cold and hot weld line. Plastics Technology article (June 2018): Technical capabilities of the process have advanced to erase former cycle-time penalties, and ongoing developments address creation of a materials database and new applications in hybrid composite injection overmolding. Formation of knit line. When injection molding complex parts, often knit-lines are formed during the mold filling stage. Islyn Thomas summarized the need for a particular vent location better than I ever could. 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. Weld lines also can be visible after a part is painted and can cause wrinkles on in-mold-label injection-molded products. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Injection molding flow lines typically fall into one of the categories mentioned in the following table: Category: Type of Flow Line: Appearance (What It Looks Like) 1. For those processes in which the plastic fills out a mold (cold press, compression, injection, reaction injection, resin transfer, structural foam, and transfer molding ), openings in the part can be molded into the part through the use of cores. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. The defect may be in part appearance or mechanical strength. Edge Gates. sinks, knit lines, and shrinkage,” Spalding says. To account for variations in viscosity, nylon injection molding machines need to maintain an appropriate injection pressure. In an injection mold, the plastic fluid flows and spreads out in many directions as it comes out of the gate. The quality of the answer is directly proportional to the information we have to work with. Kurt W. 3. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). TWIM=Thin Wall Injection Molding; TSL=Toys,Sports and Leisure; NB=No Break; IMR=Inter Material Replacement. Parts molded with ABS are susceptible to forming knit lines, which are visible lines on the surface of the part. As a result, the portion has a faint, perhaps undetectable line. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Description: Flow lines are streaks, patterns, or lines - commonly off-toned in color - that show up on the prototype part as a consequence of the physical path and cooling profile of the molten plastic as it flows into the injection mold tooling cavity. Below is a list of items that should be checked both during normal molding operations and if defects are detected. Depending on the design of the mould and the material being injected, a knit line may: present no problem at all, be a cosmetic issue, or cause a potentially. Our plastic injection molding glossary provides key terms. Contact Universal Plastic Mold Today. Venting at Weld Lines. In this way, the mold supports distribute the force and minimize the stresses on the mold plates. Notched weld lines then remain near the cavity walls. This month, we covered an array of topics including injection mold venting, business strategies and runnerless micro molds. Bubbles are caused by melting flow fronts colliding in a mold cavity. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. While mold-filling simulation is a very common tool for predicting the fill patterns of an injection mold, in our judgment there is not yet a commercially available, satisfactory filling simulation for microcellular foam molding. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. Designers are able to specify seamless design features with compression molding. 5 to 3. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. 3. Industrial Knitting Machines. 1. Resin cools as it is injected into a mold. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. Why. Know about the cause of these lines and the potential solutions. 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. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. 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. Place vents at last place to fill and at converging flow fronts. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. In fact, knit line strength will decrease with higher filler content and with longer fibers. The following are the conclusion drawn from the present research: 1. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU. Inject the molten material into a mold. The injection molding process uses a granular plastic that is grav ity fed from a hopper. 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. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Plastic injection force exceeding the clamping pressure of the press. Sequential valve gate technology. The Problems & Solutions course is designed to train injection molding personnel in. 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. Surface Finish: The injection molding process may result in visible knit lines or parting lines on the part’s surface. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. A weld or meld line is a weakness or visible. . Injection Pressure 0r Speed Too Low Explanation: If the injection speed or pressure is too low, the molten plastic will not be pushed into the mold cavity fast enough to fill and knit at converging flow fronts because it cools down and solidifies too soon. Injection Molding Materials When using PolyJet molds, both tool life and part quality will be dependent on the thermoplastic material used during the injection molding process. 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. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. It emerges and becomes visible when the flow fronts cannot mold or knit during the molding process. Molding analysis study: An example of the low patterns and knit (weld) lines formation (MoldFlow® data) of injection molded round plastic part with a complex shape and with a ring. These knit lines affect the parts aesthetics. These knit-lines are well-known as particularly critical regions in the mold when mechanically. com support@makenica. Holes in the part will always cause knit lines. Plastic injection molding is a complex and highly intricate process. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. There are times when porous materials like Porcerax are used in problem or backfill areas. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. On a hydraulic machine you can program hold pressure: For example, if you set 850 psi (59 bar), you will get 850 psi hold pressure for the time you set on. The point of meeting creates a weak spot because the edges of the molten plastic, already cooling, don’t mix together very well. 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. Remedies: Increasing the barrel temperatures will allow the flow fronts to stay hotter longer and. A knit line is the spot where two flows meet. 6. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rates, and holding pressures. wall thickness, knit lines, draft. As these flow fronts come together. 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. Contact Us. This will help the mold designer to determine the allowable gate and knit line locations. weak knit lines and fracture points. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. On this page you will find the online, condensed version of this guide, offering quick answers to your injection molding questions. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. 197 in. Fewer knit lines are produced and a smaller amount of fiber-length degradation is noticeable when compared to injection molding. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Change gate locations. Piccarolo, S. Plastic injection molding is the industry’s most common way to manufacture parts. 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. 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. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Knit Lines. 6. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Inadequate injection pressure can result in knit lines and a surface that. This is a video excerpt from our Problems & Solutions Course - Weldlines. Still, they are almost always a cosmetic issue. Flow Lines. Knit lines, also known as weld lines are areas in the. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all,. Weld lines, also known as knit lines or meld lines, occur when two or more flow fronts meet during the plastic injection molding process. The diameter of the secondary runner would be the diameter of the tertiary runner times the number of branches to the 1/3 power (cube root). PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. They again get resolidified along the surface. land and using maximum vent depths to get them as close to self-cleaning as possible. Molding parts with multiple gates will almost certainly produce a weld line at right-angles to the line joining the two gates which could cause the weld lines to be exceptionally weak (see Figure 1. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. As the polymer resin is injected into a mold, it flows through all parts of the mold. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. These defects are not visible, like small. In this paper, two different injection molding tests were completed. Parts with abrupt geometry changes or holes are more prone to knit lines. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Flashing can be a common defect in injection moulding and can affect the appearance and functionality of the finished product. Injection molding is an efficient, often cost-effective way to manufacture custom plastics that are strong, durable, and long-lasting. The pipe underwent brittle fracture into many pieces because of the high residual stresses in the wall of the pipe. Obstructions in the part create weld lines or knit lines during injection molding. Sink Marks Cause 5: Improper Part Geometry. Insufficient injection pressure and speed can cause weld lines. A component of the injection-molding machine wherein the resin pellets are melted, compressed and injected into the mold's runner system. Thick sections take longer to cool than thin ones. That’s the air escaping out of the nozzle until the hose is full of pressurized water. . 7. Weld lines defects are formed when two flow fronts are merged together. Revisiting the '5 M's' of Molding. Weld lines are formed during cavity. There is high defect rate (surface defects/knit line). TEFABLOC™ TESI 744 TPE compound for injection molding processing provides superior adhesion properties when processed using injection molding. As a result, prototyping is strongly recommended for parts with. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. In the case of mold. 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. (1. Polym Compos 1982; 3: 88–96. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. 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. It has low shrink and high dimensional stability, and it has good resistance to acids and bases. Finally, knit lines occur when molten plastic flows around an object and rejoins on the far side, a phenomenon that is quite possible when inserts. 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. Weld lines are a common imperfection to be found in most plastic injected molded parts. The injection molding design process, much like all industrial design processes, deals primarily with the creation, look, and feel of a product. 3 /sec. Don’t forget to eliminate entrapped air in the weld line injection molding; otherwise, it’ll create unfilled portions in your part design, causing more weakening. incomplete filling or shorts. Part thickness control is through stacking of. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. A knit line is any line, visible or not, where two resin flows meet. Depending on the design of the mold. Adjust the design for the flow pattern to be a single source flow. It tells them that you visualized how injection molded parts cool and harden. Temperature is another factor that can cause weld or knit lines in injection molding. weld line in injection molding. It is one of the most common blemishes for manufactured products. In compression molding, molds are closed around the charge, and in injection molding, the charge is injected into a closed mold cavity. Polypropylene can be processed over a wide range of mold temperatures; however, for applications where aesthetics are critical, a surface temperature of 80-95˚CSink Marks Cause 1: Incorrect Melt Temperature. Take these steps to avoid knit lines. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. You don't give us much to go on. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. Because viscosity is a variable, keeping fill time constant minimizes the influence of these variations and provides a more stable process, and therefore. 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. Increase the injection speed. If you need injection molding expertise, we’re here to help. How weld lines form. Shear Controlled Orientation Injection Molding of Polymeric Composites with Enhanced Properties. Adding vents, using overflows, or using porous metal. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. 4. To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. Poor venting. Knit Lines in Injection Molding. Make sure the venting is not too large. 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. It’s also relatively inexpensive. Excessive mould lubricant. A meld line occurs when two moving melt fronts converge and flow parallel to each other. ABS is a good choice for handheld consumer devices. The structural stability of. 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. 3,000 ton machines can cost $700,000. 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. These defects are not visible, like small. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. Knit line / Meld. Increase injection speed. Short shots and knit lines are two phenomena that are caused by using highly viscousHowever, they can also create weld lines or knit lines in the part where the flow fronts meet. Avoid areas where the plastic must suddenly flow upward or downward. The total amount of scrap being produced during injection molding will usually be higher than that for compression molding because of the additional material loss created. 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. As melt temperature, viscosity and abrasiveness rise, tool life will decline. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. Mold Venting. Knit lines are typically much weaker. BURN MARKS Burn Marks: burn marks can occur when the design of a plastic part, and the subsequent injection mold design, causes air to be trapped during the injection (or filling stage) of the molding cycle. Inadequate venting. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. These defects are not visible, like small. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Reduce the barrel temperature and increase the injection pressure. This is easier to accomplish on. Weld Lines-3 Ways for Detecting and Correcting. Short shots Trapped air in the mold can inhibit the flow of the material during injection, resulting in an incomplete part. Figure 1: Knit lines in a cover plate. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. 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. ABS. These knit lines affect the parts aesthetics, but also they generally decrease the strength of the part. In addition, the company is now providing three. occupied frequently with troubleshooting injection molding. Understanding types of injection molding process can help to avoid some design challenges early in the process. 7. With the right nozzle, you can boost cycle. 12515 NE 95th Street , Vancouver, WA 98682 CALL TODAY: 1-800-839-0366Contact FU CHUN SHIN MACHINERY MANUFACTURE CO. 18/06/2021. If the plastic has cooled too much during the injection process it can lead to knit lines in plastic parts when they meet past an the obstruction. One of the common defects that can occur in injection molded parts is weld line. (See Fig. doc), PDF File (. On average, larger injection molding machinery can cost from $50,000-$200,000 or more. Knit/Weld Lines. It explored the use of. 2. They again get resolidified along the surface. Injection molded plastic begins its journey through the part tooling via an entry section called a. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Polym. 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 are “knit” together). This production method is particularly popular when manufacturing in large quantities. Weld lines occur where two flow fronts meet and always provide a source of weakness as the two fronts do not knit together. Knit Lines. Advantages Excellent moldability in thin sections Outstanding chemical resistance Heat resistance Limitations Cost Knit line strength OverviewLiquid crystal polymer (LCP) exhibits a highly ordered structure in both the melt and solid states. This course outlines mold filling and how different gating configurations affect filling. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause. When the temperature is not very high, there are chances of premature solidification, which can cause weld lines to form. They again get resolidified along the surface. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. Also known as a knit line, this is the point at which two flow formations meet and are unable to. 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 . Meld and knit lines are actually both different types of weld lines. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. In injection molding, it is often important to maintain consistent color throughout the part. A knit line, also. Long shapes are produced without multiple drops or hot runner systems, eliminating knit lines and lowering tooling costs. Part Shorts and has burn marks. Recent developments were oriented on the analysis of the mechanical performance at local (knit lines and welds) and bulk (molded part) areas, with the influence of molding and welding conditions. During injection, support pillars keep closed the two halves of the plastic injection mold. Reduction of sink can possibly be had by switching to an ABS/PC-blended material. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. For example, increasing gate size can improve part filling. Venting at Weld Lines. The resin is transferred to the mold cavity under positive. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Remove the hardened material from the mold. Weld / Knit Lines; Assumptions. Some. Thermoplastic Elastomer Molding Guidelines. Weld lines or knit lines and meld lines formed when two melt fronts run into each other or join together can be improved by. Contact Universal Plastic Mold Today. The injection of molding compound into the parts through one or two gates may produce parts that have knit lines. 3 s, mold temperature of 60 °C and melt temperature of 250 °C. Plasti-Co ® manufactures a wide range of injection molding nozzles from standard nozzle tips, extended nozzle tips, nozzle bodies, extended nozzles bodies, custom bodies, general purpose to full taper, shut-off, mixing and filtering applications. See full list on fathommfg. With ABS injection molding, you get the collective benefits and properties of three monomers. The Mold Tools toolbar provides tools for creating mold tooling (cores, cavities, etc. Generally all plastic components should be designed with draft where possible. One exception: ribs should be about 50. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. 140 in. Such molds or tools aren’t intended to be used in operation. Thanks to the low air counter pressure in the cavity, this allows injection parameters to be managed in a larger window, optimizing injection time, part aesthetics and mechanical characteristics. Therefore various injection molding defects can be eliminated. An injection mold that produces pieces while the final tool is being built. Parting lines placed at intricate joints. For this study, a special injection mold was designed and constructed (Figure 1) in order to produce specimens of various thicknesses (from 2 to 6 mm). These knit lines are usually the weakest areas of the part. The part is cooled in the mold until it is solid enough to be ejected. Injection molding is a simple and efficient process that produces high-quality plastic parts. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. Knit Lines and Resins A knit line is any line, visible or not, where two resin flows meet (see Figure 2). Design bosses with an outer diameter equal 2x the nominal diameter of the screw or insert. 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. Place a vent in the weld line area to remove the entrapped air. Mold cooling is one of the most important variables in injection molding. "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. Injection moulding (U. Weld line. Prevent Flow and Knit Lines Through Mold Adjustments. Orientation of these knit (weld) lines, are perpendicular to the tensile stresses, applied to the ring (Figure 6-8). Solution: People. While knit lines can be present it does not always mean the structural integrity of the plastic part is compromised. 3. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. 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. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates. Consider adding mold release (can be added to the polymer itself by the polymer vendor) or at machine side Knit lines Weak knit lines Increase melt temperature Mold temperature too cold Increase injection speed Avoid nucleated products if possible Inadequate ventingWhat you should know is that there are various failure modes for injection molding. The fluid path has an inlet and a radially continuous, downwardly. Contact us. Incompletely fused extrusion knit Line. In the present work, the micro specimens were investigated. 8 mm relief at the edges of the thread. Causes 1. The mold maker may think that some minor defects are acceptable, or they may not even consider them from the beginning, which can cause problems when the injection mold is being manufactured. One solution is to use optimal wall thickness to help slow cooling during the ABS plastic molding process. However, with any practice, when the proper care and planning aren’t taken, problems can occur, and with injection molding, knit lines are one of the most common problems. 2) Vents in an injection mold should let the air out, but not the liquid plastic. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. The effect of holding variables and of injection and mould temperature was explored. 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. From Plastic Materials and Processing by A. As these flow fronts come together. Table 2 lists the<br /> properties of common tool steels and the typical mold components for which they are<br /> used. 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. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. 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. 080" – 0. suppressed cooling and possibly warp. 040-in. Poor Knit Lines. Following lists causes and solutions for weld or knit lines. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. Macromol Symp 1988;21/21: 489-500. The injection molding was carried out in a DK-Codim 175/410 injection molding machine. The design of the mold, as well as the part being molded, has a significant impact on the success of the process. One common problem that occurs in injection molding is the formation of knit lines. They again get resolidified along the surface. 0 and Table 1). Vacuum. Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. They occur when two resin flows meet at different. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Below is a list of items that should be checked both during normal molding operations and if defects are detected. The most common location of knit line formation is behind molded-in holes that are made by core pins in the mold. Since our material is injected through a. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. If the load is applied in the transverse direction relative to the knit line, matrix cracking is easily initiated, and the part can fail. The gate architecture and its location affects cycle times, tooling costs, lead times, the location of witness marks and many other potential defects that are commonplace for. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. 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 []. Knit lines are formed when two or more plastic flow fronts collide and solidify or “knit” together during the molding process. 120 in.