A tube that leaves the saw or the bender is rarely finished. The end usually has to slip over another tube, step down into a fitting, flare for a seal or carry a bead for a hose clamp. Tube end forming is the process that does this by moving metal instead of removing it, and it is the reason a muffler pipe, an air-conditioning line or a hydraulic manifold can be one piece of tube rather than a tube with a welded adapter.
This article explains tube end forming from the start. It covers the four operations, how the metal behaves, how a hydraulic tube end forming machine is built, what dies and stations do, and where parts go wrong. It uses Telhoo’s SG range as the machine example, takes its figures from the published data sheets, and ends with what to send for a quote. How the tube is cut before forming is covered in pipe cutting methods compared.
What Tube End Forming Is and Why It Is Used
Tube end forming changes the shape of a tube end by pressing it against a die. Nothing is cut away, and nothing is added. The end is made larger, smaller, conical or ribbed by moving the existing metal, and the tube stays in one piece from end to end.
The reasons to form an end are practical. A formed end can join to another tube with a socket joint and a single weld or clamp, where a plain end needs a coupling. It can seal against a cone or a hose, or lock a hose on with a bead. It removes parts from the bill of materials, and every part removed is one less weld, one less leak path and one less thing to inspect. For high volume parts such as exhaust pipes, furniture frames and refrigeration lines, a forming cycle of a few seconds is far cheaper than machining or fitting an adapter.
People search for this under several names. A tube end forming machine is the general name. A tube expanding machine, a tube swaging machine and a tube flaring machine describe single operations, and in practice they are the same type of machine fitted with a different die. That point matters when buying, because one machine with several dies usually covers all of them.
The Four Basic Operations
Almost every formed end is one of four operations or a combination of them. Each moves the metal a different way and each has its own typical failure, which is why it helps to name the operation on the drawing and not just the finished shape.
| Operation | What happens to the end | Typical use | Main risk |
|---|---|---|---|
| Expanding | The end is enlarged so another tube of the same size slips inside | Socket joints on exhaust and HVAC lines | Wall thins and the end can split |
| Reducing, also called swaging or necking | The end is made smaller, straight or tapered | Stepping down into a fitting, tapered ends, nested tube | Wall thickens and the transition can wrinkle |
| Flaring | The end opens into a cone | Seals, fittings and hose connections | Cracks at the lip, uneven cone |
| Beading | A raised ring is rolled or pressed into the tube | Hose retention, clamps, locating stops | Collapse or an uneven ring |
Expanding enlarges the end so that one tube fits over another, and it is the operation behind most socket joints in exhaust and air-conditioning lines. Reducing does the opposite and is the process buyers often call swaging. Flaring turns the end into a cone, and beading adds a ring a short way back from the end. Beyond these four there are variations such as curling the edge, forming a rib, or shaping a square section down to a flat. They are made of the same moves with different dies.
How the Metal Moves
Metal is not created or destroyed in forming, and a change in diameter has to be paid for somewhere. When an end is reduced, the circumference gets shorter, and the material that was in that circumference has to go into wall thickness or length. When an end is expanded, the circumference gets longer, and the wall has to thin or the tube has to draw in from behind. This is the single idea that explains most forming behaviour.
A simple model shows the size of the effect. Take the cross section area of the tube wall as roughly the wall times the mean circumference, which is proportional to t × (D − t) for outside diameter D and wall t. If no metal moves along the tube, that product stays constant when the diameter changes. The relationship is only a bound, because real forming always moves some metal along the axis, but it shows the direction and scale.
| Illustrative case | Start | After forming | Result with no axial flow |
|---|---|---|---|
| Reduce the end | Φ40 × 2.0 mm | Φ34 mm outside | Wall rises to about 2.4 mm, roughly 20 percent thicker |
| Expand the end | Φ40 × 2.0 mm | Φ46 mm outside | Wall falls to about 1.7 mm, roughly 14 percent thinner |
These numbers are illustrations of the method, not Telhoo test results. A modest change in diameter moves the wall by a noticeable amount. A 15 percent expansion thins the wall by about 14 percent in this model, and a thin-wall tube has little margin to give. A reduction thickens the wall, and a thick wall resists the die, which raises the force needed and the risk of wrinkles at the start of the taper.
This is also why forming is done in steps. A large reduction in one stroke asks the metal to pile up faster than it can flow. Several smaller reductions, each on its own station or stroke, move the metal gradually, keep the wall inside what the tube can bear and keep the transition smooth. Telhoo’s SG40-2 page shows a thin-wall tube reduced in several steps down its length, with each step a separate stroke and the part never leaving the clamp.
How a Hydraulic Tube End Forming Machine Works
A hydraulic tube end forming machine has three jobs, which are to hold the tube, push the die and repeat. The Telhoo SG range does all three with hydraulics, and both the forming and the clamping are hydraulically controlled, which keeps the force steady from cycle to cycle.
- The tube is clamped. A firm clamp leaves only the end free, and the forming force goes into the tube end and not into sliding the tube backward.
- The ram advances. A hydraulic ram pushes the forming die onto the tube end with steady force along the tube axis.
- The end takes the die shape. The metal expands, reduces, flares or beads to match the die, and the stroke sets how far along the tube the form reaches.
- The next station repeats. Multi-station tooling moves the tube to another die so one end can receive several forms in order.
The machine does not decide the operation. The same frame that expands a socket on one job reduces a taper on the next, and the change is the die set. That is why a tube end forming machine is sold by capacity, meaning the largest tube, the stroke and the force, and why the quote depends on the drawing of the part more than on the name of the operation.
Dies, Stations and Sequences
The die is the tool that carries the shape, and in practice it is the part of the system that takes the wear and sets the quality. Telhoo’s standard tooling is Cr12 steel, and each die set is made to the customer’s drawing, and the forming route is agreed against the part before the machine is built.
A station is one position in the cycle with its own die. Telhoo’s SG machines come with two stations as standard, and the data sheets list three station, four station and double head forming as options. Two stations let a tube that needs reducing and then flaring come off finished in one handling. More stations allow longer sequences, such as reduce, bead, then flare, without moving the tube to another machine. Double head forming works on both ends of the tube in the cycle, which keeps the two ends in line with each other because the tube is not re-clamped.
Sequences matter because the order changes the result. Beading before reducing puts a ring where the die will later try to push it. Flaring before a reduction tends to split the lip. As a working rule, reduce first, form the shape that needs the most metal movement next, and finish with the feature that is most delicate. The order is set when the die routes are designed, and it is one of the things to confirm with the engineers on a new part.
Ram, Rotary and Segmented Forming in Brief
The SG range is a ram machine, in which a hydraulic ram pushes a shaped die straight onto the end. It is the most common route and suits the four operations above in repeatable high volume work. Two other families exist. Rotary forming spins the tube or the tool and shapes the end by progressive pressure, and it can reach shapes a straight push cannot. Segmented forming uses an expanding or contracting ring of fingers to reach into features that a one-piece die cannot enter or leave.
The choice depends on the part and not on preference. A straight socket or a taper is a ram job. A deep or complex feature may need rotary or segmented tooling. The comparison, with the questions to ask a supplier, is in the article on ram, rotary and segmented end forming.
The Telhoo SG Range for Tube End Forming
Telhoo’s tube end forming machines are the SG range, four models named for the largest tube they take. All four are two-station hydraulic machines running at 14 MPa, and all figures below come from the published data sheets.
| Model | Max fitting | Working stroke | Working speed | Weight | Dimensions |
|---|---|---|---|---|---|
| SG40-2 | Φ40 × 2.0 mm | 120 mm | 110 mm in 3 to 4 s | 800 kg | 190 × 50 × 130 cm |
| SG60-2 | Φ60 × 2.0 mm | 120 mm | 120 mm in 5 to 6 s | 1200 kg | 210 × 60 × 140 cm |
| SG80-2 | Φ80 × 2.0 mm | 200 mm | 130 mm in 5 to 6 s | 1800 kg | 260 × 75 × 145 cm |
| SG120-2 | Φ110 × 2.0 mm | 200 mm | 140 mm in 8 to 9 s | 2500 kg | 350 × 90 × 180 cm |
Two readings of the table help. First, the 40 and 60 models share the same 120 mm stroke and pressure, and the choice between them is a question of tube diameter alone. If the tube fits the SG40-2, there is no capability reason to move to the SG60-2, and the smaller machine cycles faster. The cycle is slower on larger sections because more metal moves and the flow must be controlled, since rushing a form wrinkles the transition and scraps the part.
Second, the 200 mm stroke of the SG80-2 and SG120-2 is what separates them from the smaller two. Stroke decides how far back from the tube end the formed section can sit. On exhaust assemblies, air-conditioning lines and hydraulic manifolds the feature is often well inside the tube and not right at the lip, and that is a stroke question and not a diameter question. A feature whose far edge sits 150 mm from the end lies beyond a 120 mm stroke and inside a 200 mm one, though the final check belongs to the engineers with your drawing.
Telhoo’s data sheets note that working speed varies with pipe size, wall thickness and end shape. The figures are a guide to the cycle, and the final tooling for a part is confirmed before ordering. The whole range is on the tube end forming machine page.
Materials and Sections
The SG data sheets list mild steel, stainless steel, copper and aluminium, in round, square and rectangular section. Whether a particular tube can take a particular form is a matter of the part, and Telhoo confirms the forming route against the customer’s drawing before the machine is built. What can be said in general is how the materials behave.
Mild steel forms readily and tolerates moderate expansion and reduction. Stainless steel work-hardens as it is formed. It asks for more force, benefits from smaller steps and has less margin for a deep draw. Copper and aluminium are soft and move easily, though thin-wall copper tube is easy to over-expand and aluminium can crack at a flared lip if the tube is hard-tempered. Temper matters as much as the alloy name, and an annealed tube forms very differently from a hard one.
Section matters too. Round tube is the easiest, because the circumference closes evenly all the way round. Square and rectangular tube is harder to form than round, because the corners work-harden first and the flat sides tend to bow. Telhoo’s SG40-2 page shows a square section tapered down to a flat for this reason, as an example of work that needs a planned route and not a single stroke. For tube that is also bent, the behaviour of the material is covered in tube bending materials.
Where Tube End Forming Is Used
Forming turns up wherever a tube has to connect, seal or carry a feature at its end. The industries on Telhoo’s machine pages show the range of work.
- Automotive exhaust and frames. Muffler and exhaust pipe need socket ends and tapers so sections slip together, and seat frames and chassis tube use reduced or flattened ends.
- HVAC and refrigeration. Air-conditioning and heat pump lines use expanded sockets and reduced ends, and the cleanliness of the tube matters because the lines carry refrigerant.
- Furniture and fitness equipment. Chair and table frames use reduced and shaped ends that slip into the next member.
- Hydraulic and fluid lines. Flared and beaded ends on lines and manifolds carry seals and hoses.
- Boiler and heat exchanger tube. Tube ends are expanded or reduced to fit headers and joints.
The same tube often goes through bending and forming in the same job, which is why the two processes are usually planned together. The use cases are described further in tube end forming applications.
Forming Compared with Other Ways to Shape a Tube End
Forming is not the only route to a shaped end, and it is not always the right one. The alternatives are machining the end, welding on an adapter or fitting, and using a separate fitting with a clamp or a press joint. The table sets out the trade.
| Route | Strength | Weakness | Fits best |
|---|---|---|---|
| End forming | One piece, no joint, a few seconds a cycle | Needs dies per shape, limited by wall and material | Repeated parts at volume |
| Machining | Exact geometry, any shape | Slow, wastes metal, needs thick wall | Thick-wall one-offs and precision ends |
| Welded adapter | Any size or fitting, no die | Extra part, extra weld, leak path | Low volume and odd sizes |
| Separate fitting | Fast to fit, field repair | Added cost per joint, bulk | Service and assembly on site |
The economics depend on volume. A die set is an upfront cost, and it pays back when the same shape is made again and again. For a few pieces, a welded adapter or a purchased fitting is often cheaper. For thousands of exhaust or furniture parts, forming wins on cycle time and on parts removed. Telhoo’s engineers can work through the break-even if you send the drawing and the quantity.
Why Formed Ends Go Wrong
Most defects in forming come from asking the metal to move faster or farther than it can, and each has a recognisable cause. Naming the defect points to the fix.
| Defect | Usual cause | What to change |
|---|---|---|
| Wrinkles at the start of a taper | Reduction too large in one stroke, wall too thick for the die angle | Split into steps, soften the die angle |
| Split or crack at the end | Expansion too large, hard temper, seam or burr at the edge | Anneal, add a step, deburr and orient the seam |
| Thin wall after expanding | Metal not drawn in from behind | Allow a longer straight, reduce the ratio |
| Oval or off-centre end | Loose clamp or worn die | Check clamp pressure and die condition |
| Cone with an uneven lip | Cut end not square, burr in the bore | Cut square, deburr and chamfer before forming |
The last row deserves attention because it is the cheapest to fix. A tube end that is not square, or that carries a burr, forms unevenly, since the die meets the metal at one point before the others. A square, clean cut is the best preparation for any forming, and the tube should be deburred first. The difference between deburring and chamfering is in beveling vs chamfering pipe and how deburring differs, and how a cut end is prepared is in pipe cutting and beveling machine choices.
Welded tube adds one more variable. The weld seam is a different structure from the parent tube, and a seam on the outside of a flare is where a crack is most likely to start. Setting the seam position and agreeing it with the tube supplier is a small step that avoids a recurring scrap cause.
Designing a Part for Forming
A few rules in the design keep forming simple and cheap. They are the same ones a supplier will ask about, so settling them early saves a revision.
- Keep the change in diameter modest. Where a large step is unavoidable, accept that it will need several stations and a longer cycle.
- Leave a straight length behind the feature. The clamp needs somewhere to hold, and the metal needs room to move from behind.
- Check the stroke. A feature set back from the end needs a machine whose stroke reaches it.
- Specify the tolerance that matters. The inside diameter of a socket, the outside of a spigot or the cone angle each need a figure on the drawing, with the others left open.
- State the material and temper. A change of temper can change the whole route.
The principles are the same as for bent parts, where the drawing sets what is achievable. Designing tube parts for bending sets out that thinking for the bending side, and it is worth reading together with this section when a part is both bent and formed.
Forming Before or After Bending
When a part is bent and formed, the order is a real decision. Forming first gives a straight tube that is easy to clamp and keeps the ends square, and the bend then follows. Bending first leaves the end where the bender put it, and forming a bent tube needs a fixture that holds the curved part against the die. The usual choice is to form the ends while the tube is straight, then bend, but a feature close to a bend can be damaged by bending, and an end that the bender must grip cannot be formed beforehand without protection.
The order also depends on length. A straight tube is easy to handle on the end former. A long bent assembly can foul the frame or the clamp. Many fabricators therefore form both ends of a straight blank and bend afterward, and they keep a straight tail long enough for the bender to hold. The right answer is specific to the part. State the sequence you intend when you enquire and the engineers will confirm or change it.
What to Send for a Tube End Forming Enquiry
- Tube outside diameter, wall and section, round, square or rectangular, for every size you form.
- Material and temper, including whether the tube is welded or drawn.
- The operation and the drawing of the finished end, with the socket, taper, flare or bead dimensions and how far back from the end the feature sits.
- Quantity and cycle target, so the number of stations and the die plan can be sized.
- The sequence, including whether bending comes before or after forming.
- Cleanliness and inspection needs, such as refrigerant-line cleanliness or a leak test.
Send those and the reply on tube end forming can say which SG model, how many stations and what to confirm on a sample. Tell us about the tube, and see the range on the tube end forming machine page. The wider plan for a line that cuts, bends and forms is on our tube bending solutions page.
