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Cause analysis of die flash
发布日期: 2019.09.27 Back to list source: Release date: 2019.09.27

Flash material, also known as flashing, flashing, or dart, mostly occurs at the mold closing position, such as: the mold's parting surface, the sliding part of the slider, the gap between the inserts, and the hole of the ejector. If the flash material is not resolved in time, it will be further enlarged, which will cause the local collapse of the stamping mold, causing permanent damage. The overflow of insert gaps and ejector pores can also cause the product to jam on the mold and affect demolding. In terms of equipment (1) the true clamping force of the machine 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 during injection, otherwise it will cause the mold to expand and flash.

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(2) The clamping device is poorly adjusted, the toggle lever mechanism is not straightened, or the mold is not balanced, or the mold is not balanced, and the mold parallelism cannot be achieved, which results in the mold being closed on one side and not adhered on the other side. A flash will appear during the injection.

(3) The parallelism of the mold itself is not good, or the mounting is not parallel, or the template is not parallel, or the force distribution of the tie rods is uneven, and the deformation is uneven.

(4) Severe wear of check loops; failure of spring nozzle springs; excessive wear of barrels or screws; failure of the cooling system at the inlet caused a "bridge" phenomenon; insufficient injection volume adjusted by the barrel, too small cushions, etc. Both may cause flashing to occur repeatedly and must be repaired or replaced in time.

Second, the mold (1) mold parting surface accuracy is poor. The movable template (such as the middle plate) is deformed and warped; foreign matter is contaminated on the parting surface or there are protruding burrs on the periphery of the mold frame; the old mold is fatigued and collapsed due to the previous flashing extrusion.

(2) The mold design is unreasonable. The opening position of the mold cavity is too biased, which will cause tension on one side of the mold during injection, causing flashing; the fluidity of plastics is too good, such as polyethylene, polypropylene, nylon, etc., in the molten state, the viscosity is very low, and it is easy to enter The fixed or fixed gap requires high precision in the manufacture of the mold; it should be placed on the center of mass symmetry as much as possible without affecting the integrity of the product, and the material should be fed in the thick part of the product, which can prevent flashing while the material is missing. Situation; when there is a molding hole in or near the center of the product, it is customary to open a side gate on the hole. Under large injection pressure, if the clamping force is insufficient, the support force of this part of the mold is not enough to cause slight warpage. Flashing, such as when the side of the mold is equipped with a movable member, the projected area of the side is also affected by the molding pressure. If the supporting force is not enough, it will cause flashing; the sliding core has poor precision or the fixed core and the cavity installation position are offset Flashing occurs; cavity exhaust is poor, no vent groove is opened on the parting surface of the mold or the exhaust groove is too shallow or too deep or blocked by foreign objects will cause flashing; for multi-cavity molds, Note The reasonable design of the runners and gates is not to be avoided, otherwise the mold filling force will be uneven and the flash will occur.

Three process aspects (1) The injection pressure is too high or the injection speed is too fast. Due to the high pressure and high speed, the opening force on the mold is increased, resulting in flash. The injection speed and injection time should be adjusted according to the thickness of the product. Thin products should be filled with high speed and rapid injection, and no injection is required after filling. Thick products should be filled with low speed, and the epidermis should be fixed before the final pressure is reached. (2) Flashing due to excessive feed. It is worth noting that you do not inject too much molten material in order to prevent the depression, so that the depression may not be "filled in", but flashing will occur. This situation should be solved by extending the injection time or holding time. (3) If the temperature of the barrel or nozzle is too high or the temperature of the mold is too high, the viscosity of the plastic will decrease, and the fluidity will increase, which will cause flashing when the mold is smoothly fed.

Fourth, raw materials (1) plastic viscosity is too high or too low may appear flash. Plastics with low viscosity, such as nylon, polyethylene, polypropylene, etc., should increase the clamping force; plastics with strong water absorption or plastics that are sensitive to water will greatly reduce the flow viscosity at high temperatures, increasing the possibility of flashing These plastics must be thoroughly dried; the viscosity of plastics with too much recycled content will also decrease, and if necessary, retentive ingredients will be added. If the viscosity of the plastic is too high, the flow resistance will increase, and a large back pressure will increase the cavity pressure, resulting in insufficient clamping force and flashing. (2) When the particle size of the plastic raw material is not uniform, the feeding amount may vary, the product may be dissatisfied, or flash.

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