Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . 15 shows the frozen layer and weld lines at the end of mold filling. Sink marks. The thin weld line is the result of weak material bonding, which lowers the strength of the part. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. 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. 1. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. 18/06/2021. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Flash. Increase the melting temperature. 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. 1. 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. So today we are going to take a look at the five most common defects in injection molding and their solutions. (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. 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. The terahertz time-domain spectroscopy (THz-TDS) imaging technique was used to detect the weld line defect of an injection-moulded short glass fiber-reinforced composite. Sink Marks 2. . 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. Prediction of the weld lines in injection molding process using neural networks. Emerging Materials Research. Remedies: Raise the temperature of the mold or molten plastic. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. 6. 5. In injection molded parts, there are 2 types of weld lines: The first type of weld mark is called cold-melt joints and is formed when the melt front enters the cavity with different gates. Specifically, injection-mold lines are often associated with poor mechanical strength. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. When this fails to happen correctly, a weld line defect occurs. In Fig. Sink marks, 2. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. 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. The performance of weld lines in talc filled polypropylene box moldings produced with a. Since it is often impossible to avoid weld lines as well as a limited possibility to increase the weld line strength by adjusting the injection molding parameters, a method to predict the weld line strength in the product development process is shown below. This is particularly true if the wall thickness in the weld is thin – i. Weld-line is a weak area which reduces the strength of the part locally. Weld lines have been one of the common defects puzzling the injection molding industry. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. You can expect a mold shrinkage percentage of. 1. Provide a gas vent. This customary mark is caused by differential rates of cooling in the resin where. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. Weld Lines. Gate Placement: Properly positioning the gate can direct the melt flow to minimize weld lines or relocate the weld line to non-visible areas of the part. In. 000 0. Injection molding could be applied with many polymer materials, such as. 18/06/2021. Flow-induced filler orientation manifests in higher tensile prop-erties in the direction of flow compared to those normal to the direction of flow. Increase the injection speed. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. 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 not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. 005 0. Some of the common fixes for weld lines include: Increase the resin temperature to ensure both sides of the weld line are liquid when colliding. The resulting defects don’t stop at flash only. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. The Factors that Cause Weld Line in Injection molding Pressure. 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. 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 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. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. Streaks 3. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). 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. 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. 2. 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. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Adjust the design for the flow pattern to be a single source flow. Carefully consider all the relevant aspects of the mold design specification before. What are Weld Line Defects? Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. In an injection molding process, a weld-line forms when two flow fronts meet each other. Weld lines represent the region where two separated melt fronts recombine. (3) Adjust the temperature of the barrel and nozzle: the viscosity. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Weld lines may occur depending on the product shape and gate positions. 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. (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. The weld line is then created with a higher flow front temperature and is packed with more pressure. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Weld lines appear as a result of the flow of molten plastic during the injection molding process. (1) Increase the injection pressure and prolong the injection time. 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 lines appear on the surface of a molded part where the molten material converges after splitting off into two or more directions in a mold. Molding Equipment. Shaofei Jiang. 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. [ 18 - 21 ] In addition, the effects. 2-1. Zhao, X. The gate vestige for injection molding is usually narrow. This process makes possible to produce a wide range of products with different sizes, shapes, and for varying applications. 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). While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. 2. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Three terms that often get mixed up are weld, meld, and knit lines. Maintain a holding pressure that is no more than 1/2 the. Yes, it does help, for two reasons: Often the weld line traps air and the ‘dump’ acts as a vent to allow the air to escape. When the polymer resin is injected into a mold, it flows through all portions of the mold cavity. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. investigated the impact of injection molding parameters on weld line formation and strength reduction. The welding angle can be used to differentiate weld lines and meld lines. Lesson 7: Meld and Weld Lines (Part Design) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. After that, the compounds were injection-molded into tensile samples with and without weld lines to. Weld lines are where two flow. ac. Injection molding plate for mode I testing geometry. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Polymers 2023, 15, 2440 3 of 21. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. 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. of micro injection molding process simulation by technology update and progress. In this paper, aiming at the problem of weld line defects in the injec- tion process of a key phone panel, the injection process is optimized by using Moldflow and drop simulation. Vents in the mold allow the mold to fill. Thus, it. 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. 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. Weld line is formed when two different melt flows converge, as illustrated in Fig. In addition a weld line can be moved to an area where it is less visible. Weld line. Ideally, the resin flow will split into two flow fronts to pass around the obstruction and then recombine into a single flow front. In the 1947 book, Injection Molding of Plastics, the late Dr. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. In our DFM report, we will analyze the possible weld lines. + Optimize holding pressure time. Weld lines have been one of the common defects puzzling the injection molding industry. The plaques are prepared out of 30% glass-filled Polyamide 6 material. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. [ 18 - 21 ] In addition, the effects of flow behavior of the polymer melt due to the optimal process parameters for the minimization of weld-line effects are an important consideration. Expand. Voids and bubbles, 6. 030 0. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold. A visual mold with variotherm system for weld line study in micro injection molding. 005 0. A weld-line is known as a representative defect in the field of plastic injection moulding, and also as a cause of inferior mechanical propensities and poor appearance. Weld Lines. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. Weld Lines. If the plastic encounters a pin or other obstruction, the plastic flow front must split to form two flow fronts to go around the pin. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. 1 Mold In order to study the formation of weld lines, the mold cavities has been. Meanwhile, Using more advanced cooling method such as cyclic cooling or conformal cooling. Abstract. 2. Flow rate is 24 cm3/s. – Use generous and even. (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. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. 3. 080 inches. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). 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. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 10(a) (please see Fig. • Reduce runner dimensions and maintain the same flow rate. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. Weld Line Phenomenon: Surface defect in which the weld, or the part where the flows of melted plastic meet inside the mold, shows up on the surface as a groove or pattern. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. The rule is, a higher pressure shall be required to push the material in the machine when there is excess mold. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. 3. Weld Lines. 3: Weld Lines. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. The impact behavior of weld-lines in injection molding. Optimizing the Injection Parameters. 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. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. 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 weldAmong defects of injection molding parts, weld lines are the most common defect. The flow of the material in the injection mould takes place through the gate. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. 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. Google Scholar | Crossref | ISI. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. This injection molding defect appears as a black discoloration on the surface of the molded part. The goal is to create a uniform thickness and at the smallest (thinnest) level required. Flash. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. In weak material bonding, they will appear as hair-like weld lines. In this paper, two different injection molding tests were completed. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Don’t forget to eliminate entrapped air in the weld line injection molding; otherwise, it’ll create unfilled portions in your part design, causing more weakening. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. 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. 6. (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. This study describes how the weld line was formed on the part. As these flow fronts come together. Clamping Unit. They decrease the. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. (2011) and Fig. Typical injection molding processing temperatures of TPU materials are as follows: IM Zone 60A to 75A 80A to 90A 95A to 75D Rear 315 – 40 ºF45 -370 75 400The weld line in an injection molding product can significantly impact the strength and durability of the last part [12] [13][14][15]. 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-line is a weak area which reduces the strength of the part locally. The simulated cold weld line length is consistent with the experimental one when a 115 °C mold temperature is adopted; with lower mold temperatures, the simulated lengths are smaller than the experimental ones—in accordance with the literature on the conventional injection molding process [26,27]—probably because of the definition adopted. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. Weld Lines 5. Its appearance can be improved by adjusting parameters. T. 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. Avient’s Zachary Alderman shares practical tips on designing and injection molding parts utilizing short-fiber reinforcements. They. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. The literature on the formation of weld lines, and their consequences, is more abundant on the area of injection molding [5-12] than on extrusion [13]. Mérillou, J. One of the things that can compromise an injection molded part is a weld line, also called a knit line. Weld lines in injection molding are frequently unavoidable. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. Microsyst Technol, 14 (6) (2008), pp. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Kobayashi et al. 2021年4月23日 / by admin. You can choose material of low viscosity and can increase the injection pressure. Abstract. If you are familiar with any form of scientific injection molding, regardless of the name, then you know one of the first steps is performing a viscosity curve study. The most common and one of the most challenging injection molding defects are weld and knit lines. You will have to confirm them before tooling. 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. In this case the two flow fronts will meet and. M. When it comes to injection molding, the chances you might end up making a costly mistake is too high. Process. 1. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. Solving one problem can introduce other problems to the injection molding process. Weld Lines. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. Weld line existence reduces the material strength; however, its demerit characteristics. See moreEquipment. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. An obstruction such as a core pin or holes will split the material flow and cause a weld line issue to form on the other side. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. 2. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. As compared to a weld line, the flow fronts come together at less than 135 degrees. 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). You can locate the gate at the thick part of the injection molding to prevent air pockets. The results of. Nguyen-Chung. In other words, weld lines reduce the mechanical properties of the product. Polym. Increase the injection speed to reduce the amount of cooling happening in the mold. Experimental Setup 2. <Mold> Provide a cold slug well where weld lines occur. In injection molding, it is often important to maintain consistent color throughout the part. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. The Problems & Solutions course is designed to train injection molding personnel in. 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. Controlling the mold’s temperature could also minimize the weld line’s effects. 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. 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. (3) Adjust the temperature of the barrel and nozzle: the viscosity. The Weld line result itself has a scale associated with the placement of the weld line that is directly relative to how severe the weld line will be based on the angle in which the two flow fronts meet. 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 lines have been one of the common defects puzzling the injection molding industry. Weld-line is a weak area which reduces the strength of the part locally. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. These lines occur when two or more flow fronts meet and fuse together, resulting in a visible seam on the molded part. The main types of injection molding defects are: 1. the three-plate mold often adopt this kind of gate. Plastic Injection Molding Process. 2020-01-1306. e. Adding vents, using overflows, or using porous metal. Criens, R. Features such as sharp corners or undercuts can. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). demanding injection molding and end-use requirements. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. Injection molding of large/complicated products are usually prepared by multiple compounds, which produces weldlines once the melt fronts are joined by impingement flow. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. th INTRODUCTION Injection molding is one of the mostWeld Lines in a plastic cover. Increase the injection speed. 2. Insufficient plasticizing ability of injection molding machine. Therefore, more studies covering this subject are required in order to improve the insight regarding the mechanism involved in the formation of weld lines in extrusion and,From the so-produced materials, specimens with weld lines were produced according to the first test series, but varying the injection molding parameters only twice, between the best and worst settings found in the previous study with the polypropylene types with MFR 8 g/10 min, i. Weld lines are visible to varying degrees on any molded part depending on gate location, flow length, melt/mold temperature, cavityA weld line occurs when two or more molten plastic flows meet and fuse during the injection molding process, resulting in a visible line on the surface of the molded part. In a weld line, reinforcement fibers. This paper presents the. 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. 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. They are the result of fundamental physical effects taking place inside of the mold tool cavity. Increase the injection speed to reduce the amount of cooling happening in the mold. Azieatul Azrin Dzulkipli and M. Root causes Many factors—including processing conditions, material, part design and mold design—can influence the visibility and strength of a weld line. INJECTION MOULDING DEFECTS 1 DEFECTS 1. Proceedings of ANTEC (2000) Google Scholar [9] S. and Mosle, H. 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 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. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. View 08 DEFECTS & REMEDIES (61). Jiquan Li, Taidong Li, +1 author. Participating in DFM and mold flow analysis is a good way to achieve this. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. ”. The conditions are temperature, injection speed, and injection pressure. 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. They are unavoidable even for moderate complex products. One method is the local te mpering of the affected areas to prevent weld lines. 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. This is expected to achieve maximum results while the pressure holding effect will also increase. distribution [4]. To respond to poor plasticization and uneven melt temperature,. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. 3 the path lines of selected material elements can be observed which are. 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. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. Steven. Wang. During injection. Weld lines are one of the typical quality issues of injection molded parts. Int J Adv Manuf Technol 52:131–141. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. 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. The thermo-rheological findings were used to investigate the sources of weld line weakness. Weld-Line in an injection molded part develops when two or more melt fronts are converged together. Bubbles are caused by melting flow fronts colliding in a mold cavity. Weld lines may appear like seams or scratches, but that is not what they are. * 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). 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. 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 line and the flow pattern of co-injection molding can be seen from Fig. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. 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 thermo. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. 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. To elimi- nate weld lines, you can enlarge shrinkage. avoid weld lines, and facilitate smooth. Redesign the mold to. when two or more melt flow fronts contact each other immediately after the cooling process. 6. การแก้ไข ชิ้นงานจุดที่เกิดความอ่อนแอบริเวณ weld line คือต้องใช้ความเร็วในการฉีดต่ำในจุด. The micro tensile part was prepared by the double gate injection. S. consideration in gate location. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. 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. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 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. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Runner Type Venting Plastic melt and mold temperature Injection speed and pressure Learn how to troubleshoot weld lines in injection molding. 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. Bubbles are caused by melting flow fronts colliding in a mold cavity. In an injection molding process, a weld-line forms when two flow fronts meet each other. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. 015 0. 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. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Improvement of weld line strength in injection molded FRTP articles. Polyamide-6 (PA-66) was used as. 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. 943 µm to 0. Weld lines are one of the typical quality issues of injection molded parts. Gate blush, 4. Flow-in-duced fiber orientation manifests in higher tensile properties in the direction of flow compared to normal to the direction of flow [13–15]. Try to gradually raise the mold temperature and barrel temperature. Save. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. C. 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. 4. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro.