In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 2. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. The structure is more complex with longer molding cycle . consideration in gate location. <Materials>Injection moulding (U. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. 6. Weld lines appear as a result of the flow of molten plastic during the injection molding process. Plastics manufactured by injection molding are meant to be durable and reliable, able to hold up to heavy use, high temperatures, or adverse conditions. Proceedings of ANTEC (2000), pp. Remedies: Raise the temperature of the mold or molten plastic. In the sense that the weld line is better formed before the resin temperature. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Wavy lines are another feature of weld lines. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. Wang et al. Use a less viscous plastic. When two or more streams of plastic meet and fuse together, a visible line or weakness is formed on the surface of the finished product. [ 18 - 21 ] In addition, the effects. C. They are unavoidable even for moderate complex products. 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. 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. The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM). when two or more melt flow fronts contact each other immediately after the cooling process. Kobayashi et al. Short shots. Microsyst Technol, 14 (6) (2008), pp. gasket seal leakage where the weld line crosses a gasket. 1. Multiple gates are acceptable as long as they are close enough to each other to avoid weld line issues. 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. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. 9 – Over Packing. [1-2] investigated the weld line zone of injection molded glass-fiber-filled polypropylene (PP) composites. Weld-line is a weak area which reduces the strength of the part locally. 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. Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. 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. For example, filled resins and ABS are more likely to. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for. Weld line existence reduces the material strength; however, its demerit characteristics. 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. Design. The main runner and sub-runner are too thin. 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]. Weld Lines 5. The weld line in injection molding is created when two melt streams connect, as shown in Figure 1. This is expected to achieve maximum results while the pressure holding effect will also increase. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. 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. and Mosle, H. 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. The foundation to any robust process, in my opinion, is based on choosing the correct fill time. 005 0. Wang, G. Mold vents should function the same way. 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. , 190°C mass and 20°C mold temperature, as well as. 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. 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. M. 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. 1. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. 001 in . (1)Injection Machine Poor plasticization and non-uniform melt temperature – appropriately extend the injection molding cycle, to ensure thorough plasticization, and change for a machine with a larger. 3. สาเหตุหลักชิ้นงานพลาสติกเกิดรอยเชื่อมประสาน (weld line) คือ การประสานหรือการรวมตัวกันของพลาสติกเหลวไม่ดีเท่าที่ควรThis insertion ensures the separation of the melt flow. 809-814. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. 2020-01-1306. enough to each other to avoid weld line issues. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. 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. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. Figure 2. The following are the conclusion drawn from the present research: 1. 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. See moreEquipment. with a characteristic length χ 0 =0. Weld lines are where two flow. 21: Weld line failure caused by hoop stresses. 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. Injection molding plate for mode I testing geometry. 3 the path lines of selected material elements can be observed which are. Still, it can be seen to varied degrees depending on mold. In our DFM report, we will analyze the possible weld lines. (3) Adjust the temperature of the barrel and nozzle: the viscosity. Weld lines can affect both the aesthetics and mechanical properties of the product, making them a significant concern for. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. Possible causes: Low temperature or fluidity of melted plastic during injection molding. Insufficient plasticizing ability of injection molding machine. Three terms that often get mixed up are weld, meld, and knit lines. The thermo-rheological findings were used to investigate the sources of weld line weakness. of micro injection molding process simulation by technology update and progress. 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. wall thickness, gate and runner designs and re-validate the result. 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. 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. Increase the injection speed to reduce the amount of cooling happening in the mold. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. 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. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. As the polymer resin is injected into a mold, it flows through all parts of the mold. are very minimum. Weld line formations can be weak if they fall in areas that will bear stress or impact. Wang. Blistering 4. [1] The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. Flow marks in injection molding can be avoided if adequate measures are taken. This gives a clue as to how it was formed. It forces out trapped air pockets and can prevent a vacuum void from occurring. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Introduction. 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]. Ni. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. G. 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. The weld line is then created with a higher flow front temperature and is packed with more pressure. Weld line formation in the injection molding process occurs. They. (2011) and Fig. + Adjust injection speed. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. Quality concerns in injection-molded materials can vary fr. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. If you adjust the ejection mechanism in the mold design, you also can reduce or eliminate your need for mold release agents. From Fig. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Additionally, you can get our free Design Cube, which will provide a physical aid to help understand how knit lines form as well as other injection molding design considerations. The need to minimize fiber breakage, plus the higher viscosity of materials with. 3: Weld Lines. 2. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Injected plates were generated using a double-gated mold under four different process conditions. They decrease the. 2. . <Mold> Provide a cold slug well where weld lines occur. Plastic Injection Molding Process. Try to gradually raise the mold temperature and barrel temperature. Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. 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. 000 0. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. 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. As a result this weld line will be a weak point in this part. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. Weld lines are one of the typical quality issues of injection molded parts. In many cases, you will also see that the part is hanging up on the core during ejection. This happens when the molten plastic is injected into the mold cavity and flows around an obstacle such as a pin, hole, or protrusion, and then comes back together. In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. (3-1) Increasing the Resin Temperature at the Weld Line Section. avoid weld lines, and facilitate smooth. Controlling the mold’s temperature could also minimize the weld line’s effects. Figure 2. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. In this lesson we will focus on the meld and weld lines. Injected plates were generated using a double-gated mold under four different process conditions. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. This customary mark is caused by differential rates of cooling in the resin where. A simulation process was conducted to determine the recommended setting of injection moulding parameters and the range of the variable. Controlling the mold’s temperature could also minimize the weld line’s effects. Dischler, D. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Preventing sink marks of injection molded parts using CAE analysis. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. This is a video excerpt from our Problems & Solutions Course - Weldlines. Flow Lines and Weld Lines. In the first, sequential injection moulding, the lines are displaced to noncritical areas of the moulding. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. Features such as sharp corners or undercuts can. Burn Marks. Bubbles are caused by melting flow fronts colliding in a mold cavity. Jiquan Li, Taidong Li, +1 author. Weld lines in injection molding are frequently unavoidable. The plaques are prepared out of 30% glass-filled Polyamide 6 material. Boost time too long Shorten boost time, lower boost pressure, or move transfer to an earlier position . The weld line degrades the. 015 0. This occurs either due to injection through multiple gates or as a conse-รอยประสานของเนื้อพลาสติก Weld line ตอนที่1. Therefore, it is recommended to do a moldflow study prior to the mold being built. 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. Proper venting is also required to ensure good weld-line quality. Many studies were conducted to explain the weakness at the. To explore the formation of weld lines in injection molding, a. 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. This paper presents the. After that, the compounds were injection-molded into tensile samples with and without weld lines to. As a result, the portion has a faint, perhaps undetectable line. A new kind of weld line was. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. In other words, weld lines reduce the mechanical properties of the product. In injection molding, it is often important to maintain consistent color throughout the part. This reduced thickness of the frozen skin further enhances the visual appeal of the. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. This is particularly true if the wall thickness in the weld is thin – i. Discoloration. Weld lines have been one of the common defects puzzling the injection molding industry. 6. Weld line formation in the injection molding process occurs. This injection molding defect appears as a black discoloration on the surface of the molded part. Nguyen-Chung. 3. This may require higher melt temperature or lower injection speed . Specifically, injection-mold lines are often associated with poor mechanical strength. ” Another. Place a vent in the weld line area to remove the entrapped air. Kobayashi et al. 1. This special mould has changeable inserts to be able to inject with different gate types (standard, film, special-film, multi gates, etc. Flow front tracing simulation results for weld line developing process in micro injection molding with Comsol ® Multiphysics 3. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. 2004; To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Its appearance can be improved by adjusting parameters. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. Weld lines are also known as knit lines. Our injection molding company is explaining what these imperfections are, why they can compromise. Key words: weld line strength, thermoplastic composites, injection molding, wall thickness, skin and core layers Department of Materials Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand. Therefore, it is recommended to do a moldflow study prior to the mold being built. In the sense that the weld line is better formed before the resin. the three-plate mold often adopt this kind of gate. Email him at jhenz. The hair-like weld line is the result of weak. One method is the local te mpering of the affected areas to prevent weld lines. John Bozzelli. Injection Molding Know How. Its appearance can be improved by adjusting parameters. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. This customary mark is caused by differential rates of cooling in the resin where. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a mold. 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 are a common type of injection molding defect. (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. 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 effects of fiber concentration has been studied in detail. This failure causes the product to be damaged during use. 18/06/2021. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld together. This is where the melt fronts divided by an insert, such as a pin or a. Proceedings of ANTEC (2000) Google Scholar [9] S. The specific method is that when the product is just filled and filled in the cavity, the insert. The impact behavior of weld-lines in injection molding. , 2 (3–4) (1988. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. The weld line is then created with a higher flow front temperature and is packed with more pressure. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. The literature on the formation of weld lines, and their consequences, is more abundant on the area of injection molding [5-12] than on extrusion [13]. As these flow fronts come together. The edge gate is the most popular and straightforward injection mold gate design. 4. Double push filling method. Save. 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. Weld Lines. The rule is, a higher pressure shall be required to push the material in the machine when there is excess mold. In injection molding, it is often important to maintain consistent color throughout the part. These processing changes will increase chain. 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. The formation of weld line in the injection molding method is caused by the product and mold design that is one of the common mistakes. 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. For more information on the Factors Affecting the Injection Molding Process. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. He now teaches courses in injection molding and plastic part design at the Polymers Center of Excellence and UNC-Charlotte in Charlotte, N. 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. These lines can occur due to variations in wall thickness, gate location, or the geometry of the part. 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. The flow of the material in the injection mould takes place through the gate. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Reduce the amount of release agents. Unless you are manufacturing an extremely simple part with one gate and a unidirectional flow front, your part will have weld lines. It is possible to pre. Weld line, 5. You will have to confirm them before tooling. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. Weld Lines-3 Ways for Detecting and Correcting. (1998) for clear photographs. 5. 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. Weld lines. Controlling the mold’s temperature could also minimize the weld line’s effects. Another way to eliminate weld lines in plastic injection molding is to adjust the molding conditions. Participating in DFM and mold flow analysis is a good way to achieve this. Weld lines have been one of the common defects puzzling the injection molding industry. 015 0. , a post that forms a hole) and then rejoins, or when polymer melt fronts meet, from multiple injection points. . Abstract. 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. Silver Streak. Therefore, the. Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. Google Scholar | Crossref | ISI. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Download : Download high-res image (856KB) Download : Download full-size image; Fig. Weld lines may appear like seams or scratches, but that is not what they are. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Sink Marks 2. 5. Besides, possibly it would be. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. Thereby creating localized pressure within the mold. [ 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. It is a zone with reduced mechanical properties negatively influencing on the molding behavior in exploitation. Steven. Weld lines are formed when two or more flow fronts join, as the liquid polymer fills the. The formation of weld line in the injection molding method is caused by the product and mold design that is one of the common mistakes. when two or more melt flow fronts contact each other immediately after the cooling process. 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. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. Sequential valve gate technology. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. 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. Here are some ways to avoid. * Corresponding author, e-mail: fengsjpc@ku. 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. , less than 0. 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. 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. Short shots can occur in this case because the air in the mold cavity has nowhere to go while the plastic is entering. The edge gate is the most popular and straightforward injection mold gate design. ). 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. 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. Flash. 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. Five injection molding process parameters, including mold temperature, melt temperature, packing pressure, injection. Definition: A seam that appears where two areas of molten plastics meet. In spite of its cosmetic attributes, a bad knit line can significantly. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Weld lines are the most common defects in injection molded products. 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]. Clamping unit berfungsi untuk memegang dan mengatur gerakan mold unit, serta gerakan ejector saat melepas benda dari molding unit, pada clamping unit lah kita bisa mengatur berapa panjang gerakan molding saat dibuka dan seberapa panjang ejector harus bergerak. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. (1) Increase the injection pressure and prolong the injection time. The most common method for the weld-line characterization is mechanical testing by means of a tensile or bend stage [6,7]. 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. 005 0. when two or more melt flow fronts contact each other immediately after the cooling process. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. Weld lines not only detract from an injection-molded part’s surface quality, but also significantly reduce its mechanical strength. This process makes possible to produce a wide range of products with different sizes, shapes, and for varying applications. Knit lines are hard to eliminate for injection molded plastic parts but. The weld lines in blow molding occur wherever the pari son knits together in the head, mold tacking areas and mold parting pinch-off region. 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].