Cost-effective material for tube bending tool

The best material for a tube-bending tool is the most cost-effective. This means more than the ratio of tool life to tool cost, usually expressed as the per-bend cost of a tool. Cost-effectiveness must take into account process control - i.e., stability in a tube-bending machine's operation that optimises productivity. In terms of tool life, this translates into exhausting that life through wear rather than failure. This is because, tool failure often causes a process failure, which in turn can shut down a tube-bending machine and reduce its hours of operation.

So cost-effective tube-bending tools should tend to wear out and not break at the end of their life. To bring about this outcome, the tooling set-up on a machine is the most important factor. Next is the tooling material. The full tool kit for a rotary-draw tube-bending machine includes a die set, a mandrel, and a wiper. Rotary-draw die set has three components: Bend die, clamp die, and pressure die. The key material requirement for these dies is that they are tough. A tough die has hard working surfaces that can absorb a shock without breaking. So a tough die has some give. It is not brittle. For the same reason we do not use glass hammers, we should avoid materials and heat treatments for bending dies that make them brittle instead of tough and so break instead of wear out.

Consequently, the tool steels that are sometimes specified for rotary-draw die sets, such as A2, D2, or even a shock-resistant material like S7, are not the best materials in terms of cost-effectiveness. While they can be heat treated to a high level of hardness, they are designed to hold a sharp edge in metal-cutting operations. So the brittleness that comes with this hardness is acceptable for that use. However, tube-bending is, of course, not a metal-cutting process. There is no need for tooling materials that hold a sharp edge.

There is a need for the durability of work surfaces, specifically the tube cavities of the bending dies, which brittleness degrades. This is why die sets made of tool steel must be drawn back (i.e., softened) during heat treatment to eliminate their inherent brittleness - but also their superior hardness. Therefore, the extra cost of tool steel as a material for die sets does not deliver the maximal hardness that is the rationale for it.

For almost all tube-bending jobs, the best choice of material is alloy steel that can be heat treated to a high level hardness without inducing brittleness and then can be cased without significant dimensional distortion to further harden the working surfaces of the die set. Nitriding and carburising are effective methods of casing to make die sets tough. This is why heat-treated alloy steels are used for NASCAR engine components. They are durable and shock-absorbent, whereas tool steel parts would catastrophically fail under the stress of a NASCAR competition. Likewise heat-treated alloy steel bending dies will tend to wear out over a long life rather than fail from breakage.

Aluminium-bronze and hard-chrome plated steel have been the most common material specifications for tube bending tool. The former has been preferred for ferrous and titanium tubing while the latter for aluminium, copper-based, and, in some cases, mild steel tubing. Even with the advent of remarkable life-extending thermal diffusion and titanium coatings, there remain good reasons for preferring aluminium-bronze and hard-chromed plated steel.

To offset this defective set-up, frequently coated tool steel is specified to make the tools last longer. This typically works, although at the unnecessary extra cost of expensive materials and surface treatments and at a significantly increased risk of the tool breaking rather than wearing out. Therefore, aluminium-bronze and hard-chrome plated steel material specifications remain the most cost-effective for almost all tube-bending applications. Some of the dissatisfaction witNike Air Max