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| Flow
forming |
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| Flow forming
is a process for forming rotationally symmetrical hollow parts. A pre-formed
blank is clamped between mandrel and tailstock and rotated. A characteristic
of the process is the fact that the metal is formed by localised compression
resulting from the radial pressure of the rollers. The metal is made to
flow and, in a single roller pass, assumes the contour of the mandrel
on the inside. Process accuracy is equivalent to that of close-tolerance machining. Uninterrupted grain flow and an increase in mechanical strength as a function of the reduction act in favour of flow forming. All malleable metals and their alloys up to a tensile strength of 2200N/mm² and including stainless steels and aluminium alloys can be formed. A distinction is made between shear and cylindrical flow forming. a) Cylindrical flow forming enables external profiles to be generated - steps, transition radii and tapered intersections, not normally achievable by other methods such as deep drawing and deep drawing and ironing. Three work rollers, offset at 120° are in contact with the metal |
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The principle of flow forming (work zone and work loads) |  |
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| In forward flow forming, the direction of roller feed and material flow are the same. Short, closed-base parts can be cost-effectively produced by flow forming combined with a prior cupping operation, all in the same pass. Important applications include the production of internally splined hollow forms as well as car and commercial vehicle wheels. | |||
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| Internally splined component produced from a disc blank by forward flow forming. | |
Close-up of a flow former showing the three forming rollers set at 120° and a formed wheel. | |
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| In reverse flow forming, axial material flow in the same direction as roller traverse is prevented by a stop, causing the metal to flow beneath the rollers in the opposite direction. This enables very long cylindrical parts to be produced. | |||
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Pre-form (left) and finished part formed by reverse flow forming. | |
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| b)
Shear flow forming A flat blank is formed onto an angular the mandrel by a single work roller. During the forming process, the metal in the work zone is axially displaced - the diameter of the blank equals the diameter of the finished part. In this way, conical, concave or convex parts can be produced. |
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Shear formed parts | |
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| The simplest example of shear forming is where a flat disc blank is formed onto a conical mandrel. The finished wall thickness, S1, is a direct function of the inclined angle (angle of shear α) and the blank thickness, S0. | |||
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The principle of shear forming | |
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| For precision parts, two opposed work rollers are used. | |||
