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. Effect of geometry and injection-molding parameters on weld-line strength. Mechanical properties of the weld line defect in micro injection molding for various nano filled polypropylene composites. . 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. For glass-filled grades, the thickness at the weld line can be slightly larger than the nominal value due to lower shrinkage associated with vertical fiber orientation at the weld line cross. Weld or knit lines result wherever two or more polymer flow fronts unite. Re-balancing entire manufacturing lines may be required to effectively deliver and sustain SMED excellence. 2. Flash. Redesign the mold to prevent the weld line. NX Mold Flow Analysis. Weld lines form where two or more flow fronts come together and can create a cosmetic or structural problem. Steven. 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 often generate mechanically weak areas, because of the unfavorable perpendicular orientation of the macromolecules, fibers and/or other fillers to the direction of the main flow. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. One of the factors that determines the quality of injection molded parts is the weld line [50,75,76]. Fracture behavior of weld lines in injection molded components loaded under real operating conditions. Weld line is one of the plastic injection molding defects. Plast. A weld line region is typically filled at the end of an injection stroke or during the pressure phase. The gate is the critical bridge between the runners (the channels through which the molten plastic travels) and the actual mold. 020 0. 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. Weld lines in injection molding are frequently unavoidable. Wavy lines are another feature of weld lines. The optimum injection molding parameters to manufacture the product was determined by . 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. 1. 2. In. Munich, Germany: Carl Hanser Verlag, 1994. . The schematic diagram of a weld line formation is illustrated in Figure 7, where is the welding angle of two melt fronts. Thoroughly clean molding machine cylinders. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked. Inadequate back pressure. Weld line strength is important in blow molding as well as injection molding. Effects of mold temperature and pressure on shrinkage 0. As these flow fronts come together on the. 010 0. 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. An evaluation model based on artificial neural network method. 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 can be caused by material flowing around holes or inserts in the part, multiple injection gates or variable wall thickness where hesitation or "race tracking" can occur. The optimal process condition is very likely to appear in this second part's fine-tune group. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPEffects of mold temperature and pressure on shrinkage 0. Possible causes: Low temperature or fluidity of melted plastic during injection molding. 1. Weld lines can lower the integrity of the part. 3. Improper fusion of two fluid flows, a state before weld line. Weld-line yield strength, yield strain, and failure strain of talc-filled polypropylene increase with increasing melt temperature and increasing hold pressure. Weld Lines. This consequently produces weld lines. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. Weld lines in injection molding are frequently unavoidable. Meld Lines. 030 0. During injection. Figure 2. The wheel has to be gated at three places on the hub and. The impact behavior of weld-lines in injection molding. Since 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. They occur when melt flow fronts collide in a mold cavity. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. 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 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. (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. According to the weld line distribution map of six gate schemes shown in . A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Failure may result due to the assembly torque, or end-use application loads (temperature, creep). 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. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. 13 shows the best gate location for which the weld lines . In this study, the effects of injection temperature, injection pressure, and fiber content on the mechanical properties of weld lines were studied for carbon fiber-reinforced nylon. A 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. When molten plastic flows, it forms a smooth continuous flow until it meets an obstruction. The thermo-rheological findings were used to investigate the sources of weld line weakness. Weld lines. Meld and knit lines are actually both different types of weld lines. In our DFM report, we will analyze the possible weld lines. Weld line existence reduces the material strength; however, its. Weld-line is a weak area which reduces the strength of the part locally. Xie L, Ziegmann G (2008) A visual mold with variotherm system for weld line studying micro injection molding. This paper presents the. Miron MC, Major Z, Adachi T. 020 0. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. One of the things that can compromise an injection molded part is a weld line, also called a knit line. 8. 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. 1. This paper analyzes production data from injection molding processes to identify key interactions between the process variables from different material categories using the network inference method called “bagging conservative causal core network” (BC3net). Increase the injection speed. In this study, the effects of injection temperature, injection pressure, and fiber content on the mechanical properties of weld lines were studied for carbon fiber-reinforced nylon. As such, optimizing mold designs should always be incorporated in your production model. Figure 1a illustrates how the weld line is produced when two melt streams merge during the final filling process. There are several possible causes that need to be investigated to troubleshoot weld lines in injection molding. Remember, by avoiding weld lines, you can lessen operations cost. In this study, one injection mold. G. As a defect of micro injection molding parts, weld line is unfavorable since it will influence the surface quality and mechanical properties of micro parts. Multi-Shot Molding – A molding process that uses two or more plastic materials to form a single part. This results in a region of a different level of molecular entanglements than the bulk material. Weld lines occur when melt flow fronts meet during the injection molding of plastic parts. on conventional reciprocating screw injection molding machines using molding practices standard for filled engineering thermoplastics . DescriptionThis insertion ensures the separation of the melt flow. Bubbles are caused by melting flow fronts colliding in a mold cavity. Tekanan. Increase the injection speed. 298 µm and the weld line on the heated region was almost eliminated with the aid of induction heating. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole. Change the gate locations. 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. 1 Prediction of weld lines with injection molding simulation softwareWeld lines in design for manufacture. Polym Eng Sci 45(7):1021–1030. Weld Lines are formed when two or more molten polymer flows meet during the injection molding process. A visual mold with variotherm system for weld line study in micro injection molding. 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. Increase the injection speed. Simulation of polymer molding filling process with an adaptive weld line capturing algorithm. Consequently, weld regions have been observed to have inferior mechanical properties compared to the bulk. 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. Increase the mold temperature. 18/06/2021. In. 2. Weld line formation in the injection molding process occurs. สาเหตุรองของการเกิดปัญหาการเกิดประกายเงิน (silver streak) 1. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Again, consult with professionals as to how you could improve mold designs. Weld lines are a kind of Achilles heel of plastics. Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. Investigate for potential contamination. 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. [1] Kobayashi et al. As a result this. Munich, Germany: Carl Hanser Verlag, 1994. When this fails to happen correctly, a weld line defect occurs. Weld line defects are a common part defect that occurs when the injected plastic flows around a solid piece of the mold and does not knit back together. Knit lines in injection molding are undesirable, especially when surface appearance and part strength are significant concerns. It provides scientific basis for designers toWeld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. Our injection molding company is explaining what these imperfections are, why they can compromise. 5. Weld lines are formed when two melt fronts come in contact with each other. These flow. Install an ultrared light inside the hopper. Install an ultrared light inside the hopper. If the injection molding speed is too slow, however, there may be an insufficient filling of the mold. As a result this weld line will be a weak point in this part. Penyebab Weld Line. 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. These potential causes include:Known methods to reduce weld-line effects are the optimization of injection molding parameters, enhanced tool temperature, and using special molding tool devices. With Ixef® PARA compounds, the strength of a weld line is typically 90 MPa (13,000 psi). Figure 1 below shows the development of a weld line. 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. demanding injection molding and end-use requirements. In injection molding, it is often important to maintain consistent color throughout the part. This type of injection molding resolves any trouble caused by undesired welding lines. (1) Increase the injection pressure and prolong the injection time. 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. 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. If it only affects the appearance, it can change the position of the burn four to change the position of the weld line. 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. 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. th INTRODUCTION Injection molding is one of the mostWeld lines have been one of the common defects puzzling the injection molding industry. They decrease the. 5. In this mold, a visualization design and a rapid heating/cooling system were integrated, and specimens with different cross section. To prevent weld lines, increase the pressure and temperature. Injection molding can be performed with only one of these materials like glass, plastics, etc. poor flow fronts that are too cold, this can also lead to a deterioration in the mechanical properties. Weld lines are visually undesirable and a plastic part is structurally weak at weld line positions. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection. 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]. 2. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. (2) Causes & Countermeasures (See the table below) *Note: Flash also tends to occur when the injection pressure/speed are too high, but molding time is too long and mold temperature is too low. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. This defect occurs due to the temperature and pressure not being high enough, causing premature solidification. Criens, R. As such, optimizing mold designs should always be incorporated in your production model. Injection speed is too low. Injection molding could be applied with many polymer materials, such as. This remains as a challenge for control engineers. In this lesson we will focus on the meld and weld lines. Flow marks in injection molding can be avoided if adequate measures are taken. The. 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 injected. The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. How to Reduce Weld Line in Injection Molding? Weld lines are a common issue that occurs in injection molding. <Materials> Pre-dry thoroughly. A visible weld line is observed, due to a combina-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 appear as a result of the flow of molten plastic during the injection molding process. 030 0. Below is one of the examples: !NOTE: if the weld lines is important to the cosmetic surface of your part, please bring this up to your mold maker during quoting phase. Weld lines 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. Meld and knit lines are actually both different types of weld lines. C. The weld line length was selected as part of the quality index to investigate the effects of gate location on weld. Why You Should Avoid Weld Lines. + Optimize holding pressure time. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Machine Shot Capacity – The maximum volume of resin that can be injected in a single stroke of the injection machine. 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. They are the result of fundamental physical effects taking place inside of the mold tool cavity. Procedia Mater Sci 2014; 3: 2048–2053. The main runner and sub-runner are too thin or too long. Kagitci YC, Tarakcioglu N (2015) The effect of weld line on tensile strength in a polymer composite part. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. It occupies a major part in the plastics industry ranking second to plastic extrusion in terms of production and the utilization of both thermoplastic and thermosetting plastic materials. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at. In some cases, a weld line can also cause a loss of strength and impact resistance. Cited by (41) Effect of mould surface roughness adjustments to increase the flow path length in the injection moulding process. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. We have various types and models available. Weld Lines. Tekanan yang kurang mampu untuk mendorong aliran dan kembali pada posisi semula dapat menimbulkan weld line. 3. , 509 (2) (2011), pp. In injection molded parts, there are 2 types of weld lines: The first type of weld mark is called cold-melt joints and is formed when the melt front enters the cavity with different. Edge Gates. It is not always easy to completely eliminate weld lines by simply adjusting the relevant injection mold design or the molding conditions. In a meld line, the plastic comes together at an angle greater than 135 degrees. A simulation of mold filling with multi-inlets or an insert in the cavity is pursued with an improved Level Set Method. Processing Optimization Reduced frozen skin thickness: High injection speeds also contribute to a thinner frozen skin at the weld line. , Ziegmann G. (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. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Investigations on WLs in micro injection molded parts were performed in Refs. + Adjust injection speed. Injection molding is nothing without molds. In this experiment, several ejector. 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. 226-233. Injection moulding (U. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. Berikut beberapa di antaranya: 1. Fig 13:- Detailed view of weld lines. Investigate for potential contamination. 1. If you turn on the spigot to a garden hose, you will hear a hissing sound at the nozzle end for the first few seconds. Email him at jhenz@polymer-center. The impact behavior of weld-lines in injection molding. Mechanical properties of the weld line defect in micro injection molding for various nano filled polypropylene composites. 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. J. What causes them? The primary cause is weak bondage between two or more flow fronts. Abstract and Figures. 666 Azieatul Azrin Dzulkipli and M. Wu CY, Ku CC, Pai HY (2011) Injection molding optimization with weld line design constraint using distributed multi-population genetic algorithm. Figure 2. It is important to investigate the weld line because the weld line area can induce potential failure of structural application. 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. Known also as knit lines and. as warpage, shrinkage and weld line of the plastic parts. 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. As the plastic flows through the mold it. * Corresponding author, e-mail: [email protected] an injection molding process, a weld-line forms when two flow fronts meet each other. 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]. The thermo. 4. These lines can weaken the strength of the part, and they can also be unsightly. Weld line defects are a common part defect that occurs when the injected plastic flows around a solid piece of the mold and does not knit back together. . Nguyen-Chung. For multiple gate and complex part, molding weld-lines are unavoidable, therefore mechanical behavior of the weld-line needs to be predicted. It is important to investigate the weld line because the weld line area can. The effects of these two injection molding process parameters are explained in terms of their influence on the skin-core morphology observed on the fracture surfaces in the weld zone. Wang, G. In an injection molding process, a weld-line forms when two flow fronts meet each other. 2. (2011) and Fig. Visualization analysis of flow behavior during weld-line formation in injection molding process. Injection pressure or. 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. 1. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. For thick-walled parts, slow injection rates result in more uniform polymer distribution . Weld lines appear as a result of the flow of molten plastic during the injection molding process. (2) Adjust the injection speed: high speed allows the melt to reach the confluence without cooling down, and low speed allows time for the air in the cavity to be discharged. They are unavoidable even for moderate complex products. The Solutions for Poor Welding Lines. Weld lines have been one of the common defects puzzling the injection molding industry. 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. Reduce the amount of release agents. They. Effects of cavity surface temperature on mechanical properties of specimens with and without a weld line in rapid heat cycle. 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. 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 most simple design modification for eliminating the weakening effect of a weld line is to increase the wall thickness in the weld line zone (Figure 4). As a defect of micro injection molding parts, weld line is unfavorable since it will influence the surface quality and mechanical properties of micro parts. Gate blush, 4. 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. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. Slow down injection speed. + Improve vent inside the mold. Bin-Xin Yang Ouyang Jie Supei Zheng Qiang Li Wen Zhou. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Compd. The weld lines are an integral part of plastic injection molding and can seldom be prevented, even by specifically planning the mold with inserts for holes or the like. Poor weld line quality can lead to short-term or long-term product failures, initiated at the weld line. 6. S. 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. In the present work, the micro specimens were investigated. (+86) 760 2222 2556 enquiry@starrapid. Optimization of Injection Molding Process to Minimize Weld-line and Sink. In this paper, a weld line factor (W-L factor) was adopted to. They decrease 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. Bociaga and Jaruga (2007) investigated flowing weld line in injection process by injection molding machine, which the part surface was observed in reflected light using the optimal microscope and. That helps. Its design significantly impacts the final product’s appearance, strength, and functionality, making it crucial for manufacturers to understand its intricacies and variations thoroughly. 2. Here are some strategies. The Problems & Solutions course is designed to train injection molding personnel in. Controlling the mold’s temperature could also minimize the weld line’s effects. 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. Figure 1 below shows the development of a weld line. The following are the conclusion drawn from the present research: 1. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Adjust the position of the gate and include a venting slot. Methodology. Therefore, the length of flowing weld lines must be additionally defined. Weld lines are one of the typical quality issues of injection molded parts. Flashes, 3. The terahertz time-domain spectroscopy (THz-TDS) imaging technique was used to detect the weld line defect of an injection-moulded short glass fiber-reinforced composite. To respond to poor plasticization and uneven melt temperature, the molding cycle can be extended to make. Valve gates also make weld lines less of. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. M. Burn Marks. If so, look for an alternative resin. 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,. 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. (3-1) Increasing the Resin Temperature at the Weld Line Section. when two or more melt flow fronts contact each other immediately after the cooling process. – Use generous and even. Weld-line is a weak area which reduces the strength of the part locally. 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. Increase the injection speed to reduce the amount of cooling happening in the mold. injection molding. Weld Line defect analysis, the most common of many defects in injection moulding products. 4. But none of the current packages can predict weld lines’ properties qualitatively. They happen when two flow fronts of melted plastic meet and solidify, leaving a visible line on the surface of the part. (3-1) Increasing the Resin Temperature at the Weld Line Section. In the case of PC, the model predicts satisfactorily the weld-line strength as a function of injection temperature. 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. 2002), the use of simulation approaches (Berti and. To position weld-line to avoid critical areas for the sake of aesthetics or mechanical strength is the key to the success of bi-injection molding. identi fy a s urface defect i n th e for m of a weld line, which occurs due to the two injection points at x = 5 mm and 34 mm ( see Fig. They. In. Weld-line, a common occurrence in plastic injection moulding, is a representative defect compromising mechanical qualities and product appearance [16]. <Mold> Increase (or decrease) the size of the runners and gates. (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. 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. An injection molding processor who can analyze the process from the plastics point of view, can quickly solve any molding problem, regardless of the machine or plastic type. Venting at Weld Lines. Article Google Scholar Xie L, Ziegmann G (2009) Influence of processing parameters on micro injection molded weld line mechanical properties of polypropylene (PP). Insufficient plasticizing ability of injection molding machine. Weld line problem which occurs in polymer parts produced by plastic injection method and affects appearance and strength on a large scale was researched in this paper.