冰露礦泉水瓶瓶蓋的注塑模具設計-螺紋伺服脫模含14張CAD圖
冰露礦泉水瓶瓶蓋的注塑模具設計-螺紋伺服脫模含14張CAD圖,礦泉水瓶,瓶蓋,注塑,模具設計,螺紋,羅紋,伺服,脫模,14,cad
1．外文資料翻譯譯文（約3000漢字）：
注塑件模擬焊縫成形的實驗驗證
J.G. Kovács*, B. Sikló
布達佩斯技術經濟大學高分子工程系
摘要：近幾年來，由于對注塑件性能要求的不斷提高，人們對注塑件的焊縫分析越來越感興趣。當兩個熔化前沿相互接觸時形成焊縫。如果不修改零件的幾何結構，就不可能完全消除焊縫，但可以將其對零件性能和外觀的負面影響降到最低。這可以通過試錯實驗或模型預測來實現。后者的成本和時間效率使其成為焊縫分析的首選方法。注射成形計算機模擬軟件包能夠準確預測焊縫位置，但現有的軟件包都不能定量預測焊縫接觸角和力學性能。本文對焊縫成形過程進行了分析，提出了改進有限元網格的方法，以獲得較好的效果。
關鍵詞：焊縫；注塑成型；模擬；有限元網格
1、介紹
注塑成型是用于成型塑料零件的最有效的工藝之一[1–6]。該方法的有效性取決于產品的質量，這可能會受到工藝設置不足或模具結構造成各種缺陷的阻礙。許多缺陷如焊縫、翹曲、噴射或凹陷等都會降低注塑件的質量，降低生產效率。在注塑件的設計中，焊縫的產生是一個重要的美學和機械問題。當兩個熔化前沿相互接觸時形成焊縫。在具有多個澆口的零件中，在模具填充過程中，可變壁厚、孔或型芯形成單獨的熔體前沿，而分離的熔體前沿形成焊縫，從而在零件中造成許多故障[7,8]。它不僅惡化了局部的機械性能，而且會產生光學缺陷，特別是在使用高光澤材料時。Chen等人在ABS拉伸鋼筋上研究了感應加熱在表面溫度控制中的應用，消除了焊縫表面的痕跡 [9]。 的確許多參數對焊縫的性能有影響，這些因素已經從多個方面進行了研究。在力學性能方面，對焊縫強度和模量進行了分析，結果表明焊縫對拉伸模量沒有顯著影響[10,11]。一些研究人員[12-15]使用焊縫系數（WL factor），定義為：有焊縫的試樣強度/沒有焊縫的試樣強度，來評估他們的實驗。采用高熔體溫度、高保壓壓力和低結晶器溫度對未填充材料的影響系數最高。利用激光引伸計和聲發(fā)射對焊縫進行了研究，得出的結論是焊縫不是材料中的簡單不連續(xù)，而是應力應變分布的局部擴展擾動[16]。
近年來，由于對注塑件性能要求的不斷提高，人們對注塑件焊縫分析的興趣大大增加。如果不修改零件的幾何結構，就不可能完全消除焊縫，但可以將其對零件性能和外觀的負面影響降到最低。這可以通過試錯實驗或模型預測來實現。后者的成本和時間效率使其成為焊縫分析的首選方法。注射成型計算機模擬軟件包能夠準確預測焊縫位置，但現有的軟件包都不能定量預測焊縫性能。這主要是因為迄今為止，焊縫特性的數學模型不可用[17]。
在他們的文章中，周和李[17]提出了一個基于人工神經網絡方法（ANN）的焊縫強度評估模型。對于網絡的輸入，選擇了影響焊縫性能的因素，即材料的取向系數、相遇角和熔體流動歷史系數。與試驗結果的比較表明，該模型能夠定量地預測焊縫性能，為工程設計提供了依據。Zhou等人 [18] 研究了熔體溫度和保壓對焊縫試件力學性能的影響，發(fā)現隨著保壓和熔體溫度的升高，焊縫試件的屈服強度和疲勞強度增加。他們解釋了觀察到的不同性質的皮膚核心形態(tài)，這是受熔體溫度和保持壓力的影響。
Au [19]使用幾何方法來生成塑料部件的填充圖案，并確定可能的焊接線的大致位置。Fathi和Behravesh[20]用可視化技術研究了焊縫成形過程中的流動動力學行為，而Zhou和Li[17]開發(fā)了一個人工網絡來預測焊縫性能。為了確定網絡的輸入參數，對影響因素進行了詳細的分析。對不可避免的焊縫非關鍵區(qū)域的形成和定位進行了仿真分析。多澆口零件焊縫定位的流量控制采用流道尺寸調整方法[21]。Mezghani[22]將模擬的焊縫位置結果與注塑件的實際位置進行了比較。Zhou和Li[23]提出了一種基于初始相遇節(jié)點特征的焊縫檢測算法。Chen[24]在零件仿真模型中應用模糊理論，通過改變壁厚和澆口位置來控制焊縫位置。Chun[25]通過模擬研究了壁厚和澆口位置對焊縫形成和位置的影響。
2、實驗
實驗在Arburg Allrounder 320C 600-250注塑機上使用雙腔注射模進行。這種特殊的模具有可更換的插入件，可以用不同的澆口類型（標準、薄膜、特殊薄膜等）具有不同的模具表面光潔度（拋光、細腐蝕、粗腐蝕），并注入不同厚度的試樣（0.5–4 mm）。樣品的厚度是由一個移動的部分來設置的，以定位空腔的深度。注射模的頂出系統(tǒng)不同于傳統(tǒng)的頂出系統(tǒng)，它不包括頂出銷，而是在整個零件表面積上工作，從而消除了試樣的變形。澆口類型可以隨插入型腔之間的嵌件的變化而變化，而無需從注塑機上拆下模具。實驗中，采用了精細的腐蝕表面光潔度，并在模具中設置了雙標準澆口鑲塊。
每個零件的標稱尺寸為80 mm×80mm×2mm，從兩點注射成型。兩個標準澆口位于腔的一側，距零件邊緣10 mm，相距60 mm。
采用聚酰胺6（Durethan B30S，Lanxess）進行研究。在注射成型之前，材料在80℃注射工藝條件保持恒定，模具溫度為90℃， 當熔體溫度設定在280℃ 使用不同的切換點設置使用短射技術制作試樣。在樣品上測量熔體前沿的相遇角，作為流動距離的函數。
測量結果繪制在圖5上。從中可以清楚地看出，會合角隨流長的增加而增大。在7毫米的流動距離，它達到了一個可測量的焊縫角約28°，當距離為22毫米時，角度為100°。在較長的流動中，由于熔體前沿的輪廓，無法測量會合角。
通過在澆口位置中心使用同心圓對熔體前沿進行可視化，還構建了會合角。結果表明，拉伸會合角的增加沒有測量值高。在理論流動距離為10毫米時，它很好地代表了測量值，但在較長的距離時，它低估了實驗尺度。
3、分析
有限元模擬注射成型是目前設計注射模最先進的技術。市場上有不同級別的節(jié)目。這些基礎知識對產品設計有一定的幫助，可以在不了解塑料制造的情況下使用。更復雜的程序能夠模擬整個注射成型過程，這樣人們就可以看到模具是否能夠完美工作。這種軟件覆蓋了大量的材料和機械數據庫，設計者必須具備塑料制造的專業(yè)知識。
對于注塑模擬，在大多數情況下，采用二維三角形單元或三維四面體單元來描述型腔，其中兩節(jié)點管單元用于流道、連接件和通道。用控制體積法計算了熔體前沿的變化。在每一步中都可以得到壓力場、溫度場和速度場。這些結果構成了應力和變形分析以及焊縫結果的基礎。
Moldflow Plastics Insight 6.2用于模擬分析實驗中使用的零件模型。在分析過程中，使用了三種不同的中間平面網格類型：原始網格、理想網格和平滑網格。每種網格類型在4個網格邊長度中完成：1、2、2.5和5 mm。
原始網格是指模型由等邊三角形組成，沿估計焊縫的節(jié)點不產生直線。這種網格類型的優(yōu)點是具有良好的長寬比。網格單元的長寬比非常重要，因為它影響結果的精度。比率定義了三角形的最長邊與三角形面積之間的相關性，而中面網格的推薦最大縱橫比為約6。可以看出，在每一條邊的長度上，這種網格三角形的平均長寬比都大于1.5。
理想網格由具有共線節(jié)點的等腰三角形構成。生成這種網格類型的優(yōu)點是，它可以很好地自動化，但是，由于較差的縱橫比，即2，它不如原始網格那樣精確。在平滑網格的情況下，原始網格的節(jié)點收斂形成一條線，在預測的焊縫區(qū)域中創(chuàng)建網格三角形邊的更均勻路徑。它是從原始網格類型生成的，并在焊縫區(qū)域進行了修改。將焊縫上的節(jié)點靠近理想焊縫位置。
模擬分析的工藝設置與實驗注射成型相同，模具恒溫，熔體溫度為90℃和280℃。
焊縫分析結果與實驗結果進行了比較。在大多數情況下，理想的網格類型最適合測量結果。在邊長為1mm的情況下，采用理想和平滑網格類型的分析接近于流量長度為7-10mm之間的測量結果。原始網格類型計算的值沿整個檢測流長在測量結果周圍波動，不接近測量值，而其他網格類型與流動開始時的測量值不同。同時觀察到，在距離為10 mm后，所有網格都預測出焊縫角急劇增加。
當網格長度為2 mm且流動距離較短時，振動再次明顯。與測量結果相比，原始網格給出的結果最不準確。角度值變化較大：計算出焊縫角為0°距離10.6毫米但147°12毫米。除原始網格外，在較長的流動路徑下與測量結果的差異小于在邊緣長度為2 mm時的差異。
邊緣長度增加到2.5mm，測量結果和模擬結果之間的相似性降低。在流動距離為15～20 mm的區(qū)域，用理想網格模擬計算的焊縫線角與實測值接近，但其它網格變化不符合實測值的變化趨勢。
使用5 mm的邊緣長度，曲線之間的一致性很弱。盡管分析結果顯示出一些相似性，但出乎意料的是，結果僅在少數流動長度下接近測量值。
比較每個邊緣長度處的不同網格類型，可以注意到在每種情況下，理想網格與測量數據的相關性最好，在0.95和0.98之間變化。結果還表明，理想網格的最佳相關度在高邊長處，即5mm處，但隨著邊長的減小，相關度降低的幅度相對較小。對于原始網格類型，相關性最低，但隨著邊緣長度的增加，相關性顯著提高，但這種網格類型并沒有達到理想的相關性值。使用平滑網格，相關度隨著邊緣長度的增加而提高，但也沒有達到理想網格類型的值。
參考文獻
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2．外文資料原文（與課題相關，至少1萬印刷符號以上）：
Experimental validation of simulated weld line formation in injection moulded parts
J.G. Kovács*, B. Sikló
Abstract：The interest in weld line analysis of injection-moulded parts has increased in the past few years, mainly because of the ever-increasing requirements for the performance of injec- tion-moulded items. Weld lines are formed when two melt fronts come in contact with each other. Whereas the total elimination of weld lines is not always possible without modifying the part geometry, their negative in?uence on part performance and appear- ance can be minimized. This can be done by trial and error experiments or by model prediction. The cost and time ef?ciency of the latter makes it a preferred route for weld lines analysis. Computer simulation packages of injection moulding are capable of accu- rately predicting the weld line location, but none of the current ones can predict the weld line contact angle or mechanical properties quantitatively. This paper focuses on the analysis of weld line formation and suggests ways to modify the ?nite element mesh to get better results.
Keywords：Weld line ；Knit line；Injection moulding ；Simulation；Finite element mesh
1.Introduction
Injection moulding is one of the most productive processes used to form plastic parts [1–6]. The effectiveness of the method depends on the quality of the product, which can be hindered by inadequate process settings or mould construction causing various de?ciencies. Many kind of defect such as weld lines, warpage, jetting or sink marks can reduce the quality of the injection moulded parts, worsening productivity. The occurrence of a weld line means a signi?cant problem both aesthetically and mechanically in the design of injection moulded parts.
Weld lines are formed when two melt fronts come in contact with each other. In a part with multiple gates, variable wall thicknesses, holes or cores form separate melt fronts during mould ?lling and the separated melt fronts create weld lines, causing numerous troubles in the part [7,8]. It not only worsens the local mechanical properties, but creates optical imperfections, especially when using high gloss materials. The surface marks of weld lines can be eliminated by the application of induction heating in surface temperature control, which was investigated on ABS tensile bars by Chen et al. [9].
Many parameters have an effect on the properties of a weld line and these factors have been investigated from many aspects. As regards mechanical properties, analysis of weld line strength and modulus was performed and showed that the weld line did not have a signi?cant effect on tensile modulus [10,11]. Several researchers [12–15] used the weld line factor (WL-factor), de?ned as: strength of specimens with weld line/strength of specimens without weld line, to evaluate their experiments. Highest WL- factors were obtained for un?lled materials and using high melt temperature, high holding pressure and low mould temperature. Weld lines were studied using laser exten- someter and acoustic emission, and the conclusion was that a weld line is not a simple discontinuity in the material, but a locally extended disturbance of the stress and strain distribution [16].
The interest in weld line analysis of injection-moulded parts has increased greatly in the past few years, mainly because of the ever-increasing requirements for the performance of injection-moulded items. Whereas the total elimination of weld lines is not always possible without modifying the part geometry, their negative in?uence on part performance and appearance can be minimized. This can be done by trial and error experiment or by model prediction. The cost and time ef?ciency of the latter makes it a preferred route for weld line analysis. Computer simulation packages of injection moulding are capable of accurately predicting the weld line location, but none of the current ones can predict the weld line prop- erties quantitatively. This is mainly because a mathematical model for weld line properties is, to date, unavailable [17].
In their article, Zhou and Li [17] presented an evaluation model for weld line strength based on the arti?cial neural network method (ANN). For the input of the network, the factors affecting weld line properties were chosen; those are the orientation coef?cient of the material, the meeting angle and the melt mobility history coef?cient. Comparison with experimental results shows that the presented model is capable of predicting weld line properties quantitatively for engineering design. Zhou et al. [18] examined the effects of melt temperature and hold pressure on the mechanical properties of specimens with weld lines and found that the yield and fatigue strengths of the specimens increased with increasing hold pressure as well as increasing melt temperature. They explained the observed differences in properties in terms of a skin-core morphology, which was in?uenced by both the melt temperature and the holding pressure.
Au [19] used a geometrical approach to generate the ?lling patterns of plastic parts and determine the approx- imate location of possible weld lines. Fathi and Behravesh[20] studied the kinematical behaviour of the ?ow during weld formation with a visualization technique, while Zhou and Li [17] developed an arti?cial network to predict weld line properties. The affecting factors were analyzed in detail in order to identify the input parameters for the network. The formation and positioning in noncritical areas of unavoidable weld lines are also investigated with simula- tion analyses. The controlling of the ?ow for weld line positioning for multi-gated parts was carried out with a runner resizing method [21]. Mezghani [22] compared the simulated weld line location results with the real position on injection moulded parts. Zhou and Li [23] presented a weld detector algorithm, which is based on the characteristics of the initial meeting node. Chen [24] applied fuzzy theory for controlling the weld line position by varying the wall thickness and the gate location in part simulation models. Chun [25] showed by simulation the effect of wall thickness and gate location on the formation and position of weld lines.
2.Experimental
The experiments were performed on an Arburg Allrounder 320C 600-250 injection moulding machine using a two cavity-injection mould (Fig. 1.). This special mould has changeable inserts to be able to inject with different gate types (standard, ?lm, special-?lm, multi gates, etc.), with different mould surface ?nishes (polished, ?ne eroded, rough eroded) and to inject different thickness specimens (0.5–4 mm). The thickness of the samples is set by a moving part to position the depth of the cavities. The ejection system of the injection mould differs from the conventional one; it does not include ejector pins but operates on the whole part surface area, so eliminating deformation of the sample. The gate type can be varied with the change of an insert interposed between the cavi- ties without dismounting the mould from the injection moulding machine. For the experiments, a ?ne eroded surface ?nish was used and an insert with double standard gates was set in the mould.
Each part, having nominal dimensions of 80 mm 80 mm 2 mm, was injection moulded from two points (Fig. 2.). The two standard gates are located on one side of the cavity 10 mm from the part edge and 60 mm apart.
Polyamide 6 (Durethan B30S, Lanxess) was used for the investigations. Before injection moulding, the material was dried at 80 ○C for 4 h. The injection processing conditions were kept constant; the mould temperature was 90 ℃while the melt temperature was set at 280 ○C. The speci- mens were produced with short shot technology using different switch-over point settings (Fig. 3.). The meeting angle of the melt front was measured on the samples as a function of the ?ow distance (Fig. 4.).
The results of the measurement are plotted on Fig. 5. It can be clearly seen that the meeting angle increased with the ?ow length. At a ?ow distance of 7 mm, it reached a measurable weld line angle of about 28○, while at a distance of 22 mm the angle achieved was 100○. At longer ?ows the measurement of the meeting angle was not possible because of the pro?le of the melt front.
The meeting angles were also constructed from the visualization of the melt fronts using concentric circles centred at the gate locations. The results showed that the increase of the drawn meeting angle was not as high as the measured values (Fig. 5.). At a theoretical ?ow distance of 10 mm it represented the measured values well but at a longer distance it underestimated the experimental scale.
3、Analysis
Injection moulding simulation with the ?nite element method is the most advanced technique for designing injection moulds. There are different levels of program available on the market. The basic ones are helpful in product design, which can be used without having deep knowledge of plastic manufacturing. The more complex programs are able to simulate the whole injection moulding process so one can see whether the mould will be able to work perfectly or not. Such software cover enor- mous databases of materials and machines and the designers must have professional knowledge of plastic manufacturing.
For an injection moulding simulation, in most cases two-dimensional triangular elements or three-dimensional tetrahedron elements are used to describe the cavity, with two-node tube elements for the runners, connectors and channels. The melt front advancements are calculated by the control volume method. The pressure, temperature and velocity ?eld can be obtained in each time step. These results constitute the basis of the stress and deformation analysis as well as results for weld lines.
Mold?ow Plastics Insight 6.2 was used for the simulation analyses with a model of the part used in the experiments (Fig. 6.). During the analyses, three different mid plane mesh types were used and compared: original mesh, ideal mesh and smoothed mesh. Each mesh type was completed in 4 mesh edge lengths: 1, 2, 2.5 and 5 mm.
Original mesh means that the model consists of equilateral triangles and the nodes along the estimated weld line did not produce a straight line. The advantage of this mesh type is the good aspect ratio. The aspect ratio of the mesh elements is important because it affects the accuracy of the results. The ratio de?nes the correlation between the longest side of the triangle and the triangle area, and the recommended maximum aspect ratio for a mid plane mesh is about 6. It can be seen that at every edge length this type of mesh triangle was greater than an average aspect ratio of 1.5.
Ideal mesh is made up of isosceles triangles with collinear nodes. The advantage of the generation of this mesh type is that it can be well automated, however, because of the worse aspect ratio, namely 2, it was not as accurate as the original mesh (Fig. 7). In the case of the
smoothed mesh, the nodes of the original mesh are converged to form a line creating a more uniform path of the mesh triangle sides in the area of the predicted weld line. It was generated from the original mesh type with modi?cation at the weld line region. The nodes positioned on the weld line were made nearer to the ideal weld line position.
The process settings for the simulation analyses were identical to the experimental injection moulding, constant mould temperature and melt temperature namely 90 ℃ and 280 ℃。
The weld line analysis results were compared to the experimental. In most cases, the ideal mesh type best ?tted the results of the measurements. At an edge length of 1 mm, the analyses with ideal and smoothed mesh type came close to the measurement results between flow lengths of 7 and 10 mm (Fig. 8.). The values calculated with original mesh type flucated around the measured results along the whole examined flow length and did not approach them, while the other mesh types differed from the measured at the beginning of the ?ow. It was also observed that after a distance of 10 mm a steep weld line angle increase was predicted by all of the meshes.
At a mesh length of 2 mm and a short ?ow distance an oscillation was again noticeable (Fi
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