The areas in the cavity where such buildup tends to be common are at end-of-fill areas, details that trap gas, and knit lines. holes, multi-point injection. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. Vertical Plastic Injection Molding. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause. Injection molding machines with footprints similar to desktop FDM and SLA 3D printers are now available. When designing for injection molding, consider these steps to prevent knit lines Resin cools as it is injected into a mold. Exploring common molding defects and. Commonly seen at the edge of a hole or other cored feature, knit lines are—as a. What you should know is that there are various failure modes for injection molding. When injection molding complex parts, often knit-lines are formed during the mold filling stage. 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. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Weld-lines look like cracks on the appearance of plastic. 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. a specific area on one side lens, a warp line, and a weft line. Chris Newmarker | Dec 27, 2013. Injection Molding Press. The final molding process may be dependent upon factors. Below is a list of items that should be checked both during normal molding operations and if defects are detected. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. Specifically, Stokes and. Reduction of sink can possibly be had by switching to an ABS/PC-blended material. 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. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. and Titomanlio, G. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. For the metal feedstock, injection and mold-wall temperatures were 130 ºC. (If parts are to be molded by Protomold’s rapid injection molding process, our Design Guidelines should be used. Weld lines are a common imperfection to be found in most plastic injected molded parts. sinks, knit lines, and shrinkage,” Spalding says. N174W21430 Alcan Doctor Jackson, WI 53037 262-677-9700; 16685 State Road 32 Mountain, WE 54149 715-276-4200; Prime. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. 5 : 1 and 3. Lower the melt and mold temperature to prevent overheating. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Gate design is another critical piece of part function in plastic injection molding. Knit lines don’t always compromise the structural integrity of plastic parts. Below is a list of items that should be checked both during normal molding operations and if defects are detected. H-13 Good general purpose tool steel. Weld or knit lines occur when melt flow fronts collide in a mold cavity. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. But any. 250 in. 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. occupied frequently with troubleshooting injection molding. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. In. 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. More about the knit lines in injection molding. The packing pins are sequentially. to prevent improperly placed knit lines or sinking in the plastic downstream from the hinge. 4. Weld / Knit Lines; Assumptions. 160"). Other common issues associated with thin walls include uneven cooling, warp, cracks, cosmetic texture inconsistencies, and weak knit lines or fracture points. (1987). Encapsulating the metal insert with plastic creates a single. C. They appear around holes or seams of an injection molded part, and some may call them “flow lines” or “weld lines”. 015in wall. Thick walls are not recommended because of POM’s high shrinkage rate. A medical device designer might look up a polymer's physical properties and game out. How weld lines form. Here are some of the most common cosmetic defects and how to avoid or fix them. Please read on, stay posted, subscribe, and we welcome you to tell us what you think. [8] Bevis, MJ, Reis RL, Cunha AM. Long shapes are produced without multiple drops or hot runner systems, eliminating knit lines and lowering tooling costs. Because viscosity is a. Thin walls often lead to material flow problems, which can cause unformed areas. Given the cosmetic requirements, there is a good chance the mold would require. Most failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold. From Plastic Materials and Processing by A. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Possible causes: Low temperature or fluidity of melted plastic during injection molding. Imagine a river splitting to go around a rock, then meeting up again on the other side. , 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. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Edge Gates. 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. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. As. wall thickness, knit lines, draft. Remedies: Raise the temperature of the mold or molten plastic. It recently obtained a $4. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. If the plastic has cooled too. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Starting in September, the CoPilot process control system developed by RJG will come equipped with valve gate control. Venting at Weld Lines. Knit lines are formed in injection moulding when two flow fronts meet in the middle of a part (a line where two sides of the plastic are “knit” together). 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. 5 kN/cm2 (4 T/in2 ) is required. See UNDERCUT. Be wary of saving too much weight or you might end up with: cracking. A. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. The Goldilocks principle applied to wall thickness. Design with Plastics - for Injection Molding process. Knit Lines. To avoid these problems and create the best possible. 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. This defect is caused when the polymer resin is injected into a mold and flows around a solid piece and forms when the resin collides back together without completely fusing back together. 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. Optimizing Mechanical Performance of Injection Molded Multiple Gated Rotating Thermoplastic Components: Part 1 - Consideration of Structural Analysis and Knit Line Effects March 2001 DOI: 10. These seams are known as “knit lines. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Second, the runner leading to a tab gate takes up real estate within the. 4271. The mold-opening force varies widely depending on the type and size of the molding machine. Troubleshooting Injection Molding Weld Lines. 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. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Steven. Flow Lines. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. 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. They are very much related but independent disciplines. 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. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses, elastomers, confections, and most commonly thermoplastic and. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. Wall Thickness: The recommended wall thickness for injection molded POM parts is between 0. 3. Weld-lines or knit-lines are formed during the mold filling process when the split melt flow fronts meet at the same downstream location. RJG announced that its injection molding process control system, CoPilot, will begin offering valve gate control technology for hot runners starting in September 2021. Injection molding, producing, and forming resin materials are three core components of injection molding technology. Troubleshooting Injection Molding Weld Lines. 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. In addition, keep these in mind: Scrap rates can range from less than 1 to 5%. Meld and knit lines are actually both different types of weld lines. The leading edge of the molten material is often the coolest point and the closest to solidifying. Learn how HPP maximizes these specialized processes. Our On-demand. Knit Lines. Know about the cause of these lines and the potential solutions. End-of-arm tooling can make or break a program. 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. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Weld lines may appear like seams or scratches, but that is not what they are. The depth of the texture or letters is somewhat limited, and extra draftParts were molded at a maximum injection pressure of 235 MPa, a maximum clamping force of 800 kN, a maximum injection speed of 900 mm/s, and a maximum injection stroke of 120 mm. Injection Molding: How to Set Second. Meld and knit lines are actually both different types of weld lines. Flow Lines / Knit Lines Flow/Knit Lines 11. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. Weld line. The recommended minimum production volume for injection molding is 500 units. The definition of weld lines: When multiple plastic flow fronts meet in the cavity after encountering inserts, holes, or areas with inconsistent flow rates or interrupted melt flows, or in the case of gate injection filling, the inability of two or more flow fronts to fully “knit” together will cause the linear weld marks. 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). These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. 3—Another issue with the four-gate design was that knit lines ended on or near mounting holes, causing a. 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. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. Here are a few ways to prevent knit lines in your plastic parts: Increase material temperature: Higher temperatures on both materials prevent one section from cooling too quickly. Looking to Your Knit Lines with Molding. These data were obtained from many andKnit lines in injection molding are common defects of the molded parts. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Self-mating parts. Weld line are formed whenever melt fronts separate and recombine at some downstream location. 18/06/2021. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. Step 3: The injection mold undergoes rotation to align in position with injection Barrel B. As a result, prototyping is strongly recommended for parts with. Core out parts to eliminate thick walls. What Are Cosmetic Standards for Plastic Parts?. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Family molds. This will help the mold designer to determine the allowable gate and knit line locations. Once the plastic sets, the mold opens to eject the product. Prevent Flow and Knit Lines During the Injection Molding Process. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). The injection molding process uses a granular plastic that is grav ity fed from a hopper. 040-in. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. Weld Lines-3 Ways for Detecting and Correcting. Enlarge gas vents and gates to allow trapped air to escape the mold. Most failures occur at what are called “weld lines” or “knit lines”. Understanding types of injection molding process can help to avoid some design challenges early in the process. 05-million grant for MIM R&D from the National Institute of Standards and Technology (NIST) in Washington, D. 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. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Increase the injection speed. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. Figure 1: D-shaped through-hole in center of gear part accepts the drive shaft. ” Depending on the material you use, the knit lines could be invisible or obvious—work with an injection molding company to figure out. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. Piccarolo, S. The mold opens and closes on a vertical axis in the vertical injection molding. 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. injection molding machines using standard industry practices . Meld and knit lines are actually both different types of weld lines. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. Bociaga and Jaruga (2007) investigated flowing weld line in injection process by injection molding machine, which the part surface was observed in reflected light using the optimal microscope and. 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. All the while, the material could be the correct material," Hill says. Ideally, a safety strap should be strong enough to prevent the mold from opening under various unforeseen circumstances, but always less than the holding power of the mold clamps and the machine’s mold-opening force. Still, they are almost always a cosmetic issue. A parting-line vent. 030 and 0. Injection molding weld lines refer to a line on an injection molded part that is generated where the two halves of the mold come together. 1. 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. 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. Knit lines don’t. Plastic injection molding is a complex and highly intricate process. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Image credit: The Rodon Group. Use the fewest number of gates possible. To avoid walls that are too fat or too thin, designing a wall thickness between 0. Typically, this fillet radius should be somewhere near 0. Understanding Knit Lines in Injection Molding: Causes and Solutions. This design aid shows the mechanics of how the A-side and B-side of a tool work together during the injection molding process to create plastic parts. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. 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. All the while, the material could be the correct material," Hill says. 3. occupied frequently with troubleshooting injection molding. Pitfall #1 – Knit Lines. This continues until the weld lines in plastic injection molding disappear. 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. Insufficient injection pressure and speed can cause weld lines. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. All that considered, for a specific simple part with specific quality requirements. By understanding material fill, injection mold designers can better position gates, anticipate where knit lines will appear, and locate difficult to fill spots in the mold. Knit Lines and Resins. They are formed when two or more flow frontKnit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection. 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. Investigate the mold for signs that a water leak is present, and correct the condition. Mold filling simulation software should be used to ensure that waterExpand. Those are knit lines, formed when two opposing flows of material join together in the mold cavity. Compression molding can also support large part sizes, and it has a tendency to. Runner and gates must be balanced. (See Fig. Multiple gates will always cause knit lines. 3 To get the most out of your Xometry Injection Molding experience, we offer the following part Design Guide with. Weld Line Phenomenon: Surface defect in which the weld, or the part where the flows of melted plastic meet inside the mold, shows up on the surface as a groove or pattern. While this process is largely efficient and reliable, it's not without its potential issues. Plating and painting applications usually require slower fill rates to keep orientation low. The Jabil Molding Institute empowers employees, customers and suppliers to utilize the most advanced plastics and related manufacturing techniques in the world. This can dramatically reduce the effects of material changes, according to the injection molding technology company. 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. Imagine a river splitting to go around a rock, then meeting up again on the other side. Following lists causes and solutions for weld or knit lines. Mold venting is critical to the quality and consistency of the finished part. Slower injection provides less orientation and stress. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. It is caused by the incomplete joining of the uncured. 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. While injection molding itself is a straightforward process involving melting. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. Knit lines; Knit lines always occur once 2 melted materials meet with hair-like discolorations. 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. ITAR. The advantages of compression molding include more isotropic fiber distribution, dimensional stability, and surface finish. Even parts with metal inserts can be produced. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. To learn more about us or to get a quote, click here or call 1. 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. knit line formation, application of draft angle and design for assembly. Reduce the injection pressure. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Factors were ordered. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. 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. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. (1. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Weld lines, also called knit lines, are a defect that occurs with molded parts caused by two different flows of plastic resin that do not adequately join together or weld together correctly during injection molding. 7584. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. (for example, a hole on the plastic part), the knit line will be unavoidable. The recommended minimum production volume for injection molding is 500 units. Injection mold design and custom tooling can make or break the success of a finished plastic product. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. Learn how to troubleshoot weld lines in injection molding. It has low shrink and high dimensional stability, and it has good resistance to acids and bases. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. What Are Cosmetic Standards for Plastic Parts?. Core Geometry. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Islyn Thomas summarized the need for a particular vent location better than I ever could. 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. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Starting with small part size, students learned to think about detailing on a product at thisTable 2. mixed manually and quickly stored in the tank of an injection machine just before the start of the resin injection or (2) the components are stored separately in different tanks of an injection machine with a mixing head. [1]Weld Lines. Release of trapped air in those cases will. It is best practice to maintain a uniform thickness throughout an injection-molded part. Meld and knit lines are actually both different types of weld lines. In injection molding, a thermoplastic material is melted to a liquid state and injected into a custom, double-sided mold. There are times when porous materials like Porcerax are used in problem or backfill areas. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. weld line in injection molding. But we can’t talk about the injection molding process without discussing the injection molding machine. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. 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. There is high defect rate (surface defects/knit line). Gating. S. They are formed downstream through holes, and between multiple gate locations. 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. PTI has five injection molding presses suitable for MIM. 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. Knit lines. We ensure customers receive accurate, fast, on-time, sufficient support and services. 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. The comment on melt flow index is correct, but, I've molded straight PC down to . Knit Lines 11: 1. Flow lines typically manifest as visible marks, often slightly. High mold temperatures usually provide less residual stress. PTI, a plastics and metal parts molder, is a leading developer of the MIM process. Knit Lines. They appear around holes or seams of an injection. 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. Over the years, I have developed two separate “5M” systems. 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. Thermoplastic Elastomer Molding Guidelines. Material contamination, for example, can cause several molding issues. Other materials, like LCP are great for thin wall micro molding but also notorious for having a bad knit line, potentially snapping from excessive torque in later manufacturing processes. Fortunately, there is a technique that provides almost unlimited control over which parts of a tool fill when and how fast. Knit Lines and Resins. 3. 11) The part design must take into account possible knit line locations and work to direct them away from higher stress areas. Here are some of the most common cosmetic defects and how to avoid or fix them. Excessive injection pressure can result in part defects such as overflow or flash. Venting. Round Rock, TX 78660. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. thickness with a spacing of about 0. The areas in the cavity where such buildup tends to be common are at end-of-fill areas, details that trap gas, and knit lines. thick. extend mold service life. 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. Weld Line defect analysis, the most common of many defects in injection moulding products. injection molding. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. Understanding Knit Lines in Injection Molding: Causes and Solutions. Legend: a-in. The chart below shows recommended wall thicknesses for common injection molding resins. (called also weld marks or knit lines), and meld lines. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022injection-molding machine (Arburg allrounder 320C, Germany). Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. 5. Thin wall injection molding can produce walls as thin as 0. Plastic is then injected at high pressure into the mold, and it solidifies with any surface features or defects in. As the polymer resin is injected into a mold, it flows through all parts of the mold. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Imagine a river splitting to go around a rock, then meeting up again on the other side. Focus - Injection Molding - Free download as PDF File (. be impressed by improvements of bubbles (vacuum voids), short shots, unequal thickness, jetting marks, weld lines, knit lines, black streaks, strain 2. even though injection molding temperatures are _____ compared to metals, the thermal expansion of plastics is _____ to _____ times that of metals. They need the interference of about 0. Mold Flow Analysis computer. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. RE: Knit Line Affect On Material Strength lorelei5607 (Automotive). 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. Reduce the temperature of the mold and plastic being injected. The last cause of flow lines may be the operators running your daily operations. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. Visual indicating with an finished part that are formed by the junction from two plastic flow fronts. Runner Type. The following are general guidelines for molding acetal. Solution: People. Because they can be shut off independently you can control flow fronts and knit-line locations. Table 2. While this process is largely efficient and reliable, it's not without its potential issues. Three terms that often get mixed up are weld, meld, and knit lines. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Injection moulding (U. Redesign the mold: Redesigning the mold to. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 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. One of the most common ways of adding venting is by manually machining it into the mold (Figs.