That’s the air escaping out of the nozzle until the hose is full of pressurized water. Such molds or tools aren’t intended to be used in operation. 060 and 0. Product designers encounter a wide range of challenges when. Part thickness control is through stacking of. 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. When injection molding complex parts, often knit-lines are formed during the mold filling stage. suppressed cooling and possibly warp. In injection molding, it is often important to maintain consistent color throughout the part. Mold cooling is one of the most important variables in injection molding. 040-in. There. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. Weld lines also can be visible after a part is painted and can cause wrinkles on in-mold-label injection-molded products. Contact us. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. When the plastic cools, it takes the shape of the mold and is then ejected and finished. It is also one of the most important weapons in a molder’s arsenal for making process changes. Using abrasives in a pressurized air blast to create a surface texture on the part. 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. Resin cools as it is injected into a mold. 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. Learn how HPP maximizes these specialized processes. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. The part weight x number of cavities + runner weight should. turbulent flow of Injection speed set too high. Weld lines have a significant effect on manufactured products. The gate is the entry point to the part-forming cavity, where plastic material is injected from the molding machine barrel, through the sprue and runner, into the mold. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. 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. menu. They are the result of fundamental physical effects taking place inside of the mold. The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. Why. Knit Line occurs where different flow fronts of material meet while flowing through the mold. Islyn Thomas summarized the need for a particular vent location better than I ever could. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. SEA-LECT Plastics has 16 MILACRON injection molding machines that range from 33-ton with a 2. 1 in. 156 x 2 1/3 = 0. Below is a list of items that should be checked both during normal molding operations and if defects are detected. 02 in. The defect may be in part appearance or mechanical strength. As the polymer resin is injected into a mold, it flows through all parts of the mold. In the case of mold. Polypropylene can be processed over a wide range of mold temperatures; however, for applications where aesthetics are critical, a surface temperature of 80-95˚CSink Marks Cause 1: Incorrect Melt Temperature. In this video, Chris Burda, applications engineer at Protolabs, shares what can be done to reduce knit lines and how they can impact your part's functionality. They occur when melt flow fronts collide in a mold cavity. Redesign the mold: Redesigning the mold to. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. SPI surface finishes are the most common set of injection molding finishing standards around the world with over 12 different grades. Learn more. Increase the injection speed. Meld and knit lines are actually both different types of weld lines. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. Understanding Knit Lines in Injection Molding: Causes and Solutions. Material contamination, for example, can cause several molding issues. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. a knit line will form 180°on the opposite side from the gate location. Double push filling method. Let’s stop for a second and think about the logos we usually see on a daily basis. To briefly describe, weld lines are also called knit lines. They occur when melt flow fronts collide in a mold cavity. Because edge gates are easy to machine, they can be widened or modified to help material flow. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. One exception: ribs should be about 50. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. Place vents at last place to fill and at converging flow fronts. 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. From: Polylactic Acid (Second Edition. . When designing for injection molding, consider these steps to prevent knit lines. AS9100:2016. 2. This will helpTroubleshooting Injection Molding Weld Lines. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. The present. However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. Steven. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. In addition to the main factory and development. Generally all plastic components should be designed with draft where possible. Plastic injection molding is a complex and highly intricate process. Last month, in the first part of this two-part installment we focused on the reasons viscosity can change during injection molding. Tooling & Injection Molding Services High-Quality Complex Parts. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. The above guidelines for initial heater band settings are for most injection molded parts. The last cause of flow lines may be the operators running your daily operations. But applying excessive force can create problems with the part, mold, and machine. opposed to two or more gates. The depth of the texture or letters is somewhat limited, and extra draftInjection molding tool design and build for complex parts, with precision tooling and molding capabilities for industries demanding high-quality, critical components. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. injection molding. 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. Description: Flow lines are streaks, patterns, or lines - commonly off-toned in color - that show up on the prototype part as a consequence of the physical path and cooling profile of the molten plastic as it flows into the injection mold tooling cavity. Notched weld lines then remain near the cavity walls. 2. 3 /sec. Venting at Weld Lines. Knit lines are most common downstream of holes created in parts where the molten material meets. Weld Lines-3 Ways for Detecting and Correcting. Sprue bushing too long. placed usually in the areas last to fill, near knit lines, as well as on the runner system. This is a video excerpt from our Problems & Solutions Course - Weldlines. Our Injection Molding Capabilities • Horizontal Injection Molding up to 3300 TONS • Structural Foam Molding + Structural Web • 1oz to 600oz part capacity. Part Shorts No burn marks. Crossref. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. S. "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. Because viscosity is a variable, keeping fill time constant minimizes the influence of these variations and provides a more stable process, and therefore. incomplete filling or shorts. Knit Lines. Temperature is another factor that can cause weld or knit lines in injection molding. Therefore various injection molding defects can be eliminated. Whereas conventional injection molding uses. Plastic injection molding is the industry’s most common way to manufacture parts. A knit line is any line, visible or not, where two resin flows meet. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause. Inappropriate temperature. Holes in the part will always cause knit lines. Anisotropy. excessive or premature wear at the parting line. 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. Solution: People. A screw-type plunger forces the material into a heated chambe r,. 2. Undercuts add cost to tooling and molding, which is recommended to eliminate or minimize as possible. 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. Parting lines placed at intricate joints. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. 203 in. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. Injection moulding (U. Increase the size of the gate and runners to alter the mold design. The Difference Between Knit and Meld Lines–and Why It Matters. In working with the injection molding service offered by Protolabs, you provide. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. thick. This will help the mold designer to determine the allowable gate and knit line locations. Mold venting should be checked and increased if necessary, injection molding service. Some of the most popular brands include:Harshal Bhogesra has 9+ years of combined experience in molding, customer & supplier development. 5 inches) dispersed throughout the structural automotive sub frame component ( 10 ). Shear Controlled Orientation Injection Molding of Polymeric Composites with Enhanced Properties. 11) The part design must take into account possible knit line locations and work to direct them away from higher stress areas. 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. 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. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. 8 mm relief at the edges of the thread. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. Weld Lines-3 Ways for Detecting and Correcting. 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 []. All injection molding ultimately comes down to the “Man, Mold, Machine, Material and Method. The area generally has lower strength than the other areas of the part. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Reducing the dimensions of the runner system. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Knit Lines. A weld line can also be called a knit line. Because they can be shut off independently you can control flow fronts and knit-line locations. 156 x 1. Weld line. Injection moulding (U. Depending on the design of the mould and the material being injected, a knit line may: present no problem at all, be a cosmetic issue, or cause a potentially. 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. Injection molding is a manufacturing process that involves injecting molten plastic into a mold cavity to create a specific shape or design. 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. It’s also relatively inexpensive. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. (1987). ABOUT THE AUTHOR. Causes 1. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. One common problem that occurs in injection molding is the formation of knit lines. Revisiting the '5 M's' of Molding. On average, larger injection molding machinery can cost from $50,000-$200,000 or more. 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. The goal is to create a uniform thickness and at the smallest (thinnest) level required. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. Make sure the venting is not too large. Adding draft or slope to vertical walls of a part makes it easier to eject or remove the part from the mold. The parting line will always be visible, but can be minimized by its location, draft allowance and part geometry. Injection molding is the process of injecting liquid thermoplastic into a mold. May happen at first shots while mold is being dialed in. Runner and gates must be balanced. TEFABLOC™ TESI 744 TPE compound for injection molding processing provides superior adhesion properties when processed using 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. doc), PDF File (. Obstructions in the part create weld lines or knit lines during injection molding. POROUS MOLD MATERIALS. This month, we covered an array of topics including injection mold venting, business strategies and runnerless micro molds. 3. 0 mm) is crucial to ensuring that parts cool evenly. ABS is a good choice for handheld consumer devices. 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. Adjust the design for the flow pattern to be a single source flow. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. A thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold to produce a specific part geometry. Three terms that often get mixed up are weld, meld, and knit lines. Contact Universal Plastic Mold Today. Parts molded with ABS are susceptible to forming knit lines, which are visible lines on the surface of the part. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Meld and knit lines are actually both different types of weld lines. Figures courtesy of CAE Services. weak knit lines and fracture points. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. 140 in. Possible causes: Low temperature or fluidity of melted plastic during injection molding. They again get resolidified along the surface. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. 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. 040-in. Quotes for 25+ Manufacturing Processes. 27-ounce shot size to 600-ton with a 105-ounce shot size. Extreme geometries can cause knit lines. More about the knit lines in injection molding. 7. To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. 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. 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. “A knit line in a colored part will result in glaring visual-effect problems, while a knit through a glass-filled part would have a negative effect on both the aesthetics and the performance,” agrees Kurt Weiss, manager of part performance and new material introductions at GE Plastics. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Use gradients. Wavy lines are another feature of weld lines. Weld line. These are caused by the shot of molten plastic moving at different speeds throughout the injection. 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 knit line, also. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. The effect of holding variables and of injection and mould temperature was explored. 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. Formation of knit line. Also known as knit lines. This defect is caused when the polymer resin is injected into a mold and flows around a solid piece and forms when the resin collides back together without completely fusing back together. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. It tells them that you visualized how injection molded parts cool and harden. More about the knit lines in injection molding. The packing pins are sequentially. Weld lines are formed during cavity. They have their origins in material choice, part design, tooling, and processingIn 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. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Flow rate and flow speed are cut in half at every runner branch. 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. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Mold Flow Analysis computer. 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! A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). Very high quality and an extreme fit may. Gas-assisted Injection Molding: Influence of Processing Conditions and Material Properties. The packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. These lines can manifest as visible marks on the component’s surface and potentially affect its structural integrity. Let’s. Increasing injection speed. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. Injection molding is an efficient, often cost-effective way to manufacture custom plastics that are strong, durable, and long-lasting. Thermoplastic Elastomer Molding Guidelines. 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 Lines. 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. It emerges and becomes visible when the flow fronts cannot mold or knit during the molding process. Criens}, journal={Materials Chemistry and Physics}, year={1986}, volume={14}, pages={69-83} }A structural automotive sub frame component ( 10 ) that is formed from a sheet molding compound having carbon fibers. 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. Each mold produces as specific part. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. incomplete filling or shorts. A thermoset injection molding process may save as much as 50% of machine time per shot with a faster cycle time compared to a thermoset compression molding process, allowing molders to produce high quantities of thermoset components per day in multi-cavity tools. He is passionate about optimizing product design, tool development, molding processes, and quality. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. It has low shrink and high dimensional stability, and it has good resistance to acids and bases. Obstructions in the part create weld lines or knit lines during injection molding. The injection of molding compound into the parts through one or two gates may produce parts that have knit lines. Example of a gate location in a finished part Example of knit lines in a finished part. A wide variety of tool steels are available for injection mold construction. Orientation of these knit (weld) lines, are perpendicular to the tensile stresses, applied to the ring (Figure 6-8). Fewer knit lines. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. 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. These defects are not visible, like small. 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. Flow Lines. RELATED CONTENT. Plasti-Co. 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. Reduce the injection pressure. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all,. 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. Knit lines in injection molding are common defects of the molded parts. This will help the mold designer to determine the allowable gate and knit line locations. Determine the time duration of the molten state. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. We complete the part to your precise specifications with CNC Milling operations. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. A component of the injection-molding machine wherein the resin pellets are melted, compressed and injected into the mold's runner system. 030- to 0. Inadequate injection pressure can result in knit lines and a surface that. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. 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. 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. Kurt W. Injection mold design and custom tooling can make or break the success of a finished plastic product. 3. Legend: a-in. Whenever possible, vents should be located in the movable half of the mold wherever a gas void or knit line is seen on a part. 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. An injection molding machine having a first mold portion and a second mold portion. 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. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. This picture shows a. A poor knit line can cause cosmetic blemishes and significantly weaken the structural integrity of a part. Venting at Weld Lines. Multiple gates will always cause knit lines. 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. 250 in. Koelling, Ronald C. Introduction to Knit Line Injection Molding Knit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection molding. Material. Back to News Page. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. 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. Mold vents should function the same way. Knit line / Meld. Reduce the temperature of the mold and plastic being injected. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Short shots Trapped air in the mold can inhibit the flow of the material during injection, resulting in an incomplete part. The thermo-rheological findings were used to investigate the sources of weld line weakness. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. These knit-lines are well-known as particularly critical regions in the mold when mechanically. Kaminski, in Specialized Molding Techniques,. 3. This production method is particularly popular when manufacturing in large quantities. Solution: Increase the injection pressure or speed. 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. Also known as “stitch lines” or “weld lines”. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. Compression molding produces solid parts that are free of flow and knit lines. POROUS MOLD MATERIALS. We then. In the injection molding process, melting takes place via two factors that work together: shear and heat. pdf), Text File (. The plastic melt that passes through the gate at high speed directly enters the cavity, then contacts the surface of the cavity to solidify, and then is pushed by the subsequent plastic melt, leaving traces of meandering. Meld and knit lines are actually both different types of weld lines. 2. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. But those key aspects can be viewed differently if you’re auditing mold changes before startup or troubleshooting changes for an already validated process. 040 and 0. Another name given to weld lines is meld line. 08 KICKOFF PRODUCTION. In this way, the mold supports distribute the force and minimize the stresses on the mold plates. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. ISO 9001:2015. Knit Mark – A witness mark on a molded part, often occurring at the midpoint between two transfer or injection sprue locations. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. Weld lines, which are also referred to as knit lines, are among the most common of these blemishes. Venting. Getting started; Knit Line Injection Molding; Knit Line Injection Molding - China Manufacturers, Factory, Suppliers. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. This continues until the weld lines in plastic injection molding disappear. Having uniform wall thicknesses between 0. Solid or semi‐solid, this material leaves a distinct border with adjacent melted material similar in. Left: L-shaped perform. 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. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. Notched weld lines then remain near the cavity walls. The melt is forced to split up during filling of the cavity.