Solution: People. Weld lines may appear like seams or scratches, but that is not what they are. shows some obvious locations for vents, a brief molding trial should be conducted to observe where the gas voids occur. These knit-lines are well-known as particularly critical regions in the mold when mechanically. Since our material is injected through a. Also known as knit lines. 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. placed usually in the areas last to fill, near knit lines, as well as on the runner system. (1987). What Are Knit Lines? When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. Meld and knit lines are actually both different types of weld lines. It is. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). 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 []. These knit lines are usually the weakest areas of the part. 3. To briefly describe, weld lines are also called knit lines. 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. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. 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. In an injection mold, the plastic fluid flows and spreads out in many directions as it comes out of the gate. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. The part is cooled in the mold until it is solid enough to be ejected. (1. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. 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. Part thickness control is through stacking of. 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. This production method is particularly popular when manufacturing in large quantities. One exception: ribs should be about 50. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. 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. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Flow Lines. This will help the mold designer to determine the allowable gate and knit line locations. Reduce the screw speed and adjust the backpressure. Solution: People. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. 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. Islyn Thomas summarized the need for a particular vent location better than I ever could. Meld and knit lines are actually both different types of weld lines. Place a vent in the weld line area to remove the entrapped air. turbulent flow of Injection speed set too high. To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. Crossref. In injection molding, it is often important to maintain consistent color throughout the part. Gating. A component of the injection-molding machine wherein the resin pellets are melted, compressed and injected into the mold's runner system. 120 in. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. Parts as thin as 0. Use the fewest number of gates possible. The comment on melt flow index is correct, but, I've molded straight PC down to . Double push filling method. Injection molding is capable of producing a lot of aesthetic options as well. CURE: Run the mold in. Three terms that often get mixed up are weld, meld, and knit lines. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. Participating in DFM and mold flow analysis is a good way to achieve this. Examples of different causes of PVC pipe failure. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. 080" – 0. The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. Submarine Gates. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. 040-in. 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. Knit lines don’t always compromise the structural integrity of plastic parts. Thermoplastic Elastomer Molding Guidelines. Multiple gates will always cause knit lines. Injection moulding (U. 5-3. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. 0 mm) is crucial to ensuring that parts cool evenly. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. 1. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. H-13 Good general purpose tool steel. From Plastic Materials and Processing by A. Meld and knit lines are actually both different types of weld lines. 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. The injection molding was carried out in a DK-Codim 175/410 injection molding machine. 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. com support@makenica. Injection moulding (U. Common causes of flashing in injection moulding. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. Fewer knit lines. The recommended minimum production volume for injection molding is 500 units. com. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. 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. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. We complete the part to your precise specifications with CNC Milling operations. Temperature is another factor that can cause weld or knit lines in injection molding. Determine the time duration of the molten state. These knit lines affect the parts aesthetics, but also they generally decrease the strength of the part. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. The company provides an array of digital manufacturing expertise. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different. However, the weld line may not continue throughout the flow. When designing for injection molding, consider these steps to prevent knit lines. Injection molding weld lines refer to a line on an injection molded part that is generated where the two halves of the mold come together. The goal is to create a uniform thickness and at the smallest (thinnest) level required. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all,. The process involves feeding the material into a press, where it is cooled or heated as per. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. Thin wall injection molding can produce walls as thin as 0. This continues until the weld lines in plastic injection molding disappear. Redesign the mold: Redesigning the mold to. 3 s, mold temperature of 60 °C and melt temperature of 250 °C. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Weld lines often leave witness marks in the moulding surface. This is a video excerpt from our Problems & Solutions Course - Weldlines. Weld lines occur where two flow fronts meet and always provide a source of weakness as the two fronts do not knit together. , Rallis, A. A knit line, also. In compression molding, molds are closed around the charge, and in injection molding, the charge is injected into a closed mold cavity. Plastic injection molding is a complex and highly intricate process. In spite of its cosmetic attributes, a bad knit line can significantly. To avoid these defects, manufacturers can check molds for the following: Low Mold Temperature: A mold temperature that’s too low will cause the material temperature to drop fast. 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. Crossref. 015in wall. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. When injection molding complex parts, often knit-lines are formed during the mold filling stage. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. RapidDirect – Your Best. Avoid adding threads directly on your injection molded part. They again get resolidified along the surface. Knit Lines in Injection Molding. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. Table 2 lists the<br /> properties of common tool steels and the typical mold components for which they are<br /> used. Over the years, I have developed two separate “5M” systems. TEFABLOC™ TESI 744 TPE compound for injection molding processing provides superior adhesion properties when processed using injection molding. Weld or knit lines occur when melt flow fronts collide in a mold cavity. There. The effect of holding variables and of injection and mould temperature was explored. Reducing the dimensions of the runner system. 26 = 0. 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. They again get resolidified along the surface. Molding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesivePrevents flow and knit lines. The areas in the cavity where such buildup tends to be common are at end-of-fill areas, details that trap gas, and knit lines. Knit lines in injection molding are common defects of the molded parts. Runner Type. Cold Slug: First material to enter mold during injection. Learn about the key characteristics of common injection molding materials, recommended applications, and how common thermoplastics compare to one another. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. 4. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Contact Universal Plastic Mold Today. 8 mm relief at the edges of the thread. Steven. 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. However, the process involves forcing the material through small holes into the mold cavity. Knit line / Meld. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. (Overpacking. As always, feel free to contact us at 877-479-3680 or [email protected] if questions or concerns emerge. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Weld Lines. ABS. Here is a look at the. Meld and knit lines are actually both different types of weld lines. 5mm (0. 5 inches) dispersed throughout the structural automotive sub frame component ( 10 ). Product designers encounter a wide range of challenges when. Reducing the dimensions of the runner system. Gate design is another critical piece of part function in plastic injection molding. See full list on fathommfg. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. 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 knit (weld) line is in the direction perpendicular to applied stress. Knit Lines. Left: L-shaped perform. Setting that Delta P is the secret to consistent fill time. a knit line will form 180°on the opposite side from the gate location. As the polymer resin is injected into a mold, it flows through all parts of the mold. 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. 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. – Change the thickness of the product. 2. Below is a list of items that should be checked both during normal molding operations and if defects are detected. Notched weld lines then remain near the cavity walls. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. Three terms that often get mixed up are weld, meld, and knit lines. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. Tooling & Injection Molding Services High-Quality Complex Parts. ) Mold Analysis Tools. 827 Holes and Bosses. Kurt W. The injection molding machine includes a fluid path extending through the first mold portion. 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. Bead Blasting. 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. Compression molding produces solid parts that are free of flow and knit lines. Depending on the resin, resin temperature, mold temperature, and filling. When the plastic cools, it takes the shape of the mold and is then ejected and finished. , 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. Design. 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 . 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. 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. Move the injection unit away from the mold during short breaks . Troubleshooting Injection Molding Weld Lines. It is important when selecting an injection molder that the right process conditions are used to reduce or eliminate the effects of. Holes in the part will always cause knit lines. 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. From: Polylactic Acid (Second Edition. 0 to 3. Knit lines, holes, part configuration and the talent of your molder all come into play. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Recommended for the bonding of nylon (polyamide) and polypropylene materials, this thermoplastic elastomer delivers wide compatibility and thermal stability, allowing for use in demanding conditions. 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. Also known as a knit line, this is the point at which two flow formations meet and are unable to. 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. 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. Two major sources of weld lines are multiple gating and flow around pins. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Gas trapping/ poor venting. These knit lines affect the parts aesthetics. 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. The packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. ) 2. Mold Venting. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 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). Our glossary of terms provides definitions for a wide range of injection molding terms. Meld and knit lines are actually both different types of weld lines. 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. This picture shows a. 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. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms. Knit lines. Obstructions in the part create weld lines or knit lines during injection molding. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. 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. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. Increasing injection speed. 060 and 0. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. This production method is particularly popular when manufacturing in large quantities. Knit lines are most common downstream of holes created in parts where the molten material meets. 0mm) throughout will ensure that the parts cool evenly and will prevent warping. 0 mm) is crucial to ensuring that parts cool evenly. These defects are not visible, like small. In layman’s terms, injection molding boils down to four simple steps: Melt material. 040-in. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. . Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. Sink Marks Cause 3: Improper Pack or Hold Pressure. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Sink Marks Cause 4: High Mold Temperature. Make sure the venting is not too large. As the polymer resin is injected into a mold, it flows through all parts of the mold. 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. DFM Helps Prevent Sink Marks In Plastic Injection Molding. As melt temperature, viscosity and abrasiveness rise, tool life will decline. Because injection mold design and processing is complex, a set solution will not solve all problems. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. Mold Flow Analysis computer. The injection molding process uses a granular plastic that is grav ity fed from a hopper. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. The influence of knit-lines on the tensile properties of injection molded parts. A thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold to produce a specific part geometry. In addition to the main factory and development. 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. Weld lines or knit lines and meld lines formed when two melt fronts run into each other or join together can be improved by. Get a free des. Injection molding machine and automation supplier Engel offers an array of technologies to simplify and speed up mold changes, including magnetic clamping platens and quick couplings; intelligent assistance systems; and the famox mold changing system for automating the set-up process. such as knit lines and other imperfections. 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. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. 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. As. More about the knit lines in injection molding. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 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 weld or knit line may develop on the opposite side of the obstruction as the two fronts of material join. Thick sections take longer to cool than thin ones. This makes the casting process as efficient and accurate as possible. But those key aspects can be viewed differently if you’re auditing mold changes before startup or troubleshooting changes for an already validated process. Draft. Gas-assisted Injection Molding: Influence of Processing Conditions and Material Properties. 030- to 0. สาเหตุรองของการเกิดปัญหาการเกิดประกายเงิน (silver streak) 1. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. 1. thick. PROBLEM: FLOWLINES (ALSO CALLED WELD LINES OR KNIT LINES) Definition: Streaks, orange skin, or visible flow lines in parts . A meld line occurs when two moving melt fronts converge and flow parallel to each other. 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. Plastic injection molding is the industry’s most common way to manufacture parts. 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. 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. Because they can be shut off independently you can control flow fronts and knit-line locations. Having uniform wall thicknesses between 0. This month, we covered an array of topics including injection mold venting, business strategies and runnerless micro molds. Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. These lines occur usually around holes or obstructions and cause locally weak areas in the molded part. Runner and gates must be balanced. 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. 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. This will helpTroubleshooting Injection Molding Weld Lines. . 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. ABS is a good choice for handheld consumer devices. S. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. For injection molding of the multi-blade fans and various rotating plastic parts, the complex of multiple gating injection molding tools were used. Poor venting. No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. And like all manufacturing industries, plastic injection molding lines are more profitable the shorter the cycle time — so long as they produce quality parts. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. Industrial Knitting Machines. Rapid heat-and-cool molding technologies have attracted increasing. 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. This is easier to accomplish on. Add a 0. Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon. A knit line may only be a cosmetic issue and affect. Mold venting should be checked and increased if necessary, injection molding service. These are imperfections in the part. Anisotropy. Near-Net-Shape Molding enables us to eliminate knit lines, add undercuts, increase options for geometry and tolerances, and reduce tooling cost for low. Compression molding and injection molding are very similar, but they have one major difference. Let’s. 0 and Table 1). 197 in. Let the molten material cool to a solid-state. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. 1050 Walnut Ridge Drive. Exploring common molding defects and. Macromol Symp 1988;21/21: 489-500. Contact us. 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. Injection mold design and custom tooling can make or break the success of a finished plastic product. As a result, prototyping is strongly recommended for parts with. Plastic injection force exceeding the clamping pressure of the press. This line does not normally impact the overall shape or dimensions of the item. Weld lines are also known as “stitch lines” or “knit lines”. The point I am making here is, if you’re injecting 14. 140 in. the thin blades. Find out more by calling 573-437-4154 today or email us. 5 to 3. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near. 160"). 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. 2. Flashing can be a common defect in injection moulding and can affect the appearance and functionality of the finished product. Incompletely fused extrusion knit Line. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. 45 in. One of the common defects that can occur in injection molded parts is weld line. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. It is also where a slide mechanism might meet where it shuts off on one of the mold halves. 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. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. More about the knit lines in injection molding. After the solidification of molten plastic, the finished part is ejected out. Improve venting and/or relocate to burned area. 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. Remedies: Raise the temperature of the mold or molten plastic. (1.