【正文】 ions is reinforced and unreinforced ,solid and foamed, rigid and soft, virgin and regrind, pigmented and unpigmented , etc. Multimaterial molding and its problems and solutions is a plex subject that cannot be explored thoroughly in a short article . The acpanying table indicates the range of variables involved. A few of the more important factors bear a brief discussion. Time and temperature One cause of insufficient bonding between materials relates to the timing of the injection of the materials and temperature of the first material when it is joined with the second . Too much cooling of the first material tends to weaken bonding. On the other hand, the first shot must be cooled enough not to be deformed or displace when you shoot the second one. If the second shot es too soon, while the first material is still soft, the second material can press and flash over the first one ,causing ”splash marks”. When running parts on two injection machines(molding the first shot on machine one and inserting it into the mold of the second machine ),bonding is not apt to be as good ad on a twoshot machine with rotating table. Even when using patible materials, the delay time between the two shots is relatively long and the first shot is likely to be too cold . A higher part temperature is remended for better chemical /mechanical bonding. Also, if the first shot picks up dust while being transferred to the second mold , bonding will also be negatively affected. 36 Apart from process conditions, material choice can greatly affect bonding . Some materials naturally tend to adhere better than others, and resin suppliersparticularly makers of TPES— have been working hard to optimize certain gradesfor overmolding by increasing their range of adhesion to other polymers. Additives and pigments can affect bonding. Glass fibers in one materials can enhance bonding with the second . Fibers on the surface of the material promote a mechanical bond with the second shot . Note that materials containing fillers like talc or calcium carbonate should be dried adequately . These fillers hold a hot of moisture, which can detract from bonding. Elements of quality To prevent underfilling or overfilling (and flashing)of either material, the shotto shot accuracy of the machine is obviously a critical factor. Shot variability of less than %to %is remended. A machine with closedloop injectionspeed control is the best choice. Next, pick a mold maker with experience in multimaterial parts. You can save a lot of money if you have the mold designed well from the start . For example, it can be helpful to supplement the thermal/chemical bonding between two materials with a mechanical joint achieved by using undercuts or similar designs. Make sure multicavity molds are well balanced . Hotrunner manifolds must be balanced too, and the number and size of drops must be sufficient for lowpressure filling. Mold temperature is another important factor. Accurate control of the temperature is mandatory when running molds with core lifters for the 37 second shot . Incorrect mold temperature can cause a lifter to wedge or jam, because of differential thermal expansion of the steel or steel/brass bination. Operators must be well trained for successful multimaterial molding . Wrong machine settings are often the culprits when parts don’t turn out right . Because of its plexities ,only people who understand the process should be allowed to attempt corrections if something goes wrong . Achieving a good bond between materials is often dependent on the temperature of the first material when the second is injected. 。 當塑件制造結果不好時，錯誤的制造環(huán)境經(jīng)常是罪魁禍首。因為鋼或鋼合金有不同 的熱膨脹，所以不正確的 溫度會引起 lifter的契入和堵塞。 模具的溫度是另一個重要因素。例如，它有助于增加那些有通過用 undercuts或相似設計獲得 的機械結合的材料之間的熱化結合。 第二是選擇一個有多種材料塑件成型經(jīng)驗的模具制造者。一般建議注射量少于 %到%。 注意包含有像滑石或碳酸鈣一樣的填充物的材料應被足夠烘干，因為這些填充物含有很多能是結合減弱的濕氣。在第一材料里面的玻璃纖維能提高與第二材料的結合質(zhì)量。為了 overmolding ,樹脂供應者 — 特別是 TPES的制造者 —通過提高對其它聚合物的粘附范圍努力地將某一等級最佳化。如果當?shù)谝淮巫⑸滢D移到第二個模具上時吸附了一些灰塵，那么將會對結合有很大的影響。甚至當用相容材料時兩次注射之間延長的時間相對要長，并且地一槍可能會太冷。引起“流涎”現(xiàn)象。另外，第一次注射必須足夠冷卻才能不使第二 次注射時不引起變形和錯位。 時間和溫度 引起材料之間結合不足的原因與材料注射時間和第二材料熔合時第一材料的溫度有關。 這些情況能發(fā)生是否材料組合加強的和沒被加強的，實心的和起泡的，剛硬的和軟的，原料和再研磨，有色素和無色素，等等。不管使用程序如何，造模者在達到高質(zhì)量塑件方面面對相同的挑戰(zhàn)。 4. 在型腔和主流道下面用更重的支持板（通常是 2~3英寸厚）和較重的導柱（一般是增加 ） 5. 比傳統(tǒng)的模具使用更大更多的推桿，以減少推桿的壓力 6. 考慮滑塊和導套的放置。 2. 模具的鎖定有時是彎曲的不對齊。 這里是一些薄壁的工具設計上的技巧： 1. 對于主要薄壁工作的應用，一般用硬度大于鋼 p20的材料，尤其是要求有大的磨損和腐蝕 的時候。實際上，薄壁的注塑的方法是經(jīng)常用于省錢途徑之一。） 不過，比標準的零件來說精密的模具可能要多花費 30%~40%。 H13鋼和其它的堅韌的鋼為薄壁的工具提供了額外的安全保證。 模具的材料也應該被檢查。隨著主要壁厚的減少，循環(huán)周期能減少 50%，熔化狀態(tài)下的系統(tǒng)的小心的管理能使分流道和主流道縮小循環(huán)周期的時間。如果標準零件注射時間在 2sec內(nèi)，如果它的厚度減少 25%那么充型時間就能減少 50%，即 1sec鐘就能充滿型腔。 模子：本身的精度 速度是薄壁模能否做成功的關鍵的因素之一。在薄壁注射的應用中經(jīng)常能見到的大大地減少的總循環(huán)周期時間可以使把最小注射量降低到型腔容量的20%~30%成為可能，但是 ，只有在徹底了解零件因材料變化而引起的其特性的變化的情況下才能實現(xiàn)。 27 附錄：外文翻譯 薄壁模具成功的秘密 要求生產(chǎn)一種小的輕的零件 ,就要我們尋找一個能夠注出薄壁工件的注塑模具 .現(xiàn)在 ,” 薄壁 ” 在微電子方面通常定義為少于 1m壁厚 .在大的自動化方面 ,” 薄 ” 可能意味是 2mm左右 .無論怎么樣 ,越薄壁的地方 ,在生產(chǎn)過程中要求的變化就越多 :更高的壓力和速度 ,更短的冷卻時間 ,和改注射的方法和工作排列的方式 .這些過程的改變在模具 ,機構和零件設計中要引起一系列的思考 機械方面的思考 : 標準的注塑機都能夠應用于大多數(shù)的薄壁注射 .新標準的注塑機的容量遠超過了十幾年前的機器 .先進的材料和技術 ,高超過的設計水平大大的增加了薄壁零件對標準注塑機的要求 . 但是當薄壁不斷的收縮 ,要求有更大的高速帶來的特殊壓 力 .例如微電子零件的壁厚少于 1m,填充時間要少于 30000psi是不