The most common and one of the most challenging injection molding defects are weld and knit lines. To explore the formation of weld lines in injection molding, a. ” Another. Our injection molding company is explaining what these imperfections are, why they can compromise. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). The injection molding gate generates heat by dissipation. If the injection gate is not properly designed, it can cause the formation of defects like sink-mark, warpage, short shot, weld-line, air traps, and other faults [15]. 3. Flow Lines. Thus, it. Change the flow pattern to a single-source flow. 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. This study describes how the weld line was formed on the part. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Sink Marks Cause 3: Improper Pack or Hold Pressure. Meld and knit lines are actually both different types of weld lines. Kobayashi et al. 005 0. 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. Use a less viscous plastic. This leads to a better molecular chain entanglement, which in turn creates a better weld. Weld lines have been one of the common defects puzzling the injection molding industry. Thus, it is important to understand (i). In this paper, two different injection molding tests were completed. Participating in DFM and mold flow analysis is a good way to achieve this. As these flow fronts come together. Prediction of the weld lines in injection molding process using neural networks. The weld line can either be a minor cosmetic issue or potentially bad enough to negatively impact the part's strength. Mold vents should function the same way. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. The more gate points there are, the more weld lines will occur. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. S. 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. Consequently, it causes viscous dissipation which leads to the generation of heat. Weld line injection molding troubleshooting. These processing changes will increase chain. In some cases, a weld line can also cause a loss of strength and impact resistance. The molded plastic part may also appear to be rust-colored. Fig. This paper presents the. Weld lines are a kind of Achilles heel of plastics. Injection Molding Know How. The impact behavior of weld-lines in injection molding. The Problems & Solutions course is designed to train injection molding personnel in. e. 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 line strength is important in blow molding as well as injection molding. 22: Weld line formation when melt splits around core pins. In injection molding weld lines are formed whenever two flow fronts are joined. Weld line. Sink Marks Cause 2: Low Pack and Hold time. (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. 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. Increasing the temperature of the mold or plastic material. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Melt temperature does effect the weld. 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. 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. From Fig. Nguyen-Chung. The Influence of Knit-lines on the Tensile Properties of Injection Molded Parts, Polymer Engineering and Science, 23(10): 591-596. Int. 1 Prediction of weld lines with injection molding simulation softwareReduced frozen skin thickness: High injection speeds also contribute to a thinner frozen skin at the weld line. This is particularly true if the wall thickness in the weld is thin – i. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Which means engineers need to know how to account for this phenomenon in an efficient way. Venting at Weld Lines. Discoloration. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. 9 – Over Packing. Adding vents, using overflows, or using porous metal. The solution to an internal part cracking problem is to change the packing pressure. 7 in Kobayashi et al. The impact behavior of weld-lines in injection molding. In the sense that the weld line is better formed before the resin. (1) Increase the injection pressure and prolong the injection time. Many researchers had emerged with several. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. 2017-01-0481. Weld Lines. g. 3 the path lines of selected material elements can be observed which are. GlossFlow-induced fiber orientation and weld lines are com-mon features of the injection molding process. Weld line location. There is excess air inside the mold (1) make the mold vent larger at location with weld line; (2) Check if the mold vent is blocked or not or use vacuumized forming. Increase the injection speed. There will be too many weld lines ; 6. Proceedings of ANTEC (2000) Google Scholar [9] S. In an injection molding process, a weld-line forms when two flow fronts meet each other. [1] The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. (1) Increase the injection pressure and prolong the injection time. Google Scholar | Crossref | ISI. 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 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. 2017-01-0481. 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. When an external load is applied to a weld line region, the part’s potential for mechanical failure is increased. 1. 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. 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. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Improvement of weld line strength in injection molded FRTP articles. Fig. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. 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. 1. Injected plates were generated using a double-gated mold under four different process conditions. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. Raise the injection speed. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. 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. In the above diagram, the converging flow fronts (indicated by red arrows. [ 18 - 21 ] In addition, the effects. Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. Weld line formations can be weak if they fall in areas that will bear stress or impact. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. Polym. Move injection locations to make weld lines form closer to the gates. Mérillou, J. Sink Marks Cause 1: Incorrect Melt Temperature. Amongst weld line. Steven. This process makes possible to produce a wide range of products with different sizes, shapes, and for varying applications. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. 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, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. After that, the compounds were injection-molded into tensile samples with and without weld lines to. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. The holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. These are preferred over weld lines as they will normally result in improved cosmetics and structure. 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. These weld lines occur usually around holes or at the material flow joint area in the injeciton molded part, some welding lins is very small, specially if. In this lesson we will focus on the meld and weld lines. Or increase the number of gates. 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. Injection Molding defect:molding weld_and_meld_line. 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. 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. M. (2011) and Fig. Weld lines defects are formed when two flow fronts are merged together. Poor mold spot Spot mold to ensure fit and vent depths at ~0 . Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. 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]. th INTRODUCTION Injection molding is one of the mostWeld Lines in a plastic cover. Three terms that often get mixed up in injection molding are weld, meld and knit lines. 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. when two or more melt flow fronts contact each other immediately after the cooling process. Meld and knit lines are actually both different types of weld lines. The. As the injection process continues, the two separated melt fronts meet again along the longitudinal section of the plate forming a weld line. A meld line occurs when two moving melt fronts converge and flow parallel to each other. 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 . Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. The structure is more complex with longer molding cycle . Weld lines have been one of the common defects puzzling the injection molding industry. 8. 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. 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. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. Causes and Remedies of Sink Marks In Injection Molding. 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. The governing equations for the melt and the air in the cavity are united into…. 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. The edge gate is the most popular and straightforward injection mold gate design. You can choose material of low viscosity and can increase the injection pressure. The rule is, a higher pressure shall be required to push the material in the machine when there is excess mold. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). In an injection molding process, a weld-line forms when two flow fronts meet each other. Figure 2. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Weld lines have been one of the common defects puzzling the injection molding industry. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. Gambar 2. To elimi- nate weld lines, you can enlarge shrinkage. Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. The wheel has to be gated at three places on the hub and. To respond to poor plasticization and uneven melt temperature,. This is where the melt fronts divided by an insert, such as a pin or a. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. 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. Weld lines are a reality in the injection moulding of complex parts. In this study, the effects of injection temperature, injection pressure, and fiber cont. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms of weld-line, etc. 010 0. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. Abstract. Meddad and Fisa [3] found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. 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. Optimizing the Injection Parameters. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. Insufficient injection pressure and speed can cause weld lines. In this study, epoxy molding compounds (EMC) filled with glass beads were fabricated with a twin-screw-extruder (TSE) and tempered before further processing to generate different degrees of cross-linking (0–15%) in the compounds. 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. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. (1983). Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Double push filling method. Vacuum voids. Expand. Weld-line is a weak area which reduces the strength of the part locally. • Reduce runner dimensions and maintain the same flow rate. Redesign the mold to prevent the weld line. The position, length, and angle of weld lines are dependent on the. Sink Marks 2. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. The main runner and sub-runner are too thin. A viscosity curve is developed using calculations of the fill time and plastic pressure at. Weld lines appear as a result of the flow of molten plastic during the injection molding process. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. 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. ). 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. ) . 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 choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. Clamping Unit. Abstract. A knit line may be unnoticeable or may look like a crack. 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. 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. Weld line existence reduces the material strength; however, its demerit characteristics. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. This paper presents the. In this paper, a weld line computer determination method based on filling simulation with surface model is proposed, from which the positions and lengths of the weld lines can be predicted. The hair-like weld line is the result of weak. 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. ac. But none of the current packages can predict weld lines’ properties qualitatively. In spite of its cosmetic attributes, a bad knit line can significantly. Thereby creating localized pressure within the mold. . 18/06/2021. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. They. In this study, polypropylene (PP) was compounded respectively with carbon nano fibers (CNFs) and TiO 2 nano particles at various weight fractions (10, 20, 30, 35. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow path. avoid weld lines, and facilitate smooth. Thus, it is important to understand (i). 10 in Nguyen-Chung et al. This paper presents the. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Maintain a holding pressure that is no more than 1/2 the. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. 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 may appear like seams or scratches, but that is not what they are. In. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. 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. Here are some ways to avoid. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. This can occur when a polymer flow splits to go around an interruption (e. , 2 (3–4) (1988. Knit and meld lines are inherent to plastic. Injection molding can be performed with only one of these. investigated the impact of injection molding parameters on weld line formation and strength reduction. Weld line existence reduces the material strength; however, its demerit characteristics. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. This study focus on the formation of. Redesign the mold to. Controlling the mold’s temperature could also minimize the weld line’s effects. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. 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. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. • Optimize the design of the runner system. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. The thermo. Mold Design. Weld Line Factors for Thermoplastics. Redesign the mold to prevent the weld line. Avient’s Zachary Alderman shares practical tips on designing and injection molding parts utilizing short-fiber reinforcements. Flow Lines and Weld Lines. the meeting angle by optimizing variation over time in the cavity. 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. (3-1) Increasing the Resin Temperature at the Weld Line Section. 2) Vents in an injection mold should let the air out, but not the liquid plastic. injection molding is followed by the welding. Weld line, 5. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. <Materials>Injection moulding (U. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Wang. Instead, a line that looks like a seam forms. Optimizing the injection parameters through combination of adjusting the molding temperature, varying the gate pressure, and increasing the dwell time. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. The thin weld line is the result of weak material bonding, which lowers the strength of the part. Weld line is formed when two different melt flows converge, as illustrated in Fig. That helps. 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. 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 in an injection molded part develops when two or more melt fronts are converged together. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 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. Knit lines are hard to eliminate for injection molded plastic parts but. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. <Mold> Provide a cold slug well where weld lines occur. Improper fusion of two fluid flows, a state before weld line. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. Weld lines are the unfavorable defect not only in normal injection molding process but in micro injection molding process. They decrease the. Known also as knit lines and weld marks, weld lines are difficult to eliminate completely, especially if your injection molded part requires holes. Definition: A seam that appears where two areas of molten plastics meet. When this fails to happen correctly, a weld line defect occurs. 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. Mold vents should function the same way. The plastic injection molding process, including thermoplastic injection, is nowadays used in several industrial processes, including in the automotive industry for bowden cables. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. Its appearance can be improved by adjusting parameters. 298 µm and the weld line on the heated region was almost eliminated with the aid of induction heating. 000 0. Weld-line is a weak area which reduces the strength of the part locally. In order to prepare the weld line specimen by micro injection molding, a mould integrated with visual system and variotherm system was designed and constructed, shown as Fig. analyzed the heat transfer during heating and cooling phases of RHCM process. 2) Vents in an injection mold should let the air out, but not the liquid plastic. 4. A knit line, also called a weld line, occurs when the liquid plastic moves through the mold and hits more melted plastic and they don’t flow or fuse together. Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. 015 0. They are the result of fundamental physical effects taking place inside of the mold tool cavity. Fig 13:- Detailed view of weld lines. In injection molding weldlines are generated when two separate melt streams join either in multigated molds or as a consequence of flow around. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. Weld lines may occur on a molded part’s surface where, after breaking off into two or more directions in a mold, the molten material has converged. Here we are looking at most common part defect that can come from injection molding called weld line. Kobayashi et al. This is a video excerpt from our Problems & Solutions Course - Weldlines. Weld Lines. 000 0. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. Besides, possibly it would be. In. This line does not normally impact the overall shape or dimensions of the item. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. 1. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Founder, Injection Molding Solutions. Weld lines in injection molding are frequently unavoidable. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. injection molding. Weld Lines. The four sets of plaques are produced by changing the magnitude of packing pressure equal to 60% of filling pressure, with increment of 20% up to 120% of filling pressure. 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. Fellahi et al. The weld line is an inevitable defect in the most injection molded components. Three terms that often get mixed up are weld, meld, and knit lines. Sink marks, 2. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. 5. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Save. In the 1947 book, Injection Molding of Plastics, the late Dr. 2. It is normally at the meeting points of two flow fonts. Wavy lines are another feature of weld lines. If the different flow fronts have cooled. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. * Corresponding author, e-mail: [email protected] recently had a few pieces (2-3%) crack after assembly, while in storage (not installed, still in the package). Islyn Thomas summarized the need for a particular vent location better than I ever could. 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. Insufficient plasticizing ability of injection molding machine. This customary mark is caused by differential rates of cooling in the resin where. ppt from SCIENCE 101 at Symbiosis International University. You can expect a mold shrinkage percentage of. Weld Lines-3 Ways for Detecting and Correcting. 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 weld line and the flow pattern of co-injection molding can be seen from Fig. Bubbles are caused by melting flow fronts colliding in a mold cavity. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. During the plastic injection molding process, one of the biggest challenges is. A weld line can also be called a knit line. Email him at jhenz. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses.