水杯模具設(shè)計(jì)
機(jī)電工程學(xué)院模具設(shè)計(jì)與制造專業(yè) 阮靖皓
摘要：嵌件成型（Insert Molding）指在模具內(nèi)裝入預(yù)先準(zhǔn)備的異材質(zhì)嵌件后注入樹(shù)脂，熔融的材料與嵌件接合固化，制成一體化產(chǎn)品的成型工法。為了增加塑料制品整體或某一部位的強(qiáng)度與剛度，滿足使用的要求，常在塑件體內(nèi)設(shè)置金屬嵌件。
隨著產(chǎn)品的功能的日益提高，嵌件模的應(yīng)用也越來(lái)越廣泛，目前已廣泛應(yīng)用于汽車零配件，家用電器，電腦，手機(jī)，連接器等的模具里。嵌件模有它的獨(dú)有的特點(diǎn)，設(shè)計(jì)嵌件模時(shí)，塑膠件要放縮水，而嵌件一般是不放縮水的，這就涉及到塑件和嵌件的位置尺寸的處理問(wèn)題。由于嵌件的種類繁多，形狀大小不一，嵌件的安裝和定位，也是這類模具設(shè)計(jì)的另一難點(diǎn)。
關(guān)鍵詞：水杯 模具結(jié)構(gòu)
目錄
水杯模具設(shè)計(jì) 1
引言 3
1 塑件工藝性分析 3
1.1 塑件的原材料分析 3
(1) 塑件材料性能分析 3
(2) 成型工藝性分析 5
1.2 塑件結(jié)構(gòu)分析 5
2 擬定模具結(jié)構(gòu)形式 6
2.1 分型面位置確定 6
2.2 型腔數(shù)量及排列方式確定 7
2.3 注塑機(jī)選擇和參數(shù)校核 7
2.3.1 注射量計(jì)算 7
2.3.2 投影面積及鎖模力的計(jì)算 8
2.3.3 選擇注射機(jī) 8
根據(jù)注射機(jī)的注射容量需大于46.2cm3、鎖模力需大于366.24kN， 9
2.3.4 注射機(jī)有關(guān)參數(shù)的校核 9
3 成型零件有關(guān)尺寸的計(jì)算 10
1）型腔徑向尺寸按以下公式計(jì)算 11
2）型腔深度尺寸按以下公式計(jì)算 11
4 澆注系統(tǒng)的設(shè)計(jì) 14
4.1 澆口套的選用 14
4.2分流道的設(shè)計(jì) 15
（1）分流道截面形狀 15
（2）分流道的尺寸 15
4.3分流道的布置 16
4.4澆口設(shè)計(jì) 17
4.5澆口位置的選擇 18
5 合模導(dǎo)向機(jī)構(gòu)以及定位裝置的設(shè)計(jì) 19
5.1導(dǎo)向機(jī)構(gòu)的設(shè)計(jì) 19
5.2定位裝置的設(shè)計(jì) 20
6 脫模結(jié)構(gòu)的設(shè)計(jì) 20
7 排氣系統(tǒng)的設(shè)計(jì) 22
8 繪制模具裝配圖以及模具的安裝試模 22
裝配的繪制 22
結(jié)論 25
謝辭 25
引言
近年來(lái)，中國(guó)塑料模具制造水平已有較大提高。目前，塑料模具在整個(gè)模具行業(yè)中所占比重約為30%，在模具進(jìn)出口中的比重高達(dá)50～70%。目前，帶嵌件模具發(fā)展也是相當(dāng)?shù)目臁，F(xiàn)在最常見(jiàn)帶嵌件模具是帶金屬嵌件的模具以及帶樹(shù)脂嵌件的模具。結(jié)合Pro/E、Moldex3D等CAE分析軟件一起對(duì)帶嵌件模具進(jìn)行模擬分析，從而來(lái)指導(dǎo)帶嵌件模具設(shè)計(jì)及其工藝方案的優(yōu)化，已經(jīng)成為了當(dāng)今社會(huì)的一個(gè)的重要研究手段。但是總體說(shuō)來(lái)，對(duì)帶嵌件的模具設(shè)計(jì)仍然還不成熟。
塑料產(chǎn)品從設(shè)計(jì)到成型生產(chǎn)是一個(gè)十分復(fù)雜的過(guò)程，它包括塑料制品設(shè)計(jì)、模具結(jié)構(gòu)設(shè)計(jì)、模具加工制造和模塑生產(chǎn)等幾個(gè)主要方面，它需要產(chǎn)品設(shè)計(jì)師、模具設(shè)計(jì)師、模具加工工藝師及熟練操作工人協(xié)同努力來(lái)完成，它是一個(gè)設(shè)計(jì)、修改、再設(shè)計(jì)的反復(fù)迭代，不斷優(yōu)化的過(guò)程。傳統(tǒng)的手工設(shè)計(jì)已越來(lái)越難以滿足市場(chǎng)激烈競(jìng)爭(zhēng)的需要。計(jì)算機(jī)技術(shù)的運(yùn)用，正在各方面取代傳統(tǒng)的手工設(shè)計(jì)方式，并取得了顯著的經(jīng)濟(jì)效益。
1 塑件工藝性分析
1.1 塑件的原材料分析
產(chǎn)品名稱: 水杯
型腔數(shù):一模四腔
生產(chǎn)類型:大批量
材料: PP
圖 1-1
(1) 塑件材料性能分析
PP塑料，化學(xué)名稱：聚丙烯 ??
英文名稱:Polypropylene（簡(jiǎn)稱PP）
比重:0.9-0.91克/立方厘米 成型收縮率:1.0-2.5% 成型溫度：160-220℃ 。
成分結(jié)構(gòu)
PP為結(jié)晶型高聚物，常用塑料中PP最輕，密度僅為0.91g/cm3（比水?。?。通用塑料中，PP的耐熱性最好，其熱變形溫度為80-100℃，能在沸水中煮。PP有良好的耐應(yīng)力開(kāi)裂性，有很高的彎曲疲勞壽命，俗稱“百折膠”。PP的綜合性能優(yōu)于PE料。PP產(chǎn)品質(zhì)輕、韌性好、耐化學(xué)性好。PP的缺點(diǎn)：尺寸精度低、剛性不足、耐候性差，它具有后收縮現(xiàn)象，脫模后，易老化、變脆、易變形。
成型特性
1)結(jié)晶料,吸濕性小,易發(fā)生融體破裂,長(zhǎng)期與熱金屬接觸易分解。
2)流動(dòng)性好,但收縮范圍及收縮值大,易發(fā)生縮孔.凹痕,變形。
3)冷卻速度快,澆注系統(tǒng)及冷卻系統(tǒng)應(yīng)緩慢散熱,并注意控制成型溫度。料溫低溫高壓時(shí)容易取向,模具溫度低于50度時(shí),塑件不光滑,易產(chǎn)生熔接不良,流痕,90度以上易發(fā)生翹曲變形
4)塑料壁厚須均勻,避免缺膠,尖角,以防應(yīng)力集中。
PP與其它幾種主要的通用塑料的性能比較
表1-1 材料性能表
材料性能、種類
PP
PE
PVC
PS
ABS
密度
最小
小于水
較大
略高于水
略高于水
剛性
較好
差
好
好
好
收縮率
差
一般
好
好
好
韌性
低溫下差
好
差
差
好
強(qiáng)度
較高
低
較高
高
高
耐熱性
好
一般
差
較差
較差
化學(xué)穩(wěn)定性
好
好
好
好
好
耐候性
差
差
一般
一般
較差
毒性
無(wú)毒
無(wú)毒
可以無(wú)毒
無(wú)毒
無(wú)毒
粘合劑粘合
差
差
好
一般
一般
熱合性
一般
好
一般
一般
一般
成型加工性
好
好
不易
好
好
(2) 成型工藝性分析
PP在熔融溫度下有較好的流動(dòng)性，成型性能好，PP在加工上有兩個(gè)特點(diǎn)：其一：PP熔體的粘度隨剪切速度的提高而有明顯的下降（受溫度影響較?。?；其二：分子取向程度高而呈現(xiàn)較大的收縮率。
PP的加工溫度在200-300℃左右較好，它有良好的熱穩(wěn)定性（分解溫度為310℃），但高溫下（270-300℃），長(zhǎng)時(shí)間停留在炮筒中會(huì)有降解的可能。因PP的粘度隨著剪切速度的提高有明顯的降低，所以提高注射壓力和注射速度會(huì)提高其流動(dòng)性，改善收縮變形和凹陷。模溫宜控制在30-50℃范圍內(nèi)。PP熔體能穿越很窄的模具縫隙而出現(xiàn)披鋒。PP在熔化過(guò)程中，要吸收大量的熔解熱（比熱較大），產(chǎn)品出模后比較燙。PP料加工時(shí)不需干燥，PP的收縮率和結(jié)晶度比PE低。
1.2 塑件結(jié)構(gòu)分析
塑件的具體結(jié)構(gòu)如圖所示。其中塑件外形結(jié)構(gòu)大致圓柱形，帶有拔模角度，注塑重點(diǎn)在于，注塑時(shí)不能出現(xiàn)澆不足，收縮均勻。同時(shí)外觀要求不能有熔接痕、脫模痕, 不能有劃傷、變形、飛邊，必須符合GB/T 2828.1、QC/T 32-2006和GB/T 3730.1-2001。
制品尺寸精度分析。該塑件尺寸無(wú)特殊要求，尺寸精度按MT5查取公差。該塑件內(nèi)外尺寸均受到模具活動(dòng)的影響，故為B類尺寸。據(jù)國(guó)家標(biāo)準(zhǔn)塑件尺寸公差（GB/T144486-1993）查得，該零件主要尺寸如下所示：
表1-2
塑件標(biāo)注尺寸
尺寸公差（MT5）
塑件標(biāo)注尺寸
尺寸公差（MT5）
尺寸
18
18±0.3
尺寸
1
1±0.3
20
20±0.3
32
32±0.3
23
23±0.3
33
33±0.3
25
25±0.3
27
27±0.3
圖1-2 水杯三維圖
2 擬定模具結(jié)構(gòu)形式
2.1 分型面位置確定
在模具設(shè)計(jì)初期階段，應(yīng)首先確定分型面的位置，然后才選擇模具的結(jié)構(gòu)。分型面設(shè)計(jì)是否合理，對(duì)塑件質(zhì)量、工藝操作難易程度和模具的設(shè)計(jì)制造都有很大影響。因此，分型面的選擇是在注射模設(shè)計(jì)中的一個(gè)關(guān)鍵因素。
分型面的選擇主要應(yīng)遵循以下原則：
（1) 分型面應(yīng)選在塑件外形最大截面處。
（2) 便于塑件順利脫模，盡可能使塑件留在動(dòng)模一側(cè)。
（3) 有利于保證塑件的精度要求。
（4) 滿足塑件的外觀質(zhì)量要求。
（5) 有利于簡(jiǎn)化模具結(jié)構(gòu)。
（6) 盡量減少塑件在合模方向上的投影面積。
（7) 有利于排氣。
綜合上述的各原則，分型面可取在制件的最大投影面積處。
圖 2-1 分型面
2.2 型腔數(shù)量及排列方式確定
該塑件三維是?54上×?40下×66高mm，為中小型尺寸工件，采用一模四腔，大批量生產(chǎn)。排列如圖所示。
圖 2-2 型腔排列
2.3 注塑機(jī)選擇和參數(shù)校核
2.3.1 注射量計(jì)算
模具所需塑料熔體注射量m = nm1 + m2 (3-1)
式中： m— 一副模具所需塑料的質(zhì)量或體積（g或cm3）;
n — 初步選定的型腔數(shù)量；
m1— 單個(gè)塑件的質(zhì)量或體積（g或cm3）
m2— 澆注系統(tǒng)的質(zhì)量或體積（g或cm3）
其中m2是個(gè)未知值（注塑廠的統(tǒng)計(jì)資料），在做設(shè)計(jì)時(shí)以0.6nm1來(lái)估算，即
m = 1.6n m1 (3-2)
經(jīng)proe分析，塑件質(zhì)量m1= 5.9480.91=5.412g，所以注射量m=1.6nm1=1.645.4=34.56g
2.3.2 投影面積及鎖模力的計(jì)算
塑件和流道凝料（包括澆口）在分型面上的投影面積及所需鎖模力為：
A = nA1+A2 (3-3)
Fm=(nA1+A2)P型 (3-4)
式中： A —塑件及流道凝料在分型面上的投影面積（mm2）;
A1—單個(gè)塑件在分型面上的投影面積（mm2）；
A2—流道凝料（包括澆口）在分型面上的投影面積（mm2）;
Fm —模具所需的鎖模力（N）；
P型—塑料熔體對(duì)型腔的平均壓力（MPa）。
表5-1 常用塑料注射成型時(shí)型腔平均壓力 單位：MPa
塑件特點(diǎn)
P型
舉例
容易成型塑件
25
PE、PP、PS等壁厚均勻的日用品，
一般塑件
30
容器類
中等黏度塑件及有精度要求塑件
35
在模溫較高的情況下，成型薄壁容器類
高黏度塑料及高精度、難充模塑料
40
ABS、POM等有精度要求的零件，如殼類等高精度的機(jī)械零件，如齒輪、凸輪等
流道凝料(包括澆口)在分型面上的投影面積A2，在模具設(shè)計(jì)前是個(gè)未知值，根據(jù)多型腔模的統(tǒng)計(jì)分析，A2是每個(gè)塑件在分型面上的投影面積的0.2倍到0.5倍，因此可用0.45nA1來(lái)估算，另外部分塑料注射壓力P可查相關(guān)數(shù)據(jù)。經(jīng)過(guò)moldex 3D 的計(jì)算，總投影面積為：9156mm2。
所以：A=4（3.14*27*27）=9156mm2
Fm =AP型=9156×40=366.24kN
2.3.3 選擇注射機(jī)
根據(jù)上面計(jì)算得到的m和Fm值來(lái)選擇一種注射機(jī)，注射機(jī)的最大注射量（額定注射量G）和額定鎖模力F滿足
G≥ m/α (3-5)
式中α—注射系數(shù)，無(wú)定型塑料取0.85，結(jié)晶型塑料取0.75。
F>Fm (3-6)
則：G≥m/α→G≥34.56g/0.85=40.66g
生產(chǎn)原料密度為1.76g/cm3 注射容量為23.1 cm3
一般注塑機(jī)澆注塑料原料時(shí), 其每次注射量?jī)H達(dá)標(biāo)準(zhǔn)注射量的75 %。為了提高制件質(zhì)量及尺寸穩(wěn)定, 表面光澤、色調(diào)的均勻, 要求注射量為標(biāo)定注射量的50 %為宜，即46.2cm3。
根據(jù)注射機(jī)的注射容量需大于46.2cm3、鎖模力需大于366.24kN，
又由于《模具設(shè)計(jì)與制造簡(jiǎn)明手冊(cè)》表2-40選擇注射機(jī)XS-ZY-1000螺桿式注射機(jī)，其參數(shù)如下：
額定注射量：1000
螺桿直徑：85mm
注射壓力：178Mpa
鎖模力：4500KN
模板行程：700-mm
模具最大厚度：700mm
模具最小厚度：300mm
模板尺寸：700×850mm
拉桿空間：650×550mm
定位孔直徑：150mm
合模方式：液壓—機(jī)械
2.3.4 注射機(jī)有關(guān)參數(shù)的校核
（1） 最大注塑量校核
模具成型塑料制品和流道凝料總質(zhì)量應(yīng)小于注塑機(jī)的額定注塑量的80%，所以額定注塑量Ｍ≥138.24g÷80%=172.8g，選定的注塑機(jī)額定注塑量為1000cm3×1.76g/cm3=1760g，注塑量校核合格。
（2） 鎖模力校核
F≥kAp型=1.2*366.24KN =439.482KN，所選注塑機(jī)的鎖模力為4500KN，鎖模力校核合格。
（3） 注射壓力的校核
注射機(jī)的最大壓力應(yīng)大于塑件成型所需的壓力，即
(3-7)
式中：——注射機(jī)最大注射壓力(Mpa)；
——塑件成型所需的注射壓力(Mpa)；
采用柱塞式注塑機(jī)PPA注射壓力為140～180MPa，螺桿式注塑機(jī)則取120～140MPa為宜，因此選定的注塑機(jī)的注射壓力：178 Mpa，滿足要求。
3 成型零件有關(guān)尺寸的計(jì)算
（1）型芯設(shè)計(jì)
圖3-1 型芯
型芯的尺寸計(jì)算
型芯的尺寸按以下公式計(jì)算
D=〈〔1+〕d+xΔ〉
式中D—型芯外徑尺寸
d—塑件內(nèi)形尺寸
Δ—塑件公差
—塑料平均收縮率
—成形零件制造公差,取Δ/2。
（2） 型腔設(shè)計(jì)
圖3-2 型腔
1）型腔徑向尺寸按以下公式計(jì)算
D=〈〔1+〕d－xΔ〉
式中D—型腔的內(nèi)形尺寸
d—塑件外形基本尺寸
Δ— 塑件公差
—塑料平均收縮率
—成形零件制造公差,取Δ/2。
2）型腔深度尺寸按以下公式計(jì)算
=
式中—型腔深度
—塑件外形高度尺寸
Δ— 塑件公差
—塑料平均收縮率
—成形零件制造公差,取
（3） 由于該產(chǎn)品不是透明的，所以型芯的表面粗糙度要求不需那么高。一般取Ra1.6,在機(jī)床上加工就可以直接投入使用，不需要經(jīng)過(guò)其它的特殊加工?？紤]模具的修模以及型芯的磨損，在精度范圍內(nèi)，型芯尺寸盡量取大值。而型腔則取大值，型腔的表面粗糟將決定產(chǎn)品的外觀，因此型腔的表面粗糙度則要求較高，一般取Ra0.8～0.4。在本次設(shè)計(jì)中，型腔取Ra0.8。
（4） X——綜合修正系數(shù)（考慮塑料收縮率的偏差和波動(dòng)，成型零件的磨損等因素），塑件精度低、批量較小時(shí)，X取1/2；塑件精度高、批量比較大，X取3/4，根據(jù)設(shè)計(jì)要求取X為0.5。
要計(jì)算型芯、型腔的工作尺寸，必先確定塑件的公差及模具的制造公差。根據(jù)要求塑件精度取五級(jí)精度。根據(jù)塑料制件公差數(shù)值表（SJ1372—78）塑件在五級(jí)精度下，基本尺寸對(duì)應(yīng)的尺寸公差如下：
表3-4 基本尺寸公差
基本尺寸㎜
公差㎜
基本尺寸㎜
公差㎜
＜3
0.16
3~6
0.18
6~10
0.20
10~14
0.22
14~18
0.24
18~24
0.28
24~30
0.32
30~40
0.36
40~50
0.40
50~65
0.46
65~80
0.52
80~100
0.60
100~120
0.68
（1）型腔：寬度方向d=240；取=0.25%（以下收縮率都取0.25%）
D=[（1+0.0025）×240－0.5×0.60]=240.3
長(zhǎng)度方向 d2’=240;
D2’=[（1+0.0025）×240－0.5×0.68]=240.26
（2）型腔深度：H=66.4 ; X=0.4
H=[(1+0.0025) ×66.4+0.4×0.18]=66.638
（3）型芯：
寬度方向d=46
D=[（1+0.0025）×46+0.5×0.60]=46.415
高度方向d=64.4
D=[（1+0.0025）×64.4+0.5×0.68]=64.9
（5）型腔的強(qiáng)度及剛度要求
塑料模具型腔的側(cè)壁和底壁厚度計(jì)算是模具設(shè)計(jì)中經(jīng)常遇到的問(wèn)題，尤其對(duì)大型模具更為突出。目前常用的計(jì)算方法有按強(qiáng)度條件計(jì)算和按剛度條件計(jì)算兩類，但塑料模具要求既不許因強(qiáng)度不足而發(fā)生明顯變形，甚至破壞，也不許剛度不足而變形過(guò)大的情況，因此要求對(duì)強(qiáng)度和剛度加以考慮。對(duì)于型腔主要受到的力是塑料熔體的壓力，在塑料熔體的壓力作用下，型腔將產(chǎn)生內(nèi)應(yīng)力及變形。如果型腔側(cè)壁和底壁厚度不夠。當(dāng)型腔中產(chǎn)生的內(nèi)應(yīng)力超過(guò)材料的許用應(yīng)力時(shí)，型腔發(fā)生強(qiáng)度破壞，與此同時(shí)，剛度不足則發(fā)生彈性變形，從而產(chǎn)生溢料現(xiàn)象，將影響塑件成型質(zhì)量，所以模具對(duì)強(qiáng)度和剛度都有要求。
但是，實(shí)踐證明，模具對(duì)強(qiáng)度和剛度的要求并非同時(shí)兼顧，對(duì)大型腔，按剛度條件，對(duì)小型腔則按強(qiáng)度條件計(jì)算即可。（在本設(shè)計(jì)中按強(qiáng)度條件來(lái)計(jì)算）
對(duì)長(zhǎng)方形型腔壁厚和底板厚度的計(jì)算
1）型腔底板厚度：
式中——型腔內(nèi)塑料熔體的壓力（MPa），一般取25~45MPa
L——型腔側(cè)壁邊長(zhǎng)（mm）
b——型腔寬度（mm）
B——凹模寬度（mm）
[σ]——材料的許用應(yīng)力，一般取100Mpa
——型腔側(cè)壁長(zhǎng)邊尺寸（mm）
=36.65mm
由于根據(jù)標(biāo)準(zhǔn)模架查得定模板的厚度為40mm，綜合各方面考慮，現(xiàn)確定定模板厚為40mm，可以滿足型腔的強(qiáng)度要求。
2）確定型腔的壁厚
表3-5 型腔壁厚關(guān)系表
型腔寬度
鑲拼式腔壁厚
40
9
＞40～50
9～10
＞50～60
10～11
＞60～70
11～12
＞70～80
12～13
＞80～90
13～14
＞90～100
14～15
＞100～120
15～17
＞120～140
17～19
＞140～160
19～21
4 澆注系統(tǒng)的設(shè)計(jì)
澆注系統(tǒng)它是獲得優(yōu)良性能和理想外觀的塑件以及最佳的成型效率有直接影響。 此塑件采用普通流道系統(tǒng)，它是主由流道、分流道、澆口、冷料穴組成的。澆注系統(tǒng)是一副模具的重要的內(nèi)容之一。從總體來(lái)說(shuō)，它的作用可以作如下歸納：它是將來(lái)自注塑機(jī)噴嘴的塑料熔體均勻而平穩(wěn)地輸教送到型腔，同時(shí)使型腔的氣體能及時(shí)順利排出，在塑件熔體填充凝固的過(guò)程中，將注塑壓力有效地傳遞到型的各個(gè)部位，以獲得形完整、內(nèi)外在質(zhì)量?jī)?yōu)良的塑件制件。
澆注系統(tǒng)的設(shè)計(jì)的一般原則：了解塑件的成型性能和塑件熔料的流動(dòng)特性。采用盡量短的流程，以降低熱量與壓力損失。澆注系統(tǒng)的設(shè)計(jì)應(yīng)該有利于良好的排氣，澆注系統(tǒng)應(yīng)能順利填充型腔。便于修整澆口以保證塑件外觀質(zhì)量。確保均勻進(jìn)料。
4.1 澆口套的選用
主流道通常位于模具中心塑料熔體的入口處，它將注射機(jī)噴嘴注射出的熔體導(dǎo)入分流道或型腔中。主流道的形狀為圓錐形，以便熔體的流動(dòng)和開(kāi)模時(shí)主流道凝料的順利拔出。主流道的尺寸直接影響到熔體的流動(dòng)速度和充模時(shí)間。另外，由于其與高溫熔體及注射機(jī)噴嘴反復(fù)接觸，因此設(shè)計(jì)中常設(shè)計(jì)成可拆卸更換的澆口套。
主流道襯套為標(biāo)準(zhǔn)件可選購(gòu)。主流道小端入口處與注射機(jī)噴嘴反復(fù)接觸，易磨損，對(duì)材料要求較嚴(yán)格，因而盡管小型注射?？梢詫⒅髁鞯罎部谂c定位圈設(shè)計(jì)成一個(gè)整體，但考慮上述因素通常仍然將其分開(kāi)來(lái)設(shè)計(jì)，以便于拆卸更換。同時(shí)，也便于選用優(yōu)質(zhì)鋼材進(jìn)行單獨(dú)加工和熱處理。設(shè)計(jì)中常采用碳素工具鋼（T8A或T10A），熱處理淬火表面硬度為50～55HRC，澆口套屬于標(biāo)準(zhǔn)件，在選夠澆口套時(shí)應(yīng)注意：澆口套進(jìn)料口直徑和球面坑半徑。因此，所選澆口套如圖所示：
圖4-1 澆口套
4.2分流道的設(shè)計(jì)
（1）分流道截面形狀
分流道截面形狀可以是圓形、半圓形、矩形、梯形和U形等，圓形和正方形截面流道的比表面積最?。鞯辣砻娣e與體積之比稱為比表面積），塑料熔體的溫度下降少，阻力亦小，流道的效率最高。但加工較困難，而且正方形截面不易脫模，所以在實(shí)際生產(chǎn)中較常用的截面形狀為梯形、半圓形及U形。
（2）分流道的尺寸
分流道尺寸由塑料品種、塑件的大小及長(zhǎng)度確定。對(duì)于重量在200g以下，壁厚在3mm以下的塑件可用下面經(jīng)驗(yàn)公式計(jì)算分流道的直徑，如式。
D=0.2654W1/2 L1/4
式中：D---分流道的直徑，mm;
W---塑件的質(zhì)量，g；
L---分流道的長(zhǎng)度，mm.
此式計(jì)算的分流道直徑限于3.2mm～9.5mm.對(duì)于HPYC和PMMA。應(yīng)將計(jì)算結(jié)果增加25％。對(duì)于梯形分流道，H=2D/3；對(duì)于U形分流道，H=1.25R，R=0.5D。D算出后一般取整數(shù)；對(duì)于半圓形H=0.45R
對(duì)于流動(dòng)性極好的塑料（如PE，PA等），當(dāng)分流道很短時(shí)，其直徑可小到2mm左右；對(duì)于流動(dòng)性差的塑料（如PC，HPVC及PMMA等），分流道直徑可以大到13mm;大多數(shù)塑料所用分流道的直徑為6mm～10mm。
圖4-2 分流道布局
4.3分流道的布置
(1）在保證足夠的注塑壓力使塑料熔體順利充滿型腔的前提下，分流道截面面積與長(zhǎng)度盡量取小值，分流道轉(zhuǎn)折處應(yīng)圓弧過(guò)度。
（2）分流道較常時(shí)，在分流道的末端應(yīng)開(kāi)設(shè)冷料井。
（3）分流道的位置可單獨(dú)開(kāi)設(shè)在定模板上或動(dòng)模板上，也可以同時(shí)開(kāi)設(shè)在動(dòng)、定模板上，合模后形成分流道截面形狀。
（4）分流道與澆口連接處應(yīng)加工成斜面，并用圓弧過(guò)度。
在單腔模中，常不設(shè)分流道，而在多腔模中，一般都設(shè)置有分流道，塑料沿分流道流動(dòng)時(shí)，要求通過(guò)它盡快地充滿型腔，流動(dòng)中溫度降低盡可能小，阻力盡可能低。同時(shí)，應(yīng)能將塑料熔體均衡地分配到各個(gè)型腔。從前兩點(diǎn)出發(fā)，分流道應(yīng)短而粗。但為了減少澆注系統(tǒng)的加回料量，分流道亦不能過(guò)粗。過(guò)粗的分流道冷卻緩慢，還倒增長(zhǎng)模塑的周期。而該設(shè)計(jì)中使用了梯形斷面形狀的分流道。如圖所示；
圖4-3 分流道橫截面
4.4澆口設(shè)計(jì)
澆口亦稱進(jìn)料口，是連接分流道與型腔的通道。它是整個(gè)澆注系統(tǒng)的關(guān)鍵的部位，也是最薄點(diǎn)。其形狀、大小及位置應(yīng)根據(jù)塑件大小、形狀、壁厚、成型材料及塑件技術(shù)要求等進(jìn)行而確定。澆口分限制性澆口和非限制性澆口，該塑件采用的是限制性澆口，它一方面通過(guò)截面積的突然變化，使分流道輸送來(lái)的塑料熔體的流速產(chǎn)生加速度，提高剪切速率，有利于塑料進(jìn)入，使其充滿型腔。另一方面改善塑料熔體進(jìn)入型腔的流動(dòng)特性，調(diào)節(jié)澆口尺寸，可使多型腔同時(shí)充滿，可控制填充時(shí)間、冷卻時(shí)間及塑件表面質(zhì)量，，同時(shí)還起著封閉型腔防止塑料熔體倒流，并便于澆口凝料與塑件分開(kāi)的作用。
設(shè)計(jì)中，澆口的位置及尺寸的要求是比較嚴(yán)格的，初步試模，必要時(shí)還需要修改。因此澆口的位置的開(kāi)設(shè)，對(duì)成型性能及成型質(zhì)量的影響是很大的。一般在選擇澆口位置時(shí)，需要根據(jù)塑件的結(jié)構(gòu)工藝及特征，成型質(zhì)量和技術(shù)要求，綜合分析。一般要滿足以下原則：
(1) 盡量縮短流動(dòng)距離。
(2) 澆口應(yīng)開(kāi)設(shè)在塑件的壁厚。
(3) 必須盡量減少或避免產(chǎn)生熔接痕。
(4) 應(yīng)有利于型腔中氣體的排除。
(5) 考慮分子定向的影響。
(6) 避免產(chǎn)生噴射和蠕動(dòng)。
(7) 在承受彎曲沖擊載荷的部位設(shè)置澆口。
(8) 澆口位置的選擇應(yīng)注意塑件的外觀質(zhì)量。
澆口的形狀和尺寸對(duì)制品質(zhì)量影響很大，澆口在多情況下，系整個(gè)流道斷面尺寸最小的部分（除主流道型的澆口外），一般匯報(bào)口的斷面積與分流道的斷面積之比約為0.03～0.09。斷面形狀如圖5.4所示，澆口臺(tái)階長(zhǎng)1～1.5㎜左右．雖然澆口長(zhǎng)度比分流道的長(zhǎng)度短的多，但因?yàn)槠鋽嗝娣e甚小，澆口處的阻力與分流道相比，澆口的阻力仍然是主要的，故在加工澆口時(shí)，更應(yīng)注意其尺寸的準(zhǔn)確性。
然而，根據(jù)塑件的樣品圖、生產(chǎn)的批量等，采用一模四腔結(jié)構(gòu)。澆口采用點(diǎn)澆口 具體尺寸見(jiàn)圖。
圖 4-4 澆點(diǎn)
4.5澆口位置的選擇
（1）澆口的位置的應(yīng)使填充型腔的流程最短這樣的結(jié)構(gòu)使壓力損失最小，易保證料流充滿整個(gè)型腔。對(duì)于型塑件，要進(jìn)行流動(dòng)比的校核。流動(dòng)比K由流動(dòng)通道的長(zhǎng)度L與厚度t之比來(lái)確定。如下式：
K=Σ（Lτ/tτ）
式中：Lτ---各段流程的長(zhǎng)度，mm;
tτ---各段流程的厚度或直徑，mm;
流動(dòng)比的允許值隨塑料熔體的性質(zhì)、溫度壓力等的不同而變化。流動(dòng)比的計(jì)算公式為：
①K=L1/t 1+L 2+L 3/t 2
②K= L1/t 1+L 2/t 2+L 3/t 3+2L 4/t 4+L 5/t 5
(2) 澆口位置的選擇要避免塑件變形
（3）澆口位置的設(shè)置應(yīng)減少或避免產(chǎn)生熔接痕
熔接痕是充型時(shí)前端較冷的料流在型腔中的對(duì)接部位，它的存在會(huì)降低塑件的強(qiáng)度，所以設(shè)置澆口時(shí)應(yīng)考慮料流的方向。為提高熔接痕處強(qiáng)度，可在熔接處增設(shè)溢流槽，使冷料進(jìn)入逸流槽。筒形塑件采用環(huán)行澆口無(wú)熔接痕，而輪輻式澆口會(huì)有熔接痕產(chǎn)生。澆口的位置塑與件質(zhì)量有直接影響,位置選擇不當(dāng)會(huì)使塑件產(chǎn)生變形、熔接痕等缺陷。澆口位置的選擇如總裝圖所示。
5 合模導(dǎo)向機(jī)構(gòu)以及定位裝置的設(shè)計(jì)
5.1導(dǎo)向機(jī)構(gòu)的設(shè)計(jì)
本次設(shè)計(jì)采用的是簡(jiǎn)化型三板模標(biāo)準(zhǔn)模架其中沒(méi)有導(dǎo)柱導(dǎo)向機(jī)構(gòu)。其導(dǎo)向機(jī)構(gòu)可以用大拉桿代替，大拉桿的具體設(shè)計(jì)如圖所示：
圖 5-1大拉桿
5.2定位裝置的設(shè)計(jì)
由于本設(shè)計(jì)為多分型面開(kāi)模，在定模一側(cè)設(shè)置了脫澆道板，即分流道推板，故必須設(shè)置限位導(dǎo)柱，以便在澆注系統(tǒng)順利脫模后，開(kāi)始進(jìn)行塑件的開(kāi)模及頂出，限位導(dǎo)柱的設(shè)計(jì)結(jié)構(gòu)如圖所示：
圖 5-2限位導(dǎo)柱的裝配形式
限位導(dǎo)柱的長(zhǎng)度由各模板厚度及開(kāi)模行程決定，限位導(dǎo)柱的長(zhǎng)度：
L=200mm
定距螺釘?shù)闹睆剑篋=16mm
6 脫模結(jié)構(gòu)的設(shè)計(jì)
在注塑成型的每一個(gè)循環(huán)中，塑件必須由模具型腔中脫出，在該設(shè)計(jì)中，為了使符合脫模機(jī)構(gòu)的要求：
使塑件留于動(dòng)模；
塑件不變形損壞
這是脫模機(jī)構(gòu)應(yīng)當(dāng)達(dá)到的基本要求。要做到這一點(diǎn)首先必須分析塑件對(duì)模腔的附著力的大小和所在部位，以便選擇合適的脫模方式和脫模位置，使脫模力得以均勻合理的分布。
良好的塑件外觀
頂出塑件的位置應(yīng)盡量設(shè)在塑件內(nèi)部，以免損壞塑件的外觀。
結(jié)構(gòu)可靠
因此，根據(jù)裝配圖，其模具結(jié)構(gòu)的脫模機(jī)構(gòu)主要由脫料板將余料打出模外，然后由司筒推動(dòng)塑件使工件推出，還有在設(shè)計(jì)主型芯時(shí)也會(huì)有一定的撥模作斜度3°～5°。
本次設(shè)計(jì)的制件需要用點(diǎn)澆口進(jìn)行入澆 這樣我們就需要設(shè)計(jì)為三板模，三板模相對(duì)普通的模具多了一個(gè)脫料板，脫料板的作用是將凝料與產(chǎn)品分開(kāi)切斷以及將凝料打出模外。
本次設(shè)計(jì)的模具的運(yùn)動(dòng)過(guò)程大致如下：
開(kāi)模的時(shí)候，動(dòng)模板13在如圖12彈簧的作用下首先分開(kāi)，這樣分流道的凝料將會(huì)被18拉料銷拉住留在14脫料板一側(cè)，當(dāng)動(dòng)模板13運(yùn)動(dòng)一定距離帶動(dòng)11小拉桿的限位桿運(yùn)動(dòng) 從而帶動(dòng)脫料板將留在脫料板一側(cè)的凝料以及主流道的余料打出模外，小拉桿運(yùn)動(dòng)一些距離被定模座板固定不能運(yùn)動(dòng)后 小拉桿拉住定模版使其靜止不動(dòng) 而動(dòng)模部分繼續(xù)開(kāi)模運(yùn)動(dòng) 注塑機(jī)的頂輥?zhàn)饔庙敆U固定板作用在復(fù)位桿上 使復(fù)位桿作用推件板運(yùn)動(dòng) 推件板將產(chǎn)品頂出模外，至此一次完整的注塑過(guò)程就完成了。
7 排氣系統(tǒng)的設(shè)計(jì)
塑料在熔化時(shí)，會(huì)產(chǎn)生氣體，所以當(dāng)塑料在充滿型腔時(shí)及澆注系統(tǒng)內(nèi)的空氣，如果在型腔中不及時(shí)排除干凈，可以會(huì)在塑件上形成氣泡、接縫、表面輪廓不清及充填缺料等缺陷。另一方面氣體的受壓產(chǎn)生反向壓力而降低充模速度，還可能造成塑件碳化或燒焦。注射成型時(shí)的排氣可采用如下四種方式排氣：
（1） 利用配合間隙排氣；
（2） 在分型面上開(kāi)設(shè)排氣槽排氣；
（3） 利用排氣守排氣；
（4） 強(qiáng)制性排氣；
該模具是采用利用配合間隙排氣。其間隙值約為0.03~0.05mm.它常用于中小型的簡(jiǎn)單模具。
8 繪制模具裝配圖以及模具的安裝試模
裝配的繪制
模具整體設(shè)計(jì)也就是模體的設(shè)計(jì)，隨著現(xiàn)代工業(yè)的發(fā)展，模體設(shè)計(jì)已接近標(biāo)準(zhǔn)化，可以從市場(chǎng)上購(gòu)買相應(yīng)的模體。標(biāo)準(zhǔn)模體一般包括定模板、動(dòng)模板、墊塊、頂出固定板、頂板、導(dǎo)柱、導(dǎo)套、復(fù)位桿等。標(biāo)準(zhǔn)模架有12種結(jié)構(gòu)，15876種規(guī)格。在本次設(shè)計(jì)中，澆口套、導(dǎo)柱、導(dǎo)套、頂桿、水嘴都采用標(biāo)準(zhǔn)件，可以外購(gòu)?？傃b圖主視圖如圖所示：
圖 8-1 定模板
圖 8-2 動(dòng)模板
圖 8-3 裝配三維圖
圖 8-4 總裝配二維圖
結(jié)論
為期一個(gè)學(xué)期的畢業(yè)設(shè)計(jì)即將結(jié)束，也就意味著我的大學(xué)生活即將結(jié)束，但在這一個(gè)學(xué)期的時(shí)間里我學(xué)到了很多知識(shí)和技能。
雖然每學(xué)期都安排了課程設(shè)計(jì)或者實(shí)習(xí)，但是沒(méi)有一次課程設(shè)計(jì)能與此次相比，設(shè)計(jì)限定了時(shí)間長(zhǎng)，而且是一人一個(gè)課題要求更為嚴(yán)格，任務(wù)更加繁多、細(xì)致、要求更加嚴(yán)格、設(shè)計(jì)要求的獨(dú)立性更加高。要我們充分利用在校期間所學(xué)的課程的專業(yè)知識(shí)理解、掌握和實(shí)際運(yùn)用的靈活度。在對(duì)設(shè)計(jì)的態(tài)度上的態(tài)度上是認(rèn)真的積極的。
通過(guò)近一學(xué)期畢業(yè)設(shè)計(jì)的學(xué)習(xí)，給我最深的感受就是我的設(shè)計(jì)思維得到了很大的鍛煉與提高。作為一名設(shè)計(jì)人員要設(shè)計(jì)出有創(chuàng)意而功能齊全的產(chǎn)品，就必須做一個(gè)生活的有心人。多留心觀察思考我們身邊的每一個(gè)機(jī)械產(chǎn)品，只有這樣感性認(rèn)識(shí)豐富了，才能使我們的設(shè)計(jì)思路具有創(chuàng)造性。
謝辭
首先感謝吳國(guó)洪老師在我完成該論文過(guò)程中給予的悉心指導(dǎo)，指出本人設(shè)計(jì)中的錯(cuò)誤與不足，使得本人能按時(shí)完成本課題的設(shè)計(jì)。并與其他同學(xué)的共同討論下，掌握了注塑模設(shè)計(jì)基本原則以及設(shè)計(jì)中對(duì)軟件的應(yīng)用能力。
設(shè)計(jì)中還引用了不少工廠的經(jīng)驗(yàn)以及多位專家學(xué)者的著作，從中學(xué)到了很多設(shè)計(jì)技巧。使我初步認(rèn)識(shí)到了以后工作中可能出現(xiàn)的問(wèn)題，如何去解決，這將對(duì)我以后的工作有很好的幫助作用，在這里一并表示感謝。
最后，通過(guò)本設(shè)計(jì)我鞏固了所學(xué)專業(yè)知識(shí)，并得到了不少心得。但由于是第一次系統(tǒng)的做這樣規(guī)模的設(shè)計(jì)，會(huì)有不少缺點(diǎn)和錯(cuò)誤，歡迎審核答辯的老師批評(píng)指正，在此再次表示感謝。
參考文獻(xiàn)
[1] 黃毅宏 模具制造工藝. 北京：機(jī)械工業(yè)出版社 1999
[2] 周四新,和清芳 Pro/ENGINEER野火版基礎(chǔ)設(shè)計(jì). 北京:機(jī)械工業(yè)出版社 2004
[3] 中國(guó)機(jī)械工業(yè)教育協(xié)會(huì)組編 塑料模設(shè)計(jì)與制造. 北京:機(jī)械工業(yè)出版社 2005
[4] 馬廣、王志明 模具CAD/CAM項(xiàng)目化實(shí)訓(xùn)教程. 北京：科學(xué)出版社 2009
[5] 伍先明等 塑料模具設(shè)計(jì)指導(dǎo). 北京：國(guó)防工業(yè)出版社 2006.5
[6] 李學(xué)鋒等 模具設(shè)計(jì)與制造實(shí)訓(xùn)教程. 北京：化學(xué)工業(yè)出版社 2004
[7] 黃虹 塑料成型加工與模具. 北京：化學(xué)工業(yè)出版社 2006
英文原文
Session VA4
I ntelligent Mold Design Tool For Plastic Injection Molding
Jagannath Yammada, Terrence L. Chambers, Suren N. Dwivedi
Department of Mechanical Engineering
University of Louisiana at Lafayette
Abstract
Plastic Injection molding is one of the most popular manufacturing processes for making thermoplastic products, and mold design is a key aspect of the process. Design of molds requires knowledge, expertise and most importantly experience in the field. When one of these is lacking, selection of an appropriate mold for manufacturing a plastic component is done on a trial-and-error basis. This increases the cost of production and introduces inconsistencies in the design.
This paper describes the development of an intelligent mold design tool. The tool captures knowledge about the mold design process and represents the knowledge in logical fashion. The knowledge acquired will be deterministic and non-deterministic information about the mold design process. Once developed the mold design tool will guide the user in selecting an appropriate mold for his plastic part based on various client specifications.
Introduction
The plastic injection molding process demands knowledge, expertise and, most important, experience for its successful implementation. Often it is the molding parameters that control the efficiency of the process. Effectively controlling and optimizing these parameters during themanufacturing process can achieve consistency, which takes the form of part quality and part cost.
The level of experience of the manufacturer(s) determines how effectively the process parameters are controlled. This sometimes leads to inconsistency introduced by human error. There is also the case where there is inexperience, shortage of time, resources and little scope for innovation. Knowledge-based engineering provides a feasible solution to all these problems by creating what is called an “intelligent model” of the problem.
1 IKEM
Intelligent Knowledge based Engineering modules for the plastic injection molding process (IKEM) is a software technology that is a step ahead of the concurrent engineering and CAD/CAM systems. It integrates current knowledge about the design and manufacturing processes and helps to reduce several man-hours by reducing engineering changes in the design phase of product development by giving users instruction about various design aspects. The system will be used for injection molding design, design iterations, and process integration. The current process consists of many manual computations, CAD graphical constructions, and experience attained from previous projects. Once the engineer completes the design, it will be evaluated for performance. The IKEM project has been divided into three major modules.
1. The cost estimation module
2. The mold design module
3. The Manufacturing module
Input to the IKEM system is of two forms. Input in the form of a CAD model (Pro-E file) and input given at the User Interface form. Figure 1 illustrates the kind of input that goes into each module and the output given to the user.
Figure 1. Organization of the IKEM Project
2 Intelligent Mold Design Tool
The mold design tool in its basic form is a Visual Basic application taking input from a text file that contains information about the part and a User Input form. The text file contains information about the part geometry parsed from a Pro/E information file. The input is used to estimate the dimensions of mold and variousother features.
2.1 Literature Review
Design of molds is another stage of the injection molding process where the experience of an engineer largely helps automate the process and increase its efficiency. The issue that needs attention is the time that goes into designing the molds. Often, design engineers refer to tables and standard handbooks while designing a mold, which consumes lot of time. Also, a great deal of time goes into modeling components of the mold in standard CAD software. Differen
researchers have dealt with the issue of reducing the time it takes to design the mold in different ways. Koelsch and James have employed group technology techniques to reduce the mold design time. A unique coding system that groups a class of injection molded parts, and the tooling required ininjection molding is developed which is general and can be applied to other product lines.
A software system to implement the coding system has also been developed. Attempts were also directed towards the automation of the mold design process by capturing experience and knowledge of engineers in the field. The development of a concurrent mold design system is one such approach that attempts to develop a systematic methodology for injection mold design processes in a concurrent engineering environment. The objective of their research was to develop a mold development process that facilitates concurrent engineering-based practice, and to develop a knowledge-based design aid for injection molding mold design that accommodates manufacturability concerns, as well as product requirements.
Researchers have been trying to automate the mold design process either by capturing only the deterministic information on the mold design process or the non-deterministic information, in various ways. This research uniquely attempts to develop a mold design application that captures information in both forms; deterministic and non-deterministic.
2.2 Approach Adopted
In order to develop an intelligent mold design tool, the conventional method of designing molds is studied. The application developer and the design engineer work together in designing a mold for a particular plastic part. During this time, the approach adopted by the engineer to select the mold base is closely observed and aspects of the selection process that require his knowledge/experience are identified. Also, there will be times when the engineer will refer to tables and handbooks in order to standardize his selection process. This time consuming process is also recorded to incorporate it later in the application.
Formulating the problem for the application in terms of inputs and outputs is the next stage. This involves defining what information about the mold layout is most required for the user and also the minimum number of inputs that can be taken from him to give those outputs.
In injection molding, the polymer melt at high temperature is injected into the mold under high pressure [1]. Thus, the mold material needs to have thermal and mechanical properties capa ble of withstanding the temperatures and pressures of the mold ing cycle. The focus of many studies has been to create the
injection mold directly by a rapid prototyping (RP) process. By eliminating multiple steps, this method of tooling holds the best promise of reducing the time and cost needed to create low-volume quantities of parts in a production material. The potential of integrating injection molding with RP technologies has been demonstrated many times. The properties of RP molds are very different from those of traditional metal molds. The key differ ences are the properties of thermal conductivity and elastic mod ulus (rigidity). For example, the polymers used in RP-fabricated stereolithography (SL) molds have a thermal conductivity that is less than one thousandth that of an aluminum tool. In using RP technologies to create molds, the entire mold design and injection-molding process parameters need to be modi?ed and optimized from traditional methodologies due to the completely different tool material. However, there is still not a fundamen tal understanding of how the modi?cations to the mold tooling method and material impact both the mold design and the injec tion molding process parameters. One cannot obtain reasonable results by simply changing a few material properties in current models. Also, using traditional approaches when making actual parts may be generating sub-optimal results. So there is a dire need to study the interaction between the rapid tooling (RT) pro cess and material and injection molding, so as to establish the mold design criteria and techniques for an RT-oriented injection molding process.
In addition, computer simulation is an effective approach for predicting the quality of molded parts. Commercially available simulation packages of the traditional injection molding process have now become routine tools of the mold designer and pro cess engineer [2]. Unfortunately, current simulation programs for conventional injection molding are no longer applicable to RP molds, because of the dramatically dissimilar tool material. For instance, in using the existing simulation software with alu minum and SL molds and comparing with experimental results, though the simulation values of part distortion are reasonable for the aluminum mold, results are unacceptable, with the error exceeding 50%. The distortion during injection molding is due to shrinkage and warpage of the plastic part, as well as the mold. For ordinarily molds, the main factor is the shrinkage and warpage of the plastic part, which is modeled accurately in cur rent simulations. But for RP molds, the distortion of the mold has potentially more in?uence, which have been neglected in current models. For instance, [3] used a simple three-step simulation process to consider the mold distortion, which had too much deviation.
In this paper, based on the above analysis, a new simula tion system for RP molds is developed. The proposed system focuses on predicting part distortion, which is dominating defect in RP-molded parts. The developed simulation can be applied as an evaluation tool for RP mold design and process opti mization. Our simulation system is veri?ed by an experimental example.
Although many materials are available for use in RP tech nologies, we concentrate on using stereolithography (SL), the original RP technology, to create polymer molds. The SL pro cess uses photopolymer and laser energy to build a part layer by layer. Using SL takes advantage of both the commercial domi nance of SL in the RP industry and the subsequent expertise base that has been developed for creating accurate, high-quality parts. Until recently, SL was primarily used to create physical models for visual inspection and form-?t studies with very limited func tional applications. However, the newer generation stereolitho graphic photopolymers have improved dimensional, mechanical and thermal properties making it possible to use them for actual functional molds.
Based on the information gathered in the mold design exercise, the conventions followed by the engineer are transformed into if-then rules. Decision tables are used to account for all possible cases that arise when dealing with a particular aspect of the mold design process. The rules so framed are then organized into modules interacting with each other, using an application development environment. Finally the application is tested for its validity when it comes to designing molds for plastic parts manufactured in the industry.
2.3 Selection of Appropriate Mold Base
Typically, selection of appropriate mold base for manufacturing a plastic part involves
Estimating the number of cavities
The number of cavities is decided depending on the number of parts required within a given time. There are also other issues like the plasticizing capacity of the machine, reject rate etc that affect the number of cavities to be present in the mold base.
Deciding on the presence of inserts and their dimensions
Inserts facilitate the reusability of the mold base and therefore help in reducing cost of manufacturing. When it comes to selecting the dimensions and the number, a decision is made depending on the reusability of existing old inserts and cost of ordering new ones.
Determining the size and location of runners
The runner size depends on the material being molded. Although there are other considerations material properties determines the channel size required for its flow. Location of runners mainly depends on the topology of runners being used. Though a circular runner system is always preferable, the branched runner system that avoids runner balancing is the one most widely used.
Determining the diameter of sprue
The diameter of the sprue is decided based on the size of the mold, number of cavities, or the amount of plastic that is to be filled within a given time.
Locating gates
Plastic enters the cavity at a point where it can uniformly fill the cavity. A gate can be located at any point on the perimeter of a circular cavity but has to enter at the midsection when it comes to filling rectangular cavities.
Determining the size and location of water lines
Water lines are located at standard distances form each other and from any wall in the mold. The convention is not to locate a waterline within one diameter range on the mold wall.
Deciding mold dimensions based on above conclusions
Based on all the above decisions the approximate mold dimensions can be estimated and rounded off to the nearest catalog number. Considering all the above aspects before even modeling the mold base reduces the cost and time that go into redesigning.
The emergence of mold can be traced back thousands of years ago, pottery and bronze foundry, but the large-scale use is with the rise of modern industry and developed.The 19th century, with the arms industry (gun's shell), watch industry, radio industry, dies are widely used. After World War II, with the rapid development of world economy, it became a mass production of household appliances, automobiles, electronic equipment, cameras, watches and other parts the best way. From a global perspective, when the United States in the forefront of stamping technology - many die of advanced technologies, such as simple mold, high efficiency, mold, die and stamping the high life automation, mostly originated in the United States; and Switzerland, fine blanking, cold in Germany extrusion technology, plastic processing of the Soviet Union are at the world advanced. 0's, mold industry focus is based on subscriber demand, production can meet the product requirements of the mold. Multi-die design rule of thumb, reference has been drawing and perceptual knowledge, on the design of mold parts of a lack of real understanding of function. From 1955 to 1965, is the pressure processing of exploration and development of the times - the main components of the mold and the stress state of the function of a mathematical sub-bridge, and to continue to apply to on-site practical knowledge to make stamping technology in all aspects of a leap in development. The result is summarized mold design principles, and makes the pressure machine, stamping materials, processing methods, plum with a structure, mold materials, mold manufacturing method, the field of automation devices, a new look to the practical direction of advance, so that pressing processing apparatus capable of producing quality products from the first stage.
Into the 70's to high speed, launch technology, precision, security, development of the second stage. Continue to emerge in this process a variety of high efficiency, business life, high-precision multi-functional automatic school to help with. Represented by the number of working places as much as other progressive die and dozens of multi-station transfer station module. On this basis, has developed both a continuous pressing station there are more slide forming station of the press - bending machine. In the meantime, the Japanese stand to the world's largest - the mold into the micron-level precision, die life, alloy tool steel mold has reached tens of millions of times, carbide steel mold to each of hundreds of millions of times p minutes for stamping the number of small presses usually 200 to 300, up to 1200 times to 1500 times. In the meantime, in order to meet product updates quickly, with the short duration (such as cars modified, refurbished toys, etc.) need a variety of economic-type mold, such as zinc alloy die down, polyurethane rubber mold, die steel skin, also has been very great development.
From the mid-70s so far can be said that computer-aided design, supporting the continuous development of manufacturing technology of the times. With the precision and complexity of mold rising, accelerating the production cycle, the mold industry, the quality of equipment and personnel are required to improve. Rely on common processing equipment, their experience and skills can not meet the needs of mold. Since the 90's, mechanical and electronic technologies in close connection with the development of NC machine tools, such as CNC wire cutting machine, CNC EDM, CNC milling, CNC coordinate grinding machine and so on. The use of computer automatic programming, control CNC machine tools to improve the efficiency in the use and scope. In recent years, has developed a computer to time-sharing by the way a group of direct management and control of CNC machine tools NNC system.
With the development of computer technology, computers have gradually into the mold in all areas, including design, manufacturing and management. International Association for the Study of production forecasts to 2000, as a means of links between design and manufacturing drawings will lose its primary role. Automatic Design of die most fundamental point is to establish the mold standard and design standards. To get rid of the people of the past, and practical experience to judge the composition of the design center, we must take past experiences and ways of thinking, for series, numerical value, the number of type-based, as the design criteria to the computer store. Components are dry because of mold constitutes a million other differences, to come up with a can adapt to various parts of the design software almost impossible. But some products do not change the shape of parts, mold structure has certain rules, can be summed up for the automatic design of software. If a Japanese company's CDM system for progressive die design and manufacturing, including the importation of parts of the figure, rough start, strip layout, determine the size and standard templates, assembly drawing and parts, the output NC program (for CNC machining Center and line cutting program), etc., used in 20% of the time by hand, reduce their working hours to 35 hours; from Japan in the early 80s will be three-dimensional cad / cam system for automotive panel die. Currently, the physical parts scanning input, map lines and data input, geometric form, display, graphics, annotations and the data is automatically programmed, resulting in effective control machine tool control system of post-processing documents have reached a high level; computer Simulation (CAE) technology has made some achievements.At high levels, CAD / CAM / CAE integration, that data is integrated, can transmit information directly with each other. Achieve network. Present.Only a few foreign manufacturers can do it.
2.4 Formulation of the Problem
Based on issues that require human knowledge/experience, and aspects of mold design that consume time referring to tables, data sheets etc., the problem for developing the application is defined as shown in Figure 2.
While most of the input, like the number of cavities, cavity image dimensions, cycle time are based on the client specifications, other input like the plasticizing capacity, shots per minute etc., can be obtain