Sink marks are a common type of injection molding defect. Wavy lines are another feature of weld lines. 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. Munich, Germany: Carl Hanser Verlag, 1994. injection molded pipe-fittings with and without weld line. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. One solution is to prevent the weld lines from forming in regions that are. 943 µm to 0. 3 cc/sec, the weld lines are no longer perceivable above 130 C. Fig. In this paper, two different injection molding tests were completed. In injection molding weld lines are formed whenever two flow fronts are joined. From: Polylactic Acid (Second Edition), 2019. The effects of fiber concentration has been studied in detail. Maintain a holding pressure that is no more than 1/2 the. Silver Streak. Unfortunately, the 3D layering process creates ‘weld lines’ (an injection molding term) between layers which is essentially two layers of polymer that meet. 2. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. 6. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. This paper presents the. In the RHCM, the mold temperature profile plays a crucial. 1 Prediction of weld lines with injection molding simulation softwareWeld lines in design for manufacture. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Or, the part where the weld line is produced shall. Adjust the design for the flow pattern to be a single source flow. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. , 509 (2) (2011), pp. Our weld line injection molding is essential for the best result of finished molded products. (3-1) Increasing the Resin Temperature at the Weld Line Section. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. As a result this. This study focuses on the effect of melt temperature on. Machine Shot Capacity – The maximum volume of resin that can be injected in a single stroke of the injection machine. Polym Eng Sci 45(7):1021–1030. The problem with ‘weld lines. Weld Line defect analysis, the most common of many defects in injection moulding products. 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. The effects of these two injection molding process parameters are explained in terms of their influence on the skin-core morphology observed on the fracture surfaces in the weld zone. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow path. [ 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. 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]. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). A good weld typically occurs when the melt temperature where the weld line is formed is no more than 20°C below the injection temperature. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. (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. 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. Polyamide-6 (PA-66) was used as. Procedia Mater Sci 2014; 3: 2048–2053. Instead of using flow leaders and deflectors to control the locations of the weld lines, this paper presents an approach to specify the locations of the weld. Sequential valve gate technology. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. They. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Weld lines are formed when two orAbout Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. Thus, it is important to understand (i). Strength measurements should be made to. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. of micro injection molding process simulation by technology update and progress. This leads to a better molecular chain entanglement, which in turn creates a better weld. Reposition gates and runners to allow resin to flow around the obstruction from a. 3. * Corresponding author, e-mail: fengsjpc@ku. Information about PA6/PA66 (Nylon) Injection Molding. 1007/s00397-003-0339-2 ORIGINAL CONTRIBUTIONCauses and Remedies of Sink Marks In Injection Molding. The injection pressure is too lowEffect 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. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. 4 at different time steps (legend scale is volume fraction of. Increase the melting temperature. Microsyst Technol, 14 (6) (2008), pp. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. The second technique, cascade injection moulding, can produce parts free from weld lines. [23, 24]. This study describes how the weld line was formed on the part. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. 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. 7 in Kobayashi et al. It occupies a major part in the plastics industry ranking second to plastic extrusion in terms of production and the utilization of both thermoplastic and thermosetting plastic materials. ). Weld lines. Facebook. ”Weld Lines in a plastic cover. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Five industry pros with more than 200 years of combined molding experience provide step-by-step best practices on mounting a mold in a horizontal injection molding machine. In an injection molding process, a weld-line forms when two flow fronts meet each other. Slow down injection speed. Redesign the mold to prevent the weld line. Figure 1 below shows the development of a weld line. We have various types and models available. The. As a result this weld line will be a weak point in this part. 22 shows how the weld lines are formed when the melt splits around core pins during the injection molding process. Furthermore, injection molding was applied by filling these pellets into a micro-injection molding machine (C. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. 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. 4. In an injection molding process, a weld-line forms when two flow fronts meet each other. Figure 2. This can occur when a polymer flow splits to go around an interruption (e. 020 0. 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. A weld line can also be called a knit line. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. . Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. In injection molding, it is often important to maintain consistent color throughout the part. 2011; 509 (2):226–233. The wheel has to be gated at three places on the hub and. Compd. Injection molding weld lines where two or more flow fronts come together in the mold. We recently had a few pieces (2-3%) crack after assembly, while in storage (not installed, still in the package). 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. 10 in Nguyen-Chung et al. Flow Lines. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). (3) Adjust the temperature of the barrel and nozzle: the viscosity. From Understanding Weld-line Integrity by Sabic Innovative Plastics, p. The main types of injection molding defects are: 1. A weld line is often unavoidable. 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. A visual mold with variotherm system for weld line study in micro injection molding. Xie L, Zhu D, Ziegmann G, Steuernagel L (2016) Investigation on correlation between cold/hot weld line mechanical properties and micro injection molding processing parameters. Poor weld line Ⅰ. In this study, one injection mold. The molded plastic part may also appear to be rust-colored. Thus, it is important to understand (i). Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Injection molding is a complex multi-variable, nonlinear and time-varying unsteady process, which makes it more difficult to optimize the process parameters. , 47 (2008. 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. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. 9 – Over Packing. The most common and one of the most challenging injection molding defects are weld and knit lines. 298 µm and the weld line on the heated region was almost eliminated with the aid of induction heating. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are. The resulting defects don’t stop at flash only. Recently, injection molding process has generated growing interest, exhibiting great potential to easily fabricate unique polymeric materials for industrial applications. However, even with advanced technologies and precise control, the process is not without its challenges. A weld line is a mark left on the surface of a plastic injected molded part. Cracking and/or Crazing can be defined as a fracture or surface breakage in the material of a molded part, usually found in weld line areas, but also on the surface in general. 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. In this regard, Taguchi orthogonal experimental design is adopted, and five processing parameters, the mold temperature, melt temperature, cooling time, packing. 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. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. <Mold> Increase (or decrease) the size of the runners and gates. Again, consult with professionals as to how you could improve mold designs. Injection molding. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. Weld Lines and Fibers There are two basic types of weld lines: the stagnant and the flowing [1]. They can affect the strength and. • Move injection locations to make flow fronts meet more obliquely, turning the weld line into a meld line. Improper fusion of two fluid flows, a state before weld line. The defects encountered could be caused by mechanical factors, such as poor mold design and mold manufacturing, or by processing related factors, such as incomplete kneading, inadequate molding pressure, injection. In the 1947 book, Injection Molding of Plastics, the late Dr. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold temperature control, significantly increasing mold temperature beyond typical values observed in conventional processes. 2 mm to 1. If not, the speed will drop, and it could create weld lines. At a low volumetric injection flow rate of 33. Table 2-Glass Fiber Glass Fiber Glass Fiber Glass Fiber A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Email him at jhenz@polymer-center. One of the factors that determines the quality of injection molded parts is the weld line [50,75,76]. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. 1, right). a) Multi-fiber connector micro injection molding simulation b) 3D simulation of micro gear with 150µm diameter for weld line position prediction c) 3D micro injection molding filling simulation of micro gear with 180µm diameter Fig. The design of the mold, as well as the part being molded, has a significant impact on the success of the process. 226-233. The weld lines in injection molded parts arise as a result of the collision of two fronts of the flowing material, which fills the mold cavity and are sometimes unavoidable [1][2][3] [4]. 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. Another relevant topic in injection molding is the presence of weld lines (WLs) and their properties, which could lead to part weakness through surface disturbances, optical issues and reduced bonding [21, 22]. , Ziegmann G. A simulation process was conducted to determine the recommended setting of injection moulding parameters and the range of the variable. Weld lines may appear like seams or scratches, but that is not what they are. 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. As the plastic flows through the mold it. ABS is a commonly used plastic in injection molding due to its excellent mechanical properties and chemical resistance. 6. In manufacturing, the Weld line or Knit line or Meld line is the line where two flow fronts meet when there is the inability of two or more flow fronts to "knit" together, or "weld", during the molding process. 2(a, b). Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. Alloys. 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. A 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. Powder injection molding comprises several processing steps, and defects may occur in each step if care is not taken. As such, optimizing mold designs should always be incorporated in your production model. They. The impact behavior of weld-lines in injection molding. Weld Lines-3 Ways for Detecting and Correcting. In recent years, researchers have. and Mosle, H. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. ResourcesTo study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. 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. In. This reduced thickness of the frozen skin further enhances the visual appeal of the. Meld and knit lines are actually both different types of weld lines. 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. Causes. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 Fig. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. th INTRODUCTION Injection molding is one of the most 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. T. The weld line in an injection molding product can significantly impact the strength and durability of the last part [12] [13][14][15]. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. 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. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. From Understanding Weld-line Integrity by Sabic Innovative Plastics, p. A weld line is a visible seam where two areas of the molten plastic meet. . What causes them? The primary cause is weak bondage between two or more flow fronts. . 2. when two or more melt flow fronts contact each other immediately after the cooling process. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. Weld line. Here are some strategies. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. The injection molding simulation software used offers a method for the detection of weld lines that has shown to be only reliable for the detection of stagnating weld lines. Cited by (41) Effect of mould surface roughness adjustments to increase the flow path length in the injection moulding process. Weld lines. 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. Meld and knit lines are actually both different types of weld lines. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. They decrease the. Many researchers had emerged with several. 3 and 53. 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. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Siemens PLM Software. A weld line is a mark left on the surface of a plastic injected molded part. This study examines the impact of injection parameters on the weld line strength of the polyamide 6 and 30% fiberglass (PA6 + 30% FG) composite samples. Weld Line defect analysis, the most common of many defects in injection moulding products. The injection molding gate generates heat by dissipation. <Materials> Pre-dry thoroughly. reinforcement type and amount in nylon 6/6. 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. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. This failure causes the product to be damaged during use. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. 5. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. Xie L, Ziegmann G (2008) A visual mold with variotherm system for weld line studying micro injection molding. Adjust the design for the flow pattern to be a single source flow. Minimize the use of release agent. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. 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. are very minimum. Fisa et al. The weld line refers to the process in which the liquid material is divided into two or more flows in the cavity during the injection process and merged together after a period of time [51,77,78,79]. Zhao, X. In recent years new methods for quality prediction and optimization of the injection molding process have been proposed and applied. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 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. Ada berbagai penyebab mengapa weld line bisa muncul pada permukaan produk plastik. Sink Marks Cause 1: Incorrect Melt Temperature. 005 0. The Solutions for Poor Welding Lines. Penyebab Weld Line. Alloys. Characteristic: Basically, there are PA6 AND PA66(Nylon 6 or Nylon 66), Nylon has tenacious and wearable, self-lubricious and smooth characteristics with non-toxic and antibiosis and high water absorbability. Park et al. When an external load is applied to a weld line region, the part’s potential for mechanical failure is increased. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. To prevent weld lines, increase the pressure and temperature. The parts are molded flat and are slightly stressed once installed in an arced position, but not excessively. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Crack growth behavior. Three terms that often get mixed up are weld, meld, and knit lines. 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. 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. [ 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. g. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. The graph shows clearly how an increasing cavity temperature correlates with a reduction in the weld lines. The gate vestige for injection molding is usually narrow. on conventional reciprocating screw injection molding machines using molding practices standard for filled engineering thermoplastics . <Materials> Pre-dry thoroughly. This paper presents the. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. ชิ้นงานเกิดเป็นเส้นรอยประสาน Weld line. Just check out some of it on the above lists. If so, look for an alternative 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. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. JENIS-JENIS DEFECT (CACAT) PADA PRODUK INJECTION MOLDING PT. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. The thermo-rheological findings were used to investigate the sources of weld line weakness. Gate blush, 4. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. Avient’s Zachary Alderman shares practical tips on designing and injection molding parts utilizing short-fiber reinforcements. Which means engineers need to know how to account for this phenomenon in an efficient way. a) Multi-fiber connector micro injection molding simulation b) 3D simulation of micro gear with 150µm diameter for weld line position prediction c) 3D micro injection molding filling simulation of micro gear with 180µm diameter Fig. Vertical Plastic Injection Molding Machine [10, 11, 12] 2. 1. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. Sink marks, 2. A visible weld line is observed, due to a combina-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. Ideally, the resin flow will split into two flow fronts to pass around the obstruction and then recombine into a single flow front. Bubbles are caused by melting flow fronts colliding in a mold cavity. Plastic Rapid Injection Molding is popular not only in low volume manufacturing but also in large quantities molding, it is the most common way to manufacture plastic parts. The injection molding process can be optimized to maximize weld line strength by increasing. Weld line Weld line dikatakan ketika dua atau lebih aliran lelehan depan. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 2. 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. One common issue that frequently arises during injection molding is the formation of weld lines. Stagnant weld lines are formed when melt streams meet head-on. Poor weld line Ⅰ. Some of the approaches include the application of machine learning methods (Chen 2008; Manjunath and Krishna 2012; Kuo et al. (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. Known also as knit lines and. In spite of the symmetry of the molding the formed weld line was not straight, due to a slight unbalance of the two injection gates. 21: Weld line failure caused by hoop stresses. 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. 666 Azieatul Azrin Dzulkipli and M. Investigate for potential contamination. [ 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. Steven. Meld and knit lines are actually both different types of weld lines. Clamping unit berfungsi untuk memegang dan mengatur gerakan mold unit, serta gerakan ejector saat melepas benda dari molding unit, pada clamping unit lah kita bisa mengatur berapa panjang gerakan molding saat dibuka dan seberapa panjang ejector harus bergerak. The occurrence of a weld line means a significant problem both aesthetically and mechanically in the design of injection moulded parts. 2012. Mold. We'll show you how. Which means engineers need to know how to account for this phenomenon in an efficient way. The Solutions for Poor Welding Lines. If the injection molding speed is too slow, however, there may be an insufficient filling of the mold. This study addresses the effects of injection molding weld line on the fatigue crack resistance of commercial CPVC in the temperature range of −10 to 70 °C. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. Inadequate back pressure. Munich, Germany: Carl Hanser Verlag, 1994. 1. This can allow the. Flow-induced filler orientation and weld lines are un-avoidable facets of the injection molding process. When two or more strands of molten plastics meet in the mold, a weld. ing weld line properties of injection molded thermo-. In our DFM report, we will analyze the possible weld lines. A tensile test specimen mold, which allows cavity thickness varying from 2. (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. Therefore, it is recommended to do a moldflow study prior to the mold being built. Various measures are taken at production sites to address these problems. Injection moulding (U. 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. (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. ” Another. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. – Use generous and even. ac. To respond to poor plasticization and uneven melt temperature, the molding cycle can be extended to make. Physics. [1-2] investigated the weld line zone of injection molded glass-fiber-filled polypropylene (PP) composites. 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.