薄壁塑件注射压缩成型热残余应力仿真研究

使用Moldflow MPI/Injection-compression模块对薄壁塑件顺序注射压缩成型工艺进行了仿真,采用单因素试验研究了熔体温度、模具温度、延迟时间、压缩距离、压缩速度、压缩压力和保压压力对脱模后热残余应力的影响。仿真结果表明,顺序注射压缩成型薄壁制件热残余应力分布规律与常规注射成型相似,但是前者热残余应力较小且沿流动方向更为均匀;热残余应力随熔体温度、模具温度、压缩距离、压缩速度的增加而减小,随延迟时间和保压压力的增加而增大;压缩压力大于熔体流动阻力后,继续增大压缩力对热残余应力无影响。     

压缩工艺参数对注射压缩成型聚碳酸酯透明件残余应力的影响

基于注射压缩成型技术,以聚碳酸酯为原材料,采用不同的压缩工艺参数制备出聚碳酸酯透明件。结合成型过程中的模具型腔压力测试,采用定性（应力偏光法）和定量（小孔法）两种方法,对成型透明件的残余应力进行了测试,分析了压缩启动位置、压缩距离、熔体温度及模具温度等压缩过程的核心工艺参数对聚碳酸酯透明件残余应力的影响规律。结果表明,随着压缩启动位置的推迟或压缩距离的增大,型腔压力上升,使得制品的残余应力降低,当压缩启动位置从10 %延迟至70 %时,或者压缩距离从0.5 mm增大至2.0 mm,透明件测试点的Von Mises等效残余应力平均下降幅度达到82.0 %和64.7 %;随着熔体温度的升高或模具温度的升高,型腔压力变化并不明显,但制品的残余应力降低,当熔体温度从290 ℃升至320 ℃,或者模具温度从80 ℃升至120 ℃,透明件测试点的Von Mises等效残余应力平均下降幅度达到56.2 %和77.0 %。     

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。     

基于响应面法的注塑件残余应力优化

考虑模具温度、熔体温度、保压压力和保压时间等4个注塑工艺参数,利用响应面法进行实验设计,通过Moldflow注塑模拟软件对所设计的实验进行有限元分析,得到注塑工艺参数对制品残余应力值的影响.结果发现4个工艺参数中,熔体温度和保压压力对注塑制品残余应力值的影响极为显著,而模具温度和保压时间对制品残余应力值的影响则不显著.文章的研究结果为注塑工艺参数的调整、选取和优化,为获得残余应力值最小的优质塑料制品提供了方法和思路.     

薄壁制品微结构充填注射压缩成型中关键因素分析

利用正交实验和注射压缩成型方法,考察了温度和压缩工艺参数对薄壁制品不同位置3处微结构充填的影响。结果表明,距离浇口远近不同的微结构,其充填的影响因素不同;与温度因素相比,压缩工艺参数对微结构的充填起关键作用;压缩工艺参数中的打开距离和压缩速度对3处微结构的充填影响都较大,且打开距离越小,压缩速度越大越有利于微结构的充填。     

退火对注射成型PC制品力学性能的影响

注射成型的塑料光学制品应用日益广泛,但注射成型加工的聚碳酸酯制品通常有较大的残余应力,会对制品的光学性能、力学性能有负面的影响,而退火可减少/消除制品的残余应力。本文考察了退火对不同工艺条件下注射制品残余应力和力学性能的影响。研究的工艺条件包括三水平的变化的模具温度、熔体温度、保压压力、冷却时间等;残余应力的变化通过光弹实验的应力干涉条纹表示,力学性能的变化以拉伸强度、延伸率的变化表示。实验发现,退火前后,不同工艺条件下注塑PC制品拉伸强度平均提高4.5%,最大达9.0%;同时,断裂延伸率平均降低3%,最多减少14%。     

注塑工艺参数对制品残余应力和收缩的影响

注塑成型工艺参数对制品的最终残余应力和收缩有着直接的影响。基于线性黏弹性模型模拟计算了注塑成型过程中由温度和压力引起的残余应力和收缩。以无定型材料PS和ABS为例，系统地研究了不同成型工艺条件下平板制件的最终残余应力和收缩，并和实验结果进行对比验证。结果表明：在流动方向上无定型材料的收缩基本保持不变，残余应力沿壁厚分布的形状也基本相同，但流动末端处的应力值稍大于流动入口处；保压压力是影响制品收缩的关键因素，提高保压压力和注射温度可以降低制品的最终收缩，而模具温度对收缩的影响较小。     

微孔塑料注射成型制品体积收缩与翘曲变形数值分析

采用Moldflow软件，通过微孔注射成型过程的数值模拟，系统研究了熔体注射温度、模具温度对其体积收缩、翘曲变形和残余应力的影响规律，并基于流变学理论，揭示了其影响机理。研究结果表明，随着熔体注射温度和模具温度增加，微孔注射制品翘曲变形和残余应力均增加，成型制品的体积收缩随着熔体注射温度升高而增加，而随着模具温度升高而减小。本研究为微孔注射成型工艺和模具的设计提供理论指导。     

温度外场对注塑制品微观结构调控的数值模拟研究

利用数值模拟软件重点研究了由快变模温工艺提供的不同温度外场对注塑制品微观结构的影响规律。对结晶型聚丙烯注塑成型的模拟结果表明:提高模具型腔表面温度能有效减薄冷凝层,并降低注射压力;残余应力则随之呈现先降后升的趋势,其分布更均匀。结晶分析模块的结果表明:制品的结晶取向因子整体上随模具型腔表面温度的升高而下降;模具型腔表面温度的升高有利于增大制品晶体的平均粒径,但模具表面温度过高会导致制品晶体的平均粒径减小。     

基于Moldflow Insight2010的降低制品残余应力分析

注塑制品的残余应力影响制品的形状、表面质量及使用性能.在分析残余应力产生的机理和原因的基础上,应用软件模拟实验方法,介绍了降低残余应力的方法,结果发现冷却方式与熔体温度对残余应力的影响很大,其次是模具温度、保压压力和保压时间的影响,程度依次递减.得出的结论对工程实际应用有一定的指导意义.     

工艺条件对夹芯注射制品残余应力的影响

采用Moldflow公司MPI软件中的Co-injection分析模块，对ABS／PS夹芯注射成型过程进行动态模拟分析，以揭示工艺参数对夹芯注射成型过程中残余应力影响的规律。结果发现：在各种成型工艺参数中，保压条件对残余应力影响较为突出，模温条件对残余应力影响次之；最大残余应力主要分布在浇口位置和芯层最厚处，芯层前缘处残余应力次之，壳层最厚处残余应力最小。     

Hot Pressing of Annular Alumina–Zirconia Composites

An analysis is performed to predict the densification during and the state of residual stress after hot pressing of annular alumina/zirconia (3Y-TZP) composites. The objective of the analysis was to study the residual stresses resulting from stress gradients during pressing and those from thermal expansion mismatch during the cooling of the compact from the pressing temperature to room temperature. It is predicted that the residual stresses are affected by the respective densification rates of the core and the annulus, their elastic modulus, and thermal expansion coefficient. For the system analyzed in this study, it is predicted that hot pressing reduces the residual stresses that result from the mismatch in thermal expansion coefficients. This is due in part to the high densification rate and in part to the high elastic modulus of the alumina annulus compared to the zirconia core. For surface compression strengthening, a system where the annulus would have similar elastic modulus but lower densification rate and lower thermal expansion coefficient than the core would be more beneficial.     

Fracture surface morphology in thermosets modified with hollow microspheres

Fracture surface morphology in relation with toughening of thermosets modified with hollow microspheres was studied. Two different toughening methods were employed—one was with (MEH) and the other without (ME) compressive residual stresses around microspheres, respectively. The compressive residual stresses were to increase effective stress intensity factor. Various conditions arising from toughening method, properties of constituent materials, bonding between matrix and microspheres, relativity between bonding and microsphere strengths, and plane stress/strain were derived for part of generalization of fracture surface morphology. Mohr circle representations were employed for relative stress components analysis. New deformation mechanisms contributing to toughening were proposed. A major difference in toughening mechanism between ME and MEH methods was found to be in the location of plastic deformation under plane strain. The plastic deformation of ME was dominantly in matrix and appeared in the form of matrix cavitation. In the case of MEH, it was dominantly in microspheres. It was suggested that compressive residual stress promotes plastic deformation of microspheres caused by “extrusion” effect. The microsphere deformation in MEH was found also under plane stress although it was not as much as under plane strain. Matrix cavitation in ME under plane stress, however, was not found. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

基于盲孔法的ABS热焊板件残余应力测量

采用盲孔法对4种丙烯腈–丁二烯–苯乙烯塑料(ABS)热焊板进行了残余应力的测量,获得了这4种热焊板焊趾区的残余应力数据,结果发现,ABS经过热焊成型后容易在焊趾区形成较高的残余应力,随着测量时间的延长,热焊板焊趾区的残余应力逐渐增大,在测量7 min后释放完全。为了验证盲孔法应用于塑料热焊板残余应力检测的可行性,对ABS热焊板母材区和焊趾区以及热处理前后焊趾区的残余应力进行了测量,同时测试了4种热焊板的焊接强度,发现母材区的残余应力低于焊趾区,80℃热处理后焊趾区的残余应力比热处理前的低,残余应力较低的热焊板具有较高的焊接强度,这些结果均表明盲孔法对塑料热焊板件残余应力测量结果具有一定的参考价值。     

Process-induced residual stresses in compression molded UHMWPE

Non-isothermal cooling during processing causes the development of residual stresses, which are analyzed for compression molded UHMWPE, and affects the dimensional stability. The development of thermal residual stresses was predicted using an incremental stress analysis that included temperature-dependent material properties. Strain gauges were used to measure the residual stresses as layers were removed from a molded disk using a Process Simulated Laminate (PSL) approach. The PSL technique has not previously been applied to a compression molded neat polymer. For initial surface cooling rates of ～ 11°C/min, the model predicted a compressive stress at the bottom surface of 14 MPa and a tensile stress near the center of 2.5 MPa and matched the experimental distribution well. Because the compressive residual stress was 70% of the yield strength (～20 MPa), a lower cooling rate was also tested (2.6°C/min). The maximum tensile and compressive stresses for this cooling rate were, 0.91 MPa and 2.5 MPa, respectively. The model demonstrated its use for predicting thermal residual stresses in compression molded parts, instead of trial-and-error experimentation. UHMWPE is shown to develop residual stresses continually from ～ 120°C to 23°C.     

基于正交试验的塑料件残余应力优化分析

基于模流分析技术,以塑料件最小残余应力为目标,采用正交试验进行分析,得到最优工艺参数组合:熔体温度为260℃,模具温度为30℃,注射时间为2.5 s,保压压力设置为100%,保压时间为28 s,冷却时间为15 s。在该工艺条件下注塑件平均残余应力为8.847 MPa,该值小于各次正交试验下得到的各平均残余应力值。研究结果表明:塑料件离浇口越近则残余应力越小,塑料件离浇口越远则其中心区域残余应力越大;增加保压时间、降低冷却水温均能有效降低残余应力。