Machinery's Handbook, 31st Edition
1434 Spinning The ideal tangential force in forward tube spinning may be calculated by the following formula: (51) where F t = ideal tangential force (lb or N); σ f(m) = average flow stress of the material (lb/in 2 or MPa); T = thickness of the initial blank (inch or mm); T w = wall thickness of the spun part (inch or mm); and, f = feed (inch or mm). Because of friction and other influencing factors, the force exerted is about twice that of the ideal force. F t T T f f m w = σ − ^ ^ h h
Roller
Workpiece
f
T
T w
F
Mandrel
Fig. 26. Tube Spinning Rubber Pad and Hydroforming Processes
In the rubber pad forming process, one of the dies in a set (punch or die) is replaced with a flexible material such as rubber or polyurethane. Polyurethane is widely used because of its resistance to abrasion and its long fatigue life. Several processes utilize rubber pad forming techniques. Fig. 27 schematically illustrates the Verson-Wheelon, Marform, and hydroforming processes.
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b) Marform
c) Hydroforming
a) Verson-Wheelon
7. Flexible fluid cell 8. Trown rubber pad 9. Loading tray 10. Hydraulic inlet 11. Body of press 12. Rubber pad
13. Support rods 14. Piston 15. Pressure control valve 16. Seal 17. Press ram 18. Hydraulic servo valve
1. Form block 2. Blank 3. Workpiece 4. Hydraulic fluid 5. Container 6. Blankholder
Fig. 27. Rubber Pad Forming Processes: a) Verson-Wheelon; b) Marform; c) Hydroforming Guerin Process.— Fig. 28 shows the Guerin process, synonymous with the term “rubber pad forming,” in which a rigid forming block is placed on the lower bed of the press; on top of this block, the blank is positioned and a soft die of rubber or polyurethane (hardness 50 to 70 Shore) is forced over the rigid block and blank into its required shape. The thickness of the rubber pad, which is held in a sturdy cast-iron or steel container, is usually three times the height of the formed block, but it must be a minimum of 1.5 times thicker than the
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