BENDING TUBE WITHOUT A MANDREL

Understanding how it works & its applications

In today's competitive environment, there is a relentless push toward greater efficiency. As a result, the tube industry demands that parts be bent faster, cleaner, easier, and at a lower cost, while at the same time improving the quality of the finished product.

Nonmandrel bending is an option for meeting these demands. It dates back about 40 years to the vertical ram-type machines that used what was then referred to as "heart-shaped tooling."

In the 1970s, the heart-shaped tooling evolved into the semi-automated rotary draw bender. However, it was employed with a static pressure die, often with unsatisfactory results.

Nonmandrel bending saw its greatest advancement in the late 1980s and early 1990s with the completely automated computer numerical-controlled (CNC) bending machines. Refinements to the engineering of the shaped tube groove were also made. The tube groove often allows better control of the manufacturing process, and therefore, the finished product.

This article will answer questions about how nonmandrel bending works, when it is applicable, what kind of results can be expected, and what primary machine requirements are necessary to successfully employ nonmandrel bending.

How it works

Nonmandrel bending's primary objective is to bend tubing that would normally require some form of internal support without using that support. To achieve this goal of bending round tubing without internal support, a combination of two factors are applied to the tube simultaneously during the bending process.

First, the diameter of the tube is reduced at the point of bend, while at the same time, the circumference of the tube is reshaped into a structural form for support.

When the tubing is hard, such as stainless steel, hard copper, or titanium, good bends can be achieved with a fairly generous structural shape. Soft tubing is much more difficult to control and may require a more radically-shaped tube groove.

Because the tube at the point of bending is in a state of plastic deformation, that deformation will remain permanent after removing the load that caused it. So, after bending, the result is a piece of tubing that used to be round, but which has taken on a very new and distinctive shape during the bending process.