How Do You Keep a Long Curved Printed Section From Warping?
A long curved printed section is kept straight with four controls: build orientation and supports, stress relief before machining, re-datum within 24 h, and 1.0 mm of machining allowance. The order matters more than any single setting.
What causes the movement?
The section cools unevenly. A 1.0 mm wall loses heat faster than the thicker flange it runs into, and the difference is stored as stress while the part is still on the plate.
Cutting the supports releases that stress, and the curve moves. The movement is not elastic: the metal has already yielded at temperature, so clamping it back does not remove it.
Long curved sections are worse than straight ones because the movement accumulates along the length. A 300 mm runner can show several tenths of a millimetre at the ends even when the middle stays put, and a flange at the end of the curve inherits the whole error.
The mechanism is covered in the tolerance risk guide; this page stays with the four controls that keep the section inside its allowance.
The number to watch is flatness across the flange, not straightness along the curve. A runner that bows 0.3 mm over 300 mm can still be machined flat if the flange has stock; a flange that twists has no stock to cut.
Which four steps control it?
Orientation, relief, re-datum and allowance — in that order:
Orient the curve so supports land off the sealing faces and the long axis builds with fewer section changes.
Relieve at 850 °C for 1.5 h after support removal, with furnace cooling.
Re-datum within 24 h of relief, before any cut.
Leave 1.0 mm of machining allowance and cut from the measured datum.
The steps are cheap in the plan and expensive in the rework. A part that skips relief and goes straight to the machine will move after the cut, and the second setup costs more than the furnace slot. The stress relief slot is booked with the build for that reason.
The allowance is split between the faces: 1.0 mm on the sealing face and 0.4 mm on the bolt holes, so the cut can clean both without running out on one side. The 24-hour window is a scheduling rule: the re-datum has to finish before the machining slot opens, so the measurement and the cut stay in one plan.
What do you do if it still moves?
Measure first. Compare the post-relief datum with the pre-relief datum; if the movement is inside the 1.0 mm allowance, machine it out.
If it exceeds the allowance, the part is re-relieved or re-designed, not shimmed. Shimming a curved flange only moves the leak path to a different place on the face. If the same geometry moves twice after relief, the orientation is the first thing to change, and the wall thickness the second.
Then record the movement against the orientation and the support plan. The next build uses the record, not the same settings — that is how the four controls get tuned for a given geometry.
When does this approach not apply?
It does not apply to sections thinner than 1.0 mm or longer than the build envelope. Those are split into segments with joints, and the joints become the datum, not the curve. The joints are machined and bolted, so the curve is built in pieces that each hold their own datum.
It does not apply when the material is a precipitation-hardening grade that changes dimension during ageing. The relief and ageing cycles have to be sequenced first, or the re-datum measures a shape that is still changing.
And it is not a guarantee. The four steps reduce movement; they do not make a thin curved section rigid. Stainless steel 3D printing keeps the section in one build where the geometry allows it, and the controls keep that build inside the allowance.
Send the runner geometry, the alloy and the machining allowance to Neway; we will check the orientation and the relief slot before quoting.
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