FM全新卡车顶篷把手气辅成型技术

研究了气辅成型过程中气体穿透聚合物熔体的扩散特征和气.熔界面形态.以FM全新卡车顶篷把手为典型件进行气辅成型实验研究,研究了气体保压压力、熔体温度、气体保压时间、气体注射延迟时间四个重要工艺参数对气熔界面的影响规律.结果表明,在气体注射点近区,气体对聚合物熔体冲击程度较大.呈现出复杂流动形态及扩散特征;低的保压压力和熔体温度,较短的保压时间和较长的气体注射延迟时间可获得较好的气熔界面.     

气辅注射成型-维充填过程的最小注射量分析

对气辅注射成型-堆充填过程的初始注射量进行了研究，井推导出了熔体最小注射量的计算公式．为气辅注射成型工艺的实际应用起到了指导作用．     

气辅成型工艺参数交互作用对气指缺陷的影响

采用正交实验方法和数值模拟方法对气辅成型制品“气指”缺陷进行了研究。研究了熔体温度与气体注射延迟时间、熔体温度与气体注射压力及气体注射延迟时间与气体注射压力三对工艺参数的交互作用对气辅成型制品“气指”缺陷的影响关系。结果表明:熔体温度与气体注射延迟时间的交互作用对“气指”影响较为严重,其它两对工艺参数对“气指”的影响较小。较长的延迟时间可以减轻气指的程度,但延时过长会造成气体无法穿透或穿透不足等问题,因此选择合适的熔体温度和气体延时组合尤为重要。     

气辅成型过程气体穿透行为的MPI三维模拟及实验

采用MPI/GAS-3D模块分析了不同延迟时间和气体压力条件下的气体穿透效果,并与该工艺条件下实验测定的高密度聚乙烯(HDPE)气体辅助注射成型(GAIM)制品的气体穿透长度(GPL)及残余壁厚(RWT)进行比较,探讨了气辅成型中延迟时间和气体压力等关键工艺参数对制品气体穿透长度和残余壁厚的影响,利用实验数据分析了气体穿透长度与残余壁厚之间的定性关系。     

工艺参数对气辅成型过程的影响

为了精确描述气体辅助充填成型中气体穿透推进过程,研究各工艺参数对成型结果的影响,本文基于气体穿透机理的研究分析,将三明治成型理论应用于气辅成型.以矩形平板型腔为例,结合Hele-Shaw流动模型,建立了气辅充填成型首次气体充填过程的压力控制方程和气/液交界面运动方程,对其应用有限元进行数值模拟.对气辅成型气体穿透过程及其基本规律和各工艺参数对成型结果的影响进行了分析和讨论.箅例结果表明:三明治成型理论应用于气辅成型所建数学模型能较好地揭示气体穿透推进过程的基本特征,并可作为气辅成型过程与实验手段相辅相成的研究工具.     

气体辅助注塑成型制件开发工艺研究

对塑料家俱制件进行了气辅注塑工艺开发与研究,考察了塑料转奇扶手的气辅加工中气嘴位置,熔体注入量,熔体注射温度,延迟时间、气休注射压力等对充模过程的影响,应用气辅注射模拟软件Ｃ－Ｍｏｌｄ对该制件的气辅助才不同工艺条件对气辅制件的影响做了模拟,并和生产实际进行了比较。     

气体辅助注射成型工艺及充模过程CAE分析

描述了气体辅助注射成型的工艺过程及熔体充填和气体穿入的数学模型，采用有限元／有限差分／控制体积法计算充填阶段的压力场和温度场，确定两类移动边界—熔体前沿和熔体／气体边界。并对典型制件进行模拟以验证模型的可行性。     

聚合物熔体环绕型芯充型流动行为的物理可视化分析

利用自行开发的超声振动辅助注射成型可视化实验装置,对不同注射速度下聚丙烯(PP)在环形型腔内环绕型芯充型流动特性进行可视化试验,观测分析不同注射速度对熔体充型流动行为的影响。分析结果表明,不同注射速度对环形制件注塑成型充型流动行为产生不同程度的影响,在较低注射速度时,型腔内的气体压力变化平稳,熔体流动速度比较平稳无明显变化;在较高注射速度时,在充填过程中型腔内的气体压力急剧变化,熔体速度出现波动且在流动后期熔体的流动速度出现骤降,注射速度对熔体流动前沿的面积变化也有直接影响。在高速注射时,型腔内气体压力的变化是影响熔体充型流动特性的主因;在低速注射时,熔体与型腔表面的热交换是影响熔体充型流动特性的主因。     

气辅注射成型一维充填过程的最小注射量分析

对气辅注射成型一维充填过程的初始注射量进行了研究,并推导出了熔体最小注射量的计算公式。为气辅注射成型工艺的实际应用起到了指导作用。     

基于气液两相流的聚合物气辅挤出数值模拟

为了更准确地反映气辅挤出中气体对熔体成型的影响机理,建立了气液两相流模型,对不同气压作用下的熔体挤出成型进行了有限元数值模拟,得到了气辅作用下熔体的流速、压力降和第一法向应力差等分布。与完全滑移边界条件的模拟结果对比发现,基于气液两相流的气辅挤出,熔体的流速、压力降和第一法向应力差等物理场均存在较大变化。实验也验证了熔体挤出成型受气压的影响较大。对模拟和实验结果分析表明,气体的辅助作用对熔体产生的第一法向应力差,是造成熔体流速、压力降和成型产生变化的主要原因。而这些是以完全滑移边界条件气辅模拟方法无法体现出来的。因此,气辅挤出模拟需要考虑气体层对熔体成型的影响,并且在实际气辅挤出加工中,需要合理地设置气压等工艺参数。     

Visualization of counter pressure mechanism in gas-assisted injection molding process

Abstract

Gas-assisted injection molding (GAIM) refers to injecting gas into the short shot melt during the filling stage. Compressed gas is used as the medium to push the melt and to provide the packing pressure. In GAIM, the hollow area and penetration length are the main factors that will affect the quality of molded parts. This study has applied a Gas Counter Pressure (GCP) mechanism and has discussed the effect of GCP in the GAIM process with in-mold visualization of this complex molding flow. This study introduces a counter pressure mechanism in a thick paper-clip-shaped cavity design. The flow field under different counter pressure conditions is observed by high-speed photography, the fiber orientations are analyzed with SEM, and the affected penetration length and hollow area are measured relatively. The experimental results show that when the GCP is applied to GAIM, although the hollow area is reduced, the penetration length will be increased, so as to make the quality of molded part more uniform and reduce the shrinkage. And a quantitative measuring method of two-stage penetration time span is proposed to get more in-depth discussion about the interactions between GCP and GAIM.     

The role of gas penetration on morphological formation of polycarbonate/polyethylene blend molded by gas-assisted injection molding

Polycarbonate (PC)/polyethylene (PE) blend was molded respectively by short shot (SS) and gas-assisted injection molding (GAIM). In order to investigate the origin of the “skin-core” structure during GAIM process, the morphology of the two parts molded by SS and GAIM, far from skin, was studied. The results indicate that the structure of the SS part (SSP) is similar to that molded by conventional injection molding (CIM), while the structure of the GAIM part (GAIMP) shows an unusual gradient structure. Many coarse, short PC fibrils arise in sub skin, while such fibrils become more well-defined and reduce in number towards core layer. And the PC phase at the non-gate end, experiences more severe deformation than that at the gate end, which is also different from that in CIM parts. In addition, Moldflow 5.1, a commercial simulation package, was employed to determine the flow behaviors during SS and gas penetration processes. The experimental and simulated results indicate that shear rate and cooling rate are significant for the gradient structure formation during GAIM.     

玻纤增强HDPE气体辅助注射成型制品的形态

采用气体辅助注射成型(GAIM)和普通注射成型(CIM)制备了玻纤(GF)增强高密度聚乙烯(HDPE)复合材料。通过扫描电镜对复合材料中的玻纤取向进行了研究,发现CIM试样的玻纤仅在表层有轻微取向,而GAIM试样在整个横截面上玻纤均发生了明显的取向,且在次表层处取向强烈,排列十分规整。在此前研究工作的基础上,进一步探讨了玻纤取向结构的形成机理。     

Melt flow characteristics in gas-assisted laser cutting

We present a study on laser cutting of mild steel with oxygen as an assist gas. We correlate the cut surface quality with the melt film thickness. We estimate the optimum pressure required for melt ejection under laminar flow regime. The thickness of melt film inside the kerf is estimated using mass balance and the shear force acting on the cutting front assuming melt flow profile as linear. The dependence of melt film thickness on gas pressure, cutting velocity and work piece thickness is estimated and compared with experimental results.     

Flow-induced fiber orientation in gas-assisted injection molded part

Polyamide 66 with 33 wt.% glass fiber (DuPont, Zytel 70G33) was molded by gas-assisted injection molding (GAIM). Scanning electron microscope (SEM) micrographs indicated that fibers orientated notably in the core layer and slightly in the region near the mold wall, but aligned disorderly in the region near the gas channel. However, fibers orientated remarkably in the center of the thickness of the GAIM part, which was greatly different from the fiber orientation behavior in the samples molded by the conventional injection molding (CIM) and the water-assisted injection molding (WAIM) as reported in the literatures. Combining with a previous simulation dealing with gas penetration, the mechanisms for fiber orientation in the GAIM part are also discussed.     

气体辅助注射成型PC/PE共混物的形态

通过扫描电镜(SEM)对气体辅助注射成型(GA IM)PC/PE共混物制品相形态的观察,发现作为分散相PC的形变规律与在常规注射成型(C IM)制品中的情况有很大差异。在形态分析的基础上,探讨了气体穿透对气体辅助注射成型制品形态的形成和形态分布影响的机理。     

Influence of coating thickness and sand fineness on mold filling in the lost foam casting process

The effects of coating thickness and sand fineness on the mold filling characteristics of aluminum alloy 319 have been investigated. Experiments have been conducted with strip patterns and transparent molds have been used to visually record the flow behavior. The results indicate that a higher fill time is observed in thicker coatings and finer sands. Typical flow velocities are on the order of 80 mm/s and 90 mm/s for sands with AFS numbers of 80 and 20 respectively. By comparison, when a completely impermeable mold is used, the flow velocity is reduced to about 20 mm/s. Under normal casting conditions, the gases formed at the metal front are eliminated rapidly into the sand, so that there is no substantial gas layer ahead of the flowing melt. A gas layer may build up at the metal front if the permeability of the mold medium is not adequate and eventually the gas bubbles may escape by penetration through the liquid metal. Factors affecting polymer degradation may have strong effect on mold filling while parameters associated with the elimination of degradation products may control defect formation.