Injection molding refers to the plasticization and melting of plastic by injection molding machine, and then injection into the cavity of the molding die to form, after cooling and cooling, the melt is solidified and demoulded, and the injection molding machine is injection molded. Flash, also known as flash, overflow, and draping, mostly occurs at the position of the mold, such as: the parting surface of the mold, the sliding part of the slider, the gap of the insert, the pores of the ram, etc. . If the flash is not resolved in time, it will be further expanded, so that the stamping die forms a local collapse, causing permanent damage. The gap between the insert gap and the ejector pin also causes the article to get stuck on the mold, affecting demolding.
First, the equipment aspect
(1) The machine's true clamping force is insufficient. When selecting an injection molding machine, the rated clamping force of the machine must be higher than the tension formed by the longitudinal projection area of the injection molded product at the time of injection, otherwise it will cause expansion and flash.
(2) The clamping device is not well adjusted, the toggle mechanism is not straightened, and the left or right or upper and lower molds are not balanced. The phenomenon that the parallelism of the mold cannot be reached causes the one side of the mold to be tightly closed and the other side not to be closely attached. There will be flash on the injection.
(3) The parallelism of the mold itself is not good, or it is not parallel, or the template is not parallel, or the force distribution of the tie rod is uneven, and the deformation is uneven, which will cause the mold to be tight and the flash is generated.
(4) The ring of the check ring is seriously worn; the spring nozzle spring is ineffective; the wear of the barrel or the screw is too large; the failure of the cooling system of the inlet port causes the phenomenon of “bridge”; the amount of shots set by the barrel is insufficient, the cushion is too small, etc. Both may cause the flash to appear repeatedly, and the parts must be repaired or replaced in time.
Second, the mold aspect
(1) The mold parting surface has poor precision. The movable template (such as the middle plate) is deformed and warped; the foreign matter on the parting surface or the protruding spur burr around the mold frame; the old mold is collapsed due to the extrusion of the previous flash.
(2) The mold design is unreasonable. The opening position of the mold cavity is too biased, which will cause tension on the unilateral side of the mold during injection, causing flashing; plastic fluidity is too good, such as polyethylene, polypropylene, nylon, etc., the viscosity is very low in the molten state, easy to enter the activity Or fixed gaps, requiring high precision of the mold; under the premise of not affecting the integrity of the product, it should be placed on the center of mass symmetry as much as possible, and the material can be fed in the thick part of the product to prevent the side from being missing. In the case of a molded hole in or near the center of the product, it is customary to open a side gate on the hole. Under a large injection pressure, if the clamping force is insufficient, the supporting force of the part is insufficient to cause slight warpage. The flashing edge, if there is a movable member on the side of the mold, the projected area of the side is also affected by the forming pressure. If the supporting force is insufficient, the flashing edge may be caused; the sliding core has poor matching precision or the fixed core and the cavity mounting position are offset. The flash is generated; the cavity is poorly exhausted, and there is no open exhaust groove on the parting surface of the mold or the exhaust groove is too shallow or too deep or blocked by foreign matter; the multi-cavity mold should be Note
Third, the process aspect
(1) The injection pressure is too high or the injection speed is too fast. Due to the high pressure and high speed, the expansion force of the mold is increased to cause flashing. According to the thickness of the product to adjust the injection speed and injection time, thin products should be quickly filled with high speed, no longer inject after filling; thick products should be filled with low speed, and the skin is generally fixed before reaching the final pressure.
(2) The amount of feed is too large to cause flash. It is worth noting that you should not inject too much melt to prevent dents, so the dents may not be “filled in” and the burrs will appear. This situation is solved by prolonging the injection time or holding time.
(3) If the temperature of the barrel and nozzle is too high or the mold temperature is too high, the viscosity of the plastic will decrease, the fluidity will increase, and the flash will be caused in the case of smooth advancement.
Fourth, raw materials
(1) If the viscosity of the plastic is too high or too low, flashing may occur. Plastics with low viscosity, such as nylon, polyethylene, polypropylene, etc., should improve the clamping force; plastics with high water absorption or plastics sensitive to water will greatly reduce the flow viscosity at high temperatures and increase the possibility of flash. These plastics must be thoroughly dried; the viscosity of the plastics that incorporate too much recycled material will also decrease, and if necessary, the retention components should be added. If the viscosity of the plastic is too high, the flow resistance is increased, and a large back pressure is generated to increase the pressure of the cavity, resulting in insufficient clamping force to generate a flash.
(2) When the particle size of plastic raw materials is not uniform, the amount of feed will vary, and the parts may be dissatisfied or flashed.
