Consequently, it causes viscous dissipation which leads to the generation of heat. There are a few adjustments that you can make to your injection molding process to prevent flow lines, including: Increase the injection speed, pressure, or material temperature: Slow-moving molten plastic is more likely to cool. How to recognize, prevent, and counteract flow lines defects in injection molding? Learn flawless products from professional manufacturers. Avoiding Voids and Sinks. Draft – Add 0. 10(a) (please see Fig. Faster injection increases pressure in front of a flow front. Weld lines have been one of the common defects puzzling the injection molding industry. Flow marks occur as circles or lines that occur around the gate. Mold Design. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. [22]. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. low of a melting time will cause flow lines to occur. The process involves the injection of heated, liquefied plastic into a temperature-controlled mold under high pressure. Weld lines are a kind of Achilles heel of plastics. injection molding. Weld Line defect analysis, the most common of many defects in injection moulding products. Mold flow analysis is also used to help designers locate difficult spots to fill within the mold. If performing a resin change from one polymer to another a difference in viscosity can cause flow lines or gels. Weld lines are formed during cavity filling whenever two separated melt flow font recombine. Each needle valve nozzle opens only when the melt front has moved across its gating point. These data were obtained from many andGenerally, injection molding resins are characterized as having medium, high or very high flow. This production method is particularly popular when manufacturing in large quantities. The streaks form from plastic in the mold overlapping with plastic following it. injection mould simulation at steady flow rate. Mold design is a key aspect of injection molding. It can also aid in material selection since fill. This can prevent the opportunity for trapping air. Flow lines. This “inside-out” flow of the plastic mimics the flow in a water fountain, therefore it is called fountain flow. ABS resin has low thermal deformation temperature, but poor heat resistance. The moldability validation and flow analysis tools enable you to iden-tify and correct potential injection molding problems as you design the product. Poor mold surface n Refinish a poor or worn mold surface. That means that for each injection pressure, the flow length for a mould temperature of 80°C and 180°C shows a constant difference of ca. Obviously, as the resin front moves through the mold, the fill material will always be behind the front. Also called “Weld Line. Kobayashi et al. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Remedies: Increasing the injection pressure will force the molten plastic against the mold cavity. Consider the following examples of cooling channel configurations in P20 mold steel with a water line diameter (D) of 11. Reduce the injection pressure to prevent overpacking at the gate. Production was set according to an experimental design (DoE), varying injection flow rate, mold temperature, and melt temperature. 7 of the reference. Lower speeds allow gas more time to escape through vents. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPFor 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. 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. I’ve been writing about plastic flow simulation since 1984, and I. The Table 2 categorically reports Melt Temperature, Injection Pressure and Injection Speed are the main contributors in the defects such as the short-shot, weld-lines, flow marks, burn-marks etc. Injection molding could develop knit lines if one front cools before it reaches the other. Injection molding produces defects. These defects include the following: 1. While some molds or inserts have simple, straightforward cooling circuits, many have multiple circuits of various sizes and configurations. Edge Gates. Hamstra: For the OEMs, having a good baseline of what our cooling flow and temperature through a mold is going to give us a good optimization into the next supply chain for the injection molders. Sink Marks. Mold flow analysis is a software-enabled process that. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. If the mold itself has cracks or defects, the finished product will also have various problems. Flow Lines Defect in Injection Molding Process Flow lines can be defined as linear grooving, or circular ripples, on the surface of a molded part that indicate the. FLOW – A qualitative description of the fluidity of a plastic material during the process of molding. The Reynolds number takes into account the pressure, volume and viscosity of the coolant, the resistance to flow, length and diameter of the channels and the pressure loss in the cir-cuit. If it is farther down the flow part, increase injection speed to decrease viscosity and allow more packing pressure. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. The proposed method is first applied to the simulation of HDPE melt in a classic Poiseuille flow case, and then two. On a small four-cavity tool, the part had a U-shaped notch in the center. This can be achieved by connecting ribs to each other. Cascade Moulding Avoids Weld Lines. 3) Poor Preventative Maintenance. In this example, the flow ratio is 80 (10 Fig 2 – The spiral flow chart provides data about maximum flow length based on several Monday, 01 December 2014 Page 1 of 2Automatic in-line process quality control plays a crucial role to enhance production efficiency in the injection molding industry. Three terms that often get mixed up are weld, meld, and knit lines. Flow lines are linear grooving or circular ripples on the surface of an injection molded part that indicate the direction of material flow within the cavity. 5. Some of the most popular brands include:Fiber reinforced thermoplastics (FRTP), reinforced with glass or carbon fibers, are used to improve the mechanical strength of injection-molded products. Seven Common Defects and Solutions for PC/ABS injection molding Products,Flow Lines, Pitting,Product Delamination,Stretch Marks. Flow Rate. Incorrect gate positions cause multiple flow fronts that struggle to merge. When the gate depth is much smaller than the cavity entrance depth, and the mold filling rate is very high, when the melt flow becomes unstable jet flow, the front jet has solidified and the later flowing melt fills the mold cavity, and the product will be Snake flow lines appear on the surface. Flow marks are a phenomenon in which a pattern of the flow tracks of the molten plastic remains on the surface of the molded product. Remedies: Raise the temperature of the mold or molten plastic. Lower speeds allow gas more time to escape through vents. The last cause of flow lines may be the operators running your daily operations. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. Take these steps to avoid knit lines. (All Illustrations: S. Injection molding tool life is the number of production cycles that an injection mold can complete before it needs to be replaced. Mold design. 010 0. Melt delivery management has a major impact on final part quality and the ultimate success of the production line. 1 a. On-Line Solutions To Injection Molding Problems. They are caused by improper bonding and low injection pressure and speed [ 46 ]. Flow lines and weld lines are lines or streaks in the final molded part. Flow lines are ripples in the plastic after the part is formed. On larger parts where knit lines or flow lines are a concern, you can use sequential valve gates to control the flow and move the knit lines. Note: It is applicable to thermoplastic materials only. Using a thermoplastic that stays in a. Just multiply the area of the barrel × the injection velocity. Causes: The issue might be varying flow rates as the molten plastic moves through the mold or changes in the thickness of the mold’s walls. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. By understanding material fill, injection mold designers can better position gates, anticipate where knit lines will appear, and locate difficult to fill spots in the mold. Image 4: Top, HDPE streamlined structure. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. Accept All. 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. 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. Use high-quality, temperature-controlled materials for better mold filling. When the mold is full, the machine continues its injection pressure and compresses the plastic. In Fig. (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 injection molding a part, a knit line may present no problem, or can cause a serious structural problem. ³/sec. Flow lines. Warping. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. Different gate sizes and locations using flow simulation have been detected for defects reduction such as weld lines and air traps, air traps and warpage can be managed by varying process parameters [17]. The thermo-rheological findings were used to investigate the sources of weld line weakness. Our injection molding company is explaining what these imperfections are, why they can compromise. The recommended minimum production volume for injection molding is 500 units. The Bottom Line. The article has been structured just for you to gain an understanding of the same so that when you plan to buy plastic injection molding, you do understand what it means to do so. Flow lines and flow marks. Known as thermolators, water cooling systems require a cooling source such as a tower. The accompanying table lists the flow rates for various barrel diameters at various injection velocities. After an hour of running, the steel temperature stabilized at 78°F. 1. Low melt temperature. Impurities in the resin will prevent a smooth flow through the mold. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Weld line. (2011) and Fig. It is also useful for finalized prototypes that are used for consumer and/or product testing. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. 7 of the reference. Weld lines have been one of the common defects puzzling the injection molding industry. Caused by: Non-uniform cooling times and flow rates; excessively narrow part features. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. Apart from the shape, it is important to design ribs for optimal mold performance. (1) Increase the injection pressure and prolong the injection time. Before injection molding, there is a large amount of air in the flow path and the cavity. On average, larger injection molding machinery can cost from $50,000-$200,000 or more. Look for signs of stickiness or burning. Flow marks in injection molding are defects that manifest as a line or series of lines forming a pattern different in color from the other parts of the molded material. Flow lines are lines or streaks that appear on the surface of molded parts and occur due to variations in the flow of molten material during the injection molding process. Like flow lines, burn marks do not usually compromise the item's integrity, but they may become a problem once the product is burnt to the point of degradation. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. Prevent Flow and Knit Lines During the Injection Molding Process. In addition to the recommended wall thickness, it’s important to consider a material’s flow characteristics. In the development of our calculator. Secondly, it is easy to form obvious. Increase the injection speed, pressure, or temperature of the material. Mold flow analysis is a powerful tool for optimizing the design and performance of injection molding processes. The thermo-rheological findings were used to investigate the sources of weld line weakness. • u. Plastic injection molding is a complex and highly intricate process. c. The flow line is usually connected to injection specifications, mold and injection material, it can be defined as linear grooving, or round surges, on the surface of an injection molded part that shows the instructions of product flow within the cavity of the mold. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. diverse parameters of the injection-molding process, needs a lot of experience in order to achieve optimum results, especially if. 0005 in. These defects include the following: 1. Common injection Mold Flow Lines. Pushing the air out or not is the difference between a good part or burns and flow lines. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. Help prevent warping with these measures: Raise the mold or material cylinder temperature. Typically, flow lines are caused by the liquid plastic cooling at different rates. Introduction. This may involve adjusting the temperature and pressure of the mold, using different mold materials, or adjusting the injection speed or cycle time. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. Industry 4. When trying to establish process control in plastic injection, watering the tool is a key variable that is often overlooked. For injection molding grades, the MFR (MI) values for polyethylenes are generally determined at 190°C (374°F) using a static load of 2,160 g. These lines form as a result of material flow and solidification during the injection molding process. On a small four-cavity tool, the part had a U-shaped notch in the center. Fast injection gives you a glossy part, which is what we wanted in this. 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. Flow marks, also known as flow lines or weld lines, are common defects that can occur in plastic molded parts. Possible Causes & Remedies: Machine Cause. Check that the machine is creating enough clamping force to keep the mold halves together. Mold makers should also pay attention to sprue, runner, or gate design. Flow Lines and Flow Marks. The position, length, and angle of weld lines are dependent on the gate location, injection speed, injection pressure, mold temperature, and, especially, the direction and degree of the polymer melt velocity in the. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Clean all parting line and core vents. Tatjana Geminger, Stefan Jarka, in Specialized Injection Molding Techniques, 2016. Flow lines are a defect in injection molding and can be a significant issue for manufacturers. 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. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. In the injection molding process of plastic parts, flow mark is a common defect due to the defects of parts design and injection molding process [4]. If you’re seeing flow lines, try extending the. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. When combined with low injection pressure, this problem leads to decreasing melt speeds and can cause flow lines. Injection molding is one of the best plastic production methods. 004 m, a characteristic velocity ν 0 =0. , 1 IN, 1 OUT, 2 IN, 2 OUT). In this guide, we cover evaluation and also the remedy of flow lines in. The injection speed has a great impact on the degree of molecular orientation in the component and therefore influences the shrinkage and the development of a joint line. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the weld line can be seen clearly from the Fig. Plastic is injected into a mold at a specific rate of flow—typically in. Acetal is a funny material in how it reacts to certain injection speeds and mold temperatures. distance from the cooling lines and mold cavity surface varies and results in uneven cooling in molded part. 5 gal/min through this circuit we will get turbulent flow—the optimum cooling situation. 020"). On thicker sections of the mold, there may be sinks caused by bosses designed into the backside of the surface. The Priamus Fill system is designed for automatic closed-loop control of multi-cavity and family molds, multi-material injection, sequential valve-gated molds, as well as LSR molds. He is currently a tooling manager for a large, multi. tall, and 0. Here are some of the most common scenarios for cracks in injection molded parts: Cracks in the Direction of Flow – If the crack develops in the direction of the plastic’s flow into the mold cavity, the cause is molecular orientation. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Electronic flowmeters featuring FCI (Flow Characteristic Indicator). 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. Contact us to learn more about SMARTFLOW flowmeters. Countermeasures to Injection. Figures 3A, B and C depict different examples of “spot” vents. Polycarbonate is a tough, optically clear or opaque, biocompatible plastic with good thermal resistance. MFR values for polypropylenes are determined at the same load but at a higher temperature 230°C (446°F). During the injection molding process, one of the most important requirements of the mold is to deliver melt from the barrel to the cavity. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to. Mold Venting. The size, shape, and location of the gate have a significant impact on the finished product. 2. The Analysis and countermeasures of flow lines in injection molded products Read more. They may also appear as ring-shaped bands on a product’s surface near the entry points of the mold, or “gates”, which the molten material flows through. A method of melt flow visualization was used to record the weld line location on the surface of molding prepared at the proper injection conditions (method of "record grooves effect" formation. The steel that cored out and created the notch was very thin—roughly 0. This slight depression is a tiny line called the weld line or knit line. This is defined for each material by the length-to-thickness (L/T) ratio of the part. Flow marks are caused by a variety of factors in the injection molding making technology, and they happen at the gate. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Injection molding can be performed with only one of these materials like glass, plastics, etc. Splay is a cosmetic defect that occurs in plastic injection molding, when silver or white streaks appear on the surface of the part. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. The molding process is the leading cause of defects in injection molding parts. In the process of injection molding, the quality of the mold plays a decisive role in the quality of the finished product. Weld lines may appear like seams or scratches,. Errors like these manifest when processing is done incorrectly. google-site-verification: google03af4f4fcb62a9d5. Flow direction is essential for mold mapping because when water flow reverses, poor turbulence and hot spots occur. This review process showcases a company’s technical expertise, the capabilities of its design team, and overall quality. These lines. 182-185, 2013. The flow rate should ensure the material does not lose its. For each investigated mould temperature, a linear relationship can be observed. Let’s take a look at some defects that are caused purely due to faults in the injection mould process. 2. The material is kept poured into the mold for some time. This results in an incomplete part at the end of injection molding. Injection molding could develop knit lines if one front cools before it reaches the other. These streaks or patterns can affect a part's aesthetics, value, and. Injection Molding works with molten fluid created by heating the plastic granules above their melting point. Thin walls often increase the pressure required to fill the part, and. Unraveling Flow Lines. Another tactic to promote more chain entangling at the weld line is to raise the mold temperature 10° C (50° F). We offer this Mold Cooling Calculator tool as a free service to the injection molding industry. Manifesting as wavy lines or streaks on the surface of the molding, flow lines generally occur when molten material flows. Below are ways through which you can remove and prevent flow lines; a. One cause of flow lines is low injection speed, which can result in the molten plastic cooling too quickly and creating a. They can be caused by variations in cooling speeds of the material as it flows through the mold. 100 to 0. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no. Flow Lines Or Flow Marks. We started the mold with 100% water circulating at 60°F at a flow rate sufficient for turbulence. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Over time polymer will degrade creating carbon (black specks). This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Cooling lines impact. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. 000 0. Plastic Purity. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. Weld Lines. There are important differences between an injection mold sprue and its runner system. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. Low cushion and hold time. (1) Reduction of injection time and shortening of the molding cycle. Part walls thinner than 4mm (0. This most often occurs when you have a core or shutoff. 750 in. Sufficient draft is an important part of any mold design, and quick-turn tooling is no exception. Thick sections take longer to cool than thin ones. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Listed below are some factors to consider when designing ribs for injection-molded parts. 1) Snake flow lines. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause temperature. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rates, and holding pressures. Knit Line. This requires skilled labor to mold new parts that have less molding defects. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. When it comes to injection-molded products, here are several typical solutions for flow lines: To make sure the liquid reaches the mold fully before cooling, enhance the. This can be caused by a poor mold design, or plastic temperatures, mold temperatures, injection speeds, or. (3) Improving the surface gloss of the product. Flow lines are lines or streaks visible on the surface of a part. Flow Lines: Flow lines on thinner areas of molded components appear as a wavy pattern, often a different color than the surrounding area. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. 0 seconds, depending on part volume, runnergate style and size, cavity location and injection pressure. 020 0. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. These marks remain and are visible in the cooled product. Mold design is a key aspect of injection molding. Flow marks won. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. In this guide, we cover evaluation and also the remedy of flow lines in injection molding. thick, 0. g. . Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. They appear as waves or lines, usually of a different color tone from the surrounding area. Defects like this make it harder to market the finished parts to the end user. Flow lines are lines or streaks that appear on the surface of molded parts and occur due to variations in the flow of molten material during the injection molding. Flow lines can be minimized in injection molding by optimizing the design of the part and the mold, as well as the processing conditions. Weld lines may appear like seams or scratches, but that is not what they are. If larger gates are used, expect a longer molding cycle time. plastic mold venting. While the sprue is milled through the entire thickness of the injection mold, passing from the outer surface to the parting line (where the two mold halves meet), the runners are comparatively shallow channels milled into the face of one or two mold halves. There are two types of weld lines, cold and hot weld line. This “inside-out” flow of the plastic mimics the flow in a water fountain, therefore it is called fountain flow. At some point in time, it can no. If so, look for an alternative resin. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Picture the flow of a liquid resin filled with, for example, glass fiber. Basic Repairs for Warping. This continues until the weld lines in plastic injection molding disappear. Polycarbonate Injection molding defects. Flow lines are. Depending on the resin, resin temperature, mold temperature, and filling. It explored the use of. The problem could be the result of machine settings made before the gate was installed. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. The weld line and the flow pattern of co-injection molding can be seen from Fig. Weld lines represent the region where two separated melt fronts recombine. However, the weld line may not continue throughout the flow. Mold is not vented properly causing slow flow at knit lines. What are Flow Lines in Injection Molding? Flow lines, also known as weld lines or knit lines, are discontinuous lines or streaks that appear on the surface of an. Several factors can contribute to shrinkage in injection moulding, including material, part design, mould design and processing parameters. The most common and one of the most challenging injection molding defects are weld and knit lines. Add or increase vents as needed. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses, elastomers, confections, and most commonly thermoplastic and. Conformal cooling channels (CCCs) are a cooling passageway which follows the profile of the mold cavity or core to perform uniform cooling process effectively in the injection molding process. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. Flow lines are a typical problem for injection molding faults that appear as visible streaks or lines on the surface of the molded part. Once you have a cool shell formed the rest of the mold entering absorbs heat from the layer next to the wall. Increase the injection speed. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPWhen it comes to injection molding, the chances you might end up making a costly mistake is too high. I’ve been noodling that question around in my head for the last three years, since injection machine suppliers like Arburg, Engel, Wittmann Battenfeld and Sumitomo (SHI) Demag started showing up at trade shows with mold-filling displays on their machine controller screens. Burn Marks. Flow Lines. Peering into the Flow. Flow marks in injection molding can be avoided if adequate measures are taken. 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. with a characteristic length χ 0 =0. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and. Water set-up and design are every bit as important as establishing and recording a repeatable process. 20 mm. Flow lines are linear marks on the surface of a molded product, which indicate the flow direction of the molten plastic. Injection Molding of Multimaterial Systems. In this regard, the gate form with less shunt should be used, and the gate position should be selected reasonably. Increase injection speeds and pressure to ensure the cavities are filled properly. Shear; There are two causes of splay brought on by shear. They again get resolidified along the surface. 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. 008 to 0. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. The material is poured into a mold, which shapes the size and looks of the article. They are visible on one side of the parts. Depending on the extent, these can become defects in the case of molded products in which their external appearance is an important aspect of quality, such as in the case of home electrical appliances, containers for. Fictiv provides you with DFM feedback so that you can minimize injection molding defects. Walls thicker than 8mm (0. When mapping mold circuits, label each circuit with a number exclusive to the circuit and a supply or return designation (e. We stopped the machine and added glycol to the chiller to a concentration of about 40%. Fig. 1. A meld line occurs when two moving melt fronts converge and flow parallel to each other. 1) Snake flow lines. In addition, when the melt is solidified in the cavity, there is a vacuum between the product and the cavity wall, also the air must enter the mold. The Plastic Troubleshooter Defect - Flow Lines.