CONCEPT OF PRESS TOOLS
The general nomenclature of tools
used in press are called press tools
i.e. punch and die. The punch is the
male part of a die used for making
holes, fix either with top plate or
bottom plate. It determines the
dirnensions of opening. The material
preferably high carbon high
crornium (HcHcr) steel, hardened
and tempered 60-62 HRC. The punch
forces the sheet/strip down and may
pierce it or draw it. It should be made
as small as possible consistent with
required strength and rigidity and is secured by punch holder
The die is the female counter part of the punch and therefore fixed on the opposite side of the punch on a plate. The die opening determines the dimensions of the outer shape of component. The material preferably high carbon high cromium (HcHcr) steel, hardened and tempered 60-62 HRC. The die is usually held in the die holder which is again clamped to the bolster plate mounted on the press table and remains stationary. Fig. 1.1 shows the shearing action between die and punch.
The punch and die are also made of cast steel, hardened and tempered or of one of alloy steel recommended for this purpose. The advantages of alloy steel are that the risk of the distortion or cracking in hardening is minimized and the working edges of the tools are less likely to chip or crumble.
The punch is fitted on the ram of the press and the die is fitted on the table of the press. The die is fixed member and punch is moved in upward and downward direction. The strip is moved between the die and strip guide. The punch comes downward and the shearing action takes place. Thus we get the finished component.
PRESS TOOL OPERATIONS
SHEARING OPERATIONS
To cut sheet metal we need basically two cutting edges, acting against each other or developing that effect. In tool making we fulfill this requirement by providing punch and die, one of these cutting members stationery and the other moving. The cutting takes place when the cutting edges of punch forces the stock against the cutting edges of die. This process can be divided into different four stages.
Stage A
The punch starts to penetrate into the stock material. The material is subjected to pressure below the elastic limit. This means that if we would now to retract the punch, the so far compressed stock material would come back to the original state. The formation of radii starts at both cutting edges.
Stage B
Further penetration takes place, the pressure exceed the elastic limits. Permanent deformation would now to be noted if the punch is retracted. The radius is formed and dish shaped deformation starts penetration is completed and the ultimate tensile strength is more or less reached.
Stage C
Further the penetration then the fractures start., Due topenetration the fracture now to occur at the two cutting sides. hfr 23 diketiv fracture occur at the both side of the cutting edges.
Stage D
Fractures from both sides meet and cutting is completed. Wk. rt;ate theextent of permanent deformation on the edge radii, for blanks it appears ori side and for piercing it appears on the punch side. The softer the material the the radii and vice versa . The shape of blank edge and its elements is shown in Fig. 24.
Parts description of Press Tool
Depending upon the design of the die assembly the press could be used for a variety of operations and jobs. Specific tooling is necessary to adopt the press for a particular operation. The die assembly for any operation consists of two halves, one being mounted in the reciprocating ram and the other bolted or clamped to the stationary bolster plate. The most important components in the complete assembly are punch (male member) and die block or die (female member). Other components are also necessary in order to retain and fix the two members in a fixed and aligned position and to produce the desired action efficient. A typical sketch of die assembly is shown in Fig. 3.1 and all the components used in it are described below
1. Punch. Punch is the male part of a die used for making holes fixed either with the top or bottom plate. It determines the dimensions of opening.
Material : Preferably High Carbon High Cromium (HcHcr) steel. Hardened and tempered 60-62 HRC.
2. Die. Die is the female counter part of the punch and therefore fixed on the opposite side of the punch on a plate. The die opening determines the dimensions of
the outer shape of component.
Material : Preferably High Carbon High Cromium (HcHcr) steel. Hardened and
tempered 60-62 HRC.
3. Bottom Plate (Die Shoe). Supports usually the die, except for inverted or
compound die and locates guide pillars.Material : Graded cast iron or ENS/C40 steel (40 kgs/mm2)