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. Weld / Knit Lines; Assumptions. Based on the resin. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. These structures are often small surfaces of about a tenth of an inch in diameter. In fact, knit line strength will decrease with higher filler content and with longer fibers. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. One common problem that occurs in injection molding is the formation of knit lines. Molding is a manufacturing process in which resin in a barrel is. Injection moulding (U. Any of the above can result in “knit lines” on final products, but mold flow analysis prior to mold machining can keep these issues from cropping up at all in iteration and production. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Commonly seen at the edge of a hole or other cored feature, knit lines are—as a rule—purely cosmetic, but may create a physical failure point if present in an area of the part that receives substantial stress, such as the head of a screw. 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. While injection molding itself is a straightforward process involving melting. Fictiv can help you avoid injection mold design and plastic part design for injection molding problems. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. Injection molding a red component, for example, can pose a challenge because at time the component may be too thin for the pigment itself!. As these flow fronts come together. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. . 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). 4. It is caused by the incomplete joining of the uncured. RELATED CONTENT. The comment on melt flow index is correct, but, I've molded straight PC down to . Excessive injection pressure can result in part defects such as overflow or flash. Resin pellets are loaded into a barrel where. Enlarge gas vents and gates to allow trapped air to escape the mold. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. 4. 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. Refers to portion of injection molding part that has some taper to make it easier to remove from the mold. As a result, prototyping is strongly recommended for parts with. Troubleshooting Injection Molding Weld Lines. This is a video excerpt from our Problems & Solutions Course - Weldlines. com Discover why you should avoid knit lines when designing and manufacturing injection moulded parts. Monoform parts. 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. 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. 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. A plastic product formed by the injection mold is divided into two parts, and the line separating the product is called the parting line. 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. pdf), Text File (. This makes the casting process as efficient and accurate as possible. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. In this, work, metal inserts were joined with polyamide 6 by using the injection-molding technique. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. com. From Plastic Materials and Processing by A. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. The Demo Mold helps those new to injection molding easily visualize the process and is a great teaching device for educators. When the mold adopts the multi-gate pouring scheme, the plastic melt. We have two unique offers to meet your needs wherever you are in the product lifecycle. The definition of weld lines: When multiple plastic flow fronts meet in the cavity after encountering inserts, holes, or areas with inconsistent flow rates or interrupted melt flows, or in the case of gate injection filling, the inability of two or more flow fronts to fully “knit” together will cause the linear weld marks. Steven. This slight depression is a tiny line called the weld line or knit line. This production method is particularly popular when manufacturing in large quantities. 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. Vertical Plastic Injection Molding. Knit lines, holes, part configuration and the talent of your molder all come into play. (2) Undesired movement of certain materials in a plastic. 5. 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. 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. Typically, the wall thickness is somewhere in the neighborhood of 50%-75% of your nominal wall thickness. Meld and knit lines are actually both different types of weld lines. 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. 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. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. They occur when melt flow fronts collide in a mold cavity. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. Following lists causes and solutions for weld or knit lines. The knit line strength and other packing related properties both aesthetic and functional of injection molded polymeric products is improved by equipping the mold with packing pins. LS Mtron Injection Molding Machine (IMM) has opened a new business unit in Mexico. This article will look at two common venting options—using traditional machined vents and venting through porous materials—to help you decide which is right for your application. Learn how to troubleshoot weld lines in injection molding. Compression molding is one of the earliest forms of molding. 5 kN/cm2 (4 T/in2 ) is required. weld line in injection molding. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. 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. A parting-line vent. And the lead-time for overmolded and insert molded parts is 15 days, a bit longer than FacFox’ single-part injection molding turnaround, but still much faster than traditional insert molding. INJECTION MOLDING GUIDE V2. (See Fig. Drying Considerations For both virgin and rework, hopper dryers sized to afford theWhen establishing the parting line, we must first define the shape and position of the parting line on the plastic molded item. Depends how hard you want to push it. (called also weld marks or knit lines), and meld lines. Reducing the dimensions of the runner system. . Weld / knit plane forms as flow fronts recombine Weld line and failure due to flow around core. Still, they are almost always a cosmetic issue. 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. 3D printed molds in the injection molding process to lower costs and lead time. End-of-arm tooling can make or break a program. The resin is transferred to the mold cavity under positive. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. 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. Wax or ceramic core size or location See Section 3. Remove holes if possible. Islyn Thomas summarized the need for a particular vent location better than I ever could. holes, multi-point injection. The thermoplastic injection molding process at BEPL is a standard process involving an aluminum mold with no heating or cooling lines running through it, which means cycle times are a bit longer. All the while, the material could be the correct material," Hill says. 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. Anisotropy. 6 Monate. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Knit and meld lines are inherent to plastic. IM: hot or warm knit lines are cause by _____ while cold knit lines are caused by _____. [1] Plastic injection molding is the industry’s most common way to manufacture parts. Even parts with metal inserts can be produced. Knit Lines and Resins. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. and Titomanlio, G. 008 to 0. Injection molding weld lines refer to a line on an injection molded part that is generated where the two halves of the mold come together. Injection molding, producing, and forming resin materials are three core components of injection molding technology. Three terms that often get mixed up are weld, meld, and knit lines. Notched weld lines then remain near the cavity walls. Possible causes: Low temperature or fluidity of melted plastic during injection molding. In working with the injection molding service offered by Protolabs, you provide. (2) Undesired movement of certain materials in a plastic. To learn more about us or to get a quote, click here or call 1. Weld lines are also known as “stitch lines” or “knit lines”. Knit lines. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. This course outlines mold filling and how different gating configurations affect filling. The metal parts, made of steel grade. Mold venting is critical to the quality and consistency of the finished part. PTI, a plastics and metal parts molder, is a leading developer of the MIM process. These materials have beenThe wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. Gate design is another critical piece of part function in plastic injection molding. Meld and knit lines are actually both different types of weld lines. As a result, a rib at the weld line junction can strengthen the bosses at the mold line. Finally, knit lines occur when molten plastic flows around an object and rejoins on the far side, a phenomenon that is quite possible when inserts. Ham Lake, MN 55304. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Weld line are formed whenever melt fronts separate and recombine at some downstream location. C. BLEED – (1) To give up color when in contact with water or a solvent. Also known as knit lines. Gate and Knit Line Locations<br />. 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. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. While mold-filling simulation is a very common tool for predicting the fill patterns of an injection mold, in our judgment there is not yet a commercially available, satisfactory filling simulation for microcellular foam molding. 4271. They again get resolidified along the surface. Mold Venting. 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. 040-in. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. It allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. 2 mm. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. These are caused by the shot of molten plastic moving at different speeds throughout the injection. [1]Weld Lines. ABS. Probable Cause Suggested RemedyI am working on a thin PC/ASA injection moulded component which has a tendency to snap at the Knit-point (the final point of travel at which the…Opening and closing all the valve gates at the same time necessarily limits the degree of control over weld or knit lines, gas traps, localized packing, and unbalanced flow. Submarine gates are another injection molding types of gate that is located below the surface of the part, typically on the underside or back of the part. The example. occupied frequently with troubleshooting injection molding. 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 screw-type plunger forces the material into a heated chambe r,. Plastic injection molding is the industry’s most common way to manufacture parts. 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. 1. Proper venting is essential to molding a defect-free part. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. Complex parts can be reproduced with low cost once mold is manufactured. Weld Lines. But any. It’s called sequential valve gating, or SVG. But we can’t talk about the injection molding process without discussing the injection molding machine. Here are some of the most common cosmetic defects and how to avoid or fix them. Weld-lines look like cracks on the appearance of plastic. Observation on a “trial and error” basis may be required. 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. reduce mold maintenance cost. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. This type of molding uses a single tool to create both the part's geometry and surface finish in one step. Steven. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 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. 5 : 1 and 3. 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). The specific method is that when the product is just filled and filled in the cavity, the insert is used to cut the soft material melt in. Understanding Knit Lines in Injection Molding: Causes and Solutions. To learn more about us or to get a quote, click here or call 1-888-893-1587 now. Reduce the temperature of the mold and plastic being injected. Reducing the size and depth of depressions helps minimize the impact of knit lines. ”. 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 injection molding terms, these are called “living hinges” and are made right into the design instead of adding them later. 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. A medical device designer might look up a polymer's physical properties and game out. 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. Thin wall injection molding can produce walls as thin as 0. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. occupied frequently with troubleshooting injection molding. When working with customers, our design guidelines for living hinges are 0. Contact us. Not always a problem, but can cause serious structural issues. This will helpWeld line. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. Flow Lines. Quick Guide to Injection Molding Amodel® polyphthalamide (PPA) equipment Amodel® PPA resins can be processed on conventional injection molding equipment. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Knit and Meld lines are inherent to plastic injection. Weld/Meld/Knit lines are all terms describing the effect of two or more flow fronts of material joining or meeting together in the part. 030 and 0. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. In the case of mold details, knits will occur on the lee side of a detail. There are times when porous materials like Porcerax are used in problem or backfill areas. While this process is largely efficient and reliable, it's not without its potential issues. Als einer der führenden deutschen Hersteller von Masterbatches stellen wir nicht nur Farb-Masterbatches, Additiv-Masterbatches und funktionelle Kunststoff-Compounds her – wir leben deutsches Forscher-, Ingenieurs- und Unternehmertum. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. RE: Knit Line Affect On Material Strength lorelei5607 (Automotive). The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Let the molten material cool to a solid-state. Mold Venting. Three terms that often get mixed up in injection molding are weld, meld and knit lines. High mold temperatures usually provide less residual stress. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Knit/Weld Lines. 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. Reduce the injection speed to limit the risk of trapping air inside the mold. 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. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. This article will look at two common venting options—using traditional machined vents and venting through porous materials—to help you decide which is right for your application. The result is a consistent flow of molten plastic during injection and a quicker filling time. Submarine Gates. Kim, who has worked for hot runner system and auxiliary equipment supplier Yudo-Abiman for 12 years, most recently as. Gate size can be increased or moved to a section with greater wall thickness to help eliminate. Release of trapped air in those cases will. extend mold service life. What you should know is that there are various failure modes for injection molding. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. 453. 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. Our plastic injection molding glossary provides key terms. - 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. Contact Universal Plastic Mold Today. 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. These flaws can affect the aesthetic and structural integrity of the. Changing the. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. Observation on a “trial and error” basis may be required. Change gate locations. Its superior flowability allows for precise and flawless filling of injection molds without the risk of flow marks and knit lines. Our glossary of terms provides definitions for a wide range of injection molding terms. be impressed by improvements of bubbles (vacuum voids), short shots, unequal thickness, jetting marks, weld lines, knit lines, black streaks, strain 2. Flow Lines / Knit Lines Flow/Knit Lines 11. This defect is caused when the polymer resin is injected into a mold and flows around a solid piece and forms when the resin collides back together without completely fusing back together. While the presence of knit lines does not always compromise the structural integrity of the plastic part, they are almost always a cosmetic issue. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. Weld lines are a common imperfection to be found in most plastic injected molded parts. 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. Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon. Understanding Knit Lines in Injection Molding: Causes and Solutions. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. Ductile Injection Molding 101 - Injection Molding Varying. This defect is caused from excessive lube or oily stock. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. 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. Wall Thickness: The recommended wall thickness for injection molded POM parts is between 0. Knit Mark – A witness mark on a molded part, often occurring at the midpoint between two transfer or injection sprue locations. More about the knit lines in injection molding. TRADITIONAL MACHINES VENTS. The process is extremely versatile, and can produce very complex shaped parts, with the use of multi-sided molds. . Weld lines may appear like seams or scratches,. It’s economical, efficient, and can produce simple to complex parts with low waste. Valve gates are most efficiently. 0 and Table 1). The recommended minimum production volume for injection molding is 500 units. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. The knit line is generally opposite the gate in thermoset. Give us a call at (425) 339-0288 or email us at info@sealectplastics. Knit Lines: Holes in the part will always cause knit lines. Knit Lines. More about the knit lines in injection molding. When injection molding complex parts, often knit-lines are formed during the mold filling stage. Thermoplastic Elastomer Molding Guidelines. 3. Inadequate injection pressure can result in knit lines and a surface that appears corrugated. Inject the molten material into a mold. Also, since this part will likely be painted or chrome plated, knit lines are a concern. A meld line occurs when two moving melt fronts converge and flow parallel to each other. 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). 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. The last cause of flow lines may be the operators running your daily operations. To avoid these problems and create the best possible. Learn how HPP maximizes these specialized processes. 01 inches between parts fitted together to work best. It recently obtained a $4. These flaws can affect the aesthetic and structural integrity of the. 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. , 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. A meld line occurs when two moving melt fronts converge and flow parallel to each other. More about the knit lines in injection molding. 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. Chris Newmarker | Dec 27, 2013. Generally all plastic components should be designed with draft where possible. The mold’s sprue bushing and locating ring is placed in a way that makes sure the injection molding nozzle is properly aligned and centered. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). What Are Cosmetic Standards for Plastic Parts?. Injection Molding Press. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. In addition, keep these in mind: Scrap rates can range from less than 1 to 5%. Double push filling method. First, they carry resin to the mold via a runner. Below is a list of items that should be checked both during normal molding operations and if defects are detected. When the mold body is closed, the contact surface of the cavity and core plates makes a parting line. You don't give us much to go on. Islyn Thomas summarized the need for a particular vent location better than I ever could. Injection molding can form complex geometries easily, apply single part with multiple functions. Gate locations can be directly behind or on the edge of the graphic. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. What is copper electrode in injection mold? hashtag#plasticinjectionmold hashtag#moldmaking "Copper electrode," also known as "electrode," is a common component in mold manufacturing. 08 KICKOFF PRODUCTION. Knit Lines 11: 1. Multiple gates will always. Three terms that often get mixed up are weld, meld, and knit lines. Given the cosmetic requirements, there is a good chance the mold would require. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). 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. Be wary of saving too much weight or you might end up with: cracking. Back to News Page. thick. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. 5T, where T is your nominal wall thickness. 1050 Walnut Ridge Drive. They need the interference of about 0. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. Increase the injection speed. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. 060 in. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and holding. Venting. The cooler flow fronts of the resin aren’t forced into the mold surface texture as well as the hotter resin behind the flow front. After samples have been approved, it’s time to kickoff. 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. A screw-type plunger forces the material into a heated chamber, called a barrel, where it is melted.