Injected plates were generated using a double-gated mold under four different process conditions. 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. 4. Injection Molding defect:molding weld_and_meld_line. th INTRODUCTION Injection molding is one of the mostWeld Lines in a plastic cover. This occurs mainly in the presence of barriers that divide the melt flow in. 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. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. In injection molding, a V-notch-shaped weld line [1] is generated in the melt front meeting area. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. 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]. The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. Better weld line quality was obtained by Huang. 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. Weld line and warping are two critical defects for injection-moulded part. 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). The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. The main types of injection molding defects are: 1. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Figure 2. carried out to mass-produce molded products with complex shapes. Meddad and Fisa [3] found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost. 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. Flash. In. Improper fusion of two fluid flows, a state before weld line. In this paper, a kind of polypropylene (PP) foam plastic parts with special weld lines were obtained by core-back foam injection molding with chemical blowing agent. As these flow fronts come together. Move injection locations to make weld lines form closer to the gates. (3-1) Increasing the Resin Temperature at the Weld Line Section. Lesson 6: Meld and Weld Lines (Processing) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. 1. Injection molding, polypropylene, talc. Sequential valve gate technology. This is expected to achieve maximum results while the pressure holding effect will also increase. Short shots can occur in this case because the air in the mold cavity has nowhere to go while the plastic is entering. 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. 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. Redesign the mold to prevent the weld line. Weld Line defect analysis, the most common of many defects in injection moulding products. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. Thereby creating localized pressure within the mold. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. 2020-01-1306. If you have critical requirements for strength of knit lines, please call a Protolabs applications engineer at 877-479-3680 to discuss, or email at [email protected]. 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. However, research about the computer determination of weld lines in injection molding remains scarce. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld together. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. 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. 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. What is weld lines. 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. Sink Marks Cause 3: Improper Pack or Hold 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. Plastic Rapid Injection Molding is popular not only in low volume manufacturing but also in large quantities molding, it is the most common way to manufacture plastic parts. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. 2004; To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Weld lines are a common occurrence in injection molding that affects the overall quality and strength of a finished product. e. The following are the conclusion drawn from the present research: 1. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow path. ), with different mould surface finishes (polished, fine eroded, rough. Proper venting is also required to ensure good weld-line quality. Discoloration. Weld line location. Mérillou, J. The weld line and the flow pattern of co-injection molding can be seen from Fig. Experimental Setup 2. Carefully consider all the relevant aspects of the mold design specification before. Figure 1 below shows the development of a weld line. M. Weld Lines-3 Ways for Detecting and Correcting. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. 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. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Multiple gating, splitting of the melt flow due to inserts in the cavity or through holes, as well as changes of thickness give rise to points within the structure where the flowing fronts will recombine and weld. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. In an injection molding process, a weld-line forms when two flow fronts meet each other. Weld line formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. 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. A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. This is where the melt fronts divided by an insert, such as a pin or a. 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. Sink marks, 2. analyzed the heat transfer during heating and cooling phases of RHCM process. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). 3. Weld Line defect analysis, the most common of many defects in injection moulding products. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Weld line section presents notch or gloss difference. Consequently, it causes viscous dissipation which leads to the generation of heat. Participating in DFM and mold flow analysis is a good way to achieve this. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. A weld line is a mark left on the surface of a plastic injected molded part. The authors [5, 6] attempted to reduce the weld lines and clamping force of plastic injection moulding through numerical and experimental investigation, and discovered that the 3D cooling channel. 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. Published 5 July 2019. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. There are various types of injection molding defects that can cause such interruptions in the manufacturing cycle. Weld lines are also known as knit lines. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. For multiple gate and complex part. 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. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. (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. The weld line can either be a minor cosmetic issue or potentially bad enough to negatively impact the part's strength. 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. . 22 shows how the weld lines are formed when the melt splits around core pins during the injection molding process. These potential causes include:Weld lines Weld lines are weak areas formed by converging flows of plastic that can lead to mechanical part failure if not properly accounted for in the part design. Gambar 2. Weld-line is a weak area. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Introduction. Criens, R. This customary mark is caused by differential rates of cooling in the resin where. 5. A simulation process was conducted to determine the recommended setting of injection moulding parameters and the range of the variable. 3. The Solutions for Poor Welding Lines. 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. Injection Molding Know How. 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. Weld lines not. Steven. In the sense that the weld line is better formed before the resin temperature. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. 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. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. G. 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. The simulated cold weld line length is consistent with the experimental one when a 115 °C mold temperature is adopted; with lower mold temperatures, the simulated lengths are smaller than the experimental ones—in accordance with the literature on the conventional injection molding process [26,27]—probably because of the definition adopted. Ghazanfarpour. It is a zone with reduced mechanical properties negatively influencing on the molding behavior in exploitation. A new kind of weld line was. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Abstract. In this paper, two different injection molding tests were completed. Weld Line Factors for Thermoplastics. Sink MarksWeld lines, also known as knit lines, are a common defect in injection molding where two or more flow fronts of molten plastic meet but don’t properly fuse together. Emerging Materials Research. 5. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). Silver Streak. Therefore, it is recommended to do a moldflow study prior to the mold being built. This failure causes the product to be damaged during use. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. 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. 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. Meld lines are formed when two separate flow fronts meets. Bubbles are caused by melting flow fronts colliding in a mold cavity. The relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. The thermo. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. 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. This weld line can act as a weak spot in the material. 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. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. 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]. – Use generous and even. 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. A visual mold with variotherm system for weld line study in micro injection molding. Besides, possibly it would be. Blistering 4. Flow Lines and Weld Lines. 3: Weld Lines. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. 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]. They decrease the. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. Weld-line is a weak area which reduces the strength of the part locally. They. The injection molding temperature and the mold temperature were fixed respectively at 230 °C and 50 °C. Mold temperature controlInjection mold designers can alter the position of weld line by changing the gate locating. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. In some cases, a weld line can also cause a loss of strength and impact resistance. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the weld line can be seen clearly from the Fig. Poor mold spot Spot mold to ensure fit and vent depths at ~0 . One test mold was used to mold three different materials using heat/cool and conventional molding techniques. 5. + Adjust injection speed. The need to minimize fiber breakage, plus the higher viscosity of materials with. injection molding. The. Effects of mold temperature and pressure on shrinkage 0. ” Another. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. So today we are going to take a look at the five most common defects in injection molding and their solutions. Vents in the mold allow the mold to fill. This may require higher melt temperature or lower injection speed . spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. My polymer material selection courses 👉 Find Out About Plastics Blog👉 ht. When this fails to happen correctly, a weld line defect occurs. In this experiment, several ejector. Email him at jhenz. Meld and knit lines are actually both different types of weld lines. Fig 13:- Detailed view of weld lines. 1. Weld lines in injection molding are frequently unavoidable. The structure is more complex with longer molding cycle . Remedies: Reduce packing and fill rates by adjusting until the part is properly filled with minimum stresses. 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. Use a less viscous plastic. This customary mark is caused by differential rates of cooling in the resin where. Figure 1 below shows the development of a weld line. Figure 1 a illustrates how the weld line is produced when two melt streams merge during the final filling process. A weld line is often unavoidable. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. 2. The flow of the material in the injection mould takes place through the gate. Weld or knit lines occur when melt flow fronts collide in a mold cavity. 15 shows the frozen layer and weld lines at the end of mold filling. If the injection gate is not properly designed, it can cause the formation of defects like sink-mark, warpage, short shot, weld-line, air traps, and other faults [15]. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. 000 0. Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. 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. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. To respond to poor plasticization and uneven melt temperature,. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Many researchers had emerged with several. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. Usually it’s a straight line, and often to be found radiating. 015 0. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. In the present work, the micro specimens were investigated. Recently, the injection molding of fiber reinforced thermoplastics (FRTP) containing short fibers has been widely carried out to mass-produce molded products with complex shapes. 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. Weld lines can appear on the surface of a molded part where the molten material has converged after splitting off into two or more directions in a mold. Wavy lines are another feature of weld lines. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. 7 in Kobayashi et al. Alter the mold design. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. Venting at Weld Lines. Plastic Injection Molding Process. 1. injection molding. e. Burn Marks. 3. (1983). Weld lines are the unfavorable defect not only in normal injection molding process but in micro injection molding process. Ni. In this paper, a weld line factor (W-L factor) was adopted to describe the. Download : Download high-res image (856KB) Download : Download full-size image; Fig. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. 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) Causes & Countermeasures (See the table below) *Note: Flash also tends to occur when the injection pressure/speed are too high, but molding time is too long and mold temperature is too low. Weld lines have been one of the common defects puzzling the injection molding industry. Dischler, D. 21: Weld line failure caused by hoop stresses. Solving one problem can introduce other problems to the injection molding process. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). This is particularly true if the wall thickness in the weld is thin – i. Injection molding is an efficient manufacturing process for mass-producing parts with complicated geometry. Mold vents should function the same way. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. Weld Lines. 030 0. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the. ”. Flashes, 3. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. The micro tensile part was prepared by the double gate injection. (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. In addition a weld line can be moved to an area where it is less visible. 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. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. Weld lines. To determine the effect of the weld lines on tensile strength, tensile tests were conducted with the specimens fabricated with NORYL (amorphous blends of. Injection molding weld lines where two or more flow fronts come together in the mold. + Move gate (to where it is not visible). Here are some strategies. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. In weak material bonding, they will appear as hair-like weld lines. In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. Weld lines may appear like seams or scratches, but that is not what they are. 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. Sink marks are a common type of injection molding defect. when two or more melt flow fronts contact each other immediately after the cooling process. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. Injection pressures too high Reduce pressure . , 2 (3–4) (1988. 5. weld lines in injection molded thermoplastic composites. 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 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. Islyn Thomas summarized the need for a particular vent location better than I ever could. 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. • Reduce runner dimensions and maintain the same flow rate. Weld line. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. These lines. are very minimum. Some of these are listed below: Plastic warpage. Steven. enough to each other to avoid weld line issues. In a weld line, reinforcement fibers. 1. If the different flow fronts have cooled. CrossRef View in Scopus Google Scholar [17] G. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. Weld Lines. 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. (2011) and Fig. Park et al. <Materials>Injection moulding (U. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. The thin weld line is the result of weak material bonding, which lowers the strength of the part. consideration in gate location. The Solutions for Poor Welding Lines. They become more critical when particulate fillers are compounded with the polymer. 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. In. Weld lines are a surface defect caused when two or more flow fronts come together during the injection process. Gates should be designed larger than normal and located to minimize weld line formation. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. In many cases, you will also see that the part is hanging up on the core during ejection. Sink Marks Cause 2: Low Pack and Hold time. The impact behavior of weld-lines in injection molding. 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. 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. Save. Too much injection molding pressure lost and increase the operation difficulty of the injection molding machine; 7. <Mold> Provide a cold slug well where weld lines occur. 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. (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. gasket seal leakage where the weld line crosses a gasket. 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. 030 0. Causes and Remedies of Sink Marks In Injection Molding. Change the gate locations. According to the characteristics. So today we are going to take a look at the five most common defects in injection molding and their solutions. 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. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. The calculation was carried out on a mesh with solid elements obtained in ANSYS Meshing and transferred to Moldex3D by means Rhinoceros. T. Mold flow marks, also known as flow lines or weld lines, are often caused by variations in the flow of molten plastic material during the injection molding process. , less than 0. Weld lines are the most common defects in injection molded products. 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. In this lesson we will focus on the meld and weld lines. Weld Lines. 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. Cracks in Corners – When cracks appear in the corners of plastic parts, the cause is too much plastic shrinkage onto the mold core in that corner. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. 000 0. 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 hair-like weld line is the. Weld Lines. Some of the common fixes for weld lines include: Increase the resin temperature to ensure both sides of the weld line are liquid when colliding. 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. 020 0. 1. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. For more information on the Factors Affecting the Injection Molding Process. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. 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. Weld Lines. Here’s how to decrease the chances of weld lines: Increase the temperature of the mold or the molten plastic. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. One common issue that frequently arises during injection molding is the formation of weld lines. Weld Line Factors for Thermoplastics. Weld lines have been one of the common defects puzzling the injection molding industry. th INTRODUCTION Injection molding is one of the most Weld Lines in a plastic cover. Remedies: Raise the temperature of the mold or molten plastic. A weld line is often unavoidable. Wang, G. From Fig. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. 2. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. Premature partial solidification of the molten plastic leads to inadequate bonding — the primary cause of weld lines. 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. Nguyen-Chung. Materials Science. The melt stream is separated at the part’s cutout and reunited at the other end of the cutout. The Influence of Knit-lines on the Tensile Properties of Injection Molded Parts, Polymer Engineering and Science, 23(10): 591-596. That’s the air escaping out of the nozzle until the hose is full of pressurized water.