Dr. Roger N. Wright 2017-11-07 01:20:43
Tips From WireDrawing 101® by: Dr. Roger N. Wright Roger N. Wright, LLC 600 State Street Lawrenceville, IL 62439 USA E-mail: firstname.lastname@example.org www.rnwinc.com This is the fourth in a series of columns on drawing with shaped dies and roller dies, and we are taking a look at unpowered roller-die systems. These are systems that simply involve the wire being drawn, or pulled, through rolls that are free to turn, with the drawing force, or power, being provided by a capstan. Some simple roll configurations are shown in Figure 1(a), Figure 1(b) and Figure 1(c). Figure 1(a) shows a basic open rolling or roll flattening configuration. Figure 1(b) involves the presence of “edging” rolls. Four-roll configurations such as those of Figure 1(b) and Figure 1(c), are often referred to as “turksheads”. Much more complex configurations have been developed, involving multiple passes. Analysis of these types of configurations is beyond the scope of this series of columns, as was analysis of one-piece die sequences en route to complex shapes. We will, however, address the rolling of rectangular cross sections in single passes. This is a major technology, and sequences of such passes can be employed to many ends. Wire drawing analysis often involves the relationship of drawing stress, sd, to uniform work (volume averaged), wu, redundant work (volume averaged), wr, and friction work (volume averaged), wf. That is: Such analysis can be simplified by use of the deformation zone geometry index, D, where, for conventional drawing dies: and where a is the die half-angle in radians and r is the decimal reduction (10% = 0.1, etc.). Geometrically, D is the deformation zone dimension perpendicular to the axis of extension, divided by the length of the deformation zone. In this context: where sa is the flow stress or strength of the wire and m is the coefficient of friction. This approach will be used in this series of columns. Now, drawing or pulling the wire or workpiece through rollers to effect a change in cross-sectional area or shape, differs from simple, fixed-die drawing in that very little friction is created by the rollers, and a lubricant may not be necessary. Hence it is reasonable to eliminate friction and friction work from the drawing analysis, so that: In the spirit of this analysis, we can estimate drawing forces and stresses for roller-die systems where the rolls are not powered. In order to do this, we must define D for a tworoll roller die, which we will call D'. That will be one of our objectives for next time. So much for now. By the way, have your shops had any experience with roller-die systems? Check it out, and good luck!!!! The WireDrawing 101® short course, presented and developed by Roger N. Wright, LLC, and Wire & Cable Technology International magazine, is the comprehensive two-day course that teaches the fundamentals of wire drawing to manufacturers of ferrous and nonferrous wire. WireDrawing 101 features a unique handbook, with practical process design and trouble-shooting exercises suitable for work-a-day formats and continuing study. www.rnwinc.com
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