Look for signs of stickiness or burning. Flow Lines The problem with flow lines is that they. This happens when the molten plastic is injected into the mold cavity and flows around an obstacle such as a pin, hole, or protrusion, and then comes back together. personnel to assess cooling lines in the mold design. There are two types of weld lines, cold and hot weld line. More Control. 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. The main causes for short shots are inappropriate injection pressure and speed. 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. All mold cooling lines must have adequate flow to produce a turbulent flow condition. Increase the injection speed, pressure, or temperature of the material. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. If so, look for an alternative resin. Picture the flow of a liquid resin filled with, for example, glass fiber. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. After an hour of running, the steel temperature stabilized at 78°F. This. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. Inadequate cooling time. 4. Round the corners of the mold where wall thickness increases: This. Flow Lines Defect in Injection Molding Process Flow lines can be defined as linear grooving, or circular ripples, on the surface of a molded part that indicate the. Note: It is applicable to thermoplastic materials only. G. 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. 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. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. They are off tone wavy lines/streaks or patterns in the molded part around the injection ports. Flow lines are a defect in injection molding and can be a significant issue for manufacturers. If you’re a mold designer with one of those vent-depth “rule-of. This method can be helpful in. It affects its structural integrity and exterior appearance. 000 0. The settings and optimization of the injection molding process dictate the geometric precision and mechanical properties of the final. When mapping mold circuits, label each circuit with a number exclusive to the circuit and a supply or return designation (e. INADEQUATE INJECTION PRESSURE. 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. tall, and 0. The proposed method is first applied to the simulation of HDPE melt in a classic Poiseuille flow case, and then two. Sufficient draft is an important part of any mold design, and quick-turn tooling is no exception. 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. industry, to deliver intuitive injection mold-ing simulations embedded in NX. Flow lines are linear marks on the surface of a molded product, which indicate the flow direction of the molten plastic. ABS resin has low thermal deformation temperature, but poor heat resistance. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. The molding process is the leading cause of defects in injection molding parts. Drain the hopper if you were working with 100% regrind, clean if necessary. To further improve productivity, the injection mold was equipped with CCCs to shorten the cooling. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Flow direction is essential for mold mapping because when water flow reverses, poor turbulence and hot spots occur. This is achieved by using the needle valve nozzles to control mould filling so that only one flow front exists at a time. Flow Lines and Flow Marks. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. 2. 2. 5. Plugged or inadequate vents n Clean plugged or dirty vents, particularly those along the parting line. 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 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. 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 part surface was observed in reflected light using optical microscope and the pictures of. Tip #6: Pick Which Molding Defects Are Acceptable. Inadequate mold wall thickness leads to uneven cooling and hindered plastic flow, resulting in weld lines. The weld lines are formed when there is an obstacle in the cavity of the injection mold. Adjustments to injection speeds are the best way to determine which of these two are the specific cause. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 2), the plastic enters the mold at a relatively fast rate and forms the skin. 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. 6 T) as thick as the nominal wall. Kobayashi et al. Fast injection gives you a glossy part, which is what we wanted in this. Description: Flow lines are streaks, patterns, or lines - commonly off-toned in color - that show up on the prototype part as a consequence of the physical path and cooling profile. How to solve flow lines in injection molded products?Injection molding is a heat-transfer process. Lenticular, or Silver Dollar type pigments, are thicker than cornflakes, with a narrower particle size distribution. Strengthening. With a minimum of 1. Flow lines and flow marks. b. Introduction. In injection molding, it is often important to maintain consistent color throughout the part. What Are Flow and Knit Lines? Flow lines are defects that appear as wavy. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Contact us to learn more about SMARTFLOW flowmeters. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. Another tactic to promote more chain entangling at the weld line is to raise the mold temperature 10° C (50° F). Symptoms: Flow lines will typically appear as discolored “bands,” or sometimes “wavy. Injection molding could develop knit lines if one front cools before it reaches the other. Edge Gates. Mold Design. A ‘parting line’ is the line of separation on the plastic part where the two halves of the plastic injection mold meet. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. Weld lines are injection molding defects that can be mitigated by a number of tactics that depend on your part design. 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. The last cause of flow lines may be the operators running your daily operations. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. Non-uniform cooling of mold causes warping, creating internal stresses within the part and resulting in distortions. They are also known as flow lines. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. Reasons and solutions. 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. 7 in Kobayashi et al. They appear as waves or lines, usually of a different color tone from the surrounding area. Increase molten plastic temperature during injection molding. Injection molding is one of the most significant material processing methods for mass production of plastic products. 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. Plastic injection molding is a complex and highly intricate process. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. 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. Conformal cooling channels (CCCs) are a cooling passageway which follows the profile of the mold cavity or core to perform uniform cooling process effectively in the injection molding process. The production cost is closely related to productivity. These properties make it ideal for. The position, length, and angle of weld lines are dependent on the. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow. The Bottom Line. It explored the use of. Polycarbonate is a tough, optically clear or opaque, biocompatible plastic with good thermal resistance. Figure 7 below shows the cooling channels, defined in this case using simple sketch lines. Flow marks mainly occur in the. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. Ensure sufficient cooling time to avoid locking residual stresses into the part. 2. MMT Chats. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. Sink marks are like little craters formed on an injection-molded product. Flow marks occur as circles or lines that occur around the gate. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. The injection molding gate generates heat by dissipation. injection mould simulation at steady flow rate. Adjust resin and cooling temperatures. Here are the top 5 injection molding defects that can occur, and how to solve them: Flow / Weld Lines. Haagh, in Encyclopedia of Materials: Science and Technology, 2001 3 Modeling. 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. 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. Here are some of the most common scenarios for cracks in injection molded parts: Cracks in the Direction of Flow – If the crack develops in the direction of the plastic’s flow into the mold cavity, the cause is molecular orientation. Polycarbonate Injection molding defects. This. Utilize advanced injection molding machines with increased injection speed and pressure. Mold flow analysis is an invaluable skill for injection molding engineers and designers, as it can help them create better products, reduce costs, and increase customer satisfaction. (2011) and Fig. If packing around a detail is causing cracks/ shorts/burns on the knit line, reduce the heat to improve knit line seal and strength. flow rate, in turn, causes the heat transfer effi ciency of the cooling cha nnels to vary from one. , 1 IN, 1 OUT, 2 IN, 2 OUT). These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. These defects include the following: 1. 060 and 0. 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. Burn Marks. Flow lines. This review process showcases a company’s technical expertise, the capabilities of its design team, and overall quality. Flow lines. The co-simulation of mold flow and structure plays an important role in the design of injection molded fiber-reinforced thermoplastic (FRT) parts. Learn how to determine it, and the role of SPI Mold Classes. (3) Improving the surface gloss of the product. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. Chart 1: Diameter versus turbulent flow. 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. We will now look at the problem you are likely to encounter and how to fix them. In spite of its cosmetic attributes, a bad knit line can significantly. 10 in Nguyen-Chung et al. The mold should have a fine matte finish to allow air to vent quickly and the parison to conform to the mold surface while it is still hot. However, the weld line may not continue throughout the flow. On the contrary, for the conformal cooling. 1 Caused By The Quality of Injection Mold. This results in a much greater amount of vent flow area for the compressed air to exhaust through, and still protects the corners. 10(a) (please see Fig. 030 0. 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). FIG 1 Depiction of fountain flow. Help prevent warping with these measures: Raise the mold or material cylinder temperature. They are evidence of nonuniformity in flow pattern upon entry into the mold. May 17, 2023. Weld lines appear as a result of the flow of molten plastic during the injection molding process. If you experience flash on your injection blow molding products, consider redesigning a worn out or faulty 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. They follow the flow of the molten resin from the gate along the finished part. We stopped the machine and added glycol to the chiller to a concentration of about 40%. 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. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Flow lines are surface irregularities, wavy patterns, or a rippled effect, perhaps of a slightly different color, that can appear in injection molded parts. or too much shear heat burning the material prior to injection. The materials used in the plastic injection molding process can vary in rigidity and pliability, among other differentiating characteristics. The Table 2 categorically reports Melt Temperature, Injection Pressure and Injection Speed are the main contributors in the defects such as the short-shot, weld-lines, flow marks, burn-marks etc. Flow lines or marks appear as banded discolouration on the surface. Thereby creating localized pressure within the mold. Weld lines are formed during cavity filling whenever two separated melt flow font recombine. 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. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. 0010 in. Basic Repairs for Warping. We restarted the mold at the same coolant flow rate and temperature. Mold Flow - Position ribs such that the plastic has an optimal flow path. When trying to establish process control in plastic injection, watering the tool is a key variable that is often overlooked. 3) Poor Preventative Maintenance. Shear; There are two causes of splay brought on by shear. By contrast, a slow injection speed will give you a matte finish and a cold mold, such as 50F, will give you a more flexible part. 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. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. 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. While some molds or inserts have simple, straightforward cooling circuits, many have multiple circuits of various sizes and configurations. This software simulation can show how a resin will fill the mold during the injection molding process. When the mold is full, the machine continues its injection pressure and compresses the plastic. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. 31″) will require more. Reducing the dimensions of the runner system. Adjust the design for the flow pattern to be a single source flow. If the mold itself has cracks or defects, the finished product will also have various problems. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. Spatter lines formed on the surface of the plastic along the direction of melt flow are called silver marks. injection molding. A meld line occurs when two moving melt fronts converge and flow parallel to each other. When the melt enters the cavity quickly, it is necessary to discharge the air quickly. A. 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. 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. Weld lines may appear like seams or scratches, but that is not what they are. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. Fig. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Mold Venting. 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. Flow Lines. See. They commonly occur when there is a large variation between cooling speeds of sections of the material as it flows through the mold. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. Email Sales@Aberdeentech. 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. FLOW LINE – A mark on a molded piece made by the meeting of two flow fronts during molding. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. Facebook. Clean all parting line and core vents. Weld lines have been one of the common defects puzzling the injection molding industry. The best method of venting this type of part (Fig. Injection molding tool life is the number of production cycles that an injection mold can complete before it needs to be replaced. Vertical walls, meaning those part surfaces parallel to the direction of mold operation, should have a minimum draft angle of a 1/2 degree, and 2 degrees is even better; heavily textured surfaces may require 5 degrees or. It is widely used in various industry sectors, and its products are ubiquitous in our daily life. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. I’ve been writing about plastic flow simulation since 1984, and I. To explore the formation of weld lines in injection molding, a flow model based on viscoelastic constitutive equation is presented in this article to predict and evaluate of weld lines location. (All Illustrations: S. 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. "Design and Mould Flow Analysis of Injection Mould for Connecting Link," International Journal on Emerging Technologies, vol. 1) Snake flow lines. This means that the skin of the part is always formed by. FIG 1 Depiction of fountain flow. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. 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. On a small four-cavity tool, the part had a U-shaped notch in the center. 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. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. This article continues our series of troubleshooting reports from one of the leading on-the-spot problem solvers in the molding industry. Flow lines result from uneven cooling of the plastic within the mold. Acetal is a funny material in how it reacts to certain injection speeds and mold temperatures. Vacuum Voids. ” FLOW MARKS – Wavy surface appearance on a molded object caused by improper flow of the material into the mold. Let’s take a look at some defects that are caused purely due to faults in the injection molding process. Flow lines can be defined as linear grooving, or circular ripples, on the surface of a molded part that indicate the direction of material flow within the cavity of the mold. If it’s too thin or small, material flow, pressure, and temperature will. They usually are a slightly different color than the rest of the piece, and typically occur on more narrow sections of the molded item. Flow marks can be caused by any or all of the following factors: Slow melt injection speed. This action could indicate that one portion of the plastic flow will move more quickly than the other. Countermeasures to Injection. Ensure sufficient cooling time to avoid locking residual stresses into the part. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. The accompanying table lists the flow rates for various barrel diameters at various injection velocities. That’s an easy calculation to perform. 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. Shear; There are two causes of splay brought on by shear. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. These defects are not visible, like small. Fixing Process Variables That Can Cause Flash. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Reduce the temperature of the mold and plastic being injected. It is generally a three phase process comprising filling, packing and cooling phases. Increase the mold temperature. There are important differences between an injection mold sprue and its runner system. Faster injection increases pressure in front of a flow front. An improper flow rate and injection speed also cause flow marks. Novel Nozzle Tip Prevents Stringing, Saving Molds & Cycle Time. Plastic is injected into a mold at a specific rate of flow—typically in. In any case, you’d prefer to create polycarbonate parts of different sizes; then this is the best technique that you need to use. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. as a stand-alone, wholly owned. Give a good distance between mold gates and. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. The Smartflow Reynolds Number Calculator is provided as a service to the injection molding community as an easy-to-use online resource. 5 to 2. How to recognize, prevent, and counteract flow lines defects in injection molding? Learn flawless products from professional manufacturers. The formation process of weld lines can be described as follows: Injection moulding (U. This is defined for each material by the length-to-thickness (L/T) ratio of the part. Once you have a cool shell formed the rest of the mold entering absorbs heat from the layer next to the wall. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. In the process of injection molding, the quality of the mold plays a decisive role in the quality of the finished product. 2). Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Flow marks, also known as flow lines, are molding defects that can occur in the manufacturing process of injection molding. Leadtime Leader 2024. 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. Energy use by thermoplastics injection molding machines is estimated to result in global CO 2 emissions in the order of 80 million metric tons annually. 2) Material Changes. Several factors can contribute to shrinkage in injection moulding, including material, part design, mould design and processing parameters. The formation process of weld lines can be described as. Plastic is injected into a mold at a specific rate of flow—typically in. In this lesson we will focus on the meld and weld lines. Plastic injection molding is the industry’s most common way to manufacture parts. When trying to establish process control in plastic injection, watering the tool is a key variable that is often overlooked. According to the design requirements of the back shell of mobile phone and the performance of materials, ABS is selected as the raw material for injection molding in consideration of economy [ 8 ]. 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. (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. 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. They are typically the same color as the part but are a different tone. Remedies: Raise the temperature of the mold or molten plastic. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. [22]. Turbulent Flow IS Always Better. The edge gate is the most popular and straightforward injection mold gate design. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. 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. Most flow lines don’t impact the functio…Flow lines are a defect in injection molding and can be a significant issue for manufacturers. Vary injection speed, screw rpm, and backpressure. Use high-quality, temperature-controlled materials for better mold filling. Ensure that injection pressures are appropriate (under 70 MPa [10,000 psi]). NX Mold Flow Analysis. Cascade Moulding Avoids Weld Lines. 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. Flow lines are. 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. The process involves the injection of heated, liquefied plastic into a temperature-controlled mold under high pressure. Learn more. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. 3 the path lines of selected material elements can be observed which are. Flow Rate. The Analysis and countermeasures of flow lines in injection molded products Read more. What it is:Jan 04, 1999. He is currently a tooling manager for a large, multi. Minimum turbulent flow would be 12-14 GPM, while numbers in the 20’s would be identified as an excellent flow rate. Our glossary of terms provides definitions for a wide range of injection molding terms. Water cooling pumps coolant through lines on the outside of the mold cavity. By heating the solid material, it is converted into a fluid state with a low resistance to flow. Improper gate design. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. 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. Heat: Too much heat can have an appearance similar to moisture splay. The formation of weld lines and their location along the flow path is a well-studied phenomenon in conventional injection molding; however, only a few papers are devoted to micro-injection molding [11,13,14,15,16]. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. Mold flow analysis is a powerful tool for optimizing the design and performance of injection molding processes. These data were obtained from many andGenerally, injection molding resins are characterized as having medium, high or very high flow. They are best described as "off tone" wavy lines/streaks or patterns in the molded part around the injection ports. Part walls thinner than 4mm (0. Mold is not vented properly causing slow flow at knit lines. The flow fronts at different times (Fig. Typically, flow lines are caused by the liquid plastic cooling at different rates. Finite differences method offers strong consent for methodological solutions. One way to reduce the changes in speed of the flow front is to tailor the injection-speed profile. 0 is leading the productivity and efficiency of companies to minimize scrap rates and strive for zero-defect production, especially in the injection molding industry. The gate in injection molding is an essential component that directly connects to the plastic part and controls the flow of melted plastic resin into the cavity. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. 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. Known as thermolators, water cooling systems require a cooling source such as a tower. After exhaustive research, testing and pilot-scale demonstration, the team developed a breakthrough new technology utilizing low constant injection pressure. This steel section retained heat, not allowing the plastic to cool and requiring an excessively long cycle time of 40 sec. 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. Flow lines appear like off-tone patterns on the surface of your finished parts. google-site-verification: google03af4f4fcb62a9d5. 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. Higher numbers assure that water flow is adequate, and that turbulent flow is at an acceptable level. 750 in. 120 in. These lines. Apart from the shape, it is important to design ribs for optimal mold performance. 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. Reduce the injection pressure. Injection molding has been the most popular method for making plastic products due to. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. [1]#TROUBLESHOOTING #FLOWLINES #INJECTIONMOLDINGStudy more about troubleshooting flow lines : lines occur when two flow fronts meet and fuse together in the injection molding process. Flow lines arise from variations in the flow of molten plastic material as it fills the mold. This can be achieved by connecting ribs to each other. thick, 0. Select a plastic that is less prone to shrinkage. 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. 5mm (0. Flow Line Phenomenon: Surface defect in which wavy streaks form like a ripple centered around the gate. 160"). Increasing pack or hold pressure helps to eliminate low-pressure conditions at the weld line. 2. Flow lines. Flow marks in injection molding can be avoided if adequate measures are taken. The edge gate is the most popular and straightforward injection mold gate design. Possible Causes & Remedies: Machine Cause. Where wall thickness increases, round the corners of the mold in those regions. 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. 750 in. PROBLEM: FLASH ON PARTING LINE There are a few key reasons why flash appears on the parting line of a part. . Mold flow analysis is also used to help designers locate difficult spots to fill within the mold. Designers can easily set up and perform analysis with only a few clicks. Cracking is commonly seen at the weld line area but sometimes on the entire surface.