Influence of material properties on spontaneous buckling of thin-walled injection molded parts

摘要

Injection molding technology is widely used for manufacturing of thin-walled parts (such as covers and packagings). In those applications minimizing of wall thickness is crucial to improve economical aspects of production. Along with thin walls high injection and packing pressure must be used to obtain good quality parts. After injection molding process the residual stress is present in the part which lead to part shrinkage (reduction of dimensions). With compressive nature of residual stress and its relatively high magnitude (in comparison to part stiffness) the buckling phenomenon should be considered during the design of the part. Buckling is characterized by the sudden out-of-plane deflection of the part (well-known example of this instability is compressed ruler that bends when too high axial load is applied). This phenomenon can be present in thin walled parts with high length-to-thickness ratio and low area moment of inertia. During the packing phase of injection molding process compressive stress builds up in the part, so spontaneous buckling can occur. In the research the relation between material properties of the polymer and part stability was investigated. In this study several different thicknesses and geometries were investigated to obtain information about minimal wall thickness value that should be used to avoid the buckling occurrence.