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Technology . A digression on tube end forming technology

transfluid® invites you to take a little foray into tube end forming technology, with fascinating practical insights.

Axial tube end bending:

This procedure is most frequently used to achieve a final result or to carry out pre-forming for a subsequent process, e.g. roller burnishing. The benefits: It is highly efficient, fast and economical. Loading can occur at any time and is both simple and automated. Components such as flanges can also be reliably supplied automatically and, if necessary, compressed. The clamping process is normally carried out vertically, although for particular requirements it can also be performed horizontally. Production of the forming geometry is strictly based on the respective tool. Clamping lengths are usually dependent on the forming geometry and the material. Up to six different tools in succession can usually be used to produce a particular geometry – in exceptional cases, even more. In such a case, the different tools are positioned one after the other automaticaly.

The required compression load (tonnage) is dependent on several factors; on the one hand the diameter of the tube, and on the other the material – but particularly the desired forming geometry. As a basic rule, the tighter the angle, the more forming stages and the greater forming force that is required.

Standard compression loads of transfluid® machines:

  • up to 20 mm tube diameter: compression force 6.5 to
  • up to 32 mm tube diameter: compression force 10 to
  • up to 45 mm tube diameter: compression force 15 to
  • up to 60 mm tube diameter: compression force 25 to

Beyond these figures, plants for up to 130 to are possible.

Useful additional equipment

For progressive geometries, an additional clamping device can be used to avoid high tool expenses. This often makes it possible to produce complex geometries both simply and reliably. It also usually allows you to save on a machining step.

A second tube stop in conjunction with the additional clamp allows the two ends of the tube to be formed consecutively – even if entirely different geometries must be applied at the ends.

The use of a hydraulic/digitally controlled forming axis makes it possible to monitor forming, achieve shorter cycle times, and store or call up process parameters. These benefits can obviously also be realised with fully electric drives.

If extremely short machining times are required, instead of performing a tool change, an automatic transfer system can also be employed. This results in cycle times of approx. 6 sec. per component.

There are some typical axial forming processes:

  • Expanding or reducing (symmetrical or asymmetrical)
  • Calibrating
  • Flanging
  • Wall thickness thickening or wall thickness ironing
  • Compressing of components (flanges, compression sleeves, etc.)
  • Preparatory forming for the rolling process
  • Punching
  • Bends between 90º and 180º with narrow radii can be axially compressed.

The tools

A clamping jaw is required for each different diameter. However, this is also partially dependent on the forming geometry. If the clamping lengths between bends and the forming location are too short, form clamping pieces can be used. If the distances between the bends and the finished shape vary from product to product, this difference can be compensated for both easily and cost-effectively using additional clamping jaws. The nature of this requirement is dependent on the geometry.

For some forming processes, it may be either necessary or useful to use spring-loaded progressive clamping jaws (jaw sliding tools). This reduces the cycle time, because complex shapes can be produced in a single step.

The forming tools are composed of several parts to enable worn components to be replaced at a low price.

If external components need to be attached or, for example, the wall thickness is to be thickened or reduced, spring-loaded forming tools (so-called spring progressive tools) can also be used.

Forming tools can also be used magazines, in order to improve the already short tool change times even further.

Forming tools can also be used magazines, in order to improve the already short tool change times even further.

This type of forming also allows for components to be compressed onto the tube – both axially and radially. In order to reduce tool wear to a minimum, the forming tools are produced either from carbide or ceramic or specially coated.

Particular features and limits of this technology:

  • The degree of forming often presents a limit.
  • The material is cold hardened.
  • Max. possible expansion 80% (in relation to the initial diameter)
  • The forming operation in the first stage must be as large as possible.
  • Degree of forming possible: 1. stage: 50%, accordingly less for each subsequent stage
  • Weld seams may become visible.
  • The surface quality may change.
  • Extremely sharp-angled forms cannot be produced.
  • Wall thickness increases during a reduction
  • Wall thickness if reduced by an expansion
  • Reducing by a large amount is particularly critical for stainless steel tubes.
  • Tool closing edges may become visible.

Do you want to know more? Or perhaps you would like to complement your knowledge on this and the topics already covered by attending a workshop. If so, we would be delighted to hear from you!