This allows the melt to keep enough velocity to ensure proper filing. Reduce the injection pressure to prevent overpacking at the gate. Too hot and the plastic will start to degrade, but too low and flow marks increase. ” 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. Certain injection molding processes may not be effective for the production of some parts. The main. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. Prevent Flow and Knit Lines During the Injection Molding Process. Surface Delamination. Flow lines or flow marks are a common visual defect in injection molding. They are visible on one side of the parts. G. Solution: If possible, operate the machine on. This can be achieved by connecting ribs to each other. Voids . 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. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Inadequate cooling time. It is crucial to manage flow lines to ensure. The flow rate should ensure the material does not lose its. Injection molding is one of the best plastic production methods. AnalysisInjection moulding simulation with the finite element method is the most advanced technique for designing injection moulds. plastic mold venting. In other words, the long-chain polymer. Bob Hatch is manager of technical service and customer support for Prime Alliance, the Des Moines-based resin distributor. The most common and one of the most challenging injection molding defects are weld and knit lines. 3. 1mm (7/16"), coolant temperature of 30ºC and cycle time of 17 seconds (see Fig. Haagh, in Encyclopedia of Materials: Science and Technology, 2001 3 Modeling. 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. These streaks or patterns can affect a part's aesthetics, value, and overall quality. [12] or the flow lines shown in Ref. Adjust the sprue bushing length: If the face of the sprue bushing is sealing off on the parting line, adjust the length to ensure that nozzle pressure or thermal expansion does not hold the mold open and allow the plastic to flow out. In the area of lettering, ribs, domes or sharp wall thickness changes, air which cannot escape quickly enough is swept along, overrun by the melt and embedded. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Mold Design. 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. Contact us to learn more about SMARTFLOW flowmeters. Flow Lines particles, during injection molding, will produce visible flow and weld lines. 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. 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. An improper flow rate and injection speed also cause flow marks. The material is kept poured into the mold for some time. Increase injection speeds and pressure to ensure the cavities are filled properly. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. 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. Edge Gates. Below are ways through which you can remove and prevent flow lines; a. 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. What Are Flow and Knit Lines? Flow lines are defects that appear as wavy. The materials used in the plastic injection molding process can vary in rigidity and pliability, among other differentiating characteristics. (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. 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. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. 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. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. 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. Injection molding has been the most popular method for making plastic products due to. Flow marks can be caused by any or all of the following factors: Slow melt injection speed. Lookalikes include surface scratches, scuffs, flow lines, delamination from contamination, and flaking. Peering into the Flow. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. 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. Fast injection gives you a glossy part, which is what we wanted in this. Flow lines are surface irregularities, wavy patterns, or a rippled effect, perhaps of a slightly different color, that can appear in injection molded parts. Flow lines – A common plastic injection molding defect in which discolored ring-shaped streaks, patterns, or wavy lines appear around gates or narrow sections of the finished product. Molds for investment casting are more accurate and have fewer defects, thanks to flow control over wax injection. By using proven methods for cooling line design, warp and cooling time are minimized. This means that the skin of the part is always formed by. 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. Fictiv provides you with DFM feedback so that you can minimize injection molding defects. How to solve flow lines in injection molded products?Injection molding is a heat-transfer process. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Reducing injection speed will allow more time for the air to escape from the cavity through the vents, but this leads to other problems, such as short shots (incomplete parts). Mold Flow - Position ribs such that the plastic has an optimal flow path. 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. Turbulent Flow IS Always Better. Also called “Weld Line. Expand. 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. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. to 0. 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. Let’s take a look at some defects that are caused purely due to faults in the injection mould process. NX Mold Flow Analysis. • Reduce runner dimensions and maintain the same flow rate. Purpose: The examination of melt flow lines in injection moulded parts was the purpose of this research, as well as a new method of flow visualization was applied. Weld lines have been one of the common defects puzzling the injection molding industry. Mold design is a key aspect of injection molding. On a small four-cavity tool, the part had a U-shaped notch in the center. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Weld Lines-3 Ways for Detecting and Correcting. ABS resin has low thermal deformation temperature, but poor heat resistance. 2. Increase the mold temperature. Faster injection increases pressure in front of a flow front. We started the mold with 100% water circulating at 60°F at a flow rate sufficient for turbulence. The location of the crack can tell us a lot about its specific cause. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. They appear as waves or lines, usually of a different color tone from the surrounding area. The last cause of flow lines may be the operators running your daily operations. 4. 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. 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. A. Figures 3A, B and C depict different examples of “spot” vents. They again get resolidified along the surface. 5° draft to each side of the rib. 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. Select a plastic that is less prone to shrinkage. As a result, the lower degree of stress when gating with valve gate systems becomes relevant. The type of gate for manufacturing often depends on the material used and the parts’ shape. Water cooling pumps coolant through lines on the outside of the mold cavity. Solution: Molding Process: This defect can be reduced by raising the material temperature and the nozzle temperature, and slowing down the injection speed, etc. The formation process of weld lines can be described as. S. 015 0. Our glossary of terms provides definitions for a wide range of injection molding terms. The flow fronts at different times (Fig. MFR values for polypropylenes are determined at the same load but at a higher temperature 230°C (446°F). Mold surface is too cold. However, the weld line may not continue throughout the flow. 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. Novel Nozzle Tip Prevents Stringing, Saving Molds & Cycle Time. They also can appear as ring-shaped patterns near the entry points of the mold. This design is deliberate in order to help the mold. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. 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. Consider the following examples of cooling channel configurations in P20 mold steel with a water line diameter (D) of 11. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. These defects include the following: 1. The goal when locating cooling channels in the mold is uniform mold surface temperature, which is determined by cooling channel depth and pitch. Plastic Purity. The Plastic Troubleshooter Defect - Flow Lines. 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. These marks remain and are visible in the cooled product. Prior to this late stage in production, however, 3D printing is much more affordable and flexible for products in the early stages of design. 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. Furthermore, jetting is frequently visible as a squiggly line on the surface of the final component, typically leading from the original injection gate. Injection molding machine . This results in an incomplete part at the end of injection molding. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. Polycarbonate is a tough, optically clear or opaque, biocompatible plastic with good thermal resistance. Rubber injection molding is defined as a process where uncured rubber is transformed into a usable product by injecting raw rubber material into a mold cavity made of metal. They can be unsightly and unpleasant in high-end sunglasses. html. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. Common injection Mold Flow Lines. The injection molding process involves the injection of a polymer melt into a mold where the melt cools and solidifies to form a plastic product. Possible Causes & Remedies: Machine Cause. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. With a minimum of 1. 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. Source: Google. The material is poured into a mold, which shapes the size and looks of the article. 3,000 ton machines can cost $700,000. Weld lines may appear like seams or scratches, but that is not what they are. Ensure sufficient cooling time to avoid locking residual stresses into the part. Poor mold surface n Refinish a poor or worn mold surface. Flow marks won. Quality concerns in injection-molded materials can vary fr. The mold designer cannot know your goals without your input, which is why you will be asked to approve a gate and ejector layout prior to manufacturing a mold. In Fig. Flow lines are the results of slow injection rate and disparities. 5 to 0. Excess Mold ReleasePoor mold design, including inappropriate mold wall thickness and faulty gate placements, is a common cause of weld line formation in injection molding. Clean all parting line and core vents. One of the best ways to determine part shrinkage for complex components is with a mold flow analysis. injection mould simulation at steady flow rate. 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. It can help you reduce defects, improve quality, and save costs by simulating how. 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. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. 1 Caused By The Quality of Injection Mold. Round the corners of the mold where wall thickness increases: This. 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. Mold Design. 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. Purpose: The examination of melt flow lines in injection moulded parts was the purpose of this research, as well as a new method of flow visualization was applied. Symptoms: Flow lines will typically appear as discolored “bands,” or sometimes “wavy. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. 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. In injection molding weld lines are formed whenever two flow fronts are joined. Laminar flow in a plastic mold, described by. Listed below are some factors to consider when designing ribs for injection-molded parts. Adjust the design for the flow pattern to be a single source flow. 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. 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. Injection Molding (IM) Solutions 1019 Balfour St. with a characteristic length χ 0 =0. Flow lines. You must also note that non-fill can be an extension of a flow line or knit line condition. 18/06/2021. See. Just multiply the area of the barrel × the injection velocity. Well, what this simply implies is that injection polycarbonate molding makes it possible for you to create a wide range of part sizes. 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. At the high end of SOLIDWORKS Plastics simulation in Plastics Premium, mold-level analysis can be performed by representing the runners, cooling channels and a mold body around the cavity. Injection Molding works with molten fluid created by heating the plastic granules above their melting point. These defects are not visible, like small. This may involve adjusting the temperature and pressure of the mold, using different mold materials, or adjusting the injection speed or cycle time. 150 in. They are evidence of nonuniformity in flow pattern upon entry into the mold. 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. Chart 1: Diameter versus turbulent flow. Setting the proper pressure on the injectors to push the plastic into the mold with enough speed that the plastic will coat the mold and fuse with other flow lines. 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. 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. Too hot and the plastic will start to degrade, but too low and flow marks increase. Water set-up and design are every bit as important as establishing and recording a repeatable process. They are off tone wavy lines/streaks or patterns in the molded part around the injection ports. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. The size, shape, and location of the gate have a significant impact on the finished product. 010 0. For example, filled resins and ABS are more likely to. On the contrary, for the conformal cooling. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. Burn Marks. 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. diverse parameters of the injection-molding process, needs a lot of experience in order to achieve optimum results, especially if. If it is farther down the flow part, increase injection speed to decrease viscosity and allow more packing pressure. As these flow fronts come together. tall, and 0. Thus, with an injection pressure of 1800 MPa, the flow length with 80°C is 47 mm and accordingly for. Flow lines are ripples in the plastic after the part is formed. First, excessive injection pressures may be forcing the mold apart. vent the ejector pins and vent the lifters and the parting lines. Image 4: Top, HDPE streamlined structure. Increasing injection speed. Remedies: Raise the temperature of the mold or molten plastic. Troubleshooting Injection Molding Sink Marks. Flow lines are linear marks on the surface of a molded product, which indicate the flow direction of the molten plastic. This method can be helpful in. Flow marks: Flow lines Directionally "off tone" wavy lines or patterns Injection speeds too slow (the plastic has cooled down. 5. We will now look at the problem you are likely to encounter and how to fix them. Which means engineers need to know how to account for this phenomenon in an efficient way. 2), the plastic enters the mold at a relatively fast rate and forms the skin. Flow marks occur as circles or lines that occur around the gate. 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. 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. Each needle valve nozzle opens only when the melt front has moved across its gating point. The weld line and the flow pattern of co-injection molding can be seen from Fig. The definition of weld lines: When multiple plastic flow fronts meet in the cavity after encountering inserts, holes, or areas with inconsistent flow rates or interrupted melt flows, or in the case of gate injection filling, the inability of two or more flow fronts to fully “knit” together will cause the linear weld marks. as a stand-alone, wholly owned. For instance, the plastic used for gears must be completely smooth. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. For the measurement of the crystallinity a DSC analysis was performed. Raise the mold temperature, maintain a high. How to recognize, prevent, and counteract flow lines defects in injection molding? Learn flawless products from professional manufacturers. Within more basic plastic part design plans this plane can be a simple, flat surface, but it is often a complex form that. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. In terms of viscosity, higher heat equals faster flow and lower heat equals slower flow. 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. 5. Tip #6: Pick Which Molding Defects Are Acceptable. In addition to the recommended wall thickness, it’s important to consider a material’s flow characteristics. Injection molding, in addition to extrusion, is the most important technology in the polymer processing industry. The primary reason is insufficient plastic fluidity. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. This can prevent the opportunity for trapping air. In this lesson we will focus on the meld and weld lines. Remedies: Increasing the injection pressure will force the molten plastic against the mold cavity. 1．Mold Temperature Too Low. Here are the top 5 injection molding defects that can occur, and how to solve them: Flow / Weld Lines. Detecting Water Flow Restrictions. 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. 1, pp. 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. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. When mapping mold circuits, label each circuit with a number exclusive to the circuit and a supply or return designation (e. sufficiently melted to a molten state in the barrel of the machine before the injection. This can be accomplished by reducing the substance’s viscosity. The barrel temperature is too high. Mold Design. The other parameters such as Mold temperature and Cooling Time also contribute in the defects appropriately. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow molten plastic to flow down between the pin and hole surface. How a mold is watered is key to a processor's goal of consistency. Flow lines and flow marks. There are different levels of program available on the market. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). 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. They usually are a slightly different color than the rest of the piece, and typically occur on more narrow sections of the molded item. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. FLOW – A qualitative description of the fluidity of a plastic material during the process of molding. Effects of mold temperature and pressure on shrinkage 0. 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. 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. 100 to 0. Inadequate mold wall thickness leads to uneven cooling and hindered plastic flow, resulting in weld lines. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Polymer Injection Molding: Gas-assisted Molding. 000 0. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. 1. Flow Rate. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 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. 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. Sink marks are like little craters formed on an injection-molded product. 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. Mold venting is critical to the quality and consistency of the finished part. (1) Reduction of injection time and shortening of the molding cycle. to 0. Injection Molding of Multimaterial Systems. 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. 1 – In plastic injection molding, the flow ratio is the distance molten plastic must travel, divided by the wall thickness of the part. Circuit Identification. Insufficient injection pressure or time. The problem could be the result of machine settings made before the gate was installed. Flow lines. Do not keep the hopper full; hand-feed if necessary. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. If necessary, the mold designer may simulate the flow of solidification of resin using an injection molding simulation program. Cascade Moulding Avoids Weld Lines. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. 182-185, 2013. thick, 0. Investigate the mold for signs that a water leak is present, and correct the condition. google-site-verification: google03af4f4fcb62a9d5. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Drain the hopper if you were working with 100% regrind, clean if necessary. 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. Each needle valve nozzle opens only when the melt front has moved across its gating point. These lines form as a result of material flow and solidification during the injection molding process. Knit Line. Possible defect causes. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. Incorrect gate positions cause multiple flow fronts that struggle to merge. Injection molding tool life is the number of production cycles that an injection mold can complete before it needs to be replaced. b. 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. Below, we’ll look at five of the most common types of injection molding defects, and how you can prevent or repair them. Injection molding could develop knit lines if one front cools before it reaches the other. 005 0. Peering into the Flow. 7 in Kobayashi et al. In the process of injection molding, the quality of the mold plays a decisive role in the quality of the finished product. WeInjection molding is the most widely used form of plastics processing worldwide. Waterlines control heat within three diameters of themselves. Learn how to determine it, and the role of SPI Mold Classes. Using a thermoplastic that stays in a. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. Weld lines are formed during cavity filling whenever two separated melt flow font recombine. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. Causes – Remedies. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. We stopped the machine and added glycol to the chiller to a concentration of about 40%. 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. At a theoretical flow distance of 10 mm it represented the measured values well but at a longer distance it underestimated the experimental scale. Knit and meld lines are inherent to plastic. As a result this weld line will be a weak point in this part. Vacuum on the mold does help and many times eliminates the weld line. Injection molding could develop knit lines if one front cools before it reaches the other. You can avoid having any weld lines with cascade injection moulding. 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. 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. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. Part walls thinner than 4mm (0. Weld line. The most important factors to consider during molding are the mold temperature, melt temperature, and injection pressure and speed. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Flow lines are lines or streaks visible on the surface of a part. 2. This can be caused by a poor mold design, or plastic temperatures, mold temperatures, injection speeds, or. Siemens PLM Software. Injection molding is one of the most significant material processing methods for mass production of plastic products. 1) Snake flow lines. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. Injection molding gates occur in different forms, taking distinct sizes and shapes – appearing narrow, wide, tapered, etc. If during the design and development stage, watering is put on the back burner as an ". Each material has a maximum flow length for a given injection pressure and wall thickness — this is known as the flow ratio. By heating the solid material, it is converted into a fluid state with a low resistance to flow. The weld line is then created with a higher flow front temperature and is packed with more pressure. The recommended minimum production volume for injection molding is 500 units. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. This is defined for each material by the length-to-thickness (L/T) ratio of the part. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process.