. In this paper, a weld line factor (W-L factor) was adopted to describe the. Weld Lines. Weld lines have been one of the common defects puzzling the injection molding industry. ”. 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. The most common and one of the most challenging injection molding defects are weld and knit lines. 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. Melt temperature does effect the weld. 453-455. 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. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. 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. 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. Weld Lines. 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. Injection molding weld lines where two or more flow fronts come together in the mold. Remedies: Raise the temperature of the mold or molten plastic. 7 of the reference. Weld lines are a reality in the injection moulding of complex parts. Weld Lines. Sink Marks Cause 5: Improper Part Geometry. Weld line. Knit lines are hard to eliminate for injection molded plastic parts but. 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. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Weld line existence reduces the material strength; however, its demerit characteristics. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. The more gate points there are, the more weld lines will occur. Increase the melting temperature. 3. Flow analysis of the weld line formation during injection mold filling of thermoplastics. 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. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Redesign the mold to. • Optimize the design of the runner system. But none of the current packages can predict weld lines’ properties qualitatively. 020 0. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. Flow marks in injection molding can be avoided if adequate measures are taken. CrossRef View in Scopus Google Scholar [17] G. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Flow lines. distribution [4]. This failure causes the product to be damaged during use. 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. Knit and meld lines are inherent to plastic. 025 mm (0 . 005 0. 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. enough to each other to avoid weld line issues. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. The most common and one of the most challenging injection molding defects are weld and knit lines. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. 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. 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. Weld line formation in the injection molding process occurs. Flow lines are lines, waves, or ring patterns that appear on the surface of a part, noted by their slightly different color from the rest of the piece. The injection molding temperature and the mold temperature were fixed respectively at 230 °C and 50 °C. 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. Emerging Materials Research. Injected plates were generated using a double-gated mold under four different process conditions. Ni. Flow Lines. 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. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. 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. Molding calculation in Moldex3D: (а) melt front and weld line, (b). They. Tosello et al. 1. Injection molding of large/complicated products are usually prepared by multiple compounds, which produces weldlines once the melt fronts are joined by impingement flow. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. The plaques are prepared out of 30% glass-filled Polyamide 6 material. In the sense that the weld line is better formed before the resin. 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. This leads to a better molecular chain entanglement, which in turn creates a better weld. Meanwhile, Using more advanced cooling method such as cyclic cooling or conformal cooling. The performance of weld lines in talc filled polypropylene box moldings produced with a. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. The wheel has to be gated at three places on the hub and. This is expected to achieve maximum results while the pressure holding effect will also increase. Thus, it is important to understand (i). These are preferred over weld lines as they will normally result in improved cosmetics and structure. Weld line and warping are two critical defects for injection-moulded part. If the different flow fronts have cooled. Preventing sink marks of injection molded parts using CAE analysis. 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. The injection molding simulation software used offers a method for the detection of weld lines that has shown to be only reliable for the detection of stagnating weld lines. Which means engineers need to know how to account for this phenomenon in an efficient way. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. Injection-molding machine is the Negri Bossi VE210-1700 with screw diameter 60 mm. 2. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. weld lines in infill analysis of injection molding simulation was observed [5]. 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. A weld or meld line on plastic parts can cause structural problems and/or be visibly unacceptable. Weld lines appear on the molded part where molten plastic meets. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. 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. A. The goal is to create a uniform thickness and at the smallest (thinnest) level required. 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. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Weld Lines. 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). Ghazanfarpour. Vibration assisted injection molding. 1. In injection molding, it is often important to maintain consistent color throughout the part. injection molding. Gate location should set to avoid weld lines, keep clean of the important position of the products,. (1) Increase the injection pressure and prolong the injection time. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. 2017-01-0481. 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]. 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. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. Weld lines represent the region where two separated melt fronts recombine. Weld lines may occur depending on the product shape and gate positions. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. In this experiment, several ejector. In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. They have their origins in material choice, part design, tooling, and processingIncrease the mold temperature and smooth out any sharp corners or turns in the mold to facilitate even melt flow. 18/06/2021. The pressurized air restricts the flow of the plastic resin. Weld lines are one of the typical quality issues of injection molded parts. Proper venting is also required to ensure good weld-line quality. Or increase the number of gates. carried out to mass-produce molded products with complex shapes. – Use generous and even. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Int J Adv Manuf Technol 52:131–141. In weak material bonding, they will appear as hair-like weld lines. For the production of these weld-line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527-2) and impact (ISO 179-1/1eU) properties were measured, and statistical analyses were performed to gain insight on the correlation between melt flow rate and weld-line behavior. Weld lines are also known as knit lines. You will have to confirm them before tooling. You can choose material of low viscosity and can increase the injection pressure. The hair-like weld line is the. That’s the air escaping out of the nozzle until the hose is full of pressurized water. In this case the two flow fronts will meet and. Weld line problem which occurs in polymer parts produced by plastic injection method and affects appearance and strength on a large scale was researched in this paper. 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. To explore the formation of weld lines in injection molding, a flow model based on viscoelastic constitutive equation is presented in this article to predict and evaluate of weld lines location and properties, in which Rolie. In addition a weld line can be moved to an area where it is less visible. During the plastic injection molding process, one of the biggest challenges is. 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. These lines. Sink Marks Cause 2: Low Pack and Hold time. 010 0. Steven. T. Weld line (also known as a knit 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. Edge Gates. 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. Mostly, this happens when two or more flow fronts do not “knit” during the injection molding process. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. Where the weld lines are, where the sink marks or voids will be, and how the part warps—all of these are determined by where the molten plastic is injected into the part cavity. 10. Save. 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. When this fails to happen correctly, a weld line defect occurs. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Mold flow marks, also known as flow lines or weld lines, are often caused by variations in the flow of molten plastic material during the injection molding process. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. They become more critical when particulate fillers are compounded with the polymer. ). Weld lines have been one of the common defects puzzling the injection molding industry. . Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. Weld-line is a weak area which reduces the strength of the part locally. The next type of injection molding defect is ‘Weld Lines’. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. ” Another. 2-1. The governing equations for the melt and the air in the cavity are united into…. The conditions are temperature, injection speed, and injection pressure. This is expected to achieve maximum results while the pressure holding effect will also increase. Redesign the mold to prevent the weld line. Molding Equipment. If the melt temperature is low or the injection speed and pressure are low, you may end up with a more pronounced weld line. (3-1) Increasing the Resin Temperature at the Weld Line Section. If you are familiar with any form of scientific injection molding, regardless of the name, then you know one of the first steps is performing a viscosity curve study. The effects of fiber concentration has been studied in detail. Park et al. Injection molding plate for mode I testing geometry. The thermo. 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. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. Here we are looking at most common part defect that can come from injection molding called weld line. Runner Type Venting Plastic melt and mold temperature Injection speed and pressure Learn how to troubleshoot weld lines in injection molding. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 21: Weld line failure caused by hoop stresses. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Streaks 3. การแก้ไข ชิ้นงานจุดที่เกิดความอ่อนแอบริเวณ weld line คือต้องใช้ความเร็วในการฉีดต่ำในจุด. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. 6. Design. The impact behavior of weld-lines in injection molding. 8. 9 – Over Packing. One method is the local te mpering of the affected areas to prevent weld lines. Since it is often impossible to avoid weld lines as well as a limited possibility to increase the weld line strength by adjusting the injection molding parameters, a method to predict the weld line strength in the product development process is shown below. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. Quality concerns in injection-molded materials can vary fr. M. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. + Move gate (to where it is not visible). Weld line injection molding troubleshooting. 4. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. Many studies were conducted to explain the weakness at the. 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. 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. Change the flow pattern to a single-source flow. 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. 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. Weld lines can. 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. In this work, the weldline strength of injection molded short-glass-fiber reinforced polycarbonate was derived by an analytical method of modified rule-of-mixtures as a function of the area fraction between skin and core layers. In a weld line, reinforcement fibers. Increase the injection speed. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. Weld line section presents notch or gloss difference. Weld lines not. Controlling the mold’s temperature could also minimize the weld line’s effects. Plastic Injection Molding Process. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. Weld line strength is important in blow molding as well as injection molding. injection molding is followed by the welding. Weld lines. Weld lines may appear like seams or scratches, but that is not what they are. In other words, weld lines reduce the mechanical properties of the product. Thereby creating localized pressure within the mold. the meeting angle by optimizing variation over time in the cavity. Therefore, more studies covering this subject are required in order to improve the insight regarding the mechanism involved in the formation of weld lines in extrusion and,From the so-produced materials, specimens with weld lines were produced according to the first test series, but varying the injection molding parameters only twice, between the best and worst settings found in the previous study with the polypropylene types with MFR 8 g/10 min, i. 2017-01-0481. The weld line is an inevitable defect in the most injection molded components. Double push filling method. Ejector System (Pötsch, 1995) . Mold vents should function the same way. Injection pressures too high Reduce pressure . Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. 005 0. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. 020 0. This paper presents the. Injection molding, polypropylene, talc. consideration in gate location. Figure 2. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. 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. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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. Kobayashi et al. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Meld lines are formed when two separate flow fronts meets. 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. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. 10 in Nguyen-Chung et al. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. Increasing the temperature of the mold or plastic material. Weld lines are the result of fundamental physical effects taking place inside of the mold tool cavity, they are common imperfection to be found in most plastic injection molded parts. A viscosity curve is developed using calculations of the fill time and plastic pressure at. The impact behavior of weld-lines in injection molding. Weld Lines. the three-plate mold often adopt this kind of gate. One solution is to prevent the weld lines from forming in regions that are. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). This weld line can act as a weak spot in the material. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. The Solutions for Poor Welding Lines. Ideally, the resin flow will split into two flow fronts to pass around the obstruction and then recombine into a single flow front. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU. This customary mark is caused by differential rates of cooling in the resin where. Shaofei Jiang. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. 3. avoid weld lines, and facilitate smooth. Three terms that often get mixed up in injection molding are weld, meld and knit lines. There are various types of injection molding defects that can cause such interruptions in the manufacturing cycle. 030 0. e. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. For example, filled resins and ABS are more likely to. Fig 13:- Detailed view of weld lines. The Solutions for Poor Welding Lines. The calculation was carried out on a mesh with solid elements obtained in ANSYS Meshing and transferred to Moldex3D by means Rhinoceros. Our injection molding company is explaining what these imperfections are, why they can compromise. Vents in the mold allow the mold to fill. Controlling the mold’s temperature could also minimize the weld line’s effects. (1983). In this experiment, several ejector. Alter the mold design. The rule is, a higher pressure shall be required to push the material in the machine when there is excess mold. Sink marks are a common type of injection molding defect. This failure causes the product to be damaged during use. Introduction. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. The default weld line result recognizes 135º as the maximum angle of collision and as that angle decreases, the severity increases as it. 298 µm and the weld line on the heated region was almost eliminated with the aid of induction heating. A weld line is often unavoidable. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . 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. A new kind of weld line was. Five injection molding process parameters, including mold temperature, melt temperature, packing pressure, injection. 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 or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. The molded plastic part may also appear to be rust-colored. Azieatul Azrin Dzulkipli and M. Steven. 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. Weld lines are where two flow. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Increase the injection speed. (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. Wavy lines are another feature of weld lines. Expand. a) Multi-fiber connector micro injection molding simulation b) 3D simulation of micro gear with 150µm diameter for weld line position prediction c) 3D micro injection molding filling simulation of micro gear with 180µm diameter Fig. In this lesson we will focus on the meld and weld lines. 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. Edge Gates. 000 0. Figure 2. 1. [ 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. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. Wang et al. 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 plaques are prepared out of 30% glass-filled Polyamide 6 material. Specifically, injection-mold lines are often associated with poor mechanical strength. In the present work, the micro specimens were investigated. 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 appear on the surface of a molded part where the molten material has converged after splitting off in a mold. The primary cause of cracking is stress and deformation brought on by the external environment, cold mold surfaces, and low injection rates. Materials Science.