口與流道設計 澆口設計的影響衝擊 澆口形式 流道系統的形式 流道形式的考慮 決定模穴的數目 流道平衡 Cycle The cycle time may vary depending on process conditions, material, and part geometry. 2

澆口尺寸對模穴充填保壓的影響 狹窄澆口 較大澆口 Higher Pressure Lower Pressure Gate size falls into the category of mold design. If you make the gate smaller, the injection pressure increases. A larger gate requires lower pressure to fill the part because it is less restrictive to the plastic. The length of the gate or the “land” also influences injection pressure. You must be careful when sizing gates to not make them so restrictive that they burn the plastic due to overshearing. On the other hand, you don’t want too large of a gate because of the gate mark it will create, the difficulty in removing the gate, and the time required to freeze off at the gate as well as several other potential problems (jetting, drool, etc.). Higher Pressure Lower Pressure

Gate Diameter/Thickness 澆口尺寸對體積收縮的影響 較小的澆口更大的限制性 較低的保壓壓力會有較高的收縮 較小的澆口較易凝結 較低的保壓時間會有較高的收縮 Shrinkage Well, that was pretty technical information. You cannot really do much about the characteristics of the plastic resin except for changing to a different resin. However, there are a few things that you can control that have an impact on part shrinkage. These are shown in Figure 9-2. Among these are the melt and mold temperature, which reduce shrinkage as you reduce temperature. The injection rate has some affect, though not as dominant. Gate Diameter/Thickness

澆口形式 人工修整澆口 自動脫模澆口 聯結到 KnowHow! 在典型的模具中澆口更容易設計 典型的兩板模具 在模具設計中更加困難 經常需要使用兩板模或熱流道設計3 聯結到 KnowHow!

模具形式 We can also classify runner types in terms of cold or hot. Here are a couple types of cold runner. The most common is the 2-plate mold (left) because it’s easier to make. Another type is the 3-plate mold like the one on the right. Why do you think someone would use a 3-plate mold? (to decrease flow length, to get automatic degating, to achieve uniform part filling, and gain better control over shrinkage) The downside of using a 3-plate mold is cost. It’s more expensive to make due to slightly more complexity. 二板模模具 三板模模具

流道系統形式 熱流道 隔熱式 內熱式 外熱式 Cartridge Shut-Off Heater Pin Nozzle Frozen Layer Heater These are some common types of hot runners. A hot runner keeps the plastic in the runner system molten at all times. The runner is never ejected, so one benefit is lower cycle time. Another benefit is lower injection pressure requirement since the viscosity is lower due to increased melt temperature in the runner. Insulated runners are not as widely used as the others. These are basically very large “cold runners” that keep the plastic molten inside the runner by running very fast cycle times. Two other most commonly used hot runners use heaters to keep the plastic hot inside the runner. These can be either internally or externally heated as shown. An advantage of using hot runners is that they often have shut off valve gates so that after packing the gates can be closed sealing in pressure and minimizing stresses at the gate. Gate Melt Cavity Melt Melt 隔熱式 內熱式 外熱式

好的流道系統設計特性。 正確的流道設計將: 必須迅速充滿整個模穴 在流道系統中使廢料減到最少 盡可能一致地傳送熔膠 不須額外冷卻時間進而增加整個生產週期時間 43

模穴數的決定 有幾個原素涉及了 在指定時間內所須之產品數量 射出機的射出容量 射出機的塑化能力 由公式計算來決定決定的公式

如何決定流道直徑尺寸? 由別處推薦 使用 Moldflow 圖表 經驗 充填分析 流道平衡 冷卻分析 剪應力 溫度的上升/下降 人工的平衡 檢查所需要之冷卻時間 There are three ways to determine the size of your runners: *guess *calculate (making many assumptions) *Use a filling analysis like C-MOLD C-MOLD is the most accurate of these three ways. 8

一般所建議的流道直徑 Material Diameter (in.) Diameter (mm.) ABS, SAN 0.187 - 0.375 4.7 - 9.5 Acetal 0.125 - 0.375 3.1 - 9.5 Acrylic 0.312 - 0.375 7.5 - 9.5 Cellulosics Ionomer 0.093 - 0.375 2.3 - 9.5 Nylon 0.062 - 0.375 1.5 - 9.5 Polycarbonate Polyester Polyethylene Polypropylene PPO 0.250 - 0.375 6.3 - 9.5 Polysulfone Polystyrene PVC Above are some recommended runner diameters for various polymers. This way of choosing a runner diameter is not recommended. 9

使用Moldflow 預估流道直徑 利用充填分析決定澆口及流道的尺寸 剪應力 < 所建議的最大值 熔膠在流道中的溫度變化應小於 8 ℃ 在不平衡的多模穴系統中利用流道平衡分析(Runner Balance analysis)決定流道的直徑 在相同形狀之多模穴系統中使用不對稱的流道路線 不同形狀的多模穴系統(Family mold) C-MOLD Filling tells you the pressure, temperature, and shear stress at any point in the runner and gate. The runner diameters can be changed until either the pressure or shear stress is at the value you want it to be. Of these three methods, using C-MOLD is the most accurate and can save you the most money. 10

平衡與不平衡流道設計 自然平衡 人工平衡 Let’s first talk about the types of runners in terms of layout. The layout of a runner system determines whether it is naturally balanced or not. The runners on the left are all naturally balanced runner layouts because they have the same flow length to each cavity from the sprue. Assuming all the diameters are the same, each part cavity should fill at relatively the same time. The runner layouts on the right are not naturally balanced because either the flow lengths from the sprue to the part are different or because the part volumes are different as shown in the lower right corner. We call this a family mold. In order to fill all parts at the same time, these types of runners must be artificially balanced. We do this by changing the diameters of various runners to either restrict or promote flow to a certain cavity.

人工平衡之家族模穴 Here is an example of a family mold. The part on the left is drastically larger (in terms of volume) than the lid on the right. It is very difficult to get these two parts to fill in a balanced manner, even in a simulation because of the drastic volume difference.

一些注意細節 流道/澆口有突然急遽變化 非圓形之流道系統 對稱性多模穴配置 模具之熱流道與閥澆口的使用

建立具有錐度的流道及澆口 具有錐度的流道可由啟始直徑(Din)及半錐用( )來建立   Dia. Taper Angle If the taper angle is positive the ending diameter is larger than the specified starting diameter. Taper Angle  4

利用形狀因子( Shape Factors) 來建構非圓形流道 等似直徑 (deq) = 2 其中 A 是流道實際的橫斷面積 p 實際橫斷面之周長 周界長 Shape Factor = = 圓形橫斷面的周界長 p d b a  A The table for the shape factors is on page 3-10 in the C-MOLD Modeler and Visualizer handbook. deq 5