Experimental Study On The Influence Of The Size Of Runner And Gate On Melt's Filling In Micro Injection Molding

Micro injection molding, for its advantages in micro size, high accuracy and suitable for mass production, has become one of the most effective manufacturing methods of products in MEMS. It is now widely used in automobile manufacture, electronics, bio-medical, precision instruments, aerospace and other relative fields. While, due to the micro scale effects, the flow behavior of polymer melt in micro cavities changes significantly, and the design of the micro injection mold is different from that of the conventional injection mold. In this paper, the current situation for the research of the technology in micro injection molding home and abroad was comprehensively analyzed. For the key issues in the design of the micro injection mold, based on the theory of polymer rheology, the influence of the size of runner and gate on the flow behavior and the filling rate of polymer in micro cavities were studied combining theoretical analysis with micro injection molding experiments.The influence of the process parameters on the melt's filling rate in micro cavities and the quality of the micro molding products was also studied.Firstly, a four-cavity micro injection mold was designed and manufactured for the thin circular slice with the diameter ofΦ800μm and the thickness of 200μm. The side gate was adopted, and the gate widths of the mold were 115μm,130μm,145μm and 160μm, with the same thickness of 100μm. The single factor experiment of PP and POM was conducted with different process parameters. The filling rates of the four cavities with different gate sizes were measured. The results show that the size of gate is a principal factor to the filling rate in micro cavities. The filling rate decreases gradually with the decrease of gate size. For the same size of gate, mold temperature is more significant to the filling rate than the other process parameters. The filling rate varies for different materials.Secondly, with the same gate size, runner's cross section shape and length, the influnce of the dimension of runner's cross section on the filling rate of micro cavities was studied by enlarging the runner's cross section. The results show that, for the same gate size, the filling rate increases with the increase of the runner's cross section size. But, compared with the gate size, the influence of the runner size is less.Lastly, according to the experimental results of the filling rates for the cavities in the micro injection mold of the thin circular slice, a four-cavity mold with the side gates of the same dimension was designed for micro gears. The pitch diameter wasΦ1mm and the cross section of the runner was trapezoid. Through the single factor experiment, the influence of the injection pressure, injection rate, melt temperature, mold temperature, packing pressure and packing time on the filling rate of micro cavities was studied. It is indicated that, injection pressure, injection rate, melt temperature, mold temperature, are more significant to the filling rate than packing pressure and packing time.