DEEP DRAWING DIES

11.1 Introduction

11.2 Draw Rings

11.3 Clearances and Tolerances

11.4 Blank Holders

11.5 Single-Operation Dies

11.6 Multi-Operation Dies

11.7 Progressive Dies

11.8 Drawing Dies for Pieces of

Spherical and Parabolic Shape

11.9 Ironing Dies

11.1 INTRODUCTION

The important variables in the technical components of deep drawing dies are the punch corner radius, the die ring profile, the clearance between punch and die ring, and the configuration of the surfaces of the die rings and the blank holder that are in contact with the blank.

11.2 DRAW RINGS

The die ring profile substantially influences both the deep drawing process and the quality of the drawn workpieces. Because the material is pulled over the profile, it is necessary that the die ring profile have an optimum value. The most frequently used draw rings use a corner radius or conic profile, even though other kinds of draw rings are used as well.

11.2.1 Draw Ring with Corner Radius

A draw ring with a corner radius ( R p ) is the most frequently used for the first drawing operation without a reduction of the thickness of the materials, whether a blank holder is used or not. Fig. 11.1 shows a deep drawing die with a draw ring having a corner radius.

A draw ring with a corner radius, as shown in Fig. 11.2, can also be used for subsequent drawing operations without any reduction in the thickness of the materials if a blank holder is not used. If a blank holder is used, however, the conditions for drawing are much better using a draw ring with a conic profile than one with a corner radius.

     a) Cylindrical shells. The value for the optimum radius on the draw ring is defined experimentally, and it depends on the type and thickness of material being drawn, the order of the drawing operation, the height

Fig. 11.1 Die for the first drawing operation: die ring with corner radius.

of the workpiece, and the drawing ratio. The smaller the draw ring corner radius, the greater the force needed to draw the shell. If the corner radius of the draw ring is too large, too much of the material will not be confined as it passes over the radius. The material will thicken, fold, and wrinkle. Recommendations for approximating the draw ring radius can be found in the technical literature,. E. Kaczmarek recommends the following formula for defining the draw ring corner radius for the first drawing operation:

     (11.1)

where:

     D = blank diameter

     d 1 = inside workpiece diameter after the first drawing operation

     T = material thickness

The draw ring corner radius for the next drawing operation is:

Fig. 11.2 Typical die for subsequent drawing operations using a draw ring with corner radius.

where:

     d n = inside shell diameter after nth drawing operation.

The height of the cylindrical part of the draw ring ( h 0 ) in Fig. 11.1 can be calculated by the following formula:

     (11.2)

     b) Noncylindrical shell. The die draw radius ( R p ) for drawing a rectangular or square shell is given by the following formulas:

For longer side ( a )

     (11.3)

For shorter side ( b )

     (11.3a)

For a corner radius ( Re ), the draw radius is:

     (11.3b)

where:

     L a , L b = blank dimensions

     a 1 , b 1 = shell dimensions after

     T = material thickness.