Production of Special Tubes with a Variety Cross-Sectional Shapes by Bunch Drawing and Fluid-Mandrel Drawing

Abstract

Recently, special tubes for high efficiency heat exchangers, high functionality electrodes, and super-micro medical needles have attracted attention. In order to produce such special tubes, however, a special processing method or tool is required. In this study, fabrication of special tube by bunch drawing and fluid-mandrel drawing were attempted. And it was revealed that the fabrication of special tubes with a variety of cross-sectional shape is possible, when a bunch of tubes, or a tube of large diameter in which a number of fine tubes are inserted, is drawn. Presumption of cross-sectional shapes after bunch drawing was examined by FE analysis. Cross-sectional shapes and the distribution of Vickers hardness which has relation to equivalent strain were compared between tubes obtained virtually by FE analysis and fabricated actually in this study. It was found that they correspond very well and FE analysis is useful for the presumption of cross-sectional shapes after bunch drawing. Meanwhile, downsizing of medical needles and heat exchanger tubes has been required from the market. So it is necessary to fabricate an inner-grooved fine tube with thin wall-thickness, and at that time the inner grooved geometry must be homothetic. Hollow sinking was carried out to reduce the diameter of a tube. And cross-sectional shape, groove geometry, and the change of wall thickness after processing were examined. In hollow sinking, increase of wall-thickness, change of inner groove geometry, and poor inner surface quality were found. Therefore, newly-devised fluid-mandrel drawing was applied. And it was revealed that it is possible to obtain an inner grooved tube of which groove shape is nearly similar to that of pre-processed tube, even after the processing of diameter reduction. Also, it was clarified that the production of a medical painless needle of 0.2mm in diameter by fluid-mandrel drawing was possible.

Review on Advances in Metal Micro-Tube Forming

“…Recent developments in the fabrication of micro-tubes aim in particular to provide improved semi-finished products, with more economic manufacturing processes, for use in microsystem-based applications of medical engineering and microfluidics for heat exchangers. When primarily considering the fabrication of seamless metallic tubes, the investigated technologies can be divided into (a) dieless drawing techniques [5,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35], (b) process chains, applying scaled-down and partly modified tube drawing [36][37][38][39][40][41][42][43][44][45][46][47], and (c) manufacturing techniques of grooved micro-tubes for applications in heat exchange [43,[48][49][50][51][52][53][54]. Apart from this research into tube manufacturing processes, notable progress was also achieved in the design of the process and tools for the profile extrusion of tubular micro-profiles with a number of channels [55][56][57][58][59].…”

“…A possible way of avoiding complications in removing a rigid mandrel from the drawn micro-tube consists in the use of liquids, such as water or oil, within the sealed tube during the drawing process, instead of the mandrel [45]. For the fabrication of micro-tubes made from stainless steel, with d o = 2.0 mm, by performing 21 passes, without intermediate annealing, the application of this fluid-mandrel drawing technique resulted in an increase of the wall thickness that was about 42% lower compared to that of the use of sinking [43], as shown in Figure 5.…”

“…Furthermore, an excessive increase in the wall thickness could be observed [49,53]. Investigations into drawing such grooved tubes with a liquid medium inside-according to fluid mandrel drawing [45]-have shown that these drawing limits of tube sinking could be extended considerably [43,49]. Figure 6 illustrates the change in wall thickness for the multi-pass drawing of a grooved micro-tube with different media, as an example.…”

“…Comparison of fluid-mandrel drawing and sinking: (a) development of the wall thickness ratio versus the ratio R t of the reduction of the outer tube diameter and (b) the cross-section shapes of the initial tube (above) and the drawn micro-tubes (below). Republished with the permission of Trans Tech Publications, from reference[43], copyright 2014; permission conveyed through Copyright Clearance Center, Inc.…”

Cold Drawing of AISI 321 Stainless Steel Thin-Walled Seamless Tubes on a Floating Plug

“…The results of numerical FE-based analysis showed that the drawing force can be reduced and that the drawing force is nearly independent of the length of the The work of frictional forces on the above-mentioned surfaces is completely transformed into heat, resulting in a local increase in the temperature of the drawing die, tube, and floating plug, as well as the lubricating film on the outer and inner surfaces of the tube [6,7]. The intensity of the heat released is a function of the following factors [8,9]:…”