Features such as sharp corners or undercuts can. Flow Linesparticles, during injection molding, will produce visible flow and weld lines. Thin walls often increase the pressure required to fill the part, 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. Knit and Meld lines are inherent to plastic injection. In the development of our calculator. The last cause of flow lines may be the operators running your daily operations. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. 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. Polycarbonate is a tough, optically clear or opaque, biocompatible plastic with good thermal resistance. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. They may also take the form of ring-shaped patterns when staying close to the mold's entry point, which is the plastic injection nozzle. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and. Detecting Water Flow Restrictions. The molding process is the leading cause of defects in injection molding parts. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 3C) is to put a vent along the entire edge, but just shy of the corners. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. wide. As discussed above, one of the things that contribute to plastic injection molding defects like sink marks and flow lines is the type of injection molding machine used. In this regard, the gate form with less shunt should be used, and the gate position should be selected reasonably. Possible causes: Low temperature of injected melted plastic or slow injection speed during injection molding resulting in low fluidity of plastic inside the mold. Knit and meld lines are inherent to plastic. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Too hot and the plastic will start to degrade, but too low and flow marks increase. Vertical walls, meaning those part surfaces parallel to the direction of mold operation, should have a minimum draft angle of a 1/2 degree, and 2 degrees is even better; heavily textured surfaces may require 5 degrees or. Caused by: Non-uniform cooling times and flow rates; excessively narrow part features. He is currently a tooling manager for a large, multi. This slight depression is a tiny line called the weld line or knit line. Slower flow results in thicker and shorter knits. The importance of understanding the causes of flow lines is critical for preventing them from occurring during the injection molding process. Available with a number of options including thermometers, pressure gauges, liquid-filled pressure gauges and quick change socket and plug. html. Surface Delamination. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. This design is deliberate in order to help the mold. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. 000 0. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Image 4: Top, HDPE streamlined structure. Increase the injection speed. These lines. Flow Rate. One exception: ribs should be about 50. 2) Material Changes. Solution: Utilize a material that has the stiffest flow possible without causing non-fill. The CoolingCare system tests cooling channels for leaks and blockages. With this new discovery, P&G decided to launch iMFLUX Inc. FOW Mould is one of the best companies that use injection molding. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. Part walls thinner than 4mm (0. How to recognize, prevent, and counteract flow lines defects in injection molding? Learn. thick, 0. Flow lines are unwanted streaks, waves, or lines on a part’s surface. 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. Weld Line defect analysis, the most common of many defects in injection moulding products. For example, baffles require water to flow in a. Possible Causes & Remedies: Machine Cause. Fig. There are important differences between an injection mold sprue and its runner system. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. Walls thicker than 8mm (0. Introduce automation into the injection molding process for improved efficiency. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. Weld Lines-3 Ways for Detecting and Correcting. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. This is defined for each material by the length-to-thickness (L/T) ratio of the part. low of a melting time will cause flow lines to occur. Flow lines or marks appear as banded discolouration on the surface. 150 in. This requires skilled labor to mold new parts that have less molding defects. I’ve been writing about plastic flow simulation since 1984, and I. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. If you’re seeing flow lines, try extending the. Weld Lines. 2. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Plastic is injected into a mold at a specific rate of flow—typically in. com. Select a plastic that is less prone to shrinkage. 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. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. Draft – Add 0. 2. Flow direction is essential for mold mapping because when water flow reverses, poor turbulence and hot spots occur. 1 Caused By The Quality of Injection Mold. Reducing the dimensions of the runner system. Flow lines appear like off-tone patterns on the surface of your finished parts. Errors like these manifest when processing is done incorrectly. Increase injection speeds and pressure to ensure the cavities are filled properly. Flow lines are linear grooves or circular ripples on the surface of a molded object caused by uneven cooling, improper residence time, or cycle time, or low mold. Injection molding has been the most popular method for making plastic products due to. So when two. 2. Plastic is injected into a mold at a specific rate of flow—typically in. Flow lines and weld lines are lines or streaks in the final molded part. The 7/16-inch size is a happy medium between many small lines and the fact that larger lines don’t particularly increase the heat exchange benefit. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. They appear as visible lines or streaks on the surface of the molded part and can negatively impact its aesthetics and mechanical properties. Reasons and solutions. Also, heating the material in the cylinder. 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. 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. Lastly, you can only acquire the benefits of parting lines in injection molding during plastic production if you design the parting line correctly. Plastic Purity. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. This can be accomplished by reducing the substance’s viscosity. These benzene rings also increase the viscosity, reduce shrink rate, and increase strength with the exception of knit and/or meld lines. 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. with a characteristic length χ 0 =0. There are two types of weld lines, cold and hot weld line. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. May 17, 2023. Let’s review some methods to prevent flow and knit lines in plastic injection molding. Sprues are usually tapered, and they come with ends that are bigger at the top. Prior to this late stage in production, however, 3D printing is much more affordable and flexible for products in the early stages of design. Increase injection speeds and pressure to ensure the cavities are filled properly. 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. Here are some common remedies for flow lines in injection-molded products: Increase the injection speed, pressure and material temperature to ensure the material fills the mold before cooling. New design is said to eliminate mold damage from nozzle stringing or work-arounds that slow cycles. Flow marks occur as circles or lines that occur around the gate. #TROUBLESHOOTING #FLOWLINES #INJECTIONMOLDINGStudy more about troubleshooting flow lines :. Polymer Injection Molding: Gas-assisted Molding. When designing a new injection mold, a moldmaker’s main goal should be to put its client in the best position to make quality parts consistently and efficiently. Troubleshooting Injection Molding Sink Marks. Low melt temperature. Flow marks, also known as flow lines, are molding defects that can occur in the manufacturing process of injection 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. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of injection parts. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Flow Lines: Flow lines on thinner areas of molded components appear as a wavy pattern, often a different color than the surrounding area. Help prevent warping with these measures: Raise the mold or material cylinder temperature. 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. 1. This results in a much greater amount of vent flow area for the compressed air to exhaust through, and still protects the corners. Three terms that often get mixed up are weld, meld, and knit lines. This steel section retained heat, not allowing the plastic to cool and requiring an excessively long cycle time of 40 sec. 3. Flow lines appear as a wavy pattern on the surface of your plastic parts. They are evidence of nonuniformity in flow pattern upon entry into the mold. 7 in Kobayashi et al. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. How to solve flow lines in injection molded products?Injection molding is a heat-transfer process. thick, 0. As these flow fronts come together. Impurity. In this article, a multiscale simulation method of polymer melt injection molding filling flow is established by combining an improved smoothed particle hydrodynamics method and clustered fixed slip-link model. They can be off-color or discolored material compared to the intended color of the part. The molding process is the leading cause of defects in injection molding parts. [1]#TROUBLESHOOTING #FLOWLINES #INJECTIONMOLDINGStudy more about troubleshooting flow lines : lines occur when two flow fronts meet and fuse together in the injection molding process. The plant water system is a critical component of an injection molding facility. In this guide, we cover evaluation and also the remedy of flow lines in. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. 6 T) as thick as the nominal wall. They decrease the. Insufficient injection pressure or time. Picture the flow of a liquid resin filled with, for example, glass fiber. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Flow lines were created during injection moulding process. Flow lines are. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Reduce the injection pressure to prevent overpacking at the gate. This can be caused by a poor mold design, or plastic temperatures, mold temperatures, injection speeds, or. (1998) for clear photographs. They again get resolidified along the surface. Tip #6: Pick Which Molding Defects Are Acceptable. Weld lines are usually pointed out as the weak region in molded parts. RapidDirect – Your Best Injection Molding Partner. 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 the surface of the finished parts. This production method is particularly popular when manufacturing in large quantities. When trying to establish process control in plastic injection, watering the tool is a key variable that is often overlooked. An improper flow rate and injection speed also cause flow marks. The accompanying table lists the flow rates for various barrel diameters at various injection velocities. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. To further improve productivity, the injection mold was equipped with CCCs to shorten the cooling. 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. You must also note that non-fill can be an extension of a flow line or knit line condition. Jetting occurs in a molded component when molten material is injected into the mold cavity and starts solidifying before it fills the cavity. (2011) and Fig. The following are the main elements of a gating system designed for injection molding. The settings and optimization of the injection molding process dictate the geometric precision and mechanical properties of the final. Flow Lines The problem with flow lines is that they. If during the design and development stage,. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. mold temperature con-trol fluid flow in a mold, either laminar or turbulent, is by a dimensionless number. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. 7 of the reference. If you have critical requirements for strength of knit lines, please call a Protolabs applications engineer at 877-479-3680 to discuss, or email at [email protected]. This slight depression is a tiny line called the weld line or knit line. Results have shown that, although anisotropy is more pronounced in injection moldings, the mean of values for modulus along and at 90° to radial mold flow lines of an optimum modulus cure are the. Finite differences method offers strong consent for methodological solutions. We stopped the machine and added glycol to the chiller to a concentration of about 40%. These are typically found near the narrow sections of the mould gate and can. Peering into the Flow. 9 – Over Packing. 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. A knit line may be unnoticeable or may look like a crack. 1 Injection molding From Wikipedia, the free encyclopedia Injection molding (British: moulding ) is a manufacturing technique for making parts from. Below are ways through which you can remove and prevent flow lines; a. For example, filled resins and ABS are more likely to. FLOW – A qualitative description of the fluidity of a plastic material during the process of molding. There is a level of insulation from the plastic layer on the wall. 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. The Plastic Troubleshooter Defect - Flow Lines. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. 008 to 0. The recommended minimum production volume for injection molding is 500 units. tall, and 0. 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. Leadtime Leader 2024. As the material properties of. 3,000 ton machines can cost $700,000. This action could indicate that one portion of the plastic flow will move more quickly than the other. Shortening the molding cycle time is a key factor in improving energy efficiency and since cooling occupies a major part of the cycle, effective design and operation of cooling systems is essential. Molds gain streaks through molten plastic cooling and solidifying at different rates. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. The model of polymer melting is fundamental for the development of. 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. Water set-up and design are every bit as important as establishing and recording a repeatable process. Flow marks won. MMT Chats. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. 100 to 0. Locally black discolorations of the molded part occur in the area of the weld lines, at the end of the flow path or of individual areas of the molded part (for example, a rib). It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. We offer this Mold Cooling Calculator tool as a free service to the injection molding industry. Production was set according to an experimental design (DoE), varying injection flow rate, mold temperature, and melt temperature. 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. They can be unsightly and unpleasant in high-end sunglasses. Weld lines are a kind of Achilles heel of plastics. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. • u. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. In the plastic injection moulding industry, we work with materials that are by-products of oil refinement and moulds made of metal casting, so our terminology is bound to be at least slightly confusing. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). That’s an easy calculation to perform. They appear around holes or seams of an injection molded part, and some may call them “flow lines” or “weld lines”. They can also appear as ring-shaped bands on the surface of a product near the mold’s “gates. However, FRTP has problems such as the formation of weld lines, the deterioration of appearance due to the exposure of fibers on the molded product surface, and the deterioration of the strength of. If performing a resin change from one polymer to another a difference in viscosity can cause flow lines or gels. The chart below shows recommended wall thicknesses for common injection molding resins. Flow rates and a fluid are input to the cooling channels,. 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. 6. 0mm) throughout will ensure that the parts cool evenly and will prevent warping. google-site-verification: google03af4f4fcb62a9d5. Plastic injection molding is the industry’s most common way to manufacture parts. We started the mold with 100% water circulating at 60°F at a flow rate sufficient for turbulence. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. Flow lines appear as a wavy pattern often of a slightly different color than the surrounding area and generally on narrower sections of the molded component. When incorporating multiple gates it’s important to consider where the flows will meet as the meeting area can cause aesthetic issues and part weakness. Mold Design. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. They are visible on one side of the parts. More viscous amorphous materials, such as PC, TPU or PEEK, can have a recommended vent depth range from 0. Here are some ways to avoid. If a mold cavity has a significant flow length-to-thickness ratio, the material should have a low enough viscosity to enable a continuous flow. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. We stopped the machine and added glycol to the chiller to a concentration of about 40%. • Optimize the design of the runner system. Contact the material supplier for help in deciding which flow rate should be used for a specific application. Precise control of resin flow, pressure and temperature is critical. The strong molecular. Injection molding could develop knit lines if one front cools before it reaches the other. Aberdeen Technolgies makes the mold manufacturing process for injection molding. For the measurement of the crystallinity a DSC analysis was performed. Flow lines can occur if any of the following affect the mold: A runner, gate, or sprue that is too small for purpose creates more flow resistance. (All Illustrations: S. Listed below are some factors to consider when designing ribs for injection-molded parts. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. 0010 in. At some point in time, it can no. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Thereby creating localized pressure within the mold. Recently hired at plastic injection molding simulation software provider Moldex3D, Nicholson was spurred to undertake the research study following a conversation with a customer experiencing weld-line woes. Learn how mold flow analysis can support the development of complex and customized injection molded products by identifying defects, optimizing materials, enhancing performance, and reducing costs. The co-simulation of mold flow and structure plays an important role in the design of injection molded fiber-reinforced thermoplastic (FRT) parts. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no. 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. Increase the injection speed, pressure, or temperature of the material. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. Sink Marks. Weld‐line is a defect that arises in injection molding when two or more flow fronts collide. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. Also called “Weld Line. Introduction. By contrast, a slow injection speed will give you a matte finish and a cold mold, such as 50F, will give you a more flexible part. Flow lines. They follow the flow of the molten resin from the gate along the finished part. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Lenticular, or Silver Dollar type pigments, are thicker than cornflakes, with a narrower particle size distribution. Thickness – Make the ribs 50% to 60% (0. Flow marks, also known as flow lines, are molding defects that occur in the manufacturing process of injection molding. On that note, we. Flow lines are a defect in injection molding and can be a significant issue for manufacturers. In injection molding weld lines are formed whenever two flow fronts are joined. Kobayashi et al. process can be fully completed. Increase molten plastic temperature during injection molding. The formation process of weld lines can be described as. We heat the plastic to a molten phase, inject it into the mold and cool it into a preferred shape. Possible defect causes. Study shows that the root cause of jetting is related to the mold design on the one hand and the viscoelasticity of the material on the other. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. 005 0. 1). Each needle valve nozzle opens only when the melt front has moved across its gating point. The mold flow model is usually a single-part model, that is, the FRT part itself, but the mechanics model is often a multi-part model, an assembly of the FRT part and others. Flow velocity is very high in the area of the gate as it enters the mold, but slows down as the flow front extends away from the gate and into the cavity on a widening circle. Here are some common remedies for flow lines in injection-molded products: Increase the injection speed, pressure and material temperature to ensure the material fills the mold before cooling. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. Weld line. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. The most common and one of the most challenging injection molding defects are weld and knit lines. Too hot and the plastic will start to degrade, but too low and flow marks increase. Although injection molding is considered a fairly well-established manufacturing process, several independent parameters must be properly set to achieve a high quality of the molded parts. Edge Gates. Look for signs of stickiness or burning. AnalysisInjection moulding simulation with the finite element method is the most advanced technique for designing injection moulds. Weld lines have been one of the common defects puzzling the injection molding industry. ”. 5mm (0. The goal when locating cooling channels in the mold is uniform mold surface temperature, which is determined by cooling channel depth and pitch. It is therefore important to work with reliable injection mold makers for quality services and products. 160"). Injection Molding works with molten fluid created by heating the plastic granules above their melting point. Otherwise, the heat transfer of. Known as thermolators,. Since these materials behave and respond differently, it is crucial. Heat Input and Cooling Calculator for Injection Molding. Water cooling pumps coolant through lines on the outside of the mold cavity. There are three stages of flow – laminar, transient and turbulent. reduce the ability to positively influence the strength. Mold flow analysis is a software-enabled process that. The materials used in the plastic injection molding process can vary in rigidity and pliability, among other differentiating characteristics. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. We restarted the mold at the same coolant flow rate and temperature. Round the corners of the mold where wall thickness increases to help keep flow rate consistent and prevent flow lines. Cascade Moulding Avoids Weld Lines. 750 in. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. This article explains the causes and. 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. 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. Within more basic plastic part design plans this plane can be a simple, flat surface, but it is often a complex form that. Inadequate mold wall thickness leads to uneven cooling and hindered plastic flow, resulting in weld lines. Lower speeds allow gas more time to escape through vents. Known as thermolators, water cooling systems require a cooling source such as a tower. We restarted the mold at the same coolant flow rate and temperature. Injection Molding of Multimaterial Systems. Expand. The linear mold shrinkage of injection molded parts will vary from 0. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. One cause of flow lines is low injection speed, which can result in the molten plastic cooling too quickly and creating a. Here's a list of the commonest injection moulding defects and how you can avoid them: 1. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. Energy use by thermoplastics injection molding machines is estimated to result in global CO 2 emissions in the order of 80 million metric tons annually. [12] or the flow lines shown in Ref. While some molds or inserts have simple, straightforward cooling circuits, many have multiple circuits of various sizes and configurations. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Facebook. Thin walls of greater length require greater pressure, which requires larger injection molding machines and. 0 is leading the productivity and efficiency of companies to minimize scrap rates and strive for zero-defect production, especially in the injection molding industry. 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. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Parting Lines. Sources of defect: Material: Material too high viscosity; Method: Injection speed in the critical area too high (too low)Flow lines are one of the most common problems with injection molding. The main causes for short shots are inappropriate injection pressure and speed. These streaks or patterns can affect a part's aesthetics, value, and overall quality. Plastic Injection Molding Defects series-Flow Marks or Flow Lines Aug 23, 2019 What should we keep in mind when designing for injection molding?1. It can also aid in material selection since fill. Plastic injection molding is a complex and highly intricate process. A knit line is when two flow fronts come together but, rather than merging, it’s like a head-on collision at a 4-way stop. Each material has a maximum flow length for a given injection pressure and wall thickness — this is known as the flow ratio. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. If larger gates are used, expect a longer molding cycle time. 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. ; Burn marks – Often appears as black or rust-toned discoloration streaks on the edge or surface of a molded product. From the perspective of the mold, when the molten plastic reaches the gate through a larger-sized runner, the flow resistance of the melt is greatly increased because the gate size is usually very small. These data were obtained from many andGenerally, injection molding resins are characterized as having medium, high or very high flow. Aesthetics, such as injection molding gate marks, sink marks, voids and flow lines In some cases, more than one gate may be necessary to achieve the desired outcome. On-Line Solutions To Injection Molding Problems. Manifesting as wavy lines or streaks on the surface of the molding, flow lines generally occur when molten material flows. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. Raise the mold temperature, maintain a high. Increase the size of the gate and reduce the thickness of the walls of the molded part. This is often a sign that injection speed and/or pressure are. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Heat: Too much heat can have an appearance similar to moisture splay. Although they typically do not impact the functionality of a product, flow lines—off-color streaks or patterns across a product’s surface—may look unprofessional when visible to consumers. Flow Lines Or Flow Marks.