Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Flashing can be a common defect in injection moulding and can affect the appearance and functionality of the finished product. Two major sources of weld lines are multiple gating and flow around pins. 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. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. One solution is to use optimal wall thickness to help slow cooling during the ABS plastic molding process. Compression molding and injection molding are very similar, but they have one major difference. Injection molding machine and automation supplier Engel offers an array of technologies to simplify and speed up mold changes, including magnetic clamping platens and quick couplings; intelligent assistance systems; and the famox mold changing system for automating the set-up process. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all, be a cosmetic issue, or cause a potentially serious structural problem. Long shapes are produced without multiple drops or hot runner systems, eliminating knit lines and lowering tooling costs. Injection Molding Guide. Meld and knit lines are actually both different types of weld lines. Mold filling simulation software should be used to ensure that waterInjection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022Main causes of knit lines in injection molding: 1. For. Weld lines have a significant effect on manufactured products. lines are formed when there is an obstacle in the cavity of the injection mold. Sink Marks Cause 2: Low Pack and Hold time. 3 /sec. 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. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. Such molds or tools aren’t intended to be used in operation. shows some obvious locations for vents, a brief molding trial should be conducted to observe where the gas voids occur. Formation of knit line. Also known as a knit line, this is the point at which two flow formations meet and are unable to. This will help the mold designer to determine the allowable gate and knit line locations. Material contamination, for example, can cause several molding issues. Meld and knit lines are actually both different types of weld lines. matte or smooth texture on the part’s surface gives a more desirable aesthetic and hides small imperfections such as knit lines, flow lines, shadow marks, and sink marks that were caused by the mold. But we can’t talk about the injection molding process without discussing the injection molding machine. Gas-assisted Injection Molding: Influence of Processing Conditions and Material Properties. Poorly constructed or worn out mold. Therefore, with the cooling process, the resin in the central part shrinks and expands to the surface, resulting in insufficient filling in the central part, which is called vacuum. These knit-lines are well-known as particularly critical regions in the mold when mechanically. ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. ” What else can you do about weld lines—besides redesigning the mold or gate locations or adjust the flow pattern during fill with sequential valve gating? I recently saw a report on this issue from Moldex3D, the maker of molding simulation software. Injection molding is a simple and efficient process that produces high-quality plastic parts. Rynite® PET is usually processed with melt temperatures between 280 to 285 °C (535 to 545 °F) . Injection molded plastic begins its journey through the part tooling via an entry section called a. LCP can replace such materials as ceramics, metals, composites and other plastics because of its outstanding strength. Weld line, also known as knit line or meld line, is a visible line or mark on the surface of a plastic part where two or more flow fronts of molten plastic meet and fuse together. It is one of the most common blemishes for manufactured products. 4. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. Anisotropy. Fewer knit lines. Remove holes if possible. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Plastic melt and mold temperature. 015in wall. Contact Us. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. The defect may be in part appearance or mechanical strength. Specifically, by having a single, continuous injection outlet 140, molding material can be uniformly distributed throughout mold cavity 120 quickly and consistently without resulting in undesirable molding seams or knit lines. Bead Blasting. In this way, the mold supports distribute the force and minimize the stresses on the mold plates. These flaws can affect the aesthetic and structural integrity of the. In fact, knit line strength will decrease with higher filler content and with longer fibers. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Knit Lines and Resins A knit line is any line, visible or not, where two resin flows meet (see Figure 2). In working with the injection molding service offered by Protolabs, you provide. 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. This type of molding uses a single tool to create both the part's geometry and surface finish in one step. By using this method, theHowever, injection molding is not without its challenges. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. So. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. Compression-molding is also suitable for ultra-large basic. Overall, injection molding is a relatively simple process. Specifically, by having a single, continuous injection outlet 140, molding material can be uniformly distributed throughout mold cavity 120 quickly and consistently without resulting in undesirable molding seams or knit lines. 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 Ventings Knit/Weld Lines. The structural stability of. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. While this process is largely efficient and reliable, it's not without its potential issues. land and using maximum vent depths to get them as close to self-cleaning as possible. In the 1947 book, Injection Molding of Plastics, the late Dr. 1. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky 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. They again get resolidified along the surface. com Three terms that often get mixed up in injection molding are weld, meld and knit lines. opposed to two or more gates. 827 Holes and Bosses. This slight depression is a tiny line called the weld line or knit line. Weld lines also can be visible after a part is painted and can cause wrinkles on in-mold-label injection-molded products. Flow rate and flow speed are cut in half at every runner branch. Steven. Below is a list of items that should be checked both during normal molding operations and if defects are detected. Understanding Knit Lines in Injection Molding: Causes and Solutions. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. 5 mm (0. SPI surface finishes are the most common set of injection molding finishing standards around the world with over 12 different grades. SEA-LECT Plastics has 16 MILACRON injection molding machines that range from 33-ton with a 2. A knit line is any line, visible or not, where two resin flows meet. Left: L-shaped perform. The influence of knit-lines on the tensile properties of injection molded parts. More about the knit lines in injection molding. Learn about the key characteristics of common injection molding materials, recommended applications, and how common thermoplastics compare to one another. 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. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. 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. Depending on the design of the mold. Knit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection. Use the fewest number of gates possible. Knit Lines 11: 1. The above guidelines for initial heater band settings are for most injection molded parts. It tells them that you visualized how injection molded parts cool and harden. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. 040-in. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. A thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold to produce a specific part geometry. After the solidification of molten plastic, the finished part is ejected out. 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. [email protected] 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. After samples have been approved, it’s time to kickoff. Snake Lines: The appearance of snake lines is caused by the formation of a jet effect as the melt travels through a gate and into the mold cavity. menu. See full list on fathommfg. As these flow fronts come together. Knit Lines. In an injection mold, the plastic fluid flows and spreads out in many directions as it comes out of the gate. Meld and knit lines are actually both different types of weld lines. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. Holes in plastic parts are normally cut with a router (or drilled if round. These lines can manifest as visible marks on the component’s surface and potentially affect its structural integrity. Knit lines, also known as weld lines are areas in the. 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. The part is cooled in the mold until it is solid enough to be ejected. A knit line is any line, visible or not, where two resin flows meet. Observation on a “trial and error” basis may be required. Meld and knit lines are actually both different types of weld lines. 0 mm) is crucial to ensuring that parts cool evenly. Using abrasives in a pressurized air blast to create a surface texture on the part. Parts as thin as 0. Figure 1: Knit lines in a cover plate. Knit line / Meld line / Transfer line Discoloured line where two flow fronts meet Mould or material temperatures set too low (the material is cold when they meet, so they don't bond). They occur when melt flow fronts collide in a mold cavity. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. In the injection molding process, melting takes place via two factors that work together: shear and heat. . This production method is particularly popular when manufacturing in large quantities. com TYPICAL PROPERTIES MECHANICAL THERMAL OPTICAL. Learn how to troubleshoot weld lines in injection molding. How to Eliminate Knit Lines In Injection Molding - Xcentric Mold Want to learn how to eliminate knit lines that form during the injection molding process? Then. injection molding. Weld lines may appear like seams or scratches,. This normally occurs around holes or obstructions and causes locally weak areas in the molded parts. The fluid path has an inlet and a radially continuous, downwardly. Example of a gate location in a finished part Example of knit lines in a finished part. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. Plastic injection molding is the industry’s most common way to manufacture parts. These knit lines affect the parts aesthetics, but also they generally decrease the strength of the part. Back to News Page. A. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. Knit Lines. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. 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. These lines occur usually around holes or obstructions and cause locally weak areas in the molded part. Many materials can be. An injection molding machine having a first mold portion and a second mold portion. Very high quality and an extreme fit may. If the plastic has cooled too much during the injection process it can lead to knit lines in plastic parts when they meet past an the obstruction. excessive or premature wear at the parting line. 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. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. 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. From Plastic Materials and Processing by A. 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 packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. Weld Lines. ISO 9001:2015. Comprehensive. 2. 2. Knit lines and other aesthetic characteristics of the part are strictly related to the plastic’s temperature during molding, so efficient filling time is essential for achieving proper welding lines and quality parts. As these flow fronts come together. Check/add vacuum; Check mold lube; Check/increase venting. The main types of injection molding defects are: 1. Insert injection molding is a process that requires an insert — typically metal — to be pre-placed in the tool for injected plastic to flow around. Exploring common molding defects and. The last cause of flow lines may be the operators running your daily operations. The most common and one of the most challenging injection molding defects are weld and knit lines. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied. a specific area on one side lens, a warp line, and a weft line. . In the process of injection molding, when the wall thickness of the product is large, the cooling speed of the outer surface is faster than that of the central part. ABS is a good choice for handheld consumer devices. Knit lines are most common downstream of holes created in parts where the molten material meets. The process involves feeding the material into a press, where it is cooled or heated as per. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. Some. More about the knit lines in injection molding. Macromol Symp 1988;21/21: 489-500. When the temperature is not very high, there are chances of premature solidification, which can cause weld lines to form. 5 mm (0. Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon. 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. Using the design cube, learn how knit lines are formed on plastic parts and tips to avoid knit lines in your plastic injection molding design. With ABS injection molding, you get the collective benefits and properties of three monomers. Injection moulding (U. 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. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). Undercuts add cost to tooling and molding, which is recommended to eliminate or minimize as possible. LOCATION: Along any parting line. Legend: a-in. The Difference Between Knit and Meld Lines–and Why It Matters. One common problem that occurs in injection molding is the formation of knit lines. The last cause of flow lines may be the operators running your daily operations. For instance, three widely used processes are insert molding, overmolding, and undercuts. The injection molding machine includes a fluid path extending through the first mold portion. Weld lines or knit lines and meld lines formed when two melt fronts run into each other or join together can be improved by. Weld line. Without adequate support pillars, flashing of the parting line faces and bowing of the plates may occur. 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. Based on the resin. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. Quotes for 25+ Manufacturing Processes. Parting lines placed at intricate joints. Temperature is another factor that can cause weld or knit lines in injection molding. The goal is to create a uniform thickness and at the smallest (thinnest) level required. 5. The area generally has lower strength than the other areas of the part. Fewer knit lines are produced and a smaller amount of fiber-length degradation is noticeable when compared to injection molding. A knit line is the spot where two flows meet. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 0 mm) is crucial to ensuring that parts cool evenly. Part thickness control is through stacking of. In injection molding, it is often important to maintain consistent color throughout the part. 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. 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. Troubleshooting Injection Molding Weld Lines. What Are Knit Lines? When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. It is important when selecting an injection molder that the right process conditions are used to reduce or eliminate the effects of. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. 2. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. Different plastics make different types of knit lines. Knit/Weld Lines. RapidDirect – Your Best. Venting. Weld lines are a common imperfection to be found in most plastic injected molded parts. This will helpTroubleshooting Injection Molding Weld Lines. Inappropriate temperature. Knit / Weld Lines. Weld or knit lines occur when melt flow fronts collide in a mold cavity. Also, since this part will likely be painted or chrome plated, knit lines are a concern. Advantages Excellent moldability in thin sections Outstanding chemical resistance Heat resistance Limitations Cost Knit line strength OverviewLiquid crystal polymer (LCP) exhibits a highly ordered structure in both the melt and solid states. If the parting line is located on a sidewall of the part, it is nearly impossible to construct a mold without a slight mismatch between the force and the cavity. 8 mm relief at the edges of the thread. With plastic finishing plugs and end caps, we can help you keep your products protected while giving. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Weld Lines-3 Ways for Detecting and Correcting. To avoid these defects, manufacturers can check molds for the following: Low Mold Temperature: A mold temperature that’s too low will cause the material temperature to drop fast. Disadvantage: May rust if improperly stored. Venting. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. They again get resolidified along the surface. incomplete filling or shorts. Move the injection unit away from the mold during short breaks . These are imperfections in the part. This production method is particularly popular when manufacturing in large quantities. Don’t forget to eliminate entrapped air in the weld line injection molding; otherwise, it’ll create unfilled portions in your part design, causing more weakening. 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. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. 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. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates. 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. , LTD. Much of this research has focussed on the materials which. 45 in. A majority of these investigations concern amorphous polymers, whereas a number of engineering polymers are semicrystalline and also contain reinforcing fillers and fibers. Runner and gates must be balanced. The Mold Tools toolbar provides tools for creating mold tooling (cores, cavities, etc. Knit lines. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. 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. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. These materials have beenDetermining the correct tonnage provides a foundation that must be rock-solid to avoid flash and damage. txt) or read online for free. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. com support@makenica. Be wary of saving too much weight or you might end up with: cracking. In fact, knit line strength will decrease with higher filler content and with longer fibers. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. Mold venting should be checked and increased if necessary, injection molding service. This is a video excerpt from our Problems & Solutions Course - Weldlines. Weld lines are formed during cavity. Sink Marks Cause 3: Improper Pack or Hold Pressure. ABOUT THE AUTHOR. The gate architecture and its location affects cycle times, tooling costs, lead times, the location of witness marks and many other potential defects that are commonplace for. 1. Let’s. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. Three terms that often get mixed up are weld, meld, and knit lines. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. New blog post is up! What Are Knit Lines in Injection Molding, and How Do You Prevent Them? #injectionmolding #moldsmart #howto #rjg…Injection moulding is a well established mass production tool for polymeric products of all shapes and sizes which is now drawing the attention of companies and researchers who seek to utilise this high throughput fabrication technique to produce devices with nanoscale dimensions []. 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. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. An edge gate introduces material at the main parting line, or where the two halves of the mold meet, with a perpendicular runner. 0 and Table 1). Solution: Increase the injection pressure or speed. Trapped air in a mold manifests itself as a burn mark on the molded part. Transfer molding also utilizes a press and a mold. A wide variety of tool steels are available for injection mold construction. As. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. The specific method is that when the product is just filled and filled in the cavity, the insert. 120 in. and Titomanlio, G. This picture shows a. occupied frequently with troubleshooting injection molding. Knit Line occurs where different flow fronts of material meet while flowing through the mold. Misra A. What Causes Knit and Meld Lines? Like many part inconsistencies, these unwanted features are rooted in product design. 5 to 3. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. 5-3. 3. Meld and knit lines are actually both different types of weld lines. A screw-type plunger forces the material into a heated chambe r,. Achieving a high-quality surface finish can be challenging, and other methods, such as polishing or coating, may be required. , Rallis, A. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022What is copper electrode in injection mold? hashtag#plasticinjectionmold hashtag#moldmaking "Copper electrode," also known as "electrode," is a common component in mold manufacturing. But those key aspects can be viewed differently if you’re auditing mold changes before startup or troubleshooting changes for an already validated process. Weld lines are a common imperfection to be found in most plastic injected molded parts. (for example, a hole on the plastic part), the knit line will be unavoidable. Because injection mold design and processing is complex, a set solution will not solve all problems. The thermo-rheological findings were used to investigate the sources of weld line weakness. 11) The part design must take into account possible knit line locations and work to direct them away from higher stress areas. Weld / Knit Lines; Assumptions. For this study, a special injection mold was designed and constructed (Figure 1) in order to produce specimens of various thicknesses (from 2 to 6 mm). 140 in. Parting lines lie along the edge of the molded part, between the core and the cavity. Knit Lines. These knit lines affect the parts aesthetics, but also they generally decrease the strength. Adding draft or slope to vertical walls of a part makes it easier to eject or remove the part from the mold. Remedies: Increasing the barrel temperatures will allow the flow fronts to stay hotter longer and. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Also known as “stitch lines” or “weld lines”. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different. The parting line will always be visible, but can be minimized by its location, draft allowance and part geometry. There are times when porous materials like Porcerax are used in problem or backfill areas. On this page you will find the online, condensed version of this guide, offering quick answers to your injection molding questions. 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. Additional venting along the parting line perimeter will improve overall venting significantly. a knit line will form 180°on the opposite side from the gate location. Injection molding flow lines typically fall into one of the categories mentioned in the following table: Category: Type of Flow Line: Appearance (What It Looks Like) 1. In a well-designed mold, this is generally not a problem. Whereas conventional injection molding uses. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. 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. Injection molding is a plastic manufacturing process to achieve a high production rate. They appear around holes or seams of an injection molded part, and some may call them. Most failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold.