By the time a part reaches the welding bench, most of its accuracy has already been decided. A flattened bend, a cone that is slightly out of round or a flange formed without enough allowance will fight the welder for the whole job. Shaping steps are not preparation for the real work; they are where the real work is set.
Two processes carry most of it in sheet and tube fabrication. The press brake produces straight bends in sheet and plate. Rolls produce curvature, including the cones and transitions that join one diameter to another.
A press brake drives a punch into a die, trapping the sheet between them and forcing it to bend along a line. The operator controls where the bend line sits, how far the material goes in relative to the die opening, and how deep the punch travels. Those three things decide the angle that comes out.
Air bending, where the punch does not bottom out in the die, is the common approach because one tool set can produce a range of angles. The angle actually achieved depends on the material, its thickness and how much it springs back, which is why a test piece is usually bent before a run starts.
Back gauging matters as much as the bend itself. If the part has to match a drawing feature, the distance from the bend line to a reference edge is what the operator sets, and that reference has to be the same one the drawing used. A good bend in the wrong place is still a bad part.
Metal does not stay where it is pushed. Once the punch retracts, the material relaxes and the bend opens slightly. This spring back is predictable for a given material and thickness, but it is not the same for titanium, stainless and aluminium, and it changes with the temper of the stock.
The allowance for that relaxation is built into the setup rather than corrected after the fact. A part formed to a nominal angle and then forced straight during welding is a part with locked-in stress, and it will move again as soon as the assembly sees heat.
Bend allowance handles the same problem in the flat pattern. Because the material stretches on the outside of a bend and compresses on the inside, the flat blank has to be longer than the sum of the finished legs. Cut the blank at the finished length and the part comes out short.
Rolls form curvature by passing the sheet between three rolls and progressively tightening the middle one. A cylindrical section is the simple case. A cone or a transition is harder, because the two edges of the blank are different lengths, and the geometry has to be developed as a flat pattern before anything is rolled.
The developed pattern is the whole job. If the flat blank is wrong, no amount of rolling skill recovers it. Where a part has to match an existing diameter at one end and a larger one at the other, both diameters and the length between them have to be confirmed before the blank is cut.
After rolling, the seam edges have to meet evenly along their whole length. A cone that closes at one end and gaps at the other cannot be welded to a consistent standard, so the fit is checked dry before any tack goes on.
Formed edges rarely meet perfectly. Press brake bends are exact on the line, but the material has thickness, so the inside and outside of a corner behave differently. The usual fixes are a relief notch, a set-down, or a small amount of hand adjustment at the joint.
Where two formed sections join, the target is an even gap and matching edges. An uneven gap is what produces a weld that looks different along its length, and on thin material it is also what draws the joint out of alignment as the metal shrinks.
Thin sheet and thin-wall tube amplify every forming error. Spring back is proportionally larger, the bend radius is limited by the material's tendency to crack or thin out, and a small amount of distortion in the sheet becomes a visible wave after welding.
On titanium and stainless, the forming itself is less forgiving than on mild steel. Both work harden, so a section that is rolled or bent twice behaves differently from one formed in a single pass, and that difference shows up later as uneven spring back across the part.
Once the shaped sections fit, the welder's job is to lock that fit without disturbing it. The tacks go on in an order that balances the pull rather than in the order that is convenient, and the full welds follow the same logic. Forming that left the part stress-free makes that much easier; forming that left it fighting itself makes every run of weld a correction.
This is also where the shaping decision pays off or not. A part that was formed once, correctly, is a part that can be welded quickly and repeatably. A part that was formed in several attempts carries the history of those attempts into the joint.
You can see formed work in our exhaust tube range, and the same blanks feed into finished systems. Our fabricated metal components and TIG welded parts show what the shaping steps ultimately produce, the custom work page explains how a forming job is specified from a drawing or a sample, and our material pages cover how titanium, stainless and aluminium each respond to a bend.
Forming problems are cheapest to solve on paper. These are the questions that keep them there.
Shaping and welding are two halves of the same job, and the fit between them is what you receive. The work that comes off these forming steps appears in our finished titanium systems and in the wider fabricated range, and the custom work page covers how each job is set up from the first drawing.
