The mold maker may think that some minor defects are acceptable, or they may not even consider them from the beginning, which can cause problems when the injection mold is being manufactured. In compression molding, molds are closed around the charge, and in injection molding, the charge is injected into a closed mold cavity. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. Remove the hardened material from the mold. Possible causes: Low temperature or fluidity of melted plastic during injection molding. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. They again get resolidified along the surface. Excessive mould lubricant. Weld Lines. Minimizing or eliminating flow and knit lines is an additional benefit of using this material. com Three terms that often get mixed up in injection molding are weld, meld and knit lines. PVC pipes are manufactured by an extrusion process. Fig. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. The most common and one of the most challenging injection molding defects are weld and knit lines. It is important when selecting an injection molder that the right process conditions are used to reduce or eliminate the effects of. With plastic finishing plugs and end caps, we can help you keep your products protected while giving. 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. Example of a gate location in a finished part Example of knit lines in a finished part. 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. By using this method, theHowever, injection molding is not without its challenges. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. The thermo-rheological findings were used to investigate the sources of weld line weakness. (See Fig. Parting lines placed at intricate joints. weak knit lines and fracture points. Viscosity represents a broad concept with huge effects on any efforts to standardize an injection molding process. 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. Be wary of saving too much weight or you might end up with: cracking. In a well-designed mold, this is generally not a problem. Also discussed are weld and meld lines and their effects on molded. 020"). Adjust the design for the flow pattern to be a single source flow. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. 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. 2. Submarine Gates. Knit lines. An injection molding machine having a first mold portion and a second mold portion. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. Holes in the part will always cause knit lines. Weld lines occur where two flow fronts meet and always provide a source of weakness as the two fronts do not knit together. May happen at first shots while mold is being dialed in. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Design. Knit lines, holes, part configuration and the talent of your molder all come into play. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. directly! FCS Group, based in Taiwan, was established 40 years ago and is well known in Asia as a quality manufacturer of machinery, offering several lines of injection molding machines and other specialty and customized equipment. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Below is a list of items that should be checked both during normal molding operations and if defects are detected. If you need injection molding expertise, we’re here to help. An injection mold that produces pieces while the final tool is being built. One exception: ribs should be about 50. ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. Compression molding produces solid parts that are free of flow and knit lines. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. In layman’s terms, injection molding boils down to four simple steps: Melt material. An obstruction such as a core pin or holes will split the material flow and cause a weld line issue to form on the other side. The Goldilocks principle applied to wall thickness. Dedicated to strict quality management and thoughtful client services, our experienced staff customers are generally available to discuss your demands and guarantee full client pleasure for Knit Line Injection Molding, Electronics. 1. Compression molded parts can vary in thickness without issue. 2. These defects are not visible, like small. Parting lines lie along the edge of the molded part, between the core and the cavity. the thin blades. 1016/0254-0584(86)90019-2 Corpus ID: 136712450; Impact strength of knit-lines in injection moulded parts @article{Criens1986ImpactSO, title={Impact strength of knit-lines in injection moulded parts}, author={R. 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. 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. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Polym Compos 1982; 3: 88–96. ) Mold Analysis Tools. AS9100:2016. Let the molten material cool to a solid-state. Strength at the knit line can be as little as 20% of the. 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. Increase size of the vents. 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. excessive or premature wear at the parting line. Operating Conditions • Fast injection fill speeds, supporting short injection times (1–3 s), especially in thin sectionsGate and Knit Line Locations<br />. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. Runner and gates must be balanced. txt) or read online for free. Knit lines in injection molding are common defects of the molded parts. More about the knit lines in injection molding. 5mm (0. Whereas conventional injection molding uses. Flow rate and flow speed are cut in half at every runner branch. 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. Injection molding is the predominant manufacturing process used for producing transparent polymer products. 2020-01-1306. PROBLEM: POOR ADHESION OF LSR MATERIAL TO. Brent Strong, p. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. A knit line is the spot where two flows meet. Molding analysis study: An example of the low patterns and knit (weld) lines formation (MoldFlow® data) of injection molded round plastic part with a complex shape and with a ring. They are the result of fundamental physical effects taking place inside of the mold. Knit lines. So. No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. Solid or semi‐solid, this material leaves a distinct border with adjacent melted material similar in. LOCATION: Along any parting line. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. They occur when two resin flows meet at different. 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. Increase the melt and/or mold temperature. The company provides an array of digital manufacturing expertise. Fewer knit lines are produced and a smaller amount of fiber-length degradation is noticeable when compared to injection molding. Weld Lines-3 Ways for Detecting and Correcting. These are caused by the shot of molten plastic moving at different speeds throughout the injection. This normally occurs around holes or obstructions and causes locally weak areas in the molded parts. The most common location of knit line formation is behind molded-in holes that are made by core pins in the mold. 3,000 ton machines can cost $700,000. What Causes Knit and Meld Lines? Like many part inconsistencies, these unwanted features are rooted in product design. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause temperature. 5-3. While mold-filling simulation is a very common tool for predicting the fill patterns of an injection mold, in our judgment there is not yet a commercially available, satisfactory filling simulation for microcellular foam molding. Inappropriate temperature. Table 2. Compression-molding is also suitable for ultra-large basic. Weld lines, melt lines or Knit lines could be caused by different causes: - Low temperature of molding machine barrel - Inadequate back pressure - Injection pressure or injection speed is too low - Low mold temperature - Small injection gates and/or runners - Improper location of injection gate - Excessive gate land length1. Since our material is injected through a. Back to News Page. It’s also relatively inexpensive. In fact, for a 32-cavity mold, the flow rate in this example drops down to 0. The injection molding machine includes a fluid path extending through the first mold portion. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. (1. 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. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. In the injection molding process, melting takes place via two factors that work together: shear and heat. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Here are some reasons why design is important for injection molding. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. Part thickness control is through stacking of. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. land and using maximum vent depths to get them as close to self-cleaning as possible. 11) The part design must take into account possible knit line locations and work to direct them away from higher stress areas. 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. Knit Lines 11: 1. 26 = 0. 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. Multiple parts with complex design and differing wall. The resulting line has the. The fluid path has an inlet and a radially continuous, downwardly. 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. Based on the resin. Injection molding is an efficient, often cost-effective way to manufacture custom plastics that are strong, durable, and long-lasting. While this process is largely efficient and reliable, it's not without its potential issues. Injection molding is a manufacturing process that involves injecting molten plastic into a mold cavity to create a specific shape or design. Plastic melt and mold temperature. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. Crossref. Let’s. 0 and Table 1). Last month, in the first part of this two-part installment we focused on the reasons viscosity can change during injection molding. S. ABS. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. All the while, the material could be the correct material," Hill says. The depth of the texture or letters is somewhat limited, and extra draftInjection molding tool design and build for complex parts, with precision tooling and molding capabilities for industries demanding high-quality, critical components. Setting that Delta P is the secret to consistent fill time. Additionally. Venting at Weld Lines. It is one of the most common blemishes for manufactured products. Some. This can result in cosmetic defect or a weak point in the part. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. In addition to the main factory and development. Knit line / Meld. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Criens}, journal={Materials Chemistry and Physics}, year={1986}, volume={14}, pages={69-83} }A structural automotive sub frame component ( 10 ) that is formed from a sheet molding compound having carbon fibers. Knit line / Meld line / Transfer line Discoloured line where two flow fronts meet Mould or material temperatures set too low (the material is cold when they meet, so they don't bond). Steven. It tells them that you visualized how injection molded parts cool and harden. 5. The melt is forced to split up during filling of the cavity. wall thickness, knit lines, draft. 080" – 0. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. Knit lines, also known as weld lines are areas in the. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. 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. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. 5. As these flow fronts come together. Notched weld lines then remain near the cavity walls. 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. . Currently working with plastic, rubber, LSR, MIM molding companies to help them eliminate their complex molding challenges like air entrapment. 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. Using abrasives in a pressurized air blast to create a surface texture on the part. Gating. Additional venting along the parting line perimeter will improve overall venting significantly. The thickness of the part plays an important role in how difficult the molding process will be. The following are the conclusion drawn from the present research: 1. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. These knit lines are usually the weakest areas of the part. It can also aid in material selection since fill. 040-in. Obstructions in the part create weld lines or knit lines during injection molding. Part Shorts and has burn marks. 030- to 0. Let’s stop for a second and think about the logos we usually see on a daily basis. shows some obvious locations for vents, a brief molding trial should be conducted to observe where the gas voids occur. . Injection Molding: How to Set Second. The gate architecture and its location affects cycle times, tooling costs, lead times, the location of witness marks and many other potential defects that are commonplace for. 3. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. Plastic injection force exceeding the clamping pressure of the press. Weld / Knit Lines; Assumptions. Misra A. A knit line is any line, visible or not, where two resin flows meet. It emerges and becomes visible when the flow fronts cannot mold or knit during the molding process. 7. There are times when porous materials like Porcerax are used in problem or backfill areas. 2. Contact Universal Plastic Mold Today. They again get resolidified along the surface. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. The defect may be in part appearance or mechanical strength. Plasti-Co ® manufactures a wide range of injection molding nozzles from standard nozzle tips, extended nozzle tips, nozzle bodies, extended nozzles bodies, custom bodies, general purpose to full taper, shut-off, mixing and filtering applications. 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. 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. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. 0mm) throughout will ensure that the parts cool evenly and will prevent warping. Injection molding is capable of producing a lot of aesthetic options as well. They are formed downstream through holes, and between multiple gate locations. In this video, Chris Burda, applications engineer at Protolabs, shares what can be done to reduce knit lines and how they can impact your part's functionality. Troubleshooting Injection Molding Weld Lines. In fact, knit line strength will decrease with higher filler content and with longer fibers. Knit lines are formed when two or more plastic flow fronts collide and solidify or “knit” together during the molding process. When injection molding complex parts, often knit-lines are formed during the mold filling stage. 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. Learn how to troubleshoot weld lines in injection molding. Still, they are almost always a cosmetic issue. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. Poorly constructed or worn out mold. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Transfer molding also utilizes a press and a mold. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Meld and knit lines are actually both different types of weld lines. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. The most common and one of the most challenging injection molding defects are weld and knit lines. Double push filling method. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Such molds or tools aren’t intended to be used in operation. 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 . 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. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. weld line in injection molding. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. 4. And often, the mold is the same color as the plastic polymer, or can appear that way due to a lack of contrast caused by difficulties lighting the inside of the mold. Gas trapping/ poor venting. During injection, support pillars keep closed the two halves of the plastic injection mold. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Product designers encounter a wide range of challenges when. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. 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. But those key aspects can be viewed differently if you’re auditing mold changes before startup or troubleshooting changes for an already validated process. Nicolet Plastics LLC. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. – Change the thickness of the product. The Difference Between Knit and Meld Lines–and Why It Matters. Weld / Knit Lines; Assumptions. Using the design cube, learn how knit lines are formed on plastic parts and tips to avoid knit lines in your plastic injection molding design. Take these steps to avoid knit lines. Knit Lines. com. This will helpTroubleshooting Injection Molding Weld Lines. material Knit Lines Weld lines Small lines on the Caused by the melt-front flowing around backside of core an object standing proud in. A thermoset injection molding process may save as much as 50% of machine time per shot with a faster cycle time compared to a thermoset compression molding process, allowing molders to produce high quantities of thermoset components per day in multi-cavity tools. 120 in. It is also where a slide mechanism might meet where it shuts off on one of the mold halves. 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. Material contamination, for example, can cause several molding issues. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. Left: L-shaped perform. Here is a look at the. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. 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. In a weld line, reinforcement fibers. Prototype Tool In Soon As 10 Days; Production Tool In As Soon As 3 Weeks; 10k Parts in 10 Days; GET YOUR 30 SECOND QUOTE NOW. sinks, knit lines, and shrinkage,” Spalding says. Comprehensive. Moldflow is computer software that is widely used across the plastic injection molding industry to predict and optimize the injection molding process and assist with mold design. Plastic injection molding is the industry’s most common way to manufacture parts. They occur when melt flow fronts collide in a mold cavity. For. 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. Injection molding flow lines typically fall into one of the categories mentioned in the following table: Category: Type of Flow Line: Appearance (What It Looks Like) 1. Since the intention is to preserve fiber length in LFRTs by reducing. Trapped air in a mold manifests itself as a burn mark on the molded part. Bead Blasting. Therefore various injection molding defects can be eliminated. 3 /sec of material into a mold, don’t think the material is going into each cavity of a multi-cavity mold at the same 14. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. ”. Typically, injection molded parts will be between 0. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. Introduction to Knit Line Injection Molding Knit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection molding. 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. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. 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. Over the years, I have developed two separate “5M” systems. such as knit lines and other imperfections. Weld lines may appear like seams or scratches,. In addition, the force of the gas holds the appearance side of the part in contact with. 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. Weld lines may appear like seams or scratches, but that is not what they are. Weld lines have a significant effect on manufactured products. Compression molding produces solid parts that are free of flow and knit lines. incomplete filling or shorts. Refers to portion of injection molding part that has some taper to make it easier to remove from the mold. 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. These materials have beenDetermining the correct tonnage provides a foundation that must be rock-solid to avoid flash and damage. Common causes of flashing in injection moulding. Injection speed and pressure. To learn more about us or to get a quote, click here or call 1-888-893-1587 now. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. They appear around holes or seams of an injection molded part, and some may call them. placed usually in the areas last to fill, near knit lines, as well as on the runner system. Plastic melt and mold temperature. Expand. Using restrictors helps push visible knit lines into less conspicuous areas. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. More about the knit lines in injection molding. The specimens with a weld line at the center were obtained by double gate molding and the specimens without a weld line wereTherefore, 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. 3. The main types of injection molding defects are: 1. 12515 NE 95th Street , Vancouver, WA 98682 CALL TODAY: 1-800-839-0366Contact FU CHUN SHIN MACHINERY MANUFACTURE CO. These defects are not visible, like small. (1. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. Plastics Injection Molding Expert John Bozzelli covers. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Increase the size of the gate and runners to alter the mold design. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary from virtually invisible to something that looks like cracks in the plastic. land and using maximum vent depths to get them as close to self-cleaning as possible. opposed to two or more gates. The weld line can either be a minor cosmetic issue. We complete the part to your precise specifications with CNC Milling operations. 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. A thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold to produce a specific part geometry. 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. Meld and knit lines are actually both different types of weld lines. 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. The Fusion of Weld Lines. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Bubbles are caused by melting flow fronts colliding in a mold cavity. Flashing can be a common defect in injection moulding and can affect the appearance and functionality of the finished product. Insufficient injection pressure and speed can cause weld lines. When the temperature is not very high, there are chances of premature solidification, which can cause weld lines to form. Depending on the material you use, the knit lines could be invisible or obvious—work with an injection molding company to figure out how to reduce the mold lines on your product. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. There. A screw-type plunger forces the material into a heated chambe r,. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. Knit lines don’t. These lines occur usually around holes or obstructions and cause locally weak areas in the molded part. Sink. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. 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. 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. Meld and knit lines are actually both different types of weld lines. Islyn Thomas summarized the need for a particular vent location better than I ever could. The packing pins are sequentially. The structural stability of. In fact, strength at the knit line can be as little as 20 percent of the nominal strength of the part. The area generally has lower strength than the other areas of the part. POROUS MOLD MATERIALS. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). Disadvantage: May rust if improperly stored. Knit lines generally occur around holes or other obstructions to the melt flow. 120 in. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. But applying excessive force can create problems with the part, mold, and machine.