Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. are very minimum. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. This is where the melt fronts divided by an insert, such as a pin or a. Fig. To determine the effect of the weld lines on tensile strength, tensile tests were conducted with the specimens fabricated with NORYL (amorphous blends of. Weld lines are a kind of Achilles heel of plastics. They are unavoidable even for moderate complex products. Silver Streak. 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. The edge gate is the most popular and straightforward injection mold gate design. Recently, the injection molding of fiber reinforced thermoplastics (FRTP) containing short fibers has been widely carried out to mass-produce molded products with complex shapes. 22: Weld line formation when melt splits around core pins. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). 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. The conditions are temperature, injection speed, and injection pressure. According to the characteristics. 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. So today we are going to take a look at the five most common defects in injection molding and their solutions. Islyn Thomas summarized the need for a particular vent location better than I ever could. 5. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Weld-line is a weak area which reduces the strength of the part locally. In injection molding, it is often important to maintain consistent color throughout the part. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. During the plastic injection molding process, one of the biggest challenges is. Sequential valve gate technology. Weld line formations can be weak if they fall in areas that will bear stress or impact. 8. A weld line is a mark left on the surface of a plastic injected molded 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. Founder, Injection Molding Solutions. Weld lines have been one of the common defects puzzling the injection molding industry. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. Weld lines are one of the typical quality issues of injection molded parts. This paper presents the. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. 1. 4. • Optimize the design of the runner system. Sink marks are a common type of injection molding defect. 15 shows the frozen layer and weld lines at the end of mold filling. In injection molding, it is often important to maintain consistent color throughout the part. The injection molding gate generates heat by dissipation. Increase the injection speed to reduce the amount of cooling happening in the mold. Typical injection molding processing temperatures of TPU materials are as follows: IM Zone 60A to 75A 80A to 90A 95A to 75D Rear 315 – 40 ºF45 -370 75 400The weld line in an injection molding product can significantly impact the strength and durability of the last part [12] [13][14][15]. The thermo. (1) Increase the injection pressure and prolong the injection time. In this study, the effects of injection temperature, injection pressure, and fiber cont. 020 0. Figure 2. 18/06/2021. Its appearance can be improved by adjusting parameters. CrossRef View in Scopus Google Scholar [17] G. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Weld line injection molding troubleshooting. Weld lines: Cold feedstock in the die: Increase injection speed, mold temperature, and feedstock temperature, enlarge gate opening, add venting channels or overflow wells near weld line locations, move gate location, redesign parts to avoid stream partition: Flow mark: Cold feedstock in the dieWeld lines are a common imperfection to be found in most plastic injected molded parts. Weld line, 5. These are preferred over weld lines as they will normally result in improved cosmetics and structure. Weld line location. Weld lines appear on the molded part where molten plastic meets. You will have to confirm them before tooling. Increase the injection speed to reduce the amount of cooling happening in the mold. 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. 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-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms. Gate location should set to avoid weld lines, keep clean of the important position of the products,. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Polym Eng Sci 45(7. The structure is more complex with longer molding cycle . Therefore, the. . 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. Thus, it is important to understand (i). The flow fronts at different times (Fig. Figure 2. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. In an injection molding process, a weld-line forms when two flow fronts meet each other. 4 at different time steps (legend scale is volume fraction of. Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. Weld line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. 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. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Possible Sources of Weld/Knit Lines: Temperature from the injection molding machine, runners, and/or the mold itself in order to ensure the plastic resin flows properly;Weld line is one of the plastic injection molding defects. 21: Weld line failure caused by hoop stresses. Expand. This occurs either due to injection through multiple gates or as a conse-รอยประสานของเนื้อพลาสติก Weld line ตอนที่1. The weld line is then created with a higher flow front temperature and is packed with more pressure. This failure causes the product to be damaged during use. 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. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Injected plates were generated using a double-gated mold under four different process conditions. 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. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. 2. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Weld line existence reduces the material strength; however, its demerit characteristics. Carefully consider all the relevant aspects of the mold design specification before. In the first stage, the two part halves are injection molded and then, in a second process step outside of the molding machine, they are welded together. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Increase the injection speed. This is expected to achieve maximum results while the pressure holding effect will also increase. (3) Adjust the temperature of the barrel and nozzle: the viscosity. 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. Streaks 3. 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. 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. Int J Adv Manuf Technol 52:131–141. Bubbles are caused by melting flow fronts colliding in a mold cavity. 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. injection molding, (b) weld line and meld line, and (c) injection sample size and shape. The gate vestige for injection molding is usually narrow. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. 1. Figure 1 below shows the development of a weld line. Weld lines can appear on the surface of a molded part where the molten material has converged after splitting off into two or more directions in a mold. The weld line degrades the. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPThree terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Experimental Setup 2. It is normally at the meeting points of two flow fonts. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. Evaluate and optimize your part design The advantages of using the moldflow analysis to avoid potential defect like deformation, shrinkage, welding line etc, part designers can change the wall thickness or enhance the ribs to improve their part design. Increasing the temperature of the mold or plastic material. Weld lines are a common imperfection to be found in most plastic injected molded parts. The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. Mold Design Most conventional mold designs will work with TPU’s. 10. Change the gate locations. Steven. Its appearance can be improved by adjusting parameters. 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. Weld lines are a kind of Achilles heel of plastics. The most common and one of the most challenging injection molding defects are weld and knit lines. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. In injection molding, a V-notch-shaped weld line is generated in the melt front meeting area. Weld lines have been one of the common defects puzzling the injection molding industry. The pressurized air restricts the flow of the plastic resin. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. Weld Lines. (1998) for clear photographs. Discoloration. G. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. As a result, the portion has a faint, perhaps undetectable line. 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. These processing changes will increase chain. Introduction Weld lines are formed during mold filling whenever two separated melt streams recombine. 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. The Solutions for Poor Welding Lines. But none of the current packages can predict weld lines’ properties qualitatively. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. The Difference Between Knit and Meld Lines–and Why It Matters. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. This paper presents the. Gate Placement: Properly positioning the gate can direct the melt flow to minimize weld lines or relocate the weld line to non-visible areas of the part. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. M. 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]. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. It is a zone with reduced mechanical properties negatively influencing on the molding behavior in exploitation. You can expect a mold shrinkage percentage of. 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. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. They are the result of fundamental physical effects taking place inside of the mold tool cavity. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. This occurs mainly in the presence of barriers that divide the melt flow in. Weld line. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. Wavy lines are another feature of weld lines. The weld line’s strength is reduced when. Weld lines in design for manufacture. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. Steven. In the sense that the weld line is better formed before the resin temperature. A meld line occurs when two moving melt fronts converge and flow parallel to each other. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Solving one problem can introduce other problems to the injection molding process. Weld Lines. Weld Lines-3 Ways for Detecting and Correcting. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. 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. The next type of injection molding defect is ‘Weld Lines’. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. 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. Weld or knit lines occur when melt flow fronts collide in a mold cavity. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. the meeting angle by optimizing variation over time in the cavity. The thermo-rheological findings were used to investigate the sources of weld line weakness. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. 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. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. 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. This line does not normally impact the overall shape or dimensions of the item. An obstruction such as a core pin or holes will split the material flow and cause a weld line issue to form on the other side. , 190°C mass and 20°C mold temperature, as well as. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld together. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. Wang, G. Weld line formation in the injection molding process occurs. + Improve vent inside the mold. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. The welding angle can be used to differentiate weld lines and meld lines. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. [ 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 Lines-3 Ways for Detecting and Correcting. Venting at Weld Lines. Maintain a holding pressure that is no more than 1/2 the. Flow lines. A simulation process was conducted to determine the recommended setting of injection moulding parameters and the range of the variable. 1. If the different flow fronts have cooled. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. 1 Prediction of weld lines with injection molding simulation softwareReduced frozen skin thickness: High injection speeds also contribute to a thinner frozen skin at the weld line. The hair-like weld line is the result of weak. As the injection process continues, the two separated melt fronts meet again along the longitudinal section of the plate forming a weld line. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. Sink Marks 2. (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. An evaluation model based on artificial neural network method. 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. Weld lines are one of the typical quality issues of injection molded parts. (3) Adjust the temperature of the barrel and nozzle: the viscosity. There will be too many weld lines ; 6. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of injection parts. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 8. The Factors that Cause Weld Line in Injection molding Pressure. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. Multiple gates are acceptable as long as they are close enough to each other to avoid weld line issues. 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. 6. One method is the local te mpering of the affected areas to prevent weld lines. 1. 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. So today we are going to take a look at the five most common defects in injection molding and their solutions. 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. Cracks in Corners – When cracks appear in the corners of plastic parts, the cause is too much plastic shrinkage onto the mold core in that corner. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. Try to gradually raise the mold temperature and barrel temperature. Weld line formation in the injection molding process occurs. Injection molding of large/complicated products are usually prepared by multiple compounds, which produces weldlines once the melt fronts are joined by impingement flow. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). In a meld line, the plastic comes together at an angle greater than 135 degrees. weld lines in infill analysis of injection molding simulation was observed [5]. 7 of the reference. Valve. In an injection molding process, a weld-line forms when two flow fronts meet each other. (1983). In. when two or more melt flow fronts contact each other immediately after the cooling process. , 2 (3–4) (1988. This article will review how and why weld lines occur, how mold gates effects weld line location and strength, the importance of material selection and Injection molding weld lines refer to a line on an injection molded part that is generated where the two halves of the mold come together. + Optimize holding pressure time. The weld line can either be a minor cosmetic issue or potentially bad enough to negatively impact the part's strength. The main types of injection molding defects are: 1. The calculation was carried out on a mesh with solid elements obtained in ANSYS Meshing and transferred to Moldex3D by means Rhinoceros. 000 0. 3. For more information on the Factors Affecting the Injection Molding Process. The performance of weld lines in talc filled polypropylene box moldings produced with a. This leads to a better molecular chain entanglement, which in turn creates a better weld. Weld-line is a weak area. Ejector System (Pötsch, 1995) . Figure 1 below shows the development of a weld line. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. Improper fusion of two fluid flows, a state before weld line. Here are some strategies. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. 2) Vents in an injection mold should let the air out, but not the liquid plastic. Some of these are listed below: Plastic warpage. 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. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. T. Flash. The goal is to create a uniform thickness and at the smallest (thinnest) level required. 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. The thin weld line is the result of weak material bonding, which lowers the strength of the part. My polymer material selection courses 👉 Find Out About Plastics Blog👉 ht. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. 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. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. 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. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. You can choose material of low viscosity and can increase the injection pressure. Flow marks in injection molding can be avoided if adequate measures are taken. Clamping Unit. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. 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. 10(a) (please see Fig. Weld Line Factors for Thermoplastics. It forces out trapped air pockets and can prevent a vacuum void from occurring. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. 18/06/2021. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. 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. 3. Remedies: Raise the temperature of the mold or molten plastic. Jiquan Li, Taidong Li, +1 author. Poor mold spot Spot mold to ensure fit and vent depths at ~0 . Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. 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. As compared to a weld line, the flow fronts come together at less than 135 degrees. When two or more streams of plastic meet and fuse together, a visible line or weakness is formed on the surface of the finished product. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a mold. Injection pressures too high Reduce pressure . 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. Injection Molding defect:molding weld_and_meld_line. 13. Dischler, D. To respond to poor plasticization and uneven melt temperature,. Fig 13:- Detailed view of weld lines. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Download : Download high-res image (856KB) Download : Download full-size image; Fig. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. 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. This study examines the impact of injection parameters on the weld line strength of the polyamide 6 and 30% fiberglass (PA6 + 30% FG) composite samples. distribution [4]. Vents in the mold allow the mold to fill. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. 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. 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 most common and one of the most challenging injection molding defects are weld and knit lines. 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. Gate blush, 4. Injection molding plate for mode I testing geometry. The hair-like weld line is the. Multiple gating, splitting of the melt flow due to inserts in the cavity or through holes, as well as changes of thickness give rise to points within the structure where the flowing fronts will recombine and weld. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. Yes, it does help, for two reasons: Often the weld line traps air and the ‘dump’ acts as a vent to allow the air to escape. The need to minimize fiber breakage, plus the higher viscosity of materials with. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. 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. Instead, a line that looks like a seam forms. 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. In this paper, aiming at the problem of weld line defects in the injec- tion process of a key phone panel, the injection process is optimized by using Moldflow and drop simulation. Yes, it does help, for two reasons: Often the weld line traps air and the ‘dump’ acts as a vent to allow the air to escape. Except for a few injection molded parts with very simple geometry, they occur on most injection molding parts (the shape is usually a line or V-shaped groove), especially Large complex items requiring the use of multi-gate molds and inserts. Emerging Materials Research. To elimi- nate weld lines, you can enlarge shrinkage. Weld Lines. Polyamide-6 (PA-66) was used as. 025 mm (0 . Bubbles are caused by melting flow fronts colliding in a mold cavity. 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. (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. (3-1) Increasing the Resin Temperature at the Weld Line Section. 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. This can occur when a polymer flow splits to go around an interruption (e. When two or more streams of plastic meet and fuse. During injection. That helps. ). In conclusion, reducing weld lines in injection molding requires a combination of factors, including adjusting the melt temperature, injection speed, pressure, and gate size, as well as using a hot runner system, modifying the part design, using a different material, reducing the wall thickness, using a mold release agent, and working. (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. Weld Line defect analysis, the most common of many defects in injection moulding products. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. When this fails to happen correctly, a weld line defect occurs. 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.