1 Mold In order to study the formation of weld lines, the mold cavities has been. This is where the melt fronts divided by an insert, such as a pin or a. Jiquan Li, Taidong Li, +1 author. The main runner and sub-runner are too thin. Too high barrel temperature ( abnormal temperature control, deviation of material performance, and increasing cycle time); 8. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. Bubbles are caused by melting flow fronts colliding in a mold cavity. * Corresponding author, e-mail: fengsjpc@ku. Weld line existence reduces the material strength; however, its demerit characteristics. 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. 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. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Wavy lines are another feature of weld lines. Bubbles are caused by melting flow fronts colliding in a mold cavity. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Remedies: Raise the temperature of the mold or molten plastic. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. The position, length, and angle of weld lines are dependent on the. Weld line. 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. Carefully consider all the relevant aspects of the mold design specification before. When two or more streams of plastic meet and fuse. Introduction. 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. 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. Improvement of weld line strength in injection molded FRTP articles. 5. In injection molding, it is often important to maintain consistent color throughout the part. The edge gate is the most popular and straightforward injection mold gate design. + Improve vent inside the mold. Reduce the amount of release agents. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. 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. When the two such melt flows. 2) Vents in an injection mold should let the air out, but not the liquid plastic. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 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. Ejector System (Pötsch, 1995) . Increase the injection speed. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 10 in Nguyen-Chung et al. Besides, possibly it would be. Change the flow pattern to a single-source flow. 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. The injection molding simulation software used offers a method for the detection of weld lines that has shown to be only reliable for the detection of stagnating weld lines. Melt temperature does effect the weld. Vibration assisted injection molding. Known also as knit lines and weld marks, weld lines are difficult to eliminate completely, especially if your injection molded part requires holes. Remedies: Raise the temperature of the mold or molten plastic. M. 7 of the reference. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. Mold vents should function the same way. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. 7 in Kobayashi et al. This is a video excerpt from our Problems & Solutions Course - Weldlines. (1983). That’s the air escaping out of the nozzle until the hose is full of pressurized water. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Increase the injection speed to reduce the amount of cooling happening in the mold. and Mosle, H. Weld lines appear as a result of the flow of molten plastic during the injection molding process. An evaluation model based on artificial neural network method. 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 line and warping are two critical defects for injection-moulded part. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. This study describes how the weld line was formed on the part. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. How Are They Formed? Molten plastic resin is injected into a mold cavity through an opening known as a gate. Better weld line quality was obtained by Huang. 2(a, b). Proper venting is also required to ensure good weld-line quality. In injection molding weldlines are generated when two separate melt streams join either in multigated molds or as a consequence of flow around. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Experimental Setup 2. . Flow lines are lines, waves, or ring patterns that appear on the surface of a part, noted by their slightly different color from the rest of the piece. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. 2. In a meld line, the plastic comes together at an angle greater than 135 degrees. 2017-01-0481. To explore the formation of weld lines in injection molding, a. In Fig. Causes and Remedies of Sink Marks In Injection Molding. 015 0. + Adjust injection speed. The Solutions for Poor Welding Lines. The thin weld line is the result of weak material bonding, which lowers the strength of the part. Weld line (also known as a knit line) is the line where two flow fronts meet when there is the inability of two or more flow fronts to “knit” together, or “weld,” during the molding process. 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 is a mark left on the surface of a plastic injected molded part. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. If the large molded product is. The plaques are prepared out of 30% glass-filled Polyamide 6 material. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. 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. (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. * 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). + Optimize holding pressure time. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. The impact behavior of weld-lines in injection molding. 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. The injection molding temperature and the mold temperature were fixed respectively at 230 °C and 50 °C. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. 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. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Gate blush, 4. Injection molding, polypropylene, talc. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Wang. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. 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. Sink marks, 2. Steven. The weld lines in blow molding occur wherever the pari son knits together in the head, mold tacking areas and mold parting pinch-off region. In the 1947 book, Injection Molding of Plastics, the late Dr. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. 4. The most common and one of the most challenging injection molding defects are weld and knit lines. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. , less than 0. The spreading mold release agent on the part cavity surface might eventually cumulate at the V-notch groove of the weld line after each injection molding shot. When this fails to happen correctly, a weld line defect occurs. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. This failure causes the product to be damaged during use. weld lines in injection molded thermoplastic composites. Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. Weld lines may occur on a molded part’s surface where, after breaking off into two or more directions in a mold, the molten material has converged. • Optimize the design of the runner system. They decrease the. Adjust the position of the gate and include a venting slot. Increase the size of the gate and runners to alter the mold design. The Influence of Knit-lines on the Tensile Properties of Injection Molded Parts, Polymer Engineering and Science, 23(10): 591-596. One solution is to prevent the weld lines from forming in regions that are. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. They occur when melt flow fronts collide in a mold cavity. Figure 2. Weld lines may appear like seams or scratches, but that is not what they are. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. 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. 10. Park et al. Plastic Injection Molding Process. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. 001 in . 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. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. 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. Prediction of the weld lines in injection molding process using neural networks. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. 2. This failure causes the product to be damaged during use. 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. 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. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. Azieatul Azrin Dzulkipli and M. One of the defects observed in injection molding parts is weld line strength, which forms when two or more separate melt fronts traveling from different directions meet and join as the mold cavity is filled. This leads to a better molecular chain entanglement, which in turn creates a better weld. Weld line formations can be weak if they fall in areas that will bear stress or impact. Figure 2. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Root causes Many factors—including processing conditions, material, part design and mold design—can influence the visibility and strength of a weld line. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. 9 – Over Packing. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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 line in injection molding is created when two melt streams connect, as shown in Figure 1. Save. Flow rate is 24 cm3/s. Weld lines in injection molding are frequently unavoidable. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. . Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. 453-455. 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. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. 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. investigated the impact of injection molding parameters on weld line formation and strength reduction. (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. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. 025 mm (0 . As the polymer. 015 0. Weld lines can appear on the surface of a molded part where the molten material has converged after splitting off in a mold. The need to minimize fiber breakage, plus the higher viscosity of materials with. 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 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 line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. Abstract. Weld Lines-3 Ways for Detecting and Correcting. This process makes possible to produce a wide range of products with different sizes, shapes, and for varying applications. 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). Vacuum voids. This is expected to achieve maximum results while the pressure holding effect will also increase. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. 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. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. 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 holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. Provide a gas vent. See moreEquipment. The weld line and the flow pattern of co-injection molding can be seen from Fig. 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. According to the special features of micro injection molding process compared with normal injection molding process, the main related factors to weld line’s properties were classified as 3 group, named as processing conditions, mold design and structure, external process. During injection. Fellahi et al. 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. 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. Flow analysis of the weld line formation during injection mold filling of thermoplastics. Increase the injection speed to reduce the amount of cooling happening in the mold. In addition a weld line can be moved to an area where it is less visible. 010 0. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. Poor mold spot Spot mold to ensure fit and vent depths at ~0 . Weld-line is a weak area which reduces the strength of the part locally. Weld Line Factors for Thermoplastics. Weld lines may appear like seams or scratches, but that is not what they are. Our injection molding company is explaining what these imperfections are, why they can compromise. carried out to mass-produce molded products with complex shapes. Injection Molding defect:molding weld_and_meld_line. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. Meld lines are formed when two separate flow fronts meets. A. (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. Weld line formation in the injection molding process occurs. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Weld lines. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro. These lines usually appear on the narrowest portion of the part, and appear to originate from the mold’s gates, where the molten resin flows into the mold to form. Injected plates were generated using a double-gated mold under four different process conditions. when two or more melt flow fronts contact each other immediately after the cooling process. 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. Adjust the design for the flow pattern to be a single source flow. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Kobayashi et al. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Flow lines. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. There are various types of injection molding defects that can cause such interruptions in the manufacturing cycle. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. The performance of weld lines in talc filled polypropylene box moldings produced with a. If the different flow fronts have cooled. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Weld lines are one of the typical quality issues of injection molded parts. are very minimum. 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. To explore the formation of weld lines in injection molding, a. , 190°C mass and 20°C mold temperature, as well as. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. Increase the melting temperature. (3-1) Increasing the Resin Temperature at the Weld Line Section. When injection molding large products, molding is usually performed with multi-point gates, but weld lines can occur depending on the product shape and gate position. 10(a) (please see Fig. The following are the conclusion drawn from the present research: 1. Weld lines are where two flow. Weld Lines. 3. In narrow fields, a limited amount of molten liquid can solidify and block the flow. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. 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 material flowing around holes or inserts in the part, multiple injection gates or variable wall thickness where hesitation or "race tracking" can occur. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. Weld line. 5. S. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. The weld lines in injection moulded parts arise as a result of the collision of two fronts of the flowing material, which fills the mould cavity and are sometimes unavoidable. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. 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. Tosello et al. Process. Injected plates were generated using a double-gated mold under four different process conditions. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. Three terms that often get mixed up are weld, meld, and knit lines. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the. 030 0. The impact behavior of weld-lines in injection molding. injection molding is followed by the welding. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. As a result this weld line will be a weak point in this part. In weak material bonding, they will appear as hair-like weld lines. Short shots. So today we are going to take a look at the five most common defects in injection molding and their solutions. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. 22 shows how the weld lines are formed when the melt splits around core pins during the injection molding process. Proceedings of ANTEC (2000) Google Scholar [9] S. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Redesign the mold to. Steven. 2) Vents in an injection mold should let the air out, but not the liquid plastic. Therefore, the. Insufficient injection pressure and speed can cause weld lines. They are the result of fundamental physical effects taking place inside of the mold tool cavity. Weld lines in design for manufacture. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. From Fig. It forces out trapped air pockets and can prevent a vacuum void from occurring. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. This is particularly true if the wall thickness in the weld is thin – i. 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. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. A visible weld line is observed, due to a combina-Cracking is commonly seen at the weld line area but sometimes on the entire surface. Microsyst Technol, 14 (6) (2008), pp. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. 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. Alter the mold design. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Abstract. In this experiment, several ejector. Weld Lines. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. Gate Placement: Properly positioning the gate can direct the melt flow to minimize weld lines or relocate the weld line to non-visible areas of the part. Dischler, D. Polym Eng Sci 45(7. My polymer material selection courses 👉 Find Out About Plastics Blog👉 ht. [ 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. 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 . The Factors that Cause Weld Line in Injection molding Pressure. 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. 5. The conditions are temperature, injection speed, and injection pressure. The effects of filling time, packing time, packing pressure, melt temperature, and mold temperature on the ultimate tensile strength (UTS) and the elongation value of the weld. Weld-line is a weak area which reduces the strength of the part locally. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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 lines defects are formed when two flow fronts are merged together. 5. 3. 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. (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. 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]. Meld and knit lines are actually both different types of weld lines. The molded plastic part may also appear to be rust-colored. Double push filling method. Thus, it is important to understand (i). Avient’s Zachary Alderman shares practical tips on designing and injection molding parts utilizing short-fiber reinforcements. 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. <Mold> Provide a cold slug well where weld lines occur. Controlling the mold’s temperature could also minimize the weld line’s effects.