The results of. The thin weld line is the result of weak material bonding, which lowers the strength of the part. It is possible to pre. 4. The weld line and the flow pattern of co-injection molding can be seen from Fig. They become more critical when particulate fillers are compounded with the polymer. Yes, it does help, for two reasons: Often the weld line traps air and the ‘dump’ acts as a vent to allow the air to escape. The next type of injection molding defect is ‘Weld Lines’. Sink marks are a common type of injection molding defect. 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. Improvement of weld line strength in injection molded FRTP articles. 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. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of injection parts. 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. Alter the mold design. . Increase the melting temperature. 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. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. The second technique, cascade injection moulding, can produce parts free from weld lines. Ejector System (Pötsch, 1995) . In. Recently, the injection molding of fiber reinforced thermoplastics (FRTP) containing short fibers has been widely carried out to mass-produce molded products with complex shapes. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. 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). 1. 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. CrossRef View in Scopus Google Scholar [17] G. These lines usually appear on the narrowest portion of the part, and appear to originate from the mold’s gates, where the molten resin flows into the mold to form. 1. Knit and meld lines are inherent to plastic. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. A knit line may be unnoticeable or may look like a crack. 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. 2020-01-1306. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. 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. When this fails to happen correctly, a weld line defect occurs. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPAccording to the weld line distribution map of six gate schemes shown in . These are caused by the shot of molten plastic moving at different speeds throughout the injection. Thus, it. Weld lines not. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. 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. 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. 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. The following are the conclusion drawn from the present research: 1. 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. 21: Weld line failure caused by hoop stresses. For example, filled resins and ABS are more likely to. During the plastic injection molding process, one of the biggest challenges is. In this paper, two different injection molding tests were completed. Injected plates were generated using a double-gated mold under four different process conditions. This can occur when a polymer flow splits to go around an interruption (e. For more information on the Factors Affecting the Injection Molding Process. 18/06/2021. You can expect a mold shrinkage percentage of. (3-1) Increasing the Resin Temperature at the Weld Line Section. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. 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. In addition a weld line can be moved to an area where it is less visible. Weld lines may occur depending on the product shape and gate positions. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. 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. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. . Molding Equipment. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. You can locate the gate at the thick part of the injection molding to prevent air pockets. 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. 2. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Weld lines are common defects in injection-molded plastic parts that occur when two flow fronts of molten plastic meet and fuse together during the molding process. 2. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. Short shots. The weld line degrades the. Change the gate locations. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. This is a video excerpt from our Problems & Solutions Course - Weldlines. technical ulletin SPECIALTY POLYME RS Design and Production of Injection Molding ToolsIncrease the injection speed in order to fill the mold more quickly and ensure the material does not prematurely cool down; in addition, when the speed is adjusted the flow fronts may meet at a different spot and move the weld line location. Bubbles are caused by melting flow fronts colliding in a mold cavity. Runner Type Venting Plastic melt and mold temperature Injection speed and pressure Learn how to troubleshoot weld lines in injection molding. Park et al. – Use generous and even. 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. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. 5. They found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in whichEffects of mold temperature and pressure on shrinkage 0. Sink Marks Cause 4: High Mold Temperature. Controlling the mold’s temperature could also minimize the weld line’s effects. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. การแก้ไข ชิ้นงานจุดที่เกิดความอ่อนแอบริเวณ weld line คือต้องใช้ความเร็วในการฉีดต่ำในจุด. Weld line injection molding troubleshooting. This line does not normally impact the overall shape or dimensions of the item. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. carried out to mass-produce molded products with complex shapes. gasket seal leakage where the weld line crosses a gasket. 000 0. 025 mm (0 . Increase the size of the gate and runners to alter the mold design. They occur when melt flow fronts collide in a mold cavity. One of the things that can compromise an injection molded part is a weld line, also called a knit line. 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. After that, the compounds were injection-molded into tensile samples with and without weld lines to. 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. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Weld-line is a weak area which reduces the strength of the part locally. Its appearance can be improved by adjusting parameters. 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. 3: Weld Lines. Flow marks in injection molding can be avoided if adequate measures are taken. 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 into two or more directions in a mold. 010 0. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. In this experiment, several ejector. Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. avoid weld lines, and facilitate smooth. Weld lines defects are formed when two flow fronts are merged together. That helps. wall thickness, gate and runner designs and re-validate the result. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Insufficient plasticizing ability of injection molding machine. Weld line formation in the injection molding process occurs. Investigations on WLs in micro injection molded parts were performed in Refs. Gates should be designed larger than normal and located to minimize weld line formation. Wang et al. 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 are one of the typical quality issues of injection molded parts. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. 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. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. • Reduce runner dimensions and maintain the same flow rate. Features such as sharp corners or undercuts can. Experimental Setup 2. Sink Marks Cause 2: Low Pack and Hold time. 8. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. 3. Azieatul Azrin Dzulkipli and M. My polymer material selection courses 👉 Find Out About Plastics Blog👉 ht. Controlling the mold’s temperature could also minimize the weld line’s effects. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. 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. Therefore, the. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. 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. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. The weld line is then created with a higher flow front temperature and is packed with more pressure. This leads to a better molecular chain entanglement, which in turn creates a better weld. Prediction of the weld lines in injection molding process using neural networks. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. 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. 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. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. 2. 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. In. 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. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. These lines. Flow rate is 24 cm3/s. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Insufficient plasticizing ability of injection molding machine. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. Shaofei Jiang. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. The hair-like weld line is the result of weak. injection molding is followed by the welding. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. As compared to a weld line, the flow fronts come together at less than 135 degrees. Published 5 July 2019. Increase the injection speed. It forces out trapped air pockets and can prevent a vacuum void from occurring. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. Fig 13:- Detailed view of weld lines. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). The type of resin used during injection molding plays a large role in whether or not a knit line will be present. + Move gate (to where it is not visible). 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. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. <Mold> Provide a cold slug well where weld lines occur. The gate vestige for injection molding is usually narrow. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. 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. Reduce the amount of release agents. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. In the sense that the weld line is better formed before the resin temperature. In injection molding, it is often important to maintain consistent color throughout the part. The performance of weld lines in talc filled polypropylene box moldings produced with a. Injection molding, polypropylene, talc. Weld line and warping are two critical defects for injection-moulded part. 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. th INTRODUCTION Injection molding is one of the mostWeld Lines in a plastic cover. Effect of process parameters on the relative weld line strength From injection molding practice and literature, 1, 3,4 it is generally accepted that: if a weld line forms before the filling is. This study describes how the weld line was formed on the part. Amongst weld line. The weld line is an inevitable defect in the most injection molded components. 2021年4月23日 / by admin. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Mérillou, J. 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. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. ) . Injection Molding defect:molding weld_and_meld_line. The weld line can either be a minor cosmetic issue or potentially bad enough to negatively impact the part's strength. Wavy lines are another feature of weld lines. 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. Weld lines cause significant reject rates and are a common problem that all molders face. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. In addition a weld line can be moved to an area where it is less visible. Weld lines appear on the molded part where molten plastic meets. 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. 6. The resulting defects don’t stop at flash only. * Corresponding author, e-mail: fengsjpc@ku. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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. 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. 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. 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. In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. 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. They decrease the. 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. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and. Polyamide-6 (PA-66) was used as. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Abstract. are very minimum. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow path. Vents in the mold allow the mold to fill. Weld Line Factors for Thermoplastics. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. 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. If the large molded product is. 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. 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. Cracks in Corners – When cracks appear in the corners of plastic parts, the cause is too much plastic shrinkage onto the mold core in that corner. 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. Weld lines are formed when two orThe experiments were performed on an Arburg Allrounder 320C 600-250 injection moulding machine using a two cavity-injection mould (Fig. Sink Marks Cause 3: Improper Pack or Hold Pressure. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. The edge gate is the most popular and straightforward injection mold gate design. investigated the impact of injection molding parameters on weld line formation and strength reduction. (1) Increase the injection pressure and prolong the injection time. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. View 08 DEFECTS & REMEDIES (61). Stop using mold parting agents. 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. See moreEquipment. (1)Injection Machine Poor plasticization and non-uniform melt temperature – appropriately extend the injection molding cycle, to ensure thorough plasticization, and change for a machine with a larger. A weld line can also be called a knit line. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. (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. This injection molding defect appears as a black discoloration on the surface of the molded part. The structure is more complex with longer molding cycle . Weld lines represent the region where two separated melt fronts recombine. Blistering 4. M. 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. It is normally at the meeting points of two flow fonts. Gambar 2. Usually it’s a straight line, and often to be found radiating. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). 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. Mold Design Most conventional mold designs will work with TPU’s. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. Figure 1a illustrates how the weld line is produced when. The Influence of Knit-lines on the Tensile Properties of Injection Molded Parts, Polymer Engineering and Science, 23(10): 591-596. Weld line formation in the injection molding process occurs. 2) Vents in an injection mold should let the air out, but not the liquid plastic. The weld line’s strength is reduced when. Sink marks, 2. This customary mark is caused by differential rates of cooling in the resin where. As the polymer. Remedies: Raise the temperature of the mold or molten plastic. Weld lines, generated during injection molding, can significantly reduce the mechanical performance of structures. The impact behavior of weld-lines in injection molding. This customary mark is caused by differential rates of cooling in the resin where. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. consideration in gate location. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. The Difference Between Knit and Meld Lines–and Why It Matters. 3. One common issue that frequently arises during injection molding is the formation of weld lines. The goal is to create a uniform thickness and at the smallest (thinnest) level required. 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. distribution [4]. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Here are some ways to avoid. 080 inches. . 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. Materials Science. 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. This is where the melt fronts divided by an insert, such as a pin or a. 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. 2. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. The weld lines in blow molding occur wherever the pari son knits together in the head, mold tacking areas and mold parting pinch-off region. Proceedings of ANTEC (2000), pp. If the different flow fronts have cooled. This reduced thickness of the frozen skin further enhances the visual appeal of the. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. The edge gate is the most popular and straightforward injection mold gate design. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. and Mosle, H. Except for a few injection molded parts with very simple geometry, weld lines occur in most injection molded parts (usually with one line or V-shaped groove), especially in large-scale complex products requiring multi gate mold and inserts. Short shots can occur in this case because the air in the mold cavity has nowhere to go while the plastic is entering. , less than 0. 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. 2. 1. The relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. 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. Wavy lines are another feature of weld lines. Change the flow pattern to a single-source flow. Weld lines in injection molding are frequently unavoidable. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. The weld line is then created with a higher flow front temperature and is packed with more pressure. [ 18 - 21 ] In addition, the effects. In injection molding weldlines are generated when two separate melt streams join either in multigated molds or as a consequence of flow around. In many cases, you will also see that the part is hanging up on the core during ejection. + Optimize holding pressure time. Weld line. 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 or knit lines are perhaps the most common and difficult injection molding defect to eliminate. 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. This is expected to achieve maximum results while the pressure holding effect will also increase. 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. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. The injection molding gate generates heat by dissipation. The weld lines in injection molded parts arise as a result of the collision of two fronts of the flowing material, which fills the mold cavity and are sometimes unavoidable [1][2][3] [4]. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. 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. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. A flat product case was considered as an example of a typical aircraft structural element. . Int. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line.