Active Air Venting of Mold Cavity to Improve Performance of Injection Molded Direct Joining

A surface micro-/nano-structured metal plate can be joined with an injection molded plastic piece in a mold,which has been named injection molded direct joining(IMDJ).The injected plastic melt infiltrates the micro-/nano-structure,e.g.,a porous structure with micro/nano pores,on the metal plate while flowing in the mold cavity where the metal plate is inserted.After solidification of the plastic,the metal and plastic materials are directly joined via the micro-/nano-structured metal surface.Since air is trapped by the plastic melt,it is easily imagined that the air in the mold cavity prevents the melt plastic from contacting the metal surface and infiltrating the micro-/nano-structure,which could result in poorer joining performance.To avoid the prevention of the air for the better joining performance,the present study proposes a system actively venting the mold cavity during injection molding.To apply the active venting to IMDJ,venting and sealing systems were newly developed.In addition,a system measuring air pressure of the mold cavity was developed.The proposed system was evaluated by a measurement of joining strengths of IMDJ specimens that were produced under various conditions.From the results,it is concluded that the active venting does not necessarily have a positive effect in any cases:the effect depends on the type of surface micro-/nano-structure.

Measurement Method of Internal Residual Stress in Plastic Parts Using Terahertz Spectroscopy

Since internal residual stress in polymers causes dimension errors over time,a measurement method for residual stress in polymers,especially in opaque engineering plastics,is strongly required.In this study,we propose to utilize terahertz(THz)spectroscopy to non-destructively measure internal residual stress in polymers.To verify the validity of the proposed method,we manufactured polytetrafluoroethylene ring samples with and without residual stress,and studied them with THz time domain spectroscopy system.THz spectra of samples without residual stress showed almost no polarization difference,whereas spectra of samples with residual stress showed clear polarization difference.Dimension changes between the samples with and without residual stress were also estimated and it was found that the change had a correlation with THz polarization difference.These experimental analyses confirm the validity for the proposed non-destructive measurement of residual stress in polymer.