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Injection molding manufacturing is immensely popular nowadays because of its excellent manufacturability for complex designs produced from a wide range of different engineering plastic materials. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms of weld-line, etc. The presence of a weld-line weakens components locally due to insufficient intermolecular diffusion, v-notch formation, fiber anisotropy, insufficient process conditions, and so on. When a component is under load, crack propagation usually begins with a weak weld-line area. Therefore, the designer should anticipate the presence of weld-lines and their strength to avoid failure of components during operation. In this article, the review of published research work on weld-line formation during injection molding has been summarized. The review focuses on the phenomenon of weld-line formation, the type of weld-lines, and the importance of weld-line evaluations. The theoretical, experimental, and computational approaches to analyzing weld-line and its strength are covered in detail. At last, methods for reducing weld-lines and increasing the strength of weld-line area have been discussed. This review also gathers data on weld-line strength with respect to different materials. Highlights * Details of weld-line formation and its types. * Importance of weld-line evaluation. * Methods of weld-line strength evaluation. * Methods of reduction of the number of weld-line and its effect. * Summary of weld-line strength for different material. KEYWORDS injection molding, Moldflow simulation, polyamides, thermoplastics, weld-line, 1 | INTRODUCTION Injection molding is a great invention made by the Hyatt brothers in back 1872. Nowadays injection molding is one of the most general manufacturing methods used to [...]

The injection molding process is widely accepted for the processing of engineering thermoplastics due to the ease of manufacturing complex designs. Weld-line is a defect occurring in injection molded parts when two flow fronts join each other. At weld-line locations, parts exhibit lower mechanical strength mainly due to inadequate intermolecular diffusion and fiber orientation anisotropy. The present work is aimed at investigating and comparing weld-line strength for unfilled and glass-filled polyamide-6 materials. To achieve this, polyamide-6 unfilled, 30% glass-filled, and 50% glass-filled materials are used to manufacture plaques. The special-purpose mold is designed to obtain plaques with and without weld-lines with help of Moldflow simulations. The specimens for tensile tests are then cut from molded plaques and experimental testing is conducted to evaluate tensile properties. Fractured surfaces of specimens are examined using a scanning electron microscope. The results demonstrated a significant drop in tensile strength and modulus for glass-filled material weld-line specimens when compared to specimens of no weld-line. However, for unfilled specimens, tensile strength and modulus are almost the same for samples with and without weld-line. A reduction in tensile strength of 13%, 49%, and 57% is observed for unfilled, 30% glass-filled, and 50% glassfilled polyamide-6 material respectively. KEYWORDS injection molding method, polyamide-6, tensile properties, weld-line strength, orcid.org/0000-0002-3720-9268 orcid.org/0000-0001-7043-3141 1 | INTRODUCTION The injection molding manufacturing process is used to produce thin-walled plastic components. In general, the shape and size of the part are reproduced in the [...]

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. [ABSTRACT FROM AUTHOR]

Dental education is considered as a complex, challenging and often stressful educational procedure. Acquisition of psychomotor skills by undergraduate students is an important step in many health professions to become a successful professional. During under graduation, class II cavity preparation exercise is of utmost important in dentistry. To compare class II cavities prepared by students after hands-on live demonstration and pre-recorded video demonstration using well-organised evaluation rubrics. Preclinical dental students (n= 50) were divided into two groups. The students in group I (n= 25) attended a hands-on live demonstration performed by one faculty while students in group II (n= 25) watched a 15-minute pre-recorded procedural video on the projector. Both groups were appealed to prepare class II cavity for amalgam involving disto-occlusal surface of mandibular second molar articulated on jaw model (TRU LON study model, Jayna industries, Ghaziabad U.P., India). Following completion of the preparations, all teeth were collected, and labelled grades of prepared cavities were given according to prespecified rubrics. The data of scores were presented as means and standard deviation. Statistical analysis of data was executed using SPSS software. A paired t-test was used to compare scores between groups. The study shows that the video-supported demonstration of a cavity preparation was better than the live hands-on demonstration. A higher mean response for the procedural video group was found compared to the live demonstration group (p= 0.000133). Pre-recorded video-supported demonstration along with guidance by a tutor may be a viable alternative to hands-on live demonstration in cavity preparation procedures during undergraduate dental training. Moreover, rubric methods can be implemented in the teaching of various preclinical exercises for conservative dentistry and endodontics. [ABSTRACT FROM AUTHOR]

Background: Accurate working length (WL) determination is necessary in achieving optimal healing by non-surgical root canal therapy in teeth with inflammatory apical root resorption. Electronic apex locators (EALs) are one of the mainstays in determination of WL of teeth.

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. [ABSTRACT FROM AUTHOR]

In an injection molding process, a weld-line forms when two flow fronts meet each other. Weld-line is a weak area which reduces the strength of the part locally. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. This paper presents the effect of weld-lines on tensile properties of glass fibers reinforced polyamide-6 composite. An injection molding plaque tool has been designed and manufactured with the inputs from mold flow simulation software. The gating system is designed in such a way that the angle between two flow fronts is as minimum as possible, which theoretically gives the lowest strength at weld locations. The plaques are manufactured with BASF material Ultramid B3WG6 grade (glass filled 30%) which is a widely used engineering plastic material. Test specimens have been cut on a plaque for various angular positions. Experimental evaluation for tensile testing, tensile modulus, and stressstrain behavior for specimens with and without weld-line at different angular positions was evaluated as per ISO 527-2 standards. It has been established that the weld line significantly influences the tensile properties of the part. The presence of a weld line results in a significant decrease in the tensile strength of the part. Experimental results show approximately 58% reduction in tensile modulus and 49% reduction in stress at break values in specimen with weld-lines as compared to specimen without weld-lines. [ABSTRACT FROM AUTHOR]

Objective: This prospective, block randomized clinical trial was conducted to evaluate the effect of aromatherapy on the success rate of inferior alveolar nerve block (IANB) in teeth with irreversible pulpitis. Method and materials: In this clinical trial, 46 patients fulfilling the inclusion criteria were randomly divided into two equal groups: group I (n = 22) received IANB in a closed operatory without any fragrance, whereas group II (n = 24) received IANB in a separate closed operatory saturated with lavender fragrance using a candle warmer. The modified dental anxiety scale (MDAS) for anxiety and visual analog scale (VAS) for pain were recorded preoperatively as well as during access cavity preparation. For MDAS, a total score of more than 18 was considered as tremendously anxious or dental phobic. No or mild pain on VAS was considered as success. Data were analyzed using paired t test and independent sample t test. P < .05 was considered as statistically significant. Results: Difference in mean VAS (P = .749) and MDAS (P = 1.000) between both the groups was statistically nonsignificant. However there was a statistically significant difference in mean VAS (P = .000) and MDAS (P = .001) during access opening. Conclusion: Lavender aromatherapy can be used successfully to alleviate dental anxiety as well as to increase the anesthetic success rate of IANB in teeth with irreversible pulpitis. [ABSTRACT FROM AUTHOR]