BLANK HOLDER 4g handbook vukotaboljanovicsheetmetalformingprocesses

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. Forming Dies 7 1 2 169 1 -nosing die ring 2-workpiece 3-outside support 4-guide bushing 5-inside support 6-cushion pin 7-upper shoe 8-lower shoe Fig. 12.3 Schematic illustration of a Type nosing die. a without inside support of workpiece. b with inside support of workpiece. 8 4 2 1 I VIEW A 1 -nosing die ring 6-slide 2-nut 7-handle of slide 3-segmental cam slide 4-driver 9-lower shoe 5-inside support Fig. 12.4 Nosing die. 170 Forming Dies To place the workpiece on the inside support the slide 6 needs to be pulled out of the work zone of the die before the nosing operation begins. The stop pin not shown positions the slide for nosing, which is done in three phases. In the first phase, the top of the workpiece is formed as a conic shape with a cen- tral angle of 40 degrees. In the second phase, the top of the workpiece is formed as a conic shape with a central angle of 75 degrees. In the third and last phase, the top of the workpiece is formed into a final hemi- spherical shape. For all three phases, the same die is used except that the nosing die ring 1 is changed. When the press slide has gone down, the driver pushes the segmental cam slides so they hold the outside of the workpiece, and with the inside support the die is provided with a positive location, resulting in a good quality workpiece. When the press slide is moved up, the driver pushes the segmental cam slides to the sides and the workpiece is freed.

12.2 EXPANDING AND BULGING DIES

Drawn shells of varying sizes and shapes, including tubular stock, can be expanded or bulged to produce such articles as teapots, water pitchers, kettles, doorknobs, parts of musical instruments, and various air- craft components.

12.2.1 Expanding Dies

Expanding dies are commonly used to enlarge the open end of a drawn shell or tubular stock with a punch. In most such operations, the workpiece is first annealed. Fig. 12.5 shows a die for expanding one end of a tube 3. The die consists of a punch holder 5 and a die shoe 6 with guide post 7. To the punch hold- er is fixed the punch and to the die shoe is attached the expanding die ring and the stripper 2. 1 5 3 1 -punch 5-punch holder 2-stripper 6-die shoe 3-blank tube 7-guide post 4-workpiece 8-die Fig. 12.5 Expanding die. Various Forming Dies 171 The die consists of a punch holder 5 and a die shoe 6 with a guide post 7. To the punch holder is fixed the punch and to the die shoe are attached the die 8 and the stripper 2. After the tube has been inserted in the die, the punch moves downward and expands the end of the tube. When the press slide is moved up, the stripper 2 pulls the workpiece 4 from the punch.

12.2.2 Bulging

Dies Vertical or horizontal segmented dies are commonly used for bulging, the force being applied by either hydraulic or mechanical means. In Fig. 12.6 is shown a schematic design for a mechanical bulging die with a segmental punch for bulging a ring of a tube. This die does not have a die cavity, the tube being pulled on the segmental punch 1. The force is applied to the segmental punch 1 by the ram pressing down onto the support plate 3. The segmental punch slides down over the cone 2 and forms the tube into its final shape. When the press slide moves up, the stripper plate lifts the segmental punch, which is pulled inward by springs, so that the workpiece is freed. This type of bulging die is used for the production of symmet- rical cylindrical components. 3 ....... .... .............. ................... Bolster plate 1-segmental punch 2-cone 3-support plate 4-stripper 5-cushion pin Fig. 12.6 Mechanical bulging die. In Fig. 12.7 is shown a schematic design for a bulging die with an elastic insert. The form of the fin- ished piece is machined into a split die so that when pressure is applied to the rubber insert the workpiece is forced into the forming cavity. When the press slide is moved up, the die is opened and the rubber insert is removed from the com- ponent. For this type of die, medium-hard rubber or polyurethane is used and is easy to handle. The major advantage of using polyurethane inserts is that they are resistant to abrasion, water, and lubricants. Furthermore, they do not damage the surface finish of the piece. Hydraulic means can also be used for bulging operations, but they require sealing and control of the hydraulic pressure. 172 Various Forming Dies Fig. 12.7 Bulging die with an elastic -split die 2-rubber insert 3-punch 4-insert 5-ring 6-workpiece 7-conic ring 8-outside support insert.

12.3 FLANGING DIES

There are two kinds of flanges: the convex-shrink flange and the concave-stretch flange. The convex flange is subjected to compressive hoop stresses, which, if excessive, cause the flange edges to wrinkle. In con- cave flanging, the flanges are subjected to tensile stresses which, if excessive, cause cracks at the edges. This section discusses only dies for the flanging of a hole; they can be single-operation dies or combi- nation dies. In Fig. 12.8 is shown a single-operation die for flanging a hole on the bottom of a drawn shell. The die consists of the upper shoe 7 and the die lower shoe which are located by the guide post 3. The flanging die ring 1 and the ejector 6 are attached to the die shoe. The flanging punch 2 and the pressure pad with the springs are fixed to the punch holder. When the angle of the flange is less than 90 degrees, the process is called dimpling. The dimpling operation has been used very exten- sively in aircraft production. 1 -flanging die ring 2-flanging punch 3-guide post 4-workpiece holder 5-spring 6-ejector 7-upper shoe 8-lower shoe Fig. 12.8 Flanging die. A combination die for punching, blanking, and flanging is shown in Fig. 12.9. The die consists of the The punch holder carries the punch a blanking punch a pressure pad and knockout pins punch holder 12 and the die shoe 1 3; they are guided by posts and bushings not shown. 1 plate and knockout pin plate 3.