Question

10.5. Injection pressure (A) and hold pressure (B) are used as the variables in an injection molding operation to study the effect on flash. Flash results in wasted mate- rial. Each of the variables is tried at two levels: Flash, mm (1) 2.5 2.92.4 7.5 6.8 7.1 10.8 11.6 11.1 9.9 9.6 10.1 ab Find the main effects and the interaction effects. Draw your conclusions. ighler a tyne of wood (A), feed rate

Answer 1

Flash is a defect where excessive material is found at locations where the mold separates, notably the parting surface, movable core, vents, or venting ejector pins. Flash is a molding defect that occurs when some molten plastic escapes from the mold cavity. Typical routes for escape are through the parting line or ejector pin locations. This extrusion cools and remains attached to the finished product.

Injection pressure and holding pressure are sometimes used interchangeably however, they are not the same. Injection pressure is that pressure under which the mold fills; sometimes this is called the first-stage pressure. The holding pressure is the pressure that is maintained on the melt after the mold is filled and until the gate freezes or the pressure is removed by cycle timer-control. In most cases, it is the holding pressure that determines the shrinkage and control flash rather than the initial injection pressure.

Main Effects:

Increase the mold clamping force or reduce the injection pressure and holding pressure to optimum value cause the decrease the flash.

The improvement of poor appearance of the moldings, the reduction of size unevenness between the molding shots, and the measures against sink marks, warpage and flash can be achieved by controlling the injection rate, holding pressure, screw rotation speed and back pressure with multistep program control at the time of injection.

The defective phenomena such as sink marks, warpage and flash are related to the holding pressure. The measure against these phenomena becomes possible by controlling the holding pressure.

The injection pressure and holding pressure are set to optimum value if the flash sink marks and voids do not occur in the molded pieces.

Conclusion:

The flash increase with the Insufficient mold clamping force and too high injection pressure. The flash decrease with the optimum holding pressure and injection pressure.

The flash first increases with the significant amount of increase in the holding pressure and it decreases with the decrease in the holding pressure.

The flash decrease with the reduction in the injection pressure and increase with a further decrease in the injection pressure.

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