The chart below shows recommended wall thicknesses for common injection molding resins. Walls thicker than 8mm (0. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright. Also called “Weld Line. The position, length, and angle of weld lines are dependent on the gate location, injection speed, injection pressure, mold temperature, and, especially, the direction and degree of the polymer melt velocity in the. 030 0. The last cause of flow lines may be the operators running your daily operations. Flow Lines. The weld lines are formed when there is an obstacle in the cavity of the injection mold. They occur as a result of different flow rates of molten plastic in the mold cavity. 015 0. Weld Lines. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. The Problems & Solutions course is designed to train in the recognition and analysis. 000 0. MMT Chats. Increase the size of the gate and reduce the thickness of the walls of the molded part. Poor mold surface n Refinish a poor or worn mold surface. This action could indicate that one portion of the plastic flow will move more quickly than the other. What Are Flow and Knit Lines? Flow lines are defects that appear as wavy. If it is farther down the flow part, increase injection speed to decrease viscosity and allow more packing pressure. Pack (hold time) is usually 2 to 3 times the mold fill times, depending on gate size. If I can answer any questions you may have on optimizing the plastic part design, CNC plastic prototype, mold manufacturing, and injection molding or if I can be of any other help, please feel. Mold makers should also pay attention to sprue, runner, or gate design. ”. Kulkarni) During the fill phase (Fig. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Several factors can contribute to shrinkage in injection moulding, including material, part design, mould design and processing parameters. Then the melt is injected into the mold and the surface of injection-molded products is. Figure 1 below shows the development of a weld line. 4, no. By understanding material fill, injection mold designers can better position gates, anticipate where knit lines will appear, and locate difficult to fill spots in the mold. Common injection Mold Flow Lines. Warping. It is a type of distortion caused by this premature solidification. 5. The streaks form from plastic in the mold overlapping with plastic following it. Flow marks are caused by a variety of factors in the injection molding making technology, and they happen at the gate. Fixing Process Variables That Can Cause Flash. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. Part walls thinner than 4mm (0. 1). The injection molding process involves the injection of a polymer melt into a mold where the melt cools and solidifies to form a plastic product. Raising the temperature of the mold slightly can help to prevent flow lines, as it prevents the molten material from cooling immediately upon impact with the cavity walls. The definition of weld lines: When multiple plastic flow fronts meet in the cavity after encountering inserts, holes, or areas with inconsistent flow rates or interrupted melt flows, or in the case of gate injection filling, the inability of two or more flow fronts to fully “knit” together will cause the linear weld marks. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. 015 0. Circuit Identification. In addition, when the melt is solidified in the cavity, there is a vacuum between the product and the cavity wall, also the air must enter the mold. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. "Design and Mould Flow Analysis of Injection Mould for Connecting Link," International Journal on Emerging Technologies, vol. Flow lines. Weld line. In this regard, the gate form with less shunt should be used, and the gate position should be selected reasonably. As the material properties of. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPWhen it comes to injection molding, the chances you might end up making a costly mistake is too high. Shortening the molding cycle time is a key factor in improving energy efficiency and since cooling occupies a major part of the cycle, effective design and operation of cooling systems is essential. 20 mm. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. The resulting defects don’t stop at flash only. Address 272 Commonwealth Drive, Carol Stream, IL 60188. All mold cooling lines must have adequate flow to produce a turbulent flow condition. Request a same-day quote to see how our medical injection molding experts at Aberdeen Technologies can help move your project forward. The flow fronts at different times (Fig. If necessary, the mold designer may simulate the flow of solidification of resin using an injection molding simulation program. Flow marks: Flow lines Directionally "off tone" wavy lines or patterns Injection speeds too slow (the plastic has cooled down. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. A ‘parting line’ is the line of separation on the plastic part where the two halves of the plastic injection mold meet. Flow lines are aesthetic defects that occur on plastic products. 0030 in. Flow Lines. 750 in. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. For example, baffles require water to flow in a. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Avoid Drag in Molded Parts. The flow rate should ensure the material does not lose its. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. Thin walls often increase the pressure required to fill the part, and. By heating the solid material, it is converted into a fluid state with a low resistance to flow. Excess Mold Release Poor mold design, including inappropriate mold wall thickness and faulty gate placements, is a common cause of weld line formation in injection molding. Unexpected flow lines, so-called tear drops, occur. Learn how to troubleshoot weld lines in injection molding. In other words, the long-chain polymer. For injection molding grades, the MFR (MI) values for polyethylenes are generally determined at 190°C (374°F) using a static load of 2,160 g. 1. Lower speeds allow gas more time to escape through vents. Weld lines are usually pointed out as the weak region in molded parts. These are caused by the shot of molten plastic moving at different speeds throughout the injection mold, which ultimately causes the resin to solidify at different rates. Molds for investment casting are more accurate and have fewer defects, thanks to flow control over wax injection. 2. Image 4: Top, HDPE streamlined structure. The other parameters such as Mold temperature and Cooling Time also contribute in the defects appropriately. 0010 in. Flow lines – A common plastic injection molding defect in which discolored ring-shaped streaks, patterns, or wavy lines appear around gates or narrow sections of the finished product. Commercial injection molding simulation packages, such as Moldflow and C-MOLD, have been incorporating GAIM options to provide computerized design and optimization tools for GAIM processes and. 6. The moldability validation and flow analysis tools enable you to iden-tify and correct potential injection molding problems as you design the product. A. Low-quality and poorly designed molds can also result in flow lines on injection molded parts, particularly those with uneven wall thickness, insufficient lubrication, and poor venting. This defect compromises aesthetics. Kulkarni) During the fill phase (Fig. It can help you reduce defects, improve quality, and save costs by simulating how. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. 160"). Injection molding machine . 4) Extended Shutdowns. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. How to recognize, prevent, and counteract flow lines defects in injection molding? Learn. The line where two resin flows “knit” or “weld” together during injection molding is called a weld or knit line. Inadequate cooling time. Features such as sharp corners or undercuts can. Remedies: Increasing the injection pressure will force the molten plastic against the mold cavity. They can be off-color or discolored material compared to the intended color of the part. Each needle valve nozzle opens only when the melt front has moved across its gating point. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. Here’s a rundown of helpful tricks to keep in mind when designing and choosing a material for molded parts with walls: In general, ensuring your design has uniform wall thickness between 0. Mold Design. As a result this weld line will be a weak point in this part. reduce the ability to positively influence the strength. Excess Mold ReleasePoor mold design, including inappropriate mold wall thickness and faulty gate placements, is a common cause of weld line formation in injection molding. RapidDirect – Your Best Injection Molding Partner. The mold flow model is usually a single-part model, that is, the FRT part itself, but the mechanics model is often a multi-part model, an assembly of the FRT part and others. Weld lines have been one of the common defects puzzling the injection molding industry. Shear; There are two causes of splay brought on by shear. One of the things that can compromise an injection molded part is a weld line, also called a knit line. Accept All. Basic Repairs for Warping. The weld line and the flow pattern of co-injection molding can be seen from Fig. Reduce the injection pressure to prevent overpacking at the gate. This depends on a. This can prevent the opportunity for trapping air. Energy use by thermoplastics injection molding machines is estimated to result in global CO 2 emissions in the order of 80 million metric tons annually. Depending on the resin, resin temperature, mold temperature, and filling. In terms of viscosity, higher heat equals faster flow and lower heat equals slower flow. Insufficient injection pressure or time. Reduce the temperature of the mold and plastic being injected. Vents have three components. Raise the mold temperature, maintain a high. The CoolingCare system tests cooling channels for leaks and blockages. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. Injection molding could develop knit lines if one front cools before it reaches the other. After exhaustive research, testing and pilot-scale demonstration, the team developed a breakthrough new technology utilizing low constant injection pressure. 2) Material Changes. Description: Flow lines are streaks, patterns, or lines - commonly off-toned in color - that show up on the prototype part as a consequence of the physical path and cooling profile. 3,000 ton machines can cost $700,000. One of the best ways to determine part shrinkage for complex components is with a mold flow analysis. Incorrect gate positions cause multiple flow fronts that struggle to merge seamlessly. 080" – 0. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. Flow lines are ripples in the plastic after the part is formed. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. Flow lines are a defect in injection molding and can be a significant issue for manufacturers. Flow lines can occur if any of the following affect the mold: A runner, gate, or sprue that is too small for purpose creates more flow. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. 2) show that the weld line is formed as expected from the middle of the cavity towards the wall. In injection molded parts, there are 2 types of weld lines: The first type of weld mark is called cold-melt joints and is formed when the melt front enters the cavity with different gates. 182-185, 2013. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Minimum turbulent flow would be 12-14 GPM, while numbers in the 20’s would be identified as an excellent flow rate. html. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. In. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. Flow lines arise from variations in the flow of molten plastic material as it fills the mold. Injection molding, in addition to extrusion, is the most important technology in the polymer processing industry. The edge gate is the most popular and straightforward injection mold gate design. Production was set according to an experimental design (DoE), varying injection flow rate, mold temperature, and melt temperature. (1) Increase the injection pressure and prolong the injection time. In the plastic injection moulding industry, we work with materials that are by-products of oil refinement and moulds made of metal casting, so our terminology is bound to be at least slightly confusing. ³/sec. or too much shear heat burning the material prior to injection. Possible Sources of Weld/Knit Lines: Temperature from the injection molding machine, runners, and/or the mold itself in order to ensure the plastic resin flows properly; Insufficient pressure resulting in the flow fronts not being merged back together with strong enough; Mold design, especially location of gates and runners impacting the resin flow Knit lines are formed in injection molding when two flow fronts meet in the middle of a part (a line where two sides of the plastic are “knit” together). Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. Secondly, it is easy to form obvious. Incorrect gate positions cause multiple flow fronts that struggle to merge. 750 in. Let’s take a look at some defects that are caused purely due to faults in the injection molding process. Industry 4. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. In this lesson we will focus on the meld and weld lines. The primary cause of cracking is stress and deformation brought on by the external environment, cold mold surfaces, and low injection rates. With this new discovery, P&G decided to launch iMFLUX Inc. Although they typically do not impact the functionality of a product, flow lines—off-color streaks or patterns across a product’s surface—may look unprofessional when visible to consumers. Possible Causes & Remedies: Machine Cause. An improper flow rate and injection speed also cause flow marks. Meld and knit lines are actually both different types of weld lines. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Setting the proper pressure on the injectors to push the plastic into the mold with enough speed that the plastic will coat the mold and fuse with other flow lines. They are also known as flow lines. They follow the flow of the molten resin from the gate along the finished part. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. The material is poured into a mold, which shapes the size and looks of the article. Look for signs of stickiness or burning. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary. Finite differences method offers strong consent for methodological solutions. • Reduce runner dimensions and maintain the same flow rate. Kobayashi et al. Flow lines are lines or streaks that appear on the surface of molded parts and occur due to variations in the flow of molten material during the injection molding. 020 0. Another solution may be to pull a vacuum on the mold just before injection. Definition: Off-tone streaks, patterns or lines that appear on parts. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). The formation process of weld lines can be described as. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. If so, look for an alternative resin. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Mold flow analysis is a powerful tool for optimizing the design and performance of injection molding processes. Thin wall injection molding can produce walls as thin as 0. Increase injection speeds and pressure to ensure the cavities are filled properly. Possible causes: Low temperature of injected melted plastic or slow injection speed during injection molding resulting in low fluidity of plastic inside the mold. 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. S. Knit lines are formed in injection molding when two flow fronts meet in the middle of a part (a line where two sides of the plastic are “knit” together). Plugged or inadequate vents n Clean plugged or dirty vents, particularly those along the parting line. Source: Google. Flow lines. 1) Snake flow lines. ; Burn marks – Often appears as black or rust-toned discoloration streaks on the edge or surface of a molded product. Learn how mold flow analysis can support the development of complex and customized injection molded products by identifying defects, optimizing materials, enhancing performance, and reducing costs. Too hot and the plastic will start to degrade, but too low and flow marks increase. If near the gate, check the gate seal time. Too hot and the plastic will start to degrade, but too low and flow marks increase. For the measurement of the crystallinity a DSC analysis was performed. Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. If during the design and development stage, watering is put on the back burner as an ". Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. 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. However, FRTP has problems such as the formation of weld lines, the deterioration of appearance due to the exposure of fibers on the molded product surface, and the deterioration of the strength of. This article continues our series of troubleshooting reports from one of the leading on-the-spot problem solvers in the molding industry. 2. They usually are a slightly different color than the rest of the piece, and typically occur on more narrow sections of the molded item. Plastic Defect # 2: Flow Lines. Do not keep the hopper full; hand-feed if necessary. They are best described as "off tone" wavy lines/streaks or patterns in the molded part around the injection ports. Sink Marks. Low cushion and hold time. After an hour of running, the steel temperature stabilized at 78°F. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. Vertical walls, meaning those part surfaces parallel to the direction of mold operation, should have a minimum draft angle of a 1/2 degree, and 2 degrees is even better; heavily textured surfaces may require 5 degrees or. The Reynolds number takes into account the pressure, volume and viscosity of the coolant, the resistance to flow, length and diameter of the channels and the pressure loss in the cir-cuit. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. On the contrary, for the conformal cooling. Fast injection gives you a glossy part, which is what we wanted in this. 3). The most important factors to consider during molding are the mold temperature, melt temperature, and injection pressure and speed. 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. Solution: Molding Process: This defect can be reduced by raising the material temperature and the nozzle temperature, and slowing down the injection speed, etc. Just multiply the area of the barrel × the injection velocity. Flow Lines The problem with flow lines is that they. 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. [22]. Using cooling simulation to circuit your cooling lines properly. 1．Mold Temperature Too Low. As a result, the lower degree of stress when gating with valve gate systems becomes relevant. If a mold cavity has a significant flow length-to-thickness ratio, the material should have a low enough viscosity to enable a continuous flow. Mold design is a key aspect of injection molding. 005 0. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. I’ve been writing about plastic flow simulation since 1984, and I. A significant part of that is the cooling design, where there are many things to consider. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. The flow line is usually connected to injection specifications, mold and injection material, it can be defined as linear grooving, or round surges, on the surface of an injection molded part that shows the instructions of product flow within the cavity of the mold. personnel to assess cooling lines in the mold design. In injection molding, it is often important to maintain consistent color throughout the part. We stopped the machine and added glycol to the chiller to a concentration of about 40%. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. 1mm (7/16"), coolant temperature of 30ºC and cycle time of 17 seconds (see Fig. The Fill system analyzes the filling of each cavity by sensing the melt presence at the end of flow with a cavity temperature sensor and compares the fill-time. (All Illustrations: S. The formation process of weld lines can be described as follows: Injection moulding (U. 010 0. The plastic pellets must be. The 7/16-inch size is a happy medium between many small lines and the fact that larger lines don’t particularly increase the heat exchange benefit. That’s an easy calculation to perform. 6 T) as thick as the nominal wall. During the injection molding process, one of the most important requirements of the mold is to deliver melt from the barrel to the cavity. This design is deliberate in order to help the mold. Flow marks, also known as flow lines, are molding defects that can occur in the manufacturing process of injection molding. FIG 1 Depiction of fountain flow. That means that for each injection pressure, the flow length for a mould temperature of 80°C and 180°C shows a constant difference of ca. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Bubbles are caused by melting flow fronts colliding in a mold cavity. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. Weld Line defect analysis, the most common of many defects in injection moulding products. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. So what does the 140F mold temperature give us? The molding technician thought the 140F mold water was OK because the data sheet provided by the material supplier suggested mold temperatures from 75 to 180F. Causes – Remedies. Flow Lines. Flow marks occur as circles or lines that occur around the gate. The thermo-rheological findings were used to investigate the sources of weld line weakness. The goal when locating cooling channels in the mold is uniform mold surface temperature, which is determined by cooling channel depth and pitch. An on-line compounding injection molding machine, incorporating the co-rotating, intermeshing twin-screw extruder and a reciprocating screw injection molding machine fitted with the oscillating pressure valve, has been developed. Well, what this simply implies is that injection polycarbonate molding makes it possible for you to create a wide range of part sizes. Its popularity is typified by the numerous products produced in this way at the present time. The plant water system is a critical component of an injection molding facility. You can avoid having any weld lines with cascade injection moulding. These lines form as a result of material flow and solidification during the injection molding process. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. The Priamus Fill system is designed for automatic closed-loop control of multi-cavity and family molds, multi-material injection, sequential valve-gated molds, as well as LSR molds. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. They are evidence of nonuniformity in flow pattern upon entry into the mold. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. Solution: Utilize a material that has the stiffest flow possible without causing non-fill. Flow marks, also known as flow lines or weld lines, are common defects that can occur in plastic molded parts. This defect is caused when plastic cools too rapidly during the injection molding process. Imperfections in manufactured plastic goods, such as a flow line defect in injection molding, are unacceptable. The flow line is usually connected to injection specifications, mold and injection material, it can be defined as linear grooving, or round surges, on the surface of an injection molded part that shows the instructions of product flow within the cavity of the mold. Cooling for slender cores (≤3 mm) uses air cooling instead of water. It can also aid in material selection since fill. Help prevent warping with these measures: Raise the mold or material cylinder temperature. 120 in. In these cases each circuit might remove a different. Look for signs of stickiness or burning. Let’s review some methods to prevent flow and knit lines in plastic injection molding. Flow lines result from uneven cooling of the plastic within the mold. 1. 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. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. Reposition gates and runners to allow resin to flow around the obstruction from a different direction. We restarted the mold at the same coolant flow rate and temperature. 4 Injection Speed. Steven. Select a plastic that is less prone to shrinkage. Improper gate design. Using a thermoplastic that stays in a. The polymer material is melted by the heat from the heaters and viscous heating due to the screw rotation in the plasticization stage as shown in Fig. thick, 0. Effects of mold temperature and pressure on shrinkage 0. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. 1 Injection molding From Wikipedia, the free encyclopedia Injection molding (British: moulding ) is a manufacturing technique for making parts from. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. Weld‐line is a defect that arises in injection molding when two or more flow fronts collide. Jetting occurs in a molded component when molten material is injected into the mold cavity and starts solidifying before it fills the cavity. Mold Flow - Position ribs such that the plastic has an optimal flow path. low of a melting time will cause flow lines to occur. Water cooling pumps coolant through lines on the outside of the mold cavity. . Plastic Purity. Tip #6: Pick Which Molding Defects Are Acceptable. The mold designer cannot know your goals without your input, which is why you will be asked to approve a gate and ejector layout prior to manufacturing a mold. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow molten plastic to flow down between the pin and hole surface. We started the mold with 100% water circulating at 60°F at a flow rate sufficient for turbulence. If you’re a mold designer with one of those vent-depth “rule-of. The model of polymer melting is fundamental for the development of. We stopped the machine and added glycol to the chiller to a concentration of about 40%. They can be unsightly and unpleasant in high-end sunglasses. The Analysis and countermeasures of flow lines in injection molded products Read more. There are several factors that can contribute to the formation of weld lines, including: Part design: The design of the part can impact the flow of the material and the likelihood of weld lines forming. These streaks or patterns can affect a part's aesthetics, value, and overall quality. Flow lines were created during injection moulding process. Over time polymer will degrade creating carbon (black specks). thick, 0. This results in a much greater amount of vent flow area for the compressed air to exhaust through, and still protects the corners. Basic Repairs for Warping. Weld Lines-3 Ways for Detecting and Correcting. wide. Note: It is applicable to thermoplastic materials only.