Preventing Voids, Bubbles, and other part defects in injection molding makenica.com/preventing-voids-bubbles-and-other-part-defects-in-injection-molding April 19, 2021
Injection molding service has increased the efficiency of the plastics manufacturing industry, but these parts do not always work out as anticipated. If you know what these problems are and what is causing them, you will work with your injection molding companies to detect and fix them before they arise.
What is the source of these flaws? Several factors, including: can cause defects in plastic parts 1. There may be a problem with the mold. When this happens, all of the components manufactured from that mold can be faulty and must be recalled. 2. Another concern is how the material is handled when within the mold. If mishandled, the plastic could not set properly, resulting in complications. 3. Finally, the material itself could be at fault. If the material is not suitable for the part, it can result in low quality or faulty parts. To avoid these errors from arising in the plastic injection molding service, all of these various aspects of the procedure must be tested daily by the injection molding companies. Mold Design Errors or Poor Maintenance 1/5
The majority of issues in injection molding service caused by mold construction flaws or poor maintenance would fall into one of four categories: Jetting - happens when a line of plastic cools faster or slower than the plastic around it. This is due to faulty construction and can typically only be fixed by creating a new mold. Warping – The cooling mechanism is most likely to blame for bent or warped plastic parts. Warping occurs where the plastic inside the mold is not adequately cooled. Drag Marks – If the part is removed from the mold with streaks on it, there is a problem with the ejector mechanism or the part's draft angles. It was most likely a flawed design and would need to be replaced or have tool work performed to fix the problem. Short shot - happens where there is insufficient plastic injected into the mold to fill it appropriately. Plastic Resins or Other Additives These problems in the injection molding service are caused by a flaw in the resin or other forms of plastic used to make the components. Streaks – If the color has streaks going through it, this usually indicates that the resins or dyes were not correctly blended. To achieve a solid hue, the colorant must be evenly mixed into the resin. Delamination – This problem causes a crispy coating of resin to form on the piece's surface. It is most likely that the resin has gathered moisture/ contaminant on the surface before being melted and injected into the mold. Embedded Debris – If you see any unusual or foreign materials embedded in your components, you can clean the barrel of your injector mold. It could contain debris that is contaminating the resin. Marks or other Streaks – Moisture is likely to blame if you find silver-colored lines or markings in the plastic near the spot where it is injected into the mold. The resin may have been handled in an environment where it absorbed an excessive amount of moisture. Processing of Resin The resin is processed after being injected into the mold. Several issues will arise during this time, including: Blistering – If the resin is not adequately cooled or is subjected to a high level of heat, bubbles (or blisters) will appear. Burn Marks – When the mold isn't well ventilated, or the resin is left in for too long, it will burn. The resin will have brown or black spots. Flow Marks – This condition causes discoloration or wavy lines in the resin. It occurs as a result of the material being inserted too slowly. As a result, the resin cools sooner than it should.
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Stress cracks - also known as stress crazing, form when the resin is overexposed to incredibly high temperatures. Degradation - is a form of defect that causes the resin to lose some of its hardness, toughness, or other properties. Degradation often happens to the essential property, allowing the generated part to malfunction as used. Bubble issues If the bubbles produced in the injection molded product are not processed promptly, it will directly impact the plastic injection molding service. Why do bubbles occur during the injection molding manufacturing process? The injection molded part's bubble is a bubble formed within the plastic that forms a round protrusion on the top. Bubbles can appear anywhere, not only where the wall of the plastic component is dense, and they come in a variety of sizes and shapes. The injection molded parts will create bubbles and vacuum bubbles for the three reasons listed below. 1. Inadequate injection molding condition regulation Many process parameters directly affect the bubble and vacuum bubble generation in the plastic injection molding service. Suppose the injection molding pressure is too low. In that case, the injection molding speed is too fast. The injection molding time and cycle are too short. The amount of material added is too much or too little. The pressure is insufficient, the cooling is uneven or inadequate, and the material temperature and mold temperature are not adequately controlled; bubbles would be produced in the plastic molded parts. The gas in the mold is discharged too late, particularly during high-speed injection molding, resulting in too much gas remaining in the melt. To do this, the injection molding speed should be lowered accordingly. However, if the speed is too low and the injection molding pressure is too low, it is difficult to exhaust the gas in the melt, and bubbles, dents, and undershot are common. As a result, extra care should be taken when tuning the injection molding speed and injection mold strength. Furthermore, by changing the injection and keeping pressure times, optimizing the cooling conditions, regulating the volume of feed, and using other techniques to prevent the formation of bubbles and vacuum bubbles. If the cooling state of the plastic molded component is bad, the plastic injection molded part should be immersed in hot water and slowly cooled directly after demolding so that the cooling rate on the inside and outside is similar. When regulating the mold temperature and melt temperature, keep in mind that too much high temperature will melt to depolymerize and decompose. This will create a lot of gas or shrink unnecessarily and shape bubbles or shrinkage holes; too low a temperature
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will cause the filling pressure to be insufficient. The plastic parts will be vulnerable to voids and bubbles. The melt temperature should be kept slightly lower, and the mold temperature kept somewhat higher. It is difficult to manufacture a significant volume of gas under certain process conditions, and it is also challenging to produce shrinkage gaps. When controlling the temperature of the barrel, the temperature of the feeding portion should not be too high, as this can induce material backflow and return, as well as bubbles. 2. Flaws in injection molds Suppose the injection mold's gate position is incorrect or the gate portion is too short. In that case, the leading runner and runner are too long and thin, there are dead corners in the runner, or the mold is not adequately exhausted; this can result in bubbles or vacuum in the injection molding service. As a result, injection molding companies must decide whether the injection mold defect causes bubbles and the primary cause of vacuum bubbles. Adjust the structural parameters of the injection mold according to the particular circumstance, particularly the gate location, which should be set at the thick wall of the plastic molded component. Since the vacuum hole created by the direct gate is more visible, it should be avoided as much as possible when choosing the gate form. It is due to the pressure in the cavity is greater than the pressure before the gate after the pressure retention period has ended. If the direct gate is open, pressure in the cavity is greater than the pressure in front of the gate. Since the molten material has not been frozen, the process of molten material backflow can occur, allowing holes to appear within the plastic component. If the gate shape cannot be modified, it can be altered by increasing the holding time, decreasing the taper of the gate, and expanding the holding time. The gate section should not be too thin, particularly when injection molding multiple plastic parts in different shapes simultaneously. It should also be noted that the size of each gate should be equal to the weight of the plastic molded component, as larger plastic parts are vulnerable to air bubbles. Furthermore, the slim and narrow runners could be shortened and widened to avoid dead corners and the loss of low mold exhaust. The injection molding companies must avoid any extra-thick bits of significant disparities in the thickness of the plastic component when constructing the mold. 3. The raw materials do not satisfy the use criteria. Suppose the moisture or reactive content of the injection molding raw material exceeds the norm. In that case, the material particles are too small or irregular in size, resulting in too much air mixing in the feeding phase, the raw material shrinkage is too high, and the 4/5
melt index is too large or too small. The production of bubbles and vacuum bubbles in plastic molded pieces will be hampered if the material quality is too high in recycled content. It can be addressed in this respect by pre-drying raw materials, sieving out fine materials, replacing resins, and reducing the number of recycled materials. Voids Voids are a fairly common form of defect in injection molding service. They appear as "air pockets" in transparent molding but can also be used in colored or opaque molding. Voids are more common on thicker part surfaces and can arise as the outer layer of the part cools and solidifies quicker than the internal layer, resulting in a hole. When the injection molding companies find voids, many variables can come into play, and they can be induced by machine (process), mold, or material problems. The process is the most common source of voids, and there are some changes you may make to help fill the component out and reduce the chances of void defects. The most popular recommendations are to increase the shot length, injection pressure, screw forward time, melt temperature, or injection speed. Mold may also be the source of the void. These areas should be included in those situations. Is the gate used too narrow for the part's design? Is the gate placed incorrectly for the part? Is the runner's shape or scale incorrect? The mold temperature could either be too low, or there could be insufficient venting in the mold. The final factor to remember is the material. Voids may also be affected by damp material that has an undue amount of moisture. If this is possible, you can dry the material for a longer period to remove any residual moisture. Taking Care of These Problems Many of these problems in the injection molding service are common and relatively simple to solve. Working with professional plastic injection molding companies frequently is the only way to prevent many of these issues. Plastic Injection experts at the top injection molding companies maintain and disinfect their machines on a routine basis to avoid these issues. Makenica: One of the top plastic injection molding companies is an excellent option if you choose to work with an accomplished injection molding firm. We take pride in getting skilled experts who can collaborate with you to produce the ideal products.
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