Metal Extrusions and Roll Forming. Chapters 3.1 and 3.11. http://www.world-aluminium.org/About+Aluminium/Production/Processing/Extrusion. http://www.aec.org/techinfo/expro.html. http://www.aec.org/techinfo/expro.html. Videos. Pacific Bearing introduction to Extrusion:.
Chapters 3.1 and 3.11
Pacific Bearing introduction to Extrusion:
Spanish Extrusion Company:
It is also possible to produce hollow sections using extrusion. In this case, the die contains a short piece (or mandrel) in the shape of the hole. This mandrel is attached to the die by one or more ‘bridges’. As the extruded material encounters the bridges it is forced to separate, but it flows around the bridges and joins up again, much the same as water flowing around the piers of a bridge. Figure 30 shows such a ‘bridge die’. This works successfully even for processing of solid metals.
Steel Forming Systems overview of their Roll Forming process
SME description of bow twist, etc
is another tolerance consideration. Factors that establish material straightness include camber, curve or sweep, bow, and twist. The terms camber, curve, and bow are many times interchanged when describing material straightness, but they actually have slightly different meanings. A formed part's horizontal and vertical planes are determined by their position in the roll forming process.
Material straightness terms include:
Camber Camber is the variation of a side edge from a straight line. Extreme camber contributes to curve, bow, and/or twist in the finished part.
Curve or SweepCurve or sweep is the variation from a straight line in the horizontal plane measured after the part has been roll formed. Causes of curve or sweep included incorrect horizontal roll alignment and uneven forming pressure.
Bow Bow is the variation from a straight line in the vertical plane. It can be either cross bow or longitudinal bow. Bow is often caused by the existence of irregular vertical spaces on symmetrical sections and from uneven forming areas on unsymmetrical sections. [could use an illustration here!]
Twist A formed part is said to have twist when it resembles a corkscrew effect. This is often caused by excessive forming pressure in the final formed part. For most roll forming operations, twist is typically less than 5° in 10 feet of formed parts.