Metal spinning
Conventional spinning, shear forming and flow forming; tooling and material state, wall-thickness control, defects and finished-part acceptance.
Tags: processes, shaping, sheet-metal, spinning
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For ideal conical shear forming of a 3.00 mm blank, a 30° half-angle from the axis gives 1.500 mm wall by the sine relation. Using the 60° included angle gives 2.598 mm, overstating the ideal wall by 1.098 mm. Specify the angle convention and measure local wall thickness on the formed part.
LEIFELD's conventional spinning arrangement clamps and rotates the blank while a roller brings it onto the tool contour. Identify the starting form and whether the route intentionally reduces wall thickness. LEIFELD: spinning process
Separate three related routes
| Route | Main process distinction | Requirement to retain |
|---|---|---|
| Conventional spinning | Successive roller passes progressively change the blank's shape. | Do not assume the finished local thickness equals the incoming gauge everywhere. |
| Shear forming | Material is projected onto a tool contour with deliberate thickness change tied to the forming geometry. | Specify the angle convention and required remaining wall. |
| Flow forming | Rollers reduce a tubular or cup-like preform's wall while material extends axially. | Define preform, final wall distribution and forward/reverse arrangement. |
LEIFELD describes shear forming separately from gradual spinning and gives the ideal conical wall relationship s₁ = s₀ sin α. Its flow-forming description explicitly identifies wall reduction and axial lengthening and distinguishes forward and backward routes. Neither description supplies a universal reduction limit for every alloy or machine. LEIFELD: shear forming, LEIFELD: flow forming
Li and Long's original paper, published March 21, 2026, likewise distinguishes conventional multi-pass spinning from thickness-reducing shear spinning. Its process classification is not a guarantee of perfectly constant local wall in a manufactured conventional-spun part. The drawing must define the actual minimum wall and how it is measured. Original research: spinning and wrinkling
Geometry, tooling and extraction
Provide the full part model, starting material and intended final condition. Identify inside and outside surfaces, the axis and locating features, trimmed edges, flanges, steps and any undercuts. Check how the part is clamped and removed before accepting a contour merely because it can be drawn in CAD.
LEIFELD describes combining spinning with contour profiling, edge bordering and separation of marginal or base material in the same setup. These are available operations to discuss, not proof that every rim, flange or opening is produced directly without trimming or a secondary operation. Agree the sequence and the resulting datum relationships. LEIFELD: additional operations
Distinguish mandrel-defined geometry from surfaces governed by material flow and thickness. A qualified inside contour does not by itself establish the outside dimension. Define the surfaces that must remain concentric after unclamping and any later machining, trimming or thermal operation. Tool marks and contact witnesses should have explicit acceptance regions.
Starting material and process development
Specify alloy, temper or heat-treatment condition, incoming thickness range, surface condition and blank/preform geometry. Review whether cold work, heating or intermediate treatment changes the delivered state. The availability of a machine for one alloy and gauge is not evidence that another material has the same forming limit or final properties.
For a trial, retain the tool and roller configuration, path sequence, feed convention, rotation, lubrication and any heating/annealing route. Compare thickness, profile and surface results at relevant positions. Feed per minute and feed per revolution are different quantities, and neither can be transferred between machines without the rest of the setup.
The 2026 Li–Long study investigates wrinkling with experiments and finite-element simulation of shear spinning and proposes a test involving in-plane compression and out-of-plane bending. It relates wrinkle initiation to cyclic strain accumulation in the unsupported flange under its investigated conditions. This supports treating blank support and roller loading/path as interacting variables; it does not establish a universal feed limit or an approved fix for every conventional-spinning wrinkle. Same study: experimental scope
Inspect wrinkles, splits, local thinning, surface damage and dimensional change as different observations. Do not assume a wrinkle will disappear in a later pass or that additional roller force will resolve an underformed feature. Agree the permitted condition after forming and after the final ordered operations.
Bounded equipment examples
LEIFELD's ST 560 H flow-forming family is described for rotationally symmetric hollow bodies with constant or varying wall. Its published forward and reverse length figures are different, and the reverse figures carry a condition involving 50% wall reduction and lateral tailstock displacement. Retain that condition instead of advertising the larger length as an unrestricted machine envelope. The quoted part still needs a compatible preform, material, tooling and route. LEIFELD: ST 560 H specifications
A different implementation, NIHON SPINDLE SR150-T4, describes rollers traveling around a tube that does not rotate and operation without an internal die for the identified exhaust/catalyst applications. This demonstrates that a rotating workpiece and full internal mandrel are not universal features of every industrial spinning system. It does not qualify an arbitrary unsupported tube or sealed assembly for that process. Producer: SR150-T4
Original idealized thickness example
Apply the conical shear-forming relationship above to an invented 3.00 mm blank. Here α is the half-angle between the cone wall and its rotation axis, and s₁ is wall thickness normal to the wall:
| Assumed half-angle | Ideal calculation | Ideal wall |
|---|---|---|
| 30° | 3.00 × sin 30° | 1.500 mm |
| 45° | 3.00 × sin 45° | 2.121 mm |
| 60° | 3.00 × sin 60° | 2.598 mm |
For the 30° case, incorrectly using the 60° included cone angle would predict 2.598 mm, overstating this ideal wall by 1.098 mm. State the angle convention rather than simply writing “cone angle.”
The formula is a simplified geometry relationship, not a guaranteed local thickness or a process window. If a hypothetical measured local wall were 10% below the 1.500 mm ideal value, it would be 1.350 mm and fail an assumed 1.400 mm minimum. The model cannot replace measurement, material forming limits or trial qualification. Do not apply it unchanged to conventional spinning or to a different flow-forming geometry.
Finished-part acceptance
Specify the inspection stage after forming, release, trimming, thermal treatment and finishing as applicable. Separate profile/diameter, roundness, runout relative to datums, local thickness, edge condition and surface texture. A part that fits a contour template can still have insufficient wall or an unacceptable datum relationship.
For service components, agree any required material-condition, pressure/leak, fatigue or other functional evidence. Work hardening or absence of a welded seam does not establish every required property. A proposed alternate route must meet the actual drawing, material and application requirements.
A useful manufacturing handoff has four groups:
- Starting state: material specification/edition, condition, lot, gauge range and blank/preform definition.
- Geometry and route: full model/drawing, process variant, tool access/extraction, clamping and secondary operations.
- Final requirements: datums, profile, minimum wall, edge and surface limits, delivered material condition.
- Acceptance: measurement locations/methods and stage, relevant material/functional tests, sampling and traceability.
The producer pages have no separately verified technical issue date here. Their DIN references identify their process descriptions and are not used to claim a current contractual edition. The paper's publication date is verified. The thickness calculation and handoff structure are original applications of the stated relationship.