一种塑料精密成型复合工艺的研究

介绍了一种注射微压缩成型工艺及其特点,探讨了注射微压缩成型对制件成型精度,制件密实度和残余应力的影响,分析了制件力学性能的变化。采用常规注射成型和注射微压缩成型制件,对比两种成型工艺制件的拉伸强度,密度及残余应力。结果表明,相对于注射成型,注射微压缩丙烯腈-丁二烯-苯乙烯(ABS)和聚苯乙烯(PS)试样拉伸强度分别增加3.4%和4.48%,试样密度更高,残余应力减小。     

注射压缩成型工艺对长玻璃纤维增强聚丙烯注塑制品力学性能的影响

以长玻璃纤维增强聚丙烯(LFT-PP)为材料,利用自行设计带有压缩功能的模具,基于单因素实验方法,研究了压缩距离、压缩速度和压缩力对注射压缩成型(ICM)试样的玻璃纤维残余长度和力学性能的影响规律,在此基础上,对比了常规注塑成型(IM)和ICM方法成型的LFT-PP的玻璃纤维残余长度和力学性能差异。结果表明,玻璃纤维残余长度是引起ICM试样力学性能变化的主要因素,随着压缩距离、压缩速度以及压缩力的增大,试样内的纤维残余长度均先增加后减少,力学性能也随之先上升后下降;与拉伸强度相比,工艺参数对缺口冲击强度的影响更为明显。与IM相比,ICM可减少充模过程中纤维的断裂程度,提高玻璃纤维增强效率,增加制品的力学性能。ICM样品的平均玻璃纤维长度增加了44.1%,拉伸强度增加了18.4%,缺口冲击强度增加了243%。     

模具结构和熔体温度对PC透明制品性能的影响

用光弹实验测试不同浇口类型、不同熔体温度下聚碳酸酯透明注塑制品的应力分布,并测试了制品的拉伸强度和透光率。研究发现,模具结构对残余应力的分布形式影响显著,高应力区的拉伸强度较低,相对于无应力区最高降幅达2.69MPa;在同一成型条件下扇形浇口试样的透光率普遍要高于潜伏式浇口试样;熔体温度对试样的残余应力分布影响不大,但随着温度的升高,拉伸强度缓慢提高;要满足最佳透光率效果,不同模具结构的试样成型温度不同,试样的透光率最高达89.93%,浇口高应力区的透光率明显较低。     

液压脉动注射成型聚乳酸力学性能及生物降解性能的研究

在不同振动工艺参数下,研究液压脉动注射成型对聚乳酸(PLA)制品力学性能、结晶性能及生物降解性能的影响.结果表明,与普通注射成型相比,液压脉动注射成型的PLA制品拉伸强度提高了10.6%,冲击强度提高了29.7%,结晶度提高了11.9%.在蛋白酶K催化降解下,其生物降解过程是从表面侵蚀到内部整体侵蚀的逐步演变过程,制品总降解速率比普通注射成型的小.     

注射压缩成型聚碳酸酯制品的低温拉伸力学性能

以聚碳酸酯为材料,利用自行设计带有压缩功能的模具,采用常规注塑成型(IM)和注射压缩成型方法(ICM)对比研究制品在常温和低温环境下的拉伸力学性能;基于单因素实验方法,研究熔体温度、模具温度、模板压缩距离、延迟时间和压缩力对ICM制品残余应力和低温拉伸性能的影响规律。结果表明:在相同的环境温度下,ICM制品较IM制品有较大的屈服应力和弹性模量;低温环境下样品的拉伸性能有所提升,并在-40℃附近出现了聚碳酸酯分子的次级玻璃化转变;残余应力是影响ICM制品低温拉伸性能的主要因素,较高的熔体温度、模具温度、模板压缩距离,以及较短的延迟时间,较小的压缩力会减小ICM制品的残余应力,提高制品的低温拉伸性能。     

退火对微注射成型HDPE制品的增强增韧作用

分别在3个不同温度(85,105,125℃)进行退火3h,考察了退火前后高密度聚乙烯(HDPE)制品微结构和力学性能的变化。拉伸测试结果表明,退火显著提高了制品的拉伸强度和断裂韧性。利用差示扫描量热仪和X-射线衍射仪对退火后制品微结构的变化进行表征。结果表明,退火诱导新晶体的形成,促进初级晶体的完善、增厚,制品的结晶度提高。通过分析微结构的变化,阐明了微注射成型HDPE制品的增强增韧机理。     

微孔发泡模内表面装饰复合成型工艺参数对泡孔结构与力学性能影响

微孔发泡模内表面装饰复合成型工艺是高表观质量、轻量化塑料制品的重要成型方法,成型制品的泡孔结构与力学性能对其最终质量具有决定性影响.以典型拉伸样条为例,采用数值模拟的方法,通过对比分析不同工艺参数条件下平均气泡半径、密度和力学性能的变化规律,研究该工艺过程中主要工艺参数对泡孔结构及其力学性能的影响.结果表明,注射速率、...     

薄壁塑件注射压缩成型工艺的模拟分析

基于正交分析法和单因素分析法,用Moldflow软件数值模拟注射压缩成型中不同工艺条件对薄壁制品残余应力的影响.计算的残余应力沿厚度方向的分布表明:薄壁制品残余应力主要为流动诱导残余应力.模具温度与压缩距离对制品残余应力影响显著,模具温度越高,压缩距离越大,制品残余应力越小;其他工艺参数对残余应力均有不同程度的影响.     

PA12试件多射流熔融成型工艺研究

采用多射流熔融增材制造技术制备了PA12试件,研究了PA12试件不同的构建取向对其成型精度和力学性能以及致密度的影响规律。结果表明,当位置尺寸为宽度方向时,尺寸精度总是呈正偏差,并且在不同得成型角度下,无明显变化规律,与宽度方向相比,厚度方向与长度方向尺寸精度随成型角度增加,变化规律较为明显;试件的力学性能与延伸率受成型角度影响规律相似,当成型角度从0 °增加到45 °时,试件拉伸强度与延伸率逐渐降低,在成型角度大于45 °后,拉伸强度与延伸率显著提升;致密度变化趋势与力学性能保持一致;综合分析可得,当成型角度为45 °时,试件的尺寸精度达到最佳水平;最佳力学性能成型角度为0 °,此时PA12试件的平均拉伸强度为50.95 N/mm²,平均延伸率为37.02 %;致密度最高成型角度为0 °,平均致密度可达到99.311 %。     

退火对LLDPE/MWCNTs超薄制品的增强增韧作用

通过微注射成型技术制备了线性低密度聚乙烯/多壁碳纳米管(LLDPE/MWCNTs)超薄制品,分别在55,70,85,100℃下退火3h。通过拉伸测试、差示扫描量热分析和X-射线衍射表征考察了退火对LLDPE/MWCNTs制品结构及力学性能的影响。结果表明:退火显著提高了LLDPE/MWCNTs超薄制品的拉伸强度和断裂韧性。退火诱导新晶体的形成,促进初级晶体的完善,提高制品的结晶度。基于微结构的变化,讨论了退火后LLDPE/MWCNTs超薄制品的增强增韧机理。     

Effects of processing conditions on birefringence development in injection molded parts. II. Experimental measurement

The birefringence of injection molded parts was measured using a digital photoelasticity system, which combines a digital image analysis technique and the half-fringe photoelasticity (HFP) method The effects of processing conditions, including melt temperature, mold temperature, filling time and packing pressure, on the birefringence development in the molded parts were investigated. It was found that temperature and pressure are the two dominant factors that determine the birefringence development in the parts during the molding process. Frozen-in birefringence of the molded parts decreases with increasing melt temperature, mold temperature and injection speed. Birefringence of the parts also increases with increased packing pressure, especially around the gate area. Numerical simulations using the Leonov viscoelastic fluid model predict similar dependence of birefringence of parts on processing conditions. Simulated results are also consistent with measured values.     

注射成型聚苯乙烯制品双折射的光弹测试与分析

分析了无定形聚合物注射成型双折射行为及其产生机理,利用光弹法测试了不同工艺条件下聚苯乙烯(PS)平面内双折射分布,考察了熔体温度和保压压力变化对制品双折射和流动残余应力的影响。结果表明,PS制品残余双折射值在流动方向上从浇口附近至流动末端逐渐降低,并且最大双折射值随保压压力增加和熔体温度降低而升高;保压压力对浇口附近双折射分布影响明显。根据双折射的光弹测试结果分析了P制品分子取向和流动残余应力的分布趋势。     

Optimization and numerical simulation analysis for molded thin‐walled parts fabricated using wood‐filled polypropylene composites via plastic injection molding

Plastic injection molding is discontinuous and a complicated process involving the interaction of several variables for control the quality of the molded parts. The goal of this research was to investigate the optimal parameter selection, the significant parameters, and the effect of the injection‐molding parameters during the post‐filling stage (packing pressure, packing time, mold temperature, and cooling time) with respect to in‐cavity residual stresses, volumetric shrinkage and warpage properties. The PP + 60 wt% wood material is not suitable for molded thin‐walled parts. In contrast, the PP + 50 wt% material was found to be the preferred type of lignocellulosic polymer composite for molded thin‐walled parts. The results showed the lower residual stresses approximately at 20.10 MPa and have minimum overpacking in the ranges of ?0.709% to ?0.174% with the volumetric shrinkage spread better over the part surface. The research found that the packing pressure and mold temperature are important parameters for the reduction of residual stresses and volumetric shrinkage, while for the reduction of warpage, the important processing parameters are the packing pressure, packing time, and cooling time for molded thin‐walled parts that are fabricated using lignocellulosic polymer composites. POLYM. ENG. SCI., 55:1082–1095, 2015. © 2014 Society of Plastics Engineers     

Numerical prediction of residual stresses and birefringence in injection/compression molded center‐gated disk. Part II: Effects of processing conditions

The accompanying paper, Part I, has presented the physical modeling and basic numerical analysis results of the entire injection molding process, in particular with regard to both flow‐induced and thermally‐induced residual stress and birefringence in an injection molded center‐gated disk. The present paper, Part II, investigates the effects of various processing conditions of injection/compression molding process on the residual stress and birefringence. The birefringence is significantly affected by injection melt temperature, packing pressure and packing time. However, the thermally‐induced birefringence in the core region is insignificantly affected by most of the processing conditions. On the other hand, packing pressure, packing time and mold wall temperature affect the thermally‐induced residual stress rather significantly in the shell layer, but insignificantly in the core region. The residual stress in the shell layer is usually compressive, but could be tensile if the packing time is long, packing pressure is large, and the mold temperature is low. The lateral constraint type turns out to play an important role in determining the residual stress in the shell layer. Injection/compression molding has been found to reduce flow‐induced birefringence in comparison with the conventional injection molding process. In particular, mold closing velocity and initial opening thickness for the compression stage of injection/compression molding have significant effects on the flow‐induced birefringence, but not on the thermal residual stress and the thermally‐induced birefringence.     

The influence of injection molding parameters and blowing agent addition on selected properties,surface state,and structure of HDPE parts

The investigation of the influence of injection molding parameters (injection velocity, mold temperature and injection temperature, and additionally, as a result of these three parameters change, injection time, hold time, and cooling time) and blowing agent percentage on selected properties of HDPE molded parts such as weight, density, mechanical properties (tensile strength and elongation at maximum force), surface state (gloss and color), and structure was the aim of this work. The examination showed, that the mold temperature has the main influence on properties and surface state of molded parts from solid and foam HDPE. The weight, density, mechanical properties and gloss of molded parts increased with the increase in mold temperature. The mold temperature also influences significantly the number and size of pores in molded parts. The addition of blowing agent in a quantity of 2% is sufficient to obtain parts with favorable mechanical properties and good surface quality. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Influence of processing condition and carbon nanotube on mechanical properties of injection molded multi‐walled carbon nanotube/poly(methyl methacrylate) nanocomposites

In this work, multi‐walled carbon nanotubes (MWCNT) and poly(methyl methacrylate) (PMMA) pellets were compounded via corotating twin‐screw extruder. The produced MWCNT/PMMA nanocomposite pellets were injection molded. The effect of MWCNT concentration, injection melt temperature and holding pressure on mechanical properties of the nanocomposites were investigated. To examine the mechanical properties of the MWCNT/PMMA nanocomposites, tensile test, charpy impact test, and Rockwell hardness are considered as the outputs. Design of experiments (DoE) is done by full factorial method. The morphology of the nanocomposites was performed using scanning electron microscopy (SEM). The results revealed when MWCNT concentration are increased from 0 to 1.5 wt %, tensile strength and elongation at break were reduced about 30 and 40%, respectively, but a slight increase in hardness was observed. In addition, highest impact strength belongs to the nanocomposite with 1 wt % MWCNT. This study also shows that processing condition significantly influence on mechanical behavior of the injection molded nanocomposite. In maximum holding pressure (100 bar), the nanocomposites show highest tensile strength, elongation, impact strength and hardness. According to findings, melt temperature has a trifle effect on elongation, but it has a remarkable influence on tensile strength. In the case of impact strength, higher melt temperature is favorable. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43738.     

Numerical prediction of residual stresses and birefringence in injection/compression molded center‐gated disk. Part I: Basic modeling and results for injection molding

The present study attempted to numerically predict both the flow‐induced and thermally‐induced residual stresses and birefringence in injection or injection/compression molded center‐gated disks. A numerical analysis system has been developed to simulate the entire process based on a physical modeling including a nonlinear viscoelastic fluid model, stress‐optical law, a linear viscoelastic solid model, free volume theory for density relaxation phenomena and a photoviscoelasticity and so on. Part I presents physical modeling and typical numerical analysis results of residual stresses and birefringence in the injection molded center‐gated disk. Typical distribution of thermal residual stresses indicates a tensile stress in the core and a compressive stress near the surface. However, depending on the processing condition and material properties, the residual stress sometimes becomes tensile on the surface, especially when fast cooling takes place near the mold surface, preventing the shrinkage from occurring. The birefringence distribution shows a double‐hump profile across the thickness with nonzero value at the center: the nonzero birefringence is found to be thermally induced, the outer peak due to the shear flow and subsequent stress relaxation during the filling stage and the inner peak due to the additional shear flow and stress relaxation during the packing stage. The combination of the flow‐induced and thermally‐induced birefringence makes the shape of predicted birefringence distribution quite similar to the experimental one.     

Effects of annealing time and temperature on the crystallinity and heat resistance behavior of injection‐molded poly(lactic acid)

The effects of annealing time and temperature on the crystallinity of injection‐molded poly(lactic acid) (PLA) were investigated using differential scanning calorimetry and wide‐angle x‐ray diffraction. Differential scanning calorimetry, tensile test, and dynamic mechanical analysis showed that an increase in crystallinity in the PLA parts from the annealing treatment offers several benefits such as a higher glass transition temperature, better heat resistance, and greater storage modulus and tensile strength. Based on the experimental data, the degree of crystallinity, annealing time, and annealing temperature were found to closely follow the time–temperature superposition relationship. Namely, a master curve could be constructed based on either the Williams–Landel–Ferry equation or the Arrhenius relationship by shifting the crystallinity isotherms in the logarithmic scale horizontally along the log‐time axis. This relationship provides a quantitative guideline for annealing postinjection‐molded PLA parts to improve the heat resistance and mechanical properties. An increase of over 17% and 26% in tensile strength was achieved at an annealing temperature of 80°C for 30 min and 65°C for 31 h, respectively. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Improvement of optical quality and vibration characteristics of injection molded disk with processing condition control

Increased application of optical disks has required a rotating disk with more dynamic stability and better optical quality. A new concept of controlling the processing condition of injection molded disks is developed to improve their optical quality and vibration characteristics. To assess the effect of process conditions on residual stresses, birefringence, and critical speed, an orthogonal array for design of experiments is used. Melt temperature, filling speed, and packing pressure were effective parameters, but mold temperature and interactions among process conditions were not. The birefringence and critical speed were affected by the residual stress distribution, which varied according to the distance from the gate and processing condition. Considering the effect of the processing conditions and distance from the gate, we calculated the weight factors on residual stresses along the radial direction. Choosing weighted stress to be the target value for optimization of residual stresses, processing conditions control was accomplished. Under the newly proposed conditions, optical quality and stability of injection molded disk were simultaneously improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3275–3285, 2006     

Residual stresses and density gradient in injection molded starch/synthetic polymer blends

Residual stress distribution in injection molded starch/synthetic polymer blends was evaluated using the layer removal technique. The synthetic polymers in the blend were either polybutylene succinate (PBS) or polycaprolactone (PCL). The starch content ranged from 0 to 70% by weight in the PBS blend and was held constant at 70% in the PCL blend. The effects of various molding conditions, aging and starch content were investigated. The residual stress profiles were found to be parabolic in nature with surface compressive stresses and interior tensile stresses. Increasing the injection pressure and mold temperature decreased the tensile stresses but had no significant effect on the surface compressive stresses. Decreasing the packing pressure produced a significant decrease in the magnitude of residual stresses. Varying melt temperature and packing time did not significantly affect the residual stress distribution for the range of values investigated. The residual stresses relaxed with time, decreasing over a period of 57 days. The magnitude of residual stresses increased as the starch content in the PBS blends was varied from 0 to 70%. Density gradient measurements were made in a 70% starch/PBS blend. The density was found to be higher in the interior than at the surface with a steep gradient close to the surface. Varying the molding conditions had a complex effect on the average density and the density distribution.