, less than 0. If weld lines are unavoidable due to multiple gates in a moulding, they should be positioned in the non-critical region. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. 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. This failure causes the product to be damaged during use. As a result this weld line will be a weak point in this part. 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. (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. Other possible causes include: Low mold or material temperature; Insufficient holding time or. Multiple gates are acceptable as long as they are close enough to each other to avoid weld line issues. Weld lines have been one of the common defects puzzling the injection molding industry. Or increase the number of gates. Weld Line Occurrence in Plastic Injection Molded Parts Weld lines, also commonly known as knit lines, may be present in a plastic molded part depending on the partsí geometry. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. Here are some ways to avoid. 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. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Instead, a line that looks like a seam forms. 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. Three terms that often get mixed up are weld, meld, and knit lines. Redesign the mold to prevent the weld line. Still, it can be seen to varied degrees depending on mold. and Mosle, H. In many cases, you will also see that the part is hanging up on the core during ejection. 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. 010 0. [1-2] investigated the weld line zone of injection molded glass-fiber-filled polypropylene (PP) composites. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. A weld line is a mark left on the surface of a plastic injected molded part. Increase the injection speed. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. 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. Weld line defects in injection molding is a line or lines on the part surface that caused the part looking ugly or cuased part lifetime, or even broken easily. Specifically, injection-mold lines are often associated with poor mechanical strength. Weld line and warping are two critical defects for injection-moulded part. In. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Weld-line is a weak area. . Kobayashi et al. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and. A weld-line is known as a representative defect in the field of plastic injection moulding, and also as a cause of inferior mechanical propensities and poor appearance. The governing equations for the melt and the air in the cavity are united into…. The molded plastic part may also appear to be rust-colored. Weld lines have been one of the common defects puzzling the injection molding industry. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. Problem: Weld lines are formed when plastic resin is forced around an obstruction in a mold tool and reforms on the side opposite the gate. [ 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. 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. Weld Lines. Polym Eng Sci 45(7. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. The Factors that Cause Weld Line in Injection molding Pressure. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. They are unavoidable even for moderate complex products. John Bozzelli. Therefore, it is recommended to do a moldflow study prior to the mold being built. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. Sink MarksWeld 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. Cracking and/or Crazing can be defined as a fracture or surface breakage in the material of a molded part, usually found in weld line areas, but also on the surface in general. 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. Weld lines are visible to varying degrees on any molded part depending on gate location, flow length, melt/mold temperature, cavityA 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. But none of the current packages can predict weld lines’ properties qualitatively. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. Ghazanfarpour. Fig 13:- Detailed view of weld lines. Weld line location. This customary mark is caused by differential rates of cooling in the resin where. Improper fusion of two fluid flows, a state before weld line. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. However, research about the computer determination of weld lines in injection molding remains scarce. Expand. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. Venting at Weld Lines. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPAccording to the weld line distribution map of six gate schemes shown in . Which means engineers need to know how to account for this phenomenon in an efficient way. Int. 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. Wavy lines are another feature of weld lines. When two or more streams of plastic meet and fuse. 1 Mold In order to study the formation of weld lines, the mold cavities has been. gasket seal leakage where the weld line crosses a gasket. 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. For multiple gate and complex part. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Try to gradually raise the mold temperature and barrel temperature. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . The more gate points there are, the more weld lines will occur. 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]. Its appearance can be improved by adjusting parameters. 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 together? Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. 2(a, b). Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. Specifically, injection-mold lines are often associated with poor mechanical strength. In the sense that the weld line is better formed before the resin temperature. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. Runner Type Venting Plastic melt and mold temperature Injection speed and pressure Learn how to troubleshoot weld lines in injection molding. This injection molding defect appears as a black discoloration on the surface of the molded part. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. Meld lines are formed when two separate flow fronts meets. Adjust the design for the flow pattern to be a single source flow. Weld line formation in the injection molding process occurs. Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. In a meld line, the plastic comes together at an angle greater than 135 degrees. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. In a weld line, reinforcement fibers. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. 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. Our injection molding company is explaining what these imperfections are, why they can compromise. This line does not normally impact the overall shape or dimensions of the item. The following are the conclusion drawn from the present research: 1. 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. Weld lines are the unfavorable defect not only in normal injection molding process but in micro injection molding process. Mérillou, J. wall thickness, gate and runner designs and re-validate the result. In the feeding system of injection molding, the flow of plastic melt begins from the nozzle of the injection molding machine, traverses through the sprue and runners, and ultimately reaches the mold gate(you can call it the injection molding gate as well)—the entry point to the mold cavity. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. Injection molding plate for mode I testing geometry. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. In injection molded parts, there are 2 types of weld lines: The first type of weld mark is called cold-melt joints and is formed when the melt front enters the cavity with different gates. Weld-line is a weak area which reduces the strength of the part locally. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. Flashes, 3. In this paper, a weld line computer determination method based on filling simulation with surface model is proposed, from which the positions and lengths of the weld lines can be predicted. Flow-in-duced fiber orientation manifests in higher tensile properties in the direction of flow compared to normal to the direction of flow [13–15]. 004 m, a characteristic velocity ν 0 =0. In an injection molding process, a weld-line forms when two flow fronts meet each other. 3: Weld Lines. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. Flash. 030 0. The results of. Typical injection molding processing temperatures of TPU materials are as follows: IM ZONE 60A TO 75A 80A TO 90A 95A TO 75D REAR 315 – 340 °F 345 – 370 °F 375 – 400 °FTo study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. 2. Raise the injection speed. 5. 000 0. Weld lines can appear on the surface of a molded part where the molten material has converged after splitting off in a mold. Meld and knit lines are actually both different types of weld lines. 015 0. Figure 2. Figure 1 below shows the development of a weld line. Figure 1a illustrates how the weld line is produced when. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. The injection molding temperature and the mold temperature were fixed respectively at 230 °C and 50 °C. Second, depending on the size of the overflow well, you get a little bit of flow melding together, and that helps strength so that you have some intertwining of the polymer chains. This paper presents the. In an injection molding process, a weld-line forms when two flow fronts meet each other. The authors [5, 6] attempted to reduce the weld lines and clamping force of plastic injection moulding through numerical and experimental investigation, and discovered that the 3D cooling channel. Weld lines represent the region where two separated melt fronts recombine. technical ulletin SPECIALTY POLYME RS Design and Production of Injection Molding ToolsIncrease the injection speed in order to fill the mold more quickly and ensure the material does not prematurely cool down; in addition, when the speed is adjusted the flow fronts may meet at a different spot and move the weld line location. 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. The weld line and the flow pattern of co-injection molding can be seen from Fig. Carefully consider all the relevant aspects of the mold design specification before. Controlling the mold’s temperature could also minimize the weld line’s effects. Lesson 7: Meld and Weld Lines (Part Design) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. One test mold was used to mold three different materials using heat/cool and conventional molding techniques. Sink Marks Cause 5: Improper Part Geometry. They found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in whichEffects of mold temperature and pressure on shrinkage 0. Thus, it is important to understand (i). 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. Mold Design Most conventional mold designs will work with TPU’s. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). Google Scholar [10] S. The parts are molded flat and are slightly stressed once installed in an arced position, but not excessively. The calculation was carried out on a mesh with solid elements obtained in ANSYS Meshing and transferred to Moldex3D by means Rhinoceros. This is expected to achieve maximum results while the pressure holding effect will also increase. 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. Place a vent in the weld line area to remove the entrapped air. Improvement of weld line strength in injection molded FRTP articles. The. That helps. The spreading mold release agent on the part cavity surface might eventually cumulate at the V-notch groove of the weld line after each injection molding shot. Tosello et al. 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. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. In this paper, a weld line factor (W-L factor) was adopted to. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. Increase the melting temperature. According to the special features of micro injection molding process compared with normal injection molding process, the main related factors to weld line’s properties were classified as 3 group, named as processing conditions, mold design and structure, external process. 5. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Flow marks in injection molding can be avoided if adequate measures are taken. Weld line formation in the injection molding process occurs. Weld Lines. Burn Marks. Weld lines in design for manufacture. Thus, it is important to understand (i). The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. In this paper, two different injection molding tests were completed. Weld line section presents notch or gloss difference. 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. The effects of fiber concentration has been studied in detail. In other words, weld lines reduce the mechanical properties of the product. 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. In addition a weld line can be moved to an area where it is less visible. The weld line’s strength is reduced when. Meld and knit lines are actually both different types of weld lines. This leads to a better molecular chain entanglement, which in turn creates a better weld. Weld line. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. 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. Weld Lines. (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. A weld line can also be called a knit line. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. To determine the effect of the weld lines on tensile strength, tensile tests were conducted with the specimens fabricated with NORYL (amorphous blends of. when two or more melt flow fronts contact each other immediately after the cooling process. 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. + Adjust injection speed. When the polymer resin is injected into a mold, it flows through all portions of the mold cavity. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. In this experiment, several ejector. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. investigated the impact of injection molding parameters on weld line formation and strength reduction. Weld or knit lines occur when melt flow fronts collide in a mold cavity. When the two such melt flows. 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). 2) Vents in an injection mold should let the air out, but not the liquid plastic. Injection molding can be performed with only one of these. There are several factors that can contribute to the formation of weld lines, including: Part design: The design of the part can impact the flow of the material and the likelihood of weld lines forming. Weld Line Factors for Thermoplastics. Alter the mold design. (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. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. This process makes possible to produce a wide range of products with different sizes, shapes, and for varying applications. 030 0. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. In addition a weld line can be moved to an area where it is less visible. C. The hair-like weld line is the. The weld line degrades the. Optimizing the injection parameters through combination of adjusting the molding temperature, varying the gate pressure, and increasing the dwell time. In the present work, the micro specimens were investigated. The solution to an internal part cracking problem is to change the packing pressure. 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. The Solutions for Poor Welding Lines. Vacuum voids. 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. The second technique, cascade injection moulding, can produce parts free from weld lines. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. Weld-line is a weak area which reduces the strength of the part locally. Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. A new kind of weld line was. Injection molds: (a) mold type A, (b) fixed plate of the mold type B, and (c) moving plate of mold type B The second mold (mo ld type B) was used for the ISO D2 specimen, as shown in Figure 2b,c . About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. Edge Gates. The main types of injection molding defects are: 1. This reduced thickness of the frozen skin further enhances the visual appeal of the. In this study, the effects of injection temperature, injection pressure, and fiber cont. Weld lines. A viscosity curve is developed using calculations of the fill time and plastic pressure at. S. To explore the formation of weld lines in injection molding, a. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. One of the things that can compromise an injection molded part is a weld line, also called a knit line. 1. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. They are the result of fundamental physical effects taking place inside of the mold tool cavity. Weld lines have been one of the common defects puzzling the injection molding industry. Clamping Unit. Known also as knit lines and weld marks, weld lines are difficult to eliminate completely, especially if your injection molded part requires holes. You can choose material of low viscosity and can increase the injection pressure. 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]. Short shots. If the different flow fronts have cooled. Second, depending on the size of the overflow well, you get a little bit of flow melding together, and that helps strength so that you have some intertwining of the polymer chains. Kobayashi et al. Weld lines are a common imperfection to be found in most plastic injected molded parts. Injected plates were generated using a double-gated mold under four different process conditions. injection molding, (b) weld line and meld line, and (c) injection sample size and shape. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Remedies: Raise the temperature of the mold or molten plastic. Weld lines may occur on a molded part’s surface where, after breaking off into two or more directions in a mold, the molten material has converged. g. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. th INTRODUCTION Injection molding is one of the mostWeld Lines in a plastic cover. There will be too many weld lines ; 6. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. 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. This may require higher melt temperature or lower injection speed . In injection molding weldlines are generated when two separate melt streams join either in multigated molds or as a consequence of flow around. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. A. Root causes Many factors—including processing conditions, material, part design and mold design—can influence the visibility and strength of a weld line. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld together. [ 18 - 21 ] In addition, the effects. Insufficient plasticizing ability of injection molding machine. 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. Increase the injection speed. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. The impact behavior of weld-lines in injection molding. Weld lines appear on the molded part where molten plastic meets. Weld lines are common defects in injection-molded plastic parts that occur when two flow fronts of molten plastic meet and fuse together during the molding process. 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. 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. 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. <Materials>Injection moulding (U. 2. 015 0. Bubbles are caused by melting flow fronts colliding in a mold cavity. The effects of these two injection molding process parameters are explained in terms of their influence on the skin-core morphology observed on the fracture surfaces in the weld zone. The goal is to create a uniform thickness and at the smallest (thinnest) level required. As these flow fronts come together. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. Gates should be designed larger than normal and located to minimize weld line formation. Increase the injection speed to reduce the amount of cooling happening in the mold. Weld line, 5. 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. • Reduce runner dimensions and maintain the same flow rate. 943 µm to 0. ac. In an injection molding process, a weld-line forms when two flow fronts meet each other. Sink Marks Cause 1: Incorrect Melt Temperature. This is a video excerpt from our Problems & Solutions Course - Weldlines. 8. In injection molding weld lines are formed whenever two flow fronts are joined. 2. When an external load is applied to a weld line region, the part’s potential for mechanical failure is increased. Flow-induced filler orientation manifests in higher tensile prop-erties in the direction of flow compared to those normal to the direction of flow. 1. 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]. The quality of the weld line can be improved through optimized processing conditions, increased mold and melt temperatures, and increased injection speed to reduce the viscosity of the polymer. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Wang et al. 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. 1. 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. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. Weld lines may occur depending on the product shape and gate positions. A weld or meld line on plastic parts can cause structural problems and/or be visibly unacceptable. * Corresponding author, e-mail: fengsjpc@ku. Here are some strategies. The vents must be deep enough to allow the trapped air and gasses to escape but not deep enough to allow the plastic to flash. weld lines in injection molded thermoplastic composites. In narrow fields, a limited amount of molten liquid can solidify and block the flow. These are caused by the shot of molten plastic moving at different speeds throughout the injection. Flow Lines and Weld Lines. The thermo-rheological findings were used to investigate the sources of weld line weakness. For example, filled resins and ABS are more likely to. A visual mold with variotherm system for weld line study in micro injection molding. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Wang, G. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. (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. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Weld Lines. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. 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. of micro injection molding process simulation by technology update and progress. + Move gate (to where it is not visible). They are the result of fundamental physical effects taking place inside of the mold tool cavity. Sink marks, 2. 020 0. Weld lines are a reality in the injection moulding of complex parts.