Generally all plastic components should be designed with draft where possible. The design of the mold, as well as the part being molded, has a significant impact on the success of the process. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. Sequential valve gate technology. The injection molding was carried out in a DK-Codim 175/410 injection molding machine. 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. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. The Injection Mold Core A mold core is any member that forms the interior of a plastic part, usually on the "B" side of the mold parting line. Knit lines generally occur around holes or other obstructions to the melt flow. It’s also relatively inexpensive. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. In injection molding, a thermoplastic material is melted to a liquid state and injected into a custom, double-sided mold. Take these steps to avoid knit lines. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Plastic melt and mold temperature. A meld line occurs when two moving melt fronts converge and flow parallel to each other. In addition, the force of the gas holds the appearance side of the part in contact with. There are times when porous materials like Porcerax are used in problem or backfill areas. TWIM=Thin Wall Injection Molding; TSL=Toys,Sports and Leisure; NB=No Break; IMR=Inter Material Replacement. Too cool a melt. Knit Lines and Resins A knit line is any line, visible or not, where two resin flows meet (see Figure 2). The melt is forced to split up during filling of the cavity. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. Inject the molten material into a mold. In an injection molded structural plastic part, a weld line (also called a knit line) will result in a region of mechanical weakness as soon as the part is submitted to an external load. Injection Molding Guide. Compression-molding is also suitable for ultra-large basic. 5. Injection molding is an efficient, often cost-effective way to manufacture custom plastics that are strong, durable, and long-lasting. 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. Improve venting and/or relocate to burned area. opposed to two or more gates. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates. The Mold Tools toolbar provides tools for creating mold tooling (cores, cavities, etc. These are imperfections in the part where separated flows of cooling material meet and. The parting line location on the injection mold will have an effect on how the cavity and core (both halves of the injection mold) come together and seal. Knit line / Meld. Increase injection speed. 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. Plastic melt and mold temperature. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Here are some reasons why design is important for injection molding. Injection moulding (U. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. POROUS MOLD MATERIALS. As the polymer resin is injected into a mold, it flows through all parts of the mold. 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. Double push filling method. Getting started; Knit Line Injection Molding; Knit Line Injection Molding - China Manufacturers, Factory, Suppliers. Knit lines in injection molding are common defects of the molded parts. SEA-LECT Plastics has 16 MILACRON injection molding machines that range from 33-ton with a 2. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Weld lines are formed during cavity. 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. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. In the injection molding process, melting takes place via two factors that work together: shear and heat. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. If the plastic has cooled too much during the injection process it can lead to knit lines in plastic parts when they meet past an the obstruction. Plastic injection molding is the industry’s most common way to manufacture parts. a weld or knit line may develop on the opposite side of the obstruction as the two fronts of material join. material Knit Lines Weld lines Small lines on the Caused by the melt-front flowing around backside of core an object standing proud in. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses, elastomers, confections, and most commonly thermoplastic and. ” 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. 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. , Rallis, A. lines are formed when there is an obstacle in the cavity of the injection mold. Bubbles are caused by melting flow fronts colliding in a mold cavity. 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. A poor design can lead to many visual defects in the final part. weld line in injection molding. Contact Universal Plastic Mold Today. In the 1947 book, Injection Molding of Plastics, the late Dr. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Having uniform wall thicknesses between 0. 45 in. Mold cores can be machined from a solid piece of copper alloy or inserted to aid in construction or allow for easier replacement if a com-ponent would ever be damaged in molding. Mold filling simulation software should be used to ensure that waterInjection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022Main causes of knit lines in injection molding: 1. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Molding parts with multiple gates will almost certainly produce a weld line at right-angles to the line joining the two gates which could cause the weld lines to be exceptionally weak (see Figure 1. They again get resolidified along the surface. More about the knit lines in injection molding. 0mm) throughout will ensure that the parts cool evenly and will prevent warping. ) or as thick as 25 mm (1 in. This makes the casting process as efficient and accurate as possible. A structural finite element analysis (FEA) can be used to compare locations of high stress to the locations of the knit lines identified in the mold-filling analysis. ) are easy to produce. Alter the mold design. 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. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. We originally thought it may be caused by a silicone release agent that was occasionally sprayed on the injection mold, but testing with minimal agent and later built-in slip agent showed no change. Find out more by calling 573-437-4154 today or email us. Knit Lines. Vents for phenolic parts should be approximately ¼" (6 mm) wide and 0. The structural stability of. Steven. Disadvantage: May rust if improperly stored. Let’s stop for a second and think about the logos we usually see on a daily basis. The point I am making here is, if you’re injecting 14. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. 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. Nozzles for Injection Molding Machines. 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. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. In addition, the company is now providing three. CAUSE: 1. Plasti-Co. Venting at Weld Lines. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. The quality of the answer is directly proportional to the information we have to work with. The last cause of flow lines may be the operators running your daily operations. Weld line are formed whenever melt fronts separate and recombine at some downstream location. As a result, prototyping is strongly recommended for parts with. J (left) shows embossed feature and S (right) shows debossed feature in plastics through injection molding. Flow rate and flow speed are cut in half at every runner branch. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. It emerges and becomes visible when the flow fronts cannot mold or knit during the molding process. The point of meeting creates a weak spot because the edges of the molten plastic, already cooling, don’t mix together very well. doc), PDF File (. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. 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. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Short shots and knit lines are two phenomena that are caused by using highly viscousHowever, they can also create weld lines or knit lines in the part where the flow fronts meet. An injection mold that produces pieces while the final tool is being built. 2) Vents in an injection mold should let the air out, but not the liquid plastic. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. The specific method is that when the product is just filled and filled in the cavity, the insert. 02 in. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. RELATED CONTENT. Flow Lines. Gating. The recommended minimum production volume for injection molding is 500 units. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. Once the plastic cools, the mold is removed, and the object is ready for post-processing. Also known as a knit line, this is the point at which two flow formations meet and are unable to. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. 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. 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. This production method is particularly popular when manufacturing in large quantities. The second mold portion being movable relative to the first mold portion and together defining a mold cavity. Also known as “stitch lines” or “weld lines”. 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. When the mold adopts the multi-gate pouring scheme, the plastic melt. Meld and knit lines are actually both different types of weld lines. (for example, a hole on the plastic part), the knit line will be unavoidable. Consider adding mold release (can be added to the polymer itself by the polymer vendor) or at machine side Knit lines Weak knit lines Increase melt temperature Mold temperature too cold Increase injection speed Avoid nucleated products if possible Inadequate ventingWhat you should know is that there are various failure modes for injection molding. It can also aid in material selection since fill. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Some of the most popular brands include:Harshal Bhogesra has 9+ years of combined experience in molding, customer & supplier development. 827 Holes and Bosses. Use a thread with a pitch greater than 0. Knit/Weld Lines. Change gate locations. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. When injection molding complex parts, often knit-lines are formed during the mold filling stage. Part Shorts and has burn marks. It is also one of the most important weapons in a molder’s arsenal for making process changes. The main types of injection molding defects are: 1. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. As the polymer resin is injected into a mold, it flows through all parts of the mold. Knit and Meld lines are inherent to plastic injection. The runner and gate system used in plastic injection molding is responsible for directing molten plastic from the nozzle of the molding machine into the cavity of the tool. Polym Compos 1982; 3: 88–96. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. Knit lines form during the injection molding process when two resin flows meet. Parts as thin as 0. and Titomanlio, G. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. such as knit lines and other imperfections. 3. These defects are not visible, like small. The thermo-rheological findings were used to investigate the sources of weld line weakness. POROUS MOLD MATERIALS. There are times when porous materials like Porcerax are used in problem or backfill areas. 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. 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. 1 in. In a weld line, reinforcement fibers. This is easier to accomplish on. Short shots Trapped air in the mold can inhibit the flow of the material during injection, resulting in an incomplete part. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Therefore, with the cooling process, the resin in the central part shrinks and expands to the surface, resulting in insufficient filling in the central part, which is called vacuum. The resin is transferred to the mold cavity under positive. 040-in. In the present work, the micro specimens were investigated. Check/add vacuum; Check mold lube; Check/increase venting. They are the result of fundamental physical effects taking place inside of the mold. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. This can enable the. The injection of molding compound into the parts through one or two gates may produce parts that have knit 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. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. They occur when melt flow fronts collide in a mold cavity. 120 in. Three terms that often get mixed up are weld, meld, and knit lines. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. Injection mold design and custom tooling can make or break the success of a finished plastic product. Rynite® PET is usually processed with melt temperatures between 280 to 285 °C (535 to 545 °F) . Additionally. 2020-01-1306. Near-Net-Shape Molding enables us to eliminate knit lines, add undercuts, increase options for geometry and tolerances, and reduce tooling cost for low. 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. And like all manufacturing industries, plastic injection molding lines are more profitable the shorter the cycle time — so long as they produce quality parts. 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. Injection. Compression molded parts can vary in thickness without issue. 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. Undercuts add cost to tooling and molding, which is recommended to eliminate or minimize as possible. 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. Weld / Knit Lines; Assumptions. 3. M. 5. Injection molding is a manufacturing process that involves injecting molten plastic into a mold cavity to create a specific shape or design. Kurt W. In the 1947 book, Injection Molding of Plastics, the late Dr. Weld line in injection molding is line where two or more flow molten plastics knit together. A knit line may only be a cosmetic issue and affect. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. Mold cooling is one of the most important variables in injection molding. 453. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. How to Eliminate Knit Lines In Injection Molding - Xcentric Mold Want to learn how to eliminate knit lines that form during the injection molding process? Then. 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. 3,000 ton machines can cost $700,000. As a result, the portion has a faint, perhaps undetectable line. com TYPICAL PROPERTIES MECHANICAL THERMAL OPTICAL. Contact Us. mold venting is at the last filling point, whereby, while the melt flows forward in the cavity, air and gases flow out through the valve. 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. You can avoid knit lines and other problems by creating designs with smooth geometries. PROBLEM: FLOWLINES (ALSO CALLED WELD LINES OR KNIT LINES) Definition: Streaks, orange skin, or visible flow lines in parts . This image shows a PVC pipe after it was accidentally dropped on the ground. However, the weld line may not continue throughout the flow. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. sinks, knit lines, and shrinkage,” Spalding says. Knit lines. Such molds or tools aren’t intended to be used in operation. The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. Weld / Knit Lines; Assumptions. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. For instance, three widely used processes are insert molding, overmolding, and undercuts. The injection molding process offers a vast array of plastic resins to work with. Participating in DFM and mold flow analysis is a good way to achieve this. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. turbulent flow of Injection speed set too high. Weld Lines-3 Ways for Detecting and Correcting. (1. 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. Therefore various injection molding defects can be eliminated. Injection molding is capable of producing a lot of aesthetic options as well. Meld and knit lines are actually both different types of weld lines. In injection molding, it is often important to maintain consistent color throughout the part. The mold’s sprue bushing and locating ring is placed in a way that makes sure the injection molding nozzle is properly aligned and centered. Injection moulding (U. 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. Knit Lines. excessive or premature wear at the parting line. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. If you turn on the spigot to a garden hose, you will hear a hissing sound at the nozzle end for the first few seconds. 4. Draft. Thick sections take longer to cool than thin ones. These are imperfections in the part. 120 in. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Venting at Weld Lines. 1 in. 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. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Learn more. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Remove the hardened material from the mold. It is caused by the incomplete joining of the uncured. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022What is copper electrode in injection mold? hashtag#plasticinjectionmold hashtag#moldmaking "Copper electrode," also known as "electrode," is a common component in mold manufacturing. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. Let’s. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. "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. Three terms that often get mixed up are weld, meld, and knit lines. 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. A good injection mold design will take all of these factors into consideration, ensuring that the final product looks great. 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. 156 x 2 1/3 = 0. The process parameters were fixed as follows: Packing pressure of 40 MPa, injection time of 2. If I can answer any questions you may have on optimizing the plastic part design, CNC plastic prototype, mold manufacturing, and injection molding or if I can be of any other help, please feel. 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. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Because they can be shut off independently you can control flow fronts and knit-line locations. Edge Gates. 6 Monate. In injection molded parts, there are 2 types of weld lines: The first type of weld mark is called cold-melt joints and is formed when the melt front enters the cavity with different gates. Again, you would round this value up or down based on a standard cutter size, which is 13/64 or 0. Increase size of the vents. When setting a heat profile, consider residence time, screw RPM and filler type. No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. The company provides an array of digital manufacturing expertise. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Macromol Symp 1988;21/21: 489-500. 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. One solution is to use optimal wall thickness to help slow cooling during the ABS plastic molding process. New blog post is up! What Are Knit Lines in Injection Molding, and How Do You Prevent Them? #injectionmolding #moldsmart #howto #rjg…Injection moulding is a well established mass production tool for polymeric products of all shapes and sizes which is now drawing the attention of companies and researchers who seek to utilise this high throughput fabrication technique to produce devices with nanoscale dimensions []. This defect is caused when the polymer resin is injected into a mold and flows around a solid piece and forms when the resin collides back together without completely fusing back together. 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. Additional venting along the parting line perimeter will improve overall venting significantly. Obstructions in the part create weld lines or knit lines during injection molding. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. As. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Weld lines may appear like seams or scratches,. Material contamination, for example, can cause several molding issues. However, the process involves forcing the material through small holes into the mold cavity. A. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. Place vents at last place to fill and at converging flow fronts. Increase the melt and/or mold temperature. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). I am working on a thin PC/ASA injection moulded component which has a tendency to snap at the Knit-point (the final point of travel at which the…Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. Download : Download full-size image; 3. Meld and knit lines are actually both different types of weld lines. This defect is caused from excessive lube or oily stock. (1. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Meld and knit lines are actually both different types of weld lines. As these flow fronts come together. Knit / Weld Lines. 015in wall. 030- to 0. Temperature is another factor that can cause weld or knit lines in injection molding. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. In working with the injection molding service offered by Protolabs, you provide. Reduce the injection pressure. Inadequate injection pressure can result in knit lines and a surface that. ) Mold Analysis Tools. Another name given to weld lines is meld line. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. 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. Material contamination, for example, can cause several molding issues. Learn how small changes to an injection molding design like wall thickness or material choice can lead to more durable parts that are free of cosmetic defects. Left: L-shaped perform. Very high quality and an extreme fit may. 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. Weld lines or knit lines and meld lines formed when two melt fronts run into each other or join together can be improved by. Part Shorts No burn marks. 18/06/2021. Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon. Let’s. Adjust the design for the flow pattern to be a single source flow. Vacuum. LOCATION: Along any parting line. Brent Strong, p. Gate design is another critical piece of part function in plastic injection molding. The comment on melt flow index is correct, but, I've molded straight PC down to . Obstructions in the part create weld lines or knit lines during injection molding. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that.