A simple analysis of the causes of “flash” of injection molded products

Flash, also known as edge overflow, sharp edge, burr, etc., mostly occurs at the opening and closing position of the die, such as the parting surface of the moving die and the static die, the sliding part of the slider, the absolute gap of the insert, the hole of the ejector rod, etc. to a large extent, flash is caused by the failure of the die or machine clamping force. There may be the following reasons:

If the high clamping force of the machine is not enough, the machine with large clamping force shall be selected. The die locking force decreases due to the wear of the die locking machine hinge or the wear of the sealing element of the die locking cylinder. If the actual temperature is too high due to out of control of the heating system, check whether there are problems with the thermocouple and heating ring.

2. (1) if the uneven distribution of the mold cavity or insufficient parallelism leads to unbalanced stress, resulting in local flash and local dissatisfaction, the flow channel shall be placed at the center of mass symmetry as far as possible without affecting the integrity of the parts.

(2) Flash will be caused when the force on the movable member and sliding core in the die is unbalanced.

(3) When the mold exhaust is poor, the compressed air will expand the parting surface of the mold and flash. A good exhaust system should be set up or an exhaust ditch should be dug on the parting surface.

3. If the fluidity of plastics is too large or too much lubricant is added, the pressure, speed and temperature shall be appropriately reduced to reduce the use of lubricant. If necessary, plastics with low fluidity shall be selected.

4. Processing and adjustment:

(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) When adjusting, the die locking machine hinge is not straightened, the die adjusting nut often moves during die locking, resulting in insufficient die locking 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.

5. the reasons for the repeated occurrence of flash and parts are:

(1) When the particle size of plastic raw materials is uneven, the dosage will be uncertain.

(2) The wear of the rubber head, rubber ring and rubber washer of the screw is too large, so that the molten material may slide and return between the screw and the barrel, resulting in flash or dissatisfaction.

(3) The cooling system at the inlet fails, resulting in the adjustment of the feed.

The injection amount set by the barrel is insufficient, that is, the buffer pad is too small, which will lead to flash or dissatisfaction of parts due to more and less injection time.

from：