Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Venting. Not always a problem, but can cause serious structural issues. 6. 5 : 1 and a L/D (length toMold flow analysis is a software simulation which show how the resin fill in the mold in injection molding process. 040 and 0. While not always visible, weld lines (aka knit lines) are where two resin flows meet. Injection Molding Injection molding is perhaps the most common and important of all plastic processing processes. Meld and knit lines are actually both different types of weld lines. Piccarolo, S. Knit lines may also be called stitch lines, weld lines, or meld lines. Meld and knit lines are actually both different types of weld lines. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Solution: People. Observation on a “trial and error” basis may be required. PTI, a plastics and metal parts molder, is a leading developer of the MIM process. The injection molding process offers a vast array of plastic resins to work with. Reduce the injection speed to limit the risk of trapping air inside the 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. C. In this phenomenon, some portions of the mold cavity are filling, while others undergo over. 5. The linear mold shrinkage of injection molded parts will vary from 0. Monoform parts. 5 kN/cm2 (4 T/in2 ) is required. (1987). There are processes such as gas assist that do not require the injection unit to pressurize (pack out) the cavity, but for our discussion, we will stay with conventional injection molding. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. Imagine a river splitting to go around a rock, then meeting up again on the other side. Rapid heat-and-cool molding technologies have attracted increasing. These flaws can affect the aesthetic and structural integrity of the. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. It is. It’s our responsibility to make sure your design comes out of the mold working properly. 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. These are imperfections in the part where separated flows of cooling material meet and. thickness with a spacing of about 0. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. Because viscosity is a. Trapped air in a mold manifests itself as a burn mark on the molded part. Increase the injection speed. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. 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. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. (called also weld marks or knit lines), and meld lines. Also known as a knit line, this is the point at which two flow formations meet and are unable to connect during injection molding. Weld lines: Also known as knit lines, these are molding defects that occur when two flow fronts meet without the ability to “weld. 020"). Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. 0 mm) is crucial to ensuring that parts cool evenly. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. Hardware components. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. injection molding. Encapsulating the metal insert with plastic creates a single. A well-designed injection-molded part will usually have draft, but the same draft that helps eject a part from the. . The weld line can either be a minor cosmetic issue. These lines. Holes in the part will always cause knit lines. What Are Cosmetic Standards for Plastic Parts?. Step 3: The injection mold undergoes rotation to align in position with injection Barrel B. Thermoplastic Elastomer Molding Guidelines. extend mold service life. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Look for signs of stickiness or burning. Adjusting features to be suitable for molding will help resin flow well into the mold, allow it to cool evenly, and reduce the chance of cosmetic defects such as sink, knit lines, flash, and warp. It is best practice to maintain a uniform thickness throughout an injection-molded part. Mold venting should be checked and increased if necessary, injection molding service. Only then can we move on to determining the parting line itself. It has low shrink and high dimensional stability, and it has good resistance to acids and bases. 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. Brent Strong, p. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. Shorter knit lines must equate to a stronger part. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Steps involved in Multiple Material 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 adhesiveIt tells them that you visualized how injection molded parts cool and harden. Mold Venting. It’s called sequential valve gating, or SVG. Also known as knit lines. 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. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. 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 course outlines mold filling and how different gating configurations affect filling. Understanding Knit Lines in Injection Molding: Causes and Solutions. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause. Figure 1: D-shaped through-hole in center of gear part accepts the drive shaft. Fig. This defect is caused from excessive lube or oily stock. Injection molding is a popular manufacturing process used to fabricate parts in large volumes. 125 inches. This production method is particularly popular when manufacturing in large quantities. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. The comment on melt flow index is correct, but, I've molded straight PC down to . 7. 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. reduce mold maintenance cost. 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. 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. Services Group. A. Weld / knit plane forms as flow fronts recombine Weld line and failure due to flow around core. Discover why you should avoid knit lines when designing and manufacturing injection moulded parts. This radius should not be smaller than 0. Enlarge gas vents and gates to allow trapped air to escape the mold. What Are Cosmetic Standards for Plastic Parts?. Multiple gates will always. knit line. Solution: Increase the injection pressure or speed. 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. 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. 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. BLEED – (1) To give up color when in contact with water or a solvent. (2) Undesired movement of certain materials in a plastic. When the mold adopts the multi-gate pouring scheme, the plastic melt. 1. 1-3). Investigate the mold for signs that a water leak is present, and correct the condition. 1513 Sam Bass Rd. 120 in. 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. 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. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. Because this allows some cooling and thickening of the resin, tab gates require a relatively large opening into the mold cavity. Understanding Knit Lines in Injection Molding: Causes and Solutions. 030 and 0. Users will be able to use in-cavity pressure or temperature sensors to control when the valves open or close. 3—Another issue with the four-gate design was that knit lines ended on or near mounting holes, causing a. To avoid walls that are too fat or too thin, designing a wall thickness between 0. , under its Advanced Technology Program (ATP). 040 and 0. (See Fig. Injection molding is the most widely used method for mass-producing plastic parts. ”. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. Adding a border around an embossed logo is a good way to protect it from abrasion. 4271. 763-755-7575. High mold temperatures usually provide less residual stress. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. RE: Knit Line Affect On Material Strength lorelei5607 (Automotive). To avoid these problems and create the best possible. Weld Lines. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Back to News Page. 0 to 3. Looking to Your Knit Lines with Molding. RJG announced that its injection molding process control system, CoPilot, will begin offering valve gate control technology for hot runners starting in September 2021. 5. As a result, prototyping is strongly recommended for parts with. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. A mold with too few gates is susceptible to cooling problems, but a mold with too many gates. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Reduce the temperature of the mold and plastic being injected. . So much. This continues until the weld lines in plastic injection molding disappear. injection molding. 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. • Holes formed by core pins are, in essence, 360° inside corners and should follow. Knit lines. Weld lines are a common imperfection to be found in most plastic injected molded parts. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. These lines are the result of the molten plastic material recombining after splitting and flowing around an obstacle in the mold cavity. 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. Weld lines defects are formed when two flow fronts are merged 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. Those are knit lines, formed when two opposing flows of material join together in the mold cavity. Resin pellets are loaded into a barrel where. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. [8] Bevis, MJ, Reis RL, Cunha AM. Remove holes if possible. When needed, crush ribs can allow for draft and a tight fit for a part that requires both. "As soon as that part or material is stressed, it can be real conducive to fracture, cracking, breaking, just because of the way it's been molded. (If parts are to be molded by Protomold’s rapid injection molding process, our Design Guidelines should be used. 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. Edge gates, which can include fan and tab-shaped gates, are the most common ways to gate a tool. Injection molding a red component, for example, can pose a challenge because at time the component may be too thin for the pigment itself!. 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. Know about the cause of these lines and the potential solutions. For example, increasing gate size can improve part filling. Wall Thickness: The recommended wall thickness for injection molded POM parts is between 0. 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. RELATED CONTENT. See UNDERCUT. In layman’s terms, injection molding boils down to four simple steps: Melt material. 2. weld line in injection molding. In an injection molded structural plastic part, a weld line (also called a knit line) will result in a region of mechanical weakness as soon as the part is submitted to an external load. They occur when melt flow fronts collide in a mold cavity. Knit lines, holes, part configuration and the talent of your molder all come into play. Starting in September, the CoPilot process control system developed by RJG will come equipped with valve gate control. In a weld line, reinforcement fibers. and 0. After samples have been approved, it’s time to kickoff. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. 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. Get a free des. Core out parts to eliminate thick walls. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. In the 1947 book, Injection Molding of Plastics, the late Dr. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. The parting line location on the injection mold will have an effect on how the cavity and core (both halves of the injection mold) come together and seal. 25T-0. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. 040-in. It is best practice to maintain a uniform thickness throughout an injection-molded part. This makes the casting process as efficient and accurate as possible. Venting. In fact, knit line strength will decrease with higher filler content and with longer fibers. They again get resolidified along the surface. To learn more about us or to get a quote, click here or call 1-888-893-1587 now. Here are some of the most common cosmetic defects and how to avoid or fix them. 2. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. See full list on fathommfg. Runner and gates must be balanced. A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to. 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. There is high defect rate (surface defects/knit line). As a result, the portion has a faint, perhaps undetectable line. 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. 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. The injection molding process uses a granular plastic that is grav ity fed from a hopper. (for example, a hole on the plastic part), the knit line will be unavoidable. Other Excessive mold release Clean die and use minimal mold release. If life safety is involved, or reliably or efficacy are absolutely required, every part should. Our plastic injection molding glossary provides key terms. In this paper, a general and efficient approach was proposed for dual-scale infiltration flow balancing based on numerical simulation. With this option, users can utilize in-cavity pressure or temperature sensors to control when the valves open or close. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. By using this method, theMolding analysis study: An example of the low patterns and knit (weld) lines formation (MoldFlow® data) of injection molded round plastic part with a complex shape and with a ring. Multiple parts with complex design and differing wall. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. We have two unique offers to meet your needs wherever you are in the product lifecycle. Core out parts to eliminate thick walls. Troubleshooting Injection Molding Weld Lines. 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. 5 : 1 and 3. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022injection-molding machine (Arburg allrounder 320C, Germany). The goal is to create a uniform thickness and at the smallest (thinnest) level required. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. The parting lines is where the two injection mold halves (A side and B side) meet. They are formed downstream through holes, and between multiple gate locations. IM: hot or warm knit lines are cause by _____ while cold knit lines are caused by _____. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. 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. The melt is forced to split up during filling of the cavity. They appear around holes or seams of an injection. Learn more about the process by reading this white paper. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. wall thickness injection molding ribs. This can dramatically reduce the effects of material changes, according to the injection molding technology company. Valve gates are most efficiently. Some are: Knit lines (discontinuities where two flows merged, creating a weak point)In some situations where a mold has parting line damage, reducing heat can actually improve flash that was a direct result of that damage. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. 05-million grant for MIM R&D from the National Institute of Standards and Technology (NIST) in Washington, D. 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. While this process is largely efficient and reliable, it's not without its potential issues. Three terms that often get mixed up in injection molding are weld, meld and knit lines. [8] Bevis, MJ, Reis RL, Cunha AM. Reinforcing ribs play a pivotal role in the strength of a plastic part. Wax Cold wax Increase wax temperature. 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. Knit Lines and Resins. 2. The advantages of compression molding include more isotropic fiber distribution, dimensional stability, and surface finish. Temperature is another factor that can cause weld or knit lines in injection molding. Even parts with metal inserts can be produced. We look forward to offering support and advice on your next project. Imagine a river splitting to go around a rock, then meeting up again on the other side. 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 adhesiveWeld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. The quality of the answer is directly proportional to the information we have to work with. Understanding types of injection molding process can help to avoid some design challenges early in the process. 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. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic. 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. 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. a specific area on one side lens, a warp line, and a weft line. The metal parts, made of steel grade. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. They occur when melt flow fronts collide in a mold cavity. Learn how material selection, part design, and optimizing process parameters can help eliminate knit lines. Knit lines, holes, part configuration and the talent of your molder all come into play. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. Adding vents, using overflows, or using porous metal. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Islyn Thomas summarized the need for a particular vent location better than I ever could. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Weld line are formed whenever melt fronts separate and recombine at some downstream location. 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. Knit Lines 11: 1. 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. Other common issues associated with thin walls include uneven cooling, warp, cracks, cosmetic texture inconsistencies, and weak knit lines or fracture points. Take these steps to avoid knit lines. Meld and knit lines are actually both different types of weld lines. Also known as string lines. The following are general guidelines for molding acetal. In spite of its cosmetic attributes, a bad knit line can significantly. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. 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. Injection moulding (U. 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. This is why the leading edge of the resin flow within a. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. Those are knit lines, formed when two opposing flows of material join together in the mold cavity. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. Reducing the dimensions of the runner system. 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). These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. Learn how to troubleshoot weld lines in injection molding. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). 080" – 0. 6 Monate. , 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. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. 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. thick. Depending on the resin, resin temperature, mold temperature, and filling. A parting-line vent. Factors were ordered. ISO 9001:2015. As. While injection molding itself is a straightforward process involving melting. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. Plastic injection molding is the industry’s most common way to manufacture parts. Design With Plastics. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). One common problem that occurs in injection molding is the formation of knit lines. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. These defects are not visible, like small. 3. The Problems & Solutions course is designed to train injection molding personnel in. Also, since this part will likely be painted or chrome plated, knit lines are a concern. 008 in. Reduce the injection pressure. Knit Lines. If debossed pattern is indispensable, it should have a depth of no less than 0. All the while, the material could be the correct material," Hill says. Inject the molten material into a mold. Injection molding a part with Class-A surface finish and ribs or bosses has proven an elusive goal for molders, despite their best efforts with conventional injection or internal gas-assist technology. Plastic melt and mold temperature. This is a video excerpt from our Problems & Solutions Course - Weldlines. 847-952-8088. knit line formation, application of draft angle and design for assembly. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. Subscribe to Our Newsletter. 5mm (0. Therefore various injection molding defects can be eliminated. 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. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. How weld lines form. 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. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. When the plastic cools, it takes the shape of the mold and is then ejected and finished. Three terms that often get mixed up are weld, meld, and knit lines. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. The gate is the entry point to the part-forming cavity, where plastic material is injected from the molding machine barrel, through the sprue and runner, into the mold. Mold venting is critical to the quality and consistency of the finished part. The mold opens and closes on a vertical axis in the vertical injection molding. sinks, knit lines, and shrinkage,” Spalding says. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 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. But we can’t talk about the injection molding process without discussing the injection molding machine. Changing the. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. 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. Knit/Weld Lines. placed usually in the areas last to fill, near knit lines, as well as on the runner system. Called LS IMM Mexico, the subsidiary is based in Monterrey and led by plastics industry veterans Kevin Kim and Fulvio Menconi. The melt is forced to split up during filling of the cavity. The bottom of your rib must also feature a fillet. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills.