injection molding. The authors [5, 6] attempted to reduce the weld lines and clamping force of plastic injection moulding through numerical and experimental investigation, and discovered that the 3D cooling channel. Move injection locations to make weld lines form closer to the gates. In our DFM report, we will analyze the possible weld lines. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. Here we are looking at most common part defect that can come from injection molding called weld line. Proper venting is also required to ensure good weld-line quality. Fisa et al. In this paper, two different injection molding tests were completed. 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. analyzed the heat transfer during heating and cooling phases of RHCM process. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. Weld lines have been one of the common defects puzzling the injection molding industry. Founder, Injection Molding Solutions. (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. 020 0. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro. 10. , 190°C mass and 20°C mold temperature, as well as. Weld lines are also known as knit lines. The weld line is an inevitable defect in the most injection molded components. 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 lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. Usually it’s a straight line, and often to be found radiating. 4 at different time steps (legend scale is volume fraction of. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. Discoloration. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. The second technique, cascade injection moulding, can produce parts free from weld lines. Int. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). A knit line may be unnoticeable or may look like a crack. 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]. Figure 2. The results of. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. 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. examined the relationship between the structural and mechanical qualities in HDPE/PA6 mixture which is molded with weld line and without weld line in plastic injections [6]. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. 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. 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. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. See moreEquipment. The weld lines in injection moulded parts arise as a result of the collision of two fronts of the flowing material, which fills the mould cavity and are sometimes unavoidable. 809-814. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. Weld Line defect analysis, the most common of many defects in injection moulding products. Sink marks, 2. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Still, it can be seen to varied degrees depending on mold. Instead, a line that looks like a seam forms. Mold vents should function the same way. 080 inches. e. 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. Download : Download high-res image (856KB) Download : Download full-size image; Fig. 1. Weld-line is a weak area which reduces the strength of the part locally. Clamping Unit. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. So today we are going to take a look at the five most common defects in injection molding and their solutions. 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. 48 applied high-frequency induction heating to eliminate weld lines in an injection-molded plastic part, and experimental observation indicated that weld depth was reduced from 2. For more information on the Factors Affecting the Injection Molding Process. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. They are the result of fundamental physical effects taking place inside of the mold tool cavity. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. To explore the formation of weld lines in injection molding, a. Weld lines may occur on a molded part’s surface where, after breaking off into two or more directions in a mold, the molten material has converged. Improper fusion of two fluid flows, a state before weld line. 15 shows the frozen layer and weld lines at the end of mold filling. The thermo-rheological findings were used to investigate the sources of weld line weakness. 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. This paper presents the. 3. Abstract. This customary mark is caused by differential rates of cooling in the resin where. injection molding. Its appearance can be improved by adjusting parameters. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. Wavy lines are another feature of weld lines. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow path. Sequential valve gate technology. 1. micro injection molded weld line’s mechanical properties. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. They decrease the. Or increase the number of gates. + Move gate (to where it is not visible). Flow marks in injection molding can be avoided if adequate measures are taken. Adjust the design for the flow pattern to be a single source flow. The wheel has to be gated at three places on the hub and. Weld Lines. Injection molding weld lines where two or more flow fronts come together in the mold. Injected plates were generated using a double-gated mold under four different process conditions. [ 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. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. The weld line’s strength is reduced when. Try to gradually raise the mold temperature and barrel temperature. 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. 298 µm and the weld line on the heated region was almost eliminated with the aid of induction heating. (1)Injection Machine Poor plasticization and non-uniform melt temperature – appropriately extend the injection molding cycle, to ensure thorough plasticization, and change for a machine with a larger. 2. Flow-induced filler orientation and weld lines are un-avoidable facets of the injection molding process. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and. Voids and bubbles, 6. Reduce the amount of release agents. Weld Lines. 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. In weak material bonding, they will appear as hair-like weld lines. 22: Weld line formation when melt splits around core pins. Azieatul Azrin Dzulkipli and M. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. Mold Design. It is possible to pre. Weld lines are one of the typical quality issues of injection molded parts. Google Scholar | Crossref | ISI. One of the things that can compromise an injection molded part is a weld line, also called a knit line. These are caused by the shot of molten plastic moving at different speeds throughout the injection. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. These lines. 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. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. Vents in the mold allow the mold to fill. The thin weld line is the result of weak material bonding, which lowers the strength of the part. This occurs mainly in the presence of barriers that divide the melt flow in. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. 005 0. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. [ 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. Weld line. 3. An evaluation model based on artificial neural network method. 18/06/2021. The Solutions for Poor Welding Lines. It will degrade materials performance; 9. Many researchers had emerged with several. T. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. 1 Mold In order to study the formation of weld lines, the mold cavities has been. Quality concerns in injection-molded materials can vary fr. 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. The impact behavior of weld-lines in injection molding. This weld line can act as a weak spot in the material. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. This is a video excerpt from our Problems & Solutions Course - Weldlines. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. 5. Fellahi et al. 3. Gate location should set to avoid weld lines, keep clean of the important position of the products,. 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. Injection-molding machine is the Negri Bossi VE210-1700 with screw diameter 60 mm. Weld line existence reduces the material strength; however, its demerit characteristics. Nguyen-Chung. Edge Gates. Therefore, it is recommended to do a moldflow study prior to the mold being built. Google Scholar [10] S. Where the weld lines are, where the sink marks or voids will be, and how the part warps—all of these are determined by where the molten plastic is injected into the part cavity. Flow-induced filler orientation manifests in higher tensile prop-erties in the direction of flow compared to those normal to the direction of flow. Except for a few injection molded parts with very simple geometry, weld lines occur in most injection molded parts (usually with one line or V-shaped groove), especially in large-scale complex products requiring multi gate mold and inserts. Jiquan Li, Taidong Li, +1 author. Optimizing the injection parameters through combination of adjusting the molding temperature, varying the gate pressure, and increasing the dwell time. As the polymer. Introduction Weld lines are formed during mold filling whenever two separated melt streams recombine. Redesign the mold to prevent the weld line. Preventing sink marks of injection molded parts using CAE analysis. In narrow fields, a limited amount of molten liquid can solidify and block the flow. Weld Lines-3 Ways for Detecting and Correcting. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. Weld lines are visible lines or seams formed when molten plastic flow fronts meet and fuse together, often due to obstacles or flow interruptions in the. Int J Adv Manuf Technol 52:131–141. 015 0. If the different flow fronts have cooled. 10(a) (please see Fig. 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. ac. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. A weld line can also be called a knit line. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. 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. 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 form where two or more flow fronts come together and can create a cosmetic or structural problem. The thermo. 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. Here are some strategies. A weld line is a mark left on the surface of a plastic injected molded part. 2. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. are very minimum. This leads to a better molecular chain entanglement, which in turn creates a better weld. Increasing the temperature of the mold or plastic material. The welding angle can be used to differentiate weld lines and meld lines. Injected plates were generated using a double-gated mold under four different process conditions. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. Weld lines appear as a result of the flow of molten plastic during the injection molding process. carried out to mass-produce molded products with complex shapes. Weld lines represent the region where two separated melt fronts recombine. (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. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. 10 in Nguyen-Chung et al. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Abstract. The weld line and the flow pattern of co-injection molding can be seen from Fig. Weld Lines. 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. 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. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 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. Weld lines: Cold feedstock in the die: Increase injection speed, mold temperature, and feedstock temperature, enlarge gate opening, add venting channels or overflow wells near weld line locations, move gate location, redesign parts to avoid stream partition: Flow mark: Cold feedstock in the dieWeld lines are a common imperfection to be found in most plastic injected molded parts. 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. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. 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. injection molding is followed by the welding. This paper presents the. Carefully consider all the relevant aspects of the mold design specification before. (1998) for clear photographs. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. This study describes how the weld line was formed on the part. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Weld line and warping are two critical defects for injection-moulded part. 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 of weld-line, etc. In injection molding weldlines are generated when two separate melt streams join either in multigated molds or as a consequence of flow around. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. 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. Zhao, X. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. The more gate points there are, the more weld lines will occur. (3) Adjust the temperature of the barrel and nozzle: the viscosity. 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. They. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Injected plates were generated using a double-gated mold under four different process conditions. avoid weld lines, and facilitate smooth. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. A flat product case was considered as an example of a typical aircraft structural element. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. The edge gate is the most popular and straightforward injection mold gate design. Amongst weld line. In addition a weld line can be moved to an area where it is less visible. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. Below is one of the examples: !NOTE: if the weld lines is important to the cosmetic surface of your part, please bring this up to your mold maker during quoting phase. The hair-like weld line is the. 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. . when two or more melt flow fronts contact each other immediately after the cooling process. You will have to confirm them before tooling. . Blistering 4. 9 – Over Packing. Thus, it is important to understand (i). Therefore, more studies covering this subject are required in order to improve the insight regarding the mechanism involved in the formation of weld lines in extrusion and,From the so-produced materials, specimens with weld lines were produced according to the first test series, but varying the injection molding parameters only twice, between the best and worst settings found in the previous study with the polypropylene types with MFR 8 g/10 min, i. EasyFill Advanced provides the weld-line temperature distribution and meeting angle prediction. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. 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. 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. When two or more streams of plastic meet and fuse. Vacuum voids. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Which means engineers need to know how to account for this phenomenon in an efficient way. 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 in injection molding are frequently unavoidable. The vents must be deep enough to allow the trapped air and gasses to escape but not deep enough to allow the plastic to flash. Weld line formation in the injection molding process occurs. Weld-line is a weak area which reduces the strength of the part locally. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Weld lines appear as a result of the flow of molten plastic during the injection molding process. A visual mold with variotherm system for weld line study in micro injection molding. Our injection molding company is explaining what these imperfections are, why they can compromise. Mostly, this happens when two or more flow fronts do not “knit” during the injection molding process. As the injection process continues, the two separated melt fronts meet again along the longitudinal section of the plate forming a weld line. In a weld line, reinforcement fibers adopt an orthogonal orientation with respect to the filling direction, which results in a significant reduction in the strength and. Weld lines are the most common defects in injection molded products. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. Increase the injection speed. when two or more melt flow fronts contact each other immediately after the cooling process. Weld-line is a weak area which reduces the strength of the part locally. 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. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. 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. 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. Sink marks are a common type of injection molding defect. ”. 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. If the melt temperature is low or the injection speed and pressure are low, you may end up with a more pronounced weld line. Edge Gates. To respond to poor plasticization and uneven melt temperature,. In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Flow Lines. In injection molding weld lines are formed whenever two flow fronts are joined. In this paper, a weld line computer determination method based on filling simulation with surface model is proposed, from which the positions and lengths of the weld lines can be predicted. 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. In injection molding, it is often important to maintain consistent color throughout the part. , 2 (3–4) (1988. ), with different mould surface finishes (polished, fine eroded, rough. 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]. 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 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. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. Thus, it is important to understand (i). Email him at jhenz. 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. They appear on the surface of injection molded parts like lines. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. What is weld lines. 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. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. Tosello et al. Wang et al. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Features such as sharp corners or undercuts can. Sink Marks Cause 2: Low Pack and Hold time. The solution to an internal part cracking problem is to change the packing pressure. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. One solution is to prevent the weld lines from forming in regions that are. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. 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 occur when melt flow fronts meet during the injection molding of plastic parts. Weld line location. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. 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. The specific method is that when the product is just filled and filled in the cavity, the insert. 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. Steven. * 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). Ghazanfarpour. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. 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. 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. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. It forces out trapped air pockets and can prevent a vacuum void from occurring. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. This is where the melt fronts divided by an insert, such as a pin or a. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. 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. The weld line degrades the. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. 1. 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. The weld line can either be a minor cosmetic issue or potentially bad enough to negatively impact the part's strength. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. If the large molded product is. 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. Fig. Weld lines appear on the surface of a molded part where the molten material converges after splitting off into two or more directions in a mold. Change the gate locations. 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. 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. You can expect a mold shrinkage percentage of. Sink Marks 2. 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. Weld lines are a common occurrence in injection molding that affects the overall quality and strength of a finished product. 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.