【正文】 l or mechanical bonding of the polymers, inplete 35 filling of one or more ponents, and flashing of one or more ponents. These conditions can occur whether the materials binations 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(dāng)塑件制造結(jié)果不好時(shí)，錯(cuò)誤的制造環(huán)境經(jīng)常是罪魁禍?zhǔn)住? 模具的溫度是另一個(gè)重要因素。 第二是選擇一個(gè)有多種材料塑件成型經(jīng)驗(yàn)的模具制造者。 注意包含有像滑石或碳酸鈣一樣的填充物的材料應(yīng)被足夠烘干，因?yàn)檫@些填充物含有很多能是結(jié)合減弱的濕氣。為了 overmolding ,樹(shù)脂供應(yīng)者 — 特別是 TPES的制造者 —通過(guò)提高對(duì)其它聚合物的粘附范圍努力地將某一等級(jí)最佳化。甚至當(dāng)用相容材料時(shí)兩次注射之間延長(zhǎng)的時(shí)間相對(duì)要長(zhǎng)，并且地一槍可能會(huì)太冷。另外，第一次注射必須足夠冷卻才能不使第二 次注射時(shí)不引起變形和錯(cuò)位。 這些情況能發(fā)生是否材料組合加強(qiáng)的和沒(méi)被加強(qiáng)的，實(shí)心的和起泡的，剛硬的和軟的，原料和再研磨，有色素和無(wú)色素，等等。 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(dǎo)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(dǎo)套的放置。 這里是一些薄壁的工具設(shè)計(jì)上的技巧： 1. 對(duì)于主要薄壁工作的應(yīng)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(shí)候。） 不過(guò)，比標(biāo)準(zhǔn)的零件來(lái)說(shuō)精密的模具可能要多花費(fèi) 30%~40%。 模具的材料也應(yīng)該被檢查。如果標(biāo)準(zhǔn)零件注射時(shí)間在 2sec內(nèi)，如果它的厚度減少 25%那么充型時(shí)間就能減少 50%，即 1sec鐘就能充滿型腔。在薄壁注射的應(yīng)用中經(jīng)常能見(jiàn)到的大大地減少的總循環(huán)周期時(shí)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(shí)現(xiàn)。 在本次水桶模具設(shè)計(jì)中承蒙老師的悉心指導(dǎo)和幫助，在畢業(yè)設(shè)計(jì)過(guò)程中提供了很多寶貴的資料、設(shè)計(jì)和方向、設(shè)計(jì)思路，以及模具結(jié)構(gòu)原理方面的知識(shí)，在此向他表示衷心的感謝。但由于實(shí)踐工程經(jīng)驗(yàn)的欠缺 ，在設(shè)計(jì)中對(duì)零件的加工精度和成型零件的加工工藝的確定由很多不足之處，在以后的工作學(xué)習(xí)中還有待改進(jìn)。 通過(guò)這 次畢業(yè)設(shè)計(jì)我對(duì)模具結(jié)構(gòu)有了清楚的認(rèn)識(shí)，了解了注塑模具的工作方式，對(duì)型腔、型芯等主要零件的設(shè)計(jì)及要求有了初步知識(shí)。如圖所示 圖 43 程序的創(chuàng)建 19 工藝 在上圖對(duì)話框中，主選項(xiàng)選擇 軸加工，子選項(xiàng)中選擇素材環(huán)切 刀具確定后，會(huì)切換到加工對(duì)象功能下。進(jìn)入加工模塊后，模型的放置位置和旋轉(zhuǎn)角度按默認(rèn)方式，即直接放置到坐標(biāo)系的原點(diǎn)，同時(shí)不做旋轉(zhuǎn)。 CAD文件 打開(kāi) cimatron ，在主菜單上選擇“文件” “打開(kāi)文檔”，在 cimatron 瀏覽器中選擇凹模，打開(kāi)文件后，在 CAD方式下檢驗(yàn)?zāi)Ｐ偷耐暾浴? D．毛坯的選擇： 考慮到零件所需的性能，選用鑄件作毛坯；確定毛坯的形狀、尺寸：選用模具鋼 45鑄件 ? 650 520（ mm）； 基準(zhǔn)選擇 加工中心的一次裝夾希望能夠進(jìn)行在該基準(zhǔn)下的全部加工，這樣可以降低由于基準(zhǔn)不重合而導(dǎo)致的基準(zhǔn)不重合度誤差。由于型芯在注塑時(shí)需要承受一定的壓力和溫度，故該零件需要有足夠的強(qiáng)度、剛度、耐磨性和韌性。側(cè)芯在動(dòng)模一邊，開(kāi)模后，首先由氣缸抽出側(cè)芯，然后再頂出塑件，頂出系統(tǒng)復(fù)位后，側(cè)芯再?gòu)?fù)位。如圖 36所示。氣動(dòng)頂出閥裝設(shè)計(jì)在型芯鑲件上，進(jìn)氣道設(shè)計(jì)在動(dòng)模固定板上。