Fabrication of Inner Micro-Grooved Pipes

Heat pipes have been applied popularly in microelectronic cooling, in which grooved heat pipes are the one of main types. Most of commercial grooved heat pipes with OD 6mm have 55 grooves and the groove width is larger than 200μm, which causes the biggest drawback of grooved heat pipes having no fine anti-gravity performance. In this paper, a fabrication method of inner micro-grooved pipes is investigated. First, a die with micro-tooth was fabricated by micro wire electrical discharge machining (WEDM). Utilizing micro wire with diameter in 30μm, it can machine micro slot with minimum size of 45μm wide, the surface roughness (Ra) is smaller than 0.1μm. Then, the die forms the micro grooves on the inner wall of pipes by high-speed spinning process. Last, the grooved pipes were draw to reduce the pipe diameter further, and then smaller grooves can be formed. The experiment results show that the width of obtained grooves is less than 100μm and the depth is about 250μm. The depth-to-width ratio increases significantly. The capillary force improves by double times, so the anti-gravity performance is better.