Weld Line Factors for Thermoplastics. 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. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. The four sets of plaques are produced by changing the magnitude of packing pressure equal to 60% of filling pressure, with increment of 20% up to 120% of filling. Injected plates were generated using a double-gated mold under four different process conditions. 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. 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. Three terms that often get mixed up are weld, meld, and knit lines. Bubbles are caused by melting flow fronts colliding in a mold cavity. weld lines in injection molded thermoplastic composites. Figure 2. weld lines in infill analysis of injection molding simulation was observed [5]. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. You will have to confirm them before tooling. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. 4. Change the flow pattern to a single-source flow. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. Weld-line is a weak area. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. investigated the impact of injection molding parameters on weld line formation and strength reduction. 010 0. Polymers 2023, 15, 2440 3 of 21. The resulting defects don’t stop at flash only. 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. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. 453-455. Here we are looking at most common part defect that can come from injection molding called weld line. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. 2. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are. 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. Weld Line Phenomenon: Surface defect in which the weld, or the part where the flows of melted plastic meet inside the mold, shows up on the surface as a groove or pattern. Weld lines are a common occurrence in injection molding that affects the overall quality and strength of a finished product. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. When this fails to happen correctly, a weld line defect occurs. Heating and cooling mould systems, which cost extremely high, are a typical technology to prevent the weld-line. 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. Meld and knit lines are actually both different types of weld lines. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. They decrease the. Weld. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. 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. are very minimum. These lines. Thus, it is important to understand (i) if the melt is able to fill the cavity up to the weld line location, (ii) where the weld line forms, and (iii) if the weld line is a cold or flowing one. A weld line is often unavoidable. Our injection molding company is explaining what these imperfections are, why they can compromise. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. In a weld line, reinforcement fibers. Carefully consider all the relevant aspects of the mold design specification before. 015 0. 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 relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. Injection pressures too high Reduce pressure . Kobayashi et al. In this study, we apply the technique of SAW to explore the acoustic properties near injection-weld lines by comparing the velocity of (V R) in locations close to and locations distant from the weldAmong defects of injection molding parts, weld lines are the most common defect. 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. 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. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. 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. ” Another. Injected plates were generated using a double-gated mold under four different process conditions. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. Weld lines have been one of the common defects puzzling the injection molding industry. G. Expand. To explore the formation of weld lines in injection molding, a. In conclusion, reducing weld lines in injection molding requires a combination of factors, including adjusting the melt temperature, injection speed, pressure, and gate size, as well as using a hot runner system, modifying the part design, using a different material, reducing the wall thickness, using a mold release agent, and working. (a) (b) Figure 1. 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. As a result, the portion has a faint, perhaps undetectable line. Plastic Injection Molding Process. M. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Ni. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. 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. 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. Increasing the temperature of the mold or plastic material. Increase the injection speed. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). Weld Lines. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. 298 µm and the weld line on the heated region was almost eliminated with the aid of induction heating. Fisa et al. An obstruction such as a core pin or holes will split the material flow and cause a weld line issue to form on the other side. So today we are going to take a look at the five most common defects in injection molding and their solutions. 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. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. 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. 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. 2004; To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Adjust the design for the flow pattern to be a single source flow. Causes and Remedies of Sink Marks In Injection Molding. Weld lines defects are formed when two flow fronts are merged together. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. The need to minimize fiber breakage, plus the higher viscosity of materials with. Participating in DFM and mold flow analysis is a good way to achieve this. [ 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. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. 2. Weld lines are common defects in injection-molded plastic parts that occur when two flow fronts of molten plastic meet and fuse together during the molding process. enough to each other to avoid weld line issues. 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. 18/06/2021. The weld line is then created with a higher flow front temperature and is packed with more pressure. This may require higher melt temperature or lower injection speed . The flow of the material in the injection mould takes place through the gate. Reduce the amount of release agents. S. But none of the current packages can predict weld lines’ properties qualitatively. (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. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. when two or more melt flow fronts contact each other immediately after the cooling process. 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. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. 7 of the reference. Effects of mold temperature and pressure on shrinkage 0. 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. Strength measurements should be made to. (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. A. Wavy lines are another feature of weld lines. Redesign the mold to. with a characteristic length χ 0 =0. Short shots. Blistering 4. (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. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Weld lines may appear like seams or scratches, but that is not what they are. This customary mark is caused by differential rates of cooling in the resin where. In injection molding, it is often important to maintain consistent color throughout the part. In injection molding, a V-notch-shaped weld line is generated in the melt front meeting area. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. This study describes how the weld line was formed on the part. The holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. analyzed the heat transfer during heating and cooling phases of RHCM process. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. Injection molding of large/complicated products are usually prepared by multiple compounds, which produces weldlines once the melt fronts are joined by impingement flow. This occurs mainly in the presence of barriers that divide the melt flow in. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. Weld lines can appear on the surface of a molded part where the molten material has converged after splitting off into two or more directions in a mold. 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. Abstract. These processing changes will increase chain. Flow LinesThe most simple design modification for eliminating the weakening effect of a weld line is to increase the wall thickness in the weld line zone (Figure 4). Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. (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. Quality concerns in injection-molded materials can vary fr. 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. In this paper, a weld line factor (W-L factor) was adopted to. This paper presents the. ), with different mould surface finishes (polished, fine eroded, rough. (2011) and Fig. The weld lines are an integral part of plastic injection molding and can seldom be prevented, even by specifically planning the mold with inserts for holes or the like. In the feeding system of injection molding, the flow of plastic melt begins from the nozzle of the injection molding machine, traverses through the sprue and runners, and ultimately reaches the mold gate(you can call it the injection molding gate as well)—the entry point to the mold cavity. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. Maintain a holding pressure that is no more than 1/2 the. • Move injection locations to make flow fronts meet more obliquely, turning the weld line into a meld line. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . 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. Other possible causes include: Low mold or material temperature; Insufficient holding time or. In narrow fields, a limited amount of molten liquid can solidify and block the flow. The thermo. Adding vents, using overflows, or using porous metal. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Flow Lines. 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. They have their origins in material choice, part design, tooling, and processingIncrease the mold temperature and smooth out any sharp corners or turns in the mold to facilitate even melt flow. when two or more melt flow fronts contact each other immediately after the cooling process. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. If weld lines are unavoidable due to multiple gates in a moulding, they should be positioned in the non-critical region. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. 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. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the. Founder, Injection Molding Solutions. Flash. 2. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. If the melt temperature is low or the injection speed and pressure are low, you may end up with a more pronounced weld line. 22 shows how the weld lines are formed when the melt splits around core pins during the injection molding process. The welding angle can be used to differentiate weld lines and meld lines. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. Weld lines in design for manufacture. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Figure 1 below shows the development of a weld line. The Difference Between Knit and Meld Lines–and Why It Matters. In our DFM report, we will analyze the possible weld lines. 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. Weld lines in injection molding are frequently unavoidable. 4. This paper presents the. The simulated cold weld line length is consistent with the experimental one when a 115 °C mold temperature is adopted; with lower mold temperatures, the simulated lengths are smaller than the experimental ones—in accordance with the literature on the conventional injection molding process [26,27]—probably because of the definition adopted. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Edge Gates. From Fig. 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. When the two such melt flows. 2. Fig 13:- Detailed view of weld lines. demanding injection molding and end-use requirements. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. 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. The second technique, cascade injection moulding, can produce parts free from weld lines. Injection Molding Know How. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. Fig. In addition a weld line can be moved to an area where it is less visible. 9 – Over Packing. Root causes Many factors—including processing conditions, material, part design and mold design—can influence the visibility and strength of a weld line. Weld-line is a weak area which reduces the strength of the part locally. There are several factors that can contribute to the formation of weld lines, including: Part design: The design of the part can impact the flow of the material and the likelihood of weld lines forming. In the 1947 book, Injection Molding of Plastics, the late Dr. The edge gate is the most popular and straightforward injection mold gate design. Weld lines have been one of the common defects puzzling the injection molding industry. Effect of process parameters on the relative weld line strength From injection molding practice and literature, 1, 3,4 it is generally accepted that: if a weld line forms before the filling is. This customary mark is caused by differential rates of cooling in the resin where. Wavy lines are another feature of weld lines. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. Alter the mold design. This reduced thickness of the frozen skin further enhances the visual appeal of the. 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 spite of its cosmetic attributes, a bad knit line can significantly. Proceedings of ANTEC (2000), pp. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Sink MarksWeld lines, also known as knit lines, are a common defect in injection molding where two or more flow fronts of molten plastic meet but don’t properly fuse together. When the polymer resin is injected into a mold, it flows through all portions of the mold cavity. the meeting angle by optimizing variation over time in the cavity. 5. Meld and knit lines are actually both different types of weld lines. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. Weld lines have been one of the common defects puzzling the injection molding industry. John Bozzelli. Controlling the mold’s temperature could also minimize the weld line’s effects. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near. Gate location should set to avoid weld lines, keep clean of the important position of the products,. injection molding. 5. + Move gate (to where it is not visible). 2) Vents in an injection mold should let the air out, but not the liquid plastic. – Use generous and even. 1. Ejector System (Pötsch, 1995) . 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. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Park et al. Here are some ways to avoid. 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]. The Problems & Solutions course is designed to train injection molding personnel in. As compared to a weld line, the flow fronts come together at less than 135 degrees. See moreEquipment. If the plastic encounters a pin or other obstruction, the plastic flow front must split to form two flow fronts to go around the pin. 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 gates. when two or more melt flow fronts contact each other immediately after the cooling process. The conditions are temperature, injection speed, and injection pressure. Possible Sources of Weld/Knit Lines: Temperature from the injection molding machine, runners, and/or the mold itself in order to ensure the plastic resin flows properly;Weld line is one of the plastic injection molding defects. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. [ 18 - 21 ] In addition, the effects. 6. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near. gasket seal leakage where the weld line crosses a gasket. , less than 0. When two or more streams of plastic meet and fuse. Micro-injection molding (µIM) is a widespread process for the production of plastic parts with at least one dimension, or feature, in the microscale (conventionally below 500 µm). Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. * 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). Process. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. Place a vent in the weld line area to remove the entrapped air. 2021年4月23日 / by admin. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. The weld line’s strength is reduced when. avoid weld lines, and facilitate smooth. One method is the local te mpering of the affected areas to prevent weld lines. In this experiment, several ejector. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 10(a) (please see Fig. [ 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. 000 0. Int J Adv Manuf Technol 52:131–141. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Weld line. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. Thereby creating localized pressure within the mold. 1. The plaques are prepared out of 30% glass-filled Polyamide 6 material. In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. 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. Islyn Thomas summarized the need for a particular vent location better than I ever could. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. 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]. 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. You can choose material of low viscosity and can increase the injection pressure. Poor mold spot Spot mold to ensure fit and vent depths at ~0 . GlossFlow-induced fiber orientation and weld lines are com-mon features of the injection molding process. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld lines may occur depending on the product shape and gate positions. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Vibration assisted injection molding. Figure 1a illustrates how the weld line is produced when. • Optimize the design of the runner system. Weld lines cause significant reject rates and are a common problem that all molders face. To elimi- nate weld lines, you can enlarge shrinkage. Thus, it is important to understand (i). Weld line is formed when two different melt flows converge, as illustrated in Fig. 5. Flow lines. The thermo-rheological findings were used to investigate the sources of weld line weakness. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Silver Streak. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. 000 0. 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. Weld line. You can locate the gate at the thick part of the injection molding to prevent air pockets. 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. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. 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. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. A meld line occurs when two moving melt fronts converge and flow parallel to each other. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. In this study, polypropylene (PP) was chosen as the processing material and a micro dog-bone tensile test sample was selected as the objective part. Wang. The weld line can either be a minor cosmetic issue or potentially bad enough to negatively impact the part's strength. The next type of injection molding defect is ‘Weld Lines’. consideration in gate location. 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. You can expect a mold shrinkage percentage of. Which means engineers need to know how to account for this phenomenon in an efficient way. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. In. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. 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. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. In some cases, a weld line can also cause a loss of strength and impact resistance. Voids and bubbles, 6. The Factors that Cause Weld Line in Injection molding Pressure. 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. ) . Try to gradually raise the mold temperature and barrel temperature. 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. Jiquan Li, Taidong Li, +1 author. Dischler, D. Weld line formation in the injection molding process occurs. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. The micro tensile part was prepared by the double gate injection. This happens when the molten plastic is injected into the mold cavity and flows around an obstacle such as a pin, hole, or protrusion, and then comes back together. In this paper, a kind of polypropylene (PP) foam plastic parts with special weld lines were obtained by core-back foam injection molding with chemical blowing agent. Venting at Weld Lines. 2-1. The wheel has to be gated at three places on the hub and. Sink Marks Cause 2: Low Pack and Hold time. According to the characteristics. Weld Lines. The results of. Azieatul Azrin Dzulkipli and M. Materials Science. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at.