If you were to read a collection of tube bending articles written at various times over the last three decades, you might be surprised by how much bending technology has changed, especially within the last 20 years. Benders have advanced, new features have been developed, and bending knowledge has improved and spread.
The aircraft industry has always been one of innovation. From the first flight in 1903, the technology it used to build aircraft was almost unrecognizable a mere 50 years later. Wooden frames covered in cloth and internal combustion engines had been replaced by aluminum airframes, aluminum skins, and jet-powered engines. The first flights were measured in seconds for time and feet for distance; five decades later, jets were flying for hours and hundreds of miles. Always space- and weight-conscious, aircraft companies led the way in reducing component size and weight. In tube bending or pipe bending machine, this means tighter bending radii and thinner walls. By the 1990s, it wasn’t uncommon for a tubular aircraft part to have a bending radius equal to the tube’s diameter, known as a 1D bend.
In the early to mid-1990s the straights between bends shortened to less than 2D. Stack benders become the coveted machines of the time. The early stack machines were limited to either two or three tools: The so-called two-stack and three-stack machines with shearing machine. The latest generation of machines is more advanced still. They have a specific stack height but can accommodate as many tools as can fit onto the stack.
In that same time period a three-stack machine held a single straight clamp and two bend dies, so part designers still had limitations: either use the same straight clamp for every bend on a given part, or design the part so it used several straight clamps, which required additional tooling setups. The tradeoff was design creativity versus production efficiency.
The auto industry followed the aircraft industry by reducing the bend radii, which ultimately led to a new machine equipment feature: Boost. This process, a pushing force that advances the tube into the bend die, gave manufacturers the ability to make several 1D bends in succession with no straight length between the bends. In other words, make a 1D bend, rotate the tube a bit, and make another 1D bend right after the previous one. Voila! A compound 1D bend.
As materials have gotten thinner and bending radii smaller, more pressure has been applied to make good bends without wrinkles, and the wiper tower needs to be rigid enough to maintain position when this additional force is applied. While machine builders, including slip roll machine, incorporated one innovation after another, the one area that seemed to be neglected was the wiper towers, the posts to which the wipers were mounted. Bends have increased in severity, but among many bending machine manufacturers, wiper die towers have stayed the same.
Any experienced bend technician knows that a wiper tower that deflects during bending creates several problems, especially wrinkles. The setup person has a difficult time setting the wiper because all of the rules he or she knows no longer apply and uncertainty sets in. How to set the wiper on a tower that moves during bending? It’s impossible to say. A wiper tower that moves introduces a variable that nobody wants to deal with.