Gas-assisted injection molding has the advantages of improved appearance, material saving, cycle shortening, and reduction of internal stress. However, due to the short development of the gas-assisted process, the gas is difficult to control during commissioning, and the experience of many first-time process technicians is insufficient, which often leads to an increase in waste in production. This article focuses on gas-assisted molding processes, structural features, and countermeasures for molding defects. Process principle Gas-assisted molding (GIM) refers to the injection of high-pressure inert gas when the plastic is filled into the cavity (90%~99%). The gas pushes the molten plastic to continue filling the full cavity, and the gas pressure is used instead of the plastic pressure-maintaining process. An emerging injection molding technology. The molten resin is injected into the cavity through high pressure, high speed, and then the high pressure gas is introduced into the wall thickness part of the workpiece to produce a hollow section, driving the melt to complete the filling process and holding the pressure during the gas assisted molding process debugging. Need to pay attention to the following factors: 1. For the gas needle type panel mold, when the gas needle is pressed into the deflation, the intake imbalance is most easily generated, which makes the debugging more difficult. The main phenomenon is shrinking. The solution is to check the gas fluency when deflation. 2. The temperature of the rubber compound is one of the key factors affecting the normal production. The quality of the gas-assisted product is more sensitive to the temperature of the compound. If the temperature of the nozzle material is too high, it will cause the product to be flowered, burnt, etc.; if the temperature of the material is too low, it will cause cold glue, cold mouth, and sealing the gas needle. The phenomenon reflected by the product is mainly shrinkage and flowering. The solution is to check if the temperature of the compound is fair. 3. Check if there is any flashing phenomenon when the needle-type nozzle is returned in the manual state. If this phenomenon occurs, the gas-assisted sealing needle fails to seal the nozzle. When injecting gas, the high pressure gas will flow back into the feed pipe. The main phenomenon is that the water is large in area and burned, and the returning time is greatly reduced. When the sealing needle is opened, gas is discharged. The main solution is to adjust the right and wrong of the sealing rod. 4. Check if the gas auxiliary sensor switch is sensitive, otherwise it will cause unnecessary loss. 5. Gas-assisted products are kept by gas, and the product can be appropriately reduced when the product shrinks. Mainly to reduce the pressure and space inside the product, so that the gas can be easily puncture to the thick plastic place to fill the pressure. Gas-assisted molding advantages 1. Reduce residual stress and reduce warpage. Conventional injection molding requires sufficient high pressure to push the plastic from the main flow path to the outermost area; this high pressure causes high active shear stress, and residual stress causes deformation of the product. The formation of a gas channel in the GIM can effectively transfer pressure and reduce internal stress, so as to reduce the warpage of the finished product. 2. Eliminate the sag marks. Traditional injection molding products form a Sink Mark behind thick areas such as Rib&Boss, which is the result of uneven shrinkage of the material. GIM can be pressed by a hollow gas pipe to cause the product to shrink from the inside when it shrinks, so there is no such trace on the appearance after curing. 3. Reduce the clamping force. In the traditional injection molding, high holding pressure requires high clamping force to prevent plastic overflow, but the pressure holding pressure required by GIM is not high, which can reduce the clamping force requirement by 25%~60%. 4. Reduce the length of the runner. The large thickness of the gas circulation pipe can guide the circulation of the plastic, and does not require special external flow channel design, thereby reducing the cost of mold processing and controlling the position of the weld line. 5. Save materials. Products produced by gas-assisted injection molding can save up to 35% compared to conventional injection molding, saving a lot depending on the shape of the product. In addition to the internal hollow material savings, the material and number of gates (nozzles) of the product are also greatly reduced. 6. Shorten production cycle time. Due to the thick product and the large number of columns, traditional injection molding requires a certain amount of injection and pressure to ensure the shape of the product. Gas-assisted products, the appearance of the product seems to be very thick, but because of the internal hollow, the cooling time is shorter than the traditional solid products, and the total cycle time is shortened due to the reduction of holding pressure and cooling time. 7. Extend the life of the mold. In the traditional injection molding process, when the product is hit, the injection speed and pressure are often used, so that the “peak†is easily generated around the gate (the nozzle), and the mold often needs maintenance; after the gas-assisted, the injection pressure, the injection pressure and the lock are used. The mold pressure is simultaneously reduced, the pressure on the mold is also reduced, and the number of mold repairs is greatly reduced. 8. Reduce the mechanical loss of the injection molding machine. Due to the reduction of injection pressure and clamping force, the pressure on the main parts of the injection molding machine: Colin column, machine hinge, and machine plate are also reduced accordingly. Therefore, the wear of all major parts is reduced, the life is extended, and maintenance is reduced. The number of replacements. Mold features 1. The cross section of the airway is generally semi-circular, and the design of the diameter is as small as possible and consistent, generally 2-3 times the wall thickness. Too big or too small will be a bad penetration at the end of the airway. There should be a large arc transition at the bend of the airway; the air passage can be arranged at the root of the structure such as the rib and the self-Tapping Screw column to use the structural member as the airway to feed. 2. The matching clearance of the gas needle should be less than 0.02mm to prevent the melt from entering the gap of the inlet needle; the seal between the outer circumference of the gas needle and the mold must be good, and the sealing ring with high temperature resistance is required. 3. The structural form of the gas needle is required to prevent nitrogen from escaping from the gap between the gas needle and the product during the cooling process. 4. The position of the gas needle should not be too close to the gate. Since the temperature of the gate is the highest around the gate during filling, the viscosity is low, and the melt is easily introduced into the gap of the inlet needle, causing defects such as shrinkage and blowpage of the product. 5. When designing the runners and gates, since the gas-assisted molding eliminates the injection compensation phase, fewer runners and gates can be set. In order to ensure a faster filling speed, the runners and gates should be enlarged. The thickness of the latent gate is generally about 1.5mm. Excessive gate size increases gate solidification time, affects production efficiency, and may also cause nitrogen to enter the drum after passing through the gate and runner. Features The gas-assisted injection molding system usually consists of a low-pressure nitrogen gas source generation system, a nitrogen pressure boosting system, and a control system. Specifically, it includes a closed system composed of an air compressor, a freeze dryer, a nitrogen generator, a nitrogen buffer tank, a tube pass filter, a diaphragm type nitrogen booster, a high pressure nitrogen storage tank, and a gas auxiliary console. Common defects and troubleshooting methods 1. Gas crosses. Such defects can be addressed by increasing the degree of pre-filling, speeding up the injection temperature, increasing the melt temperature, shortening the gas delay time, or selecting a material with higher activity. 2. No chamber or chamber is too small. By reducing the degree of pre-filling, improving the melt temperature and gas pressure, shortening the gas delay time, prolonging the gas holding pressure and decompression time, selecting a material with higher activity, increasing the gas passage, and using a side cavity method, etc. Kind to solve. In addition, the gas needle can be inspected for failure or blockage, and the gas line is leak-free. 3. Shrink marks. The methods for eliminating sink marks can be reduced by reducing the degree of pre-filling and melt temperature, increasing the pressure of the melt holding pressure, shortening the gas delay time, improving the gas pressure, prolonging the gas epoch time, reducing the mold temperature, increasing the gate diameter and flow. Crossing and airway, etc. In addition, the pressure curve of the gas injection can be adjusted to check whether the pipeline and the gas needle are working properly. 4. The weight is not stable enough. Reducing the injection speed, improving the back pressure, improving the mold venting, changing the gate position and increasing the gate are all beneficial to overcome this drawback. 5. The airway wall is too thin. This can be overcome by reducing the injection speed, lowering the barrel temperature and gas pressure, extending the gas delay time, and adding atmospheric channels. 6. Finger effect. When this phenomenon occurs, it can be considered to improve the filling degree, reduce the injection speed, reduce the barrel temperature and gas pressure, prolong the gas delay time, shorten the gas and pressure time, reset the pressure curve of the gas injection, and select the activity less. Materials, methods to reduce mold temperature and reduce wall thickness. In addition, changes in gate location and increased air passages also help to improve this defect. 7. Gas enters the Screw barrel. When this phenomenon occurs, it can be considered to improve the melt holding pressure and holding time, reduce the nozzle temperature and gas pressure, shorten the gas holding time and pressure time, reset the pressure curve of the gas injection, and select the activity is lower. The material, the way to reduce the gate diameter and change the gate position. 8. Burst after demolding. When this phenomenon occurs, you can consider reducing the gas pressure, extending the dwell time, resetting the pressure curve of the gas injection, reducing the gas volume, etc., and checking whether the gas needle is clogged. Bluetooth Speaker,Portable Bluetooth Speaker,Mini Bluetooth Speaker,bluetooth Wireless Speaker,portable wireless speaker Shenzhen Lanejoy Technology Co.,LTD , https://www.copper-nut.com