(a) (b) Figure 1. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). Although they often cannot be avoided it’s possible to minimize their cosmetic effects to an acceptable degree through careful product design and manufacturing. gas, which can cause blistering, as well as poor weld lines, warpage and the formation of cold slugs that affect filling and part mechanical properties. In an injection molding process, a weld-line forms when two flow fronts meet each other. 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. Weld line defects in injection molding is a line or lines on the part surface that caused the part looking ugly or cuased part lifetime, or even broken easily. Weld lines can. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Kobayashi et al. 21: Weld line failure caused by hoop stresses. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. The performance of weld lines in talc filled polypropylene box moldings produced with a. The welding angle can be used to differentiate weld lines and meld lines. micro injection molded weld line’s mechanical properties. Weld lines are also known as knit lines. This study describes how the weld line was formed on the 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. CrossRef View in Scopus Google Scholar [17] G. A viscosity curve is developed using calculations of the fill time and plastic pressure at. Weld lines can appear on the surface of a molded part where the molten material has converged after splitting off in a mold. The Solutions for Poor Welding Lines. C. 13 shows the best gate location for which the weld lines . Try to gradually raise the mold temperature and barrel temperature. Solving one problem can introduce other problems to the injection molding process. 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. + Optimize holding pressure time. Weld line is formed when two different melt flows converge, as illustrated in Fig. 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. Clamping Unit. 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. As the polymer. Figure 2. Effect of the processing conditions on the variations of the bulk temperature, T b , at the end of mold filling at the two locations: in (left) and away (right) from the weld-line (T w , T inj. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. Weld lines may appear like seams or scratches, but that is not what they are. In this study the polycarbonate (PC) and carbon fiber (CF) are used as the experimental materials to investigate the impact of injection molding process parameters on tensile strength of weld line. Weld lines have been one of the common defects puzzling the injection molding industry. This is expected to achieve maximum results while the pressure holding effect will also increase. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. Insufficient plasticizing ability of injection molding machine. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. They become more critical when particulate fillers are compounded with the polymer. , 190°C mass and 20°C mold temperature, as well as. Meld and knit lines are actually both different types of weld lines. 1. the meeting angle by optimizing variation over time in the cavity. Weld-line is a weak area which reduces the strength of the part locally. Weld lines are a reality in the injection moulding of complex parts. The hair-like weld line is the result of weak. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. One method is the local te mpering of the affected areas to prevent weld lines. 15 it can be found that for the opposite position of melt injection the weld lines forming under higher temperature would produce better plastics. 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. You will have to confirm them before tooling. 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. An excess mold release is a major cause of weld line due to two variables: high pressure and speed. 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. Weld lines are the unfavorable defect not only in normal injection molding process but in micro injection molding process. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. As the plastic flows through the mold it forms a smooth and continuous flow front. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. and Mosle, H. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Google Scholar [10] S. Weld line strength is important in blow molding as well as 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 still rather few. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. So today we are going to take a look at the five most common defects in injection molding and their solutions. Email him at jhenz. [ 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 the sense that the weld line is better formed before the resin. However, research about the computer determination of weld lines in injection molding remains scarce. Wang. Dischler, D. Instead, a line that looks like a seam forms. Flash. Sink Marks Cause 4: High Mold Temperature. Injection molding of large/complicated products are usually prepared by multiple compounds, which produces weldlines once the melt fronts are joined by impingement flow. 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. Weld lines are a kind of Achilles heel of plastics. Improvement of weld line strength in injection molded FRTP articles. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. Which means engineers need to know how to account for this phenomenon in an efficient way. In this study, the effects of injection temperature, injection pressure, and fiber cont. distribution [4]. The most common and one of the most challenging injection molding defects are weld and knit lines. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Weld Lines 5. There will be too many weld lines ; 6. Instead of using flow leaders and deflectors to control the locations of the weld lines, this paper presents an approach to specify the locations of the weld. In this experiment, several ejector. 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. If the different flow fronts have cooled. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. In. Injection molds: (a) mold type A, (b) fixed plate of the mold type B, and (c) moving plate of mold type B The second mold (mo ld type B) was used for the ISO D2 specimen, as shown in Figure 2b,c . Weld Line defect analysis, the most common of many defects in injection moulding products. 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. 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 micro tensile part was prepared by the double gate injection. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. Meanwhile, Using more advanced cooling method such as cyclic cooling or conformal cooling. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. In spite of its cosmetic attributes, a bad knit line can significantly. 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. Wolfgang Homes, head of the applications department of Eurotool, a manufacturer of hot runner systems, clarified the two methods for IMI, noting that. This paper presents the. 3: Weld Lines. Mold Design. Weld lines are one of the typical quality issues of injection molded parts. Participating in DFM and mold flow analysis is a good way to achieve this. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Besides, possibly it would be. Causes and Remedies of Sink Marks In Injection Molding. 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]. 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. They are unavoidable even for moderate complex products. One common issue that frequently arises during injection molding is the formation of weld lines. 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. Weld lines appear on the surface of a molded part where the molten material converges after splitting off into two or more directions in a mold. 015 0. Place a vent in the weld line area to remove the entrapped air. T. 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. Injected plates were generated using a double-gated mold under four different process conditions. Weld lines are a kind of Achilles heel of plastics. e. Polym. Weld line formations can be weak if they fall in areas that will bear stress or impact. Mérillou, J. This can allow the. Try to gradually raise the mold temperature and barrel temperature. consideration in gate location. when two or more melt flow fronts contact each other immediately after the cooling process. enough to each other to avoid weld line issues. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). Thus, it is important to understand (i) if the melt is able to fill the cavity up to the weld line location, (ii) where the weld line forms, and (iii) if the weld line is a cold or flowing one. Injection Molding Know How. 5. 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. Figure 1a illustrates how the weld line is produced when. The goal is to create a uniform thickness and at the smallest (thinnest) level required. The relative weld-line strength is defined as the ratio of the strength of specimens with a weld line. Where the weld lines are, where the sink marks or voids will be, and how the part warps—all of these are determined by where the molten plastic is injected into the part cavity. (3) Adjust the temperature of the barrel and nozzle: the viscosity. The injection molding gate generates heat by dissipation. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. In this experiment, several ejector. In this paper, aiming at the problem of weld line defects in the injec- tion process of a key phone panel, the injection process is optimized by using Moldflow and drop simulation. (2) Causes & Countermeasures (See the table below) *Note: Flash also tends to occur when the injection pressure/speed are too high, but molding time is too long and mold temperature is too low. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. John Bozzelli. 3. It is normally at the meeting points of two flow fonts. 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. Here we are looking at most common part defect that can come from injection molding called weld line. Steven. 1. Short shots can occur in this case because the air in the mold cavity has nowhere to go while the plastic is entering. 5. The impact behavior of weld-lines in injection molding. Thereby creating localized pressure within the mold. 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. (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. 2. injection molding. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. Weld lines cause significant reject rates and are a common problem that all molders face. In spite of its cosmetic attributes, a bad knit line can significantly compromise a part. So today we are going to take a look at the five most common defects in injection molding and their solutions. In. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. Discoloration. The weld line’s strength is reduced when. The Solutions for Poor Welding Lines. Weld lines are weak regions in thermoplastic injection moldings, due to low molecular entanglement and unfavorable orientation. If the large molded product is. The impact behavior of weld-lines in injection molding. 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. Sink Marks Cause 5: Improper Part Geometry. It occurs when melting plastic material is injected into a mold, it flows through all parts of th. Injected plates were generated using a double-gated mold under four different process conditions. Weld Line Phenomenon: Surface defect in which the weld, or the part where the flows of melted plastic meet inside the mold, shows up on the surface as a groove or pattern. In this lesson we will focus on the meld and weld lines. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. G. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. The governing equations for the melt and the air in the cavity are united into…. The parting line in injection molding is which one of the following: (a) the lines formed where polymer melt meets after flowing around a core in the mold, (b) the narrow gate sections where the parts are separated from the runner, (c) where the clamping unit is joined to the injection unit in the molding machine, or (d) where the two mold halves come together? Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. • Move injection locations to make flow fronts meet more obliquely, turning the weld line into a meld line. 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 defects are formed when two flow fronts are merged together. Flow analysis of the weld line formation during injection mold filling of thermoplastics. Weld-line is a weak area which reduces the strength of the part locally. Increase the injection speed to reduce the amount of cooling happening in the mold. Published 5 July 2019. 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. Fisa et al. This study focus on the formation of. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. The main types of injection molding defects are: 1. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. They are unavoidable even for moderate complex products. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. In the above diagram, the converging flow fronts (indicated by red arrows. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. Many studies were conducted to explain the weakness at the. As a result this weld line will be a weak point in this part. Int. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. 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. 4. 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. The conditions are temperature, injection speed, and injection pressure. Increase the melting temperature. 13. Still, it can be seen to varied degrees depending on mold. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a mold. Polyamide-6 (PA-66) was used as. Molding Equipment. 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. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. 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 formation in the injection molding process occurs when two or more melt flow fronts contact each other immediately after the cooling process. When this fails to happen correctly, a weld line defect occurs. This is where the melt fronts divided by an insert, such as a pin or a. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. ), with different mould surface finishes (polished, fine eroded, rough. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. 1. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. In weak material bonding, they will appear as hair-like weld lines. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro. Amongst weld line. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. + Move gate (to where it is not visible). Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. (1983). g. Figure 2. Gambar 2. The weld line is an inevitable defect in the most injection molded components. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Its appearance can be improved by adjusting parameters. Flow lines. Venting at Weld Lines. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. The plaques are prepared out of 30% glass-filled Polyamide 6 material. 2. 020 0. If the plastic encounters a pin or other obstruction, the plastic flow front must split to form two flow fronts to go around the pin. Criens, R. Its properties make it possible to create thin-walled parts having close tolerances in fast cycles over long. when two or more melt flow fronts contact each other immediately after the cooling process. 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. Azieatul Azrin Dzulkipli and M. 15 shows the frozen layer and weld lines at the end of mold filling. Change the gate locations so that the weld lines occur in locations less susceptible to external forces if weld strength is an issue. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. In a meld line, the plastic comes together at an angle greater than 135 degrees. Weld lines not. Weld 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. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. The parts are molded flat and are slightly stressed once installed in an arced position, but not excessively. 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. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Weld lines occur when two flow fronts meet and fuse together in the injection molding process. 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. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. 943 µm to 0. To explore the formation of weld lines in injection molding, a. 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. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. This model provides the necessary information. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Vacuum voids. 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. 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. The position, length, and angle of weld lines are dependent on the. 5. (1) Increase the injection pressure and prolong the injection time. 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]. 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. Other possible causes include: Low mold or material temperature; Insufficient holding time or. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. If so, look for an alternative resin. injection molding is followed by the welding. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. with a characteristic length χ 0 =0. Weld lines have been one of the common defects puzzling the injection molding industry. 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. In this case the two flow fronts will meet and. 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]. 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. This paper evaluates the shrinkage and strength of weld line using Design of Experiment and Response Surface Methodology in multi-objective optimisation utilising the injection moulding parameters. 005 0. Weld line and warping are two critical defects for injection-moulded part. Voids and bubbles, 6. Sink marks. Problem: Weld lines are formed when plastic resin is forced around an obstruction in a mold tool and reforms on the side opposite the gate. Polymers 2023, 15, 2440 3 of 21. 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. 809-814. Weld-line is a weak area. INJECTION MOULDING DEFECTS 1 DEFECTS 1. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. 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]. According to the studies, the most important factor to reduce weld lines is increasing the mold temperature. demanding injection molding and end-use requirements. 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. 000 0. Weld lines are the result of fundamental physical effects taking place inside of the mold tool cavity, they are common imperfection to be found in most plastic injection molded parts. Weld lines represent the region where two separated melt fronts recombine. Our injection molding company is explaining what these imperfections are, why they can compromise. When the two such melt flows. Maintain a holding pressure that is no more than 1/2 the. [ 18 - 21 ] In addition, the effects. e. This principle has been implemented on a complex component in the case of the spring-loaded cogwheel shown in Figure 5, for instance. 1. This is particularly true if the wall thickness in the weld is thin – i. Materials Science. Founder, Injection Molding Solutions. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. Weld line section presents notch or gloss difference. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. Weld Lines. Additionally, you can get our free Design Cube, which will provide a physical aid to help understand how knit lines form as well as other injection molding design considerations. Some of these are listed below: Plastic warpage. Weld lines are where two flow. Wavy lines are another feature of weld lines. Sink marks, 2. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Ideally, the resin flow will split into two flow fronts to pass around the obstruction and then recombine into a single flow front. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Provide a gas vent. In an injection molding process, a weld-line forms when two flow fronts meet each other. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. Change the flow pattern to a single-source flow. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. The rule is, a higher pressure shall be required to push the material in the machine when there is excess mold. The most common and one of the most challenging injection molding defects are weld and knit lines. Weld line, 5. 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. That’s the air escaping out of the nozzle until the hose is full of pressurized water. (3-1) Increasing the Resin Temperature at the Weld Line Section. In our DFM report, we will analyze the possible weld lines. Stop using mold parting agents. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. 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. For multiple gate and complex part. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. 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. Injection molding could be applied with many polymer materials, such as. A knit line may be unnoticeable or may look like a crack.