Because the tube is being resized and reshaped during the nonmandrel bending process, tool alignment is a consideration that is just as important as it is in, for example, thin-walled tube mandrel tooling. Tool alignment in nonmandrel bending is achieved by using interlocking tooling.
Now that bending by the nonmandrel method requires a closed die operation. This means that the pressure die must close up and operate surface-to-surface with the bend die throughout the bending process. The idea behind this is to achieve complete cavity control, and therefore, maximum material control. Material control is necessary to realize the full potential of the nonmandrel bending process.
The final tooling consideration is the overall quality of the tooling itself. Consider the quality and comprehension of the engineering involved in developing an acceptable, workable shape for the current application. The shape of nonmandrel tooling will vary with the difficulty of the bend, the material being bent, and the application of the finished product.
Also consider the choice of materials for manufacturing the dies. Because of the constant abrasion involved in resizing and reshaping the tube, only high-quality tool steel should be considered for nonmandrel tooling.
In cases of extreme production, it is also advisable to invest in a titanium nitride (TiN) coating or some other long-wearing surface coating.
Note that medium carbon alloy steels do not belong in the nonmandrel tooling business or on today's high-speed bending machines. The additional cost in purchasing a tool manufactured from quality materials is often outweighed by the benefits of added tool life. A properly engineered, quality set of tools is capable of constant, consistent performance.