A clearance hole should be provided in the stripper plate

Bending Dies 139

10.3 DIES OF COMPLEX DESIGN

“Complex” refers to dies that are made up of many elaborately interrelated or interconnected parts. Considerable study and knowledge are needed to design complex die systems.

10.3.1 Closing Profile Dies

A bent profile often is used as a starting point for the next bending operation to be performed on the final piece. The composite drawing in Fig. illustrates both “before” and “after” stages of a bending die for closing a U-profile bend. The closing die consists of a punch holder 1 and die shoe which is guided by two guide posts and guide post bushings. The punch holder carrries a housing with movable side slides 4 that function as punches. Segments 6 are held in die shoe recesses with screws and dow- els. The workpiece U-profile, seen at the right, and in the die, with the insert 5 inside, is located on the central die segment. When the press ram is moved down, the side slides of the punch slide toward the die segment and with a single stroke of the press, the workpiece is bent to shape. The springs 7 return the slides to the start position when the ram press moves up. 1 -punch holder 1 -punch holder 2-die shoe 4-side slide 5-insert 6-segment of die 8-axle 9-security screw 10-workpiece Final piece 2-die shoe 3-holder 4-side slide 5-insert Tnitial form 6-segment of die 7-spring 8-axle 9-security screw 10-workpiece Final piece Fig. 10.6 Closing profile

10.3.2 Special Bending Dies

If great precision is required in the bent pieces, a special design of die is used for bending and coining operations. One design of such a die is shown in Fig. 10.7. The die consists of a punch holder 1 and die shoe 2 with guide post and guide post bushing. The punch holder carries the punch, which consists of an immovable segment 3 and two movable segments which are arranged to move transversely as the die closes. Attached to the die shoe are the die with stop pin 8 and stop latch 9. After the bending operation is finished, the fixed segment of the punch 3 pushes the slide punches 4 so they move transversely and coin the outside of the workpiece. 140 Bending Dies If the inside dimensions of the workpiece need to be more precise, the punch is made of one piece, and the die is made of both movable and immovable segments. After the bending operation is finished, the punch bears against the movable segments of the die additionally so they move transversely and coin the inside of the workpiece. 1-punch holder 2-die shoe 3-fixed punch 4-slide punch 5-spring 6-die 7-slide punch 8-stop pin 9-guide lath 0-blank -security ring Final piece Fig. 10.7 Special bending die. In Fig. 10.8 is shown a die for bending a double closed L-profile. The die is shown in Fig. and includes the die shoe and the punch which is directly attached to the press ram by means of the shank 5 . The die shoe embodies the die block, which consists of the immovable part of the die movable seg- ments the workpiece stop a pressure pad pegs and Belleville springs 7. The pressure pad holds the blank in position while it is being worked on, and provides the resistance to the bending operation needed to perform the operation. An air cushion or hydraulic cylinders are used to power this resistance. In the first bending phase, the punch 2 bends the blank to a double L-profile of 90 degrees. In the first bending phase, the pegs hold the movable segments of the die in the horizontal position. The Belleville springs are used to provide resistance until the blank has been bent to 90 degrees. The second bending phase begins at the moment when the punch touches the die segments 6. At this moment, the resistance of the Belleville springs 7 begins to be less than the force of the punch, the segments incline, and the workpiece is bent past 90 degrees. The stop 4 limits the inclination of the segments 6. When the press ram is moved up, the springs return the segments to the horizontal position, and the pressure pad ejects the workpiece. Bending Dies 141 1-die 4 2-punch \ I \ 3-die segment Blank 5-shank 7-Bellevillespring 8-die shoe 9-pressure pad first 10-cushion pin 1 1 -rocking roller 12-roller stop 13-spring I Final piece 13 11 Fig. 10.8 Double closed L- profile die. Instead of the segments shown in Fig. roller cylinders may be used, as shown in Fig. This concept is simpler but has a weakness, which is the possibility of the blank slipping because it is not held during the bending operation.

10.3.3 Curling and Hinge Dies

Curling dies provide a curled or coiled-up end or edge to the piece. Hinge dies make use of a curling operation. The curl may be centered, or it may be tangential to the sheet as shown in Fig. 10.9. The edge of the blank should have a starting bend and, if possible, the burr should be inside the bend. The blank 1 3 is located on the lower plate 12 where it is held by the pressure pad 6. The pressure pad holds the blank in position while it is being worked on. It also provides resistance to sideways move- ment of the blank. The spring 7 is used to provide force to power this resistance. At the start of the operation, the bent edge of the blank is curled by a horizontally-moving cam slide die 1 that is forced inward by the cam driver 2. On the upstroke of the press, the spring 10 returns the sliding die to the starting position. The swallowtail die guide latch 1 1 provides a reliable guide for the cam slide die. 142 Bending Dies Blank Final A 1 -cam slide 2-driver 3-driver plate 4-upper shoe 5-shank 6-pressure pad 7-spring 8-slide 9-spring suport 1 1 -die guide lath 12-lower shoe 13-workpiccc Fig. 10.9 Curling die design.

10.3.4 Tube-Forming Dies

Tube-forming dies may be single or multiple. Fig. 10.10 shows a single die for forming a tube in three phases. The edges of the blank are bent in the first phase between the punch 1 and the die 2. The pressure pad 10 holds the blank in position while it is being worked on, and provides the resistance needed to perform the operation. The spring 1 1 provides resistance to the pressure pad. The work- piece is transferred by hand from the first position, phase one, to the second position, phase two. At the same time, a new blank is located at the first position. In the second phase, the workpiece is bent between the punch 3 and the die 4. The workpiece is then transferred to the third position, the sec- ond workpiece moves to the second position, a new blank is located at the first position, and so on. At phase three, the third position, forming of the workpiece is completed between the punch the die and the insert 7. Even though each single press stroke makes one new piece after the completion of the first, produc- tivity of this die design is low because the workpiece is transferred by hand. For mass production, the process needs to be automated. For production of more precise tubular pieces, a much better design for the die is shown in Fig. 10.1 1. The tube-forming die in Fig. 10.1 consists of the punch holder 1 0, die shoe 1 with guide sys- tem: guide post 8 and guide bushing 9. The punch 1 and driver 5 are attached to the punch holder. The die cam the die segment and the cam slide die with springs 6 and are fixed to the die shoe.