4. In an injection molding process, a weld-line forms when two flow fronts meet each other. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. These are preferred over weld lines as they will normally result in improved cosmetics and structure. The effects of fiber concentration has been studied in detail. Mobile 0813; Shinko Sellbic Co. S. 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. . If you turn on the spigot to a garden hose, you will hear a hissing sound at the nozzle end for the first few seconds. 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. They occur when melt flow fronts collide in a mold cavity. Poor weld line Ⅰ. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. Its appearance can be improved by adjusting parameters. This leads to a better molecular chain entanglement, which in turn creates a better weld. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. 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. CrossRef View in Scopus Google Scholar [17] G. 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. Injection molding is one of the most established and well-known methods of plastic processing. 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. Gambar 2. 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. Google Scholar | Crossref | ISI. 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 can allow the. . Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. 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]. 1. Weld lines are a kind of Achilles heel of plastics. Fiber content dependence on. That helps. That’s the air escaping out of the nozzle until the hose is full of pressurized water. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. (3) Adjust the temperature of the barrel and nozzle: the viscosity. 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. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. Thoroughly clean molding machine cylinders. 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 main types of injection molding defects are: 1. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber. To prevent weld lines, increase the pressure and temperature. To respond to poor plasticization and uneven melt temperature, the molding cycle can be extended to make. 1. A weld line can also be called a knit line. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. 7 of the reference. Weld Lines. 3. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. (2) Causes & Countermeasures (See the table below) *Note: Flash also tends to occur when the injection pressure/speed are too high, but molding time is too long and mold temperature is too low. ABS is a commonly used plastic in injection molding due to its excellent mechanical properties and chemical resistance. If there’s too much mold release, you may require a higher pressure to push it through the machine. Weld lines are also known as knit lines. 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. Causes. Interestingly, these materials have been shown to outperform long fiber thermoplastic (LFT) composites (in. This study focuses on the analysis of fill time by optimizing the injection molding parameters to reduce the defects that are always found on the plastics part such as poor weld line and part not. Materials Science. They decrease the. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. In this work, the weldline strength of injection molded short-glass-fiber reinforced polycarbonate was derived by an analytical method of modified rule-of-mixtures as a function of the area fraction between skin and core layers. 030 0. Injection Molding Glossary; Weld Lines; Weld Lines. Fig. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. Machine Shot Capacity – The maximum volume of resin that can be injected in a single stroke of the injection machine. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. Meld and knit lines are actually both different types of weld lines. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. when two or more melt flow fronts contact each other immediately after the cooling process. The formation of weld lines and their location along the flow path is a well-studied phenomenon in conventional injection molding; however, only a few papers are devoted to micro-injection molding [11,13,14,15,16]. Sequential valve gate technology. Mold flow analysis can predict the location of weld lines. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Micro injection molded polymeric parts coated with functional thin films/layers show off the promising applications in microsystems area. This study focus on the. 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. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Or, the part where the weld line is produced shall. 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. Flow-induced filler orientation and weld lines are un-avoidable facets of the injection molding process. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. Valve gates also make weld lines less of. Learn more about ABS injection molding here. It is important to investigate the weld line because the weld line area can. One common issue that frequently arises during injection molding is the formation of weld lines. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. This article will introduce you the usage, types, and advantages of the Sequence Injection Timer. Injection molding could be applied with many polymer materials, such as. Zhao, X. For this purpose, the width of the weld line calculated by Sigmasoft is. See moreIncreasing the temperature of the mold or plastic material. ” Another. 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. 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. 000 0. This paper presents the. + Increase mold temp, or materials’ temp, or holding pressure. These potential causes include: Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Expand. When two or more strands of molten plastics meet in the mold, a weld. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. ”Weld Lines in a plastic cover. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Crack growth behavior. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. 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. 2-1. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. After that, the compounds were injection-molded into tensile samples with and without weld lines to. (3-1) Increasing the Resin Temperature at the Weld Line Section. In the present study, Moldflow® software is applied to simulate the injection molding of automobile instrument light guide bracket and optimize the injection gate position. T he decreased gloss level at the position of. . Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. In this regard, Taguchi orthogonal experimental design is adopted, and five processing parameters, the mold temperature, melt temperature, cooling time, packing. Polyamide 6 (Lanxess, Durethan B 30 S 000000, non-reinforced, ISO 1874-PA 6, GR, 14-030, Cologne, Germany) was used for this experiment. <1> As illustrated in Figure 4, the existence of. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Int J Adv Manuf Technol 52:131–141. 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. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Kondisi ini juga bisa menandakan bahwa mesin injection. . Gate position in injection mold. 2. Munich, Germany: Carl Hanser Verlag, 1994. Investigate for potential contamination. 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. Berikut beberapa di antaranya: 1. 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. in the cavity of the injection mold. Processing OptimizationReduced frozen skin thickness: High injection speeds also contribute to a thinner frozen skin at the weld line. Fellahi et al. The next type of injection molding defect is ‘Weld Lines’. 3 cc/sec, the weld lines decrease over temperatures up to 150 C, while at higher volumetric injection flow rates of 43. As the plastic flows through the mold it. When this fails to happen correctly, a weld line defect occurs. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. Mechanical properties of the weld line defect in micro injection molding for various nano filled polypropylene composites. A micro-photography study on the cross-section of the weld-line was also carried out. Adjust the position of the gate and include a venting slot. Published 5 July 2019. This model provides the necessary information. Weld lines are a common imperfection to be found in most plastic injected molded parts. 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. 32–24. 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. A weld line is often unavoidable. Save. Adjust the design for the flow pattern to be a single source flow. Effects of mold temperature and pressure on shrinkage 0. 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. In the heating step, the heatingOverview of the injection molding process. Injection molding can be performed with only one of these materials like glass, plastics, etc. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). 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. Mechanical properties of the weld line defect in micro injection molding for various nano filled polypropylene composites. Weld lines can lower the integrity of the part. The weld line in an injection molding product can significantly impact the strength and durability of the last part [12] [13][14][15]. 2011; 509 (2):226–233. 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. The gate is the critical bridge between the runners (the channels through which the molten plastic travels) and the actual mold. Star Rapid offers tips and tricks to improve your prototypes and production parts. Problem: Weld lines are formed when plastic resin is forced around an obstruction in a mold tool and reforms on the side opposite the gate. The weld line’s strength is reduced when. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPEffects of mold temperature and pressure on shrinkage 0. Nozzle – The nozzle is at the end of the barrel and contacts the injection mold. To resolve this issue, rapid heat cycle molding (RHCM) has attracted attention as an innovative PIM technology. Its appearance can be improved by adjusting parameters. Weld line strength is influenced by the temperature at which the weld line is formed and the pressure exerted on the weld until the part freezes, (pressure is 0 at the weld line). Injection molding is nothing without molds. [ 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. Joe Henz is a chemical engineer with 30 years of experience in the plastics industry, primarily with GE. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole. Abstract. Consequently, it causes viscous dissipation which leads to the generation of heat. Controlling injection molding weld lines with good design and process control. 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 injected. It is possible to pre. Wavy lines are another feature of weld lines. 22: Weld line formation when melt splits around core pins. Burn Marks. Procedia Mater Sci 2014; 3: 2048–2053. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. Flash. 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. Email him at jhenz@polymer-center. In this experiment, several ejector. Procedia Mater Sci 2014; 3: 2048–2053. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. injection molded pipe-fittings with and without weld line. This is a video excerpt from our Problems & Solutions Course - Weldlines. 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. Mold vents should function the same way. 4. But the unfavorable and unavoidable defect of weld line in micro injection molding part leads to detrimental mechanical and surface properties. 000 0. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. 8. 2. 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 line strength is important in blow molding as well as injection molding. If the injection molding speed is too slow, however, there may be an insufficient filling of the mold. The Solutions for Poor Welding Lines. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. The optimum injection molding parameters to manufacture the product was determined by . Weld line section presents notch or gloss difference. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. Weld lines Weld lines are weak areas formed by converging flows of plastic that can lead to mechanical part failure if not properly accounted for in the part design. Weld line. In injection molding, it is often important to maintain consistent color throughout the part. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Weld line, 5. 1. Methodology. , 509 (2) (2011), pp. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. 9 – Over Packing. In. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld. 005 0. We'll show you how. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. Introduction. During the plastic injection molding process, one of the biggest challenges is. 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. 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]. For thick-walled parts, slow injection rates result in more uniform polymer distribution . Just check out some of it on the above lists. 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. Here are some strategies. g. 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 can weaken the strength of the part, and they can also be unsightly. Flashes, 3. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. Increase the injection speed to reduce the amount of cooling happening in the mold. 22 shows how the weld lines are formed when the melt splits around core pins during the injection molding process. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. weld lines in infill analysis of injection molding simulation was observed [5]. 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 is a weak area which reduces the strength of the part locally. As a result, the portion has a faint, perhaps undetectable line. The problem with ‘weld lines. To increase the sustainability of the process, determinative parameters and their effects should be examined. Injection pressure or. As such, optimizing mold designs should always be incorporated in your production model. 2-1. org or visit 80-ton Victor injection molding machine, equipped with an accumulator capable of delivering maximum flow rate of 138 cm 3 /s and providing maximum injection pressure of 210 MPa, is utilized for experiments. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. In this experiment, several ejector. 2. In this blog post, we will explore the causes of weld lines in. technical ulletin SPECIALTY POLYME RS Design and Production of Injection Molding Tools. 666 Azieatul Azrin Dzulkipli and M. The weld line length was selected as part of the quality index to investigate the effects of gate location on weld. 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. 2007; Lotti 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. replication and poor weld line strength . box, along the region of weld line formation (wc, wm, we and wl) and away from the weld line, in a radial position along the flow direction (R), as shown in Figure 2. As compared to a weld line, the flow fronts come together at less than 135 degrees. In this lesson we will focus on the meld and weld lines. Weld-line is a weak area which reduces the strength of the part locally. The Influence of Knit-lines on the Tensile Properties of Injection Molded Parts, Polymer Engineering and Science, 23(10): 591-596. Ideally, the resin flow will split into two flow fronts to pass around the obstruction and then recombine into a single flow front. The microstructure of weld lines is clearly observed from the micrographs. 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 line reduction is one of the major concerns in plastic injection molding (PIM) that results in high surface appearance and high strength of a plastic product. For example, filled resins and ABS are more likely to. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPAbstract. Various measures are taken at production sites to address these problems. In addition a weld line can be moved to an area where it is less visible. 5. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Figure 2. Adding vents, using overflows, or using porous metal. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. In this paper, aiming at the problem of weld line defects in the injec- tion process of a key phone panel, the injection process is optimized by using Moldflow and drop simulation. 015 0. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. According to the weld line distribution map of six gate schemes shown in . 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. Gava and co-workers implemented an investigation devoted to the de-weld lines in injection molded thermoplastic composites. What causes them? The primary cause is weak bondage between two or more flow fronts. Wang, G. Int J Adv Manuf Technol:1–11In addition to the weld line, the exposure of fibers on the molded product surface results in a rough surface, which degrades the appearance of the product. Minimize the use of release agent. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. The impact behavior of weld-lines in injection molding. Vertical Plastic Injection Molding Machine [10, 11, 12] 2. 020 0. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms. Weld lines have been one of the common defects puzzling the injection molding industry. Weld line existence reduces the material strength; however, its. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. The following are the conclusion drawn from the present research: 1. ”. Weld line formation in the injection molding process occurs. 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 this study, one injection mold. 010 0. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. 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 formation of weld lines and their location along the flow path is a well-studied phenomenon in conventional injection molding; however, only a few papers are devoted to micro-injection molding [11,13,14,15,16]. It provides scientific basis for designers toWeld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. If the different flow fronts have cooled. 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. 226-233. Reposition gates and runners to allow resin to flow around the obstruction from a. This defect occurs due to the temperature and pressure not being high enough, causing premature solidification. 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. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. 6. A visual mold with variotherm system for weld line study in micro injection molding. 1007/s00397-003-0339-2 ORIGINAL CONTRIBUTIONCauses and Remedies of Sink Marks In Injection Molding. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. A meld line is defined as the re-merging of two flow fronts. Change the gate locations. industry, to deliver intuitive injection mold-ing simulations embedded in NX. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Consequently, weld regions have been observed to have inferior mechanical properties compared to the bulk. Its design significantly impacts the final product’s appearance, strength, and functionality, making it crucial for manufacturers to understand its intricacies and variations thoroughly. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. Injection moulding (U. 4If the injection gate is not properly designed, it can cause the formation of defects like sink-mark, warpage, short shot, weld-line, air traps, and other faults [15]. Xie L, Ziegmann G (2008) A visual mold with variotherm system for weld line studying micro injection molding. 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. Weld or knit lines result wherever two or more polymer flow fronts unite. 020 0. Increase the injection speed. The tensile stresses of the weld lines with ultrasonic functions are 8. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. 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 one of the plastic injection molding defects. 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. Since weldline in plastic injection molding (PIM) has an influence on not only the strength but also the surface appearance of a plastic product, it is preferable to reduce it as much as possible for high product quality. 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. [23, 24]. Again, consult with professionals as to how you could improve mold designs. Make the size of runner channel wider and/or shorter. 1% higher than the ones without ultrasonic assistant, which indicates that the weld line strength in micro injection molding can be well reinforced by the ultrasonic oscillation due to the fact that ultrasonic oscillation induces better diffusion among the melting. molding Æ Thermoplastics Æ Weld line Æ Simulation Rheol Acta (2004) 43: 240–245 DOI 10. Jiquan Li, Taidong Li, +1 author. Weld line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. An injection molding processor who can analyze the process from the plastics point of view, can quickly solve any molding problem, regardless of the machine or plastic type. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm.