” FLOW MARKS – Wavy surface appearance on a molded object caused by improper flow of the material into the mold. Adjustments to injection speeds are the best way to determine which of these two are the specific cause. This may involve adjusting the temperature and pressure of the mold, using different mold materials, or adjusting the injection speed or cycle time. Manifesting as wavy lines or streaks on the surface of the molding, flow lines generally occur when molten material flows. injection mould simulation at steady flow rate. Flow marks, also known as flow lines or weld lines, are common defects that can occur in plastic molded parts. During plastic injection molding, molten material flows through an opening called a gate and fills a mold cavity. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. The weld line is then created with a higher flow front temperature and is packed with more pressure. Certain injection molding processes may not be effective for the production of some parts. 750 in. How a mold is watered is key to a processor's goal of consistency. Aberdeen Technolgies makes the mold manufacturing process for injection molding. 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. flow rate, in turn, causes the heat transfer effi ciency of the cooling cha nnels to vary from one. The most important factors to consider during molding are the mold temperature, melt temperature, and injection pressure and speed. All mold cooling lines must have adequate flow to produce a turbulent flow condition. 2) Material Changes. Secondly, it is easy to form obvious. The plastic pellets must be. A mark on a molded piece made by the meeting of two flow fronts during molding. Another solution may be to pull a vacuum on the mold just before injection. Look for signs of stickiness or burning. thick, 0. 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. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. As these flow fronts come together. 1 Caused By The Quality of Injection Mold. They are visible on one side of the parts. 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. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Flow lines. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Weld lines have been one of the common defects puzzling the injection molding industry. 4. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. • Reduce runner dimensions and maintain the same flow rate. 1, pp. The polymer material is melted by the heat from the heaters and viscous heating due to the screw rotation in the plasticization stage as shown in Fig. If the mold itself has cracks or defects, the finished product will also have various problems. Flow rates and a fluid are input to the cooling channels,. SMARTFLOW ® flowmeters effectively and accurately measure flow rate. 0030 in. The streaks form from plastic in the mold overlapping with plastic following it. Tatjana Geminger, Stefan Jarka, in Specialized Injection Molding Techniques, 2016. 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. Weld lines are a kind of Achilles heel of plastics. Flow marks, also known as flow lines, are molding defects that occur in the manufacturing process of injection molding. Weld Lines. html. 5. Available with a number of options including thermometers, pressure gauges, liquid-filled pressure gauges and quick change socket and plug. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. Non-uniform cooling of mold causes warping, creating internal stresses within the part and resulting in distortions. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. This action could indicate that one portion of the plastic flow will move more quickly than the other. Wavy lines are another feature of weld lines. Depending on the resin, resin temperature, mold temperature, and filling. This allows the melt to keep enough velocity to ensure proper filing. Minimum turbulent flow would be 12-14 GPM, while numbers in the 20’s would be identified as an excellent flow rate. As a result this weld line will be a weak point in this part. 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. injection molding. A knit line may be unnoticeable or may look like a crack. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. 6. The article has been structured just for you to gain an understanding of the same so that when you plan to buy plastic injection molding, you do understand what it means to do so. Edge Gates. 2). More viscous amorphous materials, such as PC, TPU or PEEK, can have a recommended vent depth range from 0. 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. It is widely used in various industry sectors, and its products are ubiquitous in our daily life. Kobayashi et al. This injection molding defect appears as black or rust-colored discoloration on the molded part's surface or edge. Increase the size of the gate and reduce the thickness of the walls of the molded part. with a characteristic length χ 0 =0. Investigate the mold for signs that a water leak is present, and correct the condition. Polycarbonate injection molding is a process that is used to create polycarbonate products at high production volumes and at a low cost per part by injecting melted plastic pellets into a mold. On larger parts where knit lines or flow lines are a concern, you can use sequential valve gates to control the flow and move the knit lines. The following are the main elements of a gating system designed for injection molding. The best method of venting this type of part (Fig. Select a plastic that is less prone to shrinkage. These lines. The process involves the injection of heated, liquefied plastic into a temperature-controlled mold under high pressure. Errors like these manifest when processing is done incorrectly. Vents have three components. 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 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. Heat Input and Cooling Calculator for Injection Molding. Weld line. Known as thermolators,. They are also known as flow lines. 7. That’s an easy calculation to perform. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. Shear; There are two causes of splay brought on by shear. They are off tone wavy lines/streaks or patterns in the molded part around the injection ports. Increase the injection speed, pressure, or temperature of the material. 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. Precise control of resin flow, pressure and temperature is critical. Impurities in the resin will prevent a smooth flow through the mold. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. Excess Mold Release Poor mold design, including inappropriate mold wall thickness and faulty gate placements, is a common cause of weld line formation in injection molding. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. 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. Flow marks are caused by a variety of factors in the injection molding making technology, and they happen at the gate. 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. Utilize hot. The co-simulation of mold flow and structure plays an important role in the design of injection molded fiber-reinforced thermoplastic (FRT) parts. reduce the ability to positively influence the strength. Too hot and the plastic will start to degrade, but too low and flow marks increase. The barrel temperature is too high. The steel that cored out and created the notch was very thin—roughly 0. If the melt speed of each gate entering the cavity is inconsistent, it is easy to cause weld lines at the intersection. Reduce the injection pressure to prevent overpacking at the gate. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Thickness –Make the bottom of the boss 60% (0. Plastic Injection Molding Process. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. The weld‐lines are undesirable from both aesthetic and functional points of view and their effect. 005 0. 6 T) as thick as the nominal wall. Expand. or too much shear heat burning the material prior to injection. How a mold is watered is key to a processor's goal of consistency. Contact us to learn more about SMARTFLOW flowmeters. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. For example, baffles require water to flow in a. All of these can slow down the plastic flow, causing it to cool too quickly and lose pressure, both of which are the most likely reasons for weld lines in injection molding. Learn how to troubleshoot weld lines in injection molding. Where wall thickness increases, round the corners of the mold in those regions. Kulkarni) During the fill phase (Fig. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. The material is poured into a mold, which shapes the size and looks of the article. Incorrect gate positions cause multiple flow fronts that struggle to merge seamlessly. This most often occurs when you have a core or shutoff. thick, 0. Add or increase vents as needed. 31″) will require more. Flow lines were created during injection moulding process. (1. 3. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Inadequate mold wall thickness leads to uneven cooling and hindered plastic flow, resulting in weld lines. The molding process is the leading cause of defects in injection molding parts. The edge gate is the most popular and straightforward injection mold gate design. In narrow fields, a limited amount of molten liquid can solidify and block the flow. . Investigate the mold for signs that a water leak is present, and correct the condition. The recommended minimum production volume for injection molding is 500 units. 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. (3) Improving the surface gloss of the product. This method can be helpful in. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. An on-line compounding injection molding machine, incorporating the co-rotating, intermeshing twin-screw extruder and a reciprocating screw injection molding machine fitted with the oscillating pressure valve, has been developed. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no. How weld lines form. 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. However, the weld line may not continue throughout the flow. The formation process of weld lines can be described as follows: Injection moulding (U. Injection molding is one of the most significant material processing methods for mass production of plastic products. 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. 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. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Flow Lines. One exception: ribs should be about 50. Thickness – Make the ribs 50% to 60% (0. These streaks or patterns can affect a part's aesthetics, value, and overall quality. Flow Lines. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. 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. Circuiting Done Right. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. They are typically the same color as the part but are a different tone. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. By heating the solid material, it is converted into a fluid state with a low resistance to flow. In the process of injection molding, the quality of the mold plays a decisive role in the quality of the finished product. During the injection molding process, one of the most important requirements of the mold is to deliver melt from the barrel to the cavity. Lower speeds allow gas more time to escape through vents. Flow Lines. 0010 in. With a minimum of 1. Injection Molding of Multimaterial Systems. In terms of viscosity, higher heat equals faster flow and lower heat equals slower flow. Another tactic to promote more chain entangling at the weld line is to raise the mold temperature 10° C (50° F). 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. (1998) for clear photographs. Plastic is injected into a mold at a specific rate of flow—typically in. ³/sec. Bubbles are caused by melting flow fronts colliding in a mold cavity. Plastic Defect # 2: Flow Lines. Bob Hatch is manager of technical service and customer support for Prime Alliance, the Des Moines-based resin distributor. This can be accomplished by reducing the substance’s viscosity. Flow marks mainly occur in the. There are important differences between an injection mold sprue and its runner system. 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. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. 5 to 2. This defect compromises aesthetics. This is a video excerpt from our Problems & Solutions Course - Jetting. Flow lines result from uneven cooling of the plastic within the mold. They are the result of fundamental physical effects taking place inside of the mold. com. 4 Injection Speed. There are three stages of flow – laminar, transient and turbulent. 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. In injection molding weld lines are formed whenever two flow fronts are joined. 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. While the sprue is milled through the entire thickness of the injection mold, passing from the outer surface to the parting line (where the two mold halves meet), the runners are comparatively shallow channels milled into the face of one or two mold halves. 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. 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. Ensure sufficient cooling time to avoid locking residual stresses into the part. Common injection Mold Flow Lines. Flow lines are linear marks on the surface of a molded product, which indicate the flow direction of the molten plastic. Weld lines have been one of the common defects puzzling the injection molding industry. Within more basic plastic part design plans this plane can be a simple, flat surface, but it is often a complex form that. Bottom, PC with random structure. 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. Causes – Remedies. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Insufficient injection pressure or time. These defects include the following: 1. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. Listed below are some factors to consider when designing ribs for injection-molded parts. 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. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. Mold Flow Analysis. 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. Jetting occurs in a molded component when molten material is injected into the mold cavity and starts solidifying before it fills the cavity. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. 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. 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. wide. to 0. In some areas, the option is evident, while in others, it. The weld lines are formed when there is an obstacle in the cavity of the injection mold. This slight depression is a tiny line called the weld line or knit line. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. The injection molding gate generates heat by dissipation. Increase injection speeds and pressure to ensure the cavities are filled properly. Weld lines are formed during cavity filling whenever two separated melt flow font recombine. This study focus on the formation of weld lines of molten polypropylene and. Walls thicker than 8mm (0. 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. One of the things that can compromise an injection molded part is a weld line, also called a knit line. Raise the mold temperature, maintain a high. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding 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. 1．Mold Temperature Too Low. Inadequate mold wall thickness leads to uneven cooling and hindered plastic flow, resulting in weld lines. So when two. Consider the following examples of cooling channel configurations in P20 mold steel with a water line diameter (D) of 11. On-Line Solutions To Injection Molding Problems. Allows you to accommodate a variety of part sizes. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. If the mold temperature is too low, the material temperature will drop very fast, so the injection pressure and the holding pressure will not be high enough to press the solidified layer against the mold surface, thus leaving flow lines along the melt flow direction. Fast injection gives you a glossy part, which is what we wanted in this. Quality concerns in injection-molded materials can vary fr. Weld lines have been one of the common defects puzzling the injection molding industry. 4, no. Features such as sharp corners or undercuts can. The location of the crack can tell us a lot about its specific cause. FIG 1 Depiction of fountain flow. 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. 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. personnel to assess cooling lines in the mold design. In this example, the flow ratio is 80 (10 Fig 2 – The spiral flow chart provides data about maximum flow length based on several Monday, 01 December 2014 Page 1 of 2Automatic in-line process quality control plays a crucial role to enhance production efficiency in the injection molding industry. 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. The thermo-rheological findings were used to investigate the sources of weld line weakness. 10(a) (please see Fig. They appear around holes or seams of an injection molded part, and some may call them “flow lines” or “weld lines”. 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. 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. This can be achieved by connecting ribs to each other. 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. 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. Injection molding can be performed with only one of these materials like glass, plastics, etc. Contact the material supplier for help in deciding which flow rate should be used for a specific application. These streaks or patterns can affect a part's aesthetics, value, and. As the polymer resin is injected into a mold, it flows through all parts of the mold. When mapping mold circuits, label each circuit with a number exclusive to the circuit and a supply or return designation (e. If necessary, the mold designer may simulate the flow of solidification of resin using an injection molding simulation program. This continues until the weld lines in plastic injection molding disappear. 020 0. New design is said to eliminate mold damage from nozzle stringing or work-arounds that slow cycles. They again get resolidified along the surface. Poor mold surface n Refinish a poor or worn mold surface. Flow Lines particles, during injection molding, will produce visible flow and weld lines. 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. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. Typically, flow lines are caused by the liquid plastic cooling at different rates. Ensure sufficient cooling time to avoid locking residual stresses into the part. Impurity. Occasionally, the molded part has. PROBLEM: FLASH ON PARTING LINE There are a few key reasons why flash appears on the parting line of a part. 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. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. 3. It explored the use of. This is achieved by using the needle valve nozzles to control mould filling so that only one flow front exists at a time. Knit Line. 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. Possible Sources of Weld/Knit Lines: Temperature from the injection molding machine, runners, and/or the mold itself in order to ensure the plastic resin flows properly; Insufficient pressure resulting in the flow fronts not being merged back together with strong enough; Mold design, especially location of gates and runners impacting the resin flow Knit lines are formed in injection molding when two flow fronts meet in the middle of a part (a line where two sides of the plastic are “knit” together). This results in a much greater amount of vent flow area for the compressed air to exhaust through, and still protects the corners. Burn Marks. On average, larger injection molding machinery can cost from $50,000-$200,000 or more. 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. as a stand-alone, wholly owned. Faster injection increases pressure in front of a flow front. On thicker sections of the mold, there may be sinks caused by bosses designed into the backside of the surface. It can be difficult to determine what is truly splay, as its appearance is very similar to other defects. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. By using proven methods for cooling line design, warp and cooling time are minimized. Let’s review some methods to prevent flow and knit lines in plastic injection molding. Below are ways through which you can remove and prevent flow lines; a. One of the best ways to determine part shrinkage for complex components is with a mold flow analysis. Take these steps to avoid knit lines. This review process showcases a company’s technical expertise, the capabilities of its design team, and overall quality. They can be unsightly and unpleasant in high-end sunglasses. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. 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. The plant water system is a critical component of an injection molding facility. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. That means that for each injection pressure, the flow length for a mould temperature of 80°C and 180°C shows a constant difference of ca. Flow lines appear as a wavy pattern on the surface of your plastic parts. Mold Flow - Position ribs such that the plastic has an optimal flow path. Mold flow analysis is a powerful tool for optimizing the design and performance of injection molding processes. In the process of injection molding, the quality of the mold plays a decisive role in the quality of the finished product. 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. 0005 in. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Remedies: Increasing the injection pressure will force the molten plastic against the mold cavity. Otherwise, the heat transfer of. Turbulent Flow IS Always Better. While some molds or inserts have simple, straightforward cooling circuits, many have multiple circuits of various sizes and configurations. The formation process of weld lines can be described as. Mold venting is critical to the quality and consistency of the finished part. If larger gates are used, expect a longer molding cycle time. Definition: Off-tone streaks, patterns or lines that appear on parts. As a result, the lower degree of stress when gating with valve gate systems becomes relevant. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. Injection Molding works with molten fluid created by heating the plastic granules above their melting point. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. The position, length, and angle of weld lines are dependent on the. Increase the injection speed. • Move injection locations to make flow fronts meet more obliquely, turning the weld line into a meld line. 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. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. They appear as waves or lines, usually of a different color tone from the surrounding area. 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. Certain injection molding processes may not be effective for the production of some parts. In the development of our calculator. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Address 272 Commonwealth Drive, Carol Stream, IL 60188. You can avoid having any weld lines with cascade injection moulding. Injection molded parts can have several different issues. The formation process of weld lines can be described as. When the melt enters the cavity quickly, it is necessary to discharge the air quickly. ” 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. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. Weld lines are usually pointed out as the weak region in molded parts. 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. These benzene rings also increase the viscosity, reduce shrink rate, and increase strength with the exception of knit and/or meld lines. 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. Voids . Weld lines are similar to flow lines, but they appear similar to a plane than a line when compared to flow lines. Finite differences method offers strong consent for methodological solutions. Add more cooling circuits. When trying to establish process control in plastic injection, watering the tool is a key variable that is often overlooked. Sink Marks. The recommended minimum production volume for injection molding is 500 units. They also can appear as ring-shaped patterns near the entry points of the mold. This is often a sign that injection speed and/or pressure are.