A visual mold with variotherm system for weld line study in micro injection molding. Injection molding can be performed with only one of these. 001 in . 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. Poor mold spot Spot mold to ensure fit and vent depths at ~0 . The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. 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 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. • Reduce runner dimensions and maintain the same flow rate. Evaluate and optimize your part design The advantages of using the moldflow analysis to avoid potential defect like deformation, shrinkage, welding line etc, part designers can change the wall thickness or enhance the ribs to improve their part design. Weld. Wang, G. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Weld Lines. Weld lines have been one of the common defects puzzling the injection molding industry. As the plastic flows through the mold it forms a smooth and continuous flow front. Increase the injection speed. Weld line. 943 µm to 0. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. In this experiment, several ejector. To explore the formation of weld lines in injection molding, a. 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. 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. 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]. 025 mm (0 . The thermo. 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. (3-1) Increasing the Resin Temperature at the Weld Line Section. 15 shows the frozen layer and weld lines at the end of mold filling. Figure 2. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). 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. To explore the formation of weld lines in injection molding, a flow model based on viscoelastic constitutive equation is presented in this article to predict and evaluate of weld lines location and properties, in which Rolie. distribution [4]. Usually it’s a straight line, and often to be found radiating. Remedies: Raise the temperature of the mold or molten plastic. When the two such melt flows. 3. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. This customary mark is caused by differential rates of cooling in the resin where. Mold flow marks, also known as flow lines or weld lines, are often caused by variations in the flow of molten plastic material during the injection molding process. In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. Weld lines appear as a result of the flow of molten plastic during the injection molding process. 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. Materials Science. The Difference Between Knit and Meld Lines–and Why It Matters. A weld or meld line on plastic parts can cause structural problems and/or be visibly unacceptable. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. [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. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. See moreEquipment. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. injection molding is followed by the welding. Injected plates were generated using a double-gated mold under four different process conditions. They are unavoidable even for moderate complex products. 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. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. 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. Weld line existence reduces the material strength; however, its demerit characteristics. These lines are formed when two or more flowing molten plastic streams meet and fuse together, creating a visible line on the surface of the molded part. Weld Line 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. They are the result of fundamental physical effects taking place inside of the mold tool cavity. This study focus on the formation of. Tosello et al. These processing changes will increase chain. Weld lines are one of the typical quality issues of injection molded parts. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. 22: Weld line formation when melt splits around core pins. 2) Vents in an injection mold should let the air out, but not the liquid plastic. The solution to an internal part cracking problem is to change the packing pressure. the three-plate mold often adopt this kind of gate. In other words, weld lines reduce the mechanical properties of the product. Flow marks in injection molding can be avoided if adequate measures are taken. Nguyen-Chung. Flow lines. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. Sink marks are a common type of injection molding defect. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. weld lines in infill analysis of injection molding simulation was observed [5]. injection molding. This is a video excerpt from our Problems & Solutions Course - Weldlines. 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. 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. For the production of these weld-line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527-2) and impact (ISO 179-1/1eU) properties were measured, and statistical analyses were performed to gain insight on the correlation between melt flow rate and weld-line behavior. 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. 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. 453-455. Weld or knit lines occur when melt flow fronts collide in a mold cavity. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. carried out to mass-produce molded products with complex shapes. 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. 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. 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. Weld Line Factors for Thermoplastics. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. Which means engineers need to know how to account for this phenomenon in an efficient way. 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. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. Molding calculation in Moldex3D: (а) melt front and weld line, (b). Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Here are some ways to avoid. and Mosle, H. Improper fusion of two fluid flows, a state before weld line. The position, length, and angle of weld lines are dependent on the. 6. They. 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. Specifically, injection-mold lines are often associated with poor mechanical strength. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. Abstract. [ 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. Thus, it. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. Weld lines. Improvement of weld line strength in injection molded FRTP articles. 7 in Kobayashi et al. That helps. Insufficient plasticizing ability of injection molding machine. Our injection molding company is explaining what these imperfections are, why they can compromise. In the sense that the weld line is better formed before the resin temperature. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. 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. The main types of injection molding defects are: 1. , less than 0. The conditions are temperature, injection speed, and injection pressure. + Increase mold temp, or materials’ temp, or holding pressure. This leads to a better molecular chain entanglement, which in turn creates a better weld. During the plastic injection molding process, one of the biggest challenges is. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. 21: Weld line failure caused by hoop stresses. In this paper, a weld line factor (W-L factor) was adopted to. Blistering 4. Meld and knit lines are actually both different types of weld lines. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. Sink Marks Cause 1: Incorrect Melt Temperature. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Edge Gates. 2017-01-0481. Mostly, this happens when two or more flow fronts do not “knit” during the injection molding process. Solving one problem can introduce other problems to the injection molding process. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. Steven. The formation of weld line in the injection molding method is caused by the product and mold design that is one of the common mistakes. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. The pressurized air restricts the flow of the plastic resin. The plaques are prepared out of 30% glass-filled Polyamide 6 material. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Meld Lines. It is possible to pre. 005 0. In injection molding, it is often important to maintain consistent color throughout the part. For multiple gate and complex 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. 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. The hair-like weld line is the result of weak. Weld lines may appear like seams or scratches, but that is not what they are. The second technique, cascade injection moulding, can produce parts free from weld lines. 4. Prediction of the weld lines in injection molding process using neural networks. Weld lines are also known as knit lines. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. Try to gradually raise the mold temperature and barrel temperature. Injection molding weld lines where two or more flow fronts come together in the mold. The resulting defects don’t stop at flash only. 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. Short shots. 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. According to the characteristics. What is weld lines. 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]. 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. Increase the injection speed. In narrow fields, a limited amount of molten liquid can solidify and block the flow. 2. The relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. 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. ac. Therefore, it is recommended to do a moldflow study prior to the mold being built. 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. From Fig. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). Criens, R. 9 – Over Packing. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. A knit line may be unnoticeable or may look like a crack. Streaks 3. 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. Investigations on WLs in micro injection molded parts were performed in Refs. 1. The default weld line result recognizes 135º as the maximum angle of collision and as that angle decreases, the severity increases as it. Weld lines are the unfavorable defect not only in normal injection molding process but in micro injection molding process. 8. A viscosity curve is developed using calculations of the fill time and plastic pressure at. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. 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. To respond to poor plasticization and uneven melt temperature,. Optimizing the injection parameters through combination of adjusting the molding temperature, varying the gate pressure, and increasing the dwell time. 2. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a 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. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Flow rate is 24 cm3/s. 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. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. Fellahi et al. • Move injection locations to make flow fronts meet more obliquely, turning the weld line into a meld line. 5. It forces out trapped air pockets and can prevent a vacuum void from occurring. Controlling the mold’s temperature could also minimize the weld line’s effects. Int J Adv Manuf Technol 52:131–141. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. + Adjust injection speed. 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. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. It is normally at the meeting points of two flow fonts. 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 formation of weld line in the injection molding method is caused by the product and mold design that is one of the common mistakes. C. That’s the air escaping out of the nozzle until the hose is full of pressurized water. So today we are going to take a look at the five most common defects in injection molding and their solutions. The thermo-rheological findings were used to investigate the sources of weld line weakness. Mérillou, J. Three terms that often get mixed up in injection molding are weld, meld and knit lines. 3: Weld Lines. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Google Scholar [10] S. In the present work, the micro specimens were investigated. The wheel has to be gated at three places on the hub and. are very minimum. This model provides the necessary information. 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. 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. The Problems & Solutions course is designed to train injection molding personnel in. Weld Lines. – Use generous and even. The welding angle can be used to differentiate weld lines and meld lines. Known also as knit lines and weld marks, weld lines are difficult to eliminate completely, especially if your injection molded part requires holes. 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. It will degrade materials performance; 9. In the feeding system of injection molding, the flow of plastic melt begins from the nozzle of the injection molding machine, traverses through the sprue and runners, and ultimately reaches the mold gate(you can call it the injection molding gate as well)—the entry point to the mold cavity. ” Another. 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. Weld lines in injection molding are frequently unavoidable. Injected plates were generated using a double-gated mold under four different process conditions. But none of the current packages can predict weld lines’ properties qualitatively. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. 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. When it comes to injection molding, the chances you might end up making a costly mistake is too high. Download : Download high-res image (856KB) Download : Download full-size image; Fig. Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. Increase the melting temperature. Silver Streak. 2. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. 2. (1) Increase the injection pressure and prolong the injection time. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow path. In the sense that the weld line is better formed before the resin. Heating and cooling mould systems, which cost extremely high, are a typical technology to prevent the weld-line. This is expected to achieve maximum results while the pressure holding effect will also increase. Weld line formation in the injection molding process occurs. Weld line formation in the injection molding process occurs. 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. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. Abstract. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. injection molding. They become more critical when particulate fillers are compounded with the polymer. Weld line and warping are two critical defects for injection-moulded part. 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 . This occurs mainly in the presence of barriers that divide the melt flow in. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Injected plates were generated using a double-gated mold under four different process conditions. 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. (1) Increase the injection pressure and prolong the injection time. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Weld lines have been one of the common defects puzzling the injection molding industry. Many researchers had emerged with several. 5. 1. 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. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. 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. 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. Polymers 2023, 15, 2440 3 of 21. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. One solution is to prevent the weld lines from forming in regions that are. They are the result of fundamental physical effects taking place inside of the mold tool cavity. This gives a clue as to how it was formed. Weld line formations can be weak if they fall in areas that will bear stress or impact. 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 addition a weld line can be moved to an area where it is less visible. A weld line is often unavoidable. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. e. 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 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 appear on the surface of a molded part where the molten material has converged after splitting off in a mold. One method is the local te mpering of the affected areas to prevent weld lines. 1. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. ). 000 0. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. Definition: A seam that appears where two areas of molten plastics meet. injection molding, (b) weld line and meld line, and (c) injection sample size and shape. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. 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 not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. 3. Weld lines have been one of the common defects puzzling the injection molding industry. Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. You can choose material of low viscosity and can increase the injection pressure. 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). . 5. , 190°C mass and 20°C mold temperature, as well as. 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]. The flow of the material in the injection mould takes place through the gate. Multiple gates are acceptable as long as they are close enough to each other to avoid weld line issues. • Optimize the design of the runner system. Kobayashi et al. These are caused by the shot of molten plastic moving at different speeds throughout the injection. 2020-01-1306. 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. Materials Science. enough to each other to avoid weld line issues. 7 of the reference. 1. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. In this experiment, several ejector. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. Discoloration. John Bozzelli. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. ppt from SCIENCE 101 at Symbiosis International University. . 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. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld together. The weld line is an inevitable defect in the most injection molded components. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. Redesign the mold to prevent the weld line. Mold Design Most conventional mold designs will work with TPU’s. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. Weld Line Factors for Thermoplastics. A simulation process was conducted to determine the recommended setting of injection moulding parameters and the range of the variable. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Figure 1 below shows the development of a weld line. 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. Jiquan Li, Taidong Li, +1 author. of micro injection molding process simulation by technology update and progress. Vibration assisted injection molding. To explore the formation of weld lines in injection molding, a. 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. 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. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. Sink Marks Cause 2: Low Pack and Hold time. Weld lines are a kind of Achilles heel of plastics. e. In injection molding weldlines are generated when two separate melt streams join either in multigated molds or as a consequence of flow around. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Weld Lines-3 Ways for Detecting and Correcting. Weld lines are where two flow. G. In an injection molding process, a weld-line forms when two flow fronts meet each other. (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. When two or more streams of plastic meet and fuse. Move injection locations to make weld lines form closer to the gates. 010 0. 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. This paper presents the. This injection molding defect appears as a black discoloration on the surface of the molded part. 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.