5. Weld lines may occur depending on the product shape and gate positions. Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. The solution to an internal part cracking problem is to change the packing pressure. In addition a weld line can be moved to an area where it is less visible. The thermo-rheological findings were used to investigate the sources of weld line weakness. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. 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. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. when two or more melt flow fronts contact each other immediately after the cooling process. You will have to confirm them before tooling. Weld-Line in an injection molded part develops when two or more melt fronts are converged together. Tosello et al. Email him at jhenz. 9 – Over Packing. 1. Weld Lines. M. 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. Except for a few injection molded parts with very simple geometry, they occur on most injection molding parts (the shape is usually a line or V-shaped groove), especially Large complex items requiring the use of multi-gate molds and inserts. One solution is to prevent the weld lines from forming in regions that are. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. 2021年4月23日 / by admin. Redesign the mold to prevent the weld line. Increase the injection speed. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. ” Another. Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. 453-455. Clamping Unit. In a meld line, the plastic comes together at an angle greater than 135 degrees. injection molding is followed by the welding. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. Remedies: Raise the temperature of the mold or molten plastic. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. There are various types of injection molding defects that can cause such interruptions in the manufacturing cycle. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. 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. This weld line can act as a weak spot in the material. The weld lines in injection molded parts arise as a result of the collision of two fronts of the flowing material, which fills the mold cavity and are sometimes unavoidable [1][2][3] [4]. Shaofei Jiang. 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. 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. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Meld and knit lines are actually both different types of weld lines. are very minimum. Plastic Injection Molding Process. 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. (1983). This paper presents the. 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. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. The Problems & Solutions course is designed to train injection molding personnel in. This is where the melt fronts divided by an insert, such as a pin or a block, in a mold cavity rejoin each other downstream of the insert. 6. Expand. Gate location should set to avoid weld lines, keep clean of the important position of the products,. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. Adjust the design for the flow pattern to be a single source flow. The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. In other words, weld lines reduce the mechanical properties of the product. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. when two or more melt flow fronts contact each other immediately after the cooling process. 3: Weld Lines. Therefore, it is recommended to do a moldflow study prior to the mold being built. micro injection molded weld line’s mechanical properties. Raise the injection speed. Abstract. 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. 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. 10(a) (please see Fig. 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. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. 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. 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. Redesign the mold to. This gives a clue as to how it was formed. In manufacturing, the Weld line or Knit line or Meld line is the line where two flow fronts meet when there is the inability of two or more flow fronts to "knit" together, or "weld", during the molding process. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. This article will review how and why weld lines occur, how mold gates effects weld line location and strength, the importance of material selection and Injection molding weld lines refer to a line on an injection molded part that is generated where the two halves of the mold come together. In this paper, a weld line factor (W-L factor) was adopted to describe the. Mold vents should function the same way. 8. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are still rather few. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. A weld line is a mark left on the surface of a plastic injected molded part. There is excess air inside the mold (1) make the mold vent larger at location with weld line; (2) Check if the mold vent is blocked or not or use vacuumized forming. ). Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. 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]. 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. INJECTION MOULDING DEFECTS 1 DEFECTS 1. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. To prevent knit lines, injection molders can increase the temperature of the molten resin to prevent solidification from starting too soon, and increasing injection speeds and pressure are also potential solutions. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. A weld line can also be called a knit line. 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 lines in design for manufacture. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. Here are some ways to avoid. 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. 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. You can expect a mold shrinkage percentage of. 1. 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. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. 22 shows how the weld lines are formed when the melt splits around core pins during the injection molding process. Weld line formation in the injection molding process occurs. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. (3) Adjust the temperature of the barrel and nozzle: the viscosity. 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. Injected plates were generated using a double-gated mold under four different process conditions. 2. As the polymer. Some of these are listed below: Plastic warpage. Since it is often impossible to avoid weld lines as well as a limited possibility to increase the weld line strength by adjusting the injection molding parameters, a method to predict the weld line strength in the product development process is shown below. EasyFill Advanced provides the weld-line temperature distribution and meeting angle prediction. Weld Line Factors for Thermoplastics. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. Weld line section presents notch or gloss difference. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. examined the relationship between the structural and mechanical qualities in HDPE/PA6 mixture which is molded with weld line and without weld line in plastic injections [6]. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. With tighter heat controls, you can keep the material at the proper temperature to make sure the plastic keeps flowing and fills the mold cavity completely. + Improve vent inside the mold. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. Weld Lines. Except for a few injection molded parts with very simple geometry, weld lines occur in most injection molded parts (usually with one line or V-shaped groove), especially in large-scale complex products requiring multi gate mold and inserts. Discoloration. 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. Wavy lines are another feature of weld lines. Injection molding can be performed with only one of these. The following are the conclusion drawn from the present research: 1. Weld line formation in the injection molding process occurs. 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. If you are familiar with any form of scientific injection molding, regardless of the name, then you know one of the first steps is performing a viscosity curve study. (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. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. 2(a, b). The most common and one of the most challenging injection molding defects are weld and knit lines. 025 mm (0 . Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. In this lesson we will focus on the meld and 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. Weld-line is a weak area which reduces the strength of the part locally. Maintain a holding pressure that is no more than 1/2 the. Knit lines are hard to eliminate for injection molded plastic parts but. Figure 2. Figure 2. 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. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Weld lines have been one of the common defects puzzling the injection molding industry. Molding Equipment. A weld or meld line on plastic parts can cause structural problems and/or be visibly unacceptable. Weld lines are formed when two orThe experiments were performed on an Arburg Allrounder 320C 600-250 injection moulding machine using a two cavity-injection mould (Fig. But none of the current packages can predict weld lines’ properties qualitatively. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. 015 0. 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. They appear on the surface of injection molded parts like lines. The wheel has to be gated at three places on the hub and. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. This study focus on the formation of. GlossFlow-induced fiber orientation and weld lines are com-mon features of the injection molding process. Improvement of weld line strength in injection molded FRTP articles. To prevent knit lines, injection molders can increase the temperature of the molten resin to prevent solidification from starting too soon, and increasing injection speeds and pressure are also potential solutions. Possible causes: Low temperature or fluidity of melted plastic during injection molding. These are caused by the shot of molten plastic moving at different speeds throughout the injection. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. The weld line is then created with a higher flow front temperature and is packed with more pressure. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. The Solutions for Poor Welding Lines. That helps. For more information on the Factors Affecting the Injection Molding Process. Multiple gates are acceptable as long as they are close enough to each other to avoid weld line issues. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. One test mold was used to mold three different materials using heat/cool and conventional molding techniques. 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. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Polymers 2023, 15, 2440 3 of 21. g. [1] The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. Ideally, the resin flow will split into two flow fronts to pass around the obstruction and then recombine into a single flow front. 000 0. 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. The more gate points there are, the more weld lines will occur. This is where the melt fronts divided by an insert, such as a pin or a. 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 not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. Weld line. Ghazanfarpour. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. The relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. 5. After that, the compounds were injection-molded into tensile samples with and without weld lines to. with a characteristic length χ 0 =0. That helps. การแก้ไข ชิ้นงานจุดที่เกิดความอ่อนแอบริเวณ weld line คือต้องใช้ความเร็วในการฉีดต่ำในจุด. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. * 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). This paper presents the. <Materials>Injection moulding (U. 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. Adjust the design for the flow pattern to be a single source flow. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. Consequently, it causes viscous dissipation which leads to the generation of heat. What is weld lines. Thus, it is important to understand (i). The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. 080 inches. In. Place a vent in the weld line area to remove the entrapped air. Its appearance can be improved by adjusting parameters. Figure 1 below shows the development of a weld line. 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. In the above diagram, the converging flow fronts (indicated by red arrows. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Founder, Injection Molding Solutions. ) . 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 order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. Weld lines are visible to varying degrees on any molded part depending on gate location, flow length, melt/mold temperature, cavityA weld line occurs when two or more molten plastic flows meet and fuse during the injection molding process, resulting in a visible line on the surface of the molded part. Materials Science. Controlling the mold’s temperature could also minimize the weld line’s effects. Weld lines are a reality in the injection moulding of complex parts. The gate vestige for injection molding is usually narrow. 1. Increase the melting temperature. Better weld line quality was obtained by Huang. 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. Criens, R. In the present work, the micro specimens were investigated. ppt from SCIENCE 101 at Symbiosis International University. Meld lines are formed when two separate flow fronts meets. Thus, it is important to understand (i). 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. 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 pressure. Controlling the mold’s temperature could also minimize the weld line’s effects. Jiquan Li, Taidong Li, +1 author. Five injection molding process parameters, including mold temperature, melt temperature, packing pressure, injection. 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. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. The formation of weld line in the injection molding method is caused by the product and mold design that is one of the common mistakes. 030 0. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. Insufficient injection pressure and speed can cause weld lines. Nguyen-Chung. [ 18 - 21 ] In addition, the effects. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. a) Multi-fiber connector micro injection molding simulation b) 3D simulation of micro gear with 150µm diameter for weld line position prediction c) 3D micro injection molding filling simulation of micro gear with 180µm diameter Fig. 020 0. One method is the local te mpering of the affected areas to prevent weld lines. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. C. This injection molding defect appears as a black discoloration on the surface of the molded part. What are Weld Line Defects? Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. In this experiment, several ejector. The weld line is then created with a higher flow front temperature and is packed with more pressure. 1 Mold In order to study the formation of weld lines, the mold cavities has been. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms. Weld lines are a common imperfection to be found in most plastic injected molded parts. Vacuum voids. 2. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. 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. 4 at different time steps (legend scale is volume fraction of. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. This reduced thickness of the frozen skin further enhances the visual appeal of the. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. S. Redesign the mold to prevent the weld line. 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. 015 0. 21: Weld line failure caused by hoop stresses. 15 shows the frozen layer and weld lines at the end of mold filling. If so, look for an alternative resin. Effects of mold temperature and pressure on shrinkage 0. 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. Here we are looking at most common part defect that can come from injection molding called weld line. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. In injection molding weld lines are formed whenever two flow fronts are joined. Double push filling method. Participating in DFM and mold flow analysis is a good way to achieve this. 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. In many cases, you will also see that the part is hanging up on the core during ejection. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. The impact behavior of weld-lines in injection molding. Weld lines. Meld Lines. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Avient’s Zachary Alderman shares practical tips on designing and injection molding parts utilizing short-fiber reinforcements. 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. 1. 1. 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. 2. Mold vents should function the same way. Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. Weld lines appear on the molded part where molten plastic meets. Steven. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Three terms that often get mixed up are weld, meld, and knit lines. Many studies were conducted to explain the weakness at the. When two or more streams of plastic meet and fuse. Weld line existence reduces the material strength; however, its demerit characteristics. If the large molded product is. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Download : Download high-res image (856KB) Download : Download full-size image; Fig. Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. 3 the path lines of selected material elements can be observed which are. 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]. Abstract. (1) Increase the injection pressure and prolong the injection time. Flow analysis of the weld line formation during injection mold filling of thermoplastics. The main types of injection molding defects are: 1. [ 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. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. investigated the impact of injection molding parameters on weld line formation and strength reduction. 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. Sink marks, 2. 6. 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. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. Flow rate is 24 cm3/s. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. The flow fronts at different times (Fig. + Increase mold temp, or materials’ temp, or holding pressure. Short shots can occur in this case because the air in the mold cavity has nowhere to go while the plastic is entering. ac. 943 µm to 0. 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 weldSince weldline in plastic injection molding (PIM) has an influence on not only the strength but also the surface appearance of a plastic product, it is preferable to reduce it as much as possible for high product quality. Kobayashi et al. Injection Molding Know How. . Injection molding could be applied with many polymer materials, such as. 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. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. Vents in the mold allow the mold to fill. 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. 2. 7 of the reference.