* Corresponding author, e-mail: fengsjpc@ku. distribution [4]. 2021年4月23日 / by admin. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Weld line location. Thus, it is important to understand (i). In the sense that the weld line is better formed before the resin. Fig. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. (1998) for clear photographs. Melt temperature does effect the weld. Vents in the mold allow the mold to fill. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. The Difference Between Knit and Meld Lines–and Why It Matters. Some of the common fixes for weld lines include: Increase the resin temperature to ensure both sides of the weld line are liquid when colliding. 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. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. The impact behavior of weld-lines in injection molding. The position, length, and angle of weld lines are dependent on the. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. In this experiment, several ejector. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Weld or knit lines occur when melt flow fronts collide in a mold cavity. 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. The weld line’s strength is reduced when. In the above diagram, the converging flow fronts (indicated by red arrows. In an injection molding process, a weld-line forms when two flow fronts meet each other. Here we are looking at most common part defect that can come from injection molding called weld line. Silver Streak. Weld line and warping are two critical defects for injection-moulded part. From Fig. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. In weak material bonding, they will appear as hair-like weld lines. Weld lines are among the most critical structural defects in parts made by the injection molding of fiber-reinforced thermoplastics, explained Sirmax in a press release. If the large molded product is. One of the defects observed in injection molding parts is weld line strength, which forms when two or more separate melt fronts traveling from different directions meet and join as the mold cavity is filled. e. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. Weld lines are where two flow. + Increase mold temp, or materials’ temp, or holding pressure. e. Insufficient injection pressure and speed can cause weld lines. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. When an external load is applied to a weld line region, the part’s potential for mechanical failure is increased. A visible weld line is observed, due to a combina-Cracking is commonly seen at the weld line area but sometimes on the entire surface. 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. Weld Lines. Mold flow marks, also known as flow lines or weld lines, are often caused by variations in the flow of molten plastic material during the injection molding process. These lines are formed when two or more flowing molten plastic streams meet and fuse together, creating a visible line on the surface of the molded part. avoid weld lines, and facilitate smooth. The performance of weld lines in talc filled polypropylene box moldings produced with a. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. The conditions are temperature, injection speed, and injection pressure. in the cavity of the injection mold. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. Increase the injection speed to reduce the amount of cooling happening in the mold. Weld line injection molding troubleshooting. Published 5 July 2019. Save. The weld line’s strength is reduced when. injection molding. injection molding. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. In this study, the effects of injection temperature, injection pressure, and fiber cont. In many cases, you will also see that the part is hanging up on the core during ejection. Vacuum voids. Weld-line is a weak area. 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 still rather few. Flow analysis of the weld line formation during injection mold filling of thermoplastics. The wheel has to be gated at three places on the hub and. . Solving one problem can introduce other problems to the injection molding process. Experimental Setup 2. Increasing the temperature of the mold or plastic material. The next type of injection molding defect is ‘Weld Lines’. Weld lines are a kind of Achilles heel of plastics. 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. Polym. Injection molding plate for mode I testing geometry. Meddad and Fisa [3] found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost. + Optimize holding pressure time. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. John Bozzelli. Therefore, it is recommended to do a moldflow study prior to the mold being built. Insufficient plasticizing ability of injection molding machine. (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. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. Weld line formation in the injection molding process occurs. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. 943 µm to 0. The Solutions for Poor Welding Lines. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. Gambar 2. The main types of injection molding defects are: 1. Flow Lines. In our DFM report, we will analyze the possible weld lines. 000 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. + Improve vent inside the mold. Here are some strategies. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. They are the result of fundamental physical effects taking place inside of the mold tool cavity. In this work, the weldline strength of injection molded short-glass-fiber reinforced polycarbonate was derived by an analytical method of modified rule-of-mixtures as a function of the area fraction between skin and core layers. The flow of the material in the injection mould takes place through the gate. Ni. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. Move injection locations to make weld lines form closer to the gates. 9 – Over Packing. Usually it’s a straight line, and often to be found radiating. Proceedings of ANTEC (2000) Google Scholar [9] S. 2. the three-plate mold often adopt this kind of gate. This can occur when a polymer flow splits to go around an interruption (e. , 2 (3–4) (1988. การแก้ไข ชิ้นงานจุดที่เกิดความอ่อนแอบริเวณ weld line คือต้องใช้ความเร็วในการฉีดต่ำในจุด. Better weld line quality was obtained by Huang. 5. Weld lines cause significant reject rates and are a common problem that all molders face. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). when two or more melt flow fronts contact each other immediately after the cooling process. Expand. The holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. 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. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld together. Adding vents, using overflows, or using porous metal. Bubbles are caused by melting flow fronts colliding in a mold cavity. You can expect a mold shrinkage percentage of. Knit lines are hard to eliminate for injection molded plastic parts but. 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. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPThree terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. (2) Causes & Countermeasures (See the table below) *Note: Flash also tends to occur when the injection pressure/speed are too high, but molding time is too long and mold temperature is too low. Adjust the design for the flow pattern to be a single source flow. 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. 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). For more information on the Factors Affecting the Injection Molding Process. Flow-induced filler orientation manifests in higher tensile prop-erties in the direction of flow compared to those normal to the direction of flow. Increase the injection speed. Figure 1 below shows the development of a weld line. 10. Flashes, 3. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are. 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]. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. Dischler, D. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. One test mold was used to mold three different materials using heat/cool and conventional molding techniques. The Weld line result itself has a scale associated with the placement of the weld line that is directly relative to how severe the weld line will be based on the angle in which the two flow fronts meet. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Valve. Weld line, 5. Materials Science. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. 2. This is where the melt fronts divided by an insert, such as a pin or a block, in a mold cavity rejoin each other downstream of the insert. Key words: weld line strength, thermoplastic composites, injection molding, wall thickness, skin and core layers Department of Materials Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand. 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. 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]. 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. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. Possible causes: Low temperature or fluidity of melted plastic during injection molding. 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. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. In. The gate vestige for injection molding is usually narrow. Flash. Weld lines in injection molding are frequently unavoidable. Fisa et al. Root causes Many factors—including processing conditions, material, part design and mold design—can influence the visibility and strength of a weld line. These lines. Flow-induced filler orientation and weld lines are un-avoidable facets of the injection molding process. 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. A flat product case was considered as an example of a typical aircraft structural element. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. In this study, epoxy molding compounds (EMC) filled with glass beads were fabricated with a twin-screw-extruder (TSE) and tempered before further processing to generate different degrees of cross-linking (0–15%) in the compounds. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. + Adjust injection speed. Increase the size of the gate and runners to alter the mold design. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. 1. Sequential valve gate technology. Alter the mold design. This gives a clue as to how it was formed. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. Google Scholar [10] S. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. You can choose material of low viscosity and can increase the injection pressure. Wang et al. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. In an injection molding process, a weld-line forms when two flow fronts meet each other. In narrow fields, a limited amount of molten liquid can solidify and block the flow. The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Weld lines often generate mechanically weak areas, because of the unfavorable perpendicular orientation of the macromolecules, fibers and/or other fillers to the direction of the main flow. Weld line. In this paper, aiming at the problem of weld line defects in the injec- tion process of a key phone panel, the injection process is optimized by using Moldflow and drop simulation. 005 0. They are unavoidable even for moderate complex products. The second technique, cascade injection moulding, can produce parts free from weld lines. 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. Participating in DFM and mold flow analysis is a good way to achieve this. During the plastic injection molding process, one of the biggest challenges is. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. 3. Investigations on WLs in micro injection molded parts were performed in Refs. 7 of the reference. Clamping Unit. 2020-01-1306. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. In this case the two flow fronts will meet and. In some cases, a weld line can also cause a loss of strength and impact resistance. Weld Lines-3 Ways for Detecting and Correcting. 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. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. This occurs mainly in the presence of barriers that divide the melt flow in. In injection molding weld lines are formed whenever two flow fronts are joined. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. Preventing sink marks of injection molded parts using CAE analysis. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. 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. 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. In this lesson we will focus on the meld and weld lines. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. They decrease the. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. Except for a few injection molded parts with very simple geometry, they occur on most injection molding parts (the shape is usually a line or V-shaped groove), especially Large complex items requiring the use of multi-gate molds and inserts. Azieatul Azrin Dzulkipli and M. Molding calculation in Moldex3D: (а) melt front and weld line, (b). It is normally at the meeting points of two flow fonts. Bubbles are caused by melting flow fronts colliding in a mold cavity. (3) Adjust the temperature of the barrel and nozzle: the viscosity. This study focus on the formation of. Polymers 2023, 15, 2440 3 of 21. In this study, polypropylene (PP) was compounded respectively with carbon nano fibers (CNFs) and TiO 2 nano particles at various weight fractions (10, 20, 30, 35. 025 mm (0 . Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. Streaks 3. Download : Download high-res image (856KB) Download : Download full-size image; Fig. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. 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. 4. When this fails to happen correctly, a weld line defect occurs. The quality of the weld line can be improved through optimized processing conditions, increased mold and melt temperatures, and increased injection speed to reduce the viscosity of the polymer. But none of the current packages can predict weld lines’ properties qualitatively. This occurs either due to injection through multiple gates or as a conse-รอยประสานของเนื้อพลาสติก Weld line ตอนที่1. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. 004 m, a characteristic velocity ν 0 =0. the meeting angle by optimizing variation over time in the cavity. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. The calculation was carried out on a mesh with solid elements obtained in ANSYS Meshing and transferred to Moldex3D by means Rhinoceros. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. If the different flow fronts have cooled. These lines usually appear on the narrowest portion of the part, and appear to originate from the mold’s gates, where the molten resin flows into the mold to form. If the injection gate is not properly designed, it can cause the formation of defects like sink-mark, warpage, short shot, weld-line, air traps, and other faults [15]. (2) Adjust the injection speed: high speed allows the melt to reach the confluence without cooling down, and low speed allows time for the air in the cavity to be discharged. 005 0. They become more critical when particulate fillers are compounded with the polymer. Carefully consider all the relevant aspects of the mold design specification before. Park et al. This reduced thickness of the frozen skin further enhances the visual appeal of the. Weld lines are common defects in injection-molded plastic parts that occur when two flow fronts of molten plastic meet and fuse together during the molding process. A weld line is often unavoidable. Meld Lines. Weld line problem which occurs in polymer parts produced by plastic injection method and affects appearance and strength on a large scale was researched in this paper. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. As these flow fronts come together. Effects of mold temperature and pressure on shrinkage 0. The literature on the formation of weld lines, and their consequences, is more abundant on the area of injection molding [5-12] than on extrusion [13]. This is particularly true if the wall thickness in the weld is thin – i. Weld Lines-3 Ways for Detecting and Correcting. Wavy lines are another feature of weld lines. As the injection process continues, the two separated melt fronts meet again along the longitudinal section of the plate forming a weld line. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. The pressurized air restricts the flow of the plastic resin. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Weld lines can. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. 5. Use a less viscous plastic. Instead, a line that looks like a seam forms. Place a vent in the weld line area to remove the entrapped air. 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. Weld Lines. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Sink Marks Cause 5: Improper Part Geometry. 2. Figure 2. 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. M. S. Figure 1a illustrates how the weld line is produced when. Flow lines. The solution to an internal part cracking problem is to change the packing pressure. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. They appear on the surface of injection molded parts like lines. The weld line degrades the. Redesign the mold to. As a result, the portion has a faint, perhaps undetectable line. 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. Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. The weld line is an inevitable defect in the most injection molded components. GlossFlow-induced fiber orientation and weld lines are com-mon features of the injection molding process. That’s the air escaping out of the nozzle until the hose is full of pressurized water. If the plastic encounters a pin or other obstruction, the plastic flow front must split to form two flow fronts to go around the pin. This model provides the necessary information. This paper presents the. Plastic Injection Molding Process. This is a video excerpt from our Problems & Solutions Course - Weldlines. gas, which can cause blistering, as well as poor weld lines, warpage and the formation of cold slugs that affect filling and part mechanical properties. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. Adjust the position of the gate and include a venting slot. Try to gradually raise the mold temperature and barrel temperature. A knit line may be unnoticeable or may look like a crack. Fig 13:- Detailed view of weld lines. Poor mold spot Spot mold to ensure fit and vent depths at ~0 . A visual mold with variotherm system for weld line study in micro injection molding. Change the gate locations. (1) Increase the injection pressure and prolong the injection time. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Mold vents should function the same way. Injection molding of large/complicated products are usually prepared by multiple compounds, which produces weldlines once the melt fronts are joined by impingement flow. The four sets of plaques are produced by changing the magnitude of packing pressure equal to 60% of filling pressure, with increment of 20% up to 120% of filling. Increase the melting temperature. 809-814. 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. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Weld line existence reduces the material strength; however, its demerit characteristics. The flow fronts at different times (Fig. Optimizing the injection parameters through combination of adjusting the molding temperature, varying the gate pressure, and increasing the dwell time. A. As compared to a weld line, the flow fronts come together at less than 135 degrees. Meld and knit lines are actually both different types of weld lines. 010 0. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. 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 still rather few. To explore the formation of weld lines in injection molding, a flow model based on viscoelastic constitutive equation is presented in this article to predict and evaluate of weld lines location and properties, in which Rolie. If you turn on the spigot to a garden hose, you will hear a hissing sound at the nozzle end for the first few seconds. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold.