Edge Gates. 100 to 0. Flow lines. 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. (All Illustrations: S. A ‘parting line’ is the line of separation on the plastic part where the two halves of the plastic injection mold meet. wide. First, excessive injection pressures may be forcing the mold apart. Sufficient draft is an important part of any mold design, and quick-turn tooling is no exception. 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. ”. Flow Line. Mold flow analysis is a software-enabled process that. 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. It is therefore important to work with reliable injection mold makers for quality services and products. Lower speeds allow gas more time to escape through vents. Knit Line. This method can be helpful in. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. Vacuum Voids. Impurities in the resin will prevent a smooth flow through the mold. 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. Help prevent warping with these measures: Raise the mold or material cylinder temperature. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. ” What else can you do about weld lines—besides redesigning the mold or gate locations or adjust the flow pattern during fill with sequential valve gating? I recently saw a report on this issue from Moldex3D, the maker of molding simulation software. Weld Line defect analysis, the most common of many defects in injection moulding products. 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. Avoiding Voids and Sinks. Here are some ways to avoid. INADEQUATE INJECTION PRESSURE. In other words, the long-chain polymer. Flow marks occur as circles or lines that occur around the gate. If necessary, the mold designer may simulate the flow of solidification of resin using an injection molding simulation program. These are off-tone streaks or lines on the surface of the plastic, and while they don’t affect the structural integrity, they are unattractive and prevent a uniform and consistent appearance. If you’re a mold designer with one of those vent-depth “rule-of. This carbon will hang up in areas and is difficult to remove. The cause can vary. Vents have three components. The formation process of weld lines can be described as. Mold is not vented properly causing slow flow at knit lines. Flow lines are the results of slow injection rate and disparities. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. You must also note that non-fill can be an extension of a flow line or knit line condition. Flow Lines Or Flow Marks. They can also appear as ring-shaped bands on the surface of a product near the mold’s “gates. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. 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. ³/sec. This injection molding defect appears as black or rust-colored discoloration on the molded part's surface or edge. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. 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. The Fill system analyzes the filling of each cavity by sensing the melt presence at the end of flow with a cavity temperature sensor and compares the fill-time. Polycarbonate Injection molding defects. 0010 in. Cooling for slender cores (≤3 mm) uses air cooling instead of water. They are off tone wavy lines/streaks or patterns in the molded part around the injection ports. 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. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. Adjustments to injection speeds are the best way to determine which of these two are the specific cause. For runny, non-viscous, crystalline resins such as nylon, PE, or PP, the recommended vent depth can range from 0. Known as thermolators,. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. 2. The melt holds enough temperature to maintain a low enough viscosity. The main causes for short shots are inappropriate injection pressure and speed. 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. 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. Weld line. (4) It can improve the strength of the fusion line. Each needle valve nozzle opens only when the melt front has moved across its gating point. Weld lines have been one of the common defects puzzling the injection molding industry. g. If I can answer any questions you may have on optimizing the plastic part design, CNC plastic prototype, mold manufacturing, and injection molding or if I can be of any other help, please feel. FIG 1 Depiction of fountain flow. Introduction. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Increase injection speeds and pressure to ensure the cavities are filled properly. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. On a small four-cavity tool, the part had a U-shaped notch in the center. If you’re seeing flow lines, try extending the. 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. Weld Lines. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. Increase the mold temperature. The material is poured into a mold, which shapes the size and looks of the article. Injection moulding (U. The. 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. 000 0. Molds separate into two sides at a parting line, the A side , and the B side , to permit the part to be extracted. (1. The main. The weld line is then created with a higher flow front temperature and is packed with more pressure. The change in flow-front velocity can bring about the surface defects. Edge Gates. Imperfections in manufactured plastic goods, such as a flow line defect in injection molding, are unacceptable. They appear around holes or seams of an injection molded part, and some may call them “flow lines” or “weld lines”. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Cooling lines impact. Once you have a cool shell formed the rest of the mold entering absorbs heat from the layer next to the wall. Troubleshooting Injection Molding Sink Marks. By using proven methods for cooling line design, warp and cooling time are minimized. Each gate type has specifications that significantly affect the end product’s structure and appearance. 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. Allows you to accommodate a variety of part sizes. Flow lines were created during injection moulding process. Use high-quality, temperature-controlled materials for better mold filling. As the material properties of. 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. mold temperature con-trol fluid flow in a mold, either laminar or turbulent, is by a dimensionless number. 020"). In the development of our calculator. How to solve flow lines in injection molded products?Injection molding is a heat-transfer process. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. Thus, with an injection pressure of 1800 MPa, the flow length with 80°C is 47 mm and accordingly for. Raise the mold temperature, maintain a high. 1 a. Flow lines are. Injection Molding works with molten fluid created by heating the plastic granules above their melting point. In injection molding weld lines are formed whenever two flow fronts are joined. They follow the flow of the molten resin from the gate along the finished part. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. Thin walls of greater length require greater pressure, which requires larger injection molding machines and. Known as thermolators, water cooling systems require a cooling source such as a tower. 004 m, a characteristic velocity ν 0 =0. Injection molding tool life is the number of production cycles that an injection mold can complete before it needs to be replaced. Round the corners of the mold where wall thickness increases to help keep flow rate consistent and prevent flow lines. Mold surface is too cold. Flow marks in injection molding can be avoided if adequate measures are taken. 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]. 3. 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. The speed of an injection moldingRepeat the two previous steps two or three times, starving the screw periodically to allow the screw to rotate without building a shot. After four years in development, an injection machine nozzle tip has been commercialized that is said to eliminate problems of stringing and all the compromises. 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. Solution: Molding Process: This defect can be reduced by raising the material temperature and the nozzle temperature, and slowing down the injection speed, etc. 008 to 0. The linear mold shrinkage of injection molded parts will vary from 0. Utilize hot. These are typically found near the narrow sections of the mould gate and can. 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. 010 0. A void occurs during cooling while the part is inside or outside the mold. Plastic is injected into a mold at a specific rate of flow—typically in. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. 1. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. A. This can be achieved by reducing the flow. Too hot and the plastic will start to degrade, but too low and flow marks increase. 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. Walls thicker than 8mm (0. 0010 in. 7 of the reference. Flow marks, also known as flow lines, are molding defects that occur in the manufacturing process of injection molding. 16″) will be difficult to inject, leading to flow lines, surface imperfections, and short shots. Sink marks are like little craters formed on an injection-molded product. They can be caused by variations in cooling speeds of the material as it flows through the mold. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. 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. In injection molding, it is often important to maintain consistent color throughout the part. low of a melting time will cause flow lines to occur. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. 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. When trying to establish process control in plastic injection, watering the tool is a key variable that is often overlooked. 2. Increase the injection speed, pressure, or temperature of the material. The emergence of silver marks is generally due to the rapid start of the injection which causes the air in the melt and mold cavity unable to be discharged quickly enough. Flow lines are unwanted streaks, waves, or lines on a part’s surface. Flow marks can be caused by any or all of the following factors: Slow melt injection speed. Add or increase vents as needed. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. If you experience flash on your injection blow molding products, consider redesigning a worn out or faulty mold. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow. Wavy lines are another feature of weld lines. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. In narrow fields, a limited amount of molten liquid can solidify and block the flow. Injection molded parts can have several different issues. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Acetal is a funny material in how it reacts to certain injection speeds and mold temperatures. Impurities in the resin will prevent a smooth flow through the mold. More viscous amorphous materials, such as PC, TPU or PEEK, can have a recommended vent depth range from 0. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. Commercial injection molding simulation packages, such as Moldflow and C-MOLD, have been incorporating GAIM options to provide computerized design and optimization tools for GAIM processes and. 10 in Nguyen-Chung et al. If packing around a detail is causing cracks/ shorts/burns on the knit line, reduce the heat to improve knit line seal and strength. [12] or the flow lines shown in Ref. Flow lines are linear marks on the surface of a molded product, which indicate the flow direction of the molten plastic. Splay is a cosmetic defect that occurs in plastic injection molding, when silver or white streaks appear on the surface of the part. Facebook. Well, what this simply implies is that injection polycarbonate molding makes it possible for you to create a wide range of part sizes. Investigate the mold for signs that a water leak is present, and correct the condition. 060 and 0. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. These benzene rings also increase the viscosity, reduce shrink rate, and increase strength with the exception of knit and/or meld lines. This can be accomplished by reducing the substance’s viscosity. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. The edge gate is the most popular and straightforward injection mold gate design. Water set-up and design are every bit as important as establishing and recording a repeatable process. Because you have control over exactly when and how much material enters the tool, you have tighter control of the parameters that go into making a quality part. The last cause of flow lines may be the operators running your daily operations. It explored the use of. 4, no. Kulkarni) During the fill phase (Fig. Sink Marks. In addition to accurate temperature control, optimizing flow through a mold is critical and, quite often, results in decreased cycle times and increased product quality and repeatability, even after increasing chilled water temperature. Design for Manufacturing (DFM), also known as pre-mold review, is a collaborative process in the injection mold industry where technical negotiations take place to meet customer requirements. On average, larger injection molding machinery can cost from $50,000-$200,000 or more. Take these steps to avoid knit lines. In this study, a new specimen design is introduced for the tensile testing of micro parts. That’s an easy calculation to perform. 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. This design is deliberate in order to help the mold. New design is said to eliminate mold damage from nozzle stringing or work-arounds that slow cycles. (All Illustrations: S. Its popularity is typified by the numerous products produced in this way at the present time. Raising the temperature of the mold slightly can help to prevent flow lines, as it prevents the molten material from cooling immediately upon impact with the cavity walls. Learn how to troubleshoot weld lines in injection molding. Features such as sharp corners or undercuts can. Furthermore, jetting is frequently visible as a squiggly line on the surface of the final component, typically leading from the original injection gate. This. 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. Contact us to learn more about SMARTFLOW flowmeters. This can be achieved by connecting ribs to each other. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. The weld line and the flow pattern of co-injection molding can be seen from Fig. Weld lines have been one of the common defects puzzling the injection molding industry. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. (1) Increase the injection pressure and prolong the injection time. We heat the plastic to a molten phase, inject it into the mold and cool it into a preferred shape. In terms of viscosity, higher heat equals faster flow and lower heat equals slower flow. Thin wall injection molding can produce walls as thin as 0. So much. 020 0. Incorrect gate positions cause multiple flow fronts that struggle to merge seamlessly. Weld lines may appear like seams or scratches, but that is not what they are. Weld lines represent the region where two separated melt fronts recombine. This defect is caused when plastic cools too rapidly during the injection molding process. In this regard, the gate form with less shunt should be used, and the gate position should be selected reasonably. The recommended minimum production volume for injection molding is 500 units. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. There are different levels of program available on the market. In injection molding, it is often important to maintain consistent color throughout the part. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. 0 seconds, depending on part volume, runnergate style and size, cavity location and injection pressure. Mold Flow Analysis. Another solution may be to pull a vacuum on the mold just before injection. These data were obtained from many andGenerally, injection molding resins are characterized as having medium, high or very high flow. The size, shape, and location of the gate have a significant impact on the finished product. 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. Parting Lines. These lines. Select a plastic that is less prone to shrinkage. However, the weld line may not continue throughout the flow. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. 6T) as thick as the nominal wall. This slight depression is a tiny line called the weld line or knit line. Look for signs of stickiness or burning. This means that the skin of the part is always formed by. 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. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. After an hour of running, the steel temperature stabilized at 78°F. Secondly, it is easy to form obvious. Another tactic to promote more chain entangling at the weld line is to raise the mold temperature 10° C (50° F). This requires skilled labor to mold new parts that have less molding defects. Countermeasures to Injection. You might have come across the aforementioned terminology before and did not know what any of the words meant. The line actually indicates the parting ‘plane’ that passes through the part. However, surface quality is difficult to predict due to many influencing factors and their complex interactions. The flow rate should ensure the material does not lose its. thick, 0. 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. One of the best ways to determine part shrinkage for complex components is with a mold flow analysis. In injection molding weldlines are generated when two separate melt streams join either. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no. Weld Lines. Spatter lines formed on the surface of the plastic along the direction of melt flow are called silver marks. The process involves the injection of heated, liquefied plastic into a temperature-controlled mold under high pressure. 750 in. Remedies: Raise the temperature of the mold or molten plastic. Flow speed too fast or too slow. A meld line occurs when two moving melt fronts converge and flow parallel to each other. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. At a theoretical flow distance of 10 mm it represented the measured values well but at a longer distance it underestimated the experimental scale. As a result this weld line will be a weak point in this part. Pack (hold time) is usually 2 to 3 times the mold fill times, depending on gate size. Obviously, as the resin front moves through the mold, the fill material will always be behind the front. More about the knit lines in injection molding. Unraveling Flow Lines. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. Thickness – Make the ribs 50% to 60% (0. From a technical point of view, valve gate technology enables the production of low-stress injection molding parts, which almost always meet the requirements of a very low vestige. 5° draft to each side of the rib. Then the melt is injected into the mold and the surface of injection-molded products is. Burn Marks. For each investigated mould temperature, a linear relationship can be observed. 015 0. This new process enables thinking differently about how parts and molds can be designed. A look at how taking the time and data to analyze a mold problem will help you repair it right—and permanently—the first time. Our glossary of terms provides definitions for a wide range of injection molding terms. Flow lines are surface irregularities, wavy patterns, or a rippled effect, perhaps of a slightly different color, that can appear in injection molded parts. 5-3. Reposition gates and runners to allow resin to flow around the obstruction from a different direction. To avoid these defects, manufacturers can check molds for the following: Low Mold Temperature: A mold temperature that’s too low will cause the material temperature to drop fast. Weld lines are a common imperfection to be found in most plastic injected molded parts. Flow lines. 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 are a typical problem for injection molding faults that appear as visible streaks or lines on the surface of the molded part. Lookalikes include surface scratches, scuffs, flow lines, delamination from contamination, and flaking. It can also aid in material selection since fill. The plant water system is a critical component of an injection molding facility. 3,000 ton machines can cost $700,000. If it’s too thin or small, material flow, pressure, and temperature will. The thermo-rheological findings were used to investigate the sources of weld line weakness. 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. SMARTFLOW ® flowmeters effectively and accurately measure flow rate. 2. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Impurity. 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. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Weld line. Heat: Too much heat can have an appearance similar to moisture splay. Bob Hatch is manager of technical service and customer support for Prime Alliance, the Des Moines-based resin distributor. 1. When a poor-quality plastic that has impurities in it is used for injection molding, it is less likely to flow smoothly through the mold. Strengthening. The following advantages exist for the use of high injection speed in the injection process. Examine the flow pattern of each part to see if the plastic flow front is coming around on itself, or if there is a hesitation of the flow front in filling a thin section of the part. On the surface of a molded object, flow lines (also called flow marks) refer to the phenomenon that linear grooves or circular ripples showing the direction of material flow inside the mold cavity. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. 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. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. The problem could be the result of machine settings made before the gate was installed. Increase the size of the gate and reduce the thickness of the walls of the molded part. Lenticular, or Silver Dollar type pigments, are thicker than cornflakes, with a narrower particle size distribution. Within more basic plastic part design plans this plane can be a simple, flat surface, but it is often a complex form that. industry, to deliver intuitive injection mold-ing simulations embedded in NX. Mold Design. After exhaustive research, testing and pilot-scale demonstration, the team developed a breakthrough new technology utilizing low constant injection pressure. Tatjana Geminger, Stefan Jarka, in Specialized Injection Molding Techniques, 2016. Part Design: One of the important rules in part design is to have flow lengths that will let the plastic be fluid enough not just to flow into the end of fill but also until all the packing of the part is achieved. 2) Material Changes. Flow Lines. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and. 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. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. 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. Injection molding is a great technology for finished production on a massive scale.