Experimental study on the influence of the cross section of cavity on water penetration during overflow water-assisted injection molding (OWAIM) process was conducted based on a lab-developed water-assisted injection molding system. The lab-developed water-assisted injection molding system consisted of a water injection unit

an injection machine

a mold with changeable inserts and control unit. Seven cross sections were used as characteristic sections. Circle ratio was introduced to characterize the shape of cross section. Area of cross-section (ACS)

the maximum distance between inscribed circle center and wall (Max_D)

radius of inscribed circle (RIC) of cross-section

and circle ratio were calculated as import geometry information of cross-sections. Hollow ratio was used to describe the relative void volume of water penetration. The influences of the shape and area size of cavity cross section on the shape of water penetration section and hollow ratio and residual wall thickness (RWT) were studied. In the OWAIM process

the shape of water penetration tended to approach the shape of mold cavity cross section. If the mold cavities had the same or similar cross section area

the mold cavity with a larger circle ratio would have a larger hollow ratio. If the mold cavities had the same or similar circle ratio

the area size of cavity cross section had little effect on hollow ratio. The size of water penetration section was relatively constant in a cavity with constant cross section. The residual wall thickness of a cavity with circular section was uniform. The larger the cross section

the thicker the RWT. For the cross sections with the same radius of inscribed circle (RIC)

the maximum RWT increased proportionally as Max_D increased

while the minimum RWT decreased proportionally as Max_D increased. And the RWT inhomogeneity increased significantly as Max_D increased. For these cross sections with close Max_D

the higher the RIC

the thicker the maximum RWT and the minimum RWT.