Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. However, research about the computer determination of weld lines in injection molding remains scarce. Weld line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. + Increase mold temp, or materials’ temp, or holding pressure. [ 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. In this study, polypropylene (PP) was compounded respectively with carbon nano fibers (CNFs) and TiO 2 nano particles at various weight fractions (10, 20, 30, 35. This is a video excerpt from our Problems & Solutions Course - Weldlines. Other possible causes include: Low mold or material temperature; Insufficient holding time or. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. In this study, 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. In this lesson we will focus on the meld and weld lines. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. 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 defect that arises in injection molding when two or more flow fronts collide. . Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Weld lines in injection molding are frequently unavoidable. 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. Steven. 2017-01-0481. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. 943 µm to 0. The most common and one of the most challenging injection molding defects are weld and knit lines. 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. 020 0. Lesson 7: Meld and Weld Lines (Part Design) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. 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. Mold Design Most conventional mold designs will work with TPU’s. Figure 2. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Injection-molding machine is the Negri Bossi VE210-1700 with screw diameter 60 mm. Introduction. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 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. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. 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. This model provides the necessary information. This reduced thickness of the frozen skin further enhances the visual appeal of the. Weld line formation in the injection molding process occurs. injection molding. Some of these are listed below: Plastic warpage. Usually it’s a straight line, and often to be found radiating. Increase the injection speed. 8. The second technique, cascade injection moulding, can produce parts free from weld lines. Figure 2. A weld-line is known as a representative defect in the field of plastic injection moulding, and also as a cause of inferior mechanical propensities and poor appearance. Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. (1) Flash: Extra plastic material in the shape of films or burrs, which appears on the parting surface, around the runner or in the insert crevice. The vents must be deep enough to allow the trapped air and gasses to escape but not deep enough to allow the plastic to flash. 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. 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. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. When the same pressure is maintained or lower than that, the drop in speed shall create the weld lines. GlossFlow-induced fiber orientation and weld lines are com-mon features of the injection molding process. 6. In this experiment, several ejector. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. * 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). Here are some ways to avoid. Meanwhile, Using more advanced cooling method such as cyclic cooling or conformal cooling. This failure causes the product to be damaged during use. 2(a, b). The structure is more complex with longer molding cycle . Specifically, injection-mold lines are often associated with poor mechanical strength. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. 2-1. 005 0. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. Weld Lines-3 Ways for Detecting and Correcting. Weld lines have been one of the common defects puzzling the injection molding industry. Injection pressures too high Reduce pressure . Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. This occurs either due to injection through multiple gates or as a conse-รอยประสานของเนื้อพลาสติก Weld line ตอนที่1. 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. The weld line degrades the. Weld-line is a weak area which reduces the strength of the part locally. One common issue that frequently arises during injection molding is the formation of weld lines. Which means engineers need to know how to account for this phenomenon in an efficient way. Materials Science. Weld. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Weld lines have been one of the common defects puzzling the injection molding industry. 1. In our DFM report, we will analyze the possible weld lines. 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. 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]. 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. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. 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. In this paper, a weld line factor (W-L factor) was adopted to. 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. T. technical ulletin SPECIALTY POLYME RS Design and Production of Injection Molding ToolsIncrease the injection speed in order to fill the mold more quickly and ensure the material does not prematurely cool down; in addition, when the speed is adjusted the flow fronts may meet at a different spot and move the weld line location. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. 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. 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. The thermo. Flow Lines. If the plasticizing ability of the plastics injection molding machine is insufficient, the plastic cannot be fully plasticized, resulting in weld lines when filling the mold. Weld line 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. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. The injection molding temperature and the mold temperature were fixed respectively at 230 °C and 50 °C. This paper presents the. 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. A knit line may be unnoticeable or may look like a crack. 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. The performance of weld lines in talc filled polypropylene box moldings produced with a. 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. In other words, weld lines reduce the mechanical properties of the product. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Introduction. 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. View 08 DEFECTS & REMEDIES (61). “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. injection molding, (b) weld line and meld line, and (c) injection sample size and shape. Streaks 3. Weld lines. A knit line, also called a weld line, occurs when the liquid plastic moves through the mold and hits more melted plastic and they don’t flow or fuse together. The molded plastic part may also appear to be rust-colored. Increase the injection speed. 8. ) . 000 0. The results of. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Weld Lines. In the feeding system of injection molding, the flow of plastic melt begins from the nozzle of the injection molding machine, traverses through the sprue and runners, and ultimately reaches the mold gate(you can call it the injection molding gate as well)—the entry point to the mold cavity. Weld lines may appear like seams or scratches, but that is not what they are. A flat product case was considered as an example of a typical aircraft structural element. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. To explore the formation of weld lines in injection molding, a. 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. Blistering 4. demanding injection molding and end-use requirements. Process. Int. The difference between a weld and meld line is simply determined by the angle at which the converging flow fronts meet. An evaluation model based on artificial neural network method. This failure causes the product to be damaged during use. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. The edge gate is the most popular and straightforward injection mold gate design. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. 3. 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). Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Prediction of the weld lines in injection molding process using neural networks. 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 . In injection molding, a V-notch-shaped weld line is generated in the melt front meeting area. In an injection molding process, a weld-line forms when two flow fronts meet each other. Five injection molding process parameters, including mold temperature, melt temperature, packing pressure, injection. 10(a) (please see Fig. The effects of fiber concentration has been studied in detail. 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. 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. 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. 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. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. 2. In order to prepare the weld line specimen by micro injection molding, a mould integrated with visual system and variotherm system was designed and constructed, shown as Fig. John Bozzelli. In addition a weld line can be moved to an area where it is less visible. Weld Lines. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. 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. The weld line is then created with a higher flow front temperature and is packed with more pressure. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. 22 shows how the weld lines are formed when the melt splits around core pins during the injection molding process. Weld Lines 5. Injection Molding Know How. Sink Marks 2. 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 not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. 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. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. They decrease the. The hair-like weld line is the result of weak. Steven. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. 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. In an injection molding process, a weld-line forms when two flow fronts meet each other. Use a less viscous plastic. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. of micro injection molding process simulation by technology update and progress. Materials Science. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. This is expected to achieve maximum results while the pressure holding effect will also increase. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 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 create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 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. (a) (b) Figure 1. This weld line can act as a weak spot in the material. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. Shaofei Jiang. 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. Discoloration. 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. The welding angle can be used to differentiate weld lines and meld lines. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Abstract. 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 are a reality in the injection moulding of complex parts. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . The Weld line result itself has a scale associated with the placement of the weld line that is directly relative to how severe the weld line will be based on the angle in which the two flow fronts meet. In narrow fields, a limited amount of molten liquid can solidify and block the flow. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 665 2. The plaques are prepared out of 30% glass-filled Polyamide 6 material. In an injection molding process, a weld-line forms when two flow fronts meet each other. Insufficient injection pressure and speed can cause weld lines. The weld line’s strength is reduced when. 5. As the injection process continues, the two separated melt fronts meet again along the longitudinal section of the plate forming a weld line. Insufficient plasticizing ability of injection molding machine. 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. A new kind of weld line was. Figure 2. (1) Increase the injection pressure and prolong the injection time. Increase the size of the gate and runners to alter the mold design. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 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. The hair-like weld line is the. Bubbles are caused by melting flow fronts colliding in a mold cavity. ), with different mould surface finishes (polished, fine eroded, rough. The Factors that Cause Weld Line in Injection molding Pressure. 015 0. Sink Marks Cause 5: Improper Part Geometry. 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. The Solutions for Poor Welding Lines. wall thickness, gate and runner designs and re-validate the result. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. 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. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. For more information on the Factors Affecting the Injection Molding Process. Runner Type Venting Plastic melt and mold temperature Injection speed and pressure Learn how to troubleshoot weld lines in injection molding. This study focus on the formation of. Adjust the design for the flow pattern to be a single source flow. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of injection parts. Weld lines, generated during injection molding, can significantly reduce the mechanical performance of structures. The Solutions for Poor Welding Lines. Weld lines have been one of the common defects puzzling the injection molding industry. 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. As the polymer resin is injected into a mold, it flows through all parts of the mold. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. The main runner and sub-runner are too thin. 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]. Controlling the mold’s temperature could also minimize the weld line’s effects. Double push filling method. During injection. 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. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold. G. 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. 3. The most common and one of the most challenging injection molding defects are weld and knit lines. 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. when two or more melt flow fronts contact each other immediately after the cooling process. The thin weld line is the result of weak material bonding, which lowers the strength of the part. Many researchers had emerged with several. e. The special injection mold is designed and fabricated to produce plaques having stagnation weld-line. For example, filled resins and ABS are more likely to. Abstract. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. As the plastic flows through the mold it forms a smooth and continuous flow front. Plastic Injection Molding Process. but the injection pressure will loss and injection molding pressure of this gate is bigger than that of direct gate. 3. g. Participating in DFM and mold flow analysis is a good way to achieve this. When an external load is applied to a weld line region, the part’s potential for mechanical failure is increased. e. 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. You will have to confirm them before tooling. In this study, the effects of injection temperature, injection pressure, and fiber cont. Weld Line Factors for Thermoplastics. Weld-line is a weak area. 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]. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. You can choose material of low viscosity and can increase the injection pressure. In injection molding, it is often important to maintain consistent color throughout the part. Weld line and warping are two critical defects for injection-moulded part. In the sense that the weld line is better formed before the resin. Proper venting is also required to ensure good weld-line quality. Download : Download high-res image (856KB) Download : Download full-size image; Fig. + Adjust injection speed. That helps. 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. Remedies: Raise the temperature of the mold or molten plastic. Fig 13:- Detailed view of weld lines. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. Weld lines can. The parts are molded flat and are slightly stressed once installed in an arced position, but not excessively. Injected plates were generated using a double-gated mold under four different process conditions. M. Weld-Line in an injection molded part develops when two or more melt fronts are converged together. Weld lines. 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. Therefore, it is recommended to do a moldflow study prior to the mold being built. Improper fusion of two fluid flows, a state before weld line. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. Weld line injection molding troubleshooting. Meld lines are formed when two separate flow fronts meets. Here we are looking at most common part defect that can come from injection molding called weld line. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties [3,4,5]. The gate vestige for injection molding is usually narrow. weld lines in injection molded thermoplastic composites. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a mold. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. Injected plates were generated using a double-gated mold under four different process conditions. In. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. That helps. 030 0. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. Jiquan Li, Taidong Li, +1 author. Adding vents, using overflows, or using porous metal. Meld and knit lines are actually both different types of weld lines. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. 5. 2. 4. Weld line section presents notch or gloss difference. analyzed the heat transfer during heating and cooling phases of RHCM process. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. When it comes to injection molding, the chances you might end up making a costly mistake is too high. The holding pressure was set as approximately equal to the maximum injection pressure obtained at the time of filling the resin. The part becomes partially solidified and won’t sufficiently bond where the two halves meet, resulting in. Weld Lines-3 Ways for Detecting and Correcting. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). In weak material bonding, they will appear as hair-like weld lines. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. 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. A viscosity curve is developed using calculations of the fill time and plastic pressure at. Tosello et al. Short shots. The edge gate is the most popular and straightforward injection mold gate design. Gate blush, 4. Zhao, X. Weld lines may appear like seams or scratches, but that is not what they are. This can allow the. Mold vents should function the same way. 4 at different time steps (legend scale is volume fraction of. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. In addition a weld line can be moved to an area where it is less visible. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. micro injection molded weld line’s mechanical properties. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. 13 shows the best gate location for which the weld lines . They are the result of fundamental physical effects taking place inside of the mold tool cavity. In this case the two flow fronts will meet and. Weld line existence reduces the material strength; however, its demerit characteristics. The wheel has to be gated at three places on the hub and. If the different flow fronts have cooled. Maintain a holding pressure that is no more than 1/2 the. 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. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. They. Edge Gates. * Corresponding author, e-mail: fengsjpc@ku. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). 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. To respond to poor plasticization and uneven melt temperature,. The flow fronts at different times (Fig. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. They appear on the surface of injection molded parts like lines. 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. In the sense that the weld line is better formed before the resin temperature. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. Proceedings of ANTEC (2000), pp. As the polymer. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. The Difference Between Knit and Meld Lines–and Why It Matters. Weld-line is a weak area which reduces the strength of the part locally. In some cases, a weld line can also cause a loss of strength and impact resistance. Molding calculation in Moldex3D: (а) melt front and weld line, (b). From Fig. 48 applied high-frequency induction heating to eliminate weld lines in an injection-molded plastic part, and experimental observation indicated that weld depth was reduced from 2. 6.