The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. The depth of the texture or letters is somewhat limited, and extra draftParts were molded at a maximum injection pressure of 235 MPa, a maximum clamping force of 800 kN, a maximum injection speed of 900 mm/s, and a maximum injection stroke of 120 mm. While this process is largely efficient and reliable, it's not without its potential issues. Take these steps to avoid knit lines. Figure 1: D-shaped through-hole in center of gear part accepts the drive shaft. 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. Thermoplastic Elastomer Molding Guidelines. As the polymer resin is injected into a mold, it flows through all parts of the mold. 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. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. Understand the causes of knit lines in injection molding and explore effective solutions to minimize their impact. After samples have been approved, it’s time to kickoff. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. PCS Company, Fraser, Michigan, has launched the Polimold Valve Gate Sequencer, providing injection molders with more precise control of the mold-filling sequence when using valve-gate hot runner systems. Knit and Meld lines are inherent to plastic injection. These seams are known as “knit lines. When injection molding complex parts, often knit-lines are formed during the mold filling stage. In injection molding, it is often important to maintain consistent color throughout the part. 2. Our glossary of terms provides definitions for a wide range of injection molding terms. Having a basic understanding of the injection molding process will aid in understanding how to design for injection molding as well as how to forecast production schedules. Anisotropy. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. (1. In this, work, metal inserts were joined with polyamide 6 by using the injection-molding technique. 6. 08 KICKOFF PRODUCTION. suppressed cooling and possibly warp. Visual indicating with an finished part that are formed by the junction from two plastic flow fronts. Injection molding is an excellent way to create plastic parts in bulk, but there are many problems that can cause cosmetic defects ranging from minor to major. Adjust the design for the flow pattern to be a single source flow. Our plastic injection molding glossary provides key terms. These data were obtained from many andKnit lines in injection molding are common defects of the molded parts. PCS says each module of the Polimold Valve Gate Sequencer controls two zones, with the option to control up to 14. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. A knit line is any line, visible or not, where two resin flows meet. For non-reinforced or non-filled nylon, the mechanical performance in the knit lines (planes) areas are approximately equal to the mechanical performance of the resin (polyamide) used. S. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. On the opposite side. 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. Knit lines, also known as weld lines or meld lines, are visible lines or seams that appear on a molded part where two or more flow fronts meet during the injection molding process. One of the most important aspects of hot runner system design is the gate location, which is the point where the molten plastic enters the cavity. Thick walls are not recommended because of POM’s high shrinkage rate. Change gate locations. Troubleshooting Injection Molding Weld Lines. This is a quick rundown on how to handle common features in injection molding designs:What are the advantages of injection molding 1. 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. Islyn Thomas summarized the need for a particular vent location better than I ever could. The injection molding processing conditions for filling are given in Table 1. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. You don't give us much to go on. In the injection molding process, knit lines are a common occurrence when two or more plastic flow fronts collide and solidify, resulting in a visible seam or line on the molded part. Injection Molding. 1-3). Runner Type. 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. What causes knit lines? Knit lines are formed when the molten plastic flowing into the mold cavity runs into an obstruction, such as a core pin that forms the through hole on a flange of an enclosure. 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. Short shots and knit lines are two phenomena that are caused by using highly viscousTherefore, changing the edges and corners of the mold core to make it buffer transition and keep the melt flow stable can prevent the occurrence of wavy lines. This configuration positions the injection mechanism at the top of the mold, allowing gravity to play a role in filing the mold cavities. Weld Line Phenomenon: Surface defect in which the weld, or the part where the flows of melted plastic meet inside the mold, shows up on the surface as a groove or pattern. We recommend walls to be no less than 40 to 60 percent of adjacent wall thickness, and all should fit within recommended thickness ranges for the selected resin. With this option, users can utilize in-cavity pressure or temperature sensors to control when the valves open or close. Injection molding a part with Class-A surface finish and ribs or bosses has proven an elusive goal for molders, despite their best efforts with conventional injection or internal gas-assist technology. Core out parts to eliminate thick walls. (1. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. 5 : 1 and a L/D (length toMold flow analysis is a software simulation which show how the resin fill in the mold in injection molding process. Specifically, Stokes and. Also known as knit lines. The most common and one of the most challenging injection molding defects are weld and knit lines. Example of a gate location in a finished part Example of knit lines in a finished part. This radius should not be smaller than 0. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. Even parts with metal inserts can be produced. The mold-opening force varies widely depending on the type and size of the molding machine. So. Plastic Injection Molding Part Design Guidelines, Plastic part Design Guidance, Parting Line Draft Undercuts Wall Thickness & Uniformity Bosses Gussets and Ribs Radii and Corners Material Shrinkage Gating. Fig. Meld and knit lines are actually both different types of weld lines. Learn how material selection, part design,. Wax or ceramic core size or location See Section 3. Molding is a manufacturing process in which resin in a barrel is heated to a molten state,. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. These defects are not visible, like small. First, they carry resin to the mold via a runner. Injection speed and pressure. Steven. They need the interference of about 0. Valve gates are most efficiently. Any of the above can result in “knit lines” on final products, but mold flow analysis prior to mold machining can keep these issues from cropping up at all in iteration and production. Be wary of saving too much weight or you might end up with: cracking. What you should know is that there are various failure modes for injection molding. High mold temperatures usually provide less residual stress. The leading edge of the molten material is often the coolest point and the closest to solidifying. Increase the injection speed. This is a video excerpt from our Problems & Solutions Course - Weldlines. We all know that injection moulding is great for producing both custom prototypes and end-use production parts, but if you are not careful it can cause some. To learn more about us or to get a quote, click here or call 1. Weld line in injection molding is line where two or more flow molten plastics knit together. Flow Lines. (2) Undesired movement of certain materials in a plastic. They need the interference of about 0. Services Group. In the injection molding process, knit lines are a common occurrence when two or more plastic flow fronts collide and solidify, resulting in a visible seam or line on the molded part. Because viscosity is a. Gating. Gate locations can be directly behind or on the edge of the graphic. 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. Learn how to troubleshoot weld lines in injection molding. Undercuts add cost to tooling and molding, which is recommended to eliminate or minimize as possible. sheet metal fabrication, rapid tooling, and plastic injection molding. Injection molding is the process of injecting plastic material into a mold cavity where it cools and hardens to configuration of the cavity — is best used to mass-produce highly accurate, & often complex, 3dimensional (3D) end-use parts and products. Meld and knit lines are actually both different types of weld lines. They again get resolidified along the surface. The comment on melt flow index is correct, but, I've molded straight PC down to . 2. ABS. Factors were ordered. Bubbles are caused by melting flow fronts colliding in a mold cavity. We have an elite team that designs for injection molding, rapid prototyping with metal and plastic, and produces world-class products under the same roof. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Flash: All plastic injection molds contain parting lines, which create the potential for small amounts of molten plastic to escape the mold cavity’s boundaries. 453. 3. Incorrectly placed single gates may cause knit lines. Trapped gas is one of the most common causes of part burns, and it can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. The cooler flow fronts of the resin aren’t forced into the mold surface texture as well as the hotter resin behind the flow front. The gate is the entry point to the part-forming cavity, where plastic material is injected from the molding machine barrel, through the sprue and runner, into the mold. Many of these tips are geared around injection-molded parts, but some apply to machined and 3D-printed parts as well. land and using maximum vent depths to get them as close to self-cleaning as possible. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. Knit lines are formed in injection molding when two flow fronts meet in the middle of a part (a line where two sides of the plastic. For injection molding of the multi-blade fans and various rotating plastic parts, the complex of multiple gating injection molding tools were used. Gate design is another critical piece of part function in plastic injection molding. The weld line can either be a minor cosmetic issue. A. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. Contact us. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. It can also aid in material selection since fill. RELATED CONTENT. molding run to be sure that the temperature does not exceed the recommended limits . Weld lines, also called knit lines, are a defect that occurs with molded parts caused by two different flows of plastic resin that do not adequately join together or weld together correctly during injection molding. 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. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon. Depends how hard you want to push it. A medical device designer might look up a polymer's physical properties and game out. injection molding. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Knit / Weld Lines. Weld or knit lines occur when melt flow fronts collide in a mold cavity. Temperature is another factor that can cause weld or knit lines in injection molding. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. A parting-line vent. "As soon as that part or material is stressed, it can be real conducive to fracture, cracking, breaking, just because of the way it's been molded. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022injection-molding machine (Arburg allrounder 320C, Germany). Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. Inappropriate temperature. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. The chart below shows recommended wall thicknesses for common injection molding resins. Weld / Knit Lines; Assumptions. Knit and meld lines are inherent to plastic. 5 : 1 and 3. H-13 Good general purpose tool steel. Proper venting is essential to molding a defect-free part. What is copper electrode in injection mold? hashtag#plasticinjectionmold hashtag#moldmaking "Copper electrode," also known as "electrode," is a common component in mold manufacturing. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. com Discover why you should avoid knit lines when designing and manufacturing injection moulded parts. 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. These data were obtained from many andKnit lines in injection molding are common defects of the molded parts. Plastic injection molding is the industry’s most common way to manufacture parts. They occur when melt flow fronts collide in a mold cavity. With fast accurate, injection-mold simulations, designing injection-molded products, developing injection molds, and shooting parts is more collaborative, accurate, and efficient, saving time and driving down costs. Second, the runner leading to a tab gate takes up real estate within the. We look forward to offering support and advice on your next project. To prevent knit lines, injection molders can increase the temperature of the molten resin to prevent solidification from starting too soon, and increasing injection speeds and pressure are also potential solutions. Als einer der führenden deutschen Hersteller von Masterbatches stellen wir nicht nur Farb-Masterbatches, Additiv-Masterbatches und funktionelle Kunststoff-Compounds her – wir leben deutsches Forscher-, Ingenieurs- und Unternehmertum. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). This performance can ultimately impact many part properties, including surface quality, knit line strength, part ejection force (sticking), dimensions, tolerances. Monoform parts. Knit lines. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. 0 Items. Reinforcing ribs play a pivotal role in the strength of a plastic part. Troubleshooting Injection Molding Weld Lines. The advantages of compression molding include more isotropic fiber distribution, dimensional stability, and surface finish. There are processes such as gas assist that do not require the injection unit to pressurize (pack out) the cavity, but for our discussion, we will stay with conventional injection molding. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Learn how material selection, part design, and optimizing process parameters can help eliminate knit lines. Family molds. Flash: All plastic injection molds contain parting lines, which create the potential for small amounts of molten plastic to escape the mold cavity’s boundaries. 01 inches between parts fitted together to work best. 5. Reduce the injection speed to limit the risk of trapping air inside the mold. Knit/Weld Lines. These lines are the result of the molten plastic material recombining after splitting and flowing around an obstacle in the mold cavity. Depending on the resin, resin temperature, mold temperature, and filling. Additionally. 18/06/2021. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. Weld/Meld/Knit lines are all terms describing the effect of two or more flow fronts of material joining or meeting together in the part. 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. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. These knit lines affect the parts aesthetics, but also they generally decrease the strength. Mold Venting. C. Vacuum. The quality of the answer is directly proportional to the information we have to work with. 012 in. Imagine a river splitting to go around a rock, then meeting up again on the other side. weld lines may form during the injection molding process and work closely with the plastic injection molder and tool builder to choose the best possible gate location. The Demo Mold helps those new to injection molding easily visualize the process and is a great teaching device for educators. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. a knit line will form 180°on the opposite side from the gate location. . As these flow fronts come together. 0 mm) is crucial to ensuring that parts cool evenly. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. • Repair parting line • Weld up vent depth Gate blush • Melt Fracture • Adjust injection speed (fast/slow) • Increase melt/mold temperatures • Resize gateFeedstocks for injection molding show two rheological behaviors: Pseudoplastic (shear thinning) and Dilatant (shear thickening) behaviors. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. , under its Advanced Technology Program (ATP). Knit lines are formed in injection moulding when two flow fronts meet in the middle of a part (a line where two sides of the plastic are “knit” together). Gate and Knit Line Locations<br />. Mold cooling is one of the most important variables in injection molding. These lines occur usually around holes or obstructions and cause locally weak areas in the molded part. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. Knit lines and other aesthetic characteristics of the part are strictly related to the plastic’s temperature during molding, so efficient filling time is essential for achieving proper welding lines and quality parts. If you want to better understand the process of injection molding, there are a few critical terms you need to know. These flaws can affect the aesthetic and structural integrity of the. Injection Molding Injection molding is perhaps the most common and important of all plastic processing processes. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. Subscribe to Our Newsletter. Also known as a knit line, this is the point at which two flow formations meet and are unable to. 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. Causes 1. 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. An edge gate introduces material at the main parting line, or where the two halves of. . The result is a consistent flow of molten plastic during injection and a quicker filling time. What causes knit lines? Knit lines are formed when the molten plastic flowing into the mold cavity runs into an obstruction, such as a core pin that forms the through hole on a flange of an enclosure. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. BURN MARKS Burn Marks: burn marks can occur when the design of a plastic part, and the subsequent injection mold design, causes air to be trapped during the injection (or filling stage) of the molding cycle. 3D printed molds in the injection molding process to lower costs and lead time. Usually the parting line of the mold is perpendicular to the mold opening direction of the injection molding machine. Also known as weld lines, knit lines. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. As a result, a rib at the weld line junction can strengthen the bosses at the mold line. 125 inches. Facebook. Gate size can be increased or moved to a section with greater wall thickness to help eliminate. The most common and one of the most challenging injection molding defects are weld and knit lines. extend mold service life. Use the fewest number of gates possible. A machine heats and mixes the plastic until it is in a pliable molten shape, then a screw device turns to force the plastic into an outlet that leads to the mold. A knit line is any line, visible or not, where two resin flows meet. Starting in September, the CoPilot process control system developed by RJG will come equipped with valve gate control. Services. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Trapped air in a mold manifests itself as a burn mark on the molded part. Depends how hard you want to push it. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with. In a weld line, reinforcement fibers. Notched weld lines then remain near the cavity walls. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. Call 800-985-6750 or email your inquiry to sales@customgasketmfg. Holes in the part will always cause knit lines. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. 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 adhesiveWeld 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. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Possible causes: Low temperature or fluidity of melted plastic during injection molding. All the while, the material could be the correct material," Hill says. Weld Lines-3 Ways for Detecting and Correcting. even though injection molding temperatures are _____ compared to metals, the thermal expansion of plastics is _____ to _____ times that of metals. For the metal feedstock, injection and mold-wall temperatures were 130 ºC. 3 To get the most out of your Xometry Injection Molding experience, we offer the following part Design Guide with. ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. Strength at the knit line can be as little as 20% of the. Venting. Basic rule of thumb air in mold must be able to escape at theInjection molding is the predominant manufacturing process used for producing transparent polymer products. Having uniform wall thicknesses between 0. Heat resistance. Its superior flowability allows for precise and flawless filling of injection molds without the risk of flow marks and knit lines. 008 to 0. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow molten plastic to flow down between the pin and hole surface. These include: Symmetrical parts. Starting with small part size, students learned to think about detailing on a product at thisTable 2. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. The Problems & Solutions course is designed to train injection molding personnel in. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. It is best practice to maintain a uniform thickness throughout an injection-molded part. wall thickness injection molding ribs. Understanding Knit Lines in Injection Molding: Causes and Solutions. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. These structures are often small surfaces of about a tenth of an inch in diameter. See full list on fathommfg. Find out more by calling 573-437-4154 today or email us. This line does not normally impact the overall shape or dimensions of the item. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different. ABOUT THE AUTHOR. Kim, who has worked for hot runner system and auxiliary equipment supplier Yudo-Abiman for 12 years, most recently as. Given the cosmetic requirements, there is a good chance the mold would require. It’s called sequential valve gating, or SVG. 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. The knit line strength and other packing related properties both aesthetic and functional of injection molded polymeric products is improved by equipping the mold with packing pins. occupied frequently with troubleshooting injection molding. In layman’s terms, injection molding boils down to four simple steps: Melt material. 015in wall. All the while, the material could be the correct material," Hill says. Unsymmetrical filling makes knit lines in samples, leading to the failure of part, so it must be avoided. They are the result of fundamental physical effects taking place inside of the mold. Look for signs of stickiness or burning. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Different plastics make different types of knit lines. In fact, knit line strength will decrease with higher filler content and with longer fibers. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. One common problem that occurs in injection molding is the formation of knit lines. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Remove the hardened material from the mold. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. This summary represents a key subset of the detailed molding information found in the remainder of this molding guide . While this process is largely efficient and reliable, it's not without its potential issues. Complex parts can be reproduced with low cost once mold is manufactured. Weld-lines, also referred to as spider-lines or knit-lines, are regions in the wall of an extruded plastic pipe, running the whole length of the pipe, at which there is a change in dimension and a. Nicolet Plastics LLC. They again get resolidified along the surface. This slight depression is a tiny line called the weld line or knit line. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. , 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. ” 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. Submarine gates are another injection molding types of gate that is located below the surface of the part, typically on the underside or back of the part. The Difference Between Knit and Meld Lines–and Why It Matters. 5. Weld lines defects are formed when two flow fronts are merged together. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. Those are knit lines, formed when two opposing flows of material join together in the mold cavity. This can dramatically reduce the effects of material changes, according to the injection molding technology company. As a result of weak coupling along the knit-line, the weld-line strength can be only about 60% of that of an unreinforced resin. The depth of the texture or letters is somewhat. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. This, in turn, leaves a large tab to be trimmed, a process that can mar the finished surface. BURN MARKS Burn Marks: burn marks can occur when the design of a plastic part, and the subsequent injection mold design, causes air to be trapped during the injection (or filling stage) of the molding cycle. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. A plastic product formed by the injection mold is divided into two parts, and the line separating the product is called the parting line. Plastic melt and mold temperature. 008 to 0. The area generally has lower strength than the other areas of the part. Plastic is then injected at high pressure into the mold, and it solidifies with any surface features or defects in. End-of-arm tooling can make or break a program. Macromol Symp 1988;21/21: 489-500. Contact Universal Plastic Mold Today. Venting at Weld Lines. 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. Mold Flow Analysis computer. . 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. Imagine a river splitting to go around a rock, then meeting up again on the other side. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. 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. Vacuum on the mold does help and many times eliminates the weld line. If life safety is involved, or reliably or efficacy are absolutely required, every part should. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. To account for variations in viscosity, nylon injection molding machines need to maintain an appropriate injection pressure. Submarine Gates. Knit lines, holes, part configuration and the talent of your molder all come into play. Exploring common molding defects and. injection molding machines using standard industry practices . A screw-type plunger forces the material into a heated chamber, called a barrel, where it is melted. They appear around holes or seams of an injection.