Weld Line Strength Research Articles

Optimizing the Tensile Strength of Weld Lines in Glass Fiber Composite Injection Molding.

Weld line defects, commonly occurring during the plastic product manufacturing process, are caused by the merging of two opposing streams of molten plastic. The presence of weld lines harms the product's aesthetic appeal and durability. This study uses artificial neural networks to forecast the ultimate tensile strength of a PA6 composite incorporating 30% glass fibers (GFs). Data were collected from tensile strength tests and the technical parameters of injection molding. The packing pressure factor is the one that significantly affects the tensile strength value. The melt temperature has a significant impact on the product's strength as well. In contrast, the filling time factor has less impact than other factors. According to the scanning electron microscope result, the smooth fracture surface indicates the weld line area's high brittleness. Fiber bridging across the weld line area is evident in numerous fractured GF pieces on the fracture surface, which enhances this area. Tensile strength values vary based on the injection parameters, from 65.51 MPa to 73.19 MPa. In addition, the experimental data comprise the outcomes of the artificial neural networks (ANNs), with the maximum relative variation being only 4.63%. The results could improve the PA6 reinforced with 30% GF injection molding procedure with weld lines. In further research, mold temperature improvement should be considered an exemplary method for enhancing the weld line strength.

Investigation of microstructural and mechanical properties of weld lines in injection‐molded short glass fiber‐reinforced polyamide 6

AbstractThis research investigates the impact of weld lines on the mechanical properties and fracture behavior of injection‐molded unfilled and glass fiber‐reinforced polyamide 6 (PA6). The study aims to predict the weld line strength by analyzing the composite's microstructure at the weld line and investigating the influence of injection molding parameters. While weld lines had minimal effects in unfilled PA6 thanks to the matrix's high healing capability, composite samples showed reduced mechanical properties due to unfavorable fiber orientation at the weld line. Fracture surfaces revealed a bell‐shaped structure linked to the ‘underflow’ process caused by flow imbalances during injection molding. This phenomenon impacts fiber orientation at the weld line, affecting mechanical properties. The ‘underflow’ is simulated using Autodesk Moldflow®, predicting enhanced fiber alignment along the flow direction. Regarding processing parameters, both melt and mold temperatures showed negligible impacts, while enhanced mechanical properties were observed at elevated packing pressures. The analysis of fracture surfaces showed intensified “underflow” with increased packing pressure. A relationship is established between weld line strength and fiber orientation at the weld line, potentially serving as a predictive tool for estimating weld line strength.Highlights Weld lines in unfilled PA6:Negligible impact on the mechanical properties. In the PA6 composite: significant drop due to unfavorable fiber orientation. Fracture behavior of the composite: Bell‐shaped weld line linked to “underflow.” Melt and mold temperature: minor effect; packing pressure enhances properties. Correlation established between the weld line strength and fiber orientation.

External gas-assisted mold temperature control and optimization molding parameters for improving weld line strength in polyamide plastics.

In this study, we present a novel approach to injection molding, focusing on the strength of weld lines in polyamide 6 (PA6) composite samples. By implementing a mold temperature significantly higher than the typical molding practice, which rarely exceeds 100°C, we assess the effects of advanced mold temperature management. The research introduces a newly engineered mold structure specifically designed for localized mold heating, distinguishing it as the 'novel cavity.' This innovative design is compared against traditional molding methods to highlight the improvements in weld line strength at elevated mold temperatures. To optimize the molding parameters, we apply an Artificial Neural Network (ANN) in conjunction with a Genetic Algorithm (GA). Our findings reveal that the optimal ultimate tensile strength (UTS) and elongation values are achieved with a filling time of 3.4 seconds, packing time of 0.8 seconds, melt temperature of 246°C, and a novel high mold temperature of 173°C. A specific sample demonstrated the best molding parameters at a filling time of 3.4 seconds, packing time of 0.4 seconds, melt temperature of 244°C, and mold temperature of 173°C, resulting in an elongation value of 582.6% and a UTS of 62.3 MPa. The most influential factor on the PA6 sample's UTS and elongation at the weld line was found to be the melt temperature, while the filling time had the least impact. SEM analysis of the fracture surfaces revealed ductile fractures with rough surfaces and grooves, indicative of the weld line areas' bonding quality. These insights pave the way for significant improvements in injection molding conditions, potentially revolutionizing the manufacturing process by enhancing the structural integrity of the weld lines in molded PA6 samples.

Simulation‐based analysis of weld line strength of glass fiber‐reinforced polymer in injection molding

AbstractThe injection molding market is expected to grow with the increasing demand from various industries, such as automotive and furniture. However, weld lines in the injection molded part reduce the structural strength and affects its appearance. This study evaluates the effect of the weld line on the structure by shifting the position of the weld line outside the area where the load is applied by manipulating the opening time of the injection gates. We examined the effect of weld lines on the strength of a chair through coupled resin flow and structural analyses. The analysis revealed that the position of the weld lines is crucial for structural strength if the knockdown factor (KDF) is low. Additionally, controlling the opening time of the gate and shifting the position of the weld line improved the structure's appearance, number of weld line and avoid the lower meeting angle. However, depending on the material, the effect may be weak. For example, when the weld line location did not change much despite changing the gate timing, little change was observed in the number of weld lines. Hence, the improvement strategy of weld line should be considered for material types and strength.Highlights Injection molding growth driven by automotive, packaging, furniture demand. Weld lines impact structural strength and appearance. Shifting weld line position outside load area improves the structural appearance and strength. Effects of shifting weld line position depended on the material types. Weld line position is crucial for low knockdown factor and affects strength.

Weld-line strength prediction for glass fiber reinforced polyamide-6 material through integrative simulation and its experimental validation

Injection molding is one of the preliminary production methods for plastic components. Typically, injection molding Moldflow simulations predicts potential issues like air void, weld-line, warpage etc. This work focuses on weld-line defect, which occurs when two or more flow fronts are meets each other during filling of the cavity. Most of the commercial algorithms are based on isotropic and homogeneous material assumptions however plastic materials are anisotropic and heterogeneous in nature. Therefore, accuracy with isotropic solvers may vary with actual reality. To consider material anisotropy and heterogeneous nature of the material, an integrative simulation is advantageous technology which gives more realistic results. A unique approach of integrative simulations has been used in this work to predict the strength of the weld-line as there is no direct standard procedure or software available to get weld-line strength. Moldflow simulation is performed on specially designed plaque wherein the weld-line is reproduced considering 30% glass-filled polyamide-6 material. The new material model is developed by mapping the structural model of tensile specimens on the Moldflow simulated plaque with integrative mapping approach. The mapped model considers fiber orientation and weld-line characteristics of the material which is then solved in the Abaqus structural solver. Experimental validation is performed by manufacturing of weld-line plaques, specimen preparation, and experimental testing. The results correlation is done for an isotropic and anisotropic material model with experimental results. The correlation study shows, a significant difference in results for isotropic simulation and integrative anisotropic simulations. The failure pattern and load-displacement behavior of integrative simulation is close match with experimental results with minimum 93% accuracy.

Effect of Wall Thickness and Flow Distance behind an Obstacle on the Weldline Strength of Thermoplastic Composites

The strength of the weldline behind an obstacle in injection molded thermoplastic composites was investigated in this study. The effects of part thickness, glass-fiber length, and concentration on the weldline strength at different positions behind the obstacle were examined. The results showed that the mechanical properties of the specimen containing weldline were much lower as the fiber length and content increased. Considering the effect of part thickness on the weldline strength, it was observed that the weldline strength decreased as the part thickness increased. This was due to the fiber orientation and the void generation within the molded parts. The results obtained for the weldline strength at various positions along the weldline indicated that the weldline strength tended to increase with the increase of flow distance, especially for polypropylene containing 40 wt% long-glass-fibers. The explanation for this could be associated with the change in fiber orientation during the flow development.

Weld Line Strength of Polyamide Fiberglass Composite at Different Processing Parameters in Injection Molding Technique.

This study examines the impact of injection parameters on the weld line strength of the polyamide 6 and 30% fiberglass (PA6 + 30% FG) composite samples. The effects of filling time, packing time, packing pressure, melt temperature, and mold temperature on the ultimate tensile strength (UTS) and the elongation value of the weld line are investigated. The results reveal that the filling time factor has the lowest influence rate. On the contrary, the packing pressure has the most considerable value of UTS standard deviation, indicating that this factor has a high impact rate. The melt temperature factor has the highest elongation standard deviation, pointing out the strong impact of melt temperature on the elongation value. In reverse, the filling time factor has the lowest elongation standard deviation, showing the low impact of this factor on the elongation value. Increasing the mold temperature enhances the elongation value greatly because a higher temperature generates a better connection in the weld line area. Although the UTS value improves modestly when the mold temperature control system is used, the elongation result from the mold temperature parameter is better than expected. The UTS result from all parameters presents a minor deviation; therefore, it is lower than expected. The optimal strength result from artificial neural networks with genetic algorithm optimization is 85.1 MPa, which is higher than the best experiment result of 76.8 MPa. Scanning electron microscopy (SEM) results show that the interface between the fiberglass and the PA matrix has high adherence. The fracture surface is smooth, indicating that the PA6 + 30% FG composite sample has a high fragility level. The findings could help to increase the injection sample's weld line strength by optimizing the injection molding conditions.

Analysis of Weld Lines in Micro-Injection Molding.

Micro-injection molding (µIM) is a widespread process for the production of plastic parts with at least one dimension, or feature, in the microscale (conventionally below 500 µm). Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are present on the parts: the so-called weld lines. As weld lines are crucial in determining mechanical part performances, it is mandatory to clarify weld line position and characteristics, especially at the industrial scale during mold design, to limit failure causes. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. This work examines the influence of mold temperature on the weld line position and strength by both experimental and simulation approaches in µIM. At mold temperatures below 100 °C, only short shots were obtained in the chosen cavity. At increased mold temperatures, weld lines show up to a 40% decrease in the whole length, and the overall tensile modulus doubles. This finding can be attributed to the reduction of the orientation at the weld line location favored by high mold temperatures. Moldflow simulations consistently reproduce the main features of the process, weld line position and length. The discrepancy between experimental and simulated results was attributed to the fact that crystallization in flow conditions was not accounted for in the model.

Enhancing the Fatigue Strength of the Weld Line in Advanced Polymer Injection Molding: Gas-Assisted Mold Temperature Control for Thermoplastic Polyurethane (TPU) Composites.

This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold temperature control, significantly increasing mold temperature beyond typical values observed in conventional processes. We investigate the effects of various heating times and frequencies on the fatigue strength of Polypropylene (PP) samples and the tensile strength of Acrylonitrile Butadiene Styrene (ABS) composite samples at different Thermoplastic Polyurethane (TPU) percentages and heating times. Using gas-assisted mold heating, mold temperatures exceeding 210 °C are achieved, which represents a significant advancement compared to the standard mold temperatures of less than 100 °C. As a result, the fatigue strength of the PP sample with mold heating at 15 s shows a remarkable increase of up to 5.4 times at 5 Hz compared to the sample without mold temperature control. Moreover, ABS/TPU blends with 15 wt.% TPU exhibit the highest ultimate tensile strength (UTS) value of 36.8 MPa, while blends with 30 wt.% TPU have the lowest UTS value of 21.3 MPa. This advancement demonstrates the potential for improved welding line bonding and fatigue strength in manufacturing. Our findings reveal that increasing the mold temperature before injection results in higher fatigue strength in the weld line, with the TPU percentage having a more significant influence on the mechanical properties of ABS/TPU blends than heating time. The results of this study contribute to a deeper understanding of advanced polymer injection molding and offer valuable insights for process optimization.

Prediction of weldline strength for injection molded short-glass-fiber composites

This paper provides a modified rule-of-mixtures relationship which allows for the calculation of weldline strength as a function of the area fraction between skin and core layers. The effects of fiber length and fiber orientation within the skin and core layers on the weldline strength of injection molded short-glass-fiber reinforced polypropylene have been studied in detail. The present theory is then applied to exiting experimental results and the agreement is found to be satisfactory.

Effect of packing pressure on stagnation weld-line strength for thermoplastic semicrystalline glass fiber reinforced material

Weld-Line in an injection molded part develops when two or more melt fronts are converged together. The weld-line is unavoidable when the design is complex where two melt flow fronts are mating each other head-to-head, this mating area is mechanically weak compared to other portions of the modeled part. The decrease in strength in the weld-line area can be attributed to several factors like molecular diffusion, fiber orientation effect, unoptimized process conditions, surface tension effect, internal residual stresses, etc. The strength of the weld-line area can be increased by optimizing injection molding process parameters like melt temperature, injection speed, packing pressure, changing gate type and location, etc. The present work focuses on studying the effect of packing pressure on strength of stagnation weld-line. This has been examined with experimental testing and scanning electron micrographs of the fractured surface on the weld-line and without weld-line specimens. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. The plaques are prepared out of 30% glass-filled Polyamide 6 material. The four sets of plaques are produced by changing the magnitude of packing pressure equal to 60% of filling pressure, with increment of 20% up to 120% of filling pressure. The tensile test specimens are machined on these plaques for two different angular orientations and testing is conducted as per ISO 527-2. The results demonstrated that, without weld-line specimens, the tensile modulus, stress at break marginally increases with an increase in packing pressure, and strain at break decreases with an increase in packing pressure. However, for specimens with stagnation weld-lines, both the tensile modulus and stress at break are observed to be 42% of without weld-lines samples for minimum packing pressure. The results obtained are evident from stress-strain graphs and scanning electron micrographs.

An integrated simulation method for analyzing mechanical properties of injection molded fiber‐reinforced polymers

AbstractInjection molded fiber‐reinforced polymers have been widely used for their excellent comprehensive properties. Due to the high cost of injection molds, how to improve the strength of the products in the design stage is a problem worthy of researching. This study presents a novel method for predicting the product strength via analysis of weld line and fiber orientation, which are two key factors in injection molding. In this study, injection molding simulation was carried out in commercial software Moldex3D to obtain the information about weld line, fiber orientation and other factors which were used for prediction of strength of products. Based on the healing theory and interdiffusion model, a weld line strength model for injection molding is established. The effects of fiber orientation distribution on strength were investigated through Abaqus structural analysis. The proposed method was used to verify the experimental results in the existing literatures and the simulation results were in good agreement with the experiments. The method was applied in the gate design of an aerospace product. This study indicated that the proposed method has great potential for mold design, product structure design and process optimization.

Effect of Vibrations on the Weld-Line Strength of Injection Molded Products

In this research, vibrations were added to the mold structure. In the molding process, each vibration was turned on during the filling process. Moreover, the mold structure was re-designed to insert the vibration equipment. The design of this equipment is an early version used to insert vibrations. This option was chosen to facilitate the process of manufacturing and installing the vibration part. However, the applied method still has some limitations, such as not exerting an impact on the exact position where the weld line occurs. To overcome this disadvantage and to help increase the vibrations of the insert, we used a flexure hinge placed inside the insert. This design helped to improve the flow disturbance and to accurately impact the position where the weld line occurred. Therefore, the results of our method are better than those of the method currently being applied.

Welding Parameter Optimization for Improvement of Mechanical Strength of Weld Line

In this study, MIG welding parameters were optimized by experts. The results showed that heat input affected the welding of all five specimens, and similar structural changes were observed. The part adjacent to the weld line, using low HI (BM) lower than the melting point, increased the grain size and decreased the average hardness (87 HV) at HAZ. In comparison, high HI (WZ) at melting point resulted in fine grain with a high hardness of 126.8 HV and tensile strength of 686 MPa. Nevertheless, fatigue testing revealed that the specimens suffered a brittle fracture under a slight load cycle of 104 Nf. Correlation analysis of HI, mechanical properties and optimization plot revealed the optimum HI of 363 J/mm, and the verification by fatigue testing showed the optimum load cycle of 106 Nf. However, the determination of maximum strength should be done using several techniques for more effective improvement of quality and yield using the research findings of this study.

Evaluation of shrinkage and weld line strength of thick flat part in injection moulding process

Evaluation of shrinkage and weld line strength of thick flat part in injection moulding process

Evaluation of healing models to predict the weld line strength of the amorphous thermoplastic polystyrene by injection molding simulation

AbstractIn many injection molded parts weld lines are often unavoidable. These cause optical defects and a reduction of the mechanical properties of the part. Therefore, the predictability of the weld line strength at an early stage of development would provide a significant advantage by avoiding costly iterations of the mold and increases the understanding of the correlation between process history of the melt and weld line strength. For this purpose, a calculation routine has been developed to predict the weld line strength based on injection molding simulation. Different models to calculate the healing of a weld line are compared and analyzed. By adding a factor to consider the shear rate in addition to the temperature and the pressure and after calibration to one design of experiment setting of the experimental data, the prediction of the weld line strength shows good agreement for all examined process setpoints of the experimental data for polystyrene.

Injection Molding Study on the Strength of Weld Line for Polycarbonate and Carbon Fiber Composite Material

In this study the polycarbonate (PC) and carbon fiber (CF) are used as the experimental materials to investigate the impact of injection molding process parameters on tensile strength of weld line using Taguchi method and response surface methodology. The experiments are conducted via 27 sets of parameter combinations designed based on carbon fiber content, melt temperature, mold temperature, injection speed, injection pressure, packing speed, and packing pressure. The process parameter combination with the highest tensile strength is identified using Taguchi method. Later on, the response surface methodology is used to establish the tensile strength predicting formula formed by process parameters in order to understand the correlation between process parameters and tensile strength. The experimental and analysis results indicate the melt temperature and mold temperature have the most significant impacts on tensile strength.

Weld line strength factors in a reinforced injection molded part: Relationship with predicted fiber orientation

In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Injected plates were generated using a double-gated mold under four different process conditions. Quantification of the weld line detrimental effect was made in base on a fracture mechanics experiment. Specimens with and without the weld line—obtained from the same plates—were tested under a clamped single edge notched tension (SENT) configuration. For each set of process conditions, a relative weld line strength factor was defined in terms of the maximum applied stress intensity factor (KImax) as: KImax of specimens with weld line/KImax of specimens without weld line. In parallel, the fiber distribution pattern was obtained by process simulation software Moldex3D. An orientation factor was determined from simulation in order to quantify the effect of the local fiber orientation around the weld line. Optimal process condition and the most significant variable influencing the weld line strength were calculated via statistical analysis. Results showed a clear correlation between the weld line strenght factors and the orientaion factor. It was demonstrated that the fracture performance of the weld line region is controlled by the fiber orientation arrangement developed on that zone.

Investigation of the effects of pre-cross-linked thermoset molding compounds on weld line strength in injection molding

In this study, epoxy molding compounds (EMC) filled with glass beads were fabricated with a twin-screw-extruder (TSE) and tempered before further processing to generate different degrees of cross-linking (0–15%) in the compounds. After that, the compounds were injection-molded into tensile samples with and without weld lines to investigate the influence of pre-cross-linking of compounds on the weld line strength. Both the referent fracture strength and the weld line strength were improved with the increase of pre-cross-linking in compounds. Especially, cavities in the weld line area were reduced presumably due to the improved venting with the increased viscosity. For the resized samples without notches, their weld line strength are higher than those with notches. The in-mold pressure of more pre-cross-linked compounds can be hold longer than less pre-cross-linked compounds. This could lead to a better compensation of the material shrinkage. This might be the reason for the improved weld line strength for more pre-cross-linked compounds.

Effect of Melt Temperature on Weld Line Strength

This article deals with the influence of the melt temperature on weld line strength in injection-molded plastic parts. A special mold was created for this investigation to make specimens with a central weld line. The experimental material was polypropylene Sabic PP 90910. Its stress at break is around 16 MPa and its melting temperature is between 200°C and 260°C. In general, the presence of weld lines has a negative impact on mechanical properties. This investigation showed that the strength depends on the melt temperature (160–260°C in this case). Strength was measured using mechanical testing. It was found to increase with the melt temperature, up to 210°C. Above 210°C, degradation of the plastic led to decreasing strengths. A melt temperature range of 190–210°C is therefore optimal for this application. Shear forces and friction were found to play a great role, as they raise the melt temperature during molding. This was confirmed by mold-flow analysis. The melt temperature during molding was up to 18% higher than the initial melt temperature. This investigation has important consequences for the plastic industry. It is relevant to evaluations of the polymer matrix strength in composite materials and the strength of 3D printed parts with multiple weld lines.