Research On In-Mold Assembly Technology And Molding Equipment Of Mesoscale Plastic Revolute Joint

In-mold assembly technology integrates assembly of plastic parts into injection molding. This technology can effectively reduce or even avoid the work of assembly after molding, shorten the cycle time of production, lower the cost and enhance the economic benefit of enterprise. Now, it has been extensively used in making parts of cars, toys, electrical equipments and military. But application of in-mold assembly technology in micro-injection molding is just on start. There are many questions to be resolved. So this master thesis takes in-mold assembly of the mesoscale polymeric joint as the research object, and makes deeply study on the molding process and molding equipments.At first, theoretical analyses are carried out for the technique principles of in-mold assembly injection molding of the mesoscale plastic hinge. The precondition for eliminating adhesive bonding is put forward, and the approach of acquiring the clearance required for rotation of the mesoscale plastic hinge is analyzed. It is inferred that whether adhesion of plastic parts appears depends on the heat transferred from the later molded plastic part to the earlier molded plastic part. And the clearance between plastic parts is decided by shrinkage of both the plastic micro pin and the plastic micro hole.Secondly, the structure of the mesoscale plastic hinge is optimized to make it more suitable for injection molding by in-mold assembly technology. Then the molding process is analyzed, and the molding sequence of making the plastic micro hole before the plastic micro pin is chosen.Thirdly, based on the theoretical analyses, the mold for assembly of the mesoscale plastic hinge by using the single cylinder injection molding machine is worked out. This mould makes multi-stage injection molding become possible on the single cylinder injection molding machine, and effevtively protects the very thin core from bending under the high pressure of the polymer melt that flows into the mold cavity with high speed.Finally, the experiments for in-mold assembly of the mesoscale plastic hinge are carried out with HDPE and PP. The experimental results show that the mesoscale plastic hinge can be successfully molded by both single kind of polymer and multi kinds of polymers as long as the precondition for no adhesive bonding is meeted. Meanwhile, the injection pressure of the later molding stage has significant influence on shapes of the plastic micro pin and the plastic micro hole. With higher injection pressure of the later molding stage, tapers of the plastic micro pin and the plastic micro hole become bigger, and the clearance between the plastic parts becomes smaller even minus to form interference fit that makes the plastic hinge can not move freely. Moreover, it is not a good idea to pursue lower temperature of polymer melt at later molding stage, because lower temprature of polymer melt needs higher injection pressure which would bring undesirable influence.