08 KICKOFF PRODUCTION. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. See UNDERCUT. When the plastic cools, it takes the shape of the mold and is then ejected and finished. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 3D printed molds in the injection molding process to lower costs and lead time. The knit line is generally opposite the gate in thermoset. When designing for injection molding, consider these steps to prevent knit lines Resin cools as it is injected into a mold. Enlarge gas vents and gates to allow trapped air to escape the mold. 250 in. Inadequate injection pressure can result in knit lines and a surface that appears corrugated. 763-755-7575. Venting. A parting-line vent. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. 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. As the polymer resin is injected into a mold, it flows through all parts of the mold. While this process is largely efficient and reliable, it's not without its potential issues. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Plasti-Co ® manufactures a wide range of injection molding nozzles from standard nozzle tips, extended nozzle tips, nozzle bodies, extended nozzles. For instance, three widely used processes are insert molding, overmolding, and undercuts. These include: Symmetrical parts. Reduce the temperature of the mold and plastic being injected. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Our prototype injection molding process helps you cut product development cycles by weeks—sometimes months—and bridge to production with injection-molded parts within days. We wanted to independently assess how a mold would fill and where knit lines would be, instead ofKnit Lines. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. Additionally. Reduce the injection pressure. For the metal feedstock, injection and mold-wall temperatures were 130 ºC. 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. and 0. ”. ABS is a good choice for handheld consumer devices. 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. Injection molding is an excellent way to create plastic parts in bulk, but there are many problems that can cause cosmetic defects ranging from minor to major. Meld and knit lines are actually both different types of weld lines. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. wall thickness, knit lines, draft. Also, since this part will likely be painted or chrome plated, knit lines are a concern. Learn how material selection, part design, and optimizing process parameters can help eliminate knit lines. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. The injection molding process uses a granular plastic that is gravity fed from a hopper. Our On-demand. 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. Get a free des. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Imagine a river splitting to go around a rock, then meeting up again on the other side. A wide variety of tool steels are available for injection mold construction. Knit lines; Knit lines always occur once 2 melted materials meet with hair-like discolorations. 13758 Johnson Street NE. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Weld lines are among the most critical structural defects in parts made by the injection molding of fiber-reinforced thermoplastics, explained Sirmax in a press release. Quick Guide to Injection Molding Amodel® polyphthalamide (PPA) equipment Amodel® PPA resins can be processed on conventional injection molding equipment. Other Excessive mold release Clean die and use minimal mold release. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Thick walls are not recommended because of POM’s high shrinkage rate. Core Geometry. Injection speed and pressure. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. thickness with a spacing of about 0. ISSUE FACED BY THE INJECTION MOLDING COMPANIES: FLOWLINES (ALSO CALLED WELD LINES OR KNIT LINES) Definition: Streaks, orange skin, or visible flow lines in parts. ISO 9001:2015. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. 040-in. 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. 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. Reduce the injection pressure. We look forward to offering support and advice on your next project. 01 inches between parts fitted together to work best. TEXAS. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. Troubleshooting Injection Molding Weld Lines. A. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. Molding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesiveMolding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesiveMost failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold. Use the fewest number of gates possible. How weld lines form. Weld lines defects are formed when two flow fronts are merged together. Core Geometry. (If parts are to be molded by Protomold’s rapid injection molding process, our Design Guidelines should be used. 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. Understanding Knit Lines in Injection Molding: Causes and Solutions. They are very much related but independent disciplines. • 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. Its superior flowability allows for precise and flawless filling of injection molds without the risk of flow marks and knit lines. The thermo-rheological findings were used to investigate the sources of weld line weakness. While this process is largely efficient and reliable, it's not without its potential issues. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. Reducing the size and depth of depressions helps minimize the impact of knit lines. These structures are often small surfaces of about a tenth of an inch in diameter. In injection molding, a thermoplastic material is melted to a liquid state and injected into a custom, double-sided mold. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. [8] Bevis, MJ, Reis RL, Cunha AM. Injection molding machines with footprints similar to desktop FDM and SLA 3D printers are now available. Bubbles are caused by melting flow fronts colliding in a mold cavity. Over the years, I have developed two separate “5M” systems. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. Call 800-985-6750 or email your inquiry to sales@customgasketmfg. Knit line Knit line Start of mold filling. Increasing injection speed. 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. Weld lines may appear like seams or scratches,. 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. txt) or view presentation slides online. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. 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. Because injection mold design and processing is complex, a set solution will not solve all problems. Looking to Your Knit Lines with Molding. Inject the molten material into a mold. This guide to thermoplastics and injection molding material selection is aimed at an engineer who plans to quantitatively analyze a part, determine loads, stresses, strains, and environments and make an optimal material decision based on the analysis. 4. Still, it can be seen to varied degrees depending on mold. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. 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. Not always a problem, but can cause serious structural issues. It allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. Observation on a “trial and error” basis may be required. - You hit on this a little, but dealing with the parting line and ejector pin marks is pretty important, and isn't as simple as it seems at first look. This defect is caused from excessive lube or oily stock. Those are knit lines, formed when two opposing flows of material join together in the mold cavity. Advantages for your Injection Molding Machine:. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. Compression molding is one of the earliest forms of molding. 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. To learn more about us or to get a quote, click here or call 1. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic. Double push filling method. These knit lines are formed as molten plastic in the injection mold flows around an obstruction like a feature. Steven. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. 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 process is extremely versatile, and can produce very complex shaped parts, with the use of multi-sided molds. While not always visible, weld lines (aka knit lines) are where two resin flows meet. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. Learn how to troubleshoot weld lines in injection molding. Also discussed are weld and meld lines and their effects on molded. Contact Universal Plastic Mold Today. As a result, prototyping is strongly recommended for parts with. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. Meld and knit lines are actually both different types of weld lines. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. 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. Injection molding is min-maxed for mass production. 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. A weld or meld line is a weakness or visible. Knit lines, also known as weld lines are areas in the. Compression molding can also support large part sizes, and it has a tendency to. The comment on melt flow index is correct, but, I've molded straight PC down to . Runner and gates must be balanced. Draft. Design with Plastics - for Injection Molding process. 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. Give us a call at (425) 339-0288 or email us at info@sealectplastics. 0 and Table 1). A weld line can also be called a knit line. You don't give us much to go on. thick. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Runner Type. 015in wall. Cooling Lines, Injection Mold Material has a great impact on injection molded part quality. The most common and one of the most challenging injection molding defects are weld and knit lines. The quality of the answer is directly proportional to the information we have to work with. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. One common problem that occurs in injection molding is the formation of knit lines. 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. Thermoplastic Elastomer Molding Guidelines. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. Because they can be shut off independently you can control flow fronts and knit-line locations. Meld and knit lines are actually both different types of weld lines. Holes in the part will always cause knit lines. Extreme geometries can cause knit lines. Remove the hardened material from the mold. 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). A knit line is any line, visible or not, where two resin flows meet. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary from virtually invisible to something that looks like cracks in the plastic. Heat resistance. But we can’t talk about the injection molding process without discussing the injection molding machine. Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. 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. In injection molding terms, these are called “living hinges” and are made right into the design instead of adding them later. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different. This, in turn, leaves a large tab to be trimmed, a process that can mar the finished surface. Submarine Gates. Design With Plastics. This continues until the weld lines in plastic injection molding disappear. Thick sections take longer to cool than thin ones. sinks, knit lines, and shrinkage,” Spalding says. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. This month, we covered an array of topics including injection mold venting, business strategies and runnerless micro molds. These structures are often small surfaces of about a tenth of an inch in diameter. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. Given the cosmetic requirements, there is a good chance the mold would require. They again get resolidified along the surface. Here are some of the most common cosmetic defects and how to avoid or fix them. Also known as weld lines, knit lines. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Multiple gates will always. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. Having a basic understanding of the injection molding process will aid in understanding how to design for injection molding as well as how to forecast production schedules. Over the years, I have developed two separate “5M” systems. These are caused by the shot of molten plastic moving at different speeds throughout the injection. 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. Sequential valve gate technology. Knit Lines. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Proper venting is essential to molding a defect-free part. It is best practice to maintain a uniform thickness throughout an injection-molded part. The parting lines is where the two injection mold halves (A side and B side) meet. Knit lines don’t always compromise the structural integrity of plastic parts. 2 mm. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. While injection molding itself is a straightforward process involving melting. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. Step 2: The injected molten plastic is cooled followed by the separation of the core and cavities. 2. Step 1: The injection of molten plastic into the injection mold from Barrel A. As a result, a rib at the weld line junction can strengthen the bosses at the mold line. End-of-arm tooling can make or break a program. When needed, crush ribs can allow for draft and a tight fit for a part that requires both. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. extend the time between mold maintenance shutdowns. Flow Lines. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. The last cause of flow lines may be the operators running your daily operations. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. As. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. Steven. ; Wood, Philip E. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. Weld-lines or knit-lines are formed during the mold filling process when the split melt flow fronts meet at the same downstream location. These data were obtained from many andKnit lines in injection molding are common defects of the molded parts. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. When the mold body is closed, the contact surface of the cavity and core plates makes a parting line. Learn how HPP maximizes these specialized processes. 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. 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. Knit lines. Rynite® PET is usually processed with melt temperatures between 280 to 285 °C (535 to 545 °F) . The injection molding design process, much like all industrial design processes, deals primarily with the creation, look, and feel of a product. Insufficient injection pressure and speed can cause weld lines. IM: hot or warm knit lines are cause by _____ while cold knit lines are caused by _____. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and holding. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. 5. Resin pellets are loaded into a barrel where. This production method is particularly popular when manufacturing in large quantities. Adding vents, using overflows, or using porous metal. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. 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. Last month, in the first part of this two-part installment we focused on the reasons viscosity can change during injection molding. The tooling engineer in the mold house will be more into venting, sprue pressure, preheating the mold, cycle times, ejector pin scheme, mold flow, getting a gate location to avoid fill issues or knit lines, excessive flash and molding pressures, and the list goes on. Wall Thickness: The recommended wall thickness for injection molded POM parts is between 0. 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. Weld / Knit Lines; Assumptions. 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. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. ). All the while, the material could be the correct material," Hill says. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Learn more. Depends how hard you want to push it. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. 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 line does not normally impact the overall shape or dimensions of the item. The mold-opening force varies widely depending on the type and size of the molding machine. Knit Lines 11: 1. 2. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near. Fathom injection molding services and tools offer a single-source global solution that supports your company’s low- to high-volume manufacturing process. Anisotropy. Unsymmetrical filling makes knit lines in samples, leading to the failure of part, so it must be avoided. If life safety is involved, or reliably or efficacy are absolutely required, every part should. com. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. 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. 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. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. This will helpWeld line. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. 160"). 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. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” 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. , 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. It’s also relatively inexpensive. Plastic melt and mold temperature. Specifically, Stokes and. , under its Advanced Technology Program (ATP). 6. Knit Lines. If you want to better understand the process of injection molding, there are a few critical terms you need to know. 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. BLEED – (1) To give up color when in contact with water or a solvent. What Are Cosmetic Standards for Plastic Parts?. This course outlines mold filling and how different gating configurations affect filling. 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). There needs to be a balance between fit of the halves, function of the part, visual quality expectations, and the cost to produce the mold. 3. The melt is forced to split up during filling of the cavity. Venting at 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. For example, increasing gate size can improve part filling. 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. 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. Typically, the wall thickness is somewhere in the neighborhood of 50%-75% of your nominal wall thickness. Plastic injection molding is the process of injecting molten plastic material into a metal tool which then cools and ejects a plastic part from the machine. Table 2 lists the<br /> properties of common tool steels and the typical mold components for which they are<br /> used. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. In working with the injection molding service offered by Protolabs, you provide. This range can be affected by the part wall thickness, melt temperature, mold temperature, injection speed, hold/pack pressures and also the time between molding and measuring. You don't give us much to go on. 847-952-8088. The advantages of compression molding include more isotropic fiber distribution, dimensional stability, and surface finish. 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. 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. ” 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. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. In the 1947 book, Injection Molding of Plastics, the late Dr. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. wall thickness injection molding ribs. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. 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. sheet metal fabrication, rapid tooling, and plastic injection molding. These lines are the result of the molten plastic material recombining after splitting and flowing around an obstacle in the mold cavity. 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. In plastic injection molding, a parting line is where two halves of a mold meet when closed. Core out parts to eliminate thick walls. They appear around holes or seams of an injection. 0 Items. 1990-03-01 00:00:00 Knit lines in reaction injection molding (RIM) are formed when a fluid flow front passes through the mold cavity and must pass around objects in its path. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. Gate locations can be directly behind or on the edge of the graphic. Weld or knit lines occur when melt flow fronts collide in a mold cavity. POROUS MOLD MATERIALS. Meld and knit lines are actually both different types of weld lines. TRADITIONAL MACHINES VENTS. , 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. Most failures occur at what are called “weld lines” or “knit lines”. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. 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. Flow lines typically manifest as visible marks, often slightly. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. Solution: People. Knit Mark – A witness mark on a molded part, often occurring at the midpoint between two transfer or injection sprue locations. Injection molding is a popular manufacturing process used to fabricate parts in large volumes. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. Gate and Knit Line Locations<br />. Disadvantage: May rust if improperly stored.