CLASSIFICATIONS AND TYPES OF DIES
Dies can be classified according to a variety of elements and in keeping with the diversity of die designs. In this section, we will discuss primarily die classifications depending on the production quantities of stamping pieces (whether high, medium, or low) and the number of stations. In choosing these, we are not trying to downplay or ignore other classifications such as the number of operations, manufacturing processes, or guide methods.
2.1.1 Die Classifications Depending on the Production Quality of Parts
Depending on the production quality of pieces—high, medium, or low—stamping dies can be classified as follows:
Class A. These dies are used for high production only. The best of materials are used. All easily worn items or delicate sections are carefully designed for easy replacement. A combination of long die life, constant accuracy throughout the die life, and ease in maintenance are prime considerations, regardless of tool cost.
Class B. These dies are applicable to medium production quantities and are designed to produce the designated quantity only. Die cost as related to total production becomes an important consideration. Cheaper materials may be used, provided they are capable of producing the full quantity. Less consideration is given to the problem of ease of maintenance.
Class C. These dies represent the cheapest usable tools that can be built. They are suitable for low-volume production of parts.
2.1.2 Die Classifications According to Number of Stations
According to the number of stations, stamping dies may be classified as:
•Single-station dies
•Multiple-station dies
a) Single-Station Dies
Single-station dies may be either compound dies or combination dies.
Compound die. A die in which two or more cutting operations are accomplished to produce a part at every press stroke is called a compound die.
Combination die. A die in which both cutting and noncutting operations are accomplished to produce a part at one stroke of the press is called a combination die.
b) Multiple-Station Dies
Multiple station dies are arranged so that a series of sequential operations is accomplished with each press stroke. Two die types are used:
•Progressive dies
•Transfer dies
Progressive die. A progressive die is used to transform coil stock or strips into a completed part. This transformation is performed incrementally, or progressively, by a series of stations that cut, form, and coin the material into the desired shape. The components that perform operations on the material are unique for every part. These components are located and guided in precision cut openings in plates, which are in turn located and guided by pins.
The entire die is actuated by a mechanical press that moves the die up and down. The press is also responsible for feeding the material through the die, progressing it from one station to the next with each stroke.
Transfer die. In transfer die operations, individual stock blanks are mechanically moved from die station to die station within a single die set. Large workpieces are done with tandem press lines where the stock is moved from press to press at which specific operations are performed.
There are 20 types of dies, and each is distinct and different from all the other types. However, as you study the descriptions to follow, observe how the elements are applied and reapplied with suitable modifications to adapt them for each particular job to be performed.
2.2.1 Blanking Dies
A blanking die (Figure 2.1) produces a blank by cutting the entire periphery in one simultaneous operation. Three advantages are realized when a part is blanked:
1.Accuracy. The edges of blanked parts are accurate in relation to each other.
2.Appearance. The burnished edge of each blank extends around its entire periphery on the same side.
3.Flatness. Blanked parts are flat because of the even compression of material between punch and die cutting edges.
The inset at A shows a material strip ready to be run through a blanking die. At B is shown the top view of the die with punches removed. The section view at C shows the die in open position with the upper punch raised to allow advance of the strip against the automatic stop. At D, the die is shown closed with a blank pushed out of the strip.
Figure 2.1 Blanking die.
Blanking dies may produce plain blanks as shown in inset E, but more frequently holes are pierced at one station and the part is then blanked out at the second station. Such dies are called “pierce and blank” dies.
2.2.2 Cut-Off Dies
The basic operation of a cut-off die (Figure 2.2) consists of severing strips into short lengths to produce blanks. The line of cut may be straight or curved, and holes or notches or both may be applied in previous operations. Cut-off dies are used for producing blanks having straight, parallel sides because they are less expensive to build than blanking dies. In operation, the material strip A is registered against stop block B. Descent of the upper die causes the cut-off punch C to separate the blank from the strip. Stop block B also guides the punch while cutting occurs to prevent deflection and excessive wear on guide posts and bushings. A conventional solid stripper is employed.
2.2.3 Piercing Dies
Piercing dies (Figure 2.3) pierce holes in stampings. There are two principal reasons for piercing holes in a separate operation instead of combining piercing with other operations:
1.When a subsequent bending, forming, or drawing operation would distort the previously pierced hole or holes
2.When the edge of the pierced hole is too close to the edge of the blank for adequate strength in the die section. This occurs in compound and combination dies in which piercing and blanking are done simultaneously.
The inset at A shows a flanged shell requiring four holes to be pierced in the flange. If the holes were pierced before the drawing operation, they would become distorted because of the blank holder pressure applied to the flange in the drawing process.
The shell is located in an accurately ground hole in the die block. Piercing punches are retained in a punch plate fastened to the punch holder, and a knockout affects