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河南機(jī)電高等?？茖W(xué)校畢業(yè)設(shè)計(jì)說明書/論文
蓋塞注塑模具設(shè)計(jì)
第1章 模具工藝規(guī)程的編制
該塑件是一個(gè)蓋塞，其零件圖如圖1-1所示。該塑件材料采用PS（聚苯乙烯塑料），生產(chǎn)類型為大批量生產(chǎn)。
1.1塑件的工藝性分析
1.1.1塑件的原材料分析
1.1.1.1.塑件的原材料分析。塑件材料采用PS（聚苯乙烯塑料），該塑料從使用性能上看，其電絕緣性（尤其是高頻絕緣性）優(yōu)良，無色透明，著色性，耐水性，化學(xué)穩(wěn)定性良好，其強(qiáng)度一般，但是質(zhì)脆，易產(chǎn)生應(yīng)力碎裂，不耐苯，汽油等有機(jī)溶劑。從成型性能上看，該塑料屬于無定形料，吸濕性小，不易分解，但熱膨脹系數(shù)大。易產(chǎn)生內(nèi)應(yīng)力。流動(dòng)性較好，可用螺桿式或柱塞式注射機(jī)成型。噴嘴用直通式或自鎖式，但應(yīng)防止飛邊，宜用高料溫，高模溫低注塑壓力，延長注射時(shí)間有利于降低內(nèi)應(yīng)力，防止縮孔，變形?？梢圆捎酶鞣N形式的澆口，澆口與塑件圓弧連接，以免去除澆口時(shí)損壞塑件。要求塑件脫模斜度大，頂出均勻，塑件壁厚均勻，最好不帶嵌件，各面應(yīng)以圓弧連接，不允許有缺口，尖角。塑件壁厚均勻，不帶嵌件，不須頂出機(jī)構(gòu)，因此在成型時(shí)注意控制成型溫度，其塑件較容易成型。
1.1.1. 2.塑件的結(jié)構(gòu)和尺寸精度及表面質(zhì)量分析
圖1-1 蓋塞零件圖
（1） 結(jié)構(gòu)分析
從零件圖上分析，該塑件的總體形狀為圓柱形。在長度方向上的一側(cè)有一段M30㎜的螺紋，長8㎜。設(shè)計(jì)時(shí)需要采用螺紋抽芯機(jī)構(gòu)。在另一側(cè)的端面上有大小相同的均布的4×Ф8的孔。該塑件的結(jié)構(gòu)形狀尺寸較簡單，因此，模具設(shè)計(jì)較容易，設(shè)計(jì)時(shí)為了成型螺紋必須設(shè)置齒輪，齒條抽芯機(jī)構(gòu)，來實(shí)現(xiàn)螺紋成型。該模具設(shè)計(jì)屬于中等復(fù)雜程度。
（2） 尺寸精度分析
該塑件的尺寸精度較簡單，未注尺寸公差等級，其公差等級取MT5。各尺寸精度要求的較低，對應(yīng)模具相關(guān)零件的尺寸加工能夠保證。
從塑件的壁厚上來看，壁厚最大處為5㎜，最小處壁厚為2.5㎜，壁厚差為2.5㎜，其壁厚在成型范圍內(nèi)，塑件較容易成型。
（3） 表面質(zhì)量分析
該塑件的表面除了要求沒有缺陷，毛刺外，沒有特別的表面質(zhì)量要求，故比較容易成型。
綜合上述分析可以看出，注塑時(shí)在工藝參數(shù)控制好的情況下，零件的成型要求可以得到保證。
1.2計(jì)算塑件的體積和質(zhì)量
計(jì)算塑件的質(zhì)量是為了選用注塑機(jī)以及確定模具型腔數(shù)量。
計(jì)算塑件的體積V
V=V1+V2+V3
≈8731mm
計(jì)算塑件的質(zhì)量，根據(jù)設(shè)計(jì)手冊，可以查得PS塑料的密度為
ｐ=1.05g/㎝。故塑件的質(zhì)量M
M=ｐV
=1.05×10×8731g
≈9.06g
模具采用一模兩腔的結(jié)構(gòu)，考慮其外形尺寸，以及注塑時(shí)所需的壓力等情況，初步選用注塑機(jī)為XS-ZY-125型。
1.3塑件注塑工藝參數(shù)的確定
查找相關(guān)文獻(xiàn)，對PS塑料的成型工藝參數(shù)作如下選擇（試模時(shí)，根據(jù)
實(shí)際情況作適當(dāng)?shù)恼{(diào)整）：
注塑溫度：包括料筒溫度和噴嘴的溫度。
料筒溫度：后段溫度選用150℃；
中段溫度選用160℃；
后段溫度選用180℃；
噴嘴溫度：選用170℃；
模具溫度：選用45℃；
注塑壓力：選用80MPa；
注塑時(shí)間：選用40ｓ；
保壓壓力：選用60MPa；
保壓時(shí)間：選用30ｓ；
冷卻時(shí)間：選用40ｓ；
成型周期：110ｓ。
第2章注塑模的結(jié)構(gòu)設(shè)計(jì)
注塑模的結(jié)構(gòu)設(shè)計(jì)主要包括：分型面的選擇，模具型腔數(shù)目的確定，型腔的排列方式，冷卻水道的布局，澆口位置的設(shè)置，模具工作零件的結(jié)構(gòu)設(shè)計(jì)，側(cè)向分型與抽芯機(jī)構(gòu)的設(shè)計(jì)，推出、頂出機(jī)構(gòu)的設(shè)計(jì)等內(nèi)容。
2.1 分型面的選擇
分型面的選擇決定了模具的結(jié)構(gòu)，選擇時(shí)應(yīng)根據(jù)分型面選用原則和塑件的成型要求來選擇分型面。
該塑件為蓋塞，其表面質(zhì)量無特殊要求。塑件高度為23㎜，除一端有M30的螺紋外，其截面形狀簡單，如果選擇端面為分型面，在脫模時(shí)不容易螺紋抽芯，抽芯困難。如果選擇臺階處為分型面，脫模較容易，可以利用4×Ф8的孔止轉(zhuǎn)，減少了模具加工的難度，便于成型后取出塑件。故應(yīng)選用如下圖1-2所示的分型方式較為合理。
圖2-2 分型面的選擇
2.2 確定型腔的排列方式
該塑件在注塑時(shí)采用一模兩腔的形式，即模具需要兩個(gè)型腔。綜合考慮澆
注系統(tǒng)，模具結(jié)構(gòu)的復(fù)雜程度等因素，擬采用下圖1-3所示型腔排列方式。
圖1-3 型腔的排列方式
采用上圖所示的型腔排列方式便于設(shè)計(jì)齒輪，齒條螺紋抽芯機(jī)構(gòu)，其齒條布置在開模方向上，結(jié)構(gòu)較簡單，并且結(jié)構(gòu)較為緊湊。
2.3澆注系統(tǒng)的設(shè)計(jì)
2.3.1主流道設(shè)計(jì)
根據(jù)設(shè)計(jì)手冊查得XS-ZY-125型注塑機(jī)噴嘴的有關(guān)尺寸：
噴嘴的前端孔徑：ｄ0=Ф4㎜；
噴嘴的前端半徑： R0=S12㎜；
根據(jù)模具主流道與噴嘴的關(guān)系：
R=R0+（1～2）㎜；
D=ｄ0+（0.5～1）㎜；
故取主流道的球面半徑R=14㎜；
取主流道的小端直徑ｄ=5㎜.
為了便于將凝料從主流道中拔出，將主流道設(shè)計(jì)成圓錐形，其錐度取 1°～3°，該主流道錐度選取3°。經(jīng)換算得到主流道大端直徑D=9㎜。為了使熔料順利的進(jìn)入分流道，可以在主流道出料端設(shè)計(jì)半徑R=1㎜的圓弧過渡。
2.3.2分流道的設(shè)計(jì)
分流道的形狀以及尺寸的設(shè)計(jì)，根據(jù)塑件的體積，壁厚，形狀的復(fù)雜程度，注射速率，分流道長度等因素來確定。
因?yàn)樵撍芗欢蜯30的螺紋外，其形狀簡單，熔料填充型腔較容易。根據(jù)型腔的排列方式可知其分流道的長度較短，為了便于加工，選用半圓形截面形狀的分流道，查表選取半圓形截面半徑R=4㎜。
2.3.3澆口的設(shè)計(jì)
根據(jù)塑件的成型要求以及型腔的排列方式，選用側(cè)澆口較為合適。其澆口的截面形狀簡單，加工也比較方便。
進(jìn)料時(shí)考慮從臺階處進(jìn)料，并且在模具結(jié)構(gòu)上可以利用分型面排氣。采用矩形截面的側(cè)澆口，在澆口的連接處型腔的部位應(yīng)成圓角，有利于料流。
查表初選矩形截面尺寸為（ｂ×ｌ×ｈ）=1.2㎜×1.0㎜×0.8㎜，試模時(shí)加以修整。
2.3.4排氣槽的設(shè)計(jì)
因?yàn)槟＞叱叽巛^小擬采用分型面處排氣，即可滿足要求。
2.4 成型零件的結(jié)構(gòu)設(shè)計(jì)
2.4.1型腔的結(jié)構(gòu)設(shè)計(jì)
該塑件的模具結(jié)構(gòu)采用一模兩腔的形式，考慮其結(jié)構(gòu)的加工難易程度和材料的合理利用等因素，凹模擬采用與定模固定板作成一體，可以節(jié)省材料也能滿足使用要求。其結(jié)構(gòu)形式如零件圖01所示，圖中的孔分別用來安裝齒條和導(dǎo)柱孔。根據(jù)分流道與澆口的設(shè)計(jì)要求，分流道，主流道均可開設(shè)在定模固定板上，節(jié)省材料，也可以滿足使用要求。
2.4.2型芯的結(jié)構(gòu)設(shè)計(jì)
型芯主要是與型腔相結(jié)合構(gòu)成模具型腔，考慮其加工的難易程度，其型芯分為三個(gè)部分，一是成型螺紋部分的螺紋型環(huán)。二是成型端面圓孔的部分將其作成四個(gè)小型芯，便于加工。三是成型塑件內(nèi)部的形狀部分。其具體結(jié)構(gòu)形式如零件圖02.03.04所示。其中小型芯03與型芯04上的四個(gè)孔過盈配合。
第3章 模具設(shè)計(jì)的有關(guān)計(jì)算
查手冊可知，PS塑料的收縮率為S=0.1﹪～0.8﹪，故其平均收縮率為
Sｃｐ=（0.1+0.8）﹪/2=0.45﹪?？紤]生產(chǎn)實(shí)際，模具制造的公差選取
δｚ=Δ/3。
3.1型腔和型芯工作尺寸的計(jì)算
型腔，型芯工作尺寸計(jì)算如下表：
類別
模具零件名稱
塑件尺寸
計(jì)算公式
工作尺寸
型腔的尺寸
型腔
15
Hm1=Hmax+HmaxSmid﹪-C-0.5（Tｚ+Tｍ）
14.68
35
Dｍ=Dmax +Dmax Ｓmax﹪-Tｚ
34.84
型芯的尺寸
大型芯
Φ25
d =d +d Smax ﹪+Tz
25.27
17
Dm=Dmax+DmaxSmax﹪
-Tz
16.89
小型芯
6
Hm=Hmax+HmaxSmax﹪
-0.5(Tz+Tm)
5.92
Φ8
Dm=dmin+dminSmin﹪
+Tz
8.14
3.2螺紋型環(huán)徑向尺寸計(jì)算
螺紋的基本尺寸為M30㎜，為粗牙螺紋。查手冊可知，其螺距為
3.5㎜，中徑尺寸為27.727㎜，小徑尺寸為26.21㎜。中徑的制造公
差Δ中=0.03，大小徑的制造公差Δ中=0.04。
螺紋型環(huán)的中徑為
由公式Dm中=[Ds中+Ds中Scp-Δ中] 得
Dm中=[27.727+27.727×0.45﹪-0.15]
=27.7
螺紋型環(huán)的外徑為
由公式Dm外=[Ds外+Ds外Scp-1.2Δ中]
Dm外=[30+30×0.45﹪-1.2×0.2]
=27.73
螺紋型環(huán)的內(nèi)徑為：
由公式Dm內(nèi)=Ds內(nèi)Scp-Δ中]
=[26.211+26.211×0.45﹪-1.2×0.2]
=26.13
3.3 型腔底板厚度計(jì)算
在注塑成型過程中，型腔所受的力有塑料熔體的壓力，合模時(shí)的壓力開模時(shí)的拉力等。其中最主要的是塑料的熔體的壓力。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。對于該塑料，其強(qiáng)度不足是主要問題型腔底板厚度應(yīng)按強(qiáng)度條件計(jì)算。
由強(qiáng)度計(jì)算公式th= 得
th=
=21.4㎜
式中th—型腔底板的計(jì)算厚度（㎜）；
Pm—模腔的壓力（MPａ）；
ｒ—型腔內(nèi)孔半徑（㎜）；
б—材料許用應(yīng)力（MPａ）；
（材料為45鋼，其許用應(yīng)力160 MPａ）
3.4 螺紋抽芯機(jī)構(gòu)設(shè)計(jì)
該塑件的一端有一段M30的外螺紋，脫模時(shí)阻礙成型后塑件從模具中脫出，其成型螺紋的軸線與快模方向一致，設(shè)計(jì)時(shí)需要在齒輪齒條傳動(dòng)后再用圓錐齒輪或其他方式換向。在其塑件結(jié)構(gòu)上要求塑件或模具的一側(cè)又回轉(zhuǎn)又軸向運(yùn)動(dòng)，來實(shí)現(xiàn)塑件的自動(dòng)脫螺紋。該塑件模具設(shè)計(jì)擬采用動(dòng)模一側(cè)設(shè)置回轉(zhuǎn)運(yùn)動(dòng)，利用端面上的4×Φ8㎜的孔可以防止塑件隨螺紋型環(huán)一起旋轉(zhuǎn)當(dāng)止動(dòng)部分長度H和螺紋長度ｈ相等時(shí)，回轉(zhuǎn)終了即使沒有頂出機(jī)構(gòu)塑件也
能落下。其齒輪齒條脫螺紋機(jī)構(gòu)如下圖1-4所示，其旋轉(zhuǎn)方向如圖。
圖1-4 齒輪齒條脫螺紋機(jī)構(gòu)
模具的開模時(shí)所需的時(shí)間：
t = s/v
=270/40 s
=6.75s
由齒條直線運(yùn)動(dòng)的速度V與齒輪分度圓直徑ｄ，轉(zhuǎn)速ｎ之間的關(guān)系為
V=3.14dn/60 (mm/s)
選用與齒條嚙合的齒輪分度圓直徑為20㎜，
故n=60V/3.14d
≈3.8r/s
選取脫螺紋的時(shí)間為3ｓ，則螺紋型環(huán)的轉(zhuǎn)速為
n5=r/s
故齒輪1與齒輪5之間的傳動(dòng)比i為
i = n1/n5
=3.8/1r/s
=3.8r/s
則斜齒輪2的轉(zhuǎn)速為3.8 r/s；
齒輪5的轉(zhuǎn)速為1 r/s；
取斜齒輪2，3之間的傳動(dòng)比為2；
則齒輪4，5之間的傳動(dòng)比為
i 15 =i5/i23
=3.8/2
=1.9
齒輪3的轉(zhuǎn)速為 n 3=n2/i3
=3.8/2 r/s
=1.9 r/s
螺紋旋轉(zhuǎn)脫模力矩M，由公式
M=f cPSr2= f cP2r2
P2=1.5aE(Tf-Tj)(d2-d1)
=1.5×7×10 ×20.7×10 (90-60)(30 -26.211 )
=1811.4N
M= f cP2r2
=0.45×1811.4×(27.727/2)
=11297.7N㎜
式中a—塑料的線膨脹系數(shù)；
E—脫模溫度下，塑料的抗拉彈性模量（MPa）；
Tf—軟化溫度；
= Tｊ—脫模頂出時(shí)制品的溫度；
d—螺紋外徑；
d1—螺紋內(nèi)徑；
f c —脫模系數(shù)；
P2 —制品外螺紋齒形對鋼型芯牙形的軸向包緊力（N）；
r2 —螺紋中徑的半徑值；
直齒輪分度圓直徑的計(jì)算：
由公式d≥2.32
選用載荷系數(shù)K=1.3；
齒寬系數(shù)φｄ=0.8；
查得彈性影響系數(shù)ZE=189.8 ；
其齒輪材料選用45鋼，查得接觸疲勞強(qiáng)度極限[б]=470MPａ；
對于減速傳動(dòng)，其齒輪的齒數(shù)比等于傳動(dòng)比ｉ
ｕ=ｉ=1.9
選取齒輪5的齒數(shù)為30，
則大齒輪齒數(shù)Z2=ｕZ1
=30×1.9
=57
d ≥2.32
=36.3㎜
由公式
d1=×d
=×36.3㎜
=35㎜
查得式中載荷系數(shù)K=1.20；
取模數(shù)為標(biāo)準(zhǔn)值ｍ=1；
則分度圓直徑：d5=mZ5=30×1=30㎜
d4=mz4=57×1=57㎜
齒輪的寬度：b=φdd5
=30×0.8㎜
=24㎜
第4章 模具加熱和冷卻系統(tǒng)的計(jì)算
塑件在注塑成型時(shí)模具溫度為45℃，其溫度低于80℃。因而模具在結(jié)
構(gòu)上不需要設(shè)置加熱系統(tǒng)，是否需要冷卻系統(tǒng)做如下設(shè)計(jì)計(jì)算：
設(shè)定模具的平均工作溫度為45℃，用20℃的常溫水作為冷卻介質(zhì)，其
出口冷卻水溫度為25℃，其產(chǎn)量為（初算每三分鐘一套）0.36kg/h
4.1 求塑件在硬化時(shí)每小時(shí)釋放的熱量Q1
查有關(guān)文獻(xiàn)資料得到PS塑料的單位熱流量為27.2×10 J/kg
Q1=WQ2
=0.36×27.2×10J
=9.8×10J
根據(jù)熱平衡條件Qout=Qin可得
Mw=(Δim)/[cw(tout- tin)]
Mw=Ρv
V=(Δim)/ [cwρ(tout- tin)]
式中 mw —冷卻水每小時(shí)用量；
cw —冷卻水的比熱容（4.187KJ/kg℃）
tout —模具的出水口溫度；
tin —模具冷卻水進(jìn)水溫度；
V —冷卻水的體積；
V= (0.36×27.2×10)/[60×4.187×10×(25-20)]
=7.8×10mm/min
由體積流量V查表可知所需的冷卻水管的直徑很小。
由上述計(jì)算可知，因?yàn)槟＞呙糠昼娝璧睦鋮s水體積流量很小，故可不設(shè)定冷卻冷卻系統(tǒng)，依靠空冷的方式冷卻模具即可。
第5章 模具閉合高度的確定
在支承與固定零件中，其尺寸設(shè)計(jì)根據(jù)經(jīng)驗(yàn)確定：
取定模固定板（型腔板）的厚度40㎜。
固定板厚度取30㎜，墊板的厚度取50㎜；
支承板厚度取20㎜，支架的高度取60㎜；
因而模具的閉合高度H=H1+H2+H3+H4+H5
=40+30+50+20+60㎜
=200㎜
第6章 注塑機(jī)有關(guān)參數(shù)的校核
該模具的外形尺寸為350㎜×200㎜×200㎜，選用的XS-ZY-125型注塑機(jī)模板最大安裝尺寸370㎜×320㎜。故該注塑機(jī)能夠滿足模具的安裝要求。由上述計(jì)算可知模具的閉合高度H=200㎜。XS-ZY-125型注塑機(jī)所允許的最小模具厚度Hmin=150mm,最大模具閉合高度Hmax=300mm。模具的安裝條件：
Hmin≤H≤Hmax
150mm≤200mm≤300mm
即滿足模具的安裝條件。
查資料可知，XS-ZY-125型注塑機(jī)的最大開模行程S=270㎜，模具
頂出塑件要求開模行程
S=H1+H2+（5～10）㎜
=15+8+10㎜
=33㎜
注塑機(jī)的開模行程能夠滿足頂出塑件的要求。
由于螺紋的抽芯距離較短，不會(huì)過大的增加開模行程，注塑機(jī)的開模行程足夠。
經(jīng)過驗(yàn)證，XS-ZY-125型注塑機(jī)能夠滿足使用要求，可以采用。
第7章 結(jié)構(gòu)與輔助零部件的設(shè)計(jì)
7.1 導(dǎo)柱的選用
導(dǎo)柱選用帶頭導(dǎo)柱，由導(dǎo)柱直徑與模板外形尺寸關(guān)系，其尺寸選用
Φ16㎜×100㎜×25㎜，材料選用20鋼。GB/T4169.4-1984
其結(jié)構(gòu)形式如下圖1-5所示：
圖1-5 導(dǎo)柱的結(jié)構(gòu)形式
其導(dǎo)柱的安裝時(shí)與模板之間的配合的公差取IT7級，安裝沉孔直徑比導(dǎo)柱直徑大（1～2）㎜。
7.2 導(dǎo)套的選用
導(dǎo)套選用直導(dǎo)套，與導(dǎo)柱的配合。尺寸選Φ16×40，材料選用20鋼。GB/T4169.2-1984 其結(jié)構(gòu)形式如下圖1-6所示：
圖1-6 導(dǎo)套的結(jié)構(gòu)形式
導(dǎo)套與模板的安裝孔徑之間的配合公差I(lǐng)T7級，安裝后下平面磨平。
該模具由于塑件的精度要求較低，可以采用兩根導(dǎo)柱即可滿足塑件的精度，兩根導(dǎo)柱，導(dǎo)套尺寸選用相同直徑，不對稱布置。其布置形式如零件圖定模固定板上所示。
第8章 繪制模具總裝配圖和非標(biāo)零件工作圖
該蓋塞注塑模具總裝配圖，非標(biāo)零件圖如附圖所示。
蓋塞注塑模具的工作原理：開模時(shí)，塑件被帶到動(dòng)模上的同時(shí)，
定板在定模上的齒條，與在動(dòng)模上的齒輪的作用下，使螺紋型環(huán)16沿著塑件脫出方向旋轉(zhuǎn)，至塑件完全脫出螺紋型環(huán)16為止。
第9章 注塑模主要零件加工工藝規(guī)程的編制
主要零件的加工工藝過程如下表1-2，1-3，1-4所示。
第10章 模具的裝配與調(diào)試
10.1 模具的裝配
由于型芯，型腔在合模后很難找正相對位置，故應(yīng)先安裝齒輪，齒條
作為安裝基準(zhǔn)。裝配過程如下：
（1） 裝配前按照零件圖檢驗(yàn)其工作零件的尺寸及其他零件是否齊備；
（2） 將型芯1裝配到型芯15上，保證軸線與端面的垂直度；
（3） 將導(dǎo)套壓入到定模固定板2中，并保證其軸線與端面的垂直度；
（4） 將齒條13壓入到定模固定板2中，保證其垂直度；
（5） 將圓套7壓入到支架14中；
（6） 將齒輪軸6穿過支架上的圓套7后，安放在齒條13上，找正位置，將其放上支座25。在其銷釘孔打入銷釘，擰緊螺釘；
（7） 將圓錐齒輪4裝在齒輪軸6的端面上，并用鍵5固定；
（8） 將導(dǎo)柱打入固定板19中，保證軸線與端面的垂直度；
（9） 型芯15套入螺紋型環(huán)16中后，放入固定板19中定位；
（10） 將圓錐齒輪套入固定軸9中，將固定軸定位于固定板19中；
（11） 在固定板6與支撐板10之間加上墊板20，調(diào)整圓錐齒輪和螺紋型環(huán)，使其正確嚙合后，將其用螺母固定。在固定板19與支撐板10以及墊板上投窩，打孔，擰緊螺釘；
（12） 最后，將支架14與固定板用螺釘固定；
（13） 裝配完成，試模。
10.2試模
（1） 試模前，先對設(shè)備的油路，水路以及電路進(jìn)行檢查；
（2） 選取的原料必須合格，根據(jù)選用的工藝參數(shù)將料筒和噴嘴加熱；
（3） 開始試模時(shí)，應(yīng)該先選擇選定的壓力，溫度和注塑時(shí)間的條件下成型，制品不符合要求然后按壓力，注塑時(shí)間，溫度
這樣的先后順序變動(dòng)，注意一次只改變一個(gè)參數(shù)；
（4） 在試模過程中作出詳細(xì)的記錄，并將結(jié)果填入試模記錄卡，注明模具是否合格，如果需要返修，提出返修意見；
（5） 通過不斷的試模和返修，生產(chǎn)出合格的制件后，將模具清理干凈，涂上防銹油，入庫。
10.3 試?？赡墚a(chǎn)生的問題及改善措施
試模中所獲得的樣件是對模具整體質(zhì)量的一個(gè)全面反映。以檢驗(yàn)樣件來修正和驗(yàn)收模具，是塑料模具這種特殊產(chǎn)品的特殊性。首先，在初次試模中我們最常遇到的問題是根本得不到完整的樣件。常因塑件被粘附于模腔內(nèi)，或型芯上，甚至因流道粘著制品被損壞。這是試模首先應(yīng)當(dāng)解決的問題。
10.3.1 粘著模腔
制品粘著在模腔上，是指塑件在模具開啟后，與設(shè)計(jì)意圖相反，離開型芯一側(cè)，滯留于模腔內(nèi)，致使脫模機(jī)構(gòu)失效，制品無法取出的一種反?，F(xiàn)象。其主要原因是：
（1） 注射壓力過高，或者注射保壓壓力過高。
（2） 注射保壓和注射高壓時(shí)間過長，造成過量充模。
（3） 冷卻時(shí)間過短，物料未能固化。
（4） 模芯溫度高于模腔溫度，造成反向收縮。
（5） 型腔內(nèi)壁殘留凹槽，或分型面邊緣受過損傷性沖擊，增加了脫模阻力。
10.3.2 粘著模芯
（1） 注射壓力和保壓壓力過高或時(shí)間過長而造成過量充模。
（2） 冷卻時(shí)間過長，制件在模芯上收縮量過大。
（3） 模腔溫度過高，使制件在設(shè)定溫度內(nèi)不能充分固化。
（4） 機(jī)筒與噴嘴溫度過高，不利于在設(shè)定時(shí)間內(nèi)完成固化。
（5） 可能存在不利于脫模方向的凹槽或拋光痕跡需要改進(jìn)。
10.3.3 粘著主流道
（1） 閉模時(shí)間太短，使主流道物料來不及充分收縮。
（2） 料道徑向尺寸相對制品壁厚過大，冷卻時(shí)間內(nèi)無法完成料道物
料的固化。
（3） 主流道襯套區(qū)域溫度過高，無冷卻控制，不允許物料充分收縮。
（4） 主流道襯套內(nèi)孔尺寸不當(dāng)，未達(dá)到比噴嘴孔大0.5～1 ㎜。
（5） 主流道拉料桿不能正常工作。
一旦發(fā)生上述情況，首先要設(shè)法將制品取出模腔（芯），不惜破壞制件，保護(hù)模具成型部位不受損傷。仔細(xì)查找不合理粘模發(fā)生的原因，一方面要對注射工藝進(jìn)行合理調(diào)整；另一方面要對模具成型部位進(jìn)行現(xiàn)場修正，直到認(rèn)為達(dá)到要求，方可進(jìn)行二次注射。
10.3.4 成型缺陷
當(dāng)注射成型得到了近乎完整的制件時(shí)，制件本身必然存在各種各樣的缺陷，這種缺陷的形成原因是錯(cuò)綜復(fù)雜的，一般很難一目了然，要綜合分析，找出其主要原因來著手修正，逐個(gè)排出，逐步改進(jìn)，方可得到理想的樣件。下面就對度模中常見的成型制品主要缺陷及其改進(jìn)的措施進(jìn)行分析。
（1） 注射填充不足
所謂填充不足是指在足夠大的壓力、足夠多的料量條件下注射不滿型腔而得不到完整的制件。這種現(xiàn)象極為常見。其主要原因有：
a. 熔料流動(dòng)阻力過大
這主要有下列原因：主流道或分流道尺寸不合理。流道截面形狀、尺寸不利于熔料流動(dòng)。盡量采用整圓形、梯形等相似的形狀，避免采用半圓形、球缺形料道。熔料前鋒冷凝所致。塑料流動(dòng)性能不佳。制品壁厚過薄。
b. 型腔排氣不良
這是極易被忽視的現(xiàn)象，但以是一個(gè)十分重要的問題。模具加工精度超高，排氣顯得越為重要。尤其在模腔的轉(zhuǎn)角處、深凹處等，必須合理地安排頂桿、鑲塊，利用縫隙充分排氣，否則不僅充模困難，而且易產(chǎn)生燒焦現(xiàn)象。
c. 鎖模力不足
因注射時(shí)動(dòng)模稍后退，制品產(chǎn)生飛邊，壁厚加大，使制件料量增加而引起的缺料。應(yīng)調(diào)大鎖模力，保證正常制件料量。
（2） 溢邊（毛刺、飛邊、批鋒）
與第一項(xiàng)相反，物料不僅充滿型腔，而且出現(xiàn)毛刺，尤其是在分型面處毛刺更大，甚至在型腔鑲塊縫隙處也有毛刺存在，其主要原因有：
a. 注射過量
b. 鎖模力不足
c. 流動(dòng)性過好
d. 模具局部配合不佳
e. 模板翹曲變形
（3） 制件尺寸不準(zhǔn)確
初次試模時(shí)，經(jīng)常出現(xiàn)制件尺寸與設(shè)計(jì)要求尺寸相差較大。這時(shí)不要輕易修改型腔，應(yīng)行從注射工藝上找原因:
a. 尺寸變大
注射壓力過高，保壓時(shí)間過長，此條件下產(chǎn)生了過量充模，收縮率趨向小值，使制件的實(shí)際尺寸偏大；模溫較低，事實(shí)上使熔料在較低溫度的情況下成型，收縮率趨于小值。這時(shí)要繼續(xù)注射，提高模具溫度降低注射壓力，縮短保壓時(shí)間，制件尺寸可得到改善。
b. 尺寸變小
注射壓力偏低、保壓時(shí)間不足，制在冷卻后收縮率偏大，使制件尺寸變??；模溫過高，制件從模腔取出時(shí)，體積收縮量大，尺寸偏小。此時(shí)調(diào)整工藝條件即可。通過調(diào)整工藝條件，通常只能在極小范圍內(nèi)使尺寸京華，可以改變制件相互配合的松緊程度，但難以改變公稱尺寸。
10.3.5 調(diào)整措施
調(diào)整時(shí)應(yīng)注意調(diào)節(jié)進(jìn)料速度，增加排氣孔，正確設(shè)計(jì)澆注系統(tǒng)。注意控制成型周期。
結(jié)論
此次畢業(yè)設(shè)計(jì)的題目為蓋塞注塑模具設(shè)計(jì)，蓋塞為生活中常用零件，需要大批量生產(chǎn)，以降低生產(chǎn)成本，該塑件對精度要求較低，便于加工生產(chǎn)。為該零件設(shè)計(jì)的注塑模采用了螺紋抽芯機(jī)構(gòu)。其中螺紋的成型較復(fù)雜。該模具采用一模兩腔，提高了生產(chǎn)效率，由于制件尺寸較小，采用空冷及能滿足冷卻要求，故此模具未開設(shè)流道。通過計(jì)算該模具能夠滿足零件的生產(chǎn)要求，結(jié)構(gòu)較為合理，由于本人能力所學(xué)知識有限，定有許多不足之處，望老師批評指正。
編號：
畢業(yè)設(shè)計(jì)(論文)外文翻譯
（原文）
學(xué) 院： 機(jī)電工程學(xué)院
專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化
學(xué)生姓名： 韋良華
學(xué) 號： 1000110129
指導(dǎo)教師單位： 機(jī)電工程學(xué)院
姓 名： 陳虎城
職 稱： 助教
2014年 5 月 26 日
a r t i c l e i n f o
Article history:
Received 25 October 2010
Received in revised form
12 January 2011
Accepted 14 January 2011
Available online 21 January 2011
Keywords:
Microcellular injection molding
Plastic foaming
Swirl-free surface
a b s t r a c t
Microcellular injection molding is the manufacturing method used for producing foamed plastic parts.Microcellular injection molding has many advantages including material, energy, and cost savings as well as enhanced dimensional stability. In spite of these advantages, this technique has been limited by its propensity to create parts with surface defects such as a rough surface or gas flow marks. Methods for improving the surface quality of microcellular plastic parts have been investigated by several researchers. This paper describes a novel method for achieving swirl-free foamed plastic parts using the microcellular injection molding process. By controlling the cell nucleation rate of the polymer/gas solution through material formulation and gas concentration, microcellular injection molded parts free of surface defects were achieved. This paper presents the theoretical background of this approach as well as the experimental results in terms of surface roughness and profile, microstructures, mechanical properties, and dimensional stability.
l Introduction
The commercially available microcellular injection molding process (a.k.a. the MuCell Process) consists of four distinctive steps, namely, gas dissolution, nucleation, cell growth, and shaping [1]. In the gas dissolution stage, polymer in the injection barrel is mixed with supercritical fluid (SCF) nitrogen, carbon dioxide, or another type of gas using a special screw which is designed to maximize the mixing and dissolving of the gas in the polymer melt. During injection, a large number of nucleation sites (orders of magnitude higher than conventional foaming processes) are formed by a rapid and substantial pressure drop as the polymer/gas solution is injected into the mold cavity, thus causing the formation of cells (bubbles). During the rest of the injection molding cycle, cells continue to grow to fill and pack out the mold and subsequently compensate for the polymer shrinkage as the material cools inside the mold. The cell growth is driven by the amount and spatial distribution of the dissolved gas. The cell growth is also controlled by processing conditions such as melt pressure and temperature as well as material properties such as melt strength and gas solubility. Finally, the shaping of the part takes place inside the mold until the mold opens allowing the part to be ejected.
Since the microcellular injection molding process was invented, there have been numerous studies on process, material, and technical developments aimed at materializing the full process potential. According to previous studies [1-5], microcellular injection molding offers a number of advantages such as cost savings, weight reduction, ease in processing due to low viscosity, and outstanding dimensional accuracy. Due to these advantages, the microcellular injection molding process has been used in many industries such as automotive, electrical goods, and home appliances using a broad range of thermoplastics. Despite these advantages, however, the surface imperfections associated with microcellular injection molded partsdsuch as unique gas flow marks, referred to as swirl marks throughout this paper, and a lack of smoothnessdstill remain one of the main drawbacks surrounding microcellular injection molding. In order to eliminate or reduce these surface imperfections there have been several studies attempted, as reported in Refs. [6-14]. Some researchers have focused on temperature modification of the mold surface to improve the surface quality of microcellular injection molded parts [6-8]. With polymeric foam, it was found that bubbles forming at the advancing melt front are first stretched by the fountain flow behavior toward the mold surface and subsequently dragged against the mold wall causing swirl marks [9]. During the filling stage of polymer melts, keeping the mold wall temperature high enough for bubbles at the mold surface to beeliminated improves the surface quality of microcellular injection molded parts. By controlling the mold temperature rapidly and precisely using mold temperature control units or other kinds of thermal or surface heating devices, microcellular foamed plastics with glossy and swirl-free surfaces can be produced.
There have also been efforts to eliminate the swirl marks on microcellular injection molded parts without any mold temperature controller. In particular, it was proposed that inserting an insulator onto the mold wall might help keeping the interface temperature between the mold and the polymer melt high. This technique basically yields the same result as temperature modification of the mold [10]. Thermal analysis and experimental results prove that the addition of an insulator layer on the mold can improve the surface quality of microcellular injection parts [11].
Another method of producing parts with an improved surface quality leads to a microcellular co-injection molding process [12]. In this technique, a proper amount of solid skin material is injected prior to the injection of a foaming core material. This can yield a sandwiched (solid skinefoamed coreesolid skin) structure with a surface finish similar to a conventionally molded component while partially maintaining the advantages of microcellular injection molding.
Another approach for improving the surface quality of microcellular
injection molded parts is the gas counter pressure process [13,14]. In this process, a high-pressure gas is injected into the mold prior to the polymer/gas solution to suppress cell nucleation and bubble growth while the polymer/gas solution is being injected into the mold cavity. Toward the end of injection, counter gas pressure is released and bubbles begin to form within the cavity. Since a majority of the part surface is already solidified, gas flow marks are eliminated.
In spite of these efforts to improve the surface quality, there have been difficulties in applying the microcellular injection molding process in industries requiring parts with high surface qualities because these techniques entail additional equipment which results in high costs or maintenance. There have been no reported studies on improving the surface quality of microcellular injection molded parts without any additional equipment or modification to existing equipment.
This paper proposes a novel approach to improve the surface quality of microcellular injection molded parts by controlling the cell nucleation rate. In this study, the cell nucleation rate was dramatically lowered or delayed by controlling the degree of supersaturation so that cell nucleation was delayed during the filling stage. After the polymer/gas solution volumetrically filled the mold cavity, intentionally delayed nucleation occurred and bubbles formed in the polymer matrix, except on the surface where the material had already solidified upon touching the mold surface. Theoretical background and experimental results are described in this paper. Microstructure, surface profile, surface roughness,mechanical properties, and dimensional stability are also investigated in this study.
2. Theoretical
2.1. Nucleation theory for polymeric foams
In polymeric foams, nucleation refers to the initial stage of the formation of gas bubbles in the polymeregas solution. For nucleation,
gas bubbles must overcome the free energy barrier before they can survive and grow to macroscopic size [15]. According to classical nucleation theories [16-18], the nucleation rate is controlled by the macroscopic properties and states of the polymer and gas such as solubility, diffusivity, surface tension, gas concentration, temperature, and the degree of super saturation.
One representative equation for the nucleation rate of polymeric foams was reported by Colton and Suh [19,20]. In addition to the mathematical representation, they also verified their nucleation theory experimentally for a batch foaming process using a high pressure vessel. The nucleation equation for microcellular foams dominated by the classical nucleation theory [16e18] can be expressed as
N=fCex(-?G**/kT)
where N is the nucleation rate, f is the frequency of atomic molecular lattice vibration, C is the concentration of gas molecules, k is the Boltzmann’s constant, T is the absolute temperature, and ?G**is the activation energy barrier for nucleation.
According to previous studies [19,20], the nucleation rate of polymeric foams is composed of two components: a homogeneous term and a heterogeneous term. The activation energy for homogeneous nucleation is given by
?Ghom**?16πr33?P2
where g is the surface energy of the bubble interface and ?P.is
assumed to be the gas saturation pressure. More precisely,
?P=|Pr'-Pr| where Pr` is the pressure that is exerted in a high
pressure vessel and Pr is the pressure of the supersaturated vapor in
the sample [16]. That is, DP is the pressure difference between the
pressure that is applied to the sample and the pressure of the supersaturated vapor in the sample. When the pressure that saturates
the gas in a high pressure vessel is suddenly released to trigger the so-called thermodynamic instability by rendering the sample into the supersaturated state, Pr` becomes 1 bardso low compared to Pr that DP can be approximated as Pr.
On the other hand, the activation energy for heterogeneous nucleation is affected by a geometric factor that depends on the contact (wetting) angle between the polymer and the particle and can be expressed as
?Ghet**=?Ghom**×f(θ) (3a)
fθ=12-34cosθ+14cosθ3 (3b)
where f(q) is a geometric factor that is dependent upon the contact
angle, θ, of the interface between the polymer and a second phase,
and has values of less than or equal to 1. For a typical wetting angle
of around 200 on the interface between a solid particle and the polymer melt, the geometric factor is 2.7X10-3, suggesting that the energy barrier for heterogeneous nucleation can be reduced by three orders of magnitude with the presence of an interface [20,21].
l 2.2. Nucleation theory for microcellular injection molding
In the batch foaming process, the theory of Colton and Suh was verified by their experiments. Due to the large difference between the pressure exerted in a high pressure vessel and the pressure of the supersaturated vapor in the sample, the gas pressure dissolved in the polymer, the?P in the Gibbs free energy equation, can be approximately assumed to be the saturation gas pressure. The assumption that ?P is the gas saturation pressure is fairly reasonable in a batch foaming process although the ?Pcan still have an error of about 30-40% due to overestimation as reported in a previous study [15].
The nucleation theory by Colton and Suh is a simplified form derived and modified from classic nucleation theories [16-18] and is generally adequate for the batch foaming process. However, there is a need for this theory to be modified in cases of microcellular injection molding and extrusion systems because ?P cannot be directly controlled and measured. To predict nucleation in microcellular injection molding and extrusion processes more precisely, this paper proposes a cell nucleation theory of a different form, which includes a term for the degree of supersaturation because it is a directly controllable factor.
To avoid misestimating ?P, and to consider the degree of supersaturation, a more proper activation energy equation for nucleation can be derived from the following equation [16,17]
?P=|Pr'-Pr|=2rrc （4）
where rc is the radius of a characteristic droplet, and the W.
Thomson equation
RTlnPrP∞=2r?Mr?p （5）
where P∞ is the pressure of the saturated vapor (i.e., the equilibrium
pressure), R is the universal gas constant, M is the molar mass, and p is the density. These equations yield
?P=RTρlnPrP∞M （6）
which can be alternatively expressed as
?P=ktρ1lnS (7)
whereρ1is the molecular density of the bulk liquid, and S(=PrP∞)
is defined as the degree of supersaturation.
Thus, the activation energy equation (cf. Equation (2)) for nucleation in the microcellular injection molding process can be given by
?G**=16πr33(kTρ1lnS)2 （8）
Hence it can be stated that the activation energy for nucleation is inversely proportional to the square of the natural logarithm of the supersaturation degree.
In the microcellular injection molding process, the polymer/gas
solution becomes a metastable supersaturation solution when it is
injected into the mold cavity. This is because the amount of gas able to be dissolved in the polymer in the presence of a rapid pressure drop is less than the gas amount originally dissolved in polymer melts. In particular, assuming the air in the cavity is properly vented, the pressure at the advancing melt front is at the atmospheric pressure. The solubility of a gas in a polymer at atmospheric pressure and processing temperature can be obtained by an Arrhenius-type expression with regard to temperature [22]
S@1 atm; melt temperature=S@STPexp?(-?HsR(1Tmelt-1298)) (9)
where S@STP is the solubility of the gas in the polymer at standard
temperature and pressure conditions (298 K and 1 atm). The parameter DHs is the molar heat of sorption, and Tmelt is the polymer melt temperature.
Thus, the degree of supersaturation is given by
S=mgS@STPexp?(-?HsR(1Tmelt-1298)) (10)
where mg is the gas dosage which can be controlled by the supercritical
fluid (SCF) supply system.
The heat of sorption, ?HsRg, of various polymer/gas systems at standard temperature has been studied and summarized in many previously published studies. In order to obtain the degree of supersaturation for a polymer/gas solution in the microcellular injection molding process, one has to either measure the solubility of the gas in the polymer at standard temperature and pressure or consult published data on the solubility of the gas in the polymer. Then, the activation energy barrier for nucleation in Equation (8), ?G**, can be obtained based on the calculated degree of supersaturation and the surface energy of the bubble interface, γ. Given the activation energy barrier and the frequency factor, f, the nucleation rate (expressed in Equation (1)) can then be calculated.The estimate of the surface energy of the bubble interface and the frequency factor is discussed below.
In microcellular injection molding, the polymer/gas solution can
be treated as a liquid mixture. Thus, the surface energy of the
bubble interface, g, can be expressed as [23,24]
γmix=γpolymerρmixρpolymer4(1-wgas) （11）
where γpolymer is the surface energy of the polymer, P′S are the
densities, and wgas is the weight fraction of gas.
In addition, a frequency factor for a gas molecule, f, in Eq. (1) can
be expressed as [24-26]
f=Zβ(4πrc2) (12)
where z is the Zeldovich factor, which accounts for the many clusters that have reached the critical size, rc., but are still unable to grow to sustainable bubbles. The parameter b is the impingement rate at which gas molecules collide with the wall of a cluster. The parameter Zβcan be used as a correction factor and is determined experimentally.
Once the nucleation rate as a function of the degree of supersaturation
is obtained, one can control the gas (SCF) content in the polymer melt to control or delay the onset of cell nucleation so that no bubble will form at the advancing melt front during the injection filling stage, thus, allowing microcellular parts with solid, swirl-free surface to be injection molded.
3. Experimental
3.1. Materials
The material used in this study was an injection molding grade
low density polyethylene, LDPE (Chevron Phillips Chemical Company, Texas, USA). It has a melt index of 25 g/10 min and a density of 0.925 g/cm3.
To confirm the theory for improving surface quality by controlling
the degree of supersaturation, a random copolymer polypropylene (PP)was also used in this study. The PP used in this study was Titanpro SM668 (Titan Chemicals Corp., Malaysia), with a melt flow index of 20 g/10 min and a density of 0.9 g/cm3. Both materials were used as received without any colorant, fillers, or additives.
Commercial grade nitrogen was used as a physical blowing agent for the microcellular injection molding trials.
3.2. Microcellular injection molding
In this study, an Arburg 320S injection molding machine (Arburg,Germany) was used for both the solid conventional and microcellular injection molding experiments. The supercritical fluid (SCF) supply system used in this study was the S11-TR3 model (Trexel, Woburn,MA, USA). The total gas dosagewas controlled by adjusting the gas injection time, t, and the gas injection flowrate,m_ g. A tensile test mold, which produces tensile test specimens that meet the ASTM D638 Type I standards, was used for this experiment.
For injectionmolding of both LDPE and PP tensile test specimens,
nozzle and mold temperatures were set at 221 。C and 25 。C, respectively. The cycle time was 40 s. An injection speed of 80 cm3/s was employed. In this study, six different gas dosages (concentrations) were used for injection molding of LDPE as shown in Table 1. Also, four different gas dosages were employed for microcellular injection molding of PP. The supercritical fluid was injected into the injection barrel at 140 bar pressure to be mixed with the polymer melts in this experiment. The weight reduction of foamed versus solid plastic partswas targeted at 8 _ 0.5% for each specimen. For the conventional injectionmolding experiment, the shot size of 20.2 cm3 and a packing pressure of 800 bars were employed for 6 s. For the microcellular injection molding experiments, the shot size of the polymer melt was 19.2 cm3 and the packing stage was eliminated.
3.3. Analysis methods
To analyze the surface roughness of the molded tensile bar specimens, a Federal Surfanalyzer 4000 (Federal Product Corporation, RI, USA)was used. The surface roughnesses of conventional and microcellular injection molded parts were evaluated at three locations shown in Fig. 1 and the averaged surface roughness based on measurementsdone at all three locationswas recordedandreported. The cutoff, drive speed, and drive length for the test were 0.75 mm, 2.5 mm/s, and 25 mm, respectively. For each process condition, ten specimens and three points on each specimen were tested.
In addition to the surface roughness, swirl marks commonly observed in microcellular injection molded samples can also be clearly revealed by a 3-D surface profiler. Zygo NewView (Zygo Corporation, CT, USA), a non-contact 3-D surface profiler, was employed to examine the surface profile of injection molded parts in this study using a scan distance of ±10 mm.
A JEOL JSM-6100 scanning electron microscope with an accelerating
voltage of 15 kV was employed for observing the microstructures of the foamed parts. To observe the cross section of the microcellular injection molded parts, test specimens were frozen by liquid nitrogen and subsequently fractured. Representative images of each process condition were selected and cell sizes and densities were analyzed. A UTHSCSA Image Tool was employed as the ima