Injection molding is the process of injecting liquid thermoplastic into a mold. Reduce the injection pressure. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Conversely, texturing of part surfaces is often effective in hiding flaws and imparting a “grippy” or leather-like. Misra A. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Meld and knit lines are actually both different types of weld lines. Tooling & Injection Molding Services High-Quality Complex Parts. wall thickness, knit lines, draft. Melt temperature does. 5 inches) dispersed throughout the structural automotive sub frame component ( 10 ). Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. Trapped gas is one of the most common causes of part burns, and can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part. Excessive mould lubricant. Solution: Increase the injection pressure or speed. , 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. In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. Anisotropy. Participating in DFM and mold flow analysis is a good way to achieve this. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. weak knit lines and fracture points. The plastic in the ‘flow front’ cannot pass through the core pin, so it flows around the core pin splitting into 2 distinct flow fronts. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. 0 mm) is crucial to ensuring that parts cool evenly. Reducing the dimensions of the runner system. That’s the air escaping out of the nozzle until the hose is full of pressurized water. 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. ) Mold Analysis Tools. 250 in. 3 s, mold temperature of 60 °C and melt temperature of 250 °C. 26 = 0. The parting lines is where the two injection mold halves (A side and B side) meet. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Two major sources of weld lines are multiple gating and flow around pins. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. The Mold Tools toolbar provides tools for creating mold tooling (cores, cavities, etc. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. These defects are not visible, like small. 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. The plastic melt that passes through the gate at high speed directly enters the cavity, then contacts the surface of the cavity to solidify, and then is pushed by the subsequent plastic melt, leaving traces of meandering. Short shots Trapped air in the mold can inhibit the flow of the material during injection, resulting in an incomplete part. The resulting line has the. Legend: a-in. The plastics used by injection molding processes are relatively cheap and can be used to achieve a wide variety of properties, so injection molding is popular for creating many packaging and consumer products, like LEGO! A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. CURE: Run the mold in. But those key aspects can be viewed differently if you’re auditing mold changes before startup or troubleshooting changes for an already validated process. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. Koelling, Ronald C. It is also where a slide mechanism might meet where it shuts off on one of the mold halves. 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. These are imperfections in the part. Draft. Polypropylene Consumer and Injection Molding Containers, Crates, Garden Furniture, Housewares, Luggage, TSL, TWIM lyondellbasell. They again get resolidified along the surface. injection-molding machine (Arburg allrounder 320C, Germany). Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 6 Monate. While not always visible, weld lines (aka knit lines) are where two resin flows meet. and Titomanlio, G. Learn how HPP maximizes these specialized processes. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. (1. An injection mold that produces pieces while the final tool is being built. Knit lines are formed when two or more plastic flow fronts collide and solidify or “knit” together during the molding process. 2. Knit lines. Double push filling method. Increase the size of the gate and runners to alter the mold design. After samples have been approved, it’s time to kickoff. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. 080" – 0. Flow Lines. Macromol Symp 1988;21/21: 489-500. 6. For this study, a special injection mold was designed and constructed (Figure 1) in order to produce specimens of various thicknesses (from 2 to 6 mm). This can result in cosmetic defect or a weak point in the part. Edge gates, which can include fan and tab-shaped gates, are the most common ways to gate a tool. 120 in. Inject the molten material into a mold. Disadvantage: May rust if improperly stored. 08 KICKOFF PRODUCTION. 0 to 3. There needs to be a balance between fit of the halves, function of the part, visual quality expectations, and the cost to produce the mold. Weld lines, also known as knit lines or meld lines, occur when two or more flow fronts meet during the plastic injection molding process. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. suppressed cooling and possibly warp. com support@makenica. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Here’s a rundown of helpful tricks to keep in mind when designing and choosing a material for molded parts with walls: In general, ensuring your design has uniform wall thickness between 0. Flashing can be a common defect in injection moulding and can affect the appearance and functionality of the finished product. It is also one of the most important weapons in a molder’s arsenal for making process changes. 020"). 3. Also known as knit lines. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. 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. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. There is high defect rate (surface defects/knit line). Orientation of these knit (weld) lines, are perpendicular to the tensile stresses, applied to the ring (Figure 6-8). A weld line, also known as a knit line, is a visible line or mark that occurs in an injection-molded part where two or more melt fronts meet and fuse together during the molding process. Contact Universal Plastic Mold Today. Get a free des. Also known as a knit line, this is the point at which two flow formations meet and are unable to connect during injection molding. Knit lines. While knit lines can be present it does not always mean the structural integrity of the plastic part is compromised. Using restrictors helps push visible knit lines into less conspicuous areas. Many materials can be. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. excessive or premature wear at the parting line. Some of the most popular brands include:Harshal Bhogesra has 9+ years of combined experience in molding, customer & supplier development. “A knit line in a colored part will result in glaring visual-effect problems, while a knit through a glass-filled part would have a negative effect on both the aesthetics and the performance,” agrees Kurt Weiss, manager of part performance and new material introductions at GE Plastics. ISSUE FACED BY THE INJECTION MOLDING COMPANIES: FLOWLINES (ALSO CALLED WELD LINES OR KNIT LINES) Definition: Streaks, orange skin, or visible flow lines in parts. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. A good injection mold design will take all of these factors into consideration, ensuring that the final product looks great. Weld line, also known as knit line or meld line, is a visible line or mark on the surface of a plastic part where two or more flow fronts of molten plastic meet and fuse together. Meld and knit lines are actually both different types of weld lines. And the lead-time for overmolded and insert molded parts is 15 days, a bit longer than FacFox’ single-part injection molding turnaround, but still much faster than traditional insert molding. 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. 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. Potential Knit Lines • Knit lines occur where to or mold melt fronts come together-Holes, slots, multiple gates, variations in wall thickness-Meld lines occur when the melt comes together in the same flow direction • Knit lines are areas of weakness and should be located in low stress areas . Parting lines lie along the edge of the molded part, between the core and the cavity. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. A poor design can lead to many visual defects in the final part. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Some. In fact, knit line strength will decrease with higher filler content and with longer fibers. Weld lines are also known as “stitch lines” or “knit lines”. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. When these areas are visible, it can pose no problem at all to the piece, be nothing more than a cosmetic flaw, or can be. Learn more about the process by reading this white paper. Weld lines are formed during cavity. However, with any practice, when the proper care and planning aren’t taken, problems can occur, and with injection molding, knit lines are one of the most common problems. Near-Net-Shape Molding enables us to eliminate knit lines, add undercuts, increase options for geometry and tolerances, and reduce tooling cost for low. Each mold produces as specific part. 4. (1. From Plastic Materials and Processing by A. Specifically, by having a single, continuous injection outlet 140, molding material can be uniformly distributed throughout mold cavity 120 quickly and consistently without resulting in undesirable molding seams or knit lines. [1] Here are a few ways to prevent knit lines in your plastic parts: Increase material temperature: Higher temperatures on both materials prevent one section from cooling too quickly. You can avoid knit lines and other problems by creating designs with smooth geometries. PVC pipes are manufactured by an extrusion process. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. This picture shows a. The part weight x number of cavities + runner weight should. These defects are not visible, like small. Adding vents, using overflows, or using porous metal. Product designers encounter a wide range of challenges when. The data suggest that either local sample thickening or grooves form at knit line when complete section solidification takes place first at weld zone or. Knit lines are most common downstream of holes created in parts where the molten material meets. Additionally, it may produce sinks and voids caused by localized shrinkage during the part’s cooling process. Causes 1. It is. 197 in. 2. Depends how hard you want to push it. Incorrectly placed single gates may cause knit lines. Whereas conventional injection molding uses. Obstructions in the part create weld lines or knit lines during injection molding. Injection molding is a manufacturing process that involves injecting molten plastic into a mold cavity to create a specific shape or design. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Sink Marks Cause 4: High Mold Temperature. The injection molding process offers a vast array of plastic resins to work with. Yet a smooth finish sometimes actually highlights flaws like knit lines and blemishes in the part. Part Design Summary Bosses:Welds and/or Knit lines can be defined as the inability of two or more flow fronts to “knit” together, or "weld", during the molding process. SEA-LECT Plastics has 16 MILACRON injection molding machines that range from 33-ton with a 2. suppressed cooling and possibly warp. Knit lines don’t. com Three terms that often get mixed up in injection molding are weld, meld and knit lines. Mold Flow Analysis computer. Some are: Knit lines (discontinuities where two flows merged, creating a weak point)Those are knit lines, formed when two opposing flows of material join together in the mold cavity. What Are Knit Lines? When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. RELATED CONTENT. Crossref. 2. It tells them that you visualized how injection molded parts cool and harden. 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. Surface Finish: The injection molding process may result in visible knit lines or parting lines on the part’s surface. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Meld and knit lines are actually both different types of weld lines. menu. Parting Lines. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. Polym. There are two primary reasons for this occurrence: 1. Gas trapping/ poor venting. With plastic finishing plugs and end caps, we can help you keep your products protected while giving. mixed manually and quickly stored in the tank of an injection machine just before the start of the resin injection or (2) the components are stored separately in different tanks of an injection machine with a mixing head. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. (See Fig. Reduce the screw speed and adjust the backpressure. A knit line is any line, visible or not, where two resin flows meet. 5 mm (0. The most common location of knit line formation is behind molded-in holes that are made by core pins in the mold. Runner and gates must be balanced. However, the weld line may not continue throughout the flow. Injection Molding Materials When using PolyJet molds, both tool life and part quality will be dependent on the thermoplastic material used during the injection molding process. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. Injection Pressure 0r Speed Too Low Explanation: If the injection speed or pressure is too low, the molten plastic will not be pushed into the mold cavity fast enough to fill and knit at converging flow fronts because it cools down and solidifies too soon. By using this method, theHowever, injection molding is not without its challenges. What Causes Knit and Meld Lines? Like many part inconsistencies, these unwanted features are rooted in product design. Vents for phenolic parts should be approximately ¼" (6 mm) wide and 0. This production method is particularly popular when manufacturing in large quantities. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. The last cause of flow lines may be the operators running your daily operations. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different. Injection molding weld lines refer to a line on an injection molded part that is generated where the two halves of the mold come together. The comment on melt flow index is correct, but, I've molded straight PC down to . Weld line are formed whenever melt fronts separate and recombine at some downstream location. Knit Lines. This defect is caused from excessive lube or oily stock. The main causes of Weld Line or Knit lines are: Convergence of two flowing polymer melt streams during injection molding process: This is the most common cause of weld lines, as the two melt streams coming from different runners or gates in the mold meet and do not fully mix, creating a weak point in the finished product. Whenever possible, vents should be located in the movable half of the mold wherever a gas void or knit line is seen on a part. The plastic in the ‘flow front’ cannot pass through the core pin, so it flows around the core pin splitting into 2 distinct flow fronts. The chart below shows recommended wall thicknesses for common injection molding resins. 3 /sec. thick. Product designers encounter a wide range of challenges when. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. Knit/Weld Lines. The only parts that count are the ones that meet quality standards, and keeping pressure evenly distributed across a mold’s parting lines is one of the many critical tasks to get those good parts molded. sinks, knit lines, and shrinkage,” Spalding says. S. These knit lines are usually the weakest areas of the part. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. How weld lines form. In injection molding, it is often important to maintain consistent color throughout the part. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. opposed to two or more gates. They again get resolidified along the surface. There are times when porous materials like Porcerax are used in problem or backfill areas. Wavy lines are another feature of weld lines. Reduce the temperature of the mold and plastic being injected. Commonly seen at the edge of a hole or other cored feature, knit lines are—as a rule—purely cosmetic, but may create a physical failure point if present in an area of the part that receives substantial stress, such as the head of a screw. Knit Lines 11: 1. com. . Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Kaminski, in Specialized Molding Techniques,. The Difference Between Knit and Meld Lines–and Why It Matters. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. Long shapes are produced without multiple drops or hot runner systems, eliminating knit lines and lowering tooling costs. This slight depression is a tiny line called the weld line or knit line. In this way, the mold supports distribute the force and minimize the stresses on the mold plates. 2. Injection molding is an efficient, often cost-effective way to manufacture custom plastics that are strong, durable, and long-lasting. Multiple gates will always cause knit lines. 1. 5-3. land and using maximum vent depths to get them as close to self-cleaning as possible. SPI surface finishes are the most common set of injection molding finishing standards around the world with over 12 different grades. As a result, molten plastic takes the injection mold core and cavity shape. turbulent flow of Injection speed set too high. Plastic injection molding is a process where a thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold. If the parting line is located on a sidewall of the part, it is nearly impossible to construct a mold without a slight mismatch between the force and the cavity. – Change the thickness of the product. These knit-lines are well-known as particularly critical regions in the mold when mechanically. Understanding Knit Lines in Injection Molding: Causes and Solutions. Injection moulding (U. More about the knit lines in injection molding. When injection molding complex parts, often knit-lines are formed during the mold filling stage. This is why the leading edge of the resin flow within a mold is always the coolest area of the resin, and, therefore, the closest to solidifying. (1987). Let’s. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. Molding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesivePrevents flow and knit lines. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. Weld lines also can be visible after a part is painted and can cause wrinkles on in-mold-label injection-molded products. It explored the use of. Again, you would round this value up or down based on a standard cutter size, which is 13/64 or 0. Weld lines are a common imperfection to be found in most plastic injected molded parts. Having uniform wall thicknesses between 0. Exploring common molding defects and. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. Flow rate and flow speed are cut in half at every runner branch. Crossref. Increase injection speed. Over the years, I have developed two separate “5M” systems. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. Three terms that often get mixed up are weld, meld, and knit lines. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Increase the melt and/or mold temperature. Viscosity represents a broad concept with huge effects on any efforts to standardize an injection molding process. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. 0mm) throughout will ensure that the parts cool evenly and will prevent warping. Cold Slug: First material to enter mold during injection. a weld or knit line may develop on the opposite side of the obstruction as the two fronts of material join. This range can be affected by the part wall thickness, melt temperature, mold temperature, injection speed, hold/pack pressures and also the time between molding and measuring. This range can be affected by the part wall thickness, melt temperature, mold temperature, injection speed, hold/pack pressures and also the time between molding and measuring. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. 2. Use gradients. Injection molding is typically a better choice for more complex parts, while compression molding is a great option for relatively simple designs, including ultra-large basic shapes that cannot be produced using extrusion techniques. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. As the polymer resin is injected into a mold, it flows through all parts of the mold. Mold Venting. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. A majority of these investigations concern amorphous polymers, whereas a number of engineering polymers are semicrystalline and also contain reinforcing fillers and fibers. Compression molding produces solid parts that are free of flow and knit lines. Polym Compos 1982; 3: 88–96. The three dimensional structure is formed of a resin fiber mixture having a resin material infused with carbon fibers having a length of about 12. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Another name given to weld lines is meld line. Meld and knit lines are actually both different types of weld lines. 02 in. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. Injection Pressure 0r Speed Too Low Explanation: If the injection speed or pressure is too low, the molten plastic will not be pushed into the mold cavity fast enough to fill and knit at converging flow fronts because it cools down and solidifies too soon. Knit lines occur at points where resin flows converge after molding around an obstruction or protrusion within the mold, usually away from the gate area. Avoid adding threads directly on your injection molded part. (1. Back to News Page. Gas-assisted Injection Molding: Influence of Processing Conditions and Material Properties. Plastic melt and mold temperature. Injection molding machine and automation supplier Engel offers an array of technologies to simplify and speed up mold changes, including magnetic clamping platens and quick couplings; intelligent assistance systems; and the famox mold changing system for automating the set-up process. Prevent Flow and Knit Lines Through Mold Adjustments. Release of trapped air in those cases will. Weld line. Alter the mold design. The injection molding process uses a granular plastic that is grav ity fed from a hopper. The injection molding was carried out in a DK-Codim 175/410 injection molding machine. Cooling Lines, Injection Mold Material has a great impact on injection molded part quality. As. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Advantages Excellent moldability in thin sections Outstanding chemical resistance Heat resistance Limitations Cost Knit line strength OverviewLiquid crystal polymer (LCP) exhibits a highly ordered structure in both the melt and solid states. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. A knit line may only be a cosmetic issue and affect. Troubleshooting Injection Molding Weld Lines. The goal is to create a uniform thickness and at the smallest (thinnest) level required. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Let’s. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Because viscosity is a variable, keeping fill time constant minimizes the influence of these variations and provides a more stable process, and therefore. Mold venting should be checked and increased if necessary, injection molding service. In addition to the main factory and development. Plastic injection molding is the process of injecting molten plastic material into a metal tool which then cools and ejects a plastic part from the machine. 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. Injection Molding: How to Set Second. POROUS MOLD MATERIALS. Therefore various injection molding defects can be eliminated. There is no need to worry about flow or knit lines that may appear with injection molding. Improve venting and/or relocate to burned area. In the process of injection molding, when the wall thickness of the product is large, the cooling speed of the outer surface is faster than that of the central part. RapidDirect – Your Best. In the 1947 book, Injection Molding of Plastics, the late Dr. To learn more about us or to get a quote, click here or call 1-888-893-1587 now. 12515 NE 95th Street , Vancouver, WA 98682 CALL TODAY: 1-800-839-0366Contact FU CHUN SHIN MACHINERY MANUFACTURE CO. Expand. Here are some reasons why design is important for injection molding. 2020-01-1306. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. land and using maximum vent depths to get them as close to self-cleaning as possible. 5mm (0. Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. Notched weld lines then remain near the cavity walls. Injection molding is a simple and efficient process that produces high-quality plastic parts. cold and hot weld line. Resin cools as it is injected into a mold. Incompletely fused extrusion knit Line. Figure 1: Knit lines in a cover plate. Meld and knit lines are actually both different types of weld lines. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. We complete the part to your precise specifications with CNC Milling operations. In the injection molding process, melting takes place via two factors that work together: shear and heat. As a result, prototyping is strongly recommended for parts with. Remove the hardened material from the mold. Too cool a melt. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. As. Find out more by calling 573-437-4154 today or email us. 3. Figures courtesy of CAE Services. Misra A. 5 mm (0. They again get resolidified along the surface. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. In an injection mold, the plastic fluid flows and spreads out in many directions as it comes out of the gate. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. Sink. The point I am making here is, if you’re injecting 14. Polym Compos 1982; 3: 88–96. ITAR. This can enable the. Snake Lines: The appearance of snake lines is caused by the formation of a jet effect as the melt travels through a gate and into the mold cavity. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. When the temperature is not very high, there are chances of premature solidification, which can cause weld lines to form. Three terms that often get mixed up are weld, meld, and knit lines.