Technology . A digression on tube end forming technology (continued)
You are now well acquainted with the possibilities and particular features of axial tube end forming from our last t time(s) issue. Time now to cast our eye over a second forming procedure.
Rotary tube end forming:
Roll forming often complements axial forming, though it can also be used to create its own discrete shaping forms. Rolling is frequently used to increase the surface quality in forming processes and to produce polished surfaces. Sharp-angled forms, which cannot be produced axially (or only with great difficulty) are relatively simple to create by rolling. Even complex and highly structured geometries can be produced in this way. This ensures a geometric concentricity of +/- 0.01. The clamping surfaces are usually substantially shorter than for axial forming.
Roll forming is also used on so-called combination machines. This is useful if axial forming will be carried out, followed by rolling, as the entire forming process can then be performed in one clamping position.
In contrast to axial tube forming, the design of the machine for roll forming is not dependent upon either the geometry or the force, but exclusively on the size of the tube being processed.
This process is not always suitable for axial expansion. The internal diameter must be large enough that it is possible to use a tool to roll from the inside to the outside. This is usually the case at diameters > 15 mm. In order to guarantee lasting deformation, the degree of deformation during the rolling process must also be outside of the elastic range of the material.
Standard sizes for transfluid® rotary endforming machines:
- for tube diameter 6–22 mm: SRM 622-E (300–1000 rpm)
- For tube diameter 15–50 mm: SRM 1550-E (100–500 rpm)
- For tube diameter 40–115 mm: SRM 40115-E (40–280 rpm)
Mode of operation of the rotary endforming machines
The workpiece is positioned against a stop and the clamping device closes. The roller head is then positioned axially via a servo motor and a ball screw. Its position is freely programmable. The roller head, controlled by a conical system, is then closed.
This position is also freely programmable. The closing speed and duration are programmed according to the geometry and the material. In the case of new products, only the tool needs replacing. All process parameters are programmed and can be easily called up. Manual settings are not necessary.
In addition to rolling from outside to inside and from inside to outside, these machines can also cut in both directions. Particularly subsequent cutting followed by shaping is often very economical in such cases. When it comes to forms with functional surfaces on the inside and outside, it is also possible to roll both sides at the same time.
In all these cases, the process is dependent on the particular tool. The processing time is dependent on the form and is mostly between 8 and 12 seconds. It is however also possible to produce complex geometries regardless of the tool which is used. If the machine is equipped with a CNC control system, it works in principle like a controlled lathe. However instead of the turning tool, it uses rollers. This makes it possible, for instance, to reduce small stainless steel tubes and simultaneously form them. Thus different geometries and tube sizes can be formed with a single tool.
Useful additional equipment
A suitable lubrication device contributes to achieving a good forming result and good surface properties, as well as to extending tool life.
For steel and stainless steel, it makes sense to use a microlubrication device. This makes it possible to apply a minimal quantity of lubricant, in a targeted manner, to the relevant points. If aluminium tubes are being rolled, pressure flushing with an emulsion is wise. Without recirculating lubrication, oxidated particles may appear, which has a negative impact on surface quality.
To clean the lubricating emulsion, the pressure flushing devices have two reversible filters. The benefits: If a filter has to be replaced, the second filter can be used, and production can continue without interruption. To filter out coarse particles of dirt, a belt filter can also be used. This is fitted upstream of the fine filters, thus increasing their service life.
Typical rotary forming processes:
- Sharp-angled forming
- Complex and heavily structured geometries
- Improving surface quality
- Cutting off excess length
Special machines for producing flaring
Our type-UMR rotary flaring machines have been developed to produce beading between 20° and 90°. This machine model produces a perfect sealing surface from a short clamping length of just 1xD. Even weld seams can be levelled out. Beading up to 90° can be produced in one step by a tumbling motion of the tool and tool changes can be performed in next to no time.
Standard sizes for transfluid® rotary flaring machines, type UMR:
- for tube diameter 6–28 mm: UMR 628 (603 rpm)
- for tube diameter 6–42 mm: UMR 642 (200 rpm)
- for tube diameter 6–65 mm: UMR 665 (95 rpm)
- for tube diameter 30–115 mm: UMR 30115 (70 rpm)
- for tube diameter 40–220 mm: UMR 40220 (60 rpm)
A clamping jaw is required for both the type-SRM bead rolling machine and the type-UMR rotary flaring machine, for each 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 forms to be produced are tool-dependent, corresponding forming rollers are required. It is not possible for any wear to occur to these rollers during this process. The cutting tools are composed of several parts to enable worn components to be replaced.
Particular features and limits of this technology:
- The degree of forming often presents a limit.
- Additional components cannot be applied.
- The material is cold hardened.
- The tube wall thickness is lower in the vicinity of the form.
- Reducing over a long distance is particularly critical for stainless steel tubes.
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!