weld line injection molding. Learn more about ABS injection molding here. weld line injection molding

 
 Learn more about ABS injection molding hereweld line injection molding  The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at

+ Improve vent inside the mold. In this paper, a kind of polypropylene (PP) foam plastic parts with special weld lines were obtained by core-back foam injection molding with chemical blowing agent. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. NX Mold Flow Analysis. Zhao, X. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. Gava and co-workers implemented an investigation devoted to the de-weld lines in injection molded thermoplastic composites. + Optimize holding pressure time. Machine Shot Capacity – The maximum volume of resin that can be injected in a single stroke of the injection machine. Maintain a holding pressure that is no more than 1/2 the. Controlling the mold’s temperature could also minimize the weld line’s effects. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. Int J Adv Manuf Technol 52:131–141. In an injection molding process, a weld-line forms when two flow fronts meet each other. When this fails to happen correctly, a weld line defect occurs. This occurs mainly in the presence of barriers that divide the melt flow in. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Injection molding weld lines where two or more flow fronts come together in the mold. However, even with advanced technologies and precise control, the process is not without its challenges. สาเหตุรองของการเกิดปัญหาการเกิดประกายเงิน (silver streak) 1. Weld line usually is not allowed on some critical area, and weld line on the part also weaken the strength. 2. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. T he decreased gloss level at the position of. The most common and one of the most challenging injection molding defects are weld and knit lines. A weld line is a mark left on the surface of a plastic injected molded part. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. In this study, we apply the technique of SAW to explore the acoustic properties near injection-weld lines by comparing the velocity of. Figure 2. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. Plast. and most commonly, thermoplastic polymers are used. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. As a result this. Miron MC, Major Z, Adachi T. Weld line, 5. This failure causes the product to be damaged during use. If so, look for an alternative resin. Amongst weld line. In. The weld line in an injection molding product can significantly impact the strength and durability of the last part [12] [13][14][15]. Weld lines are injection molding defects that can be mitigated by a number of tactics that depend on your part design. replication and poor weld line strength . Description Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. It is important to investigate the weld line because the weld line area can. Int J Adv Manuf Technol:1–11In addition to the weld line, the exposure of fibers on the molded product surface results in a rough surface, which degrades the appearance of the product. Weld-line is a weak area which reduces the strength of the part locally. If you have critical requirements for strength of knit lines, please call a Protolabs applications engineer at 877-479-3680 to discuss, or email at [email protected]. After that, the compounds were injection-molded into tensile samples with and without weld lines to. DYNAPLAST Tbk. Figure 1 below shows the development of a weld line. Injection Molding Glossary; Weld Lines; Weld Lines. une, 13: 15. Instead, a line that looks like a seam forms. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. 2. (2) Causes & Countermeasures (See the table below) *Note: Flash also tends to occur when the injection pressure/speed are too high, but molding time is too long and mold temperature is too low. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. But the unfavorable and unavoidable defect of weld line in micro injection molding part leads to detrimental mechanical and surface properties. The diameter of the hole is 12 mm. Wavy lines are another feature of weld lines. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. The Problems & Solutions course is designed to train injection molding personnel in. The impact behavior of weld-lines in injection molding. As a defect of micro injection molding parts, weld line is unfavorable since it will influence the surface quality and mechanical properties of micro parts. They. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are still rather few. Injection molding is one of the most established and well-known methods of plastic processing. <Materials> Pre-dry thoroughly. Or, the part where the weld line is produced shall. Kagitci YC, Tarakcioglu N (2015) The effect of weld line on tensile strength in a polymer composite part. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. Examples of such failure are shown in Figure 1. CrossRef View in Scopus Google Scholar [17] G. Weld lines represent the region where two separated melt fronts recombine. Below is one of the examples: !NOTE: if the weld lines is important to the cosmetic surface of your part, please bring this up to your mold maker during quoting phase. 010 0. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. In the 1947 book, Injection Molding of Plastics, the late Dr. When two or more strands of molten plastics meet in the mold, a weld. Weld line Weld line dikatakan ketika dua atau lebih aliran lelehan depan. . This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. Flow lines arise when at least two melt fronts meet at an acute an-Weld line is aesthetically unpleasant and affects the mechanical strength of injection molded parts. Various measures are taken at production sites to address these problems. Its appearance can be improved by adjusting parameters. Berikut beberapa di antaranya: 1. If the injection molding speed is too slow, however, there may be an insufficient filling of the mold. The weld lines in injection moulded parts arise as a result of the collision of two fronts of the flowing material, which fills the mould cavity and are sometimes unavoidable. That helps. Unfortunately, the 3D layering process creates ‘weld lines’ (an injection molding term) between layers which is essentially two layers of polymer that meet. Weld line formation in the injection molding process occurs. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near. Munich, Germany: Carl Hanser Verlag, 1994. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. a) Multi-fiber connector micro injection molding simulation b) 3D simulation of micro gear with 150µm diameter for weld line position prediction c) 3D micro injection molding filling simulation of micro gear with 180µm diameter Fig. In. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. Thus, it is important to understand (i). Weld lines have been one of the common defects puzzling the injection molding industry. Thus, it is important to understand (i) if the melt is able to fill the cavity up to the weld line location, (ii) where the weld line forms, and (iii) if the weld line is a cold or flowing one. Weld lines are the result of fundamental physical effects taking place inside of the mold tool cavity, they are common imperfection to be found in most plastic injected. Again, consult with professionals as to how you could improve mold designs. g. Key words: weld line strength, thermoplastic composites, injection molding, wall thickness, skin and core layers Department of Materials Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are still rather few. This study addresses the effects of injection molding weld line on the fatigue crack resistance of commercial CPVC in the temperature range of −10 to 70 °C. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. If the plasticizing ability of the plastics injection molding machine is insufficient, the plastic cannot be fully plasticized, resulting in weld lines when filling the mold. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are. 1. The. (3) Adjust the temperature of the barrel and nozzle: the viscosity. when two or more melt flow fronts contact each other immediately after the cooling process. Weld Line defect analysis, the most common of many defects in injection moulding products. 2017-01-0481. + Adjust injection speed. Investigate for potential contamination. Weld lines are among the most critical structural defects in parts made by the injection molding of fiber-reinforced thermoplastics, explained Sirmax in a press release. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. Weld lines can be caused by material flowing around holes or inserts in the part, multiple injection gates or variable wall thickness where hesitation or "race tracking" can occur. A weld line is often unavoidable. 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). This is expected to achieve maximum results while the pressure holding effect will also increase. Article Google Scholar Xie L, Ziegmann G (2009) Influence of processing parameters on micro injection molded weld line mechanical properties of polypropylene (PP). Consequently, weld regions have been observed to have inferior mechanical properties compared to the bulk. 1. In this work, the weldline strength of injection molded short-glass-fiber reinforced polycarbonate was derived by an analytical method of modified rule-of-mixtures as a function of the area fraction between skin and core layers. [ 18 - 21 ] In addition, the effects of flow behavior of the polymer melt due to the optimal process parameters for the minimization of weld-line effects are an important consideration. In this regard, Taguchi orthogonal experimental design is adopted, and five processing parameters, the mold temperature, melt temperature, cooling time, packing. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. To prevent weld lines, increase the pressure and temperature. Weld lines are formed when two melt fronts come in contact with each other. Meld and knit lines are actually both different types of weld lines. As a result, the portion has a faint, perhaps undetectable line. Weld lines can be caused by several different problems: Low temperature of injection moulding machine barrel. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. Facebook. . Abstract. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. 9. A flat product case was considered as an example of a typical aircraft structural element. This happens when the molten plastic is injected into the mold cavity and flows around an obstacle such as a pin, hole, or protrusion, and then comes back together. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Emerging Materials Research. Weld lines Weld lines are weak areas formed by converging flows of plastic that can lead to mechanical part failure if not properly accounted for in the part design. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. Injection moulding (U. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. Polyamide 6 (Lanxess, Durethan B 30 S 000000, non-reinforced, ISO 1874-PA 6, GR, 14-030, Cologne, Germany) was used for this experiment. They are the result of fundamental physical effects taking place inside of the mold tool cavity. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. In an injection molding process, a weld-line forms when two flow fronts meet each other. Learn more about ABS injection molding here. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole. Sink marks are a common type of injection molding defect. Vibration assisted injection molding. Double push filling method. In a weld line, reinforcement fibers adopt an orthogonal orientation with respect to the filling direction, which results in a significant reduction in the strength and. Fracture behavior of weld lines in injection molded components loaded under real operating conditions. If not, the speed will drop, and it could create weld lines. Many researchers had emerged with several. Just check out some of it on the above lists. To prevent weld lines, increase the pressure and temperature. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. 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. Weld lines, generated during injection molding, can significantly reduce the mechanical performance of structures. Weld lines. Our injection molding company is explaining what these imperfections are, why they can compromise. Meld and knit lines are actually both different types of weld lines. Burn Marks. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. Polymer Engineering and Science (2005) There are more references available in the full text version of this article. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. 48 applied high-frequency induction heating to eliminate weld lines in an injection-molded plastic part, and experimental observation indicated that weld depth was reduced from 2. Compd. 1. Since it is often impossible to avoid weld lines as well as a limited possibility to increase the weld line strength by adjusting the injection molding parameters, a method to predict the weld line strength in the product development process is shown below. 005 0. The terahertz time-domain spectroscopy (THz-TDS) imaging technique was used to detect the weld line defect of an injection-moulded short glass fiber-reinforced composite. Set up the process overflow and use it as the place where the weld line is generated, and then cut off and remove it after forming. The molded plastic part may also appear to be rust-colored. The formation of weld line in the injection molding method is caused by the product and mold design that is one of the common mistakes. This consequently produces weld lines. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. These lines are formed when two or more flowing molten plastic streams meet and fuse together, creating a visible line on the surface of the molded part. Slow down injection speed. By the reflection method and a high speed camera, the visual system can be used to record and observe the forming process of micro weld lines during the. To respond to poor plasticization and uneven melt temperature, the molding cycle can be extended to make. Weld-line is a weak area which reduces the strength of the part locally. Xie L. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU. 1, right). This can occur when a polymer flow splits to go around an interruption (e. The parts are molded flat and are slightly stressed once installed in an arced position, but not excessively. . Sink Marks Cause 4: High Mold Temperature. oped which factors the weld lines into the virtual design of chopped-strand-rein-forced thermoplastic parts. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. Flash. The present work focuses on studying the effect of packing pressure on strength of stagnation weld-line. Flow Lines. If the different flow fronts have cooled. 4. (2) Adjust the injection speed: high speed allows the melt to reach the confluence without cooling down, and low speed allows time for the air in the cavity to be discharged. Bin-Xin Yang Ouyang Jie Supei Zheng Qiang Li Wen Zhou. 5 mm, 1. Weld lines are also known as knit lines. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. + Move gate (to where it is not visible). The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. Polym Eng Sci 45(7. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. % glass fibers – PA6 Aramid SV 30-1ETM (figure 1b). Additionally, you can get our free Design Cube, which will provide a physical aid to help understand how knit lines form as well as other injection molding design considerations. Weld lines can lower the integrity of the part. Some of the approaches include the application of machine learning methods (Chen 2008; Manjunath and Krishna 2012; Kuo et al. Gate blush, 4. 2011; 509 (2):226–233. 5. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. Insufficient plasticizing ability of injection molding machine. Sink Marks Cause 1: Incorrect Melt Temperature. 666 Azieatul Azrin Dzulkipli and M. The default weld line result recognizes 135º as the maximum angle of collision and as that angle decreases, the severity increases as it. Weld-Line in an injection molded part develops when two or more melt fronts are converged together. Mold. Make the size of runner channel wider and/or shorter. 2. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Multi-Shot Molding – A molding process that uses two or more plastic materials to form a single part. This model provides the necessary information. A visual mold with variotherm system for weld line study in micro injection molding. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU. 2-1. A family of short carbon fiber-reinforced thermoplastic (CFRTP) compounds specifically formulated for injection molding is being used to extend the capabilities of thermoplastic composites in a variety of part sizes and complexities. C. One common issue that frequently arises during injection molding is the formation of weld lines. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Three terms that often get mixed up in injection molding are weld, meld and knit lines. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. When two or more streams of plastic meet and fuse. 2012. when two or more melt flow fronts contact each other immediately after the cooling process. 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. gas, which can cause blistering, as well as poor weld lines, warpage and the formation of cold slugs that affect filling and part mechanical properties. 005 0. Ozcelik studied the influence of the injection parameters and weld line on the mechanical properties of polypropylene (PP) during IM process via the design of experiment (DOE). II. 10(a) (please see Fig. 2-1. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. Weld line formation in the injection molding process occurs. In the end, the total amount of time that running a complete Taguchi DOE (L18) to occupy an injection. In the present work, the micro specimens were investigated. In this study, one injection mold. In injection molding of thermosoftening plastics, an important aspect having a bearing on the quality of articles is the appearance of weld lines that are formed when there are inserts, barriers, molding signs, reinforcements, etc. An injection molding gate is the designed opening in a mold through which molten plastic is introduced into the mold cavity, initiating the process of taking the shape of the desired part. One of the things that can compromise an injection molded part is a weld line, also called a knit line. This type of injection molding resolves any trouble caused by undesired welding lines. Procedia Mater Sci 2014; 3: 2048–2053. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. 2021年4月23日 / by admin. + Increase mold temp, or materials’ temp, or holding pressure. A tensile test specimen mold, which allows cavity thickness varying from 2. 2. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Weld Lines-3 Ways for Detecting and Correcting. A weld line is a mark left on the surface of a plastic injected molded part. Minimize the use of release agent. Three terms that often get mixed up are weld, meld, and knit lines. ”. Information about PA6/PA66 (Nylon) Injection Molding. Procedia Mater Sci 2014; 3: 2048–2053. Lesson 6: Meld and Weld Lines (Processing) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. com1. At a low volumetric injection flow rate of 33. The weld line is an inevitable defect in the most injection molded components. A weld line is a visible seam where two areas of the molten plastic meet. With tighter heat controls, you can keep the material at the proper temperature to make sure the plastic keeps flowing and fills the mold cavity completely. 6. Weld lines can be caused by material flowing around holes or inserts in the part, multiple injection gates or variable wall thickness where hesitation or "race tracking" can occur. These potential causes include:Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. , Ltd. The parting line in injection molding is which one of the following: (a) the lines formed where polymer melt meets after flowing around a core in the mold, (b) the narrow gate sections where the parts are separated from the runner, (c) where the clamping unit is joined to the injection unit in the molding machine, or (d) where the two mold halves come. are very minimum. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Weld line reduction is one of the major concerns in plastic injection molding (PIM) that results in high surface appearance and high strength of a plastic product. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 Fig. Weld line is one of the plastic injection molding defects. This leads to a better molecular chain entanglement, which in turn creates a better weld. In addition a weld line can be moved to an area where it is less visible. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. 943 µm to 0. These lines can weaken the strength of the part, and they can also be unsightly. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. Another relevant topic in injection molding is the presence of weld lines (WLs) and their properties, which could lead to part weakness through surface disturbances, optical issues and reduced bonding [21, 22]. injection molding, (b) weld line and meld line, and (c) injection sample size and shape. In order to prepare the weld line specimen by micro injection molding, a mould integrated with visual system and variotherm system was designed and constructed, shown as Fig. The Solutions for Poor Welding Lines. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Injection molding is nothing without molds. We investigate the effects of various heating times and. In a meld line, the plastic comes together at an angle greater than 135 degrees. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). These potential causes include: Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. ac. Visualization analysis of flow behavior during weld-line formation in injection molding process. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. This weld line can act as a weak spot in the material. Because of the ever-increasing requirements for parts performance, lots of researchers have perf. Weld line and warping are two critical defects for injection-moulded part. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. 1 Prediction of weld lines with injection molding simulation softwareWeld lines in design for manufacture. Star Rapid offers tips and tricks to improve your prototypes and production parts. Penyebab Weld Line. They found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in whichTo investigate the effect of hot gas heating in injection molding on the weld line appearance, an experiment was conducted with the molding parameters listed in Table 2. On the other hand, the mechanical strength at the weld line area of an injection molding part is always a concern. Which means engineers need to know how to account for this phenomenon in an efficient way. on conventional reciprocating screw injection molding machines using molding practices standard for filled engineering thermoplastics . ”Weld Lines in a plastic cover. 4. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. A knit line, also called a weld line, occurs when the liquid plastic moves through the mold and hits more melted plastic and they don’t flow or fuse together. Micro injection molded polymeric parts coated with functional thin films/layers show off the promising applications in microsystems area. Shaofei Jiang. 2. identi fy a s urface defect i n th e for m of a weld line, which occurs due to the two injection points at x = 5 mm and 34 mm ( see Fig. ). In some cases, a weld line can also cause a loss of strength and impact resistance. Voids and bubbles, 6. To prevent knit lines, injection molders can increase the temperature of the molten resin to prevent solidification from starting too soon, and increasing injection speeds and pressure are also potential solutions. 22: Weld line formation when melt splits around core pins. In this paper, two different injection molding tests were completed. Remedies: Raise the temperature of the mold or molten plastic. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. Insufficient plasticizing ability of injection molding machine. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Table 2-Glass Fiber Glass Fiber Glass Fiber Glass Fiber A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. Our weld line injection molding is essential for the best result of finished molded products. Materials Science.