) . 18/06/2021. To determine the effect of the weld lines on tensile strength, tensile tests were conducted with the specimens fabricated with NORYL (amorphous blends of. In this paper, two different injection molding tests were completed. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). Increase the size of the gate and runners to alter the mold design. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Emerging Materials Research. 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. 2. 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. The. Increasing the temperature of the mold or plastic material. 2. In this study, we apply the technique of SAW to explore the acoustic properties near injection-weld lines by comparing the velocity of (V R) in locations close to and locations distant from the weldAmong defects of injection molding parts, weld lines are the most common defect. Mold vents should function the same way. Since it is often impossible to avoid weld lines as well as a limited possibility to increase the weld line strength by adjusting the injection molding parameters, a method to predict the weld line strength in the product development process is shown below. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Short shots. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. The default weld line result recognizes 135º as the maximum angle of collision and as that angle decreases, the severity increases as it. They appear on the surface of injection molded parts like lines. Weld lines are the most common defects in injection molded products. 6. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. In conclusion, reducing weld lines in injection molding requires a combination of factors, including adjusting the melt temperature, injection speed, pressure, and gate size, as well as using a hot runner system, modifying the part design, using a different material, reducing the wall thickness, using a mold release agent, and working. Weld Lines. 5. They decrease the. Expand. ” Another. Sink marks are a common type of injection molding defect. So today we are going to take a look at the five most common defects in injection molding and their solutions. 6. In the first stage, the two part halves are injection molded and then, in a second process step outside of the molding machine, they are welded together. This weld line can act as a weak spot in the material. The holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. 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. In this lesson we will focus on the meld and weld lines. 943 µm to 0. Prediction of the weld lines in injection molding process using neural networks. 005 0. 2021年4月23日 / by admin. 2. It will degrade materials performance; 9. The thermo. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. Therefore, the. Weld line formation in the injection molding process occurs. 3: Weld Lines. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. Int J Adv Manuf Technol 52:131–141. 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. The edge gate is the most popular and straightforward injection mold gate design. Weld lines have been one of the common defects puzzling the injection molding industry. Recently, the injection molding of fiber reinforced thermoplastics (FRTP) containing short fibers has been widely carried out to mass-produce molded products with complex shapes. The impact behavior of weld-lines in injection molding. The relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Change the gate locations. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. They are the result of fundamental physical effects taking place inside of the mold tool cavity. gasket seal leakage where the weld line crosses a gasket. Injected plates were generated using a double-gated mold under four different process conditions. Experimental Setup 2. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. An evaluation model based on artificial neural network method. The gate vestige for injection molding is usually narrow. Consequently, it causes viscous dissipation which leads to the generation of heat. The weld line and the flow pattern of co-injection molding can be seen from Fig. Its appearance can be improved by adjusting parameters. 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 are where two flow. Better weld line quality was obtained by Huang. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. They occur when melt flow fronts collide in a mold cavity. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. 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. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. Weld Line defect analysis, the most common of many defects in injection moulding products. 7 of the reference. 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. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. The Problems & Solutions course is designed to train injection molding personnel in. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. Injection molding can be performed with only one of these. 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. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPAccording to the weld line distribution map of six gate schemes shown in . Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Weld lines may appear like seams or scratches, but that is not what they are. 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. The following are the conclusion drawn from the present research: 1. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. The next type of injection molding defect is ‘Weld Lines’. Flow Lines and Weld Lines. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Weld lines are a reality in the injection moulding of complex parts. 001 in . . 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. The resulting defects don’t stop at flash only. Mostly, this happens when two or more flow fronts do not “knit” during the injection molding process. The impact behavior of weld-lines in injection molding. Weld line formation in the injection molding process occurs. Meld Lines. Weld line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. Effect of process parameters on the relative weld line strength From injection molding practice and literature, 1, 3,4 it is generally accepted that: if a weld line forms before the filling is. injection molding is followed by the welding. 080 inches. 004 m, a characteristic velocity ν 0 =0. Many studies were conducted to explain the weakness at the. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Fisa et al. 020 0. 2. These weld lines occur usually around holes or at the material flow joint area in the injeciton molded part, some welding lins is very small, specially if. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. 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. The molded plastic part may also appear to be rust-colored. ac. Mérillou, J. [ 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. As these flow fronts come together. It is a zone with reduced mechanical properties negatively influencing on the molding behavior in exploitation. Weld Lines. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. The thin weld line is the result of weak material bonding, which lowers the strength of the part. Design. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. e. 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. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. This failure causes the product to be damaged during use. 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. wall thickness, gate and runner designs and re-validate the result. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. Possible causes: Low temperature or fluidity of melted plastic during injection molding. <Materials>Injection moulding (U. To explore the formation of weld lines in injection molding, a. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. Figure 2. (3-1) Increasing the Resin Temperature at the Weld Line Section. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. Definition: A seam that appears where two areas of molten plastics meet. Here are some strategies. The rule is, a higher pressure shall be required to push the material in the machine when there is excess mold. For multiple gate and complex part. If you are familiar with any form of scientific injection molding, regardless of the name, then you know one of the first steps is performing a viscosity curve study. This gives a clue as to how it was formed. That helps. Flow LinesThe most simple design modification for eliminating the weakening effect of a weld line is to increase the wall thickness in the weld line zone (Figure 4). In some cases, a weld line can also cause a loss of strength and impact resistance. 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. Ni. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. For more information on the Factors Affecting the Injection Molding Process. The Solutions for Poor Welding Lines. Wavy lines are another feature of weld lines. The Difference Between Knit and Meld Lines–and Why It Matters. 8. 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. This occurs mainly in the presence of barriers that divide the melt flow in. 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. 3 the path lines of selected material elements can be observed which are. The governing equations for the melt and the air in the cavity are united into…. Weld lines have been one of the common defects puzzling the injection molding industry. Injected plates were generated using a double-gated mold under four different process conditions. injection molding. Wang et al. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. The edge gate is the most popular and straightforward injection mold gate design. 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. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Materials Science. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. Root causes Many factors—including processing conditions, material, part design and mold design—can influence the visibility and strength of a weld line. Injection Molding Know How. avoid weld lines, and facilitate smooth. The plastic injection molding process, including thermoplastic injection, is nowadays used in several industrial processes, including in the automotive industry for bowden cables. A weld line is a mark left on the surface of a plastic injected molded part. Weld lines have been one of the common defects puzzling the injection molding industry. Sequential valve gate technology. Introduction. The structure is more complex with longer molding cycle . Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Redesign the mold to prevent the weld line. Weld. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Weld line formations can be weak if they fall in areas that will bear stress or impact. This paper presents the. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. This is expected to achieve maximum results while the pressure holding effect will also increase. 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. when two or more melt flow fronts contact each other immediately after the cooling process. 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. The injection molding process can be optimized to maximize weld line strength by increasing mold and melt temperatures, and by increasing pack pressure at the weld line. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. They are unavoidable even for moderate complex products. 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. Alter the mold design. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. They decrease the. In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. 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. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. This is particularly true if the wall thickness in the weld is thin – i. Weld line. The Factors that Cause Weld Line in Injection molding Pressure. Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. In this lesson we will focus on the meld and weld lines. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. 2) Vents in an injection mold should let the air out, but not the liquid plastic. This paper presents the. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. Steven. Weld lines are formed when two orThe experiments were performed on an Arburg Allrounder 320C 600-250 injection moulding machine using a two cavity-injection mould (Fig. Five injection molding process parameters, including mold temperature, melt temperature, packing pressure, injection. Known also as knit lines and weld marks, weld lines are difficult to eliminate completely, especially if your injection molded part requires holes. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Weld line injection molding troubleshooting. The position, length, and angle of weld lines are dependent on the. 1. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. Weld-line is a weak area. 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. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. 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. 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 melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Knit and meld lines are inherent to plastic. 2. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. Flow rate is 24 cm3/s. 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 represent the region where two separated melt fronts recombine. Shaofei Jiang. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. In the present work, the micro specimens were investigated. In the sense that the weld line is better formed before the resin temperature. Flash. of micro injection molding process simulation by technology update and progress. The weld line is then created with a higher flow front temperature and is packed with more pressure. injection molding. Heating and cooling mould systems, which cost extremely high, are a typical technology to prevent the weld-line. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. They are the result of fundamental physical effects taking place inside of the mold tool cavity. The foundation to any robust process, in my opinion, is based on choosing the correct fill time. Runner Type Venting Plastic melt and mold temperature Injection speed and pressure Learn how to troubleshoot weld lines in injection molding. They found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in whichEffects of mold temperature and pressure on shrinkage 0. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. 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. ac. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Int. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. Weld-line is a weak area which reduces the strength of the part locally. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. 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. 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. the three-plate mold often adopt this kind of gate. The impact behavior of weld-lines in injection molding. 22: Weld line formation when melt splits around core pins. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow path. Injection Molding defect:molding weld_and_meld_line. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. They have their origins in material choice, part design, tooling, and processingIncrease the mold temperature and smooth out any sharp corners or turns in the mold to facilitate even melt flow. The parting line in injection molding is which one of the following: (a) the lines formed where polymer melt meets after flowing around a core in the mold, (b) the narrow gate sections where the parts are separated from the runner, (c) where the clamping unit is joined to the injection unit in the molding machine, or (d) where the two mold halves come together? Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Molding Equipment. When injection molding large products, molding is usually performed with multi-point gates, but weld lines can occur depending on the product shape and gate position. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. (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. 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. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. 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. 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. The solution to an internal part cracking problem is to change the packing pressure. In. The spreading mold release agent on the part cavity surface might eventually cumulate at the V-notch groove of the weld line after each injection molding shot. Weld lines in design for manufacture. 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. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. One solution is to prevent the weld lines from forming in regions that are. One common issue that frequently arises during injection molding is the formation of weld lines. • Optimize the design of the runner system. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Weld lines have been one of the common defects puzzling the injection molding industry. Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. EasyFill Advanced provides the weld-line temperature distribution and meeting angle prediction. • Reduce runner dimensions and maintain the same flow rate. Introduction. g. <Mold> Provide a cold slug well where weld lines occur. In Fig. As the polymer resin is injected into a mold, it flows through all parts of the mold. 010 0. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. 1. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. This can allow the. micro injection molded weld line’s mechanical properties. The weld line is an inevitable defect in the most injection molded components. In an injection molding process, a weld-line forms when two flow fronts meet each other. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Second, depending on the size of the overflow well, you get a little bit of flow melding together, and that helps strength so that you have some intertwining of the polymer chains. Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. If the different flow fronts have cooled. demanding injection molding and end-use requirements. Google Scholar | Crossref | ISI. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. They. G. Kobayashi et al. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. Steven. 8. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Meld lines are formed when two separate flow fronts meets. Clamping Unit. 2. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. When the polymer resin is injected into a mold, it flows through all portions of the mold cavity. 6. 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. 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. Insufficient plasticizing ability of injection molding machine. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. 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. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. 030 0. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. carried out to mass-produce molded products with complex shapes. Zhao, X. 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. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. This failure causes the product to be damaged during use. Weld lines are also known as knit lines. This happens when the molten plastic is injected into the mold cavity and flows around an obstacle such as a pin, hole, or protrusion, and then comes back together. Proceedings of ANTEC (2000) Google Scholar [9] S. Wavy lines are another feature of weld lines. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. 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. 18/06/2021. Optimizing the injection parameters through combination of adjusting the molding temperature, varying the gate pressure, and increasing the dwell time. 10(a) (please see Fig. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. When two or more streams of plastic meet and fuse together, a visible line or weakness is formed on the surface of the finished product. 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. Weld lines. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Preventing sink marks of injection molded parts using CAE analysis. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Improper fusion of two fluid flows, a state before weld line. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. As compared to a weld line, the flow fronts come together at less than 135 degrees. This model provides the necessary information. 2. Effect of the processing conditions on the variations of the bulk temperature, T b , at the end of mold filling at the two locations: in (left) and away (right) from the weld-line (T w , T inj. Weld line defects in injection molding is a line or lines on the part surface that caused the part looking ugly or cuased part lifetime, or even broken easily. 025 mm (0 . This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. Venting at Weld Lines. Sink Marks Cause 3: Improper Pack or Hold Pressure. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. 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. Knit lines are hard to eliminate for injection molded plastic parts but. Meld and knit lines are actually both different types of weld lines. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. Weld lines are one of the typical quality issues of injection molded parts. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. The pressurized air restricts the flow of the plastic resin. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. in the cavity of the injection mold. Possible Sources of Weld/Knit Lines: Temperature from the injection molding machine, runners, and/or the mold itself in order to ensure the plastic resin flows properly;Weld line is one of the plastic injection molding defects. A simulation process was conducted to determine the recommended setting of injection moulding parameters and the range of the variable. 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.