Effects of Molding Conditions On Injection Molded Direct Joining Using a Metal with Nano-Structured Surface

Recent advances in metal-plastic joining techniques require that the two materials be joined directly without further use of adhesives, bolts or rivets. As a result, direct joining techniques have attracted undivided attention recently. This can be attributed to the fact that these novel techniques possess desirable advantages such as: reduced weight of the composite material, eases design restrictions and simplifies the manufacturing process. Basically, the joining means are categorized into two groups by virtue of the method of forming plastic structures, namely: the separated type and the in-situ type. This work majors on the in situ type where the plastic structure is formed and joined to its metal base simultaneously while utilizing an injection molding by inserting a special metal piece, the injection molded direct joining technique. Here, the desired nano structures on the metal piece are formed using chemical processing. However, the injection molded direct joining technique using micro/nano-structure forming has not been well applied to real industries due to some remaining challenges; nevertheless, the injection molded direct joining is quite a promising process.

In a recent research paper published in the journal, Precision Engineering, Fuminobu Kimura, Shotaro Kadoya, and Yusuke Kajihara at the Institute of Industrial Science, The University of Tokyo in Japan, set out to investigate the effects of molding conditions on strength of the injection molded direct joining samples, of which the metal pieces used had surface nano-structures. The team aimed at applying a chemical process as the special surface treatment to form the nano-structures on the metal piece. More so, they sought to look into the relationship between joining strengths and molding conditions; focusing on pressure of a mold cavity and injection speed as the molding conditions.

Briefly, the research team started by forming the nano structures on the metal piece by chemical processing. They then produced the injection molded direct joining samples where shape was a single lap joint geometry so as to measure the shear strength of the joint by tensile shear test. Lastly, the results of the tests were compared and analyzed.

The authors of this paper observed that the joining strength had positive correlations with both cavity pressure conditions. Secondly, they noted that the joining strength had a negative correlation with the injection speed. This was a novel finding and unique to the injection molded direct joining technique using nanostructures only. More so, it was seen that the injection speed was much higher than the one of the cavity pressures.

Within, an empirical investigation on the effects of molding conditions on the joining strength has been presented. The effects of processing conditions, where the surface structures of the metal piece are in nanometer scale, have been thoroughly analyzed. As a result, interesting effects of the injection speed, which is unique to the injection molded direct joining technique using a metal piece with nano-structures, have been uncovered. Moreover, this technique could help achieve coveted advantages such as reduced weight of the composite material, ease in design restrictions and simplification of the manufacturing process. In totality, the findings of this study will help promote a better understanding of the injection molded direct joining technique.