A knit line may be unnoticeable or may look like a crack. are very minimum. 2. Weld lines are among the most critical structural defects in parts made by the injection molding of fiber-reinforced thermoplastics, explained Sirmax in a press release. Weld Line defect analysis, the most common of many defects in injection moulding products. The specific method is that when the product is just filled and filled in the cavity, the insert. 2. Weld line and warping are two critical defects for injection-moulded part. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. ac. Sink Marks Cause 4: High Mold Temperature. Vacuum voids. 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. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. The Problems & Solutions course is designed to train injection molding personnel in. การแก้ไข ชิ้นงานจุดที่เกิดความอ่อนแอบริเวณ weld line คือต้องใช้ความเร็วในการฉีดต่ำในจุด. 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. In injection molding weld lines are formed whenever two flow fronts are joined. 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. ”. Weld line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. 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. 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. Maintain a holding pressure that is no more than 1/2 the. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. 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. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Silver Streak. ” Another. To elimi- nate weld lines, you can enlarge shrinkage. (1) Increase the injection pressure and prolong the injection time. 1. 1. and Mosle, H. weld lines in infill analysis of injection molding simulation was observed [5]. So today we are going to take a look at the five most common defects in injection molding and their solutions. Gate location should set to avoid weld lines, keep clean of the important position of the products,. Improvement of weld line strength in injection molded FRTP articles. Blistering 4. In other words, weld lines reduce the mechanical properties of the product. Injection molding, polypropylene, talc. Weld lines may appear like seams or scratches, but that is not what they are. That helps. 5. (3) Adjust the temperature of the barrel and nozzle: the viscosity. As the polymer resin is injected into a mold, it flows through all parts of the mold. Yes, it does help, for two reasons: Often the weld line traps air and the ‘dump’ acts as a vent to allow the air to escape. Instead, a line that looks like a seam forms. [ 18 - 21 ] In addition, the effects. Weld lines, generated during injection molding, can significantly reduce the mechanical performance of structures. 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. Some of these are listed below: Plastic warpage. 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. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. Weld lines are the most common defects in injection molded products. This study focus on the formation of. They occur when melt flow fronts collide in a mold cavity. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. 2. The edge gate is the most popular and straightforward injection mold gate design. Other possible causes include: Low mold or material temperature; Insufficient holding time or. Weld line location. This occurs either due to injection through multiple gates or as a conse-รอยประสานของเนื้อพลาสติก Weld line ตอนที่1. The thermo. 4. Double push filling method. In addition a weld line can be moved to an area where it is less visible. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. These lines occur when two or more flow fronts meet and fuse together, resulting in a visible seam on the molded part. 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. Weld lines are visible lines or seams formed when molten plastic flow fronts meet and fuse together, often due to obstacles or flow interruptions in the. Abstract. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. This failure causes the product to be damaged during use. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. Or increase the number of gates. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. 2. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. Proceedings of ANTEC (2000) Google Scholar [9] S. As the injection process continues, the two separated melt fronts meet again along the longitudinal section of the plate forming a weld line. Weld lines are a kind of Achilles heel of plastics. distribution [4]. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. One method is the local te mpering of the affected areas to prevent weld lines. 2. Weld lines have been one of the common defects puzzling the injection molding industry. 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. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. In this paper, two different injection molding tests were completed. Gava and co-workers implemented an investigation devoted to the de-Injection-mold weld lines may or may not be easily identified by naked eye or straightforward optical microscopy. Proper venting is also required to ensure good weld-line quality. This model provides the necessary information. Proceedings of ANTEC (2000), pp. Wang et al. Molding Equipment. This can occur when a polymer flow splits to go around an interruption (e. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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. In this paper, a weld line factor (W-L factor) was adopted to describe the. In this study, epoxy molding compounds (EMC) filled with glass beads were fabricated with a twin-screw-extruder (TSE) and tempered before further processing to generate different degrees of cross-linking (0–15%) in the compounds. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. Consequently, it causes viscous dissipation which leads to the generation of heat. Insufficient plasticizing ability of injection molding machine. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Weld line defects in injection molding is a line or lines on the part surface that caused the part looking ugly or cuased part lifetime, or even broken easily. Weld Lines-3 Ways for Detecting and Correcting. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. Introduction Weld lines are formed during mold filling whenever two separated melt streams recombine. Vibration assisted injection molding. Solving one problem can introduce other problems to the injection molding process. 2017-01-0481. 2. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPThree terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Weld line is formed when two different melt flows converge, as illustrated in Fig. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. When an external load is applied to a weld line region, the part’s potential for mechanical failure is increased. 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. 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. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. To explore the formation of weld lines in injection molding, a. 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 this study, the effects of injection temperature, injection pressure, and fiber cont. ). <Materials>Injection moulding (U. In injection molding, it is often important to maintain consistent color throughout the part. 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. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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. Increase the melting temperature. 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]. Weld-line is a weak area which reduces the strength of the part locally. 010 0. Typical injection molding processing temperatures of TPU materials are as follows: IM Zone 60A to 75A 80A to 90A 95A to 75D Rear 315 – 40 ºF45 -370 75 400The weld line in an injection molding product can significantly impact the strength and durability of the last part [12] [13][14][15]. This customary mark is caused by differential rates of cooling in the resin where. If the different flow fronts have cooled. Weld lines are one of the typical quality issues of injection molded parts. The performance of weld lines in talc filled polypropylene box moldings produced with a. The literature on the formation of weld lines, and their consequences, is more abundant on the area of injection molding [5-12] than on extrusion [13]. the meeting angle by optimizing variation over time in the cavity. They found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in whichEffects of mold temperature and pressure on shrinkage 0. 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. In this case the two flow fronts will meet and. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. The goal is to create a uniform thickness and at the smallest (thinnest) level required. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. 2017-01-0481. Discoloration. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. when two or more melt flow fronts contact each other immediately after the cooling process. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. weld lines in injection molded thermoplastic composites. (2011) and 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. Sequential valve gate technology. 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. They. (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. The most common and one of the most challenging injection molding defects are weld and knit lines. The need to minimize fiber breakage, plus the higher viscosity of materials with. M. They appear on the surface of injection molded parts like lines. 5. Weld lines represent the region where two separated melt fronts recombine. Gate blush, 4. 7 of the reference. Optimizing the Injection Parameters. 1. To explore the formation of weld lines in injection molding, a. During the plastic injection molding process, one of the biggest challenges is. Therefore, it is recommended to do a moldflow study prior to the mold being built. 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 have been one of the common defects puzzling the injection molding industry. Gates should be designed larger than normal and located to minimize weld line formation. Weld lines cause significant reject rates and are a common problem that all molders face. In some cases, a weld line can also cause a loss of strength and impact resistance. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Bubbles are caused by melting flow fronts colliding in a mold cavity. 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. In spite of its cosmetic attributes, a bad knit line can significantly. • Optimize the design of the runner system. By the reflection method and a high speed camera, the visual system can be used to record and observe the forming process of micro weld lines during the. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. In the first stage, the two part halves are injection molded and then, in a second process step outside of the molding machine, they are welded together. In an injection molding process, a weld-line forms when two flow fronts meet each other. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. Possible causes: Low temperature or fluidity of melted plastic during injection molding. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. A weld line can also be called a knit line. e. 453-455. 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. Criens, R. INJECTION MOULDING DEFECTS 1 DEFECTS 1. Injection molding weld lines where two or more flow fronts come together in the mold. Weld Line Occurrence in Plastic Injection Molded Parts Weld lines, also commonly known as knit lines, may be present in a plastic molded part depending on the partsí geometry. Increase the injection speed to reduce the amount of cooling happening in the mold. Besides, possibly it would be. 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). 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. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. 2004; To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. In an injection molding process, a weld-line forms when two flow fronts meet each other. Try to gradually raise the mold temperature and barrel temperature. Injection Molding Know How. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. In this lesson we will focus on the meld and weld lines. 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. Founder, Injection Molding Solutions. If the different flow fronts have cooled. In the above diagram, the converging flow fronts (indicated by red arrows. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Weld lines appear as a result of the flow of molten plastic during the injection molding process. 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. A weld line is often unavoidable. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. That’s the air escaping out of the nozzle until the hose is full of pressurized water. They become more critical when particulate fillers are compounded with the polymer. Molding calculation in Moldex3D: (а) melt front and weld line, (b). In a weld line, reinforcement fibers adopt an orthogonal orientation with respect to the filling direction, which results in a significant reduction in the strength and. Weld. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. 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. Weld lines defects are formed when two flow fronts are merged together. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. The second technique, cascade injection moulding, can produce parts free from weld lines. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. 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. Weld line section presents notch or gloss difference. Quality concerns in injection-molded materials can vary fr. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. gasket seal leakage where the weld line crosses a gasket. 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. Voids and bubbles, 6. Increase the injection speed. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. Weld line strength is important in blow molding as well as injection molding. Islyn Thomas summarized the need for a particular vent location better than I ever could. Int. 1. The solution to an internal part cracking problem is to change the packing pressure. There will be too many weld lines ; 6. 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. 22: Weld line formation when melt splits around core pins. 3. Google Scholar | Crossref | ISI. Burn Marks. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPAccording to the weld line distribution map of six gate schemes shown in . It forces out trapped air pockets and can prevent a vacuum void from occurring. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. Controlling the mold’s temperature could also minimize the weld line’s effects. 1. 6. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. The thermo-rheological findings were used to investigate the sources of weld line weakness. Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. This line does not normally impact the overall shape or dimensions of the item. Injected plates were generated using a double-gated mold under four different process conditions. Weld line, 5. The main runner and sub-runner are too thin. injection molding. Fig. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a mold. [ 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 hair-like weld line is the result of weak. In injection molding, a V-notch-shaped weld line is generated in the melt front meeting area. Streaks 3. The authors [5, 6] attempted to reduce the weld lines and clamping force of plastic injection moulding through numerical and experimental investigation, and discovered that the 3D cooling channel. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and. Int J Adv Manuf Technol 52:131–141. 030 0. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. 809-814. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. Typical injection molding processing temperatures of TPU materials are as follows: IM ZONE 60A TO 75A 80A TO 90A 95A TO 75D REAR 315 – 340 °F 345 – 370 °F 375 – 400 °FTo study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. In Fig. A visual mold with variotherm system for weld line study in micro injection molding. For multiple gate and complex part. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. Venting at Weld Lines. 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. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. 21: Weld line failure caused by hoop stresses. 9 – Over Packing. Experimental Setup 2. Flow-induced filler orientation and weld lines are un-avoidable facets of the injection molding process. Sink Marks Cause 3: Improper Pack or Hold Pressure. Three terms that often get mixed up in injection molding are weld, meld and knit lines. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. Introduction. Flow 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. Edge Gates. Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. 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. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. 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. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. 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. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. Mostly, this happens when two or more flow fronts do not “knit” during the injection molding process. Dischler, D. Don’t forget to eliminate entrapped air in the weld line injection molding; otherwise, it’ll create unfilled portions in your part design, causing more weakening. carried out to mass-produce molded products with complex shapes. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. One solution is to prevent the weld lines from forming in regions that are. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. In weak material bonding, they will appear as hair-like weld lines. It will degrade materials performance; 9. Therefore, the. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Tosello et al. The injection molding process can be optimized to maximize weld line strength by increasing mold and melt temperatures, and by increasing pack pressure at the weld line. The structure is more complex with longer molding cycle . Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Specifically, injection-mold lines are often associated with poor mechanical strength. A new kind of weld line was. (1) Increase the injection pressure and prolong the injection time. Kobayashi et al. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro. Remedies: Raise the temperature of the mold or molten plastic. View 08 DEFECTS & REMEDIES (61). 10. (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. 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 lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Increase the injection speed to reduce the amount of cooling happening in the mold. In many cases, you will also see that the part is hanging up on the core during ejection. G. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Which means engineers need to know how to account for this phenomenon in an efficient way. This study describes how the weld line was formed on the part. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. The next type of injection molding defect is ‘Weld Lines’. when two or more melt flow fronts contact each other immediately after the cooling process. The hair-like weld line is the. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. But none of the current packages can predict weld lines’ properties qualitatively. 10(a) (please see Fig. If the melt temperature is low or the injection speed and pressure are low, you may end up with a more pronounced weld line. Injection molding can be performed with only one of these. 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). In the present work, the micro specimens were investigated. You can expect a mold shrinkage percentage of. Flash. Bubbles are caused by melting flow fronts colliding in a mold cavity.