The "flash" of injection mold is caused by the failure of mold or machine clamping force

The "flash" of injection mold is caused by the failure of mold or machine clamping force

The "flash" of injection mold is caused by the failure of mold or machine clamping force


Injection mold is an important process equipment for producing various industrial products. With the rapid development of the plastic industry and the promotion and application of plastic products in aviation, aerospace, electronics, machinery, shipbuilding and automotive industries, the requirements of products on molds are increasingly high.


During the injection mold process, flash (also known as overflow, flaring, burr, etc.) may occur. The flash mostly occurs at the opening and closing position of the mold, such as the parting surface of the moving mold and the static mold, the sliding fitting part of the slider, the absolute clearance of the insert, the pin hole, etc. The flash is largely caused by the failure of the mold or machine clamping force.


Some specific reasons are summarized:

  1. If the maximum clamping force of the machine is not enough, the machine with enough clamping force shall be selected. The clamping force is reduced due to the wear of the clamping machine hinge or the wear of the sealing element of the clamping cylinder and the occurrence of oil dripping or backflow. If the actual temperature is too high due to out of control heating system, check the thermocouple and heating coil for problems.
  2. Several situations and solutions of "flash" generated by injection mold:

  3. (1) The uneven distribution of the mold cavity or the insufficient parallelism of the mold cavity cause the unbalanced stress, which causes local flash, and local dissatisfaction. The runner should be placed at the center of mass symmetry as far as possible without affecting the integrity of the parts.
    (2) When the force on the moving components and sliding core in the die is unbalanced, flash will be caused.
    (3) When the mold has poor exhaust, the pressurized air will cause the parting surface of the mold to expand and flash. A good exhaust system should be set up, or an exhaust ditch should be dug on the parting surface.
  4. If the fluidity of plastic is too high or too much lubricant is added, the pressure, speed, temperature, etc. should be appropriately reduced to reduce the amount of lubricant used. If necessary, the plastic with low fluidity should be selected.
  5. Injection mold processing and adjustment:

  6. (1) If the set temperature, pressure and speed are too high, segmented injection shall be adopted. Excessive injection time, pressure holding time and feeding amount will cause flash.
    (2) During adjustment, the hinge of the mold locking machine is not straight, or the mold adjusting nut often moves when opening and locking the mold, resulting in insufficient clamping force and flash.
    (3) The parallelism between the regulating head and the two poles is not enough or the regulated system pressure is too large.
  7. Reasons for repeated occurrence of flash and part dissatisfaction of injection mold:

  8. (1) When the particle size of plastic raw materials is uneven, the feeding amount will be uncertain.
    (2) The excessive wear of the rubber overshoot head, rubber overshoot ring and rubber overshoot washer of the screw may cause flash or dissatisfaction due to the sliding and backflow of molten materials between the screw and the barrel.
    (3) The cooling system at the inlet fails, causing the feed to be adjusted.
    (4) Inadequate filling amount set by the charging barrel, that is, too small buffer pad will cause flash or insufficient parts due to more and less feeding time.
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