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. Wang. A flow mark is commonly referred to as a flow line occurs during the process of injection molding. They found that the weld line is a zone between 2 and 8 mm wide extending throughout the thickness in whichTo investigate the effect of hot gas heating in injection molding on the weld line appearance, an experiment was conducted with the molding parameters listed in Table 2. If the different flow fronts have cooled. An injection molding gate is a critical component in mold design, acting as the passage through which molten plastic travels from the runners into the mold cavity. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. (2011) and Fig. They can affect the strength and. This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold temperature control, significantly increasing mold temperature beyond typical values observed in conventional processes. During injection. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. ABS is a commonly used plastic in injection molding due to its excellent mechanical properties and chemical resistance. Powder injection molding comprises several processing steps, and defects may occur in each step if care is not taken. With unchangeable and fixed requirements for the final product, their avoidance often proves difficult. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. Xie L, Ziegmann G (2008) A visual mold with variotherm system for weld line studying micro injection molding. The main runner and sub-runner are too thin or too long. 030 0. Knit lines in injection molding are undesirable, especially when surface appearance and part strength are significant concerns. Or, the part where the weld line is produced shall. This failure causes the product to be damaged during use. The weld line is then created with a higher flow front temperature and is packed with more pressure. 1. For thick-walled parts, slow injection rates result in more uniform polymer distribution . Microsyst Technol. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. The impact behavior of weld-lines in injection molding. 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. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. Set up the process overflow and use it as the place where the weld line is generated, and then cut off and remove it after forming. org or visit 80-ton Victor injection molding machine, equipped with an accumulator capable of delivering maximum flow rate of 138 cm 3 /s and providing maximum injection pressure of 210 MPa, is utilized for experiments. Flow-induced filler orientation manifests in higher tensile prop-erties in the direction of flow compared to those normal to the direction of flow. 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. Consequently, it causes viscous dissipation which leads to the generation of heat. [ 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. Effects of mold temperature and pressure on shrinkage 0. The optimal process condition is very likely to appear in this second part's fine-tune group. 3. For example, filled resins and ABS are more likely to. The resulting defects don’t stop at flash only. This may require higher melt temperature or lower injection speed . Weld-line is a weak area which reduces the strength of the part locally. This is expected to achieve maximum results while the pressure holding effect will also increase. Weld line additionally called as knit line, is a defect that occurs when the injected plastic meets within a. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. Weld line strength is important in blow molding as well as injection molding. We recently had a few pieces (2-3%) crack after assembly, while in storage (not installed, still in the package). If the different flow fronts have cooled. 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]. Figure 2. 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. Thoroughly clean molding machine cylinders. Weld lines are a common defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are still rather few. Weld lines appear on the surface of a molded part where the molten material converges after splitting off into two or more directions in a mold. The most common and one of the most challenging injection molding defects are weld and knit lines. The impact behavior of weld-lines in injection molding. A flat product case was considered as an example of a typical aircraft structural element. 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. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. open access Abstract Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. The injection molding gate generates heat by dissipation. Strength at weld the line location and warpage problem in injection molding plastic component were not new problems in injection molding industries. The three parameters affecting operation were called injection pressure, injection time, and packing pressure which influence the quality of weld line. Remedies: Raise the temperature of the mold or molten plastic. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. Alloys. 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. Venting at Weld Lines. The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. 2011; 509 (2):226–233. In narrow fields, a limited amount of molten liquid can solidify and block the flow. Weld line. A weld line is often unavoidable. Fracture Toughness of Weld Lines in Thermoplastic Injection Molding, Polymer Engineering and Science, 33(15): 996-1001. The gate location should enable the two flow fronts to merge easily and continue to flow beyond the weld line. Polym Eng Sci 45(7. 3. In injection molding, it is often important to maintain consistent color throughout the part. Injection molding can be performed with only one of these materials like glass, plastics, etc. 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. Weld lines are one of the typical quality issues of injection molded parts. This will produce parts with aExperimental results show that the weld-line strength from a standard test is not applicable in microinjection molding. “I realized weld -line problems are a very common issue for injection molded parts,” Nicholson told Plastics Technology. In an injection molding process, a weld-line forms when two flow fronts meet each other. 0 mm, is designed to conduct the. Lugs size is 65 х 24 х 4 mm. (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. 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. This consequently produces weld lines. Abstract. 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 design of the mold, as well as the part being molded, has a significant impact on the success of the process. They occur when melt flow fronts collide in a mold cavity. Injection molding is a manufacturing process that involves injecting molten plastic into a mold cavity to create a specific shape or design. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. Five injection molding process parameters, including mold temperature, melt temperature, packing pressure, injection. Insufficient clamp tonnage Increase clamp pressure or move to machine with more tonnage . For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. 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. For this purpose, the width of the weld line calculated by Sigmasoft is. 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. Consultant @ Effinno Technologies, BSME, MBA - Bridge between Plastics Injection Molding Knowledge and Practice. 3 and 53. and most commonly, thermoplastic polymers are used. Table 2-Glass Fiber Glass Fiber Glass Fiber Glass Fiber A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. Miron MC, Major Z, Adachi T. Meld and knit lines are actually both different types of weld lines. 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. The parts are molded flat and are slightly stressed once installed in an arced position, but not excessively. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. To prevent weld lines, increase the pressure and temperature. 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. Slow down injection speed. In this study, we apply the technique of SAW to explore the acoustic properties near injection-weld lines by comparing the velocity of. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld. One of the things that can compromise an injection molded part is a weld line, also called a knit line. Remedies: Raise the temperature of the mold or molten plastic. The possibility of the functional thin film for. [1-2] investigated the weld line zone of injection molded glass-fiber-filled polypropylene (PP) composites. 2. Try to gradually raise the mold temperature and barrel temperature. That helps. 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. injection molded pipe-fittings with and without weld line. During injection moulding, a weld-line occurs when two or more flow fronts collide in the hollow cavity. This month, in our FREE SimTech™ series of webinars, we will explore weld lines and how they develop. <Mold> Increase (or decrease) the size of the runners and gates. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. Materials Science. In an injection molding process, a weld-line forms when two flow fronts meet each other. Mobile 0813; Shinko Sellbic Co. Weld lines can impact the strength and appearance of the final part, and are often considered a defect. This reduced thickness of the frozen skin further enhances the visual appeal of the. Weld lines can be caused by material flowing around holes or inserts in the part, multiple injection gates or variable wall thickness where hesitation or "race tracking" can occur. Threadline gap in-between part due to improper gate location in complex design parts including excess of holes (multipoint. Improper fusion of two fluid flows, a state before weld line. Description Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. To increase the sustainability of the process, determinative parameters and their effects should be examined. A weld line can appear during the absence of enough pressure to push the plastic flow and then meld. Xie L. This study addresses the effects of injection molding weld line on the fatigue crack resistance of commercial CPVC in the temperature range of −10 to 70 °C. 4If 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]. industry, to deliver intuitive injection mold-ing simulations embedded in NX. [ 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. Recently, injection molding process has generated growing interest, exhibiting great potential to easily fabricate unique polymeric materials for industrial applications. Insufficient plasticizing ability of injection molding machine. 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. So today we are going to take a look at the five most common defects in injection molding and their solutions. Install an ultrared light inside the hopper. This failure causes the product to be damaged during use. When two or more streams of plastic meet and fuse. • Reduce runner dimensions and maintain the same flow rate. Weld lines in injection molding are a type of cosmetic defect that detracts from a plastic part’s appearance. 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. when two or more melt flow fronts contact each other immediately after the cooling process. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. The injection pressure is too lowEffect 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. Injection molding is nothing without molds. Fracture behavior of weld lines in injection molded components loaded under real operating conditions. From Understanding Weld-line Integrity by Sabic Innovative Plastics, p. This study focuses on the effect of melt temperature on. In. If so, look for an alternative resin. 2. Nguyen-Chung. Abstract and Figures. Published 5 July 2019. When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. These lines are formed when two or more flowing molten plastic streams meet and fuse together, creating a visible line on the surface of the molded part. Weld Lines-3 Ways for Detecting and Correcting. Flow lines arise when at least two melt fronts meet at an acute an-Weld line is aesthetically unpleasant and affects the mechanical strength of injection molded parts. Criens, R. Maintain a holding pressure that is no more than 1/2 the. Weld lines can appear on the components when the molten plastics meet each other as they are flowing from two different parts of the mold. If weld lines are unavoidable due to multiple gates in a moulding, they should be positioned in the non-critical region. Article Google Scholar Deng YM, Zheng D, Lu XJ (2008) Injection moulding optimization of multi-class design variables using a PSO algorithm. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. ). According to the weld line distribution map of six gate schemes shown in . But the unfavorable and unavoidable defect of weld line in micro injection molding part leads to detrimental mechanical and surface properties. And how to use the 3 modes of the sequential controller correctly to prevent burn marks, weld line, short shot, and other part defects in injection molding. In. reinforcement type and amount in nylon 6/6. 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. Figure 1. As the unfavorable defect in micro injection molding parts, weld line brings reduced mechanical and physical properties, especially for nano filled composites. The weld line and the flow pattern of co-injection molding can be seen from Fig. Visualization analysis of flow behavior during weld-line formation in injection molding process. Sink marks, 2. In addition, its tensile strength and stiffness will be sharply decreased. Tekanan yang kurang mampu untuk mendorong aliran dan kembali pada posisi semula dapat menimbulkan weld line. Inadequate back pressure. Injection Molding Glossary; Weld Lines; Weld Lines. Silver Streak. High-density PE was also moulded in the same conditions but in a lower temperature range (145 to 220°C). Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Increase the injection speed. Effect of process parameters on the relative weld line strength From injection molding practice and literature, 1, 3,4 it is generally accepted that: if a weld line forms before the filling is. This method was adopted. One common issue that frequently arises during injection molding is the formation of weld lines. In order to prepare the weld line specimen by micro injection molding, a mould integrated with visual system and variotherm system was designed and constructed, shown as Fig. Poor weld line quality can lead to short-term or long-term product failures, initiated at the weld 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. In this experiment, several ejector. 2. C. The problem with ‘weld lines. Known also as knit lines and. 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. , 47 (2008. A weld line develops when two or more flow fronts come together but do not meld completely because of partial solidification. 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. Bin-Xin Yang Ouyang Jie Supei Zheng Qiang Li Wen Zhou. Machine Shot Capacity – The maximum volume of resin that can be injected in a single stroke of the injection machine. Its design significantly impacts the final product’s appearance, strength, and functionality, making it crucial for manufacturers to understand its intricacies and variations thoroughly. 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. 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. Weld line is one of the plastic injection molding defects. One solution is to prevent the weld lines from forming in regions that are. Examples of such failure are shown in Figure 1. Micro injection molded polymeric parts coated with functional thin films/layers show off the promising applications in microsystems area. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. technical ulletin SPECIALTY POLYME RS Design and Production of Injection Molding Tools. In. 7 in Kobayashi et al. Rapid heat and cool injection molding is an example of a measure to prevent the generation of weld lines. Ejector System (Pötsch, 1995) . It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. Plastic Injection Molding Process. Another relevant topic in injection molding is the presence of weld lines (WLs) and their properties, which could lead to part weakness through surface disturbances, optical issues and reduced bonding [21, 22]. (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. T. In the 1947 book, Injection Molding of Plastics, the late Dr. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. (3-1) Increasing the Resin Temperature at the Weld Line Section. Usually it’s a straight line, and often to be found radiating away from a hole, inclusion or other such part feature. 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. This model provides the necessary information. Fellahi et al. Siemens PLM Software. Gava and co-workers implemented an investigation devoted to the de-weld lines in injection molded thermoplastic composites. The occurrence of a weld line means a significant problem both aesthetically and mechanically in the design of injection moulded parts. We have various types and models available. We'll show you how. The choosing optimal gate location technique has been developed to set weld lines as far as possible from the region of maximum stresses. When an external load is applied to a weld line region, the part’s potential for mechanical failure is increased. A knit line, also called a weld line, occurs when the liquid plastic moves through the mold and hits more melted plastic and they don’t flow or fuse together. If not, the speed will drop, and it could create weld lines. This line does not normally impact the overall shape or dimensions of the item. (3-1) Increasing the Resin Temperature at the Weld Line Section. II. But none of the current packages can predict weld lines’ properties qualitatively. To respond to poor plasticization and uneven melt temperature, the molding cycle can be extended to make. Weld Lines. molding Æ Thermoplastics Æ Weld line Æ Simulation Rheol Acta (2004) 43: 240–245 DOI 10. Learn more about ABS injection molding here. When two or more strands of molten plastics meet in the mold, a weld. 13 shows the best gate location for which the weld lines . The wheel has to be gated at three places on the hub and. Azuddin / Procedia Engineering 184 ( 2017 ) 663 – 672 Fig. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. A weld or meld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. % glass fibers – PA6 Aramid SV 30-1ETM (figure 1b). 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. Injection molding is one of the most established and well-known methods of plastic processing. The strength of the weld-line area can be increased by optimizing injection molding process parameters like melt temperature, injection speed, packing pressure, changing gate type and location, etc. In the sense that the weld line is better formed before the resin temperature. Processing OptimizationReduced frozen skin thickness: High injection speeds also contribute to a thinner frozen skin at the weld line. In this mold, a visualization design and a rapid heating/cooling system were integrated, and specimens with different cross section. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. Shaofei Jiang. 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 study focus on the. Figure 2. CrossRef View in Scopus Google Scholar [17] G. 226-233. 4. 2012. This study describes how the weld line was formed on the part. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. 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. Injection molding is a complex multi-variable, nonlinear and time-varying unsteady process, which makes it more difficult to optimize the process parameters. In the sense that the weld line is better formed before the resin. Weld line Weld line dikatakan ketika dua atau lebih aliran lelehan depan. Valve gates also make weld lines less of. Bubbles are caused by melting flow fronts colliding in a mold cavity. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. 015 0. 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. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. 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 defect generated in injection molding, which apparently affects the performance of final products, but the available reports on carbon fiber-reinforced thermoplastics are. Fig 13:- Detailed view of weld lines. 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. At a low volumetric injection flow rate of 33. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. 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. Weld lines in injection molding are frequently unavoidable. In this paper, a weld line factor (W-L factor) was adopted to describe the. In order to reduce these weak points, a special ram technique for injection molding, which can be integrated into the mold, was investigated. Mold vents should function the same way. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Islyn Thomas summarized the need for a particular vent location better than I ever could. To prevent weld lines, increase the pressure and temperature. Wu CH, Liang WJ (2005) Effects of geometry and injection-molding parameters on weld-line strength. (+86) 760 2222 2556 enquiry@starrapid. 2. Thereby creating localized pressure within the mold. They. Because of the ever-increasing requirements for parts performance, lots of researchers have perf. Figure 1 below shows the development of a weld line. Abstract. Weld lines are a common imperfection to be found in most plastic injected molded parts. 1. In this paper, two different injection molding tests were completed. 2007; Lotti et al. Here are some reasons why design is important for injection molding. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. 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. Flow-induced filler orientation and weld lines are un-avoidable facets of the injection molding process. Flash. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. A quantitative evaluation of the appearance quality of weld lines in RHCM parts. 18 ชิ้นงานเกิดเป็นเส้นรอยประสาน Weld line. These master batches and PP pellets were dry-blended by adjusting the ratio such that the fiber contents were 10, 20, and 30 wt%. Molding with weld line model Moldex3D was used for calculate the molding of lugs (figure 1). Meld and knit lines are actually both different types of weld lines. Mold flow analysis is widely employed in mold making industry, utilizing data simulation software, the injection molding process can be simulated and presented on the computer,. This study focuses on the analysis of fill time by optimizing the injection molding parameters to reduce the defects that are always found on the plastics part such as poor weld line and part not. Weld line usually is not allowed on some critical area, and weld line on the part also weaken the strength. 3. To resolve this issue, rapid heat cycle molding (RHCM) has attracted attention as an innovative PIM technology. . Technol. G. Reposition gates and runners to allow resin to flow around the obstruction from a. 1. Just check out some of it on the above lists. Increase the injection speed. [ 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. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. demanding injection molding and end-use requirements. 030 0. In the RHCM, the mold temperature profile plays a crucial. A weld line is a mark left on the surface of a plastic injected molded part. [ 18 - 21 ] In addition, the effects of flow behavior of the polymer melt due to the optimal process parameters for the minimization of weld-line effects are an important consideration. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Fortunately, there are several. The flow of the material in the injection mould takes place through the gate. 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. box, along the region of weld line formation (wc, wm, we and wl) and away from the weld line, in a radial position along the flow direction (R), as shown in Figure 2. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. This paper presents the. Weld lines can be caused by many reasons, which covers the various aspects of mold, process, raw materials and product design, etc. Possible causes: Low temperature or fluidity of melted plastic during injection molding. 3 cc/sec, the weld lines decrease over temperatures up to 150 C, while at higher volumetric injection flow rates of 43. Five industry pros with more than 200 years of combined molding experience provide step-by-step best practices on mounting a mold in a horizontal injection molding machine.