View 08 DEFECTS & REMEDIES (61). Weld line, 5. 6. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. This leads to a better molecular chain entanglement, which in turn creates a better weld. 1 Mold In order to study the formation of weld lines, the mold cavities has been. The thin weld line is the result of weak material bonding, which lowers the strength of the part. 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. The holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. 2. The weld lines in injection moulded parts arise as a result of the collision of two fronts of the flowing material, which fills the mould cavity and are sometimes unavoidable. 1. Injection Molding defect:molding weld_and_meld_line. Increase the injection speed to reduce the amount of cooling happening in the mold. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. 030 0. If the large molded product is. Abstract. Use a less viscous plastic. Besides, possibly it would be. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. 2. A new kind of weld line was. The Difference Between Knit and Meld Lines–and Why It Matters. The micro tensile part was prepared by the double gate injection. This customary mark is caused by differential rates of cooling in the resin where. But none of the current packages can predict weld lines’ properties qualitatively. 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. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. In the 1947 book, Injection Molding of Plastics, the late Dr. The injection molding process can be optimized to maximize weld line strength by increasing mold and melt temperatures, and by increasing pack pressure at the weld line. Improper fusion of two fluid flows, a state before weld line. This happens when the molten plastic is injected into the mold cavity and flows around an obstacle such as a pin, hole, or protrusion, and then comes back together. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Therefore, it is recommended to do a moldflow study prior to the mold being built. This can occur when a polymer flow splits to go around an interruption (e. The weld line degrades the. Weld lines, generated during injection molding, can significantly reduce the mechanical performance of structures. Change the gate locations. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. 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. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. + Adjust injection speed. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Edge Gates. (1983). The impact behavior of weld-lines in injection molding. Weld-line is a weak area which reduces the strength of the part locally. In this lesson we will focus on the meld and weld lines. 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. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. Weld Lines. Specifically, injection-mold lines are often associated with poor mechanical strength. 020 0. <Materials>Injection moulding (U. Thereby creating localized pressure within the mold. 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. Place a vent in the weld line area to remove the entrapped air. In narrow fields, a limited amount of molten liquid can solidify and block the flow. In an injection molding process, a weld-line forms when two flow fronts meet each other. Weld lines appear as a result of the flow of molten plastic during the injection molding process. 2(a, b). A flat product case was considered as an example of a typical aircraft structural element. 298 µm and the weld line on the heated region was almost eliminated with the aid of induction heating. Weld Lines. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. Injection molding, polypropylene, talc. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. Weld lines are one of the typical quality issues of injection molded parts. Weld lines not. The primary cause of cracking is stress and deformation brought on by the external environment, cold mold surfaces, and low injection rates. • Reduce runner dimensions and maintain the same flow rate. Int. 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. gasket seal leakage where the weld line crosses a gasket. consideration in gate location. Reduce the amount of release agents. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the weld line can be seen clearly from the Fig. 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. Weld Lines-3 Ways for Detecting and Correcting. There are several factors that can contribute to the formation of weld lines, including: Part design: The design of the part can impact the flow of the material and the likelihood of weld lines forming. Weld 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 defect analysis, the most common of many defects in injection moulding products. 1. 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). Adjust the design for the flow pattern to be a single source flow. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. This line does not normally impact the overall shape or dimensions of the item. of micro injection molding process simulation by technology update and progress. 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]. The molded plastic part may also appear to be rust-colored. Process. CrossRef View in Scopus Google Scholar [17] G. 1. To respond to poor plasticization and uneven melt temperature,. The performance of weld lines in talc filled polypropylene box moldings produced with a. 5. The position, length, and angle of weld lines are dependent on the. This reduced thickness of the frozen skin further enhances the visual appeal of the. The plaques are prepared out of 30% glass-filled Polyamide 6 material. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. 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. when two or more melt flow fronts contact each other immediately after the cooling process. , 190°C mass and 20°C mold temperature, as well as. Gambar 2. You can expect a mold shrinkage percentage of. For example, filled resins and ABS are more likely to. Adjust the position of the gate and include a venting slot. g. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are still rather few. 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. [ 18 - 21 ] In addition, the effects. Meanwhile, Using more advanced cooling method such as cyclic cooling or conformal cooling. Sink Marks Cause 3: Improper Pack or Hold Pressure. 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. One solution is to prevent the weld lines from forming in regions that are. Weld line is formed when two different melt flows converge, as illustrated in Fig. So today we are going to take a look at the five most common defects in injection molding and their solutions. Controlling the mold’s temperature could also minimize the weld line’s effects. It forces out trapped air pockets and can prevent a vacuum void from occurring. This is expected to achieve maximum results while the pressure holding effect will also increase. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. This occurs mainly in the presence of barriers that divide the melt flow in. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Prediction of the weld lines in injection molding process using neural networks. [1-2] investigated the weld line zone of injection molded glass-fiber-filled polypropylene (PP) composites. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Weld line location. Fisa et al. 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 is particularly true if the wall thickness in the weld is thin – i. You can locate the gate at the thick part of the injection molding to prevent air pockets. 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. These potential causes include:Weld lines Weld lines are weak areas formed by converging flows of plastic that can lead to mechanical part failure if not properly accounted for in the part design. During the plastic injection molding process, one of the biggest challenges is. In this paper, a weld line factor (W-L factor) was adopted to describe the. Tosello et al. 13. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. 10 in Nguyen-Chung et al. Weld lines may occur depending on the product shape and gate positions. 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. Melt temperature does effect the weld. 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. Gava and co-workers implemented an investigation devoted to the de-Injection-mold weld lines may or may not be easily identified by naked eye or straightforward optical microscopy. 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. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. The authors [5, 6] attempted to reduce the weld lines and clamping force of plastic injection moulding through numerical and experimental investigation, and discovered that the 3D cooling channel. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Thus, it is important to understand (i). Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. 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. Sink marks, 2. In this study the polycarbonate (PC) and carbon fiber (CF) are used as the experimental materials to investigate the impact of injection molding process parameters on tensile strength of weld line. In this paper, a kind of polypropylene (PP) foam plastic parts with special weld lines were obtained by core-back foam injection molding with chemical blowing agent. Increasing the temperature of the mold or plastic material. Weld lines often generate mechanically weak areas, because of the unfavorable perpendicular orientation of the macromolecules, fibers and/or other fillers to the direction of the main flow. They. Still, it can be seen to varied degrees depending on mold. Better weld line quality was obtained by Huang. Weld Lines. Design. 7 of the reference. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. 809-814. After that, the compounds were injection-molded into tensile samples with and without weld lines to. Stop using mold parting agents. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. This failure causes the product to be damaged during use. 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. Weld lines have been one of the common defects puzzling the injection molding industry. 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]. This paper presents the. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. 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. In this study, we apply the technique of SAW to explore the acoustic properties near injection-weld lines by comparing the velocity of (V R) in locations close to and locations distant from the weldSince weldline in plastic injection molding (PIM) has an influence on not only the strength but also the surface appearance of a plastic product, it is preferable to reduce it as much as possible for high product quality. The solution to an internal part cracking problem is to change the packing pressure. ac. Weld lines have been one of the common defects puzzling the injection molding industry. 1. Other possible causes include: Low mold or material temperature; Insufficient holding time or. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. My polymer material selection courses 👉 Find Out About Plastics Blog👉 ht. 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. 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 . Investigations on WLs in micro injection molded parts were performed in Refs. 1. This is where the melt fronts divided by an insert, such as a pin or a. In the present work, the micro specimens were investigated. Which means engineers need to know how to account for this phenomenon in an efficient way. G. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. In. Usually it’s a straight line, and often to be found radiating. ), with different mould surface finishes (polished, fine eroded, rough. gas, which can cause blistering, as well as poor weld lines, warpage and the formation of cold slugs that affect filling and part mechanical properties. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Wang. Weld line strength is important in blow molding as well as injection molding. Some of these are listed below: Plastic warpage. Increase the injection speed. Injection molding can be performed with only one of these. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). Kobayashi et al. Therefore, the. 21: Weld line failure caused by hoop stresses. Introduction Weld lines are formed during mold filling whenever two separated melt streams recombine. 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 in injection moulded parts arise as a result of the collision of two fronts of the flowing material, which fills the mould cavity and are sometimes unavoidable. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 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. 5. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. ac. 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. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. Meld and knit lines are actually both different types of weld lines. Insufficient plasticizing ability of injection molding machine. It will degrade materials performance; 9. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. 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. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. 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. Remedies: Raise the temperature of the mold or molten plastic. Sink Marks Cause 1: Incorrect Melt Temperature. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Lesson 6: Meld and Weld Lines (Processing) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. [ 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. 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. See moreEquipment. The welding angle can be used to differentiate weld lines and meld lines. Effects of mold temperature and pressure on shrinkage 0. Strength measurements should be made to. Improvement of weld line strength in injection molded FRTP articles. Proceedings of ANTEC (2000), pp. 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 wheel has to be gated at three places on the hub and. The results of. During injection. Edge Gates. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). The rule is, a higher pressure shall be required to push the material in the machine when there is excess mold. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. The hair-like weld line is the result of weak. 2. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. The weld line’s strength is reduced when. Which means engineers need to know how to account for this phenomenon in an efficient way. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. Weld line formation in the injection molding process occurs. Weld lines are the most common defects in injection molded products. The Solutions for Poor Welding Lines. wall thickness, gate and runner designs and re-validate the result. In the above diagram, the converging flow fronts (indicated by red arrows. Solving one problem can introduce other problems to the injection molding process. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. ”. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. Google Scholar | Crossref | ISI. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. 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. When it comes to injection molding, the chances you might end up making a costly mistake is too high. Save. Kobayashi et al. When injection molding large products, molding is usually performed with multi-point gates, but weld lines can occur depending on the product shape and gate position. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. Weld line formation in the injection molding process occurs. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Weld Lines. 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. Wavy lines are another feature of weld lines. Fig. So today we are going to take a look at the five most common defects in injection molding and their solutions. This paper evaluates the shrinkage and strength of weld line using Design of Experiment and Response Surface Methodology in multi-objective optimisation utilising the injection moulding parameters. The resulting defects don’t stop at flash only. Our injection molding company is explaining what these imperfections are, why they can compromise. Many researchers had emerged with several. Ni. Adjust the design for the flow pattern to be a single source flow. 3: Weld Lines. Criens, R. The edge gate is the most popular and straightforward injection mold gate design. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. Weld lines in injection molding are frequently unavoidable. As the injection process continues, the two separated melt fronts meet again along the longitudinal section of the plate forming a weld line. In weak material bonding, they will appear as hair-like weld lines. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. Polymers 2023, 15, 2440 3 of 21. Effect of the processing conditions on the variations of the bulk temperature, T b , at the end of mold filling at the two locations: in (left) and away (right) from the weld-line (T w , T inj. These lines. 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. Wang et al. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Meld Lines. In an injection molding process, a weld-line forms when two flow fronts meet each other. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. the meeting angle by optimizing variation over time in the cavity. Weld lines appear as a result of the flow of molten plastic during the injection molding process. 1. Weld line and warping are two critical defects for injection-moulded part. Adding vents, using overflows, or using porous metal. A weld or meld line on plastic parts can cause structural problems and/or be visibly unacceptable. Valve. Weld Lines. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Figure 1a illustrates how the weld line is produced when. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. If you turn on the spigot to a garden hose, you will hear a hissing sound at the nozzle end for the first few seconds. 000 0. A weld line can also be called a knit line. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. ” Another. 020 0. Weld lines are a common issue in injection molding, and occur when two flow fronts meet and fuse together as the material cools and solidifies. The governing equations for the melt and the air in the cavity are united into…. Cracking and/or Crazing can be defined as a fracture or surface breakage in the material of a molded part, usually found in weld line areas, but also on the surface in general. Avient’s Zachary Alderman shares practical tips on designing and injection molding parts utilizing short-fiber reinforcements. Remedies: Raise the temperature of the mold or molten plastic. This customary mark is caused by differential rates of cooling in the resin where. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. They are the result of fundamental physical effects taking place inside of the mold tool cavity. 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). As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. The more gate points there are, the more weld lines will occur. 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. This weld line can act as a weak spot in the material. 2021年4月23日 / by admin. Therefore, it is recommended to do a moldflow study prior to the mold being built. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. (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. • Optimize the design of the runner system.