STRIPPER PLATES 4g handbook vukotaboljanovicsheetmetalformingprocesses

132 Blanking and Punching Dies Fig. 9.27 Single punching die with a series of punches staggered. 6 Fig. 9.28 Compound die with parallel positions for punching and blanking operations. I 1 -punch holder 2-die shoe 3-punch plate 4-punching punch 5-stripper 6-bellevile spring 7-die 8-workpiece stop 9-guide post 10-guide bushing 1 1 -security ring 13-dowel 14-workpiece 1-punch holder 2-die shoe 3-die 4-punch 5-workpiece stripper 6-scrap stripper 7-blanking punch 8-strip guide bolt 9-stop pin 1 0-guide post 1 I-guide post bushing 12-workpiece Blanking and Punching Dies 133 Fig. 9.28 shows a compound die with punching and blanking operations in parallel positions. The die consists of a punch holder 1 and a die shoe with guide post 10 and guide post bushing 1 1. The guide posts are press-fitted into the die shoe and secured. The blanking die 3 is fitted on to the punch holder, along with the punching punch and the workpiece stripper. On the lower shoe are fixed the blanking punch and the scrap-strip stripper the stop pin and the strip guide-bolts which also function as guide bolts for the scrap-strip strippers. Fig. 9.29 shows a compound die with progressively placed punching and blanking operations. On the punch holder 9 are mounted a punching punch a blanking punch and a French notch punch 5. Socket head screws and locating dowel pins are used to hold the punch plate 7 and the backing plate 8 to the punch holder. The die holder 10 carries the die block, which consists of a die plate a guide plate and a strip guide 1 1. The shank 1 3 is used to hold the upper set of the die to the press ram. The first punching holes are of 10 mm diameter; the blanking work piece is of 20 mm diameter. Pilots 3 are inserted into the blanking punches 2 to center the inner and outer contours. The die is four-serial, so that every press stroke makes four pieces. Section A-A -die 2-blanking punch 3-pilot 5-French notch 6-guide plate 7-punch plate 8-backing 9-punch holder 10-die shoe 1 1 -guide rail 12-strip guide 13-shank Final part Fig. 9.29 The four-serial compound die. 10.1 Introduction BENDING DIES

10.1 INTRODUCTION

Bending dies may be conveniently classified according to their design, whether simple or complex, and according to their universality of application, whether universal or specific. The design of bending dies depends on the complexity of the workpiece shape, its dimensions, the type of material, the tolerances, etc.

10.2 SIMPLE DIE DESIGNS

Some die sets are designed to perform a single bending operation, which may include L, U, or Z, bends and other profiles. Such dies are called single-operation dies or simple dies. One operation is accomplished with each stroke of the press.

10.2.1 U-Profile Bend Dies

Fig. illustrates a simple die for bending a U-profile. In this example, the blank of length L , width and thickness T, is positioned on the die 1 between stop pins 1 1. The die 1 is mounted on the lower plate 3 in the conventional position. The punch 2 is attached to the punch holder which is fitted a shank 6 for that purpose, to the ram of the press. The pressure pad 10 applies pressure to the blank so that as the punch pushes the blank into the die, the workpiece is formed by a single stroke of the press. The bent workpiece is ejected from the die by the pressure pad mechanism a when the press ram retracts. For bending workpieces of small dimensions and thin material, the punches and dies are made from a single block of metal. 135 136 Bending Dies 4-punch holder 8-cushion pin a-spring type pad Fig. 10.1 Simple bending die. mechanism For bending a larger workpiece, using a heavier die set see Fig. the die is made up of segments which in turn are generally made from alloy tool steel. The advantages of this design are the same as with punching and blanking dies, as described in Chapter 9. The segments 4 are fixed to the die shoe with screws and dowels. The stop pin 7 is fixed to a pres- sure pad plate which holds the blank in position while it is being worked on. The pressure plate also 2 3 1 -fixed stripper Fig. Simple bending die with 2-punch 3-punch holder 4-die segment 5-cushion pin 6-pressure pad plate 7-stop pin 8-die shoe 9-workpiece segments. Bending Dies 137 provides resistance to the bending operation, which is needed to perform the operation. An air cushion or hydraulic cylinders are used to generate the force necessary for this resistance. If the width of the piece is large, it is necessary for the die to have a stripper. In the following description of a die set console, the stripper 1 is fixed to the die shoe, and the punch holder has a slot so that the upper set of the tool can move up and down without obstruction when the press ram cycles.

10.2.2 V-Profile Bend Dies

Fig. 10.3 shows a simple die set for bending different shapes with bending angles of These types of die are known as dies for V-profile bends. The die 1 is mounted on the die plate 4 in the conventional position. The punch 2 is attached to the punch holder 3. The pad 5 holds the blank in position while it is being worked on. It also provides the resistance needed to perform the bending operation. An air cushion or hydraulic cylinders are used to power this resistance. The lower and upper parts of the die set are guided by the guide post 7. The blank is positioned on the die between the stop pins and with a single stroke of the press the workpiece is bent into its required shape. Corrections to the punch angle, if necessary, are made after a try-out, when the exact springback angle is known. 3 2 1 -die 2-punch 3-punch holder 4-die shoe 5-pressure pad 6-stop pin 7-guide post 8-cushion pin 9-workpiece Final piece Fig. 10.3 V-profile bend die. Fig. 10.4 shows a single-operation bending die for a V-profile workpiece being bent on one end, with the other end of the piece already curled. The die consists of a punch holder 3 and a die shoe 4 with guide posts 7. The guide posts are press fitted into the die shoe and secured. The bending punch 2 is fixed to the punch holder with screws and dowels. The die shoe carries the die 1 the blank guide and the stop pin 6. The pad 5 provides the resistance to the bending operation, needed to perform the operation. An air cushion or hydraulic cylin- ders are used to power this resistance. The bent piece is ejected from the die with a pressure pad mechanism when the press ram is moved to the “up” position.