《塑胶模具设计》PPT课件.ppt

塑膠產品設計Plastic Part Design徐昌煜Charles Hsu,就傳統射出成形而言，實用的最小壁厚在0.75到1.00mm 之間。如果要採用更薄的壁厚，卻又缺乏實際的經驗，可以借助CAE作科學的決定。For conventional injection molding,a practical minimum wall thickness is in the range of 0.75 to 1.00 mm.When thinner walls are required but actual experience is absent,the minimum possible thickness can be scientifically determined by CAE.,壁厚Wall Thickness,壁厚不均是注塑成形中最大的麻煩製造者。這對薄壁零件尤然。這些麻煩包括了遲滯現象、短射、凹陷、發赤、噴流、翹曲及長冷卻時間等；目前都可用CAE以直接或間接的方式預測。Non-uniform wall thickness is the biggest trouble maker in plastic injection molding.This is especially true to thin-wall part.The troubles,including hesitation,short shot,sink mark,blush,jetting,warpage and long cooling time etc.,can be predicted,directly or indirectly,by using CAE.,壁厚不均Non-uniform Wall Thickness,設計高收縮率材料成型品時，設計者應將壁厚變化限制在10%。就低收縮率材料而言，許容壁厚變化可到25%。While designing injection molded parts in high mold shrinkage factor materials,the designer should try to limit wall thickness variation to 10%.The allowable wall thickness variation for the low mold shrinkage factor materials can be up to 25%.,壁厚不均Non-uniform Wall Thickness,壁厚設計Wall Thickness Design,掏空設計(1)Coring Out Design(1),掏空設計(2)Coring Out Design(2),外側凸轂Outside Boss,空洞或/和凹陷的形成Void or/and Sink Mark Forming,肋厚和內圓角半徑的影響The Effect of Rib Thickness&Fillet Radius,突出件和公稱厚壁相交處的內圓角半徑太大，會致使凹陷、空洞、殘餘應力和長的冷卻時間。該內圓角半徑太小，會致使應力集中。一個好的折中方案是採用公稱壁厚的25%，作為內圓角半徑。A large fillet radius causes sink mark,void,residual stress and long cooling time.A small fillet radius causes stress concentration.A good compromise is to use a radius,which is 25%of the nominal wall(NW),at the junction of the NW and a projection.,內圓角半徑 Fillet Radius,肋的底部厚度Bottom Thickness of Rib,肋的設計(一)Rib Design(1),肋的設計(二)Rib Design(2),角板設計(三)Gusset Design(3),與側壁相連之凸轂(熱塑性塑膠)Boss at Wall(Thermoplastics),遠離側壁之凸轂(熱塑性塑膠)Boss Away From Wall(Thermoplastics),Wall Thickness,Rib,Conventional0.080 to 0.125 in(2.0 to 3.2 mm),Thinwall:0.050 to 0.080 in 0.050 in(1.2 to 2.0 mm)(1.2 mm),Wall Thickness,Bosses,Conventional0.080 to 0.125 in(2.0 to 3.2 mm),Thinwall:0.050 to 0.080 in 0.050 in(1.2 to 2.0 mm)(1.2 mm),Wall Thickness,Gussets,Conventional0.080 to 0.125 in(2.0 to 3.2 mm),Thinwall:0.050 to 0.080 in 0.050 in(1.2 to 2.0 mm)(1.2 mm),突出件在和公稱厚壁相交處的建議厚度：以高縮水率的結晶性塑膠而言，可採用公稱壁厚的50%。以低縮水率的非結晶性塑膠而言，可採用公稱壁厚的75%。The recommended thickness at the junction of a projection and the nominal wall(NW)is 50%of the NW thickness for high-mold-shrinkage,crystalline materials.The lower-mold-shrinkage-factor,amorphous plastics can have thicknesses of up to 75%of the parts NW thickness.,突出件壁厚Thickness of the Projection,有些情形，在美觀的考慮下，是不容許些微凹陷的。設計者應當考慮將建議厚度減少10%。In those cases where aesthetic considerations preclude even a slight sink mark,a designer should consider reducing the recommended rib thickness by an additional 10 percent.,突出件壁厚Thickness of the Projection,從成型容易的觀點來看，突出件的高度以產品公稱壁厚的2.5到3倍為宜。From an ease of molding perspective,the height of projections should be limited to 2.5 to 3 times the part nominal wall thickness.,突出件高度 Height of the Projection,強固的、脆的、剝蝕性的、黏的塑件要有大的脫模角和光滑的拋光。軟的、延展性的、和光滑的塑件則可有小的脫模角。Large draft angles and a smooth polish are required for parts molded in strong,brittle,abrasive,and sticky materials.Smaller draft angles can be used on soft,ductile,and slippery materials.,突出件脫模角 Draft Angle of the Projection,以成本和可製造性的觀點，理想的脫模角是消費者可以接受的前題下，最大的角度。就多數情況而言，每邊1應已足夠，但2 或 5 可以更好。模穴應順著開模方向打光。The ideal draft angle,from a cost and manufacturability perspective,is the largest angle that will not distract from the consumers acceptance of the product.In most cases,1 per side will be adequate,but 2 or 5 per side would be better.The cavities that form projections should be draw-polished.,突出件脫模角 Draft Angle of the Projection,距離應大於產品公稱壁厚的2倍。使得模具鋼材具備足夠的強度以抵抗彎曲，並且提供足夠的吸熱器，以免產生凹陷和成型應力。This distance should be at least 2 times the parts nominal wall thickness,so the mold steel provide enough strength to resist bending and enough heat sink to avoid sink mark and molded in stress.,突出件和側壁/突出件的距離 The Distance between Projection and Side Wall/Projection,Where 1/r:樑的曲率 curvature of the beamM:彎曲力矩 bending momentE:彈性模數 modulus of elasticityI:斷面積對中立軸的慣性矩 moment of inertia of the cross-sectional area with respect to the neutral axisEI:撓曲剛性 flexural rigidity,撓曲剛性Flexural Rigidity,Where:最大偏移 maximum deflection W:負荷 load L:樑長 length of beam E:彈性模數 modulus of elasticity I:斷面積對中立軸的慣性矩 moment of inertia of the cross-sectional area with respect to the neutral axis EI:撓曲剛性 flexural rigidity:最大應力 maximum stress:中立軸到到其斷面離其最遠的點的距離 distance from the extreme point of a cross section to the neutral axis of this cross section,Youngs Modulus,E,The ratio between stress and strain is constant,obeying Hookes Law,within the elasticity range of any material.This ratio is called Youngs modulus and is measured in Mpa or psi.,平板和肋板的比較Comparison between Plain&Ribbed Plates,和平板比，若基於相同的慣性矩(剛性)，肋板需料少了43%，I/A卻增加了1.79倍。肋板的最大厚度減為平板的1/4，使得冷卻時間驟降15/16(94%)。Based on the same moment of inertia(stiffness),ribbed plate needs 43%less material but boost I/A by 1.79 times comparing with plane plate.The maximum thickness of ribbed plate is only 1/4 of plain plates;showing a dramatic cooling time reduction of 94%(15/16).,平板和肋板的比較Comparison between Plain&Ribbed Plates,應力比(肋/無肋)Stress Ratio(Ribbed/Unribbed),偏移比(肋/無肋)Deflection Ratio(Ribbed/Unribbed),結構設計是薄殼成形零件的基礎。Structural design is the base of thin-wall molding parts.薄殼成形零件不僅僅是一趨勢，而且也是降低成本和提高競爭力的有效途徑。Thin-wall molding part is not only a trend but also an effective way to achieve cost reduction and competitiveness increase.,結構設計和薄殼成形零件Structural Design&Thin-wall Molding Parts,Living Hinge Design for PP and PE:(a)before,and(b)after Bending 180,Typical Values of Living Hinge Design for PP and PE:(a)Most Application;(b)Self-opening Hinge Design,Most Common Living Hinge Design:(a)before,and(b)after Bending 180,Recommended Living Hinge Design with the Neutral Axis in the Center:(a)before,and(b)at Bending Angle of 180,Cross Section through the Entire Hinge Showing Its Principal Dimensions,Cross Section of a Portion of a Living Hinge Design and Its Neutral Axis Position,Hinge Design Detail:(a)as Molded;(b)as Assembled,“Right Way”Assembly Hinge Detail,Cable Ignition Bracket Axonometric View,Cable Ignition Bracket Side View,Cable Ignition Bracket Top View,Hinge Detail:(a)Initial Design;(b)Improved Design,Hinge Behavior after Assembly,POLYPROPYLENE HINGE DESIGN,NOTES:1.Y DIM.PER PART DESIGN2.X DIM.=2Y+0.25,POLYPROPYLENE HINGE DESIGN,孔 Holes,以射出成型而言，圓孔形狀理想，原因是塑料冷卻時，它收縮到心型銷，若銷為圓形，應力會均勻的分布在圓銷面上。Round holes are the ideal shape for the injection molding process.The reason for this is that as plastic material cools it shrinks onto the core pin that forms a hole and,with round holes,the stress is uniformly distributed around it.,孔 Holes,這一尼龍風扇因安裝孔的直線孔緣末端的鎖入應力而損毀。This nylon fan failed due to molded-in stress at the end of the straight section on the mounting hole.,孔 Holes,孔 Holes,最初，此一玻纖補強的尼龍計時鏈輪中央的方型驅動軸孔，有四個銳角。使用幾個月後，這些鏈輪，從方孔的銳角，到其附近的鏈輪齒根，產生裂隙而報廢。後來，在方孔的四個角落，加了向外延伸的小孔之後，鏈輪便不再開裂。The glass-fiber-reinforced nylon timing sprockets were introduced with sharp corners on the square drive shaft hole.These sprockets failed after several months in the field due to cracks radiating from a corner on the square hole to the root of a nearby gear tooth.These field failures were eliminated by adding the outwardly extending radiuses.,孔 Holes,內圓角和向外延伸的內圓角(B,C,D)可以減低鎖入的應力並且使得產品變強。Inside and outwardly extending radiuses(B,C,D)reduce molded-in stress and result in a stronger part.,孔 Holes,孔A和B能以簡單直接開模的方式成形，孔C則須要一較複雜的側向運動心型，方能成形。Holes A and B can be molded with a simple,straight opening mold.Hole C requires a more complex side-acting mold.,從易於成型的觀點來看，相鄰二孔緣的距離，或是孔緣和產品邊緣的距離，至少要有壁厚的兩倍，而絕對不可小於壁厚。From an ease of molding perspective,the distance from one hole to the next,or to the edge of a part,must be at a minimum two times the parts wall thickness,and never less than the parts wall thickness,孔 Holes,孔 Holes,圖中的孔太靠近產品的邊緣，塑料的收縮使得該孔和其周圍的薄壁都因之扭曲。The hole shown here is too close to the edge of the part.Shrinkage of the plastic material has distorted this hole and the thin wall around it.,孔 Holes(Figure I),孔 Holes,圖I的盲孔A的長徑比應以2:1或3:1為限。形成圖I穿孔B的心型銷的自由端是頂在母模面上。這樣的心型銷獲得支持，而長徑比可增加到6:1。The length-to-diameter ratio of the blind hole in Figure I(A)is limited to only 2:1 or 3:1.The through hole B in Figure I allows the free end of the core pin to be seated against the cavity.This supports the core and allows its length-to-diameter to be 6:1.,孔 Holes,如圖I的C所示，將型心延伸至母模側的配合孔，可以提供額外的支撐，兩頭支撐的型心銷的長徑比可達12:1。如圖I的D所示，以二支型心銷成型深孔，可以消除型心銷和母模面的磨耗。這種方法產生的孔也可有12:1的長徑比。Telescoping the core into a mating hole in the cavity,C in Figure I,provides additional support.A core pin anchored at both ends can have a length-to-diameter ratio of 12:1.Molding a deep hole with two core pins,D in Figure I,eliminates wear between the core pin and the cavity.Holes produced in this manner can also have a 12:1 length-to-diameter ratio.,塑膠工業協會(SPI)指定12種拋光，從鑽石高度拋光，到噴砂粗度拋光。依照SPI模具拋光指南，來指定表面光滑度，已經被國際接受。The Society of the Plastics Industry(SPI)specified 12 finishes,ranging from a high diamond polish to a rough,blasted surface.The SPI Mold Finish Guide has become the internationally accepted for specifying surface finishes.,表面光滑度Surface Finish,如果型心形成的內面沒有拋光，頂出力和循環時間都會相應增加。If the core that forms the inside surfaces is not smoothly polished,the ejection forces and the cycle time will increase accordingly.,表面光滑度Surface Finish,只在成型品頂出方向拋光，可以消除側凹。這種拋光方法被稱作“抽拋”。設計工程師應於零件須要最小或0脫模角時，指定抽拋。Polishing the mold only in the direction that the molded part moves during ejection eliminates these undercuts.This polishing technique is called“draw polishing.”Design engineers would be well advised to specify draw polishing on parts requiring minimal or no draft angles.,表面光滑度Surface Finish,無論模面如何光滑，低密度聚乙烯都無法產生和聚苯乙烯接近的光亮外表。補強料加得多的塑料不能有效的產生光亮的外表。一般說來，熱模較之冷模，較能產生光滑的外表。保壓不足的產品無法忠實的複現模面的光滑。Regardless of the finish on the mold,low-density polyethylene can never produce the shiny appearance of a polystyrene part.Heavily filled or reinforced polymer cannot reliably produce shiny surfaces.Generally speaking,a hot mold will produce better surfaces than a cold mold.A poorly packed out part will not faithfully replicate the mold polish on all of the part surfaces.,表面光滑度Surface Finish,最軟的聚乙烯和聚氯乙烯、polyurethanes 和某些熱塑性elastomers 有沾黏高度拋光金屬面的傾向。這類黏的材料，一般較易從粗糙面或輕度噴砂面脫模。The softest polyethylenes and polyvinyl chlorides,polyurethanes,and some thermoplastic elastomers have a tendency to adhere to highly polished metal surfaces.Sticky materials of this type will normally release better from molding surfaces with matte or lightly blasted surface finish.,表面光滑度Surface Finish,強壯而又有些彈性的塑膠，像聚丙烯、ABS和耐衝擊聚苯乙烯，較之剛而脆的材料，如一般用途用聚丙烯和壓克力，更能接受粗略拋光的模面。對這些硬而脆的材料，抽拋是非常有益的。Strong but somewhat flexible plastics,such as polypropylene,ABS,and impact styrene,are more tolerant of roughly polished molding surfaces than rigid,brittle materials,such as general-purpose styrene and acrylics.Draw polishing is very beneficial with these hard,brittle materials.,表面光滑度Surface Finish,不能指望產品設計師、模具製造者以及拋光公司知道所有不同塑料的癖性。然而，我們可以倚賴塑料供應商和有經驗的成型者，他們知道那一種模面光滑度適合那一種特定的塑料。Product designers,moldmakers,and polishing companies cannot be expected to know the idiosyncrasies of all of the different plastic materials.Plastic material suppliers and experienced molders can,however,be relied upon to know what mold finish is optimal for a given material.,表面光滑度Surface Finish,有些工業界的內行者，估計拋光代表了模具平均成本的10%。這個平均值當然會有明顯的差異，這要看模具的尺寸和形狀、金屬的硬度、要求拋光的程度、以及拋光前模面的光滑程度。Some industry insiders have estimated that,on the average,polishing can represent 10%of a mold overall cost.This average will obviously vary,depending on the size and shape of the mold,the hardness of the metal,the level of polish required,and how well the mold was finished prior to polishing.,表面光滑度Surface Finish,對不透明件而言，大多數消費者無法分辨SPI指南中最高三級光滑度的分別，SPI的最高二級光滑度應為可以看穿的透明件保留。換言之，為何要花錢在消費者無法感激的表面光滑度上？Most consumers will not notice the differences between the SPI Guide three highest finishes on an opaque part.The two best SPI finishes should be reserved for transparent,see-through parts.In other words,why spend money on a surface finish that the consumer cannot appreciate?,表面光滑度Surface Finish,產品圖上必須標明表面光滑度，高度建議參照SPI模具光滑度指南。The surface finish must be clearly indicated on the part drawing.It is strongly recommended that surface finish be specified according to SPI Mold Finish Guide.,表面光滑度Surface Finish,一般說來，成本或交貨期，會隨著決定採用電火花加工法、噴砂法和照相化學腐蝕法的順序而增加。所有方法都能供給不同程度的表面花紋。較細的花紋像編織物或風乾木材的紋理，只能靠照相化學腐蝕提供。Generally speaking,the cost and delivery time increases with the decision to go from EDMing to blasting to PCEing.All three techniques can provide varying degrees of matte finishes.The more detailed finishes,such as fabric or weathered wood,are available only with PCEing.Note:PCE is Photo Chemical Etching,表面花紋Pattern,根據經驗法則，對母模側模壁(冷卻時，塑料從其離開)而言，每0.025mm咬花深度，單邊至少要有1.5 脫模角。有些咬花供應商要求在公模側模壁(冷卻時，塑料向其包裹)，提供2倍的脫模角。安全的作法是避免在内面採用咬花。The rule of thumb,applied to the side wall of cavities that the material shrinks away from as it cools,is a minimum of 1.5 of draft per side for each 0.025mm(0.001 inch)of texture depth.Some texture suppliers ask for twice as much draft on inside surfaces,that the material shrinks onto as it cools.A safer approach is to avoid using texture on inside surfaces.,咬花Texture,設計者必須指出咬花從那裏開始，到那裏結束。一個好的咬花標註，應該指出花紋號碼、咬花深度、咬花位置，如果要更得當的話，還要加上花紋的方向。當一產品是由數件零件組合而成，一定要指出咬花花紋的方向。The designer must indicate where the texture stops and starts.A good texturing note should indicate the pattern number,depth of texture,its location,and-if appropriate-the direction of the pattern.In those instances where several parts fit together in one product,the direction of the texture pattern absolutely must be specified.,咬花Texture,設計者完成產品設計之前，能做的最重要的單一事項，就是會同專業的咬花供應商作專案檢討。The single most important thing that a designer can do to optimize the use of texturing is to review the project with a knowledgeable texture supplier before finalizing the part design.,咬花Texture,半結晶塑料的收縮率較高，這些塑料因在平行和垂直於熔膠流動方向有著不同的收縮率，而多了一層問題。這問題又因成型條件改變致使結晶度變化而更形複雜。如果塑料冷卻得慢，結晶度和收縮率都會增加。The semi-crystalline plastics has higher mold shrinkage factors.These materials have the additional problem of different shrinkage factors parallel to and perpendicular to the direction of melt flow.This problem is further compounded by variations in the degree of crystallinity caused by changes in molding conditions.If the material is cooled slowly,there will be an increase in crystallinity and mold shrinkage.,收縮Shrinkage,非結晶塑料收縮率低，較易維持尺寸的複現性。發表的收縮率，是以3.175mm(0.125吋)的壁厚為準。It is easier to maintain dimensional reproducibility with low mold shrinkage factor amorphous materials.The published mold shrinkage data is based on a molded part with a 3.175mm(0.125inch)wall thickness.,收縮Shrinkage,設計射出成型零件，當塑料收縮率高時，應試圖限制壁厚變化在10%之內。當塑料收縮率低時，許容壁厚變化在25%以內。While designing injection molded parts in high mold shrinkage factor materials,the designer should try to limit wall thickness variations to 10%.The allowable wall thickness variation for the low mo