Premise and definition of process
In manipulation of rigid pipes for fluids, like water-cooling circuits for automotive engines, especially in the connections between metal tubes and rubber-manifolds, end-forming operations producing external beads are being used more and more.
These assemblies, commonly called rubber-manifold holders, are actually standardized by most cars manufacturers, therefore we may talk about hose-connectors as per FIAT-, or VW-norms, etc.
Connections made this way represent a really useful and practical way to join a rubber-manifold and a rigid-pipe in the engine, both for the first assembly of the vehicle, and in case will be later necessary to disconnect the parts for checking, or replacing one of the components.
Generally talking, an elastic retainer (expansion ring, or screw-driven ring) is used to ensure a safe connection of the rigid pipe, which is
introduced inside the hose for a short length (let's say from 20 to 50 mm. in the average).
'Though a certain degree of interference between the ID of the rubber manifold and the OD of the metal tube exists, the elastic retainer has the important function to prevent the assembly from loosening, especially in presence of mechanical forces (internal pressure, vibrations from the vehicle, etc.), and thermo-chemical shocks (elongations due to high
temperatures, aggression from liquids, etc.), which are typical in
the environment of a vehicle.
In order to help the function of the elastic retainer and the a.m.
interference of diameters between hose and rigid pipe, most part of
rubber-manifold holders have one-, or more beads on the outer part of tube end.
These beads - until a few years ago - used to be produced on a piece from metal-casting, or machining. In this last case, manufacturing
process started from a solid piece, or from a heavy-wall tube, then the complete part could be welded on the tubular end.
These systems are still used nowadays in a few cases (solution is admitted by some norms), anyhow modern industry trend is moving more and more towards the manufacture of rubber-manifold holders directly from tube.
A solution that comes in the times of alternative materials, yet with quite evident advantages in terms of process-technology. Some advantages have been resumed in the attached chart.

"Conventional" tube beading systems
To be honest, cold forming technology. of tubular ends for rubber-manifold holders is quite known.
In order to explain what are the peculiar advantages of rotary beading of tubes - topic of this article - we'd better mention first which are some of the existing (most commonly used) methods to produce a.m. beads, at least until a short time ago.
In addition to that, we think it could be helpful to make a more
comprehensive picture of the situation, by shortly describing a commonly used manufacturing routine to produce the rubber-manifold holders. So, we are going to explore for a while some of the conventional
technologies generally associated with the manipulation of a.m. tubes, whenever the system of welding a separate metal piece with beads is not taken in consideration.
Generally talking, water-cooling pipes inside car engines may vary in size from a minimum diameter of 16-18 mm., to a maximum of 55-65 mm. in the average.
Raw materials range from mild steels (ordinary welded tubes), to stainless steels, to aluminium alloys, in some cases. Tube blanks may present some bends, of course, and they may be as short as a few hundreds of millimetres, up to one meter, or more.
Sometimes, layout of bent tubes is quite linear, sometimes is more complex, maybe with very close return-corners, extremely short straight- parts between the bends, minimum straight ends, depending on the dimensions of engines and on the position of internal components.

A typical manufacturing cycle
Starting from tube bars of commercially available length, the first cut of blanks is generally made using automatic sawing machines. Length of these blanks should take into account the needs of the bending process, therefore - after this operation - we'll have some excess of material in comparison with the length of the finished part.
Together with the first tube cutting, a de-burring and / or cleaning operation of the ends is generally required, especially if this job is performed by tube-cutting service-shops, but also in case is the manufacturer of rubber-manifold holders to make the first cut.
Until this point - generally speaking - there are no major problems in the process.
Mandrel bending of tube blanks is generally the following operation. This procedure provides the problem that cross sections close to the bends become quite oval, unfortunately also in the areas where we're supposed to produce the beads for the rubber-manifold holders.
Beside that - due to the peculiar rotary-draw bending system - at least one of the two ends of the bent tube will result not perpendicular to the tube axis. The slice angle (or mitre cut) will be as much visible as the last bend is closer to the tube-tail, of course.
Another "physical" effect of mandrel bending (not really welcome) is the difference of wall-thickness from the extrados- and the intrados- of the bends; difference that will be as much higher as tighter is the bending radius, as everybody may expect from conventional mandrel benders.
We will see later how this phenomena may influence the results of the rubber-manifold holders.
At this point of the manufacturing routine, many tube manipulation specialists provide a trimming cut of one, or both ends of blanks. This operation is generally considered as critical, because it's quite necessary, yet slow; noisy and "dirty"; apparently simple, yet expensive; requiring attention as regards the safety environment and for the kind of special equipment that are needed.
In the conventional way, these trim-cuts are made through a manually operated-, or half automatic-sawing machine, where the operator is demanded to feed-through and un-feed the materials.
These sawing machines are sometimes equipped with special clamping jaws to grant a safe tube grip, but also oftentimes one can find problems related to the light wall-thickness of blanks, to the presence of burrs and metal chips, etc.; problems well known by all tube manipulation specialists.
Next operation is generally a manual tube de-burring, to be made both on the OD and on the ID, which could be made through different systems (see other article in this issue of TUBOLOGY, ndr).
De-burring of the ends is necessary whatever is the bead we're going to make on tube ends, and also if there is no need of end-forming at all, a smooth edge-finish is always considered as "critical" by drawing
specifications ("tubes must be free from burrs, chips and cutting edges").
Reason of this "no-burrs" recommendation is to prevent the rubber manifold from being damaged during assembly, and to avoid any possible crack / leaking during normal use on board.

Some advantages in the production of rubber-manifold holders made directly out of tubes, in comparison with the solution where a bushing is made from casting, or turning, then welded:
1 Improved technical features
- Coupling is sturdier (made from a single-piece), and concentricity is generally better;
- Roughness surfaces are smoother, therefore introduction of rubber manifold is easier;
- Neither burrs, nor sharp edges (who may damage the rubber manifold) are generated;
- With same wall, assembly is more resistant to deflection, due to cold-hardening of tube;
- Optimised weight of the assembly, and more flexible design (thanks to machine adjustments);
2 No need of welding
- Coupling is basically safer, as it's all made out from a single piece of tube, without interruptions;
- Savings on machinery, energy and skilled operators (as welding process is eliminated);
- Material is more consistent, and more resistant to thermal shocks, all the length through;
- Internal logistic problems are reduced (the welding department is generally separated);
- Process is faster: manufacturing times in the workshop are improved very much.
3 Process is less expensive
- No need of pre-assembling (prior of welding): fixtures and related procedures are eliminated;
- No need to handle the "bushing": neither from external suppliers, nor inside the company;
- Generally, there's no need to make pressure tests of the assembly (to prove the welding);
- A single operator can manage the process of end-forming and some other operations, too;
- Tools aren't dedicated: consumable materials do not influence the cost of the assembly.

"Conventional ways" of making beads on rubber-manifold holders
Now, depending on the "conventional" system used to produce the beads, our blank tube may follow two different directions. If beads are made through a bordering machine with two opposite rollers (one inside, the other outside the tube), this equipment doesn't allow to size the tube ends, which may result very oval in the cross-section due to the previous bending and trimming processes, as we said.
In this case, it is generally necessary to size first the tube ends, i.e.: to re-create a cylindrical cross-section (through different equipment) before making the beads themselves.
But this operation needs some time and some room, a specific machine, a trained operator (it's a working step more), and it generally provides no guarantee of a perfect / consistent result, because the different tube ends may result un-evenly oval depending on previous operations, and because of different parameters as the tube quality, the position of the welding-seam in comparison with the bending plane, etc.
Therefore a so-called "conventional" sizing-operation does not re-create always and exactly the same cylindrical cross-section of tubes:
oftentimes it just reduces the ovality of the ends.
Beside what reported above, the bordering machine with two rollers - 'though it's simple in the working-principle and easy to be operated - may provide some problems in the specific application.
First, we have to say the beads may result not perpendicular to the tube axis, due to the absence of whatever guide and to the difference in the resistance of material around the 360° (different wall-thickness and
different cold-hardening from intrados and extrados of the bends).
In addition to that, positioning of tube blanks into the machine is made by the operator (who can loose the contact with the length gauge),
therefore repeatability in the position of the beads with the tube end is not guaranteed by the process / equipment.
Again, bordering machines with two rollers make the tubes spinning during the cycle, that could be dangerous for the operator / for the
collision with the machine, in comparison with a machine operating with stationary tube (see following).
The next "conventional" system to make beads on tubes we're taking into consideration is the one of axial (or ram) forming, typical of horizontal presses with automatic index of dies.
By using this system, we may think to avoid the sizing operation mentioned after de-burring of tube ends, as it may be included in the process itself by using the first punches, just before beading.
However, even the system of making the rubber-manifold holder through ram-style end-forming machines, is progressively loosing some appeal in modern tube manipulation cycles, due to the following main reasons:
1. A formed-groove set of clamping-jaws (which are dedicated, therefore expensive) is necessary for each part number and - sometimes - for each end of a given tube, especially when having very short straight ends. This problem makes impossible to complete a typical rubber-manifold holder with beads on both ends in sequence on the same routine, as one have to change the clamping dies first.
2.. Profile of beads is not the best, as typical design of tooling by construction (formed clamps and punches) and spring-back of tubes do not allow the full control of the form. In addition to that, transition radii required by the norms of rubber-manifold holders are subject to raw materials variations, like un-even wall thickness, un-consistence and different position of the welding seam, etc.
3. Some scratches, or cold-welding spots, may happen on the bead sealing surfaces, caused by friction phenomena, presence of sharp edges, metal chips, lack of lubricant, premature wearing of punches, etc. Then, it's obvious those scratches may negatively influence the ideal shape, the roughness surface, and the perfect functionality of the whole assembly.
4. Even if some segmented-type dies (or split punches) have been recently developed to fit ram-style tube end-forming machines, in order to reduce a.m. problems and simultaneously increase productivity, still there are some problems in the roundness and concentricity of cross sections.
In fact, these expansion-type tools, even in most sophisticated applications, are completely free from the so-called "margarita effect"…

Innovation in production of rubber-manifold holders
Riding the wave of an always more extended use of rubber-manifold holders in the automotive market, yet with the knowledge of the "real" problems associated with a.m. "conventional" forming systems, a different technology and an innovative machine have been rapidly
developed and optimised.
This technology - that is quickly finding a large approval in different shops manipulating rigid tubes for such applications - basically consists in making the beads from inside-out , by using a set of jaws to clamp the tube, and a planetary-driven mandrel, which can perform at the same time a few different operations:
-Sizing of tube end in the area of the bead(s), at least for the length engaged by the manifold.
-Trim cutting of the excess of tube (sliced end), with no need of de-burring afterwards.
-Forming of one-, two-, or more-beads on rigid tube-end, depending on part specifications.

Some advantages of rotary tube end-forming and simultaneous trimming
1.Bent tube is firmly clamped in the machine jaws, therefore it doesn't spin during inside rolling.
This system makes the process less dangerous and more accurate than other beading systems, because the profile of the connector is fully
controlled between the punch and the clamps.
2. As - during the rolling operation - tubes are not subject to any axial force (in other words, there's no pressure to push the part out from the clamps), jaws are - generally talking - very short yet with straight-groove: this fact reduces very much the cost of the tools.
3. Just a single set of straight clamps, moreover, allows to operate both ends of the tube blank in a continuous routine (if both ends must be formed the same shape), without having to stock the parts meanwhile, and with no need to change and set-up the tooling first.
4. As we said, is not generally necessary to make any sizing of the tube end (through a separate equipment) before proceeding with the
roll-forming, because is the rolling pilot itself which re-creates a cylindrical cross-section (or a slightly expanded end), during the cycle.
5. Trimming of tube end results quiet, clean, fast, without chip-removal. Beside that, is generally not necessary to make any de-burring of tubes (neither inside, nor outside) after trimming.
Tube scrap resulting from trimming is automatically kicked-out during the process.
6. The whole operation is fast (average time ranging from 10 to 14 seconds), result is proved by the process itself, accuracy is constant, operator engagement is minimum, foot-print of the machine is compact (it can be introduced into a working cell, while operation time could be hidden by another operation, for instance: bending).
7. Operators can't influence the output consistency in a bad way, opposite to what is going to happen when considering - for instance - all manually attended operations of trimming by saw, hand de-burring, segmented tool sizing, making beads in the "conventional" way, etc.
8. Position of beads is not influenced by possible variations of the blanks-length, nor by accuracy of mandrel bending, since it's always related to the last bend, guaranteed by a mechanical gauge (or simple jig) external to the clamp, with quick release, easy to be manufactured and replaced.
9. Tools are un-expensive, long lasting, and may be considered to produce different part numbers.
Rolling pilots and cutting knives can be even used to cover some similar tube diameters (thanks to the adjustments of the machine), provided that beads have the same profile and distance.
10. Bent tubes having also complex geometries (with return corners, etc.) can be conveniently roll-formed and trimmed by these rotary-forming machines thanks to an accurate study of overall dimensions in the area of the head and of the clamping device, which minimize collisions risks.
11. On request, these machines can be used just for rolling (without
trimming), or just to make a fine re-cut of short pieces of tube. They have a broad range of applications, both in the diameters (20-65 mm.) and for the distances to the tube end.
12. All parameters which may influence the job can be programmed through a friendly digital operator's interface connected to the PLC. They can be also saved and protected through a password to speed-up the setting of the machine and make it suitable from small runs, to medium-large batches of production.
13. Tube forming and flow of material in the beads (also at max.
expansion levels) is more gradual than other systems, as tube-wall is stretched more progressively. A high-revolution speed rolling-action of the internal pilot allows a more comfortable profiling, because the number of passages on a given point is much higher than in any two-rolls bordering-machine.
14. Through rotary-type tube end-forming machine, risks of having cricks is reduced even in the welded area, even in case of very small radii, and even when quality of tubes is poor.
In comparison with axial-type tube end-forming machines, surfaces are generally better.
15. In rotary forming of beads, neither heavy lubricants (which are instead necessary in axial-forming machines), nor water-oil emulsions
(typical of metal saws) are being used.
Tooling and parts generally get micro-lubrication through a suitable device, therefore is not necessary to wash the tubes after end-forming.
16. Inside-to-outside rolling head to make external beads can be easily replaced with a different rolling head to work from outside-to-inside, so that the machine can be considered even more flexible in use (this argument will be better discussed in a future issue).

Final remarks
The process of planetary beading and trimming of tubes from inside to outside we introduced above can literally "make the difference" in costs reduction, both for the number of operations, than for the number of equipment, and for the number of workers involved in production and control, in comparison with more conventional systems associated with manufacturing of rubber-manifold holders.
This innovation technology and related equipment should be carefully considered with the intention to reduce the amount of defective-, and scrap-parts in those companies which are at the limit of profitability when actually manufacturing similar tubes, and/or those companies which are looking to improve the quality of tubes using different machinery and tooling.