Abstract: Based on a homemade extrusion platform designed for the fabrication of thermoplastic parts with micro capillaries, a novel plastic micro tube with 24 capillaries was first proposed all over the world (Micro Capillary Tube, MCT). These 24 capillaries are orderly located in the circular wall of a tube with a larger hollow channel. The effects of three processing parameters, i.e. injection air pressure, draw ratio and air gap distance, on the quality of the parts were investigated in the extrusion process with conditions of injection air pressures: 0.21~0.36 kPa, air gap distance: 35~110 mm and draw ratio: 2.4~14.1. The results indicated that larger draw ratio could result in a smaller outer and capillary diameter, and there was a negative correlation between the sizes of MCT and draw ratio. However, the draw ratio did not show any influence on the dimensional proportions of cross section of MCT, and a similar trend could be observed in the air gap distance. In contrast, the injection air gap severely damaged the dimensional proportions and changed the shape and size of micro capillary, but it did not change the external size.

Key words: micro capillary, plastic tube, extrusion , injection air pressure, draw ratio, air gap distance