In the plastic injection moulding industry, we work with materials that are by-products of oil refinement and moulds made of metal casting, so our terminology is bound to be at least slightly confusing. Learn about prevention methods and references. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Mold flow analysis is a software-enabled process that. In this lesson we will focus on the meld and weld lines. They can be unsightly and unpleasant in high-end sunglasses. ³/sec. 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. Flow marks won. Knit and Meld lines are inherent to plastic injection. Adjust the design for the flow pattern to be a single source flow. Weld lines are a kind of Achilles heel of plastics. Different gate sizes and locations using flow simulation have been detected for defects reduction such as weld lines and air traps, air traps and warpage can be managed by varying process parameters [17]. Molds for investment casting are more accurate and have fewer defects, thanks to flow control over wax injection. with a characteristic length χ 0 =0. Flow rates and a fluid are input to the cooling channels,. Turbulent Flow Rate Calculator. Flow marks can be caused by any or all of the following factors: Slow melt injection speed. 008 to 0. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. If the melt speed of each gate entering the cavity is inconsistent, it is easy to cause weld lines at the intersection. This “inside-out” flow of the plastic mimics the flow in a water fountain, therefore it is called fountain flow. Weld lines are among the most critical structural defects in parts made by the injection molding of fiber-reinforced thermoplastics, explained Sirmax in a press release. The proposed method is first applied to the simulation of HDPE melt in a classic Poiseuille flow case, and then two. Flow lines or marks appear as banded discolouration on the surface. Too hot and the plastic will start to degrade, but too low and flow marks increase. Do not keep the hopper full; hand-feed if necessary. Plastic injection molding is the industry’s most common way to manufacture parts. 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. 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. Flow marks mainly occur in the. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. The co-simulation of mold flow and structure plays an important role in the design of injection molded fiber-reinforced thermoplastic (FRT) parts. Materials that have physical fillers like glass, carbon, metal flakes, etc. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. After an hour of running, the steel temperature stabilized at 78°F. Flow lines are lines or streaks visible on the surface of a part. 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. This continues until the weld lines in plastic injection molding disappear. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). These are typically found near the narrow sections of the mould gate and can. 1) Snake flow 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 melting temperature is 217–237 °C, and the thermal. plastic mold venting. For the measurement of the crystallinity a DSC analysis was performed. Ensure that injection pressures are appropriate (under 70 MPa [10,000 psi]). If a mold cavity has a significant flow length-to-thickness ratio, the material should have a low enough viscosity to enable a continuous flow. Peering into the Flow. Just multiply the area of the barrel × the injection velocity. Heat: Too much heat can have an appearance similar to moisture splay. Phone (630) 665-8590. It can be difficult to determine what is truly splay, as its appearance is very similar to other defects. It can also aid in material selection since fill. It explored the use of. Edge Gates. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. Countermeasures to Injection. Reasons and solutions. This results in an incomplete part at the end of injection molding. 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. This results in a much greater amount of vent flow area for the compressed air to exhaust through, and still protects the corners. Optimize the runner system and locate gates near the thin walls. Avoid Drag in Molded Parts. Unexpected flow lines, so-called tear drops, occur. Fictiv provides you with DFM feedback so that you can minimize injection molding defects. Increase the size of the gate and reduce the thickness of the walls of the molded part. A ‘parting line’ is the line of separation on the plastic part where the two halves of the plastic injection mold meet. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. While some molds or inserts have simple, straightforward cooling circuits, many have multiple circuits of various sizes and configurations. Reduce the injection pressure to prevent overpacking at the gate. Injection molding is a great technology for finished production on a massive scale. 3,000 ton machines can cost $700,000. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no. ” FLOW MARKS – Wavy surface appearance on a molded object caused by improper flow of the material into the mold. Non-uniform cooling of mold causes warping, creating internal stresses within the part and resulting in distortions. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. Cascade Moulding Avoids Weld Lines. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. The edge gate is the most popular and straightforward injection mold gate design. This defect compromises aesthetics. 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. 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. 5. Flow lines and weld lines are lines or streaks in the final molded part. This can be achieved by connecting ribs to each other. Heat: Too much heat can have an appearance similar to moisture splay. 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. They commonly occur when there is a large variation between cooling speeds of sections of the material as it flows through the mold. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. Lenticular, or Silver Dollar type pigments, are thicker than cornflakes, with a narrower particle size distribution. Allows you to accommodate a variety of part sizes. 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. Flow direction is essential for mold mapping because when water flow reverses, poor turbulence and hot spots occur. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. Melt delivery management has a major impact on final part quality and the ultimate success of the production line. Consider the following examples of cooling channel configurations in P20 mold steel with a water line diameter (D) of 11. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. 0010 in. What it is:Jan 04, 1999. At some point in time, it can no. One exception: ribs should be about 50. It is widely used in various industry sectors, and its products are ubiquitous in our daily life. 750 in. Flow lines are a defect in injection molding and can be a significant issue for manufacturers. (All Illustrations: S. If the mold itself has cracks or defects, the finished product will also have various problems. Flow Lines particles, during injection molding, will produce visible flow and weld lines. Weld Lines. Water cooling pumps coolant through lines on the outside of the mold cavity. In terms of viscosity, higher heat equals faster flow and lower heat equals slower flow. 2), the plastic enters the mold at a relatively fast rate and forms the skin. V. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. 4, no. 005 0. Investigate the mold for signs that a water leak is present, and correct the condition. Cooling lines impact. 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. 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. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. 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 a small four-cavity tool, the part had a U-shaped notch in the center. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. Shear; There are two causes of splay brought on by shear. 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. low of a melting time will cause flow lines to occur. 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. 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. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Plastic is injected into a mold at a specific rate of flow—typically in. The leading edge of the flow, or the melt. If packing around a detail is causing cracks/ shorts/burns on the knit line, reduce the heat to improve knit line seal and strength. (4) It can improve the strength of the fusion line. 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). 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. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. This depends on a. Bottom, PC with random structure. They usually are a slightly different color than the rest of the piece, and typically occur on more narrow sections of the molded item. Tip #6: Pick Which Molding Defects Are Acceptable. The importance of understanding the causes of flow lines is critical for preventing them from occurring during the injection molding process. Figure 7 below shows the cooling channels, defined in this case using simple sketch lines. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. 5° draft to each side of the rib. The production cost is closely related to productivity. 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. These lines form as a result of material flow and solidification during the injection molding process. Before his present assignment, Bob managed a molding operation for 25. 18/06/2021. Part Design: One of the important rules in part design is to have flow lengths that will let the plastic be fluid enough not just to flow into the end of fill but also until all the packing of the part is achieved. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. A poorly designed or maintained water-cooling system can have a serious impact on production efficiency and cause many maintenance issues. A significant part of that is the cooling design, where there are many things to consider. Check that the machine is creating enough clamping force to keep the mold halves together. [22]. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Midland, MI. 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. google-site-verification: google03af4f4fcb62a9d5. In injection molding, it is often important to maintain consistent color throughout the part. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Thin walls often increase the pressure required to fill the part, and. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. These marks remain and are visible in the cooled product. 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 ]. Flow speed too fast or too slow. This. 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. The co-simulation of mold flow and structure plays an important role in the design of injection molded fiber-reinforced thermoplastic (FRT) parts. It affects its structural integrity and exterior appearance. Injection molding is one of the most significant material processing methods for mass production of plastic products. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. 100 to 0. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. 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. For runny, non-viscous, crystalline resins such as nylon, PE, or PP, the recommended vent depth can range from 0. 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. The speed of an injection moldingRepeat the two previous steps two or three times, starving the screw periodically to allow the screw to rotate without building a shot. This software simulation can show how a resin will fill the mold during the injection molding process. Flow lines are aesthetic defects that occur on plastic products. com. In Fig. Effects of mold temperature and pressure on shrinkage 0. Walls thicker than 8mm (0. The part surface was observed in reflected light using optical microscope and the pictures of. Improper gate design. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. 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. Lastly, you can only acquire the benefits of parting lines in injection molding during plastic production if you design the parting line correctly. Molds gain streaks through molten plastic cooling and solidifying at different rates. The main causes for short shots are inappropriate injection pressure and speed. Manifesting as wavy lines or streaks on the surface of the molding, flow lines generally occur when molten material flows. 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. Burn Marks. After an hour of running, the steel temperature stabilized at 78°F. The most important factors to consider during molding are the mold temperature, melt temperature, and injection pressure and speed. Its popularity is typified by the numerous products produced in this way at the present time. We will now look at the problem you are likely to encounter and how to fix them. mold temperature con-trol fluid flow in a mold, either laminar or turbulent, is by a dimensionless number. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. The settings and optimization of the injection molding process dictate the geometric precision and mechanical properties of the final. Select a plastic that is less prone to shrinkage. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Also called “Weld Line. There are three stages of flow – laminar, transient and turbulent. The formation process of weld lines can be described as. The model of polymer melting is fundamental for the development of. 030 0. Flow Lines. These lines. 1 – In plastic injection molding, the flow ratio is the distance molten plastic must travel, divided by the wall thickness of the part. Weld lines may appear like seams or scratches,. Unraveling Flow Lines. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. Introduction. 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. However, the weld line may not continue throughout the flow. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. Help prevent warping with these measures: Raise the mold or material cylinder temperature. The recommended minimum production volume for injection molding is 500 units. Also called “Weld Line. 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. This design is deliberate in order to help the mold. The Bottom Line. Solution: Utilize a material that has the stiffest flow possible without causing non-fill. An improper flow rate and injection speed also cause flow marks. Molds separate into two sides at a parting line, the A side , and the B side , to permit the part to be extracted. The moldability validation and flow analysis tools enable you to iden-tify and correct potential injection molding problems as you design the product. Additionally, you can get our free Design Cube, which will provide a physical aid to help understand how knit lines form as well as other injection molding design considerations. Acetal is a funny material in how it reacts to certain injection speeds and mold temperatures. Meld and knit lines are actually both different types of weld lines. Siemens PLM Software. Draft – Add 0. Flow lines result from uneven cooling of the plastic within the mold. Impurity. Round the corners of the mold where wall thickness increases to help keep flow rate consistent and prevent 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. ABS resin has low thermal deformation temperature, but poor heat resistance. Accept All. Flow lines or flow marks are a common visual defect in injection molding. The flow rate should ensure the material does not lose its. In any case, you’d prefer to create polycarbonate parts of different sizes; then this is the best technique that you need to use. This slight depression is a tiny line called the weld line or knit line. Lower speeds allow gas more time to escape through vents. Since these materials behave and respond differently, it is crucial. Short shots refer to incomplete filling of a mold cavity. Using cooling simulation to circuit your cooling lines properly. Knit and meld lines are inherent to plastic. Flow Rate. 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. As the material properties of. 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. Fast injection gives you a glossy part, which is what we wanted in this. Voids . If possible, try to choose a little glue . These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Utilize hot. As far as the mold builders are concerned, having good flow through each circuit and having a good pressure leak test that they can perform is an. 10(a) (please see Fig. 1. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Weld Line defect analysis, the most common of many defects in injection moulding products. Avoiding Voids and Sinks. Heat Input and Cooling Calculator for Injection Molding. 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. Weld lines have been one of the common defects puzzling the injection molding industry. INADEQUATE INJECTION PRESSURE. (1) Reduction of injection time and shortening of the molding cycle. 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. Figures 3A, B and C depict different examples of “spot” vents. Picture the flow of a liquid resin filled with, for example, glass fiber. This injection molding defect appears as black or rust-colored discoloration on the molded part's surface or edge. The linear mold shrinkage of injection molded parts will vary from 0. Flow lines can be minimized in injection molding by optimizing the design of the part and the mold, as well as the processing conditions. There are important differences between an injection mold sprue and its runner system. This allows the melt to keep enough velocity to ensure proper filing. Leadtime Leader 2024. 005 0. 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. 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. 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. The steel that cored out and created the notch was very thin—roughly 0. The primary reason is insufficient plastic fluidity. 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. Learn more. 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 weld‐lines are undesirable from both aesthetic and functional points of view and their effect. 5 gal/min through this circuit we will get turbulent flow—the optimum cooling situation. 5. 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. Wavy lines are another feature of weld lines. Image 4: Top, HDPE streamlined structure. ; Warping – The structural deformation that occurs. In a weld line, reinforcement fibers. Thin wall injection molding can produce walls as thin as 0. Thereby creating localized pressure within the mold. Increase the injection speed, pressure, or temperature of the material. 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. 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. Source: Google. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. Contact the material supplier for help in deciding which flow rate should be used for a specific application. 160"). Let’s take a look at some defects that are caused purely due to faults in the injection mould process. Flow Lines Or Flow Marks. c. For example, filled resins and ABS are more likely to. 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. (All Illustrations: S. Prevent Flow and Knit Lines Through Mold Adjustments. Add or increase vents as needed. 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. 150 in. Mold flow analysis is a powerful tool for optimizing the design and performance of injection molding processes. When the melt enters the cavity quickly, it is necessary to discharge the air quickly. I’ve been noodling that question around in my head for the last three years, since injection machine suppliers like Arburg, Engel, Wittmann Battenfeld and Sumitomo (SHI) Demag started showing up at trade shows with mold-filling displays on their machine controller screens. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. 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. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. Strengthening. Help prevent warping with these measures: Raise the mold or material cylinder temperature. Burn Marks. On a small four-cavity tool, the part had a U-shaped notch in the center. Raise the mold temperature, maintain a high. Seven Common Defects and Solutions for PC/ABS injection molding Products,Flow Lines, Pitting,Product Delamination,Stretch Marks. He is currently a tooling manager for a large, multi. When two or more streams of plastic meet and fuse together, a visible line or weakness is formed on the surface of the finished product. 2. 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. This can prevent the opportunity for trapping air. 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. Flow marks are caused by a variety of factors in the injection molding making technology, and they happen at the gate. Minimum turbulent flow would be 12-14 GPM, while numbers in the 20’s would be identified as an excellent flow rate. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Mold design. RapidDirect – Your Best Injection Molding Partner. 5mm (0. Injection molding can be performed with only one of these materials like glass, plastics, etc. Low-quality and poorly designed molds can also result in flow lines on injection molded parts, particularly those with uneven wall thickness, insufficient lubrication, and poor venting. Sink marks are like little craters formed on an injection-molded product. The type of gate for manufacturing often depends on the material used and the parts’ shape. PROBLEM: FLASH ON PARTING LINE There are a few key reasons why flash appears on the parting line of a part. The following are the main elements of a gating system designed for injection molding. Each material has a maximum flow length for a given injection pressure and wall thickness — this is known as the flow ratio. 000 0. 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]. If larger gates are used, expect a longer molding cycle time. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. 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. (2) Improving the flow of plastic and facilitating the molding of thin-walled parts. Because you have control over exactly when and how much material enters the tool, you have tighter control of the parameters that go into making a quality part. Incorrect gate positions cause multiple flow fronts that struggle to merge. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. It is a type of distortion caused by this premature solidification. They again get resolidified along the surface. Plugged or inadequate vents n Clean plugged or dirty vents, particularly those along the parting line. How a mold is watered is key to a processor's goal of consistency. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. So much. The flow rate should ensure the material does not lose its. This review process showcases a company’s technical expertise, the capabilities of its design team, and overall quality. The weld lines are formed when there is an obstacle in the cavity of the injection mold. 5. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. Production was set according to an experimental design (DoE), varying injection flow rate, mold temperature, and melt temperature. 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. They are best described as "off tone" wavy lines/streaks or patterns in the molded part around the injection ports. Known as thermolators, water cooling systems require a cooling source such as a tower. Lenticular, or Silver Dollar type pigments, are thicker than cornflakes, with a narrower particle size distribution. How to recognize, prevent, and counteract flow lines defects in injection molding? Learn. The. The wavy lines or patterns that form on the surface of the molded object are what we refer to as flow marks. Look for signs of stickiness or burning. Shear; There are two causes of splay brought on by shear. Defect categories.