工艺参数对注塑件熔接痕性能的影响

概述了注塑件熔接痕的分类及特点；分析了工艺参数主要包括熔体温度、模具温度、充模速度、注射时间、注射压力、保压压力、后处理等对熔接痕的外观及性能的影响。着重阐述了各工艺参数对熔接痕性能影响的研究进展；综述了优化工艺参数和研究工艺参数对熔接痕影响程度的研究以及数值模拟技术，并从工艺方面提出了减小熔接痕损害的方法。     

Effect of process conditions on the weld‐line strength and microstructure of microcellular injection molded parts

This study was aimed at understanding how the process conditions affect the weld‐line strength and microstructure of injection molded microcellular parts. A design of experiments (DOE) was performed and polycarbonate tensile test specimens were produced for tensile tests and microscopic analysis. Injection molding trials were performed by systematically adjusting four process parameters (i.e., melt temperature, shot size, supercritical fluid (SCF) level, and injection speed). For comparison, conventional solid specimens were also produced. The tensile strength was measured at the weld line and away from the weld line. The weld‐line strength of injecton molded microcellular parts was lower than that of its solid counterparts. It increased with increasing shot size, melt temperature, and injection speed, and was weakly dependent on the supercritical fluid level. The microstructure of the molded specimens at various cross sections were examined using scanning electron microscope (SEM) and a light microscope to study the variation of cell size and density with different process conditions.     

Advanced injection molding mold and molding process for improvement of weld line strengths and isotropy of glass fiber filled aromatic polyester LCP

An advanced injection molding tool for measurement of mechanical strength and anisotropy of liquid crystal polymers (LCP)/mineral filler composites was developed. The mold produces thin‐walled LCP specimens that can be used by water cutting technique for production of an injection molded flow direction test bar, a transverse‐to‐injection molded flow direction test bar, a test bar for knit line strength measurement, and a test bar for butt weld line strength measurement. This tool and its use for molding experiments were optimized by experimental research and by computational calculations based on experimental parameters obtained by molding of several LCP test materials. Different pressure profiles and different injection speeds were tested as well as application of mold overflow phenomenon in production of test specimens. It was observed that a pressure controlled X‐melt technique and on the other hand fast injection speeds with overflow in conventional molding methods gave the best strength and isotropy properties for the test specimens. Results indicate that the mold developed is useful for determination of anisotropic and weld line strength properties of LCP composites. When developing “isotropic LCP” by different possibilities of nanotechnology this tool significantly reduces time of LCP material and process development. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Untersuchung zur Vorhersage der Bindenahtfestigkeit in spritzgegossenen Formteilen

Weld lines in injection molded parts are often weak spots and should therefore be taken into account as early as possible when developing new parts. The influence of material, nozzle and mold temperature respectively injection speed on weld line strength was investigated. By obtaining the actual temperature in the weld line, the interrelated processing influences can be expressed by a common relation. Physical analysis shows that this is the molecular mobility, which in turn is dependent on temperature. It opens a route backed by experimental results to assess the weld line strength of different materials in dependence of the processing parameters.     

Effect of processing on weld line strength in five thermoplastics

Weld line strength has been measured in five engineering thermoplastics. The effect of processing parameters was studied using experimental design. Four parameters–holding pressure, injection velocity, melt temperature, and mold temperature–were varied in two levels. For each parameter setting the weld line strength was measured and compared with the bulk strength via a weld line factor (WL-factor), defined as: strength of specimens with weld line/strength of specimens without weld line. Results from flexural tests on both filled and unfilled materials showed that the weld line factors for cold weld lines varied between 0.25 and 0.98 depending on material and parameter setting. Highest WL-factors were obtained for unfilled materials and using high melt temperature, high holding pressure, and low mold temperature. Results from instrumented falling weight impact tests on weld lines sometimes showed a WL-factor higher than 1.0. There was generally a poor correlation between results from impact tests and results from flexural tests.     

半透明注塑制品熔接痕分析及控制对策

借助模流分析软件Moldnow对半透明注塑制品熔接痕位置进行模拟分析,以此来优化浇口的位置和成型工艺参数,最终使熔接痕位于半透明注塑制品不重要的部位,并提高了熔接痕的强度.     

Enhancement of weld line mechanical strength using a novel ejector‐pins compression system

This study proposes a novel ejector‐pins compression system (EPCS) to improve the mechanical strength of weld lines that are formed in the injection molding process. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. In this experiment, several ejector pins are placed intentionally near the weld lines appearing, and are initially sunken beneath the cavity surface to form a reflow trap such that some of the molten plastics are allowed to flow into it during the filling process. These molten plastics are then compressed by the arisen ejector pins. Accordingly, the compressed molten plastics reflow through the weld lines, disordering the molecular orientation. Experimental verification revealed that the use of an EPCS can efficiently eliminate the orientation of the molecules parallel to the weld line. The specimens' impact strength of using EPCS can increase to between one and two times than that of conventionally injection‐molded. Therefore, this simple and novel method is feasible for greatly improving the mechanical strength of weld lines. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

A study on weld line morphology and mechanical strength of injection molded polystyrene/poly(methyl methacrylate) blends

In this work, the mechanical strength and weld line morphology of injection molded polystyrene/poly(methyl methacrylate) (PS/PMMA) blends were investigated by scanning electron microscopy (SEM) and mechanical property test. The experimental results show that the tensile strength of PS/PMMA blends get greatly decreased due to the presence of the weld line. Although the tensile strength without the weld line of PS/PMMA (70/30) is much higher than that of the PS/PMMA (30/70) blend, their tensile strength with weld line shows reversed change. The viscosity ratio of dispersed phase over matrix is a very important parameter for control of weld‐line morphology of the immiscible polymer blend. In PS/PMMA (70/30) blend, the PMMA dispersed domains at the core of the weld line are spherically shaped, which is the same as bulk. While in the PS/PMMA (30/70) blend, the viscosity of the dispersed PS phase is lower than that of the PMMA matrix, the PS phase is absent at the weld line, and PS particles are highly oriented parallel to the weld line, which is a stress concentrator. This is why weld line strength of PS/PMMA (30/70) is lower than that of PS/PMMA (70/30) blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1856–1865, 2002; DOI 10.1002/app.10450     

Ultrasonic improvement of weld line strength of injection‐molded polystyrene and polystyrene/polyethylene blend parts

The effect of melt temperature, ultrasonic oscillations, and induced ultrasonic oscillations modes on weld line strength of polystyrene (PS) and polystyrene/polyethylene (PS/HDPE) (90/10) blend was investigated. The results show that the increase of melt temperature is beneficial to the increase of weld line strength of PS and PS/HDPE blend. Compared with PS, the increase of melt temperature can greatly enhance the strength of PS/HDPE blends. For PS, the presence of ultrasonic oscillations can enhance the weld line strength of PS at different melt temperatures. But for PS/HDPE blends, the presence of ultrasonic oscillations can improve the weld line strength when the melt temperature is 230°C, but when the melt temperature is 195°C, the induced ultrasonic oscillations hardly enhance the weld line strength. Compared with Mode I (ultrasonic oscillations were induced into the mold at the whole process of injection molding), the induced ultrasonic oscillations as Mode II (ultrasonic oscillations were induced into the mold after injection mold filling) is more effective at increasing the weld line strength of PS and PS/HDPE blends. The mechanism for ultrasonic improvement of weld line strength was also studied. POLYM. ENG. SCI., 45:1666–1672, 2005. © 2005 Society of Plastics Engineers     

基于可视化技术的注射成型熔接痕缺陷的研究

介绍了动态可视化技术在注射充模过程中的应用。借助注射成型充模过程可视化实验装置,构造并记录了成型过程中的熔接痕缺陷的形成过程。分析了该缺陷的产生机理,并通过改变工艺条件改善了缺陷,为研究和排除制品缺陷提供了理论依据。同时,表明了可视化实验研究的意义。     

Glass Fiber/Polyphthalamide Composites for 3D-Molded Interconnect Devices Application: Structure and Properties

The research work was to demonstrate the feasibility of a three-dimensional molded interconnect devices concept using the injection-molding technique and to investigate the effects of weld/meld line types on the structure and properties. Two different polymers based on polyphthalamide/glass fiber composites (PA6 T/X and PA10 T/X composites) were produced by injection molding at the different processing conditions. A mold was designed in such a way that a weld and meld line can be produced at different angles by changing an insert inside the mold. The mechanical properties such as stiffness, tensile strength, and flexural strength were determined in tensile and flexural tests, respectively. The adhesive strength and electrical resistance were studied with the pull-off process and four-point measurement, respectively, and are discussed. The dispersion of the glass fiber and types of meld/weld line were inspected using scanning electron microscopy. The results were in-line with the expectation of a reduction in mechanical properties in areas where weld/meld lines occurred. The results of tensile tests clearly showed that the weld and meld lines showed a considerable influence on mechanical properties. It was found that the tensile and flexural strength of polyphthalamide/glass fiber composites with weld line type decreased approximately 58 and 62%, respectively, compared to the composites without the weld line. On the other hand, the effects of injection time and mold temperature on the tensile strength were marginal.     

Effects of geometry and injection‐molding parameters on weld‐line strength

Polymeric flows in microchannels are found to differ significantly from those in macrogeometries. Increasing the mechanical properties of microstructures is one of the most important issues in injection‐molding processes. Weld‐line characteristics of structures with different cross‐sections are investigated in this study. The effects of process parameters and cross‐sectional dimensions on the tensile strength of a weld line are discussed. A mold was designed in such a way that specimens with and without weld lines can be developed separately. Five specimens, with different cross‐sections, are injection‐molded simultaneously. Both polypropylene (PP) and high density polyethylene (HDPE) are used in this study. With the Taguchi method, four process variables: melt temperature, mold temperature, injection speed, and packing pressure were found to be the most influential. Experimental results show that the weld‐line strength from a standard test is not applicable in microinjection molding. The microstructure of weld lines is clearly observed from the micrographs. POLYM. ENG. SCI., 45:1021–1030, 2005. © 2005 Society of Plastics Engineers     

Thermal response of an electric heating rapid heat cycle molding mold and its effect on surface appearance and tensile strength of the molded part

Rapid heat cycle molding (RHCM) is a newly developed injection molding technology in recent years. In this article, a new electric heating RHCM mold is developed for rapid heating and cooling of the cavity surface. A data acquisition system is constructed to evaluate thermal response of the cavity surfaces of the electric heating RHCM mold. Thermal cycling experiments are implemented to investigate cavity surface temperature responses with different heating time and cooling time. According to the experimental results, a mathematical model is developed by regression analysis to predict the highest temperature and the lowest temperature of the cavity surface during thermal cycling of the electric heating RHCM mold. The verification experiments show that the proposed model is very effective for accurate control of the cavity surface temperature. For a more comprehensive analysis of the thermal response and temperature distribution of the cavity surfaces, the numerical‐method‐based finite element analysis (FEA) is used to simulate thermal response of the electric heating RHCM mold during thermal cycling process. The simulated cavity surface temperature response shows a good agreement with the experimental results. Based on simulations, the influence of the power density of the cartridge heaters and the temperature of the cooling water on thermal response of the cavity surface is obtained. Finally, the effect of RHCM process on surface appearance and tensile strength of the part is studied. The results show that the high‐cavity surface temperature during filling stage in RHCM can significantly improve the surface appearance by greatly improving the surface gloss and completely eliminating the weld line and jetting mark. RHCM process can also eliminate the exposing fibers on the part surface for the fiber‐reinforced plastics. For the high‐gloss acrylonitrile butadiene styrene/polymethyl methacrylate (ABS/PMMA) alloy, RHCM process reduces the tensile strength of the part either with or without weld mark. For the fiber‐reinforced plastics of polypropylene (PP) + 20% glass fiber, RHCM process reduces the tensile strength of the part without weld mark but slightly increases the tensile strength of the part with weld mark. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Weld lines in nylon 6 melt‐blended nanocomposites

The effects of weld lines in injection moldings of nylon 6 and nylon 6 nanocomposite samples were investigated by comparing single‐end‐gated and double‐end‐gated tensile samples. The single‐gated samples have no weld line, whereas the double‐end‐gated configuration produces a weld line at the center of the gauge length. Nylon 6 shows little variation in tensile properties for samples with or without weld lines, remaining ductile and tough, even with weld lines present. However, nylon 6 nanocomposites containing organically modified montmorillonite (organoclay), produced by a melt blending technique, exhibits rigid and brittle behavior for both single (no weld line) and double‐end‐gated (with weld line) samples. The organoclay increases the tensile strength but reduces the strain‐to‐failure significantly in both cases. A modified L₁₆ orthogonal array based on the Taguchi approach with three levels was designed to run injection‐molding experiments to allow production of a modest number of samples to identify the most important process factors. The results were analyzed using the statistical tools signal‐to‐noise (S/N) ratio and analysis of variance (ANOVA), in particular showing that the principal process factors for the double‐end‐gated nylon 6 nanocomposite samples are mold and melt temperatures. POLYM. ENG. SCI., 45:1606–1614, 2005. © 2005 Society of Plastics Engineers     

The V-notch at weld lines in polystyrene injection moldings

A major factor that weakens the weld line in injection moldings is the V-notch structure. Though the existence of a V-notch is well known, its depth variation with molding conditions has not been detailed. The aim of this paper is to clarify the V-notch structure and its effect on the strength of general purpose polystyrene injection moldings. A dog bone type tensile specimen with a weld line was molded under several molding conditions. The surface of the weld line was partially eliminated by cutting with a milling machine to seven levels of cut depth (D_c). As a result, the weld strength increased with D_c to about 50%. The relationship between the weld strength and D_c made it possible to determine the V-notch depth, which vas defined as the “depth of the weld line.” From these results, a hypothesis is proposed that the V-notch has a structure with a fine groove on the surface and a poorly bonded inner layer. This study considered the relationships among the weld strength, the depth of the weld line, and molding conditions.     

Weld line improvement of short fiber reinforced thermoplastics with a movable flow obstacle

Short fiber reinforced (SFR) thermoplastics are ideal materials from which to manufacture complex technical parts in high volumes with low energy expenditure. The orientation of the fibers, and hence their reinforcing effect, depends strongly on the nature of the cavity and on the injection molding process. One disadvantage of SFR thermoplastics is a significant decrease in mechanical properties in the areas of the weld lines, due to subopt imal fiber orientation as the melt streams reunite at these points. Common mold‐based and process‐based optimization techniques alter the fiber orientation after the formation of the weld line. The mold‐based approach presented here, on the other hand, operates at the time the weld line is formed: by redirecting the melt streams, it moves the weld line and improves the fiber orientation. A prototype mold is described, and samples produced from it with both standard and modified weld lines are compared with flawless specimens. The new technique yields a large rise in flexural strength and a smaller but significant improvement in tensile properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42025.     

基于可视化技术的注射成型冷接痕的研究

借助注射成型充模过程可视化实验装置,构造了3种形状的制品,在一定的工艺条件下观察到了冷接痕的形成过程,分析了冷接痕的产生机理,通过改变保压压力、熔体温度、注射速度等工艺条件改善或消除了冷接痕,为进一步研究和排除制品缺陷提供了参考。     

纤维增强PA66注塑熔接痕性能的工艺优化

针对注塑过程中纤维增强PA66制品出现的熔接痕缺陷,利用Taguchi方法设计了L9实验矩阵,分析了注塑压力、熔体温度、注射速率和保压压力等工艺因素对注塑件熔接痕拉伸强度的影响,预测了最大拉伸强度和最佳工艺条件,与实验结果具有很好的一致性。     

Injection Molding Optimization for Minimizing the Defects of Weld Lines

Weld lines are one of the critical defects in injection molding production. They affect the strength of the plastic parts and are visually unpleasant. To address this problem, this paper proposes some strategies and methods for the formulation and implementation of an optimization procedure to minimize the defects of weld lines by minimizing their total length and by positioning them as further away as possible from, or restricting them from occurring at, the specified critical regions on the part surface. Several concepts are defined, such as the weld line relevant part qualities, types of critical regions, and constraints on the occurrence of the weld lines. Based on these, the optimization problem is modeled and a genetic algorithm (GA) based optimization procedure is proposed. The methodology can provide useful guidelines for injection molding designers in achieving the optimal part quality relevant to the weld lines. A case study is also conducted to demonstrate the effectiveness of the methodology.     

Weld line morphology of injection molded polypropylene

The weakness of plastics at weld lines provides serious difficulties for the design and long term durability of injection molded parts. The goal of this work was to identify the cause of weld line weakness in polypropylene (PP) systems. The morphology of weld lines in a high molecular weight PP has been studied. It was found that the PP contains a hindered phenolic antioxidant additive that is not soluble in the polymer at the standard processing conditions. Transmission electron microscopy (TEM) pictures reveal the additive existing as a dispersed phase in the bulk polymer. Even though very small concentrations of this additive are normally used, (0.1–0.5%) large quantities were found at weld lines in a band approximately 100 nm wide and penetrating about 10 μm into the surface of the part, hindering strength development at the weld line. X-ray photoelectron spectroscopy (XPS) results confirm enhanced concentrations of antioxidant on the flow front and mold wall surface of short shot samples. The mechanical properties (Izod impact, tensile strength) are measured for samples molded at various processing conditions, varying amounts of antioxidant additive and with and without weld lines. The results are consistent with the presence of the additive playing a key role in strength development at PP weld lines.