Depending on the resin, resin temperature, mold temperature, and filling. On a hydraulic machine you can program hold pressure: For example, if you set 850 psi (59 bar), you will get 850 psi hold pressure for the time you set on. End-of-arm tooling can make or break a program. 060 and 0. They occur when melt flow fronts collide in a mold cavity. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Refers to portion of injection molding part that has some taper to make it easier to remove from the mold. As a result, prototyping is strongly recommended for parts with. Setting that Delta P is the secret to consistent fill time. Knit Lines: Holes in the part will always cause knit lines. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses, elastomers, confections, and most commonly thermoplastic and. It’s called sequential valve gating, or SVG. Holes in the part will always cause knit lines. (If parts are to be molded by Protomold’s rapid injection molding process, our Design Guidelines should be used. 5mm (0. pdf), Text File (. In addition, keep these in mind: Scrap rates can range from less than 1 to 5%. How weld lines form. The knit line is generally opposite the gate in thermoset. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Cooling Lines, Injection Mold Material has a great impact on injection molded part quality. Drying Considerations For both virgin and rework, hopper dryers sized to afford theWhen establishing the parting line, we must first define the shape and position of the parting line on the plastic molded item. Change gate locations. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. "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. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. A knit line is any line, visible or not, where two resin flows meet. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. The Goldilocks principle applied to wall thickness. Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. It’s also relatively inexpensive. 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. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Meld and knit lines are actually both different types of weld lines. Venting. 7. In injection molding, a thermoplastic material is melted to a liquid state and injected into a custom, double-sided mold. LS Mtron Injection Molding Machine (IMM) has opened a new business unit in Mexico. Solution: People. Guideline for Design, Material Selection and General Application of Encapsulation of Electronic Circuit Assembly by Low Pressure Molding with ThermoplasticsThis was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. See full list on fathommfg. Looking to Your Knit Lines with Molding. Our glossary of terms provides definitions for a wide range of injection molding terms. The leading edge of the molten material is often the coolest point and the closest to solidifying. 140 in. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. extend the time between mold maintenance shutdowns. The recommended minimum production volume for injection molding is 500 units. Islyn Thomas summarized the need for a particular vent location better than I ever could. and Titomanlio, G. 010 inches. 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. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. As melt temperature, viscosity and abrasiveness rise, tool life will decline. Rapid heat-and-cool molding technologies have attracted increasing. 5 kN/cm2 (4 T/in2 ) is required. Knit line Knit line Start of mold filling. 015in wall. Plating and painting applications usually require slower fill rates to keep orientation low. If the plastic has cooled too. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Adding a border around an embossed logo is a good way to protect it from abrasion. Wax Cold wax Increase wax temperature. We recommend walls to be no less than 40 to 60 percent of adjacent wall thickness, and all should fit within recommended thickness ranges for the selected resin. Visual indicating with an finished part that are formed by the junction from two plastic flow fronts. Three terms that often get mixed up are weld, meld, and knit lines. 040 and 0. This, in turn, leaves a large tab to be trimmed, a process that can mar the finished surface. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. ” Depending on the material you use, the knit lines could be invisible or obvious—work with an injection molding company to figure out. 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. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Troubleshooting Injection Molding Weld Lines. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. A parting-line vent. wall thickness injection molding ribs. By contrast, a slow injection speed will give you a matte finish and a cold mold, such as 50F, will give you a more flexible part. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. Knit lines are formed in injection moulding when two flow fronts meet in the middle of a part (a line where two sides of the plastic are “knit” together). Weld lines: Also known as knit lines, these are molding defects that occur when two flow fronts meet without the ability to “weld. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. 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. Brent Strong, p. Knit/Weld Lines. – Change the thickness of the product. While this process is largely efficient and reliable, it's not without its potential issues. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. 05-million grant for MIM R&D from the National Institute of Standards and Technology (NIST) in Washington, D. These are imperfections in the part where separated flows of cooling material meet and. Monoform parts. (1987). After samples have been approved, it’s time to kickoff. Shorten the mold cycle time so that any trapped air and resin don’t have a chance to overheat. The company provides an array of digital manufacturing expertise. 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. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. The mold opens and closes on a vertical axis in the vertical injection molding. . Reduce the injection pressure. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. Reduce the injection speed to limit the risk of trapping air inside the mold. ”. ISSUE FACED BY THE INJECTION MOLDING COMPANIES: FLOWLINES (ALSO CALLED WELD LINES OR KNIT LINES) Definition: Streaks, orange skin, or visible flow lines in parts. Weld lines, also known as knit lines, are lines that appear on the surface of an injection-molded part where two or more flow fronts meet and fuse together. The thickness of the part plays an important role in how difficult the molding process will be. Such molds or tools aren’t intended to be used in operation. Injection Molding Injection molding is perhaps the most common and important of all plastic processing processes. In. This is a video excerpt from our Problems & Solutions Course - Weldlines. One of the most important aspects of hot runner system design is the gate location, which is the point where the molten plastic enters the cavity. 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. Learn how to troubleshoot weld lines in injection molding. Solution: Increase the injection pressure or speed. BLEED – (1) To give up color when in contact with water or a solvent. Contact us. Strength at the knit line can be as little as 20% of the. 7584. The specimens with a weld line at the center were obtained by double gate molding and the specimens without a weld line wereInjection runner too small Increase runner as needed. Encapsulating the metal insert with plastic creates a single. 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. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. com. We have two unique offers to meet your needs wherever you are in the product lifecycle. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. In spite of its cosmetic attributes, a bad knit line can significantly. Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. Also known as a knit line, this is the point at which two flow formations meet and are unable to connect during injection molding. A wide variety of tool steels are available for injection mold construction. Gate size can be increased or moved to a section with greater wall thickness to help eliminate. The resin is transferred to the mold cavity under positive. The following are general guidelines for molding acetal. In the case of mold details, knits will occur on the lee side of a detail. The chart below shows recommended wall thicknesses for common injection molding resins. Wavy lines are another feature of weld lines. ABS. Demo Mold. The definition of weld lines: When multiple plastic flow fronts meet in the cavity after encountering inserts, holes, or areas with inconsistent flow rates or interrupted melt flows, or in the case of gate injection filling, the inability of two or more flow fronts to fully “knit” together will cause the linear weld marks. A knit line is any line, visible or not, where two resin flows meet. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. 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. Contact Universal Plastic Mold Today. Learn how HPP maximizes these specialized processes. Steven. Let’s. Therefore various injection molding defects can be eliminated. One of the most common ways of adding venting is by manually machining it into the mold (Figs. The Jabil Molding Institute empowers employees, customers and suppliers to utilize the most advanced plastics and related manufacturing techniques in the world. As these flow fronts come together. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. 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. Additional venting along the parting line perimeter will improve overall venting significantly. Multiple gates will always. This line does not normally impact the overall shape or dimensions of the item. A weld or meld line is a weakness or visible. It is best practice to maintain a uniform thickness throughout an injection-molded part. ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. The depth of the texture or letters is somewhat limited, and extra draftParts were molded at a maximum injection pressure of 235 MPa, a maximum clamping force of 800 kN, a maximum injection speed of 900 mm/s, and a maximum injection stroke of 120 mm. The parting lines is where the two injection mold halves (A side and B side) meet. 847-952-8088. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. Shorter knit lines must equate to a stronger part. To learn more about us or to get a quote, click here or call 1-888-893-1587 now. thickness with a spacing of about 0. More about the knit lines in injection molding. The injection molding process is on the surface is fairly simple, plastic resin is heated to its melting point and forced into the cavity of the mold to produce a plastic parts. Weld-lines look like cracks on the appearance of plastic. "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. 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. Knit and meld lines are inherent to plastic. This article will look at two common venting options—using traditional machined vents and venting through porous materials—to help you decide which is right for your application. Three terms that often get mixed up are weld, meld, and knit lines. 2. We wanted to independently assess how a mold would fill and where knit lines would be, instead ofKnit Lines. Other Excessive mold release Clean die and use minimal mold release. While injection molding itself is a straightforward process involving melting. The most common and one of the most challenging injection molding defects are weld and knit lines. Typically, the wall thickness is somewhere in the neighborhood of 50%-75% of your nominal wall thickness. Because injection mold design and processing is complex, a set solution will not solve all problems. Reinforcing ribs play a pivotal role in the strength of a plastic part. When injection molding complex parts, often knit-lines are formed during the mold filling stage. a specific area on one side lens, a warp line, and a weft line. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Here are a few ways to prevent knit lines in your plastic parts: Increase material temperature: Higher temperatures on both materials prevent one section from cooling too quickly. Moisture in the material due to insufficient drying can form at the melt front, forming an interface between the two melt fronts. These data were obtained from many andKnit lines in injection molding are common defects of the molded parts. While injection molding itself is a straightforward process involving melting. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Injection Molding Press. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Gate and Knit Line Locations<br />. Prevent Flow and Knit Lines During the Injection Molding Process. 763-755-7575. Probable Cause Suggested RemedyI am working on a thin PC/ASA injection moulded component which has a tendency to snap at the Knit-point (the final point of travel at which the…Opening and closing all the valve gates at the same time necessarily limits the degree of control over weld or knit lines, gas traps, localized packing, and unbalanced flow. suppressed cooling and possibly warp. 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). (2) Undesired movement of certain materials in a plastic. Its superior flowability allows for precise and flawless filling of injection molds without the risk of flow marks and knit lines. Nicolet Plastics LLC. 040 and 0. Molding is a manufacturing process in which resin in a barrel is. Compression molding can also support large part sizes, and it has a tendency to. Example of a gate location in a finished part Example of knit lines in a finished part. 008 to 0. Release of trapped air in those cases will. Wall Thickness: The recommended wall thickness for injection molded POM parts is between 0. Depends how hard you want to push it. extend mold service life. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. 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. Other common issues associated with thin walls include uneven cooling, warp, cracks, cosmetic texture inconsistencies, and weak knit lines or fracture points. These lines occur usually around holes or obstructions and cause locally weak areas in the molded part. 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. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. A weld line can also be called a knit line. Look for signs of stickiness or burning. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. The process is extremely versatile, and can produce very complex shaped parts, with the use of multi-sided molds. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. The gate location affects the. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. 3. Knit lines, also known as weld lines or meld lines, are visible lines or seams that appear on a molded part where two or more flow fronts meet during the injection molding process. Complex parts can be reproduced with low cost once mold is manufactured. However, the weld line may not continue throughout the flow. What is copper electrode in injection mold? hashtag#plasticinjectionmold hashtag#moldmaking "Copper electrode," also known as "electrode," is a common component in mold manufacturing. The areas in the cavity where such buildup tends to be common are at end-of-fill areas, details that trap gas, and knit lines. placed usually in the areas last to fill, near knit lines, as well as on the runner system. 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. 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. 13758 Johnson Street NE. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. sheet metal fabrication, rapid tooling, and plastic injection molding. 3. Lower the melt and mold temperature to prevent overheating. Exploring common molding defects and. 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. They appear around holes or seams of an injection. Core Geometry. Short shots and knit lines are two phenomena that are caused by using highly viscousTherefore, changing the edges and corners of the mold core to make it buffer transition and keep the melt flow stable can prevent the occurrence of wavy lines. Facebook. 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. Injection molding can use thermosets or thermoplastics. opposed to two or more gates. Understand the causes of knit lines in injection molding and explore effective solutions to minimize their impact. The melt is forced to split up during filling of the cavity. A screw-type plunger forces the material into a heated chamber, called a barrel, where it is melted. • Holes formed by core pins are, in essence, 360° inside corners and should follow. Learn how to troubleshoot weld lines in injection molding. AS9100:2016. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. Based on the resin. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Jabil (formerly Nypro) is uniquely qualified to offer a state-of-the-art curriculum in injection molding and related disciplines, which require highly specialized skills and continuous. 1-3). In fact, knit line strength will decrease with higher filler content and with longer fibers. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). As a result of weak coupling along the knit-line, the weld-line strength can be only about 60% of that of an unreinforced resin. Please read on, stay posted, subscribe, and we welcome you to tell us what you think. 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. 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. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. Resin pellets are loaded into a barrel where. This is why the leading edge of the resin flow within a. Typically, injection molded parts will be between 0. Flow Lines. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. When injection molding a part, a knit. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. To avoid walls that are too fat or too thin, designing a wall thickness between 0. Reduce the injection speed to limit the risk of trapping air inside the mold. Design With Plastics. All that considered, for a specific simple part with specific quality requirements. See UNDERCUT. BURN MARKS Burn Marks: burn marks can occur when the design of a plastic part, and the subsequent injection mold design, causes air to be trapped during the injection (or filling stage) of the molding cycle. 18/06/2021. They need the interference of about 0. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Many of these tips are geared around injection-molded parts, but some apply to machined and 3D-printed parts as well. - 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. Family molds. Unsymmetrical filling makes knit lines in samples, leading to the failure of part, so it must be avoided. Knit Mark – A witness mark on a molded part, often occurring at the midpoint between two transfer or injection sprue locations. 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. Increasing injection speed. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. These structures are often small surfaces of about a tenth of an inch in diameter. Weld Lines. 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. Investigate the mold for signs that a water leak is present, and correct the condition. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Weld or knit lines occur when melt flow fronts collide in a mold cavity. For best results, keep thickness variations to within 15% of the nominal wall thickness. Short molding cycle, high production efficiency, and easy automation 2. 5 : 1 and 3. Sequential valve gate technology. 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. Undercuts add cost to tooling and molding, which is recommended to eliminate or minimize as possible. Weld lines are also known as “stitch lines” or “knit lines”. Remedies: Raise the temperature of the mold or molten plastic. The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. We all know that injection moulding is great for producing both custom prototypes and end-use production parts, but if you are not careful it can cause some. The packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. 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. Injection Molding: How to Set Second. Having uniform wall thicknesses between 0. While not always visible, weld lines (aka knit lines) are where two resin flows meet. Injection molding is a popular manufacturing process used to fabricate parts in large volumes. Vacuum on the mold does help and many times eliminates the weld line. For injection molding of the multi-blade fans and various rotating plastic parts, the complex of multiple gating injection molding tools were used. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. sinks, knit lines, and shrinkage,” Spalding says. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. 3. By contrast, a slow injection speed will give you a matte finish and a cold mold, such as 50F, will give you a more flexible part. We ensure customers receive accurate, fast, on-time, sufficient support and services. • Estimated clamp tonnage of 5. A machine heats and mixes the plastic until it is in a pliable molten shape, then a screw device turns to force the plastic into an outlet that leads to the mold. Injection Mold Tooling Options and Quality Reporting. In injection molding, it is often important to maintain consistent color throughout the part. such as knit lines and other imperfections. While this process is largely efficient and reliable, it's not without its potential issues. 6. (1. 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. They occur when melt flow fronts collide in a mold cavity. An injection mold that produces pieces while the final tool is being built. Our On-demand. This article will look at two common venting options—using traditional machined vents and venting through porous materials—to help you decide which is right for your application. Knit Lines 11: 1. As the polymer resin is injected into a mold, it flows through all parts of the mold. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. Disadvantage: May rust if improperly stored. 012 in. Remove holes if possible. The result is a consistent flow of molten plastic during injection and a quicker filling time. 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. Knit Line occurs where different flow fronts of material meet while flowing through the mold. Plastic injection molding is the industry’s most common way to manufacture parts. Learn Injection Molding Glossary with Plastopia: Using actual molded parts (with images) as examples. Knit lines, also known as weld lines are areas in the. 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. Ductile Injection Molding 101 - Injection Molding Varying. The mold’s sprue bushing and locating ring is placed in a way that makes sure the injection molding nozzle is properly aligned and centered. Tips for Avoiding Knit Lines in Injection Molding Keeping the proper temperature in the injection molding machine, runners, and within the mold are all key to ensuring. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. Meld and knit lines are actually both different types of weld lines. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Injection molding a red component, for example, can pose a challenge because at time the component may be too thin for the pigment itself!. If you want to better understand the process of injection molding, there are a few critical terms you need to know. 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. This design tip offers several ways to make your next multipart design less like a root canal and more like a day on the beach. With fast accurate, injection-mold simulations, designing injection-molded products, developing injection molds, and shooting parts is more collaborative, accurate, and efficient, saving time and driving down costs. This configuration positions the injection mechanism at the top of the mold, allowing gravity to play a role in filing the mold cavities. Weld / Knit Lines; Assumptions. These lines are the result of the molten plastic material recombining after splitting and flowing around an obstacle in the mold cavity. Remove the hardened material from the mold. The injection molding design process, much like all industrial design processes, deals primarily with the creation, look, and feel of a product. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. 01 inches between parts fitted together to work best.