Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 3 the path lines of selected material elements can be observed which are. 5-3. How a mold is watered is key to a processor's goal of consistency. Flow lines. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Shear; There are two causes of splay brought on by shear. Walls thicker than 8mm (0. 6. They decrease the. Weld lines have been one of the common defects puzzling the injection molding industry. 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. Injection moulding (U. Flow lines are unwanted streaks, waves, or lines on a part’s surface. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. 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. Troubleshooting Injection Molding Sink Marks. Flow lines arise from variations in the flow of molten plastic material as it fills the mold. PartWeld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. Learn how to troubleshoot weld lines in injection molding. [1] #TROUBLESHOOTING #FLOWLINES #INJECTIONMOLDINGStudy more about troubleshooting flow lines : Weld lines occur when two flow fronts meet and fuse together in the injection molding process. 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. 2. 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 most common and one of the most challenging injection molding defects are weld and knit lines. 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. 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. While some molds or inserts have simple, straightforward cooling circuits, many have multiple circuits of various sizes and configurations. Knit Line. Flow lines were created during injection moulding process. Effects of mold temperature and pressure on shrinkage 0. Flow lines or marks appear as banded discolouration on the surface. Flow Lines: Flow lines on thinner areas of molded components appear as a wavy pattern, often a different color than the surrounding area. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. 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. diverse parameters of the injection-molding process, needs a lot of experience in order to achieve optimum results, especially if. Hamstra: For the OEMs, having a good baseline of what our cooling flow and temperature through a mold is going to give us a good optimization into the next supply chain for the injection molders. The gate vestige for injection molding is usually narrow. 1. 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. It is crucial to manage flow lines to ensure. Incorrect gate positions cause multiple flow fronts that struggle to merge seamlessly. Typically, flow lines are caused by the liquid plastic cooling at different rates. Thick sections take longer to cool than thin ones. The accompanying table lists the flow rates for various barrel diameters at various injection velocities. If the mold itself has cracks or defects, the finished product will also have various problems. Laminar flow in a plastic mold, described by. 100 to 0. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Below are ways through which you can remove and prevent flow lines; a. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. 000 0. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. Facebook. The molding process is the leading cause of defects in injection molding parts. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. Injection molding has been the most popular method for making plastic products due to. Here are the top 5 injection molding defects that can occur, and how to solve them: Flow / Weld Lines. Non-uniform cooling of mold causes warping, creating internal stresses within the part and resulting in distortions. To avoid these defects, manufacturers can check molds for the following: Low Mold Temperature: A mold temperature that’s too low will cause the material temperature to drop fast. Prevent Flow and Knit Lines Through Mold Adjustments. Each needle valve nozzle opens only when the melt front has moved across its gating point. The material is kept poured into the mold for some time. First, excessive injection pressures may be forcing the mold apart. ”Poor venting, along with the diesel effect, can also cause the mold to wear on the mold parting lines, resulting in flash (excess plastic) on the injected part. This steel section retained heat, not allowing the plastic to cool and requiring an excessively long cycle time of 40 sec. These defects include the following: 1. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. 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. More Control. Circuiting Done Right. These lines form as a result of material flow and solidification during the injection molding process. Sink Marks. Unraveling Flow Lines. 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. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. More about the knit lines in injection molding. Shear; There are two causes of splay brought on by shear. 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. 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. 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. Plastic Injection Molding Defects series-Flow Marks or Flow Lines Aug 23, 2019 What should we keep in mind when designing for injection molding?1. mold and the blow molding process. Molds gain streaks through molten plastic cooling and solidifying at different rates. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. Thus, with an injection pressure of 1800 MPa, the flow length with 80°C is 47 mm and accordingly for. Phone (630) 665-8590. 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. 750 in. 7. Known as thermolators,. Vary injection speed, screw rpm, and backpressure. They are evidence of nonuniformity in flow pattern upon entry into the mold. Round the corners of the mold where wall thickness increases to help keep flow rate consistent and prevent flow lines. Thus, as the flow continues, the two flow fronts may gradually rejoin to. Sink Marks. The part surface was observed in reflected light using optical microscope and the pictures of. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. Here are some ways to avoid. How weld lines form. Investigate the mold for signs that a water leak is present, and correct the condition. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Waterlines control heat within three diameters of themselves. Mold venting is critical to the quality and consistency of the finished part. It is also useful for finalized prototypes that are used for consumer and/or product testing. Injection molding (or injection moulding) is a widely used manufacturing process in many different industries such as aerospace, automotive, medical, and even. 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 appear like off-tone patterns on the surface of your finished parts. Flow lines result from uneven cooling of the plastic within the mold. Defects like this make it harder to market the finished parts to the end user. The size, shape, and location of the gate have a significant impact on the finished product. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. 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. In injection molding weldlines are generated when two separate melt streams join either. There are two halves to the injection mold that must come together and at the interface there is a chance of a parting line. This review process showcases a company’s technical expertise, the capabilities of its design team, and overall quality. They also can appear as ring-shaped patterns near the entry points of the mold. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. The co-simulation of mold flow and structure plays an important role in the design of injection molded fiber-reinforced thermoplastic (FRT) parts. The formation process of weld lines can be described as follows: Injection moulding (U. • Move injection locations to make flow fronts meet more obliquely, turning the weld line into a meld line. ³/sec. Flow lines appear as a wavy pattern on the surface of your plastic parts. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. 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. S. Increase the injection speed. Lower speeds allow gas more time to escape through vents. The mold in Figure 6 is an 8-cavity with an “H” pattern runner and a lapped edge gate. More viscous amorphous materials, such as PC, TPU or PEEK, can have a recommended vent depth range from 0. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. If so, look for an alternative resin. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. 4 Injection Speed. Consider the following examples of cooling channel configurations in P20 mold steel with a water line diameter (D) of 11. Circuit Identification. Plastic injection molding is a complex and highly intricate process. V. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Also called “Weld Line. They can be off-color or discolored material compared to the intended color of the part. 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. Mold design is a key aspect of injection molding. Imperfections in manufactured plastic goods, such as a flow line defect in injection molding, are unacceptable. The edge gate is the most popular and straightforward injection mold gate design. Select a plastic that is less prone to shrinkage. The weld line and the flow pattern of co-injection molding can be seen from Fig. html. When the melt enters the cavity quickly, it is necessary to discharge the air quickly. Also, heating the material in the cylinder. After exhaustive research, testing and pilot-scale demonstration, the team developed a breakthrough new technology utilizing low constant injection pressure. When it comes to injection-molded products, here are several typical solutions for flow lines: To make sure the liquid reaches the mold fully before cooling, enhance the. These streaks or patterns can affect a part's aesthetics, value, and. Thickness –Make the bottom of the boss 60% (0. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. Injection molding tool life is the number of production cycles that an injection mold can complete before it needs to be replaced. Flow Linesparticles, during injection molding, will produce visible flow and weld lines. The Bottom Line. They again get resolidified along the surface. 5. You can avoid having any weld lines with cascade injection moulding. Drain the hopper if you were working with 100% regrind, clean if necessary. google-site-verification: google03af4f4fcb62a9d5. Steven. In spite of its cosmetic attributes, a bad knit line can significantly. On average, larger injection molding machinery can cost from $50,000-$200,000 or more. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. Figure 1 below shows the development of a weld line. Ensure sufficient cooling time to avoid locking residual stresses into the part. Help prevent warping with these measures: Raise the mold or material cylinder temperature. Slower flow results in thicker and shorter knits. 1) Snake flow lines. Remedies: Raise the temperature of the mold or molten plastic. Flow marks can be caused by any or all of the following factors: Slow melt injection speed. Injection Molding (IM) Solutions 1019 Balfour St. RapidDirect – Your Best Injection Molding Partner. I’ve been writing about plastic flow simulation since 1984, and I. In the process of injection molding, the quality of the mold plays a decisive role in the quality of the finished product. Our glossary of terms provides definitions for a wide range of injection molding terms. Remedies: Increasing the injection pressure will force the molten plastic against the mold cavity. Countermeasures to Injection. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. Plastic Injection Molding Process. Mold flow analysis is a software-enabled process that. injection molding. 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 a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Flow lines are the results of slow injection rate and disparities. Kobayashi et al. Peering into the Flow. Wavy lines are another feature of weld lines. Allows you to accommodate a variety of part sizes. 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. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Mold Design. 020"). 6 T) as thick as the nominal wall. They are the result of fundamental physical effects taking place inside of the mold. This means that the skin of the part is always formed by. Voids . Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Reduce the injection pressure to prevent overpacking at the gate. 750 in. Injection molding could develop knit lines if one front cools before it reaches the other. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. In injection molding weld lines are formed whenever two flow fronts are joined. 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. A significant part of that is the cooling design, where there are many things to consider. Before his present assignment, Bob managed a molding operation for 25. 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. 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. Since these materials behave and respond differently, it is crucial. It can also aid in material selection since fill. 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. Check that the machine is creating enough clamping force to keep the mold halves together. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. Reducing the dimensions of the runner system. The streaks form from plastic in the mold overlapping with plastic following it. By using proven methods for cooling line design, warp and cooling time are minimized. MMT Chats. Although injection molding is considered a fairly well-established manufacturing process, several independent parameters must be properly set to achieve a high quality of the molded parts. ABS resin has low thermal deformation temperature, but poor heat resistance. 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. 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. ” 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. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. You can avoid having any weld lines with cascade injection moulding. This method can be helpful in. So what does the 140F mold temperature give us? The molding technician thought the 140F mold water was OK because the data sheet provided by the material supplier suggested mold temperatures from 75 to 180F. Mold Design. Reduce the temperature of the mold and plastic being injected. 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. The leading edge of the flow, or the melt. 0005 in. Flow marks, also known as flow lines, are molding defects that can occur in the manufacturing process of injection molding. The flow rate should ensure the material does not lose its. 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. AnalysisInjection moulding simulation with the finite element method is the most advanced technique for designing injection moulds. In terms of viscosity, higher heat equals faster flow and lower heat equals slower flow. Increase the injection speed, pressure, or temperature of the material. Flow marks: Flow lines Directionally "off tone" wavy lines or patterns Injection speeds too slow (the plastic has cooled down. It can help you reduce defects, improve quality, and save costs by simulating how. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. We offer this Mold Cooling Calculator tool as a free service to the injection molding industry. Increase molten plastic temperature during injection molding. 2), the plastic enters the mold at a relatively fast rate and forms the skin. There are important differences between an injection mold sprue and its runner system. 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. As the polymer resin is injected into a mold, it flows through all parts of the mold. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating 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. as a stand-alone, wholly owned. Understanding the complexities of injection molding flow and solidification is a bit more challenging as. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. 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. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. The line actually indicates the parting ‘plane’ that passes through the part. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. 5° draft to each side of the rib. So much. 2) Material Changes. The goal when locating cooling channels in the mold is uniform mold surface temperature, which is determined by cooling channel depth and pitch. 1 Caused By The Quality of Injection Mold. The melt holds enough temperature to maintain a low enough viscosity. thick, 0. Just multiply the area of the barrel × the injection velocity. They can also appear as ring-shaped bands on the surface of a product near the mold’s “gates. Weld Lines. Another tactic to promote more chain entangling at the weld line is to raise the mold temperature 10° C (50° F). Weld lines are a common imperfection to be found in most plastic injected molded parts. This is a video excerpt from our Problems & Solutions Course - Jetting. 4, no. 1 – In plastic injection molding, the flow ratio is the distance molten plastic must travel, divided by the wall thickness of the part. 100 to 0. Meld and knit lines are actually both different types of weld lines. 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]. Three terms that often get mixed up are weld, meld, and knit lines. We restarted the mold at the same coolant flow rate and temperature. 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. Injection molding could develop knit lines if one front cools before it reaches the other. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no. 7 in Kobayashi et al. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. Plastic Defect # 2: Flow Lines. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Draft – Add 0. The strong molecular. Sufficient draft is an important part of any mold design, and quick-turn tooling is no exception. Sources of defect: Material: Material too high viscosity; Method: Injection speed in the critical area too high (too low)Flow lines are one of the most common problems with injection molding. Solution: Utilize a material that has the stiffest flow possible without causing non-fill. In narrow fields, a limited amount of molten liquid can solidify and block the flow. This can be accomplished by reducing the substance’s viscosity. In. • Optimize the design of the runner system. The 7/16-inch size is a happy medium between many small lines and the fact that larger lines don’t particularly increase the heat exchange benefit. For instance, the plastic used for gears must be completely smooth. 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. Clean all parting line and core vents. Water cooling pumps coolant through lines on the outside of the mold cavity. How to recognize, prevent, and counteract flow lines defects in injection molding? Learn flawless products from professional manufacturers. Flow marks are caused by a variety of factors in the injection molding making technology, and they happen at the gate. Flow lines are linear marks on the surface of a molded product, which indicate the flow direction of the molten plastic. Possible causes: Low temperature of injected melted plastic or slow injection speed during injection molding resulting in low fluidity of plastic inside the mold. However, the weld line may not continue throughout the flow. In this lesson we will focus on the meld and weld lines. This injection molding defect appears as black or rust-colored discoloration on the molded part's surface or edge. Flow speed too fast or too slow. The plant water system is a critical component of an injection molding facility. Knit and Meld lines are inherent to plastic injection. Learn how mold flow analysis can support the development of complex and customized injection molded products by identifying defects, optimizing materials, enhancing performance, and reducing costs. 5. The Priamus Fill system is designed for automatic closed-loop control of multi-cavity and family molds, multi-material injection, sequential valve-gated molds, as well as LSR molds. to 0. Knit and meld lines are inherent to plastic. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. 2). 1mm (7/16"), coolant temperature of 30ºC and cycle time of 17 seconds (see Fig. 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. Furthermore, jetting is frequently visible as a squiggly line on the surface of the final component, typically leading from the original injection gate. The primary cause of cracking is stress and deformation brought on by the external environment, cold mold surfaces, and low injection rates. We heat the plastic to a molten phase, inject it into the mold and cool it into a preferred shape. 0010 in. 1 Caused By The Quality of Injection Mold. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). Recently hired at plastic injection molding simulation software provider Moldex3D, Nicholson was spurred to undertake the research study following a conversation with a customer experiencing weld-line woes. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. In these cases each circuit might remove a different. It explored the use of. Within more basic plastic part design plans this plane can be a simple, flat surface, but it is often a complex form that. In a weld line, reinforcement fibers. Picture the flow of a liquid resin filled with, for example, glass fiber. If packing around a detail is causing cracks/ shorts/burns on the knit line, reduce the heat to improve knit line seal and strength. If it’s too thin or small, material flow, pressure, and temperature will. 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. In Fig. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. This software simulation can show how a resin will fill the mold during the injection molding process. Look for signs of stickiness or burning. Flow lines. (1998) for clear photographs. Flow lines are lines or streaks visible on the surface of a part. We restarted the mold at the same coolant flow rate and temperature. Tatjana Geminger, Stefan Jarka, in Specialized Injection Molding Techniques, 2016. These benzene rings also increase the viscosity, reduce shrink rate, and increase strength with the exception of knit and/or meld lines. Cooling lines impact. 20 mm. Weld lines are similar to flow lines, but they appear similar to a plane than a line when compared to flow lines. If performing a resin change from one polymer to another a difference in viscosity can cause flow lines or gels. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Utilize advanced injection molding machines with increased injection speed and pressure. Adjust resin and cooling temperatures. Increasing pack or hold pressure helps to eliminate low-pressure conditions at the weld line. 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. Spatter lines formed on the surface of the plastic along the direction of melt flow are called silver marks. 2. These marks remain and are visible in the cooled product. Its popularity is typified by the numerous products produced in this way at the present time. Increase the size of the gate and reduce the thickness of the walls of the molded part. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. For each investigated mould temperature, a linear relationship can be observed. 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. Do not keep the hopper full; hand-feed if necessary. The flow fronts at different times (Fig. Weld lines are formed during cavity filling whenever two separated melt flow font recombine. SMARTFLOW ® flowmeters effectively and accurately measure flow rate. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. Parting Lines. Inadequate cooling time. Vacuum Voids. Kobayashi et al. personnel to assess cooling lines in the mold design. 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. 1, pp. S. [22]. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. G. A look at how taking the time and data to analyze a mold problem will help you repair it right—and permanently—the first time. mold temperature con-trol fluid flow in a mold, either laminar or turbulent, is by a dimensionless number. Weld‐line is a defect that arises in injection molding when two or more flow fronts collide. Flow lines or marks appear as banded discolouration on the surface.