There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. 125 inches. . Proper venting is essential to molding a defect-free part. Weld Lines. 344. Let the molten material cool to a solid-state. Wax or ceramic core size or location See Section 3. 2. 015in wall. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. "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. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. Injection molding is a popular manufacturing process used to fabricate parts in large volumes. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. • Standard (general purpose) screws with a compression ratio between 2. Troubleshooting Injection Molding Weld Lines. For example, increasing gate size can improve part filling. Fig. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. 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. Molding is a manufacturing process in which resin in a barrel is heated to a molten state,. Specifically, Stokes and. Take these steps to avoid knit lines. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. such as knit lines and other imperfections. Fathom injection molding services and tools offer a single-source global solution that supports your company’s low- to high-volume manufacturing process. Knit Lines. Unsymmetrical filling makes knit lines in samples, leading to the failure of part, so it must be avoided. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. Injection rate plays a role—faster fill times develop more shear, molecular orientation and residual stress. Changing the. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. You don't give us much to go on. (2) Undesired movement of certain materials in a plastic. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. Mold cooling is one of the most important variables in injection molding. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. occupied frequently with troubleshooting 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. A meld line occurs when two moving melt fronts converge and flow parallel to each other. It can also aid in material selection since fill. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. 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. In addition, keep these in mind: Scrap rates can range from less than 1 to 5%. Knit lines. For instance, three widely used processes are insert molding, overmolding, and undercuts. Increasing injection speed. 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 Materials When using PolyJet molds, both tool life and part quality will be dependent on the thermoplastic material used during the injection molding process. Anisotropy. Learn how material selection, part design, and optimizing process parameters can help eliminate knit lines. . Plastics Technology article (June 2018): Technical capabilities of the process have advanced to erase former cycle-time penalties, and ongoing developments address creation of a materials database and new applications in hybrid composite injection overmolding. This is a video excerpt from our Problems & Solutions Course - Weldlines. Such molds or tools aren’t intended to be used in operation. These knit lines affect the parts aesthetics, but also they generally decrease the strength. 0 mm) is crucial to ensuring that parts cool evenly. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. 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. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. These materials have beenThe wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. 847-952-8088. Use the fewest number of gates possible. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. More about the knit lines in injection molding. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Core out parts to eliminate thick walls. Factors were ordered. 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. Still, it can be seen to varied degrees depending on mold. 5mm (0. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. TRADITIONAL MACHINES VENTS. A parting-line vent. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with. Chris Newmarker | Dec 27, 2013. The injection molding process offers a vast array of plastic resins to work with. Knit lines; Knit lines always occur once 2 melted materials meet with hair-like discolorations. "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. There is high defect rate (surface defects/knit line). Venting at Weld Lines. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Usually the parting line of the mold is perpendicular to the mold opening direction of the injection molding machine. 1-3). Holes in the part will always cause knit lines. Having a basic understanding of the injection molding process will aid in understanding how to design for injection molding as well as how to forecast production schedules. Reduce the temperature of the mold and plastic being injected. They again get resolidified along the surface. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. 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. 008 to 0. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. The linear mold shrinkage of injection molded parts will vary from 0. End-of-arm tooling can make or break a program. Gate locations can be directly behind or on the edge of the graphic. The Troubleshooting Tips below offer common solutions to challenges in IML and IMD. Shear Controlled Orientation Injection Molding of Polymeric Composites with Enhanced Properties. Learn more about the process by reading this white paper. This radius should not be smaller than 0. Advantages for your Injection Molding Machine:. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. They need the interference of about 0. This performance can ultimately impact many part properties, including surface quality, knit line strength, part ejection force (sticking), dimensions, tolerances. Enlarge gas vents and gates to allow trapped air to escape the mold. They again get resolidified along the surface. Heat: Too much heat can have an appearance similar to moisture splay. 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. The process is extremely versatile, and can produce very complex shaped parts, with the use of multi-sided molds. See UNDERCUT. Knit and Meld lines are inherent to plastic injection. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. So much. 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. Meld and knit lines are actually both different types of weld lines. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. a specific area on one side lens, a warp line, and a weft line. 008 to 0. 0 Items. Possible causes: Low temperature or fluidity of melted plastic during injection molding. Thermoplastic Elastomer Molding Guidelines. This configuration positions the injection mechanism at the top of the mold, allowing gravity to play a role in filing the mold cavities. 030 and 0. Plasti-Co® Nozzles for Injection Molding Machines. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. Causes 1. Plastic injection molding is a complex and highly intricate process. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. A wide variety of tool steels are available for injection mold construction. Adjust the design for the flow pattern to be a single source flow. When designing for injection molding, consider these steps to prevent knit lines Resin cools as it is injected into a mold. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different. With this option, users can utilize in-cavity pressure or temperature sensors to control when the valves open or close. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022 Injection Molding Problems and Solutions (16/17) – Warpage Sep 15, 2022. Proper venting is essential to molding a defect-free part. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. BLEED – (1) To give up color when in contact with water or a solvent. 3. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. In addition, the force of the gas holds the appearance side of the part in contact with. ABS. Knit Lines 11: 1. 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. It is. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. holes, multi-point injection. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. sheet metal fabrication, rapid tooling, and plastic injection molding. Also, since this part will likely be painted or chrome plated, knit lines are a concern. As. If debossed pattern is indispensable, it should have a depth of no less than 0. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. In a weld line, reinforcement fibers. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. 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. It allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. 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. As these flow fronts come together. 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). Meld and knit lines are actually both different types of weld lines. 5. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. Weld lines: Also known as knit lines, these are molding defects that occur when two flow fronts meet without the ability to “weld. Injection molding a red component, for example, can pose a challenge because at time the component may be too thin for the pigment itself!. Our prototype injection molding process helps you cut product development cycles by weeks—sometimes months—and bridge to production with injection-molded parts within days. Meld and knit lines are actually both different types of weld lines. IM: cooling accounts for _____ % of the total cycle time. The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. If life safety is involved, or reliably or efficacy are absolutely required, every part should. 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. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. It’s also relatively inexpensive. wall thickness injection molding ribs. Enlarge gas vents and gates to allow trapped air to escape the mold. 020"). 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. Main causes of knit lines in injection molding: 1. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. When the plastic cools, it takes the shape of the mold and is then ejected and finished. Knit Mark – A witness mark on a molded part, often occurring at the midpoint between two transfer or injection sprue locations. These lines. 7584. Imagine a river splitting to go around a rock, then meeting up again on the other side. What is copper electrode in injection mold? hashtag#plasticinjectionmold hashtag#moldmaking "Copper electrode," also known as "electrode," is a common component in mold manufacturing. They are formed when two or more flow frontKnit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection. INJECTION MOLDING GUIDE V2. While injection molding dies are expensive to produce, each die canHowever, they can also create weld lines or knit lines in the part where the flow fronts meet. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. Over the years, I have developed two separate “5M” systems. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. In. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. Remedies: Raise the temperature of the mold or molten plastic. Notched weld lines then remain near the cavity walls. The melt is forced to split up during filling of the cavity. The depth of the texture or letters is somewhat. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. This defect is caused from excessive lube or oily stock. ). These structures are often small surfaces of about a tenth of an inch in diameter. Edge gates, which can include fan and tab-shaped gates, are the most common ways to gate a tool. to prevent improperly placed knit lines or sinking in the plastic downstream from the hinge. Three terms that often get mixed up in injection molding are weld, meld and knit lines. In this, work, metal inserts were joined with polyamide 6 by using the injection-molding technique. For the metal feedstock, injection and mold-wall temperatures were 130 ºC. In the 1947 book, Injection Molding of Plastics, the late Dr. This makes the casting process as efficient and accurate as possible. 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. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. Reduce clamping force. Adding a border around an embossed logo is a good way to protect it from abrasion. Subscribe to Our Newsletter. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. These lines. Give us a call at (425) 339-0288 or email us at info@sealectplastics. Pitfall #1 – Knit Lines. Knit lines don’t. 5T, where T is your nominal wall thickness. wall thickness, knit lines, draft. 2. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. Draft. 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. When injection molding a part, a knit. In injection molding terms, these are called “living hinges” and are made right into the design instead of adding them later. Demo Mold. To learn more about us or to get a quote, click here or call 1. These flaws can affect the aesthetic and structural integrity of the. 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. [1] Plastic injection molding is the industry’s most common way to manufacture parts. a knit line will form 180°on the opposite side from the gate location. Prevent Flow and Knit Lines During the Injection Molding Process. Double push filling method. Plasti-Co ® manufactures a wide range of injection molding nozzles from standard nozzle tips, extended nozzle tips, nozzle bodies, extended nozzles. 250 in. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Our On-demand. Bociaga and Jaruga (2007) investigated flowing weld line in injection process by injection molding machine, which the part surface was observed in reflected light using the optimal microscope and. The injection molding process is fairly simple, plastic resin is heated to its melting point and forced through the machine and into your mold to produce your plastic parts. Temperature is another factor that can cause weld or knit lines in injection molding. Injection Molding: How to Set Second. Typically, this fillet radius should be somewhere near 0. As melt temperature, viscosity and abrasiveness rise, tool life will decline. The weld line can either be a minor cosmetic issue. In injection molding, a thermoplastic material is melted to a liquid state and injected into a custom, double-sided mold. Our plastic injection molding glossary provides key terms. Weld-lines look like cracks on the appearance of plastic. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. Weld line. Here are some of the most common cosmetic defects and how to avoid or fix them. The Difference Between Knit and Meld Lines–and Why It Matters. 030- to 0. Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. Thick walls are not recommended because of POM’s high shrinkage rate. The example. When the mold adopts the multi-gate pouring scheme, the plastic melt. Mold Flow Analysis computer. After selecting the direction in which the mold hole will be cut, it is much simpler to locate the separating line. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. 08 KICKOFF PRODUCTION. The melt is forced to split up during filling of the cavity. Knit lines don’t always compromise the structural integrity of plastic parts. They occur when melt flow fronts collide in a mold cavity. Learn how HPP maximizes these specialized processes. When the temperature is not very high, there are chances of premature solidification, which can cause weld lines to form. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. Insufficient injection pressure and speed can cause weld lines. 3 To get the most out of your Xometry Injection Molding experience, we offer the following part Design Guide with. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Thin wall injection molding design tips and tricks. . 05-million grant for MIM R&D from the National Institute of Standards and Technology (NIST) in Washington, D. 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. A meld line occurs when two moving melt fronts converge and flow parallel to each other. These structures are often small surfaces of about a tenth of an inch in diameter. IM: hot or warm knit lines are cause by _____ while cold knit lines are caused by _____. In this paper, a general and efficient approach was proposed for dual-scale infiltration flow balancing based on numerical simulation. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. 0 and Table 1). 015in wall. Three terms that often get mixed up are weld, meld, and knit lines. This course outlines mold filling and how different gating configurations affect filling. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Disadvantage: May rust if improperly stored. 040 and 0. - 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. Weld-lines or knit-lines are formed during the mold filling process when the split melt flow fronts meet at the same downstream location. Macromol Symp 1988;21/21: 489-500. However, the weld line may not continue throughout the flow. Depends how hard you want to push it. 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. Knit Line occurs where different flow fronts of material meet while flowing through the mold. placed usually in the areas last to fill, near knit lines, as well as on the runner system. 3. Excessive injection pressure can result in part defects such as overflow or flash. Observation on a “trial and error” basis may be required. 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. Knit line Knit line Start of mold filling. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Self-mating parts. This can dramatically reduce the effects of material changes, according to the injection molding technology company. Runner Type. 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. These lines. 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. . mystagingwebsite. Understand the causes of knit lines in injection molding and explore effective solutions to minimize their impact. It’s called sequential valve gating, or SVG. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. Understanding types of injection molding process can help to avoid some design challenges early in the process. Call 800-985-6750 or email your inquiry to sales@customgasketmfg. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. com . H-13 Good general purpose tool steel. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. Weld / Knit Lines; Assumptions. They have their origins in material choice, part design, tooling, and processingInjection molding is generally restrictive (not including special processes) in the cross-sectional size of the part, while blow molding allows for channels in the part that increases strength. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. What Are Cosmetic Standards for Plastic Parts?. We ensure customers receive accurate, fast, on-time, sufficient support and services. The linear mold shrinkage of injection molded parts will vary from 0. It is best practice to maintain a uniform thickness throughout an injection-molded part. These are caused by the shot of molten plastic moving at different speeds throughout the injection. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. Knit lines. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022injection-molding machine (Arburg allrounder 320C, Germany). Meld and knit lines are actually both different types of weld lines. Below is a list of items that should be checked both during normal molding operations and if defects are detected. Other Excessive mold release Clean die and use minimal mold release. Reduce. 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. 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. 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. 060 in. 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. A well-designed injection-molded part will usually have draft, but the same draft that helps eject a part from the. We have two unique offers to meet your needs wherever you are in the product lifecycle. In working with the injection molding service offered by Protolabs, you provide. 25T-0. Hardware components. Wall Thickness: The recommended wall thickness for injection molded POM parts is between 0. PCS says each module of the Polimold Valve Gate Sequencer controls two zones, with the option to control up to 14. While this process is largely efficient and reliable, it's not without its potential issues. One common problem that occurs in injection molding is the formation of knit lines. As the polymer resin is injected into a mold, it flows through all parts of the mold. Shear Controlled Orientation Injection Molding of Polymeric Composites with Enhanced Properties. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. [8] Bevis, MJ, Reis RL, Cunha AM. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. In plastic part design for injection molding, it is important to design the injection mold so that the molten plastic fills the mold cavity entirely, cools as evenly and as quickly as possible without warping, and functions as intended. Knit/Weld 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. Thin wall injection molding can produce walls as thin as 0. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. Trapped air in a mold manifests itself as a burn mark on the molded part. Inject the molten material into a mold. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Weld lines are a common imperfection to be found in most plastic injected molded parts. 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. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Weld line in injection molding is line where two or more flow molten plastics knit together. This production method is particularly popular when manufacturing in large quantities. As a result, prototyping is strongly recommended for parts with. 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. This type of molding uses a single tool to create both the part's geometry and surface finish in one step. When the mold body is closed, the contact surface of the cavity and core plates makes a parting line. Last month, in the first part of this two-part installment we focused on the reasons viscosity can change during injection molding. Fictiv can help you avoid injection mold design and plastic part design for injection molding problems. Also known as a knit line, this is the point at which two flow formations meet and are unable to. 5 kN/cm2 (4 T/in2 ) is required. even though injection molding temperatures are _____ compared to metals, the thermal expansion of plastics is _____ to _____ times that of metals. Molding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesiveMolding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesiveMost failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold.