January 16, 2024

Unison Blog: How can clever tube and pipe design save you money?

Blog by Steve Chambers.

How can clever Tube and Pipe design save you time and money?


All of us in the Tube Manipulation world know that when “a thing” is designed, the pipe and tube elements are generally the last parts to be considered.

Why is this? Well, it is perceived that pipes can be designed (in CAD anyway) to go anywhere, therefore, it doesn’t really matter. As long as the part can be fitted and whatever is being transported can get from A to B.

So what issues can be over looked when designing pipework is last minute.

When designing items to be manufactured, the complexities of tube bending are not always completely understood.

It is often assumed that tube bending is easy, but in fact there are a lot of factors that need to be considered at point of design, which does make tube bending a bit of a “Black Art!”


Distance between bends (DBB):

This should be recommended to be at least 2D in length (2 x the Diameter of the bend). This is to give the tooling enough grip on the tube when rotary draw bending. If the DBB is shorter than this, there are solutions, but they are not always ideal:

  • Clamp areas can be shot blasted or even serrated, but this can leave marks on the finished bend.
  • Bend on Bend (or Compound Tooling) may be used, but this then becomes bespoke for that specific part, and may not be used on other bent parts. Compound tooling can also be expensive to manufacture.
Bend on bend tooling
Bend on bend tooling


Serrated tube bender tooling
Serrated tube bender tooling

Differing CLRs within the Same part (Centre-line Radii):

Some parts will be designed with different CLRs within the same part, when sometimes it is not necessary. For example, if a 20mm diameter part with three bends had one bend at 40mm CLR, one at 50mm CLR and a third at 55mm CLR, immediately there would be a need for a multi-stack tube bending machine, and also the need for three toolsets or multi-stack tooling, which can be very expensive.

Now I fully understand that the part will have been drawn to miss other components within the assembly, but, if all the CLRs were homogenized to say 48mm (to take an average), does this really matter?

I recently looked at an application for an existing customer who had this such issue. Design had drawn a bent tube with three CLRs within the same part – say 6”, 8” and 10” for example. However, the bends were very shallow, with the maximum Degree of Bend (DOB) being around 15°.

We discussed with the customer, that yes, Unison can supply you a multi-stack machine, and three sets of tools, or a multi-stack set of tools, to make your part as designed, or, if you can speak to your design team and make all the CLRs 8”, we can save you a whole load of cash and simplify your process.

When the customer’s design team remodelled the part with all the CLRs at 8”, and overlaid it with the original, there was hardly any difference whatsoever!

The design was agreed, and we sold the customer a single-stack machine, with one set of tooling, rather than a multi-stack with three sets. This saved the customer over £150k.

Yes, I agree, we diddled ourselves out of overselling a machine, but that is not what we are about at Unison. We want you to have the right machine for your application, and would never sell you a sledge hammer to knock in a tack!


Picking the most Suitable CLR:

In the same vein as the above, it is also important to pick the most suitable CLR. Yes, bends may need to be tight to miss other design elements, but if the CLR can be made as generous as possible, you may eliminate the need for wiper dies and mandrels.

Depending on the material, wall thickness and CLR, tighter bend radius will need a wiper die to eliminate wrinkles from the inside of the bend, and the same parameters can affect the number of balls needed on a mandrel – if one is needed at all – to reduce ovality during bending.

Obviously, if you can potentially eliminate the need for either, you would not need to stock replacements, as these are generally consumables and also make the machine and bending process easier.


Design is Master:

Taking the above factors into consideration, it is often a good idea for the design team to have access to the operating system and simulators for the bending machines, to prove the manufacture of a part before the works order hits the shop floor.

This is why Unison recommend a seat of UniBend Office within a machine purchase package. Along with Unison’s simulation software Opt2Sim Tube, UniBend allows the mechanical design team to program and simulate the parts in full on the actual machine or machines with the actual tooling they have.

If the machine or tooling on site are not capable of bending the part, slight redesigns can be made to make it possible.

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