The weld lines in blow molding occur wherever the pari son knits together in the head, mold tacking areas and mold parting pinch-off region. Facebook. Insufficient clamp tonnage Increase clamp pressure or move to machine with more tonnage . Gate blush, 4. 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. Plastic Rapid Injection Molding is popular not only in low volume manufacturing but also in large quantities molding, it is the most common way to manufacture plastic parts. The gate is the critical bridge between the runners (the channels through which the molten plastic travels) and the actual mold. Strength measurements should be made to. Change the gate locations. The possibility of the functional thin film for. th INTRODUCTION Injection molding is one of the most 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. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. A poor knit line. A weld line is a visible seam where two areas of the molten plastic meet. The Solutions for Poor Welding Lines. Injection molding is one of the most established and well-known methods of plastic processing. Redesign the mold to prevent the weld line. Improper fusion of two fluid flows, a state before weld line. To explore the formation of. For this purpose, the width of the weld line calculated by Sigmasoft is. (1998) for clear photographs. They can affect the strength and. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld line defects are a common part defect that occurs when the injected plastic flows around a solid piece of the mold and does not knit back together. reinforcement type and amount in nylon 6/6. Increase the injection speed. The impact behavior of weld-lines in injection molding. That’s the air escaping out of the nozzle until the hose is full of pressurized water. oped which factors the weld lines into the virtual design of chopped-strand-rein-forced thermoplastic parts. The need to minimize fiber breakage, plus the higher viscosity of materials with. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. The Solutions for Poor Welding Lines. Injection molding is a complex multi-variable, nonlinear and time-varying unsteady process, which makes it more difficult to optimize the process parameters. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. Int J Adv Manuf Technol 52:131–141. Mold. Meddad and Fisa [3] found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost. The definition of weld lines: When multiple plastic flow fronts meet in the cavity after encountering inserts, holes, or areas with inconsistent flow rates or interrupted melt flows, or in the case of gate injection filling, the inability of two or more flow fronts to fully “knit” together will cause the linear weld marks. Consequently, it causes viscous dissipation which leads to the generation of heat. The. In. Mold vents should function the same way. 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. Figure 2. This defect occurs due to the temperature and pressure not being high enough, causing premature solidification. Weld lines represent the region where two separated melt fronts recombine. The following guidelines have. 5 mm, 1. The weld line’s strength is reduced when. In this paper, a weld line factor (W-L factor) was adopted to. Xie L, Zhu D, Ziegmann G, Steuernagel L (2016) Investigation on correlation between cold/hot weld line mechanical properties and micro injection molding processing parameters. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. Weld lines are a common issue in injection molding, and occur when two flow fronts meet and fuse together as the material cools and solidifies. 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. 2002), the use of simulation approaches (Berti and. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. (1) make the mold vent larger at location with weld line; (2) Check if the mold vent is blocked or not or use vacuumized forming. (1983). One of the things that can compromise an injection molded part is a weld line, also called a knit line. Munich, Germany: Carl Hanser Verlag, 1994. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. Plastic part design for injection molding – An introduction. – Use generous and even. 0 mm, is designed to conduct the. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. For those who are new to the injection molding industry, may be confused about this product. A weld line can also be called a knit line. in the cavity of the injection 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 still rather few. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 Fig. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. This paper presents the. 9. 2. Insufficient injection pressure and speed can cause weld lines. Although this phenomenon occurs in almost all the commercially important polymer. molding Æ Thermoplastics Æ Weld line Æ Simulation Rheol Acta (2004) 43: 240–245 DOI 10. <1> As illustrated in Figure 4, the existence of. 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. We'll show you how. These weld lines occur usually around holes or at the material flow joint area in the injeciton molded part, some welding lins is very small, specially if. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). 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. 2(a, b). Fracture behavior of weld lines in injection molded components loaded under real operating conditions. Information about PA6/PA66 (Nylon) Injection Molding. Designers can easily set up and perform analysis with only a few clicks. When two or more strands of molten plastics meet in the mold, a weld. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. This model provides the necessary information. In a meld line, the plastic comes together at an angle greater than 135 degrees. Sink Marks Cause 5: Improper Part Geometry. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. Visualization analysis of flow behavior during weld-line formation in injection molding process. For example, filled resins and ABS are more likely to. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. Miron MC, Major Z, Adachi T. C. technical ulletin SPECIALTY POLYME RS Design and Production of Injection Molding Tools. As compared to a weld line, the flow fronts come together at less than 135 degrees. Star Rapid offers tips and tricks to improve your prototypes and production parts. Flash. An evaluation model based on artificial neural network method. Still, it can be seen to varied degrees depending on mold. . An injection molding processor who can analyze the process from the plastics point of view, can quickly solve any molding problem, regardless of the machine or plastic type. This leads to a better molecular chain entanglement, which in turn creates a better weld. 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 Prediction of weld lines with injection molding simulation softwareWeld lines in design for manufacture. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. In order to study the weld line developing process and its influence on mechanical properties in micro injection molding, a visual mold with variotherm system mold was designed and fabricated. The moldability validation and flow analysis tools enable you to iden-tify and correct potential injection molding problems as you design the product. Many researchers had emerged with several. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Poor weld line quality can lead to short-term or long-term product failures, initiated at the weld line. Weld lines represent the region where two separated melt fronts recombine. 010 0. The welding angle can be used to differentiate weld lines and meld lines. The flow of the material in the injection mould takes place through the gate. From Understanding Weld-line Integrity by Sabic Innovative Plastics, p. What Causes Weld Lines in Plastic Injection Molding Parts? I. Injection molding. We recently had a few pieces (2-3%) crack after assembly, while in storage (not installed, still in the package). Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Meld and knit lines are actually both different types of weld lines. 1. th e use of design of e xperiment techniq ue. The weld line refers to the process in which the liquid material is divided into two or more flows in the cavity during the injection process and merged together after a period of time [51,77,78,79]. Recently hired at plastic injection molding simulation software provider Moldex3D, Nicholson was spurred to undertake the research study following a conversation with a customer experiencing weld-line woes. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. A weld line is often unavoidable. Weld Line Phenomenon: Surface defect in which the weld, or the part where the flows of melted plastic meet inside the mold, shows up on the surface as a groove or pattern. Flash. Description Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Plastic Injection Molding Process. 2. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. + Improve vent inside the mold. Molding with weld line model Moldex3D was used for calculate the molding of lugs (figure 1). These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 2. Injection speed is too low. Figure 1. Our weld line injection molding is essential for the best result of finished molded products. Weld lines have been one of the common defects puzzling the injection molding industry. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. They occur when melt flow fronts collide in a mold cavity. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. In some cases, a weld line can also cause a loss of strength and impact resistance. This weld line can act as a weak spot in the material. Fellahi et al. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. 2. If the different flow fronts have cooled. This study focuses on the effect of melt temperature on. A micro-photography study on the cross-section of the weld-line was also carried out. Weld lines are a common imperfection to be found in most plastic injected molded parts. Polymer Engineering and Science (2005) There are more references available in the full text version of this article. The weld lines in injection molded parts arise as a result of the collision of two fronts of the flowing material, which fills the mold cavity and are sometimes unavoidable [1][2][3] [4]. 3 cc/sec, the weld lines are no longer perceivable above 130 C. T he decreased gloss level at the position of. 809-814. As a result this. Weld lines are injection molding defects that can be mitigated by a number of tactics that depend on your part design. Miron MC, Major Z, Adachi T. As the plastic flows through the mold it. . Meld lines are formed when two separate flow fronts meets. Weld lines. open access Abstract Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. A weld line occurs when two or more molten plastic flows meet and fuse during the injection molding process, resulting in a visible line on the surface of the molded part. Insufficient plasticizing ability of injection molding machine. Sink Marks Cause 4: High Mold Temperature. Clamping unit berfungsi untuk memegang dan mengatur gerakan mold unit, serta gerakan ejector saat melepas benda dari molding unit, pada clamping unit lah kita bisa mengatur berapa panjang gerakan molding saat dibuka dan seberapa panjang ejector harus bergerak. CrossRef View in Scopus Google Scholar [17] G. 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. 000 0. • Reduce runner dimensions and maintain the same flow rate. Melt temperature is 250°C, mold temperature is 110°C. Edge Gates. Lugs size is 65 х 24 х 4 mm. The defects encountered could be caused by mechanical factors, such as poor mold design and mold manufacturing, or by processing related factors, such as incomplete kneading, inadequate molding pressure, injection. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. Rapid heat and cool injection molding is an example of a measure to prevent the generation of weld lines. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). Some of the common fixes for weld lines include: Increase the resin temperature to ensure both sides of the weld line are liquid when colliding. But the unfavorable and unavoidable defect of weld line in micro injection molding part leads to detrimental mechanical and surface properties. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. In addition, its tensile strength and stiffness will be sharply decreased. Munich, Germany: Carl Hanser Verlag, 1994. Three terms that often get mixed up in injection molding are weld, meld and knit lines. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. Consequently, weld regions have been observed to have inferior mechanical properties compared to the bulk. Figure 2. The optimal process condition is very likely to appear in this second part's fine-tune group. They occur when melt flow fronts collide in a mold cavity. Injection molding could be applied with many polymer materials, such as. It is important to investigate the weld line because the weld line area can. Weld lines can impact the strength and appearance of the final part, and are often considered a defect. 2. 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. The resulting defects don’t stop at flash only. Fisa et al. Increase the mold temperature. (1) Increase the injection pressure and prolong the injection time. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a. Weld line injection molding troubleshooting. Processing Optimization Reduced frozen skin thickness: High injection speeds also contribute to a thinner frozen skin at the weld line. Microsyst Technol, 14 (6) (2008), pp. This can occur when a polymer flow splits to go around an interruption (e. 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. injection molding. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. The occurrence of a weld line means a significant problem both aesthetically and mechanically in the design of injection moulded parts. Insufficient plasticizing ability of injection molding machine. Microsyst Technol. 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. Shaofei Jiang. Weld lines appear as a result of the flow of molten plastic during the injection molding process. As such, optimizing mold designs should always be incorporated in your production model. Fracture behavior of weld lines in injection molded components loaded under real operating conditions. The formation of weld lines and their location along the flow path is a well-studied phenomenon in conventional injection molding; however, only a few papers are devoted to micro-injection molding [11,13,14,15,16]. Minimize the use of release agent. Flow analysis of the weld line formation during injection mold filling of thermoplastics. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. 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. The impact behavior of weld-lines in injection molding. A meld line is defined as the re-merging of two flow fronts. , Ltd. Save. Install an ultrared light inside the hopper. 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. One solution is to prevent the weld lines from forming in regions that are. 13 shows the best gate location for which the weld lines . Instead of using flow leaders and deflectors to control the locations of the weld lines, this paper presents an approach to specify the locations of the weld. [ 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. To respond to poor plasticization and uneven melt temperature, the molding cycle can be extended to make. Weld line. Molding Equipment. Nozzle – The nozzle is at the end of the barrel and contacts the injection mold. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Thoroughly clean molding machine cylinders. Weld lines, generated during injection molding, can significantly reduce the mechanical performance of structures. When this fails to happen correctly, a weld line defect occurs. 666 Azieatul Azrin Dzulkipli and M. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. It is possible to pre. Email him at jhenz@polymer-center. The injection molding simulation software used offers a method for the detection of weld lines that has shown to be only reliable for the detection of stagnating weld lines. Moldflow is computer software that is widely used across the plastic injection molding industry to predict and optimize the injection molding process and assist with mold design. Which means engineers need to know how to account for this phenomenon in an efficient way. Re-balancing entire manufacturing lines may be required to effectively deliver and sustain SMED excellence. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and. Just check out some of it on the above lists. on conventional reciprocating screw injection molding machines using molding practices standard for filled engineering thermoplastics . Injection molding of large/complicated products are usually prepared by multiple compounds, which produces weldlines once the melt fronts are joined by impingement flow. [ 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. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. 2 mm to 1. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. (+86) 760 2222 2556 enquiry@starrapid. Effects of fillers and/or reinforcements on weld-line strength of nylon 6/6. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Wang, G. Remember, by avoiding weld lines, you can lessen operations cost. Increase the injection speed. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. From Understanding Weld-line Integrity by Sabic Innovative Plastics, p. A weld line develops when two or more flow fronts come together but do not meld completely because of partial solidification. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Multi-Shot Molding – A molding process that uses two or more plastic materials to form a single part. The second technique, cascade injection moulding, can produce parts free from weld lines. One common issue that frequently arises during injection molding is the formation of weld lines. Injection molding plate for mode I testing geometry. Controlling the mold’s temperature could also minimize the weld line’s effects. 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. Thus, it is important to understand (i). Int J Adv Manuf Technol 52:131–141. S. Possible causes: Low temperature or fluidity of melted plastic during injection molding. Causes. Weld line is one of the plastic injection molding defects. Thus, it is important to understand (i). Wavy lines are another feature of weld lines. Learn more about ABS injection molding here. Xie L. Change the gate locations. The thermo. 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. 4If the injection gate is not properly designed, it can cause the formation of defects like sink-mark, warpage, short shot, weld-line, air traps, and other faults [15]. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. However, even with advanced technologies and precise control, the process is not without its challenges. Therefore, the length of flowing weld lines must be additionally defined. This customary mark is caused by differential rates of cooling in the resin where. C. , 47 (2008. Nguyen-Chung. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. 2012. 2017-01-0481. Meld and knit lines are actually both different types of weld lines. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. Procedia Mater Sci 2014; 3: 2048–2053. Injection molding is nothing without molds. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Alloys. * Corresponding author, e-mail: fengsjpc@ku. Weld lines are formed when two orAbout Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. See moreIncreasing the temperature of the mold or plastic material. Fig 13:- Detailed view of weld lines. 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. Its appearance can be improved by adjusting parameters. 3 and 53. Weld lines, also known as knit lines, are a common defect in injection molding where two or more flow fronts of molten plastic meet but don’t properly fuse together. During the plastic injection molding process, one of the biggest challenges is. Gate position in injection mold. 10(a) (please see Fig. They are unavoidable even for moderate complex products. In injection molding, it is often important to maintain consistent color throughout the part. These are preferred over weld lines as they will normally result in improved cosmetics and structure. Short Shot Short Shot adalah suatu kondisi dimana, plastik leleh yang akan diinjeksikan kedalam cavity tidak mencapai kapasitas yang ideal atau sesuai settingan mesin. Weld lines appear on the surface of a molded part where the molten material converges after splitting off into two or more directions in a mold. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. ชิ้นงานเกิดเป็นเส้นรอยประสาน Weld line. The molded plastic part may also appear to be rust-colored. 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. The thermo-rheological findings were used to investigate the sources of weld line weakness. Injection Molding Glossary; Weld Lines; Weld Lines. 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. examined the relationship between the structural and mechanical qualities in HDPE/PA6 mixture which is molded with weld line and without weld line in plastic injections [6]. 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. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Increase the mold temperature. 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]. To determine the effect of the weld lines on tensile strength, tensile tests were conducted with the specimens fabricated with NORYL (amorphous blends of. Gambar 2. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. g. In an injection molding process, a weld-line forms when two flow fronts meet each other. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. This gives a clue as to. Fig. Weld lines can lower the integrity of the part. Avient’s Zachary Alderman shares practical tips on designing and injection molding parts utilizing short-fiber reinforcements. 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. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole. Because of the ever-increasing requirements for parts performance, lots of researchers have perf. . A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. Weld lines can. Micro injection molded polymeric parts coated with functional thin films/layers show off the promising applications in microsystems area. The thermo-rheological findings were used to investigate the sources of weld line weakness. Weld line problem which occurs in polymer parts produced by plastic injection method and affects appearance and strength on a large scale was researched in this paper. This consequently produces weld lines. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. Thoroughly clean molding machine cylinders. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. Five injection molding process parameters, including mold temperature, melt temperature, packing pressure, injection. Powder injection molding comprises several processing steps, and defects may occur in each step if care is not taken. Mold flow analysis can predict the location of weld lines. Islyn Thomas summarized the need for a particular vent location better than I ever could. Various measures are taken at production sites to address these problems. 1. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld. Polym. This reduced thickness of the frozen skin further enhances the visual appeal of the. 3. (1)Injection Machine Poor plasticization and non-uniform melt temperature – appropriately extend the injection molding cycle, to ensure thorough plasticization, and change for a machine with a larger. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . Adjust the design for the flow pattern to be a single source flow. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. Sequential valve gate technology. Weld lines can be caused by several different problems: Low temperature of injection moulding machine barrel. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Polym Eng Sci 45(7. Munich, Germany: Carl Hanser Verlag, 1994. 2) Vents in an injection mold should let the air out, but not the liquid plastic. Recently hired at plastic injection molding simulation software provider Moldex3D, Nicholson was spurred to undertake the research study following a conversation with a customer experiencing weld-line woes. 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. In the 1947 book, Injection Molding of Plastics, the late Dr.