Widening (forming process)

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Widening is a manufacturing process of the main group forming and, according to DIN 8585, together with length and stretch forming (depths), is assigned to the group of tensile forming . A hollow workpiece is expanded by a force acting radially outward. It is used to manufacture housings, drums and body parts. In addition to round parts, polygonal hollow bodies can also be machined. In this case, however, weld seams harbor the risk of damaging the tool. According to DIN 8585, a distinction is made between

  1. Widening with tools that are of the greatest importance in industrial practice,
  2. the expansion with active media that is gaining in importance and the
  3. Expansion with active energy.

A variant of widening can be assigned to the manufacturing process of the main group joining ( joining by forming ).

Expansions with tools

In principle, mandrels can be used for widening , with either only the ends being widened, which is referred to as widening , or the entire workpiece is widened.

When using an expanding tool , it is also possible to only expand the middle, which is known as bulging . The individual segments of the tool are pressed outwards by a wedge or cone. You can either use a die for machining or you can shape it freely.

In addition to rigid tools, elastic tools made of rubber , elastomers or cork are suitable for expanding . The economically producible diameters are then limited to about 100 mm. The friction between the tool and the workpiece results in higher machining forces and a shortening of the workpieces in the axial direction (with stainless steel up to 12%). In return, the circumferential stretch can be increased significantly (up to 60%).

Widening with active media

Another variant is widening with active media such as oil or water. It is used to make fittings with multiple branches in any direction. There is a direct relationship between the pressure of the active medium and the minimally deformable radius of the workpiece. For the forming of a 6 mm thick, high-strength steel pipe with a 3 mm radius, a pressure of around 1200 bar is required, whereas 120 bar is sufficient for a 10 mm radius.

Expansion with active energy

When expanding with active energy , the force used for reshaping is not applied to the workpiece from the outside, but is generated inside it by current-carrying coils. The effect is used that two current-carrying conductors can repel each other. A current pulse in the coil creates a reciprocal vortex field in the workpiece, which can be used for reshaping if it is sufficiently strong. The required energy is stored in capacitors. The coils must be wound according to the shape of the workpiece.

literature

  • Fritz, Schulze: Manufacturing technology. 11th edition, p. 482.
  • Hoffmann, Neugebauer, track: Handbook Forming. 2012, pp. 557-560.