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Precision injection molding technology of progress
Author : Masaki Mikell Chen Chun
Abstract : Introduction about precision injection molding technology of the polymer materials, and discussion about factors which impact the precision injection molding, including the precision of the mold，the control accuracy of the injection molding machine, the process control of precision injection and other computer control technology. Discussed to each of these factors, and given the relevant solutions, finally, introduce a number of advanced molding technology.
Keywords : Precision Injection, Injection Machine，Precision Injection Mold
In recent years, with the rapid development of the electronics, telecommunications, health care, automotive, and other industries，the demand to high-precision and high performance of plastic products is increasing day by day, prompted precision molding technology continues to progress, new technologies continue to emerge. Precision injection molding products not only require high dimensional accuracy, low warpage，good to write, but also require excellent optical properties [1]. Injection molding is the most important method of the plastic molding, including plastics plastics，injection, and packing, several basic cooling process, so there are many factors which can impact precision injection molding.
1 Precision Mold
To create sophisticated products, precision mold is essential. Generally the accuracy of the Mold controlled by the mold temperature, the precision manufacturing mold and the selection of plastic shrinkage rate when mold design .
1.1 The Control Precision of The Mold Temperature
General precision parts in the injection molding, temperature control of mold is to increase productivity. However，the impact of temperature control of mold for precision injection molding is great [2], it affects component of contraction, shape, crystallization, stress and so on, therefore mold design temperature loop temperature distribution at the request reasonable, control accuracy is precise. Wen preferred mode control and a cool-water machine. Mold temperature control and cooling time on product performance and the impact is as follows [3] :
(1)Melt plastic injection and the cycle time of mold cavity can make fluctuations of the temperature difference ，therefore be to minimize the volatility worse peaks.
(2)Heat transfer of mold is through the concrete and mold die within the media around the world. Mold is unchanged and therefore control of the media is the key, the general import and export of its cooling water temperature is less than 1 °Ｃ, application of the theory to the average temperature calculated [4], this can guarantee the stability of heat transfer.
(3)Stable state of mold to maintain a balance between absorption and distribution of heat, injection molding machine should strictly maintain a stable temperature.
1.2 The Design And Manufacture of Precision Mold
The premise to guarant precision component size of plastic is mold design in order to improve the precision of precision injection mold, using computer-aided analysis is necessary in the design process，especially on the gating system and the behavior of mold temperature control system heat distribution analysis.
1.3 The Use of Precision Mold Design Shrinkage Rate
Precision injection molding machine generally has larger injection of power, make difficulties to mold design, size and cavity size precision control products [5]. Precision plastic parts of the design prior to manufacture simple mold to measure the molding part of the actual shrinkage, this will greatly improve the accuracy of component size.
2 Best Precision Iinjection Molding Process Parameters Settings
To the best molding process parameters to reduce plastic products, the shrinkage rate. Parts of the wall thickness difference is generally considered by the two factors :.
（1）Melt hypertension caused by mold cavity minor deformation;
（2）When the mold cavity flexibility of the material after expansion.
3 Precision Injection Molding Machine Used to Replace Conventional Injection Molding Machine
Precision injection molding machine generally larger injection of power, Besides meet injection pressure and injection rate of requirements, Power will be injecting itself on the accuracy of a certain role in the improvement.
3.1 The consistency of molding cycle time
General typical injection molding machine with three modes：manual, semi-automatic and fully automatic. Due to the influence of various factors, in the former two models under each molding cycle time vary, this will affect the mold temperature and melt materials in the residence time, thereby affecting the precision of the parts made, so in Precision molding should maximize the use of fully automatic mode [14].
3.2 The Temperature Control of Precision Injection Molding Machine, And A New Design of Screw.
Injection barrel automatic thermostat on the cycle of sexual relations and the opening of the stove to melt density and viscosity changes. Products thus affecting the quality and accuracy of the cyclical fluctuations; injection molding machine nozzle close to the mold cavity. Therefore, the nozzle temperature of molding component will have an important impact.
4 Precision Molding Technology
4.1 Application of The Mold Injection Compression Molding (ICM) Technology ICM
Technology is the means to open a certain distance from the mold under the conditions of the beginning injection, injection of a certain amount, close to the beginning die cavity melt implementation of the compression, Die completely closed at the termination of injection, and then packing, cooling until the removal products.
4.2 The High-speed Injection Molding
High-speed injection molding method of filling melts faster than traditional fast 10 ~ 100 times, so that melt in a mold cavity to produce high shear flow and viscosity, mold filling fast, plastic surface hardening slowed, will be enhanced thin-wall molding thickness limit, inhibit excessive molding pressure and low-pressure die as mobile, products, the lower the stress.
4.3 No Guarantee Pressure Injection Molding
Without packing injection molding technology is referred to the plastic melt in high-speed, high pressure filling into the mold, then close to the nozzle needle, a plastic mold cavity melt automatically cover all parts of the product contraction Such products can greatly reduce the warpage.
4.4 Other Intelligent Control Technology
Precision injection molding process on the processing conditions for continued monitoring and accurate control is very important. With the development of computer technology, computerized injection molding has been widely used .
5 Conclusion
The growing requirement of plastic products for high accuracy and high performance requirements is the momentum for sophisticated injection molding technology forward. People of precision injection molding understanding of the principle is the continuous deepening of precision injection molding technology the basis for progress. With new materials, new techniques and new equipment has emerged, particularly plastic widely used in the computer processing, to create good conditions for precision injection technology. As long as reasonable to use, we will be able to produce sophisticated products.
References
［1］Luo WeiHua. Application Engineering Plastics, 2002, 30 (8) : 27
［2］Zhang yougen. Plastics technology, 1990 (1)
［3］Xi yongsheng. Precision Injection Mold Design. Beijing : China Light Industry Press, 1997
［4］Wang songjie. Plastics Processing, 2002, 37 (3) :40
［5］Chen Hong .Precision Plastic Molding. Beijing : National Defense Industry Press, 1999
［6］Dai wenli. Polymeric Materials Science and Engineering, 1995, 11 (5) : 97
［7］Yang S Y. Advances in Polymer Technology, 1996, 15 (4) : 289
8Chen Shi. Advances in Polymer Technology, 2003, 22 (4) : 306
［8］Zhu Xikun. Die industry, 2001，41 (11) : 37
10Kleinebrahm M. Kunstoffe Plast Europe, 1998 (1) : 12
［9］Hu haiqing. Application Engineering Plastics, 2000, 28 (10) : 18
［10］Mikell K. Plastics Technology, 2001 (4) : 54
［11］Hang Xu. Electromechanical Components, 2002, 22 (2) : 56
［12］Xu Bin. China Plastics, 2003, 17 (4) : 61
［13］Yang S Y. Advances in Polymer Technology, 1996, 15 (3) : 205
［14］Masaki Y. Polymer Engineering and Advanc e, 1998, 38 (9) : 17Peter Pokorny 1587.
［15］Peter Pokorny. Injection Molding, 2001, 91 (7) : 100029 22
［16］Wu daming. China Plastics, 2003, 17 (2) : 1
精密注射成型技術(shù)的研究進(jìn)展
作者： Masaki Mikell 陳占春
摘要：介紹聚合物材料的精密注射成型技術(shù)，論述影響精密注射成型的因素，包括模具的精度、注塑機(jī)的控制精度、精密注射工藝控制和其它一些計(jì)算機(jī)控制技術(shù)。分別對這些因素進(jìn)行分析討論，并給出了相關(guān)的解決方法，最后介紹了一些先進(jìn)的模塑成型技術(shù)。
關(guān)鍵詞：精密注射,注塑機(jī),精密注射模具
近年來，隨著電子、電信、醫(yī)療、汽車等行業(yè)的迅速發(fā)展，對塑料制品的高精度、高性能要求與日俱增，促使精密成型技術(shù)不斷地進(jìn)步，新的技術(shù)不斷地涌現(xiàn)。精密注射成型要求制品不僅具有較高的尺寸精度、較低的翹曲變形、優(yōu)良的轉(zhuǎn)寫性，而且還應(yīng)有優(yōu)異的光學(xué)性能等[ 1 ]。注射成型是最重要的塑料成型方法之一，包括塑料的塑化、注射、保壓、冷卻等幾個基本的過程，因此影響精密注射成型的因素也很多。
1 精密模具
要制造出精密的制品，精密模具是必不可少的。模具的精度一般受模具的溫度控制、模具的精密制造和模具設(shè)計(jì)時對塑料收縮率選用等影響。
1.1 模具溫度的精密控制
在一般精度零件的注射成型中，控制模具溫度主要是為了提高生產(chǎn)率。然而模具溫度控制對精密注射成型的影響極大[ 2 ] ，它影響制件的收縮、形狀、結(jié)晶、內(nèi)應(yīng)力等，因此設(shè)計(jì)模具冷熱回路時要求溫度分布合理，控制精度精確，最好采用模溫機(jī)和冷水機(jī)控制。模具溫度控制和冷卻時間對制品性能的影響及其影響因素如下[ 3 ] ：
(1)塑料熔體注入和模具開模的循環(huán)時間二者會在模具中產(chǎn)生溫度差的波動，因此應(yīng)該盡量減小這種波動差峰。
(2)模具內(nèi)的熱量轉(zhuǎn)移模具的熱量是通過模具體和模具內(nèi)的媒體傳遞出去的，模具是不變的，因此對媒體的控制是關(guān)鍵，一般其冷卻水出入口溫度差小于1℃，應(yīng)用平均溫度理論來計(jì)算[ 4 ] ，這樣能夠保證熱量傳遞的穩(wěn)定性。
(3)模具穩(wěn)定狀態(tài)為使模具所吸收和散發(fā)的熱量保持平衡，注塑機(jī)注射出的熔體要嚴(yán)格保持穩(wěn)定的溫度。
1.2 精密模具的設(shè)計(jì)與制造
模具設(shè)計(jì)的好壞是保證塑料制件尺寸精度的前提，為了提高精密注塑模的精度，在設(shè)計(jì)過程中采用計(jì)算機(jī)輔助分析是必要的，特別是對澆注系統(tǒng)的流動行為和模具溫度調(diào)節(jié)系統(tǒng)熱量分布的分析等。
1.3 精密模具設(shè)計(jì)時物料收縮率的選用
熱塑性塑料制品成型時收縮率波動較大，給模具設(shè)計(jì)、確定型腔尺寸和控制制品尺寸精度帶來困難[ 5 ]。對高精度塑料件可在設(shè)計(jì)前先制造簡易模具，以測出成型時各部位的實(shí)際收縮率，這樣便可大大提高制件的尺寸精度。
2 精密注射成型最佳工藝參數(shù)的設(shè)定
選取最佳的成型工藝參數(shù)能夠減少塑料制品的收縮率。制件壁厚的差異一般認(rèn)為是由兩個方面的因素引起的：
(1)高壓熔體引起的模具型腔輕微變形;
(2)當(dāng)模具開模后材料的彈性膨脹。
3 用精密注塑機(jī)代替常規(guī)注塑機(jī)
精密注塑機(jī)一般都采用較大的注射功率，這樣除了可以滿足注塑壓力和注射速率方面的要求外，注射功率本身還會對制品精度起一定的改進(jìn)作用。
3.1 成型制件循環(huán)時間的一致性
一般典型的注塑機(jī)有三種模式：手動、半自動、全自動。由于各種因素的影響，在前兩種模式下每次模塑的循環(huán)時間不盡相同，這會影響到模具溫度和物料在料筒中的停留時間，進(jìn)而影響到制件的精度，因此在精密成型中應(yīng)盡量采用全自動的模式[ 14 ]。
3.2 精密注塑機(jī)的溫度控制和新型螺桿的設(shè)計(jì)
注塑機(jī)筒上自動調(diào)溫器的循環(huán)性開和關(guān)導(dǎo)致了料筒內(nèi)熔料密度和粘度的變化，從而影響制件質(zhì)量和尺寸精度的周期性波動;注塑機(jī)的噴嘴緊靠模具型腔，所以噴嘴的溫度對模塑制件也有重大的影響。
4 精密成型新技術(shù)
4.1 在模具中應(yīng)用注射壓縮成型( ICM)技術(shù)
ICM技術(shù)是指模具開啟一定距離的條件下開始注射，注射到一定量后，模具開始閉合對型腔內(nèi)的熔體實(shí)施壓縮，模具完全閉合時注射終止，然后保壓、冷卻直到取出制品。
4.2 高速注射成型
高速注射成型方法的熔體填充速度較傳統(tǒng)的快10 ～100倍，使熔體在模腔內(nèi)產(chǎn)生高剪切的流動，粘度下降，充模速度快，塑料表面硬化減慢，因而可提高薄壁制品的成型厚度極限，抑制過度的成型壓力，同時由于模內(nèi)低壓流動，制品的內(nèi)應(yīng)力降低。
4.3 無保壓的注射成型
無保壓注射成型技術(shù)是指將塑料熔體以高速、高壓充填入模具，然后關(guān)閉設(shè)于噴嘴的針閥，以模腔內(nèi)的塑料熔體自動彌補(bǔ)制品各部分的收縮，這樣可以大大降低制品的翹曲變形。
4.4 其它的智能控制技術(shù)
精密注射成型過程中對加工條件實(shí)行持續(xù)性監(jiān)測和精確控制非常重要。隨著計(jì)算機(jī)技術(shù)的發(fā)展，計(jì)算機(jī)化的注射成型已得到廣泛的應(yīng)用。
5結(jié)語
對塑料制品高精度、高性能要求的日益增長是精密注射成型技術(shù)前進(jìn)的動力，人們對精密注射成型原理理解的不斷深化是精密注射成型技術(shù)進(jìn)步的基礎(chǔ)。隨著新材料、新工藝和新設(shè)備的相繼出現(xiàn)，尤其是計(jì)算機(jī)在塑料加工中的廣泛應(yīng)用，為精密注射技術(shù)創(chuàng)造了良好的條件。對只要合理的利用這些技術(shù)，就一定能生產(chǎn)出精密的制品。
參考文獻(xiàn)
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