Other possible causes include: Low mold or material temperature; Insufficient holding time or. Gate blush, 4. Injection molding could be applied with many polymer materials, such as. Weld lines are the most common defects in injection molded products. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. 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. Wavy lines are another feature of weld lines. The pressurized air restricts the flow of the plastic resin. Provide a gas vent. 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. Weld line and warping are two critical defects for injection-moulded part. These lines occur when two or more flow fronts meet and fuse together, resulting in a visible seam on the molded part. Molding calculation in Moldex3D: (а) melt front and weld line, (b). Introduction. The Solutions for Poor Welding Lines. 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. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Bubbles are caused by melting flow fronts colliding in a mold cavity. Try to gradually raise the mold temperature and barrel temperature. See moreEquipment. The weld lines are an integral part of plastic injection molding and can seldom be prevented, even by specifically planning the mold with inserts for holes or the like. 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. 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. Azieatul Azrin Dzulkipli and M. Short shots can occur in this case because the air in the mold cavity has nowhere to go while the plastic is entering. Weld line formation in the injection molding process occurs. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. Tosello et al. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. 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. 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. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Introduction. The thermo. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. 080 inches. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. (1) Flash: Extra plastic material in the shape of films or burrs, which appears on the parting surface, around the runner or in the insert crevice. injection molding. 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]. Wang. Meld lines are formed when two separate flow fronts meets. 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. Gambar 2. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. 8. 010 0. 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. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Gates should be designed larger than normal and located to minimize weld line formation. In this lesson we will focus on the meld and weld lines. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. The weld line is then created with a higher flow front temperature and is packed with more pressure. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. 1. The simulated cold weld line length is consistent with the experimental one when a 115 °C mold temperature is adopted; with lower mold temperatures, the simulated lengths are smaller than the experimental ones—in accordance with the literature on the conventional injection molding process [26,27]—probably because of the definition adopted. Usually it’s a straight line, and often to be found radiating. Weld line location. ”. Weld line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. 1 Mold In order to study the formation of weld lines, the mold cavities has been. If weld lines are unavoidable due to multiple gates in a moulding, they should be positioned in the non-critical region. Stop using mold parting agents. Weld lines are a common imperfection to be found in most plastic injected molded parts. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. 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. 2. They are the result of fundamental physical effects taking place inside of the mold tool cavity. 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 weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. 1. Optimizing the injection parameters through combination of adjusting the molding temperature, varying the gate pressure, and increasing the dwell time. 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. 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. Weld line injection molding troubleshooting. The impact behavior of weld-lines in injection molding. Weld line. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. The gate vestige for injection molding is usually narrow. (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. Proceedings of ANTEC (2000) Google Scholar [9] S. 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. In an injection molding process, a weld-line forms when two flow fronts meet each other. Wavy lines are another feature of weld lines. Optimizing the Injection Parameters. If the different flow fronts have cooled. Weld lines are visible lines or seams formed when molten plastic flow fronts meet and fuse together, often due to obstacles or flow interruptions in the. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. 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. The more gate points there are, the more weld lines will occur. 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. One of the defects observed in injection molding parts is weld line strength, which forms when two or more separate melt fronts traveling from different directions meet and join as the mold cavity is filled. analyzed the heat transfer during heating and cooling phases of RHCM process. Polyamide-6 (PA-66) was used as. 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. 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. 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. 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. Weld lines are a kind of Achilles heel of plastics. It will degrade materials performance; 9. Fellahi et al. Its appearance can be improved by adjusting parameters. These processing changes will increase chain. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling 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. Controlling the mold’s temperature could also minimize the weld line’s effects. Flow lines. The most common and one of the most challenging injection molding defects are weld and knit lines. 13. Weld line is formed when two different melt flows converge, as illustrated in Fig. 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. Remedies: Raise the temperature of the mold or molten plastic. 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). Mold vents should function the same way. INJECTION MOULDING DEFECTS 1 DEFECTS 1. Improvement of weld line strength in injection molded FRTP articles. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. 1. (1983). This is expected to achieve maximum results while the pressure holding effect will also increase. Mérillou, J. The next type of injection molding defect is ‘Weld Lines’. In this lesson we will focus on the meld and weld lines. Weld lines represent the region where two separated melt fronts recombine. The second technique, cascade injection moulding, can produce parts free from weld lines. Mostly, this happens when two or more flow fronts do not “knit” during the injection molding process. In the sense that the weld line is better formed before the resin temperature. Increase the size of the gate and runners to alter the mold design. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. [ 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. You can locate the gate at the thick part of the injection molding to prevent air pockets. Increasing the temperature of the mold or plastic material. Weld lines in design for manufacture. Ghazanfarpour. In this study, the effects of injection temperature, injection pressure, and fiber content on the mechanical properties of weld lines were studied for carbon fiber-reinforced nylon. As the polymer resin is injected into a mold, it flows through all parts of the mold. ), with different mould surface finishes (polished, fine eroded, rough. 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. 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 resulting defects don’t stop at flash only. Weld lines not. 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. Molding Equipment. When the two such melt flows. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Zhao, X. Vibration assisted injection molding. Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. From Fig. ppt from SCIENCE 101 at Symbiosis International University. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. The impact behavior of weld-lines in injection molding. and Mosle, H. In other words, weld lines reduce the mechanical properties of the product. The foundation to any robust process, in my opinion, is based on choosing the correct fill time. Weld line strength is important in blow molding as well as injection molding. 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. Injection-molding machine is the Negri Bossi VE210-1700 with screw diameter 60 mm. Weld Lines-3 Ways for Detecting and Correcting. 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. During the plastic injection molding process, one of the biggest challenges is. Prediction of the weld lines in injection molding process using neural networks. The goal is to create a uniform thickness and at the smallest (thinnest) level required. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Abstract. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Our injection molding company is explaining what these imperfections are, why they can compromise. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. 2. Adjust the design for the flow pattern to be a single source flow. <Materials>Injection moulding (U. As the plastic flows through the mold it forms a smooth and continuous flow front. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. Weld. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Mold Design Most conventional mold designs will work with TPU’s. Weld lines appear as a result of the flow of molten plastic during the injection molding process. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. The weld line degrades the. Remedies: Raise the temperature of the mold or molten plastic. Gate location should set to avoid weld lines, keep clean of the important position of the products,. 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. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. View 08 DEFECTS & REMEDIES (61). 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 Lines. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. In the sense that the weld line is better formed before the resin. 3 the path lines of selected material elements can be observed which are. Flow marks in injection molding are defects that manifest as a line or series of lines forming a pattern different in color from the other parts of the molded material. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. 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 . The literature on the formation of weld lines, and their consequences, is more abundant on the area of injection molding [5-12] than on extrusion [13]. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Redesign the mold to prevent the weld line. 6. They. 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. 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. 020 0. The micro tensile part was prepared by the double gate injection. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Controlling the mold’s temperature could also minimize the weld line’s effects. This is where the melt fronts divided by an insert, such as a pin or a block, in a mold cavity rejoin each other downstream of the insert. [ 18 - 21 ] In addition, the effects. The relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. One common issue that frequently arises during injection molding is the formation of weld lines. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. The primary cause of cracking is stress and deformation brought on by the external environment, cold mold surfaces, and low injection rates. A visual mold with variotherm system for weld line study in micro injection molding. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. Weld Lines. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. enough to each other to avoid weld line issues. Injection Molding defect:molding weld_and_meld_line. 3. + Adjust injection speed. (1) Increase the injection pressure and prolong the injection time. 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. Flow LinesThe most simple design modification for eliminating the weakening effect of a weld line is to increase the wall thickness in the weld line zone (Figure 4). As these flow fronts come together. injection molding, (b) weld line and meld line, and (c) injection sample size and shape. The performance of weld lines in talc filled polypropylene box moldings produced with a. Many studies were conducted to explain the weakness at the. 22: Weld line formation when melt splits around core pins. 2-1. 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. 1. 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. Weld Lines. In the above diagram, the converging flow fronts (indicated by red arrows. The injection molding temperature and the mold temperature were fixed respectively at 230 °C and 50 °C. In injection molding, a V-notch-shaped weld line is generated in the melt front meeting area. This line does not normally impact the overall shape or dimensions of the item. 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. Increase the injection speed. They are unavoidable even for moderate complex products. Weld line formation in the injection molding process occurs. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. 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. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). 1. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. the meeting angle by optimizing variation over time in the cavity. The weld line’s strength is reduced when. 2) Vents in an injection mold should let the air out, but not the liquid plastic. ” Another. A flat product case was considered as an example of a typical aircraft structural element. Vents in the mold allow the mold to fill. 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. Flash. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Double push filling method. , less than 0. 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. 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. 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. What are Weld Line Defects? Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. 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. This is expected to achieve maximum results while the pressure holding effect will also increase. In manufacturing, the Weld line or Knit line or Meld line is the line where two flow fronts meet when there is the inability of two or more flow fronts to "knit" together, or "weld", during the molding process. Thereby creating localized pressure within the mold. In narrow fields, a limited amount of molten liquid can solidify and block the flow. Nguyen-Chung. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld-line is a weak area which reduces the strength of the part locally. Weld lines have been one of the common defects puzzling the injection molding industry. Figure 1 below shows the development of a weld line. (1998) for clear photographs. Place a vent in the weld line area to remove the entrapped air. Voids and bubbles, 6. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. 3. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. Three terms that often get mixed up are weld, meld, and knit lines. A visible weld line is observed, due to a combina-Cracking is commonly seen at the weld line area but sometimes on the entire surface. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Better weld line quality was obtained by Huang. Sequential valve gate technology. 2. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. 1. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. Thus, it. 005 0. Some of these are listed below: Plastic warpage. 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. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. Int J Adv Manuf Technol 52:131–141. Weld lines appear on the molded part where molten plastic meets. Google Scholar | Crossref | ISI. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. Emerging Materials Research. This process makes possible to produce a wide range of products with different sizes, shapes, and for varying applications. Dischler, D. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. Fig 13:- Detailed view of weld lines. Founder, Injection Molding Solutions. 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. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. Google Scholar [10] S. 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 have been one of the common defects puzzling the injection molding industry. Burn Marks. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. 010 0. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. 4 at different time steps (legend scale is volume fraction of. 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. distribution [4]. However, research about the computer determination of weld lines in injection molding remains scarce. They appear on the surface of injection molded parts like lines. 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. Heating and cooling mould systems, which cost extremely high, are a typical technology to prevent the weld-line. Weld lines are one of the typical quality issues of injection molded parts. This reduced thickness of the frozen skin further enhances the visual appeal of the. In the 1947 book, Injection Molding of Plastics, the late Dr. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Injection pressures too high Reduce pressure . The main runner and sub-runner are too thin. 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. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. Fisa et al. Weld line formation in the injection molding process occurs. Except for a few injection molded parts with very simple geometry, weld lines occur in most injection molded parts (usually with one line or V-shaped groove), especially in large-scale complex products requiring multi gate mold and inserts. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. 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. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. Injected plates were generated using a double-gated mold under four different process conditions. 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. In an injection molding process, a weld-line forms when two flow fronts meet each other. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. If the different flow fronts have cooled. Effect of process parameters on the relative weld line strength From injection molding practice and literature, 1, 3,4 it is generally accepted that: if a weld line forms before the filling is. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Weld lines have been one of the common defects puzzling the injection molding industry. 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. When it comes to injection molding, the chances you might end up making a costly mistake is too high. (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.