Summary:The thinning of the bumper is easy to cause warping deformation, and the warping...
The thinning of the bumper is easy to cause warping deformation, and the warping deformation is the result of the release of internal stress. Thin-walled bumpers generate internal stresses for various reasons during various stages of injection molding.
Generally, it mainly includes orientation stress, thermal stress and mold release stress. Orientation stress is the internal attraction caused by insufficient relaxation of fibers, macromolecular chains or segments in the melt oriented in a certain direction. The degree of orientation is related to the thickness of the product, melt temperature, mold temperature, injection pressure, and holding time. The greater the thickness, the lower the degree of orientation; the higher the melt temperature, the lower the degree of orientation; the higher the mold temperature, the lower the degree of orientation; the higher the injection pressure, the higher the degree of orientation; the longer the dwell time, the greater the degree of orientation .
Thermal stress is due to the high temperature of the melt and the low temperature of the mold to form a large temperature difference, and the cooling rate of the melt near the mold cavity area is fast, resulting in uneven distribution of mechanical internal stress.
The demolding stress is mainly caused by insufficient strength and rigidity of the mold, elastic deformation under the action of injection pressure and ejection force, and uneven force when the product is ejected due to unreasonable distribution of ejector rods.
The thin wall of the bumper will also have the problem of difficulty in demoulding. Due to the small wall thickness and small shrinkage, the product is tightly adhered to the mold; due to the relatively high injection speed, the pressure holding time is reduced. Control is more difficult; thinner wall thicknesses and stiffeners are also prone to damage during demolding. The normal opening of the mold requires the injection machine to provide sufficient mold opening force, which should be able to overcome the resistance during mold opening.yongfengchina.com