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Defect analysis and elimination of molding flash

Posted by: Mu Ju 2021-11-07 Comments Off on Defect analysis and elimination of molding flash

What is molding flash?

Molding flash, also known as overflow, overflow, seam and so on, mostly occurs in the opening and closing position of the mold, such as the interface of the mold, the sliding part of the slider, the gap of the insert, the hole of the ejector pin and so on. If the flash is not solved in time, it will be further enlarged, resulting in local collapse of the impression die, which may eventually cause permanent damage. The overflow of the insert gap and the top bar hole will also make the product stuck on the mold and affect the demoulding. The flash of the product is shown in the figure

(1) Insufficient clamping force

When the injection pressure is greater than the clamping force, the die parting surface is not well closed, and the overflow flash is easy to occur. In this regard, we should check whether the pressurization is excessive, and check whether the product of plastic projection area and molding pressure exceeds the clamping force of the equipment. The forming pressure is the average pressure in the mold, which is usually calculated as 40MPa. The forming pressure of polyethylene, polypropylene, polystyrene and ABS is about 30MPa when producing box shaped plastic parts, about 36Mpa when producing deep shaped plastic parts, and about 60MPa when producing small plastic parts with volume less than 10cm3. If the result is that the clamping force is less than the product of the projected area of the plastic part and the molding pressure, it indicates that the clamping force is insufficient or the injection positioning pressure is too high. It is necessary to reduce the injection pressure or the cross-sectional area of the injection port, shorten the holding and pressurization time, reduce the injection stroke, or consider reducing the number of cavities and using the injection machine with large clamping tonnage.

(2) The material temperature is too high

The melt viscosity of high temperature melt is small, the flow performance is good, and the molten material can flow into a small gap in the mold to produce overflow flash. Therefore, it is necessary to reduce the temperature of barrel, nozzle and mold to shorten the injection cycle.

For low viscosity melt such as polyamide, it is very difficult to solve the flash defect only by changing the molding conditions. At the same time, we should reduce the temperature of the material properly, and try our best to process and repair the die to reduce the die gap.

(3) Mold defects

Die defect is the main cause of overflow flash. When there are more overflow flash, the die must be checked carefully. The parting surface should be checked again to make the moving die and the fixed die align. The parting surface should be checked to see if it fits closely, and the wear clearance of the sliding parts in the cavity and die core is out of tolerance. Whether there is adhesion or falling foreign matter on the parting surface, whether the templates are parallel, whether there is bending deformation, whether the opening distance of the templates is apintejinusted to the correct position according to the mold thickness, whether the surface of the guide pin is damaged, whether the pull rod is deformed unevenly, and whether the exhaust slot hole is too large and deep. According to the results of the above step-by-step inspection, the error can be eliminated by machining.

(4) Improper control of process conditions

If the injection speed is too fast, the injection time is too long, the injection pressure is unevenly distributed in the mold cavity, the mold filling rate is not balanced, and the amount of feeding is too much, the excessive use of lubricant will lead to overflow flash, so corresponding measures should be taken according to the specific situation.

It is worth noting that the elimination of overflow flash fault must start from the elimination of mold fault. If the forming conditions or raw material formula are changed due to overflow flash, it often has adverse effects on other aspects and is easy to cause other forming faults.


About PTJMould Industrial Company Limited

PTJmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.

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