CLEARANCES AND TOLERANCES 4g handbook vukotaboljanovicsheetmetalformingprocesses

164 Deep Drawing Dies

11.9 IRONING DIES

Frequently, the final operation in a series of draws consists in ironing the shell walls to reduce the thick- ness of the material and ensure a smooth uniform surface throughout. This work is done by making the clearance between the punch and the die ring slightly less than the thickness of the workpiece wall, so that the material is both thinned and elongated. Fig. 1 1.18 shows an ironing die. The ironing die consists of the punch holder 9 and the die shoe without a guide system. The punch is attached to the punch holder by the ring whose inner side has a conic profile and whose out- side is threaded. The punch is made of two parts: the technical part of the punch 1 is made of tool steel, and the extension part is made of carbon steel. The upper set of the die is fixed to the ram 1 2, by a clamp 15. In the die shoe 10 are fixed the die ring the workpiece centering ring and the seg- mental stripper with the helical spring 6. The lower set of the die is attached to the bed of the press by the clamp 1 6. The segmental stripper consists of four segments connected by the ring of the helical spring located in slots in the segments. When the ram moves down, the segments are moved apart by the radial pressure on the workpiece, and when the ram is moved up, the sharp edges of the stripper strip the workpiece from the punch. The most efficient drawing process occurs when the first drawing achieves a reduction by diameter; reduction of the wall thickness of the workpiece occurs after that. Deformation by diameter done separately from deformation by wall-thickness reduction is advisable not only because of the favorable drawing ratio but because for wall-thickness reduction operations, ironing dies are simple and may be used on single-action \ I J 1 -punch 2-die ring 7-punch extension 8-ring 13-bed of press 3-workpiece 4-workpiece centering ring 14-holder plate 5-clamp 10-die shoe 5-segmental stripper 11-backing plate 6-helical spring 16-clamp Fig. 1.18 An ironing die Deep Drawing Dies 165 presses. However, reduction by both diameter and wall thickness of the workpiece may be combined in one multi-stage drawing die. Fig. 1 1.19 shows one design for a multi-stage ironing die. In the multi-stage ironing die, a precut blank is inserted into a nest and held there by the pneumatic pressure pad 10. The blank is pushed through the die ring 2 for reduction by diameter, and then it is drawn. I Ironing operations are then done by the punch 1 and three reduction draw rings 3, 4, and 5. The distance rings and 6b assure the correct distances between the draw rings. If the workpiece, in process of drawing, leaves one draw ring before beginning to enter into the next draw ring, the machinery may perform another stroke that will often cause a crack or cracks in the workpiece. 1 -punch 2-die ring for deformation by diameter 3-die ring for 1 reduction 4-die ring for 2nd reduction 5-die ring for 3rd reduction 6, ring 7-segmental stripper spring 9-die shoe 1 O-pressure pad 1 1-air pressure cilinder 12-screw 13-workpiece Fig. 1.19 Multi-stage ironing die I VARIOUS FORMING DIES

12.1 NOSING DIES

Deep drawn shells or tubes are used as initial working material in nosing type dies. Chapter 7 describes three types of nosing processes. Fig. 12.1 shows a schematic arrangement of a nosing die of Type I. Nosing type dies are designed in two simple variations: In the first, shown in Fig. the top of the workpiece is reduced from a larger to a smaller diameter. An immovable nosing die ring 1 is fixed to the lower shoe, and a movable punch 3 fixed to the upper shoe of this die. Fig. 12.1 Schematic illustration of a Type I 167 1 -nosing die ring 2-workpiece 3 -punch 4-outside holder 5-ejector nosing die. 168 Various Forming Dies In the second variation, shown in Fig. the top of the workpiece diameter is reduced so that the workpiece, after nosing, has a conic shape. In this second die, the nosing die ring 1 is fixed to the upper shoe so that it is movable, and the workpiece is held with an outside holder attached to the lower shoe. In both variations, the workpiece is ejected by the ejector 5 after the nosing operation is finished. The weakness of these kinds of die designs is that there is no provision for the die components to locate the workpiece: if the height of the workpiece is greater than the diameter, deflections or wrinkles may appear in the workpiece during the nosing operation. Fig. 12.2 shows a design for a Type nosing die. To the upper shoe 9 is attached the nosing die ring the inside support 6 with the spring and the driver ring 5. To the lower shoe 10 are attached the out- side support 3 and the segmental bushing 4 with helical springs 7. A pre-drawn workpiece is inserted into a nest on the outside support 3. When the press slide moves down, the driver ring 5 pushes the segmental ring which then holds the workpiece; at the same time, the inside support 6 enters the the workpiece to provide a positive guide and prevent deflection and development of wrinkles during the nosing operation. 1 -nosing die ring 2-workpiece 3-outside support 4-segmental bushing 5-driver 6-inside support 7-spring 8-spring 9-upper shoe 10-lower shoe Fig. 12.2 Schematic illustration of a Type nosing die. During the nosing operation, a die of Type as shown in Fig. 12.3, provides the best location for the workpiece. The Type die consists of the upper shoe 7 and the lower shoe 8. To the upper shoe is attached the nosing die ring and to the lower shoe is fixed the outside support 3. The workpiece, which has been pre-drawn, is inserted into a nest on the outside support 3 and located by the outside bushing which is powered by a mechanism positioned below the bed of the press. The workpiece is not then sup- ported from the inside Fig. Fig. shows a similar die design for nosing a tube, but this type of die has an inside support 5 that holds the workpiece during the nosing operation. A complete nosing die design is shown in Fig. 12.4. The die consists of the upper shoe 8 and the lower shoe guided by a guide post and guide post bushing. To the upper shoe is attached the nosing die ring with the nut which holds the die ring and the driver 4. To the lower shoe is fixed the inside support the slide 6 with handle and the segmental cam slide 3.