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.
Forming
Dies
173 1
-punching punch 2-blanking punch
3-knockout pin plate
4-blanking die plate 5-workpiece ejector
6-punching die ring 7-cushion pin
8-strip stop pin
9-pressure pad 1 0-plate
1 1 -knockout pin 12-punch holder
13-die shoe Fig. 12.9
Combination die
for
punching,
blanking, and
flanging. To the die shoe are attached the blanking plate
the punching ring the workpiece ejector plate
and the strip stop pin 8.
The strip stock is positioned by the stop in and guided by a guide rail not shown and held by the
pressure pad which functions as a scrap stripper. First, the blank is cut out with the punch
2 and the blanking plate
so that the hole is simultaneously punched with the punch
and the punching die ring 6. The hole is then flanged with the inside of the blanking punch 2 and the outside of the punching die
ring 6. The workpiece is ejected from the die by the knockout plate 3 and the workpiece ejector 5.
13.1
Introduction
13
13.2
Carbon and
Alloy Steels
13.3 Tool
Steels
13.4
Nonferrous Metals
13.5
Nonmetallic
Materials
TOOL AND DIE MATERIALS
13.1 INTRODUCTION
The composition and physical properties of the principal materials used in die design for sheet metal form- ing are discussed in this chapter. A die component must be made of
a
material that has properties suitable for the conditions of service. The die material is just as important as are considerations of the loads and
stresses, dimension, and form of the piece, as well the quantity of the pieces which need to be manufac- tured with the die. Frequently, the limitations imposed by available materials are the controlling factor in
a die design. The designer must be familiar with the effects that the methods of manufacture of die com- ponents and heat treatment have on the properties of the die materials. The manufacturing processes used
for fabrication of workpieces will also influence the types of material that can be used. Sometimes, the
help of a professional metallurgist is needed to ensure the best possible choice of material and heat treat- ment. The emphasis of this text will be on the steels needed to produce dies for sheet-metal forming. Other
materials, such as nonferrous and nonmetallic materials, will be included to complete the picture.
13.2 CARBON AND ALLOY STEELS
Steel is an alloy of iron and carbon, or of iron, carbon, and other alloying elements. Carbon must be pres- ent to the extent of about
0.05 by weight in order for the material to be known as steel rather than com- mercial iron.
Carbon and alloy steels are among the most commonly used metals and have a wide variety of appli- cations. The composition and processing of steels are controlled in a manner that makes them suitable for
numerous applications. They are available in various basic product shapes: plate, sheet, strip, bar, wire, tube, and they may also be cast or forged.
175
