An Investigation of Weldline Strength in Injection Molded Rubber Parts

Compression molding of randomly oriented strands (ROS) composites offers the possibility to manufacture complex parts with a fast processing cycle. In this paper, effects of pressure, strand size, temperature, and material placement in the mold cavity on the quality of a T-shape part were studied experimentally with carbon/polyether ether ketone ROS composites. Minimum filling pressure was obtained for the consolidation of a 25-mm deep cavity. Parts processed at filling pressure showed a void content no greater than 1.2%. Increasing pressure to 70 bar resulted in decreased void content as low as 0.03%. Mechanical testing of the T-shape showed similar strengths for parts processed at filling pressure and higher (70 bar). At the component level, initial strand placement greatly affected mechanical performance as the presence of a knit line was responsible for a reduction of 60% in tensile strength. The main findings show that processing a complex feature at filling pressure P fill was sufficient to reach nominal mechanical properties. This suggested that moderate porosity was not detrimental to the mechanical performance for the given tests where fatigue performance was not evaluated.

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“…The presence of merging flow fronts or of a knit line has been showed to be detrimental for injection-molded parts (Ref. 10).…”

Section: Manufacturing Proceduresmentioning

confidence: 99%

Study of Processing Conditions on the Forming of Ribbed Features Using Randomly Oriented Strands Thermoplastic Composites

Leblanc¹,

Landry²,

Lévy³

et al. 2015

j am helicopter soc

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“…From injection molding practice and literature, 1,3,4 it is generally accepted that: if a weld line forms before the filling is complete and is immediately subject to additional packing pressure, the weld line will typically be less visible and stronger. Additionally, if the Tw increases, intermolecular diffusion tend to increases due to the molecular chains gain an increasing ability to flow at the higher temperature.…”

Section: Discussionmentioning

confidence: 99%

“…Its presence causes reduced mechanical properties and visual defects due to the poor intermolecular entanglement, the molecular orientation induced by the fountain flow at this region, and the stress concentration effect of a surface V-notch. 1–4 Such effects may be worsened when considering discontinuous fiber-reinforced components. In general, the degree of change in the physical and mechanical properties produced by a weld line will depend on the ability of the two flow fronts to unite in the most homogeneous way possible.…”

Section: Introductionmentioning

confidence: 99%

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

Quintana

Frontini

2019

Journal of Reinforced Plastics and Composites

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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.

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“…Very limited research has been done on the formation of weld-lines in SMCs, whereas the effect of WLDs on short fibre reinforced (thermoplastic) composites has been studied to a great extent. In these cases, the effect of WLDs on the mechanical and physical properties was shown to depend on how homogeneously the two flow fronts unite [9]. Such previous studies showed that discontinuous fibres tend to reorient parallel to the WLD, decreasing the cohesion at the weld-region [10,11].…”

Section: Introductionmentioning

confidence: 88%

Quality Analysis of Weld-Line Defects in Carbon Fibre Reinforced Sheet Moulding Compounds by Automated Eddy Current Scanning

Fereshteh-Saniee

Reynolds

Norman

et al. 2022

JMMP

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Discontinuous fibre reinforced composites enable the manufacture of integrated structural components via the complex flow process of compression moulding. However, such processes can lead to the formation of detrimental weld-lines. Here, the meso-structure of carbon fibre sheet moulding compounds (C-SMC) was analysed using conventional non-destructive techniques and automated eddy current (EC) scanning, as well as destructive methods, in an attempt to identify defects such as weld-lines in this class of materials. Compression-moulded plaques with forced weld-lines in two different configurations (adjacent and opposing flow joints) were analysed, showing up to 80% strength reduction versus a defect-free plaque. The EC-determined local fibre orientation and elucidated local microstructure matched those obtained using conventional techniques, showing a dramatic fibre tow alignment parallel to the weld-lines. It was found that failure occurred in proximity to the “non-uniformity” defect regions identified by EC analyses, demonstrating the use of robot-guided EC for successful defect detection in C-SMC structures.

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An Investigation of Weldline Strength in Injection Molded Rubber Parts

Cited by 9 publications

References 13 publications

Study of Processing Conditions on the Forming of Ribbed Features Using Randomly Oriented Strands Thermoplastic Composites

Study of Processing Conditions on the Forming of Ribbed Features Using Randomly Oriented Strands Thermoplastic Composites

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

Quality Analysis of Weld-Line Defects in Carbon Fibre Reinforced Sheet Moulding Compounds by Automated Eddy Current Scanning

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