Texturing may also hide surface defects such as knit lines and other imperfections. They are very much related but independent disciplines. Knit Lines 11: 1. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. 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. (1987). The process is extremely versatile, and can produce very complex shaped parts, with the use of multi-sided molds. Look for signs of stickiness or burning. Bubbles are caused by melting flow fronts colliding in a mold cavity. The main causes of Weld Line or Knit lines are: Convergence of two flowing polymer melt streams during injection molding process: This is the most common cause of weld lines, as the two melt streams coming from different runners or gates in the mold meet and do not fully mix, creating a weak point in the finished product. These defects are not visible, like small. 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. Islyn Thomas summarized the need for a particular vent location better than I ever could. To avoid these problems and create the best possible. 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. 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. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Last month, in the first part of this two-part installment we focused on the reasons viscosity can change during injection molding. For injection molding of the multi-blade fans and various rotating plastic parts, the complex of multiple gating injection molding tools were used. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. 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. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. txt) or view presentation slides online. Change gate locations. Knit / Weld Lines. This makes the casting process as efficient and accurate as possible. It’s economical, efficient, and can produce simple to complex parts with low waste. Injection moulding (U. Mold venting is critical to the quality and consistency of the finished part. What causes knit lines? Knit lines are formed when the molten plastic flowing into the mold cavity runs into an obstruction, such as a core pin that forms the through hole on a flange of an enclosure. We all know that injection moulding is great for producing both custom prototypes and end-use production parts, but if you are not careful it can cause some. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. Press fits for injection-molded parts can be challenging. Knit and Meld lines are inherent to plastic injection. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. We all know that injection moulding is great for producing both custom prototypes and end-use production parts, but if you are not careful it can cause some. 847-952-8088. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. Knit/Weld Lines. Quick Guide to Injection Molding Amodel® polyphthalamide (PPA) equipment Amodel® PPA resins can be processed on conventional injection molding equipment. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. In addition, keep these in mind: Scrap rates can range from less than 1 to 5%. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Meld and knit lines are actually both different types of weld lines. a specific area on one side lens, a warp line, and a weft line. 18/06/2021. All the while, the material could be the correct material," Hill says. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Solution: Increase the injection pressure or speed. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). Multiple gates will always. Weld Lines. Notched weld lines then remain near the cavity walls. 140 in. Core out parts to eliminate thick walls. Which affect parts aesthetics and decrease parts strength. • Standard (general purpose) screws with a compression ratio between 2. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. What is copper electrode in injection mold? hashtag#plasticinjectionmold hashtag#moldmaking "Copper electrode," also known as "electrode," is a common component in mold manufacturing. Weld-lines or knit-lines are formed during the mold filling process when the split melt flow fronts meet at the same downstream location. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Knit lines, also known as weld lines or meld lines, are visible lines or seams that appear on a molded part where two or more flow fronts meet during the injection molding process. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. These defects are not visible, like small. Meld and knit lines are actually both different types of weld lines. Disadvantage: May rust if improperly stored. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. Also known as a knit line, this is the point at which two flow formations meet and are unable to connect during injection molding. 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. With this option, users can utilize in-cavity pressure or temperature sensors to control when the valves open or close. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause. An edge gate introduces material at the main parting line, or where the two halves of. Also known as weld lines, knit lines. Imagine a river splitting to go around a rock, then meeting up again on the other side. ITAR. 3D printed molds in the injection molding process to lower costs and lead time. Holes in the part will always cause knit lines. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. 7584. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. Lower the melt and mold temperature to prevent overheating. Call 800-985-6750 or email your inquiry to sales@customgasketmfg. 008 to 0. 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. If life safety is involved, or reliably or efficacy are absolutely required, every part should. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Two major moldability pitfalls to avoid are sink and voids. When the mold adopts the multi-gate pouring scheme, the plastic melt. . H-13 Good general purpose tool steel. 2 mm. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Consider adding mold release (can be added to the polymer itself by the polymer vendor) or at machine side Knit lines Weak knit lines Increase melt temperature Mold temperature too cold Increase injection speed Avoid nucleated products if possible Inadequate venting7. The chart below shows recommended wall thicknesses for common injection molding resins. Basic rule of thumb air in mold must be able to escape at theInjection molding is the predominant manufacturing process used for producing transparent polymer products. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. 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. End-of-arm tooling can make or break a program. Weld / Knit Lines; Assumptions. (1. We have two unique offers to meet your needs wherever you are in the product lifecycle. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Typically, this fillet radius should be somewhere near 0. Bubbles are caused by melting flow fronts colliding in a mold cavity. We have an elite team that designs for injection molding, rapid prototyping with metal and plastic, and produces world-class products under the same roof. Gating. Get a free des. Obstructions in the part create weld lines or knit lines during injection molding. In injection molding, it is often important to maintain consistent color throughout the part. The comment on melt flow index is correct, but, I've molded straight PC down to . Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. Reduce the injection speed to limit the risk of trapping air inside the mold. Extreme geometries can cause knit lines. Injection Pressure 0r Speed Too Low Explanation: If the injection speed or pressure is too low, the molten plastic will not be pushed into the mold cavity fast enough to fill and knit at converging flow fronts because it cools down and solidifies too soon. In fact, knit line strength will decrease with higher filler content and with longer fibers. wall thickness, knit lines, draft. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. Below is a list of items that should be checked both during normal molding operations and if defects are detected. Submarine Gates. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. A parting-line vent. 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. First, they carry resin to the mold via a runner. 5. 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. But we can’t talk about the injection molding process without discussing the injection molding machine. 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. Reducing the size and depth of depressions helps minimize the impact of knit lines. - Mold flow analysis to control fill and knit lines. Weld line in injection molding is line where two or more flow molten plastics knit together. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Take these steps to avoid knit lines. Anisotropy. For best results, keep thickness variations to within 15% of the nominal wall thickness. 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. Hartland, WI 53029. 3. Step 1: The injection of molten plastic into the injection mold from Barrel A. Lower the melt and mold temperature to prevent overheating. Operating Conditions • Fast injection fill speeds, supporting short injection times (1–3 s), especially in thin sectionsKnit lines in reaction injection moldings Knit lines in reaction injection moldings Maier, Christian; Hrymak, Andrew N. [8] Bevis, MJ, Reis RL, Cunha AM. 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. 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. While injection molding itself is a straightforward process involving melting. Understanding Knit Lines in Injection Molding: Causes and Solutions. Knit lines may also be called stitch lines, weld lines, or meld lines. Investigate the mold for signs that a water leak is present, and correct the condition. Draft. In fact, knit line strength will decrease with higher filler content and with longer fibers. Know about the cause of these lines and the potential solutions. It has low shrink and high dimensional stability, and it has good resistance to acids and bases. As. 125 inches. 1. Most failures occur at what are called “weld lines” or “knit lines”. RJG announced that its injection molding process control system, CoPilot, will begin offering valve gate control technology for hot runners starting in September 2021. Encapsulating the metal insert with plastic creates a single. 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. Once the plastic sets, the mold opens to eject the product. Trapped air in a mold manifests itself as a burn mark on the molded part. An obstruction such as a core pin or holes will split the material flow and cause a weld line issue to form on the other side. Step 3: The injection mold undergoes rotation to align in position with injection Barrel B. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. This will helpWeld line. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. 05-million grant for MIM R&D from the National Institute of Standards and Technology (NIST) in Washington, D. Image credit: The Rodon Group. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. It’s our responsibility to make sure your design comes out of the mold working properly. Weld lines are a common imperfection to be found in most plastic injected molded parts. Three terms that often get mixed up in injection molding are weld, meld and knit lines. TRADITIONAL MACHINES VENTS. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. 4. 120 in. 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. Plastic injection molding is a complex and highly intricate process. knit line. In a weld line, reinforcement fibers. 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. And, for those who can work within its limitations, rapid injection molding may be suitable for producing some optical parts (and cost as much as 90 percent less than traditional tooling). Inject the molten material into a mold. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. Plastic injection molding is the industry’s most common way to manufacture parts. It is typically used for thermoset materials, but can be used with thermoplastics. Remedies: Raise the temperature of the mold or molten plastic. Those are knit lines, formed when two opposing flows of material join together in the mold cavity. Meld and knit lines are actually both different types of weld lines. As the polymer resin is injected into a mold, it flows through all parts of the mold. ABS. 040 and 0. Three terms that often get mixed up are weld, meld, and knit lines. They are formed when two or more flow frontFor more information on our custom rubber molding services or to speak with one of our knowledgeable professionals, please feel free to Contact Us or complete our online Request For Quote form. com . The company provides an array of digital manufacturing expertise. In injection molding terms, these are called “living hinges” and are made right into the design instead of adding them later. Weld lines, also known as knit lines, are lines that appear on the surface of an injection-molded part where two or more flow fronts meet and fuse together. The last cause of flow lines may be the operators running your daily operations. Also known as a knit line, this is the point at which two flow formations meet and are unable to. 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. "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. "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. Meld and knit lines are actually both different types of weld lines. Discover why you should avoid knit lines when designing and manufacturing injection moulded parts. A wide variety of tool steels are available for injection mold construction. 13758 Johnson Street NE. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Adjust the design for the flow pattern to be a single source flow. 3. Thin wall injection molding can produce walls as thin as 0. In the 1947 book, Injection Molding of Plastics, the late Dr. Steps involved in Multiple Material Molding. 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. The Demo Mold helps those new to injection molding easily visualize the process and is a great teaching device for educators. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Learn more. In working with the injection molding service offered by Protolabs, you provide. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Mold cooling is one of the most important variables in injection molding. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. When the plastic cools, it takes the shape of the mold and is then ejected and finished. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. Ham Lake, MN 55304. They need the interference of about 0. In plastic part design for injection molding, it is important to design the injection mold so that the molten plastic fills the mold cavity entirely, cools as evenly and as quickly as possible without warping, and functions as intended. These knit lines affect the parts aesthetics, but also they generally decrease the strength. , 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. Notched weld lines then remain near the cavity walls. See UNDERCUT. Gates that are too small can also cause the uneven flow of material or result in knit lines, blemishes that occur where two resin flows meet. When the molten plastic meets an obstruction. weld line in injection molding. The injection molding process uses a granular plastic that is grav ity fed from a hopper. The linear mold shrinkage of injection molded parts will vary from 0. 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). 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. Compression molding can also support large part sizes, and it has a tendency to. Islyn Thomas summarized the need for a particular vent location better than I ever could. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. By contrast, a slow injection speed will give you a matte finish and a cold mold, such as 50F, will give you a more flexible part. The 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. For example, increasing gate size can improve part 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). Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. suppressed cooling and possibly warp. 01 inches between parts fitted together to work best. , 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. PTI, a plastics and metal parts molder, is a leading developer of the MIM process. 11) The part design must take into account possible knit line locations and work to direct them away from higher stress areas. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. We recommend walls to be no less than 40 to 60 percent of adjacent wall thickness, and all should fit within recommended thickness ranges for the selected resin. Material contamination, for example, can cause several molding issues. So. (1. Runner Type. Vacuum. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. The depth of the texture or letters is somewhat. Injection molding a red component, for example, can pose a challenge because at time the component may be too thin for the pigment itself!. Weld lines may appear like seams or scratches,. 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. Knit Lines. Injection molding is the most widely used method for mass-producing plastic parts. . Knit lines don’t always compromise the structural integrity of plastic parts. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Also known as weld lines, knit lines. 01 inches between parts fitted together to work best. The metal parts, made of steel grade. The injection molding process offers a vast array of plastic resins to work with. even though injection molding temperatures are _____ compared to metals, the thermal expansion of plastics is _____ to _____ times that of metals. To avoid walls that are too fat or too thin, designing a wall thickness between 0. It is best practice to maintain a uniform thickness throughout an injection-molded part. Additionally. 2. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. You don't give us much to go on. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. 160"). Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. Find out more by calling 573-437-4154 today or email us. These flaws can affect the aesthetic and structural integrity of the. Second, the runner leading to a tab gate takes up real estate within the. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. 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. 4. 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. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. The injection molding process is on the surface is fairly simple, plastic resin is heated to its melting point and forced into the cavity of the mold to produce a plastic parts. Let’s. Molding is a manufacturing process in which resin in a barrel is heated to a molten state,. 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. POROUS MOLD MATERIALS. Tips for Avoiding Knit Lines in Injection Molding Keeping the proper temperature in the injection molding machine, runners, and within the mold are all key to ensuring. reduction on the side the part is folding towards. RELATED CONTENT. Kim, who has worked for hot runner system and auxiliary equipment supplier Yudo-Abiman for 12 years, most recently as. Knit and meld lines are inherent to plastic. To learn more about us or to get a quote, click here or call 1-888-893-1587 now. Trapped gas is one of the most common causes of part burns, and can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Macromol Symp 1988;21/21: 489-500. (See Fig. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Injection molding machines with footprints similar to desktop FDM and SLA 3D printers are now available. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. injection molding. 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. Knit Lines. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. Flow Lines / Knit Lines Flow/Knit Lines 11. 080" – 0. Reinforcing ribs play a pivotal role in the strength of a plastic part. The area generally has lower strength than the other areas of the part. 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. Redesign the mold: Redesigning the mold to. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. 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. Use the fewest number of gates possible. 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. This is a video excerpt from our Problems & Solutions Course - Weldlines. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. 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. extend mold service life. 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. 2. If you have questions about the suitability of the Protolabs process for your optical parts, contact an applications engineer at 877-479-3680. Weld line. The injection molding process uses a granular plastic that is gravity fed from a hopper. 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. 453. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. Mold venting should be checked and increased if necessary, injection molding service. land and using maximum vent depths to get them as close to self-cleaning as possible. Only then can we move on to determining the parting line itself. Long shapes are produced without multiple drops or hot runner systems, eliminating knit lines and lowering tooling costs. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. TRADITIONAL MACHINES VENTS. The Goldilocks principle applied to wall thickness. Observation on a “trial and error” basis may be required. incomplete filling or shorts. LS Mtron Injection Molding Machine (IMM) has opened a new business unit in Mexico. extend the time between mold maintenance shutdowns. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different. ). Reducing the dimensions of the runner system. 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. Wavy lines are another feature of weld lines. 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. The mold opens and closes on a vertical axis in the vertical injection molding. Enlarge gas vents and gates to allow trapped air to escape the mold.