模具设计技术2-DESIGN FOR PRODUCTIVITY AND PERANCE.ppt

1、(一),学习模具 设计,(二),DESIGN FOR PRODUCTIVITY 這種技術如圖3所示. 起泡器不僅用于冷卻公模,也用于冷卻不能裝配(鑽孔或銑管道)的扁平模具.,Bubblers are commercially available and are usually screwed into the core, as shown in Figure 3 below. Up to a diameter of 4 mm, the tubing should be beveled at the end to enlarge the cross section of the outlet;

2、this technique is illustrated in Figure 3. Bubblers can be used not only for core cooling, but are also for cooling flat mold sections, which cant be equipped with drilled or milled channels.,FIGURE 3. (左) 起泡器鎖入公模內 (右) 有斜面的起泡器放大排氣口,FIGURE 3. (Left) Bubblers screwed into core. (Right) Bubbler beveled

3、 to enlarge outlet,NOTE: 因為擋板與起泡器都使流動面積變窄,流動阻力增加.因此, 必須注意這些裝置的尺寸設計.擋板與起泡器的流動與熱傳送行為可以通過C-MOLD冷卻分析來作為樣板分析.,NOTE: Because both baffles and bubblers have narrowed flow areas, the flow resistance increases. Therefore, care should be taken in designing the size of these devices. The flow and heat transfer

4、 behavior for both baffles and bubblers can be readily modeled and analyzed by C-MOLD Cooling analysis.,電熱棒 電熱棒可以用來取代擋板與起泡器.它是填滿流體的密封圓筒. 流體從模具鋼材中吸熱蒸發并隨對冷卻劑的熱量釋放而濃縮如圖 4.電熱棒的熱傳輸性能幾乎是銅套管的10倍大.鑒于良好的熱傳導性,避免產生電熱棒與模具之間的氣隙.,Thermal pins A thermal pin is an alternative to baffles and bubblers. It is a sealed

5、 cylinder filled with a fluid. The fluid vaporizes as it draws heat from the tool steel and condenses as it releases the heat to the coolant, as shown in Figure 4. The heat transfer efficiency of a thermal pin is almost ten times as great as a copper tube. For good heat conduction, avoid an air gap

6、between the thermal pin and the mold, or fill it with a highly conductive sealant.,FIGURE 4. 電熱棒熱傳輸性能,FIGURE 4. Thermal pin heat transfer efficiency,細長型公模冷卻 如果直徑或寬度太小(小于 3 mm),只有氣體冷卻是可行的.氣體在模具打開時從外面吹向公模或從內部流向中心孔,如圖5所示.這種程序當然不允許保持一個确切的模溫.,Cooling slender cores If the diameter or width is very small (

7、less than 3 mm), only air cooling is feasible. Air is blown at the cores from the outside during mold opening or flows through a central hole from inside, as shown in Figure 5. This procedure, of course, does not permit maintaining an exact mold temperature.,FIGURE 5. 細長公模氣體冷卻,FIGURE 5. Air cooling

8、of a slender core,通過使用帶高熱傳導性的鑲件如銅或鈹銅材質來實現較好的細長公模氣體冷卻(量測小于 5 mm).這種技術使用如圖6所示. 那種鑲件是壓配合進公模的并擴展到它們的基部,冷卻管道有一個盡可能大的剖面.,Better cooling of slender cores (those measuring less than 5 mm) is accomplished by using inserts made of materials with high thermal conductivity, such as copper or beryllium-copper ma

9、terials. This technique is illustrated in Figure 6 below. Such inserts are press-fitted into the core and extend with their base, which has a cross section as large as is feasible, into a cooling channel.,FIGURE 6. 使用高熱傳導性材料來冷卻細長型公模,FIGURE 6. Using high thermal conductivity material to cool a slende

10、r core,大號公模冷卻 大公模直徑 (40 mm 或更大),必須确保冷卻劑的良好傳輸.這可以與鑲件一起完成,冷卻劑通過中心孔達到公模的頂端如圖7所示.這種設計大大削弱了公模.,Cooling large cores For large core diameters (40 mm and larger), a positive transport of coolant must be ensured. This can be done with inserts in which the coolant reaches the tip of the core through a central

11、 bore and is led through a spiral to its circumference, and between core and insert helically to the outlet, as shown in Figure 7. This design weakens the core significantly.,FIGURE 7. 使用螺旋狀的擋板來冷卻大公模,FIGURE 7. Use of helical baffle to cool large core,圓柱形公模冷卻 圓柱形公模冷卻與其它圓形件應該如圖所示用兩個螺旋形物來完成.冷卻劑用一個螺旋形料筒

12、流向公模頂端用另一個回流. 鑒于設計原因,這種場合公模壁厚必須至少3 mm.,Cooling cylinder cores Cooling of cylinder cores and other round parts should be done with a double helix, as shown below. The coolant flows to the core tip in one helix and returns in another helix. For design reasons, the wall thickness of the core should be

13、at least 3 mm in this case.,FIGURE 8. 帶中心起泡器的兩個螺旋物.,FIGURE 8. Double helix with center bubbler,冷卻系統公式 冷卻時間 理論上,冷卻時間與最重件產品厚度成平方比或最大流道直徑的1.6次冪.也就是:,Cooling system equations Cooling time Theoretically, cooling time is proportional to the square of the heaviest part wall thickness or the power of 1.6 fo

14、r the largest runner diameter. That is:,where the thermal diffusivity of polymer melt is defined as,如聚合物熔融的熱散佈性所定義的一樣, 換言之,壁厚加倍,冷卻時間成四倍數.,In other words, doubling the wall thickness quadruples the cooling time.,Reynolds number and coolant flow 無論怎樣,冷卻劑湍流可以由Reynolds數字(Re)來決定,如在目錄1中所列舉. Reynolds 數字定義如

15、下: 在冷卻劑的密集度處,U 散熱劑的平均粘度,d 是冷卻道的直徑,是冷卻劑的動態粘度.,Reynolds number and coolant flow Whether or not the coolant flow is turbulent can be determined by the Reynolds number (Re), as listed in Table 1. The Reynolds number is defined as: where is the density of the coolant, U is the averaged velocity of the co

16、olant, d is the diameter of the cooling channel, and is the dynamic viscosity of the coolant.,TABLE 1. 冷卻流動類型與相應的Reynolds 數字範圍 Reynolds 數字 (Re) 流動類型 10,000 Re Turbulent Flow 2,300 Re 10,000 Transition Flow 100 Re 2,300 Laminar Flow Re 100 Stagnated Flow,TABLE 1. Coolant flow types andcorresponding R

17、eynolds number ranges Reynolds Number (Re) Type of Flow 10,000 Re Turbulent Flow 2,300 Re 10,000 Transition Flow 100 Re 2,300 Laminar Flow Re 100 Stagnated Flow,設計規則 模具冷卻設計考量 這里描述的設計規則提供了一些有效的模具冷卻綱要.冷卻管道為了使用標準機器工具,標準裝配,與快速分開,應該使用標準尺寸大小. 基于產品厚度與體積,模具設計者必須決定以下設計變數來設計冷卻系統:,Design rules Mold cooling des

18、ign considerations The design rules presented here provide some guidelines for attaining proper and efficient mold cooling. Cooling channels should be of standard sizes in order to use standard machine tools, standard fittings, and quick disconnects. Based on the part thickness and volume, the mold

19、designer needs to determine the following design variables when designing a cooling system:,* 冷卻管道的位置與大小. * 冷卻管道的類型. * 冷卻管道的布局與連接. * 冷卻管道回路的長度. * 流率與冷卻劑的熱傳輸.,*Location and size of channels of cooling channels. * Type of cooling channels. * Layout and connection of cooling channels. * Length of cooli

20、ng-channel circuits. * Flow rate and heat transfer of coolant.,冷卻管道的位置與大小 產品厚度 為保持可接受的經濟的冷卻時間,應該避免厚度過厚的產品. 冷卻時間隨產品厚度快速增加.這種計算如在冷卻系統公式中所示.產品厚度應該盡量保持均勻一致如圖16所示.,Location and size of channels Part thickness To maintain an economically acceptable cooling time, excessive part wall thickness should be avo

21、ided. Required cooling time increases rapidly with wall thickness. This calculation is shown in Cooling system equations. Part thickness should be as uniform as possible, as shown in Figure 16 below.,FIGURE 16. 用于取代保持均勻產品厚度的設計方案.,FIGURE 16. An alternative design can be used to maintain uniform part

22、thickness.,冷卻管道位置與大小 冷卻管道最佳的位置在含公母模的區段.把冷卻管道放置在母模外面或公模上會充分冷卻模具,通常,冷卻道表面 (如深度)應該是公母模一個或兩個管道的直徑.基本原則是鋼材深度直徑必須為1,鈹銅直徑為1.5,鋁為2.坡度(冷卻道的中心距离)應該是冷卻管道直徑的三到五倍.典型的冷卻管道直徑從10 14 mm (7/16 to 9/16 英吋),如圖17.,Cooling-channel location and size The best location for cooling channels is in the blocks that contain the

23、mold cavity and core. Placing the cooling channels outside the cavity or core block will cool the mold less adequately. Generally, the surface of the cooling channels (i.e., depth) should be one to two channel diameters from the cavity or core. The rule of thumb is that the depth should be 1 diamete

24、r for steel, 1.5 diameters for beryllium copper, and 2 for aluminum. The pitch (distance between cooling channels centers) should be three to five times the channel diameter. A typical cooling channel diameter ranges from 10 to 14 mm (7/16 to 9/16 inches), as shown in Figure 17 below.,FIGURE 17. 冷卻道

25、直徑尺寸(d), 寬度 (D), 行程 (P).,FIGURE 17. Typical dimensions for cooling channel diameter (d), depth (D), and pitch (P).,流率與冷卻劑的熱傳輸 溫差 保持產品反面的溫差至最低限度,產品公差不應超過10 C.,Flow rate and heat transfer Temperature difference Keep the temperature difference on opposite sides of the part to a minimum; it should not e

26、xceed 10C for parts that require tight tolerance.,冷卻液流動的熱傳輸 熱傳輸效果隨冷卻液由層流改為湍流而增加,熱量經由熱傳導逐層傳送.然而在湍流過程中,在半徑方向的大量熱傳送使熱量通過傳導與轉變轉移.最終效率大大提昇.以下圖示闡明這種概念.,Heat transfer of coolant flow The effect of heat transfer increases as the flow of coolant changes from laminar flow to turbulent flow. For laminar flow,

27、heat can be transferred only by means of heat conduction from layer to layer. However, in turbulent flow, the mass transfer in the radial direction enables the heat to be transferred by both conduction and convection. As a result, the efficiency increases dramatically. The diagram below illustrates

28、this concept.,FIGURE 18. 層流無定形的材料縮水較多小.當結晶材料冷卻至它們過渡溫度之下時,分子以更為有序的方式自動排列形成結晶,另一方面, 無定形的材料的微觀結構不隨階段的變更而變更.這種不同之處導致結晶狀或半結晶狀材料在其流動與凝固階段產生更大的差异, 如Figure 1所示.我們想要指出的是冷卻率同時也會影響結晶狀或半結晶狀材料快速冷卻的pvT行為.,Shrinkage The shrinkage of molded plastic parts can be as much as 20 percent by volume, when measured at the

29、processing temperature and the ambient temperature. Crystalline and semi-crystalline materials are particularly prone to thermal shrinkage; amorphous materials tend to shrink less. When crystalline materials are cooled below their transition temperature, the molecules arrange themselves in a more or

30、derly way, forming crystallites. On the other hand, the microstructure of amorphous materials does not change with the phase change. This difference leads to crystalline and semi-crystalline materials having a greater difference in specific volume ( ) between their melt phase and solid (crystalline)

31、 phase. This is illustrated in Figure 1 below. Wed like to point out that the cooling rate also affects the fast-cooling pvT behavior of crystalline and semicrystalline materials.,圖 1. 加工階段無定形的pvT 曲線 結晶性聚合物 (A點) 與室溫狀態及空氣壓力(B點).,FIGURE 1. The pvT curves for amorphous and crystalline polymers and the

32、specific volume variation ( ) between the processing state (point A) and the state at room temperature and atmospheric pressure (point B). Note that the specific volume decreases as the pressure increases.,過多的產品縮水原因 超出可接受範圍的過多縮水的原因可能由以下因素造成.縮水關系對幾種加工參數及產品厚度如草圖2所展示. * 低射出壓力 *短保壓時間或冷卻時間 *高流動溫度 *高模具溫度

33、* 低保壓壓力.,Causes of excessive part shrinkage Excessive shrinkage, beyond the acceptable level, can be caused by the following factors. The relationship of shrinkage to several processing parameters and part thickness is schematically plotted in Figure 2. *low injection pressure * short pack-hold time

34、 or cooling time *? high melt temperature *high mold temperature * low holding pressure.,產品縮水造成的問題 未測定體積的收縮要麼導致縮水痕要麼導致成型內部空點. 管制產品縮水在產品,模具,與制程設計中是重要的,尤其在需要較小公差的應用中.縮水導致縮水痕或空點可以通過充填後模穴保壓來減少或消除.模具設計應將縮水列入考量以便與產品尺寸相符. C-MOLD 預測的產品縮水為正确的模具設計提供了一個有用的指南.,Problems caused by part shrinkage Uncompensated vol

35、umetric contraction leads to either sink marks or voids in the molding interior. Controlling part shrinkage is important in part, mold, and process designs, particularly in applications requiring tight tolerances. Shrinkage that leads to sink marks or voids can be reduced or eliminated by packing th

36、e cavity after filling. Also, the mold design should take shrinkage into account in order to conform to the part dimension. Part shrinkage predicted by C-MOLD offers a useful guideline for proper mold design.,FIGURE 2. 影響產品縮水的加工或設計參數,FIGURE 2. Processing and design parameters that affect part shrink

37、age,變形 變形是在模壓產品表面不能按設計要求的形狀產出的一種扭曲.產品變形由模壓內的殘余應力,它又是由模壓件中材料的差動縮水引起的一種變形.如果通過產品的縮水是均勻的,成型不會變形,它僅僅變小,然而,由于諸多的因素的存在與相互作用如分子與纖維的定向,模具冷卻與設計及制程加工條件,要達到低的均勻的縮水并不是一件簡單的任務.,Warpage Warpage is a distortion where the surfaces of the molded part do not follow the intended shape of the design. Part warpage resul

38、ts from molded-in residual stresses, which, in turn, is caused by differential shrinkage of material in the molded part. If the shrinkage throughout the part is uniform, the molding will not deform or warp, it simply becomes smaller. However, achieving low and uniform shrinkage is a complicated task

39、 due to the presence and interaction of many factors such as molecular and fiber orientations, mold cooling, part and mold designs, and process conditions.,差動縮水造成的變形 模壓產品變形由差動縮水造成.縮水的變化由分子與纖維定向,產品溫度變异及不同的保壓造成,如澆口處過保壓與遠离澆口區域的低保壓或產品厚度材料固化的不同壓力等級.這些原因在下面更為全面地描述. * 充填與未充填材料區別 * 越過產品厚度或產品上的非均衡模具冷卻 * 產品厚度

40、不同造成的冷卻率 * 產品外形不對稱或彎曲,Warpage due to differential shrinkage Warpage in molded parts results from differential shrinkage. Variation in shrinkage can be caused by molecular and fiber orientation, temperature variations within the molded part, and by variable packing, such as over-packing at gates and

41、under-packing at remote locations, or different pressure levels as material solidifies across the part thickness. These causes are described more fully below. *Differences in filled and unfilled materials *Non-uniform mold cooling across the part thickness or over the part *Cooling rates that differ

42、 because of Part thickness variation *Part geometry asymmetry or curvature,充填材料與未充填材料中的區別 在充填與未充填材料中的差動縮水如圖3 所示.當縮水差動與非等向性穿過產品或產品厚度時,內部產生的應力會導致產品變形.,Differences in filled and unfilled materials Differential shrinkage for filled and unfilled materials is shown in Figure 3 below. When shrinkage is dif

43、ferential and anisotropic across the part and part thickness, the internal stresses created can lead to part warpage.,充填的材料 纖維充填熱塑性材料由于它們較小的熱收縮與較高的系數,加強纖維植入縮水.因此,纖維充填材料在纖維流動方向的縮水相對于橫向縮水較小.同樣地,顆粒充填熱塑比未充填等級縮水更小.,Filled materials For fiber-filled thermoplastics, reinforcing fibers inhibit shrinkage due

44、 to their smaller thermal contraction and higher modulus. Therefore, fiber-filled materials shrink less along the direction in which fibers align (typically the flow direction) compared to the shrinkage in the transverse direction. Similarly, particle-filled thermoplastics shrink much less than unfi

45、lled grades.,未充填的材料 另一方面,如果未充填模壓件包括高速的分子定向,縮水是非等向性的.因為定位方向上更大程度上的一系列縮水. 液晶聚合物 對液晶聚合物(LCPs)排列緊密的結構易顯示出非等向性的縮水.,Unfilled materials On the other hand, if an unfilled molded part contains high levels of molecular orientation, shrinkage is anisotropic because aligned chains shrink to a greater extent in

46、the direction of orientation. Liquid crystal polymers For liquid crystal polymers (LCPs) the tightly ordered self-reinforcing structure tends to exhibit anisotropic shrinkage.,FIGURE 3. 充填與未充填材料的差動縮水,FIGURE 3. Differential shrinkage for both unfilled and filled materials,穿過產品厚度不均衡的模具冷卻 從模穴到模仁穿過產品厚度的

47、產品中不均衡的冷卻與不對稱冷卻也能引致差動縮水.材料冷卻并從模壁到中心不一致地縮水,從而造成頂出後變形.,Non-uniform mold cooling across the part thickness Non-uniform cooling in the part and asymmetric cooling across the part thickness from the moldcavity and core can also induce differential shrinkage. The material cools and shrinks inconsistently

48、from the mold wall to the center, causing warpage after ejection.,FIGURE 4. 產品冷卻產均衡造成的變形(a)與(b)產品厚度冷卻不相稱造成的變形.,FIGURE 4. Part warpage due to (a) non-uniform cooling in the part, and (b) asymmetric cooling across the part thickness.,產品厚度變异 縮水隨壁厚增加而增加.由不均衡壁厚造成的差動縮水是在未加強的熱塑產品中變形的主要原因.更具體地說,隨著厚度的變化通常會產生

49、不同的冷卻率與結晶等級.這種現象造成差動縮水,導致如圖5所未的產品變形.,Part thickness variation Shrinkage increases as the wall thickness increases. Differential shrinkage due to non-uniform wall thickness is a major cause of part warpage in unreinforced thermoplastics. More specifically, different cooling rates and crystallization

50、levels generally arise within parts with wall sections of varying thickness. This causes differential shrinkage, resulting in part warpage, as shown in Figure 5 below.,圖 5. 由高結晶等級造成的大面積縮水 (如厚壁部分) 致使差動的縮水與產品相應的變形.,FIGURE 5. Larger volumetric shrinkage due to the high crystallization level in the slow

51、 cooling areas (e.g., the thick sections) leads to differential shrinkage and thus part warpage,產品外形不對稱或彎曲 幾何形狀不對稱將引致不均勻冷卻與差動縮水而帶來產品的變形如圖6所示.,Part geometry asymmetry or curvature Geometric asymmetry (e.g., a flat plate with a large number of ribs that are aligned in one direction or on one side of t

52、he part) will introduce non-uniform cooling and differential shrinkage that can lead to part warpage, as shown in Figure 6 below.,圖 6. 加強肋一邊的模壁不良冷卻造成一邊材料較慢的冷卻,這會導致產品變形.,FIGURE 6. The poor cooling of the mold wall on the ribbed side causes a slower cooling of the material on that one side, which can

53、lead to part warpage,縮水與變形設計規則 指南 你可以通過正當設計產品,模具與加工及材料的選擇來減少或控制縮水與變形. 以下設計規則為開發低縮水,無變形的產品提供一些指南. 壁厚 避免非均勻壁厚或設計薄件三倍長度之過渡,如下所示,Design rules for shrinkage and warpage Guidelines You can reduce or control shrinkage and warpage by properly designing the part, mold, and process, as well as through careful

54、 material selection. The following design rules provide some guidelines for developing low-shrinkage, warp-free parts. Wall thickness Avoid non-uniform wall thickness or design a transition length of three times the thickness of the thinner region, as illustrated below.,FIGURE 1. 不同厚度的產品設計.,FIGURE 1

55、. Part design with thickness variation.,厚度選擇 改變設計來替代造成嚴重縮水與變形或內部空點的厚部.一個薄的均勻的帶肋的壁(以下Figure 2 所示)提供了均衡的縮水,強度對重量的比率及成本效果.,Thick sections Alter the design to replace thick sections that cause significant shrinkage and lead to sink marks or internal voids. A thin, uniform wall with ribs (shown in Figure

56、 2 below) provides for uniform shrinkage, strength to weight ratio, and cost effectiveness.,FIGURE 2. 在許多應用程序中, 帶肋的均勻的薄壁件優先于厚壁件.,FIGURE 2. In most applications, a thin uniform wall with ribs is preferred to a thick wall.,平衡充填 設計傳送系統提供一個平衡的常量流動速度充填模式. 保壓壓力 高保壓力能幫助減少縮水,它同時也可能會增加殘余應力等級與夾緊力需求.為了達到一個較好的制

57、程加工設計,使用一個適當的保壓壓力等級,允許足夠的保壓時間與灌點冷卻後移除壓力. 保壓壓力應該能夠傳送額外的材料來補救產品內的面積縮水.,Balanced filling Design the delivery system to provide a balanced filling pattern with a constant melt-front velocity. Packing pressure While high packing pressure can help reduce the shrinkage, it also potentially increases the le

58、vel of residual stress and the clamp force requirement. For a better process design, use a proper packing pressure level, allow sufficient packing time, and remove the pressure after the gate freezes off. The packing pressure should be able to deliver additional material to compensate for the volume

59、tric shrinkage within the part.,冷卻系統 應用穿過產品厚度及整個產品上的均勻的平衡的冷卻來設計冷卻系統. 殘余應力 通過增加流動溫度,模壁溫度,充填時間與型穴厚度或減少保壓壓力與流道來減少殘余應力與分子或纖維方向.,Cooling system Design the cooling system to apply uniform, balanced cooling, both across the thickness and throughout the part. Residual stress Reduce residual stress and molecular or fiber orientation by increasing the melt temperature, mold-wall temperature, fill time, and cavity thickness, or by decreasing the packing pressu