Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. This summary represents a key subset of the detailed molding information found in the remainder of this molding guide . Rynite® PET is usually processed with melt temperatures between 280 to 285 °C (535 to 545 °F) . 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. Visual indicating with an finished part that are formed by the junction from two plastic flow fronts. Injection molding can use thermosets or thermoplastics. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Weld lines may appear like seams or scratches,. Three terms that often get mixed up are weld, meld, and knit lines. Remedies: Raise the temperature of the mold or molten plastic. 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. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. All the while, the material could be the correct material," Hill says. For example, increasing gate size can improve part filling. 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. 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. 030 and 0. Weld line are formed whenever melt fronts separate and recombine at some downstream location. This performance can ultimately impact many part properties, including surface quality, knit line strength, part ejection force (sticking), dimensions, tolerances. 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. Mold cooling is one of the most important variables in injection molding. H-13 Good general purpose tool steel. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. 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. 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. These are caused by the shot of molten plastic moving at different speeds throughout the injection. 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. Different plastics make different types of knit lines. Injection molding can form complex geometries easily, apply single part with multiple functions. RELATED CONTENT. They again get resolidified along the surface. In a weld line, reinforcement fibers. The weld line can either be a minor cosmetic issue. So much. • Holes formed by core pins are, in essence, 360° inside corners and should follow. 3. 012 in. 5. Thin walls often lead to material flow problems, which can cause unformed areas. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. Double push filling method. Meld and knit lines are actually both different types of weld lines. 1513 Sam Bass Rd. This, in turn, leaves a large tab to be trimmed, a process that can mar the finished surface. Kim, who has worked for hot runner system and auxiliary equipment supplier Yudo-Abiman for 12 years, most recently as. The melt is forced to split up during filling of the cavity. Following lists causes and solutions for weld or knit lines. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Here are some of the most common cosmetic defects and how to avoid or fix them. Heat resistance. 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. Core out parts to eliminate thick walls. While injection molding dies are expensive to produce, each die canHowever, they can also create weld lines or knit lines in the part where the flow fronts meet. Injection molding is the most widely used method for mass-producing plastic parts. A knit line is any line, visible or not, where two resin flows meet. BLEED – (1) To give up color when in contact with water or a solvent. ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. In a weld line, reinforcement fibers. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. Mold venting should be checked and increased if necessary, injection molding service. Holes in the part will always cause knit lines. The recommended minimum production volume for injection molding is 500 units. The company provides an array of digital manufacturing expertise. In plastic injection molding, a parting line is where two halves of a mold meet when closed. The final molding process may be dependent upon factors. Draft. land and using maximum vent depths to get them as close to self-cleaning as possible. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Plastic injection molding is the industry’s most common way to manufacture parts. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. 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. Reducing the size and depth of depressions helps minimize the impact of knit lines. Weld lines are a common imperfection to be found in most plastic injected molded parts. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. Proper venting is essential to molding a defect-free part. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. The injection molding process is on the surface is fairly simple, plastic resin is heated to its melting point and forced into the cavity of the mold to produce a plastic parts. (2) Undesired movement of certain materials in a plastic. Example of a gate location in a finished part Example of knit lines in a finished part. Quick Guide to Injection Molding Amodel® polyphthalamide (PPA) equipment Amodel® PPA resins can be processed on conventional injection molding equipment. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Be wary of saving too much weight or you might end up with: cracking. Reducing the dimensions of the runner system. Flow Lines / Knit Lines Flow/Knit Lines 11. Still, it can be seen to varied degrees depending on mold. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. From Plastic Materials and Processing by A. Still, they are almost always a cosmetic issue. The goal is to create a uniform thickness and at the smallest (thinnest) level required. Not always a problem, but can cause serious structural issues. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022 Injection Molding Problems and Solutions (16/17) – Warpage Sep 15, 2022. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. 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. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. They occur when melt flow fronts collide in a mold cavity. In fact, knit line strength will decrease with higher filler content and with longer fibers. Piccarolo, S. A weld or meld line is a weakness or visible. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Knit lines, also known as weld lines or meld lines, are visible lines or seams that appear on a molded part where two or more flow fronts meet during the injection molding process. In fact, knit line strength will decrease with higher filler content and with longer fibers. 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. 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. Also known as weld lines, knit lines. A wide variety of tool steels are available for injection mold construction. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Venting at 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. Also, since this part will likely be painted or chrome plated, knit lines are a concern. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. With fast accurate, injection-mold simulations, designing injection-molded products, developing injection molds, and shooting parts is more collaborative, accurate, and efficient, saving time and driving down costs. Islyn Thomas summarized the need for a particular vent location better than I ever could. The packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. Venting. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. extend the time between mold maintenance shutdowns. This configuration positions the injection mechanism at the top of the mold, allowing gravity to play a role in filing the mold cavities. such as knit lines and other imperfections. 060 in. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. Advantages for your Injection Molding Machine:. knit lines and parting lines are at the discretion of MIC-ZG. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Step 1: The injection of molten plastic into the injection mold from Barrel A. Such molds or tools aren’t intended to be used in operation. 01 inches between parts fitted together to work best. 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. ). Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. This production method is particularly popular when manufacturing in large quantities. It is caused by the incomplete joining of the uncured. 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. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. 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. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. These lines. They are the result of fundamental physical effects taking place inside of the mold. Also discussed are weld and meld lines and their effects on molded. Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon. Adjusting features to be suitable for molding will help resin flow well into the mold, allow it to cool evenly, and reduce the chance of cosmetic defects such as sink, knit lines, flash, and warp. 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. Gate size can be increased or moved to a section with greater wall thickness to help eliminate. 1 Gate Location. They are the result of fundamental physical effects taking place inside of the mold. Press fits for injection-molded parts can be challenging. While injection molding itself is a straightforward process involving melting. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. Typically, this fillet radius should be somewhere near 0. The Problems & Solutions course is designed to train injection molding personnel in. Depends how hard you want to push it. All that considered, for a specific simple part with specific quality requirements. Learn more. 0 mm) is crucial to ensuring that parts cool evenly. In spite of its cosmetic attributes, a bad knit line can significantly. Reduction of sink can possibly be had by switching to an ABS/PC-blended material. Wall Thickness: The recommended wall thickness for injection molded POM parts is between 0. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Knit/Weld Lines. Demo Mold. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. The thermoplastic injection molding process at BEPL is a standard process involving an aluminum mold with no heating or cooling lines running through it, which means cycle times are a bit longer. Release of trapped air in those cases will. Most failures occur at what are called “weld lines” or “knit lines”. . Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Multiple parts with complex design and differing wall. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. • Repair parting line • Weld up vent depth Gate blush • Melt Fracture • Adjust injection speed (fast/slow) • Increase melt/mold temperatures • Resize gateFeedstocks for injection molding show two rheological behaviors: Pseudoplastic (shear thinning) and Dilatant (shear thickening) behaviors. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. Knit Lines. Knit Lines and Resins. See full list on fathommfg. One common problem that occurs in injection molding is the formation of knit lines. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. 140 in. Second, the runner leading to a tab gate takes up real estate within the. occupied frequently with troubleshooting injection molding. 030- to 0. Plastic Injection Molding Part Design Guidelines, Plastic part Design Guidance, Parting Line Draft Undercuts Wall Thickness & Uniformity Bosses Gussets and Ribs Radii and Corners Material Shrinkage Gating. Below is a list of items that should be checked both during normal molding operations and if defects are detected. The melt is forced to split up during filling of the cavity. Understand the causes of knit lines in injection molding and explore effective solutions to minimize their impact. "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. If debossed pattern is indispensable, it should have a depth of no less than 0. Behind the obstruction, the flows try to merge again, but this is made more difficult by a low temperature of the mold surface and a low melt pressure. You don't give us much to go on. The mold-opening force varies widely depending on the type and size of the molding machine. Slower injection provides less orientation and stress. Step 2: The injected molten plastic is cooled followed by the separation of the core and cavities. . Not always a problem, but can cause serious structural issues. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. Meld and knit lines are actually both different types of weld lines. 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. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. and 0. After samples have been approved, it’s time to kickoff. Thermoplastic Elastomer Molding Guidelines. 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. It is best practice to maintain a uniform thickness throughout an injection-molded part. This makes the casting process as efficient and accurate as possible. Knit lines are formed in injection molding when two flow fronts meet in the middle of a part (a line where two sides of the plastic. The recommended minimum production volume for injection molding is 500 units. Imagine a river splitting to go around a rock, then meeting up again on the other side. 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. 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. [1] Plastic injection molding is the industry’s most common way to manufacture parts. What causes knit lines? Knit lines are formed when the molten plastic flowing into the mold cavity runs into an obstruction, such as a core pin that forms the through hole on a flange of an enclosure. A machine heats and mixes the plastic until it is in a pliable molten shape, then a screw device turns to force the plastic into an outlet that leads to the mold. 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. Bubbles are caused by melting flow fronts colliding in a mold cavity. 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. Runner Type. The Jabil Molding Institute empowers employees, customers and suppliers to utilize the most advanced plastics and related manufacturing techniques in the world. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Trapped air in a mold manifests itself as a burn mark on the molded part. Our glossary of terms provides definitions for a wide range of injection molding terms. 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. Obstructions in the part create weld lines or knit lines during injection molding. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. pdf), Text File (. Wavy lines are another feature of weld lines. (called also weld marks or knit lines), and meld lines. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. Weld Lines-3 Ways for Detecting and Correcting. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. txt) or view presentation slides online. 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. Some are: Knit lines (discontinuities where two flows merged, creating a weak point)In some situations where a mold has parting line damage, reducing heat can actually improve flash that was a direct result of that damage. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Over the years, I have developed two separate “5M” systems. Inject the molten material into a mold. Knit lines. These include: Symmetrical parts. It’s also relatively inexpensive. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. Submarine Gates. For best results, keep thickness variations to within 15% of the nominal wall thickness. Short shots and knit lines are two phenomena that are caused by using highly viscousTherefore, changing the edges and corners of the mold core to make it buffer transition and keep the melt flow stable can prevent the occurrence of wavy lines. Starting with small part size, students learned to think about detailing on a product at thisTable 2. 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. ABOUT THE AUTHOR. You don't give us much to go on. Hardware components. Chris Newmarker | Dec 27, 2013. 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. [1]Weld Lines. CNC-Bearbeitung; Spritzgusswerkzeuge und -teile; Stereolithographie (SLA) Selektives. Plastic is then injected at high pressure into the mold, and it solidifies with any surface features or defects in. weld lines may form during the injection molding process and work closely with the plastic injection molder and tool builder to choose the best possible gate location. Because injection mold design and processing is complex, a set solution will not solve all problems. Weld Lines-3 Ways for Detecting and Correcting. To avoid these problems and create the best possible. One of the most common ways of adding venting is by manually machining it into the mold (Figs. It can also aid in material selection since fill. The last cause of flow lines may be the operators running your daily operations. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. Generally all plastic components should be designed with draft where possible. What you should know is that there are various failure modes for injection molding. Knit and Meld lines are inherent to plastic injection. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. They are formed downstream through holes, and between multiple gate locations. Facebook. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. This is the first article in a new series that will examine the injection molding process by breaking down the path a plastic pellet takes as it is transformed from Pellet 2 Part. mystagingwebsite. Only then can we move on to determining the parting line itself. Plastic melt and mold temperature. (1987). This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. 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. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. These flaws can affect the aesthetic and structural integrity of the. These seams are known as “knit lines. Fictiv can help you avoid injection mold design and plastic part design for injection molding problems. Insert injection molding is a process that requires an insert — typically metal — to be pre-placed in the tool for injected plastic to flow around. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. 7584. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. To account for variations in viscosity, nylon injection molding machines need to maintain an appropriate injection pressure. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Mold Venting. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. They need the interference of about 0. 453. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. Increase the injection speed. Vertical Plastic Injection Molding. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Plating and painting applications usually require slower fill rates to keep orientation low. These data were obtained from many andKnit lines in injection molding are common defects of the molded parts. Reduce the injection pressure. Macromol Symp 1988;21/21: 489-500. Having uniform wall thicknesses between 0. While injection molding itself is a straightforward process involving melting. Runner and gates must be balanced. Learn more about the process by reading this white paper. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. , 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. Commonly seen at the edge of a hole or other cored feature, knit lines are—as a. See UNDERCUT. A parting-line vent. Weld lines: Also known as knit lines, these are molding defects that occur when two flow fronts meet without the ability to “weld. 3. RJG announced that its injection molding process control system, CoPilot, will begin offering valve gate control technology for hot runners starting in September 2021. Unsymmetrical filling makes knit lines in samples, leading to the failure of part, so it must be avoided. First, they carry resin to the mold via a runner. Image credit: The Rodon Group. An injection mold that produces pieces while the final tool is being built. They occur when melt flow fronts collide in a mold cavity. 250 in. [8] Bevis, MJ, Reis RL, Cunha AM. Make sure the venting is not too large. 6. The injection molding processing conditions for filling are given in Table 1. 3. After selecting the direction in which the mold hole will be cut, it is much simpler to locate the separating line. Depends how hard you want to push it. 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. – Change the thickness of the product. When the molten plastic meets an obstruction. Trapped gas is one of the most common causes of part burns, and it can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. Insufficient injection pressure and speed can cause weld lines. PCS Company, Fraser, Michigan, has launched the Polimold Valve Gate Sequencer, providing injection molders with more precise control of the mold-filling sequence when using valve-gate hot runner systems. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. 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. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. The gate location affects the. com . Gating. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with. The linear mold shrinkage of injection molded parts will vary from 0. 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. The injection molding process offers a vast array of plastic resins to work with. The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. A well-designed injection-molded part will usually have draft, but the same draft that helps eject a part from the. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. to prevent improperly placed knit lines or sinking in the plastic downstream from the hinge. injection molding. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. 008 to 0. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Steven. As. Bubbles are caused by melting flow fronts colliding in a mold cavity. Exploring common molding defects and. Looking to Your Knit Lines with Molding. A knit line is any line, visible or not, where two resin flows meet. It is typically used for thermoset materials, but can be used with thermoplastics. Refers to portion of injection molding part that has some taper to make it easier to remove from the mold. Specific attention to processing details will enhance quality and productivity . Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Also known as weld lines, knit lines. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. For the metal feedstock, injection and mold-wall temperatures were 130 ºC. Understanding Knit Lines in Injection Molding: Causes and Solutions. Additional venting along the parting line perimeter will improve overall venting significantly. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. 05-million grant for MIM R&D from the National Institute of Standards and Technology (NIST) in Washington, D. S. End-of-arm tooling can make or break a program. ” 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. Knit lines don’t. weld line in injection molding. Most issues occur before entry into the mold.