Various reasons for the mold to produce flash

- May 07, 2019-

What is the cause of the flash? The causes and elements of the production of flash are multifaceted and complex. I will answer from several aspects.


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What is a flash? The flash edge, also known as the overflow edge, the edgy, the burr, etc., mostly occurs at the position of the mold, such as the parting surface of the movable mold and the static mold, the sliding part of the slider, the gap of the insert, and the apex of the ejector. At the same time, the flash is largely due to the failure of the mold or machine clamping force. In general, due to various factors, it is impossible for plastic parts to produce no flash.

Flash edge generation

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However, how to reduce the flash to improve the quality of plastic parts is an important research topic in the field of plastic molding and precision injection molding. The occurrence of flashing may be caused by the following reasons:

1. The highest clamping force of the machine should be enough to use the machine with sufficient clamping force. The clamping machine wears the hinge or the clamping element of the clamping cylinder wears and drops or recirculates, causing the clamping force to decrease. If the heating system is out of control and the actual temperature is too high, check whether there are any problems with the thermocouple or heating coil.

(1) If the mold cavity is unbalanced or the parallelism is insufficient, the force is unbalanced and local burrs are caused. If the parts are not full, the flow path should be placed in the center of mass symmetry as much as possible without affecting the integrity of the parts.

(2) When the movable member and the sliding core in the mold are unbalanced, they will cause flash.

(3) When the mold is exhausted, the compressed air will expand the parting surface of the mold and flash, and a good exhaust system should be opened, or the exhaust groove should be dug on the parting surface.

2. If the fluidity of the plastic is too large, or if too much lubricant is added, the pressure, speed, temperature, etc. should be appropriately reduced, the amount of lubricant used should be reduced, and if necessary, a plastic with low fluidity should be selected.

3. Processing and adjustment:

(1) If the set temperature, pressure and speed are too high, segmental injection should be used. Excessive injection time, dwell time, and too much feed will cause flash.

(2) When adjusting, the hinge of the clamping machine is not straightened, or the mold nut is often moved when the mold is opened or locked, and the clamping force is insufficient to cause flashing.

(3) The parallelism of the adjustment head and the two poles is insufficient or the system pressure of the adjustment is too large.

4. Reasons for repeated occurrences of flashing and manufacturing dissatisfaction:

(1) When the particle size of the plastic raw material is unevenly distributed, the amount of the added material may be indefinite.

(2) The wear of the rubber head, the rubber ring and the rubber gasket of the screw is too large, so that the melt may slide or return between the screw and the cylinder to cause flashing or dissatisfaction.

(3) The cooling system of the inflow port is invalid, so that the feed is adjusted.

(4) The amount of shots set by the barrel is insufficient, that is, if the cushion is too small, there will be a lot of burrs or dissatisfaction of the parts.

Flash edge solution

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The first reason is the occurrence of flash: 1, the mold parting surface (PL) sliding surface does not match; 2, the injection pressure is too high; 3, the injection machine offset; 4, the locking force is insufficient.

Problems associated with the mold: 1. The parting surface PL of the mold, the sliding mating surface, the demolding pin, the spacer, and the like. The gap between the various grooves of the mold is formed, and if the material flows, it becomes a flash. The flash edge is a wedge block. There is a tendency to gradually become larger; 2, to eliminate the flash of the product is generally based on the principle of repairing the mold, because the forming conditions are not good, and the flashing occurs temporarily, the temperature of the barrel should be reduced. The direction in which the mold temperature is lowered and the injection speed is lowered causes the material fluidity to decrease. However, it should be noted that this will cause residual internal stress in the product.

Solution: 1, instant: reduce the injection pressure, reduce the temperature of the heating barrel. Reduce the injection speed; 2, short-term: grinding the surface of the mold with flash; 3, long-term: the mold uses hard steel material.

Due to the difference of materials: 1, due to the fluidity of the material is easy to produce flash, so the mold parting surface to be done tightly; 2, the crystalline material is very low in viscosity due to melting. In particular, the tightness of the mold parting surface is required.

References: 1. It should be noted that excessive pressure on the mold will also produce flash edges. Between the parting surfaces, foreign objects will damage the mold and produce flash edges. 2. The mold material usually uses materials such as S50C. Japan's JJS standard is equivalent to domestically produced 50# steel. Using HRC30's pre-hardened special steel, it is difficult to produce flash on the parting surface.