Effects of molding conditions on injection molded direct joining using a metal with nano-structured surface

• Direct joining of injection molded plastic on metal work with surface nano-structure.
• Experimentally investigation of effects of molding conditions on joining strength.
• The joining strength had a positive correlation with cavity pressures.
• Injection speed had a negative correlation: unique for nanometer scale structures.
• The injection speed affected much higher than the cavity pressures.

Injection molded direct joining (IMDJ) is one of the metal-plastic direct joining processes and is based on a combination of a special surface treatment of a metal piece and an insert molding. This study employed a chemical processing as the special surface treatment to form nano-structures on the metal piece. We investigated relationship between joining strengths and molding conditions; we focused on pressure of a mold cavity and injection speed as molding conditions in this work. To evaluate the IMDJ samples processed under various molding conditions, we carried out tensile-shear tests. Then we compared the results of the tests to discuss how much each condition variation affected the joining strength. From the discussion, we found an interesting effect of the injection speed, which is unique to the IMDJ using a metal piece with nano-structures. The findings of this study will promote a better understanding of the IMDJ.