Our prototype injection molding process helps you cut product development cycles by weeks—sometimes months—and bridge to production with injection-molded parts within days. 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. Knit Lines and Resins. 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. The recommended minimum production volume for injection molding is 500 units. In the 1947 book, Injection Molding of Plastics, the late Dr. 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. As these flow fronts come together. A. 0 and Table 1). This performance can ultimately impact many part properties, including surface quality, knit line strength, part ejection force (sticking), dimensions, tolerances. These data were obtained from many andKnit lines in injection molding are common defects of the molded parts. 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. Learn about the key characteristics of common injection molding materials, recommended applications, and how common thermoplastics compare to one another. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. 1 Gate Location. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022injection-molding machine (Arburg allrounder 320C, Germany). 080" – 0. 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. Facebook. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. 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. The Jabil Molding Institute empowers employees, customers and suppliers to utilize the most advanced plastics and related manufacturing techniques in the world. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. You don't give us much to go on. 120 in. When injection molding complex parts, often knit-lines are formed during the mold filling stage. These flaws can affect the aesthetic and structural integrity of the. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Weld lines are a common imperfection to be found in most plastic injected molded parts. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. Pitfall #1 – Knit Lines. Injection molding crush ribs are small, protruding features added to molding designs to support and improve the stability of press-fit connections. Which affect parts aesthetics and decrease parts strength. The Difference Between Knit and Meld Lines–and Why It Matters. Observation on a “trial and error” basis may be required. Such molds or tools aren’t intended to be used in operation. The knit line is generally opposite the gate in thermoset. 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. It’s economical, efficient, and can produce simple to complex parts with low waste. While injection molding itself is a straightforward process involving melting. Over the years, I have developed two separate “5M” systems. This slight depression is a tiny line called the weld line or knit line. When working with customers, our design guidelines for living hinges are 0. 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. Venting at Weld Lines. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. An edge gate introduces material at the main parting line, or where the two halves of. 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. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. The goal is to create a uniform thickness and at the smallest (thinnest) level required. Depends how hard you want to push it. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Weld / Knit Lines; Assumptions. Knit and meld lines are inherent to plastic. The chart below shows recommended wall thicknesses for common injection molding resins. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. 060 in. 1-3). While the presence of knit lines does not always compromise the structural integrity of the plastic part, they are almost always a cosmetic issue. injection molding. Steps involved in Multiple Material Molding. 763-755-7575. 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. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Monoform parts. occupied frequently with troubleshooting injection molding. Services Group. Injection molding, producing, and forming resin materials are three core components of injection molding technology. 1-3). Find out more by calling 573-437-4154 today or email us. Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 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. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. BACK TAPER – Reverse draft used in mold to prevent molded articles from drawing freely. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. Injection molding weld lines refer to a line on an injection molded part that is generated where the two halves of the mold come together. Second, the runner leading to a tab gate takes up real estate within the. A wide variety of tool steels are available for injection mold construction. opposed to two or more gates. A mold with too few gates is susceptible to cooling problems, but a mold with too many gates. Knit lines. Learn how HPP maximizes these specialized processes. 3. Reduce the injection speed to limit the risk of trapping air inside the mold. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. 040-in. Piccarolo, S. This makes the casting process as efficient and accurate as possible. In fact, knit line strength will decrease with higher filler content and with longer fibers. 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. BLEED – (1) To give up color when in contact with water or a solvent. Submarine gates are another injection molding types of gate that is located below the surface of the part, typically on the underside or back of the part. In an injection molded structural plastic part, a weld line (also called a knit line) will result in a region of mechanical weakness as soon as the part is submitted to an external load. Those are knit lines, formed when two opposing flows of material join together in the mold cavity. ISO 9001:2015. Most issues occur before entry into the mold. Call 800-985-6750 or email your inquiry to sales@customgasketmfg. These lines. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. If life safety is involved, or reliably or efficacy are absolutely required, every part should. land and using maximum vent depths to get them as close to self-cleaning as possible. Injection Molding: How to Set Second. • Standard (general purpose) screws with a compression ratio between 2. Molding is a manufacturing process in which resin in a barrel is. It allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. MINNESOTA. Nicolet Plastics LLC. 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. When injection molding complex parts, often knit-lines are formed during the mold filling stage. LS Mtron Injection Molding Machine (IMM) has opened a new business unit in Mexico. RJG announced that its injection molding process control system, CoPilot, will begin offering valve gate control technology for hot runners starting in September 2021. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. wall thickness injection molding ribs. Flow lines typically manifest as visible marks, often slightly. Knit Lines and Resins. Learn how material selection, part design, and optimizing process parameters can help eliminate knit lines. They appear around holes or seams of an injection. So. 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. 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. A weld or meld line is a weakness or visible. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. You don't give us much to go on. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. 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. Also known as weld lines, knit lines. Injection moulding (U. pdf), Text File (. Injection molding is a popular manufacturing process used to fabricate parts in large volumes. . "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 11: 1. 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. Understanding Knit Lines in Injection Molding: Causes and Solutions. Knit Lines. High mold temperatures usually provide less residual stress. Macromol Symp 1988;21/21: 489-500. In addition, the force of the gas holds the appearance side of the part in contact with. These structures are often small surfaces of about a tenth of an inch in diameter. Inadequate injection pressure can result in knit lines and a surface that appears corrugated. Temperature is another factor that can cause weld or knit lines in injection molding. Disadvantage: May rust if improperly stored. com Discover why you should avoid knit lines when designing and manufacturing injection moulded parts. Read on to find out more! 800. Vacuum. This production method is particularly popular when manufacturing in large quantities. TRADITIONAL MACHINES VENTS. Many of these tips are geared around injection-molded parts, but some apply to machined and 3D-printed parts as well. Thin wall injection molding design tips and tricks. holes, multi-point injection. Because injection mold design and processing is complex, a set solution will not solve all problems. 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. Weld lines, also called knit lines, are a defect that occurs with molded parts caused by two different flows of plastic resin that do not adequately join together or weld together correctly during injection molding. Weld-lines, also referred to as spider-lines or knit-lines, are regions in the wall of an extruded plastic pipe, running the whole length of the pipe, at which there is a change in dimension and a. 3. Imagine a river splitting to go around a rock, then meeting up again on the other side. While this process is largely efficient and reliable, it's not without its potential issues. In the case of mold details, knits will occur on the lee side of a detail. Injection Molding Press. Table 2 lists the<br /> properties of common tool steels and the typical mold components for which they are<br /> used. The Troubleshooting Tips below offer common solutions to challenges in IML and IMD. Reducing the size and depth of depressions helps minimize the impact of knit lines. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. When injection molding a part, a knit. The final molding process may be dependent upon factors. The Demo Mold helps those new to injection molding easily visualize the process and is a great teaching device for educators. 2 mm. BACKING PLATE – In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc. Injection molding is the process of injecting plastic material into a mold cavity where it cools and hardens to configuration of the cavity — is best used to mass-produce highly accurate, & often complex, 3dimensional (3D) end-use parts and products. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. This radius should not be smaller than 0. 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. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Observation on a “trial and error” basis may be required. The Problems & Solutions course is designed to train injection molding personnel in. The packing pins are sequentially. Steven. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. 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. 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. 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. 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. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). Resin pellets are loaded into a barrel where. Know about the cause of these lines and the potential solutions. Trapped gas is one of the most common causes of part burns, and it can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part. Macromol Symp 1988;21/21: 489-500. This continues until the weld lines in plastic injection molding disappear. 125 inches. Lower the melt and mold temperature to prevent overheating. 5. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. 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. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic 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 article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. So what does the 140F mold temperature give us? The molding technician thought the 140F mold water was OK because the data sheet provided by the material supplier suggested mold temperatures from 75 to 180F. Sequential valve gate technology. Molding parts with multiple gates will almost certainly produce a weld line at right-angles to the line joining the two gates which could cause the weld lines to be exceptionally weak (see Figure 1. When designing for injection molding, consider these steps to prevent knit lines Resin cools as it is injected into a mold. H-13 Good general purpose tool steel. Knit lines. 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. Thermoplastic Elastomer Molding Guidelines. Increase the injection speed. All the while, the material could be the correct material," Hill says. be impressed by improvements of bubbles (vacuum voids), short shots, unequal thickness, jetting marks, weld lines, knit lines, black streaks, strain 2. 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. Generally, the mold structure is roughly divided into two main parts: fixed half and moving half. As a result, the portion has a faint, perhaps undetectable line. When needed, crush ribs can allow for draft and a tight fit for a part that requires both. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. However, the weld line may not continue throughout the flow. We have an elite team that designs for injection molding, rapid prototyping with metal and plastic, and produces world-class products under the same roof. Knit Lines: Holes in the part will always cause knit lines. Still, they are almost always a cosmetic issue. Meld and knit lines are actually both different types of weld lines. Other Excessive mold release Clean die and use minimal mold release. It’s our responsibility to make sure your design comes out of the mold working properly. What Are Cosmetic Standards for Plastic Parts?. So much. , under its Advanced Technology Program (ATP). 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. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. The injection molding process uses a granular plastic that is gravity fed from a hopper. C. knit lines and parting lines are at the discretion of MIC-ZG. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. 13758 Johnson Street NE. Adjust the design for the flow pattern to be a single source flow. The depth of the texture or letters is somewhat. In. PCS says each module of the Polimold Valve Gate Sequencer controls two zones, with the option to control up to 14. Core out parts to eliminate thick walls. RELATED CONTENT. Injection molding a red component, for example, can pose a challenge because at time the component may be too thin for the pigment itself!. Injection molding can form complex geometries easily, apply single part with multiple functions. Depends how hard you want to push it. We ensure customers receive accurate, fast, on-time, sufficient support and services. 015in wall. Knit lines don’t always compromise the structural integrity of plastic parts. to prevent improperly placed knit lines or sinking in the plastic downstream from the hinge. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. Generally all plastic components should be designed with draft where possible. Three terms that often get mixed up in injection molding are weld, meld and knit lines. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. Knit lines don’t. The linear mold shrinkage of injection molded parts will vary from 0. Gate locations can be directly behind or on the edge of the graphic. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Obstructions in the part create weld lines or knit lines during injection molding. Three terms that often get mixed up are weld, meld, and knit lines. Complex parts can be reproduced with low cost once mold is manufactured. They again get resolidified along the surface. S. - Mold flow analysis to control fill and knit lines. Example of a gate location in a finished part Example of knit lines in a finished part. 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. The following are general guidelines for molding acetal. Proper venting is essential to molding a defect-free part. Typically, the wall thickness is somewhere in the neighborhood of 50%-75% of your nominal wall thickness. mixed manually and quickly stored in the tank of an injection machine just before the start of the resin injection or (2) the components are stored separately in different tanks of an injection machine with a mixing head. Gating. TEFABLOC™ TOSI 431 75A is a high-flow thermoplastic elastomer (TPE) designed for large-part injection molding applications, offering exceptional flexibility and weather resistance. 344. Shorter knit lines must equate to a stronger part. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Please read on, stay posted, subscribe, and we welcome you to tell us what you think. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. mystagingwebsite. The injection molding process is fairly simple, plastic resin is heated to its melting point and forced through the machine and into your mold to produce your plastic parts. Injection molding is min-maxed for mass production. Weld/Meld/Knit lines are all terms describing the effect of two or more flow fronts of material joining or meeting together in the part. PTI, a plastics and metal parts molder, is a leading developer of the MIM process. Thermoplastic Elastomer Molding Guidelines. One common problem that occurs in injection molding is the formation of knit lines. Understanding Knit Lines in Injection Molding: Causes and Solutions. May 24th, 2019 Posted in Injection Molding Flaw Repair Preventing Flow Lines, Knit Lines, & Blush Injection molding isn’t an exact science, and there is a lot that can go. Excessive injection pressure can result in part defects such as overflow or flash. 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. First, they carry resin to the mold via a runner. As these flow fronts come together. Inappropriate temperature. Material contamination, for example, can cause several molding issues. 040 and 0. Usually the parting line of the mold is perpendicular to the mold opening direction of the injection molding machine. 012 in. 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. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary from virtually invisible to something that looks like cracks in the plastic. Ductile Injection Molding 101 - Injection Molding Varying. The cooler flow fronts of the resin aren’t forced into the mold surface texture as well as the hotter resin behind the flow front. For example, increasing gate size can improve part filling. Take these steps to avoid knit lines. It can also aid in material selection since fill. This is a video excerpt from our Problems & Solutions Course - Weldlines. Weld Lines-3 Ways for Detecting and Correcting. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. The uneven thickness of the product will make the melt flow resistance larger and smaller, resulting in unstable melt flow. suppressed cooling and possibly warp. Venting at Weld Lines. (called also weld marks or knit lines), and meld lines. Injection molding is the most widely used method for mass-producing plastic parts. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. The quality of the answer is directly proportional to the information we have to work with. Obstructions in the part create weld lines or knit lines during injection molding. 11) The part design must take into account possible knit line locations and work to direct them away from higher stress areas. The comment on melt flow index is correct, but, I've molded straight PC down to . A parting-line vent. Injection Molding. Called LS IMM Mexico, the subsidiary is based in Monterrey and led by plastics industry veterans Kevin Kim and Fulvio Menconi. Weld-lines look like cracks on the appearance of plastic. N174W21430 Alcan Doctor Jackson, WI 53037 262-677-9700; 16685 State Road 32 Mountain, WE 54149 715-276-4200; Prime. 030- to 0. Increase the injection speed. Change gate locations. 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. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. RE: Knit Line Affect On Material Strength lorelei5607 (Automotive). S. com. 160"). The Difference Between Knit and Meld Lines–and Why It Matters. Our plastic injection molding glossary provides key terms. 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. knit line formation, application of draft angle and design for assembly. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Hardware components. sinks, knit lines, and shrinkage,” Spalding says. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. They are formed when two or more flow frontKnit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection. Adding vents, using overflows, or using porous metal. From Plastic Materials and Processing by A. These defects are not visible, like small. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic. injection molding machines using standard industry practices . In plastic part design for injection molding, it is important to design the injection mold so that the molten plastic fills the mold cavity entirely, cools as evenly and as quickly as possible without warping, and functions as intended. So what does the 140F mold temperature give us? The molding technician thought the 140F mold water was OK because the data sheet provided by the material supplier suggested mold temperatures from 75 to 180F. Last month, in the first part of this two-part installment we focused on the reasons viscosity can change during injection molding. a knit line will form 180°on the opposite side from the gate location. End-of-arm tooling can make or break a program. It’s called sequential valve gating, or SVG. Bubbles are caused by melting flow fronts colliding in a mold cavity. In this, work, metal inserts were joined with polyamide 6 by using the injection-molding technique. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Demo Mold. Release of trapped air in those cases will. Remove the hardened material from the mold. Meld and knit lines are actually both different types of weld lines. Islyn Thomas summarized the need for a particular vent location better than I ever could. Remedies: Raise the temperature of the mold or molten plastic. Multiple gates will always. To learn more about us or to get a quote, click here or call 1. Weld / knit plane forms as flow fronts recombine Weld line and failure due to flow around core. One of the most common ways of adding venting is by manually machining it into the mold (Figs. Figure 1: D-shaped through-hole in center of gear part accepts the drive shaft. Most failures occur at what are called “weld lines” or “knit lines”. TRADITIONAL MACHINES VENTS. Molding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesiveMolding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesiveMost failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc.