Below, we’ll look at five of the most common types of injection molding defects, and how you can prevent or repair them. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Flow Lines. They again get resolidified along the surface. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. html. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. Although they typically do not impact the functionality of a product, flow lines—off-color streaks or patterns across a product’s surface—may look unprofessional when visible to consumers. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. Several factors contribute to the formation of flow lines, including material properties, mold design, and process parameters. The mold material 6 can have several effects on. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. The cause can vary. However, FRTP has problems such as the formation of weld lines, the deterioration of appearance due to the exposure of fibers on the molded product surface, and the deterioration of the strength of. Additionally, you can get our free Design Cube, which will provide a physical aid to help understand how knit lines form as well as other injection molding design considerations. Mold Design. When combined with low injection pressure, this problem leads to decreasing melt speeds and can cause flow lines. Ensure sufficient cooling time to avoid locking residual stresses into the part. In this example, the flow ratio is 80 (10 Fig 2 – The spiral flow chart provides data about maximum flow length based on several Monday, 01 December 2014 Page 1 of 2Automatic in-line process quality control plays a crucial role to enhance production efficiency in the injection molding industry. 1). We heat the plastic to a molten phase, inject it into the mold and cool it into a preferred shape. 6 T) as thick as the nominal wall. Warping. Flow marks in injection molding are defects that manifest as a line or series of lines forming a pattern different in color from the other parts of the molded material. Precise control of resin flow, pressure and temperature is critical. Effects of mold temperature and pressure on shrinkage 0. ; Warping – The structural deformation that occurs. Fig. Plastic Purity. For the measurement of the crystallinity a DSC analysis was performed. Typically, flow lines are caused by the liquid plastic cooling at different rates. Laminar flow in a plastic mold, described by. 5-3. 10(a) (please see Fig. In addition to accurate temperature control, optimizing flow through a mold is critical and, quite often, results in decreased cycle times and increased product quality and repeatability, even after increasing chilled water temperature. (3) Improving the surface gloss of the product. Increase injection speeds and pressure to ensure the cavities are filled properly. These defects include the following: 1. The Mold. 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. A meld line occurs when two moving melt fronts converge and flow parallel to each other. 182-185, 2013. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. There are important differences between an injection mold sprue and its runner system. Inadequate mold wall thickness leads to uneven cooling and hindered plastic flow, resulting in weld lines. Cooling lines impact. Leadtime Leader 2024. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Certain injection molding processes may not be effective for the production of some parts. 5. Possible defect causes. Plastic Injection Molding Defects series-Flow Marks or Flow Lines Aug 23, 2019 What should we keep in mind when designing for injection molding?1. Flow lines can be minimized in injection molding by optimizing the design of the part and the mold, as well as the processing conditions. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. Too hot and the plastic will start to degrade, but too low and flow marks increase. This results in a much greater amount of vent flow area for the compressed air to exhaust through, and still protects the corners. 3 the path lines of selected material elements can be observed which are. It is a type of distortion caused by this premature solidification. Mold Venting. One way to reduce the changes in speed of the flow front is to tailor the injection-speed profile. This requires skilled labor to mold new parts that have less molding defects. AnalysisInjection moulding simulation with the finite element method is the most advanced technique for designing injection moulds. Occasionally, the molded part has. As these flow fronts come together. Here are some ways to avoid. They appear as visible lines or streaks on the surface of the molded part and can negatively impact its aesthetics and mechanical properties. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. A mark on a molded piece made by the meeting of two flow fronts during molding. Commercial injection molding simulation packages, such as Moldflow and C-MOLD, have been incorporating GAIM options to provide computerized design and optimization tools for GAIM processes and. The moldability validation and flow analysis tools enable you to iden-tify and correct potential injection molding problems as you design the product. They appear around holes or seams of an injection molded part, and some may call them “flow lines” or “weld lines”. They usually are a slightly different color than the rest of the piece, and typically occur on more narrow sections of the molded item. The formation process of weld lines can be described as. A method of melt flow visualization was used to record the weld line location on the surface of molding prepared at the proper injection conditions (method of "record grooves effect" formation. The flow fronts at different times (Fig. Strengthening. The formation of weld lines and their location along the flow path is a well-studied phenomenon in conventional injection molding; however, only a few papers are devoted to micro-injection molding [11,13,14,15,16]. Turbulent Flow IS Always Better. Flow Lines. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. As the material properties of. Vacuum on the mold does help and many times eliminates the weld line. Adjust the sprue bushing length: If the face of the sprue bushing is sealing off on the parting line, adjust the length to ensure that nozzle pressure or thermal expansion does not hold the mold open and allow the plastic to flow out. A poorly designed or maintained water-cooling system can have a serious impact on production efficiency and cause many maintenance issues. Fixing Process Variables That Can Cause Flash. In injection molding, it is often important to maintain consistent color throughout the part. Flow lines or flow marks are a common visual defect in injection molding. plastic mold venting. 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. 20 mm. The melt holds enough temperature to maintain a low enough viscosity. Remedies: Raise the temperature of the mold or molten plastic. Flow direction is essential for mold mapping because when water flow reverses, poor turbulence and hot spots occur. I’ve been noodling that question around in my head for the last three years, since injection machine suppliers like Arburg, Engel, Wittmann Battenfeld and Sumitomo (SHI) Demag started showing up at trade shows with mold-filling displays on their machine controller screens. Consider the following examples of cooling channel configurations in P20 mold steel with a water line diameter (D) of 11. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. The materials used in the plastic injection molding process can vary in rigidity and pliability, among other differentiating characteristics. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. Flow lines are a defect in injection molding and can be a significant issue for manufacturers. Source: Google. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). The plant water system is a critical component of an injection molding facility. So when two. [12] or the flow lines shown in Ref. Flow lines are. As a result, the lower degree of stress when gating with valve gate systems becomes relevant. When mapping mold circuits, label each circuit with a number exclusive to the circuit and a supply or return designation (e. Jetting occurs in a molded component when molten material is injected into the mold cavity and starts solidifying before it fills the cavity. You can avoid having any weld lines with cascade injection moulding. Round the corners of the mold where wall thickness increases to help keep flow rate consistent and prevent flow lines. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. flow rate, in turn, causes the heat transfer effi ciency of the cooling cha nnels to vary from one. G. When the mold is full, the machine continues its injection pressure and compresses the plastic. 1) Snake flow lines. So much. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. In Fig. . 2), the plastic enters the mold at a relatively fast rate and forms the skin. Higher numbers assure that water flow is adequate, and that turbulent flow is at an acceptable level. Known as thermolators,. Water cooling pumps coolant through lines on the outside of the mold cavity. They are evidence of nonuniformity in flow pattern upon entry into the mold. Thus, with an injection pressure of 1800 MPa, the flow length with 80°C is 47 mm and accordingly for. If larger gates are used, expect a longer molding cycle time. Peering into the Flow. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. This slight depression is a tiny line called the weld line or knit line. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. 750 in. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. Mold Design. Description: Flow lines are streaks, patterns, or lines - commonly off-toned in color - that show up on the prototype part as a consequence of the physical path and cooling profile. Short Shots. with a characteristic length χ 0 =0. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. The formation process of weld lines can be described as follows: Injection moulding (U. Setting the proper pressure on the injectors to push the plastic into the mold with enough speed that the plastic will coat the mold and fuse with other flow lines. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Listed below are some factors to consider when designing ribs for injection-molded parts. The primary reason is insufficient plastic fluidity. This depends on a. Weld lines are a kind of Achilles heel of plastics. In injection molding weldlines are generated when two separate melt streams join either. The proposed method is first applied to the simulation of HDPE melt in a classic Poiseuille flow case, and then two. Symptoms: Flow lines will typically appear as discolored “bands,” or sometimes “wavy. 3) Poor Preventative Maintenance. Tip #6: Pick Which Molding Defects Are Acceptable. The chart below shows recommended wall thicknesses for common injection molding resins. Study shows that the root cause of jetting is related to the mold design on the one hand and the viscoelasticity of the material on the other. Otherwise, the heat transfer of. 1 Caused By The Quality of Injection Mold. Weld lines have been one of the common defects puzzling the injection molding industry. Flow LinesWeld lines are the def ects in. There are a few adjustments that you can make to your injection molding process to prevent flow lines, including: Increase the injection speed, pressure, or material temperature: Slow-moving molten plastic is more likely to cool. This article continues our series of troubleshooting reports from one of the leading on-the-spot problem solvers in the molding industry. ³/sec. Increasing pack or hold pressure helps to eliminate low-pressure conditions at the weld line. These properties make it ideal for. SMARTFLOW ® flowmeters effectively and accurately measure flow rate. Acetal is a funny material in how it reacts to certain injection speeds and mold temperatures. Kobayashi et al. With a minimum of 1. These data were obtained from many andGenerally, injection molding resins are characterized as having medium, high or very high flow. 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. or too much shear heat burning the material prior to injection. Injection moulding (U. This can be achieved by connecting ribs to each other. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Introduction. There are two types of weld lines, cold and hot weld line. 020 0. Injection molding can be performed with only one of these materials like glass, plastics, etc. thick, 0. 3. We restarted the mold at the same coolant flow rate and temperature. 3). The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Non-uniform cooling of mold causes warping, creating internal stresses within the part and resulting in distortions. Where wall thickness increases, round the corners of the mold in those regions. 0010 in. Let’s review some methods to prevent flow and knit lines in plastic injection molding. com. 2), the plastic enters the mold at a relatively fast rate and forms the skin. Low-quality and poorly designed molds can also result in flow lines on injection molded parts, particularly those with uneven wall thickness, insufficient lubrication, and poor venting. Errors like these manifest when processing is done incorrectly. One cause of flow lines is low injection speed, which can result in the molten plastic cooling too quickly and creating a. For the production of these weld-line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527-2) and impact (ISO 179-1/1eU) properties were measured, and statistical analyses were performed to gain insight on the correlation between melt flow rate and weld-line behavior. Thin walls of greater length require greater pressure, which requires larger injection molding machines and. Thin walls often increase the pressure required to fill the part, and. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Surface Delamination. The accompanying table lists the flow rates for various barrel diameters at various injection velocities. According to the design requirements of the back shell of mobile phone and the performance of materials, ABS is selected as the raw material for injection molding in consideration of economy [ 8 ]. Email Sales@Aberdeentech. to 0. Lesson 6: Meld and Weld Lines (Processing) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. Basic Repairs for Warping. Which means engineers need to know how to account for this phenomenon in an efficient way. Figure 7 below shows the cooling channels, defined in this case using simple sketch lines. After exhaustive research, testing and pilot-scale demonstration, the team developed a breakthrough new technology utilizing low constant injection pressure. See. Look for signs of stickiness or burning. When a poor-quality plastic that has impurities in it is used for injection molding, it is less likely to flow smoothly through the mold. Several factors contribute to the formation of flow marks in plastic molds: Mold Design:. Water cooling pumps coolant through lines on the outside of the mold cavity. A. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near the surface of the finished parts. Impurity. Molds separate into two sides at a parting line, the A side , and the B side , to permit the part to be extracted. FLOW – A qualitative description of the fluidity of a plastic material during the process of molding. If the mold itself has cracks or defects, the finished product will also have various problems. 1 Caused By The Quality of Injection Mold. There is a level of insulation from the plastic layer on the wall. How a mold is watered is key to a processor's goal of consistency. Vacuum Voids. The streaks form from plastic in the mold overlapping with plastic following it. 010 0. Investigate the mold for signs that a water leak is present, and correct the condition. If you have critical requirements for strength of knit lines, please call a Protolabs applications engineer at 877-479-3680 to discuss, or email at [email protected]. The most important factors to consider during molding are the mold temperature, melt temperature, and injection pressure and speed. Lower speeds allow gas more time to escape through vents. 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. 3C) is to put a vent along the entire edge, but just shy of the corners. Ensure that injection pressures are appropriate (under 70 MPa [10,000 psi]). Use high-quality, temperature-controlled materials for better mold filling. If it’s too thin or small, material flow, pressure, and temperature will. Weld lines, also known as knit lines, are a common defect in injection molding where two or more flow fronts of molten plastic meet but don’t properly fuse together. Defects like this make it harder to market the finished parts to the end user. Flow marks are a phenomenon in which a pattern of the flow tracks of the molten plastic remains on the surface of the molded product. We restarted the mold at the same coolant flow rate and temperature. Reduce the temperature of the mold and plastic being injected. google-site-verification: google03af4f4fcb62a9d5. Lenticular, or Silver Dollar type pigments, are thicker than cornflakes, with a narrower particle size distribution. Flow Rate. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. 1) Snake flow lines. Injection Molding works with molten fluid created by heating the plastic granules above their melting point. After an hour of running, the steel temperature stabilized at 78°F. , 1 IN, 1 OUT, 2 IN, 2 OUT). Flow lines are linear grooves or circular ripples on the surface of a molded object caused by uneven cooling, improper residence time, or cycle time, or low mold. 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. 020 0. Chart 1: Diameter versus turbulent flow. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. If I can answer any questions you may have on optimizing the plastic part design, CNC plastic prototype, mold manufacturing, and injection molding or if I can be of any other help, please feel. 31″) will require more. In this regard, the gate form with less shunt should be used, and the gate position should be selected reasonably. On-Line Solutions To Injection Molding Problems. 6. These defects include the following: 1. In the plastic injection moulding industry, we work with materials that are by-products of oil refinement and moulds made of metal casting, so our terminology is bound to be at least slightly confusing. Known as thermolators, water cooling systems require a cooling source such as a tower. 0 seconds, depending on part volume, runnergate style and size, cavity location and injection pressure. Figures 3A, B and C depict different examples of “spot” vents. Weld lines have been one of the common defects puzzling the injection molding industry. FOW Mould is one of the best companies that use injection molding. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. The main. to 0. Weld lines are a common imperfection to be found in most plastic injected molded parts. On the surface of a molded object, flow lines (also called flow marks) refer to the phenomenon that linear grooves or circular ripples showing the direction of material flow inside the mold cavity. Increase the mold temperature. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. Three terms that often get mixed up are weld, meld, and knit lines. Flow lines can be defined as linear grooving, or circular ripples, on the surface of a molded part that indicate the direction of material flow within the cavity of the mold. In this guide, we cover evaluation and also the remedy of flow lines in injection molding. The best method of venting this type of part (Fig. Adjustments to injection speeds are the best way to determine which of these two are the specific cause. If the melt speed of each gate entering the cavity is inconsistent, it is easy to cause weld lines at the intersection. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Utilize advanced injection molding machines with increased injection speed and pressure. These flaws might have an impact on the product’s functionality as well as its appearance. The Mold. 5. Depending on the resin, resin temperature, mold temperature, and filling. They can be unsightly and unpleasant in high-end sunglasses. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the weld line can be seen clearly from the Fig. We stopped the machine and added glycol to the chiller to a concentration of about 40%. It is widely used in various industry sectors, and its products are ubiquitous in our daily life. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. Figure 1 below shows the development of a weld line. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. This software simulation can show how a resin will fill the mold during the injection molding process. V. In narrow fields, a limited amount of molten liquid can solidify and block the flow. Wavy lines are another feature of weld lines. Introduce automation into the injection molding process for improved efficiency. Unraveling Flow Lines. Troubleshooting Injection Molding Sink Marks. Understanding the complexities of injection molding flow and solidification is a bit more challenging as. On the contrary, for the conformal cooling. Energy use by thermoplastics injection molding machines is estimated to result in global CO 2 emissions in the order of 80 million metric tons annually. Flow Rate. If performing a resin change from one polymer to another a difference in viscosity can cause flow lines or gels. We started the mold with 100% water circulating at 60°F at a flow rate sufficient for turbulence. As the polymer resin is injected into a mold, it flows through all parts of the mold. ; Burn marks – Often appears as black or rust-toned discoloration streaks on the edge or surface of a molded product. Phone (630) 665-8590. They occur as a result of different flow rates of molten plastic in the mold cavity. Polycarbonate Injection molding defects. This article explains the causes and. Faster injection increases pressure in front of a flow front. Designers can easily set up and perform analysis with only a few clicks. 1．Mold Temperature Too Low. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. In addition, when the melt is solidified in the cavity, there is a vacuum between the product and the cavity wall, also the air must enter the mold. While the sprue is milled through the entire thickness of the injection mold, passing from the outer surface to the parting line (where the two mold halves meet), the runners are comparatively shallow channels milled into the face of one or two mold halves. If I can answer any questions you may have on optimizing the plastic part design, CNC plastic prototype, mold manufacturing, and injection molding or if I can be of any other help, please feel. process can be fully completed. This may involve adjusting the temperature and pressure of the mold, using different mold materials, or adjusting the injection speed or cycle time. Design for Manufacturing (DFM), also known as pre-mold review, is a collaborative process in the injection mold industry where technical negotiations take place to meet customer requirements. One of the best ways to determine part shrinkage for complex components is with a mold flow analysis. Novel Nozzle Tip Prevents Stringing, Saving Molds & Cycle Time. PROBLEM: FLASH ON PARTING LINE There are a few key reasons why flash appears on the parting line of a part. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. Plastic is injected into a mold at a specific rate of flow—typically in. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. Drain the hopper if you were working with 100% regrind, clean if necessary. However, the weld line may not continue throughout the flow. Flow Lines. The position, length, and angle of weld lines are dependent on the gate location, injection speed, injection pressure, mold temperature, and, especially, the direction and degree of the polymer melt velocity in the. Melt delivery management has a major impact on final part quality and the ultimate success of the production line. They may also appear as ring-shaped bands on a product’s surface near the entry points of the mold, or “gates”, which the molten material flows through. Purpose: The examination of melt flow lines in injection moulded parts was the purpose of this research, as well as a new method of flow visualization was applied. g. In this guide, we cover evaluation and also the remedy of flow lines in. Inadequate mold wall thickness leads to uneven cooling and hindered plastic flow, resulting in weld lines. The following advantages exist for the use of high injection speed in the injection process. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Injection Molding of Multimaterial Systems. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow. Flow Lines Defect in Injection Molding Process Flow lines can be defined as linear grooving, or circular ripples, on the surface of a molded part that indicate the. The type of gate for manufacturing often depends on the material used and the parts’ shape. Since these materials behave and respond differently, it is crucial. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. 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. 5. Another advantage to using valve gating is the amount of control it gives you over the injection molding process. This is often a sign that injection speed and/or pressure are. Accept All. Waterlines control heat within three diameters of themselves. Examine the flow pattern of each part to see if the plastic flow front is coming around on itself, or if there is a hesitation of the flow front in filling a thin section of the part. Effects of mold temperature and pressure on shrinkage 0. 020"). INADEQUATE INJECTION PRESSURE. They follow the flow of the molten resin from the gate along the finished part. Flow marks, also known as flow lines, are molding defects that can occur in the manufacturing process of injection molding. On thicker sections of the mold, there may be sinks caused by bosses designed into the backside of the surface. They are best described as "off tone" wavy lines/streaks or patterns in the molded part around the injection ports. 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. The Smartflow Reynolds Number Calculator is provided as a service to the injection molding community as an easy-to-use online resource. Inadequate cooling time. Midland, MI. Mold Flow - Position ribs such that the plastic has an optimal flow path. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Mold flow analysis is a powerful tool for optimizing the design and performance of injection molding processes. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. The weld lines are formed when there is an obstacle in the cavity of the injection mold. Flow lines are the results of slow injection rate and disparities. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. (1998) for clear photographs. All mold cooling lines must have adequate flow to produce a turbulent flow condition. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near. The position, length, and angle of weld lines are dependent on the. Utilize hot. They commonly occur when there is a large variation between cooling speeds of sections of the material as it flows through the mold. Injection molding is a great technology for finished production on a massive scale. Adjust resin and cooling temperatures. The formation process of weld lines can be described as. The emergence of silver marks is generally due to the rapid start of the injection which causes the air in the melt and mold cavity unable to be discharged quickly enough. If possible, try to choose a little glue . 1, pp. There are three stages of flow – laminar, transient and turbulent. This method can be helpful in. Injection molding is one of the best plastic production methods. We started the mold with 100% water circulating at 60°F at a flow rate sufficient for turbulence. Solution: If possible, operate the machine on. They are the result of fundamental physical effects taking place inside of the mold. • Reduce runner dimensions and maintain the same flow rate. Weld lines may appear like seams or scratches, but that is not what they are. Pushing the air out or not is the difference between a good part or burns and flow lines. These are off-tone streaks or lines on the surface of the plastic, and while they don’t affect the structural integrity, they are unattractive and prevent a uniform and consistent appearance. The most common and one of the most challenging injection molding defects are weld and knit lines. Slower flow results in thicker and shorter knits. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. Mold surface is too cold.