Material contamination, for example, can cause several molding issues. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. 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. First, they carry resin to the mold via a runner. 763-755-7575. A parting-line vent. Most failures occur at what are called “weld lines” or “knit lines”. - 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. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. Usually the parting line of the mold is perpendicular to the mold opening direction of the injection molding machine. These seams are known as “knit lines. But any. (1. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. Here are some of the most common cosmetic defects and how to avoid or fix them. Contact us. 120 in. 4. Reduction of sink can possibly be had by switching to an ABS/PC-blended material. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. They again get resolidified along the surface. Solution: People. Injection Molding Materials When using PolyJet molds, both tool life and part quality will be dependent on the thermoplastic material used during the injection molding process. sinks, knit lines, and shrinkage,” Spalding says. Over the years, I have developed two separate “5M” systems. You don't give us much to go on. 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. Learn how to troubleshoot weld lines in injection molding. Reduce the temperature of the mold and plastic being injected. Consider adding mold release (can be added to the polymer itself by the polymer vendor) or at machine side Knit lines Weak knit lines Increase melt temperature Mold temperature too cold Increase injection speed Avoid nucleated products if possible Inadequate venting7. 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. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. TRADITIONAL MACHINES VENTS. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. Weld / knit plane forms as flow fronts recombine Weld line and failure due to flow around core. Also known as weld lines, knit lines. knit line. ABS is a good choice for handheld consumer devices. The result is a consistent flow of molten plastic during injection and a quicker filling time. 0 mm) is crucial to ensuring that parts cool evenly. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. 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. 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. In spite of its cosmetic attributes, a bad knit line can significantly. When the mold body is closed, the contact surface of the cavity and core plates makes a parting line. wall thickness injection molding ribs. Temperature is another factor that can cause weld or knit lines in injection molding. Because viscosity is a. 5 : 1 and 3. In injection molding, it is often important to maintain consistent color throughout the part. Contact Universal Plastic Mold Today. What Are Cosmetic Standards for Plastic Parts?. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. Weld / Knit Lines; Assumptions. 3. The injection molding process uses a granular plastic that is grav ity fed from a hopper. 4. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. 3. Knit / Weld Lines. Flow lines typically manifest as visible marks, often slightly. ; Wood, Philip E. They are formed when two or more flow frontFor more information on our custom rubber molding services or to speak with one of our knowledgeable professionals, please feel free to Contact Us or complete our online Request For Quote form. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. 4271. Mold cooling is one of the most important variables in injection molding. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). An injection mold that produces pieces while the final tool is being built. The injection molding processing conditions for filling are given in Table 1. Gates that are too small can also cause the uneven flow of material or result in knit lines, blemishes that occur where two resin flows meet. In addition, the force of the gas holds the appearance side of the part in contact with. Given the cosmetic requirements, there is a good chance the mold would require. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. 1-3). What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. 1 Gate Location. These defects are not visible, like small. And, for those who can work within its limitations, rapid injection molding may be suitable for producing some optical parts (and cost as much as 90 percent less than traditional tooling). Injection molding can be a real challenge if you don’t follow the “Five M’s”: Man, Mold, Machine, Material and Method. The parting lines is where the two injection mold halves (A side and B side) meet. Observation on a “trial and error” basis may be required. Many of these tips are geared around injection-molded parts, but some apply to machined and 3D-printed parts as well. See UNDERCUT. 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. While the presence of knit lines does not always compromise the structural integrity of the plastic part, they are almost always a cosmetic issue. But we can’t talk about the injection molding process without discussing the injection molding machine. Contact Universal Plastic Mold Today. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Rapid heat-and-cool molding technologies have attracted increasing. Plasti-Co® Nozzles for Injection Molding Machines. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. While not always visible, weld lines (aka knit lines) are where two resin flows meet. Causes 1. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. Flow lines, also known as weld lines or knit lines, are discontinuous lines or streaks that appear on the surface of an injection-molded part. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Only then can we move on to determining the parting line itself. 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. Take these steps to avoid knit lines. Injection molding can use thermosets or thermoplastics. Multiple parts with complex design and differing wall. Learn how to troubleshoot weld lines in injection molding. End-of-arm tooling can make or break a program. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Reducing the dimensions of the runner system. Finally, knit lines occur when molten plastic flows around an object and rejoins on the far side, a phenomenon that is quite possible when inserts. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Most issues occur before entry into the mold. ” Depending on the material you use, the knit lines could be invisible or obvious—work with an injection molding company to figure out. opposed to two or more gates. 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. Users will be able to use in-cavity pressure or temperature sensors to control when the valves open or close. These lines. extend mold service life. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. to prevent improperly placed knit lines or sinking in the plastic downstream from the hinge. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Over the years, I have developed two separate “5M” systems. We wanted to independently assess how a mold would fill and where knit lines would be, instead ofKnit Lines. 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. This will helpWeld line. Learn more about the process by reading this white paper. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. This range can be affected by the part wall thickness, melt temperature, mold temperature, injection speed, hold/pack pressures and also the time between molding and measuring. Multiple gates will always cause knit lines. This type of molding uses a single tool to create both the part's geometry and surface finish in one step. Adjust the design for the flow pattern to be a single source flow. The last cause of flow lines may be the operators running your daily operations. Gating. This production method is particularly popular when manufacturing in large quantities. Lower the melt and mold temperature to prevent overheating. 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. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. knit lines and parting lines are at the discretion of MIC-ZG. Meld and knit lines are actually both different types of. Understanding Knit Lines in Injection Molding: Causes and Solutions. ). Injection mold design and custom tooling can make or break the success of a finished plastic product. We have two unique offers to meet your needs wherever you are in the product lifecycle. Know about the cause of these lines and the potential solutions. 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. Knit lines, holes, part configuration and the talent of your molder all come into play. Our plastic injection molding glossary provides key terms. A weld or meld line is a weakness or visible. such as knit lines and other imperfections. We look forward to offering support and advice on your next project. RE: Knit Line Affect On Material Strength lorelei5607 (Automotive). From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. 060 in. Knit lines, holes, part configuration and the talent of your molder all come into play. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. , 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. 015in wall. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. . He is currently a tooling manager for a large, multi-plant molding and manufacturing company. In. 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. Imagine a river splitting to go around a rock, then meeting up again on the other side. 2. Multiple gates will always. Draft. Mold Flow Analysis computer. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with. Nicolet Plastics LLC. The comment on melt flow index is correct, but, I've molded straight PC down to . Increase the injection speed. Reduce the temperature of the mold and plastic being injected. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. 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. Weld Lines-3 Ways for Detecting and Correcting. Other materials, like LCP are great for thin wall micro molding but also notorious for having a bad knit line, potentially snapping from excessive torque in later manufacturing processes. Injection molding is the most widely used method for mass-producing plastic parts. com. Image credit: The Rodon Group. For injection molding of the multi-blade fans and various rotating plastic parts, the complex of multiple gating injection molding tools were used. Injection Mold Tooling Options and Quality Reporting. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Adding a border around an embossed logo is a good way to protect it from abrasion. Three terms that often get mixed up are weld, meld, and knit lines. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. This is why the leading edge of the resin flow within a. The specific method is that when the product is just filled and filled in the cavity, the insert is used to cut the soft material melt in. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. Plasti-Co ® manufactures a wide range of injection molding nozzles from standard nozzle tips, extended nozzle tips, nozzle bodies, extended nozzles. Enlarge gas vents and gates to allow trapped air to escape the mold. Injection speed and pressure. Weld lines may appear like seams or scratches,. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. Once the plastic sets, the mold opens to eject the product. The packing pins are sequentially. This will help the mold designer to determine the allowable gate and knit line locations. Compression molding is one of the earliest forms of molding. land and using maximum vent depths to get them as close to self-cleaning as possible. 012 in. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. It’s also relatively inexpensive. A weld line can also be called a knit line. Looking to Your Knit Lines with Molding. Focus - Injection Molding - Free download as PDF File (. Remedies: Raise the temperature of the mold or molten plastic. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. wall thickness, knit lines, draft. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. Injection moulding (U. 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. These lines. Vertical Plastic Injection Molding. Dimensional stability. ABS (Acrylonitrile Butadiene Styrene) Benefits: ABS is a tough, impact-resistant plastic that is widely used across many different industries. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. While injection molding itself is a straightforward process involving melting. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. Weld lines are a common imperfection to be found in most plastic injected molded parts. Second, the runner leading to a tab gate takes up real estate within the. Inappropriate temperature. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. A meld line occurs when two moving melt fronts converge and flow parallel to each other. placed usually in the areas last to fill, near knit lines, as well as on the runner system. Plastic melt and mold temperature. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. 250 in. Very high quality and an extreme fit may. The mold opens and closes on a vertical axis in the vertical injection molding. (1987). 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. Plastic injection molding is a complex and highly intricate process. Vacuum. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). In this, work, metal inserts were joined with polyamide 6 by using the injection-molding technique. One of the most common ways of adding venting is by manually machining it into the mold (Figs. When the mold adopts the multi-gate pouring scheme, the plastic melt. Let the molten material cool to a solid-state. Injection molding is a popular manufacturing process used to fabricate parts in large volumes. Disadvantage: May rust if improperly stored. occupied frequently with troubleshooting injection molding. Pitfall #1 – Knit Lines. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Gate and Knit Line Locations<br />. It explored the use of. Knit and meld lines are inherent to plastic. 080" – 0. Molding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesiveWeld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. If debossed pattern is indispensable, it should have a depth of no less than 0. Weld lines are also known as “stitch lines” or “knit lines”. 5. 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. They occur when melt flow fronts collide in a mold cavity. Be wary of saving too much weight or you might end up with: cracking. Meld and knit lines are actually both different types of weld lines. Enlarge gas vents and gates to allow trapped air to escape the mold. Long shapes are produced without multiple drops or hot runner systems, eliminating knit lines and lowering tooling costs. It is best practice to maintain a uniform thickness throughout an injection-molded part. Weld line. Inject the molten material into a mold. IM: hot or warm knit lines are cause by _____ while cold knit lines are caused by _____. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. 0 to 3. The most common and one of the most challenging injection molding defects are weld and knit lines. The company provides an array of digital manufacturing expertise. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all, be a. They appear around holes or seams of an injection molded part, and some may call them “flow lines” or “weld lines”. Most failures occur at what are called “weld lines” or “knit lines”. Also known as string lines. Weld-lines look like cracks on the appearance of plastic. Different plastics make different types of knit lines. Adjust the design for the flow pattern to be a single source flow. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. Plastic melt and mold temperature. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Injection moulding (U. 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. The knit line strength and other packing related properties both aesthetic and functional of injection molded polymeric products is improved by equipping the mold with packing pins. Injection molding is an efficient, often cost-effective way to manufacture custom plastics that are strong, durable, and long-lasting. Knit lines. Incorrectly placed single gates may cause knit lines. 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. Generally all plastic components should be designed with draft where possible. Knit Lines and Resins. and Titomanlio, G. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. When the temperature is not very high, there are chances of premature solidification, which can cause weld lines to form. Visual indicating with an finished part that are formed by the junction from two plastic flow fronts. Additional venting along the parting line perimeter will improve overall venting significantly. In plastic injection molding, a parting line is where two halves of a mold meet when closed. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. PTI has five injection molding presses suitable for MIM. Understanding Knit Lines in Injection Molding: Causes and Solutions. The Difference Between Knit and Meld Lines–and Why It Matters. Injection molding a red component, for example, can pose a challenge because at time the component may be too thin for the pigment itself!. AS9100:2016. One common problem that occurs in injection molding is the formation of knit lines. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. From Plastic Materials and Processing by A. It is best practice to maintain a uniform thickness throughout an injection-molded part. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. As a result, prototyping is strongly recommended for parts with. POROUS MOLD MATERIALS. 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. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and holding. By using this method, theMolding analysis study: An example of the low patterns and knit (weld) lines formation (MoldFlow® data) of injection molded round plastic part with a complex shape and with a ring. Weld Line defect analysis, the most common of many defects in injection moulding products. 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. After selecting the direction in which the mold hole will be cut, it is much simpler to locate the separating line. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates. 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. A well-designed injection-molded part will usually have draft, but the same draft that helps eject a part from the. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. This performance can ultimately impact many part properties, including surface quality, knit line strength, part ejection force (sticking), dimensions, tolerances. Reduce clamping force. Injection Molding Process Guidelines The following is given as a potential process starting point. Trapped air in a mold manifests itself as a burn mark on the molded part. , under its Advanced Technology Program (ATP). The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. 2. 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. Runner Type. 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. So. Following lists causes and solutions for weld or knit lines. Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. More about the knit lines in injection molding. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. An edge gate introduces material at the main parting line, or where the two halves of. Knit Lines. Other common issues associated with thin walls include uneven cooling, warp, cracks, cosmetic texture inconsistencies, and weak knit lines or fracture points. Find out more by calling 573-437-4154 today or email us. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. Such molds or tools aren’t intended to be used in operation. 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. Ideally, a safety strap should be strong enough to prevent the mold from opening under various unforeseen circumstances, but always less than the holding power of the mold clamps and the machine’s mold-opening force. Obstructions in the part create weld lines or knit lines during injection molding. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Weld lines: Also known as knit lines, these are molding defects that occur when two flow fronts meet without the ability to “weld. Get a free des. Not always a problem, but can cause serious structural issues. Imagine a river splitting to go around a rock, then meeting up again on the other side. Please read on, stay posted, subscribe, and we welcome you to tell us what you think. Strength at the knit line can be as little as 20% of the. Steps involved in Multiple Material Molding. Fathom injection molding services and tools offer a single-source global solution that supports your company’s low- to high-volume manufacturing process. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Thick walls are not recommended because of POM’s high shrinkage rate. Specifically, Stokes and. occupied frequently with troubleshooting injection molding. They appear around holes or seams of an injection. H-13 Good general purpose tool steel. These structures are often small surfaces of about a tenth of an inch in diameter. 040 and 0. Edge gates, which can include fan and tab-shaped gates, are the most common ways to gate a tool. More about the knit lines in injection molding. The process is extremely versatile, and can produce very complex shaped parts, with the use of multi-sided molds. Adding vents, using overflows, or using porous metal. 125 inches. Inadequate injection pressure can result in knit lines and a surface that appears corrugated. Learn more. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. In the 1947 book, Injection Molding of Plastics, the late Dr. [8] Bevis, MJ, Reis RL, Cunha AM. So much. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. 18/06/2021. INJECTION MOLDING GUIDE V2. The melt is forced to split up during filling of the cavity. Let’s. Steven. When designing for injection molding, consider these steps to prevent knit lines The Resin Cooling Process. Knit lines and other aesthetic characteristics of the part are strictly related to the plastic’s temperature during molding, so efficient filling time is essential for achieving proper welding lines and quality parts. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Chris Newmarker | Dec 27, 2013. 040-in. 160"). The quality of the answer is directly proportional to the information we have to work with. 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. Mold filling simulation software should be used to ensure that waterExpand. 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. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. 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. PTI, a plastics and metal parts molder, is a leading developer of the MIM process. Injection molding is min-maxed for mass production. 4. Knit Lines. Also known as weld lines, knit lines.