Knit Lines 11: 1. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. We have two unique offers to meet your needs wherever you are in the product lifecycle. 7. These lines occur usually around holes or obstructions and cause locally weak areas in the molded part. Probable Cause Suggested RemedyI 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…Opening and closing all the valve gates at the same time necessarily limits the degree of control over weld or knit lines, gas traps, localized packing, and unbalanced flow. Our glossary of terms provides definitions for a wide range of injection molding terms. Jabil (formerly Nypro) is uniquely qualified to offer a state-of-the-art curriculum in injection molding and related disciplines, which require highly specialized skills and continuous. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. This slight depression is a tiny line called the weld line or knit line. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Learn more. Core Geometry. In. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. You don't give us much to go on. Heat resistance. ABOUT THE AUTHOR. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. Not always a problem, but can cause serious structural issues. BLEED – (1) To give up color when in contact with water or a solvent. In the 1947 book, Injection Molding of Plastics, the late Dr. LS Mtron Injection Molding Machine (IMM) has opened a new business unit in Mexico. The injection molding process is fairly simple, plastic resin is heated to its melting point and forced through the machine and into your mold to produce your plastic parts. 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. They are formed when two or more flow frontFor more information on our custom rubber molding services or to speak with one of our knowledgeable professionals, please feel free to Contact Us or complete our online Request For Quote form. Notched weld lines then remain near the cavity walls. The process is extremely versatile, and can produce very complex shaped parts, with the use of multi-sided molds. 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. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. These are caused by the shot of molten plastic moving at different speeds throughout the injection. Reduction of sink can possibly be had by switching to an ABS/PC-blended material. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. Weld lines, also known as knit lines, are lines that appear on the surface of an injection-molded part where two or more flow fronts meet and fuse together. Three terms that often get mixed up are weld, meld, and knit lines. Understanding Knit Lines in Injection Molding: Causes and Solutions. The linear mold shrinkage of injection molded parts will vary from 0. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. Observation on a “trial and error” basis may be required. Specifically, Stokes and. Weld Lines-3 Ways for Detecting and Correcting. RJG announced that its injection molding process control system, CoPilot, will begin offering valve gate control technology for hot runners starting in September 2021. Excessive injection pressure can result in part defects such as overflow or flash. These structures are often small surfaces of about a tenth of an inch in diameter. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. Wavy lines are another feature of weld lines. PTI, a plastics and metal parts molder, is a leading developer of the MIM process. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. Knit lines, also known as weld lines are areas in the. occupied frequently with troubleshooting injection molding. Having uniform wall thicknesses between 0. 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. This course outlines mold filling and how different gating configurations affect filling. Meld and knit lines are actually both different types of weld lines. com . In addition, the force of the gas holds the appearance side of the part in contact with. Operating Conditions • Fast injection fill speeds, supporting short injection times (1–3 s), especially in thin sectionsKnit lines in reaction injection moldings Knit lines in reaction injection moldings Maier, Christian; Hrymak, Andrew N. While injection molding itself is a straightforward process involving melting. The Troubleshooting Tips below offer common solutions to challenges in IML and IMD. 5 : 1 and a L/D (length toMold flow analysis is a software simulation which show how the resin fill in the mold in injection molding process. You don't give us much to go on. 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. Injection moulding (U. Ham Lake, MN 55304. Because viscosity is a. 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. A weld or meld line is a weakness or visible. This defect is caused from excessive lube or oily stock. The recommended minimum production volume for injection molding is 500 units. It allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. 6. Also known as string lines. In a weld line, reinforcement fibers. They need the interference of about 0. This will helpWeld line. H-13 Good general purpose tool steel. 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. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. On the opposite side. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. 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. The area generally has lower strength than the other areas of the part. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. injection molding machines using standard industry practices . We recommend walls to be no less than 40 to 60 percent of adjacent wall thickness, and all should fit within recommended thickness ranges for the selected resin. Users will be able to use in-cavity pressure or temperature sensors to control when the valves open or close. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. After samples have been approved, it’s time to kickoff. Nicolet Plastics LLC. Tips for Avoiding Knit Lines in Injection Molding Keeping the proper temperature in the injection molding machine, runners, and within the mold are all key to ensuring. Knit line Knit line Start of mold filling. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. txt) or view presentation slides online. Flow Lines. . "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. 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 venting7. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. [8] Bevis, MJ, Reis RL, Cunha AM. They are the result of fundamental physical effects taking place inside of the mold. And, for those who can work within its limitations, rapid injection molding may be suitable for producing some optical parts (and cost as much as 90 percent less than traditional tooling). Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. such as knit lines and other imperfections. Our plastic injection molding glossary provides key terms. 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. C. 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 adhesiveMolding 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 adhesiveMost failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold. Also known as a knit line, this is the point at which two flow formations meet and are unable to connect during injection molding. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all, be a. suppressed cooling and possibly warp. 05-million grant for MIM R&D from the National Institute of Standards and Technology (NIST) in Washington, D. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. • Holes formed by core pins are, in essence, 360° inside corners and should follow. 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. For example, increasing gate size can improve part filling. In injection molding terms, these are called “living hinges” and are made right into the design instead of adding them later. A wide variety of tool steels are available for injection mold construction. While injection molding itself is a straightforward process involving melting. Increase the injection speed. Injection molding can use thermosets or thermoplastics. Meld and knit lines are actually both different types of weld lines. Following lists causes and solutions for weld or knit lines. Other common issues associated with thin walls include uneven cooling, warp, cracks, cosmetic texture inconsistencies, and weak knit lines or fracture points. ISO 9001:2015. Heat: Too much heat can have an appearance similar to moisture splay. If you want to better understand the process of injection molding, there are a few critical terms you need to know. 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. be impressed by improvements of bubbles (vacuum voids), short shots, unequal thickness, jetting marks, weld lines, knit lines, black streaks, strain 2. Adjust the design for the flow pattern to be a single source flow. Corrosion resistance. Throughout the molding process the press operator visually inspects the molded parts as they come out of the mold for any imperfections such as air trap, knit lines, backrinding, or tearing. Drying Considerations For both virgin and rework, hopper dryers sized to afford theWhen establishing the parting line, we must first define the shape and position of the parting line on the plastic molded item. . Weld line. Bubbles are caused by melting flow fronts colliding in a mold cavity. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. knit lines and parting lines are at the discretion of MIC-ZG. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. The advantages of compression molding include more isotropic fiber distribution, dimensional stability, and surface finish. While not always visible, weld lines (aka knit lines) are where two resin flows meet. Weld-lines, also referred to as spider-lines or knit-lines, are regions in the wall of an extruded plastic pipe, running the whole length of the pipe, at which there is a change in dimension and a. The final molding process may be dependent upon factors. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. As the polymer resin is injected into a mold, it flows through all parts of the mold. Molding is a manufacturing process in which resin in a barrel is heated to a molten state,. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. Learn how to troubleshoot weld lines in injection molding. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. With the help of mold flow analysis and mold flow service, mold designers understand how the material fill to position gates better, anticipate where the knit line will appear and locate difficult to fill spots in the injection mold. These materials have beenThe wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. This is a video excerpt from our Problems & Solutions Course - Weldlines. The weld line can either be a minor cosmetic issue. Disadvantage: May rust if improperly stored. In situ injection molding of continuous fiber reinforced thermoplastic composites is challenged by unbalanced dual-scale infiltration flow due to the pronounced capillary effect. 4. , 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. 5 to 3. Gating. 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). These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. [8] Bevis, MJ, Reis RL, Cunha AM. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Submarine gates are another injection molding types of gate that is located below the surface of the part, typically on the underside or back of the part. Shorter knit lines must equate to a stronger part. Vertical Plastic Injection Molding. Knit lines don’t always compromise the structural integrity of plastic parts. The tooling engineer in the mold house will be more into venting, sprue pressure, preheating the mold, cycle times, ejector pin scheme, mold flow, getting a gate location to avoid fill issues or knit lines, excessive flash and molding pressures, and the list goes on. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Resin pellets are loaded into a barrel where. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. As a result of weak coupling along the knit-line, the weld-line strength can be only about 60% of that of an unreinforced resin. Most failures occur at what are called “weld lines” or “knit lines”. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Increasing injection speed. Molding is a manufacturing process in which resin in a barrel is. 030 and 0. Brent Strong, p. This makes the casting process as efficient and accurate as possible. Contact us. Take these steps to avoid knit lines. An injection mold that produces pieces while the final tool is being built. 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. In fact, knit line strength will decrease with higher filler content and with longer fibers. 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 is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. Macromol Symp 1988;21/21: 489-500. Flow lines, also known as weld lines or knit lines, are discontinuous lines or streaks that appear on the surface of an injection-molded part. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. Solution: Increase the injection pressure or speed. - Mold flow analysis to control fill and knit lines. This design tip offers several ways to make your next multipart design less like a root canal and more like a day on the beach. To learn more about us or to get a quote, click here or call 1. Weld Line defect analysis, the most common of many defects in injection moulding products. Use the fewest number of gates possible. This article will look at two common venting options—using traditional machined vents and venting through porous materials—to help you decide which is right for your application. There are processes such as gas assist that do not require the injection unit to pressurize (pack out) the cavity, but for our discussion, we will stay with conventional injection molding. The main causes of Weld Line or Knit lines are: Convergence of two flowing polymer melt streams during injection molding process: This is the most common cause of weld lines, as the two melt streams coming from different runners or gates in the mold meet and do not fully mix, creating a weak point in the finished product. 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. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. As a result, the portion has a faint, perhaps undetectable line. More about the knit lines in injection molding. This can dramatically reduce the effects of material changes, according to the injection molding technology company. This radius should not be smaller than 0. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. And the lead-time for overmolded and insert molded parts is 15 days, a bit longer than FacFox’ single-part injection molding turnaround, but still much faster than traditional insert molding. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. placed usually in the areas last to fill, near knit lines, as well as on the runner system. 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. This configuration positions the injection mechanism at the top of the mold, allowing gravity to play a role in filing the mold cavities. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. Understanding Knit Lines in Injection Molding: Causes and Solutions. Steven. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Gates that are too small can also cause the uneven flow of material or result in knit lines, blemishes that occur where two resin flows meet. These lines. - You hit on this a little, but dealing with the parting line and ejector pin marks is pretty important, and isn't as simple as it seems at first look. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. 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 adhesiveIt tells them that you visualized how injection molded parts cool and harden. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. Round Rock, TX 78660. Increase the injection speed. Weld/Meld/Knit lines are all terms describing the effect of two or more flow fronts of material joining or meeting together in the part. Thick sections take longer to cool than thin ones. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. 01 inches between parts fitted together to work best. Adding vents, using overflows, or using porous metal. 250 in. Core out parts to eliminate thick walls. Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. 015in wall. Knit lines, holes, part configuration and the talent of your molder all come into play. Specific attention to processing details will enhance quality and productivity . injection molding. 008 in. Gating. Undercuts add cost to tooling and molding, which is recommended to eliminate or minimize as possible. 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. For best results, keep thickness variations to within 15% of the nominal wall thickness. This production method is particularly popular when manufacturing in large quantities. 13758 Johnson Street NE. 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. Figure 1: D-shaped through-hole in center of gear part accepts the drive shaft. A weld line can also be called a knit line. Injection rate plays a role—faster fill times develop more shear, molecular orientation and residual stress. . This will help the mold designer to determine the allowable gate and knit line locations. S. 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. Knit lines may also be called stitch lines, weld lines, or meld lines. The linear mold shrinkage of injection molded parts will vary from 0. To avoid walls that are too fat or too thin, designing a wall thickness between 0. Plating and painting applications usually require slower fill rates to keep orientation low. 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. Back to News Page. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. com Discover why you should avoid knit lines when designing and manufacturing injection moulded parts. Make sure the venting is not too large. Anisotropy. Shear Controlled Orientation Injection Molding of Polymeric Composites with Enhanced Properties. Starting with small part size, students learned to think about detailing on a product at thisTable 2. Troubleshooting Injection Molding Weld Lines. 3. A mold with too few gates is susceptible to cooling problems, but a mold with too many gates. Know about the cause of these lines and the potential solutions. Usually the parting line of the mold is perpendicular to the mold opening direction of the injection molding machine. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. opposed to two or more gates. ” 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. Injection molding is the most widely used method for mass-producing plastic parts. Weld-lines or knit-lines are formed during the mold filling process when the split melt flow fronts meet at the same downstream location. Injection molding is an excellent way to create plastic parts in bulk, but there are many problems that can cause cosmetic defects ranging from minor to major. Reduce the temperature of the mold and plastic being injected. Notched weld lines then remain near the cavity walls. Knit Lines: Holes in the part will always cause knit lines. Find out more by calling 573-437-4154 today or email us. Gate and Knit Line Locations<br />. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 2. What Are Cosmetic Standards for Plastic Parts?. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. knit line. Dimensional stability. They have their origins in material choice, part design, tooling, and processingInjection molding is generally restrictive (not including special processes) in the cross-sectional size of the part, while blow molding allows for channels in the part that increases strength. sinks, knit lines, and shrinkage,” Spalding says. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. The last cause of flow lines may be the operators running your daily operations. 1. Once the plastic sets, the mold opens to eject the product. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. Typically, this fillet radius should be somewhere near 0. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022injection-molding machine (Arburg allrounder 320C, Germany). Depends how hard you want to push it. 18/06/2021. Runner Type. AS9100:2016. Hardware components. 5mm (0. Demo Mold. Proper venting is essential to molding a defect-free part. knit line formation, application of draft angle and design for assembly. RE: Knit Line Affect On Material Strength lorelei5607 (Automotive). 5. 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. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. All the while, the material could be the correct material," Hill says. 4. They again get resolidified along the surface. This, in turn, leaves a large tab to be trimmed, a process that can mar the finished surface. When the molten plastic meets an obstruction. Weld Lines-3 Ways for Detecting and Correcting. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Looking to Your Knit Lines with Molding. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Weld lines may appear like seams or scratches,. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. The leading edge of the molten material is often the coolest point and the closest to solidifying. As a result, prototyping is strongly recommended for parts with. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. As a result, a rib at the weld line junction can strengthen the bosses at the mold line. Knit / Weld Lines. Visual indicating with an finished part that are formed by the junction from two plastic flow fronts. One of the most important aspects of hot runner system design is the gate location, which is the point where the molten plastic enters the cavity. The following are general guidelines for molding acetal. If debossed pattern is indispensable, it should have a depth of no less than 0. Below is a list of items that should be checked both during normal molding operations and if defects are detected. [1]Weld Lines. When designing for injection molding, consider these steps to prevent knit lines Resin cools as it is injected into a mold. The specific method is that when the product is just filled and filled in the cavity, the insert is used to cut the soft material melt in. The comment on melt flow index is correct, but, I've molded straight PC down to . Thermoplastic Elastomer Molding Guidelines. Weld line are formed whenever melt fronts separate and recombine at some downstream location. Table 2. During the injection molding process, molten plastic is injected into a mold cavity through a gate. Obstructions in the part create weld lines or knit lines during injection molding. These include: Symmetrical parts. This month, we covered an array of topics including injection mold venting, business strategies and runnerless micro molds. Because injection mold design and processing is complex, a set solution will not solve all problems. 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. The injection molding processing conditions for filling are given in Table 1. ; Wood, Philip E. A weld line, also known as a knit line, is a visible line or mark that occurs in an injection-molded part where two or more melt fronts meet and fuse together during the molding process. Knit lines, holes, part configuration and the talent of your molder all come into play. Temperature is another factor that can cause weld or knit lines in injection molding. reduce mold maintenance cost. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. We all know that injection moulding is great for producing both custom prototypes and end-use production parts, but if you are not careful it can cause some. A parting-line vent. , under its Advanced Technology Program (ATP). Look for signs of stickiness or burning. Complex parts can be reproduced with low cost once mold is manufactured. Also, since this part will likely be painted or chrome plated, knit lines are a concern. Weld / knit plane forms as flow fronts recombine Weld line and failure due to flow around core.