Application And Mechanism Research On Compound Spinning And Multi-pass Drawing Manufacturing Technology Of Micro Copper Tube With Straight Grooves

Recently,with the trend of electronics processors towards higher performance andsmaller packaging, the heat dissipation from these devices is growing and the heat flux isgreater than ever, and the size of micro heat pipe,with high thermal conductivity,goodisotherm performance, rapid heat response and no extra power, is becoming smaller andsmaller. Micro heat pipe provide an effective solution for a variety of extremely small spaceand the cooling problem of high heat flux components. And will be wildly used inultra-samllelectronic compents and application systems, special in surgical thermalmanagement. However, it has proven hard tomanufacture micro heat pipe having an outerdiameter less than6mm (especially less than Ф4mm) by the traditional manufacturing methodsuch as extrusion-ploughing or high speed Ball-spinning.The compound spinning anddrawing manufacture technique is developed for the efficient and economical manufacture ofthe micro-grooved copper pipe.then, micro straight groove of copper tube with outer diameterabout Ф2~6mm was obtained using a compound technology of high-speed oil-filledspinning and multi-pass drawing in this paper.Micro straight groove of copper tube which had an outer diameter of Ф6mm wasobtained by high-speed oil-filled spinning method first.After that,multi-pass drawingprocessing method was designed to manufacture micro straight groove of copper tube withouter diameter about Ф2~6mm.In this paper, the optimal design theory is presented tosimplified the forming process of multi-pass drawing,and then,the drawing force of microstraight groove of copper tube and the model of admissible velocity field,the deformationpower and the arch effect have been established. Use the analytical method to derived thedrawing force,the height of the arch effect and the deformation power. The mechanism ofarch effect of the grooves in the drawing process were investigated. And devided to foursteps,and they are:grooves accumulation extrusion, grooves cracking, arch effect formationand grooves saturation.On the basis of elastic-plastic finite element analysis of large deformationtheory,three-dimensional finite analysis model are established by MSC.MARC for muti-passdrawing.The metal flow rule,distribution rule of stress and strain, the influence of formingprocess parameters on drawing quality and the corresponding forming mechanism by themuti-pass drawing has been simulated. Results indicate that the grooves generated the arch effect andswallow tailed during the fourth passes drawing with the outer diameter reduces from3mm to 2.5mm. Moreover,the drawing force decreases firstly and then increases with the increases ofreduction. And when the value of reduction is13.1%, the drawing force is smallest. when thevalue of reduction is21.9%, the drawing become maximum. The value of the height of thearch effect is0.5mm on the reducing area,while the value is0.62mm on the calibrating area.To reveal the mechanism of high-speed oil-filled spinning and multi-pass drawingcomposite forming technique, scanning electron microscopy, ultra-deep microscope andmetallurgical microscop methods are performed. The structure evolution of micro straightgroove of copper tube by composite forming was concluded.Results show that the groovesgenerated the arch effect during the third passes drawing and swallow tailed at the fourthpasses. However,arch coefficient increases firstly at0~16%and then decreases above16%asthe increase of drawing reduction. The process of drawing force are generally classified intothree stages: the initial contact, stable drawing deformation, and leaving the drawing die. Thedrawing force decreases firstly and then increases with the increases of die angle. And whendie angle is16°,the drawing force is smallest.Furthermore,There are many kinds of flawseasily generated during multi-pass tube drawing,such as surface scratches,metal pressed into,bonding or segmental teeth, Spiral, vertical or horizontal crack,bending and so on.The capillary performance of the micro straight groove with outer diameter of Ф6mm,Ф5mm, Ф4mm, Ф3mm, Ф2.5mm and Ф2mm are done by infrared thermal imagingtechnology.The results show that the capillary force increases firstly with outer diameter about3~6mm and then decreases with outer diameter about2~2.5mm as the decrease of drawingdiameter.Moreover,boiling experimental apparatus of the micro straight groove are alsoestablished,and the heat transfer charateristics were analyzed.Results indicated that the valueof N_u decreases as the decrease of drawing diameter.At last,the start-up and isothermalperformance of micro copper heat pipe with straight grooves are tested. The results show thatthe startup time of micro-heat pipe is about10s,and the value of temperature difference isabout3℃.