Still, they are almost always a cosmetic issue. Learn about the key characteristics of common injection molding materials, recommended applications, and how common thermoplastics compare to one another. Inadequate injection pressure can result in knit lines and a surface that. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. In this case it would be 0. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Excessive mould lubricant. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. cold and hot weld line. When setting a heat profile, consider residence time, screw RPM and filler type. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Depending on the material you use, the knit lines could be invisible or obvious—work with an injection molding company to figure out how to reduce the mold lines on your product. 5. 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. Three terms that often get mixed up are weld, meld, and knit lines. For instance, three widely used processes are insert molding, overmolding, and undercuts. The specific method is that when the product is just filled and filled in the cavity, the insert. Strength at the knit line can be as little as 20% of the. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Injection molding is the process of injecting liquid thermoplastic into a mold. When injection molding complex parts, often knit-lines are formed during the mold filling stage. Having uniform wall thicknesses between 0. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. The packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. Draft. While this process is largely efficient and reliable, it's not without its potential issues. thick. . That’s the air escaping out of the nozzle until the hose is full of pressurized water. Plasti-Co. They occur when melt flow fronts collide in a mold cavity. 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. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. A weld line can also be called a knit line. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. Injection moulding is a manufacturing process that melts, injects and sets plastic into a metal mould. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 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. , Rallis, A. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. Polypropylene Consumer and Injection Molding Containers, Crates, Garden Furniture, Housewares, Luggage, TSL, TWIM lyondellbasell. Place a vent in the weld line area to remove the entrapped air. POROUS MOLD MATERIALS. These knit-lines are well-known as particularly critical regions in the mold when mechanically. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Reduce the screw speed and adjust the backpressure. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Venting at Weld Lines. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. Injection. Moldflow is computer software that is widely used across the plastic injection molding industry to predict and optimize the injection molding process and assist with mold design. Brent Strong, p. It’s also relatively inexpensive. We complete the part to your precise specifications with CNC Milling operations. 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 appear around holes or seams of an injection molded part, and some may call them. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. 5 to 3. This can result in cosmetic defect or a weak point in the part. 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. 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. Weld line. Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. 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. It has low shrink and high dimensional stability, and it has good resistance to acids and bases. Different plastics make different types of knit lines. Solution: People. An edge gate introduces material at the main parting line, or where the two halves of the mold meet, with a perpendicular runner. They again get resolidified along the surface. Knit / Weld Lines. The plastic in the ‘flow front’ cannot pass through the core pin, so it flows around the core pin splitting into 2 distinct flow fronts. However, with any practice, when the proper care and planning aren’t taken, problems can occur, and with injection molding, knit lines are one of the most common problems. The melt is forced to split up during filling of the cavity. Basic rule of thumb air in mold must be able to escape at theAbstract The knit line structure of injection moulded PA 6 samples was analysed by SEM and optical microscopy. 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. a specific area on one side lens, a warp line, and a weft line. Also known as knit lines. land and using maximum vent depths to get them as close to self-cleaning as possible. Anisotropy. Use gradients. Overall, injection molding is a relatively simple process. In a weld line, reinforcement fibers. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. 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. wall thickness, knit lines, draft. 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. 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. 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. 0035"Weld lines:Witness line where 2 or more fronts of molten plastic converge, also called knit lines or flow lines, the weld around the holes, the line between the injection gate. Near-Net-Shape Molding enables us to eliminate knit lines, add undercuts, increase options for geometry and tolerances, and reduce tooling cost for low. txt) or read online for free. Contact Universal Plastic Mold Today. Plastic injection molding is the industry’s most common way to manufacture parts. 040 and 0. The injection molding process uses a granular plastic that is grav ity fed from a hopper. Injection molded plastic begins its journey through the part tooling via an entry section called a. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Part Design Summary Bosses:Welds and/or Knit lines can be defined as the inability of two or more flow fronts to “knit” together, or "weld", during the molding process. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. 4. Knit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection. 11) The part design must take into account possible knit line locations and work to direct them away from higher stress areas. With ABS injection molding, you get the collective benefits and properties of three monomers. 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. When 2 flows meet, small hair-like discolorations may develop. There is high defect rate (surface defects/knit line). PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. Resin cools as it is injected into a mold. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. This article looks at the issues presented by a weld line in injection molding and the techniques manufacturers can use to avoid them. As the polymer resin is injected into a mold, it flows through all parts of the mold. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary from virtually invisible to something that looks like cracks in the plastic. Designers are able to specify seamless design features with compression molding. Knit lines. CURE: Run the mold in. Industrial Knitting Machines. Very high quality and an extreme fit may. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Rapid heat-and-cool molding technologies have attracted increasing. Place vents at last place to fill and at converging flow fronts. 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. Runner Type. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. incomplete filling or shorts. Sink Marks Cause 4: High Mold Temperature. 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. The thermo-rheological findings were used to investigate the sources of weld line weakness. This continues until the weld lines in plastic injection molding disappear. 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. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. Another name given to weld lines is meld line. An injection mold that produces pieces while the final tool is being built. These materials have beenDetermining the correct tonnage provides a foundation that must be rock-solid to avoid flash and damage. 1 in. Near-Net-Shape production uses injection molding to account for 70-90% of the final geometry of a part. This makes the casting process as efficient and accurate as possible. 040 and 0. No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. When injection molding complex parts, often knit-lines are formed during the mold filling stage. Gating. weak knit lines and fracture points. "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. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Gate design is another critical piece of part function in plastic injection molding. Orientation of these knit (weld) lines, are perpendicular to the tensile stresses, applied to the ring (Figure 6-8). A knit line is the spot where two flows meet. Weld lines have a significant effect on manufactured products. Weld / Knit Lines; Assumptions. The second mold portion being movable relative to the first mold portion and together defining a mold cavity. 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. Koelling, Ronald C. The defect may be in part appearance or mechanical strength. When the plastic cools, it takes the shape of the mold and is then ejected and finished. Meld and knit lines are actually both different types of weld lines. Knit lines. The quality of the answer is directly proportional to the information we have to work with. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. Solution: People. Knit lines, also known as weld lines are areas in the. The goal is to create a uniform thickness and at the smallest (thinnest) level required. I 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…Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. a weld or knit line may develop on the opposite side of the obstruction as the two fronts of material join. Meld and knit lines are actually both different types of weld lines. Injection molding is a simple and efficient process that produces high-quality plastic parts. The area generally has lower strength than the other areas of the part. Bubbles are caused by melting flow fronts colliding in a mold cavity. 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. Recent developments were oriented on the analysis of the mechanical performance at local (knit lines and welds) and bulk (molded part) areas, with the influence of molding and welding conditions. It is also where a slide mechanism might meet where it shuts off on one of the mold halves. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. A. 3 /sec of material into a mold, don’t think the material is going into each cavity of a multi-cavity mold at the same 14. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. ) are easy to produce. [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. 2020-01-1306. Know about the cause of these lines and the potential solutions. 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. The Injection Mold Core A mold core is any member that forms the interior of a plastic part, usually on the "B" side of the mold 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. First of all, ABS is prone to knit lines — or the places where two flows of plastic resin meet during the manufacturing process. In fact, for a 32-cavity mold, the flow rate in this example drops down to 0. Venting. Short shots Trapped air in the mold can inhibit the flow of the material during injection, resulting in an incomplete part. 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. Steven. Since the intention is to preserve fiber length in LFRTs by reducing. Plastic injection force exceeding the clamping pressure of the press. For injection molding of the multi-blade fans and various rotating plastic parts, the complex of multiple gating injection molding tools were used. Change gate locations. Learn about the key characteristics of common injection molding materials, recommended applications, and how common thermoplastics compare to one another. 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 adhesivePrevents flow and knit lines. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. More about the knit lines in injection molding. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. Examples of different causes of PVC pipe failure. Polym Compos 1982; 3: 88–96. 040-in. The most common location of knit line formation is behind molded-in holes that are made by core pins in the mold. Edge Gates. 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. For fiber-glass reinforced thermoplastics, the strength in these local areas (knit/weld and meld lines) is less than in bulk areas, dueMolding 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 adhesiveThe best option once you have the approximate tonnage required is to find a molding partner that has machines in that range. 060 and 0. Also known as “stitch lines” or “weld lines”. 0 mm) is crucial to ensuring that parts cool evenly. 5. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all,. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause. 0 and Table 1). An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. One solution is to use optimal wall thickness to help slow cooling during the ABS plastic molding process. Sink Marks Cause 2: Low Pack and Hold time. 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. 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. Cold Slug: First material to enter mold during injection. 17. However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Make sure the venting is not too large. Legend: a-in. 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. Gate size can be increased or moved to a section with greater wall thickness to help eliminate. Use the fewest number of gates possible. (Overpacking. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. 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. Transfer molding also utilizes a press and a mold. Short shots and knit lines are two phenomena that are caused by using highly viscousHowever, they can also create weld lines or knit lines in the part where the flow fronts meet. ” 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. Misra A. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. You don't give us much to go on. In the case of mold. Remedies: Raise the temperature of the mold or molten plastic. 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. How weld lines form. (1. Design. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. Product designers encounter a wide range of challenges when. The three dimensional structure is formed of a resin fiber mixture having a resin material infused with carbon fibers having a length of about 12. com. Also known as a knit line, this is the point at which two flow formations meet and are unable to. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. . With plastic finishing plugs and end caps, we can help you keep your products protected while giving. H-13 Good general purpose tool steel. (1. Injection molding is a plastic manufacturing process to achieve a high production rate. Steven. ITAR. Meld and knit lines are actually both different types of weld lines. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. 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 []. Thanks to the low air counter pressure in the cavity, this allows injection parameters to be managed in a larger window, optimizing injection time, part aesthetics and mechanical characteristics. 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. They occur when melt flow fronts collide in a mold cavity. They occur when two resin flows meet at different. In injection molding, it is often important to maintain consistent color throughout the part. The quality of the weld line can be improved through optimized processing conditions, increased mold and melt temperatures, and increased injection speed toInjection molding, producing, and forming resin materials are three core components of injection molding technology. It is caused by the incomplete joining of the uncured. As a result, molten plastic takes the injection mold core and cavity shape. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. Such molds or tools aren’t intended to be used in operation. 3. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. 060 and 0. An injection mold that produces pieces while the final tool is being built. Plastics Injection Molding Expert John Bozzelli covers. Parting Lines. The primary rule is to apply 1 degree of draft per. 3—Another issue with the four-gate design was that knit lines ended on or near mounting holes, causing a. The Problems & Solutions course is designed to train injection molding personnel in. In fact, knit line strength will decrease with higher filler content and with longer fibers. 156 x 2 1/3 = 0. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. Sprue bushing too long. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. Insufficient injection pressure and speed can cause weld 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. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). Plastic melt and mold temperature. Considerations: ABS-molded parts will show. Contact us. Encapsulating the metal insert with plastic creates a single molded plastic piece that’s generally stronger than one created using secondary assembly. This will helpTroubleshooting Injection Molding Weld Lines. Our glossary of terms provides definitions for a wide range of injection molding terms. Dedicated to strict quality management and thoughtful client services, our experienced staff customers are generally available to discuss your demands and guarantee full client pleasure for Knit Line Injection Molding, Electronics. directly! FCS Group, based in Taiwan, was established 40 years ago and is well known in Asia as a quality manufacturer of machinery, offering several lines of injection molding machines and other specialty and customized equipment. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. 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. In this paper, two different injection molding tests were completed. 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. lines are formed when there is an obstacle in the cavity of the injection mold. (1987). 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. This type of molding uses a single tool to create both the part's geometry and surface finish in one step. Solution: Increase the injection pressure or speed. Setting that Delta P is the secret to consistent fill time. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. All the while, the material could be the correct material," Hill says. 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. Revisiting the '5 M's' of Molding. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. Increase the mold temperature and reduce the barrel temperature for injection molding of thin-walled products. Disadvantage: May rust if improperly stored. Because injection mold design and processing is complex, a set solution will not solve all problems. 203 in. Temperature is another factor that can cause weld or knit lines in injection molding. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. 1 in. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. Two major sources of weld lines are multiple gating and flow around pins. 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. Viscosity represents a broad concept with huge effects on any efforts to standardize an injection molding process. Weld lines also can be visible after a part is painted and can cause wrinkles on in-mold-label injection-molded products. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. In working with the injection molding service offered by Protolabs, you provide. The plastics used by injection molding processes are relatively cheap and can be used to achieve a wide variety of properties, so injection molding is popular for creating many packaging and consumer products, like LEGO!. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Getting started; Knit Line Injection Molding; Knit Line Injection Molding - China Manufacturers, Factory, Suppliers. Crossref. Contact Universal Plastic Mold Today. 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. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. These are imperfections in the part. Causes 1. The above guidelines for initial heater band settings are for most injection molded parts. Common causes of flashing in injection moulding. The process involves feeding the material into a press, where it is cooled or heated as per. Figures courtesy of CAE Services. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Weld line. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Knit line strength is improved since. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). 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. Adjust the design for the flow pattern to be a single source flow. Increase size of the vents. Mold cores can be machined from a solid piece of copper alloy or inserted to aid in construction or allow for easier replacement if a com-ponent would ever be damaged in molding. 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 knit line may only be a cosmetic issue and affect. 02 in. pdf), Text File (. Depends how hard you want to push it. Since our material is injected through a. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. 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. Bubbles are caused by melting flow fronts colliding in a mold cavity. Support pillar suppliers can help determine the. 060 and 0.