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附件1：外文資料翻譯譯文
微型模具成型的熱量和擠壓控制
在這篇文章中,我們?yōu)榱擞行У貜椭瞥鲈撐⑿湍＞弋a(chǎn)品的微小結(jié)構(gòu),將一個擠壓機器和一個小核心傳感器組合起來，構(gòu)建一個注射模具的擠壓系統(tǒng)。在一些重要的部位，由一個壓力裝置，它作為原動力，驅(qū)動中心模具工作。舉例說吧，在注射以后，模腔中的壓力會從二十兆帕上升到三十四兆帕。那些小小的感應器形成感受到壓力，那些周圍的裝置和熱敏傳感器，排列在洞腔的同圍。我們可以根據(jù)這些信號推測里面狀況朝著有利的方向發(fā)展。為了評估該注射系統(tǒng)，我們做了一個厚度為1lm角度為140℃ 三角凹朝槽 來進行工作。
說明
大部分的醫(yī)療信息設(shè)備都有一個基礎(chǔ)工作部分，另外還有一些輔助部件來完成某種特定的功能。模具成型技術(shù) 在現(xiàn)實中廣泛應用，而且在大批量生產(chǎn)中多有應用，這篇文章即是研究成型過程在傳統(tǒng)的成型壓力系統(tǒng)中,其為系統(tǒng)提供很大的壓力差,這種特點為模具成型過程提供了很好的動力源.然而,傳統(tǒng)的成型過程在注射成型的過程中,特別是在微型模具的成型過程中,有兩個很明顯的問題.首先,在用單模腔成型微小結(jié)構(gòu)的模具時,不同的溫度和硬度會引起不一致的成型壓力.一般來說,模腔中心的溫度越高,中心周圍的溫度也會越高.其次,即使通過冷卻和控制壓力的方法來展平那些不平的區(qū)域,但是通過檢測發(fā)現(xiàn),熱流量和壓力仍是高于成型微型模具工作時所規(guī)定的壓力,而且腔內(nèi)的這種情況很不好控制,這樣以來就只好通來偵測熱流面不是溫度來控制型腔中各種成型條件.
這篇文章的作者，也就是該機器的設(shè)計者，他通過在模具重要部位安放一個叫做模具核心擠壓機的部件來及時了解并控制模腔內(nèi)成型的具體情況。這個部件配備有特殊裝置來控制模腔內(nèi)的壓力、溫度，并反饋回到顯示裝置上。這篇文章就向我們詳細地闡述了這種機器的模型。
模具成型的壓力系統(tǒng)設(shè)計
如圖1所示，該結(jié)構(gòu)為我們常用的模具結(jié)構(gòu)圖。首先，我們描述一下裝備有piezo設(shè)備的模具成型壓力機。我們用的pie20設(shè)備有一個最大厚度為13LM的裝置，而且可以產(chǎn)生一個最大值為6KN的壓力。因此，該注射壓力系統(tǒng)所能產(chǎn)生的壓力在0~6KN之間，注射機的壓力系統(tǒng)有一個壓力設(shè)備，該裝置有一個特置的中心軸，并與一個傳感反饋裝置連在一塊。這個壓力裝置是圓柱形的，直徑為25mm，高度為54mm，它的溫度約在20℃和120℃之間。壓力傳動裝置的設(shè)計是對稱的，它把動力和運動從壓力裝置上以一定的規(guī)律和方式傳出去，這個圓柱體的傳動裝置向一個方向上不停地進行著傳遞工作，并由一個平面的輔助裝置保證其只能在平面內(nèi)作旋轉(zhuǎn)運動。
為了研究之便，我們特地用一個很小的傳感器，使位移，壓力、傳感器、熱量傳感器很好地相互協(xié)調(diào)起來協(xié)同工作，當注射機的注射孔開始有位移并要接觸到模腔時，位移傳感器裝置就會測出其位移，并作出下一步的控制動作。該位移傳感器是非接觸式傳感器，其最大是量程為500lm ,誤差可以控制在0.2lm以下。
我們把一個核心模型放在模腔的中央，其結(jié)構(gòu)是一個三角形的凹槽，以深度1lm順次排列。核心表面有32768個三角形的凹槽組成，凹槽相鄰的角度為140o ，距離為1μm完成加工的產(chǎn)品組成一個直徑為12mm厚度為1mm的盤狀物。由是由在鋼里面加入鎳和磷元素制成的合金做的。有很好的硬度和耐磨性。三角槽的切制是由精度非常高的NC機切制而成的，有著異常高的精確度。
有二組深度為12lm的廢氣排放口，依次排列在圓洞的周圍。用一個真空泵抽出由于樹脂的分解而產(chǎn)生的廢氣物。為保證精細模具的硬度，統(tǒng)一冷卻那些盤狀產(chǎn)品。我對使冷卻水做曲線的循環(huán)運動。注射機依靠一個伺服馬達系統(tǒng)，使其可以具備最高達150KN的夾緊力。
評估微型注射系統(tǒng)
以下是成型時的條件：材料：聚苯乙烯；注射溫度：190℃；成型設(shè)備溫度：80℃；注射速度：10mm/s；注射壓力：34mpa；夾緊力：150KN。在這些條件下，我們分別對如下情景作了比較分析。第一種情況是在約1000Vr 電壓下推動注射壓力機工作，第二種是沒有電壓作用。圖表3和4顯示的是模具里邊傳感器的測量結(jié)果。注射壓力的測量由位于注射壓力機后面的壓力計來測量，并以數(shù)字表格形式在輸出裝置上顯示。
第三組表格顯示了成型一個周期的數(shù)據(jù)。首先，在第5.16秒，注射動作開始注射，注射壓力也隨之上升，從第5.6s開始注射壓力在2秒之內(nèi)迅速升至34MPA，模腔內(nèi)的應力實行如圖所標的傳感器檢測表明，也隨著增加，只不過有大約0.35秒的延遲，最終可達到20MPA，約是注射壓力的59%。在注射壓力保持不變的那一階段，模腔內(nèi)的應力迅速下降到零。這充分證明，盡管存在著由注射機提供注射壓力，但其中一部分由于模腔內(nèi)的摩擦力的存在而被抵消，熔料在模腔內(nèi)凝固的過程中，熔料因漸成為固體而其余部分也隨之降低為零。在此過程中，中心位移也經(jīng)歷了與模腔內(nèi)壓力變化規(guī)律相似的變化。這說明注射中心也受到了反作用力，在經(jīng)歷大約14S的冷卻過程后模具被打開了。
比較低的表格表明了表面溫度和熱量擴散的過程。其中比較平直的那一段曲線顯示的是保壓階段或者說是壓力持續(xù)過程。圖表顯示的是表面溫度連續(xù)上升的過程，此時，熔料經(jīng)澆口源源不斷地流經(jīng)流道，最終達到成型模腔。在注射完成后，溫度迅速上升，而后隨即下降（在冷卻作用下）特別是澆口附近的熱量散的比較快，溫度下降也比較明顯。
在圖表4中，在第5.6s的時候，壓力裝置得到約1000V的電壓，由于電壓作用，模腔內(nèi)的壓力升至34MPA，中心的溫度和壓力也隨之上升。切斷電壓后，中心也恢復到原始狀態(tài)，但我們無法看到這一過程。
下面，我們對是否微型注射壓力機時產(chǎn)品的表面特征作一比較。圖表5、6顯示的是SEM照片而AFM的測量結(jié)果。從圖片來看，三角形凹槽的表面粗糙度和均勻程度在這兩種情況下并無明顯區(qū)別。原因就是因與注射時的速度與模具微小結(jié)構(gòu)的質(zhì)量有關(guān)，另外三角形凹槽的深度和排列密度也是其原因之一。
附件2：外文原文
Injection molding for microstructures controlling mold-core extrusion and cavity heat-flux
Abstract In this work we constructed an injection press molding system with a mold-core extrusion mechanism and a small sensor assembly for effectively duplicating microstructures to the mold products. The mold-core extrusion mechanism is driven by a piezo element to apply force on important area with microstructures. For example, after injection it increases the cavity pressure from 20 to 34 MPa. Small sensors consist of the pressure, displacement, and heat flux sensor assemblies,arranged around the small cavity. The signals showed us the physical phenomena inside the mold and may be further used as control signal. In order to evaluate this injection press molding system, we formed micro triangular grooves of pitch 1 lm and angle 140o. The mold-core extrusion gave better diffraction intensity by several percents.
1
Introduction
Many information and medical equipment contain functional parts with microstructures in the order of 1 lm and overall size of several millimeters. Molding is a mass production method widely used in duplicating three dimensional forms of these parts [1–4]. This paper reports our study on one of the molding processes, namely, the injection press molding process.
In contrast to regular injection molding process that injects molten resin at high pressure into the cavity for simultaneous filling and forming, injection press molding process separates the time of the two processes. Injection press molding process injects molten resin into a mold cavity at low pressure to keep the flow resistance small,and once the cavity is filled, applies large clamping force on molds to form microstructures. Injection press molding has superb transforming capability used for example, in forming optical disks and LCD light guiding plates.
Conventional injection press molding applies large clamping force on molds for forming after the filling process. However, conventional injection press molding process has two problems for forming micro parts described above. First, in forming multiple micro parts with a single set of molds, the temperature and rigidity distributions are not uniform causing difference in forming pressure [5, 6]. Generally, the temperature is higher around the mold center and the pressing force is higher around the perimeter. Secondly, even if one tries to flatten the uneven distribution with cooling or pressure control, sensors to monitor the heat flux or pressure are larger than the micro parts and cannot find these conditions within the cavity.Note that measuring heat flux instead of temperature allows monitoring resin solidification in the cavity.
The authors of this paper devised mechanisms to (1) individually press each important micro structure area (we call this area the ‘‘core’’) with a mold-core extrusion mechanism equipped with a small piezo element and (2) control pressure temperature, and especially the cavity heat flux for each core by arranging a set of sensors around each core and feeding back the sensor signals to the above piezo element. This paper reports our prototype of these mechanisms.
2
Designing the injection press molding system
Figure 1 shows the mold we used. First we describe the mold-core extrusion mechanism design equipped with a piezo element. The piezo element used (KISTLER,Z17294X2) has a maximum free displacement of 13 lm and produces a maximum force of 6 kN with no displacement,thus the pressing force varies between 0 and 6 kN depending on the piezo element extension. The piezo element has a single axis force sensor (KISTLER, 9134A) integrated in it for pressing force feedback control. The piezo element unit size is 25 mm in diameter, 54 mm long and its temperature
Fig. 1. Test mold range is )20 to 120oC. The
symmetric design of the force transferring structure uniformly transfers the pressing force from the piezo element. This cylindrical force transfer mechanism moves in one direction and a planar surface keeps the shaft from rotating.
A small sensor assembly was developed for our study in this paper. Displacement, pressure, and heat flux sensors compose the assembly. The displacement sensor measures the displacement at the mold-core extrusion mechanism where it presses the mold-core, and the displacement in the parting direction at the parting line.
The displacement sensor is an eddy-current type noncontact displacement sensor (SINKAWA Electric, VC-202N) with range of 500 lm and resolution of 0.2 lm. The above 1 axis force sensor served as the pressure sensor to measure the cavity internal pressure.
The heat flux sensor measured the cavity surface temperature and the heat flux. A pair of thermocouples embedded at depths 0.3 and 0.6 mm enabled these measurements with the principle of inverse heat conduction.We mounted the diameter 3.5 mm heat flux sensors on the gate, cavity and sprue lock pin (Fig. 2).
We placed one mold-core at the mold center. The microstructure was triangular grooves arranged with pitch 1 lm. The core surface had 32,768 triangular grooves with 140_ angle that are 0.2 mm long on the
perimeter of a 10.5 mm circle.
Fig. 2. Cavity details and mold-core The finished product formed into
a 1 mm thick disk with diameter 12 mm. The core was made of steel (UDDEHOLM, STAVAX, 52 Rockwell hardness), with Ni-P plating. We cut the triangular grooves with an ultra precision NC machine (FANUC ROBOnano Ui).
Two 12 lm deep air vent grooves were placed on the perimeter of the cavities. A vacuum pump pumped out residual air and gas from molten resin. To provide rigidity similar to a regular mold, we kept the entire 80 kgf mold size the same. For uniformly cooling the disk shaped product, we ran cooling water in a circular path. The injection molding machine (FANUC, ROBOSHOT a-15) has a servo motor type drive with maximum clamping force of 150 kN.
3
Evaluating the injection press molding system
Here are the molding conditions: Resin: Polystyrene, Resin temperature at injection: 190 oC, Mold set temperature:80 oC, Injection speed: 10 mm/s, Holding pressure:34 MPa, and Clamping force: 150 kN. Under these conditions,we compared the case with a constant voltage of 1000 V applied to push the mold-core extrusion mechanism,and the case without pushing. Figures 3 and 4 show the measurements from the sensors inside the mold. The injection force measured with a load cell placed behind the injection molding machine screw derived the injection pressure in the figure.
Fig. 3. Measurements Fig. 4. Measurements
of sensors (without) of sensors (with)
Upper figures of Fig. 3 show the molding cycle. First at 5.15 s, the injection starts and the injection pressure suddenly rises. At 5.6 s, the injection pressure is held at 34 MPa for 2 s. The cavity pressure, measured by the 1 axis force sensor, increase with a 0.35 s delay, to reach only 20 MPa, which is 59% of the injection pressure. The cavity pressure quickly went down to about zero during the injection pressure holding period. This shows that despite the pushing force at the source of the injection molding machine, friction reduces pressure which is dropped at cavity. Also, when the resin solidified in the cavity, it parted from the mold to drop the pressure to zero. The core displacement shows a transition similar to the cavity pressure indicating that it was pressed back by the resin. After further cooling to 14 s, the mold was opened.
Lower figures of Fig. 3 show the surface temperature and heat flux transitions. The horizontal axes are magni-fied in the lower figures around the pressure holding period.The figure shows the sequential surface temperature rise at the lock pin, gate, and cavity as resin passed over them. The heat flux maximized immediately after injection and gradually decreased. Especially at the gate, the heat flux went down to about zero during pressure holding.
In Fig. 4, a voltage of 1000 V was applied to the piezo element for 2 s starting at 5.6 s. The voltage raised the cavity pressure to 34 MPa. The core gradually advanced with drop in cavity pressure from the position pressed in by the resin to eventually reach 9 lm ahead of its original position. Cutting the voltage retracted the core to its original position. But, we were not able to observe change in surface temperature and heat flux due to change in heat transfer from applying voltage.
Next we compare form features on the product with and without the mold-core extrusion. Figures 5 and 6 show the SEM photographs and the AFM measurement results. The photographs reveal that the triangular grooves had a uniform pitch with smooth surface regardless of mold-core extrusion, and good form transfer to the products. The reasons are smooth flow of polystyrene and the small aspect ratio of the groove depth and pitch.
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