+ Move gate (to where it is not visible). การแก้ไข ชิ้นงานจุดที่เกิดความอ่อนแอบริเวณ weld line คือต้องใช้ความเร็วในการฉีดต่ำในจุด. These are preferred over weld lines as they will normally result in improved cosmetics and structure. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. demanding injection molding and end-use requirements. Place a vent in the weld line area to remove the entrapped air. This may require higher melt temperature or lower injection speed . 7 in Kobayashi et al. With tighter heat controls, you can keep the material at the proper temperature to make sure the plastic keeps flowing and fills the mold cavity completely. However, research about the computer determination of weld lines in injection molding remains scarce. The molded plastic part may also appear to be rust-colored. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. • Reduce runner dimensions and maintain the same flow rate. 18/06/2021. Weld-line is a weak area. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. Materials Science. Adjust the design for the flow pattern to be a single source flow. In injection molding, it is often important to maintain consistent color throughout the part. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. See moreEquipment. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. 2. This failure causes the product to be damaged during use. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. Better weld line quality was obtained by Huang. Weld lines have been one of the common defects puzzling the injection molding industry. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Weld lines are a common imperfection to be found in most plastic injected molded parts. S. Cracks in Corners – When cracks appear in the corners of plastic parts, the cause is too much plastic shrinkage onto the mold core in that corner. The formation of weld line in the injection molding method is caused by the product and mold design that is one of the common mistakes. Flash. a) Multi-fiber connector micro injection molding simulation b) 3D simulation of micro gear with 150µm diameter for weld line position prediction c) 3D micro injection molding filling simulation of micro gear with 180µm diameter Fig. A weld line is often unavoidable. Prediction of the weld lines in injection molding process using neural networks. Problem: Weld lines are formed when plastic resin is forced around an obstruction in a mold tool and reforms on the side opposite the gate. There will be too many weld lines ; 6. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. For more information on the Factors Affecting the Injection Molding Process. (1998) for clear photographs. Weld lines are the result of fundamental physical effects taking place inside of the mold tool cavity, they are common imperfection to be found in most plastic injection molded parts. 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. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Flashes, 3. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are. Experimental Setup 2. Usually it’s a straight line, and often to be found radiating. Adjust the design for the flow pattern to be a single source flow. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. This occurs either due to injection through multiple gates or as a conse-รอยประสานของเนื้อพลาสติก Weld line ตอนที่1. 030 0. Flow lines are lines, waves, or ring patterns that appear on the surface of a part, noted by their slightly different color from the rest of the piece. + Adjust injection speed. The injection molding temperature and the mold temperature were fixed respectively at 230 °C and 50 °C. Proceedings of ANTEC (2000) Google Scholar [9] S. 080 inches. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. ” Another. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. Participating in DFM and mold flow analysis is a good way to achieve this. In weak material bonding, they will appear as hair-like weld lines. 1. The flow fronts at different times (Fig. The simulated cold weld line length is consistent with the experimental one when a 115 °C mold temperature is adopted; with lower mold temperatures, the simulated lengths are smaller than the experimental ones—in accordance with the literature on the conventional injection molding process [26,27]—probably because of the definition adopted. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. According to the characteristics. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. The structure is more complex with longer molding cycle . This paper presents the. 5. Mold Design Most conventional mold designs will work with TPU’s. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. It is normally at the meeting points of two flow fonts. The Factors that Cause Weld Line in Injection molding Pressure. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. This leads to a better molecular chain entanglement, which in turn creates a better weld. After that, the compounds were injection-molded into tensile samples with and without weld lines to. analyzed the heat transfer during heating and cooling phases of RHCM process. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. (1) Increase the injection pressure and prolong the injection time. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. Raise the injection speed. (3) Adjust the temperature of the barrel and nozzle: the viscosity. In a meld line, the plastic comes together at an angle greater than 135 degrees. As compared to a weld line, the flow fronts come together at less than 135 degrees. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. You will have to confirm them before tooling. A knit line, also called a weld line, occurs when the liquid plastic moves through the mold and hits more melted plastic and they don’t flow or fuse together. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Weld line is formed when two different melt flows converge, as illustrated in Fig. Increase the injection speed. Weld-line is a weak area which reduces the strength of the part locally. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. Figure 1 below shows the development of a weld line. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. This paper evaluates the shrinkage and strength of weld line using Design of Experiment and Response Surface Methodology in multi-objective optimisation utilising the injection moulding parameters. Stop using mold parting agents. Weld lines are visible to varying degrees on any molded part depending on gate location, flow length, melt/mold temperature, cavityA weld line occurs when two or more molten plastic flows meet and fuse during the injection molding process, resulting in a visible line on the surface of the molded part. You can locate the gate at the thick part of the injection molding to prevent air pockets. injection molding. Try to gradually raise the mold temperature and barrel temperature. Multiple gating, splitting of the melt flow due to inserts in the cavity or through holes, as well as changes of thickness give rise to points within the structure where the flowing fronts will recombine and weld. (3) Adjust the temperature of the barrel and nozzle: the viscosity. 1. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. This article will review how and why weld lines occur, how mold gates effects weld line location and strength, the importance of material selection and 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. The weld lines in blow molding occur wherever the pari son knits together in the head, mold tacking areas and mold parting pinch-off region. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. investigated the impact of injection molding parameters on weld line formation and strength reduction. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. Its appearance can be improved by adjusting parameters. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. Fellahi et al. Weld line. 1. Weld Line Factors for Thermoplastics. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. 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. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. Adjust the position of the gate and include a venting slot. Melt temperature does effect the weld. Vacuum voids. Increase the injection speed. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. with a characteristic length χ 0 =0. The holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. They. Weld lines can be caused by material flowing around holes or inserts in the part, multiple injection gates or variable wall thickness where hesitation or "race tracking" can occur. Effects of mold temperature and pressure on shrinkage 0. In injection molding of thermosoftening plastics, an important aspect having a bearing on the quality of articles is the appearance of weld lines that are formed when there are inserts, barriers, molding signs, reinforcements, etc. In. If the different flow fronts have cooled. 1. The weld line’s strength is reduced when. 025 mm (0 . Which means engineers need to know how to account for this phenomenon in an efficient way. Mold Design. Remedies: Raise the temperature of the mold or molten plastic. 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. Sequential valve gate technology. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. 2. . 004 m, a characteristic velocity ν 0 =0. Maintain a holding pressure that is no more than 1/2 the. Plastic Rapid Injection Molding is popular not only in low volume manufacturing but also in large quantities molding, it is the most common way to manufacture plastic parts. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Islyn Thomas summarized the need for a particular vent location better than I ever could. Weld lines are a common issue in injection molding, and occur when two flow fronts meet and fuse together as the material cools and solidifies. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. This paper presents the. 13. [ 18 - 21 ] In addition, the effects of flow behavior of the polymer melt due to the optimal process parameters for the minimization of weld-line effects are an important consideration. 3. Weld line formation in the injection molding process occurs. Flow-in-duced fiber orientation manifests in higher tensile properties in the direction of flow compared to normal to the direction of flow [13–15]. + Increase mold temp, or materials’ temp, or holding pressure. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. In injection molding weld lines are formed whenever two flow fronts are joined. In an injection molding process, a weld-line forms when two flow fronts meet each other. What are Weld Line Defects? Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. One method is the local te mpering of the affected areas to prevent weld lines. Clamping unit berfungsi untuk memegang dan mengatur gerakan mold unit, serta gerakan ejector saat melepas benda dari molding unit, pada clamping unit lah kita bisa mengatur berapa panjang gerakan molding saat dibuka dan seberapa panjang ejector harus bergerak. Weld lines appear on the molded part where molten plastic meets. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. 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]. Thus, it is important to understand (i). In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. The hair-like weld line is the. Yes, it does help, for two reasons: Often the weld line traps air and the ‘dump’ acts as a vent to allow the air to escape. In this experiment, several ejector. Plastic Injection Molding Process. Possible causes: Low temperature or fluidity of melted plastic during injection molding. Discoloration. A weld line is often unavoidable. The effects of filling time, packing time, packing pressure, melt temperature, and mold temperature on the ultimate tensile strength (UTS) and the elongation value of the weld. Thus, it is important to understand (i) if the melt is able to fill the cavity up to the weld line location, (ii) where the weld line forms, and (iii) if the weld line is a cold or flowing one. Weld-line is a weak area which reduces the strength of the part locally. Micro-injection molding (µIM) is a widespread process for the production of plastic parts with at least one dimension, or feature, in the microscale (conventionally below 500 µm). 030 0. Gate Placement: Properly positioning the gate can direct the melt flow to minimize weld lines or relocate the weld line to non-visible areas of the part. Still, it can be seen to varied degrees depending on mold. * Corresponding author, e-mail: [email protected] recently had a few pieces (2-3%) crack after assembly, while in storage (not installed, still in the package). These are caused by the shot of molten plastic moving at different speeds throughout the injection. Yes, it does help, for two reasons: Often the weld line traps air and the ‘dump’ acts as a vent to allow the air to escape. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. , less than 0. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. By the reflection method and a high speed camera, the visual system can be used to record and observe the forming process of micro weld lines during the. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. Burn Marks. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of injection parts. Weld line, 5. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are. The thermo. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. In order to prepare the weld line specimen by micro injection molding, a mould integrated with visual system and variotherm system was designed and constructed, shown as Fig. 1. 020 0. 13 shows the best gate location for which the weld lines . It occurs when melting plastic material is injected into a mold, it flows through all parts of th. According to the special features of micro injection molding process compared with normal injection molding process, the main related factors to weld line’s properties were classified as 3 group, named as processing conditions, mold design and structure, external process. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Sink marks are a common type of injection molding defect. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. . Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. Steven. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. Weld-line is a weak area which reduces the strength of the part locally. Figure 1a illustrates how the weld line is produced when. Weld lines are also known as knit lines. Flow marks in injection molding can be avoided if adequate measures are taken. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a mold. Weld lines have been one of the common defects puzzling the injection molding industry. Weld line (also known as a knit 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. carried out to mass-produce molded products with complex shapes. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. (1983). The Influence of Knit-lines on the Tensile Properties of Injection Molded Parts, Polymer Engineering and Science, 23(10): 591-596. As these flow fronts come together. Many researchers had emerged with several. Evaluate and optimize your part design The advantages of using the moldflow analysis to avoid potential defect like deformation, shrinkage, welding line etc, part designers can change the wall thickness or enhance the ribs to improve their part design. Consequently, it causes viscous dissipation which leads to the generation of heat. In the feeding system of injection molding, the flow of plastic melt begins from the nozzle of the injection molding machine, traverses through the sprue and runners, and ultimately reaches the mold gate(you can call it the injection molding gate as well)—the entry point to the mold cavity. Email him at jhenz. 3 the path lines of selected material elements can be observed which are. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Flow lines. [1] 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. From Fig. 1 Prediction of weld lines with injection molding simulation softwareReduced frozen skin thickness: High injection speeds also contribute to a thinner frozen skin at the weld line. Jiquan Li, Taidong Li, +1 author. 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. Weld lines may occur depending on the product shape and gate positions. Meanwhile, Using more advanced cooling method such as cyclic cooling or conformal cooling. In this paper, a kind of polypropylene (PP) foam plastic parts with special weld lines were obtained by core-back foam injection molding with chemical blowing agent. (1) Flash: Extra plastic material in the shape of films or burrs, which appears on the parting surface, around the runner or in the insert crevice. . Which means engineers need to know how to account for this phenomenon in an efficient way. + Optimize holding pressure time. 6. These potential causes include:Weld lines Weld lines are weak areas formed by converging flows of plastic that can lead to mechanical part failure if not properly accounted for in the part design. Optimizing the Injection Parameters. technical ulletin SPECIALTY POLYME RS Design and Production of Injection Molding ToolsIncrease the injection speed in order to fill the mold more quickly and ensure the material does not prematurely cool down; in addition, when the speed is adjusted the flow fronts may meet at a different spot and move the weld line location. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. For example, filled resins and ABS are more likely to. Weld lines are a kind of Achilles heel of plastics. The governing equations for the melt and the air in the cavity are united into…. Some of these are listed below: Plastic warpage. In this paper, two different injection molding tests were completed. That helps. The parts are molded flat and are slightly stressed once installed in an arced position, but not excessively. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. 2. e. Knit lines are hard to eliminate for injection molded plastic parts but. An evaluation model based on artificial neural network method. Thereby creating localized pressure within the mold. The resulting defects don’t stop at flash only. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold. 015 0. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. Definition: A seam that appears where two areas of molten plastics meet. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. Weld lines not. Recently hired at plastic injection molding simulation software provider Moldex3D, Nicholson was spurred to undertake the research study following a conversation with a customer experiencing weld-line woes. Short shots. In this study, the effects of injection temperature, injection pressure, and fiber content on the mechanical properties of weld lines were studied for carbon fiber-reinforced nylon. Fisa et al. e. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. In narrow fields, a limited amount of molten liquid can solidify and block the flow. The effects of these two injection molding process parameters are explained in terms of their influence on the skin-core morphology observed on the fracture surfaces in the weld zone. Increasing the temperature of the mold or plastic material. Kobayashi et al. Shaofei Jiang. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. The terahertz time-domain spectroscopy (THz-TDS) imaging technique was used to detect the weld line defect of an injection-moulded short glass fiber-reinforced composite. (3-1) Increasing the Resin Temperature at the Weld Line Section. 3. It forces out trapped air pockets and can prevent a vacuum void from occurring. In this paper, a weld line factor (W-L factor) was adopted to describe the. You can choose material of low viscosity and can increase the injection pressure. Flow rate is 24 cm3/s. This is where the melt fronts divided by an insert, such as a pin or a. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. Blistering 4. M. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. 1. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. The weld line can either be a minor cosmetic issue or potentially bad enough to negatively impact the part's strength. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. 2. Flow analysis of the weld line formation during injection mold filling of thermoplastics. To elimi- nate weld lines, you can enlarge shrinkage. In spite of its cosmetic attributes, a bad knit line can significantly. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. There are several factors that can contribute to the formation of weld lines, including: Part design: The design of the part can impact the flow of the material and the likelihood of weld lines forming. Its appearance can be improved by adjusting parameters. Gate blush, 4. Materials Science. th INTRODUCTION Injection molding is one of the mostWeld Lines in a plastic cover. In this study the polycarbonate (PC) and carbon fiber (CF) are used as the experimental materials to investigate the impact of injection molding process parameters on tensile strength of weld line. A meld line occurs when two moving melt fronts converge and flow parallel to each other. If the plasticizing ability of the plastics injection molding machine is insufficient, the plastic cannot be fully plasticized, resulting in weld lines when filling the mold. Injection molding, polypropylene, talc. As the polymer resin is injected into a mold, it flows through all parts of the mold. Abstract. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). Redesign the mold to prevent the weld line. Injected plates were generated using a double-gated mold under four different process conditions. This can allow the. Process. Ni. When the two such melt flows. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. In addition a weld line can be moved to an area where it is less visible. 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. Venting at Weld Lines. Weld lines can be caused by material flowing around holes or inserts in the part, multiple injection gates or variable wall thickness where hesitation or "race tracking" can occur. are very minimum. Redesign the mold to. The flow of the material in the injection mould takes place through the gate. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. 6. Proper venting is also required to ensure good weld-line quality. Molding calculation in Moldex3D: (а) melt front and weld line, (b). Weld or knit lines occur when melt flow fronts collide in a mold cavity. 000 0.